Skip to main page content
U.S. flag

An official website of the United States government

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021 Dec 3;22(23):13082.
doi: 10.3390/ijms222313082.

Imidazole Analogs of Vascular-Disrupting Combretastatin A-4 with Pleiotropic Efficacy against Resistant Colorectal Cancer Models

Franziska Reipsch  1 , Bernhard Biersack  2 , Henrike Lucas  3 , Rainer Schobert  2 , Thomas Mueller  1
Affiliations

Imidazole Analogs of Vascular-Disrupting Combretastatin A-4 with Pleiotropic Efficacy against Resistant Colorectal Cancer Models

Franziska Reipsch et al. Int J Mol Sci. .

Abstract

Specific targeting of the tumoral vasculature by vascular-disrupting agents (VDA), of which combretastatin A-4 (CA-4) is a main representative, has been considered a new therapeutic strategy against multidrug-resistant tumors. In addition, CA-4 and analogs are tubulin-targeting agents and can exert direct antitumor effects by different mechanisms. Herein, we analyzed a series of synthetic CA-4 analogs featuring N-methylimidazole-bridged Z-alkenes with different halo- or amino-substituted aryl rings in vitro and in vivo, focusing on models of colorectal cancer. Combined in vitro/in vivo structure-activity relationship studies using cell lines and xenograft tumors susceptible to VDA-induced vascular damage demonstrated a clear association of cytotoxic and vascular-disrupting activity with the ability to inhibit tubulin polymerization, which was determined by specific substitution constellations. The most active compounds were tested in an extended panel of colorectal cancer (CRC) cell lines and showed activity in CA-4-resistant and chemotherapy-resistant cell lines. The bromo derivative brimamin was then compared with the known fosbretabulin (CA-4P) by activity tests on DLD-1- (multidrug-resistant) and HT29- (CA-4-resistant) derived xenograft tumors. Treatment did not induce pronounced vascular-disrupting effects in these tumors. Histological analyses revealed distinct tumor substructures and vessel compositions of DLD-1/HT29 tumors, which clearly differed from the tumor models susceptible to VDA treatment. Even so, brimamin effectively retarded the growth of DLD-1 tumors, overcoming their resistance to standard treatment, and it inhibited the outgrowth of disseminated HT29 tumor cells in an experimental metastasis model. In conclusion, combretastatin analogous N-methylimidazoles proved capable of inducing vascular-disrupting effects, comparable to those of CA-4P. In addition, they showed antitumor activities in models of drug-resistant colorectal cancer, independent of vascular-disrupting effects.

Keywords: chemotherapy resistance; colorectal cancer; combretastatin A-4; imidazoles; microtubule destabilization; vascular-disrupting agents.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Structure–activity relationship study of imidazoles C 1–C 12 compared with CA-4 and CA-4P. (a) Combined cytotoxicity and tubulin polymerization assay. Displayed are the means of IC50 values of compounds against a panel of six different cell lines (upper diagram). Tubulin polymerization is quantified as relative fluorescence units per minute and is given as percent of untreated control (lower diagram). (b) Structures of combretastatin A-4 (CA-4) and combretastatin A-4 phosphate (fosbretabulin) and of N-methyl-4-(4,5-dimethoxyphenyl)-5-phenyl-imidazolium hydrochlorides C 1–C 12 with variation in residues R1, R2, and R3 as specified. (c) Representative examples of 1411HP xenograft tumors before and 48 h after treatment, showing typical discoloration indicating a vascular-disrupting effect.
Figure 2
Figure 2
Cytotoxic activities of brimamin and Et-brimamin compared with those of conventional drugs in CRC cell lines. Displayed are the means of IC50 values ± standard deviation (n = 3).
Figure 3
Figure 3
Analysis of tumor substructure after Azan staining. (a–c) Different areas of HT29 tumors, showing small vessels or capillaries embedded in collagen-rich septal structures or compositions with abundant fibrotic tissue. (d) DLD1 tumor showing similar structure to HT29 tumors. (e) 1411HP tumor showing large vessels and less extracellular material or stromal structures. (f,g) Examples of vessels of DLD-1 tumor, representing typical vessel structures found in DLD-1/HT29 tumors, showing distinct vessels with abundant (f) or normal (g) collagen-based supporting structure. (Scale bars: (a–e)—100 µm; (f,g)—20 µm).
Figure 4
Figure 4
Antitumor activity of brimamin compared with CA-4P and standard treatment. Nude mice bearing s.c. xenograft tumors of DLD-1 (a) and HT29 (b) were treated with NaCl (control), brimamin (25 mg/kg BW), CA-4P (250 mg/kg BW), or 5-FU + irinotecan (30 mg/kg + 50 mg/kg BW) on days 0, 7, 14, 21, and 28 (only HT29). The tumor volume increase relative to the start of treatment on day 0 is shown, as mean values ± SD (n = 6).
Figure 5
Figure 5
Antimetastatic activity of brimamin in the DLD-1 tumor model. Nude mice bearing s.c. xenograft tumors of luciferase-expressing DLD-1 were treated with NaCl (control) or brimamin (20 mg/kg BW) on days 0, 7, 14, and 21. (a) The tumor volume increase on day 25 relative to the start of treatment on day 0 is shown, as mean values ± SD (n = 3). (b) Ex vivo analysis of lung metastasis using bioluminescence imaging. (c) Quantification of metastatic burden given as total flux (photons per seconds).
Figure 6
Figure 6
Antimetastatic activity of brimamin in the HT29 tumor model of disseminated tumor cells. Nude mice were injected i.v. with luciferase-expressing HT29-Luc cells, and then treated with NaCl (control) or brimamin (25 mg/kg BW) once weekly. (a) The whole tumor burden and lung metastasis are shown (mean values ± SD (n = 5)) as analyzed by bioluminescence imaging and are given as total flux (photons per seconds). (b) An example from the control group showing tumor growth in the nape, flank, chest, neck, and abdomen.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Siemann D.W., Bibby M.C., Dark G.G., Dicker A.P., Eskens F.A., Horsman M.R., Marme D., Lorusso P.M. Differentiation and definition of vascular-targeted therapies. Clin. Cancer Res. 2005;11:416–420. - PubMed
    1. Siemann D.W. The unique characteristics of tumor vasculature and preclinical evidence for its selective disruption by Tumor-Vascular Disrupting Agents. Cancer Treat. Rev. 2011;37:63–74. doi: 10.1016/j.ctrv.2010.05.001. - DOI - PMC - PubMed
    1. Siemann D.W., Chaplin D.J., Horsman M.R. Vascular-targeting therapies for treatment of malignant disease. Cancer. 2004;100:2491–2499. doi: 10.1002/cncr.20299. - DOI - PubMed
    1. Tozer G.M., Kanthou C., Baguley B.C. Disrupting tumour blood vessels. Nat. Rev. Cancer. 2005;5:423–435. doi: 10.1038/nrc1628. - DOI - PubMed
    1. Kanthou C., Tozer G.M. Tumour targeting by microtubule-depolymerizing vascular disrupting agents. Expert Opin. Ther. Targets. 2007;11:1443–1457. doi: 10.1517/14728222.11.11.1443. - DOI - PubMed

MeSH terms