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S H Friedman

Publications and source records attributed to S H Friedman.

9 recordsLinked to original sources
PubMed2001

Small molecule/nucleic acid affinity chromatography: application for the identification of telomerase inhibitors which target its key RNA/DNA heteroduplex.

The purpose of this work is to develop methods for identifying high-affinity nucleic acid binding species from soluble mixtures of compounds. We have developed and applied an affinity chromatography method for identifying small molecules with high affinity for the telomerase RNA/DNA duplex. An affinity resin was derivatized with an RNA/DNA duplex which represents the key structure that forms during telomerase's catalytic cycle. A soluble mixture of compounds was applied to this resin and the compounds which bound to the highest extent were also confirmed to be the best inhibitors of the enzyme. This correlation of affinity for the RNA/DNA duplex with telomerase inhibition both supports the duplex as the target of these compounds, and suggests that the affinity method may be applied for the identification of higher affinity inhibitors from soluble mixtures of compounds.

Catalysis↗
PubMed2001

Targeting telomerase via its key RNA/DNA heteroduplex.

Telomerase is a promising "universal" anticancer target. It has been demonstrated that inhibition of telomerase leads to mortalization and death of previously immortal cell lines. We are interested in targeting telomerase by binding to the RNA/DNA duplex that forms during its catalytic cycle. The RNA strand of this duplex is a component of telomerase and acts as a template to direct the synthesis of the single-stranded DNA telomere. We have hypothesized that molecules that bind to this duplex will inhibit the enzyme by either preventing strand dissociation or by sufficiently distorting the substrate, thereby causing a misalignment of key catalytic residues. To test this hypothesis we have examined the activity of telomerase in the presence of a range of intercalating molecules, known for their broad duplex binding properties. Of the nine compounds we examined, four show promising lead activity in the low micromolar range. A kinetic analysis of the telomeric products suggests that these compounds do not act by stabilizing G-quartets, thereby supporting the telomeric RNA/DNA heteroduplex as the site of action. We anticipate using these lead compounds as the basis for combinatorial variation to increase the affinity and specificity for the target telomerase.

DNA↗
PubMed1998

Optimizing the binding of fullerene inhibitors of the HIV-1 protease through predicted increases in hydrophobic desolvation.

We have developed and applied a computational strategy to increase the affinity of fullerene-based inhibitors of the HIV protease. The result is a approximately 50-fold increase in affinity from previously tested fullerene compounds. The strategy is based on the design of derivatives which may potentially increase hydrophobic desolvation upon complex formation, followed by the docking of the hypothetical derivatives into the HIV protease active site and assessment of the model complexes so formed. The model complexes are generated by the program DOCK and then analyzed for desolvated hydrophobic surface. The amount of hydrophobic surface desolvated was compared with a previously tested compound, and if this amount was significantly greater, it was selected as a target. Using this approach, two targets were identified and synthesized, using two different synthetic approaches: a diphenyl C60 alcohol (5) based on a cyclopropyl derivative of Bingel (Chem.Ber. 1993, 126, 1957-1959) and a diisopropyl cyclohexyl C60 alcohol (4a) as synthesized by Ganapathi et al. (J. Org.Chem. 1995, 60, 2954-2955). Both showed tighter binding than the originally tested compound (diphenethylaminosuccinate methano-C60, Ki = 5 microM) with Ki values of 103 and 150 nM, respectively. In addition to demonstrating the utility of this approach, it shows that simple modification of fullerenes can result in high-affinity ligands of the HIV protease, for which they are highly complementary in structure and chemical nature.

Binding Sites↗
PubMed1997

A prospective study of the effects of high-dose chemotherapy and bone marrow transplantation on sexual function in the first year after transplant.

Patients undergoing high-dose chemotherapy and bone marrow transplantation (BMT) may experience a variety of abnormalities of psychological and physical function including sexual dysfunction. However, no study has prospectively evaluated whether there is an association between sexual dysfunction and BMT. In a previous study in which we analyzed the sexual function of 30 patients immediately before transplant, we found that nearly half of all patients had sexual dysfunction using the Derogatis Interview for Sexual Functioning for males and females. The findings of the pilot study led us to hypothesize that the incidence of sexual dysfunction would not be significantly altered by BMT; we performed a prospective study designed to test this hypothesis. In this study a further 20 patients about to undergo BMT were surveyed, making a total of 50. Thirty-one of 38 survivors were reanalyzed 3-6 months after transplant. The major finding of the study is that the incidence of sexual dysfunction is unchanged 3 months after transplant (48 vs 36%, P = NS). The mean total score on the DISF was decreased by 7.5 points but this was also not significant. A preliminary analysis of 16 patients surveyed at 12 months post-BMT suggests little change in sexual function between 3 and 12 months post-BMT. We conclude that in the first 12 months after high-dose chemotherapy and BMT the pretreatment difficulties remain.

