Dilip K Tosh

• PhD
• Researcher at National Institutes of Health

Alterations in mitochondrial function are the linchpin in numerous disease states including in the development of chemotherapy-induced neuropathic pain (CIPN), a major dose-limiting toxicity of widely used chemotherapeutic cytotoxins. In CIPN, mitochondrial dysfunction is characterized by deficits in mitochondrial bioenergetics (e.g., decreased ATP...

Background and Purpose Adenosine, through the A1 receptor (A1R), is an endogenous anticonvulsant. The development of adenosine receptor agonists as antiseizure medications has been hampered by their cardiac side effects. A moderately A1R‐selective agonist, MRS5474, has been reported to suppress seizures without considerable cardiac action. Hypothes...

The neurotransmitter dopamine has central roles in mood, appetite, arousal and movement 1. Despite its importance in brain physiology and function, and as a target for illicit and therapeutic drugs, the human dopamine transporter (hDAT) and mechanisms by which it is inhibited by small molecules and Zn 2+ are without a high-resolution structural con...

The neurotransmitter dopamine has central roles in mood, appetite, arousal and movement¹. Despite its importance in brain physiology and function, and as a target for illicit and therapeutic drugs, the human dopamine transporter (hDAT) and mechanisms by which it is inhibited by small molecules and Zn²⁺ are without a high-resolution structural conte...

Background and Purpose Adenosine, through the A1 receptor (A1R), is an endogenous anticonvulsant. Development of adenosine receptor agonists as antiseizure medications has been hampered by their cardiac side effects. A moderately A1R-selective agonist, MRS5474, has been reported to suppress seizures without considerable cardiac action. Hypothesizin...

The A3 adenosine receptor (AR) is an important inflammatory and immunological target. However, the underlying mechanisms are not fully understood. Here, we report the gene regulation in HL-60 cells treated acutely with highly selective A3AR agonist MRS5698, positive allosteric modulator (PAM) LUF6000, or both. Both pro- and anti-inflammatory genes,...

(N)-Methanocarba adenosine derivatives were structurally modified to target 5-HT2B serotonin receptors as antagonists, predominantly containing branched N6-alkyl groups. N6-Dicycloalkyl-methyl groups, including their asymmetric variations, as well as 2-iodo, were found to generally favor 5-HT2Rs, while only N6-dicyclohexyl-methyl derivative 35 show...

Adenosine receptors (ARs) are involved in the suppression and development of inflammatory and fibrotic conditions. Specifically, AR activation promotes differentiation of lung fibroblasts into myofibroblasts, typical of a fibrotic event. Pulmonary fibrosis is a severe disease characterized by inflammation and fibrosis of unknown etiology and lackin...

COVID-19 disease is associated with progressive accumulation of SARS-CoV-2-specific mRNA, which is recognized by innate immune receptors, such as TLR3. This in turn leads to dysregulated production of multiple cytokines, including IL-6, IFN-γ, CXCL1, and TNF-α. Excessive production of these cytokines leads to acute lung injury (ALI), which conseque...

Resistance to pharmacotherapy requires the development of novel antiseizure drugs (ASDs). An adenosine A1 receptor (A1R) agonist, MRS5474, possesses anticonvulsant activity [1], without the cardiac side effects of other A1R agonists. We hypothesized that it could operate via a novel mechanism. We thus assessed its influence upon hippocampal excitat...

Resistance to pharmacotherapy requires the development of novel antiepileptic drugs (AEDs). An adenosine A1 receptor (A1R) agonist, MRS5474, possesses anticonvulsant activity (Tosh et al., 2012, J Med Chem, 55:8075), without the cardiac side effects of other A1R agonists. Hypothesizing that it operates via a novel mechanism, we assessed its influen...

Introduction: Resistance to pharmacotherapy requires the development of novel antiepileptic drugs (AEDs). An adenosine A1 receptor (A1R) agonist, MRS5474, possesses anticonvulsant activity [1] Tosh et al., 2012, J Med Chem, 55:8075, without the cardiac side effects of other A1R agonists. We hypothesized that it could operate via a novel mechanism....

Cisplatin is used to combat solid tumors. However, patients treated with cisplatin often develop cognitive impairments, sensorimotor deficits, and peripheral neuropathy. There is no FDA-approved treatment for these neurotoxicities. We investigated the capacity of a highly selective A 3 adenosine receptor (AR) subtype (A 3 AR) agonist, MRS5980, to p...

