Tumour pH drop after cryotreatment and enhancement of hyperthermia antitumour effect

Our previous study demonstrated a selective drop of pH, PO2 and blood flow in tumours under induced hyperglycaemia that enhanced the antitumour effect of hyperthermia. However, there are contraindications restricting the use of hyperglycaemia. Cryotreatment, as a method of altering tumour microphysiology similar to hyperglycaemia, was investigated. Guerin carcinoma pH was measured after cryotreatment (-15 to -20 degrees C at the tumour and normal tissue boundary; -110 to -120 degrees C at the cryoinstrument tip). It was determined that tumour pH immediately after complete tumour thawing (10 degrees C) was 6.08 (range 5.5-6.3), by 2 h it was 6.34 (range 6.2-6.4), by 4 h it was 6.42 (range 6.1-6.8) and by 24 h it was 6.54 (range 6.3-6.6). Complete tumour regression (%) and survival of rats with both the tumour regrowth and the partial tumour regression (days) after a single treatment were as follows: control -zero, 28 +/- 4; hyperthermia (2450 MHz, 43 degrees C, 60 min) -zero, 30 +/- 3; cryotreatment -14, 35 +/- 5; cryotreatment+hyperthermia -41, 46 +/- 5. It is planned to use combined cryotreatment+hyperthermia in a clinical trial for certain accessible tumours.