Dual targeting of HSP70 does not induce the heat shock response and synergistically reduces cell viability in muscle invasive bladder cancer

Abstract

Muscle invasive bladder cancer (MIBC) is a common malignancy and major cause of morbidity worldwide. Over the last decade mortality rates for MIBC have not decreased as compared to other cancers indicating a need for novel strategies. The molecular chaperones HSP70 and HSP90 fold and maintain the 3-dimensional structures of numerous client proteins that signal for cancer cell growth and survival. Inhibition of HSP70 or HSP90 results in client protein degradation and associated oncogenic signaling. Here we targeted HSP70 and HSP90 with small molecule inhibitors that trap or block each chaperone in a low client-affinity “open” conformation. HSP70 inhibitors, VER155008 (VER) and MAL3-101 (MAL), along with HSP90 inhibitor, STA-9090 (STA), were tested alone and in combination for their ability to reduce cell viability and alter protein levels in 4 MIBC cell lines. When combined, VER+MAL synergistically reduced cell viability in each MIBC cell line while not inducing expression of heat shock proteins (HSPs). STA+MAL also synergistically reduced cell viability in each cell line but induced expression of cytoprotective HSPs indicating the merits of targeting HSP70 with VER+MAL. Additionally, we observed that STA induced the expression of the stress-related transcription factor HSF2 while reducing levels of the co-chaperone TTI1.

Heat Shock Proteins Are Essential Components in Transformation and Tumor Progression: Cancer Cell Intrinsic Pathways and Beyond

“…Nevertheless, 55 of 332 chaperone genes were shown to be essential for viability in K562 human leukemia cells, which is in agreement with findings from Rodina et al, and supports the notion that key nodes within the chaperome network may be targeted in cancer in order to achieve toxicity to transformed cells [26,52,59]. This has previously been exemplified by studies demonstrating the increased toxicity of Hsp90 inhibitors upon the co-inhibition of Hsp70 [60,61].…”

“…Another class of inhibitors that target the C-terminal domain of Hsp90 induces the degradation of client oncogenes, but does not activate the HSF1-feedback loop and continue to be developed [190], along with small molecules that specifically target the constitutively expressed Hsp90 Beta paralog [191,192]. Furthermore, as HSPs operate in relay and have redundant protein folding activities, another tactic to dramatically disrupt proteostasis is to simultaneously inhibit Hsp70 and Hsp90, an approach that has shown some merit [60,84].…”

The heat shock protein 70 inhibitor VER155008 suppresses the expression of HSP27, HOP and HSP90β and the androgen receptor, induces apoptosis, and attenuates prostate cancer cell growth

“…Shown are means ± SD and statistical analysis was performed using the Student t test. 33 As was to be expected, the inhibition of HSP70 activity itself did not affect its own protein expression. Significances were defined as: *P < 0.05, ***P < 0.001 Besides other mechanisms, apoptotic properties of HSP70 are also mediated by the regulation of apoptotic cascades.…”

Hsp70 inhibitors: Implications for the treatment of colorectal cancer

“…MAL3‐101 exhibits antiproliferative and proapoptotic effects in multiple cancer cell lines . The combination of VER‐155008 along with MAL3‐101 synergistically reduced cell viability and disrupted oncogenic signaling pathway in bladder cancer cell lines while did not induce expression of other HSPs and heat shock response . It also exerts potent anticancer activity against Merkel‐cell carcinoma both in vitro and in vivo .…”