Loss Of Rb Research Articles

Circulating tumor cells (CTCs) in patients with metastatic castration resistant prostate cancer (mCRPC) treated with olaparib plus 177lutetium-prostate specific membrane antigen-617 (177Lu-PSMA-617) in the LuPARP trial.

5064 Background: LuPARP (NCT03874884) is evaluating the safety and efficacy of olaparib in combination with 177Lu-PSMA-617 in patients (pts) with mCRPC who have progressed on an androgen receptor pathway inhibitors and docetaxel. We aim to identify potential prognostic and predictive biomarkers from serial CTC profiling. Methods: Twenty-six pts with high PSMA expression on PSMA-PET received 7.4 GBq of 177Lu-PSMA-617 every 6 weeks (wk) together with an escalating dose-schedule of olaparib (50mg BD – 300mg BD, days 2 to 14 or days -4 to 14) for up to 6 cycles. For CTC analysis, 10 mls of blood was collected at baseline, 12-weekly for 48 wk, and thereafter every 24 wk and at disease progression. CK+, CD45-, and DAPI+ CTCs were enumerated from 3 mls of blood and immunoassayed for PSMA expression using the Epic Sciences platform. Correlations between total and PSMA+ CTC counts and PSA50 response (PSA reduction of ≥ 50%) were evaluated. Low pass whole genome sequencing (lpWGS) was performed on baseline and longitudinal CTC samples to identify copy number alterations. Results: At baseline, 23 of 26 pts (88%) had detectable CTCs (median 2.9 CTC/ml, range 0-30), and of these 23 pts, 17 (74%) had detectable PSMA+ CTCs (median 0.9 CTC/ml, range 0.3-27), indicating heterogeneity of PSMA expression in CTCs. The CTC positivity rates (% of cases ≥1 CTC) at week (w)12, w24, w36, w48 and at disease progression were 57%, 58%, 75%, 36% and 100%, and the PSMA positivity rates (% of cases ≥1 PSMA+ CTC) were 38%, 36%, 22%, 50% and 56%, respectively. Fifteen of 20 (75%) evaluable pts with paired baseline and w12 CTCs had a ≥50% decline in total CTC count, of which 9/15 (60%) pts also achieved a PSA50 response. Five of these 9 (56%) pts had 100% CTC clearance at w12. In terms of PSMA+ CTCs, 14/15 (93%) evaluable pts had ≥50% PSMA+ CTC decline with 13 pts (93%) achieving complete CTC clearance by w12. Six of the 13 pts with complete PSMA+ CTC clearance at w12 also achieved a PSA50 response. Beyond PSMA expression, genomic heterogeneity was evident in baseline and on-treatment CTCs, including recurrent loss of PTEN, TP53, BRCA2, ATM, and RB1, and gain of AR and MYC. lpWGS in 10 baseline samples identified 5 cases with BRCA2 loss and 5 cases with ATM loss. Two pts with BRCA2 loss and 3 pts with ATM loss had a PSA50 response by w12. Conclusions: We observed high rates of total and PSMA+ CTCs in PSMA-expressing mCRPC. Total and PSMA+ CTCs decline with combined olaparib and 177Lu-PSMA-617 treatment. Early declines in total and PSMA+ CTCs including 12w CTC clearance paralleled PSA responses. Notably, total and PSMA+ CTCs rise again in the setting of disease progression. Serial CTC profiling may assist in tracking response to 177Lu-PSMA-617 therapy. Clinical trial information: NCT03874884 .

Ferroptosis: the vulnerability within a cancer monster.

Treatment-resistant cancer, such as neuroendocrine prostate cancer (NEPC), is a lethal disease with limited therapeutic options. RB1 is a tumor suppressor gene that is lost in a majority of NEPC tumors. In this issue of the JCI, Wang and colleagues examined how RB1 loss may sensitize cancer cells to ferroptosis inducers through elevation of ACSL4, a key enzyme that promotes lipid peroxidation and triggers ferroptosis. We discuss a high potential of RB1-deficient cells to undergo ferroptosis due to the elevation of ACSL4. This is normally kept in check by abundant expression of GPX4, an antioxidant enzyme, in cancer cells. This balance, however, is tilted by GPX4 inhibitors, leading to massive ferroptosis. We highlight possible therapeutic strategies that exploit this inherent vulnerability for targeting RB1-deficient, treatment-resistant cancer.

DNA-PKcs as an upstream mediator of OCT4-induced MYC activation in small cell lung cancer

Small cell lung cancer (SCLC) is a neuroendocrine tumor noted for the rapid development of both metastases and resistance to chemotherapy. High mutation burden, ubiquitous loss of TP53 and RB1, and a mutually exclusive amplification of MYC gene family members contribute to genomic instability and make the development of new targeted agents a challenge. Previously, we reported a novel OCT4-induced MYC transcriptional activation pathway involving c-MYC, pOCT4S111, and MAPKAPK2 in progressive neuroblastoma, also a neuroendocrine tumor. Using tumor microarray analysis of clinical samples and preclinical models, we now report a correlation in expression between these proteins in SCLC. In correlating c-MYC protein expression with genomic amplification, we determined that some SCLC cell lines exhibited high c-MYC without genomic amplification, implying amplification-independent MYC activation. We then confirmed direct interaction between OCT4 and DNA-PKcs and identified specific OCT4 and DNA-PKcs binding sites. Knock-down of both POU5F1 (encoding OCT4) and PRKDC (encoding DNA-PKcs) resulted in decreased c-MYC expression. Further, we confirmed binding of OCT4 to the promoter/enhancer region of MYC. Together, these data establish the presence of a DNA-PKcs/OCT4/c-MYC pathway in SCLCs. We then disruptively targeted this pathway and demonstrated anticancer activity in SCLC cell lines and xenografts using both DNA-PKcs inhibitors and a protein-protein interaction inhibitor of DNA-PKcs and OCT4. In conclusion, we demonstrate here that DNA-PKcs can mediate high c-MYC expression in SCLCs, and that this pathway may represent a new therapeutic target for SCLCs with high c-MYC expression.

Chromophobe Renal Cell Carcinoma with Sarcomatoid Differentiation: Clinicopathologic Correlation and Molecular Findings.

