Loss of Bacillus Calmette-Guerin Viability Adversely Affects the Direct Response of Urothelial Carcinoma Cells to Bacillus Calmette-Guerin Exposure

Purpose: The attenuated mycobacterium bacillus Calmette-Guerin is widely used as intravesical immunotherapy for nonmuscle invasive urothelial carcinoma. Previous studies demonstrated that in the laboratory and clinical settings bacillus Calmette-Guerin viability is a variable that correlates with antitumor efficacy. We evaluated how loss of viability impacted a number of molecular and phenotypic intermediate end points that characterize and/or contribute to the direct effect of bacillus Calmette-Guerin on urothelial carcinoma cells. Materials and Methods: We studied the effect of loss of bacillus Calmette-Guerin viability on the tumor cell response to the treatment in 2 human urothelial carcinoma cell lines. The cellular response to bacillus Calmette-Guerin rendered nonviable by heat killing was compared to the response to viable bacillus. Response end points included the induction of oxidative stress, activation of intracellular signaling pathways, gene transactivation and phenotypic changes. Results: Loss of viability resulted in a quantitative decrease in the tumor cell response relative to that of viable bacillus Calmette-Guerin for all measured end points. The decrease in response varied by cell line, ranging from 15% to 100% of the response to viable bacillus. While responses were quantitatively different, nonviable bacillus continued to induce responses that were qualitatively similar to those of bacillus Calmette-Guerin relative to that in untreated controls. Conclusions: Bacillus Calmette-Guerin viability is an important variable influencing the direct tumor cell response to the treatment. Although the magnitude of its effects are attenuated, heat killed bacillus Calmette-Guerin remains active for the induction of bacillus Calmette-Guerin responsive biological end points.