Simultaneous evaluation of the effects of RF hyperthermia on the intra- and extracellular tumor pH

Abstract

31P-magnetic resonance spectroscopy (MRS) and a fiberoptic pH meter were used simultaneously to follow the changes in intra- (pH(i)) and extracellular pH (pH(e)), respectively, of murine RIF-1 tumors with hyperthermia. Hyperthermia was induced at 34 MHz using the same coil used for MR. The study was carried out until 3.5 hr after hyperthermia. In untreated tumors (n = 29), pH(i) was always higher than pH(e). pH(i) was reduced after hyperthermia (30 min) at both 42°C and 45°C. pile registered an increase after 42°C and a decrease after 45°C. The reduction in pH(i) was larger than the initial differential between pH(i) and pH(e), and the change in pile was relatively small. Hyperthermia changed the acidity of the intra- and extracellular compartments, such that pile became more alkaline than pH(i) by 0.15 ± 0.13 units after 42°C [pH(e) (7.20 ± 0.12) and pH(i) (7.03 ± 0.05)], and by 0.12 ± 0.14 units after 45°C [pH(e) (6.84 ± 0.24) and pH(i) (6.72 ± 0.19)]. Simultaneous measurements of pH from the intra- and extracellular compartments demonstrated reversal in the pH gradient after hyperthermic treatment.