Structure-activity relationship of ligands of the pyrimidine nucleoside phosphorylases

Eighty-seven pyrimidine base and nucleoside analogs were evaluated as inhibitors of uridine phosphorylase (UrdPase) and thymidine phosphorylase (dThdPase). These findings, together with an extensive literature review, have allowed construction of structure-activity relationships for the binding of ligands to UrdPase and dThdPase and provide a basis for the rational design of new inhibitors of these enzymes. Additionally, 2,6-pyridinediol and 6-benzyl-2-thiouracil have been identified as being potent inhibitors of UrdPase and dThdPase respectively.     

Structure-activity relationship of ligands of dihydrouracil dehydrogenase from mouse liver

One hundred and five nucleobase analogues were screened as inhibitors of dihydrouracil dehydrogenase (DHUDase, EC 1.3.1.2) from mouse liver. 5-Benzyloxybenzyluracil, 1-deazauracil (2,6-pyridinediol), 3-deazauracil (2,4-pyridinediol), 5-benzyluracil, 5-nitrobarbituric acid and 5,6-dioxyuracil (alloxan) were identified as potent inhibitors of this activity, with apparent Ki values of 0.2, 0.5, 2.1, 3.4, 3.8 and 6.6 microM respectively. Both 5-benzyloxybenzyluracil and 1-deazauracil were also potent inhibitors of DHUDase from human livers. These findings along with an extensive review of literature allowed the formulation of a structure-activity relationship. The binding to DHUDase required intact C2 and C4 oxo groups. Replacement of N1 or N3 by an endocyclic carbon enhanced binding. In contrast, replacement of C5 or C6 by an endocyclic nitrogen abolished binding. Addition of a charged group to C5 and/or C6, and of a hydrophobic group to C5 but not C6 improved the binding.     

Erythro- and threo-2-hydroxynonyl substituted 2-phenyladenines and 2-phenyl-8-azaadenines: ligands for A1 adenosine receptors and adenosine deaminase

erythro-2-Phenyl-9-(2-hydroxy-3-nonyl)adenine and its 8-aza analog were prepared and showed a very high inhibitory activity towards adenosine deaminase (ADA), with Ki 0.55 and 1.67 nM, respectively, and high affinity for A1 adenosine receptors, with Ki 28 and 2.8 nM, respectively. To increase affinity for A1 receptors we introduced a substituent on the N6 position such as alkyl or cycloalkyl groups, which are present in effective agonists or antagonists. Furthermore, for some compounds, we prepared the two diastereoisomers erythro and threo to verify whether the binding with A1 receptors is stereoselective, as in ADA. Results show that some of the synthesised compounds are good inhibitors for ADA and good ligands for A1, and the erythro diastereoisomers are more active than the threo ones. The experimental evidence allows us to hypothesise some similarity in the three dimensional structures of the binding site of the two proteins, ADA and A1 adenosine receptor, in spite of lacking any homologies in the amino acid sequences.     

Structure-activity relationship of pyrimidine base analogs as ligands of orotate phosphoribosyltransferase

Eighty pyrimidine base analogs were evaluated as inhibitors of mouse liver orotate phosphoribosyltransferase (OPRTase, EC 2.4.2.10). Based on these findings and an extensive literature review, a structure-activity relationship has been formulated for the binding of pyrimidine base analogs to OPRTase. This study provides a basis for the rational design of new inhibitors of this enzyme, and several such compounds are proposed. Additionally, 4,6-dihydroxypyrimidine has been found to be a potent OPRTase inhibitor. Eleven OPRTase inhibitors were also evaluated as inhibitors of orotidine 5'-monophosphate decarboxylase (ODCase, EC 4.1.2.23). 5-Azauracil, 5-azaorotate, and barbituric acid inhibited ODCase significantly only after preincubation with PRPP and MgCl2 in the presence of cytosol.     

