Breast Cancer Xenograft Model Research Articles

Abstract 1581: KSQ-4279, a first-in-class USP1 inhibitor shows strong combination activity with multiple PARP inhibitors in BRCA mutant cancers

Abstract Tumors harboring BRCA1/2 mutations and other homologous recombination deficiencies are sensitive to agents targeting pathways involved in DNA repair including poly (ADP-ribose) polymerase (PARP) inhibitors, which have been approved for the treatment of BRCA mutant cancers. Despite the clinical benefit with these drugs, many patients achieve incomplete disease control and often develop resistance. By employing our CRISPRomics® technology to screen over 600 cancer cell lines, we identified the deubiquitinating enzyme USP1 as one of the top targets that displays selective anti-tumor activity in ovarian and triple negative breast cancers with homologous recombination deficiencies. Subsequent drug discovery efforts identified KSQ-4279 as a potent and highly selective first-in-class small molecule USP1 inhibitor that is now in clinical development. In preclinical models, we previously demonstrated that KSQ-4279 shows therapeutic potential in combination with olaparib for treating patients who are either intrinsically resistant, or have developed acquired resistance to PARP inhibitors. We performed studies to investigate the therapeutic potential of combining KSQ-4279 across a variety of PARP inhibitors with different ‘PARP trapping’ potencies. Clonogenic assays demonstrated synergistic effects of KSQ-4279 across multiple PARP inhibitors regardless of their PARP trapping potency. Second generation PARP1 selective inhibitors such as AZD5305 are currently in clinical development and may provide a safety and efficacy advantage for patients. We have investigated the potential of combining KSQ-4279 with AZD5305 in a PARP refractory patient-derived triple negative breast cancer (TNBC) xenograft model by evaluating tolerability and anti-tumor efficacy. We observed significantly greater and more durable anti-tumor activity, including regressions, with the combination therapy compared to single agents. Our data supports the clinical testing of KSQ-4279 in combination with PARP inhibitors. Citation Format: Erica Tobin, Pamela Sullivan, Morgan Murray, Hugh Gannon, Anne Dodson, Sol Shenker, Frank Stegmeier, Andrew Wylie, Louise Cadzow. KSQ-4279, a first-in-class USP1 inhibitor shows strong combination activity with multiple PARP inhibitors in BRCA mutant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1581.

Abstract 1884: DB-1310, a novel Her3 targeting antibody-drug conjugate, exhibits therapeutic efficacy for solid tumors

Abstract Background: HER3 (ErbB3), a member of the human epidermal growth factor receptor family, is frequently overexpressed in various cancers. Its high expression is associated with poor prognosis in several solid tumors. Many anti-Her3 antibodies have been developed for cancer therapy. To date, only patritumab deruxtecan (U3-1402) showed clinical efficacy in both NSCLC and breast cancer among all Her3-targeting therapies. DB-1310 is a HER3 ADC composed of a novel humanized anti-Her3 immunoglobulin G1 (IgG1) monoclonal antibody, covalently linked to a proprietary DNA topoisomerase I inhibitor payload via a maleimide tetrapeptide-based cleavable linker with a drug antibody ratio (DAR) of approximately eight. In the present study, we aim to evaluate the efficacy and safety of DB-1310 in preclinical models. Methods: The binding of DB-1310 to Her3 and other HER families was measured by ELISA and SPR. The competition of binding epitope for DB-1310 and patritumab was tested by FACS. The sensitivity of breast cancer and lung cancer cell lines to DB-1310 was evaluated by in vitro cell killing assay. In vivo growth inhibition study evaluated the sensitivity of DB-1310 to Her3-positive breast cancer and lung cancer xenograft models. In addition, the efficacy of DB-1310 was compared to that of patritumab deruxtecan in tumor xenograft models. The pharmacokinetics and safety profile were also measured in cynomolgus monkey. Results: In this study, DB-1310 showed high affinity to both Human and Cyno Her3 without cross reacting with Her2, Her4 or EGFR. DB-1310 binds Her3 using a different epitope from patritumab. DB-1310 has high internalization capability and translocates into lysosomes after internalization. In vitro, DB-1310 exhibited cytotoxicity in a panel of Her3- expression human breast cancer and lung cancer cell lines. It also showed dose-dependent antitumor killing activity in a HER3-positive breast cancer HCC1569 xenograft model and a lung cancer NCI-H441 xenograft model. Tumor regression was observed in a NSCLC patient-derived xenograft model with EGFR mutation under DB-1310 treatment. Moreover, DB-1310 showed stronger tumor growth inhibition than that of patritumab deruxtecan at the same dose. The systemic exposure AUC0-last and Cmax of DB-1310 and total antibody increased dose proportionally from 1 mg/kg to 10 mg/kg with low released payload in serum. The DB-1310 also showed good safety profile with highest non-severely toxic dose (HNSTD) above 30mg/kg. Conclusions: DB-1310 exhibited its efficacy in tumor models both in vitro and in vivo. These studies suggest that DB-1310 as a novel HER3-targeting ADC showed antitumor efficacy for HER3 positive tumors with good safety profile. Citation Format: Xi Li, Jun Yao, Chen Qu, Luo Lan, Bing Li, Yu Zhang, Rong Shi, Haiqing Hua, Yang Qiu. DB-1310, a novel Her3 targeting antibody-drug conjugate, exhibits therapeutic efficacy for solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1884.

Active recruitment of anti-PD-1-conjugated platelets through tumor-selective thrombosis for enhanced anticancer immunotherapy.

