Inhibition of tumor cell invasiveness by chemically modified tetracyclines

COLO 205 is a cell line derived from a human colon carcinoma with high degr adative activity towards extracellular matrix (ECM). It has been shown that COLO 205 cells produce matrix metalloproteinases (MMPs). MMPs are a family of enzymes known to degrade components of the ECM and have been implicated in tumor invasion. In the present study, we have analyzed the multiple eff ects of chemically modified tetracyclines (CMTs) on the expression and acti vity of MMPs selected by COLO 205 cells in vitro with the aim of evaluating these compounds Tor potential use in management of invasive tumors. Becaus e COLO 205 cells can degrade an interstitial ECM in serum-free medium in vi tro, we have been able to compare the effects of the tetracyclines on this measure of invasive activity with their effects on proteinase expression an d activity. We demonstrate here that one of the chemically modified tetracy clines, 6-deoxy-6-demethyl-4-de(dimethylamino)tetracycline (CMT-3) can effe ctively inhibit ECM degradation mediated by COLO 205 cells or their conditi oned medium. Gelatin zymography and immunoblots show that CMT-3 has the abi lity to inhibit release of MMP-2 into conditioned medium as well as to inhi bit MMP-2 gelatinolytic activity, which correlates with the results from EC M degradation assays. On the basis of our findings with COLO 205 cells we h ave expanded our evaluation of the tetracyclines to include effects on a ge netically engineered line of MDA-MB-231 breast tumor cells overexpressing M MP-9 at levels over tenfold those of the parent cell line, and on three hum an prostate tumor cell lines, LNCaP, DU-145, and PC-3. We show here that CM T-3 displays multiple modes of action: inhibiting MR IP activity, reducing levels of MMP expression, and exhibiting selective cytotoxicity towards som e of the tumor cell lines.