Effects of mitomycin C and porfiromycin on exponentially growing and plateau phase cultures

Abstract

Laboratory studies and clinical trials are exploring the use of hypoxia-directed cytotoxic agents as adjuncts to radiotherapy. Because hypoxia and the microenvironmental inadequacies associated with hypoxia in solid tumours inhibit cell proliferation, an essential requirement for the successful use of hypoxia-directed drugs in cancer therapy is that these drugs be toxic to quiescent tumour cells, as well as tumour cells progressing rapidly through the cell cycle. The experiments reported here compared the cytotoxicities of mitomycin C and porfiromycin to exponentially growing and plateau phase cultures of EMT6 mouse mammary tumour cells. The proliferative status of the cultures did not influence the cytotoxicity of mitomycin C under either aerobic or hypoxic conditions, or the cytotoxicity of porfiromycin in air. Exponentially growing cultures were slightly more sensitive than plateau phase cultures to porfiromycin in hypoxia, but the difference between the sensitivities of proliferating and quiescent cells was much smaller than the difference between aerobic and hypoxic cells. No evidence for repair of potentially lethal damage was found after treatment with porfiromycin in air or in hypoxia; this is in agreement with previous findings for mitomycin C. Mitomycin C and porfiromycin therefore exhibit the toxicity to quiescent cells needed for effective use as hypoxia-directed drugs for the treatment of solid tumours.Laboratory studies and clinical trials are examining the effects of regimens combining concomitant treatment with radiation and the bioreductive alkylating agents mitomycin C or porfiromycin. This approach is based on the premise that the preferential toxicity of radiation to aerobic cells and the preferential toxicity of mitomycin C or porfiromycin to hypoxic cells might be combined to produce very effective treatment of solid tumours (Rockwell 1992). Because hypoxic cells in solid tumours are often forced into quiescence by the microenvironmental inadequacies associated with hypoxia, these combined modality regimens can be effective only if the drugs are toxic to quiescent cells, as well as to proliferating cells. Under aerobic conditions, mitomycin C is known to have similar toxicities to exponentially growing and plateau phase cultures of LoVo or EMT6 cells (Barlogie & Drewinko 1980, Rockwell 1986). It has been assumed that this finding could be generalized to porfiromycin and to hypoxic cells. However, recent studies demonstrating the complexities of the activation and metabolism of the quinone bioreductive alkylating agents

Preclinical evaluation of Laromustine for use in combination with radiation therapy in the treatment of solid tumors

“…This differs from our findings for the crosslinking agents mitomycin C and porfiromycin (Rockwell and Hughes 1994) and those of Twentyman and Bleehan (1975) for carmustine, lomustine, bleomycin, and cis-platin, which all showed similar cytotoxicities to exponentially growing and plateau phase EMT6 cells. The mechanism underlying the greater cytotoxicity of Laromustine to rapidly proliferating EMT6 cells is not yet known; it could imply a difference in initial alkylation, in crosslink formation after alkylation, or in recognition and repair of crosslinks caused by differences in the proliferative status, cell cycle distribution, or extracellular milieu of the exponential and plateau phase cultures.…”

“…Thus, although plateau phase EMT6 cells are proficient in PLD repair when held in quiescence after treatment with radiation or drugs (Hahn et al 1974, Rockwell 1977), PLD repair could not be responsible for the difference seen here. Moreover, PLD repair was not observed in EMT6 cells treated with mitomycin C or porfiromycin and may be less important for crosslinks than for some other lesions (Rockwell and Hughes 1994). Laromustine inhibits DNA polymerase β (Frederick et al 2009), a principal enzyme in base excision repair; a direct effect of Laromustine on the enzymatic pathways that repair the DNA crosslinks therefore could be responsible for the unanticipated proliferation-dependence of Laromustine cytotoxicity.…”

In vitro and in vivo evaluation of novel implantable collagen–chitosan–soybean phosphatidylcholine composite film for the sustained delivery of mitomycin C

“…For this reason, our group developed blends of chitosan-collagen-SPC as implantable films for the localized delivery of anti-cancer agents. Mitomycin C (MMC) is a potent anticancer drug that has enhanced activity in hypoxic environments [Rauth et al, 1983] and thus has significant potential for local-regional treatment of solid tumors as a significant percentage of viable cancer cells within a solid tumor can be hypoxic [Rockwell and Hughes, 1994]. To develop a system suitable for delivery of a wide range of anticancer drugs, we explore incorporation of MMC into the chitosan-collagen-SPC film using nanoparticles to provide cargo space for MMC together with an environment that may aid in preserving its stability and biological activity.…”

New Method to Prepare Mitomycin C Loaded PLA-Nanoparticles with High Drug Entrapment Efficiency

“…Because of MMC’s enhanced activity in hypoxic environments [1], it has great potential for loco-regional treatment of solid tumors since a significant percentage of viable cancer cells within a solid tumor can be hypoxic [2]. However, use of MMC is associated with a number of acute and chronic toxicities, such as irreversible myelosuppression and hemolyticuremic syndrome, which limit its clinical application.…”