Mary E. Abood - US grants

Marijuana is currently the most widely abused street drug. However, the functional significance of the cannabinoid receptor system in health and disease includes the use of cannabinoids as analgesics, antiemetics in cancer patients, anticonvulsants for epilepsy and as antiglaucoma agents as well as immunomodulatory agents. To date, two cannabinoid receptor subtypes, CB1 and CB2, have been fully defined as these two subtypes.. Anandamide produces the full range of behavioral effects (antinociception, catalepsy and impaired locomotor activity) in CB1 receptor knockout mice. In addition, anandamide-stimulated GTPgS activity can be elicited in brain membranes from these mice. Finally, radioligand binding studies indicate the existence of additional binding sites in brain and spinal cord. The goal of this project is to clone and characterize additional subtypes of the cannabinoid receptors in order to elucidate their role in vivo. The first specific aim is to isolate additional cannabinoid receptor subtypes using a cDNA expression library constructed from CB1 receptor knockout mice. Stable cell lines will be used to functionally characterize novel receptor subtypes using GTPgS binding and investigation of signal transduction pathways. The second specific aim will identify additional receptor-subtype selective ligands to establish structure-activity relationships for CB1 and CB2 receptors, in conjunction with other Center grant participants. The second specific aim will identify additional receptor-subtype selective ligands to establish structure-activity relationships for CB1 and CB2 receptors, in conjunction with other Center grant participants. In addition, we will characterize the ligand-receptor-G protein interactions which discriminate between the receptor subtypes. In addition, we will characterize the ligand-receptor-G protein interactions which discriminate between the receptor subtypes. A model is emerging about the specific sites of interaction for ligand recognition and signal transduction in the CB1 and CB2 receptors. The third aim is to define the regions believed to be critical to receptor subtype discrimination by site-directed mutagenesis and construction of receptor chimeras. These studies will facilitate the design of new therapeutic strategies involving the cannabinoid systems. Furthermore, insight into the molecular mechanisms of activation of cannabinoid receptors may lead to a better understanding of marijuana abuse in humans.

The goals of the proposed research are to understand the development of the opioid receptor and opioid systems. In order to simplify the multiplicity of influences exerted in the developing animal, the initial studies will be performed in a model cell line for differentiation, the PC12 rat pheochromocytoma cells. Subsequently, the information acquired in the cell line will be applied to the neonatal rat brain, specifically with respect to the development and differentiation of opioid systems in animals with drug-addicted mothers. Specifically: 1. In one subclone of PC12 cells, PC12h, low levels of opioid receptors markedly increase in response to nerve growth factor (NGF). The opioid receptor has been identified as delta, but no further characterization has been done. In this proposal, the receptor in PC12h cells will be further characterized with respect to its possible function, i.e., what are the consequences of opioid binding? 2. The possibility that NGF can induce opioid receptor expression in other subclones of PC12 cells will be explored in order to determine if PC12h cells are unique in this response to NGF or if NGF induction of opioid receptors is more universal. This relates to the question of the signals for gene expression in stem cells in the developing nervous system. 3. Once the response of receptors to opioids in PC12 cells has been established, the effect of opioids on differentiation will be examined. It is known that pre-natal morphine has numerous effects on development and differentiation. Thus, the following questions arise: Will opioids have any effect on NGF-induced differentiation in the cell line? Will opioids have a morphological or biochemical effect by themselves? 4. Recently, a novel molecule related to the neural cell adhesion molecule, N-CAM has been isolated which is related to opioid binding. The expression of this molecule, termed OB-CAM, will be examined in control and NGF treated cells, as it may be associated with the opioid receptors in PC12h cells. If it is found to be differentially expressed the molecule will be cloned from PC12h cells. 5. The level of G proteins, both mRNA and protein levels, will be examined in control and NGF treated PC12 cells as well as in opioid treated cells. These proteins are signalling molecules and probably have a role in the normal and drug-altered developing nervous system, which will be examined in the rat pup. 6. Are opioid peptides present in these cells? And if so, is their expression altered by NGF or opioid treatment? 7. In addition to examining the expression of specific molecules, such as OB-CAM and G proteins, it is a long term goal to clone molecules which are differentially expressed in control vs NGF treated PC12 cells. 8. The final aims are to determine the role of NGF on opioid receptor development in neonatal rats as well as the effects of prenatal exposure to opioids on receptor development.

