Misoprostol-induced radioprotection of oncogenic transformation

Prostaglandins are associated with a variety of both pathologic and normal physiological effects in mammals. Among this broad array of effects, prostaglandins have been shown to provide protection to tissues from a variety of injurious agents including ionizing radiation. Of the prostaglandins tested to date, an analogue of prostaglandin E1, misoprostol (cytotec) was found to be a very effective radioprotector. The purpose of this study was to assess the ability of misoprostol to protect cells from the cytotoxic and oncogenic effects of ionizing radiation.

Pregnant Syrian hamsters were injected subcutaneously with 125 micrograms misoprostol/100 g body weight 2 h before being exposed to graded doses of X rays. Embryos were excised immediately after irradiation and cells were explanted into culture dishes. Following 14 days of incubation, cells were fixed in formalin and stained with giemsa for examination of cell clonogenicity and morphological transformation.

First, misoprostol protected cells from some degree of radiation toxicity. A reduction in cell killing by a factor of 1.5 was seen at 10% cell survival. Second, based on transformation studies, a higher frequency of oncogenic transformation is seen for cells exposed in utero to graded doses of X rays alone than for cells exposed to the combination of misoprostol followed by radiation. In the presence of misoprostol, transformation is reduced by a factor of 20 at the level of 10(-3) transformants per surviving cell.

Misoprostol may have clinical utility, not only in protecting selected normal tissues during cancer therapy, but it may also be useful in protecting cells from secondary tumors caused by ionizing radiation.