We studied the synthetic matrix metalloproteinase inhibitor (MMPI) prinomastat (AG3340) in a well-established NCI-H460 orthotopic lung cancer model that exhibits highly predictable regional and systemic metastatic patterns. Both primary and metastatic tumors express the matrix metalloproteinases (MMP-2), MT1-MMP (MMP-14) and tissue inhibitor of metalloproteinases (TIMP-2). The anti-tumor activity of prinomastat was investigated both as a single agent and in combination therapy with carboplatin. Treatment with both carboplatin (at two dose levels) and prinomastat commenced when the primary lung cancer was approximately 200-300 mg in size and without gross or microscopic evidence of metastases. As single agents, prinomastat significantly reduced the incidence of kidney metastasis, but had no effect on metastatic frequency to other organs. As single agents neither drug enhanced length of survival over control animals, although microvessel counts in prinomastat-treated tumors were lower than in tumors from control animals (P<0.01). In combination prinomastat and the lower dose of carboplatin significantly enhanced survival over control animals, and over animals treated with carboplatin alone (P<0.05). Tolerance to this combination was assessed with body weight and serum biochemistries. At the higher carboplatin dose, toxicity became evident both as a single agent and in combination with prinomastat. Our results suggest that the administration of prinomastat in combination with standard cytotoxic chemotherapy during early stages of tumor growth and metastasis may prolong survival in non-small cell lung cancer (NSCLC) patients.