Striatal adenosine A(2A) receptor-mediated positron emission tomographic imaging in 6-hydroxydopamine-lesioned rats using [(18)F]-MRS5425.

INTRODUCTION: A(2A) receptors are expressed in the basal ganglia, specifically in striatopallidal GABAergic neurons in the striatum (caudate-putamen). This brain region undergoes degeneration of presynaptic dopamine projections and depletion of dopamine in Parkinson's disease. We developed an (18)F-labeled A(2A) analog radiotracer ([(18)F]-MRS5425) for A(2A) receptor imaging using positron emission tomography (PET). We hypothesized that this tracer could image A(2A) receptor changes in the rat model for Parkinson's disease, which is created following unilateral injection of the monoaminergic toxin 6-hydroxydopamine (6-OHDA) into the substantia nigra. METHODS: [(18)F]-MRS5425 was injected intravenously in anesthetized rats, and PET imaging data were collected. Image-derived percentage injected doses per gram (%ID/g) in regions of interest was measured in the striatum of normal rats and in rats unilaterally lesioned with 6-OHDA after intravenous administration of saline (baseline), D(2) agonist quinpirole (1.0 mg/kg) or D(2) antagonist raclopride (6.0 mg/kg). RESULTS: Baseline %ID/g reached a maximum at 90 s and maintained plateau for 3.5 min, and then declined slowly thereafter. In 6-OHDA-lesioned rats, %ID/g was significantly higher in the lesioned side compared to the intact side, and the baseline total %ID/g (data from both hemispheres were combined) was significantly higher compared to quinpirole stimulation starting from 4.5 min until the end of acquisition at 30 min. Raclopride did not produce any change in uptake compared to baseline or between the hemispheres. CONCLUSION: Thus, increase of A(2A) receptor-mediated uptake of radioactive MRS5425 could be a superior molecular target for Parkinson's imaging.

Molecular probes for the A2A adenosine receptor based on a pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine scaffold.

Pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine derivatives such as SCH 442416 display high affinity and selectivity as antagonists for the human A(2A) adenosine receptor (AR). We extended ether-linked chain substituents at the p-position of the phenyl group using optimized O-alkylation. The conjugates included an ester, carboxylic acid and amines (for amide condensation), an alkyne (for click chemistry), a fluoropropyl group (for (18)F incorporation), and fluorophore reporter groups (e.g., BODIPY conjugate 14, K(i) 15 nM). The potent and A(2A)AR-selective N-aminoethylacetamide 7 and N-[2-(2-aminoethyl)-aminoethyl]acetamide 8 congeners were coupled to polyamidoamine (PAMAM) G3.5 dendrimers, and the multivalent conjugates displayed high A(2A)AR affinity. Theoretical docking of an AlexaFluor conjugate to the receptor X-ray structure highlighted the key interactions between the heterocyclic core and the binding pocket of the A(2A)AR as well as the distal anchoring of the fluorophore. In conclusion, we have synthesized a family of high affinity functionalized congeners as pharmacological probes for studying the A(2A)AR.

The ERAD inhibitor Eeyarestatin I is a bifunctional compound with a membrane-binding domain and a p97/VCP inhibitory group.

BACKGROUND: Protein homeostasis in the endoplasmic reticulum (ER) has recently emerged as a therapeutic target for cancer treatment. Disruption of ER homeostasis results in ER stress, which is a major cause of cell death in cells exposed to the proteasome inhibitor Bortezomib, an anti-cancer drug approved for treatment of multiple myeloma and Mantle cell lymphoma. We recently reported that the ERAD inhibitor Eeyarestatin I (EerI) also disturbs ER homeostasis and has anti-cancer activities resembling that of Bortezomib. METHODOLOGY AND PRINCIPAL FINDINGS: Here we developed in vitro binding and cell-based functional assays to demonstrate that a nitrofuran-containing (NFC) group in EerI is the functional domain responsible for the cytotoxicity. Using both SPR and pull down assays, we show that EerI directly binds the p97 ATPase, an essential component of the ERAD machinery, via the NFC domain. An aromatic domain in EerI, although not required for p97 interaction, can localize EerI to the ER membrane, which improves its target specificity. Substitution of the aromatic module with another benzene-containing domain that maintains membrane localization generates a structurally distinct compound that nonetheless has similar biologic activities as EerI. CONCLUSIONS AND SIGNIFICANCE: Our findings reveal a class of bifunctional chemical agents that can preferentially inhibit membrane-bound p97 to disrupt ER homeostasis and to induce tumor cell death. These results also suggest that the AAA ATPase p97 may be a potential drug target for cancer therapeutics.

