New modalities providing safe and effective treatment of pain, especially prolonged pathological pain, have not appeared despite much effort. In this mini-review/overview we suggest that new paradigms of drug design are required to counter the underlying changes that occur in the nervous system that may elicit chronic pain states. We illustrate this approach with the example of designing, in a single ligand, molecules that have agonist activity at μ and σ opioid receptors and antagonist activities at cholecystokinin (CCK) receptors. Our findings thus far provide evidence in support of this new approach to drug design. We also report on a new biophysical method, plasmon waveguide resonance (PWR) spectroscopy, which can provide new insights into information transduction in g-protein coupled receptors (GPCRs) as illustrated by the δ opioid receptor.
drug design; neuropathic pain; bifunctional ligands; plasmon waveguide resonance spectroscopy; GPCRs; opioid receptors; cholecystokinin receptors
Cholecystokinin (CCK) has been identified as a pronociceptive endogenous peptide which also possesses antiopioid actions. CCK may be upregulated in conditions of chronic pain or during sustained morphine administration resulting in attenuation of opioid-mediated pain relief. These complex interactions between opioids and endogenous CCK receptor systems have suggested the need for a new paradigm in drug design for some states of chronic pain. In these circumstances the rational design of potential drugs for the treatment of these conditions must be based on one ligand for multiple targets. We have designed a single peptide which can interact with δ and μ opioid receptors as agonists and with CCK receptors as antagonists. The ligands were designed based on a model of overlapping pharmacophores of opioid and CCK peptide ligands, which incorporates opioid pharmacophores at the N-terminal and CCK tetrapeptide pharmacophores at the C-terminal of the designed ligands. We measured binding and activities of our bifunctional peptides at opioid and CCK receptors. Compound 11 (Tyr-d-Ala-Gly-d-Trp-NMeNle-Asp-Phe-NH2) demonstrated opioid agonist properties at δ and μ receptors (IC50 = 63 ± 27 nM and 150 ± 65 nM, respectively in MVD and GPI tissue assays) and high binding affinity at CCK-1 and CCK-2 receptors (Ki = 320 and 1.5 nM, respectively). Compound 9 (Tyr-d-Nle-Gly-Trp-Nle-Asp-Phe-NH2) displayed potent agonist activity at δ and μ receptors (IC50 = 23 ±10 nM and 210 ± 52 nM, respectively in MVD and GPI tissue assays), with a balanced binding affinity for CCK-1 and CCK-2 receptors (Ki = 9.6 and 15 nM, respectively). These results provide evidence supporting the concept that opioid and CCK receptors have overlapping pharmacophores required for binding affinity and biological activity and that designing overlapping pharmacophores of two peptides into a single peptide is a valid drug design approach.
Cannabinoid drugs differ in their rank order of potency to produce analgesia versus other central nervous system effects. We propose that these differences are due to unique agonist-bound cannabinoid CB1 receptor conformations that exhibit different affinities for individual subsets of intracellular signal transduction pathways. In order to test this hypothesis, we have used plasmon-waveguide resonance (PWR) spectroscopy, a sensitive method that can provide direct information about ligand-protein and protein-protein interactions, and can detect conformational changes in lipid-embedded proteins. A recombinant epitope-tagged human cannabinoid CB1 receptor was expressed in insect Sf9 cells, solubilized and purified using two-step affinity chromatography. The purified receptor was incorporated into a lipid bilayer on the surface of the PWR resonator. PWR spectroscopy demonstrated that cannabinoid agonists exhibit high affinity (KD = 0.2 ± 0.03 nM and 2 ± 0.4 nM for CP 55,940 and WIN 55,212-2, respectively) for the purified epitope tagged hCB1 receptor. Interestingly however, these structurally different cannabinoid agonists shifted the PWR spectra in opposite directions, indicating that CP 55,940 and WIN 55,212-2 binding leads to different hCB1 receptor conformations. Furthermore, PWR experiments also indicated that these CP 55,940- and WIN 55,212 - bound hCB1 receptor conformations exhibit slightly different affinities to an inhibitory G protein heterotrimer, Gi1 (KD = 27 ± 8 nM and KD = 10.7 ± 4.7 nM, respectively), whereas they strikingly differ in their ability to activate this G protein type.
