Comparative efficacy and the window of radioprotection for adrenergic and serotoninergic agents and aminothiols in experiments with small and large animals

1-Isobutanoil-2-isopropylisothiourea Phosphate, T1082: A Safe and Effective Prevention of Radiotherapy Complications in Oncology

The radioprotective effects of a new 1-isobutanoil-2-isopropylisothiourea derivative named T1082 are presented. Research methods included toxic characteristics, radioprotective activity (Till–McCulloch’s test and 30-day survival test) in γ-ray total-body-irradiated mice, and a clinical and histological study of the effect of T1082 on acute radiation skin reactions (RSR) in rats after a single or fractionated β-ray local irradiation. T1082 is more effective than its analogue, the NOS inhibitor T1023, at low concentrations and doses (1/12–1/8 LD₁₀), both parenterally and intragastrically. In this case, its therapeutic index (LD₅₀/ED₅₀) reaches 30, and the optimal radioprotective doses (ED_84–98—141–224 mg/kg) are an order less than the maximum tolerated doses—1/16–1/10 LD₁₀. These properties allowed T1082, at a low intragastrical dose (160 mg/kg; 1/14 LD10), to significantly limit the severity of acute RSR after single (40 Gy) and fractionated (78 Gy) β-ray irradiation. The results confirm T1082 as one of the safest emergency radioprotectors and indicate the prospects for its further development as a pharmacological agent for the prevention of RT complications.

An Analysis of the Serum Metabolomic Profile for the Radiomitigative Effect of the Thrombopoietin Receptor Agonist Romiplostim in Lethally Whole-Body-Irradiated Mice

The thrombopoietin receptor agonist romiplostim (RP) was recently approved by the US Food and Drug Administration for improving survival in patients acutely exposed to myelosuppressive doses of radiation. Our previous studies with mice have shown that RP administration after lethal irradiation not only completely rescues irradiated mice but also shows mitigative effects on their hematopoiesis and multiple organ injury, including that of the lung, bone marrow, small intestine, and liver. However, the mechanism by which RP functions as a radiomitigator remains unclear. In the present study, we applied a metabolomics approach, which has the ability to reflect the status of an organism directly and accurately, helping to elucidate the biology of treatment responses. Our results showed that the disruption of several metabolites and pathways in response to total body irradiation was partially corrected by RP administration. Notably, RP-corrected metabolites and pathways have been reported to be indicators of DNA damage and lung, bone marrow, small intestine, and liver injury. Taken together, the present findings suggested that the radiomitigative effect of RP is partially involved in the recovery of organ injury, and the identified metabolites may be a useful biomarker of the survival likelihood following radiation exposure.

Design, Synthesis, and Biological Evaluation of a Novel Aminothiol Compound as Potential Radioprotector

The risk of radiation damage has increased with the rapid development of nuclear technology and radiotherapy. Hence, research on radioprotective agents is of utmost importance. In the present study, a novel aminothiol compound 12, containing a linear alkylamino backbone and three terminal thiols, was synthesized. Owing to the appropriate capped groups in the chains, it has an improved permeability and oral bioavailability compared to other radioprotective agents. Oral administration of compound 12 improved the survival of mice that received lethal doses of γ-irradiation. Experimental results demonstrated that compound 12 not only mitigated total body irradiation-induced hematopoietic injury by increasing the frequencies of hematopoietic stem and progenitor cells but also prevented abdominal irradiation-induced intestinal injury by increasing the survival of Lgr5⁺ intestinal cells, lysozyme⁺ Paneth cells, and Ki67⁺ cells. In addition, compound 12 decreased oxidative stress by upregulating the expression of Nrf2 and NQO1 and downregulating the expression of NOX1. Further, compound 12 inhibited γ-irradiation-induced DNA damage and alleviated G2/M phase arrest. Moreover, compound 12 decreased the levels of p53 and Bax and increased the level of Bcl-2, demonstrating that it may suppress radiation-induced apoptosis via the p53 pathway. These results indicate that compound 12 has the possibility of preventing radiation injury and can be a potential radioprotector for clinical applications.

