Simultaneous targeting of mTOR and mLST8 in human breast cancer cells

Despite our continually increasing knowledge of cancer biology and intracellular mechanisms, identifying targets for cancer treatment remains a challenge. Cancer cells are heterogeneous and plastic, which are involved in innate and acquired resistance to molecularly targeted anticancer drugs, respectively. This project focuses on the PI3K/Akt cell signaling pathway, specifically mammalian target of rapamycin (mTOR) and GβL (mLST8), to halt cell proliferation. The breast cancer cell lines MDA-MB-231, MDA-MB-468, and AU565 were exposed to small interfering RNAs (siRNAs) targeting mTOR or mLST8, as well as a combination of both. The cell protein expression profile was studied to investigate the efficiency of protein silencing, and potential synergistic effect on downstream effectors of the pathway. Due to poor cellular internalization of siRNA, we also investigated the efficiency of small cell-penetrating peptides specifically designed as siRNA carriers. Three cyclic peptides (WR5, [R5K]W5 and [R6K]W6) incorporating ring-forming arginines (as a cationic moiety for inter-ionic interaction with nucleic acids), tryptophan (as a hydrophobic chain to enhance interaction with cell membrane, and lysine as the conjugation site for tryptophan chain were studied for in vitro siRNA delivery. The siRNA complexes formed with these amphiphilic peptides were delivered to the same breast cancer cell lines, and the efficiency of cellular internalization and mTOR and mLST8 silencing was investigated. Our findings confirm the efficiency of siRNAs in interrupting formation of mTOR complexes, and the activation of downstream proteins. Further studies are required to confirm these findings in patient cells and to evaluate the efficacy of this approach in vivo. Citation Format: Melissa Coyle, Romina Nabiee, Robert Lamboy, Parvin Mahdipoor, Keykavous Parang, Hamidreza Montazeri Aliabadi. Simultaneous targeting of mTOR and mLST8 in human breast cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr B01.