Enhancement of colorectal cancer therapy through interruption of the HSF1-HSP90 axis by p53 activation or cell cycle inhibition
The heat-shock protein 90 (HSP90) is a promising target in cancer therapy, but its inhibitors' clinical trial failures are partly due to a compensatory heat-shock response (HSR) mediated by heat-shock factor 1 (HSF1). We previously showed that wildtype p53 reduces HSR by repressing HSF1 via a p21-CDK4/6-MAPK-HSF1 axis. Here, we explore if simultaneous p53 activation or cell cycle inhibition can disrupt the HSF1-HSR axis and enhance HSP90 inhibitors' efficiency.  mRNA sequencing was performed on HCT116 cells treated for 24 hours with DMSO, 50 nM Ganetespib, 1 µM RG-7388, or their combination.  We found that the p53 activator Idasanutlin suppresses HSF1-HSR activity in HSP90 inhibitor-based therapies, synergistically reducing cell viability and accelerating cell death in p53-proficient colorectal cancer (CRC) cells and organoids. Combination therapy upregulates p53 pathways, apoptosis, and inflammation. In a CRC mouse model, dual HSF1-HSP90 inhibition represses tumor growth and alters immune cell composition.  CDK4/6 inhibition under HSP90 inhibition mimics HSR repression in p53-proficient CRC cells. In p53-deficient CRC cells and p53-mutated organoids, combined HSP90 and CDK4/6 inhibition suppresses HSF1-HSR and reduces cancer growth, offering a p53-independent strategy for CRC treatment.  In conclusion, we present new options to improve HSP90-based therapies for enhanced CRC treatment.