Design, synthesis and in vitro evaluation of novel uni- and bivalent ligands for the cannabinoid receptor type 1 with variation of spacer length and structure

The Olfactory Trail of Neurodegenerative Diseases

Alterations in olfactory functions are proposed as possible early biomarkers of neurodegenerative diseases. Parkinson's and Alzheimer's diseases manifest olfactory dysfunction as a symptom, which is worth mentioning. The alterations do not occur in all patients, but they can serve to rule out neurodegenerative pathologies that are not associated with small deficits. Several prevalent neurodegenerative conditions, including impaired smell, arise in the early stages of Parkinson's and Alzheimer's diseases, presenting an attractive prospect as a snitch for early diagnosis. This review covers the current knowledge on the link between olfactory deficits and Parkinson's and Alzheimer's diseases. The review also covers the emergence of olfactory receptors as actors in the pathophysiology of these diseases. Olfactory receptors are not exclusively expressed in olfactory sensory neurons. Olfactory receptors are widespread in the human body; they are expressed, among others, in the testicles, lungs, intestines, kidneys, skin, heart, and blood cells. Although information on these ectopically expressed olfactory receptors is limited, they appear to be involved in cell recognition, migration, proliferation, wound healing, apoptosis, and exocytosis. Regarding expression in non-chemosensory regions of the central nervous system (CNS), future research should address the role, in both the glia and neurons, of olfactory receptors. Here, we review the limited but relevant information on the altered expression of olfactory receptor genes in Parkinson's and Alzheimer's diseases. By unraveling how olfactory receptor activation is involved in neurodegeneration and identifying links between olfactory structures and neuronal death, valuable information could be gained for early diagnosis and intervention strategies in neurodegenerative diseases.

Modular One-Pot Strategy for the Synthesis of Heterobivalent Tracers

Bivalent ligands, i.e., molecules having two ligands covalently connected by a linker, have been gathering attention since the first description of their pharmacological potential in the early 80s. However, their synthesis, particularly of labeled heterobivalent ligands, can still be cumbersome and time-consuming. We herein report a straightforward procedure for the modular synthesis of labeled heterobivalent ligands (HBLs) using dual reactive 3,6-dichloro-1,2,4,5-tetrazine as a starting material and suitable partners for sequential S_NAr and inverse electron-demand Diels-Alder (IEDDA) reactions. This assembly method conducted in a stepwise or in a sequential one-pot manner provides quick access to multiple HBLs. A conjugate combining ligands toward the prostate-specific membrane antigen (PSMA) and the gastrin-releasing peptide receptor (GRPR) was radiolabeled, and its biological activity was assessed in vitro and in vivo (receptor binding affinity, biodistribution, imaging) as an illustration that the assembly methodology preserves the tumor targeting properties of the ligands.

Cannabinoid receptor CB1 and CB2 interacting proteins: Techniques, progress and perspectives

Cannabinoid receptors 1 and 2 (CB₁ and CB₂) are implicated in a range of physiological processes and have gained attention as promising therapeutic targets for a number of diseases. Protein-protein interactions play an integral role in modulating G protein-coupled receptor (GPCR) expression, subcellular distribution and signaling, and the identification and characterization of these will not only improve our understanding of GPCR function and biology, but may provide a novel avenue for therapeutic intervention. A variety of techniques are currently being used to investigate GPCR protein-protein interactions, including Förster/fluorescence and bioluminescence resonance energy transfer (FRET and BRET), proximity ligation assay (PLA), and bimolecular fluorescence complementation (BiFC). However, the reliable application of these methodologies is dependent on the use of appropriate controls and the consideration of the physiological context. Though not as extensively characterized as some other GPCRs, the investigation of CB₁ and CB₂ interacting proteins is a growing area of interest, and a range of interacting partners have been identified to date. This review summarizes the current state of the literature regarding the cannabinoid receptor interactome, provides commentary on the methodologies and techniques utilized, and discusses future perspectives.

