Abstract 5462: Antiproliferative and cytotoxic activities of 5-(nonyloxy)tryptamine derivatives in breast cancer cells

In women in the Western world, breast cancer is the most common malignancy with over 40,000 deaths attributed to this disease. Major factors for patient death include metastasis, and the loss of sensitivity or resistance to current therapies including radiation, hormonal therapy and chemotherapy. Thus, to enhance the efficacy of current therapies and prolong patient survival, there is an urgent need for the development of novel therapeutic strategies. Recently, we have discovered a potential new role for 5-(nonyloxy)tryptamine (5-NT) in the treatment of breast cancer. This study investigates potential mechanism(s) underlying the anti-proliferative and cytotoxic effects of 5-NT derivatives on breast cancer cell lines. Initial cell viability assays using the MTS reagent indicate that 5-NT has an IC50 value of 5 μM and 9 µM against MDA-MB-231 (triple-negative) and MCF-7 (ER-positive) breast cancer cell lines respectively. 5-NT is known to exert its effects through the serotonin (5-hydroxytryptamine, 5-HT) 5-HT1B/1D receptors. Hence, based on available information about the interaction between 5-NT and the 5-HT1B/1D receptors, a library of 5-NT derivatives was synthesized, and the compounds tested for their ability to inhibit breast cancer cell growth. Interestingly, structure-activity relationship (SAR) studies using cell viability assays indicate that these 5-NT derivatives do not solely exert their effects through the 5-HT1B/1D receptors. Of the 60 compounds synthesized, KD06 appears to be the most potent. Further analysis in MDA-MB-231 cells indicates that KD06 induces apoptosis in both a time-dependent and dose-dependent manner as determined by FACS analysis using Annexin-V and propidium-iodide staining. This was confirmed with a caspase-3/7 activity assay as well as by Western blotting to detect PARP cleavage. FACS analysis also indicates an arrest in the cell cycle, which is supported by reverse phase protein array (RPPA) studies. RPPA data suggest a down-regulation in global protein translation and cell proliferation through inhibition of the mTOR pathway, as indicated by decreased levels of phosphorylated 4E-BP1, p70S6K and S6 among others. Additionally, critical proteins involved in cell cycle progression such as Rb and cyclin B1 were also down-regulated. Western blotting suggests that ER stress could contribute to the observed inhibition in cell proliferation and induction of apoptosis. This was indicated by a progressive increase in levels of phospho-PERK, phospho-eIF-2α, ATF4 and CHOP, in a time-dependent and dose-dependent manner. Studies are currently being performed to assess the efficacy of KD06 in inhibiting growth of highly aggressive and metastatic human breast tumors in an in vivo orthotopic xenograft breast cancer model in nude mice. Citation Format: Clint D. J. Tavares, Jiney Jose, Ashwini K. Devkota, Jihyun Park, Tamer S. Kaoud, Eric V. Anslyn, Kevin N. Dalby. Antiproliferative and cytotoxic activities of 5-(nonyloxy)tryptamine derivatives in breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5462. doi:10.1158/1538-7445.AM2014-5462