Bortezomib inhibits the proteasome, leading to cell death via apoptosis in feline injection site sarcoma cells in vitro

Abstract

Abstract OBJECTIVE To determine the in vitro effects of the proteasome inhibitor bortezomib in feline injection site sarcoma (FISS) cell lines. SAMPLE In vitro cultures of the FISS cell lines Ela-1, Hamilton, and Kaiser. PROCEDURES Cells were treated with increasing doses of bortezomib or vehicle alone (dimethyl sulfoxide) and evaluated for cell viability via an adenosine triphosphate concentration assay, proteasome activity via a commercially available proteasome assay, accumulation of ubiquitinated proteins via Western blot, and apoptosis via flow cytometry. RESULTS All 3 cell lines were sensitive to bortezomib with a 50% inhibitory concentration after 48 hours of treatment at 17.46 nM (95% CI, 15.47 to 19.72 nM) for Ela-1, 19.48 nM (95% CI, 16.52 to 23.00 nM) for Hamilton, and 21.38 nM (95% CI, 19.24 to 23.78 nM) for Kaiser. In the Ela-1 cell line, 20 nM bortezomib inhibited 20S proteasome activity by 90.9% compared with the vehicle-only control. In the Kaiser cell line, 20 nM bortezomib decreased 20S proteasome activity by 70%, compared with the untreated vehicle-only control. Last, treatment with bortezomib (25 and 40 nM) resulted in statistically significant decreases in viable cells accompanied by a statistically significant increase in apoptotic cells. CLINICAL RELEVANCE Treatment options for FISS, especially nonresectable FISS, are currently very limited. These results support further investigation of bortezomib either alone or in combination with other treatments in such cases.