Selective Inhibitor Research Articles

Abstract PO2-05-08: ISM5043, a novel, selective KAT6 inhibitor for the treatment of advanced and refractory ER+ breast cancer

Abstract Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death among women in the US. Approximately 70% of human breast tumors are estrogen receptor positive (ER+), and endocrine therapy (ET), which inhibits the estrogen signaling pathway, remains the backbone of therapy for ER+ breast cancer. However, ET resistance often develops, and patients eventually experience disease progression. This is a significant clinical challenge and highlights the urgent need for novel therapies that may help overcome the resistance. KAT6A is a histone (lysine) acetyltransferase (HAT) belonging to the MYST family. KAT6A and its paralog KAT6B play important roles in cell cycle progression, neuron stem cell maintenance and hematopoietic development via acetylation of H3K23. Molecular dysregulation of KAT6A, including amplification and fusion, has been reported in many cancers. In breast cancer, KAT6A is amplified as part of the 8p11 amplicon in about 10-15% of the ER+ breast cancer population, where it functions as an epigenetic modulator of ER expression, and is associated with a worse clinical outcome. Therefore, inhibition of KAT6A may be a promising therapy for ER+ breast cancer. Here, we evaluated ISM5043, a novel, small molecule KAT6 inhibitor for anti-tumor effects in ER+/HER2- breast cancer cell lines and animal models. ISM5043 demonstrated potent inhibitory activity against KAT6A (IC50, 8 nM) and KAT6B (IC50, 16 nM) with selectivity over KAT7 (IC50, 344 nM) and other HATs (IC50 >2000 nM). The compound showed robust, dose-dependent, anti-proliferation activity (IC50 < 10 nM) in multiple ER+/HER2- breast cancer cell lines with KAT6A amplification, in accordance with its suppression of H3K23 acetylation. Investigation of the mechanism of action revealed that treatment with ISM5043 resulted in the downregulation of the expression of ERα in these breast cancer cells. In the ZR-75-1 (ER+, HER2-) xenograft model, ISM5043 demonstrated robust and dose-dependent anti-tumor activity, as monotherapy, with Tumor Growth Inhibition (TGI) between 80~110% at doses ranging from 0.3 to 10 mg/kg, QD. ISM5043 (0.3 mg/kg, QD), in combination with tamoxifen (20 mg/kg, QD) exhibited synergistic effect against tumor growth, with a Q value of 1.25 based on Jin’s equation. Notably, ISM5043 displayed a strong anti-tumor effect (TGI of 67.7% and 83.6% at 3 and 10 mg/kg QD, respectively) as monotherapy, in a patient-derived ER+/HER2- breast cancer xenograft model representing disease progression following multiple prior lines of treatment (including palbociclib in combination with letrozole). ISM5043 also showed favorable ADME properties as well as good pharmacokinetic and safety profiles. Taken together, these data support the clinical evaluation of ISM5043 as a targeted therapy in patients with advanced and refractory ER+ breast cancer. Citation Format: Xin Cai, Xin Cheng, Luoheng Qin, Man Zhang, Junwen Qiao, Supriya Bavadekar, Sujata Rao, Feng Ren. ISM5043, a novel, selective KAT6 inhibitor for the treatment of advanced and refractory ER+ breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-05-08.

Abstract PO3-25-09: OKI-219, a PI3KαH1047R-mutant-selective inhibitor demonstrates efficacy as a single agent and drives combination responses with standard of care therapies in pre-clinical PI3KαH1047R mutant breast cancer models

Abstract Mutations in PI3Kα lead to constitutive activation of the PI3K/AKT/mTOR pathway and are highly prevalent in cancer. PI3KαH1047R is the most common amino acid substitution mutation and represents approximately one-third of all PI3Ka mutations, with 15% of breast cancers having a PI3KαH1047R mutation. In breast cancer, PI3KαH1047R mutations are associated with resistance to targeted therapies, including HER2- and estrogen receptor (ER)- targeted agents. Although targeting PI3Kα in cancer is a therapeutically proven strategy, with the currently approved drug alpelisib showing clinical efficacy alone or in combination with other therapies, treatment with non-mutant selective PI3Kα inhibitors such as alpelisib is associated with significant toxicities such as hyperglycemia, due to on-target inhibition of the wild-type enzyme. This often leads to dose modification or discontinuation. Therefore, there is a significant need to develop new PI3Kα-targeted therapies that can avoid or minimize on-target toxicity and improve the safety and clinical benefit for patients. OKI-219 is an orally bioavailable, PI3KαH1047R mutant-selective inhibitor, with ~100-fold cellular selectivity for the H1047R mutation over wild-type. OKI-219 demonstrates selectivity across a panel of 412 kinases, with no other kinases showing >30% inhibition at 1 µM. In vitro, OKI-219 drives decreased phosphorylated AKT (pAKT) and decreased proliferation specifically in PI3KαH1047R mutant cell lines across several tumor types, including breast cancer. In vivo, as a monotherapy, OKI-219 demonstrates dose dependent antitumor activity in multiple human tumor xenograft models, including the H1047R mutant breast cancer CDX models T47D and HCC1954 and several PDX models, with regression rates up to 100% at doses that show no sign of the metabolic dysfunction (increased glucose or insulin) associated with wild-type protein inhibition. The in vivo antitumor activity correlates with pathway inhibition, measured by decreased pAKT in tumors. Moreover, OKI-219 dosed in combination with the selective estrogen receptor degraders (SERDs) fulvestrant, elacestrant or camizestrant showed significant combination benefit leading to tumor regressions of up to 100% in the ER+ H1047R mutant breast cancer model xxT47D, at doses where no regressions were observed with single agent treatment. Dosing OKI-219 in combination with HER2-inhibitors, such as tucatinib, led to tumor regressions in the ER-HER2+ and H1047R mutant breast cancer CDX model HCC1954, also at doses where no regressions were observed with single agent treatment. These data indicate that OKI-219 offers improved efficacy and a wider therapeutic window compared to non-mutant selective PI3Kα inhibitors. OKI-219 is advancing into clinical trials. Citation Format: Molly A. Taylor, Qian Zhao, David Mareska, Maria Hoh, Yevgeniy Izrayelit, Kevin Litwiler, Mark L Boys, Rich Woessner, Duncan Walker, James D Winkler, Jennifer Diamond. OKI-219, a PI3KαH1047R-mutant-selective inhibitor demonstrates efficacy as a single agent and drives combination responses with standard of care therapies in pre-clinical PI3KαH1047R mutant breast cancer models [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-25-09.

Abstract PO3-25-10: Selective and Effective Targeting of Triple-Negative Breast Cancer by CMPD1: Inhibition of MAP kinase-activated protein kinase 2 and Microtubule Dynamics