Introduction: Sarcomatoid differentiation has been reported in approximately 8% of chromophobe renal cell carcinoma (RCC) and is associated with a worse prognosis. We aim to describe the clinicopathologic and molecular findings of chromophobe RCC with sarcomatoid differentiation. Methods: Surgical pathology database was searched to identify chromophobe RCC with sarcomatoid differentiation from January 2015 to December 2021. Results: Five patients were diagnosed with chromophobe RCC with sarcomatoid differentiation. The median age at the time of diagnosis was 57 years (range 51-61 years). Three patients died after median follow-up of 12.1 months (range 1.6-18.2 months). The median tumor size was 10.7 cm (range 5.6-13.6 cm). The median percentage of sarcomatoid component was 60% (range 10-90%), and the median percentage of necrosis was 30% (range 10-50%). One tumor demonstrated osteoid formation. PAX8, keratin 7, KIT (CD117), and Hale colloidal iron were positive in the epithelial component, whereas the sarcomatoid component was positive for vimentin, CD10, and high Ki67 proliferative index. Molecular testing was performed in three specimens: all were TP53 mutated and microsatellite stable. One aggressive tumor had RB1 frameshift mutation and copy number gains for TERT and CUL4A. Conclusion: Chromophobe RCC with sarcomatoid differentiation is a rare entity with aggressive behavior. Percentage of sarcomatoid component, necrosis, and the occurrence of metastasis is associated with worse prognosis. Molecular profiling reveals frequent TP53 mutation. While TERT promoter mutation has no prognostic implication, FLCN inactivation may be associated with a less aggressive course. The clinical significance of RB1 loss is unclear.

Significance of RB Loss in Unlocking Phenotypic Plasticity in Advanced Cancers.

Cancer cells can undergo plasticity in response to environmental stimuli or under selective therapeutic pressures that result in changes in phenotype. This complex phenomenon of phenotypic plasticity is now recognized as a hallmark of cancer. Lineage plasticity is often associated with loss of dependence on the original oncogenic driver and is facilitated, in part, by underlying genomic and epigenetic alterations. Understanding the molecular drivers of cancer plasticity is critical for the development of novel therapeutic strategies. The retinoblastoma gene RB1 (encoding RB) is the first tumor suppressor gene to be discovered and has a well-described role in cell-cycle regulation. RB is also involved in diverse cellular functions beyond cell cycle including differentiation. Here, we describe the emerging role of RB loss in unlocking cancer phenotypic plasticity and driving therapy resistance across cancer types. We highlight parallels in cancer with the noncanonical role of RB that is critical for normal development and lineage specification, and the downstream consequences of RB loss including epigenetic reprogramming and chromatin reorganization that can lead to changes in lineage program. Finally, we discuss potential therapeutic approaches geared toward RB loss cancers undergoing lineage reprogramming.

BET Inhibition Sensitizes Immunologically Cold Rb-Deficient Prostate Cancer to Immune Checkpoint Blockade.

Non-T-cell-inflamed immunologically "cold" tumor microenvironments (TME) are associated with poor responsiveness to immune checkpoint blockade (ICB) and can be sculpted by tumor cell genomics. Here, we evaluated how retinoblastoma (Rb) tumor-suppressor loss-of-function (LOF), one of the most frequent alterations in human cancer and associated with lineage plasticity, poor prognosis, and therapeutic outcomes, alters the TME, and whether therapeutic strategies targeting the molecular consequences of Rb loss enhance ICB efficacy. We performed bioinformatics analysis to elucidate the impact of endogenous Rb LOF on the immune TME in human primary and metastatic tumors. Next, we used isogenic murine models of Rb-deficient prostate cancer for in vitro and in vivo mechanistic studies to examine how Rb loss and bromodomain and extraterminal (BET) domain inhibition (BETi) reprograms the immune landscape, and evaluated in vivo therapeutic efficacy of BETi, singly and in combination with ICB and androgen deprivation therapy. Rb loss was enriched in non-T-cell-inflamed tumors, and Rb-deficient murine tumors demonstrated decreased immune infiltration in vivo. The BETi JQ1 increased immune infiltration into the TME through enhanced tumor cell STING/NF-κB activation and type I IFN signaling within tumor cells, resulting in differential macrophage and T-cell-mediated tumor growth inhibition and sensitization of Rb-deficient prostate cancer to ICB. BETi can reprogram the immunologically cold Rb-deficient TME via STING/NF-κB/IFN signaling to sensitize Rb-deficient prostate cancer to ICB. These data provide the mechanistic rationale to test combinations of BETi and ICB in clinical trials of Rb-deficient prostate cancer.

Abstract 1714: CRACD/KIAA1211 loss drives cell plasticity and immune evasion of small cell lung cancer

Abstract Small cell lung carcinoma (SCLC) is a lethal neuroendocrine type of lung cancer with limited therapeutic options. Despite recent advances in cancer immunotherapy, its efficacy is limited to a small subset of SCLC patient tumors. The molecular origin of the refractoriness to immunotherapy remains elusive. CRACD (Capping protein inhibiting regulator of actin dynamics; KIAA1211/CRAD) gene is frequently mutated and transcriptionally downregulated in SCLC. Cracd knockout (KO) causes the transformation of preneoplastic neuroendocrine cells and significantly accelerates SCLC development in a mouse model initiated by the loss of Rb1, Trp53, and Rbl2 in the lung epithelium. Cracd KO induces tumor cell plasticity generating deregulated cell lineage trajectories of SCLC tumors. Strikingly, Cracd KO SCLC tumors display the complete loss of CD8+ T cells due to epigenetic suppression of the MHC-I pathway. Furthermore, single-cell transcriptomic analyses of SCLC patient samples classified SCLC by concurrent features: CRACD inactivation and tumor antigen presentation impairment. This study suggests CRACD as a tumor suppressor of SCLC that regulates proliferation and immune recognition of cells, providing novel insight into the mechanism of SCLC evading immune surveillance. Citation Format: Shengzhe Zhang, Kee-Bum Kim, Yuanjian Huang, Dong-Wook Kim, Bongjun Kim, Kyung-Pil Ko, Gengyi Zou, Jie Zhang, Sohee Jun, Nicole A. Kirk, Ye Eun Hwang, Young Ho Ban, Joseph M. Chan, Charles M. Rudin, Kwon-Sik Park, Jae-Il Park. CRACD/KIAA1211 loss drives cell plasticity and immune evasion of small cell lung cancer [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 1714.

