No abstract

Previously, we showed that a nitric oxide synthase (NOS) inhibitor, compound T1023, induces transient hypoxia and prevents acute radiation syndrome (ARS) in mice. Significant efficacy (according to various tests, dose modifying factor (DMF)—1.6–1.9 against H-ARS/G-ARS) and safety in radioprotective doses (1/5–1/4 LD10) became the reason for testing its ability to prevent complications of tumor radiation therapy (RT). Research methods included studying T1023 effects on skin acute radiation reactions (RSR) in rats and mice without tumors and in tumor-bearing animals. The effects were evaluated using clinical, morphological and histological techniques as well as RTOG classification. T1023 administration prior to irradiation significantly limited the severity of acute RSR. This was due to a decrease in radiation alteration of the skin and underlying tissues, and the preservation of the functional activity of cell populations that are critical in the pathogenesis of radiation burn. The DMF values for T1023 for skin protection were 1.4–1.7. Moreover, its radioprotective effect was fully selective to normal tissues in RT models of solid tumors—T1023 reduced the severity of acute RSR and did not modify the antitumor effects of γ-radiation. The results indicate that T1023 can selectively protect the non-malignant tissues against γ-radiation due to hypoxic mechanism of action and potentiate opportunities of NOS inhibitors in RT complications prevention.

The purpose of the work was to study the ability of the NOS inhibitor T1023 to prevent late radiation injuries. Methods: the effects of T1023 (75 mg / kg, once i.p. 30 minutes before the irradiation) on the development of post-radiation pulmonitis and pneumofibrosis in rats with thoracic exposure to g-radiation at  a dose of 12.5 Gy were studied histopathologically and morphometrically. The results of the studies showed that there wasn’t a significant objective effect of T1023 on the development of early radiation-induced lung injuries  (9 weeks after irradiation). But it prevented late radiation induced lung injuaries (26 weeks after irradiation) – there were a significant lesser pathomorphological manifestations of post-radiation pulmonitis, proliferation of connective tissue and the development of fibrotic changes in the lung parenchyma. At this stage, the action of T1023 clearly contributed to the preservation of the normal histostructure of the lungs, reducing by 40% the content of compaction zones in the parenchyma. The ability of the NOS inhibitor T1023 to significantly limit the development of lungs late radiation reaction confirms the promise of further development  of this compound as a means for prevention radiation therapy complications.