Abstract Background: Microtubule-targeting agents (MTAs) have been widely utilized in cancer treatment, but the development of novel MTAs has faced limitations. CMPD1, a highly selective inhibitor of MAP kinase-activated protein kinase 2 (MK2) with dual functions as a microtubule inhibitor, shows promise as a targeted therapy for triple-negative breast cancer (TNBC). This study aimed to investigate the effects of CMPD1, targeting MK2 and acting as a microtubule inhibitor, on cell cycle progression, microtubule dynamics, and TNBC-related processes. Methods: CMPD1 was evaluated in non-transformed retinal pigment epithelial cells (RPE1) and TNBC cell lines, including MDA-MB-231 and MDA-MB-468 cells. Time-lapse microscopy and immunofluorescence staining were employed to observe the effects of CMPD1 on mitotic progression, cellular morphology, activation of the spindle assembly checkpoint (SAC), and microtubule dynamics. Anchorage-independent growth assays and in vivo studies using a TNBC xenograft model were performed to assess the impact of CMPD1 on colony formation, tumor growth, and metastasis. Results: CMPD1 treatment induced prometaphase arrest and mitotic slippage in both non-transformed and TNBC cells. This arrest was associated with SAC activation, evidenced by increased levels of Mad1 at kinetochores. CMPD1 exhibited robust microtubule depolymerization, primarily targeting microtubule plus-ends and inhibiting microtubule polymerization in vitro. Furthermore, CMPD1 disrupted the organization of the microtubule network in interphase cells and perturbed the mitotic spindle during mitosis. Additionally, CMPD1 treatment resulted in the formation of cytoplasmic protrusions, membrane deformations, and dynamic movement of clustered mitotic chromosomes. These morphological alterations were indicative of the impact of CMPD1 on cellular structures and processes during mitosis. Notably, CMPD1 demonstrated significant efficacy in inhibiting anchorage-independent growth in TNBC cells, highlighting its potential as an anti-TNBC agent. In the TNBC xenograft model, CMPD1 exhibited superior anti-tumor activity compared to the standard chemotherapeutic agent Taxol. Tumor growth was markedly suppressed, and the formation of metastatic lesions was significantly reduced upon CMPD1 treatment. Furthermore, CMPD1 treatment effectively inhibited TNBC cell migration and invasion, likely through its modulation of microtubule dynamics. The disruption of microtubule dynamics by CMPD1 impaired the ability of TNBC cells to migrate and invade surrounding tissues, which are crucial processes in cancer metastasis. Importantly, CMPD1 showed high selectivity for TNBC cells, exerting minimal cytotoxic effects on normal cells, and could be efficiently washed out. This selectivity and washout ability enhance its potential as a targeted therapeutic agent for TNBC treatment. Conclusions: CMPD1, a highly selective MK2 inhibitor and microtubule inhibitor, exerts profound effects on cell cycle progression, microtubule dynamics, and TNBC-related processes. It induces prometaphase arrest, mitotic slippage, and microtubule depolymerization, resulting in altered cellular morphology. CMPD1 displays high selectivity for TNBC cells, while sparing normal cells and allowing efficient washout, making it a promising therapeutic agent for TNBC treatment. Its inhibition of anchorage-independent growth, suppression of tumor growth in vivo, and ability to impair TNBC cell migration and invasion further underscore its potential as a targeted anti-TNBC therapy. Citation Format: Mamoru Takada, Yu-Chia Chen, Yu Muhan, Hideyuki Yamada, Junta Sakakibara, Hiroshi Fujimoto, Takeshi Nagashima, Masayuki Otsuka, Motoki Takaku, Aussie Suzuki. Selective and Effective Targeting of Triple-Negative Breast Cancer by CMPD1: Inhibition of MAP kinase-activated protein kinase 2 and Microtubule Dynamics [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-25-10.

Abstract PO1-16-04: Targeting PKMYT1 Kinase as a Therapeutic Strategy for Treatment of Triple Negative Breast Cancer with Low Molecular Weight Cyclin E (LMW-E) Expression

Abstract Purpose: Low molecular weight isoforms of cyclin E (LMW-E) have been implicated in various human cancers, including triple negative breast cancer (TNBC), and are associated with a poor prognosis. However, targeted therapies for TNBC based on biomarkers are currently lacking. This study aims to investigate LMW-E as a potential therapeutic target in TNBC and evaluate the efficacy of RP-6306, a selective inhibitor of the Protein Kinase, Membrane Associated Tyrosine/Threonine 1 (PKMYT1), in LMW-E-positive breast tumors. Experimental Design: Immunohistochemical (IHC) analysis was performed on pre-treatment tumor specimens from TNBC patients (n=36) to assess the correlation between LMW-E expression, CDK1 phosphorylation at Threonine 14 (pT14), and pathologic complete response to neoadjuvant chemotherapy. LMW-E inducible human mammary epithelial cells (hMEC) and breast cancer cell lines were used to investigate the regulatory effect of LMW-E on PKMYT1, the kinase responsible for CDK1 phosphorylation at T14, and the response to RP-6306, a first in-class and selective inhibitor of PKMYT1. Patient-derived xenograft (PDX) models and transgenic mouse mammary tumor virus (MMTV) models of TNBC expressing human LMW-E (hLMW-E) were also utilized to assess LMW-E as a biomarker for predicting response to RP-6306. Results. Analysis of TNBC tumor biopsies revealed a significant positive correlation between LMW-E expression and CDK1 pT14, and both biomarkers were associated with a lack of pathological complete response to neoadjuvant chemotherapy. In vitro results using LMW-E inducible hMECs and breast cancer cell lines demonstrated that LMW-E up-regulates PKMYT1 and CDK1 pT14, acting as a PKMYT1 binding protein and enhancing PKMYT1 protein stability. High LMW-E protein levels predicted a favorable response to RP-6306, resulting in the accumulation of sub-G1 and polyploid cells, decreased tolerance to replication stress, increased DNA damage, chromosomal breakage, and apoptosis. In vivo treatment of TNBC PDX models and hLMW-E transgenic tumors with RP-6306 resulted in a significant reduction in tumor volume only in mice harboring high LMW-E tumors, while low cyclin E models showed no response. Immunohistochemical analysis confirmed increased γ-H2AX and decreased CDK1-pT14 and Ki67 levels, indicating the efficacy of RP-6306 in both PDX and transgenic models. Conclusion: This study highlights the regulatory axis from LMW-E to PKMYT1 and its predictive value for pathological complete response in TNBC patients receiving neoadjuvant chemotherapy. The selective PKMYT1 kinase inhibitor RP-6306 consistently induced DNA damage and inhibited tumor growth in in vitro and in vivo pre-clinical breast tumor models. Co-expression of LMW-E and CDK1-pT14 in TNBC can be used to stratify patients whose tumors are likely to respond to RP-6306, emphasizing its therapeutic significance. Citation Format: Mi Li, Amriti Lulla, Cansu Karakas, Spiridon Tsavaschidis, Yan Wang, Tuyen Nguyun, Tuyen Bui, Gary Marshall, Kelly Hunt, Khandan Keyomarsi. Targeting PKMYT1 Kinase as a Therapeutic Strategy for Treatment of Triple Negative Breast Cancer with Low Molecular Weight Cyclin E (LMW-E) Expression [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-16-04.

Discovery of the Clinical Candidate Sonrotoclax (BGB-11417), a Highly Potent and Selective Inhibitor for Both WT and G101V Mutant Bcl-2.

The approval of venetoclax, a B-cell lymphoma-2 (Bcl-2) selective inhibitor, for the treatment of chronic lymphocytic leukemia demonstrated that the antiapoptotic protein Bcl-2 is a druggable target for B-cell malignancies. However, venetoclax's limited potency cannot produce a strong, durable clinical benefit in other Bcl-2-mediated malignancies (e.g., diffuse large B-cell lymphomas) and multiple recurrent Bcl-2 mutations (e.g., G101V) have been reported to mediate resistance to venetoclax after long-term treatment. Herein, we described novel Bcl-2 inhibitors with increased potency for both wild-type (WT) and mutant Bcl-2. Comprehensive structure optimization led to the clinical candidate BGB-11417 (compound 12e, sonrotoclax), which exhibits strong in vitro and in vivo inhibitory activity against both WT Bcl-2 and the G101V mutant, as well as excellent selectivity over Bcl-xL without obvious cytochrome P450 inhibition. Currently, BGB-11417 is undergoing phase II/III clinical assessments as monotherapy and combination treatment.

Abstract SS02-02: Hormone Replacement and Alternatives for Relief of Vasomotor Symptoms in Women at Increased Risk for Breast Cancer

