Highly potent cytotoxic compounds with inhibitory effects on tubulin polymerization and topoisomerase II

C218 AEZS-112 (ZEN-012) is a novel multi-targeted cytotoxic compound with inhibitory effects on tubulin polymerization, topoisomerase II and angiogenesis. This drug has demonstrated in vivo activity after oral administration in various tumor models including mammary, colon, skin and leukemic cancers and has recently entered phase I clinical trials. Here we present results of the pharmacological characterization of three novel AEZS-112 follow-up candidates.
 All three compounds posess highly potent anti-proliferative activity in a diverse panel of about 30 cancer cell lines with IC50 values in the range of 30 to 160 nM. Mode-of-action studies revealed that all compounds inhibit tubulin polymerization comparable to AEZS-112 (IC50 = 1.49 µM) and are potent inhibitors of topoisomerase II. Compound 2 even exceeds the activity of the reference compound amsacrine in a decatenation assay.
 It could be shown that all compounds are able to arrest KB/HeLa cells in G2/M phase at nanomolar concentrations and induce apoptosis in U937 cells as proven by caspase activity, DNA fragmentation and annexin V staining. The potency ranking of the follow-up candidates in these assays is in accordance with the cytotoxic potential of the compounds. Compound 3 shows the highest potency of 13 to 16 nM EC50.
 In vitro liver microsomal and plasma stability of the potential follow-up candidates are comparable to AEZS-112 or even improved, thus demonstrating suitability for in vivo efficacy studies. In order to prepare for such studies, the impact of AEZS-112 and compound 1 on the clonogenic growth of 24 human tumor xenografts covering different classes of tumors has been analyzed. Overall, doubling of potency by compound 1 could be demonstrated. Moreover, this study allows to discriminate between more and less sensitive tumor types, hence supporting the selection of the most appropriate tumor models.
 Based on their interesting pharmacological profiles all three candidates will be subjected to human tumor xenograft in vivo models before selecting an AEZS-112 follow-up candidate for preclinical development.