| Matrix metalloproteinases (MMPs) as well as the urokinase plasminogen activator (uPA) are thought to play a significant role in tumor invasion and metastasis as well as angiogenesis. Batimastat, also known as BB-94, is a potent synthetic low-molecular weight inhibitor of MMPs. Batimastat, in previously published literature, has been shown to prolong the life of mice bearing an ovarian ascites tumor. In our study, the hormone-independent MDA435/LCC6 human breast cancer cell line was used to propagate a malignant ascites in athymic nude mice. Treatment with 50 mg/kg of batimastat intraperitoneally in our ascites model produced no increase in survival, nor significant suppression of ascites formation. However, treated animals showed dramatic tumor cell consolidation and less dispersed ascites cells as compared to control animals. In contrast, we also utilized the same MDA435/LCC6 cell line to seed solid tumors subcutaneously into the region of the mammary fat pad in nude mice. A statistically significant difference in tumor volume between batimastat-treated and control animals was measured. However, both treated and control tumors were locally invasive and showed some degree of vascularization. To investigate the nature of tumor growth retardation by batimastat we used a number of tumor proliferation assays. Tumors from batimastat-treated and control mice were examined for Ki-67 and PCNA staining, number of mitotic figures, S-phase analysis, and TUNEL. No statistically significant differences were found between treatment groups, although tumor necrosis appeared to be slightly higher in batimastat-treated tumors. Two potential targets of batimastat, gelatinase A and B (MMP-2 and -9, respectively) were examined in both tumor sites. These metalloproteinases were present in both solid tumor and ascites fluid and in both cases were host-derived and not produced by the tumor. Using in situ hybridization, we found that stromal uPA expression was significantly and reproducibly increased at the tumor-stromal junction in batimastat-treated solid tumors in comparison with the control tumors. Increased expression of uPA may be a biological response to batimastat treatment via a TNFa-mediated pathway. These results may have important implications for the clinical applications of MMP inhibitors. |
