THE TETRACYCLINE ANALOG MINOCYCLINE AND DOXYCYCLINE INHIBIT ANGIOGENESIS IN-VITRO BY A NON-METALLOPROTEINASE-DEPENDENT MECHANISM

The tetracycline analogs minocycline and doxycycline are inhibitors of metalloproteinases (MMPs) and have been shown to inhibit angiogenesis in vivo. To further study the mechanism of action of these compounds we tested them in an in vitro model of angiogenesis: aortic sprouting in fibrin gels. Angiogenesis was quantitated in this system by a uniqu e application of planar morphometry. Both compounds were found to pote ntly inhibit angiogenesis in this model. To further characterize the a ctivity of these compounds against MMPs, we determined the IC(50)s of both compounds against representatives of three classes of metalloprot einases: fibroblast collagenase, stromelysin, and gelatinase A. Doxycy cline was found to inhibit collagenase, gelatinase A and stromelysin w ith IC,,s of 452 mu M, 56 mu M and 32 mu M, respectively. Minocycline was found to inhibit only stromelysin in the micromolar range with an IC50 of 290 mu M. Since these results suggest that these compounds may not have been inhibiting in vitro angiogenesis by an MMP-dependent me chanism, we decided to test the effects of the potent MMP inhibitor BB -94. This compound failed to inhibit aortic sprouting in fibrin gels, thus strongly suggesting that both doxycycline and minocycline act by an MMP-independent mechanism. These results have implications for the mechanism of action of tetracycline analogs, particularly where they a re being considered for the treatment of disorders of extracellular ma trix degradation including periodontal disease, arthritis, and tumor a ngiogenesis.