Philip S. Portoghese

Binaltorphimine and nor-binaltorphimine, potent and selective k-opioid receptor antagonists

The opioid antagonist activities of two bivalent ligands, BNI and nor-BNI, have been evaluated in smooth muscle preparations and in mice. Both ligands are highly potent and selective as kappa opioid receptor antagonists, with relatively feeble blocking activity at mu and delta opioid receptors. BNI and nor-BNI represent the first highly selective kappa opioid receptor antagonists and should be of great utility as molecular probes for identifying the interaction of agonist ligands with kappa opioid receptors in vitro and in vivo.

Morphine promotes the growth of HIV-1 in human peripheral blood mononuclear cell cocultures.

Because morphine has been shown to alter the function of human T lymphocytes and monocytes, we postulated that morphine would promote the growth of HIV-1 in these cells. To test this hypothesis, a coculture assay was used consisting of phytohemagglutinin (PHA)-activated peripheral blood mononuclear cells (PBMC) from normal donors and PBMC which had been infected with a viral isolate from an asymptomatic patient, HIV-1AT. The growth of HIV-1AT, as reflected by the concentration of p24 antigen in coculture supernatants, was markedly increased in cocultures that contained morphine. A bell-shaped dose-response curve was observed with three- to fourfold increased growth at a morphine concentration of 10(-12) M. Augmentation of HIV-1AT growth by morphine required an interaction with the PHA-activated donor PBMC. Furthermore, potentiation of HIV-1AT growth by morphine was stereospecific and was antagonized by naloxone and beta-funaltrexamine indicating involvement of an opiate receptor mechanism. These findings provide an additional explanation of how opiates could act as a cofactor in the pathogenesis of HIV-1 in intravenous drug users.

The irreversible narcotic antagonistic and reversible agonistic properties of the fumaramate methyl ester derivative of naltrexone

The fumaramate methyl ester derivatives of naltrexone (beta-FNA) and oxymorphone (beta-FOA) were both found to be reversible agonists on the guinea pig ileal longitudinal muscle preparation. In addition, beta-FNA possessed on irreversible antagonistic effect against morphine whereas beta-FOA had no such capacity. Analysis by pA2 values revealed that beta-FOA resembled pure agonists like morphine and enkephalin while beta-FNA resembled the mixed agonist-antagonists like nalorphine and pentazocine. The antagonism by beta-FNA was very selective in that it antagonized pure agonists but had little or no effect on the effects of either mixed agonist-antagonists, ethylketocyclazocine or other non-opiate-type agonists like norepinephrine.

Effects of κ-opioid receptor ligands on intracranial self-stimulation in rats

RationaleElevations in cAMP response element binding protein (CREB) function within the mesolimbic system of rats reduce cocaine reward in place conditioning studies and increase immobility in the forced swim test. Each of these behavioral adaptations can be interpreted as a depressive-like effect (i.e., anhedonia, despair) that may reflect reduced activity of brain reward systems. Furthermore, each effect appears due to increases in CREB-mediated expression of dynorphin, since each is attenuated by intracranial injections of the κ-opioid receptor antagonist norBNI.ObjectivesIntracranial self-stimulation (ICSS) studies were conducted in rats to determine whether administration of a κ-agonist would have depressive-like effects on brain stimulation reward, and whether pretreatment with a κ-antagonist would attenuate any such effects. Conditions that have depressive effects in people (e.g., drug withdrawal) increase the threshold amounts of stimulation required to sustain ICSS in rats.MethodsSprague-Dawley rats with lateral hypothalamic stimulating electrodes were tested in a “curve-shift” variant of the ICSS procedure after systemic administration of the κ-agonist U-69593 alone, the novel κ-antagonist 5′-acetamidinoethylnaltrindole (ANTI) alone, or co-administration of both drugs.ResultsU-69593 dose dependently increased ICSS thresholds, suggesting that activation of κ-receptors reduced the rewarding impact of the brain stimulation. ANTI had no effects on its own, but it attenuated increases in ICSS thresholds caused by the agonist.ConclusionsThese data provide further evidence that stimulation of brain κ-receptors may trigger certain depressive-like signs, and that κ antagonists may have efficacy as antidepressants without having reward-related actions of their own.

Bivalent ligands and the message-address concept in the design of selective opioid receptor antagonists.

Metabolically stable receptor antagonists that are subtype selective are indispensable pharmacological tools. In this article, Philip Portoghese describes the bivalent ligand approach to drug design which has resulted in the development of several highly selective non-peptide opioid receptor antagonists, such as the kappa-selective norbinaltorphimine and the delta-selective naltrindole. Models used resemble Schwyzers message-address concept which originally described the recognition elements of peptide hormones; their success augurs well for the possibility of altering antagonist selectivity in a predictable fashion by simulating a portion of the address peptide component with a rigid nonpeptide moiety.

A highly selective δ1-opioid receptor antagonist: 7-benzylidenenaltrexone

In guinea pig brain membranes 7-benzylideneraltrexone (BNTX) possesses 100-fold greater affinity (Ki = 0.1 nM) for [3H]DPDPE [3H][D-Pen2,D-Pen5]enkephalin) binding sites (δin1) relative to those of [3H]DSLET ([3H][D-Ser2, Leu5] enkephalin-Thr6) (δ2). The ED50 dose ratio (tail flick) in mice for the antagonism of DPDPE-induced antinociception of BNTX (6.3 pmol i.c.v.) was 7.2, whereas for DSLET, morphine and U69593 it was not significantly different from unity. The fact that there was no correlation of the binding or in vivo data for BNTX with antagonist potency in smooth muscle preparations suggest that the in vitro pharmacologic activity is mediated by δ-opioid subtypes that are different from those in the brain.