trafficking; G proteins; PWR spectroscopy; functional selectivity
A procedure has been developed for directly depositing membrane fragments derived from bacterial (chromatophores from Rhodopseudomonas sphaeroides) and mammalian cells (μ-opioid receptor- and MC4 receptor-transfected HEK cells, and rat trigeminal ganglion cells) onto the silica surface of a plasmon-waveguide resonance (PWR) spectrometer. Binding of ligands (cytochrome c2 for the chromatophores, the peptide agonists DAMGO and Melanotan-II that are specific for the μ-opioid and MC4 receptors, and two non-peptide agonists that are specific for the CB1 receptor) to these membrane fragments has been observed and characterized with high sensitivity using PWR spectral shifts. The KD values obtained are in excellent agreement with conventional pharmacological assays and with prior PWR studies using purified receptors inserted into deposited lipid bilayer membranes. These studies provide a new tool for obtaining useful biological information about receptor-mediated processes in real biological membranes.
G-protein coupled receptors; bacterial chromatophores; transfected HEK cells; rat trigeminal ganglion; μ-opioid receptor; cannabinoid CB1 receptor; melanocortin-4 receptor
The conventional design of high affinity drugs targeted to a single molecule has not resulted in clinically useful therapies for pain relief. Recent reviews have suggested that newly designed analgesic drugs should incorporate multiple targets. The distributions of cholecystokinin (CCK) and CCK receptors in the central nervous system (CNS) overlap significantly with endogenous opioid systems and can be dually targeted. CCK has been shown to act as an endogenous “anti-analgesic” peptide and neuropathic pain conditions promote endogenous CCK release in CNS regions of pain modulation. Administration of CCK into nuclei of the rostral ventromedial medulla induces pronociceptive behaviors in rats. RSA 504 and RSA 601 are novel bifunctional compounds developed to target neuropathic pain by simultaneously acting as agonists at two distinct opioid receptors and antagonizing CCK receptors in the CNS. RSA 504 and RSA 601 demonstrate agonist activity in vitro and antihypersensitivity to mechanical and thermal stimuli in vivo using the spinal nerve ligation model of neuropathic pain. Intrathecal administration of RSA 504 and RSA 601 did not demonstrate antinociceptive tolerance over 7 days of administration and did not display motor impairment or sedation using a rotarod. These are the first behavioral studies that demonstrate how multi-targeted molecule design can address the pathology of neuropathic pain. These compounds with δ and μ opioid agonist activity and CCK antagonist activity within one molecule offer a novel approach with efficacy for neuropathic pain while lacking the side effects typically caused by conventional opioid therapies.
neuropathic pain; spinal nerve ligation; cholecystokinin; opioids
Plasmon-waveguide resonance (PWR) spectroscopy is an optical technique that has been developed in our laboratories and applied to the study of membrane-associated proteins, especially GPCRs. It has high sensitivity and requires no labeling of materials, and can monitor changes in proteolipid mass density and conformation in real time using plasmon excitation by light polarized both perpendicular and parallel to the resonator surface. Direct measurements will be described of the association of ligands and G-proteins to GPCRs incorporated into a self-assembled lipid bilayer deposited on the silica surface of a PWR resonator. These studies have provided new insights into the functioning of this important class of signaling proteins.