Abstract 70% of women will experience vasomotor symptoms sufficient to impact their quality of life during menopause transition and the early menopause. These symptoms are thought result from neurotransmitter imbalances resulting from ovarian hormone reductions and hypersecretion of gonadotropins. Increases in gonadotropins result in neurotransmitter triggered stimulation of the neurokinin 3 (NK3) receptor and thermoregulatory imbalance. Estrogen deficiency also reduces serotonin which can also trigger increases in hot flashes, and sleep disturbances. Vasomotor symptoms last on the average for 7 years until acclimation to persistent low estrogen levels occurs. Estrogen +/- progestin replacement therapy is associated with the greatest likelihood of vasomotor symptom relief as it reduces gonadotropin and NK3 receptor signaling and increases serotonin. Progestins also increase the neuroinhibitory transmitter gamma-aminobutyric acid (GABA) which improves sleep quality. There continues to be confusion on the part of providers and patients regarding the excess risk of breast cancer and thromboembolic events as these risks are affected by type of agent, route of delivery, age, duration of treatment, and presence of obesity. The majority of placebo controlled randomized clinical trial data on hormone replacement with estrogen or estrogen + a progestin comes from the Women’s Health Initiative (WHI) for women 50-79 in which oral conjugated estrogen (CE) 0.625 mg was used as the estrogen for women without a uterus and medroxyprogesterone acetate (MPA) was added to CE for women with a uterus to protect against endometrial hyperplasia and cancer. The median age at entry to WHI that trial was 63 and a substantial proportion had previously taken hormones. Large longitudinal cohort studies have been helpful in assessing risks in women starting hormones at a more clinically relevant age (45-55) and with hormonal preparations other than oral CE and MPA. Five to seven years of estrogen alone results in minimal if any increased risk for breast cancer. However, combined estrogen+ progestin replacement for women over 50, necessary for women with a uterus, results in an ~ 30 % relative increased risk for breast cancer if taken for up to 5 years and a doubling of risk with 10 years of treatment. So called bioidentical hormones often compounded as oral troches of estradiol, progesterone, and testosterone, are also associated with increased breast cancer risk. Vaginal hormones have not been found to increase risk for breast cancer. Increased risk of thromboembolism is predominately observed in women over 50 using oral as opposed to transdermal preparations. Increased risk for stroke and dementia was observed in the WHI again with oral hormones in women over 65. In the WHI there was no increase in cancer related, cardiovascular or overall mortality with estrogen or estrogen and progestin. For high-risk peri and post-menopausal women with who would like to reduce/alleviate their vasomotor symptoms with no increase in risk for breast cancer there are several options: 1) the tissue selective estrogen complex bazedoxifene (BZA) combined with conjugated estrogen (CE) 2) the non-hormonal option of NK3 receptor antagonists such as fezolinetant ( 3) non-hormonal options of gabapentin, selective serotonin reuptake inhibitors (SSRI) and serotonin and norepinephrine uptake inhibitors (SNRI). BZA and CE and fezolinetant are reported to reduce hot flashes in 70% or more of individuals with paroxetine effectiveness reported as 50%. All three are FDA approved for reduction of vasomotor symptoms. The combination of BZA and CE is also being investigated for breast cancer risk reduction. These agents differ with respect to side effects with increased risk of blood clots for bazedoxifene and conjugated estrogen, increased risk of nausea, diarrhea, and liver dysfunction for fezolinetant and drowsiness and dry mouth for SSRIs. Drug costs may also dramatically affect insurance coverage and patient uptake of a particular strategy. A recent online perusal of a popular site for finding the lowest drug price suggested substantial differences in the cost of drugs for relief of vasomotor symptoms. The approximate cost for a 30- day supply of oral estradiol was $30, estradiol transdermal patches $35, oral progesterone $15, combined estradiol and levonorgestrel transdermal patches $240, oral CE $200, oral CE + medoxyprogesterone acetate $240, and for BZA+ CE $200. For non-hormonal therapies the cost of 30 days of gabapentin was $11, paroxetine $30 and fezolinetant $550. Crandall, Mehta, and Manson JAMA 2023 329:405-420 Collaborative Group on Hormonal Factors in Breast Cancer Lancet 2019 394: 1159-1168 Fabian et al Ca Prev Res 2019 10:711-720 Modi and Dhillo Neuroendocrinology 2019 109:242–248 Citation Format: C. Fabian. Hormone Replacement and Alternatives for Relief of Vasomotor Symptoms in Women at Increased Risk for Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr SS02-02.

Abstract PO3-19-10: Phase 1b study of EZH1/2 inhibitor valemetostat in combination with trastuzumab deruxtecan in subjects with HER2 low/ultra-low/null metastatic breast cancer

Abstract Background Low HER2-expressing breast cancers have traditionally been classified as HER2-negative and treated as TNBC or hormone receptor (HR)-positive. Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate, composed of an anti-HER2 antibody conjugated to topoisomerase I payload, is approved for clinical use in HER2-low (IHC 1+ or IHC 2+/ISH negative) metastatic breast cancer (MBC). In the DAISY study (NCT04132960), meaningful clinical response was observed with T-DXd in HER2 IHC 0 MBC. Valemetostat is an oral, selective dual inhibitor of enhancer of zeste homolog 1 and 2 (EZH1/2, methyltransferases that specifically methylate histone H3 lysine 27. It is currently approved for patients with relapsed or refractory adult T-cell leukemia/lymphoma in Japan. EZH2-mediated PP2A inactivation has been shown to confer resistance to HER2-targeted therapy. Additionally, valemetostat has been shown to upregulate Schlafen11 (SLFN11), a putative DNA/RNA helicase, that regulates the sensitivity to DNA damaging agents such as topoisomerase I inhibitors. Consequently, this study examines the safety and anti-tumor activity of valemetostat in combination with T-DXd in subjects with HER2 low/ultra-low/null MBC. Trial Design This is a single-arm, phase-1b study to evaluate the safety and clinical activity of T-DXd in combination with valemetostat in patients with HER2 low/ultra-low/null MBC. The dosing for T-DXd is 5.4 mg/kg Q3W administered intravenously as indicated for current clinical use. Valemetostat will be evaluated at three dose levels (100 mg, 150 mg, and 200 mg orally), with starting dose (level 1) at 100 mg QD. The dose-limiting toxicity (DLT) evaluation period will be the first 2 treatment cycles (42 days). Eligibility criteria Specific aims Statistical methods Approximately 12 evaluable patients will be enrolled for the dose-escalation portion based on the Bayesian optimal interval design with a target DLT rate of 25%. Patients enrolled in cohorts of 3. The expansion will be performed at the RDE using the 2-stage Bayesian optimal dose-expansion design. In the first stage, 13 evaluable patients (including those treated at the RDE in the dose-escalation part) will be enrolled. If < 5 patients respond in the first stage, the study will be stopped for futility. If ≥ 5 responses are observed, 13 additional evaluable patients will be enrolled. If 11 or more responses are observed among the total of 26 patients the treatment will be regarded as promising. This two-stage design yields 78% power under the alternative hypothesis of ORR=50% (null ORR = 30%) while controlling the one-sided type I error at 10%. Contact information for people with a specific interest in the trial sdamodaran@mdanderson.org (NCT05633979) Citation Format: Senthil Damodaran, Toshiaki Iwase, Angela Marx, Jie Willey, Funda Meric-Bernstam, Debu Tripathy, Carlos Barcenas, Jangsoon lee, Naoto Ueno. Phase 1b study of EZH1/2 inhibitor valemetostat in combination with trastuzumab deruxtecan in subjects with HER2 low/ultra-low/null metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-19-10.

Abstract PO1-24-05: EZH2 histone methyltransferase activity promotes spindle metaplastic breast carcinoma metastasis and is induced by CCN6 knockout/b-catenin/TCF axis

