Abstract 1202: Targeting PIK3C3 to overcome drug resistance resulted from prosurvival autophagy in cancer cells

Abstract

Abstract Autophagy is an important cellular recycling mechanism in which portions of cytosol or organelles are sequestered into a double-membrane structure and delivered to lysosome for degradation. PIK3C3 is the only class III PI3K, which specifically generates phosphatidylinositol 3-phosphate (PtdIns3P). It in turn recruits proteins containing FYVE or PX domains, thereby initiating various complexes at the membranes of endosomes, phagosomes and autophagosomes. Recently, several studies have shown that autophagy is upregulated in cancer cells when exposing to chemotherapy and radiotherapy. Therefore, the rationale of targeting autophagy addiction in cancer was proposed by combining autophagy inhibition with agents that induce autophagy as a pro-survival response to increase their therapeutic efficacy. We stably knocked down PIK3C3 in cancer cell lines and combined with clinical therapeutic agents reportedly induce pro-survival autophagy. Cell viability was examined by MTT assay and combination index was determined by Compusyn software. The autophagy flux was evaluated by detecting protein levels of LC-3II and p62 through western blot analysis. The results showed PIK3C3 knockdown synergistically sensitize the killing effects of gefitinib and gemcitabine in A549 cells and Panc1 cells, respectively. Both of gefitinib and gemcitabine increased autophagy flux, as evidence by the increase of LC3-II and decrease of autophagy substrate, p62. However, the combination of PIK3C3 knockdown and therapeutic agents increased both of the protein levels of LC3-II and p62. These data suggest incomplete autophagy when the function of PIK3C3 was inhibited. The phenomenon was confirmed by bombing autophagy inducer and PIK3C3 inhibitors. Moreover, no appreciable apoptotic cell death was observed. Taken together, our study revealed a potential strategy by targeting PIK3C3 to overcome drug resistance associated with the pro-survival autophagy in cancer. Citation Format: CHUN-HAN CHEN. Targeting PIK3C3 to overcome drug resistance resulted from prosurvival autophagy in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1202. doi:10.1158/1538-7445.AM2017-1202