The management of metastatic estrogen receptor (ER) positive HER2 negative breast cancer (ER+) has improved; however, therapeutic resistance and disease progression emerges in majority of cases. Using unbiased approaches, as expected PI3K and MTOR inhibitors emerge as potent inhibitors to delay proliferation of ER+ models harboring PIK3CA mutations. However, the cytostatic efficacy of these drugs is hindered due to marginal impact on the expression of cyclin D1. Different combination approaches involving the inhibition of ER pathway or cell cycle result in durable growth arrest via RB activation and subsequent inhibition of CDK2 activity. However, cell cycle alterations due to RB loss or ectopic CDK4/cyclin D1 activation yields resistance to these cytostatic combination treatments. To define means to counter resistance to targeted therapies imparted with RB loss; complementary drug screens were performed with RB-deleted isogenic cell lines. In this setting, RB loss renders ER+ breast cancer models more vulnerable to drugs that target DNA replication and mitosis. Pairwise combinations using these classes of drugs defines greater selectivity for RB deficiency. The combination of AURK and WEE1 inhibitors, yields synergistic cell death selectively in RB-deleted ER+ breast cancer cells via apoptosis and yields profound disease control in vivo. Through unbiased efforts the XIAP/CIAP inhibitor birinapant was identified as a novel RB-selective agent. Birinapant further enhances the cytotoxic effect of chemotherapies and targeted therapies used in the treatment of ER+ breast cancer models selectively in the RB-deficient setting. Using organoid culture and xenograft models, we demonstrate the highly selective use of birinapant based combinations for the treatment of RB-deficient tumors. Together, these data illustrate the critical role of RB-pathway in response to many agents used to treat ER+ breast cancer, whilst informing new therapeutic approaches that could be deployed against resistant disease.
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The authors thank all members of the laboratory group and colleagues in the discussion and preparation of the manuscript. We thank Emily Schultz for acquiring the patient information and the genetic characteristics of the tumor tissues. Dr. Steven Pruitt provided the lentiviral vector for CDK2 sensor. Drug screening was performed through Small Molecule Screening facility at RoswellPark Cancer Center. We would like to thank Dr. Sandra Sexton, Facility director of Laboratory Animal Resources at Roswell Park for assisting us with xenografts. The research was supported by a grant to AKW and ESK from National Cancer Institute (NCI).
ESK and AKW have received research funding from Eli Lilly, Novartis and Pfizer over the last 5 years. There is no current research support from these entities and the study was written in the absence of input from any pharmaceutical company.
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Kumarasamy, V., Nambiar, R., Wang, J. et al. RB loss determines selective resistance and novel vulnerabilities in ER-positive breast cancer models. Oncogene 41, 3524–3538 (2022). https://doi.org/10.1038/s41388-022-02362-2