Abstract 419: Elevated Akt/mTOR signaling drives therapy resistance in ALM

Abstract Metastatic acral lentiginous melanoma (ALM) is the most lethal subtype of cutaneous melanoma and effective therapies for patients have not been established. Studies revealed a link between the dysregulation of CDK4/6 and ALM mortality, however CDK4/6 inhibitors (CDK4i/6i) have proved ineffective in patients with advanced ALM. The tumor suppressor Rb was recently shown to have a novel suppressive role towards mTORC2. Here, we elucidate the role of a non-canonical tumor suppressor function of Rb in negative regulation of mTOR in CDK4i/6i-resistance. We hypothesize that the loss of Rb induced by CDK4i/6i triggers phosphorylation of Akt and downstream mTORC1 signaling pathways. We characterized baseline activity of the PI3K/AKT/mTOR pathway in a panel of ALM cell lines, finding heterogeneity across signaling. We immunoblotted for key proteins involved in the signal reprogramming hypothesized: pRb, pAkt, pS6 to define activation status and found the loss of Rb phosphorylation preceded the enrichment of pAKT, supporting the non-canonical role of Rb tumor suppression and the Rb-mTORC2 signaling axis as intrinsic CDK4i/6i mechanism. In parallel, we assessed the essential protein-protein interactions required for mechanistic mTORC1 activation—mTOR and Rheb GTPase. The enrichment of these interactions shortly after introducing CDK4i/6i supported our hypothesized mechanism. Translational utility of CDK4i/6i and mTORi dual inhibition was determined via long-term Colony Formation Assays (CFAs) using Palbociclib, rapamycin and sapanisertib (TAK228), a catalytic mTOR inhibitor. We generated Palbociclib (acquired)-resistant ALM cell lines and investigated the pharmacological inhibition of PI3K signaling pathways through immunoblot and colony-formation assays. Concurrent mTORi and CDK4i/6i inhibition showed effective reduction in pRb, pS6, Cyclin D and increases in Cleaved PARP protein, suggesting apoptotic cell death was elevated with combined CDK4i/6i+mTORi treatment. Similarly, CFAs revealed dual inhibition elicited superior antiproliferative effect over the monotherapy treatments. CFAs with acquired-resistance cell lines also showed that combination inhibition decreased colony formation, showing the potential utility of concurrent CDK4i/6i and mTORi as an approach against acquired resistance. Our results show the efficacy of combined inhibition as an anti-tumor strategy. Citation Format: Jeremy A. Bravo Narula, Vito W. Rebecca. Elevated Akt/mTOR signaling drives therapy resistance in ALM [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 419.

Abstract 3891: Epigenetic rewiring promotes antiandrogen resistance and metastasis via heterogenous oncogenic drivers in prostate cancer

Abstract Prostate cancer (PCa) is the most diagnosed cancer among American men, which has traditionally been treated through hormone therapy. However, after hormone therapy many patients with PCa still develop a more aggressive stage of PCa, called metastasis castration resistant prostate cancer (mCRPC). The second- generation antiandrogens, such as enzalutamide or apalutamide, are used to competitively inhibit the androgen receptor (AR) signaling and achieved great clinical success. However, most of the mCRPC patients would develop resistance to the targeted therapy drugs within 6 months to 2 years after initial administration. Consequently, understanding the molecular mechanism of antiandrogen resistance, has become a critical endeavor to provide a greater benefit to patients. mCRPC is characterized by extensive heterogeneity of genomic copy number alterations, which may lead to antiandrogen resistance. TP53 and RB1 alterations have been reported to be dramatically enriched in mCRPC neuroendocrine cancer and we have previously found that inactivation of both TP53 and RB1 confers resistance to antiandrogen through lineage plasticity, where cancer cells can transdifferentiate from a luminal lineage to a mixture of basal and neuroendocrine lineages, which is no longer dependent on AR signaling. Despite these exciting discoveries, only 10% of patients have TP53 and RB1 loss and it is estimated that approximately 40% of patients develop antiandrogen resistance through an undiscovered mechanism.To identify more genomic alterations which confer antiandrogen resistance, we performed an in vivo library screening and identified some of the frequently depleted genes as top candidates mediating antiandrogen response, including the chromatin helicase DNA-binding factor (CHD1). Strikingly, the loss of CHD1 establishes an altered chromatin landscape and enables the activation of heterogenous resistant subclones to emerge, including clones with ectopic NR3C1/GR, POU3F2/BRN2, TBX2, and NR2F1. This work provided an innovative model to explain the dramatically increased tumor heterogeneity in therapy resistant prostate cancer and suggested potential druggable targets to overcome resistance. Building on those exciting results, we are now examining the underlying mechanism how the epigenetic rewiring in resistant tumor clones confer resistance and monitoring the evolution of those heterogenous resistant subclones. Furthermore, we are revealing the collaborative function of those four resistant driver genes in promoting metastasis to various distal organs through multidisplinary approaches including single cell transcriptomics and 3D organoid modeling. The completion of this study will not only add clarity to the mechanism of antiandrogen resistance but may also lead to the development of novel biomarker and therapeutic approaches to overcome resistance. Citation Format: Xiaong li, Su Deng, Julisa Gonzalez, Carla Rodriguez Tirado, Choushi Wang, Nickolas A. Johnson, Lauren Metang, Ping Mu. Epigenetic rewiring promotes antiandrogen resistance and metastasis via heterogenous oncogenic drivers in prostate cancer. [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 3891.

Abstract 3906: The mRNA translational plasticity of small cell lung carcinoma is associated with its phenotypic transdifferentiation

Abstract Small cell lung carcinoma(SCLC), classified as a recalcitrant cancer type, accounts for 13-15% of all lung cancers with a median overall survival less than 10 months in patients with extensive stage SCLC. SCLC was once considered as molecularly homogeneous due to nearly universal loss of TP53 and RB1, whereas subsets of MYC-driven, non-neuroendocrine (non-NE) SCLC variants, possess chemoresistance, suggesting its high plasticity and intertumoral heterogeneity related to rapid refractory to first-line chemotherapies. Current pathognomonic classification stratifies SCLC into two NE subtypes (ASCL1+, NEUROD1+) and two non-NE subtypes (POU2F3+ and triple negative), associated with different expression patterns of MYC family proteins. MYC is a master regulator of mRNA translation, whether translational regulation actively tunes SCLC plasticity and the associated chemosensitivity remains an enigma. Here, we delineate the translation landscape of NE and non-NE SCLC cells by using paired human NE SCLC cell line and constitutive or induced non-NE SCLC cells. As expected, non-NE SCLC cells are more resistant to the clinically relevant first-line chemotherapy than NE SCLC cells. With polysome profiling in combination with polysome RNA-seq, we showed differential expression at both transcription- and translation-level. However, transcription-level changes minimally overlapped with the translational changes between NE and non-NE SCLC cells, with a global reduction of translation activity observed in non-NE SCLC cells. Through analyzing the polysome profiles, we observed a striking accumulation of 60S monosomes and diminishment of 80S ribosomes derived from non-NE SCLC cells compared to those from NE SCLC cells. This unique translational pattern in non-NE SCLC cells was correlated with an increased expression of eIF6, a ‘sitting on the bench’ member of eukaryotic initiation factor (eIF) family. The eIF6 couples 60S monosome maturation and recycling, enrolling a quintessential role in functional 80S ribosome formation. Positive correlation between eIF6 expression and non-NE SCLC tumors was observed in 81 tumor samples derived from patients with limited stage SCLC and CCLE cell consortium, in which c-MYC expression was also positively correlated with eIF6 level. By using both ultracentrifugation and fraction analysis from polysome profiling, we found that less association of eIF6 with 60S may mitigate 80S ribosome assembly in non-NE SCLC cells. In addition, in vivo xenograft models showed that eIF6 expression was higher in residual tumors upon chemotherapy. Taken together, these data revealed an eIF6-dependent translational regulation in non-NE transdifferentiation of SCLC subtypes, suggesting an underappreciated function of translational regulation of SCLC plasticity and the potential therapeutic value of eIF6 for overcoming SCLC resistance to chemotherapy. Citation Format: Haoning Peng, Mengyao Wang, Lu Li, Lunxu Liu, Shensi Shen. The mRNA translational plasticity of small cell lung carcinoma is associated with its phenotypic transdifferentiation. [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 3906.

