Combretastatin A-4 derived imidazoles show cytotoxic, antivascular, and antimetastatic effects based on cytoskeletal reorganisation
Introduction Combretastatin A-4 (CA-4) is a natural cis-stilbene which interferes with the cellular tubulin dynamics and which selectively destroys tumour blood vessels. Its pharmacological shortcomings such as insufficient chemical stability, water solubility, and cytotoxicity can be remedied by employing its imidazole derivatives. Methods We studied 11 halogenated imidazole derivatives of CA-4 for their effects on the microtubule and actin cytoskeletons of cancer and endothelial cells and on the propensity of these cells to migrate across tissue barriers or to form blood vessel-like tubular structures. Results A series of N-methyl-4-aryl-5-(4-ethoxyphenyl)-imidazoles proved far more efficacious than the lead CA-4 in growth inhibition assays against CA-4-resistant HT-29 colon carcinoma cells and generally more selective for cancer over nonmalignant cells. Et-brimamin (6), the most active compound, inhibited the growth of various cancer cell lines with IC50 (72 h) values in the low nanomolar range. Active imidazoles such as 6 reduced the motility and invasiveness of cancer cells by initiating the formation of actin stress fibres and focal adhesions as a response to the extensive microtubule disruption. The antimetastatic properties were ascertained in 3D-transwell migration assays which simulated the transgression of highly invasive melanoma cells through the extracellular matrix of solid tumours and through the endothelium of blood vessels. The studied imidazoles exhibited vascular-disrupting effects also against tumour xenografts that are refractory to CA-4. They were also less toxic and better tolerated by mice. Conclusions We deem the new imidazoles promising drug candidates for combination regimens with antiangiogenic VEGFR inhibitors.
KeywordsCombretastatin A-4 Imidazoles Vascular-disrupting agents (VDA) Antimetastatic activity Transwell invasion assay Trans-endothelium migration assay CAM assay
We are indebted to Dr. Florenz Sasse (Helmholtz Centre for Infection Research, Braunschweig, Germany) for assisting with fluorescence microscopy and to Franziska Reipsch (Department of Internal Medicine IV, Halle) for technical assistance.
Conflict of interest
The authors declare that there are no conflicts of interest.
- 5.Kanthou C, Tozer GM (2009) Microtubule depolymerizing vascular disrupting agents: novel therapeutic agents for oncology and other pathologies: microtubule depolymerizing vascular disrupting agents. Int J Exp Pathol 90:284–294. doi: 10.1111/j.1365-2613.2009.00651.x CrossRefPubMedCentralPubMedGoogle Scholar
- 15.Del Conte G, Bahleda R, Morena V et al (2012) A phase I study of ombrabulin (O) combined with bevacizumab (B) in patients with advanced solid tumors. J Clin Oncol 30:(suppl); abstr 3080Google Scholar
- 18.Schobert R, Biersack B, Dietrich A et al (2010) 4-(3-Halo/amino-4,5-dimethoxyphenyl)-5-aryloxazoles and -N-methylimidazoles that are cytotoxic against combretastatin A resistant tumor cells and vascular disrupting in a cisplatin resistant germ cell tumor model. J Med Chem 53:6595–6602. doi: 10.1021/jm100345r CrossRefPubMedGoogle Scholar
- 42.Horan PK, Melnicoff MJ, Jensen BD, Slezak SE (1990) Chapter 42 Fluorescent cell labeling for in vivo and in vitro cell tracking. Methods Cell Biol. Elsevier, 469–490Google Scholar
- 47.Werr J, Xie X, I-Iedqvist P et al (1998) B-integrins are critically involved in neutrophil locomotion in extravascular tissue in vivo. J Exp Med 18712091–2096Google Scholar