Synthesis and evaluation of 1,2,4-triazolo[1,5-c]pyrimidine derivatives as A2A receptor-selective antagonists.

Movement disorders such as Parkinson's disease and Huntington's disease are serious life-limiting and debilitating movement disorders. Their onset typically occurs from mid-life to late in life, and effective diagnostic techniques for detecting and following the disease course are lacking. Our goal is to develop receptor imaging agents for positron emission tomography (PET) that selectively target the most relevant subtype of adenosine receptors (AR) that are highly expressed in the striatum, that is, the A(2A) AR. To further this goal, we have synthesized and characterized pharmacologically a family of high affinity A(2A) AR ligands, based on the known antagonist, SCH 442416 (R=-Me), which have structural variability on the terminus (R=-Et, -i-Pr, -allyl, and others). A O-fluoroethyl analogue suitable for use as a PET tracer had a K(i) value of 12.4 nM and was highly selective for the A(2A) AR in comparison to the A(1) and A(3) ARs.

Synthesis and structure activity relationship studies of novel Staphylococcus aureus Sortase A inhibitors.

Synthetic methods have been developed for lead Sortase A inhibitors identified from previous studies. Several derivatives of the lead inhibitor were synthesized to derive preliminary structure activity relationships (SAR). Different regions of the lead inhibitor that are critical for the enzyme activity have been determined by systematic SAR studies. The E stereochemistry of the lead compound was found to be critical for its activity. Replacement of the E double bond with Z double bond or a rigid triple bond reduced the enzyme inhibitory activity in most cases. Reduction of the double bond to a C-C single bond resulted in complete loss of activity. Amide carbonyl and NH groups were also found to be crucial for the activity of this class of inhibitors, as well. The morpholine ring oxygen atom was also found to be an important factor for the activity of the lead inhibitor. Preliminary SAR studies led to the identification of compounds with improved enzyme inhibition. The most active compound was found to have an IC(50) value of 58 microM against the enzyme.

Synthesis and characterization of potent inhibitors of Trypanosoma cruzi dihydrofolate reductase.

Dihydrofolate reductase (DHFR) of the parasite Trypanosoma cruzi (T. cruzi) is a potential target for developing drugs to treat Chagas' disease. We have undertaken a detailed structure-activity study of this enzyme. We report here synthesis and characterization of six potent inhibitors of the parasitic enzyme. Inhibitory activity of each compound was determined against T. cruzi and human DHFR. One of these compounds, ethyl 4-(5-[(2,4-diamino-6-quinazolinyl)methyl]amino-2-methoxyphenoxy)butanoate (6b) was co-crystallized with the bifunctional dihydrofolate reductase-thymidylate synthase enzyme of T. cruzi and the crystal structure of the ternary enzyme:cofactor:inhibitor complex was determined. Molecular docking was used to analyze the potential interactions of all inhibitors with T. cruzi DHFR and human DHFR. Inhibitory activities of these compounds are discussed in the light of enzyme-ligand interactions. Binding affinities of each inhibitor for the respective enzymes were calculated based on the experimental or docked binding mode. An estimated 60-70% of the total binding energy is contributed by the 2,4-diaminoquinazoline scaffold.

Synthesis and antiproliferative activity of benzyl and phenethyl analogs of makaluvamines.

