Tumour growth delay, cell inactivation and vascular damage following hyperthermic treatment of a human melanoma xenograft

Thermal effects of 2450 MHz microwave exposure near a titanium alloy plate implanted in rabbit limbs

This study aimed to examine the safety profile of microwave therapy on limbs with metal implants. New Zealand white rabbits were implanted with titanium alloy internal fixation plates. Femurs were exposed to 20, 40, 60, or 80 W of microwave radiation for 30 min (microwave applicator at 2450 MHz), and temperatures of the implants and muscles adjacent to implants were recorded. To evaluate thermal damage, nerves were electrodiagnostically assessed immediately after radiation, and histologic studies performed on nerve and muscle sections. As expected, implant temperature was highest in the exposure field. Temperatures of limbs with titanium alloy implants increased significantly at 60 and 80 W, with a significant decline in the nerve conduction velocity and acute thermal injuries in nerves and muscles adjacent to implants. However, temperature remained unchanged and no adverse effects were observed in nerves and muscles at 20 and 40 W. These findings are inconsistent with the current notion that surgical metal implants in the treatment field are contraindications for microwave therapy. Hence, we believe that a lower dose of continuous wave microwave irradiation is safe for limbs with titanium alloy implants.

Hyperthermia, cisplatin and radiation trimodality treatment: a promising cancer treatment? A review from preclinical studies to clinical application

This review discusses available clinical and experimental data and the underlying mechanisms involved in trimodality treatment consisting of hyperthermia, cisplatin and radiotherapy. The results of phase I/II clinical trials show that trimodality treatment is effective and feasible in various cancer types and sites with tolerable toxicity. Based on these results, phase III trials have been launched to investigate whether significant differences in treatment outcome exist between trimodality and standard treatment. In view of the clinical interest, it is surprising to find so few preclinical studies on trimodality treatment. Although little information is available on the doses of the modalities and the treatment sequence resulting in the largest degree of synergistic interaction, the results from in vivo and in vitro preclinical studies support the use of trimodality treatment for cancer patients. Animal studies show an improvement in treatment outcome after trimodality treatment compared with mono- and bimodality treatment. Studies in different human tumour cell lines show that a synergistic interaction can be obtained between hyperthermia, cisplatin and radiation and that this interaction is more likely to occur in cell lines which are more sensitive to cisplatin.

Histopathological observations of the antivascular effects of physiotherapy ultrasound on a murine neoplasm

This study evaluates the histopathological changes that follow insonation of a neoplasm with physiotherapy ultrasound. In 27 mice (C3HV/HeN strain), a subcutaneous melanoma (K1735(22)) was insonated with continuous physiotherapy ultrasound (1 MHz; spatial-average-temporal-average = 2.3 W cm(-2)). Analyses of contrast enhanced (0.1 mL Optison) power Doppler observations showed that insonation significantly (p < 0.05) increased the avascular area in the neoplasm. The predominant acute effect of insonating the neoplasm was an apparently irreparable dilation of the tumor capillaries with associated intercellular oedema; other immediate effects were haemorrage and increased intercellular fluid. Liquefactive necrosis of neoplastic cells was a delayed effect. There was a high correlation (R2 = 0.91) between the percent area affected on histologic examination and the percent increase in avascularity of the neoplasm in the Doppler study. In conclusion, physiotherapy ultrasound produced histologic changes in the tumor vasculature that were consistent with observations made by contrast enhanced power Doppler ultrasound.

The new tubulin-inhibitor combretastatin A-4 enhances thermal damage in the BT4An rat glioma

PURPOSE

To investigate the toxicity of combretastatin A-4 disodium phosphate (CA-4) and its vascular effects in the subcutaneous (s.c.) BT4An rat glioma, and additionally, to determine the tumor response of CA-4 combined with hyperthermia.

METHODS AND MATERIALS

For assessment of drug toxicity, rats were given 50, 75, or 100 mg/kg CA-4 and followed by daily registration of weight and side effects. Interstitial tumor blood flow was determined by laser Doppler flowmetry in rats injected with 50 mg/kg CA-4. In the tumor response study we administered CA-4 50 mg/kg alone or combined with hyperthermia (waterbath 44 degrees C for 60 min) 0 or 3 h later.

