Discovery And Characterization Of CDC25B Inhibitors

Cell division cycle 25(CDC25)phosphatases regulate key transitions between cell cycle phases during normal cell division by dephosphorylating and activating the CDK(cyclin-dependent kinase)complexes.And in the event of DNA damage they are the targets of the checkpoint machinery that ensures genetic stability.Since then,CDC25 was reported to be overexpressed in primary tissue samples from various human cancers.Some evidences suggested that the overexpression of CDC25 may contribute to cancer.And down-regulation of CDC25 caused cell cycle arrest and inhibition of cell proliferation.These in turn make them ideal targets for a new anticancer therapy.We purified recombinant CDC25B expressed in Escherichia coli. High-through screening(HTS)assay was set up to find out novel inhibitors of CDC25B from 48000 pure chemicals collected from different sources with wide structural diversity of National Center for Drug Screening.LGH00031 and LGH00045 were discovered and characterized.LGH00031 was thought to be an irreversible inhibitor,and LGH00045 was a reversible and mixed-type inhibitor of CDC25 with relative good selection.The studies in cellular levels showed that both of the inhibitors caused a G2/M phase arrest which in turn resulted in the inhibition of cell proliferaton,and inhibited dephosphorylation of Tyr15 of CDK1. The mechanism of the inhibition of LGH00031 against CDC25B was also studied here.The result showed that in vitro the inhibition was caused by ROS which was generated by the reaction of LGH00031 and DTT.In cultured cells,LGH00031 increased the generation of ROS,and NAC,a precursor of glutathione,impaired the action of LGH00031 in cells.The generation of ROS by the reaction of LGH00031 and dihydrolipoic acid was conjectured,which may be the reason that LGH00031 inhibited CDC25B in the absence of DTT in cultured cells.The discovery and characterization of the novel potent and selective inhibitor as well as its evaluation in cellular levels will be ground work for further structure modification,cell-based and animal-based pharmacological and efficacy studies in the future.It might be extremely powerful tools to exploit the physiological and pathological function of CDC25B.Another part of work is the study on the protection of isletsβcells by nicotinic acid.Nicotinic acid could protect isletβcells of streptozocin induced diabetic rats.This protection may be relative to the anti-oxidative stress of nicotinic acid.