Enhancement of thermoradiotherapy by glucose administration for superficial malignant tumours

A moderate elevation of blood glucose level increases the effectiveness of thermoradiotherapy in a rat tumor model. I. Relative contributions of glucose and heating to tumor acidification

PURPOSE

To establish dose-effect relationships for tumor acidification induced by heat and glucose as a basis for testing the value of adding glucose administration to combined heat and x-ray treatment at clinically achievable glucose and temperature levels.

METHODS AND MATERIALS

Rhabdomyosarcoma BA1112 was grown s.c. in the upper leg of 16-20-week-old Wag/Rij rats. Animals were given 2 consecutive 100-min periods of saline (S) or glucose (G) infusion, while keeping tumor temperature at 37 degrees, 42 degrees, or 43 degrees C for 1 or 2 periods, in various combinations, each involving 6 animals. Glucose was infused i.v. as a 20% solution at 2.4-3 g/kg/h. Tumors were heated using 2,450-MHz electromagnetic radiation, and tumor pH was measured using a 0.7 mm fiberoptic probe.

RESULTS

Mean overall baseline pH was 7.00 (SD 0.10). The change induced by G37G43 (i.e., glucose infusion for a full 200 min, first 100 min at 37 degrees C, final 100 min at 43 degrees C) was -0.48 +/- 0.03 (SEM) pH units, and -0.17 +/- 0.03 for S37S43. The effect of G37G42 was -0.37 +/- 0.03 pH units, compared with -0.08 +/- 0.02 for S37S42 and -0.28 +/- 0.04 for glucose alone (G37G37). Glucose was less effective when given after or fully parallel to heating: -0.21 +/- 0.02 pH units for S43G37 and -0.37 +/- 0.02 for G43G43.

CONCLUSION

The glucose-induced tumor pH drop is much more pronounced than that induced by heat, both of which are dose dependent. The effects of glucose and heat seem additive if heating is started when glucose-induced acidification has reached its plateau level, but the overall effect is diminished if administration is fully simultaneous or in reversed order. Schedule G37G43 is optimal with respect to tumor acidification. Its predicted superiority in thermoradiotherapy as compared with S37S42, S37S43, and G37G42 treatment regimens was confirmed in a subsequent experimental tumor control study.

A moderate elevation of blood glucose level increases the effectiveness of thermoradiotherapy in a rat tumor model II. Improved tumor control at clinically achievable temperatures

PURPOSE

To assess the therapeutic gain (at the TCD(50) level) that can be obtained by boosting thermoradiotherapy with intravenous glucose infusion at different temperatures. This completes our series of studies to determine the optimal conditions and the effectiveness of glucose administration at clinically achievable glucose levels and treatment temperatures.

METHODS AND MATERIALS

Subcutaneous rat rhabdomyosarcoma BA1112 was irradiated with graded single doses of 300-kV X-rays (dose range 0-60 Gy). Fifteen minutes after irradiation, a 100-min intravenous infusion was started, consisting of either glucose (20% solution, 2.4-3 g/kg/h) or saline as a control. Then heat was applied to the tumors at 42 degrees C or 43 degrees C (water bath) during a subsequent 100-min period of infusion. Tumor control was scored as the absence of palpable growth at 100 days after treatment.

RESULTS

Glucose infusion enhanced tumor control independent of temperature in the range 42-43 degrees C. At 42 degrees C, the TCD(50) for X-irradiation decreased by 5.9 Gy (SEM 1.8 Gy), from 41.6 (1.6) to 35.7 (1.5) Gy, and at 43 degrees C from 33.3 (1.6) to 27.3 (1.5) Gy, representing a glucose enhancement ratio of approximately 1.2. At doses corresponding to the TCD(50) at either 42 or 43 degrees C, the addition of glucose increased tumor control from 50% to 70%. An enhancement ratio of 2.1 was found for the combination of irradiation, glucose infusion, and heating at 43 degrees C, with respect to irradiation alone (TCD(50) 56.3 Gy, reanalyzed earlier data). The contribution of combined heat and glucose to tumor control represented an additive effect, probably on the hypoxic cell population.

CONCLUSION

Moderate glucose administration (blood concentration 300 mg/100 mL) sizably improves experimental tumor control after combined X-irradiation and hyperthermia under clinically feasible conditions. Clinical treatment should benefit from this additional modality, in particular if unsatisfactory local control rates are due to insufficient heating. The therapeutic gain has to be evaluated further in clinical studies.