Abstract Background: Metaplastic breast carcinomas (mBrCAs) are a highly aggressive subtype of triple negative breast cancer with histological evidence of deregulated differentiation towards non-glandular components. Previous studies have demonstrated that human mBrCA often exhibit activation of differentiation pathways, including canonical Wnt/b-catenin and EZH2-mediated transcriptional repression. Our lab has identified CCN6 as a tumor suppressor in mBrCA. MMTV-Cre;Ccn6fl/fl (CCN6KO) mice develop spindle mBrCAs and CCN6 is reduced/lost in 68% of human mBrCAs. Recently, we have demonstrated that the tumor suppressor function of CCN6 in spindle mBrCA requires activation of Wnt/b-catenin signaling pathway. Here, we tested the hypothesis that CCN6 KO leads to the upregulation of EZH2 histone methyltransferase promoting mBrCA. Furthermore, we investigated the requirement for the activation of the Wnt/b-catenin pathway in this mechanism. Methods: To test the effect of CCN6/b-catenin on EZH2 gene and protein expression we performed IHC, IF, qRT-PCR, ChIP-Seq, RNA-seq, invasion and adhesion assays, EZH2 reporter assay and immunoblots in mBrCA cell lines and MMTV-Cre;Ccn6fl/fl tumors. To investigate the role of CCN6KO-induced b-catenin activation on EZH2 activity and neoplastic functions we employed three independent approaches: i) Expression of a dominant-negative Tcf4 (dnTcf4) rescued with EZH2-WT, dSET and dNLS domain mutants versus vector in MMTV-Cre;Ccn6fl/fl tumor-derived cells; ii) Expression of a constitutively active mutant (S33Y) b-catenin in concert with treatment with recombinant human CCN6 (rhCCN6; 500 ug/ml) versus control; iii) Syngeneic orthotopic mammary tumor transplants of MMTV-Cre;Ccn6fl/fl were used for in vivo rescue experiments with rhCCN6 or BSA. To assess the therapeutic benefit of inhibiting EZH2 methyltransferase activity, MMTV-Cre;Ccn6fl/fl tumor cells (CCN6KO cells) were implanted orthotopically or intracardially in FVB mice, followed by treatment with EPZ-6438 (a selective EZH2 methyltransferase inhibitor) or vehicle. We tested CCN6, b-catenin, and EZH2 expression by IHC in a cohort of 27 human mBrCA tumor samples. Results: CCN6KO-induced b-catenin/TCF activation mediates EZH2 transcriptional upregulation and the deposition of repressive H3K27me3 in spindle mBrCAs. We found that the invasion program triggered by CCN6KO-induced Wnt/b-catenin requires EZH2 catalytic activity as WT-EZH2 (but not dSET-EZH2) rescued the reduced invasion of CCN6KO-dnTcf4 cells. RNA-seq and 3H3K27 ChIP-seq of CCN6KO-dnTcf4 cells transduced with EZH2-WT or dSET-EZH2 identify specific CCN6KO-b-catenin/Tcf targets that require EZH2 transcriptional repressor function. In vivo, administration of CCN6 protein to MMTV-Cre;Ccn6fl/fl tumor transplants reduces tumor growth and nuclear b-catenin, EZH2 and 3H3K27 in the tumors. Pharmacologic inhibition of EZH2 reduces the growth and metastasis of CCN6KO mBrCA tumors and improves survival. We identify a subset of human spindle mBrCA (54%) that display a CCN6Low/nuclear b-cat/EZH2High phenotype. Conclusion: We found a critical role for EZH2 activation in CCN6-deficient mBrCA tumor phenotypes via b-catenin/TCF Wnt canonical signaling. We demonstrate the effectiveness of pharmacological inhibition of EZH2 methyltransferase activity in reducing primary tumor growth and distant metastasis in mouse models of spindle mBrCA. In clinical samples, low CCN6 is significantly associated with activated b-catenin and high EZH2 in spindle mBrCAs compared to other subtypes. These data reveal a novel tumor suppressor mechanism of CCN6 and provide compelling evidence supporting the potential therapeutic value of CCN6 restoration, b-catenin or EZH2 inhibition as promising approaches for the treatment of spindle mBrCAs. Citation Format: Maria Gonzalez, Ahmad Eido, GIUSEPPINA AUGIMERI, Celina Kleer. EZH2 histone methyltransferase activity promotes spindle metaplastic breast carcinoma metastasis and is induced by CCN6 knockout/b-catenin/TCF axis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-24-05.

Abstract PO2-19-08: INAVO121: Phase III study of inavolisib + fulvestrant vs alpelisib + fulvestrant in patients with hormone receptor-positive, HER2-negative, PIK3CA-mutated locally advanced or metastatic breast cancer

Abstract BACKGROUND Standard-of-care (SoC) endocrine therapy (ET) for patients (pts) with hormone receptor-positive, HER2-negative, PIK3CA-mutated locally advanced or metastatic breast cancer (HR+, HER2–, PIK3CA-mut LA/mBC) was transformed by combinations with cyclin-dependent kinase 4/6 inhibitors (CDK4/6is); a CDK4/6i-based combination is approved in high-risk early BC. However, in most pts, mechanisms of resistance that emerge during or after treatment with a CDK4/6i and ET combination lead to relapse/disease progression. Dysregulating mutations in PIK3CA, occurring in ~40% of HR+, HER2– BCs, represent a common mechanism of resistance to CDK4/6is and ET combinations. Alpelisib (ALP; a selective PI3Kα inhibitor; PI3Kαi) + fulvestrant (FUL) is approved for pts with HR+, HER2–, PIK3CA-mut LA/mBC, but its widespread implementation in clinical practice has been challenging. As such, there is a significant need to develop PI3Kαis with a better therapeutic index. Inavolisib (INAVO) is a highly potent and selective PI3Kαi that also facilitates the degradation of mutated PI3Kα isoform. INAVO has demonstrated manageable safety/tolerability, alone and in combination with SoC treatments in HR+, HER2–, PIK3CA-mut LA/mBC. Moreover, an ongoing Phase I trial showed that INAVO + FUL elicited encouraging preliminary antitumor activity in heavily pretreated pts, including a CDK4/6i-based regimen. TRIAL DESIGN INAVO121 is a Phase III, randomized, open-label study. Pts are randomized 1:1 to receive INAVO (9 mg oral daily; PO QD) + FUL (500 mg intramuscularly on Days [D] 1 and 15 of Cycle 1, then D1 of subsequent cycles), or ALP (300 mg PO QD) + FUL. Randomization is stratified by visceral disease (yes vs no) and prior CDK4/6i therapy (adjuvant vs metastatic setting). Pts will receive treatment until disease progression or unacceptable toxicity. ELIGIBILITY CRITERIA Pts have HR+, HER2–, PIK3CA-mut LA/mBC (confirmed by circulating-tumor DNA or tumor tissue), adequate hematologic and organ function, and disease progression after or during treatment with a CDK4/6i-based regimen. Up to two prior lines of systemic therapy in LA/mBC, including one line of chemotherapy, are allowed. AIMS The primary endpoint is progression-free survival (PFS) by blinded independent central review (BICR). Secondary endpoints include overall survival, BICR-objective response rate, BICR-best overall response, BICR-duration of response, BICR-clinical benefit rate, safety, tolerability, pt-reported outcomes, and pharmacokinetics. STATISTICAL METHODS A stratified log-rank test at an overall 0.05 significance level (two-sided) will be used for the primary endpoint analysis. Median PFS will be estimated using Kaplan–Meier methodology. An independent data monitoring committee will be in place for safety and efficacy. ACCRUAL The study is open for enrollment and has randomized four pts; the study is targeting 400 pts at ~200 sites globally. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number NCT05646862. This abstract was originally presented at ASCO 2023 (TPS1123). Citation Format: Dejan Juric, Kevin Kalinsky, Seock-Ah Im, Eva Ciruelos, Giampaolo Bianchini, Carlos Barrios, William Jacot, Peter Schmid, Sherene Loi, Hope Rugo, Veronica Craine, Katherine Hutchinson, Aulde Flechais, Eirini Thanopoulou, Nadia Harbeck. INAVO121: Phase III study of inavolisib + fulvestrant vs alpelisib + fulvestrant in patients with hormone receptor-positive, HER2-negative, PIK3CA-mutated locally advanced or metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-19-08.

Discovery of BIO-8169─A Highly Potent, Selective, and Brain-Penetrant IRAK4 Inhibitor for the Treatment of Neuroinflammation.

Interleukin receptor associated kinase 4 (IRAK4) plays an important role in innate immune signaling through Toll-like and interleukin-1 receptors and represents an attractive target for the treatment of inflammatory diseases and cancer. We previously reported the development of a potent, selective, and brain-penetrant imidazopyrimidine series of IRAK4 inhibitors. However, lead molecule BIO-7488 (1) suffered from low solubility which led to variable PK, compound accumulation, and poor in vivo tolerability. Herein, we describe the discovery of a series of pyridone analogs with improved solubility which are highly potent, selective and demonstrate desirable PK profiles including good oral bioavailability and excellent brain penetration. BIO-8169 (2) reduced the in vivo production of pro-inflammatory cytokines, was well tolerated in safety studies in rodents and dog at margins well above the predicted efficacious exposure and showed promising results in a mouse model for multiple sclerosis.

