Inhibition of smooth muscle cell proliferation by a chemically modified tetracycline.

Introduction: Chemically modified tetracyclines (CMTs) are a group of nonantimicrobial derivatives of tetracycline, which exert antiproliferative and anticollagenolytic properties. The molecular mechanisms, however, are poorly understood.

Materials And Methods: The effect of CMT-3 on cultured, subconfluent rat aortic smooth muscle cells (SMCs) was analyzed by [(3)H]-thymidine incorporation, counting cell numbers, and flow cytometry analysis.

Results: CMT-3 inhibited the incorporation of [(3)H]-thymidine and reduced the cell number dose-dependently, with approximately 60% inhibition at the maximal CMT-3 concentration used (20 mumol/l). CMT-3 decreased the SMC proportion in S-phase and gradually increased the proportion at G2/M. Initially, the proportion of cells in G1-phase increased and then gradually decreased back to baseline as the CMT-3 concentration increased. CMT-3 treatment of confluent SMCs for 24 h did not induce apoptosis.

Conclusions: CMT-3 inhibited SMC proliferation by inducing cell cycle arrest at the G2/M restriction point. Nonetheless, CMT-3 did not induce SMC apoptosis.