Structure-activity relationships of bifunctional peptides based on overlapping pharmacophores at opioid and cholecystokinin receptors

Multitarget ligands that comprise opioid/nonopioid pharmacophores for pain management: Current state of the science

Chronic pain, which affects more than one-third of the world's population, represents one of the greatest medical challenges of the 21st century, yet its effective management remains sub-optimal. The 'gold standard' for the treatment of moderate to severe pain consists of opioid ligands, such as morphine and fentanyl, that target the µ-opioid receptor (MOP). Paradoxically, these opioids also cause serious side effects, including constipation, respiratory depression, tolerance, and addiction. In addition, the development of opioid-use disorders, such as opioid diversion, misuse, and abuse, has led to the current opioid crisis, with dramatic increases in addiction, overdoses, and ultimately deaths. As pain is a complex, multidimensional experience involving a variety of pathways and mediators, dual or multitarget ligands that can bind to more than one receptor and exert complementary analgesic effects, represent a promising avenue for pain relief. Indeed, unlike monomodal therapeutic approaches, the modulation of several endogenous nociceptive systems can often result in an additive or even synergistic effect, thereby improving the analgesic-to-side-effect ratio. Here, we provide a comprehensive overview of research efforts towards the development of dual- or multi-targeting opioid/nonopioid hybrid ligands for effective and safer pain management. We reflect on the underpinning discovery rationale by discussing the design, medicinal chemistry, and in vivo pharmacological effects of multitarget antinociceptive compounds.

BNT12, a novel hybrid peptide of opioid and neurotensin pharmacophores, produces potent central antinociception with limited side effects

The development of multitarget opioid drugs has emerged as an attractive approach for innovative pain management with reduced side effects. In the present study, a novel hybrid peptide BNT12 containing the opioid and neurotensin (NT)-like fragments was synthesized and pharmacologically characterized. In acute radiant heat paw withdrawal test, intracerebroventricular (i.c.v.) administration of BNT12 produced potent antinociception in mice. The central antinociceptive activity of BNT12 was mainly mediated by μ-, δ-opioid receptor, neurotensin receptor type 1 (NTSR1) and 2 (NTSR2), supporting a multifunctional agonism of BNT12 in the functional assays. BNT12 also exhibited significant antinociceptive effects in spared nerve injury (SNI)-neuropathic pain, complete Freund's adjuvant (CFA)-induced inflammatory pain, acetic acid-induced visceral and formalin-induced pain after i.c.v. administration. Furthermore, BNT12 exhibited substantial reduction of acute antinociceptive tolerance, shifted the dose-response curve to the right by only 1.3-fold. It is noteworthy that BNT12 showed insignificant chronic antinociceptive tolerance at the supraspinal level. In addition, BNT12 exhibited reduced or no opioid-like side effects on conditioned place preference (CPP) response, naloxone-precipitated withdrawal response, acute hyperlocomotion, motor coordination, gastrointestinal transit, and cardiovascular responses. The present investigation demonstrated that the novel hybrid peptide BNT12 might serve as a promising analgesic candidate with limited opioid-like side effects.

Development of Highly Potent Clinical Candidates for Theranostic Applications against Cholecystokinin-2 Receptor Positive Cancers

Peptide receptor radionuclide therapy (PRRT) is a promising form of systemic radiation therapy designed to eradicate cancer. Cholecystokinin-2 receptor (CCK2R) is an important molecular target that is highly expressed in a range of cancers. This study describes the synthesis and in vivo characterization of a novel series of 177Lu-labeled peptides ([177Lu]Lu-2b-4b) in comparison with the reference CCK2R-targeting peptide CP04 ([177Lu]Lu-1b). [177Lu]Lu-1b-4b showed high chemical purity (HPLC ≥ 94%), low Log D7.4 (-4.09 to -4.55) with strong binding affinity to CCK2R (KD 0.097-1.61 nM), and relatively high protein binding (55.6-80.2%) and internalization (40-67%). Biodistribution studies of the novel 177Lu-labeled peptides in tumors (AR42J and A431-CCK2R) showed uptake one- to eight-fold greater than the reference compound CP04 at 1, 24, and 48 h. Rapid clearance and high tumor uptake and retention were established for [177Lu]Lu-2b-4b, making these compounds excellent candidates for theranostic applications against CCK2R-expressing tumors.

Fentanyl Structure as a Scaffold for Opioid/Non-Opioid Multitarget Analgesics

One of the strategies in the search for safe and effective analgesic drugs is the design of multitarget analgesics. Such compounds are intended to have high affinity and activity at more than one molecular target involved in pain modulation. In the present contribution we summarize the attempts in which fentanyl or its substructures were used as a μ-opioid receptor pharmacophoric fragment and a scaffold to which fragments related to non-opioid receptors were attached. The non-opioid ‘second’ targets included proteins as diverse as imidazoline I₂ binding sites, CB₁ cannabinoid receptor, NK₁ tachykinin receptor, D₂ dopamine receptor, cyclooxygenases, fatty acid amide hydrolase and monoacylglycerol lipase and σ₁ receptor. Reviewing the individual attempts, we outline the chemistry, the obtained pharmacological properties and structure-activity relationships. Finally, we discuss the possible directions for future work.