Development of new opioid drugs that provide analgesia without producing dependence is important for pain treatment. Opioid agonist drugs exert their analgesia effects primarily by acting at the mu opioid receptor (MOR) sites. High-resolution differentiation of opioid ligands is crucial for the development of new lead drug candidates with better tolerance profiles. Here, we use a label-free integrative pharmacology on-target (iPOT) approach to characterize the functional selectivity of a library of known opioid ligands for the MOR. This approach is based on the ability to detect dynamic mass redistribution (DMR) arising from the activation of the MOR in living cells. DMR assays were performed in HEK-MOR cells with and without preconditioning with probe molecules using label-free resonant waveguide grating biosensors, wherein the probe molecules were used to modify the activity of specific signaling proteins downstream the MOR. DMR signals obtained were then translated into high resolution heat maps using similarity analysis based on a numerical matrix of DMR parameters. Our data indicate that the iPOT approach clearly differentiates functional selectivity for distinct MOR signaling pathways among different opioid ligands, thus opening new avenues to discover and quantify the functional selectivity of currently used and novel opioid receptor drugs.
Increasing evidence supports the idea that the plasma membrane bilayer is characterized by a laterally inhomogeneous mixture of lipids, having an organized structure in which lipid molecules segregate into small domains or patches. Such microdomains are characterized by high contents of sphingolipids that form thicker liquid-ordered regions having resistance to extraction with nonionic detergents. The existence of lipid lateral segregation has been demonstrated in both model and biological membranes, although its role in protein sorting and membrane function still remains unclear. In the present studies, plasmon-waveguide resonance (PWR) spectroscopy was employed to investigate the properties of microdomains in a model system consisting of a solid-supported lipid bilayer composed of a 1:1 mixture of palmitoyloleoylphosphatidylcholine (POPC) and brain sphingomyelin (SM), and their influence on the partitioning and functioning of the human delta opioid receptor (hDOR; a G-protein coupled receptor, GPCR). Resonance signals corresponding to two microdomains (POPC-rich and SM-rich) were observed in such bilayers, and the sorting of the receptor into each domain was highly dependent on the type of ligand that was bound. When no ligand was bound, the receptor incorporated preferentially into the POPC-rich domain; when an agonist or an antagonist was bound, the receptor incorporated preferentially into the SM-rich component, although with a two-fold greater propensity for this microdomain in the case of the agonist. G-protein binding to the agonist-bound receptor in the SM-rich domain occurred with a 30-fold higher affinity than to the receptor in the PC-rich domain. The binding of agonist to an unliganded receptor in the bilayer produced receptor trafficking from the PC-rich into the SM-rich component. Since the SM-rich domain is thicker than the PC-rich domain, and previous studies with the hDOR have shown that the receptor elongates upon agonist-activation, we propose that hydrophobic matching between the receptor and the lipid is a driving force for receptor trafficking to the SM-rich component.
microenvironmental effects; G-protein binding and activation; phospholipids; sphingolipids; protein sorting
Both mu opioid (MOP)† and type 2 cholecystokinin (CCK2) receptors are present in areas of the central nervous system that are involved in modulation of pain processing. We conducted bioluminescence resonance energy transfer (BRET) studies on COS cells coexpressing MOP and CCK2 receptors to determine whether receptor heterodimerization is involved in such modulation. These studies revealed the absence of constitutive or monovalent ligand-induced heterodimerization. Heterodimerization of MOP and CCK2 receptors therefore is unlikely to be responsible for the opposing effects between morphine and CCK in the CNS. However, association was induced, as indicated by a positive BRET signal, on exposure of the cells to bivalent ligands containing mu-opioid agonist and CCK2 receptor antagonist pharmacophores linked through spacers containing 16 to 22 atoms, but not with a shorter (9-atom) spacer. These studies demonstrate for the first time that an appropriately designed bivalent ligand is capable of inducing association of G protein-coupled receptors. The finding that opioid tolerance studies with these ligands in mice showed no correlation with the BRET data is consistent with the absence of association of MOP and CCK2 receptors in vivo.
