1
|
Briggs CA, Anderson DJ, Brioni JD, Buccafusco JJ, Buckley MJ, Campbell JE, Decker MW, Donnelly-Roberts D, Elliott RL, Gopalakrishnan M, Holladay MW, Hui YH, Jackson WJ, Kim DJ, Marsh KC, O'Neill A, Prendergast MA, Ryther KB, Sullivan JP, Arneric SP. Functional characterization of the novel neuronal nicotinic acetylcholine receptor ligand GTS-21 in vitro and in vivo. Pharmacol Biochem Behav 1997; 57:231-41. [PMID: 9164577 DOI: 10.1016/s0091-3057(96)00354-1] [Citation(s) in RCA: 151] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
(2.4)-Dimethoxybenzylidene anabaseine dihydrochloride (GTS-21), a compound that interacts with rat neuronal nicotinic acetylcholine receptors (nAChRs), was evaluated using human recombinant nAChRs in vitro and various pharmacokinetic and behavioral models in rodents, dogs and monkeys. GTS-21 bound to human alpha 4 beta 2 nAChR (K1-20 nM) 100-fold more potently than to human alpha 7 nAChR, and was 18- and 2-fold less potent than (-)-nicotine at human alpha 4 beta 2 and alpha 7 nAChR, respectively. Functionally. GTS-21 stimulated [5H]dopamine release from rat striatal slices with an EC50 of 10 +/- 2 microM (250-fold less potent and 70% as efficacious as (-)-nicotine), an effect blocked by the nAChR antagonist dihydro-beta-erythroidine. However, GTS-21 did not stimulate human alpha 4 beta 2 nor human ganglionic nAChRs significantly. In vivo, GTS-21 had no adverse effect on dog blood pressure (< or = 2.5 micromol/kg i.v. bolus infusion), in marked contrast with (-)-nicotine, GTS-21 (-62 micromol/kg.s.e.) also did not cross-discriminate significantly with (-)-nicotine in rats and did not reduce temperature or locomotion in mice. Neither was it active in the elevated plus maze anxiety model (0.19-6.2 micromol/kg.IP) in normal mice. However, GTS-21 did improve learning performance of monkeys in the delayed matching-to-sample task (32-130 nmol/kg.i.m.).
Collapse
|
|
28 |
151 |
2
|
Gopalakrishnan M, Buisson B, Touma E, Giordano T, Campbell JE, Hu IC, Donnelly-Roberts D, Arneric SP, Bertrand D, Sullivan JP. Stable expression and pharmacological properties of the human alpha 7 nicotinic acetylcholine receptor. Eur J Pharmacol 1995; 290:237-46. [PMID: 7589218 DOI: 10.1016/0922-4106(95)00083-6] [Citation(s) in RCA: 132] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The alpha 7 neuronal nicotinic acetylcholine receptor subtype forms a Ca(2+)-permeable homooligomeric ion channel sensitive to alpha-bungarotoxin in Xenopus oocytes. In this study, we have stably and functionally expressed the human alpha 7 cDNA in a mammalian cell line, HEK-293 and examined its pharmacologic properties. [125I] alpha-Bungarotoxin bound to transfected cells with a Kd value of 0.7 nM and a Bmax value of 973 pmoL/mg protein. No specific binding was detected in untransfected cells. Specific binding could be displaced by unlabeled alpha-bungarotoxin (Ki = 0.5 nM) and an excellent correlation was observed between binding affinities of a series of nicotinic cholinergic ligands in transfected cells and those in the human neuroblastoma IMR-32 cell line. Additionally, cell surface expression of alpha 7 receptors was detected by fluorescein isothiocyanate-conjugated alpha-bungarotoxin in transfected cells. Whole cell currents sensitive to blockade by alpha-bungarotoxin, and with fast kinetics of activation and inactivation, were recorded from transfected cells upon rapid application of (-)-nicotine or acetylcholine with EC50 values of 49 microM and 155 microM respectively. We conclude that the human alpha 7 subunit when expressed alone can form functional ion channels and that the stably transfected HEK-293 cell line serves as a unique system for studying human alpha 7 nicotinic receptor function and regulation, and for examining ligand interactions.