Functional characterization of N-octyl 4-methylamphetamine variants and related bivalent compounds at the dopamine and serotonin transporters using Ca2+ channels as sensors

The early characterization of ligands at the dopamine and serotonin transporters, DAT and SERT, respectively, is important for drug discovery, forensic sciences, and drug abuse research. 4-Methyl amphetamine (4-MA) is a good example of an abused drug whose overdose can be fatal. It is a potent substrate at DAT and SERT where its simplest secondary amine (N-methyl 4-MA) retains substrate activity at them. In contrast, N-n-butyl 4-MA is very weak, therefore it was categorized as inactive at these transporters. Here, N-octyl 4-MA and other related compounds were synthesized, and their activities were evaluated at DAT and SERT. To expedite this endeavor, cells expressing DAT or SERT were co-transfected with a voltage-gated Ca2+ channel and, the genetically-encoded Ca2+ sensor, GCaMP6s. Control compounds and the newly synthesized molecules were tested on these cells using an automated multi-well fluorescence plate reader; substrates and inhibitors were identified successfully at DAT and SERT. N-Octyl 4-MA and three bivalent compounds were inhibitors at these transporters. These findings were validated by measuring Ca2+-mobilization using quantitative fluorescence microscopy. The bivalent molecules were the most potent of the series and were further characterized in an uptake-inhibition assay. Compared to cocaine, they showed comparable potency inhibiting uptake at DAT and higher potency at SERT. These observations support a previous hypothesis that amphetamine-related (and, here, N-extended alkyl and) bivalent arylalkylamine molecules are active at monoamine transporters, showing potent activity as reuptake inhibitors, and implicate the involvement of a distant auxiliary binding feature to account for their actions at DAT and SERT.

Discovery of Homobivalent Bitopic Ligands of the Cannabinoid CB2 Receptor*

Single chemical entities with potential to simultaneously interact with two binding sites are emerging strategies in medicinal chemistry. We have designed, synthesized and functionally characterized the first bitopic ligands for the CB2 receptor. These compounds selectively target CB2 versus CB1 receptors. Their binding mode was studied by molecular dynamic simulations and site-directed mutagenesis.

Synthesis of 1-(tert-Butyl) 4-Methyl (1R,2S,4R)-2-Methylcyclohexane-1,4-dicarboxylate from Hagemann's tert-Butyl Ester for an Improved Synthesis of BMS-986251

We describe an efficient synthetic route to differentially protected diester, 1-(tert-butyl) 4-methyl (1R,2S,4R)-2-methylcyclohexane-1,4-dicarboxylate (+)-1, via palladium-catalyzed methoxycarbonylation of an enol triflate derived from a Hagemann's ester derivative followed by a stereoselective Crabtree hydrogenation. Diester 1 is a novel chiral synthon useful in drug discovery and was instrumental in the generation of useful SAR during a RORγt inverse agonist program. In addition, we describe a second-generation synthesis of the clinical candidate BMS-986251, using diester 1 as a critical component.

2016 Philip S. Portoghese Medicinal Chemistry Lectureship: Designing Bivalent or Bitopic Molecules for G-Protein Coupled Receptors. The Whole Is Greater Than the Sum of Its Parts

The genesis of designing bivalent or bitopic molecules that engender unique pharmacological properties began with Portoghese's work directed toward opioid receptors, in the early 1980s. This strategy has evolved as an attractive way to engineer highly selective compounds for targeted G-protein coupled receptors (GPCRs) with optimized efficacies and/or signaling bias. The emergence of X-ray crystal structures of many GPCRs and the identification of both orthosteric and allosteric binding sites have provided further guidance to ligand drug design that includes a primary pharmacophore (PP), a secondary pharmacophore (SP), and a linker between them. It is critical to note the synergistic relationship among all three of these components as they contribute to the overall interaction of these molecules with their receptor proteins and that strategically designed combinations have and will continue to provide the GPCR molecular tools of the future.

