Abstract 2660: Selective inhibition of HSP90 by its C-terminal inhibitors is more effective to suppress bladder cancer cell growth

Abstract

Abstract HSP90 (heat shock protein 90) is a central chaperone to regulate protein folding for a large array of client proteins as important drivers for cancer development. Its overexpression in bladder cancer, especially the most aggressive muscle-invasive subtype (MIBC), attracts a lot of attention for drug development. Although many HSP90 inhibitors have been tested in clinical trials for many cancers, none of them has been approved by FDA for cancer therapy. One of critical problems is the co-activation of heat shock response (HSR), an integrated stress response pathway with strong pro-survival function. Our previous studies also observed the robust activation of HSF1 (an effector of HSR) and HSP70 (a target gene of HSF1) associated with the inhibition of HSP90 by its N-terminal (NT) inhibitors, thereby impairing the effect of HSP90 NT inhibitor. Intriguingly, HSP90 inhibitors tested in the clinical trials so far are all NT inhibitors, further promoting us to explore the HSP90 C-terminal (CT) inhibitors as a new strategy for MIBC therapy. In this study, a number of MIBC cell lines representing different cancer stages were utilized to generate more physiologically relevant data. When UMUC3, T24, SW-780, and J82 cells were treated by novobiocin (Novo, a HSP90 CT inhibitor) at a series of concentrations, it was found that Novo inhibited the proliferation of all cells. However, their sensitivities to Novo were different in the following order: T24> SW-780> UMUC3> J82. This effect was partially correlated with the aggressiveness of cancer stage, wherein higher grade MIBC cells are less sensitive to Novo treatment. Western blotting (WB) analysis indicated that HSF1 and HSP70 were not activated. More importantly, client kinase AKT1 was highly activated in SW-780 but not in all other three cells; ERK1/2 was highly activated in UMUC3 but not in all other three cells, suggesting that the activation of kinases is differential and cell type-dependent. Confocal fluorescence microscopic analysis revealed that HSP90 cellular localization was also altered by Novo from more diffused cytoplasmic distribution to more perinuclear localization, whereas the predominant nuclear localization of HSF1 was not changed by Novo treatment, suggesting the localization of HSP90, different modified forms, or the interaction with other proteins may also contribute to HSP90’s functions in cell growth. These aspects are under investigation by various biochemical and cell biology techniques to validate the advantage of HSP90 CT inhibitors for MIBC therapy. (* corresponding authors) Note: This abstract was not presented at the meeting. Citation Format: Jun Ling, Connor Magura, Vaibhav Sharma, Maisara Rahimi, Heinric Williams. Selective inhibition of HSP90 by its C-terminal inhibitors is more effective to suppress bladder cancer cell growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2660.