Collapse
|
|
30 |
132 |
3
|
Coghlan MJ, Carroll WA, Gopalakrishnan M. Recent developments in the biology and medicinal chemistry of potassium channel modulators: update from a decade of progress. J Med Chem 2001; 44:1627-53. [PMID: 11356099 DOI: 10.1021/jm000484+] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
Review |
24 |
111 |
4
|
Sullivan JP, Donnelly-Roberts D, Briggs CA, Anderson DJ, Gopalakrishnan M, Piattoni-Kaplan M, Campbell JE, McKenna DG, Molinari E, Hettinger AM, Garvey DS, Wasicak JT, Holladay MW, Williams M, Arneric SP. A-85380 [3-(2(S)-azetidinylmethoxy) pyridine]: in vitro pharmacological properties of a novel, high affinity alpha 4 beta 2 nicotinic acetylcholine receptor ligand. Neuropharmacology 1996; 35:725-34. [PMID: 8887981 DOI: 10.1016/0028-3908(96)84644-2] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The in vitro pharmacological properties of a novel cholinergic channel ligand, A-85380 [3-(2(S)-azetidinylmethoxy)pyridine], were examined using tissue preparations that express different putative nAChR subtypes. In radioligand binding studies, A-85380 is shown to be a potent and selective ligand for the human alpha 4 beta 2 nAChR subtype (Ki = 0.05 + 0.01 nM) relative to the human alpha 7 (Ki = 148 +/- 13 nM) and the muscle alpha 1 beta 1 dg subtype expressed in Torpedo electroplax (Ki = 314 +/- 12 nM). The R-enantiomer of A-85380, A-159470, displays little enantioselectivity towards the alpha 4 beta 2 and alpha 1 beta 1 delta gamma subtypes but does not display 12-fold enantioselectivity towards the alpha 7 subtype (Ki = 1275 +/- 199 nM). (+)- and(-)-Epibatidine display similar potencies at the human human alpha 4 beta 2 (Ki = 0.04 +/- 0.02 nM and 0.07 +/- 0.02 nM, respectively), human alpha 7 (Ki = 16 +/- 2 nM and 22 +/- 3 nM, respectively) and muscle alpha 1 beta 1 delta gamma g (Ki = 2.5 +/- 0.9 nM and 5.7 +/- 1.0 nM, respectively) nAChRs. Functionally, A-85380 is a potent activator of cation efflux through the human alpha 4 beta 2 (EC50 = 0.7 +/- 0.1 microM) and ganglionic (EC50 = 0.8 +/- 0.09 microM) subtypes, effects that are attenuated by pretreatment with mecamylamine (10 microM). Further, A-85380 can activate (EC50 = 8.9 +/- 1.9 microM) currents through channels formed by injection of the human alpha 7 subunit into Xenopus oocytes, effects that are attenuated by pretreatment with the alpha 7 nAChR antagonist, methyllycaconitine (10 nM). In all cases, A-85380 is more potent than (-)-nicotine but less potent than (+/-)-epibatidine. In neurotransmitter release studies, A-85380 stimulates the release of dopamine with an EC 50 value of 0.003 +/- 0.001 microM which is equipotent to (+/-)-epibatidine, and 20-fold more potent than (-)-nicotine (EC50 = 0.04 +/- 0.009 microM). Thus, A-85380 displays a profile of robust activation of a number of nAChR subtypes with substantially less affinity for [125I] alpha-BgT sites than [3H](-)-cytisine sites, suggesting that it may serve as a more selective pharmacologic probe for the alpha 4 beta 2 subtype relative to the alpha 7 and alpha 1 beta 1 delta g nAChRs than (+/-)-epibatidine.
Collapse
|
|
29 |
100 |
5
|
Bertrand D, Bertrand S, Cassar S, Gubbins E, Li J, Gopalakrishnan M. Positive allosteric modulation of the alpha7 nicotinic acetylcholine receptor: ligand interactions with distinct binding sites and evidence for a prominent role of the M2-M3 segment. Mol Pharmacol 2008; 74:1407-16. [PMID: 18678621 DOI: 10.1124/mol.107.042820] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The alpha7 nicotinic acetylcholine receptor (nAChR), a homopentameric, rapidly activating and desensitizing ligand-gated ion channel with relatively high degree of calcium permeability, is expressed in the mammalian central nervous system, including regions associated with cognitive processing. Selective agonists targeting the alpha7 nAChR have shown efficacy in animal models of cognitive dysfunction. Use of positive allosteric modulators selective for the alpha7 receptor is another strategy that is envisaged in the design of active compounds aiming at improving attention and cognitive dysfunction. The recent discovery of novel positive allosteric modulators such as 1-(5-chloro-2-hydroxyphenyl)-3-(2-chloro-5-trifluoromethylphenyl)urea (NS-1738) and 1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)urea (PNU-120596) that are selective for the alpha7 nAChRs but display significant phenotypic differences in their profile of allosteric modulation, suggests that these molecules may act at different sites on the receptor. Taking advantage of the possibility to obtain functional receptors by the fusion of proteins domains from the alpha7 and the 5-HT(3) receptor, we examined the structural determinants required for positive allosteric modulation. This strategy revealed that the extracellular N-terminal domain of alpha7 plays a critical role in allosteric modulation by NS-1738. In addition, alpha7-5HT(3) chimeras harboring the M2-M3 segment showed that spontaneous activity in response to NS-1738, which confirmed the critical contribution of this small extracellular segment in the receptor gating. In contrast to NS-1738, positive allosteric modulation by PNU-120596 could not be restored in the alpha7-5HT(3) chimeras but was selectively observed in the reverse 5HT(3)-alpha7 chimera. All together, these data illustrate the existence of distinct allosteric binding sites with specificity of different profiles of allosteric modulators and open new possibilities to investigate the alpha7 receptor function.
