A differential low pH effect on tumour cells grown in vivo and in vitro when treated with hyperthermia

Effect of lactic acid in tumours on antitumour activity of hyperthermia

The change of lactic acid concentration in the tumour after intraperitoneal administration of 5 g/kg glucose, and the effect of the lactic acid concentration on antitumour activity of hyperthermia were studied in an experimental murine tumour. The lactic acid concentration in SCC VII tumours transplanted into the legs of C3H/HeJ male mice was measured by gas chromatography. Local hyperthermic treatment to the tumour was performed with a water bath at 43 degrees C for 40 min. Antitumour effects were evaluated by measuring tumour volume doubling time (DT) as an index. The mean concentration of lactic acid in the tumour was 10.4 mumol/g in the no-treatment group. The lactic acid concentration gradually increased after glucose administration, reaching a significantly high concentration of 20.0 mumol/g at 90 min later. The DTs in the no-treatment group and hyperthermia alone group were 2.4 and 3.7 days respectively. The DTs in the glucose administration groups shortly before, 30 and 60 min before the hyperthermia were 3.6, 3.6 and 5.6 days respectively. The DT in the 60 min group was significantly extended (p < 0.0001). Hyperthermia during the period of increased lactic acid concentration significantly prolonged the DT of the tumour. These results clearly showed that an increase of lactic acid concentration in the tumour improved the effect of local hyperthermia.

Evaluation of photodynamic therapy-induced heating of hamster melanoma and its effect on local tumour eradication

To investigate the contribution of hyperthermia on local tumour eradication by photodynamic therapy (PDT) we quantified PDT induced tumour heating and evaluated its biological effect in vivo. Syrian Golden hamsters bearing an amelanotic melanoma implanted into the dorsal skin received intravenous injections of Photofrin (5 mg kg-1). Twenty-four hours later tumours were illuminated by red light (630 nm; total energy: 100 J cm-2) at 100 and 200 mW cm-2 and tumour surface and tumour centre temperature were measured. The tumoricidally threshold temperature of 43 degrees C was exceeded at 200 mW cm-2 only, revealing a calculated equivalent treatment time at 43 degrees C of about 10 min. Melanomas treated by PDT at both light intensities disappeared within 48 h and did not reappear locally within the observation period of 32 days. Tumours treated by hyperthermia (water bath) at the maximum temperatures measured during illumination at 200 mW cm-2 (45.5 degrees C for 500 s) or animals receiving laser light at 200 mW cm-2 alone showed a significant growth delay compared to controls (p < 0.05), whereas illumination at 100 mW cm-2 alone or hyperthermia corresponding to the maximum temperature obtained at 100 mW cm-2 (39.5 degrees C for 1000 s) did not alter tumour growth. These data indicate that tumour temperature increased during PDT and exceeded the hyperthermic threshold temperature of 43 degrees C at 200 mW cm-2. In our tumour model hyperthermia was not necessary for a complete tumour eradication by PDT. Although a combination of PDT and hyperthermia might act in an additive or synergistic manner, an unrecognized overlap of both effects might complicate the interpretation of studies on the mechanisms of PDT.

Modification of human tumour and normal tissue pH during hyperthermic and normothermic antiblastic regional isolation perfusion for malignant melanoma: a pilot study

Human tumour and normal tissue pH were investigated during hyperthermic and normothermic antiblastic regional isolation perfusion and the effects of vascular occlusion, artificially induced hypoxia, hyperglycaemia, haemoglobin level of the perfusate and hyperthermia on tumour and normal tissue pH were evaluated. A pilot study was performed on 10 patients, with locally inoperable recurrent and primary malignant melanoma of the leg. The treatment consisted of a regional isolation perfusion with hyperthermia (120 min at 42-43 degrees C), at femoral level, followed by a normothermic regional isolation perfusion with Melphalan (60 min at 37-38 degrees C), at iliacal level, 7-10 can be distinguished: (1) first ischaemic anoxia period; (2) extracorporeal circulation, during which the leg is heated to the desired temperature, after which either hyperthermia or Melphalan is applied; (3) second ischaemic anoxia period. During the anoxia periods the large vessels that supply the leg are temporarily clamped and the effects on tissue pH can be investigated. During extracorporeal circulation, high-dose glucose can be administered to the isolated leg, to acutely decrease tumour tissue pH. Such a decrease is expected to sensitize tumours to hyperthermia, when applied immediately prior to or during heating. At the beginning of the treatment the mean tumour pH was significantly lower than normal tissue pH (7.14, with a mean tumour volume of 39.2 cm3, and 7.38, respectively; p < 0.01). During the perfusions with hyperthermia and Melphalan, tissue pH decreased by -0.41 units and -0.20 for tumour, and -0.11 units for normal tissue, respectively (all statistically significant). The two anoxia periods accounted for approximately half of the net decrease. During these periods tumour pH appeared to decrease more selectively, although there was great variation. The other investigated modalities, such as hyperglycaemia and hyperthermia, also decreased tissue pH, but to a lesser extent. However, a combination of more than one modality caused a larger decrease than a single one, but no preference for tumour could be detected. Before the second perfusion mean tumour pH was significantly increased by 0.14 units, and was no longer significantly different from normal tissue pH in the course of the regional isolation perfusion. This could be the reflection of the reduced tumour volume (by 30%, n.s.). Similar pH changes occurred during this Melphalan perfusion, but they were less pronounced since the total treatment time was shorter. Summarizing, tumour pH can be decreased more than normal tissue pH in the course of the regional isolation perfusion. In particular, vascular occlusion appeared to be tumour pH selective.(ABSTRACT TRUNCATED AT 400 WORDS)