PI-273, a Substrate-Competitive, Specific Small-Molecule Inhibitor of PI4KIIα, Inhibits the Growth of Breast Cancer Cells

PI-273 exhibited the greatest inhibitory effect on PI4KIIα kinase activity (IC50 = 0.47 μmol/L) and suppressed cell proliferation. Surface plasmon resonance and thermal shift assays indicated that PI-273 interacted directly with PI4KIIα. The kinetic analysis identified PI-273 as a reversible competitive inhibitor with respect to the substrate phosphatidylinositol (PI), which contrasted with most other PI kinase inhibitors that bind the ATP binding site. PI-273 reduced PI4P content, cell viability, and AKT signaling in wild-type MCF-7 cells, but not in PI4KIIα knockout MCF-7 cells, indicating that PI-273 is highly selective for PI4KIIα. Mutant analysis revealed the role of palmitoylation insertion in the selectivity of PI-273 for PI4KIIα. In addition, PI-273 treatment retarded cell proliferation by blocking cells in G2-M, inducing cell apoptosis and suppressing colony-forming ability. Importantly, PI-273 significantly inhibited MCF-7 cell-induced breast tumor growth without toxicity. PI-273 is the first substrate-competitive, a subtype-specific inhibitor of PI4KIIα, the use of which will facilitate evaluations of PI4KIIα as a cancer therapeutic target.

PI-273 (intraperitoneal injection; 25 mg/kg/day; 15 days) profoundly suppresses the tumor volume and weight in the MCF-7 xenografts[1].PI-273 (0.5 mg/kg (intravenously) or 1.5 mg/kg (intragastrically); 0.08-5 hours) has a half-life of 0.411 hours for intravenous administration and 1.321 hours for intragastrical administration, and the absolute bioavailability of PI-273 is 5.1%[1].