Abstract PO1-18-05: Combination treatment with CDK2 inhibitor (BLU-222) and either palbociclib or ribociclib is synergistic in pre-clinical models of CDK4/6 inhibitor-resistant breast cancer

Abstract Background: Cyclin-dependent-kinase-4/6 inhibitors (CDK4/6 inhibitors) plus endocrine therapy (ET) is the standard of care first-line treatment for patients with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC). However, since most patients progress following long-term treatment, resistance to CDK4/6 inhibitors plus ET remains a clinical problem with limited therapeutic options. Here we show that a potent and selective CDK2 inhibitor, BLU-222, while effective as a single agent, exhibited enhanced, synergistic activity when combined with palbociclib or ribociclib in both in vitro and in vivo (patient-derived xenografts-PDX) models of HR+/HER2- breast cancer resistant to CDK4/6 inhibitors. Methods: MCF7 and T47D palbociclib-resistant (PR) breast cancer cell lines were generated by culturing cells in media supplemented with increasing concentrations of palbociclib, starting at 1.2 µM and reaching a final concentration of 4.8 µM in a stepwise manner over a 6-month period. The single agent activity of BLU-222 and the combination effect of BLU-222 plus palbociclib in vitro were evaluated using the highest single agent model by SynergyFinder. The efficacy of BLU-222 as a single agent or in combination with palbociclib or ribociclib was also assessed in two PDX models (PR 1 and 2) from patients with acquired resistance (i.e. progressed following >6 months of treatment) to palbociclib plus letrozole treatment, and another two PDX models (PR 3 and 4) from patients who were intrinsically resistant (i.e. progressed following < 3 months of treatment) to palbociclib plus fulvestrant or letrozole, respectively. Results: In palbociclib-resistant MCF7 and T47D cells, protein levels of cyclin E and CDK2 were significantly upregulated, but Rb and p21 levels were downregulated compared to the parental cells. While these PR cells were completely refractory to palbociclib, they were significantly more sensitive to BLU-222. Moreover, combining BLU-222 with palbociclib demonstrated a strong synergistic effect in PR cells accompanied by enhanced apoptosis and cell cycle accumulation in G1 or G2/M phases. Consistent with these in vitro findings, combination treatment with BLU-222 (60 mg/kg; b.i.d.) and palbociclib (50 mg/kg; q.d.) or ribociclib (50 mg/kg; q.d.) exhibited significant antitumor activity in all four PDX models, as compared to either treatment alone. The combination of BLU-222 plus the CDK4/6 inhibitor induced durable tumor regression and prolonged survival, which continued unabated following drug removal. Mechanistically, treatment of PR cells and palbociclib-resistant PDX models with BLU-222 as a single agent, resulted in the induction of p21, which can sensitize the cells to palbociclib. Conclusions: These results show robust activity of BLU-222 in combination with CDK4/6 inhibitors in breast cancer cell lines and PDX models resistant to CDK4/6 inhibitors, providing a strong rationale for advancing BLU-222 plus CDK4/6 inhibitor treatment to clinical development in HR-positive/HER2-negative breast cancer patients who have progressed on CDK4/6 inhibitors. Citation Format: Linjie Luo, Juliana Navarro-Yepes, Yan Wang, Tuyen Bui, Nicole Kettner, Debu Tripathy, Kelly Hunt, Kerrie Faia, Khandan Keyomarsi. Combination treatment with CDK2 inhibitor (BLU-222) and either palbociclib or ribociclib is synergistic in pre-clinical models of CDK4/6 inhibitor-resistant breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-18-05.

Abstract RF01-04: Final results from the phase 2, open-label FOENIX-MBC2 study: efficacy and safety of futibatinib in adult patients with locally advanced/metastatic HR+/HER2− breast cancer harboring high-level FGFR1 gene amplification

Abstract Background: Fibroblast growth factor receptor 1 (FGFR1) gene amplification and overexpression is associated with an adverse prognosis in hormone receptor–positive (HR+)/human epidermal growth factor receptor 2–negative (HER2−) breast cancer and is observed in ~10% of all invasive breast cancers. The phase 2 FOENIX-MBC2 study (NCT04024436) was designed to evaluate the effect of futibatinib, a highly selective and potent irreversible covalent inhibitor of FGFR1–4 (FDA-approved for intrahepatic cholangiocarcinoma), used either alone or in combination with fulvestrant in patients with metastatic breast cancer. Here, we report final efficacy and safety data for the cohort of patients receiving futibatinib plus fulvestrant for HR+/HER2− breast cancer harboring high-level FGFR1 gene amplification. Methods: Patients were eligible if they had disease progression after prior therapy for advanced/metastatic disease, had measurable disease per RECIST v1.1, had an ECOG performance status of 0 or 1, were fulvestrant-naïve, and had previously received 1–2 endocrine-containing therapies, ≤1 chemotherapy regimen, and a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor for advanced cancer (unless ineligible). High-level FGFR1 gene amplification, determined in tumor tissue using next-generation sequencing, fluorescence in situ hybridization (FISH), or similar assays, was defined as FGFR1/centromere 8 ratio ≥5 or FGFR1 copy number ≥10 signals per cell. Local FGFR1 determination results were confirmed in tumor tissue by a central laboratory using FISH. Patients received oral futibatinib 20 mg once daily and standard fulvestrant dosing until disease progression, unacceptable toxicity, or other discontinuation criteria were met. The primary endpoint was the 6-month progression-free survival (PFS) rate. Key secondary endpoints included objective response rate (ORR), PFS, and overall safety. Results: Overall, 22 female patients were enrolled in this cohort. Patients were a median age of 58 years, had received a median of 3 lines of any prior systemic anticancer therapy, and had all received CDK4/6 inhibitor pretreatment. PFS at 6 months was observed in 10 (45.5%) patients (95% CI: 24.4, 67.8) and the median PFS was 7.2 (95% confidence interval [CI]: 2.1, 7.6) months. Four patients had a confirmed partial response (ORR: 18.2%; 95% CI: 5.2, 40.3). The median duration of response was 6.3 (range: 3.3–12.8) months. All patients had ≥1 treatment-related adverse event (TRAE), the most common being hyperphosphatemia (95.5%), alopecia (54.5%), constipation (45.5%), and dry mouth (40.9%). There were 5 (22.7%) patients with a Grade 3 TRAE (no Grade 4 or 5). TRAEs leading to study treatment interruption or reduction were seen in 9 (40.9%) and 15 (68.2%) patients, respectively. There were 2 (9.1%) patients who had TRAEs leading to study treatment discontinuation. No treatment-related serious adverse events were reported. Conclusions: Futibatinib plus fulvestrant showed antitumor activity in patients with advanced HR+/HER2− breast cancer with FGFR1 amplification progressing on prior CDK4/6 inhibitors, with a numerically higher ORR and doubling in PFS relative to historical fulvestrant results in post-CDK4/6 patients. The safety profile was consistent with those of the individual study drugs. Further biomarker work is ongoing. Citation Format: Senthil Damodaran, Fabrice André, Nisha Unni, Marta Ferreira, Karthik Giridhar, Brooke Daniel, Marco Colleoni, Luis Costa, Thomas Bachelot, Ciara O’Brien, Gail Wright, Masashi Shimura, Gareth Tomlinson, Maciej Gil, Nicholas Turner. Final results from the phase 2, open-label FOENIX-MBC2 study: efficacy and safety of futibatinib in adult patients with locally advanced/metastatic HR+/HER2− breast cancer harboring high-level FGFR1 gene amplification [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr RF01-04.

Upadacitinib Rapidly Improves Patient-Reported Outcomes in Atopic Dermatitis: 16-Week Results from Phase3 Clinical Trials (Measure Up1 and 2).

Atopic dermatitis (AD) is characterized by intense itch and other symptoms that negatively impact quality of life (QoL). This study evaluates the effect of upadacitinib (an oral selective Janus kinase inhibitor) monotherapy on patient-reported outcomes (PROs) among adults and adolescents with moderate-to-severe AD over 16weeks. This integrated analysis of the double-blind, placebo-controlled periods of phase3 monotherapy clinical trials Measure Up1 (NCT03569293) and Measure Up2 (NCT03607422) assessed itch (Worst Pruritus Numerical Rating Scale [WP-NRS] and SCORing Atopic Dermatitis [SCORAD]), skin pain and symptom severity (AD Symptom Scale), symptom frequency (Patient-Oriented Eczema Measure), sleep (AD Impact Scale [ADerm-IS] and SCORAD), daily activities and emotional state (ADerm-IS), QoL (Dermatology Life Quality Index [DLQI] and Children's DLQI), mental health (Hospital Anxiety and Depression Scale), and patient impressions (Patient Global Impression of Severity, Patient Global Impression of Change, and Patient Global Impression of Treatment). Data from 1683 patients (upadacitinib 15mg, n = 557; upadacitinib 30mg, n = 567; placebo, n = 559) were analyzed. A greater proportion of patients receiving upadacitinib versus placebo experienced improvements in itch (≥ 4-point improvement on WP-NRS) by week1 (upadacitinib 15mg, 11.2%; upadacitinib 30mg, 17.7%; placebo, 0.5%; P < 0.001), with response rates sustained through week16 (upadacitinib 15mg, 47.1%; upadacitinib 30mg, 59.8%; placebo, 10.4%; P < 0.001). Improvements were similar for PROs assessing skin pain/symptoms, sleep, daily activities, QoL, emotional state, mental health, and patient impressions of disease severity and treatment. Responses generally improved rapidly (within 1-2weeks), increased through weeks 4-6, and were maintained through week16. Once-daily oral upadacitinib monotherapy improved response rates across PROs compared with placebo. Upadacitinib therapy resulted in rapid, sustained improvements in PROs measuring symptom burden and QoL in adults and adolescents with moderate-to-severeAD. ClinicalTrials.gov identifiers, NCT03569293 and NCT03607422.