Abstract 6206: Combined inhibition of AXL and ATR enhances replication stress, cell death and immune response in small cell lung cancer

Abstract Small cell lung cancer (SCLC) is an aggressive neuroendocrine lung tumor. Despite high initial responses to frontline chemo-immunotherapy, therapeutic resistance develops rapidly. There are limited treatment options in the relapsed setting, where the prognosis remains dismal. SCLC tumors experience continuous and high levels of replication stress (RS) due to ubiquitous loss of key cell cycle checkpoints, RB1 and TP53. Frequent amplification and high expression of the transcription factor cMYC further contribute to increased RS. Thus, high levels of RS expose a potential SCLC vulnerability and provide a therapeutic opportunity. Our group and others have shown that AXL, a TAM family receptor tyrosine kinase that is highly expressed in mesenchymal tumors, mediates resistance to chemotherapy, radiation and targeted therapies in SCLC, non-small cell lung cancer and other cancers, through its role in driving epithelial to mesenchymal transition (EMT). More recently, a novel role for AXL in DNA damage repair and tolerance has emerged. Therefore, we hypothesize that AXL targeting may be a potential therapeutic approach in SCLC. We first investigated the transcriptomic expression profile of AXL in SCLC clinical cohorts. AXL-high tumors were seen in a subset of treatment-naïve SCLC tumors, frequently among, but not limited to, the inflamed SCLC subtype. AXL expression was also seen in many relapsed SCLC tumors. As expected, tumors with high AXL expression also expressed several mesenchymal genes and higher EMT scores. Interestingly, among the treatment-naïve SCLC tumors, AXL expression was inversely correlated with a RS signature (rho=-0.54, p<0.001). Next, we tested the effects of AXL inhibition in SCLC in vitro and in vivo models. In a panel of 30 SCLC cell lines, bemcentinib, a selective AXL inhibitor in clinical trials for various advanced solid tumors, exhibited a range of antiproliferative activity, with IC50 values ranging from 41 nM to 10 µM (median IC50 3.1 µM). Bemcentinib also significantly delayed tumor growth in in vivo SCLC models. Biomarkers associated with sensitivity to bemcentinib in SCLC cell lines included markers of RS (cMYC, replication stress score) and DNA damage response (phospho CHK1S345, phospho CHK2T68). Bemcentinib also induced RS, indicated by the activation of ATR/CHK1-mediated RS response pathway, and DNA damage, and the combination with an ATR inhibitor (ceralasertib) showed a greater than additive effect. In a syngeneic model of SCLC, the combination of bemcentinib, ceralasertib and an anti-PDL1 antibody induced significant tumor regression. Together, these promising findings demonstrate that AXL inhibition may be an effective strategy to target the RS vulnerability common in SCLC. Citation Format: Kavya Ramkumar, C. Allison Stewart, Azusa Tanimoto, Qi Wang, Yuanxin Xi, Benjamin B. Morris, Runsheng Wang, Li Shen, Robert J. Cardnell, Jing Wang, Carl M. Gay, Lauren A. Byers. Combined inhibition of AXL and ATR enhances replication stress, cell death and immune response in small cell lung cancer [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 6206.

Abstract 1143: Development of a CDK2-selective small molecule inhibitor INCB123667 for the treatment of CCNE1hi breast cancers

Abstract Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors have been approved for treatment of metastatic ER+ HER2− breast cancer as monotherapy or in combination with endocrine therapy. However, many patients become resistant to CDK4/6 therapy due to various mechanisms such as loss of tumor suppressor Rb, hyperactivation of CDK4/6, and/or CDK2/Cyclin E1 expression and activity, resulting in a highly unmet clinical need. Triple-negative breast cancers (TNBC), owing to a lack of hormone receptor (HR) expression and extensive heterogeneity, remain notoriously aggressive and unresponsive to current therapies. CCNE1 overexpression or amplification has been shown to be an oncogenic driver associated with poor clinical outcomes in ovarian, gastric, endometrial, and HR+ breast cancers. CCNE1hi cancers are dependent on CDK2 for growth and survival. CDK2 in complex with CCNE1 phosphorylates Rb, resulting in E2F target gene expression and G1 to S-phase cell cycle progression. Using a potent and selective CDK2 inhibitor, INCB123667, we demonstrate the efficacy of CDK2 inhibition in CCNE1hi breast cancer models. Analysis of genome-wide CRISPR screen data identified a subset of CCNE1hi breast cancer models dependent on CDK2 comprised of basal and luminal breast cancer subtypes, including TNBC, ER+ HER2−, and HR− HER2+ models. Two CCNE1hi cell lines, HCC1569 and MDAMB157, were evaluated in cell assays monitoring pRb, S-phase, and growth inhibition, and found to be sensitive to treatment with INCB123667 and insensitive to multiple CDK4/6 inhibitors. Through extensive biochemical studies, INCB123667 was observed to be potently active against CDK2 at subnanomolar range and inactive against other CDKs (CDK1, CDK4, CDK6, CDK7, and CDK9). INCB123667 also selectively induced senescence in CCNE1hi HCC1569 cells. In contrast, CCNE1 nonamplified cell lines, MCF7 and T47D, were inactive in pRb, S-phase, and growth inhibition assays when treated with INCB123667. Significant tumor growth inhibition was observed in CCNE1hi PDX and xenograft models with minimal body weight loss. We also observed dose-dependent inhibition of CDK2 substrates, including pRb S780, both in vitro and in vivo. To further characterize downstream signaling and transcriptional changes with CDK2 inhibition, we identified a discrete gene signature associated with cell cycle regulation, which was notably distinct from CDK4/6 responsive target genes. In conclusion, we have demonstrated CDK2 activity in CCNE1hi breast cancers using INCB123667, a potent and selective small molecule inhibitor of CDK2 currently in clinical development. Treatment resulted in cell growth inhibition and antitumor activity in vitro and in vivo. Our data demonstrate the therapeutic potential of CDK2 inhibition in CCNE1hi HR+ HER2− and TNBC breast cancer models. Acknowledgments: R&D services provided by Pharmaron, Crown Bioscience, and Champions Oncology Citation Format: Saswati Chand, Michael Hansbury, Yvonne Lo, Pat Feldman, Justine Carl, Cynthia Timmers, Joshua Hummel, Susan Wee, Sunkyu Kim. Development of a CDK2-selective small molecule inhibitor INCB123667 for the treatment of CCNE1hi breast 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 1143.

