ANGOLINE AND CHELERYTHRINE, BENZOPHENANTHRIDINE ALKALOIDS THAT DO NOTINHIBIT PROTEIN-KINASE-C

Starting with an extract derived from the I;tem of Macleaya cordata (P apaveraceae) that was active in the process of inhibiting phorbol 12,1 3-dibutyrate binding to partially purified protein kinase C (PI(C), th e benzophenanthridine alkaloid angoline was isolated and identified. T his discovery appeared in context, as a related benzophenanthridine al kaloid, chelerythrine, has been reported to mediate a variety of biolo gical activities, including potent and selective inhibition of protein kinase C (PKC). However, in our studies, angoline was not observed to function as a potent inhibitor of PHC. Moreover, we were unable to co nfirm the reported inhibitory activity of chelerythrine. In a comprehe nsive series of studies performed with various PKC isozymes derived fr om a variety of mammalian species, neither chelerythrine nor angoline inhibited activity with high potency. To the contrary, chelerythrine s timulated PKC activity in the cytosolic fractions of rat and mouse bra in in concentrations up to 100 mu M. In addition, chelerythrine and an goline did not inhibit [H-3]phorbol 12,13-dibutyrate binding to the re gulatory domain of PKC at concentrations up to 40 mu g/ml, and no sign ificant; alteration of PKC-alpha, -beta, or -gamma translocation was o bserved with human leukemia (HL-60) cells in culture. Fur ther, cheler ythrine did not inhibit 12-O-tetradecanoylphorbol 13-acetate-induced o rnithine decarboxylase activity with cultured mouse 308 cells, but ang oline was active in this capacity with an IC50 value of 1.0 mu g/ml. A I relatively large number of biological responses have been reported i n studies conducted with chelerythrine, and alteration of PI(C activit y has been considered as a potential mechanism of action. In light of the current report, mechanisms independent of PKC inhibition should be considered as responsible for these effects.