Descending input from the rostral ventromedial medulla (RVM) provides positive and negative modulation of spinal nociceptive transmission and has been proposed to be critical for maintaining neuropathic pain. This study tests the hypothesis that neuropathic pain requires the activity of a subset of RVM neurons that are distinguished by co-expression of mu opioid receptor (MOR) and cholecystokinin type 2 receptor (CCK2). Using male Sprague–Dawley rats, we demonstrate that discrete RVM neurons express MOR and CCK2; over 80% of these cells co-express both receptors. Agonist-directed cell lesion in the RVM with the cytotoxin, saporin, using either CCK-saporin to target CCK receptor expressing cells, or dermorphin-saporin to target MOR expressing cells, resulted in concomitant loss of CCK2 and MOR expressing cells, did not alter the basal sensory thresholds but abolished the hyperalgesia induced by microinjection of CCK into the RVM. The findings suggest that these CCK2-MOR co-expressing RVM neurons facilitate pain and can be directly activated by CCK input to the RVM. Furthermore, lesion of these RVM neurons did not affect the initial development of neuropathic pain in the hind paw upon injury to the sciatic nerve, but the abnormal pain states were short lived such that by about day 9 the sensory thresholds had reverted to pre-injury baselines despite the existing neuropathy. These data support our hypothesis and identify CCK2-MOR co-expressing neurons in the RVM as potential therapeutic targets for neuropathic pain.
opioid receptor; cholecystokinin receptor; neuropathy; rostral ventromedial medulla; nociception
Plasmon-waveguide resonance (PWR) sensors are particularly useful for investigation of biomolecular interactions with or within lipid bilayer membranes. Many studies demonstrated their ability to provide unique qualitative information, but the evaluation of their sensitivity as compared to other surface plasmon resonance (SPR) sensors has not been broadly investigated. We report here a comprehensive sensitivity comparison of SPR and PWR biosensors for the p-polarized light component. The sensitivity of five different biosensor designs to changes in refractive index, thickness and mass are determined and discussed. Although numerical simulations show an increase of the electric field intensity by 30–35 % and the penetration depth by four times in PWR, the waveguide-based method is 0.5 to 8 fold less sensitive than conventional SPR in all considered analytical parameters. The experimental results also suggest that the increase in the penetration depth in PWR is made at the expense of the surface sensitivity. The physical and structural reasons for PWR sensor limitations are discussed and a general viewpoint for designing more efficient SPR sensors based on dielectric slab waveguides is provided.
optical biosensors; surface plasmon resonance; plasmon-waveguide resonance; surface sensitivity; planar waveguide
Opioid receptors are G protein-coupled receptors (GPCRs) of utmost significance in the development of potent analgesic drugs for the treatment of severe pain. An accurate evaluation at the molecular level of the ligand binding pathways into these receptors may play a key role in the design of new molecules with more desirable properties and reduced side effects. The recent characterization of high-resolution X-ray crystal structures of non-rhodopsin GPCRs for diffusible hormones and neurotransmitters presents an unprecedented opportunity to build improved homology models of opioid receptors, and to study in more detail their molecular mechanisms of ligand recognition. In this study, possible entry pathways of the non-selective antagonist naloxone (NLX) from the water environment into the well-accepted alkaloid binding pocket of a delta opioid receptor (DOR) molecular model based on the β2-adrenergic receptor crystal structure are explored using microsecond-scale well-tempered metadynamics simulations. Using as collective variables distances that account for the position of NLX and of the receptor extracellular loop 2 in relation to the DOR binding pocket, we were able to distinguish between the different states visited by the ligand (i.e., docked, undocked, and metastable bound intermediates), and to predict a free energy of binding close to experimental values after correcting for possible drawbacks of the sampling approach. The strategy employed herein holds promise for its application to the docking of diverse ligands to the opioid receptors as well as to other GPCRs.
