Methoxy and ethoxy substituted 3-aroyl-2-arylbenzo[b]thiophenes and benzo[b]thiophene analogues are described for use in inhibiting tubulin polymerization. The compounds' use for treating tumor cells is also described. Additional aspects described here are certain diaryl ether benzo[b]thiophene derivatives. Also described are particular analogs derived from dihydronaphthalene which have proven particularly effective. Certain new benzofuran analogs are described, as well as certain sulfur oxide benzo[b]thiophene analogs. Important compounds described herein include the first nitrogen-containing derivatives of combretastatin. These include nitro, amino and azide combrdtastatin derivatives.