Abstract: N-methylisoindigotin is a second generation drug developed on the basis of chemical structure and activity relationship studies of the compounds derived from a traditional Chinese medicinal herb Indigofera tinctoria which has been shown to be effective in treating psoriasis in clinical trials. To research into the therapeutic mechanism of the drug in the treatment of psoriasis, the authors using the methods of crystal violet staining, hexosaminidase assay, thymidine incorporation, cell counting and quantitation of morphologic changes during differentiation, studied the effects of N-methylisoindigotin on cultured human keratinocytes. The results showed that N-methylisoindigotin inhibited proliferation of keratinocytes at the concentrations of 10^-7mol/L and 10^-8mol/L but did not inhibit anymore at 10^-9mol/L. However, the drug significantly promoted differentiation of keratinocytes even at 10^-10mol/L. This indicates that N-methylisoindigotin influences both the proliferation and the differentiation of keratinocytes and predominantly on the promotion of differentiation, suggesting the drug acts in a way different from that of ordinary cytotoxics in chemotherapy.

Key words: N-methylisoindigotin, Keratinocyte