This application is one of the three interactive research projects. We propose to study the determinants of mitomycin C (MMC) in human solid tumors. MMC is active against a wide variety of solid tumors. MMC undergoes enzymatic reduction to active DNA alkylating species by quinone reductases, i.e. DT diaphorase and NADPH:cytochrome P450 reductase. The current hypothesis is that both enzymes are involved under aerobic conditions, while the activity of NADPH:cytochrome P450 reductase predominates under hypoxic conditions. The relative contributions of these enzymes in the MMC sensitivity of multicellular patient solid tumors, which consists of both oxic and hypoxic regions, are not known. We have studied the MMC cytotoxicity in patient bladder tumors maintained as multicellular fragments. The proliferation of the tumor explants parallels their in vivo aggressiveness, which suggests the maintenance of tumor pathology in culture. Tumor explants from 30 patients showed a 120 fold difference in MMC sensitivity. The large inter-tumor variation in chemosensitivity was correlated with the tumor pathology. The variable sensitivity suggests that (a) tumor stage, grade, labeling index and DNA index are potential indicators of tumor sensitivity to MMC, and (b) there may be substantial biochemical differences among tumors. We hypothesize this may be related to the activity of the MMC activating enzymes. We recently developed the methodology to measure the gene expression of the activating enzymes in small tumor specimens (1-2 mg). A comparison of the tumor pathology, the MMC sensitivity in tumor explants with the enzyme activity and gene expression of the MMC reductases, using bladder tumors from individual patients, will indicate the relative importance of the two MMC activating enzymes in determining the MMC cytotoxicity in multicellular solid tumors. In addition, these studies will be done in parallel with the accompanying efficacy trial and target site pharmacokinetic studies of MMC in bladder cancer patients. This provides the unique opportunity to evaluate the correlations between the activity and gene expression of these enzymes, in vitro cytotoxicity of MMC (i.e., extent of inhibition of tumor cell DNA synthesis), MMC pharmacokinetics at the target site, and treatment outcome. Establishing easily identifiable biochemical and pathological prognostic indicators may allow the identification of tumors and hence patients most likely to respond to MMC.