RESULTS

We found that CA-4, at a well-tolerated dose of 50 mg/kg, induced a considerable time-dependent decrease in the tumor blood flow. Tumor blood flow was reduced by 47-55% during the first 110 min after injecting CA-4, and thereafter remained decreased until the measurements were terminated. Administering CA-4 3 h before hyperthermia yielded the best tumor response and increased tumor growth time significantly compared with simultaneous administration of CA-4 and hyperthermia (p = 0.03). Interestingly, CA-4 alone did not influence tumor growth.

CONCLUSION

CA-4 induces a gradual reduction in tumor blood flow which can be exploited to sensitize the BT4An tumor for hyperthermia.

Relationships between thermal dose and heat-induced tissue and vascular damage after thermoradiotherapy of locally advanced breast carcinoma

Twenty-four patients with locally advanced breast carcinoma were given thermoradiotherapy, and heat-induced damage to tissue and vasculature was studied in relation to thermal dose. Thermometry was performed using six to eight multi-point thermistor probes. Heat-induced damage was quantified by histopathological analysis of biopsies taken from the temperature probe locations shortly after treatment. Both tumour and normal tissue were found in the biopsies. Fraction of tissue and fraction of vessels with heat-induced damage were determined for the malignant and the normal tissue compartment separately, using stereological techniques. Clear relationships were found between these parameters and the largest thermal dose achieved in one heat fraction. The data were subjected to logit analysis, and the thermal doses (eqv. min at 43 degrees C) that caused massive necrosis in 50% of the tissue were calculated to be 116 +/- 31 for the malignant tissue compartment and 205 +/- 49 for the normal tissue compartment. Similarly, the thermal doses that caused damage to 50% of the vessels were found to be 63 +/- 34 and 144 +/- 46 for the malignant and the normal tissue compartment, respectively. Thus, the tumour tissue was more sensitive to heat than was the surrounding normal tissue, irrespective of whether necrosis or vessel damage was considered. This was probably a consequence of physiological and vascular differences between the two tissue compartments. Evidence for primary and secondary cell death was found both in the malignant and the normal tissue, although primary cell death probably was of minor importance in the normal tissue. The data indicate that selective heat-inactivation of tumour tissue is possible by external microwave hyperthermia of locally advanced breast carcinoma.

Morphologic and morphometric studies on tumor necrosis produced by radiotherapy, and hyperthermia singly and in combination

The purpose of the present study was to evaluate the therapeutic effects of hyperthermia associated with radiotherapy on neoplasia. Two transplanted experimental tumors (undifferentiated carcinoma of mouse breast and sarcoma 37) were used. A protocol was followed that included, for both models, four groups of animals: 1) control group; 2) radiotherapy group; 3) hyperthermia group; 4) radiotherapy associated with hyperthermia group. The animals were sacrificed after therapy according to a different schedule for each type of tumor. The morphology of the neoplasia in every group of treated tumors was compared with that of the control group. For quantitative evaluation of the necrosis, we studied the ratio of the tumor necrotic areas (N) to a tumor standard area (T). From the results obtained, the following conclusions were made: 1) Necrosis produced by combined treatment was significantly greater than that obtained by using one only; 2) necrosis appeared early after treatment and remained relatively unchanged; 3) The damaging effect of the hyperthermia occurred earlier than that produced by radiotherapy when these methods were used separately, thus suggesting distinct mechanisms of tumor necrosis.

Histopathologic effects of ultrasonically induced hyperthermia in intraocular malignant melanoma

Four cases of human intraocular malignant melanoma were treated with ultrasonically induced hyperthermia immediately before enucleation. Tumors were treated in two regimens: 30 minutes at 43 degrees to 45 degrees C and 5 minutes at greater than 50 degrees C. Temperatures were estimated from applied power levels, based on empirical data and mathematical models. Histopathologic changes observed in human tumors were compared with changes seen in malignant melanoma xenografts in athymic nude mice which were treated with ultrasonically induced hyperthermia for 30 minutes at 42 degrees to 46 degrees C. The effects of treatment were similar to changes seen in the animal model treated under analogous conditions: increased intercellular spacing, cytoplasmic vacuole formation, clumping of chromatin, breaks in cell membranes, and swelling and collapse of cells. Perivascular and peripheral zones sometimes showed decreased damage levels. The high temperature (greater than 50 degrees C) technique is presently being used as a means of "sterilizing" tumors before planned enucleation. The moderate temperature (43 degrees-45 degrees C) technique has been used in combination with radiotherapy to treat tumors when vision can be salvaged.