Abstract 4525: YAP1 in relapsed pulmonary high-grade neuroendocrine carcinomas (NEC) is associated with CDKN2A loss, intact RB1, EMT and therapeutic vulnerability to MEK1 and CDK4/6 inhibition

Abstract Neuroendocrine carcinomas (NECs) are clinically aggressive carcinomas commonly arising from the respiratory and gastrointestinal tracts, typically categorized as large-cell neuroendocrine carcinomas (LCNECs) or small cell carcinomas (most commonly small cell lung cancer (SCLC)). Clinically, pulmonary LCNECs (pLCNECs) mirror the course common to SCLC - initial response followed by rapid and insurmountable resistance to one-size-fits-all approaches. Recently, SCLC has been subdivided into four subtypes with unique vulnerabilities, three of which are defined by the transcription factors ASCL1, NEUROD1, and POU2F3, while a fourth group exhibits an inflamed signature. We hypothesize that pLCNEC may be similarly classified into molecularly distinct subsets with unique therapeutic vulnerabilities - a fundamental step toward personalized medicine. We applied our SCLC 1300 gene signature to pLCNEC patient tumors and, as in SCLC, found three distinct subtypes determined by differential expression of ASCL1, NEUROD1, and POU2F3, but with a unique fourth subtype marked by expression of the transcription factor YAP1. Unlike in treatment-naïve SCLC, where YAP1 is absent, YAP1 expression clearly defines pLCNEC as two, roughly equal subsets with the YAP1-low tumors encompassing tumors expressing the other three transcription factors. Conversely, YAP1-high pLCNEC is more mesenchymal and inflamed, and less neuroendocrine (NE), reminiscent of inflamed SCLC. Additionally, YAP1-high status is associated with smoking exposure (P<0.001, FC=81), high frequency of CDKN2A homozygous deletion and SMARCA4 mutations, as well as intact RB1. These features are distinct from SCLC, wherein transcriptional subtypes lack distinct genomic characteristics. Consistent with CDKN2A deletion, YAP1-high pLCNEC cell lines have increased sensitivity to MEK1 and CDK4/6 inhibition. We also demonstrate that RB1 loss downregulates YAP1 expression, which may account for the absence of YAP1 in treatment-naïve SCLC due to ubiquitous loss of RB1. In contrast to treatment-naïve SCLC, where our group and others have been unable to detect YAP1, single-cell RNAseq analysis of biopsies from patients with relapsed SCLC identified emerging YAP1-positive cancer cell populations, which are similarly associated with increased EMT, immune cell infiltration (CD8+ T-cells), and loss of NE gene expression. This suggests that the ability for cancer cells to acquire YAP1 expression and, perhaps, pLCNEC-like features, may be a resistance mechanism in relapsed SCLC, contributing to the abundant intratumoral heterogeneity and highlighting potential vulnerabilities to overcome resistance. In summary, YAP1 may be a predictive biomarker of intact RB1 and response to cellular and checkpoint immunotherapy and MEK1/CDK4/6 inhibition in pLCNEC and relapsed SCLC. Citation Format: C. Allison Stewart, Lixia Diao, Yuanxin Xi, Runsheng Wang, Kavya Ramkumar, B. Leticia Rodriguez, Benjamin B. Morris, Li Shen, Bingnan Zhang, Yan Yang, Azusa Tanimoto, Veronica Y. Novegil, Luisa M. Solis Soto, Pedro F. Simoes da Rocha, Natalie Vokes, Don L. Gibbons, Michael Frumovitz, Junya Fujimoto, Jing Wang, Bonnie Glisson, Lauren A. Byers, Carl M. Gay. YAP1 in relapsed pulmonary high-grade neuroendocrine carcinomas (NEC) is associated with CDKN2A loss, intact RB1, EMT and therapeutic vulnerability to MEK1 and CDK4/6 inhibition. [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 4525.

Abstract 3869: Short or long-term treatment with CDK4/6 inhibitors in patients with ER+ breast cancer: characterization and comparative analysis of resistance in seventeen XPDX models

Abstract Background: Mechanisms of resistance to CDK4/6 inhibitors (CDK4/6i) have been well studied and several alterations identified including RB loss and altered expression of related genes including CCNE1, E2F4 and CDK6. However, whether duration of clinical treatment might elicit specific mechanism(s) of CDK4/6i resistance is unclear. To better understand if duration of clinical treatment correlates with unique resistance mechanisms, we established, characterized, and compared a panel of ER+ breast XPDX models from patients who benefitted then progressed on a CDK4/6i. Patients were separated into two groups by time to progression (TTP): those who responded up to twelve months (RES12) and patients with clinical response greater than one year (RES13+). Methods: Seventeen breast cancer XPDX models were analyzed, including eight previously described (7xRES12; 1xRES13+: SABCS2021: T Hernandez et al). Nine new models were established from seven patients: six from fluid samples with three designated as ductal (ST3105B, ST3105C, STM001B) and three lobular carcinoma (STM182, STM229, STM229B); two from lymph node biopsies (ST5676, STM127) and one from a liver core biopsy (ST4887B), all reported as ductal carcinoma. STM182 was classified as RES12 and the remaining eight as RES13+. These models were passaged and challenged with CDK4/6i to confirm resistance. Receptor expression was determined by IHC and genomic analyses including WES and RNAseq, were performed to identify mechanisms of resistance. For in vivo studies, CDK4/6i were dosed PO once daily at 50 mg/kg; endpoints included tumor volume (TV) and time from treatment initiation (TTI) with %T/C values and tumor regression reported at study completion; a %T/C of ≤20 versus control was considered sensitive. Tumor regression (%T/C<0) versus Day 0 TV was also reported. Results: Clinical TTP for RES12 (n=8) was four to twelve months and RES13+ (n=9) from thirteen to forty-two months. All models retained ER expression in evaluated passages with similar histology compared with archival clinical samples. Sequencing identified several variants including RB1 truncations or deletions and increased gene expression in CCND1, CCNE1 and the PIK3CA/AKT pathway. Interestingly, 5/8 RES12 models reported ESR1 mutations or fusions versus 1/9 RES13+ and PIK3CA mutations were reported in 1/8 RES12 versus 5/9 RES13+. Several RES13+ models also reported variants and increased amplification in the RICTOR/TORC2 pathway versus RES12. Conclusion: We have established, characterized, and compared a panel of seventeen breast XPDX models from fourteen female patients representing early or late acquired resistance to CDK4/6i therapy and identified potential differences in each set. These models and resulting data are useful in developing novel therapies for CDK4/6i-resistant patients. Citation Format: Alyssa Simonson, Johnnie Flores, Morgan Lynch, Emily Carpenter, Justine Hruzek, Jim Lund, Natalia Baños Herraiz, Kyriakos Papadopoulos, Amy Vander Woude, Gladys Rodriguez, Sreenivasa Chandana, Thomas Gribbin, Nehal Lakhani, Tatiana Hernandez, Maria Jose de Miguel, Amy Lang, Michael J. Wick. Short or long-term treatment with CDK4/6 inhibitors in patients with ER+ breast cancer: characterization and comparative analysis of resistance in seventeen XPDX models. [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 3869.