Collapse
|
|
17 |
91 |
6
|
Zhang XF, Gopalakrishnan M, Shieh CC. Modulation of action potential firing by iberiotoxin and NS1619 in rat dorsal root ganglion neurons. Neuroscience 2003; 122:1003-11. [PMID: 14643767 DOI: 10.1016/j.neuroscience.2003.08.035] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The present study investigated the effects of iberiotoxin (IbTx), a peptide toxin blocker of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels and NS1619, a BK(Ca) channel opener, on action potential firing of small and medium size afferent neurons from L6 and S1 dorsal root ganglia of adult rats. Application of IbTx (100 nM) reduced whole-cell outward currents in 67% of small and medium size neurons. Analysis of action potential profile revealed that IbTx significantly prolonged the duration of action potential and increased firing frequency of afferent neurons. IbTx did not significantly alter the resting membrane potential, threshold for action potential activation and action potential amplitude. The benzimidazolone NS1619 (10 microM) increased opening activity of a Ca(2+)-dependent channel as assessed by single channel measurements. In contrast to IbTx, NS1619 reversibly suppressed action potential firing, attributable to increases in threshold for evoking action potential, reduction in action potential amplitude and increases in amplitude of afterhyperpolarization. The effect of NS1619 on neuronal firing was sensitive to IbTx, indicating the attenuation of neuronal firing by NS1619 was mediated by opening BK(Ca) channels. NS1619 also reduced neuronal hyperexcitability evoked by 4-aminopyridine (4-AP), a transient-inactivated K(+) channel (A-current) blocker, in an IbTx-sensitive manner. These results indicate that IbTx-sensitive BK(Ca) channels exist in both small and medium diameter dorsal root ganglion (DRG) neurons and play important roles in the repolarization of action potential and firing frequency. NS1619 modulates action potential firing and suppresses 4-AP-evoked hyperexcitability in DRG neurons, in part, by opening BK(Ca) channels. These results suggest that opening BK(Ca) channels might be sufficient to suppress hyperexcitability of afferent neurons as those evoked by stimulants or by disease states.
Collapse
|
|
22 |
84 |
7
|
Whiteaker KL, Gopalakrishnan SM, Groebe D, Shieh CC, Warrior U, Burns DJ, Coghlan MJ, Scott VE, Gopalakrishnan M. Validation of FLIPR membrane potential dye for high throughput screening of potassium channel modulators. JOURNAL OF BIOMOLECULAR SCREENING 2001; 6:305-12. [PMID: 11689130 DOI: 10.1177/108705710100600504] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A fluorescence-based assay using the FLIPR Membrane Potential Assay Kit (FMP) was evaluated for functional characterization and high throughput screening (HTS) of potassium channel (ATP-sensitive K+ channel; K(ATP)) modulators. The FMP dye permits a more sensitive evaluation of changes in membrane potential with a more rapid response time relative to DiBAC4(3). The time course of responses is comparable to ligand-evoked activation of the channel measured by patch-clamp studies. The pharmacological profile of the K+ channel evaluated by using reference K(ATP) channel openers is in good agreement with that derived previously by DiBAC4(3)-based FLIPR assays. Improved sensitivity of responses together with the diminished susceptibility to artifacts such as those evoked by fluorescent compounds or quenching agents makes the FMP dye an alternative choice for HTS screening of potassium channel modulators.
Collapse
|
Validation Study |
24 |
76 |
8
|
Molinari EJ, Delbono O, Messi ML, Renganathan M, Arneric SP, Sullivan JP, Gopalakrishnan M. Up-regulation of human alpha7 nicotinic receptors by chronic treatment with activator and antagonist ligands. Eur J Pharmacol 1998; 347:131-9. [PMID: 9650859 DOI: 10.1016/s0014-2999(98)00084-3] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
This study examined the binding and functional properties of human alpha7 neuronal nicotinic acetylcholine receptors stably expressed in human embryonic kidney (HEK) 293 cells following chronic treatment with nicotinic receptor ligands. Treatment of cells with (-)-nicotine (100 microM) for 120 h increased the Bmax values of [125I]alpha-bungarotoxin binding 2.5-fold over untreated cells. This effect was concentration-dependent (EC50) = 970 microM) and a 6-fold upregulation was observed with the maximal concentration of (-)-nicotine tested. Also, treatment of cells with ligands of varying intrinsic activities including (+/-)-epibatidine, (2,4)-dimethoxybenzylidene anabaseine (GTS-21) and 1,1-dimethyl-4-phenyl piperazinium iodide (DMPP) also upregulated [125I]alpha-bungarotoxin binding. A concentration-dependent upregulation of binding sites was also observed following treatment with the alpha7 nicotinic receptor antagonist, methyllycaconitine (EC50 = 92 microM) with a maximal upregulation of about 7-fold. Functionally, the peak amplitude of the whole-cell currents recorded by fast application of (-)-nicotine after chronic treatment of cells with concentrations of (-)-nicotine (1000 microM) or methyllycaconitine (10 microM) that elicited similar increases in binding levels (3.5-fold) resulted in increases of 2-fold (505 +/- 21 pA) and 6-fold (1820 +/- 137 pA) respectively in whole cell current amplitude compared to untreated cells (267 +/- 24 pA). These studies clearly demonstrate that long-term exposure to both activator and antagonist ligands can increase the density of alpha7 nicotinic receptors and can differentially enhance nicotinic receptor function.