Single-chain Fragment variable antibody targeting cholecystokinin-B receptor for pain reduction

The cholecystokinin B receptor and its neuropeptide ligand are upregulated in chronic neuropathic pain models. Single-chain Fragment variable antibodies were generated as preferred non-opioid targeting therapy blocking the cholecystokinin B receptor to inhibit chronic neuropathic pain models in vivo and in vitro. Engineered antibodies of this type feature binding activity similar to monoclonal antibodies but with stronger affinity and increased tissue penetrability due to their smaller size. More importantly, single-chain Fragment variable antibodies have promising biotherapeutic applications for both nervous and immune systems, now recognized as interactive in chronic pain. A mouse single-chain Fragment variable antibody library recognizing a fifteen amino acid extracellular peptide fragment of the cholecystokinin B receptor was generated from immunized spleens. Ribosome display, a powerful cell-free technology, was applied for recombinant antibody selection. Antibodies with higher affinity, stability, solubility, and binding specificity for cholecystokinin B not A receptor were selected and optimized for in vivo and in vitro efficacy. A single dose of the lead candidate reduced mechanical and cold hypersensitivity in two rodent models of neuropathic pain for at least seven weeks. Continuing efficacy was evident with either intraperitoneal or intranasal dosing. Likewise, the lead single-chain Fragment variable antibody totally prevented development of anxiety- and depression-like behaviors and cognitive deficits typical in the models. Reduction of neuronal firing frequency was evident in trigeminal ganglia primary neuronal cultures treated in vitro with the cholecystokinin B receptor antibody. Immunofluorescent staining intensity in the trigeminal neuron primary cultures was significantly reduced incrementally after overnight binding with increasingly higher dilutions of the single-chain Fragment variable antibody. While it is reported that single-chain Fragment variable antibodies are removed systemically within 2-6 h, Western blot evidence indicates the His-tag marker remained after 7 weeks in the trigeminal ganglia and in the dorsolateral medulla, providing evidence of brain and ganglia penetrance known to be compromised in overactivated states. This project showcases the in vivo efficacy of our lead single-chain Fragment variable antibody indicating its potential for development as a non-opioid, non-addictive therapeutic intervention for chronic pain. Importantly, studies by others have indicated treatments with cholecystokinin B receptor antagonists suppress maintenance and reactivation of morphine dependence in place preference tests while lowering tolerance and dose requirements. Our future studies remain to address these potential benefits that may accompany the cholecystokinin B receptor biological therapy. Both chronic sciatic and orofacial pain can be unrelenting and excruciating, reducing quality of life as well as diminishing physical and mental function. An effective non-opiate, non-addictive therapy with potential to significantly reduce chronic neuropathic pain long term is greatly needed.

Multifunctional Opioid-Derived Hybrids in Neuropathic Pain: Preclinical Evidence, Ideas and Challenges

When the first- and second-line therapeutics used to treat neuropathic pain (NP) fail to induce efficient analgesia—which is estimated to relate to more than half of the patients—opioid drugs are prescribed. Still, the pathological changes following the nerve tissue injury, i.a. pronociceptive neuropeptide systems activation, oppose the analgesic effects of opiates, enforcing the use of relatively high therapeutic doses in order to obtain satisfying pain relief. In parallel, the repeated use of opioid agonists is associated with burdensome adverse effects due to compensatory mechanisms that arise thereafter. Rational design of hybrid drugs, in which opioid ligands are combined with other pharmacophores that block the antiopioid action of pronociceptive systems, delivers the opportunity to ameliorate the NP-oriented opioid treatment via addressing neuropathological mechanisms shared both by NP and repeated exposition to opioids. Therewith, the new dually acting drugs, tailored for the specificity of NP, can gain in efficacy under nerve injury conditions and have an improved safety profile as compared to selective opioid agonists. The current review presents the latest ideas on opioid-comprising hybrid drugs designed to treat painful neuropathy, with focus on their biological action, as well as limitations and challenges related to this therapeutic approach.

In Vivo, In Vitro and In Silico Studies of the Hybrid Compound AA3266, an Opioid Agonist/NK1R Antagonist with Selective Cytotoxicity

AA3266 is a hybrid compound consisting of opioid receptor agonist and neurokinin-1 receptor (NK1R) antagonist pharmacophores. It was designed with the desire to have an analgesic molecule with improved properties and auxiliary anticancer activity. Previously, the compound was found to exhibit high affinity for μ- and δ-opioid receptors, while moderate binding to NK1R. In the presented contribution, we report on a deeper investigation of this hybrid. In vivo, we have established that AA3266 has potent antinociceptive activity in acute pain model, comparable to that of morphine. Desirably, with prolonged administration, our hybrid induces less tolerance than morphine does. AA3266, contrary to morphine, does not cause development of constipation, which is one of the main undesirable effects of opioid use. In vitro, we have confirmed relatively strong cytotoxic activity on a few selected cancer cell lines, similar to or greater than that of a reference NK1R antagonist, aprepitant. Importantly, our compound affects normal cells to smaller extent what makes our compound more selective against cancer cells. In silico methods, including molecular docking, molecular dynamics simulations and fragment molecular orbital calculations, have been used to investigate the interactions of AA3266 with MOR and NK1R. Insights from these will guide structural optimization of opioid/antitachykinin hybrid compounds.

