What is the role of environmental health science in cancer prevention?

THE USE of hypoxic cell sensitizers in improving the therapeutic ratio is the subject of much experimental and clinical investigation. Unfortunately the most widely used compound, misonidazole (MISO) increases the number of treatment complications, in particular causing peripheral neuropathies (Dische et al., 1978). It is also found in the laboratory that MISO enhances the effect of radiation on some normal tissues. Hendry & Sutton (1978) argued from experiments with hyperbaric 02 or MISO that at least some normal tissues contain a significant proportion of hypoxic cells, which should be taken into account in treatment with hypoxic cell sensitizers. It is natural to be especially cautious of radiosensitization in tissue in which direct drug toxicity has been observed, i.e. the central nervous system. Recently Yuhas (1 979) reported the results of a pilot study in which 0-2 mg/g MISO given to rats caused an increase in the incidence of paralysis due to irradiation of a segment of the spinal cord. The sensitizer enhancement ratio (SER) in these experiments was about 1P3 though the data were rather limited. However, more extensive experiments of a similar nature have been performed by van der Kogel (personal communication) on anaesthetized rats, and he found no enhanced radiation response of the spinal cord. Clearly, the effects of radiosensitizing drugs on the CNS need further investigation. A convenient method for estimatingradiation damage to neuroglia is by counting cells in the subependymal layer of the rodent forebrain. In the rat these cells divide Accepte(1 3 MIarchi 1981