Opioid receptor-mediated inhibition of dopamine and acetylcholine release from slices of rat nucleus accumbens, olfactory tubercle and frontal cortex

The modulation of the electrically evoked release of [3H]dopamine (DA) and [14C]acetylcholine (ACh) by opioid receptor activation was examined in superfused slices from rat nucleus accumbens, olfactory tubercle, and frontal cortex. In all brain areas examined, [3H]DA release was inhibited by the kappa agonist, U 50,488 (1-100 nM), and this inhibition was fully antagonized by the selective kappa antagonist, norbinaltorphimine (nor-BNI). In the frontal cortex, the mu agonist, [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO, 0.01-1 microM), also inhibited the evoked release of tritium. However, further experiments (including the use of the D2-receptor agonist, LY 171555, and the alpha 2-adrenoceptor agonist, oxymetazoline) suggest strongly that in the frontal cortex DAGO only inhibits the release of [3H]catecholamine from noradrenergic nerve terminals, despite the use of desimipramine to prevent the uptake of [3H]DA into these terminals. [14C]ACh release from both the nucleus accumbens and olfactory tubercle, but not from the frontal cortex, was inhibited by DAGO (0.01-1 microM) and the delta agonist, [D-Pen2,D-Pen5]enkephalin (DPDPE, 0.01-1 microM). These inhibitory effects were antagonized by 0.1 microM naloxone but not by 3 nM nor-BNI. The irreversible delta ligand, fentanyl isothiocyanate (FIT, 1 microM), only antagonized the inhibition caused by DPDPE. The results indicate that the inhibitory effects of opioids on the in vitro release of DA from dopaminergic nerve fibres arising from the substantia nigra and the ventral tegmental area are mediated by presynaptic kappa receptors only. In those regions where ACh release is modulated by opioids, the type of opioid receptor involved may depend on the type of neuron, i.e. interneuron or afferent neuron.

The delta opioid receptor antagonist naltrindole attenuates both alcohol and saccharin intake in rats selectively bred for alcohol preference

This study demonstrates that the selective delta receptor antagonists ICI 174864 and naltrindole (NTI) attenuate alcohol intake in a dose-dependent manner, without altering water intake, in rats selectively bred for alcohol preference. ICI 174864 had a very limited duration of action, as evidenced by the fact that suppression of alcohol intake lasted for only an hour following ICI 174864 administration. NTI, when administered in a dose of 10 mg/kg, suppressed alcohol intake by 28%. Increasing the dose of NTI to 15 mg/kg produced a 44% suppression of alcohol intake, but a further increase to 20 mg/kg did not produce greater suppression than was seen with a dose of 15 mg/kg (46% versus 44%, respectively). This suggests that NTI is maximally effective in suppressing alcohol intake at a dose of 15.0 mg/kg. NTI displayed a long duration of action, as evidenced by attenuation of alcohol drinking that lasted for at least 8 h following drug treatment. Administering the maximally effective dose of NTI (15 mg/kg) in two parts, separated by 4 h, served to prolong the duration of action of NTI and produced an attenuation of alcohol intake, but not water intake, that lasted for at least 28 h. The effect of NTI on alcohol intake was not specific for alcohol, as evidenced by the fact that NTI reduced the intake of saccharin solutions with and without alcohol.

The delta2-opioid receptor antagonist naltriben selectively attenuates alcohol intake in rats bred for alcohol preference

The relative importance of different opioid receptor types in mediating alcohol drinking behavior compared with the intake of other ingesta can be determined by characterizing the effects of selective opioid antagonists on the intake of various ingesta. Nonselective opioid receptor antagonists suppress the intake of many ingesta including alcohol, food, water, and sweets. Two distinct subtypes of delta-opioid receptors, delta 1 and delta 2, have recently been identified in rodent brain. We have previously reported that naltrindole (NTI), which blocks both delta 1 and delta 2 receptors, suppresses both alcohol and saccharin intake in rats selectively bred for high alcohol preference (P line). We now report that naltriben (NTB), an opioid antagonist that is selective for delta 2-opioid receptors, suppresses alcohol intake in rats of the P line and the effect appears to be both specific for alcohol and independent of alcohol palatability. NTB may reduce alcohol intake by attenuating the reinforcing pharmacological properties of alcohol.

Effect of Mu opioid receptor blockade on alcohol intake in rats bred for high alcohol drinking

Beta-funaltrexamine (beta-FNA), a selective mu opioid receptor antagonist, when administered in doses of 10.0, 15.0, and 20.0 mg/kg b.wt., decreased alcohol but not water intake in a dose-dependent manner in rats selectively bred for high alcohol intake (HAD line). Beta-FNA also suppressed the intake of a saccharin solution containing alcohol without altering the intake of a similar solution without alcohol. The results suggest that beta-FNA may prove useful as a pharmacotherapeutic agent for the treatment of alcohol dependence. In a second study, pituitary beta-endorphin gene expression (proopiomelanocortin or POMC messenger ribonucleic acid-mRNA) was compared in another pair of rat lines selectively bred for high or low alcohol intake (alcohol-preferring or P and alcohol-nonpreferring or NP lines). A repeated alcohol challenge (1.0 g/kg b.wt./day, IP for 4 days) produced a greater increase in POMC mRNA in the anterior and neurointermediate lobes of the pituitary of P rats compared with NP rats. The results suggest that a genetic predisposition toward high alcohol drinking may be associated with increased responsiveness of the opioid system to alcohol.