A step-wise synthetic approach is necessary to access γ-conjugates of folate: folate-conjugated prodigiosenes

Despite the vast literature that describes reacting folic acid with a pharmacophore, this route is ineffective in providing the correct regioisomer of the resulting conjugate. We herein present a step-wise route to the preparation of nine folate conjugates of the tripyrrolic prodigiosene skeleton. The strict requirement for step-wise construction of the folate core is demonstrated, so as to achieve conjugation at only the desired γ-carboxylic acid and thus maintain the α-carboxylic site for folate receptor (FRα) recognition. Linkages via ethylenediamine, polyethylene glycol and glutathione are demonstrated.

Despite the vast literature that describes reacting folic acid with a pharmacophore, this route is ineffective in providing the correct regioisomer of the resulting conjugate.

A novel synthetic ursolic acid derivative inhibits growth and induces apoptosis in breast cancer cell lines

The present study investigated the anticancer functions of ursolic acid (UA) and its novel derivatives, with a nitrogen-containing heterocyclic scaffold and the privileged fragment at the C-28 position on apoptosis induction, cell proliferation and cell cycle in human BC lines. UA was chemically modified in the present study to increase its antitumor activity and bioavailability. A novel UA derivative, FZU3010, was synthesized using a nitrogen-containing heterocyclic scaffold and a privileged fragment at the C-28 position. Sulforhodimine B assays were used to measure the effect of UA and different concentrations of FZU3010 on the viability of breast cancer (BC) SUM149PT and HCC1937 cells. FZU3010 significantly repressed the proliferation of the two cancer cell lines in a dose-dependent manner, with a half-maximal inhibitory concentration of 4-6 µM, and exhibited decreased cytotoxicity compared with vehicle-treated cell lines. The effect of FZU3010 on cell cycle distribution and cellular apoptosis was also investigated. The results of this investigation indicated that FZU3010 significantly increased the number of SUM149PT and breast cancer HCC1937 cells in the G₀/G₁ phase in a dose-dependent manner. Additionally, at a concentration of 5 µM, the capability of FZU3010 to induce BC apoptosis was significantly higher than the capability of UA. Thus, the results of the current study indicated that FZU3010 induced apoptosis in BC cells, together with induction of cell cycle arrest at the S and G₀/G₁ phase. FZU3010 may therefore be considered as a potential therapeutic agent for the treatment of BC.

An Update on Non-CB1, Non-CB2 Cannabinoid Related G-Protein-Coupled Receptors

The endocannabinoid system (ECS) has been shown to be of great importance in the regulation of numerous physiological and pathological processes. To date, two Class A G-protein-coupled receptors (GPCRs) have been discovered and validated as the main therapeutic targets of this system: the cannabinoid receptor type 1 (CB1), which is the most abundant neuromodulatory receptor in the brain, and the cannabinoid receptor type 2 (CB2), predominantly found in the immune system among other organs and tissues. Endogenous cannabinoid receptor ligands (endocannabinoids) and the enzymes involved in their synthesis, cell uptake, and degradation have also been identified as part of the ECS. However, its complex pharmacology suggests that other GPCRs may also play physiologically relevant roles in this therapeutically promising system. In the last years, GPCRs such as GPR18 and GPR55 have emerged as possible missing members of the cannabinoid family. This categorization still stimulates strong debate due to the lack of pharmacological tools to validate it. Because of their close phylogenetic relationship, the Class A orphan GPCRs, GPR3, GPR6, and GPR12, have also been associated with the cannabinoids. Moreover, certain endo-, phyto-, and synthetic cannabinoid ligands have displayed activity at other well-established GPCRs, including the opioid, adenosine, serotonin, and dopamine receptor families. In addition, the cannabinoid receptors have also been shown to form dimers with other GPCRs triggering cross-talk signaling under specific conditions. In this mini review, we aim to provide insight into the non-CB1, non-CB2 cannabinoid-related GPCRs that have been reported thus far. We consider the physiological relevance of these molecular targets in modulating the ECS.

