Evgeny Golovinsky

Natural and synthetic inhibitors of UDP-glucuronosyltransferase.

Glucuronidation is a major detoxification pathway in vertebrates. The reaction is catalyzed by a family of UDP-glucuronosyltransferases (UGTs) and involves conjugation of many endobiotic and xenobiotic substances with glucuronic acid, forming inactive water-soluble glucuronides. UGT prevents the accumulation of potentially toxic compounds and/or their subsequent bioactivation to more toxic intermediates, although biologically active glucuronides are also known. Impairment of UGTs may have important toxicological consequences. Substances found to inhibit or down-regulate UGT activity include endogenous compounds, a wide range of clinically used drugs, environmental contaminants, and natural toxic substances present in the diet. The development of selective, active-site-directed UGT inhibitors greatly enables the study of various UGT isoenzymes. A promising approach offers the design of transition-state analogs of the glucuronidation reaction.

Some pyrazoles as inhibitors of purine biosynthesis de novo

Abstract The inhibitory effect of some pyrazole derivatives on purine biosynthesis was studied in a pigeon liver cell-free system. It was demonstrated that 3-amino-4-carbethoxypyrazole, 3-amino-4-carboxypyrazole and 3-(3′3′-bis-β-chloroethyltriazenyl-1′)-4-carbethoxypyrazole were inhibitors, while N - β -hydroxyethyl-3-amino-4-carbethoxypyrazole was almost inactive. A possible mechanism of action is discussed.

Enhanced cell permeability increases the sensitivity of a yeast test for mutagens

ts1 is a mutation which causes a general increase in permeability of Sacharomyces cerevisiae cells in an unspecific manner. The introduction of the ts1 mutation under homozygous conditions into the D7 diploid strain enhanced the sensitivity of the test system described by Zimmermann et al. (1975). The newly constructed strain D7ts1 responded with a four to six times higher frequency compared to the D7 strain for all genetic end-points induced with chemical mutagens (ethyl methanesulfonate, methyl methanesulfonate, hydroxyurea, benzpyrene). The increased sensitivity of D7ts1 is specific only for mutagens active in yeast, since treatment of D7ts1 cells with 5-bromouracil or 5-bromouridine, known to be non-mutagenic in yeast, did not result in the induction of any of the measured genetic alterations. Five out of 14 water samples taken from the environment induced recombinogenic events in D7ts1, whereas all 14 water samples were without effect in the D7 test system. We concluded that D7ts1 cells show a higher sensitivity in the detection of mutagenic or carcinogenic action because of their generally enhanced permeability due to the ts1 mutation.

Pharmacobiochemistry of arylalkyltriazenes and their application in cancer chemotherapy

As a class of organic compounds tr iazenes were characterized and described a very long time ago (Griess, 1862), however, data about their biological action did not appear until considerably later. About 28 years ago Stock et al. (Clarke et al., 1955; Burchenal et al., 1956) were the first to establish the antitumor activity of certain aryldimethyltriazenes, but their therapeutic use did not become possible until the synthesis of DTIC [5(4)-(3,3-dimethyl-l-triazeno)imidazole-4(5)-carboxamide]. This compound has been the most extensively studied agent in the treatment of malignant melanoma and the subject of detailed research in the pharmacobiochemistry of this class of compounds. In the present review, data on the synthesis and mechanism of action (molecular and cellular) of arvlalkyl tr iazenes in the last 20 years have been systematized, and a summary of the activity and therapeutic use of DTIC is given.

Synthesis of thiazole, imidazole and oxazole containing amino acids for peptide backbone modification.

Novel 5‐ring heterocyclic building blocks are synthesized. These can be incorporated into analogs of peptide antibiotics such as microcin B17, which is a potent DNA‐gyrase inhibitor that exhibits eight thiazole and oxazole moieties. In particular, the syntheses of imidazole and bisoxazole amino acids as novel peptidomimetics are reported, this includes a new procedure for the oxidative conversion of the intermediates oxazoline, imidazoline as well as oxazole–oxazoline into the corresponding heteroaromatic compounds. A mixture of 1,8‐diazabicyclo‐[5.4.0.]‐undec‐7‐ene/carbon tetrachloride/acetonitrile and pyridine proved to be a very effective and mild agent. Copyright

Copper(II) complexes of hydrazides

Abstract The Cu(II) complexes of three hydrazides of aspartic and glutamic acids have been obtained and studied using electronic IR and EPR spectra, DTA, magnetic susceptibility measurements, extraction, ion exchange and elemental analysis data. It was found that depending on the reaction conditions two types of complexes are obtained, with M:L ratios 1:1 and 1:2, copper(II) being six-coordinated in both. The 1:1 complexes include one hydrazide molecule and three inorganic ligands. When CuCl 2 is used as the initial Cu(II) salt, one Cl − and two OH − are coordinated at pH 6.5–7.0 (resp. two H 2 O molecules at pH 3.0–3.5), while using CuSO 4 only OH − , resp. H 2 O are coordinated together with the hydrazide. In the 1:2 complexes two hydrazide molecules are coordinated, no other ligands being present in the coordination sphere. A possible structure of the complexes, consistent with all the experimental data is proposed and discussed.