MP17-01 DIFFERENTIAL TRANSCRIPTOMIC INDICATORS OF POTENTIAL THERAPEUTIC RESPONSE TO TARGETED THERAPY FOR AJCC IIC+ LOCALIZED PROSTATE CANCER WITH DECIPHER ≥0.95

You have accessJournal of UrologyCME1 Apr 2023MP17-01 DIFFERENTIAL TRANSCRIPTOMIC INDICATORS OF POTENTIAL THERAPEUTIC RESPONSE TO TARGETED THERAPY FOR AJCC IIC+ LOCALIZED PROSTATE CANCER WITH DECIPHER ≥0.95 Eric Li, James Proudfoot, Alex Hakansson, Xin Zhao, Yang Liu, Adam Weiner, Edward Schaeffer, Elai Davicioni, and Ashley Ross Eric LiEric Li More articles by this author , James ProudfootJames Proudfoot More articles by this author , Alex HakanssonAlex Hakansson More articles by this author , Xin ZhaoXin Zhao More articles by this author , Yang LiuYang Liu More articles by this author , Adam WeinerAdam Weiner More articles by this author , Edward SchaefferEdward Schaeffer More articles by this author , Elai DavicioniElai Davicioni More articles by this author , and Ashley RossAshley Ross More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003237.01AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Among patients with AJCC Stage IIC+ cancer, a subset of patients are genomically at highest risk of progression with very high Decipher ≥0.95 scores. This group of patients is distinct and not present with AJCC I-IIB prostate cancer. As genomic changes may predict potential benefit from molecular based therapies, we sought to identify incidence of genomic alterations in this population. METHODS: We analyzed the transcriptomes of 13,117 men diagnosed with AJCC stage IIC+ localized prostate cancer. We compared signature readouts for androgen receptor activity (AR-A), PTEN loss, homologous repair deficiency, Rb loss, immune activity, and PSMA (FOLH1) expression, as well as prostate subtyping classifier (PSC) based on cell of origin and molecular pathways. Standardized mean differences (SMD) were calculated to compare size effect, with significant effect size defined as 0.2. RESULTS: 1767 men with AJCC Stage IIC+ cancer were found to have Decipher score ≥0.95. Patients with Decipher ≥0.95 possessed lower AR activity, as well as higher rates of PTEN loss and HR deficiency compared to men with high Decipher 0.6-0.95 (SMD 0.32, 0.40, and 0.43). There was a lower incidence of luminal differentiated (LD), and higher incidence of basal immune (BI) and basal neuroendocrine (BN) subtypes among those with Decipher ≥0.95. Rates of Rb loss remained low across all Decipher subgroups, and there was no significant difference in FOLH1 expression comparing men with Decipher 0.6-0.95 and Decipher ≥0.95. CONCLUSIONS: Patients with very high Decipher ≥0.95 localized prostate cancer have a distinct molecular profile, and may benefit from PARP inhibitors. Further investigation is required to understand how these molecular signatures may drive progression and metastasis in patients who are identified as very high risk on genomic classifier testing. Source of Funding: None © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e212 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Eric Li More articles by this author James Proudfoot More articles by this author Alex Hakansson More articles by this author Xin Zhao More articles by this author Yang Liu More articles by this author Adam Weiner More articles by this author Edward Schaeffer More articles by this author Elai Davicioni More articles by this author Ashley Ross More articles by this author Expand All Advertisement PDF downloadLoading ...

The New Way to Define Key Oncogenic Drivers of Small Cell Lung Cancer

Small-cell lung cancer (SCLC) continues to be the deadliest of all lung cancer types. Its high mortality is largely attributed to the unchangeable development of resistance to standard chemo/radiotherapies, which have remained invariable for the past 30 years, underlining the need for new therapeutic approaches. Recent studies of SCLC genome revealed a large number of somatic alterations and identified remarkable heterogeneity of the frequent mutations except for the loss of both RB and P53 tumor suppressor genes (TSGs). Identifying the somatic alterations scattered throughout the SCLC genome will help to define the underlying mechanism of the disease and pave the way for the discovery of therapeutic vulnerabilities associated with genomic alterations. The new technique made it possible to determine the underlying mechanism for the discovery of therapeutic targets. To these ends, the techniques have been focused on understanding the molecular determinants of SCLC.

Abstract P4-02-13: Homologous recombination deficiency, RB-loss gene signatures, intrinsic subtype and response to neoadjuvant treatment in HR+/HER2- early breast cancer: a correlative analysis of two phase II trials

Abstract Background: Hormone-receptor (HR)+/HER2- breast cancer (BC) is a biologically heterogeneous disease. Homologous recombination deficiency (HRD) and BRCA mutations have been previously reported to be associated with worse outcomes in HR+/HER2- metastatic BC patients receiving CDK4/6 inhibitors and endocrine therapy. Here, we assess the relation between HRD and RB-loss signatures, intrinsic subtyping, the PAM50-based chemo-endocrine score, and response to chemotherapy-based therapy and endocrine treatment in HR+/HER2- early BC. Methods: GIADA is a multicentric neoadjuvant phase II trial that treated premenopausal patients with Luminal B (LumB)-like BC (HR-positive, HER2-negative, with Ki67>20% and/or histologic Grade 3) with a combination of chemotherapy, immunotherapy and endocrine treatment. Expression of 758 genes on baseline tumor samples from all 43 patients was quantified by nCounter platform. The LETLOB phase II trial randomized postmenopausal women with clinical stage II-IIIA HR+/HER2- BC to neoadjuvant letrozole + lapatinib or letrozole + placebo for 6 months (Guarneri, JCO 2014). Gene-expression data (Affymetrix platform) from pre-treatment frozen core-biopsies was available from 66 out of 92 pts enrolled. Intrinsic subtype was assigned using a research-based PAM50 subtype predictor. A published HRD signature (Peng, Nat Commun 2014) and a signature of RB loss (RBsig), previously reported to potentially predict resistance to CDK4/6 inhibitors in HR+/HER2- BC (Malorni, Oncotarget 2016) were computed. The PAM50 based chemo-endocrine score (CES) was calculated using published definition (Prat, CCR 2017). Higher values of CES indicate increased endocrine sensitivity, while lower values indicate chemosensitivity. Association between genomic signatures was assessed through Pearson’s correlation coefficient. Association of genomic signatures with pCR was assessed through logistic regression and association with PEPI scores was assessed through Kruskal-Wallis test. Results: HRD signature levels were significantly higher in non-luminal (Basal-like and HER2-enriched) tumors as compared to Luminal (A or B) tumors (p>0.001 in the GIADA trial, p=0.021 in the LETLOB trial). Moreover, higher levels of HRD signature were associated with higher levels of RB-loss signature (Pearson correlation 0.355, p=0.020 in the GIADA trial; Pearson correlation 0.942, p< 0.001 in the LETLOB trial), higher levels of Basal-like signature (Pearson correlation 0.502, p< 0.001 in the GIADA trial; Pearson correlation 0.373, p=0.002 in the LETLOB trial) and lower levels of CES (Pearson correlation -0.422, p=0.005 in the GIADA trial; Pearson correlation -0.763, p< 0.001 in the LETLOB trial), indicative of higher chemosensitivity. In the GIADA trial, higher levels of HRD signature (p=0.018) and RBloss signature (p=0.073) and lower levels of CES (p=0.007) were associated with higher pCR rates after chemo, endocrine and immunotherapy. In the LETLOB trial, lower levels of HRD signature (p=0.068) and RBloss signature (p=0.042) and higher levels of CES (p=0.050) were associated with higher sensitivity to endocrine treatment (lower PEPI scores, 0 vs 1-3 vs 4 or more, after neoadjuvant letrozole). Conclusions: In HR+/HER2- early BC, HRD gene signatures, RB-loss gene signatures and non-luminal (especially Basal-like) intrinsic subtyping are associated with each other and associated with higher sensitivity to chemotherapy-based therapy and lower sensitivity to endocrine treatment. These observations might help correctly tailor systemic therapy, including biologic agents, in patients with HR+/HER2- early and advanced BC. Citation Format: Gaia Griguolo, Federica Miglietta, Laia Paré, Daniele G. Generali, Antonio Frassoldati, Antonino Musolino, Simon Spazzapan, Grazia Vernaci, Tommaso Giarratano, Marcello Lo Mele, Giancarlo Bisagni, Federico Piacentini, Enrico Tagliafico, Katia Cagossi, Francesca Schiavi, Claudia Pinato, Aleix Prat, Valentina Guarneri, Maria Vittoria Dieci. Homologous recombination deficiency, RB-loss gene signatures, intrinsic subtype and response to neoadjuvant treatment in HR+/HER2- early breast cancer: a correlative analysis of two phase II trials [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 P4-02-13.

