Cancer cell responses to Hsp70 inhibitor JG-98: Comparison with Hsp90 inhibitors and finding synergistic drug combinations

Abstract

Hsp70 is a promising anti-cancer target. Our JG-98 series of Hsp70 inhibitors show anti-cancer activities affecting both cancer cells and tumor-associated macrophages. They disrupt Hsp70 interaction with a co-chaperone Bag3 and affect signaling pathways important for cancer development. Due to a prior report that depletion of Hsp70 causes similar responses as depletion of Hsp90, interest to Hsp70 inhibitors as drug prototypes is hampered by potential similarity of their effects to effects of Hsp90 inhibitors. Here, using the Connectivity Map platform we demonstrate that physiological effects of JG-98 are dissimilar from effects of Hsp90 inhibitors, thus justifying development of these compounds. Using gene expression and ActivSignal IPAD platform, we identified pathways modulated by JG-98. Some of these pathways were affected by JG-98 in Bag3-dependent (e.g. ERK) and some in Bag3-independent manner (e.g. Akt or c-myc), indicating multiple effects of Hsp70 inhibition. Further, we identified genes that modulate cellular responses to JG-98, developed approaches to predict potent combinations of JG-98 with known drugs, and demonstrated that inhibitors of proteasome, RNApol, Akt and RTK synergize with JG-98. Overall, here we established unique effects of novel Hsp70 inhibitors on cancer cell physiology, and predicted potential drug combinations for pre-clinical development.

HSP70 Multi-Functionality in Cancer

“…Interesting results were gained by Li and colleagues with JG-98 inhibitor. JG-98 disrupts HSP70-BAG3 complex, thereby, freezing HSP70 in its ADP state [213,214]. Similar effects were reported with YM-1, an inhibitor that targets HSP70-NEF complex, indicating that freezing of HSP70 in ADP-bound state can be the most promising strategy for the future developments of anti-cancer drugs [168].…”

Human Stress-inducible Hsp70 Has a High Propensity to Form ATP-dependent Antiparallel Dimers That Are Differentially Regulated by Cochaperone Binding*

“…Furthermore, antiparallel dimeric Hsp70 species were detected in in vitro reconstituted complexes involving Hsp90, Hop, Hsp40, and GR (Glucocorticoid receptor) (27), supporting the functional role of Hsp70 dimerization in multichaperone assemblies. The level of inducible Hsp70 is elevated under proteotoxic conditions and chronically increased in some pathologies, including cancer (73)(74)(75)(76)(77)(78). Given that intracellular concentrations of Hsp70 can reach up to tens of M under stress conditions (79,80), the physiological importance of ATP-dependent Hsp70 dimers for overcoming proteotoxic stress becomes a likely hypothesis.…”

The Molecular Chaperone Heat Shock Protein 70 Controls Liver Cancer Initiation and Progression by Regulating Adaptive DNA Damage and Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Signaling Pathways

“…Therefore, based on a previous report (85), we sought to test a model in which the negative loop on ERK activity in mutant mice that depends on the DUSP6 phosphatase activity could involve a second level of regulation with critical direct participation of BAG3, a cochaperone of HSP70 and potent regulator and enhancer of DUSP6-ERK1/2 interaction. Notably, a well-defined HSP70-BAG3 interaction network has been described to act as a broadly acting regulator of cancer cell signaling factors (86,87). According to this finding, depletion of HSP70 not only is expected to increase ERK1/2-BAG3 interaction, which in turn suppresses p-ERK1/2 activity, but also could cause disruption of HSP70-BAG3 complexes, thus amplifying the antitumor effects.…”