Immune checkpoint inhibitors (ICIs) can reinvigorate T cells to eradicate tumor cells, showing great potential in combating various types of tumors. We propose a delivery strategy to enhance tumor-selective ICI accumulation, which leverages the responsiveness of platelets and platelet-derivatives to coagulation cascade signals. A fused protein tTF-RGD targets tumor angiogenic blood vessel endothelial cells and initiates the coagulation locoregionally at the tumor site, forming a "cellular hive" to recruit anti-PD-1 antibody (aPD-1)-conjugated platelets to the tumor site and subsequently activating platelets to release aPD-1 antibody to reactivate T cells for improved immunotherapy. Moreover, on a patient-derived xenograft breast cancer model, the platelet membrane-coated nanoparticles can also respond to the coagulation signals initiated by tTF-RGD, thus enhancing the accumulation and antitumor efficacy of the loaded chemotherapeutics. Our study illustrates a versatile platform technology to enhance the local accumulation of ICIs and chemodrugs by taking advantage of the responsiveness of platelets and platelet derivatives to thrombosis.

Reprogramming anchorage dependency by adherent-to-suspension transition promotes metastatic dissemination

BackgroundAlthough metastasis is the foremost cause of cancer-related death, a specialized mechanism that reprograms anchorage dependency of solid tumor cells into circulating tumor cells (CTCs) during metastatic dissemination remains a critical area of challenge.MethodsWe analyzed blood cell-specific transcripts and selected key Adherent-to-Suspension Transition (AST) factors that are competent to reprogram anchorage dependency of adherent cells into suspension cells in an inducible and reversible manner. The mechanisms of AST were evaluated by a series of in vitro and in vivo assays. Paired samples of primary tumors, CTCs, and metastatic tumors were collected from breast cancer and melanoma mouse xenograft models and patients with de novo metastasis. Analyses of single-cell RNA sequencing (scRNA-seq) and tissue staining were performed to validate the role of AST factors in CTCs. Loss-of-function experiments were performed by shRNA knockdown, gene editing, and pharmacological inhibition to block metastasis and prolong survival.ResultsWe discovered a biological phenomenon referred to as AST that reprograms adherent cells into suspension cells via defined hematopoietic transcriptional regulators, which are hijacked by solid tumor cells to disseminate into CTCs. Induction of AST in adherent cells 1) suppress global integrin/ECM gene expression via Hippo-YAP/TEAD inhibition to evoke spontaneous cell–matrix dissociation and 2) upregulate globin genes that prevent oxidative stress to acquire anoikis resistance, in the absence of lineage differentiation. During dissemination, we uncover the critical roles of AST factors in CTCs derived from patients with de novo metastasis and mouse models. Pharmacological blockade of AST factors via thalidomide derivatives in breast cancer and melanoma cells abrogated CTC formation and suppressed lung metastases without affecting the primary tumor growth.ConclusionWe demonstrate that suspension cells can directly arise from adherent cells by the addition of defined hematopoietic factors that confer metastatic traits. Furthermore, our findings expand the prevailing cancer treatment paradigm toward direct intervention within the metastatic spread of cancer.

Discovery of a Potent and Selective CCR8 Small Molecular Antagonist IPG7236 for the Treatment of Cancer.

Recently, there has been increasing evidence indicating that the CC chemokine receptor 8 (CCR8) plays an important role in mediating the recruitment and immunosuppressive function of regulatory T (Treg) cells in the tumor microenvironment. Therefore, the development of a specific CCR8 antagonist presents a potential therapeutic strategy against cancer. Despite a few small molecules having been reported as CCR8 antagonists, none has progressed to the clinical stage. Herein, we described a potent and selective CCR8 antagonist (compound 1, IPG7236) as the first small molecule to advance to the clinical stage. IPG7236 demonstrated an anti-cancer effect via modulating Treg and cytotoxic T (CD8+ T) cells. IPG7236 alone or in combination with PD-1 antibody exhibited significant tumor suppression effects in the mouse xenograft model of human breast cancer. IPG7236 is a promising clinical candidate that targets CCR8 with excellent in vitro ADMET properties, pharmacokinetics, safety profiles, and in vivo efficacy.

ImmunoPET Imaging Identifies the Optimal Timepoint for Combination Therapy in Xenograft Models of Triple-Negative Breast Cancer.

