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Biomedical subjects

A Pavlovsky

Publications and source records attributed to A Pavlovsky.

At least 19 recordsLinked to original sources
PubMed2001

4-Hydroxy-5,6-dihydropyrones as inhibitors of HIV protease: the effect of heterocyclic substituents at C-6 on antiviral potency and pharmacokinetic parameters.

Due largely to the emergence of multi-drug-resistant HIV strains, the development of new HIV protease inhibitors remains a high priority for the pharmaceutical industry. Toward this end, we previously identified a 4-hydroxy-5,6-dihydropyrone lead compound (CI-1029, 1) which possesses excellent activity against the protease enzyme, good antiviral efficacy in cellular assays, and promising bioavailability in several animal species. The search for a suitable back-up candidate centered on the replacement of the aniline moiety at C-6 with an appropriately substituted heterocyle. In general, this series of heterocyclic inhibitors displayed good activity (in both enzymatic and cellular tests) and low cellular toxicity; furthermore, several analogues exhibited improved pharmacokinetic parameters in animal models. The compound with the best combination of high potency, low toxicity, and favorable bioavailabilty was (S)-3-(2-tert-butyl-4-hydroxymethyl-5-methyl-phenylsulfanyl)-4-hydroxy-6-isopropyl-6-(2-thiophen-3-yl-ethyl)-5,6-dihydro-pyran-2-one (13-(S)). This thiophene derivative also exhibited excellent antiviral efficacy against mutant HIV protease and resistant HIV strains. For these reasons, compound 13-(S) was chosen for further preclinical evaluation.

Animals↗
PubMed2001

Dielectrical model of cellular structures in radio frequency and microwave spectrum. Electrically interacting versus noninteracting cells.

A model of dielectrical properties of cellular structures of a tissue has been proposed. Cellular structures were presented as a composition of membrane covered spheres and cylinders that do not interact with each other. No restrictions were applied to the thickness of cellular membranes. The model was further generalized into a case of electrically interacting cells. The difference in dielectrical properties calculated with the model of electrically noninteracting versus interacting cells is inversely dependent on frequency. At biological values of cellular volume fraction near 0.7 (packed configuration) the difference is about 10%-15% in resistance and in epsilon' for frequencies near 0.1 MHz. Experimental data for myocardial tissue and theoretical data, for both interacting and noninteracting models, reasonably agree at frequencies of 1-100 MHz.

Animals↗
PubMed2000

Microwave spectroscopy of myocardial ischemia and infarction. 2. Biophysical reconstruction.

The proposed dielectrical relaxation model of the myocardium in the microwave spectrum has been verified both on test solutions and on normal canine myocardium. Furthermore, the model was utilized to reconstruct the changes in tissue properties (including myocardial bulk resistance and water content) following myocardial acute ischemia and chronic infarction. It was shown that the reconstructed myocardial resistance and water content correlate dynamically with the process of the development of acute myocardial ischemic injury. In chronic cases the reconstructed resistance and water content of infarcted myocardium are significantly different from that of normal myocardium: the resistance is lower and water content is higher than in normal myocardium.

Acute Disease↗
PubMed1999

Nonpeptidic HIV protease inhibitors possessing excellent antiviral activities and therapeutic indices. PD 178390: a lead HIV protease inhibitor.

With the insight generated by the availability of X-ray crystal structures of various 5,6-dihydropyran-2-ones bound to HIV PR, inhibitors possessing various alkyl groups at the 6-position of 5,6-dihydropyran-2-one ring were synthesized. The inhibitors possessing a 6-alkyl group exhibited superior antiviral activities when compared to 6-phenyl analogues. Antiviral efficacies were further improved upon introduction of a polar group (hydroxyl or amino) on the 4-position of the phenethyl moiety as well as the polar group (hydroxymethyl) on the 3-(tert-butyl-5-methyl-phenylthio) moiety. The polar substitution is also advantageous for decreasing toxicity, providing inhibitors with higher therapeutic indices. The best inhibitor among this series, (S)-6-[2-(4-aminophenyl)-ethyl]-(3-(2-tert-butyl-5-methyl-phenylsulfa nyl)-4-hydroxy-6-isopropyl-5,6-dihydro-pyran-2-one (34S), exhibited an EC50 of 200 nM with a therapeutic index of > 1000. More importantly, these non-peptidic inhibitors, 16S and 34S, appear to offer little cross-resistance to the currently marketed peptidomimetic PR inhibitors. The selected inhibitors tested in vitro against mutant HIV PR showed a very small increase in binding affinities relative to wild-type HIV PR. Cmax and absolute bioavailability of 34S were higher and half-life and time above EC95 were longer compared to 16S. Thus 34S, also known as PD 178390, which displays good antiviral efficacy, promising pharmacokinetic characteristics and favorable activity against mutant enzymes and CYP3A4, has been chosen for further preclinical evaluation.

Cell Line↗
PubMed1997

4-hydroxy-5,6-dihydropyrones. 2. Potent non-peptide inhibitors of HIV protease.

