A novel mechanism of action of chemically modified tetracyclines: Inhibition of COX-2-mediated prostaglandin E-2 production

Tetracyclines (doxycycline and minocycline) inhibit inducible NO synthase e xpression and augment cyclooxygenase (COX)-2 expression and PGE, production . In contrast, chemically modified tetracyclines (CMTs), such as CMT-3 and -8 (but not CMT-1, -2, and -5), that lack antimicrobial activity, inhibit b oth NO and PGE, production in LPS-stimulated murine macrophages, bovine cho ndrocytes, and human osteoarthritis-affected cartilage, which spontaneously produces NO and PGE, in ex vivo conditions. Furthermore, CMT-3 augments CO X-2 protein expression but inhibits net PGE, accumulation. This coincides w ith the ability of CMT-3 and -8 to inhibit COX-2 enzyme activity in vitro. The action of CMTs is distinct from that observed with tetracyclines becaus e 1) CMT-3-mediated inhibition of PGE, production coincides with modificati on of COX-2 protein, which is distinct from the nonglycosylated COX-2 prote in generated in the presence of tunicamycin, as observed by Western blot an alysis and 2) CMT-3 and -8 have no significant effect on COX-2 mRNA accumul ation. In contrast, CMT3 and -8 do not inhibit COX-1 expression in A549 hum an epithelial cells at the level of protein and mRNA accumulation or modifi cation of COX-1 protein. CMT-3 and -8 inhibit the sp.act. of COX-2 (but not COX-1) in cell-free extracts. These results demonstrate differential actio n of CMT-3 (Metastat) on COX-1 and -2 expression, which is distinct from ot her tetracyclines.