(1) Purpose: The glycoprotein non-metastatic melanoma B (gpNMB) is a type 1 transmembrane protein that is overexpressed in numerous cancers, including triple-negative breast cancer (TNBC). Its overexpression is associated with lower overall survival of patients with TNBC. Tyrosine kinase inhibitors such as dasatinib can upregulate gpNMB expression, which has the potential to enhance therapeutic targeting with anti-gpNMB antibody drug conjugates such as glembatumumab vedotin (CDX-011). Our primary aim is to quantify the degree and identify the timeframe of gpNMB upregulation in xenograft models of TNBC after treatment with the Src tyrosine kinase inhibitor, dasatinib, by longitudinal positron emission tomography (PET) imaging with the 89Zr-labeled anti-gpNMB antibody ([89Zr]Zr-DFO-CR011). The goal is to identify the timepoint at which to administer CDX-011 after treatment with dasatinib to enhance therapeutic efficacy using noninvasive imaging. (2) Methods: First, TNBC cell lines that either express gpNMB (MDA-MB-468) or do not express gpNMB (MDA-MB-231) were treated with 2 μM of dasatinib in vitro for 48 h, followed by Western blot analysis of cell lysates to determine differences in gpNMB expression. MDA-MB-468 xenografted mice were also treated with 10 mg/kg of dasatinib every other day for 21 days. Subgroups of mice were euthanized at 0-, 7-, 14-, and 21-days post treatment, and tumors were harvested for Western blot analysis of tumor cell lysates for gpNMB expression. In a different cohort of MDA-MB-468 xenograft models, longitudinal PET imaging with [89Zr]Zr-DFO-CR011 was performed before treatment at 0 (baseline) and at 14 and 28 days after treatment with (1) dasatinib alone (2) CDX-011 (10 mg/kg) alone, or (3) sequential treatment of dasatinib for 14 days then CDX-011 to determine changes in gpNMB expression in vivo relative to baseline. As a gpNMB-negative control, MDA-MB-231 xenograft models were imaged 21 days after treatment with dasatinib, combination of CDX-011 and dasatinib, and vehicle control. (3) Results: Western blot analysis of MDA-MB-468 cell and tumor lysates showed that dasatinib increased expression of gpNMB in vitro and in vivo at 14 days post treatment initiation. In PET imaging studies of different cohorts of MDA-MB-468 xenografted mice, [89Zr]Zr-DFO-CR011 uptake in tumors (SUVmean = 3.2 ± 0.3) was greatest at 14 days after treatment initiation with dasatinib (SUVmean = 4.9 ± 0.6) or combination of dasatinib and CDX-011 (SUVmean= 4.6 ± 0.2) compared with that at baseline (SUVmean = 3.2 ± 0.3). The highest tumor regression after treatment was observed in the combination-treated group with a percent change in tumor volume relative to baseline (%CTV) of -54 ± 13 compared with the vehicle control-treated group (%CTV = +102 ± 27), CDX-011 group (%CTV = -25 ± 9.8), and dasatinib group (%CTV = -23 ± 11). In contrast, the PET imaging of MDA-MB-231 xenografted mice indicated no significant difference in the tumor uptake of [89Zr]Zr-DFO-CR011 between treated (dasatinib alone or in combination with CDX-011) and vehicle-control groups. (4) Conclusions: Dasatinib upregulated gpNMB expression in gpNMB-positive MDA-MB-468 xenografted tumors at 14 days post treatment initiation, which can be quantified by PET imaging with [89Zr]Zr-DFO-CR011. Furthermore, combination therapy with dasatinib and CDX-011 appears to be a promising therapeutic strategy for TNBC and warrants further investigation.

Abstract P4-07-04: STX-478, a mutant-selective PI3Kα H1047X inhibitor clinical candidate with a best-in-class profile: Pharmacology and therapeutic activity as monotherapy and in combination in breast cancer xenograft models

Abstract PI3Kα is highly mutated in cancer resulting in hyperactivation of lipid kinase activity and downstream AKT signaling. H1047 is the most common site of oncogenic mutation and occurs in ~14% of all breast cancers. Initial therapeutic benefit of targeting PI3Kα was established with alpelisib, an alpha-selective PI3K inhibitor that is equipotent against wild-type and mutant forms. However, wild-type PI3Kα inhibition results in frequent dose-limiting toxicities including hyperglycemia, restricting the full potential of this drug. Selective targeting of H1047X-mutant PI3Kα is expected to both improve anti-tumor activity and reduce toxicity. STX-478 is an allosteric, CNS-penetrant, selective PI3Kα H1047X inhibitor, having excellent drug-like properties and exceptional kinome selectivity. STX-478 demonstrated minimal inhibition of CYP enzymes in vitro, supporting the potential for combinations with a wide range of therapeutics in breast cancer and a variety of other tumor types. STX-478 selectivity extended to the inhibition of other activating kinase domain mutations in biochemical assays. In a diverse panel of PI3Kα H1047X mutant cell lines, STX-478 selectively reduced the cellular levels of pAKT (S473) with a strong correlation between pAKT inhibition and cell viability (R = 0.8). In a high-throughput viability screen of 467 cancer cell lines, the presence of PIK3CA H1047X and other kinase domain mutations were the single strongest predictor of STX-478 sensitivity with potency superior to alpelisib. STX-478 also selectively inhibited the proliferation of cell lines with PI3Kα helical domain mutations, potentially due to the selective dependency of these cells on mutant PI3Kα. When combined with fulvestrant, lapatinib, or abemaciclib, STX-478 demonstrated synergistic anti-proliferative activity in cell lines with relevant ER/HER2 status. Unlike alpelisib, STX-478 did not impair glucose metabolism or cause insulin resistance at efficacious doses. In the T47D (PI3Kα H1047R) breast cancer model, STX-478 (100 mg/kg) monotherapy caused tumor regression whereas alpelisib caused only stasis. STX-478 combination with fulvestrant was well-tolerated, with more consistent and deeper tumor regression. Similar results were observed in a PI3Kα H1047R mutant ER+/HER2- PDX model, where fulvestrant monotherapy showed minimal activity, while combination with STX-478 yielded tumor regressions. In an ER+/HER2+ PDX model (PI3Kα H1047R/R108H), palbociclib and STX-478 (100 mg/kg) monotherapy resulted in similar efficacy while the combination was well tolerated and yielded tumor regression. Together these data indicate robust STX-478 monotherapy activity that was well tolerated and improved when dosed in combination with fulvestrant or CDK4/6 inhibitors. Finally, we investigated the effect of STX-478 treatment in an ER+ PDX model carrying a helical domain mutation. STX-478 treatment resulted in tumor growth inhibition at doses that did not result in metabolic dysfunction, suggesting that STX-478 may also be efficacious in treating PIK3CA mutant tumors with helical domain mutations. In summary, STX-478 efficacy was superior to alpelisib at a dose level that exceeds the clinically relevant exposure in mice without causing metabolic dysfunction. STX- 478 has a predicted low human dose, CNS exposure, low risk of DDI, and a predicted long half-life with minimal variation in peak-to-trough plasma concentrations which further supports a favorable therapeutic index. STX-478 has the potential to provide a best-in-class profile to improve outcomes in patients harboring tumors with prevalent PI3Kα H1047X mutations as well as other kinase and helical domain mutant tumors. The significant CNS exposure of STX-478 is expected to enable this treatment for patients with brain tumors and brain metastases not afforded by existing options. STX-478 is currently in IND enabling studies and is expected to enter human clinical trials in 2023. Citation Format: Leonard Buckbinder, David J. St. Jean, Brendon Ladd, Trang Tieu, Philip Jonsson, Jacob Alltucker, Samantha Manimala, Weixue Wang, Angel Guzman-Perez, Darrin D. Stuart, Gregory Dowdell. STX-478, a mutant-selective PI3Kα H1047X inhibitor clinical candidate with a best-in-class profile: Pharmacology and therapeutic activity as monotherapy and in combination in breast cancer xenograft models [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-04.