Abstract P6-10-13: An update to a Phase I trial of CFI-402257, an oral TTK inhibitor, in patients with advanced solid tumors with HER2-negative breast cancer expansion cohorts

Abstract Background: TTK (also known as MPS1), a dual-specificity serine-threonine kinase, is critical for the spindle assembly checkpoint, chromosome alignment, and error correction in mitosis. Inhibition of TTK causes premature mitotic exit with unattached chromosomes, to result in chromosomal missegregation, aneuploidy, and cell death. CFI-402257 is a potent and highly selective inhibitor of TTK. Robust suppression of tumor growth was achieved upon oral dosing of single agent CFI-402257 in ER+/HER2- cell line and patient derived xenograft models. CFI-402257 demonstrated enhanced cytotoxicity in CDK4/6 inhibitor resistant ER+ breast cancer cell line models compared to parental cell lines, including those with RB1 loss. CFI-402257 has previously exhibited monotherapy and combination efficacy with a tolerable safety profile in ER+/Her2- Breast cancer patients in an ongoing clinical study which is updated here. Methods: This is an ongoing phase I, multi-center, dose escalation study (3+3 design) to determine the safety, tolerability, and maximum tolerated dose of CFI-402257 and to evaluate anti-tumor activity at the recommended phase 2 dose (RP2D). CFI-402257 was dosed once daily on a continuous schedule in 28-day cycles at a starting dose of 5 mg. Dose escalation included patients (pts) with advanced solid tumors. Dose expansion at the RP2D included pts with advanced solid tumors (Cohort A), advanced Her2-negative (ER+ or TNBC) with 1-4 prior lines of chemotherapy for metastatic disease (Cohort B), and ER+/Her2- breast cancer in combination with Fulvestrant (500 mg IM Day 1, 15 and 29 and then every 28 days) who have had prior treatment with an aromatase inhibitor in combination with a CDK4/6 inhibitor (≥ 3 months) and ≤1 prior chemotherapy for metastatic disease (Cohort C). Results: At data cutoff of May 2, 2022, 87 pts were enrolled. 86 pts (66 pts receiving monotherapy and 20 patients receiving combination therapy received ≥1 dose of study therapy and were analyzed for safety. One pt was not dosed due to elevated liver enzymes prior to first dose. The median age for mono was 61 years (range, 35-81) and for combo was 54 (range, 31-70). The median number of prior regimens mono and combo was 5 (range, 0-17; and 1-9, respectively). Tumor types in mono were breast cancer (27 pts), ovarian cancer (7 pts), GI cancer (3 pts), pancreatic cancer (3 pts), and other (30 pts). 20 breast cancer pts were enrolled in the combo. To date, 11 dose levels have been studied (range: 5 to 294 mg) in mono. There were 4 dose limiting toxicities (neutropenia >7days at 168mg/day, febrile neutropenia at 210mg/day, and neutropenia and colitis at 294mg/day, all grade 3). The RP2D of 168 mg was established. 3 pts in mono (biliary obstruction, febrile neutropenia, and pancytopenia) and 0 pts in combo discontinued study due to adverse events (AEs).Treatment emergent adverse events (TEAE’s) occurring in ≥30% of pts were fatigue (31 pts; 47%), nausea (30 pts; 46%), decreased appetite (22 pts; 33%), and diarrhea (21 pts; 32%) in mono; and nausea (11 pts; 55%) and diarrhea (7 pts; 35%) in combo. 35% of mono and 39% of combo AEs were considered related to CFI-402257 by the investigators. Grade ≥3 AEs and serious AEs were reported in 25 pts (38%) and 17 pts (26%), respectively in mono; and 5 pts (25%) and 3 pts (15%) in combo. The investigator assessed best overall response rate (partial response [PR] or better within the efficacy population) of 6% (PR; hepatocellular carcinoma n=1, breast cancer n=2 from n=47) in mono and 18% (PR; n=2 breast cancer) in combo (n=11), with additional patients still to be assessed. Conclusion: CFI-402257 is well tolerated as mono and combination with fulvestrant. Efficacy signals are emerging with pts in the combo cohort demonstrating anti-tumor activity. Additional efficacy will be updated at the time of the presentation. Citation Format: John Hilton, Daniel Renouf, David W. Cescon, Aaron Hansen, Alibiruni Abdul Razak, Lee-Anne Stayner, Trisha A. Denny, Emily Roberts-Thomson, Dih-Yih Chen, Mark Bray, Philippe Bedard. An update to a Phase I trial of CFI-402257, an oral TTK inhibitor, in patients with advanced solid tumors with HER2-negative breast cancer expansion cohorts [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 P6-10-13.