Multivalent peptide and peptidomimetic ligands for the treatment of pain without toxicities and addiction

The current opioid crisis has created a tragic problem in medicine and society. Pain is the most ubiquitous and costly disease in society and yet all of our "treatments" have toxicities, especially for prolonged use. However, there are several alternatives that have been discovered in the past fifteen years that have been demonstrated in animals to have none of the toxicities of current drugs. Many of the compounds are multivalent and have novel biological activity profiles. Unfortunately, none of these have been in clinical trials in humans, perhaps because they were discovered in academic laboratories. A review of these novel chemicals are given in this paper.

Site-specific stabilization of minigastrin analogs against enzymatic degradation for enhanced cholecystokinin-2 receptor targeting

Minigastrin (MG) analogs show high affinity to the cholecystokinin-2 receptor (CCK2R) and have therefore been intensively studied to find a suitable analog for imaging and treatment of CCK2R-expressing tumors. The clinical translation of the radioligands developed thus far has been hampered by high kidney uptake or low enzymatic stability. In this study, we aimed to develop new MG analogs with improved targeting properties stabilized against degradation through site-specific amino acid modifications.

Method: Based on the lead structure of a truncated MG analog, four new MG derivatives with substitutions in the C-terminal part of the peptide (Trp-Met-Asp-Phe-NH₂) were synthesized and derivatized with DOTA at the N-terminus for radiolabeling with trivalent radiometals. The in vitro properties of the new analogs were characterized by analyzing the lipophilicity, the protein binding, and the stability of the Indium-111 (¹¹¹In)-labeled analogs in different media. Two different cell lines, AR42J cells physiologically expressing the rat CCK2R and A431 cells transfected with human CCK2R (A431-CCK2R), were used to study the receptor affinity and cell uptake. For the two most promising MG analogs, metabolic studies in normal BALB/c mice were carried out as well as biodistribution and imaging studies in tumor xenografted athymic BALB/c nude mice.

Results: Two out of four synthesized peptide analogs (DOTA-MGS1 and DOTA-MGS4) showed retained receptor affinity and cell uptake when radiolabeled with ¹¹¹In. These two peptide analogs, however, showed a different stability against enzymatic degradation in vitro and in vivo. When injected to normal BALB/c mice, for ¹¹¹In-DOTA-MGS1 at 10 min post injection (p.i.) no intact radiopeptide was found in the blood, whereas for ¹¹¹In-DOTA-MGS4 more than 75% was still intact. ¹¹¹In-DOTA-MGS4 showed a clear increase in injected activity per gram tissue (IA/g) for A431-CCK2R xenografts (10.40±2.21% IA/g 4 h p.i.) when compared to ¹¹¹In-DOTA-MGS1 (1.23±0.15% IA/g 4 h p.i.). The tumor uptake of ¹¹¹In-DOTA-MGS4 was also combined with a low uptake in stomach and kidney leading to high-contrast NanoSPECT/CT images.

Conclusion: Of the four new MG analogs developed, the best results in terms of enzymatic stability and increased tumor targeting were obtained with ¹¹¹In-DOTA-MGS4 showing two substitutions with N-methylated amino acids. ¹¹¹In-DOTA-MGS4 was also superior to other MG analogs reported thus far and seems therefore an extremely promising targeting molecule for theranostic use with alternative radiometals.

Impact of G protein-coupled receptor heteromers in endocrine systems

The fine-tuning of endocrine homeostasis is regulated by dynamic receptor mediated processes. The superfamily of G protein-coupled receptors (GPCRs) have diverse roles in the modulation of all endocrine axes, thus understanding the mechanisms underpinning their functionality is paramount for treatment of endocrinopathies. Evidence over the last 20 years has highlighted homo and heteromerization as a key mode of mediating GPCR functional diversity. This review will discuss the concept of GPCR heteromerization and its relevance to endocrine function, detailing in vitro and in vivo evidence, and exploring current and potential pharmacological strategies for specific targeting of GPCR heteromers in endocrine heath and disease.

Novel Molecular Strategies and Targets for Opioid Drug Discovery for the Treatment of Chronic Pain

Opioid drugs like morphine and fentanyl are the gold standard for treating moderate to severe acute and chronic pain. However, opioid drug use can be limited by serious side effects, including constipation, tolerance, respiratory suppression, and addiction. For more than 100 years, we have tried to develop opioids that decrease or eliminate these liabilities, with little success. Recent advances in understanding opioid receptor signal transduction have suggested new possibilities to activate the opioid receptors to cause analgesia, while reducing or eliminating unwanted side effects. These new approaches include designing functionally selective ligands, which activate desired signaling cascades while avoiding signaling cascades that are thought to provoke side effects. It may also be possible to directly modulate downstream signaling through the use of selective activators and inhibitors. Separate from downstream signal transduction, it has also been found that when the opioid system is stimulated, various negative feedback systems are upregulated to compensate, which can drive side effects. This has led to the development of multi-functional molecules that simultaneously activate the opioid receptor while blocking various negative feedback receptor systems including cholecystokinin and neurokinin-1. Other novel approaches include targeting heterodimers of the opioid and other receptor systems which may drive side effects, and making endogenous opioid peptides druggable, which may also reduce opioid mediated side effects. Taken together, these advances in our molecular understanding provide a path forward to break the barrier in producing an opioid with reduced or eliminated side effects, especially addiction, which may provide relief for millions of patients.

