Enhanced sensitivity of human colon tumor cell lines in vitro in response to thermochemoimmunotherapy

We have investigated the cytotoxic responses in vitro of three human colon tumor cell lines with epithelial-like morphology, DLD-1, HCT-15, and HT-29, to thermochemoimmunotherapy with hyperthermia (42 degrees C for 2 h), carboplatin, and recombinant human tumor necrosis factor (TNF). Dose ranges of carboplatin and recombinant human TNF were administered essentially simultaneously and were followed 1 h later by hyperthermia. A two-tiered approach was used to evaluate cytotoxicity. In the first tier, a 5-day microcytotoxicity assay using vital dye staining was done; the effect on surviving fraction of simultaneously varying carboplatin and recombinant human TNF doses was evaluated by response surface methodology. From this analysis doses were selected for use in the second-tier clonogenic survival assays. A similar treatment protocol was used in clonogenic assays. Both assays revealed significant interline treatment response heterogeneity. Only the HCT-15 cells were sensitive to TNF alone; carboplatin activity against all three tumor cell lines was enhanced by TNF. Hyperthermia had minimal effect as a sole agent but enhanced the effects of carboplatin and TNF in DLD-1 and HCT-15 cells. Triple modality treatment resulted in 3-4-log decreased survival and could reduce cytotoxic resistance expressed against single- or dual-modality treatments by some of these cells.