Abstract P3-07-19: Anti-depressant Amitriptyline Augments the Efficacy of Tamoxifen in ER positive breast cancer

Abstract Anti-depressant Amitriptyline Augments the Efficacy of Tamoxifen in ER positive breast cancer Pitta Venkata Prabhakar1, Arhan D Rao1, Timilsina Santosh1, Deepika Singh1, Ratna Vadlamudi1,2, Virginia Kaklamani3, Manjeet Rao1,2. 1Greehey Children’s Cancer Research Institute, University of Texas Health San Antonio, San Antonio, TX, USA. 2Mays Cancer Center, University of Texas Health San Antonio, San Antonio, TX, USA. 3Department of Medicine, UT Health, San Antonio, USA. Background: Breast cancer (BC) is the most common cancer in women and the leading cause of cancer-related deaths in women worldwide, with 1 out of 8 women being diagnosed with invasive breast cancer during their lifetime. The majority of breast cancer patients (80%) are diagnosed with Estrogen Receptor positive (ER+) breast cancer. The most commonly used treatment option for ER+ Breast cancer is endocrine therapy, such as Tamoxifen(TAM). Although survival of breast cancer patients has dramatically improved with the use of endocrine therapy, acquired resistance and debilitating side effects of treatment became major concerns. Therefore, safer treatment options that effectively suppress cancer progression, reduce treatment associated side effects, and improve efficacy of standard of care therapies are much needed. Repurposing of clinically approved or investigational drugs has become promising alternative approach for treating cancer. Therefore, we tested the repurposing potential of anti-depressant Amitriptyline for the treatment of ER+ breast cancer. Methods: The anti-cancer effect of Amitriptyline was determined in vitro using short and long-term viability, migration, and apoptosis assays. To substantiate the in vitro data, the effect of Amitriptyline on tumor growth was assessed using orthotopic xenograft model. RNA-seq analysis was performed in Vehicle and Amitriptyline treated breast cancer cells to understand the mechanism of action. Finally, to test whether amitriptyline can sensitize ER+ breast cancer cells to endocrine therapy, we performed cell viability assays after treatment with Amitriptyline and Tamoxifen. Results: Amitriptyline treatment resulted in significant reduction of short term and long term viability, as well as, migration of ER+ BC cells. Furthermore, Amitriptyline treatment significantly increased apoptosis in BC cells. Our RNA-seq analysis revealed that Amitriptyline treatment inhibited important genes involved in cancer growth and survival including E2F signaling, G2/M pathway, and DNA repair pathways. Confirming our in vitro findings, Amitriptyline treatment blocked the growth of ER+ BC growth in pre-clinical orthotopic xenograft model of breast cancer. Importantly, Amitriptyline treatment sensitized ER+ BC to TAM, showing highly synergistic effects. Amitriptyline treatment significantly improved the effects of TAM on cell viability, survival, migration, and apoptosis. Furthermore, Amitriptyline augmented the efficacy of Tamoxifen in TAM resistant BC cells. Conclusion: Our study establishes potential of Amitriptyline as a repurposable drug as safe and robust treatment option for ER+ patients, either as a monotherapy or in combination. We are poised to begin a clinical trial and test the therapeutic efficacy of Amitriptyline for treating breast cancer patients. Citation Format: Prabhakar Pitta Venkata, Arhan D. Rao, Santosh Timilsina, Deepika Singh, Ratna K. Vadlamudi, Virginia Kaklamani, Manjeet K. Rao. Anti-depressant Amitriptyline Augments the Efficacy of Tamoxifen in ER positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-07-19.

Abstract P3-07-10: CCTG IND.236: A Phase 1b trial of combined CFI-402257 and weekly paclitaxel in patients with HER2-negative (HER2-) advanced breast cancer (aBC)