Structure-activity relationships of histamine H2 receptor ligands

Recent research on histamine H2 receptor agonists was focused on quantitative structure-activity relationships and receptor models explaining the activity of imidazolylpropylguanidines. Their selectivity for guinea pig vs. human isoforms was investigated using H2 receptor-Gsalpha fusion proteins and attributed to amino acid differences in transmembrane domains 1 and 7. New antagonists result from approaches to improve pharmacokinetic properties and to design hybrid drugs which additionally have gastroprotective or anti H. pylori activity.     

Structure-activity relationships of 7-deaza-6-benzylthioinosine analogues as ligands of Toxoplasma gondii adenosine kinase

Several 7-deaza-6-benzylthioinosine analogues with varied substituents on aromatic ring were synthesized and evaluated against Toxoplasma gondii adenosine kinase (EC.2.7.1.20). Structure-activity relationships indicated that the nitrogen atom at the 7-position does not appear to be a critical structural requirement. Molecular modeling reveals that the 7-deazapurine motif provided flexibility to the 6-benzylthio group as a result of the absence of H-bonding between N7 and Thr140. This flexibility allowed better fitting of the 6-benzylthio group into the hydrophobic pocket of the enzyme at the 6-position. In general, single substitutions at the para or meta position enhanced binding. On the other hand, single substitutions at the ortho position led to the loss of binding affinity. The most potent compounds, 7-deaza- p-cyano-6-benzylthioinosine (IC 50 = 5.3 microM) and 7-deaza- p-methoxy-6-benzylthioinosine (IC 50 = 4.6 microM), were evaluated in cell culture to delineate their selective toxicity.     

Structure-activity relationship,conformation and pharmacology studies of morphiceptin analogues--selective mu-opioid receptor ligands

Morphiceptin (Tyr-Pro-Phe-Pro-NH(2)) is one of the most selective agonists for the mu-opioid receptor. In this review structure-activity relationships of morphiceptin analogues and studies resulting in defining low energy conformations are discussed. Finally, new developments in the control of tumour growth and cell proliferation by morphiceptin analogues are surveyed, which open future perspectives in the diagnosis and treatment of various cancers.     

Specificity of adenosine deaminase inhibitors

The specificity of the potent adenosine deaminase inhibitors deoxycoformycin (covidarabine), coformycin and erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), has been assessed in Ehrlich ascites tumor cells in vitro and in cultured mouse lymphoma L5178Y cells. EHNA is both less potent an inhibitor of adenosine deaminase than deoxycoformycin, and is less specific. High concentrations of deoxycoformycin and EHNA inhibit all pathways of purine ribonucleotide synthesis, and inhibit the conversion of inosinate to adenine and guanine nucleotides. These drugs also inhibit purified adenylate deaminase, but inhibition of this enzyme in intact cells can only be detected at high rates of deamination of adenylate. Deoxycoformycin potentiates the toxicity of adenine against cultured cells.     

Primary structure of bovine adenosine deaminase

Derivatized bovine adenosine deaminase is used in enzyme replacement therapy and as an adjunct to gene therapy against severe combined immunodeficiency syndrome. Although a gene sequence is known for human adenosine deaminase, the structure of the bovine enzyme has not been characterized. Structure studies using mass spectrometry are reported here that evaluate sequence, processing, post-translational modifications and the extent of homology between the human protein and its therapeutic surrogate.     

Adenosine deaminase from human erythrocytes: Purification and effects of adenosine analogs

Adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) has been purified about 3000-fold from human erythrocytes. The molecular weight of the enzyme was estimated to be 33,000. With the partially purified erythrocytic adenosine deaminase, K_m and V_max values relative to adenosine were: adenosine, 25 μM, 100 per cent; formycin A, 1000 μM, 753–850 per cent; 8-aza-adenosine, 130 μM, 310 per cent; 6-chloropurine ribonuclcoside, 1000 μM, 91 per cent; 2,6-diaminopurine ribonucleoside, 74 μM, 91 per cent; 2'-deoxyadenosine. 7 μm, 60 per cent; xylosyladenine, 33 μm, 62 per cent; arabinosyi adenine, 100 μM, 47 per cent; 3'-deoxyadenosine (cordycepin), 41 μM, 100 per cent; 3'-amino3'-deoxyadenosine. 133 μM, 89 per cent: 4'-thioadenosine, 13 μM, 43 per cent; and 6-methylselenopurine ribonucleoside, 27 μM, 88 per cent. Apparent K_ti values of reaction products and some adenosine analogs using adenosine as a substrate were as follows; inosine. 116 μM; 2'-deoxyinosine, 60 μM; guanosine, 140 μM; 2-fluoroadenosine, 60 μM; 2-fluorodeoxyadenosine. 19 μM; N⁶-methyladenosine, 17 μM; N₁-methyladenosine, 275 μM; 6-thioguanosine, 92 μM; 6-thioinosine, 330 μM; 6-methylthioinosine, 270 μM; arabinosyl 6-thiopurine, 360 μM; and coformycin, 0.01 μM. Tubercidin (7-deaza-adenosine) and toyocamycin were devoid both of substrate and inhibitor activity. Also. N⁷-methylinosine, N⁷-methylguanosine and dipyridamole (Persantin®) did not inhibit the enzymic activity.     

Structure-activity relationship of lysophosphatidylcholines in HL-60 human leukemia cells

AIM: To explore the structure-activity relationship of lysophosphatidylcholine (LPC) and lysolipid molecules from a marine sponge and ladybirds. METHODS: We tested three synthetic LPCs and four natural lysolipids on Ca2 mobilization in HL-60 human leukemia cells. RESULTS: We observed lysolipid-mediated Ca2 mobilization. The activity was the same in both ester- and ether-linked lysolipids, and introduction of a double bond or methoxy group on the alkyl chain did not significantly modulate the activity. However, replacement of trimethylammonium moiety in the choline structure with ammonium moiety reduced the activity. Furthermore, change of the alkyl chain length influenced the Ca2 response. CONCLUSION: LPC-induced Ca2 mobilization might be dependent on the length of alkyl chain and the presence of choline moiety in HL-60 leukemia cells.     

Structure-activity relationship of 1-propargyl-5-halopyrimidin-2-ones

The structure-activity relationship of 1-propargyl-5-halopyrimidin-2-ones with respect to mitotic inhibitory potential and inhibition of colchicine binding to tubulin was investigated. A correlation between accumulation in metaphase of cultured human NHIK 3025 cells and drug competition with colchicine binding to tubulin was found for each compound. Effects on division of NHIK 3025 cells were determined in stained preparations following a 6 h treatment with drugs. The four halogen-substituted compounds displayed metaphase arresting ability while the H-substituted 1-propargylpyrimidin-2-one did not. 1-Propargyl-5-fluoropyrimidin-2-one was active at 1.5 and 0.75 mM while the 5-chloro, 5-bromo and 5-iodo compounds caused metaphase arrest at 0.375 and 0.18 mM. The ability of these drugs to compete with colchicine binding to DEAE-cellulose purified tubulin was also investigated. 1-Propargylpyrimidin-2-one at 5 mM did not inhibit (3H)colchicine binding to tubulin as determined by Sephadex G-50 gel filtration. The halogen-substituted pyrimidones, however, demonstrated competitive inhibition of colchicine binding to tubulin. Five mM 1-propargyl-5-iodopyrimidin-2-one inhibited colchicine binding by 43.2%, the highest value obtained within the metahalone group. The drugs tested had no effect on vincristine binding to tubulin. With respect to the halogen substitution, the increasing order of mitotic inhibitory potential and competition with colchicine binding to tubulin is H less than less than F less than Cl less than or equal to Br less than or equal to I.     