Collapse
|
|
27 |
65 |
9
|
Parent L, Gopalakrishnan M. Glutamate substitution in repeat IV alters divalent and monovalent cation permeation in the heart Ca2+ channel. Biophys J 1995; 69:1801-13. [PMID: 8580323 PMCID: PMC1236413 DOI: 10.1016/s0006-3495(95)80050-0] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
In voltage-gated ion channels, residues responsible for ion selectivity were identified in the pore-lining SS1-SS2 segments. Negatively charged glutamate residues (E393, E736, E1145, and E1446) found in each of the four repeats of the alpha 1C subunit were identified as the major determinant of selectivity in Ca2+ channels. Neutralization of glutamate residues by glutamine in repeat I (E393Q), repeat III (E1145Q), and repeat IV (E1446Q) decreased the channel affinity for calcium ions 10-fold from the wild-type channel. In contrast, neutralization of glutamate residues in repeat II failed to significantly alter Ca2+ affinity. Likewise, mutation of neighboring residues in E1149K and D1450N did not affect the channel affinity, further supporting the unique role of glutamate residues E1145 in repeat III and E1446 in repeat IV in determining Ca2+ selectivity. Conservative mutations E1145D and E1446D preserved high-affinity Ca2+ binding, which suggests that the interaction between Ca2+ and the pore ligand sites is predominantly electrostatic and involves charge neutralization. Mutational analysis of E1446 showed additionally that polar residues could achieve higher Ca2+ affinity than small hydrophobic residues could. The role of high-affinity calcium binding sites in channel permeation was investigated at the single-channel level. Neutralization of glutamate residue in repeats I, II, and III did not affect single-channel properties measured with 115 mM BaCl2. However, mutation of the high-affinity binding site E1446 was found to significantly affect the single-channel conductance for Ba2+ and Li+, providing strong evidence that E1446 is located in the narrow region of the channel outer mouth. Side-chain substitutions at 1446 in repeat IV were used to probe the nature of divalent cation-ligand interaction and monovalent cation-ligand interaction in the calcium channel pore. Monovalent permeation was found to be inversely proportional to the volume of the side chain at position 1446, with small neutral residues such as alanine and glycine producing higher Li+ currents than the wild-type channel. This suggests that steric hindrance is a major determinant for monovalent cation conductance. Divalent permeation was more complex. Ba2+ single-channel conductance decreased when small neutral residues such as glycine were replaced by bulkier ones such as glutamine. However, negatively charged amino acids produced single-channel conductance higher than predicted from the size of their side chain. Hence, negatively charged residues at position 1446 in repeat IV are required for divalent cation permeation.
Collapse
|
research-article |
30 |
56 |
10
|
Manikandan P, Letchoumy PV, Gopalakrishnan M, Nagini S. Evaluation of Azadirachta indica leaf fractions for in vitro antioxidant potential and in vivo modulation of biomarkers of chemoprevention in the hamster buccal pouch carcinogenesis model. Food Chem Toxicol 2008; 46:2332-43. [PMID: 18442880 DOI: 10.1016/j.fct.2008.03.013] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2007] [Revised: 02/16/2008] [Accepted: 03/11/2008] [Indexed: 10/22/2022]
Abstract
We evaluated the chemopreventive potential of Azadirachta indica (neem) leaf fractions based on in vitro antioxidant assays, and in vivo inhibitory effects on 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch (HBP) carcinogenesis. In addition we also identified the major constituents in neem leaf fractions by HPLC. Analysis of the free radical scavenging activities and reducing potential of crude ethanolic extract (CEE), ethyl acetate fraction (EAF) and methanolic fraction (MF) of neem leaf revealed a concentration-dependent increase in antioxidant potential that was in the order EAF>MF>CEE. Administration of neem leaf fractions reduced the incidence of DMBA-induced HBP carcinomas at a lower concentration compared to the crude extract. Chemoprevention by neem leaf fractions was associated with modulation of phase I and phase II xenobiotic-metabolising enzymes, lipid and protein oxidation, upregulation of antioxidant defences, inhibition of cell proliferation and angiogenesis, and induction of apoptosis. However, EAF was more effective than MF in terms of antiproliferative and antiangiogenic effects, and expression of CYP isoforms. The greater efficacy of EAF may be due to higher content of constituent phytochemicals as revealed by HPLC analysis. The results of the present study suggest that the antioxidant properties of neem leaf fractions may be responsible for modulating key hallmark capabilities of cancer cells such as cell proliferation, angiogenesis and apoptosis in the HBP carcinogenesis model.
