The Effectiveness of Cyclic Hydroxamic Acid CHA-5 against Drug-Resistant P388 Leukemia Strains.

We studied the effectiveness of cyclic hydroxamic acid CHA-5 against drug-resistant and multidrug-resistant murine P388 leukemia strains. More than 60% mice receiving transplantation of rubomycin-resistant leukemia P388 strain survived after CHA-5 monotherapy; combined therapy with CHA-5 and cisplatin was also highly effective. Vincristine-resistant tumor was highly sensitive to combined treatment with CHA-5 and cyclophosphamide. It should be emphasized that standard antitumor agents were used in very low doses in combination therapy and CHA-5 significantly potentiated their effect.

[Cyclic hydroxamic acids as chemosensitizers in cytostatic therapy].

In experimental animals with tumors it was studied antitumor activity of spirocyclic hydroxamic acids which could be classified as targeted agents as their target was enzyme histonedeacetylase, which was involved in the neoplastic process. The results showed that the hydroxamic acids were chemosensitizers for anticancer agents increasing their efficacy and enabling the researchers to reduce significantly the therapeutic dose. Also it was showed that hydroxamic acid, containing nitrogen mustard, was effective in the action on tumors with phenotype and genotype of multidrug resistance.

[The use of hydroxamic acids and sodium nitrate to enhance the antitumor effect of cyclophosphamide].

It has been showed that the introduction of nitrocompounds (as nitic oxide donors) in to the compositions of cyclophosphamide and hydroxamic acids for curing animals having leukemia P-388 increased duration of life by 290%. Thereby 40% of animals have recovered. The therapeutic dose cyclophosphamide have been reduced by 6 times.

[Antileukemic activity and development of resistance to cisplatin (CPT) and platinum (IV)-nitroxyl complex VS118].

Treatment with low doses (1/10 of LD50) of cisplatin and platinum (IV)-nitroxyl complex VS118 [e-ammin-d-(4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-a,f-bi s(acetate)-b,c-dichlorplatinum (IV)] was followed by a synergistic therapeutic effect (a 100% cure of animals) as compared with monotherapy with either drug. There was no synergistic increase in toxicity. The rates of resistance development decreased in the following order: P388/cPt+VS118, P388/cPt, P388/VS118. Resistant strains P388/cPt+VS18 and P388/VS118 were highly sensitive to doxorubicin, etoposide and cyclophoshamide. Further research in cPt+VS 118 combinations should be continued.

Effect of nitric oxide donor, a modulator of tumor drug resistance, on cell death and p53 protein expression.

Exogenous NO donor 3,3-bis-(nitroxymethyl)oxetane (NMO) was synthesized at the Institute for Problems of Chemical Physics (Russian Academy of Sciences). This compound was shown to inhibit cell death (apoptosis and necrosis) in cyclophosphamide-sensitive and cyclophosphamide-resistant P388 murine tumor. p53 protein was expressed in both lines of tumor cells. NO donor NMO had little effect on p53 protein expression in cells of both stains. Our results suggest that the proapoptotic effect of NMO is mediated by the p53-independent molecular mechanisms.

Effect of drug resistance modulator, NO donor, on membrane structure and function of membrane-bound Ca2+-activated Mg2+-dependent ATPase.

Exogenous NO donor 3,3-bis-(nitroxymethyl)oxetane (NMO) was synthesized at the Institute for Problems of Chemical Physics (Russian Academy of Sciences). This compound was shown to inhibit Ca2+-ATPase isolated from normal muscular cells and tumor cells. Both hydrolytic and transport functions of the enzyme were inhibited under these conditions. These changes were probably related to changes in membrane structure caused by NO donor. Our results suggest that changes in intracellular Ca2+ concentration can modulate the formation of tumor drug resistance.

[Inhibition of active transport of calcium ions by PT(IV) and PD(II) metal complexes. Correlation between the process and antimetastatic action of drugs].

