RTK-Dependent Inducible Degradation of Mutant PI3Kα Drives GDC-0077 (Inavolisib) Efficacy

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• PIK3CA mutations are common in cancer, driving tumor cell proliferation via the p110a protein.
• PI3K inhibitors are in clinical trials for PIK3CA-mutant breast cancer, but pathway feedback can limit efficacy.
• Preclinical data suggest PI3K inhibition can activate compensatory signaling pathways, reducing drug effectiveness.

Purpose of the Study:

• To investigate the mechanism of action of PI3K inhibitors GDC-0077 and taselisib.
• To explore the potential of these inhibitors in overcoming resistance mechanisms in PIK3CA-mutant cancers.
• To establish a strategy for developing targeted therapies based on selective oncoprotein degradation.

Main Methods:

• Assessed the efficacy of GDC-0077 and taselisib in preclinical models.
• Investigated the impact of these inhibitors on PI3K pathway signaling and protein levels.
• Examined the role of HER2 in the drug-induced degradation of mutant p110a.

Main Results:

• GDC-0077 and taselisib demonstrated potent inhibition of mutant PI3K pathway signaling and cell viability.
• These inhibitors induced HER2-dependent degradation of mutant p110a protein.
• The inhibitors achieved prolonged pathway suppression compared to other PI3K inhibitors.

Conclusions:

• GDC-0077 and taselisib exhibit a unique mechanism of degrading mutant p110a, offering a novel therapeutic strategy.
• Selective degradation of mutant p110a without affecting wild-type p110a may improve the therapeutic index in PIK3CA-mutant tumors.
• These findings provide a strong rationale for developing PI3Kα degraders for HER2-positive breast cancer.