Collapse
|
Research Support, Non-U.S. Gov't |
17 |
56 |
11
|
Zhao X, Shen J, Ivaturi V, Gopalakrishnan M, Feng Y, Schmidt BJ, Statkevich P, Goodman V, Gobburu J, Bello A, Roy A, Agrawal S. Model-based evaluation of the efficacy and safety of nivolumab once every 4 weeks across multiple tumor types. Ann Oncol 2019; 31:302-309. [PMID: 31959348 DOI: 10.1016/j.annonc.2019.10.015] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 10/18/2019] [Accepted: 10/24/2019] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND Nivolumab 480 mg every 4 weeks (Q4W) is approved in the European Union, United States, and several other markets across multiple tumor types. Its approval was supported by quantitative efficacy/safety analyses bridging to 3 mg/kg every 2 weeks (Q2W). PATIENTS AND METHODS The benefit-risk profile of nivolumab 480 mg Q4W relative to 3 mg/kg Q2W was evaluated using population pharmacokinetic modeling and exposure-response (E-R) analyses for safety and efficacy. Pharmacokinetic exposures were predicted for 3203 patients with melanoma, non-small-cell lung cancer (NSCLC), renal cell carcinoma (RCC), squamous cell carcinoma of the head and neck, urothelial carcinoma, or classical Hodgkin lymphoma. Quantitative models analyzed E-R to predict 480-mg Q4W safety across all indications and efficacy for melanoma, NSCLC, and RCC. Intratumoral receptor occupancy (RO) was predicted for parameters representing different tumor types. RESULTS Time-averaged concentrations for 480 mg Q4W versus 3 mg/kg Q2W were higher during the first 28 days (26.8%) and similar at steady state (5.2%). The maximum concentration (Cmax) after the first dose was higher (110.4%), and the trough concentration at day 28 was lower (-22.1%) with 480 mg Q4W versus 3 mg/kg Q2W. The Cmax achieved with 480 mg Q4W was lower than the previously established safe dose of 10 mg/kg Q2W. The probability of adverse events for key safety end points was similar for 480 mg Q4W and 3 mg/kg Q2W. The predicted overall survival and objective response rates with 480 mg Q4W were comparable to 3 mg/kg Q2W. The predicted high intratumoral RO provided additional evidence to support 480 mg Q4W across tumor types. CONCLUSIONS The benefit-risk profile for nivolumab 480 mg Q4W was predicted to be similar to that of 3 mg/kg Q2W across tumor types while providing a convenient and flexible option for patients and their caregivers.
Collapse
|
Research Support, Non-U.S. Gov't |
6 |
54 |
12
|
Balasankar T, Gopalakrishnan M, Nagarajan S. Synthesis and antibacterial activity of some 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles. Eur J Med Chem 2005; 40:728-31. [PMID: 15935906 DOI: 10.1016/j.ejmech.2005.01.005] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2004] [Revised: 01/21/2005] [Accepted: 01/24/2005] [Indexed: 11/18/2022]
Abstract
A series of 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles were synthesized, characterized by IR, NMR and elemental analysis and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that compounds 7a-j had better activity against tested Gram-positive organisms than the reference ciprofloxacin and norfloxacin. However, the compounds were nearly inactive against Gram-negative bacteria. Compound 7c and 7d were the most active compounds against Gram-positive bacteria.
