Cytotoxic phenanthroindolizidine alkaloids in Tylophora tanakae against human gastric carcinoma cells

We have noticed the presence of cytotoxic activity in the body fluid of a b utterfly, Ideopsis similis, in family Danaidae. The cytotoxic principles we re purified and identified to be phernanthroindolizidine alkaloids. In addi tion, the cytotoxic activity was observed in the leaves of Tylophora tanaka e, which is a host plant for caterpillars of I. similis. In the present stu dy, cytotoxic principles in methanol extracts of the leaves against human g astric carcinoma TMK-1 cells were purified by acid-base partition, repeated HPLC and preparative TLC, and two cytotoxic compounds were isolated. From spectroscopic analysis of their structures, they were identified as phenant hroindolizidine alkaloids, trans-(+)-3,14 alpha -dihydroxy-4,6,7-trimethoxy phenanthrondolizidine N-oxide and (-)-7-hydroxy-2,3,6-trimethoxyphenanthroi ndolizidine. The amounts of two compounds isolated from 200 g of dried leav es were 3.5 and 4.0 mg, respectively. These alkaloids are different from th ose in the fluid of I. similis. When TMK-1 cells were treated with these ph enanthroindolizidine alkaloids, strong cytotoxic effects were observed, dos es of 6 ng/ml for trans-(+)-3, 14 alpha -dihydroxy-4,6,7-trimethoxyphenanth roindolizidine N-oxide and 3 ng/ml for (-)-7-hydroxy-2,3,6-trimethoxyphenan throindolizidine inducing 50% cell growth inhibition (IC50).