The 4-hydroxy-5,6-dihydropyrone template was utilized as a flexible scaffolding from which to build potent active site inhibitors of HIV protease. Dihydropyrone 1c (5,6-dihydro-4-hydroxy-6-phenyl-3-[(2-phenylethyl)thio]-2H-pyran-2-one) was modeled in the active site of HIV protease utilizing a similar binding mode found for the previously reported 4-hydroxybenzopyran-2-ones. Our model led us to pursue the synthesis of 6,6-disubstituted dihydropyrones with the aim of filling S1 and S2 and thereby increasing the potency of the parent dihydropyrone 1c which did not fill S2. Toward this end we attached various hydrophobic and hydrophilic side chains at the 6-position of the dihydropyrone to mimic the natural and unnatural amino acids known to be effective substrates at P2 and P2'. Parent dihydropyrone 1c (IC50 = 2100 nM) was elaborated into compounds with greater than a 100-fold increase in potency [18c, IC50 = 5 nM, 5-(3,6-dihydro-4-hydroxy-6-oxo-2-phenyl-5-[2-phenylethyl)thio] -2H-pyran-2-yl)pentanoic acid and 12c, IC50 = 51 nM, 5,6-dihydro-4-hydroxy-6-phenyl-6-(2-phenylethyl)-3- [(2-phenyl-ethyl)thio]-2H-pyran-2-one]. Optimization of the 3-position fragment to fill S1' and S2' afforded potent HIV protease inhibitor 49 [IC50 = 10 nM, 3-[(2-tert-butyl-5-methylphenyl)sulfanyl]-5,6-dihydro-4 -hydroxy-6-phenyl-6-(2-phenylethyl)-2H-pyran-2-one]. The resulting low molecular weight compounds (< 475) have one or no chiral centers and are readily synthesized.

Anti-HIV Agents↗
PubMed1996

X-ray structure of a hydroxamate inhibitor complex of stromelysin catalytic domain and its comparison with members of the zinc metalloproteinase superfamily.

BACKGROUND: Stromelysin belongs to a family of zinc-dependent endopeptidases referred to as matrix metalloproteinases (MMPs, matrixins) because of their capacity for selective degradation of various components of the extracellular matrix. Matrixins play key roles in diseases as diverse as arthritis and cancer and hence are important targets for therapeutic intervention. RESULTS: The crystal structure of the stromelysin catalytic domain (SCD) with bound hydroxamate inhibitor, solved by multiple isomorphous replacement, shows deep S1' specificity pocket which explains differences in inhibitors binding between the collagenases and stromelysin. The binding of calcium ions by loops at the two ends of a beta-strand which marks the boundary of the active site provides a structural rationale for the importance of these cations for stability and catalytic activity. Major differences between the matrixins are clustered in two regions forming the entrance to the active site and hence may be determinants of substrate selectivity. CONCLUSIONS: Structural comparisons of SCD with representative members of the metalloproteinase superfamily clearly highlight the conservation of key secondary structural elements, in spite of major variations in the sequences including insertions and deletions of functional domains. However, the three-dimensional structure of SCD, which is generally closely related to the collagenases, shows significant differences not only in the peripheral regions but also in the specificity pockets; these latter differences should facilitate the rational design of specific inhibitors.

Amino Acid Sequence↗
PubMed1996

Discovery and optimization of nonpeptide HIV-1 protease inhibitors.

Several small, achiral nonpeptide inhibitors of HIV-1 protease with low micromolar activity were identified by mass screening of the Parke-Davis compound library. Two of the compounds, structurally similar, were both found to be competitive and reversible inhibitors [compound 1, 4-hydroxy-3-(3-phenoxypropyl)-1-benzopyran-2-one: Ki = 1.0 microM; compound 2, 4-hydroxy-6-phenyl-3-(phenylthio)-pyran-2-one: Ki = 1.1 microM]. These inhibitors were chosen as initial leads for optimization of in vitro inhibitory activity based on molecular modeling and X-ray crystallographic structural data. While improvements in inhibitory potency were small with analogues of compound 1, important X-ray crystallographic structural information of the enzyme-inhibitor complex was gained. When bound, 1 was found to displace H2O301 in the active site while hydrogen bonding to the catalytic Asps and Ile50 and Ile150. The pyranone group of compound 2 was found to bind at the active site in the same manner, with the 6-phenyl and the 3-phenylthio occupying P1 and P1', respectively. The structural information was used to develop design strategies to reach three or four of the internal pockets, P2-P2'. This work led to analogues of diverse structure with high potency (IC50 < 10 nM) that contain either one or no chiral centers and remain nonpeptide. The highly potent compounds possess less anti-HIV activity in cellular assays than expected, and current optimization now focuses on increasing cellular activity. The value of the HIV-1 protease inhibitors described is their potential as better pharmacological agents with a different pattern of viral resistance development, relative to the peptide inhibitors in human clinical trials.

Benzopyrans↗
PubMed1996

Designing inhibitors of the metalloproteinase superfamily: comparative analysis of representative structures.