Prolonged opioid exposure increases the expression of cholecystokinin (CCK) and its receptors in the central nervous system, 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-NH2) showed potent binding and agonist activities at δ and µ opioid receptors while displaying some binding to CCK receptors. The NMR structure of the lead compound displayed similar conformational features of opioid and CCK ligands.
Multivalent Ligands; Bifunctional Peptides; Overlapping Pharmacophores; G-Protein Coupled Receptors; Pain; Tolerance; NMR Conformation
The myriad of side-effects that associate with morphine has been problematic in the clinical use to manage moderate to severe pain. It has been the holy grail of the pharmacologists to develop a compound, or treatment paradigm that could retain the analgesic effect of the drug while eliminating or reducing the side-effects, mainly the tolerance and addiction development associates with chronic usage of the drug. In our earlier receptor structure/activities studies, we discovered an unique mutation of a conserved Ser in the 4th transmembrane domain of the opioid receptor that the alkaloid antagonist could activate the receptor. Based on this initial finding, we decide to explore the possibility of using virus to deliver the mutant mu-opioid receptor at the various sites of the nociceptive pathway and induce the antinociceptive responses with the systemic administration of opioid antagonists. In this article, we will summarize the progress of such approach and the probable advantages over the conventional approach of drug development in the treatment of chronic pain.
morphine; pain treatment; mu-opioid receptor; naloxone
G-protein-coupled receptors (GPCRs) play key roles in cellular signal transduction and many are pharmacologically important targets for drug discovery. GPCRs can be reconstituted in planar supported lipid bilayers (PSLBs) with retention of activity, which has led to development of GPCR-based biosensors and biochips. However, PSLBs composed of natural lipids lack the high stability desired for many technological applications. One strategy is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how lipid polymerization affects GPCR structure and activity. Here we have investigated the photochemical activity of bovine rhodopsin (Rho), a model GPCR, reconstituted into PSLBs composed of lipids having one or two polymerizable dienoyl moieties located in different regions of the acyl chains. Plasmon waveguide resonance spectroscopy was used to compare the degree of Rho photoactivation in fluid and poly(lipid) PSLBs. The position of the dienoyl moiety was found to have a significant effect: polymerization near the glycerol backbone significantly attenuates Rho activity whereas polymerization near the acyl chain termini does not. Differences in cross-link density near the acyl chain termini also do not affect Rho activity. In unpolymerized PSLBs, an equimolar mixture of phosphatidylethanolamine and phosphatidylcholine (PC) lipids enhances activity relative to pure PC; however after polymerization, the enhancement is eliminated which is attributed to stabilization of the membrane lamellar phase. These results should provide guidance for the design of robust lipid bilayers functionalized with transmembrane proteins for use in membrane-based biochips and biosensors.
Z-360 is an orally active cholecystokinin-2 (CCK2)/gastrin receptor antagonist currently under development as a therapeutic drug for pancreatic cancer. It was previously reported that Z-360 treatment in combination with gemcitabine prolonged the survival period in a lethal pancreatic cancer xenograft model in mice. In a phase Ib/IIa clinical study, Z-360 treatment displayed a trend of reduced pain in patients with advanced pancreatic cancer in combination with gemcitabine including analgesics such as opioids. Here, we investigated the mechanism of analgesic action of Z-360 in a severe cancer-induced pain model in mice, which is considered to be opioid-resistant, by examining ephrin B1 gene expression, N-methyl-D-aspartate receptor NR2B subunit phosphorylation, and interleukin-1β (IL-1β) production.
In a mouse model of cancer-induced pain, ephrin B1 gene expression in dorsal root ganglia (DRGs) and the phosphorylation of NR2B in the spinal cord were induced. Z-360 treatment inhibited both ephrin B1 gene expression and the phosphorylation of NR2B. In addition, IL-1β production increased in the cancer-inoculated hind paw of mice, but could be suppressed by treatment with Z-360. Moreover, we observed that the CCK1 receptor antagonist devazepide similarly suppressed up-regulation of ephrin B1 gene expression and IL-1β production, and that the intraperitoneal injection of sulfated CCK-8 induced the production of IL-1β in the cancer-inoculated region.