Mutagenic activity of some newly synthesized cytostatic 1-(2-chloroethyl)-4-arylacyl-1-nitrososemicarbazides in theSalmonella/mammalian microsome assay

SummaryFive experimental anti-leukemic agents, 1-(2-chloroethyl)-4-arylacyl-1-nitrososemicarbazides, were synthesized and tested for genotoxicity in theSalmonella/ mammalian microsome assay. No strong mutagenic activity could be detected when tested with theS. typhimurium TA98. A clear dose-dependent base-pair-substitution mutagenic activity was observed with each compound when the tester strain TA100 was used with or without metabolic activation. The genotoxicity of the unsubstituted substance was similar to that of the known mutagenic cytostatic drugs, lomustin and carmustin, and was stronger than the mutagenicity of each substituted derivative.

The action of some orotic acid analogues on the in vitro incorporation of 14C-orotate into pyrimidine nucleotides

Abstract The effect of some orotic acid analogues on the incorporation of 14 C-orotate into uridine and cytidine nucleotides by a soluble rat liver enzyme system was investigated. The compounds studied were found to inhibit the labelling of uridine nucleotides in the following order: 5-azaorotic acid, orotic acid hydrazide, 2-thioorotic acid, uracil-6-aceticacid, orotaldehyde hydrazone, 4, 6-dihydroxypicolinicacid(“3-deazaoroticacid”). With the orotic acid hydrazide and the orotaldehyde hydrazone the labelling of cytidine nucleolides runs parallel to that of uridine nucleotides. With the four other compounds the inhibition of 14 C-orotate incorporation into cytidine nucleotides is much stronger as compared to uridine nucleotides. This effect is more pronounced in the case of 2-thioorotic acid and uraeil-6-acetic acid.

Microbial Diversity in Heavy-Metal Polluted Waters

ABSTRACT Indigenious water microflora as well as the presence of metal- and xenobiotic biotransforming bacteria were investigated in waters near the KCM Pb-Zn smelter, South Bulgaria. Content of As, Hg, Cd, Mn, Pb, Cu and Zn exceeded in times the maximum permission standart. Absence of some microbial groups demonstrated a change in the microbial community structure in the region. Ecotoxicology test ISO/DIS 10712.2 displayed toxic environmental effect of the polluted waters, especially one of them which demonstrated 72% ofn ecotoxicity. More than 20 ecologically relevant new bacteria were cultured. Three of them demonstrated tolerance to Cd, Cu and Mn and five- a tolerance to 2,4-dichlorphenoxyacetic acid. Our result revealed that the heavy metal pollutions reduced the microbial diversity in the studied waters, are ecotoxic as well as that some of newly isolated bacteria possess a capacity for a clean-up biotechnologies in the region.

Unusual reactivity of cytotoxic cis-dihydrazide Pt(II) complexes in aqueous solution

Complexes of the general structure cis-[PtX(2)(hydrazide)(2)] and cis-[PtX(2)NH(3)(hydrazide)], where X=Cl(-), Br(-) and I(-), and hydrazide=cyclohexylcarboxylic acid hydrazide (chcah), cyclopentylcarboxylic acid hydrazide (cpcah), 3-aminocyclohexanspiro-5-hydantoin (achsh) and 3-aminocyclopentanspiro-5-hydantoin (acpsh), were investigated with respect to aqueous stability, DNA platination rates and cytotoxic activity on a panel of seven human cancer cell lines as well as a cisplatin-resistant cell line. Stabilities in aqueous solution, determined by RP-HPLC and UV-Vis methods, were highly dependent on the type of halide ligand, with stability decreasing in the order I(-)>Cl(-)>Br(-). Added chloride (100 mM) only stabilized the dichloro-Pt(II) complexes containing the hydrazide as part of a hydantoin ring (i.e., achsh). Platination of calf thymus DNA determined by AAS was most rapid with dichloro-Pt(II) complexes containing achsh ligand. The mixed-amine dichloro-Pt(II) complexes with either chcah or cpcah ligands also platinated DNA >80%, but at a slower rate, while dihydrazide dichloro-Pt(II) complexes with either chcah or cpcah ligands resulted in <25% DNA platination at 24 h. cis-[PtX(2)(hydrazide)(2)], where hydrazide=chcah or cpcah, were the most potent compounds (chcah>cpcah), but activity was independent of the halide ligand (I(-)=Cl(-)=Br(-)). These complexes showed no cross-resistance with cisplatin, but they also showed little differentiation in potency over the seven cell lines. Complexes with the hydantoin ligands achsh and acpsh were inactive in all cell lines. Thus, neither stability in aqueous media nor covalent binding to DNA are correlated with biological activity, suggesting that cis-dihydrazide Pt(II) complexes act by a unique mechanism of action.