Single dose intravenous paracetamol or intravenous propacetamol for postoperative pain

BACKGROUND

This is an updated version of the original Cochrane review published in Issue 10, 2011. Paracetamol (acetaminophen) is the most commonly prescribed analgesic for the treatment of acute pain. It may be administered orally, rectally, or intravenously. The efficacy and safety of intravenous (IV) formulations of paracetamol, IV paracetamol, and IV propacetamol (a prodrug that is metabolized to paracetamol), compared with placebo and other analgesics, is unclear.

OBJECTIVES

To assess the efficacy and safety of IV formulations of paracetamol for the treatment of postoperative pain in both adults and children.

SEARCH METHODS

We ran the search for the previous review in May 2010. For this update, we searched the Cochrane Central Register of Controlled Trials (CENTRAL 2016, Issue 1), MEDLINE (May 2010 to 16 February 2016), EMBASE (May 2010 to 16 February 2016), LILACS (2010 to 2016), a clinical trials registry, and reference lists of reviews for randomized controlled trials (RCTs) in any language and we retrieved articles.

SELECTION CRITERIA

Randomized, double-blind, placebo- or active-controlled single dose clinical trials of IV paracetamol or IV propacetamol for acute postoperative pain in adults or children.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data, which included demographic variables, type of surgery, interventions, efficacy, and adverse events. We contacted study authors for additional information. We graded each included study for methodological quality by assessing risk of bias and employed the GRADE approach to assess the overall quality of the evidence.

MAIN RESULTS

We included 75 studies (36 from the original review and 39 from our updated review) enrolling a total of 7200 participants.Among primary outcomes, 36% of participants receiving IV paracetamol/propacetamol experienced at least 50% pain relief over four hours compared with 16% of those receiving placebo (number needed to treat to benefit (NNT) = 5; 95% confidence interval (CI) 3.7 to 5.6, high quality evidence). The proportion of participants in IV paracetamol/propacetamol groups experiencing at least 50% pain relief diminished over six hours, as reflected in a higher NNT of 6 (4.6 to 7.1, moderate quality evidence). Mean pain intensity at four hours was similar when comparing IV paracetamol and placebo, but was seven points lower on a 0 to 100 visual analog scale (0 = no pain, 100 = worst pain imaginable, 95% CI -9 to -6, low quality evidence) in those receiving paracetamol at six hours.For secondary outcomes, participants receiving IV paracetamol/propacetamol required 26% less opioid over four hours and 16% less over six hours (moderate quality evidence) than those receiving placebo. However, this did not translate to a clinically meaningful reduction in opioid-induced adverse events.Meta-analysis of efficacy comparisons between IV paracetamol/propacetamol and active comparators (e.g., opioids or nonsteroidal anti-inflammatory drugs) were either not statistically significant, not clinically significant, or both.Adverse events occurred at similar rates with IV paracetamol or IV propacetamol and placebo. However, pain on infusion occurred more frequently in those receiving IV propacetamol versus placebo (23% versus 1%). Meta-analysis did not demonstrate clinically meaningful differences between IV paracetamol/propacetamol and active comparators for any adverse event.

AUTHORS' CONCLUSIONS

Since the last version of this review, we have found 39 new studies providing additional information. Most included studies evaluated adults only. We reanalyzed the data but the results did not substantially alter any of our previously published conclusions. This review provides high quality evidence that a single dose of either IV paracetamol or IV propacetamol provides around four hours of effective analgesia for about 36% of patients with acute postoperative pain. Low to very low quality evidence demonstrates that both formulations are associated with few adverse events, although patients receiving IV propacetamol have a higher incidence of pain on infusion than both placebo and IV paracetamol.

Design, synthesis and biological evaluation of multifunctional ligands targeting opioid and bradykinin 2 receptors

We report here the design and synthesis of novel multifunctional ligands that act as (μ/δ) opioid agonists and bradykinin 2 receptor antagonists. These multifunctional ligands were designed to interact with the multiple receptors to show an enhanced analgesic effect, with no opioid-induced tolerance. We designed our multifunctional ligands based on the well-known second generation bradykinin 2 receptor antagonist Hoe 140 (DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH) and the opioid enkephalin analogues Tyr-DAla-Phe, Tyr-DAla-Gly-Phe and Tyr-Pro-Phe. We explored the conjugation of opioid pharmacophore to the Hoe 140 (DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH) in various positions with and without a linker. These bifunctional ligands showed very good binding affinity towards the both μ and δ opioid receptors. Among these bifunctional ligands 8, 11 and 12 showed excellent and balanced binding affinity at both μ and δ opioid receptors (0.5 nM, 2.0 nM; 0.3 nM, 2 nM; 2 nM and 3 nM), respectively. On the other hand these bifunctional ligands showed very weak and no binding affinity for rat brain bradykinin 2 receptors. Similarly, the Hoe 140 showed very low affinity (>10,000 nM and 9,000 nM) against [(3)H] BK binding in rat brain membranes and in HEK293 cells, respectively. In contrast, the Hoe 140 showed very good binding affinity in guinea pig ileum (0.43 nM) similar to that of previously reported. The bradykinin 2 receptors are known to be present in rat brain membrane, guinea pig ileum (GPI) and rabbit jugular vein. Previously the binding affinity of Hoe 140 for bradykinin 2 receptor was reported using guinea pig ileum. The above results suggest that the bradykinin 2 receptors present in rat brain membrane are a different sub type than the bradykinin 2 receptor present in guinea pig ileum (GPI).