Emerging DNA Methylome Targets in FLT3-ITD-Positive Acute Myeloid Leukemia: Combination Therapy with Clinically Approved FLT3 Inhibitors.

The internal tandem duplication (ITD) mutation of the FMS-like receptor tyrosine kinase 3 (FLT3-ITD) is the most common mutation observed in approximately 30% of acute myeloid leukemia (AML) patients. It represents poor prognosis due to continuous activation of downstream growth-promoting signaling pathways such as STAT5 and PI3K/AKT. Hence, FLT3 is considered an attractive druggable target; selective small FLT3 inhibitors (FLT3Is), such as midostaurin and quizartinib, have been clinically approved. However, patients possess generally poor remission rates and acquired resistance when FLT3I used alone. Various factors in patients could cause these adverse effects including altered epigenetic regulation, causing mainly abnormal gene expression patterns. Epigenetic modifications are required for hematopoietic stem cell (HSC) self-renewal and differentiation; however, critical driver mutations have been identified in genes controlling DNA methylation (such as DNMT3A, TET2, IDH1/2). These regulators cause leukemia pathogenesis and affect disease diagnosis and prognosis when they co-occur with FLT3-ITD mutation. Therefore, understanding the role of different epigenetic alterations in FLT3-ITD AML pathogenesis and how they modulate FLT3I's activity is important to rationalize combinational treatment approaches including FLT3Is and modulators of methylation regulators or pathways. Data from ongoing pre-clinical and clinical studies will further precisely define the potential use of epigenetic therapy together with FLT3Is especially after characterized patients' mutational status in terms of FLT3 and DNA methlome regulators.

Abstract PO4-06-07: Efficacy and safety of futibatinib in patients with locally advanced/metastatic triple-negative breast cancer harboring FGFR2 gene amplification: final results from the phase 2, open-label FOENIX-MBC2 study

Abstract Background: Triple-negative breast cancer (TNBC) accounts for ~15% of breast cancers and represents an aggressive subtype with limited targeted therapeutic options. Fibroblast growth factor receptor (FGFR) signaling plays an important role in breast tumorigenesis and metastasis. The phase 2 FOENIX-MBC2 study (NCT04024436) was designed to evaluate responses to futibatinib, a highly selective and potent irreversible covalent inhibitor of FGFR1–4 (FDA-approved for intrahepatic cholangiocarcinoma), in patients with metastatic breast cancer. Here, we report final efficacy and safety data for futibatinib in the cohort of patients with advanced/metastatic TNBC harboring FGFR2 gene amplification. Methods: Eligible patients had locally advanced/metastatic TNBC with measurable disease per RECIST v1.1, an ECOG performance status of 0/1, and progressive disease after ≥1 prior chemotherapy-containing regimen for advanced disease. Patients were positive for FGFR2 gene amplification determined by analysis of tumor tissue or circulating tumor DNA. Patients received oral futibatinib 20 mg once daily until disease progression, unacceptable toxicity, or other discontinuation criteria were met. The primary endpoint was objective response rate (ORR) by RECIST v1.1 in patients with centrally confirmed FGFR2 amplification. Responses (complete response and partial response) required confirmation after at least 4 weeks. Secondary endpoints included the 6-month progression-free survival (PFS) rate, PFS, duration of response (DOR), and overall safety. Results: Overall, 21 female patients with TNBC were enrolled (median age: 53 years) in this cohort. Patients had received a median 5 lines of prior systemic therapy. Overall, 2 patients had a confirmed partial response (ORR: 9.5%; 95% confidence interval [CI]: 1.2, 30.4), with a median DOR of 6.1 months (range: 3.1−9.2 months). Five (23.8%) patients had stable disease. PFS at 6 months was observed in 4 patients (19.0%; 95% CI: 5.4, 41.9) and the median PFS was 1.9 months (95% CI: 1.6, 4.0). Twenty patients (95.2%) had ≥1 treatment-related adverse event (TRAE), including 7 (33.3%) with a Grade 3 TRAE (no Grade 4 or 5). Common TRAEs (any grade) included hyperphosphatemia (85.7% of patients), constipation, diarrhea, fatigue, and dry skin (each in 23.8% of patients). Anemia was the only Grade 3 TRAE observed in more than 1 patient (n=2, 9.5%). Overall, 28.6% of patients had a serious adverse event (SAE; any cause), and 1 patient had an SAE leading to death (ischemic stroke). None of the SAEs or deaths were considered treatment-related. Conclusions: In heavily pretreated patients with metastatic TNBC harboring FGFR2 gene amplification, futibatinib monotherapy demonstrated modest anticancer activity. Futibatinib was tolerable and had an acceptable safety profile, consistent with previous data. Further biomarker work to identify patients who might benefit most from futibatinib is ongoing. Clinical trial information: NCT04024436 Citation Format: Antonio Giordano, Nisha Unni, Senthil Damodaran, Hope Rugo, Timothy Crook, Thomas Bachelot, Federico Piacentini, Hector Soto Parra, Ian Krop, Masashi Shimura, Gareth Tomlinson, Maciej Gil, Nicholas Turner, Fabrice André. Efficacy and safety of futibatinib in patients with locally advanced/metastatic triple-negative breast cancer harboring FGFR2 gene amplification: final results from the phase 2, open-label FOENIX-MBC2 study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-06-07.

Abstract PO1-04-14: PLK1 Inhibitor Onvansertib Extends the Response and Overcomes Resistance to Paclitaxel in Palbociclib-resistant HR+ Breast Cancer Patient-derived Xenografts

Abstract Paclitaxel is a first-line chemotherapy for hormone receptor positive (HR+) metastatic breast cancer patients after progression on a combination of endocrine and CDK4/6 inhibitor therapy. Response rate to paclitaxel ranges between 20-40%, and most patients progress due to intrinsic or acquired resistance, leaving them with limited treatment choices. Therapeutic strategies to overcome paclitaxel resistance and extend its clinical benefit are urgently needed. Paclitaxel-resistant tumors have increased expression of polo-like kinase 1 (PLK1), a serine-threonine-protein kinase that regulates mitosis and cell cycle progression. PLK1 has also been shown to mediate resistance to CDK4/6 inhibitor palbociclib in HR+ breast cancer. Onvansertib is an orally bioavailable, highly potent, and selective PLK1 inhibitor in clinical development. Onvansertib exhibited synergy in vitro and showed potent anti-tumor activity in vivo in combination with paclitaxel in ovarian cancer and triple negative breast cancer (TNBC) preclinical models. A phase 1b/2 clinical trial is ongoing to evaluate the safety and efficacy of onvansertib plus paclitaxel in advanced TNBC (NCT05383196). Here we investigated whether the potential of onvansertib and paclitaxel combination could be extended to HR+ breast cancer. Co-treatment with onvansertib and paclitaxel synergistically inhibited the viability of HR+ breast cancer cell lines (MCF-7, T-47D, EFM-19, CAMA-1, ZR-75-1). Compared to the single agents, the combination induced increased apoptosis. The combination was further tested in vivo in patient-derived xenograft (PDX) models. To this end, six HR+ breast cancer PDXs with intrinsic or acquired resistance to palbociclib were established from primary breast tumors (n=1) or metastatic bone biopsies (n=5). The PDX tumors were engrafted subcutaneously in nude mice and the effect of onvansertib (45 mg/kg, oral, 5 days a week) and paclitaxel (15-25mg/kg, IP, once a week) was investigated as monotherapy and in combination. The combination of onvansertib and paclitaxel was tolerated with minimal toxicity and showed enhanced anti-tumor activity compared to either agent alone in all 6 PDX models. Paclitaxel and onvansertib monotherapies had little to no anti-tumor activity in 4 out of 6 PDX models (HBCx124palboR25, HBCx-139 palboR5, HBCx-202 and HBCx-131). Importantly, the combination of onvansertib and paclitaxel induced strong anti-tumor activity in these 4 models. Tumor regression was observed in the 2 PDX models with acquired resistance to palbociclib, HBCx-124palboR25 and HBCx-139palboR5, with 62% (5/8 mice) and 54% (6/11 mice) complete response rates, respectively. The combination showed tumor stasis in HBCx-131 and induced tumor regression in HBCx-202, established from patient resistant to palbociclib. In 2 of the 6 PDXs, paclitaxel exhibited anti-tumor activity, inducing tumor regression in HBCx-137paboR26 and tumor stasis in HBCx-86. In comparison, the combination of onvansertib and paclitaxel had greater activity, inducing tumor regression in both models with a higher rate of complete response than the monotherapy. Complete response rates for paclitaxel versus the combination were 62% and 100% in the HBCx-137palboR26 model and 0% and 67% in the HBCx-86 model. Notably, the antitumor activity of the onvansertib and paclitaxel combination was very durable, showing a robust delay in tumor relapse after stopping therapy. Together, our data strongly support that combining paclitaxel with the PLK1 inhibitor onvansertib extends its benefit and overcomes paclitaxel resistance, and represents a promising therapeutic strategy for HR+ breast cancer patients after progression on a combination of endocrine and CDK4/6 inhibitor therapy. Citation Format: Maya Ridinger, Pierre Painsec, Sreeja Sreekumar, Dalia Gonzalez, Davis Klein, Laura Sourd, Elodie Montaudon, Paul Cottu, Tod Smeal, Elisabetta Marangoni. PLK1 Inhibitor Onvansertib Extends the Response and Overcomes Resistance to Paclitaxel in Palbociclib-resistant HR+ Breast Cancer Patient-derived Xenografts [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-04-14.