We have identified a novel pain cascade, in which IL-1β production in cancer-inoculated regions induces ephrin B1 gene expression in DRGs and then ephrin B1 enhances the tyrosine phosphorylation of NR2B via Eph B receptor in the spinal cord. Notably, Z-360 relieves cancer-induced pain by preventing this pain cascade through the suppression of IL-1β production, likely via the blockade of CCK1 receptor. The pre-clinical results presented here support the analgesic action of Z-360 in pancreatic cancer patients with severe, opioid-resistant pain. Pre-clinical and clinical results have demonstrated that Z-360 combined with gemcitabine represents a promising pancreatic cancer therapy approach with characteristic analgesic effects in addition to the prolongation of survival.
The greatest advance in pediatric pain medicine is the recognition that untreated pain is a significant cause of morbidity and even mortality after surgical trauma. Accurate assessment of pain in different age groups and the effective treatment of postoperative pain is constantly being refined; with newer drugs being used alone or in combination with other drugs continues to be explored. Several advances in developmental neurobiology and pharmacology, knowledge of new analgesics and newer applications of old analgesics in the last two decades have helped the pediatric anesthesiologist in managing pain in children more efficiently. The latter include administering opioids via the skin and nasal mucosa and their addition into the neuraxial local anesthetics. Systemic opioids, nonsteroidal anti-inflammatory agents and regional analgesics alone or combined with additives are currently used to provide effective postoperative analgesia. These modalities are best utilized when combined as a multimodal approach to treat acute pain in the perioperative setting. The development of receptor specific drugs that can produce pain relief without the untoward side effects of respiratory depression will hasten the recovery and discharge of children after surgery. This review focuses on the overview of acute pain management in children, with an emphasis on pharmacological and regional anesthesia in achieving this goal.
pediatric pain treatment; pain medication in children; pediatric regional anesthesia; pca and pcea in children; epidural additives
For years conventional drug design at G-protein coupled receptors (GPCRs) has mainly focused on the inhibition of a single receptor at a usually well-defined ligand-binding site. The recent discovery of more and more physiologically relevant GPCR dimers/oligomers suggests that selectively targeting these complexes or designing small molecules that inhibit receptor-receptor interactions might provide new opportunities for novel drug discovery. To uncover the fundamental mechanisms and dynamics governing GPCR dimerization/oligomerization, it is crucial to understand the dynamic process of receptor-receptor association, and to identify regions that are suitable for selective drug binding. This minireview highlights current progress in the development of increasingly accurate dynamic molecular models of GPCR oligomers based on structural, biochemical, and biophysical information that has recently appeared in the literature. In view of this new information, there has never been a more exciting time for computational research into GPCRs than at present. Information-driven modern molecular models of GPCR complexes are expected to efficiently guide the rational design of GPCR oligomer-specific drugs, possibly allowing researchers to reach for the high-hanging fruits in GPCR drug discovery, i.e. more potent and selective drugs for efficient therapeutic interventions.
GPCRs; dimers; computational methods; molecular modeling; rational drug design
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.1–4 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.
Opioid analgesics provide effective treatment for noncancer pain, but many physicians have concerns about adverse effects, tolerance, and addiction. Misuse of opioids is prominent in patients with chronic back pain and early recognition of misuse risk could help physicians offer adequate patient care while implementing appropriate levels of monitoring to reduce aberrant drug-related behaviors. In this review, we discuss opioid abuse and misuse issues that often arise in the treatment of patients with chronic back pain and present an overview of assessment and treatment strategies that can be effective in improving compliance with the use of prescription opioids for pain. Many persons with chronic back pain have significant medical, psychiatric and substance use comorbidities that affect treatment decisions and a comprehensive evaluation that includes a detailed history, physical, and mental health evaluation is essential. Although there is no “gold standard” for opioid misuse risk assessment, several validated measures have been shown to be useful. Controlled substance agreements, regular urine drug screens, and interventions such as motivational counseling have been shown to help improve patient compliance with opioids and to minimize aberrant drug-related behavior. Finally, we discuss the future of abuse-deterrent opioids and other potential strategies for back pain management.