Investigational peptide and peptidomimetic μ and δ opioid receptor agonists in the relief of pain

INTRODUCTION

Current methods for treating prolonged and neuropathic pain are inadequate and lead to toxicities that greatly diminish quality of life. Therefore, new approaches to the treatment of pain states are needed to address these problems.

AREAS COVERED

The review primarily reviews approaches that have been taken in the peer-reviewed literature of multivalent ligands that interact with both μ and δ opioid receptors as agonists, and in some cases, also with pharmacophores for antagonist ligands that interact with other receptors as antagonists to block pain.

EXPERT OPINION

Although there are a number of drugs currently on the market for the treatment of pain; none of them are 100% successful. In the authors' opinion, it is clear that new directions and modalities are needed to better address the treatment of prolonged and neuropathic pain; one drug or class clearly is not the answer for all pain therapy. Undoubtedly, there are many different phenotypes of prolonged and neuropathic pain and this should be one avenue to further develop appropriate therapies.

Design of peptide and peptidomimetic ligands with novel pharmacological activity profiles

Peptide hormones and neurotransmitters are of central importance in most aspects of intercellular communication and are involved in virtually all degenerative diseases. In this review, we discuss physicochemical approaches to the design of novel peptide and peptidomimetic agonists, antagonists, inverse agonists, and related compounds that have unique biological activity profiles, reduced toxic side effects, and, if desired, the ability to cross the blood-brain barrier. Designing ligands for specific biological and medical needs is emphasized, as is the close collaboration of chemists and biologists to maximize the chances for success. Special emphasis is placed on the use of conformational (ϕ-ψ space) and topographical (χ space) considerations in design.

An optical probe for noninvasive molecular imaging of orthotopic brain tumors overexpressing epidermal growth factor receptor

We have developed a near-infrared (NIR) probe that targets cells overexpressing the EGF receptor (EGFR) for imaging glioblastoma brain tumors in live subjects. A peptide specific for the EGFR was modified with various lengths of monodiscrete polyethylene glycol (PEG) units and a NIR Cy5.5 fluorescence dye. The lead compound, compound 2, with one unit of PEG displayed good binding (8.9 μmol/L) and cellular uptake in glioblastoma cells overexpressing EGFR in vitro. The in vivo studies have shown that the probe was able to selectively label glioblastoma-derived orthotopic brain tumors. In vivo image analyses of peptide binding to the tumors using fluorescence-mediated molecular tomography revealed that the compound could distinguish between tumors expressing different levels of EGFR. The data presented here represent the first demonstration of differential quantitation of tumors expressing EGFR in live animals by a targeted NIR fluorescence probe using a molecular imaging device.

Conotoxin engineering: dual pharmacophoric noradrenaline transport inhibitor/integrin binding peptide with improved stability

A dual-pharmacophoric peptide was engineered by grafting the integrin binding RGD motif between the C- and N-termini of a disulfide-rich noradrenaline transporter inhibiting χ-conotoxin resulting in a stable backbone cyclized peptide. The construct maintained two independent biological activities and showed increased plasma stability with no adverse effects observed following administration to rats, highlighting the potential value of pharmacophore grafting into constrained peptide scaffolds.

A DFT and semiempirical model-based study of opioid receptor affinity and selectivity in a group of molecules with a morphine structural core

We report the results of a search for model-based relationships between mu, delta, and kappa opioid receptor binding affinity and molecular structure for a group of molecules having in common a morphine structural core. The wave functions and local reactivity indices were obtained at the ZINDO/1 and B3LYP/6-31G^∗∗ levels of theory for comparison. New developments in the expression for the drug-receptor interaction energy expression allowed several local atomic reactivity indices to be included, such as local electronic chemical potential, local hardness, and local electrophilicity. These indices, together with a new proposal for the ordering of the independent variables, were incorporated in the statistical study. We found and discussed several statistically significant relationships for mu, delta, and kappa opioid receptor binding affinity at both levels of theory. Some of the new local reactivity indices incorporated in the theory appear in several equations for the first time in the history of model-based equations. Interaction pharmacophores were generated for mu, delta, and kappa receptors. We discuss possible differences regulating binding and selectivity in opioid receptor subtypes. This study, contrarily to the statistically backed ones, is able to provide a microscopic insight of the mechanisms involved in the binding process.