Abstract PO5-11-08: Assessing practice patterns of antidepressant medication and tamoxifen use among patients with hormone receptor-positive breast cancer

Abstract Background: Treatment with endocrine therapy such as tamoxifen has been identified as one of the most important variables linked with survival among women with hormone receptor-positive breast cancer (BC). There is significant risk reduction of BC recurrence and BC mortality at 15 years among patients treated with tamoxifen for 5 years compared to no endocrine therapy. Tamoxifen is metabolized in the liver via multiple cytochrome P (CYP) isoforms. To ensure optimal efficacy of tamoxifen, consideration must be given to concomitant use of other commonly prescribed drugs such as antidepressants. Some selective serotonin reuptake inhibitors (SSRIs) are potent inhibitors of CYP2D6, an enzyme that metabolizes tamoxifen into its active metabolite, endoxifen, which has anti-tumor effect. Such inhibition can reduce the plasma concentration of endoxifen which could lead to higher rates of BC recurrence. This resulted in an FDA black box warning discouraging concurrent prescriptions of tamoxifen and SSRIs, yet clinical data to support this warning is lacking. Our aim is to describe the practice patterns of concomitant use of tamoxifen and antidepressant medication at our institution. Methods: This is a single institution retrospective study that included adult women, ages 18-99, with stage I-IV BC, who received adjuvant tamoxifen and were taking an antidepressant medication between years 2016-2021. Patients were identified from a tumor registry database. Patient demographics and tumor characteristics were collected via electronic medical record. Results: A total of 419 patients met the inclusion criteria. At the start of tamoxifen therapy, 348 women were on at least one antidepressant, mostly for Major Depressive Disorder (86%). Of those women, 22% were prescribed a strong/moderately potent CYP inhibitor (paroxetine, fluoxetine, duloxetine, or bupropion) and 43% were prescribed weak or non-CYP inhibiting SSRIs (citalopram, escitalopram, fluvoxamine, and sertraline). The most commonly prescribed antidepressants at the start of tamoxifen, alone or in combination with a second antidepressant, were: venlafaxine (30%), escitalopram (17%), sertraline (13%), citalopram (12%) and duloxetine (10%). Main prescribers of antidepressants were primary care physicians (70%), psychiatrists (10%) followed by academic medical oncologists (7%) and regional medical oncologists (6%). Interestingly, the majority of women continued taking the same antidepressant after starting tamoxifen (76%) while, at least 10% of patients changed anti-depressant classes prior to starting tamoxifen, due to concern for drug-drug interaction. When a different class of antidepressant was chosen after starting tamoxifen (22%), serotonin and norepinephrine reuptake inhibitors (SNRIs) were the most frequent class (48%), followed by a different SSRI (42%). The time in which the antidepressant change occurred was variable, but most commonly prior to initiating tamoxifen. Conclusion: Concurrent use of tamoxifen and antidepressant medications is common. Theoretical risk of reduced efficacy of tamoxifen with inhibitors of CYP leads to medication changes for some but not all patients requiring tamoxifen and an antidepressant medication. This can have clinical implications as stability on a specific antidepressant is important for patients and adjustment may impact control of their mood disorder. In some cases, even if a drug-drug interaction was identified, some patients chose to continue their current antidepressant due to concerns of mood de-stabilization, and in other cases, aromatase inhibitors were started as an alternative. These findings highlight differences in practice patterns for which additional guidance may be helpful in bringing awareness and standardization to care. Citation Format: Mariah Ondeck, Bennett Osantowski, Nerea Lopetegui-Lia, Wei Wei, Alexandra Murray, Amanda Maggiotto, Halle Moore, Erin Roesch. Assessing practice patterns of antidepressant medication and tamoxifen use among patients with hormone receptor-positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-11-08.

Integrin αVβ3 antagonist-c(RGDyk) peptide attenuates the progression of ossification of the posterior longitudinal ligament by inhibiting osteogenesis and angiogenesis

BackgroundOssification of the posterior longitudinal ligament (OPLL), an emerging heterotopic ossification disease, causes spinal cord compression, resulting in motor and sensory dysfunction. The etiology of OPLL remains unclear but may involve integrin αVβ3 regulating the process of osteogenesis and angiogenesis. In this study, we focused on the role of integrin αVβ3 in OPLL and explored the underlying mechanism by which the c(RGDyk) peptide acts as a potent and selective integrin αVβ3 inhibitor to inhibit osteogenesis and angiogenesis in OPLL.MethodsOPLL or control ligament samples were collected in surgery. For OPLL samples, RNA-sequencing results revealed activation of the integrin family, particularly integrin αVβ3. Integrin αVβ3 expression was detected by qPCR, Western blotting, and immunohistochemical analysis. Fluorescence microscopy was used to observe the targeted inhibition of integrin αVβ3 by the c(RGDyk) peptide on ligaments fibroblasts (LFs) derived from patients with OPLL and endothelial cells (ECs). The effect of c(RGDyk) peptide on the ossification of pathogenic LFs was detected using qPCR, Western blotting. Alkaline phosphatase staining or alizarin red staining were used to test the osteogenic capability. The effect of the c(RGDyk) peptide on angiogenesis was determined by EC migration and tube formation assays. The effects of the c(RGDyk) peptide on heterotopic bone formation were evaluated by micro-CT, histological, immunohistochemical, and immunofluorescence analysis in vivo.ResultsThe results indicated that after being treated with c(RGDyk), the osteogenic differentiation of LFs was significantly decreased. Moreover, the c(RGDyk) peptide inhibited the migration of ECs and thus prevented the nutritional support required for osteogenesis. Furthermore, the c(RGDyk) peptide inhibited ectopic bone formation in mice. Mechanistic analysis revealed that c(RGDyk) peptide could inhibit osteogenesis and angiogenesis in OPLL by targeting integrin αVβ3 and regulating the FAK/ERK pathway.ConclusionsTherefore, the integrin αVβ3 appears to be an emerging therapeutic target for OPLL, and the c(RGDyk) peptide has dual inhibitory effects that may be valuable for the new therapeutic strategy of OPLL.

