In vitro activity: MK-1775 inhibits Wee1 kinase in an ATP-competitive manner. Compared to Wee1, MK-1775 displays 2- to 3-fold less potency against Yes with IC50 of 14 nM, 10-fold less potency against seven other kinases with>80% inhibition at 1 μM, and>100-fold selectivity over human Myt 1, another kinase that inhibits cyclin-dependent kinase 1 (CDC2) by phosphorylation at an alternative site (Thr14). By abrogating the DNA damage checkpoint via blockade of Wee1 activity in WiDr cells bearing mutated p53, MK-1775 treatment inhibits the basal phosphorylation of CDC2 at Tyr15 (CDC2Y15) with EC50 of 49 nM, and suppresses gemcitabine-, carboplatin- or cisplatin-induced phosphorylation of CDC2 and cell cycle arrest in a dose-dependent manner, with EC50 of 82 nM and 81 nM, 180 nM and 163 nM, as well as 159 nM and 160 nM, respectively. MK-1775 treatment alone at 30-100 nM has no significant antiproliferative effect in WiDr and H1299 cells, whereas MK-1775 at 300 nM, sufficient to inhibit Wee1 by>80%, displays moderate but significant antiproliferative effects by 34.1% in WiDr cells and 28.4% in H1299 cells.

Kinase Assay: Recombinant human Wee1 is used. Kinase reaction is conducted with 10 μM ATP, 1.0 μCi of [γ-33P]ATP, and 2.5 μg of poly(Lys, Tyr) as a substrate in the presence of increasing concentrations of MK-1775 at 30°C for 30 minutes. Radioactivity incorporated into the substrate is trapped on MultiScreen-PH plates and is counted on a liquid scintillation counter.

Cell Assay: Cells (WiDr, NCI-H1299, TOV21G, and HeLa) are treated with or without gemcitabine for 24 hours, then with MK-1775 for an additional 24 hours. Cell viability is determined with a WST-8 kit using SpectraMax. Cellular caspase-3/7 activities are determined with a Caspase-3/7 Glo kit.

Mol Cancer Ther. 2009 Nov;8(11):2992-3000.