Single dose intravenous propacetamol or intravenous paracetamol for postoperative pain

BACKGROUND

Paracetamol (acetaminophen) is the most commonly prescribed analgesic for the treatment of acute pain. It may be administered orally or intravenously. The efficacy and safety of intravenous (IV) formulations of paracetamol, IV paracetamol and IV propacetamol, compared with placebo and other analgesics, is unclear.

OBJECTIVES

To assess the efficacy and safety of IV formulations of paracetamol for treatment of postoperative pain in both adults and children.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 2), MEDLINE (1950 to May 2010), EMBASE (1980 to 2010, Week 18), LILACS (1992 to May 2010) and reference lists of retrieved articles.

SELECTION CRITERIA

Randomized, double-blind, placebo- or active-controlled single dose clinical trials of IV propacetamol or IV paracetamol for acute postoperative pain in adults or children.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the risk of bias and extracted data. We contacted study authors for additional information. We collected adverse event information from the studies.

MAIN RESULTS

Thirty-six studies (3896 participants) were included. Thirty-seven percent of participants receiving IV propacetamol/paracetamol experienced at least 50% pain relief over four hours compared with 16% of those receiving placebo (number needed to treat to benefit (NNT = 4.0; 95% confidence interval 3.5 to 4.8). The proportion of participants in IV propacetamol/paracetamol groups experiencing at least 50% pain relief diminished over six hours, as reflected in a higher NNT of 5.3 (4.2 to 6.7). Participants receiving IV propacetamol/paracetamol required 30% less opioid over four hours than those receiving placebo. However, this did not translate to a reduction in opioid-induced adverse events.Meta-analysis of efficacy comparisons between IV propacetamol/paracetamol and active comparators (opioids or nonsteroidal anti-inflammatories (NSAIDs)) were either not statistically significant, not clinically significant, or both.Adverse events occurred at similar rates with IV propacetamol or IV paracetamol and placebo. However, pain on infusion occurred more frequently in those receiving IV propacetamol versus placebo (23% versus 1%).Meta-analysis did not demonstrate statistically significant differences between IV propacetamol/paracetamol and active comparators for any adverse event except a reduction in the rate of hypotension versus NSAIDs and a reduction in the rate of gastrointestinal disorders versus opioids.

AUTHORS' CONCLUSIONS

A single dose of both IV propacetamol and IV paracetamol provides around four hours of effective analgesia for about 37% of patients with acute postoperative pain. Both formulations are associated with few adverse events, although patients receiving IV propacetamol have a higher incidence of pain on infusion than both placebo and IV paracetamol.

Twin and triplet drugs in opioid research

Twin and triplet drugs are defined as compounds that contain respectively two and three pharmacophore components exerting pharmacological effects in a molecule. The twin drug bearing the same pharmacophores is a "symmetrical twin drug", whereas that possessing different pharmacophores is a "nonsymmetrical twin drug." In general, the symmetrical twin drug is expected to produce more potent and/or selective pharmacological effects, whereas the nonsymmetrical twin drug is anticipated to show both pharmacological activities stemming from the individual pharmacophores (dual action). On the other hand, nonsymmetrical triplet drugs, which have two of the same pharmacophores and one different moiety, are expected to elicit both increased pharmacological action and dual action. The two identical portions could bind the same receptor sites simultaneously while the third portion could bind a different receptor site or enzyme. This review will mainly focus on the twin and triplet drugs with an evaluation of their in vivo pharmacological effects, and will also include a description of their pharmacology and synthesis.

Design and synthesis of trivalent ligands targeting opioid, cholecystokinin, and melanocortin receptors for the treatment of pain

It has been known that co-administration of morphine with either cholecystokinin (CCK) receptor or melanocortin (MC) receptor antagonists enhance morphine's analgesic efficacy by reducing serious side effects such as tolerance and addiction. Considering these synergistic effects, we have designed trivalent ligands in which all three different pharmacophores for opioid, CCK, and MC receptors are combined in such a way as to conserve their own topographical pharmacophore structures. These ligands, excluding the cyclic compound, were synthesized by solid phase synthesis using Rink-amide resin under microwave assistance in very high yields. These trivalent ligands bind to their respective receptors well demonstrating that the topographical pharmacophore structures for the three receptors were retained for receptor binding. Ligand 10 was a lead compound to show the best biological activities at all three receptors.

Modulation of cell surface expression of nonactivated cholecystokinin receptors using bivalent ligand-induced internalization

CCK(2) receptor antagonists potentiate pain relief by MOP receptor agonists. In an attempt to enhance this effect, we prepared bivalent ligands incorporating CCK(2) receptor antagonist and MOP receptor agonist pharmacophores. (9) Ligands with 16- to 22-atom spacers could simultaneously bind both receptors but provided no advantage in activity over individual ligands. We now examine the effect of these ligands on receptor internalization as a mechanism of receptor regulation. We prepared CHO cell lines expressing nonfluorescent halves (YN and YC) of yellow fluorescent protein attached to each receptor. Spatial approximation of constructs was needed to yield fluorescence. Monovalent MOP agonist 1 signaled normally and internalized the MOP receptor. Monovalent CCK(2) antagonist 2 did not stimulate receptor internalization. In the dual receptor-bearing cells, bivalent ligands 3a-c capable of simultaneously binding both receptors resulted in cell surface fluorescence and internalization of the fluorescent complex in a time- and temperature-dependent manner. Bivalent ligand 4 with spacer too short to occupy both receptors simultaneously yielded no signal. Receptor tethering with appropriate bivalent ligands can down-regulate signaling by moving a nonactivated receptor into the endocytic pathway.