A Direct in Vivo Comparison of the Melanocortin Monovalent Agonist Ac-His-DPhe-Arg-Trp-NH2 versus the Bivalent Agonist Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH2: A Bivalent Advantage

Bivalent ligands targeting putative melanocortin receptor dimers have been developed and characterized in vitro; however, studies of their functional in vivo effects have been limited. The current report compares the effects of homobivalent ligand CJL-1-87, Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH₂, to monovalent ligand CJL-1-14, Ac-His-DPhe-Arg-Trp-NH₂, on energy homeostasis in mice after central intracerebroventricular (ICV) administration into the lateral ventricle of the brain. Bivalent ligand CJL-1-87 had noteworthy advantages as an antiobesity probe over CJL-1-14 in a fasting-refeeding in vivo paradigm. Treatment with CJL-1-87 significantly decreased food intake compared to CJL-1-14 or saline (50% less intake 2-8 h after treatment). Furthermore, CJL-1-87 treatment decreased the respiratory exchange ratio (RER) without changing the energy expenditure indicating that fats were being burned as the primary fuel source. Additionally, CJL-1-87 treatment significantly lowered body fat mass percentage 6 h after administration (p < 0.05) without changing the lean mass percentage. The bivalent ligand significantly decreased insulin, C-peptide, leptin, GIP, and resistin plasma levels compared to levels after CJL-1-14 or saline treatments. Alternatively, ghrelin plasma levels were significantly increased. Serum stability of CJL-1-87 and CJL-1-14 (T_1/2 = 6.0 and 16.8 h, respectively) was sufficient to permit physiological effects. The differences in binding affinity of CJL-1-14 compared to CJL-1-87 are speculated as a possible mechanism for the bivalent ligand's unique effects. We also provide in vitro evidence for the formation of a MC3R-MC4R heterodimer complex, for the first time to our knowledge, that may be an unexploited neuronal molecular target. Regardless of the exact mechanism, the advantageous ability of CJL-1-87 compared to CJL-1-14 to increase in vitro binding affinity, increase the duration of action in spite of decreased serum stability, decrease in vivo food intake, decrease mice's body fat percent, and differentially affect mouse hormone levels demonstrates the distinct characteristics achieved from the current melanocortin agonist bivalent design strategy.

An in Vitro and in Vivo Investigation of Bivalent Ligands That Display Preferential Binding and Functional Activity for Different Melanocortin Receptor Homodimers

Pharmacological probes for the melanocortin receptors have been utilized for studying various disease states including cancer, sexual function disorders, Alzheimer's disease, social disorders, cachexia, and obesity. This study focused on the design and synthesis of bivalent ligands to target melanocortin receptor homodimers. Lead ligands increased binding affinity by 14- to 25-fold and increased cAMP signaling potency by 3- to 5-fold compared to their monovalent counterparts. Unexpectedly, different bivalent ligands showed preferences for particular melanocortin receptor subtypes depending on the linker that connected the binding scaffolds, suggesting structural differences between the various dimer subtypes. Homobivalent compound 12 possessed a functional profile that was unique from its monovalent counterpart providing evidence of the discrete effects of bivalent ligands. Lead compound 7 significantly decreased feeding in mice after intracerebroventricular administration. To the best of our knowledge, this is the first report of a melanocortin bivalent ligand's in vivo physiological effects.

One for the Price of Two…Are Bivalent Ligands Targeting Cannabinoid Receptor Dimers Capable of Simultaneously Binding to both Receptors?

Bivalent ligands bridging two G-protein-coupled receptors (GPCRs) provide valuable pharmacological tools to target oligomers. The success of therapeutically targeting the cannabinoid CB1 receptor has been limited, in part due to its widespread neuronal distribution. Therefore, CB1 ligands targeting oligomers that exhibit restricted distribution or altered pharmacology are highly desirable, and several bivalent ligands containing a CB1 pharmacophore have been reported. Bivalent ligand action presumes that the ligand simultaneously binds to both receptors within the dimeric complex. However, based on the current understanding of CB1 ligand binding, existing bivalent ligands are too short to bind both receptors simultaneously. However, ligands with longer linkers may not be the solution, because evidence suggests that ligands enter CB1 through the lipid bilayer and, thus, linkers are unlikely to exit the receptor through its external face. Thus, the entire premise of designing bivalent ligands targeting CB1 must be revisited.