Structure--antitubulin activity relationship in steganacin congeners and analogues. Inhibition of tubulin polymerization in vitro by (+/-)-isodeoxypodophyllotoxin.

A new series of 23 synthetic analogues of the naturally occurring antitumor lignan steganacin was tested for the inhibition of microtubule assembly in vitro. Interestingly, (+/-)-isopicrostegane (I50 = 5 microM) was found to be almost as active as (+/-)-steganacin(I50 = 3.5 microM). On the other hand, racemic isodeoxypodophyllotoxin has an inhibiting activity of microtubule assembly comparable to that of (-)-podophyllotoxin, whereas (-)-isodeoxypodophyllotoxin is totally inactive.