The biological activity and metabolic stability of peptidic bifunctional compounds that are opioid receptor agonists and neurokinin-1 receptor antagonists with a cystine moiety

In order to improve metabolic stability, a ring structure with a cystine moiety was introduced into TY027 (Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-NH-[3',5'-(CF(3))(2)Bzl]), which is a lead compound of our developing bifunctional peptide possessing opioid agonist and NK1 antagonist activities. TY038 (Tyr-cyclo[D-Cys-Gly-Phe-Met-Pro-D-Cys]-Trp-NH-[3',5'-(CF(3))(2)Bzl]) was found as a highly selective delta opioid agonist over mu receptor in conventional tissue-based assays, together with an effective NK1 antagonist activity and good metabolic stability with more than 24h half life in rat plasma.

Synthesis and investigations of double-pharmacophore ligands for treatment of chronic and neuropathic pain

Acids 9a-f as possible bivalent ligands designed as a structural combination of opioid mu-agonist (Fentanyl) and NSAID (Indomethacin) activities and produced compounds which were tested as analgesics. The obtained series of compounds exhibits low affinity and activity both at opioid receptors and as cyclooxygenase (COX) inhibitors. One explanation of the weak opioid activity could be stereochemical peculiarities of these bivalent compounds which differ significantly from the fentanyl skeleton. The absence of significant COX inhibitory properties could be explained by the required substitution of an acyl fragment in the indomethacin structure for 4-piperidyl.

Bi- or multifunctional opioid peptide drugs

Strategies for the design of bi- or multifunctional drugs are reviewed. A distinction is made between bifunctional drugs interacting in a monovalent fashion with two targets and ligands containing two distinct pharmacophores binding in a bivalent mode to the two binding sites in a receptor heterodimer. Arguments are presented to indicate that some of the so-called "bivalent" ligands reported in the literature are unlikely to simultaneously interact with two binding sites. Aspects related to the development of bi- or multifunctional drugs are illustrated with examples from the field of opioid analgesics. The drug-like properties of the tetrapeptide Dmt(1)[DALDA] with triple action as a micro opioid agonist, norepinephrine uptake inhibitor and releaser of endogenous opioid peptides to produce potent spinal analgesia are reviewed. Rationales for the development of opioid peptides with mixed agonist/antagonist profiles as analgesics with reduced side effects are presented. Progress in the development of mixed micro opioid agonist/delta opioid antagonists with low propensity to produce tolerance and physical dependence is reviewed. Efforts to develop bifunctional peptides containing a micro opioid agonist and a cholecystokinin antagonist or an NK1 receptor antagonist as analgesics expected to produce less tolerance and dependence are also reviewed. A strategy to improve the drug-like properties of bifunctional opioid peptide analgesics is presented.

The importance of micelle-bound states for the bioactivities of bifunctional peptide derivatives for delta/mu opioid receptor agonists and neurokinin 1 receptor antagonists

To provide new insight into the determining factors of membrane-bound peptide conformation that might play an important role in peptide-receptor docking and further biological behaviors, the dodecylphosphocholine (DPC) micelle-bound conformations of bifunctional peptide derivatives of delta-preferring opioid agonists and NK1 antagonists (1: Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-O-3,5-Bzl(CF 3) 2; 2: Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-NH-3,5-Bzl(CF 3) 2; 3: Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-NH-Bzl) were determined based on 2D NMR studies. Although the differences in the primary sequence were limited to the C-terminus, the obtained NMR conformations were unexpectedly different for each compound. Moreover, their biological activities showed different trends in direct relation to the compound-specific conformations in DPC micelles. The important result is that not only were the NK1 antagonist activities different (the pharmacophore located at the C-terminus)but the opioid agonist activities (this pharmacophore was at the structurally preserved N-terminus) also were shifted, suggesting that a general conformational change in the bioactive state was induced due to relatively small and limited structural modifications.

Structure-activity relationships of bifunctional cyclic disulfide peptides based on overlapping pharmacophores at opioid and cholecystokinin receptors

Prolonged opioid exposure increases the expression of cholecystokinin (CCK) and its receptors in the central nervous system (CNS), where CCK may attenuate the antinociceptive effects of opioids. The complex interactions between opioid and CCK may play a role in the development of opioid tolerance. We designed and synthesized cyclic disulfide peptides and determined their agonist properties at opioid receptors and antagonist properties at CCK receptors. Compound 1 (Tyr-c[d-Cys-Gly-Trp-Cys]-Asp-Phe-NH(2)) showed potent binding and agonist activities at delta and mu opioid receptors but weak binding to CCK receptors. The NMR structure of the lead compound displayed similar conformational features of opioid and CCK ligands.

Opioid and melanocortin receptors: do they have overlapping pharmacophores?

