Mitomycin C and Porfiromycin

Paula Marie Fracasso, Yale University.

This is an Open Access Thesis


Solid neoplasms are known to contain deficient or poorly functional vascular beds and as a result populations of cells in these solid tumors may contain hypoxic or poorly oxygenated tumor cells. These hypoxic tumor cells may form a therapeutically resistant cell population within the tumor difficult to eradicate by ionizing radiation and most existing chemotherapeutic agents. As a consequence, this dissertation has investigated the mechanism of bioactivation and cytotoxicity of mitomycin C and porfiromycin, structurally similar antibiotics which are selectively cytotoxic to hypoxic cells.Mitomycin C was preferentially cytotoxic to hypoxic EMT6 and V79 cells in culture, but was not selectively cytotoxic to CHO cells in culture. Porfiromycin produced hypoxic cell cytotoxicity comparable to that of mitomycin C in EMT6 and V79 cells, but exhibited significantly less aerobic cytotoxicity. Porfiromycin was significantly more cytotoxic to hypoxic CHO cells than to aerobic CHO cells. This increase in hypoxic cell cytotoxicity for CHO cells treated with porfiromycin, however, was substantially less than the differential cytotoxicity seen with the EMT6 and V79 cells treated with this drug.NADPH-Cytochrome c reductase, NADH-cytochrome b(,5) reductase, cytochrome b(,5), and DT-diaphorase were present in all three cell lines, whereas cytochrome P-450 was not detectable. The highest activity of NADPH-cytochrome c reductase and DT-diaphorase were observed in EMT6 cells. Sonicates of EMT6, V79, and CHO cells enzymatically formed reactive metabolites of MC under hypoxic conditions as detected by the trapping agent 4-(p-nitrobenzyl)pyridine. EMT6 cells were able to generate reactive metabolites of mitomycin C to a greater extent than V79 and CHO cells. The formation of reactive metabolites occurred most efficiently in the presence of an NADPH regenerating system and to a lesser degree with added NADPH or NADH alone. (Abstract shortened with permission of author.)