Search PubMed⌕ Search

Biomedical subjects

V M Kolb

Publications and source records attributed to V M Kolb.

At least 19 recordsLinked to original sources
PubMed1998

Biomimicry as a basis for drug discovery.

Selected works are discussed which clearly demonstrate that mimicking various aspects of the process by which natural products evolved is becoming a powerful tool in contemporary drug discovery. Natural products are an established and rich source of drugs. The term "natural product" is often used synonymously with "secondary metabolite." Knowledge of genetics and molecular evolution helps us understand how biosynthesis of many classes of secondary metabolites evolved. One proposed hypothesis is termed "inventive evolution." It invokes duplication of genes, and mutation of the gene copies, among other genetic events. The modified duplicate genes, per se or in conjunction with other genetic events, may give rise to new enzymes, which, in turn, may generate new products, some of which may be selected for. Steps of the inventive evolution can be mimicked in several ways for purpose of drug discovery. For example, libraries of chemical compounds of any imaginable structure may be produced by combinatorial synthesis. Out of these libraries new active compounds can be selected. In another example, genetic system can be manipulated to produce modified natural products ("unnatural natural products"), from which new drugs can be selected. In some instances, similar natural products turn up in species that are not direct descendants of each other. This is presumably due to a horizontal gene transfer. The mechanism of this inter-species gene transfer can be mimicked in therapeutic gene delivery. Mimicking specifics or principles of chemical evolution including experimental and test-tube evolution also provides leads for new drug discovery.

Algorithms↗
PubMed1994

Alternative bases in the RNA world: the prebiotic synthesis of urazole and its ribosides.

Urazole is a five-membered heterocyclic compound which is isosteric with uracil's hydrogen-bonding segment. Urazole reacts spontaneoulsy with ribose (and other aldoses) to give a mixture of four ribosides: alpha and beta pyranosides and furanosides. This reaction occurs in aqueous solution at mild temperatures. Thermodynamic and kinetic parameters for the reaction of urazole with ribose were determined. In contrast, uracil is completely unreactive with ribose under these conditions. Urazole's unusual reactivity is ascribed to the hydrazine portion of the molecule. Urazole can be synthesized from biuret and hydrazine under prebiotic conditions. The prebiotic synthesis of guanazole, which is isosteric in part to diaminopyrimidine and cytosine, is accomplished from dicyandiamide and hydrazine. Kinetic parameters for both prebiotic reactions were measured. Urazole and guanazole are transparent in the UV, which would be a favorable property in the absence of an ozone layer on the early Earth. Urazole makes hydrogen bonds with adenine in DMSO similar to those of uracil, as established by H NMR. All of these properties make urazole an attractive potential precursor to uracil and guanazole a potential precursor to cytosine in the RNA or pre-RNA world.

Cytosine↗
PubMed1993

Effects of the opioid antagonist naltrexone-estrone azine on the luteinizing hormone-releasing hormone induced release of luteinizing hormone from the pituitary glands of ovariectomized rats.

The effects were studied of in vivo administration of the new opioid antagonist-estrogen hybrid, naltrexone-estrone azine (EH-NX), on subsequent luteinizing hormone-releasing hormone (LHRH)-stimulated luteinizing hormone (LH) release by the pituitary gland in vitro. It is well known that administration of estrogen exerts negative and positive effects on the pituitary LH response to LHRH, respectively after short-term and long-term treatment. Rats were injected subcutaneously with either 17 beta-estradiol-3-benzoate (EB), EH-NX or oil on days 18 and 19 (long-term treatment), and on day 21 (short-term treatment) following ovariectomy. Twenty minutes later the animals were killed and the pituitary glands were incubated in the presence of LHRH (1000 ng/ml) for 4 h. Whereas short-term treatment with EB on day 21 did not affect LH release in vitro, EH-NX significantly decreased the pituitary LH response to LHRH in oil pretreated rats. This inhibitory effect was partially blocked by the opioid antagonist naltrexone. After long-term EB or EH-NX, followed by short-term oil treatment, the pituitary LH response to LHRH was increased considerably, compared to the long-term oil controls. These observations demonstrate that the opioid antagonist estrogen hybrid EH-NX has estrogenic activity at the level of the pituitary gland. This hybridized drug is more effective in time than EB and an equimolar amount of EH (estrone hydrazone) to induce the negative estrogenic effect.

Animals↗
PubMed1992

Estrogenic effects of the new opioid antagonist naltrexone-estrone azine on pituitary luteinizing hormone secretion in ovariectomized rats.