Newly synthesized compounds, namely, platinum and palladium metal complexes based on substituted pyridinecarboxylic acids inhibit both active transport of Ca ions and hydrolysis of ATP, catalyzed by sarcoplasmic reticulum Ca(2+)-ATPase. The degree of active transport of Ca ions to vesicles correlated to the inhibition of metastases of experimental melanoma B16 by compounds studied. We suggest that the mechanism responsible for inhibition of metastases by newly synthesized compounds consists in change of normal ratio of extra- and intracellular content of Ca2+ ions that influences platelet aggregation, required for adhesion of metastasizing tumor cells to vascular walls.

Ultralow doses of various drugs in chemotherapy of experimental tumors.

Antitumor activity of ultralow doses of cytostatic lonidamine and effects of various biological preparations in ultralow doses (chemosensitizer, immunomodulator, and antioxidant) on the efficiency of adriamycin and cisplatin were studied in animals with transplanted tumors. High efficiency of this method was demonstrated. Nitrotriazole chemosensitizer in ultralow doses increased the sensitivity of leukemia P388/rn substrain with multiple drug resistance phenotype to mitomycin C during combination therapy.

[Nitric oxide donor increases the effectiveness of cytostatic therapy and inhibits the development of drug resistance]. / Donor oksida azota povyshaet éffektivnost' tsitostaticheskoi terapii i zaderzhivaet razvitie lekarstvennoi rezistentnosti.

The investigation has established a potential of low-dosage chemotherapy with cytostatics when used in combination with nitric oxide (NO) donor. Such regimen resulted in more animals being cured of leukemias P388 and L1210 and longer survival. Similar effect was reported with transplantable intracerebral leukemia P388 in which case mean survival after cyclophosphamide plus NO-donor was three times as high as that after cyclophosphamide alone. Combination therapy also promoted animetastatic effect: melanoma B16 inhibition by cyclophosphamide alone was 50% vs. 80% after cyclophosphamide plus NO-donor. NO-donor inhibited development of drug resistance to cyclophosphamide.

Nitric oxide donor increases the efficiency of cytostatic therapy and retards the development of drug resistance.

The potentiality to increase the chemotherapeutic effectiveness of some cytostatics in low, subtherapeutic doses in combination with nitric oxide (NO) donor has been shown. This type of combined therapy results in significant increase in life span and number of survivors among mice bearing leukemias P388 and L-1210. A similar effect was observed for intracerebral leukemia P388 transplantation. In this case the life span of mice treated with cyclophosphamide and NO donor increased by three times in comparison to therapy with cyclophosphamide alone. The coinjection of nitric oxide donor and cytostatics improved the antimetastatic activity of the cytostatics: the index of melanoma B16 metastasis inhibition at the cyclophosphamide monotherapy is 50%; on addition of NO donor the index is over 80%. Comparative studies of NO donor (organic nitrate) and a similar compound in which ONO(2) moieties were replaced by OH groups demonstrated that the presence of NO(2) is required for adjuvant activity of compounds and confirmed that nitric oxide modifies the antitumor effects of cytostatics. It is shown also that nitric oxide donor retards the development of drug resistance to cyclophosphamide.

[Ecdysterone modulates antitumor activity of cytostatics and biosynthesis of macromolecules in tumor-bearing animals]. / Ekdisteron moduliruet protivoopukholevuiu aktivnost' tsitostatikov i ikh deistvie na biosintez makromolekul v organakh zhivotnykh-opukholenositelei.

The influence of therapeutic and half doses of cisplatin and adriamicin combination with the anabolic drug ecdisteron (20-hydroecdison) on development of subcutaneously and intraperitonially transplanted P388 and L1210 leukemia and metastasizing B16 melanoma was studied. Ecdisteron significantly stimulated the chemotherapeutic effect of low doses of the cytostatics: inhibition of tumor growth, mice survival rate, their lifespan, and the antimetastatic activity index were comparable or better than after therapy with high doses of the antitumor drugs. The influence of high and low doses of cisplatin and its low dose in combination with ecdisteron on the dynamics of protein and DNA biosynthesis in the liver, pancreas, thymus, spleen, and adrenals of tumor-bearing mice were also studied. Although the therapeutic effect of 4 mg/kg cisplatin by activated protein biosynthesis and DNA repair is comparable or better than that of its low dose (2 mg/kg) in combination with ecdisteron, in terms of chemotherapy the combination looks preferable since the therapeutic dose of cisplatin is toxic for the intact tissues.