Opioids are the most widely used analgesics for the treatment of clinical pain. They produce their therapeutic effects by binding to μ-opioid receptors (MORs), which are 7 transmembrane domain (7TM) G-protein-coupled receptors (GPCRs), and inhibiting cellular activity. However, the analgesic efficacy of opioids is compromised by side-effects such as analgesic tolerance, dependence and opioid-induced hyperalgesia (OIH). In contrast to opioid analgesia these side effects are associated with cellular excitation. Several hypotheses have been advanced to explain these phenomena, yet the molecular mechanisms underlying tolerance and OIH remain poorly understood.
We recently discovered a new human alternatively spliced isoform of MOR (MOR1K) that is missing the N-terminal extracellular and first transmembrane domains, resulting in a 6TM GPCR variant. To characterize the pattern of cellular transduction pathways activated by this human MOR1K isoform, we conducted a series of pharmacological and molecular experiments. Results show that stimulation of MOR1K with morphine leads to excitatory cellular effects. In contrast to stimulation of MOR1, stimulation of MOR1K leads to increased Ca2+ levels as well as increased nitric oxide (NO) release. Immunoprecipitation experiments further reveal that unlike MOR1, which couples to the inhibitory Gαi/o complex, MOR1K couples to the stimulatory Gαs complex.
The major MOR1 and the alternative MOR1K isoforms mediate opposite cellular effects in response to morphine, with MOR1K driving excitatory processes. These findings warrant further investigations that examine animal and human MORK1 expression and function following chronic exposure to opioids, which may identify MOR1K as a novel target for the development of new clinically effective classes of opioids that have high analgesic efficacy with diminished ability to produce tolerance, OIH, and other unwanted side-effects.
The management of advanced non-small-cell lung cancer (a-nsclc) is currently undergoing one of its rare paradigm shifts. Just as the nihilism of the 1970s gave way to the empiricism of the 1980s and 1990s, so the current decade has seen the first truly rational therapies based on informed design. In addition, molecular markers and traditional parameters can now be combined to provide a framework of knowledge that will guide the application of not just the new therapies, but also the older ones that remain effective. This framework—as important a component of the rational paradigm as the new drugs themselves are—is necessary to decide who should and, crucially, who should not receive the various components of this rapidly expanding armamentarium. Here, I have provided a historical overview of the drug treatment of a-nsclc, a mini-review of important new data, and an integrative approach that tries to ensure that patients receive the optimal treatment choice at the appropriate time.
The speed at which new knowledge now arrives, coupled with the persistent high level of unmet medical need, suggests that the traditional pace of evidence-based review needs to be accelerated. Indeed, the increased scope for personalized management constitutes something of a challenge to “business as usual” evidence-based medicine. As a result, substantial investment on the part of payers, which may or may not be possible, will be required. In the meantime, some patients may wish and may be financially able to take advantage of modern developments before they have been fully digested by the public-payer system. Responsive clinicians face difficult tradeoffs as they try to balance the pros and cons of early adoption versus excessive conservatism.
The present article is my personal view of how to navigate these waters, and although it is written especially for patients who like to be the captain of their own ship, there is good reason to believe that all patients will eventually be managed by similar, if not identical, means. Nonetheless, the recommendations herein should not be construed as appropriately reviewed provincial or national guidelines. Finally, if appropriate, a clinical trial should always be offered.