Analogs of marine alkaloid, makaluvamine, bearing substituted benzyl and substituted phenethyl side chains have been synthesized and their antiproliferative activities have been evaluated. 4-Methyl, 4-chloro, and 4-fluoro substituted benzyl analogs possessed pronounced antiproliferative effects on the breast cancer cell line, MCF-7 at IC(50) values of 2.3 microM, 1.8 microM, and 2.8 microM, respectively. 4-Methyl, 4-chloro, and 3,4-methylenedioxy derivatives showed the best activity against MCF-7 among the phenethyl analogs with IC(50) values of 2.3 microM, 2.8 microM, and 2.4muM, respectively. In general, methoxy substitutions resulted in slight loss in activity in both benzyl and phenethyl series. Benzyl, 4-fluorobenzyl, 3,4-dimethoxyphenethyl, and 3,4-methylenedioxyphenethyl analogs were tested by NCI in their 60 cell lines in vitro human cancer cell screen. All four compounds showed excellent inhibition against several tested cancer cell lines. Benzyl and 4-fluorobenzyl analogs were relatively more active than 3,4-dimethoxy phenethyl and 3,4-methylenedioxy phenethyl analogs. In NCI assays, the best LogGI(50) values were shown by the fluorobenzyl analog against the renal cancer cell line RXF-393 (<-8.0M) and dimethoxy phenethyl analog against the CNS cancer cell line, SF-268 (<-8.0M). The best LogLC(50) value was shown by the fluorobenzyl analog against the breast cancer cell line MCF-7 (-6.01 M).

Identification of novel inhibitors of bacterial surface enzyme Staphylococcus aureus Sortase A.

In-silico virtual screening of bacterial surface enzyme Staphylococcus aureus Sortase A against commercial compound libraries using FlexX software package has led to the identification of novel inhibitors. Inhibition of enzyme catalytic activity was determined by monitoring the steady state cleavage of a model peptide substrate. Preliminary structure activity relationship studies on the lead compound resulted in the identification of compounds with improved activity. The most active compound has an IC50 value of 58 microM against the enzyme.

Analogs of the marine alkaloid makaluvamines: synthesis, topoisomerase II inhibition, and anticancer activity.

Twelve analogs of makaluvamines have been synthesized. These compounds were evaluated for their ability to inhibit the enzyme topoisomerase II. Five compounds were shown to inhibit topoisomerase catalytic activity comparable to two known topoisomerase II targeting control drugs, etoposide and m-AMSA. Their cytotoxicity against human colon cancer cell line HCT-116 and human breast cancer cell lines MCF-7 and MDA-MB-468 has been evaluated. Four makaluvamine analogs exhibited better IC(50) values against HCT-116 as compared to control drug etoposide. One analog exhibited better IC(50) value against HCT-116 as compared to m-AMSA. All 12 of the makaluvamine analogs exhibited better IC(50) values against MCF-7 and MDA-MB-468 as compared to etoposide as well as m-AMSA.

Azetidin-2-ones, synthon for biologically important compounds.

Azetidin-2-one, a four-membered cyclic lactam (beta-lactam) skeleton has been recognised as a useful building block for the synthesis of a large number of organic molecules by exploiting the strain energy associated with it, in addition to its use in the synthesis of a variety of beta-lactam antibiotics. Efforts have been made in exploring such new aspects of beta-lactam chemistry using enantiomerically pure beta-lactams as versatile intermediates for the synthesis of aromatic beta-amino acids and their derivatives, peptides, polyamines, polyamino alcohols, amino sugars and polyamino ethers. The development of methodologies based on beta-lactam nucleus is now referred as 'the beta-lactam synthon methods'. The selective bond cleavage of the strained ring coupled with further interesting transformation render this fascinating molecule as a powerful building block. This provides an access to diverse structural type of synthetic target molecules lacking beta-lactam ring structure. This review provides an account of synthesis of organic compounds having biological significance at the same time lacking beta-lactam ring, by using beta-lactam as synthon.