Collapse
|
|
20 |
43 |
13
|
Kanagarajan V, Thanusu J, Gopalakrishnan M. Synthesis and in vitro microbiological evaluation of an array of biolabile 2-morpholino-N-(4,6-diarylpyrimidin-2-yl)acetamides. Eur J Med Chem 2010; 45:1583-9. [DOI: 10.1016/j.ejmech.2009.12.068] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Revised: 12/22/2009] [Accepted: 12/29/2009] [Indexed: 11/29/2022]
|
|
15 |
39 |
14
|
Gopalakrishnan M, Sureshkumar P, Kanagarajan V, Thanusu J, Govindaraju R. A simplified green chemistry approaches to organic synthesis in solid media. Activated fly ash, an industrial waste (pollutant) as an efficient and novel catalyst for some selected organic reactions in solvent-free conditions under microwave irradiation. ARKIVOC 2006. [DOI: 10.3998/ark.5550190.0007.d13] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
|
|
19 |
38 |
15
|
Harlan J, Chen Y, Gubbins E, Mueller R, Roch JM, Walter K, Lake M, Olsen T, Metzger P, Dorwin S, Ladror U, Egan DA, Severin J, Johnson RW, Holzman TF, Voelp K, Davenport C, Beck A, Potter J, Gopalakrishnan M, Hahn A, Spear BB, Halbert DN, Sullivan JP, Abkevich V, Neff CD, Skolnick MH, Shattuck D, Katz DA. Variants in Apaf-1 segregating with major depression promote apoptosome function. Mol Psychiatry 2006; 11:76-85. [PMID: 16231040 DOI: 10.1038/sj.mp.4001755] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
APAF1, encoding the protein apoptosis protease activating factor 1 (Apaf-1), has recently been established as a chromosome 12 gene conferring predisposition to major depression in humans. The molecular phenotypes of Apaf-1 variants were determined by in vitro reconstruction of the apoptosome complex in which Apaf-1 activates caspase 9 and thus initiates a cascade of proteolytic events leading to apoptotic destruction of the cell. Cellular phenotypes were measured using a yeast heterologous expression assay in which human Apaf-1 and other proteins necessary to constitute a functional apoptotic pathway were overexpressed. Apaf-1 variants encoded by APAF1 alleles that segregate with major depression in families linked to chromosome 12 shared a common gain-of-function phenotype in both assay systems. In contrast, other Apaf-1 variants showed neutral or loss-of-function phenotypes. The depression-associated alleles thus have a common phenotype that is distinct from that of non-associated variants. This result suggests an etiologic role for enhanced apoptosis in major depression.
Collapse
|
|
19 |
34 |
16
|
Gopalakrishnan M, Sureshkumar P, Kanagarajan V, Thanusu J. New environmentally-friendly solvent-free synthesis of imines using calcium oxide under microwave irradiation. RESEARCH ON CHEMICAL INTERMEDIATES 2007. [DOI: 10.1163/156856707782565822] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
|
18 |
34 |
17
|
Briggs CA, Schrimpf MR, Anderson DJ, Gubbins EJ, Grønlien JH, Håkerud M, Ween H, Thorin-Hagene K, Malysz J, Li J, Bunnelle WH, Gopalakrishnan M, Meyer MD. alpha7 nicotinic acetylcholine receptor agonist properties of tilorone and related tricyclic analogues. Br J Pharmacol 2007; 153:1054-61. [PMID: 18157163 DOI: 10.1038/sj.bjp.0707649] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE The alpha7 nicotinic acetylcholine receptor (nAChR) has attracted considerable interest as a target for cognitive enhancement in schizophrenia and Alzheimer's Disease. However, most recently described alpha7 agonists are derived from the quinuclidine structural class. Alternatively, the present study identifies tilorone as a novel alpha7-selective agonist and characterizes analogues developed from this lead. EXPERIMENTAL APPROACH Activity and selectivity were determined from rat brain alpha7 and alpha4beta2 nAChR binding, recombinant nAChR activation, and native alpha7 nAChR mediated stimulation of ERK1/2 phosphorylation in PC12 cells. KEY RESULTS Tilorone bound alpha7 nAChR (IC(50) 110 nM) with high selectivity relative to alpha4beta2 (IC(50) 70 000 nM), activated human alpha7 nAChR with an EC(50) value of 2.5 microM and maximal response of 67% relative to acetylcholine, and showed little agonist effect at human alpha3beta4 or alpha4beta2 nAChRs. However, the rat alpha7 nAChR maximal response was only 34%. Lead optimization led to 2-(5-methyl-hexahydro-pyrrolo[3,4-c]pyrrol-2-yl)-xanthen-9-one (A-844606) with improved binding (alpha7 IC(50) 11 nM, alpha4beta2 IC(50)>30 000 nM) and activity at both human and rat alpha7 nAChR (EC(50)s 1.4 and 2.2 microM and apparent efficacies 61 and 63%, respectively). These compounds also activated native alpha7 nAChR, stimulating ERK1/2 phosphorylation in PC12 cells. CONCLUSIONS AND IMPLICATIONS Tilorone, known as an interferon inducer, is a selective alpha7 nAChR agonist, suggesting utility of the fluorenone pharmacophore for the development of alpha7 nAChR selective agonists. Whether alpha7 stimulation mediates interferon induction, or whether interferon induction may influence the potential anti-inflammatory properties of alpha7 nAChR agonists remains to be elucidated.
