Design and Synthesis of a Novel Covalent Dihydropteridinone Derivative as a Highly Potent and Orally Bioavailable PLK1 Inhibitor for the Treatment of Chronic Myeloid Leukemia.

Polo-like kinase 1 (PLK1) is a validated cancer therapeutic target, but ATP-competitive PLK1 inhibitors have been limited by dose-limiting toxicities. Here, we designed covalent inhibitors that specifically engage the noncatalytic Cys67 residue of the ATP domain. Rational optimization of the warhead and core scaffold led to B9 as a highly potent lead candidate. B9 exhibited low nanomolar enzymatic inhibition and exceptional cellular potency (IC50 = 0.4 nM in K562 leukemia cells), representing a >150-fold improvement over the reversible reference compound BI2536 (61 nM). B9 also showed favorable overall selectivity against nonrelated kinases. Remarkably, B9 achieved 77.6% oral bioavailability in mice. In an orthotopic K562 leukemia xenograft model, oral administration of B9 significantly suppressed the bioluminescence of leukemia burden and extended survival rates to 100% over 42 days without observable toxicity. These findings underscore the potential of B9 as a safe, orally bioavailable, and highly potent PLK1 inhibitor for preclinical development.