The effect of the new opioid antagonist naltrexone-estrone azine (EH-NX) on pituitary luteinizing hormone (LH) secretion in the ovariectomized rat was studied. EH-NX is a hybrid between the steroid component estrone and the opioid antagonist naltrexone (NX). It is a potent and long-acting opioid antagonist in vitro and in vivo, but its effect upon in vivo LH secretion has not been tested before. The aims of the study were to investigate whether, unlike naltrexone, EH-NX can stimulate LH secretion without the need of additional estrogen pretreatment and whether EH-NX has peripheral estrogenic effects upon the uterine weight, when administered chronically to long-term ovariectomized rats. Female rats were injected subcutaneously with EH-NX 21 days after ovariectomy. The effects of EH-NX injections on LH secretion were compared to the effects of NX and estrone hydrazone (EH) alone, or in combination, with or without estradiol-benzoate (EB) pretreatment. Inhibition of LH secretion and uterine proliferation were observed in rats treated chronically with EH-NX in dosages of 0.250 mg/kg bw and higher. These effects were similar to those caused by EH and EB. In short-term OVX rats EH-NX appeared to act faster than EH. In contrast to NX, no stimulatory effect on LH secretion was seen with EH-NX in EB primed OVX rats. These results surprisingly demonstrate that EH-NX behaves like an estrogen and not like an opioid antagonist. The unexpected pharmacological profile of this new drug may open up doors for several medical applications.

Animals↗
PubMed1988

Doisynolic-type acids--uterotropically potent estrogens which compete poorly with estradiol for cytosolic estradiol receptors.

Doisynolic acids, a class of seco-steroid acids some of which exhibit greater uterotropic estrogenicity than estradiol-17 beta, are D-ring cleavage products of steroidal estrogens formed by fusion with KOH above 200 degrees C. We have found that electron-transfer reactions between estrone or estradiol and CCl4 or CBrCl3 in KOH-t-BuOH at 25 degrees C rapidly provide 16,16-dichloro- or -dibromodoisynolic acid, respectively, the former approaching estradiol in uterotropic potency. Simple esters from these highly hindered tertiary carboxylic acids, easily prepared via phase-transfer-catalyzed alkylations, also rival estradiol in uterotropic activity. Unlike natural steroidal estrogens or their commonly used artificial equivalents (DES, hexoestrol, ethynylestradiol, etc.) whose uterotropic activity is accompanied by substantial binding affinity for cytosolic estradiol receptors, these highly uterotropic doisynolic-type acids and esters exhibit binding affinities for this receptor of only about 1% that of estradiol-17 beta as determined by the usual competitive binding-inhibition studies with [3H]estradiol. Other highly uterotropic carboxylic acids may exhibit similar characteristics. These unusual results leave open the possibilities that uterotropic seco-steroid and related carboxylic acids undergo some unknown metabolic activation, are exceptionally persistent estrogens, bind to a cytosolic receptor site other than the conventional (type I) estradiol site, or bind directly to type I or type II nuclear receptor sites. At dosages of 1000 times those required for a uterotropic effect, the doisynolic-type acids (24 doses over an 8-week period) were neither toxic nor carcinogenic.

Animals↗
PubMed1987

Electron-transfer and charge-transfer clastic binding hypotheses for drug-receptor interactions.

The origins and development of clastic binding hypotheses for interaction of morphines with the opiate receptor and various hallucinogens with their putative receptors are reviewed. Possible alternative explanations of the facts which led to the clastic binding hypotheses are offered. Possible integration of the clastic binding processes into other, better-recognized processes at the receptors is considered.

Electron Transport↗
PubMed1987

A naloxone-steroid hybrid azine with selective and long-acting opioid antagonism at delta receptors in vitro.

The interaction of naloxone estrone azine (N-EH) with various opioid receptor types was studied in vitro. Its potency as an antagonist of opioid effects was compared to that of naloxone on the electrically evoked contractions of mouse vas deferens (Mvd) and guinea pig ileum myenteric plexus longitudinal muscle (Gpi) preparations. N-EH was found to be 9-fold more potent than naloxone in antagonizing the effects of D-Ala2-Leu5-enkephalin in the Mvd and 22-fold less potent in antagonizing normorphine in the Gpi. In the Mvd, the recovery half-time for N-EH was longer than 1000 min. Neither compound showed agonism. The two compounds were also compared for their capacity to displace the binding of 3H-D-Ala2-Leu5-enkephalin, 3H-dihydromorphine, and 3H-ethylketocyclazocine to rat brain membranes under conditions where delta, mu, and kappa sites were labeled. The relative affinities were 0.70, 0.16, and 0.14 for N-EH and 0.05, 0.87, and 0.08 for naloxone, respectively. Thus, compared to naloxone, which is mu selective, N-EH is a delta-selective antagonist.

Animals↗
PubMed1986

A novel comprehensive opiate-receptor model.

A new, comprehensive opiate-receptor model based on calculations of possible events at the molecular level is proposed. Agonist versus antagonist action, ultra long-lasting activity and N-dealkylation accompanying receptor binding are included.

Models, Molecular↗
PubMed1986

Stereochemistry of novel delta selective opiate antagonists.

