Abstract 715: Targeting the mTOR pathway for the prevention of er-negative breast cancer

Abstract

Abstract Background: Triple-Negative breast cancer (TNBC) is an aggressive cancer that lacks expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. These cancers have a poor prognosis and are treated predominantly with chemotherapy. Therefore, we are working to find preventive therapies for these potentially lethal cancers. Dysregulation of PI3K-mTOR pathway is commonly associated with TNBC and other ER-negative breast cancers. We hypothesized that targeting mTOR may prevent development of ER-negative breast cancers and in this study tested whether the mTOR inhibitor, everolimus, prevents cancer in several mouse models of ER-negative breast cancer. Methods: MMTV-erbB2 mice were purchased from the Jackson Laboratory. C3(1)/SV40TAg and BRCA1co/co;MMTV-Cre;p53+/- were generated through breeding. P53-null and p53-mutant mammary gland mice were generated by transplanting p53-null or p53-mutant mammary glands into cleared fat pads of p53-wild type mice. The mice were treated with either control or everolimus (5mg/kg), administered by oral gavage daily (5X/week). All mice develop palpable mammary tumors within 8-12 months. Mice were observed daily for tumor formation and drug toxicity. The percentage of tumor free mice was recorded, and time to tumor development was visualized using Kaplan-Meier curves and analyzed using the generalized Wilcoxon test. Results: Treatment with everolimus significantly increased median survival of all mouse models. Everolimus treatment was also able to completely prevent mammary tumor formation in 27% of C3(1)/SV40Tag mice and 44% p53-mutant mammary gland mice. In p53-null mammary gland mice, 46% of control mice had developed tumors after 420 days, compared to 7% of everolimus treated mice. Long term treatment of everolimus was associated with mild toxicity that includes slight weight loss (<10%) and skin changes (matted hair, skin erythema). Conclusions: Everolimus significantly delayed mammary tumorigenesis in all five breast cancer mouse models. Our results suggest that everolimus is a promising cancer preventive drug for ER-negative tumors, and that further studies of everolimus in combination with other targeted therapies are warranted. In the future, clinical trials of the everolimus should be considered for the prevention of breast cancer in high-risk patients. Supported by NCI PREVENT Cancer Preclinical Drug Development Program (HHSN-2612015000-18I (PB). Citation Format: Abhijit Mazumdar, Jamal Hill, William Tahaney, Yanxia Ma, Alejandro Contreras, Shizuko Sei, Altaf Mohammed, Powel Brown. Targeting the mTOR pathway for the prevention of er-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 715.