Granulocyte-colony stimulating factor enhances anti-tumour effect of hyperthermia

The combined effect of granulocyte-colony stimulating factor (GCSF) and hyperthermia in the treatment of experimental tumours was studied to examine the possible involvement of activated granulocytes in the antitumour effect of hyperthermia. Two weeks after transplantation of SCC VII cells (1 x 10(5)) into the instep of the left leg of C3H/HeJ male mice, the mice were given subcutaneous injections of GCSF (0.2 mg/kg) for 4 days. On day 4, hyperthermia was applied locally at 43 degrees C for 40 min. Hyperthermia inhibited the tumour growth, and this effect was enhanced by pre-treating the animals with GCSF. The numbers of circulating neutrophils in control and GCSF-treated mice were 2728 +/- 517/microl and 3124 +/- 194/microl, respectively (p = 0.53). Hyperthermia increased the number of neutrophils to 4409 +/- 700/microl (p < 0.05). Hyperthermia combined with GCSF significantly increased the number of netrophils to 5479 +/- 691/microl (p < 0.01). Chemiluminescence analysis using L-012 revealed that GCSF enhanced the generation of reactive oxygen species by about 10-fold. Glutathione contents in tumours 24 h after hyperthermia decreased by about 50% in both the hyperthermia groups with or without GCSF, as compared to those in the control. The GCSF-enhanced anti-tumour activity of hyperthermia was markedly inhibited by administration of a long-acting superoxide dismutase derivative (SM-SOD). These results suggest that GCSF activates the ability to generate active oxygen species by neutrophils and, thereby, enhances the anti-tumour effect of hyperthermia.