Radioprotective Activity of the Nitric Oxide Synthase Inhibitor T1023. Toxicological and Biochemical Properties, Cardiovascular and Radioprotective Effects

In this work, studies were performed to investigate the toxicological, biochemical, vasotropic and radiomodifying properties of the new nitric oxide synthase (NOS) inhibitor, compound T1023. Toxicological studies included the estimation of acute toxicity in mice after i.p. administration of T1023. Radiometric analysis and electron paramagnetic resonance spectroscopy were used to study NOS-inhibitory properties of T1023 in vitro and in vivo, respectively. T1023 vasoactive properties were studied in rat central hemodynamics. Radiobiological experiments were performed using endogenous and exogenous spleen colony formation as well as 30-day survival tests. The morphological changes in peripheral blood and bone marrow (BM) induced with T1023 were analyzed in mice during hematopoietic acute radiation syndrome (H-ARS). It was shown that T1023 is a sufficiently safe compound (LD10 of 317 mg/kg; LD50 of 410 mg/kg). It is an effective competitive NOS-inhibitor that is 10-to-15-fold selective to endothelial and inducible NOS (IC50 for nNOS, iNOS, eNOS: 52.3, 3.2 and 5.1 µM, respectively). Its NOS-inhibitory activity is realized in vivo and is accompanied by an increase in vascular tone. Its single i.p. administration in doses greater than 1/8 LD10 provides significant (40-50%) and long-lasting (more than 90 min) weakening of cardiac output, which can cause transient hypoxia. In radiobiological studies, T1023 proved to be a hypoxic radioprotector. Its radioprotective effect was observed only when administered prophylactically [single i.p dose, 5-120 min before total-body irradiation (TBI)] and only in doses that reduced cardiac output (1/8 LD10 and more, 40 mg/kg for mice), and was correlated in time with the dynamics of circulatory depression. Its radioprotective effect was not observed when administered in vitro and in the first 4 h after TBI. The optimal radioprotective doses of T1023 are relatively safe (1/ 5-1/4 LD10). In addition, T1023 effectively prevents H-ARS and gastrointestinal acute radiation syndrome (G-ARS) in experimental animals in vivo: dose modifying factor of 1.6-1.9. In the H-ARS mouse model, the prophylactic effect of T1023 (75 mg/kg, single i.p. injection) was accompanied by clinically significant effects. There was an express decrease in the degree of indicators of early BM devastation (by 40%) and maximal neutropenia and thrombocytopenia (2-2.5 times), in addition to a reduction in recovery time (by 30-40%). The obtained experimental results and literature data indicate that NOS inhibitors are an independent class of vasoactive radioprotectors with a specific hypoxic mechanism of action. NOS inhibitors provide new opportunities for developing effective and safe tools for the prevention of ARS.

Enhancing effect of cystamine in its amides with betulinic acid as antimicrobial and antitumor agent in vitro

Amides of betulinic acid with cystamine were synthesized to investigate their antimicrobial and antitumor activity, and their influence on the cell cycle and cell apoptosis. The former target amide (6) displayed cytotoxicity in CEM cell line after 72 h of treatment (IC₅₀ = 3.0 ± 0.7 μM; TI = 20), and induced apoptosis by caspase-3/7 activation in CEM cells. The latter target amide (9) displayed antimicrobial activity against Streptococcus mutans (MIC 3.125 μM; MBC 3.125 μM) and Bacillus cereus (MIC 25 μM; MBC 25 μM). The achieved results demonstrate enhancing of their biological activity over that of the parent compounds. However, two intermediate compounds (2 and 7) displayed either considerable cytotoxicity (2; 7.5 ± 0.8 μM; TI = 10, against G361) or antimicrobial activity (7; both against Actinomyces odontolycus and Clostridium perfrigens with MIC 12.5 µM and MBC 12.5 µM). The experimental data were compared with the in silico calculated physico-chemical and ADME parameters of the target compounds, including successful intermediates.