Adolescent↗
PubMed1989

The chloride-activated peroxidation of catechol as a mechanistic probe of chloroperoxidase reactions. Competitive activation as evidence for a catalytic chloride binding site on compound I.

Chloride ion (Cl-) effects on chloroperoxidase (CPO)-catalyzed peroxidation of catechol were used to probe the involvement of Cl- in CPO reactions. High concentrations of Cl- inhibit catechol peroxidation by competing with hydrogen peroxide (KI = 370 mM). However, at lower concentrations, Cl- is a linear competitive activator versus catechol (KDC = 35 mM). Addition of good halogenation substrates to the peroxidatic reaction mixture converts Cl- from a competitive activator to a competitive inhibitor. The KI (10 mM) for this halogenation substrate promoted Cl- inhibition is equivalent to the KM (11 mM) for Cl- in CPO-catalyzed halogenation reactions. During this inhibition, the halogenation substrate is consumed and, at the point where its consumption is complete, Cl- again becomes an activator. Also, at 2.0 mM hydrogen peroxide, CPOs chlorination reaction and its Cl- -activated peroxidatic reaction have similar apparent kcat values. All data are consistent with a mechanism in which Cl- competes with catechol for binding to CPO Compound I. Catechol binding initiates the Cl- -independent path, in which Compound I acts as the oxidizing agent for catechol. When Cl- binds to Compound I, it reacts to yield the enzymatic chlorinating intermediate which is responsible for either the oxidation of catechol in the Cl- -dependent path or the chlorination of substrates in the halogenation pathway. Cl- activation of the peroxidatic reaction is due to a shift from the Cl- -independent pathway to the Cl- -dependent process. The mechanism is unique in that exclusion of the substrate from its primary binding site leads to an increase in the catalytic efficiency of the reaction. This catechol-Cl- system also offers further potential for probing the specificity and chemistry of the key enzymatic intermediates in haloperoxidase-catalyzed reactions.

Catechols↗
PubMed1988

Cardiopulmonary exercise testing. The clinical value of gas exchange data.

Cardiopulmonary exercise testing is a noninvasive tool whose clinical value is not yet widely recognized. The technique involves breath-by-breath measurement of respiratory gas exchange during a symptom-limited exercise test, with determination of maximal oxygen uptake and anaerobic threshold. These measurements serve as objective, reproducible indices of exercise capacity that can be applied to the management of various clinical problems. In addition, by permitting simultaneous assessment of circulatory and ventilatory reserves, the test can be especially helpful in the differential diagnosis of exertional dyspnea and fatigue. This paper reviews the physiology of gas exchange, the limitations of standard exercise tests, and the methodology and clinical applications of cardiopulmonary exercise testing.

Carbon Dioxide↗
PubMed1986

Catalysis of intermolecular oxygen atom transfer by nitrite dehydrogenase of Nitrobacter agilis.

Nitrobacter agilis, which contains a very active nitrite dehydrogenase, was studied in vivo under anaerobic conditions by the 15N NMR technique. When incubated with equimolar 15NO3- and unlabeled nitrite (or 15NO2- and unlabeled nitrate) the bacterium catalyzed an isotope exchange reaction at rates about 10% those observed in the nitrite oxidase assay. When incubated with 18O-labeled 15NO2- and 18O-labeled 15NO3-, the 18O was observed to exchange at similar rates from both species into water. Finally, when incubated with equimolar [18O]nitrate and 15NO2-, intermolecular 18O transfer was observed to result in formation of double labeled nitrate and nitrite at similar rates. 18O was transferred from nitrate to a 15N species or to water at approximately equal rates under the conditions of the experiments. It is argued that the enzyme responsible for these exchange reactions is nitrite dehydrogenase and not nitrate reductase. This work and the related experiments of DiSpirito and Hooper (DiSpirito, A.A., and Hooper, A.B. (1986) J. Biol. Chem. 261, 10534-10537) represent the first demonstrations of intermolecular oxygen atom transfer among oxotransferases. Mechanistic implications are discussed.

Kinetics↗