Growth characteristics of human melanoma multicellular spheroids in liquid-overlay culture: comparisons with the parent tumour xenografts

The growth characteristics of multicellular spheroids, derived from human melanoma xenografts and cultivated in liquid-overlay culture, were studied and compared with those of the parent tumours. Six of the seven melanomas investigated formed spheroids, which grew exponentially up to a volume of 1-2 X 10(7) microns 3 (a diameter of 270-340 microns) before the growth rate tapered off. The morphology of the spheroids varied considerably among the melanomas; some spheroids grew as densely packed, spherical structures of cells whereas others were loosely packed and showed an irregular shape. Central necrosis developed when the spheroids attained a diameter of 150-200 microns. The histological and cytological appearance of the spheroids was remarkably similar to that of the parent xenograft in five of the six cases. The sixth melanoma contained two subpopulations with distinctly different DNA content, one of which was predominant in the spheroids, the other in the tumours. This gave rise to clear histological and cytological differences. The volume-doubling time of the spheroids during the exponential growth phase ranged from 1.7 +/- 0.2 to 2.7 +/- 0.4 days and the fraction of cells in S from 13 +/- 1 to 28 +/- 2%. The volume-doubling time decreased with increasing fraction of cells in S, indicating that the differences in growth rate were due mainly to differences in the growth fraction or to differences in the duration of G1. The spheroid volume-doubling times did not correlate with those of the parent xenografts (Td = 4.2-22.5 days at V = 200 mm3), possibly because the cell loss factors of the xenografts were large and varied among the melanomas. The fractions of cells in G1/G0, S and G2 + M in the spheroids and the xenografts did not correlate either, but were found to be within the same narrow ranges in the spheroids and the xenografts--i.e. 50-80% (G1/G0), 10-30% (S) and 10-20% (G2 + M).

Heterogeneity in heat sensitivity and development of thermotolerance of cloned cell lines derived from a single human melanoma xenograft

One uncloned and five cloned cell lines were isolated from a single human melanoma xenograft in passage 39 in athymic mice. Cells from passages 7-12 in vitro were heated at 42.5, 43.5 or 44.5 degrees C and the colony forming ability of the cells was assayed in soft agar. The six cell lines showed individual and characteristic responses to heat treatment. The D0 values of the survival curves were in the ranges 76 +/- 5 to 131 +/- 13 min (42.5 degrees C), 12.5 +/- 1.1 to 22.2 +/- 1.9 min (43.5 degrees C) and 9.4 +/- 1.0 to 15.6 +/- 1.5 min (44.5 degrees C). Cells from all lines developed thermotolerance during protracted treatments at 42.5 degrees C. Thermotolerance was also studied by giving the cells a priming treatment of 43.5 degrees C for 90 min and then, after different fractionation intervals at 37 degrees C, second graded treatments at 43.5 degrees C. Thermotolerance ratio (TTR), i.e. the ratio of the slopes of the survival curves for preheated and single-heated cells, was used as a quantitative measure of the thermotolerance. Thermotolerance developed rapidly for all lines, reached a maximum at 12 or 16 h, and then decayed slowly. Maximum TTR varied among the lines from 4.2 +/- 0.5 to 6.0 +/- 0.9, i.e. within a factor of about 1.4. The survival curves and the TTR-curve for the uncloned line were positioned in the midst of those of the cloned lines. A linear correlation between maximum TTR and heat sensitivity was found for the six lines; maximum TTR decreased with increasing D0 value at 43.5 degrees C. Nevertheless, the lines which were most resistant before thermotolerance developed were also most resistant at maximum thermotolerance.