We examined the cytotoxic effect of
maytanprine isolated from the
methanol extract of Maytenus diversifolia on human
leukemia K562 cells using a flow cytometer and compared its cytotoxicity with that of
maytansine, a potent cytotoxic maytansinoid.
Maytanprine at concentrations of 0.03 nM or more (up to 1 nM) attenuated cell growth with decreasing cell viability and increased the population of shrunken cells in a concentration-dependent manner. Complete inhibition of growth by
maytanprine was observed at concentrations of 0.3 nM or more. The compound at 0.03 nM markedly decreased the population at G0G1 phase in the cell cycle, but only slightly decreased that in the G2M phase, suggesting the possibility that it inhibits or delays cell division, and increased the population of cells with hypodiploidal
DNA (apoptotic cells). The potency of
maytanprine in inhibiting cell growth was greater than that of
maytansine, although the inhibitory action of
maytanprine was similar to that of
maytansine. The results suggest that
maytanprine exerts a potent inhibitory action on the growth of human
leukemia K562 cells. M. diversifolia is one natural source of
maytanprine, which is more cytotoxic than
maytansine.