Laserthermia enhances the clastogenic effects of antineoplastic agents in aerobic and chronically hypoxic HeLa cells in vitro

The interactive clastogenic effects of Nd-YAG laser induced hyperthermia (laserthermia) in combination with antineoplastic agents on normally oxygenated and chronically hypoxic HeLa cells were investigated. Exponentially growing HeLa cells were treated with bleomycin sulfate (BLM) (2–4 μg/ml), adriamycin (ADM) (2–4 μg/ml) and actinomycin D (ACT) (0.2–0.4 μg/ml) alone or in combination with laser at various powers (7–13 W) or different laser induced elevated temperatures (39.5–43.5°C). HeLa cells were incubated with 3 μg/ml cytochlasin B for 36 h after treatments and the frequency of micronuclei (MN) were determined in binucleated cells. Results showed a relatively high frequency of MN formation after drug treatments in normally oxic and chronically hypoxic cells, although there was a decrease in the frequency of MN in hypoxic cells compared to oxygenated cells. Laserthermia at various powers and different induced temperatures produced a slight increase in MN formation both in oxic and hypoxic cells. When drug treatment and laserthermia was combined, a profound synergistic effect in MN formation was observed for all three drugs used in these experiments. ACT at a concentration of ten times lower than ADM and BLM produced similar effect. Also, ADM showed a marked synergistic effect with laserthermia compared to BLM at similar concentrations. This study suggests that laserthermia in combination with ADM, BLM or ACT would have a greater genotoxic effect on hypoxic cell populations. Therefore, Nd-YAG laser induced hyperthermia may be a useful modality for elimination of the radioresistant hypoxic cells.