Abstract A20: 17-Aminogeldanamycin inhibits cytoprotective UPR pathways and cooperates with inhibitors of the MAPK signaling cascade in apoptosis induction

Abstract

Abstract Geldanamycin is an inhibitor of Heat Shock Protein 90 (HSP90). Attenuation of HSP90 activity results in accumulation of unfolded proteins, induction of endoplasmic reticulum (ER) stress, and activation of unfolded protein response (UPR). HSP90 is a chaperone protein participating in appropriate folding of more than 100 proteins, including IRE1α and BRAFV600E. In melanoma cells, BRAFV600E was correlated with chronically induced ER stress and involved in UPR-induced resistance to apoptosis. As geldanamycin is highly hepatotoxic, geldanamycin derivatives exerting similar proapoptotic properties but higher selectivity towards cancer cells are needed. In the present study, 17-aminogeldanamycin exerted higher proapoptotic activity than geldanamycin in patient-derived melanoma cell populations as demonstrated by using fluorescence time-lapse imaging (IncuCyte ZOOM). We have also shown that 17-aminogeldanamycin inhibits ERK1/2 activity and cell proliferation,as well as induces apoptosis transiently, enhancing expression of HSP70 and GRP78. GRP78 regulates activity of the UPR pathway, and we have demonstrated that 17-aminogeldanamycin inhibits IRE1α-dependent pathway of UPR responsible for degradation of unfolded proteins and reduces levels of 36 kDa product of ATF6 cleavage in selected melanoma cell populations. Moreover, we have shown that combination of 17-aminogeldanamycin and trametinib induces apoptosis earlier and more efficiently. Our study suggests that cooperation of 17-aminogeldanamycin and trametinib might result from concurrent inhibition of the MAPK and protective UPR pathways but can be also associated with the basal UPR activity, which is diverse among drug-naïve melanoma cell populations. Further studies are necessary to fully explore antimelanoma capabilities of 17-aminogeldanamycin and its combination with targeted therapy. This work was financially supported by Grant 2014/15/B/NZ7/00947 from National Science Centre (Poland), and 502-03/1-156-01/502-14-318 from Medical University of Lodz. Citation Format: Aleksandra H. Mielczarek-Lewandowska, Mariusz L. Hartman, Malgorzata M. Sztiller-Sikorska, Marta Osrodek, Anna E. Gajos-Michniewicz, Malgorzata E. Czyz. 17-Aminogeldanamycin inhibits cytoprotective UPR pathways and cooperates with inhibitors of the MAPK signaling cascade in apoptosis induction [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr A20.