PI3K-alpha

Class

small molecule PI3K inhibitor selective for the alpha isoform (p110α); induces degradation of mutant p110α protein

Pathway

inhibits PI3Kα signaling, blocking downstream AKT phosphorylation, which reduces proliferation and induces apoptosis in PIK3CA-mutated, hormone receptor-positive breast cancer cells; used in combination with palbociclib and fulvestrant

PI3K-alpha (p110α, encoded by the gene PIK3CA) is the catalytic subunit of a lipid kinase that relays signals from growth-factor receptors on the cell surface into the cell interior. When activated, it produces a lipid messenger that recruits and activates the protein AKT, which in turn promotes cell growth, survival, and metabolism. In many hormone receptor-positive breast cancers, PIK3CA carries activating mutations that lock this pathway in an "on" state, independent of normal growth-factor cues, driving uncontrolled proliferation. Selectively inhibiting the alpha isoform—rather than blocking all PI3K isoforms—aims to shut down this oncogenic signal while sparing the beta, gamma, and delta isoforms, which govern platelet function, immune cell signaling, and other processes not central to this cancer's growth. Some newer agents in this class also promote degradation of the mutant protein itself, adding a second layer of pathway suppression beyond simple enzymatic blockade. Because the PI3Kα/AKT axis also regulates normal insulin signaling and glucose metabolism, its inhibition carries mechanism-based metabolic effects. These agents are often combined with therapies targeting the cell cycle machinery and hormone receptor signaling, reflecting the idea that blocking multiple growth-driving pathways simultaneously can more durably suppress tumor growth than targeting one alone.