Nitrotriazole AK-2123 enhances mitomycin C activity in mice bearing multidrug-resistant tumors.

The often observed cross resistance of multidrug-resistant (MDR) tumors to mitomycin C (MMC) is surprising, as these tumors are, as a rule, sensitive to alkylating drugs, and the mechanism of MMC activity is connected to alkylation of DNA. This study shows that nitrotriazole AK-2123 significantly enhances the sensitivity of MDR-strains of P388 mouse leukemia (developed and characterized by authors previously) to mitomycin C. The modulating effect is dependent on the initial sensitivity of resistant tumors to MMC which is correlated with the existence or absence of sorcin (cytosole Ca2+-binding protein) gene coamplification in MDR-amplicon. In agreement with authors' previous data about AK-2123 influence on active Ca2+-transport, it is supposed that the modulatory effect of radiosensitizer is at least partially dependent on this capacity. AK-2123 has no own antitumor effect on investigated tumors and cannot modify the sensitivity of the parent tumor P388 to MMC.

[The radiosensitizer AK-2123 enhances sensitivity of MDR-tumors to Mitomycin C]. / Povyshenie chuvstvitel'nosti lekarstvenno-ustoichivykh opukholei k mitomitsinu C s pomoshch'iu radiosensibilizatora AK-2123.

It was demonstrated that radiosensitizer AK-2123 of the triazole group significantly enhanced the sensitivity of MDR-strains of P388 murine leukemia (reported by the authors earlier) to mitomycin C (MMC). There was a direct correlation between the modulating effect of AK-2123 and dose increase from 1 to 10 mg/kg. The effect depended on the initial sensitivity of the MMC-resistant strain which in turn correlated with the absence or presence of sorcin (cytosole low-molecular Ca(2+)-binding protein) gene coamplification in the mdr-amplicon. Since AK-2123 was reported earlier by us to disrupt active Ca(2+)-transport, it is suggested that the modulating effect of the radiosensitizer was at least partially due to said disruption. AK-2123 exerted no antitumor action of its own whatsoever. It could neither modify the sensitivity of parent strain P388 to MMC, nor overcome the cross resistance of one of the MDR-tumor strains under study to such drugs as etoposide and adriablastin.

[Effect of Ruboxyl (nitroxyl derivative of daunorubicin) on hepatic metastases of colorectal carcinoma]. / Aktivnost' Ruboxyla (nitroxil'nogo proizvodnogo daunomitsina) pri metastazakh v pechen' kolorektal'nogo raka.

Inhibition by ruboxyl, a nitroxyl derivative of daunorubicin, source preparation and 5-fluorouracil was compared in metastases of experimental colorectal carcinoma to murine liver. The indices of metastasis inhibition were 84.43 and 70%, respectively. In rats receiving the drugs by continuous intravenous infusion for 7 days, the number of metastases was reduced (ruboxyl--1.0 +/- 1.4; 5-fluorouracil 3.2 +/- 1.3.

[Inhibitory effect of the radiosensitizer AK-2123 on experimental liver metastasis and active transport of calcium ions]. / Ingibiruiushchii éffekt radiosensibilizatora AK-2123 na éksperimental'nye metastazy v pecheni i aktivnyi transport ionov kal'tsiia.

Radiosensitizer AK-2123, a triazol, has been shown to significantly inhibit the development of hepatic metastases induced in syngeneic mice by intrasplenic injections with cels of bowel adenocarcinoma. The antimetastatic effect was produced by use of a very low dose of the drug. A therapeutic dose of AK-2123 has been shown to inhibit active transport of calcium ions across sarcoplasmic reticular cells effected by Ca(2+)-dependent Mg(2+)-activated ATPase. It is suggested that the antimetastatic effect of AK-2123 is determined by at least partial inhibition of active transport of calcium.

Inhibitory effect of radiosensitizer AK-2123 on experimental hepatic metastases and Ca2+ active transport.

