Structure-activity relationships of a lead hydroxamic acid inhibitor of recombinant human stromelysin were systematically defined by taking advantage of a concise synthesis that allowed diverse functionality to be explored at each position in a template. An ex vivo rat model and an in vivo rabbit model of stromelysin-induced cartilage degradation were used to further optimize these analogs for oral activity and duration of action. The culmination of these modifications resulted in CGS 27023A, a potent, orally active stromelysin inhibitor that blocks the erosion of cartilage matrix.

The matrix metalloproteinase enzyme MMP-13 plays a key role in the degradation of type II collagen in cartilage and bone in osteoarthritis (OA). An effective MMP-13 inhibitor would therefore be a novel disease modifying therapy for the treatment of arthritis. Our efforts have resulted in the discovery of a series of carboxylic acid inhibitors of MMP-13 that do not significantly inhibit the related MMP-1 (collagenase-1) or tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE). It has previously been suggested (but not proven) that inhibition of the latter two enzymes could lead to side effects. A promising carboxylic acid lead 9 was identified and a convergent synthesis developed. This paper describes the optimization of 9 and the identification of a compound 24f for further development. Compound 24f is a subnanomolar inhibitor of MMP-13 (IC(50) value 0.5 nM and K(i) of 0.19 nM) having no activity against MMP-1 or TACE (IC(50) of >10000 nM). Furthermore, in a rat model of MMP-13-induced cartilage degradation, 24f significantly reduced proteoglycan release following oral dosing at 30 mg/kg (75% inhibition, p < 0.05) and at 10 mg/kg (40% inhibition, p < 0.05).

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The full three-dimensional structure of the catalytic domain of human stromelysin-1 (SCD) complexed to a novel and potent, nonpeptidic inhibitor has been determined by nuclear magnetic resonance spectroscopy (NMR). To accurately mimic assay conditions, the structure was obtained in Tris buffer at pH 6.8 and without the presence of organic solvent. The results showed that the major site of enzyme-inhibitor interaction occurs in the S1' pocket whereas portions of the inhibitor that occupy the shallow S2' and S1 pockets remained primarily solvent exposed. Because this relatively small inhibitor could not deeply penetrate stromelysin's long narrow hydrophobic S1' pocket, the enzyme was found to adopt a dramatic fold in the loop region spanning residues 221-231, allowing occupation of the solvent-accessible S1' channel by the enzyme itself. This remarkable conformational fold at the enzyme binding site resulted in constriction of the S1' loop region about the inhibitor. Examination of the tertiary structure of the stromelysin-inhibitor complex revealed few hydrogen-bonding or hydrophobic interactions between the inhibitor and enzyme that can contribute to overall binding energy; hence the resultant compact structure may in part account for the relatively high potency exhibited by this inhibitor.