Abstract CCTG IND.236: A Phase 1b trial of combined CFI-402257 and weekly paclitaxel in patients with HER2-negative (HER2-) advanced breast cancer (aBC) Philippe L. Bedard, Mihaela Mates, John Hilton, Nathalie Levasseur, Arif Awan, Amirrtha Srikanthan, David Cescon, Karen Gelmon, Andrew Robinson, Nancy Drummond-Ivars, Irene Li, Laleh Rastgou, Jackie Edwards, Linda Hagerman, Siwei Zhang, Mark Bray, Lesley Seymour, Moira Rushton-Marovac, Pierre-Olivier Gaudreau Background: CFI-402257 is a selective oral inhibitor of TTK protein kinase, a critical regulator of the mitotic spindle assembly checkpoint overexpressed in breast cancer (BC). CFI-402257 monotherapy has anti-proliferative and cytotoxic activity and enhances antitumor activity of paclitaxel in BC xenograft models. Material and methods: Primary objectives were to establish safety and Recommended Phase 2 dose (RP2D) of CFI-402257 combined with weekly paclitaxel (Phase 1b) and Overall Response Rate (ORR) as per RECIST 1.1 (Phase 2). Patients with HER2- aBC with adequate organ function, PS 0-1, previously treated with >1 non-taxane chemotherapy, were eligible. A 3+3 design was used for Phase 1b, with dose limiting toxicities (DLTs) assessed during cycle 1 (28 days). Starting dose CFI-402257 was 84mg (DL1 = 84mg, DL2 = 112mg, DL3 = 168mg, DL4 = 210mg and DL5 = 252mg) on a 2-day on, 5-day off schedule with paclitaxel 80mg/m2 day 1, 8, 15. Safety assessments were performed weekly (CTCAE v5.0) and response every 2 cycles. A Simon 2-stage design was used for Phase 2 (stage 2 required ≥4 responses in 17 evaluable patients from stage 1). Results: 37 patients received a total of 260 cycles including all 5 dose levels. Median age was 59; 92% ER+/HER2-; 49% PS1; 22% 3 prior chemotherapy lines; 41% 4 sites of metastatic disease, and 81% had received prior CDK4/6 inhibitors. Grade 3 hematological adverse events (AEs, all dose levels) were neutropenia (70%), lymphopenia (41%) and anemia (14%). Six DLTs occurred: 5 dose-related grade 4 neutropenia and 1 febrile neutropenia. Three DLTs occurred at DL3, two at DL4, and one at DL5. Three serious AEs (two at DL3, and one at DL4) at least possibly related to treatment were seen: 2 febrile neutropenia and 1 skin infection (all grade 3). Frequent AEs (˃5%; all dose levels) considered at least possibly related to treatment were: diarrhea (38%), nausea (30%), fatigue (27%), vomiting (16%), anorexia (14%), maculo-papular rash (14%), oral mucositis (11%), alopecia (11%) and pruritus (8%). DL3 (168mg) was selected as RP2D. ORR was 3/36=8% and 1/17=5.9% in all vs Phase 2 evaluable patients, respectively. Clinical Benefit Rate (CBR; defined as complete response, partial response or stable disease ˃16 weeks in duration) was 18/33=54.6% and 10/17=58.8% in all vs Phase 2 evaluable patients, respectively. During Phase 2, the 17 evaluable patients from stage 1 did not meet pre-specified threshold for anti-tumor activity to proceed to stage 2. Conclusions: CFI-402257 and paclitaxel was well tolerated, with neutropenia as the main toxicity. DL3 (168mg) was selected as RP2D. Phase 2 ORR and CBR was 5.9% and 58.8%, respectively; during Phase 2, the 17 evaluable patients from stage 1 did not meet the pre-specified threshold for anti-tumor activity to proceed to stage 2 and the trial was closed to accrual on April 7, 2022. Final analysis and correlative analyses are ongoing. Acknowledgements: Coordinated by the CCTG. Funding supported by SU2C Canada - Canadian Cancer Society Breast Cancer Dream Team Research Funding (SU2C-AACR-DT-18-15) and OICR. CFI-402257 provided by Treadwell Therapeutics. Citation Format: Philippe Bedard, Mihaela Mates, John Hilton, Nathalie Levasseur, Arif Awan, Amirrtha Srikanthan, David W. Cescon, Karen Gelmon, Andrew Robinson, Nancy Drummond-Ivars, Irene Li, Laleh Rastgou, Jackie Edwards, Linda Hagerman, Siwei Zhang, Mark Bray, Lesley Seymour, Moira Rushton, Pierre-Olivier Gaudreau. CCTG IND.236: A Phase 1b trial of combined CFI-402257 and weekly paclitaxel in patients with HER2-negative (HER2-) advanced breast cancer (aBC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-07-10.

Abstract P2-24-07: Combination of complete estrogen receptor antagonist, OP-1250, and CDK4/6 inhibitors enhances tumor suppression and inhibition of cell cycle-related gene expression

Abstract OP-1250, a complete estrogen receptor antagonist (CERAN) and selective estrogen receptor degrader (SERD), is currently in Phase I/II clinical trials for the treatment of estrogen receptor positive (ER+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer. OP-1250 has previously demonstrated efficacy in both estrogen receptor 1 (ESR1) wild-type and Y537S mutant breast cancer xenograft models. Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) are a standard first-line treatment for ER+ advanced or metastatic breast cancer in combination with endocrine therapy. To characterize OP-1250 efficacy in this setting, we explored the combination of OP-1250 with CDK4/6 inhibitors palbociclib and ribociclib in ER+/HER2- breast cancer preclinical models, and profiled the transcriptional changes associated with single agent and combination therapy. OP-1250 and CDK4/6 inhibitors were tested alone and in combination in ESR1 wild-type MCF7 and ESR1 Y537S mutant ST941 xenograft models. Higher doses of OP-1250 and either CDK4/6 inhibitor, when given as a monotherapy, suppress tumor growth and increase animal survival, while lower doses of the compounds display a modest or minimal effect on tumor growth or survival. In combination, lower doses of OP-1250 and either CDK4/6 inhibitor result in significantly greater tumor growth suppression (both xenograft models), tumor regression (MCF7) and animal survival (ST491) than each compound individually. RNA sequencing revealed substantially more gene expression changes with combination treatment than monotherapy. In particular, pathways associated with cell cycle progression displayed greater changes with combination treatment, similar to what was observed with a much higher dose of monotherapy. This study supports the clinical evaluation of OP-1250 in combination with CDK4/6 inhibitors (palbociclib or ribociclib) and provides additional context to mechanisms of combination efficacy. OP-1250 is currently being evaluated in a Phase Ib clinical trial in combination with palbociclib and a study including evaluation of the combination of OP-1250 with ribociclib is planned to initiate in Q3 2022. Citation Format: Alison D. Parisian, Gopinath S. Palanisamy, Fabian Ortega, Judevin L. Sapugay, William J. Bodell, David Kulp, Peter Kushner, Cyrus Harmon. Combination of complete estrogen receptor antagonist, OP-1250, and CDK4/6 inhibitors enhances tumor suppression and inhibition of cell cycle-related gene expression [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-24-07.

