Cryosurgical Modeling: Sequence of Freezing and Cytotoxic Agent Application Affects Cell Death.
Cryosurgery is now being used to eradicate a variety of tumors, including those that are found in the kidney. Because it is well known that cancer treatments are often most effective when combined with adjunctive therapies, we developed a model kidney cell culture system to determine: (1) if 5-fluorouracil (5-FU), a compound known to be a poor kidney tumor chemotherapeutic agent, can be more effective when combined with cryosurgery; and (2) how kidney cells die through freezing-induced injury that might occur during cryosurgery. The DNA isolated from kidney cells that died during an exposure to -15 degrees C showed nonrandom cleavage when separated on an agarose gel, indicating that cell death was attributable, in part, to apoptosis, whereas DNA isolated from kidney cells that died during exposure to -75 degrees C showed random cleavage, indicating that cell death was attributable, in part, to necrosis. The apoptotic protease inhibitor, caspase 1 inhibitor V, was able to prevent freezing-induced cell death, supporting the idea that apoptosis may be a mechanism of cell death in the periphery of the iceball created by cryosurgical procedures in vivo. Because 5-FU is known to induce apoptosis, this drug was used in combination with various freezing regimes to determine if the combination might be a better method of killing cells than either treatment alone. Whereas the addition of 5-FU at the same time or 2 days after freezing resulted in a synergistic lethal effect, many cells survived this combination treatment. When cells were treated with 5-FU 2 days prior to freezing, however, there was an apparent complete loss of viability. The reason may be that, by an unknown mechanism, freezing enhances the ability of 5-FU-treated cells to move more effectively through the apoptosis pathway. Kidney tumors may have robust antiapoptotic mechanisms that make them refractory to 5-FU, but these mechanisms might be overridden by freezing. In either case, the data suggest that chemotherapy may be more effective when followed by cryosurgery.
Clarke
DM
Department of Biological Sciences, State University of New York, Binghamton, NY.
Hollister
WR
Baust
JG
Van Buskirk RG