Abstract 3534: Inhibition of melanoma cell survival through p62/LC3B autophagic signaling

Abstract

Abstract The primary objectives of this study were i) systematic evaluation of the differences in basal autophagic activity between melanocytes and malignant melanoma cells to determine whether these differences may be selectively targeted using the ROS inducer, Nexrutine (NX); ii) determination of NX selectivity in inhibiting melanoma cell survival and iii) specific involvement of autophagy signaling protein, SQSTM1/p62 in NX-mediated autophagic cell survival. NX is obtained from the bark of the cork tree, Phellodendron amurense. A panel of melanocyte and melanoma cells was evaluated for basal autophagy level and effect of NX treatment, including protein levels and turnover of p62 and LC3B (+/- CQ), and number of autophagic puncta per cell. Trypan blue, MTT, and Annexin V-APC were used to evaluate the effect of NX on cell death, proliferation and apoptosis. Genetic approach using siRNA for p62 and overexpression using HA-p62 followed by survival, proliferation, and autophagy measurements were used to further evaluate the possibility of p62 as a molecular target for inhibition of autophagy seen using NX. We found that i) melanoma cells displayed high autophagic flux compared with melanocytes, ii) NX treatment a) inhibited autophagy in melanoma cells, b) inhibited melanoma cell survival, and c) induced apoptosis in melanoma cells, iii) knockdown of p62 resulted in a lesser inhibition of cell viability and autophagy after NX treatment in high p62-expressing melanoma cells, and iv) overexpression of p62 sensitized low p62-expressing normal melanocytes and melanoma cells to NX-mediated cell death and autophagy inhibition, suggesting that p62 is a bonafide molecular target of NX. Overall, we show that Nexrutine is able to inhibit the inherent high level of pro-survival autophagy in melanoma cells, leading to loss of cell viability and induction of apoptosis, while melanocytes remain unaffected by NX at the same doses. Further, SQSTM1/p62 was found to be a critical mediator of the NX-mediated inhibition of autophagy and cell viability. This study demonstrates that NX maybe a promising novel, non-toxic agent for melanoma. Supported by R21 CA125719 & ACRCF (RG); NIDCR T32 DE14318/COSTAR (HGH) Citation Format: Heather G. Hambright, Addanki P. Kumar, Rita Ghosh. Inhibition of melanoma cell survival through p62/LC3B autophagic signaling. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3534.