Abstract P4-08-18: Engineered Toxin Bodies Specific for TROP2 Positive Cancers

Abstract Engineered Toxin Bodies Specific for TROP2 Positive Cancers Authors: Garrett L. Cornelison, Ileana Pedraza, Kendra Garrison, Elizabeth M. Kapeel, Channing Pletka, Abdul Khan, Jessica Momb, Rebecca Martin, Adam Bartos, Joseph D. Dekker, Jay Zhao, John Majercak, Garrett L. Robinson Molecular Templates, Austin, TX Lanier Biotherapeutics, Bogart, GA Molecular Templates produces next generation immunotoxins called Engineered toxin bodies (ETBs). ETBs are comprised of a proprietarily engineered form of Shiga-like Toxin A subunit (SLT-A) genetically fused to antibody-like binding domains. ETBs work through novel mechanisms of action and are capable of forced internalization, undergoing retrograde translocation to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes resulting in the inhibition of protein synthesis and induction of apoptosis. In addition, Molecular Templates has expanded the ETB platform to include Antigen Seeding Technology (AST) to generate ETBs with the ability to deliver foreign protein antigen to targeted populations of tumor cells. This mechanism of action allows for the intracellular processing of antigen and subsequent surface MHC-I presentation required for activation of a re-directed T lymphocyte response and the capacity to restore a functional immune clearance program against the tumor. Three ETBs are in clinical development (MT-5111 targeting HER2, MT-0169 targeting CD38, and AST enabled MT-6402 targeting PD-L1). The novel mechanisms of action have potential benefit in different indications including in the relapsed setting, when disease has progressed after chemotherapies and other targeted therapies, and additionally may be able to combine with standard of care. ETBs are being developed that target other cell surface receptors expressed on solid tumors including tumor-associated calcium signal transducer 2 (TROP2). TROP2 is a clinically validated target in metastatic triple-negative breast cancer (mTNBC) and other cancers such as metastatic urothelial carcinoma (mUC) using antibody drug conjugate (ADC) therapies such as sacituzumab govitecan (Trodelvy®). In vitro, ETBs targeting TROP2 specifically and directly kill tumor cells expressing TROP2 with picomolar activity. ETBs can bind to TROP2 in the presence of the Trodelvy parent monoclonal antibody, sacituzumab, and ETBs retain potency on TROP2 positive cell lines in the presence of clinically relevant concentrations of sacituzumab. AST enabled Trop2 targeted ETBs retain direct cell killing activity and can deliver multiple viral antigens to induce cytokine secretion and T-cell mediated killing in a co-culture assay of TROP2 target cells with antigen matched HLA type and antigen specific T-cells. In vivo, TROP2 targeted ETBs demonstrate good tolerability in a murine HCC1806 triple-negative breast cancer xenograft model and significantly reduce tumor burden relative to vehicle control. These pre-clinical in vitro and in vivo data suggest AST enabled Trop2 targeted ETBs have the potential to deplete Trop2 positive malignancies through multiple unique mechanisms of action. Citation Format: Garrett L. Cornelison, Ileana Pedraza, Kendra Garrison, Elizabeth M. Kapeel, Channing Pletka, Abdul Khan, Jessica Momb, Rebecca Martin, Adam Bartos, Joseph D. Dekker, Jay Zhao, John Majercak, Garrett L. Robinson. Engineered Toxin Bodies Specific for TROP2 Positive Cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-18.

Small Molecules Targeting the RNA-Binding Protein HuR Inhibit Tumor Growth in Xenografts.

The RNA-binding protein Hu antigen R (HuR) is a post-transcriptional regulator critical in several types of diseases, including cancer, making it a promising therapeutic target. We have identified small-molecule inhibitors of HuR through a screening approach used in combination with fragment analysis. A total of 36 new compounds originating from fragment linking or structural optimization were studied to establish structure-activity relationships in the set. Two top inhibitors, 1c and 7c, were further validated by binding assays and cellular functional assays. Both block HuR function by directly binding to the RNA-binding pocket, inhibit cancer cell growth dependence of HuR, and suppress cancer cell invasion. Intraperitoneal administration of inhibitor 1c inhibits tumor growth as a single agent and shows a synergistic effect in combination with chemotherapy docetaxel in breast cancer xenograft models. Mechanistically, 1c interferes with the HuR-TGFB/THBS1 axis.

Icaritin Derivative IC2 Induces Cytoprotective Autophagy of Breast Cancer Cells via SCD1 Inhibition.

