Surendra K. Saini

A Novel Delta Opioid Receptor Antagonist, SoRI-9409, Produces a Selective and Long-Lasting Decrease in Ethanol Consumption in Heavy-Drinking Rats

BACKGROUND Naltrexone, a compound with high affinity for the mu opioid receptor (MOP-R) reduces alcohol consumption. SoRI-9409 is a derivative of naltrexone that has highest affinity at delta opioid receptors (DOP-Rs). We have investigated the effects of SoRI-9409 on ethanol consumption to determine the consequences of altering the naltrexone compound to a form with increased efficacy at DOP-Rs. METHODS Effects of the opioid receptor antagonists, SoRI-9409 (0-30 mg/kg, IP), naltrexone (0-30 mg/kg, IP), or naltrindole (0-10 mg/kg, IP) on ethanol consumption was measured in high- and low-ethanol-consuming rats with two different drinking paradigms. SoRI-9409-, naltrexone-, and naltrindole-mediated inhibition of DOP-R-stimulated [(35)S]GTP gamma S binding was measured in brain membranes prepared from high-ethanol-consuming rats. The effects of SoRI-9409 on morphine-mediated analgesia, conditioned place preference, and anxiety were also examined. RESULTS In high- but not low-ethanol-consuming animals, SoRI-9409 is threefold more effective and selective at reducing ethanol consumption when compared with naltrexone or naltrindole for up to 24 hours. SoRI-9409 administered daily for 28 days continuously reduced ethanol consumption, and when the administration of SoRI-9409 was terminated, the amount of ethanol consumed remained lower compared with vehicle-treated animals. Furthermore, SoRI-9409 inhibits DOP-R-stimulated [(35)S]GTP gamma S binding in brain membranes of high-ethanol-consuming rats. CONCLUSIONS SoRI-9409 causes selective and long-lasting reductions of ethanol consumption. This suggests that compounds that have high affinity for DOP-Rs such as SoRI-9409 might be promising candidates for development as a novel therapeutic for the treatment of alcoholism.

Design, Synthesis, and Structure–Activity Relationship Studies of a Series of [4-(4-Carboxamidobutyl)]-1-arylpiperazines: Insights into Structural Features Contributing to Dopamine D3 versus D2 Receptor Subtype Selectivity

Antagonist and partial agonist modulators of the dopamine D3 receptor (D3R) have emerged as promising therapeutics for the treatment of substance abuse and neuropsychiatric disorders. However, development of druglike lead compounds with selectivity for the D3 receptor has been challenging because of the high sequence homology between the D3R and the dopamine D2 receptor (D2R). In this effort, we synthesized a series of acylaminobutylpiperazines incorporating aza-aromatic units and evaluated their binding and functional activities at the D3 and D2 receptors. Docking studies and results from evaluations against a set of chimeric and mutant receptors suggest that interactions at the extracellular end of TM7 contribute to the D3R versus D2R selectivity of these ligands. Molecular insights from this study could potentially enable rational design of potent and selective D3R ligands.

Studies of the Biogenic Amine Transporters. 15. Identification of Novel Allosteric Dopamine Transporter Ligands with Nanomolar Potency

Novel allosteric modulators of the dopamine transporter (DAT) have been identified. We have shown previously that SRI-9804 [N-(diphenylmethyl)-2-phenyl-4-quinazolinamine], SRI-20040 [N-(2,2-diphenylethyl)-2-phenyl-4-quinazolinamine], and SRI-20041 [N-(3,3-diphenylpropyl)-2-phenyl-4-quinazolinamine] partially inhibit [125I]RTI-55 ([125I]3β-(4′-iodophenyl)tropan-2β-carboxylic acid methyl ester) binding and [3H]dopamine ([3H]DA) uptake, slow the dissociation rate of [125I]RTI-55 from the DAT, and allosterically modulate d-amphetamine–induced, DAT-mediated DA release. We synthesized and evaluated the activity of >500 analogs of these ligands and report here on 36 selected compounds. Using synaptosomes prepared from rat caudate, we conducted [3H]DA uptake inhibition assays, DAT binding assays with [3H]WIN35428 ([3H]2β-carbomethoxy-3β-(4-fluorophenyl)tropane), and DAT-mediated release assays with either [3H]MPP+ ([3H]1-methyl-4-phenylpyridinium) or [3H]DA. We observed three groups of [3H]DA uptake inhibitors: 1) full-efficacy agents with a one-site fit, 2) full-efficacy agents with a two-site fit, and 3) partial-efficacy agents with a one-site fit—the focus of further studies. These agents partially inhibited DA, serotonin, and norepinephrine uptake, yet were much less potent at inhibiting [3H]WIN35428 binding to the DAT. For example, SRI-29574 [N-(2,2-diphenylethyl)-2-(imidazo[1,2-a]pyridin-6-yl)quinazolin-4-amine] partially inhibited DAT uptake, with an IC50 = 2.3 ± 0.4 nM, without affecting binding to the DAT. These agents did not alter DAT-mediated release of [3H]MPP+ in the absence or presence of 100 nM d-amphetamine. SRI-29574 had no significant effect on the d-amphetamine EC50 or Emax value for DAT-mediated release of [3H]MPP+. These studies demonstrate the existence of potent DAT ligands that partially block [3H]DA uptake, without affecting DAT binding or d-amphetamine–induced [3H]MPP+ release. These compounds may prove to be useful probes of biogenic amine transporter function as well as novel therapeutics.