Potential use of melatonin in skin cancer treatment: A review of current biological evidence

Skin cancer, particularly melanoma, is a leading cause of death worldwide. The therapeutic methods for this malignancy are not effective, and due to the side effects of these treatments, applying an appropriate alternative or complementary treatment is important. According to available data, melatonin as the main product of the pineal gland has oncostatic and antitumoral properties. Also, melatonin acts as an anti-inflammatory and reactive oxygen species inducer agent which suppresses the growth of tumors. It also has apoptosis induction characteristics through regulating signaling pathways, including heat shock protein 70, nuclear factor-erythroid 2 p45-related factor 2 and others. Thus, adding melatonin to chemo- and radiotherapy may have synergistic therapeutic effects and increase the survival time in patients with skin cancer. Few clinical studies have evaluated the efficacy of melatonin in skin cancer. Based on the related mechanisms, this review discusses about how melatonin may improve outcomes in skin cancer patients.

Localized Delivery of Amifostine Enhances Salivary Gland Radioprotection

Radiotherapy for head and neck cancers commonly causes damage to salivary gland tissue, resulting in xerostomia (dry mouth) and numerous adverse medical and quality-of-life issues. Amifostine is the only Food and Drug Administration-approved radioprotective drug used clinically to prevent xerostomia. However, systemic administration of amifostine is limited by severe side effects, including rapid decrease in blood pressure (hypotension), nausea, and a narrow therapeutic window. In this study, we demonstrate that retroductal delivery of amifostine and its active metabolite, WR-1065, to murine submandibular glands prior to a single radiation dose of 15 Gy maintained gland function and significantly increased acinar cell survival. Furthermore, in vivo stimulated saliva secretion was maintained in retrograde-treated groups at levels significantly higher than irradiated-only and systemically treated groups. In contrast to intravenous injections, retroductal delivery of WR-1065 or amifostine significantly attenuated hypotension. We conclude that localized delivery to salivary glands markedly improves radioprotection at the cellular level, as well as mitigates the adverse side effects associated with systemic administration. These results support the further development of a localized delivery system that would be compatible with the fractionated dose regimen used clinically.

Melatonin as an adjuvant in radiotherapy for radioprotection and radiosensitization

It is estimated that more than half of cancer patients undergo radiotherapy during the course of their treatment. Despite its beneficial therapeutic effects on tumor cells, exposure to high doses of ionizing radiation (IR) is associated with several side effects. Although improvements in radiotherapy techniques and instruments could reduce these side effects, there are still important concerns for cancer patients. For several years, scientists have been trying to modulate tumor and normal tissue responses to IR, leading to an increase in therapeutic ratio. So far, several types of radioprotectors and radiosensitizers have been investigated in experimental studies. However, high toxicity of chemical sensitizers or possible tumor protection by radioprotectors creates a doubt for their clinical applications. On the other hand, the protective effects of these radioprotectors or sensitizer effects of radiosensitizers may limit some type of cancers. Hence, the development of some radioprotectors without any protective effect on tumor cells or low toxic radiosensitizers can help improve therapeutic ratio with less side effects. Melatonin as a natural body hormone is a potent antioxidant and anti-inflammatory agent that shows some anti-cancer properties. It is able to neutralize different types of free radicals produced by IR or pro-oxidant enzymes which are activated following exposure to IR and plays a key role in the protection of normal tissues. In addition, melatonin has shown the ability to inhibit long-term changes in inflammatory responses at different levels, thereby ameliorating late side effects of radiotherapy. Fortunately, in contrast to classic antioxidants, some in vitro studies have revealed that melatonin has a potent anti-tumor activity when used alongside irradiation. However, the mechanisms of its radiosensitive effect remain to be elucidated. Studies suggested that the activation of pro-apoptosis gene, such as p53, changes in the metabolism of tumor cells, suppression of DNA repair responses as well as changes in biosynthesis of estrogen in breast cancer cells are involved in this process. In this review, we describe the molecular mechanisms for radioprotection and radiosensitizer effects of melatonin. Furthermore, some other proposed mechanisms that may be involved are presented.