Breast cancer is one of the most prevalent malignancies and the leading cause of cancer-associated mortality in China. Icaritin (ICT), a prenyl flavonoid derived from the Epimedium Genus, has been proven to inhibit the proliferation and stemness of breast cancer cells. Our previous study demonstrated that IC2, a derivative of ICT, could induce breast cancer cell apoptosis by Stearoyl-CoA desaturase 1 (SCD1) inhibition. The present study further investigated the mechanism of the inhibitory effects of IC2 on breast cancer cells in vitro and in vivo. Our results proved that IC2 could stimulate autophagy in breast cancer cells with the activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling and mitogen-activated protein kinase (MAPK) signaling. Combination treatment of the AMPK inhibitor decreased IC2-induced autophagy while it markedly enhanced IC2-induced apoptosis. In common with IC2-induced apoptosis, SCD1 overexpression or the addition of exogenous oleic acid (OA) could also alleviate IC2-induced autophagy. In vivo assays additionally demonstrated that IC2 treatment markedly inhibited tumor growth in a mouse breast cancer xenograft model. Overall, our study was the first to demonstrate that IC2 induced cytoprotective autophagy by SCD1 inhibition in breast cancer cells and that the autophagy inhibitor markedly enhanced the anticancer activity of IC2. Therefore, IC2 was a potential candidate compound in combination therapy for breast cancer.

Predictors of success in establishing orthotopic patient-derived xenograft models of triple negative breast cancer

Patient-derived xenograft (PDX) models of breast cancer are an effective discovery platform and tool for preclinical pharmacologic testing and biomarker identification. We established orthotopic PDX models of triple negative breast cancer (TNBC) from the primary breast tumors of patients prior to and following neoadjuvant chemotherapy (NACT) while they were enrolled in the ARTEMIS trial (NCT02276443). Serial biopsies were obtained from patients prior to treatment (pre-NACT), from poorly responsive disease after four cycles of Adriamycin and cyclophosphamide (AC, mid-NACT), and in cases of AC-resistance, after a 3-month course of different experimental therapies and/or additional chemotherapy (post-NACT). Our study cohort includes a total of 269 fine needle aspirates (FNAs) from 217 women, generating a total of 62 PDX models (overall success-rate = 23%). Success of PDX engraftment was generally higher from those cancers that proved to be treatment-resistant, whether poorly responsive to AC as determined by ultrasound measurements mid-NACT (p = 0.063), RCB II/III status after NACT (p = 0.046), or metastatic relapse within 2 years of surgery (p = 0.008). TNBC molecular subtype determined from gene expression microarrays of pre-NACT tumors revealed no significant association with PDX engraftment rate (p = 0.877). Finally, we developed a statistical model predictive of PDX engraftment using percent Ki67 positive cells in the patient’s diagnostic biopsy, positive lymph node status at diagnosis, and low volumetric reduction of the patient’s tumor following AC treatment. This novel bank of 62 PDX models of TNBC provides a valuable resource for biomarker discovery and preclinical therapeutic trials aimed at improving neoadjuvant response rates for patients with TNBC.

BET-HDAC Dual Inhibitors for Combinational Treatment of Breast Cancer and Concurrent Candidiasis.

Breast cancer is susceptible to Candida infections, and candidiasis has an enhancing effect on the progression and metastasis of tumor. Breast cancer and concurrent candidiasis represent a significant challenge in clinical therapy. Herein, a series of novel small molecule inhibitors simultaneously targeting bromodomain and extra-terminal (BET) and histone deacetylase (HDAC) were designed for combinational treatment of breast cancer and resistant Candida albicans infections. Among them, compounds 13c and 17b exhibited excellent and balanced inhibitory activity against both BET family proteins BRD4 and HDAC1. As compared with BRD4 or HDAC1 inhibitors, dual inhibitors 13c and 17b displayed improved in vivo antitumor efficacy in MDA-MB-231 breast cancer xenograft models. Notably, they synergized with fluconazole (FLC) to effectively reduce the kidney fungal burden in a murine model of disseminated candidiasis. Thus, the BET-HDAC dual inhibitors represented a novel therapeutic strategy for combinational treatment of breast cancer and concurrent candidiasis.

Novel Chiral Ru(II) Complexes as Potential c-myc G-quadruplex DNA Stabilizers Inducing DNA Damage to Suppress Triple-Negative Breast Cancer Progression.

Currently, effective drugs for triple-negative breast cancer (TNBC) are lacking in clinics. c-myc is one of the core members during TNBC tumorigenesis, and G-rich sequences in the promoter region can form a G-quadruplex conformation, indicating that the c-myc inhibitor is a possible strategy to fight cancer. Herein, a series of chiral ruthenium(II) complexes ([Ru(bpy)2(DPPZ-R)](ClO4)2, Λ/Δ-1: R = -H, Λ/Δ-2: R = -Br, Λ/Δ-3: R = -C≡C(C6H4)NH2) were researched based on their interaction with c-myc G-quadruplex DNA. Λ-3 and Δ-3 show high affinity and stability to decrease their replication. Additional studies showed that Λ-3 and Δ-3 exhibit higher inhibition against different tumor cells than other molecules. Δ-3 decreases the viability of MDA-MB-231 cells with an IC50 of 25.51 μM, which is comparable with that of cisplatin, with an IC50 of 25.9 μM. Moreover, Δ-3 exhibits acceptable cytotoxic activity against MDA-MB-231 cells in a zebrafish xenograft breast cancer model. Further studies suggested that Δ-3 decreases the viability of MDA-MB-231 cells predominantly through DNA-damage-mediated apoptosis, which may be because Δ-3 can induce DNA damage. In summary, the results indicate that Ru(II) complexes containing alkinyl groups can be developed as c-myc G-quadruplex DNA binders to block TNBC progression.

Bioinspired Nanocomplexes Comprising Phenolic Acid Derivative and Human Serum Albumin for Cancer Therapy.

