Combination of NOS- and PDK-Inhibitory Activity: Possible Way to Enhance Antitumor Effects.

We have previously demonstrated a high antitumor potential of NOS inhibitor T1023 (1-isobutanoyl-2-isopropylisothiourea hydrobromide): antitumor antiangiogenic activity in several animal tumor models and its ability to synergistically enhance the antitumor effects of bevacizumab, cyclophosphamide and γ-radiation. At the same time, rather rapid adaptation of experimental neoplasias to T1023 treatment was often observed. We attempted to enhance the antitumor activity of this NOS inhibitor by supplementing its molecular structure with a PDK-inhibiting fragment, dichloroacetate (DCA), which is capable of hypoxia-oriented toxic effects. We synthesized compound T1084 (1-isobutanoyl-2-isopropylisothiourea dichloroacetate). Its toxic properties, NOS-inhibiting and PDK-inhibiting activity in vivo, and antitumor activity on the mouse Ehrlich carcinoma model (SEC) were investigated in compare with T1023 and Na-DCA. We found that the change of the salt-forming acid from HBr to DCA does not increase the toxicity of 1-isobutanoyl-2-isopropylisothiourea salts, but significantly expands the biochemical and anti-tumor activity. New compound T1084 realizes in vivo NOS-inhibiting and PDK-inhibiting activity, quantitatively, at the level of the previous compounds, T1023 and Na-DCA. In two independent experiments on SEC model, a pronounced synergistic antitumor effect of T1084 was observed in compare with T1023 and Na-DCA at equimolar doses. There were no signs of SEC adaptation to T1084 treatment, while experimental neoplasia rapidly desensitized to the separate treatment of both T1023 and Na-DCA. The totality of the data obtained indicates that the combination of antiangiogenic and hypoxia-oriented toxic effects (in this case, within the molecular structure of the active substance) can increase the antitumor effect and suppress the development of hypoxic resistance of neoplasias. In general, the proposed approach can be used for the design of new anticancer agents.

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 ß-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 (ED84-98-141-224 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) ß-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.

The Ability of the Nitric Oxide Synthases Inhibitor T1023 to Selectively Protect the Non-Malignant Tissues.

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.

Preclinical studies of NOS inhibitor T1059 vasopressor activity on the models of acute hemorrhagic shock in rats and dogs.

The development of new effective and safe vasopressors is one of the ways to increase the effectiveness of the treatment of hypotensive disorders, the severe forms of which remain a common cause of death in all countries of the world. Previously, we synthesized the original compound T1059, a selective inhibitor of eNOS/iNOS which has a pronounced vasoconstrictive effect. Here we show its vasopressor activity in models of the early stage of acute hemorrhagic shock in rats and dogs, as part of preclinical studies. The results indicate NOS inhibitor T1059 as a potent long-acting vasopressor. Its single parenteral administration in sufficiently safe doses (1/50-1/9 LD10), caused in rats and dogs a rapid increase in vascular tone, accompanied by a prolonged hypertensive effect (within 90-120 min in rats, and within 115 min in dogs). The repeated administration of T1059 at low doses (1/3 of the first dose) made it possible to considerably (by at least 60 min) prolong a significant vasopressor effect. In all schemes, T1059 administration considerably inhibited the development of threatening cardiorespiratory disorders and significantly (p = 0.0026-0.0098) increased the short-term survival of experimental animals, formally extending the duration of the "golden hour" by 2 times. These data indicate that NOS inhibitors and, in particular, compound T1059, are able to create new opportunities in the treatment of hypotensive disorders, including the provision of assistance at the prehospital stage of treatment of such pathologies.

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.