Radiation protection of pronormoblasts and normoblasts by 2-mercaptopropionylglycine (MPG)

Radioprotective Agents: Strategies and Translational Advances

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

Protection against radiation induced chromosome injury by sulfhydryl compounds

The radiation induced changes in a critically radiation-sensitive tissue, bone marrow of Swiss albino mice and its modification by two sulfhydryl compounds, MPG and WR-2721, were studied cytogenetically after whole body exposure to 0.5, 1.5, 3.0, 4.5 and 6.0 Gy of 60Co gamma radiation. The changes in the structural arrangements of chromosomes in the bone marrow were studied at various post-irradiation times from 1 to 28 days. Both the control (irradiated) and experimental (drug + irradiation) animals showed qualitatively similar types of aberrations; the severity of lesions increased with the radiation dose. The maximum damage in all the groups was seen on day 1, post-irradiation. Both the drugs afforded better protection at lower doses of exposure, their effectiveness decreasing with an increasing radiation dose. Of the two drugs, WR-2721 was more effective than MPG against initial aberration yield but the former, at the present drug dose, showed some toxic effect at the later post-irradiation intervals (2 weeks onward) as manifested by an increase in the chromatid breaks and polyploidy.

Protection with combinations of hydroxytryptophan and some thiol compounds against whole-body gamma irradiation

Protection of mice (as measured by survival at 30 days) against whole-body gamma exposure by prior treatment with combinations of hydroxytryptophan (HT) and some thiol drugs, is reported here. The combination of HT and aminoethylisothiuronium bromide hydrobromide (AET) was much more effective than HT alone against the effects of 10.5 and 12.5 Gy of gamma ray exposure. A combination of HT and beta-mercaptopropionylglycine (MPG) gave marked protection against a 10.5 Gy exposure but not against 12.5 Gy. The combination of HT with cysteine or cysteamine also provided reasonable protection against 10.5 Gy. The combination of HT and cystamine rendered a low level of protection against 10.5 Gy, but again it was better than HT alone. The thiol drugs by themselves in the doses used in combination were ineffective in rendering protection after whole body gamma ray exposure.