PD 0166285 is a pyridopyrimidine compound that inhibits Wee1, which is a Ser/Thr kinase that regulates the cell cycle (1,2).
This potent G2 checkpoint abrogator (FW = 512.43 g/mol; CAS 185039-89- 8; Solubility = 100 mg/mL DMSO), also named 6-(2,6-dichlorophenyl)-2- [[4-[2-(diethylamino)ethoxy]phenyl] amino]-8-methylpyrido[2,3-d] pyrimidin-7(8H)-one, targets Wee1 kinase (IC50 = 24 nM), a enzyme that is crucial for maintaining G2 cell-cycle arrest through its inhibitory phosphorylation of Cdc2. PD-166285 was identified in a screening campaign that was premised on the idea that cells that lack p53 would lack the capacity to engage effective G1 checkpoint regulation, such that they would depend on the G2 checkpoint to permit DNA repair prior to mitosis. This logic led to the hypothesis that a G2 checkpoint abrogator would preferentially kill p53-inactive cancer cells by removing the only checkpoint protecting such cells from premature mitosis in response to DNA damage. At an intracellular concentration of 0.5 μM, PD0166285 potently inhibits irradiation-induced Cdc2 phosphorylation at Tyr-15 and Thr-14 in seven of seven cancer cell lines tested, showing that this G2 checkpoint abrogator can kill cancer cells. Notably, PD0166285 is a radiosensitizer, enhancing cell sensitivity to radiation-induced cell death, showing a sensitivity enhancement ratio of 1.23 in a standard clonogenic assay. Its radiosensitizing activity is p53-dependent, showing a higher efficacy in p53-inactive cells. Treatment of B16 mouse melanoma cells with the inhibitor B16 cells also dramatically abrogates the G2 checkpoint, with arrest in the early G1 phase at 0.5 muM for 4 hours observed by flow cytometry. Cyclin D mRNA decreased within 4 hours observed by Realtime PCR. Rb was dephosphrylated for 24 hours. However, B16 cells did not undergo cell death after treatment with 0.5 μM PD0166285 for 24 hours. Immnofluoscence microscopy also showed that the cells become round and small in the morphogenesis, suggesting that microtubule stabilization is blocked and that Wee1 distribution was restricted after treatment for 4 hours. PD0166285 also abrogates the G2 checkpoint in osteosarcoma (OS) cells, pushing them into mitotic catastrophe and sensitizing them to irradiation-induced cell death. Other agents, like caffeine and UCN-01, can also abrogate the G2 checkpoint, thereby sensitizing p53 inactive cells to apoptosis. Other Targets: Myelin transcription factor-1, or Myt1 (IC50 = 72 nM); checkpoint kinase Chk1 IC50 = 3.4 μM)