DESCRIPTION (provided by applicant): Many G-protein coupled receptors involved in pain and addiction are pharmacologically and biochemically well characterized, but some orphan receptors like GPR35 and GPR55, with homology to known receptors for drugs of abuse, remain poorly characterized. GPR55 is emerging as an important target in inflammatory pain, neuropathic pain, and bone development while other studies indicate that GPR55 activation is pro-carcinogenic. GPR55 does recognize certain cannabinoid ligands, so it has been suggested to be a third cannabinoid receptor. GPR35 is an important target in pain (spinal antinociception as well as inflammatory pain), heart disease, asthma, metabolic disease, inflammatory bowel disease and cancer. Each of these areas alone is medically important and each would benefit by the use of selective agonists and antagonists to further studies in their respective animal models. However, to date, no low nanomolar potency ligands have been discovered for these receptors nor is there a radioligand developed to characterize binding. The lack of such ligands is a critical barrier to progress in this field. The goal of this proposal is to leverage our recen promising high throughput, high content screening results for GPR55 agonists and GPR35 antagonists using structure based design and cheminformatics tools to develop an SAR for selected scaffolds that leads to the identification of low nanamolar ligands that retain high receptor selectivity. We aim to discover nanomolar potency GPR55 and GPR35 ligands using a combination of structure-based design, molecular modeling, chemoinformatics, high-throughput screening and site directed mutagenesis.

DESCRIPTION (provided by applicant): Drug addiction continues to remain a major public health concern in the United States. Addictive behavior results from changes in central nervous system signaling pathways that are modified after exposure to drugs of abuse. In particular, compounds such as cannabinoids and opiates that influence mood and pain perception are commonly associated with addictive behaviors. Many receptors regulating addiction are pharmacologically and biochemically well characterized, but some orphan receptors like GPR35 with homology to known receptors of abuse remain almost totally uncharacterized. The identification of small molecules capable of selectively inhibiting or activating orphans will provide enabling tools for elucidating novel molecular pathways underlying addictive behaviors. This proposal seeks to provide new compounds for characterizing the orphan G protein-coupled receptor GPR35. We have identified pamoic acid analogs as potent GPR35 agonists using in vitro assays and have found that pamoic acid induces antinociception. We propose a strategy to identify predominantly commercially available small molecules towards the objective of identifying a useful molecular probe for GPR35. Optimizing these novel compounds will allow the characterization of GPR35 biology in vitro and in animal models of pain. Our results suggest unexpected biological functions of pamoic acid and potential application for new drug development. PUBLIC HEALTH RELEVANCE: This proposal will provide tools for delineating the pharmacology of GPR35, potentially provide compounds for targeted therapeutics of pathways underlying pain, and clarify our understanding of GPR35 biology in vitro and in animal models of pain.

DESCRIPTION (provided by applicant): GPR55 is a rhodopsin-like (Class A) G protein-coupled receptor (GPCR), highly expressed in human striatum (Genbank accession # NM-005683). Characterizations of GPR55(-/-) (knock-out) mice reveal a role for the GPR55 receptor in inflammatory pain, neuropathic pain, and bone development; while other studies indicate that GPR55 activation is pro-carcinogenic. GPR55 may also be a cannabinoid receptor, since CB1/CB2 agonists, as well as antagonists have been reported to act at GPR55. Thus, GPR55 may also have a role to play in drug abuse. Despite these potential therapeutic uses, no low nanomolar potency ligands have been confirmed for this receptor, nor is there a radioligand developed to characterize binding at this receptor. The lack of such GPR55 ligands is a critical barrier to progress in this field. During a collaborative project between our individual laboratoris and the Sanford-Burnham screening center of the Molecular Libraries Probe Production Centers Network (MLPCN), we identified a series of GPR55 antagonists that belong to novel, unreported GPR55 antagonist chemotypes with IC50s in the 0.34 to 2.72 ¿M range. The compounds that were in this potency range were also screened for agonist activity against GPR55 along with agonist/antagonist activity against GPR35, CB1, and CB2. Importantly, many of the GPR55 antagonists were completely selective, with no observed activity in the assays for related GPCRs for concentrations up to 20 ¿M. We propose here to leverage these promising high-content screen results using state-of-the-art structure- based design and cheminformatics tools combined with a synthesis strategy to develop an SAR for selected scaffolds that leads to the identification of low nanomolar IC50 GPR55 antagonists with high receptor selectivity.