薯蓣皂苷元衍生物抗肿瘤的构效关系研究

为阐明薯蓣皂苷元衍生物的体外抗肿瘤活性的构效关系,基于Bcl-2蛋白小分子抑制剂的三维药效团模型的各药效点的特点,本研究利用autodock4.2将薯蓣皂苷元衍生物和Bcl-2进行了大量对接及分析,选择性的合成了31个化合物,采用MTT法测定了这些化合物对A375、A549、HepG-2和K562等4个肿瘤细胞株的体外抗肿瘤活性。初步的构效关系研究表明,薯蓣皂苷元失F环的26-位脂肪酸酯、芳香酸酯类衍生物几乎没有活性;薯蓣皂苷元三氮唑溴盐类衍生物均具有较好的体外抗肿瘤活性,且三氮唑上连有较大的疏水基团的衍生物的活性更好;薯蓣皂苷元及其失F环的杂环类、薯蓣皂苷元失F环氨基酸酯类衍生物能形成较强氢键、偶极作用的衍生物的活性更好。     

Pharmacological characterization of novel adenosine ligands in recombinant and native human A2B receptors

The present study was designed to evaluate the effects of novel and recognised compounds at human recombinant A(2B) adenosine receptors expressed in Chinese hamster ovary (hA(2B)CHO), in human embryonic kidney 293 (hA(2B)HEK-293) and at endogenous A(2B) receptors in human mast cells (HMC-1). Saturation binding experiments performed using the new high affinity A(2B) adenosine radioligand [(3)H]-N-benzo[1,3]dioxol-5-yl-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetra hydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]-acetamide ([(3)H]-MRE 2029F20) revealed a single class of binding sites in hA(2B)CHO, hA(2B)HEK-293 and HMC-1 cells with K(D) (nM) of 1.65+/-0.18, 2.83+/-0.34, 2.62+/-0.27 and B(max) (fmol/mg protein) of 36+/-4, 475+/-50 and 128+/-15, respectively. The pharmacological profile of new compounds, determined in inhibition binding experiments in hA(2B)HEK-293 cells using [(3)H]-MRE 2029F20, showed a rank order of potency typical of the A(2B) receptors with K(i) values in the range 3.2-28nM. In functional assays, recognised agonists and antagonists were studied by evaluating their capability to modulate the cAMP production in hA(2B)CHO and in HMC-1 cells. Novel compounds were able to decrease NECA-stimulated cAMP production in hA(2B)CHO and in HMC-1 cells showing a high potency. New compounds were also able to inhibit cAMP levels in the absence of NECA and in the presence of forskolin stimulation in hA(2B)CHO and in HMC-1 cells. In HEK-293 cells MRE 2029F20 reduced cAMP basal levels with an IC(50) value of 2.9+/-0.3nM. These results suggest that novel compounds are antagonists with an inverse agonist activity in recombinant and native human A(2B) receptors.     

Structure-based design, synthesis, and structure-activity relationship studies of novel non-nucleoside adenosine deaminase inhibitors

We disclose herein optimization efforts around the novel, highly potent non-nucleoside adenosine deaminase (ADA) inhibitor, 1-[(R)-1-hydroxy-4-(6-(3-(1-methylbenzimidazol-2-yl)propionylamino)indol-1-yl)-2-butyl]imidazole-4-carboxamide 1 (K(i)= 7.7 nM), which we recently reported. Structure-based drug design (SBDD) utilizing the crystal structure of the 1/ADA complex was performed in order to obtain structure-activity relationships (SAR) for this type of compound rationally and effectively. To utilize the newly formed hydrophobic space (F2), replacement of the benzimidazole ring of 1 with a n-propyl chain (4b) or a simple phenyl ring (4c) was tolerated in terms of binding activity, and the length of the methylene-spacer was shown to be optimal at two or three. Replacement of an amide with an ether as a linker was also well tolerated in terms of binding activity and moreover improved the oral absorption (6a and 6b). Finally, transformation of indol-1-yl to indol-3-yl resulted in discovery of a novel highly potent and orally bioavailable ADA inhibitor, 1-[(R)-4-(5-(3-(4-chlorophenyl)propoxy)-1-methylindol-3-yl)-1-hydroxy-2-butyl]imidazole-4-carboxamide 8c.