Platinum complexes able to inhibit matrix metalloproteinases (MMPs) through a noncompetitive mechanism are reported for the first time in this study. [PtCl2(SMP)] and [Pt(dimethylmalonato)(SMP)], characterized by the bisphosphonate-analogue ligand diethyl[(methylsulfinyl)methyl]phosphonate (SMP), are slight inhibitors of MMP-2 (IC50 = 258 +/- 38 and 123 +/- 14 microM, respectively) but markedly inhibit MMP-9 (IC50 = 35.5 +/- 6 and 17 +/- 4 microM), MMP-3 (IC50 = 5.3 +/- 2.9 and 4.4 +/- 2.2 microM), and MMP-12 (IC50 = 10.8 +/- 3 and 6.2 +/- 1.8 microM). In contrast, cisplatin, carboplatin, and the SMP ligand are inactive, and the bisphosphonate clodronate shows a broad-spectrum inhibitory activity in the high micromolar range (mean IC50 > 200 microM). These results, along with mechanistic investigations (DNA interaction and tumor cell growth inhibition), demonstrate that ligand modifications of platinum compounds can be exploited to target also biological substrates distinct from DNA.