STX-478, a Mutant-Selective, Allosteric PI3Kα Inhibitor Spares Metabolic Dysfunction and Improves Therapeutic...

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Phosphoinositide 3-kinase α (PIK3CA) mutations are common in various cancers, including breast, gynecologic, and head and neck squamous cell carcinoma.
• Current therapies like alpelisib inhibit both wild-type and mutant PI3Kα, leading to dose-limiting toxicities such as hyperglycemia.
• There is a need for therapies that selectively target mutant PI3Kα to improve efficacy and reduce side effects.

Purpose of the Study:

• To introduce and characterize STX-478, a novel allosteric PI3Kα inhibitor designed for selective targeting of mutant PI3Kα.
• To evaluate the efficacy and toxicity profile of STX-478 in preclinical cancer models.
• To assess the potential of combining STX-478 with other cancer therapies.

Main Methods:

• STX-478 was developed as an allosteric inhibitor targeting prevalent PIK3CA helical and kinase domain mutations.
• Efficacy of STX-478 was assessed in human tumor xenografts.
• Combination studies were performed with fulvestrant and/or cyclin-dependent kinase 4/6 inhibitors in ER+HER2- xenograft models.

Main Results:

• STX-478 demonstrated robust efficacy in preclinical xenograft models.
• Unlike alpelisib, STX-478 did not cause the metabolic dysfunction (e.g., hyperglycemia) associated with wild-type PI3Kα inhibition.
• Combinations of STX-478 with fulvestrant and/or CDK4/6 inhibitors were well tolerated and achieved durable tumor regression in relevant models.

Conclusions:

• STX-478 is a promising mutant-selective PI3Kα inhibitor with a favorable preclinical efficacy and safety profile.
• Its selective targeting of mutant PI3Kα offers a potential therapeutic advantage over non-selective inhibitors by reducing toxicity.
• Clinical evaluation of STX-478 is warranted to explore its potential in treating PIK3CA-mutated cancers and expand the therapeutic window.