Identification of a novel partial inhibitor of dopamine transporter among 4-substituted 2-phenylquinazolines

In an attempt to identify novel ligands for the dopamine transporter, a series of 4-substituted-2-phenylquinazolines were synthesized and evaluated. Among the compounds studied, 4-[(diphenylmethyl)amino]-2-phenylquinazoline (4 g) was identified as a novel partial inhibitor of [(125)I]RTI-55 binding to the dopamine transporter and a partial inhibitor of [(3)H]dopamine uptake.

Design, parallel synthesis, and crystal structures of biphenyl antithrombotics as selective inhibitors of tissue factor FVIIa complex. Part 1: Exploration of S2 pocket pharmacophores

Factor VIIa (FVIIa), a serine protease enzyme, coupled with tissue factor (TF) plays an important role in a number of thrombosis-related disorders. Inhibition of TF x FVIIa occurs early in the coagulation cascade and might provide some safety advantages over other related enzymes. We report here a novel series of substituted biphenyl derivatives that are highly potent and selective TF x FVIIa inhibitors. Parallel synthesis coupled with structure-based drug design allowed us to explore the S2 pocket of the enzyme active site. A number of compounds with IC(50) value of <10 nM were synthesized. The X-ray crystal structures of some of these compounds complexed with TF x FVIIa were determined and results were applied to design the next round of inhibitors. All the potent inhibitors were tested for inhibition against a panel of related enzymes and selectivity of 17,600 over thrombin, 450 over trypsin, 685 over FXa, and 76 over plasmin was achieved. Two groups, vinyl 36b and 2-furan 36ab, were identified as the optimum binding substituents on the phenyl ring in the S2 pocket. Compounds with these two substituents are the most potent compounds in this series with good selectivity over related serine proteases. These compounds will be further explored for structure-activity relationship.

Identification of quinazoline compounds as novel potent inhibitors of Wnt/β-catenin signaling in colorectal cancer cells.

The Wnt/β-catenin signaling pathway is critical for the initiation and progression of most colon cancers, and has emerged as one of the most promising targets for colorectal cancer chemoprevention and treatment. In this study, we have discovered a structurally related series of quinazolines as potent inhibitors of Wnt/β-catenin signaling in colorectal cancer cells harboring mutations in CTNNB1 or APC. We showed that the quinazoline leads suppressed Wnt/β-catenin signaling without altering the level of β-catenin protein in colorectal cancer cells, suggesting that they act on the downstream elements of the pathway. Moreover, the quinazoline leads displayed potent anticancer activities with IC50 values between 4.9 and 17.4 μM in colorectal cancer cells. Importantly, we also found that a structurally related quinazoline lacking inhibitory effect on Wnt/β-catenin signaling was unable to suppress colorectal cancer cell proliferation. Together, these results suggest that the quinazoline lead compounds identified in this study have therapeutic potential for the prevention and treatment of colorectal cancer.

Interactions Between Cocaine and the Putative Allosteric Dopamine Transporter Ligand SRI-31142

Drugs that inhibit the dopamine (DA) transporter (DAT) include both therapeutic agents and abused drugs. Recent studies identified a novel series of putative allosteric DAT inhibitors, but the in vivo effects of these compounds are unknown. This study examined the abuse-related behavioral and neurochemical effects produced in rats by SRI-31142 [2-(7-methylimidazo[1,2-a]pyridin-6-yl)-N-(2-phenyl-2-(pyridin-4-yl)ethyl)quinazolin-4-amine], one compound from this series. In behavioral studies, intracranial self-stimulation (ICSS) was used to compare the effects produced by SRI-31142, the abused and nonselective DAT inhibitor cocaine, and the selective DAT inhibitor GBR-12935 [1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine]. In neurochemical studies, in vivo microdialysis was used to compare the effects of SRI-31142 and cocaine on levels of DA and serotonin in nucleus accumbens (NAc). The effects of SRI-31142 in combination with cocaine were also examined in both procedures. In contrast to cocaine and GBR-12935, SRI-31142 failed to produce abuse-related increases in ICSS or NAc DA; instead, SRI-31142 only decreased ICSS and NAc DA at a dose that was also sufficient to block cocaine-induced increases in ICSS and NAc DA. Pharmacokinetic studies suggested low but adequate brain penetration of SRI-31142, in vitro binding studies failed to identify likely non-DAT targets, and in vitro functional assays failed to confirm DA uptake inhibition in an assay of DAT-mediated fluorescent signals in live cells. These results indicate that SRI-31142 does not produce cocaine-like abuse-related effects in rats. SRI-31142 may have utility to block cocaine effects and may warrant further study as a candidate pharmacotherapy; however, the role of DAT in mediating these effects is unclear, and side effects may be a limiting factor.