We have discovered novel delta selective opiate antagonists of a non-peptide nature. Our lead compound at the present time is the mixed azine between estrone and naloxone, the compound named EH-NAL. In this paper we describe the stereochemistry of EH-NAL and an EH-NAL analog, the mixed azine between pregnenolone and naltrexone, the compound named PH-NX. The stereochemical assignments are based on the high-resolution 13C-NMR studies and on the X-ray structural determinations.

Estrone↗
PubMed1984

Angular dependence of the interaction energy between the N lone pair of amines and a proton: relevance to drug-receptor systems.

Ab initio molecular orbital calculations with a 4-31G basis set have been performed to study the angular dependence of the interaction energy between a lone electron pair of nitrogen and a proton. In this study ammonia and trimethylamine were used as models of biologically active amines. A proton was used as a model of an electrophilic site at the receptor. Results obtained confirm previous indications that the energy required to bend the proton from the lone pair direction decreases markedly as the two species are further separated from one another. Implications regarding the interactions of drugs and hormones at specific receptors are discussed.

Amines↗
PubMed1984

New insights in the clastic binding hypothesis for opiate-receptor interactions I: Electron-transfer mechanism.

A clastic binding hypothesis for opiate-receptor interactions, in which the key step in eliciting the opiate response is an electron transfer from the opiate nitrogen to the receptor, is analyzed from a chemical point of view and is found to be chemically feasible. An extended form of this hypothesis is proposed in order to accommodate recent observations about the N-demethylation of morphines in the brain. An in vitro model system for studying the electron-transfer reactions of morphines is proposed, and the initial experiments in this system are reported.

Carbon Tetrachloride↗
PubMed1984

New insights in the clastic binding hypothesis for opiate-receptor interactions II: Proton-transfer mechanism.

Ab initio (4-31G) molecular orbital calculations were performed on model systems to investigate the proton-transfer version of the clastic binding hypothesis for opiate-receptor interactions. Ammonia was chosen as the model for the nitrogen-containing portion of the opiate molecule, while ammonia and water were chosen as models for the proton acceptor at the receptor. The equilibrium position of a proton situated between the two molecules is found to be determined primarily by the orientation of the proton-donor molecule with some influence also from the other molecule. Misalignments of the lone pairs can significantly alter equilibrium populations when the proton affinities of the two molecules are similar.

Chemical Phenomena↗
PubMed1983

Study of the syn and anti isomerism of the long-lasting opiate antagonist naloxazone and related compounds.

A 13C-NMR study of the long-acting opiate antagonists naloxazone (I) and naltrexazone (II) and the long-acting opiate agonist oxymorphazone (III) revealed that these compounds are formed as mixtures of their anti and syn isomers. The less crowded anti isomer was found to be the major product in all cases (ca. 80%). N,N-Dimethyl derivatives of naloxazone (IV), naltrexazone (V), and oxymorphazone (VI), which are sterically more crowded than the corresponding unsubstituted hydrazones I-III, were formed as almost exclusively anti isomers. Pure anti isomer of II was obtained as a 1:1 complex with ethanol. No syn-anti equilibration was observed during the 13C-NMR experiment in any of the cases studied. The relevance of our finding about the syn-anti isomerism of the opiate hydrazones to the understanding of their interactions with the opiate receptor is discussed.

Isomerism↗
PubMed1983

Fluorescent probes for opioid receptors.

Naloxone, naltrexone and oxymorphone were labeled in position 6 with fluorescein by coupling their hydrazone analogs with fluorescein isothiocyanate. Naloxone was also coupled in a similar way with rhodamine-B. The compounds thus obtained were: "6-FN", [1-(N)-fluoresceinyl naloxone thiosemicarbazone]; "6-FNX", [1-(N)-fluoresceinyl naltrexone thiosemicarbazone]; "6-FO", [1-(N)-fluoresceinyl oxymorphone thiosemicarbazone]; "6-RN", [1-(N)-tetramethylrhodaminyl-B naloxone thiosemicarbazone]. These compounds were tested for opioid receptor binding in rat brain synaptosomal plasma membranes and for biological activity on the guinea pig ileum. All compounds retained activity, showing some changes in affinity and binding profile compared to their parent compounds. "6-FN", for example, showed decreased (approximately 10x) affinity compared to naloxone in opiate displacement analysis but retained potency in displacement of opioid peptides. Antagonist activity of "6-FN" in the guinea pig ileum bioassay was about ten-fold less than that of naloxone.

Animals↗
PubMed1982

Operation of long-range substituent effects in rigid opiates: protonated and unprotonated oxymorphone.

The structure of protonated oxymorphone (amine salt) was determined by an X-ray crystallographic study. Significant differences were found with the previously determined structure of unprotonated oxymorphone (free base). Upon protonation on nitrogen, an elongation of the N-C bound occurred, accompanied by subtle changes in bond lengths and angles distant from the site of protonation. These changes in geometry are interpreted as a reflection of long-range substituent effects.

Chemistry, Pharmaceutical↗