Inspired by the natural phenomenon of phenolic-protein interactions, we translate this "naturally evolved interaction" to a "phenolic acid derivative based albumin bound" technology, through the synthesis of phenolic acid derivatives comprising a therapeutic cargo linked to a phenolic motif. Phenolic acid derivatives can bind to albumin and form nanocomplexes after microfluidic mixing. This strategy has been successfully applied to different types of anticancer drugs, including taxanes, anthraquinones, etoposides, and terpenoids. Paclitaxel was selected as a model drug for an in-depth study. Three novel paclitaxel-phenolic acid conjugates have been synthesized. Molecular dynamics simulations provide insights into the self-assembled mechanisms of phenolic-protein nanocomplexes. The nanocomplexes show improved pharmacokinetics, elevated tolerability, decreased neurotoxicity, and enhanced anticancer efficacies in multiple murine xenograft models of breast cancer, in comparison with two clinically approved formulations, Taxol (polyoxyethylated castor oil-formulated paclitaxel) and Abraxane (nab-paclitaxel). Such a robust system provides a broadly applicable platform for the development of albumin-based nanomedicines and has great potential for clinical translation.

EPH/Ephrin-Targeting Treatment in Breast Cancer: A New Chapter in Breast Cancer Therapy

Breast cancer (BC) is the most common malignant tumor in women. Erythropoietin-producing hepatocellular receptors (EPHs), receptor tyrosine kinases binding the membrane-bound proteins ephrins, are differentially expressed in BC, and correlate with carcinogenesis and tumor progression. With a view to examining available therapeutics targeting the EPH/ephrin system in BC, a literature review was conducted, using the MEDLINE, LIVIVO, and Google Scholar databases. EPHA2 is the most studied EPH/ephrin target in BC treatment. The targeting of EPHA2, EPHA10, EPHB4, ephrin-A2, ephrin-A4, as well as ephrin-B2 in BC cells or xenograft models is associated with apoptosis induction, tumor regression, anticancer immune response activation, and impaired cell motility. In conclusion, EPHs/ephrins seem to represent promising future treatment targets in BC.

DAB2IP attenuates chemoresistance of triple-negative breast cancer through sequestration of RAC1 to prevent β-catenin nuclear accumulation.

Although chemotherapy, the most widely used systemic treatment in triple-negative breast cancer (TNBC), markedly improved the patients' outcome, chemoresistance always occurs. This study purposed to explore new therapeutic strategies for the treatment of chemoresistance. The expression and prognostic value of DAB2IP were investigated in TNBC tissues and cell lines. Low DAB2IP expression predicted high mortality risk in TNBC. Inhibition of DAB2IP expression conferred cancer stem cell capacity and chemoresistance in TNBC cell lines. Using murine breast cancer (BC) xenograft models, we evaluated the association with DAB2IP and chemoresistance. DAB2IP inhibited TNBC tumourigenesis and chemoresistance in vivo. Further, we revealed that DAB2IP inhibited β-catenin nuclear transport through competitive interaction with RAC1 and decreased β-catenin accumulation in the cell nucleus. Finally, we found that the DNA methylation level was negatively associated with DAB2IP expression in TNBC. Inhibition of DNA methylation restored the DAB2IP expression and attenuated chemoresistance in TNBC. We revealed that DAB2IP attenuates chemoresistance of TNBC via inhibition of RAC1-mediated β-catenin nuclear accumulation. Decitabine treatment results in re-expression of DAB2IP by inhibiting DNA methylation and could be a potential therapeutic strategy for chemoresistance in TNBC.

EXTH-103. DISCOVERY AND PHARMACOLOGICAL CHARACTERIZATION OF SKL27969, A NOVEL BRAIN-PENETRATING PRMT5 INHIBITOR WITH STRONG ANTITUMOR ACTIVITY, IN GLIOBLASTOMA AND BRAIN METASTASIS PRECLINICAL MODELS

Abstract Protein arginine methyltransferase 5 (PRMT5), a type II methyltransferase, regulates cellular processes such as survival, proliferation, and apoptosis by inducing symmetric arginine dimethylation of multiple cellular proteins involved in the regulation of cellular transcription and RNA splicing. Elevated tumor PRMT5 protein level has recently been correlated with poor prognosis and poor patient survival in various human cancers, including glioblastoma multiforme (GBM), lung cancer, breast cancer, and ovarian cancer. SKL27969 is a highly selective and potent PRMT5 inhibitor that is designed for brain penetration. It strongly binds to S-adenosylmethionine (SAM)-bound PRMT5/MEP50 (methylosome protein 50), leading to potent cellular symmetric dimethylarginine (SDMA) inhibition with an IC50 of 3.4 nM. Cell line panel profiling of SKL27969 revealed a broad spectrum of anti-proliferative activity in various cancer cell types, including CNS tumors, solid cancers prone to spread to brain, other solid cancers, and hematologic cancers. SKL27969 showed excellent brain exposure, with total and unbound partition coefficient (Kp and Kpuu) values of 6.57 and 1.08, respectively, and high tumor-to-plasma ratio, which resulted in significant survival benefit in orthotopic GBM xenograft models and metastatic brain cancer models such as intracranial xenograft models of non-small cell lung cancer (NSCLC) or triple-negative breast cancer (TNBC). Administration of SKL27969 showed strong tumor growth suppression in subcutaneous xenograft models of GBM, NSCLC, or TNBC. High correlation between tumor and plasma SDMA levels after SKL27969 treatment were observed in the preclinical models. Furthermore, SKL27969 showed potentiation of DNA damage when used in combination with DNA-damaging agents, which may suggest possible benefit as a combination therapy. Given the therapeutic target potential of PRMT5 in glioblastoma and other brain metastatic cancers, and the preclinical efficacy of SKL27969, these results have enabled the initiation of Phase 1/2 open-label, multicenter dose-finding study in patients with advanced solid tumors (NCT05388435).