Enhancement of misonidazole chemopotentiation by mild hyperthermia (41 degrees C) in vitro and selective enhancement in vivo

The advantageous use of hypoxic tumour cells in cancer therapy: identical chemosensitization by metronidazole and misonidazole at moderately elevated temperatures

Chemosensitization by two nitroimidazoles (NIs), metronidazole (METRO) and misonidazole (MISO), of the anti-tumour effect of alkylating agents was studied at three different temperatures: room temperature (RT), 37 and 41.5 degrees C. Three alkylating agents, cyclophosphamide (CY), 1,3 bis(2-chloroethyl)-N-nitrosourea (BCNU) and melphalan (L-PAM) were tested when the tumours reached an average diameter of 4 mm. Tumours were 4th generation isotransplants of a spontaneous fibrosarcoma, FSa-II. Treatment at 37 or 41.5 degrees C was given by immersing the tumour-bearing foot for 60 min in a water bath set at these temperatures. The test agents were injected ip immediately before immersing the foot in the water bath, whereas METRO or MISO (2.5 mmol/kg) was given ip 30 min before the injection of a test agent. Following treatment the tumour growth (TG) time, i.e. the time required for one-half of treated tumours to reach 1000 mm3 after the treatment day, was studied. For CY, MISO was a better sensitizer than METRO at RT and 37 degrees C, but the magnitude of the chemosensitization by MISO and METRO became identical at 41.5 degrees C. Notably, the chemosensitization was substantially enhanced at 41.5 degrees C, whereas neither 41.5 degrees C-heat, NIs or combined NI and heat prolonged the TG time. Although no chemosensitization was observed for BCNU at RT, both METRO and MISO equally enhanced the effect of BCNU at 41.5 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of misonidazole chemosensitization effect by mild local hyperthermia

In an attempt to increase the chemosensitization effect of the alkylating agents 1,3 bis(2-chloroethyl)-1-nitrosourea (BCNU) and cyclophosphamide (CY), by misonidazole (MISO) at the tumor site, mild hyperthermic treatment (41.5 degrees C, 1 hr) was applied at various administration sequences. C3Hf/Sed mice bearing subcutaneous FSa-II tumors in the foot were used for a tumor growth time assay. Local hyperthermic treatment increased the antitumor activities of BCNU and CY by 1.4 and 2.4 fold, respectively. MISO at 2.5 mmole/kg potentiated the antitumor activities of BCNU, but not CY, at normal body temperature. There were no significant improvement of MISO chemosensitization when heat was given before the administration of BCNU and CY. However, a significant enhancement of chemosensitization was observed when heat was given after the administration of MISO and the alkylating agents. Enhancement ratios of about 2.4 and 4.7 were observed with BCNU and CY, respectively. There may be two mechanisms responsible for this thermal enhancement. First, the MISO pre-incubation time that was required for the expression of chemosensitization effect decreased substantially at elevated temperatures. This hypothesis was supported by the pharmacokinetic studies that MISO was rapidly eliminated from tumors in the first 10 min during the local heat treatment and remained at a plateau with a concentration of about 5-fold less than the peak MISO concentration in the control tumors. This rapid elimination might result from the increase in the rate of hypoxic metabolism of MISO in heated tumors. Second, heat may increase the MISO-alkylating agent interactions, which are independent of pre-incubation time. This effect was especially pronounced in CY because pre-incubation-induced chemosensitization of CY in unheated tumor was insignificant in this study. The significant improvement of MISO chemosensitization at moderately elevated temperatures can be useful clinically in combined hyperthermia and chemotherapy treatment.