Double mutations in cis increase oncogenicity and sensitivity to PI3Kα inhibitors.

Activating mutations in are frequent in human breast cancer, and phosphoinositide 3-kinase alpha (PI3Kα) inhibitors have been approved for therapy. To characterize determinants of sensitivity to these agents, we analyzed -mutant cancer genomes and observed the presence of multiple mutations in 12 to 15% of breast cancers and other tumor types, most of which (95%) are double mutations. Double mutations are in cis on the same allele and result in increased PI3K activity, enhanced downstream signaling, increased cell proliferation, and tumor growth. The biochemical mechanisms of dual mutations include increased disruption of p110α binding to the inhibitory subunit p85α, which relieves its catalytic inhibition, and increased p110α membrane lipid binding. Double mutations predict increased sensitivity to PI3Kα inhibitors compared with single-hotspot mutations.