We have identified compound 1 as a novel ligand for opioid and melanocortin (MC) receptors, which is derived from the overlapping of a well known structure for the delta opioid receptor, 2,6-dimethyltyrosine (Dmt)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic), and a small molecule for the MC receptor, Tic-DPhe(p-Cl)-piperidin-4-yl-N-phenyl-propionamide. Ligand 1 showed that there is an overlapping pharmacophore between opioid and MC receptors through the Tic residue. The ligand displayed high biological activities at the delta opioid receptor (Ki = 0.38 nM in binding assay, EC(50) = 0.48 nM in GTP-gamma-S binding assay, IC(50) = 74 nM in MVD) as an agonist instead of an antagonist and showed selective binding affinity (IC(50) = 2.3 muM) at the MC-3 receptor rather than at the MC-5 receptor. A study of the structure-activity relationships demonstrated that the residues in positions 2, 3, and the C-terminus act as a pharmacophore for the MC receptors, and the residues in positions 1 and 2 act as a pharmacophore for the opioid receptors. Thus, this structural construct can be used to prepare chimeric structures with adjacent or overlapping pharmacophores for opioid and MC receptors.

Arylation of Phe and Tyr side chains of unprotected peptides by a Suzuki-Miyaura reaction in water

An efficient arylation in water of tyrosine and phenylalanine side chains from unprotected iodopeptides is accomplished by using Suzuki-Miyaura cross-coupling processes. The method is compatible with the hydrophilic and thermolabile nature of biologically active peptides. Also of interest, the arylated tyrosine peptides can be accessed in one-pot mode starting from native peptides.

A structure-activity relationship study and combinatorial synthetic approach of C-terminal modified bifunctional peptides that are delta/mu opioid receptor agonists and neurokinin 1 receptor antagonists

A series of bifunctional peptides with opioid agonist and substance P antagonist bioactivities were designed with the concept of overlapping pharmacophores. In this concept, the bifunctional peptides were expected to interact with each receptor separately in the spinal dorsal horn where both the opioid receptors and the NK1 receptors were found to be expressed, to show an enhanced analgesic effect, no opioid-induced tolerance, and to provide better compliance than coadministration of two drugs. Compounds were synthesized using a two-step combinatorial method for C-terminal modification. In the method, the protected C-terminal-free carboxyl peptide, Boc-Tyr( tBu)- d-Ala-Gly Phe-Pro-Leu-Trp(Boc)-OH, was synthesized as a shared intermediate using Fmoc solid phase chemistry on a 2-chlorotrityl resin. This intermediate was esterified or amidated in solution phase. The structure-activity relationships (SAR) showed that the C-terminus acted as not only a critical pharmacophore for the substance P antagonist activities, but as an address region for the opioid agonist pharmacophore that is structurally distant from the C-terminal. Among the peptides, H-Tyr- d -Ala-Gly-Phe-Pro-Leu-Trp-NH-Bzl ( 3) demonstrated high binding affinities at both delta and mu receptors ( K i = 10 and 0.65 nM, respectively) with efficient agonist functional activity in the mouse isolated vas deferens (MVD) and guinea pig isolated ileum (GPI) assays (IC 50 = 50 and 13 nM, respectively). Compound 3 also showed a good antagonist activity in the GPI assay with substance P stimulation ( K e = 26 nM) and good affinity for the hNK1 receptor ( K i = 14 nM). Consequently, compound 3 is expected to be a promising and novel type of analgesic with bifunctional activities.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Design, synthesis, and biological evaluation of novel bifunctional C-terminal-modified peptides for delta/mu opioid receptor agonists and neurokinin-1 receptor antagonists

A series of bifunctional peptides that act as agonists for delta and mu opioid receptors with delta selectivity and as antagonist for neurokinin-1 (NK1) receptors were designed and synthesized for potential application as analgesics in various pain states. The peptides were characterized using radioligand binding assays and functional assays using cell membrane and animal tissue. Optimization was performed on the fifth residue which serves as an address moiety for both receptor recognitions. It had critical effects on both activities at delta/mu opioid receptors and NK1 receptors. Among the synthesized peptides, H-Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-O-3,5-Bzl(CF3) 2 (5) and H-Tyr-D-Ala-Gly-Phe-Nle-Pro-Leu-Trp-O-3,5-Bzl(CF3)2 (7) had excellent agonist activity for both delta opioid and mu opioid receptors and excellent antagonist activity for NK1 receptors. These results indicate that the rational design of multifunctional ligands with opioid agonist and neurokinin-1 antagonist activities can be accomplished and may provide a new tool for treatment of chronic and several pain states.

Partial retro-inverso, retro, and inverso modifications of hydrazide linked bifunctional peptides for opioid and cholecystokinin (CCK) receptors

Partially modified retro-inverso, retro, and inverso isomers of hydrazide linked bifunctional peptides were designed, synthesized, and evaluated for bioactivities at delta/mu opioid receptors and CCK-1/CCK-2 receptors. All modifications of the CCK pharmacophore moiety affected bioactivities for the CCK-1 and CCK-2 receptors (up to 180-fold increase in the binding affinity with higher selectivity) and for the delta and mu opioid receptors. The results indicate that the opioid and CCK pharmacophores in one molecule interact with each other to induce topographical changes for both pharmacophores.