Abstract PO3-25-08: Artificial Intelligence-based screening of small molecule inhibitors of phosphoenolpyruvate carboxykinase 2 (PCK2), a novel cancer therapeutic target

Abstract Background: Metabolic rewiring is a hallmark of cancer that is often mediated by alterations in metabolic isozyme expression. Isozymes that are overexpressed in cancer and catalyze rate limiting steps in key metabolic processes are potential therapeutic targets. We previously identified phosphoenolpyruvate carboxykinase 2 (PCK2) as cancer dominant isoform, required for maintaining high metabolic activity and proliferation of lung, prostate, and breast cancer (BC) cells in vitro and in vivo. No PCK2 specific small molecule inhibitors exist. Methods: mRNA expression levels were assessed in the TCGA data. PCK2 MISSION shRNAs (Millipore) were used to knock-down expression of PCK2 in BC cells. Alterations in metabolic flux caused by PCK2 down-regulation were examined via 13C-labeling and mass spectrometry using a SCIEX 5500 QTRAP and SelexION instrument for mobility separation of metabolites. The AtomNetTM (Atomwise Inc.) deep convolutional neural network structure-based drug design software was used to identify candidate small molecule PCK2 inhibitors which were tested in PCK1 and PCK2 in vitro enzyme activity assays. The lead compound was assessed for drug-like properties by QickPropV4.0.001w, and its growth inhibitory activity was tested in MDA-MB-321 and BT-549 cells. Results: Analysis of mRNA levels in TNBC samples revealed a significant decrease in PCK1 expression compared to normal tissues, while PCK2 expression remained elevated or even increased. Quantification of mRNA levels in TNBC cell lines confirmed the higher expression of PCK2 compared to PCK1. To assess functional significance of PCK2 expression, we downregulated PCK2 using shRNA constructs in TNBC cell lines. Western blot analysis confirmed efficient knockdown of PCK2 protein without affecting PCK1 expression. Clonogenic assays demonstrated that PCK2-depleted BT-549 and MDA-MB-231 cells exhibited impaired proliferation, with reduced colony number and size compared to control cells. Metabolic analysis of PCK2-depleted TNBC cells demonstrated decreased levels of glycolytic and TCA intermediates and reduced flux through pyruvate carboxylase, indicating altered metabolic pathways upon PCK2 depletion. To identify potential inhibitors of PCK2, virtual screening was conducted using compound structures. We used a PCK2 protein structure homology model and designated the 3-mercaptopicolinic acid-binding site of the PCK1 structure as the site of interest to perform virtual drug screening of 7 million diverse compounds. The first screen yielded 86 structures to be tested in vitro, of which 5 demonstrated &amp;gt; 16% PCK2 inhibition. The top hit (IC50=2.4µM) was used to refine a second round of in silico screen that yielded 87 second-round candidates that were assessed for PCK2 inhibition in vitro. 3-(3,4-dihydroxyphenyl)-2-hydroxypropanoate emerged as the lead compound. QickProp predicted favorable absorption, distribution, metabolism, and excretion properties, but relatively low cell permeability (apparent Caco-2 and MDCK2 cell permeabilities 18 nm/sec and 8 nm/sec, respectively). The specificity of 3-(3,4-dihydroxyphenyl)-2-hydroxypropanoate was tested in PCK1 and PCK2 enzymatic assays and revealed IC50 of 500nM on PCK1 and an IC50 of 3 nM on PCK2. We next tested the cell growth inhibitory effect of 3-(3,4-dihydroxyphenyl)-2-hydroxypropanoate on parental MDA-MB-231 and BT-549 cells and their PCK2 knockdown clones. Cell growth and viability significantly decreased in the MDA-MD-231 and BT-549 parental cells (the IC50 for MDA-MB-231 was 173 μM) and in shRNA non-targeting control cells, but not in the PCK2 depleted clones, demonstrating PCK2-dependent inhibitory effect. Conclusion: We identified 3-(3,4-dihydroxyphenyl)-2-hydroxypropanoate as a high affinity selective PCK2 enzyme inhibitor. This compound also has significant growth inhibitory activity in BC cell lines in vitro and represents a novel therapeutic lead compound. Citation Format: Alejandro Rios Hoyo, Naing Lin Shan, Hao-Kuen Lin, Gerson Espinoza Campos, Mostafa Ahmed, Sheila Umlauf, Rebecca Cardone, Yulia V. Surovtseva, Vignesh Gunasekharan, Lajos pusztai. Artificial Intelligence-based screening of small molecule inhibitors of phosphoenolpyruvate carboxykinase 2 (PCK2), a novel cancer therapeutic target [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-25-08.

Abstract PS12-03: p53 loss enables HR+ breast cancer escape from CDK4/6 inhibitor-induced quiescence via CDK2

Abstract Background: Inhibition of CDK4/6 kinases has led to improved clinical outcomes in hormone receptor positive (HR+) breast cancer. While these are highly effective therapies, only a minority of patients experience long-term disease control. We sought to determine the genomic configurations and underlying mechanisms associated with long-term response. Methods: To identify genomic patterns associated with clinical outcomes, we analyzed a cohort of 447 patients with metastatic HR+ breast cancer treated at MSK with first-line CDK4/6 inhibitors (CDK4/6i) for which tumor-normal sequencing and long-term clinical follow up were available. To identify the pattern of genomic features associated with longer, intermediate, and short response, we implemented an elastic net Cox regression on binary pathogenic variant status of each gene as well as select clinical features (prior endocrine therapy, endocrine therapy partner, de novo metastatic status). Our principal aim was variable interpretability over pure predictive accuracy. Human HR+ breast cancer models including human breast cancer organoids and cell lines were utilized for mechanistic studies. For validation in a clinical setting, we analyzed the association between Ki67 score after neoadjuvant ribociclib plus endocrine therapy and pre-treatment gene mutation from the FELINE trial [NCT02712723] using a Fisher exact test. Results: Our model identified a “longer response” group (n = 124, 27.7%) from patients with a median progression free survival (PFS) of 32.5 months, compared with an “intermediate” (n = 224, 50.1%, median PFS = 13.7 months) and “short response” group (n = 99, 22.1%, median PFS = 5.84 months). TP53 and MDM2 pathogenic variant status were the most important variables to stratify between these groups, obtaining variable selection frequencies of 1.0 and 0.93 and mean hazard ratios of 2.02 and 1.38, respectively. To elucidate the mechanisms whereby the p53 pathway supports long term response, we generated isogenic and patient derived models of TP53 loss or MDM2 overexpression. Using immunoblotting and cell cycle assays, we found that drug-treated p53 KO cells and MDM2 overexpressing cells effectively suppressed RB1 phosphorylation and blocked in G1 after 24-48 hours. However, upon drug withdrawal, these cells could reenter the cell cycle and promote long-term tumor outgrowth. These effects we observed both in vitro and in vivo. Measures of long-term CDK4/6i response such as expression of senescence associated secretory phenotype genes was abrogated by TP53 loss. Mechanistically, we found persistent phosphorylation of the p130 RB1-like protein in the p53 KO cells. Phosphorylation of p130 impaired its interaction with E2F4, thereby blocking DREAM complex assembly and promoting cell cycle reentry. Inhibition of phosphorylation of p130 via p21 overexpression or by selective CDK2 inhibitors could restore irreversible cell cycle arrest in p53 KO cells. The combination of CDK2 and CDK4/6 inhibition led to long-term tumor growth suppression in models with mutant TP53. To validate the human relevance of TP53 mediating CDK4/6i response, we analyzed longitudinal samples from the FELINE trial that evaluated efficacy and feasibility of neoadjuvant ribociclib plus endocrine therapy. Of 45 evaluable patients, 13 (28.9%) harbored a pre-treatment TP53 loss of function variant. Of these 13 cases, 7 (53.8%) did not achieve a low ( &amp;lt; 10%) Ki-67 upon surgical resection as compared to TP53 wildtype tumors (n=32), only one (3.2%) of which did not achieve a low Ki-67 [OR 32.1, 95% CI 3.28 – 1660.3, p = 0.00026]. Conclusion: Loss of p53 was strongly associated with lack of long-term response to CDK4/6i in patients. Complete inhibition of both CDK4/6 and CDK2 appears to be necessary in order to convert quiescent HR+ tumors cells into durably inhibited and effectively dormant cancers. Citation Format: Rei Kudo, Anton Safonov, Edaise M. da Silva, Qing Li, Hong Shao, Marie Will, Harikrishna Nakshatri, Jorge Reis-Filho, Shom Goel, Andrew Koff, Britta Weigelt, Qamar Khan, Pedram Razavi, Sarat Chandarlapaty. p53 loss enables HR+ breast cancer escape from CDK4/6 inhibitor-induced quiescence via CDK2 [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS12-03.