Collapse
|
Journal Article |
18 |
31 |
18
|
El Kouhen R, Hu M, Anderson DJ, Li J, Gopalakrishnan M. Pharmacology of alpha7 nicotinic acetylcholine receptor mediated extracellular signal-regulated kinase signalling in PC12 cells. Br J Pharmacol 2009; 156:638-48. [PMID: 19226255 DOI: 10.1111/j.1476-5381.2008.00069.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE Neuronal nicotinic acetylcholine receptors (nAChR) can modulate cell survival and memory processing. The involvement of specific nAChR subtypes in downstream signalling events has been ill defined thus far, because of a lack of subtype-selective ligands. In this study, we investigated activation and modulation of alpha7 nAChR-mediated phosphorylation of extracellular signal-regulated kinases (ERK1/2) in PC12 cells, using selective agonists and positive allosteric modulators. EXPERIMENTAL APPROACH We used undifferentiated PC12 cells endogenously expressing alpha7 nAChR for both biochemical and functional studies. ERK phosphorylation changes were measured by using a novel In-Cell Western procedure. alpha7 nAChR-mediated Ca(2+) signalling was determined by using the fluorometric imaging plate reader assay. KEY RESULTS Robust induction of ERK phosphorylation followed exposure of PC12 cells to the selective agonist PNU-282987 in the presence of the alpha7 nAChR modulator PNU-120596. ERK phosphorylation was transient and was attenuated by the selective antagonist methyllycaconitine. Consistent with allosteric modulation of alpha7 nAChRs, PNU-120596 enhanced both the agonist potency and efficacy in activating ERK. Moreover, alpha7 nAChR agonists could be quantitatively differentiated based on their potency in activating ERK signalling. The rank order of potencies correlated fairly well with the corresponding binding K(i) values of these alpha7 nAChR agonists. CONCLUSIONS AND IMPLICATIONS The present work extends previous observations demonstrating the involvement of alpha7 nAChRs in ERK1/2 phosphorylation in PC12 cells. The In-Cell Western procedure allowed a detailed investigation of alpha7 nAChR function and downstream ERK signalling in response to agonist and allosteric modulators.
Collapse
|
Research Support, Non-U.S. Gov't |
16 |
30 |
19
|
Gopalakrishnan M, Molinari EJ, Shieh CC, Monteggia LM, Roch JM, Whiteaker KL, Scott VE, Sullivan JP, Brioni JD. Pharmacology of human sulphonylurea receptor SUR1 and inward rectifier K(+) channel Kir6.2 combination expressed in HEK-293 cells. Br J Pharmacol 2000; 129:1323-32. [PMID: 10742287 PMCID: PMC1571965 DOI: 10.1038/sj.bjp.0703181] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/1999] [Revised: 11/11/1999] [Accepted: 12/22/1999] [Indexed: 11/09/2022] Open
Abstract
1. The pharmacological properties of K(ATP) channels generated by stable co-expression of the sulphonylurea receptor SUR1 and the inwardly rectifying K(+) channel Kir6.2 were characterized in HEK-293 cells. 2. [(3)H]-Glyburide (glibenclamide) bound to transfected cells with a B(max) value of 18.5 pmol mg(-1) protein and with a K(D) value of 0.7 nM. Specific binding was displaced by a series of sulphonylurea analogues with rank order potencies consistent with those observed in pancreatic RINm5F insulinoma and in the brain. 3. Functional activity of K(ATP) channels was assessed by whole cell patch clamp, cation efflux and membrane potential measurements. Whole cell currents were detected in transfected cells upon depletion of internal ATP or by exposure to 500 microM diazoxide. The currents showed weak inward rectification and were sensitive to inhibition by glyburide (IC(50)=0.92 nM). 4. Metabolic inhibition by 2-deoxyglucose and oligomycin treatment triggered (86)Rb(+) efflux from transfected cells that was sensitive to inhibition by glyburide (IC(50)=3.6 nM). 5. Diazoxide, but not levcromakalim, evoked concentration-dependen decreases in DiBAC(4)(3) fluorescence responses with an EC(50) value of 14.1 microM which were attenuated by the addition of glyburide. Diazoxide-evoked responses were inhibited by various sulphonylurea analogues with rank order potencies that correlated well with their binding affinities. 6. In summary, results from ligand binding and functional assays demonstrate that the pharmacological properties of SUR1 and Kir6.2 channels co-expressed in HEK-293 cells resemble those typical of native K(ATP) channels described in pancreatic and neuronal tissues.