DESCRIPTION (provided by applicant): GPR55 has recently been identified as a lysophosphatidylinositol (LPI)-sensitive receptor that may also mediate some off-target effects of cannabinoids. The broad central nervous system (CNS) distribution of GPR55 suggests its involvement in central physiology and pathology. Characterization of GPR55-/- (knock-out) mice reveals roles for the GPR55 receptor in inflammatory pain, neuropathic pain, and bone development while other studies indicate that GPR55 activation is pro-carcinogenic. Importantly, GPR55-/- mice show decreased inflammatory and neuropathic pain. Further, inhibition of LPI-induced activation of GPR55 may reduce neuropathic pain. The main goal of this application is to uncover the functional role of this new receptor, GPR55, in the periaqueductal gray (PAG), one of the most important regions involved in pain modulation and also a primary site of action of many analgesic compounds including cannabinoids. Our preliminary data revealed activation of GPR55 receptors in the PAG produces increases in intracellular calcium and cytoplasmic and mitochondrial reactive oxygen species in primary neurons and depolarization of PAG neurons in midbrain slice cultures. Furthermore, activation of GPR55 in PAG significantly reduced the pain threshold in rats. In other words, the activation of GPR55 in the PAG has a pro-nociceptive function. Thus, manipulating GPR55 signaling could be a new target for pain management. We propose to test a new hypothesis that the activation of GPR55 in the PAG has nociceptive response and antagonizing this receptor could have analgesic function. In the experiments under specific Aim 1, we will evaluate the GPR55-dependent Ca2+ response in PAG neurons. Studies under Aim 2 will use electrophysiology to characterize the membrane and synaptic activity responses of PAG neurons to GPR55 activation. In aim 3, we will determine the in vivo effect of GPR55 agonist(s)/antagonist(s) on PAG in several pain models. These studies will demonstrate the functional role of GPR55 in PAG, with the objective of identifying novel targets for effective therapeutic interventions. Specifically, we will determine whether the inhibition of GPR55 by antagonist(s) can be used as potential therapeutics for pain management.

GPR55 is a lysophosphatidylinositol (LPI)-sensitive G-protein coupled receptor (GPCR) that recognizes a sub- set of cannabinoid CB1 and CB2 ligands. The goal of the proposed project is to understand the functional features of GPR55 that may define mechanisms of drug-receptor interactions relevant to physiological and pathophysiological function, including drug abuse. GPR55 has been implicated in inflammatory pain, neuropathic pain, metabolic disorder, bone and neurological development, and cancer, indicating the real potential of GPR55 ligands as therapeutics. Each of these areas alone is medically important and each would benefit by the use of selective agonists and antagonists to further studies. While selective agonists and antagonists for GPR55 from a number of diverse scaffolds have been identified, no low nanomolar potency ligands have been confirmed for this receptor, nor is there a radioligand developed to characterize binding. We have recently identified the first set of GPR55 residues important for agonist signaling and for GPR55 activation. This information should aid in the rational design of next generation GPR55 ligands, using our evolving molecular model. The goal of this proposal is to use structure-based design and cheminformatics tools to develop structure-activity relationships for selected scaffolds, leading to the identification of low nanomolar ligands that retain high receptor selectivity. We aim to discover nanomolar potency GPR55 ligands using a combination of molecular modeling, chemoinformatics, high-throughput screening and site directed mutagenesis. We will dissect the specific signaling pathways governing GPR55 activity as well as investigate ligand bias.