Evolution of Hsp90 targeting: From stress biology to clinical translation.

Hsp90 inhibitors represent a decades-long experimental framework that has progressively uncovered how molecular chaperone systems are organized, regulated, and rewired in disease. Early natural products established that pharmacologic engagement of Hsp90 simultaneously destabilizes broad client networks and exposes a central layer of proteostasis control. Subsequent structural, biochemical, and translational studies revealed the mechanistic importance of nucleotide-driven conformational cycling, cochaperone exchange, paralog specialization, and subcellular compartmentalization, as well as the emergence of disease-specific chaperone assemblies such as the epichaperome. In parallel, adaptive responses to Hsp90 inhibition, including heat-shock factor 1 activation, unfolded-protein-response signaling, autophagy induction, and oncogenic network rewiring, illuminated the resilience built into proteostasis architecture and the conditions under which it can be overcome. Later inhibitor classes, encompassing C-terminal allosteric ligands, middle-domain modulators, isoform-selective agents, epichaperome-directed compounds, and targeted degraders, extended the field from pan-inhibition toward increasingly precise intervention in specific chaperone states. The first regulatory approval of an Hsp90 inhibitor, Pimitespib, for refractory gastrointestinal stromal tumor, marks a translational milestone that validates this framework clinically. Combination studies have further mapped where Hsp90 inhibition is most informative and most effective, demonstrating that benefit is strongest when deployment is guided by defined client dependency, proteostasis burden, immune context, or biomarker selection. Together, these advances position Hsp90 inhibitor research as a major source of mechanistic insight into molecular chaperones and as a foundation for biomarker-guided, context-aware targeting of proteostasis in oncology and beyond.