In vitro biocompatibility between mitomycin-C (MMC) and bacillus Calmette-Guerin (BCG)

Abstract

Background: Mitomycin-C (MMC) and bacillus Calmette-Guerin (BCG) intravesical instillations are widely and effectively used as adjuvant treatment for superficial bladder cancer. In an attempt to improve the efficacy of intravesical therapy, MMC and BCG have also been used in a sequential or an alternating mode. The aim of this study was to assess the in vitro biocompatibility between these agents. Materials and Methods: The effect of MMC on BCG clumping tendency was assessed by estimating the number of colony forming units (CFU) of BCG in suspension, during incubation at 37 degrees C for 3 h, with repeated recordings of the suspension optical density (OD). Preparations containing either BCG plus MMC or BCG plus an equivalent amount of sterile water were cultivated using the non-radiometric system BACTEC MGIT 960. The final concentrations of the agents, following transfer of the preparations into the tubes of the system, were 1.25 mg/ml for BCG and 1 mg/ml for MMC. During the cultivation process, the tubes of the system were automatically checked every 60 min for fluorescence emission, which is an indication of mycobacteria growth. A comparative cultivation of the same preparations on Lowenstein-Jensen solid medium was also performed. Results: The OD of the BCG preparation remained almost unaffected for 3 h and was minimally altered by inclusion of MMC. After 34-38 h of cultivation in the BACTEC MGIT 960 system, all 7 cultures of the BCG+sterile water preparations became positive. In contrast, no BCG+MMC specimen became positive after an incubation period of 42 days. Following re-cultivation of the 7 negative BCG+MMC specimens, 6 remained negative, whereas 1 specimen became positive after an incubation period of 22 days. On Lowenstein-Jensen medium, growth of mycobacteria was noted only in the BCG+sterile water specimens and not in the BCG+MMC specimens. Conclusion: The results of this study indicate that, although MMC has no apparent effect on BCG tendency to form clumps in suspension, it may inhibit its growth in vitro. However, this does not necessarily compromise BCG anti-tumour activity. As the in vivo interaction of the drugs may be different, the efficacy of the combined BCG+MMC treatment should be defined in clinical trials.