DMAPT is an Effective Radioprotector from Long-Term Radiation-Induced Damage to Normal Mouse Tissues In Vivo

While radiotherapy is widely used in cancer treatment, the benefits can be limited by radiation-induced damage to neighboring healthy tissues. We previously demonstrated in mice that the anti-inflammatory compound dimethylaminoparthenolide (DMAPT) selectively induces radiosensitivity in prostate tumor tissue from transgenic adenocarcinoma of mouse prostate (TRAMP) mice, while simultaneously protecting healthy tissues from 6 Gy whole-body radiation-induced apoptosis. Here, we examined the radioprotective effect of DMAPT on fibrosis in normal tissues after a partial-body fractionated radiation protocol that more closely mimics the image-guided fractionated radiotherapy protocols used clinically. Male C57BL/6J mice, 16 weeks old, received 20 Gy fractionated doses of X rays (2 Gy daily fractions, five days/week for two weeks) or sham irradiation to the lower abdomen, with or without a prior 20 mGy dose to mimic an image dose. In addition, mice received thrice weekly DMAPT (100 mg/kg by oral gavage) or vehicle control from 15 weeks of age until time of analysis at 6 weeks postirradiation. In the absence of exposure to radiation, there were no significant differences observed in the tissues of DMAPT and vehicle-treated mice (P > 0.05). DMAPT treatment significantly reduced radiation-induced testis weight loss by 60.9% (P < 0.0001), protected against a decrease in the seminiferous tubule diameter by 42.1% (P < 0.0001) and largely preserved testis morphology. Inclusion of the image dose had no significant effect on testis mass, seminiferous tubule diameter or testis morphology. DMAPT reduced radiation-induced fibrosis in the corpus cavernous region of the penis (98.1% reduction, P = 0.009) and in the muscle layer around the bladder (80.1% reduction, P = 0.0001). There was also a trend towards reduced collagen infiltration into the submucosal and muscle layers in the rectum. These results suggest that DMAPT could be useful in providing protection from the radiation-induced side effects of impotence and infertility, urinary incontinence and fecal urgency resulting from prostate cancer radiotherapy. DMAPT is a very well-tolerated drug and can conveniently be delivered orally without strict time windows relative to radiation exposure. Protection of normal tissues by DMAPT could potentially be useful in radiotherapy of other cancer types as well.