A high-affinity conformation of Hsp90 confers tumour selectivity on Hsp90 inhibitors

Area of Science:

• Molecular biology
• Oncology
• Biochemistry

Background:

• Heat shock protein 90 (Hsp90) is a molecular chaperone crucial for the function of oncogenic signaling proteins.
• Hsp90 inhibitors, like 17-allylaminogeldanamycin (17-AAG), induce degradation of these client proteins and show selective cancer cell killing.
• The molecular basis for this tumor selectivity of Hsp90 inhibitors remains largely unknown.

Purpose of the Study:

• To investigate the molecular basis for the tumor selectivity of Hsp90 inhibitors.
• To compare the binding affinity of 17-AAG to Hsp90 from tumor cells versus normal cells.

Main Methods:

• Biochemical assays to measure the binding affinity of 17-AAG to Hsp90 from tumor and normal cells.
• Analysis of Hsp90 complex formation and ATPase activity in tumor and normal cells.
• In vitro reconstitution of Hsp90 chaperone complexes.

Main Results:

• Hsp90 derived from tumor cells exhibited a 100-fold higher binding affinity for 17-AAG compared to Hsp90 from normal cells.
• Tumor Hsp90 was found in active multi-chaperone complexes with high ATPase activity, while normal Hsp90 was in a latent, uncomplexed state.
• Reconstitution of Hsp90 into chaperone complexes in vitro increased its binding affinity for 17-AAG and enhanced ATPase activity.

Conclusions:

• Tumor cells possess Hsp90 complexes in an activated, high-affinity conformation that promotes malignant progression.
• This activated Hsp90 complex represents a potential unique therapeutic target for cancer treatment.