Synergistic interaction of hyperthermia and Gemcitabine in lung cancer
ABSTRACT
Hyperthermia increases cytotoxicity of various antineoplastic agents. We investigated the cytotoxic effects of Gemcitabine and/or hyperthermia on BZR-T33 (human non-small-cell lung cancer cells) in vitro and in immune-suppressed athymic nude mice. Isobologram analysis of monolayer cell cultures for cytotoxicity demonstrates a synergistic interaction between hyperthermia and Gemcitabine. Clonogenic results show significant reductions in surviving fractions and colony size for both therapies; greatest reduction was for the combined therapy group. Using cell cycle analysis, hyperthermia enhanced Gemcitabine-induced G2-M arrest resulting in destruction of 3.5 log cells. Apoptotic studies (Annexin-V FITC staining) showed that hyperthermia augmented Gemcitabine-induced apoptosis. Transmission electron microscopy demonstrated pathology observed in cultures exposed to either therapy present in cultures exposed to both therapies. Studies in nude mice show that the combination therapy group had both an initial decrease in tumor size, and a significantly delayed rate of growth. Additionally, using tumor material harvested from nude mice two days after end to treatment reveals a significantly greater apoptotic index and significantly smaller mitotic index for the combined therapy group. Western blots of the same tumor material, showed that heat shock protein 70 was not significantly increased, however, caspase-3 activity of was significantly increased because of the combined therapy. In conclusion, the combined therapy is synergistic in effect because of hyperthermia enhancing Gemcitabine-induced apoptosis.