Structural comparisons of representative members of the zinc metalloproteinase superfamily show that the key secondary structural elements are conserved, in spite of major variations in the sequences including insertions and deletions of functional domains. Major differences between the matrix metalloproteinases (matrixins) are clustered in two regions forming the entrance to the active site and hence may be determinants of substrate selectivity. A comparison of the structures of matrixin-inhibitor complexes shows that there are significant differences even among the closely related matrixins, not only in the peripheral regions but also in the specificity pockets; these differences offer an excellent opportunity for the design of specific inhibitors targetted to individual members.

Binding Sites↗
PubMed1993

Hematopoietic cytokines: similarities and differences in the structures, with implications for receptor binding.

Crystal and NMR structures of helical cytokines--interleukin-4 (IL-4), granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin-2 (IL-2)--have been compared. Root mean square deviations in the C alpha coordinates for the conserved regions of the helices were 1-2 A between different cytokines, about twice the differences observed for independently determined crystal and solution structures of IL-4. Considerable similarity in amino acid sequence in the areas expected to interact with the receptors was detected, and the available mutagenesis data for these cytokines were correlated with structure conservation. Models of cytokine-receptor interactions were postulated for IL-4 based on its structure as well as on the published structure of human growth hormone interacting with its receptors (de Vos, A.M., Ultsch, M., & Kossiakoff, A.A., 1992, Science 255, 306-312). Patches of positively charged residues on the surfaces of helices C and D of IL-4 may be responsible for the interactions with the negatively charged residues found in the complementary parts of the IL-4 receptors.

Amino Acid Sequence↗
PubMed1992

Crystal structure of human recombinant interleukin-4 at 2.25 A resolution.

The crystal structure of human recombinant interleukin-4 (IL-4) has been solved by multiple isomorphous replacement, and refined to an R factor of 0.218 at 2.25 A resolution. The molecule is a left-handed four-helix bundle with a short stretch of beta sheet. The structure bears close resemblance to other cytokines such as granulocyte-macrophage colony stimulating factor (GM-CSF). Although no sequence similarity of IL-4 to GM-CSF and other related cytokines has been previously postulated, structure-based alignment of IL-4 and GM-CSF revealed that the core of the molecules, including large parts of all four helices and extending over half of the molecule, has 30% sequence identity. This may have identified regions which are not only important to maintain structure, but could also play a role in receptor binding.

Amino Acid Sequence↗
PubMed1980

Defective function of peripheral blood monocytes in patients with Hodgkin's and non-Hodgkin's lymphomas.

Phagocytosis and lysis of C. pseudotropicalis by peripheral blood monocytes from Hodgkin's and non-Hodgkin's lymphoma were analysed. In Hodgkin's disease, there was a decrease in the phagocytic activity of blood monocytes; moreover, the candidacidal activity was significantly decreased as compared with normal controls. Although monocytes from non-Hodgkin's patients presented normal phagocytic function, the ability to kill C. pseudotropicalis was impaired. In both groups of lymphomas, the data showed that the abnormal findings were not related to treatment. These results indicate that monocytes from Hodgkin's and non-Hodgkin's lymphoma posses a deficiency in killing C. pseudotropicalis, which could be due to an intrinsic macrophage defect in the myeloperoxidase-independent mechanisms and which may be responsible for the predisposition of the se patients to candida infections.

Adolescent↗
PubMed1976

Rosette forming T-cells in human lymphomas: relationship with age and clinical parameters.

Peripheral blood spontaneous rosette forming T cells (RFC) were studied in 40 Hodgkin's Disease (HD) and 20 lymphosarcoma (LS) patients, classified according to the histological type and spread of disease and to their age, treatment, clinical condition and evolution. LS patients had near normal RFC values; in HD, the lowest values of RFC corresponded to the most severe histological picture. In all patients, differences could be seen according to the spread of the disease and the clinical condition, but none in relation with treatment nor with the clinical evolution in a one year period after the test. While in controls and LS patients, RFC were higher in younger than older subjects, in HD, values were higher after 50 years of age. The usefulness of RFC test in the evaluation of lymphoma patients is discussed.

Adolescent↗
PubMed1976

Physical, chemical and immunological studies on bovine factor VIII.

Highly purified bovine factor VII prepared according to our technique and having a specific activity of 500 U/mg protein has been studied. The chemical analysis of the preparation revealed it to be composed of amino acids, lipids (8-10%) and carbohydrates (7%). The lipid moiety can be removed by chromatography. Different mechanism of inactivation of bovine factor VII and the possible molecular changes induced by the inactivating agents were studied. EDTA and EGTA provoke a weakening of the bonds linking the structural elements of the molecule, which allows for the separation of two different components of the molecule by gel filtration. Upon treatment with thrombin, the carbohydrate content of bovine factor VIII decreases without any apparent degradation of the protein moiety of the molecule. The fact that precipitating and neutralizing antisera against factor VIII were obtained, shows that the molecules modified by EDTA and thrombin still have the antigenic properties of factor VIII. The inhibitor developed by hemophiliacs transfused with human factor VIII is bound to bovine factor VIII, forming a complex reveal that it is composed of bovine factor VIII and human gamma-globulin. Bovine factor VIII in the complex retains some antigenic determinants which bind rabbit antiserum against bovine factor VIII, as shown by neutralization of the antiserum and by precipitation studies.

Animals↗