Candidates for testing were selected based on their current availability in the NCI collection and their relatively high growth inhibition (GI50) values (Fig. ). Two of the tested compounds (cc-1 and cc-2) were structural analogs of combretastatin A-4 and had previously been characterized as antimitotic drugs, while the other two (cc-3 and cc-4) had not been examined before. All four compounds displayed tubulin-binding signals above the control level in С-MST-assay (Fig. , Fig. ), suggesting that they bound to the colchicine site of tubulin. Unfortunately, the compound cc-4 was delivered only ~75% pure, so we took an effort to obtain it in sufficient purity. As we