Abstract P3-07-19: Anti-depressant Amitriptyline Augments the Efficacy of Tamoxifen in ER positive breast cancer
Authors: Venkata Prabhakar Pitta , Rao Arhan D. , Timilsina Santosh , Singh Deepika , Vadlamudi Ratna K. , Kaklamani Virginia , Rao Manjeet K. 
Published: March 2023

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.