Antitumor effect of alpha isomer of anordrin in vitro and cell cycle arrest at G1 phase.

Alpha isomer of anordrin (2 alpha, 17 alpha-diethyl-A-norandrostane-2 beta, 17 beta-diol dipropionate, alpha-Ano) inhibited mouse hepatoma (Hep A) and P388 cell growth in vitro. alpha-Ano (20 micrograms.ml-1) inhibited the incorporation of [3H]uridine and [3H]thymidine into RNA and DNA within 3 h, but the inhibition of L-[3H]lysine incorporating into protein was not obvious. alpha-Ano had no effect on the DNA-dependent RNA synthesis with purified nuclei of Hep A cells. It is suggested that the inhibition of RNA and DNA syntheses is the major cause of the cytostatic effect. alpha-Ano blocked the P388 cells at G1/G0 phase, and the delay in G1/G0 to S phase transition plays an important role in the inhibition of P388 cell growth.