Advanced non-small-cell lung cancer; treatment; personal view
Opioid receptors are critical therapeutic targets for medications development relevant to the treatment of drug dependence and pain. With recent advances in molecular neurobiology, it has become evident that the functional activity of opioid receptors, as ligand-regulated protein complexes, is modulated by multifarious intracellular and extracellular events, that there is genetic variation in coding for receptors, and that the activity of endogenous opioid systems may underlie actions common to other addictive disorders. This supplemental issue of Drug and Alcohol Dependence, arising from an invited symposium at the 71st Annual Meeting of the College on Problems of Drug Dependence, provides a series of contemporary reviews focused on recent advances in opioid neuropharmacology. Each speaker provides herein an invited comprehensive review of the state of knowledge on a specific topic in opioid neuropharmacology. Evans and colleagues describe the multi-faceted control of the opioid G-protein coupled receptor as a dynamic “sensor” complex and identify novel targets for drug development. Von Zastrow focuses on opioid receptor-mediated events regulated by endocytosis and membrane trafficking through the endocytic pathway and differential responses to opioid agonists. Blendy and colleague provide a review of human association studies on the functional relevance of the mu opioid receptor variant, A118G, and presents data from the A112G knock-in model, an analogous mouse variant to A118G. Finally, Maldonado and colleagues provide a broader systems review from genetic, pharmacologic and behavioral studies implicating the endogenous opioid systems as a substrate for the mediation of substance use disorders spanning pharmacological classes.
opioid; pharmacology; molecular biology; receptor; genetics; analgesia; abuse
Prescription opioid formulations designed to resist or deter abuse are an important step in reducing opioid abuse. In creating these new formulations, the paradigm of drug development target should be introduced. Biological targets relating to the nature of addiction may pose insurmountable hurdles based on our current knowledge and technology, but products that use behavioral targets seem logical and feasible. The population of opioid abusers is large and diverse so behavioral targets are more challenging than they appear at first glance. Furthermore, we need to find ways to correlate behavioral observations of drug liking to actual use and abuse patterns. This may involve revisiting some pharmacodynamic concepts in light of drug effect rather than peak concentration. In this paper we present several new opioid analgesic agents designed to resist or deter abuse using physical barriers, the inclusion of an opioid agonist or antagonist, an aversive agent, and a prodrug formulation. Further, this paper also provides insight into the challenges facing drug discovery in this field. Designing and screening for opioids intended to resist or deter abuse is an important step to meet the public health challenge of burgeoning prescription opioid abuse.
Cholecystokinin (CCK) has been suggested to be both pro-nociceptive and anti-opioid by actions on pain modulatory cells within the RVM. One consequence of activation of RVM CCK2 receptors may be enhanced spinal nociceptive transmission but how this might occur, especially in states of pathological pain is unknown. Here, in vivo microdialysis was used to demonstrate that levels of RVM CCK increased by approximately 2-fold following ligation of L5/L6 spinal nerves (SNL). Microinjection of CCK into the RVM of naïve rats elicited hypersensitivity to tactile stimulation of the hindpaw. Additionally, RVM CCK elicited a time-related increase in PGE2 measured in cerebrospinal fluid from the lumbar spinal cord. The peak increase in spinal PGE2 was approximately 5-fold and was observed at approximately 80-min post-RVM CCK, a time coincident with maximal RVM CCK-induced mechanical hypersensitivity. Spinal administration of naproxen, a non-selective COX-inhibitor, significantly attenuated RVM CCK-induced hindpaw tactile hypersensitivity. RVM-CCK also resulted in a 2-fold increase in spinal 5-HIAA, a 5-HT metabolite, as compared to controls, and mechanical hypersensitivity that was attenuated by spinal application of ondansetron, a 5-HT3 antagonist. The present studies suggest that chronic nerve injury can result in activation of descending facilitatory mechanisms that may promote hyperalgesia via ultimate release of PGE2 and 5-HT in the spinal cord.
rostral ventromedial medulla; descending facilitation; cholecystokinin; serotonin; PGE2; microdialysis; tactile hypersensitivity; nerve injury