Collapse
|
research-article |
25 |
29 |
20
|
Thanusu J, Kanagarajan V, Gopalakrishnan M. Synthesis, spectral analysis and in vitro microbiological evaluation of 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-ones as a new class of antibacterial and antifungal agents. Bioorg Med Chem Lett 2010; 20:713-7. [DOI: 10.1016/j.bmcl.2009.11.074] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 10/14/2009] [Accepted: 11/13/2009] [Indexed: 10/20/2022]
|
|
15 |
27 |
21
|
Thimmapaya R, Neelands T, Niforatos W, Davis-Taber RA, Choi W, Putman CB, Kroeger PE, Packer J, Gopalakrishnan M, Faltynek CR, Surowy CS, Scott VE. Distribution and functional characterization of human Nav1.3 splice variants. Eur J Neurosci 2005; 22:1-9. [PMID: 16029190 DOI: 10.1111/j.1460-9568.2005.04155.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The focus of the present study is the molecular and functional characterization of four splice variants of the human Nav1.3 alpha subunit. These subtypes arise due to the use of alternative splice donor sites of exon 12, which encodes a region of the alpha subunit that resides in the intracellular loop between domains I and II. This region contains several important phosphorylation sites that modulate Na+ channel kinetics in related sodium channels, i.e. Nav1.2. While three of the four Nav1.3 isoforms, 12v1, 12v3 and 12v4 have been previously identified in human, 12v2 has only been reported in rat. Herein, we evaluate the distribution of these splice variants in human tissues and the functional characterization of each of these subtypes. We demonstrate by reverse transcriptase-polymerase chain reaction (RT-PCR) that each subtype is expressed in the spinal cord, thalamus, amygdala, cerebellum, adult and fetal whole brain and heart. To investigate the functional properties of these different splice variants, each alpha subunit isoform was cloned by RT-PCR from human fetal brain and expressed in Xenopus oocytes. Each isoform exhibited functional voltage-dependent Na+ channels with similar sensitivities to tetrodotoxin (TTX) and comparable current amplitudes. Subtle shifts in the V 1/2 of activation and inactivation (2-3 mV) were observed among the four isoforms, although the functional significance of these differences remains unclear. This study has demonstrated that all four human splice variants of the Nav1.3 channel alpha subunit are widely expressed and generate functional TTX-sensitive Na+ channels that likely modulate cellular excitability.
Collapse
|
|
20 |
27 |
22
|
Gopalakrishnan M, Sureshkumar P, Thanusu J, Kanagarajan V, Govindaraju R, Jayasri G. A convenient ‘one-pot’ synthesis andin vitromicrobiological evaluation of novel 2,7-diaryl-[1,4]-diazepan-5-ones. J Enzyme Inhib Med Chem 2008; 22:709-15. [PMID: 18237023 DOI: 10.1080/14756360701270618] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
|
17 |
26 |
23
|
Davis-Taber R, Choi W, Feng J, Hoogenboom L, McNally T, Kroeger P, Shieh CC, Simmer R, Brioni JD, Sullivan JP, Gopalakrishnan M, Scott VE. Molecular characterization of human SUR2-containing K(ATP) channels. Gene 2000; 256:261-70. [PMID: 11054556 DOI: 10.1016/s0378-1119(00)00338-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The distribution of human sulfonylurea receptor-2 (SUR2)-containing K(ATP) channels was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR). mRNA for SUR2B was detected in a variety of tissues including brain, skeletal, cardiac and smooth muscle, whereas SUR2A message was restricted to cardiac and skeletal muscle. An additional splice variant of SUR2 that lacked exon 17 was also identified by RT-PCR in tissues expressing both SUR2A and SUR2B or SUR2B alone. Quantification of RNA for SUR2 exon 17+ and SUR2 exon 17- splice variants using real-time Taqman PCR indicated differential levels of expression in brain, kidney, skeletal muscle, heart and small intestine. Interestingly, the SUR2 exon 17+ variant is the major species expressed in all tissues examined in this study. Each of the SUR2 splice variants transiently expressed with the inward rectifier Kir 6.2 formed functional K(ATP) channels in HEK 293 cells as assessed either by changes in DiBAC(4)(3) fluorescence responses or glyburide-sensitive whole cell currents. Collectively, our findings demonstrate that various SUR2 splice variants have distinct expression patterns and can form functional K(ATP) channels.
Collapse
|
|
25 |
26 |
24
|
Monteggia LM, Gopalakrishnan M, Touma E, Idler KB, Nash N, Arneric SP, Sullivan JP, Giordano T. Cloning and transient expression of genes encoding the human alpha 4 and beta 2 neuronal nicotinic acetylcholine receptor (nAChR) subunits. Gene X 1995; 155:189-93. [PMID: 7721089 DOI: 10.1016/0378-1119(94)00914-e] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Partial cDNA clones generated by RT-PCR were used as probes to clone the cDNAs encoding the human alpha 4 and beta 2 neuronal nicotinic acetylcholine receptor (nAChR) subunits. The 2.1-kb alpha 4 cDNA shows 84 and 76% identity to the rat and chicken cDNA sequences, respectively. The deduced amino-acid sequence shares 89 and 84% similarity, respectively, with the corresponding rat and chicken proteins, with most of the divergence occurring in the cytoplasmic domain. The 1721-nucleotide beta 2 sequence was identical to the human beta 2 sequence previously reported. Transfection of the alpha 4 and beta 2 clones into HEK293 cells resulted in the formation of binding sites that display high affinity towards [3H] cytisine, a characteristic of the alpha 4 beta 2 subtype produced in vivo.
Collapse
|
|
30 |
26 |
25
|
Gopalakrishnan M, Sureshkumar P, Kanagarajan V, Thanusu J. Organic Synthesis in Solid Media. Alumina Supported Sodium Hydrogen Sulfate as an Effective and Reusable Catalyst for One-Pot Synthesis of Amides from Ketones in Dry Media Under Microwave Irradiation. LETT ORG CHEM 2005. [DOI: 10.2174/1570178054405904] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
|
20 |
25 |