A triazole group radiosensitizer AK-2123 is shown to inhibit considerably the growth of hepatic metastases induced by the intrasplenic injection of colon adenocarcinoma cells in syngenic mice. Even an extremely low dose of the drug exhibits the antimetastatic effect. It is shown that AK-2123 injected at therapeutic dose inhibits active transport of calcium ions by the (Ca2+-Mg2+)-dependent ATP-ase. The antimetastatic effect of AK-2123 is suggested to be related, at least partially, to the inhibition of the active calcium transport.

Synthesis and antitumor activity of platinum(II) complexes with trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl.

Platinum complexes PtII(DAPO)X2 with diaminonitroxyl radical-trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl (DAPO)-were synthesized by the direct reaction of DAPO with K2PtX4 (X = Cl, I) or by the replacement of chloro ligands in PtII(DAPO)Cl2 by bromo, nitrato, oxalato, malonato, and 1,1-cyclobutanedicarboxylato ligands. The complexes thus obtained were characterized by elemental analysis, infrared,electronic, electron paramagnetic resonance spectroscopic techniques, and high-performance liquid chromatography. The toxicity of compounds in terms of LD50 strongly depends on the nature of X-ligands, and varies between 11 mg/kg (X = NO3) and 400 mg/kg (X2 = 1,1-cyclobutanedicarboxylate). Up to 66% of mice bearing leukemia L1210 survive after the administration of these complexes. This effect is comparable to the effect of cisplatin (50% survive). An increase in the life span of the rest of the animals ranges from 158 to 383%. Complex PtII(DAPO)Cl2 appears to be more efficient than cisplatin against adenocarcinoma 755. Cisplatin, cis-diamminedichloroplatinum(II); CBDCA, 1,1-cyclobutanedicarboxylic acid; DAPO, trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl; Mal, malonic acid; Ox, oxalic acid; IR, infrared; EPR, electron paramagnetic resonance; HPLC, high-performance liquid chromatography; Ca755, adenocarcinoma 755; LD50 and LD100, dose of compounds (mg/kg), causing a death of 50 or 100% or treated animals; ILS, increase in life span of mice.

[Nitroxyl radical Tempol as a modulator of toxic and antineoplastic effect of 6-mercaptopurine]. / Nitroksil'nyi radikal tempol kak moduliator toksicheskogo i protivoopukholevogo deistviia 6-merkaptopurina.

Both intact mice and those with transplantable adenocarcinoma 755 were used in the investigation. The nitroxyl radical Tempol was shown to cut down the toxicity of 6-mercaptopurine and potentiate its antitumor effect to a certain degree. The study results suggest on the basis of an investigation of cytochrome P450 and some other evidence that said effect of Tempol might be due, at least, in part to antioxidant activity.

Modulatory effect of tempol on toxicity and antitumor activity of 6-mercaptopurine and on P450 cytochrome level.

Low selectivity of contemporary antitumor drugs requires a search for its improvement. In this context, nitroxyl radicals are of interest as promising pharmacological agents. The introduction of nitroxyl radical into the structure of antitumor cytostatics was found to reduce considerably their general and specific toxicity. In this work, we demonstrate a detoxifying effect of tempol upon its combined injection with cytostatics at their absolute lethal dose in the intact mice as well as an improvement of sensitivity of tumor-bearing animals to 6-MP. Tempol is shown to normalize the level of oxidized form of P450 cytochrome in a liver, reduced as a result of the injection of 6-MP.

Radiosensitizer AK-2123 as modulating agent in the chemotherapy of experimental metastases.

Therapeutic effect of Cyclophosphamide (CPA) and radiosensitizer AK-2123 (AK) combination versus CPA alone in the same doses was investigated on transplanted LL carcinoma and B 16 melanoma. Antimetastatic efficacy of different doses of CPA and combined therapy was evaluated. Our data demonstrate that the effect of combined treatment by CPA at low uneffective doses (60 mg/kg, 40 mg/kg, 20 mg/kg at the 3rd and the 7th day after transplantation) and AK at low daily doses (1 mg/kg and 0.1 mg/kg for 3-9 days after transplantation) is equal or superior to the effect of CPA alone at the therapeutic dose (120 mg/kg).