HYPERTHERMIA, CHEMOTHERAPY, AND ONCOGENIC TRANSFORMATION

There is increasing concern for the oncogenic potential of agents used to treat cancer. To some extent, concern about the production of a second malignancy is the price of success. After all, the patient must be a long-term survivor, with the first malignancy cured--or at least controlled--before the possibility of a treatment-induced second malignancy becomes a problem. Hyperthermia is one of the few modalities used to treat cancer which does not of itself induce oncogenic transformations; by comparison, radiation is a weak oncogenic agent, while some chemotherapy agents are relatively potent. The purpose of the present application is to explore pragmatic and mechanistic aspects of the interaction of heat, chemotherapy agents, and radiation as they relate to oncogenic transformation. The first aims is to determine whether hyperthermia, used to potentiate chemotherapy agents, enhances the transformation incidence to the same extent as it enhances cell lethality. To be specific, for a given level of cell killing, does not thermochemotherapy produce an equally elevated level of oncogenic transformation, or can a sequence be found where cytotoxicity is enhanced without a concomitant increase in oncogenicity? This has proved to be the case for X rays and for the chemotherapy agents investigated to date, namely actinomycin-D, BCNU and mitomycin-C. The range of chemotherapy agents tested in combination with heat will be extended to include bleomycin, melphalan, and cis-platinum, and oncogenic transformation will be monitored in vitro using C3H 10T1/2 cells. Attention will focus also on the transient phenomenon of thermotolerance, whereby cells exposed to an initial heat treatment develop resistance to killing by subsequent heat exposures. We will determine whether or not thermotolerant cells are also resistant to the induction of transformation by X rays and chemotherapeutic agents. The development of thermotolerance will be monitored by the appearance of "heat-shock" proteins and checked by enhanced cell survival.