Abstract PD10-04: PD10-04 Combination of the next generation oral SERD camizestrant (AZD9833) with CDK4/6 and mTOR/AKT inhibitors delivers robust efficacy in a broad range of ER+ breast tumors

Abstract Next-generation oral selective estrogen receptor degraders (ngSERDs) are aiming to become the backbone endocrine therapy (ET) for patients with estrogen receptor positive (ER+) breast cancer (BC) by achieving greater ER signaling blockade than current therapies and tackling key mechanisms of resistance. Camizestrant (AZD9833) is an ngSERD for the treatment of ER+ BC which has demonstrated selective ERα degradation, pure ER antagonism and significant anti-tumor activity in ESR1 wild-type (ESR1wt) and mutant (ESR1m) tumors, as well as encouraging clinical activity in early phase trials. ER+ BC is responsive to therapies targeting ER and CDK4/6 signaling in the adjuvant and metastatic settings. To explore camizestrant combination potential as a backbone ET, camizestrant was partnered with either palbociclib or abemaciclib in CDK4/6 inhibitor (CDK4/6i) naïve and resistant in vitro and in vivo models. Combination benefit was observed in vitro in 3 parental ER+ BC cell lines, moreover camizestrant plus abemaciclib showed activity in palbociclib-resistant cell lines including lines harboring CCNE1amp and RB1 loss. In vivo, combination of camizestrant and either CDK4/6i was well tolerated with the combinations promoting improved efficacy in ESR1wt and ESR1m PDX tumor models compared to monotherapy arms. ER+ BC has a high prevalence of alterations in the PI3K/AKT/PTEN pathway which provides opportunities for treatment with PI3K/AKT pathway inhibitors. Camizestrant delivered enhanced efficacy when combined with mTORC1 inhibitor everolimus and AKT inhibitor capivasertib in CTC-174, an ESR1m and PI3KCAm tumor model. Additionally, combination with capivasertib was more efficacious than single treatments, at clinically relevant dose and schedules, in both PI3Kwt and mutated pathway in PDX models. These data demonstrate the interplay between PI3K/AKT/PTEN pathway inhibition and camizestrant mechanism of action. Finally, we explored a potential triple combination of camizestrant, capivasertib and palbociclib in Palbociclib-resistant models representative of PI3KCA/AKT/PTEN wt and altered tumors. This strategy delivered robust efficacy across these models comparing to single treatments and double combinations. The triplet led to durable regressions at clinically achievable doses of all compounds, irrespective of genetic background and aligned to biomarker modulation of the three signaling axis. These preclinical data demonstrate the potential of camizestrant to become the backbone ET, with high combinability in vivo with inhibitors of CDK4/6, mTOR and AKT. These combinations demonstrate the opportunity to impact care of patients with early and metastatic ER+BC, delivering benefit to broad patient populations including those with ESR1wt or ESR1m tumors, independent of PI3K/AKT/PTEN pathway mutation status, and in patients with both CDK4/6i sensitive and resistant tumors. Citation Format: Larissa Carnevalli, Susana Ros, Jelena Urosevic, Natalie Cureton, Sophie Darcy, Mandy Lawson, Stuart Williamson, Pablo Morentin Gutierrez, Azadeh Bashi, Jennifer Moss, Christopher Morrow, Barry Simon, Teresa Klinowska. PD10-04 Combination of the next generation oral SERD camizestrant (AZD9833) with CDK4/6 and mTOR/AKT inhibitors delivers robust efficacy in a broad range of ER+ breast tumors. [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 PD10-04.

Abstract P5-02-17: Prognostic and predictive role of RBsig and CCNE1/RB1 gene-expression signatures in patients with advanced breast cancer treated with palbociclib in combination with endocrine therapy in the PALOMA-2 and 3 trials

Abstract Background: We have previously identified two potentially predictive signatures of palbociclib resistance: the RBsig, composed of E2F1/E2F2 dependent genes, which is correlated with genetic loss of RB1, and the ratio between the gene expression levels of CCNE1 to RB1 (CCNE1/RB1). Both signatures have been previously tested in vitro and in neoadjuvant studies with palbociclib. The present analysis aims to explore the prognostic and predictive role of RBsig and CCNE1/RB1 in the pivotal phase III randomized trials PALOMA-2 and PALOMA-3. Materials and methods: Gene expression data from the PALOMA-2 and PALOMA-3 datasets were generated using the HTG EdgeSeq Oncology BM Panel, as previously described. Of the 87 genes composing RBsig, 46 were available within the EdgeSeq dataset and were used for the analyses; CCNE1 and RB1 were both available. RBsig was calculated as the mean of the Z-score scaled gene expression (log) of the 46 genes; CCNE1/RB1 was computed as the log ratio between the mRNA expression of CCNE1 and RB1. High and low values of RBsig and CCNE1/RB1 were defined based on the third quartile (Q3) as cutoff or as continuous variables. The prognostic/predictive effect of the signatures in terms of PFS was tested using Cox proportional hazard models and the Wald test. Results: The 46-genes RBsig versus the original signature showed excellent correlation in the METABRIC dataset (R=0.99), confirming its reliability as a surrogate of the original RBsig using EdgeSeq data. In both PALOMA-2 and PALOMA-3, RBsig high was significantly associated with a worse outcome compared to RBsig low in the palbociclib arm but not in the control arm [PALOMA-2: HR 1.4 (95% CI 1.0, 2.0) p=0.029 for palbociclib arm; HR 1.1 (95% CI 0.7, 1.6) p=0.71 for control arm. PALOMA-3: HR 1.7 (95% CI 1.1, 2.6) p=0.01 for palbociclib arm; HR 1.2 (95% CI 0.7, 1.9) p= 0.49 for control arm]. However, in both studies RBsig was not predictive of palbociclib resistance both when considered as a continuous variable and when dichotomized at Q3. Similarly to RBsig, in PALOMA- 3 patients with CCNE1/RB1 high tumors treated in the palbociclib arm showed a significantly worse outcome compared to those with CCNE1/RB1 low but this effect was not observed in those treated in the control arm [HR 1.6 (95% CI 1.1- 2.5) p= 0.03 for palbociclib arm; HR 1.2 (95% CI 0.7, 1.9) p=0.5 for control arm]. In addition, CCNE1/RB1 as a continuous variable was predictive of palbociclib benefit in PALOMA-3 (interaction p= 0.047). These effects were not observed in PALOMA-2. Conclusions: RBsig is a prognostic biomarker in patients treated with palbociclib, suggesting it may help in patients’ risk stratification. CCNE1/RB1 is predictive of palbociclib benefit in PALOMA-3, but not in PALOMA-2 probably due to the different patient populations and characteristics. Further studies of these biomarkers in patients treated with CDK4/6 inhibitors in the metastatic as well in the adjuvant setting are warranted. Citation Format: Luca Malorni, Matteo Benelli, Yuan Liu, Shibing Deng, Zhe Zhang, Cristina Guarducci, Angela Leo, Agostina Nardone, Francesca Galardi, Emanuela Risi, Erica Moretti, Dario Romagnoli, Chiara Biagioni, Marta Paoli, Laura Biganzoli, Ilenia Migliaccio. Prognostic and predictive role of RBsig and CCNE1/RB1 gene-expression signatures in patients with advanced breast cancer treated with palbociclib in combination with endocrine therapy in the PALOMA-2 and 3 trials [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 P5-02-17.