Various adenosine receptor nucleoside-like ligands were found to modulate ATP hydrolysis by the multidrug transporter ABCG2. Both ribose-containing and rigidified (N)-methanocarba nucleosides (C2-, N⁶- and 5′-modified), as well as adenines (C2-, N⁶-, and deaza modified), were included. 57 compounds out of 63 tested either stimulated (50) or inhibit...

Resistance to pharmacotherapy requires the development of novel antiepileptic drugs (AEDs). An adenosine A1 receptor (A1R) agonist, MRS5474, possesses anticonvulsant activity (Tosh et al., 2012, J Med Chem, 55:8075), without the cardiac side effects of other A1R agonists. We hypothesized that it could operate via a novel mechanism. We thus assessed...

Following our study of 4′-truncated (N)-methanocarba-adenosine derivatives that displayed unusually high mouse (m) A3AR affinity, we incorporated dopamine-related N⁶ substituents in the full agonist 5′-methylamide series. N⁶-(2-(4-Hydroxy-3-methoxy-phenyl)ethyl) derivative MRS7618 11 displayed Ki (nM) 0.563 at hA3AR (∼20,000-fold selective) and 1.5...

Nucleoside derivatives are well represented as pharmaceuticals due to their druglike physicochemical properties, and some nucleoside drugs are designed to act on receptors. The purinergic signaling pathways for extracellular nucleosides and nucleotides, consisting of adenosine receptors, P2Y/P2X receptors for nucleotides, and enzymes such as adenos...

Psoriasis is a chronic and relapsing inflammatory skin disease lacking a cure that affects approximately 2% of the population. Defective keratinocyte proliferation and differentiation, and aberrant immune responses are major factors in its pathogenesis. Available treatments for moderate to severe psoriasis are directed to immune system causing syst...

The heat shock protein 90 kDa (Hsp90) family of chaperones is highly sought-after for the treatment of cancer and neurodegenerative diseases. Glucose regulated protein 94 (Grp94) is the endoplasmic reticulum localized isoform that is responsible for the maturation of proteins involved in cell adhesion and the immune response, including Toll-like re...

The A3 adenosine receptor (A3AR) has emerged as a therapeutic target with A3AR agonists to tackle the global challenge of neuropathic pain; investigation into their mode of action is essential for ongoing clinical development. A3ARs on immune cells, and their activation during pathology, modulates cytokine release. Thus, immune cells as a cellular...

Introduction: Pharmaco-resistance in epilepsy requires development of novel antiepileptic drugs. An A1 adenosine receptor (A1R) agonist, MRS5474, possesses anticonvulsant activity, without the cardiac side effects of other A1R agonists [1], leading us to hypothesise that it could operate a different mechanism from classical A1R agonists. We thus te...

Rapid phosphoester hydrolysis of endogenous purine and pyrimidine nucleotides has challenged the characterization of the role of P2 receptors in physiology and pathology. Nucleotide phosphoester stabilization has been pursued on a number of medicinal chemistry fronts. We investigated the in vitro and in vivo stability and pharmacokinetics of protot...

Various (North)-methanocarba adenosine derivatives, containing rigid bicyclo[3.1.0]hexane ribose substitution, were screened for activity against representative viruses, and inhibition was observed after treatment of Enterovirus A71 with a 2-chloro-N6-1-cyclopropyl-2-methylpropan-1-yl derivative (17). μM activity was also seen when testing 17 again...

Prodrugs (MRS7422, MRS7476) of highly selective A3 adenosine receptor (AR) agonists Cl-IB-MECA and MRS5698, respectively, were synthesized by succinylation of the 2′ and 3′ hydroxyl groups, and the parent, active drug was shown to be readily liberated upon incubation with liver esterases. The prodrug MRS7476 had greatly increased aqueous solubility...

Epilepsy is a common neurological disorder but resistance to pharmacotherapy makes it necessary the development of novel antiepileptic drugs (AEDs). An A1 adenosine receptor (A1R) agonist, MRS5474, possesses anticonvulsant activity (Tosh et al.,2012- J.Med.Chem., 55,8075), without the cardiac side effects of other A1R agonists, leading us to hypoth...

Treating chronic pain using opioids, such as morphine, is hampered by the development of opioid-induced hyperalgesia (OIH; increased pain sensitivity), antinociceptive tolerance and withdrawal which can contribute to dependence and abuse. In the central nervous system, the purine nucleoside adenosine has been implicated in beneficial and detrimenta...

Pharmacological tools for chronic visceral pain management are still limited and inadequate. A3 adenosine receptor (A3AR) agonists are effective in different models of persistent pain. Recently their activity has been related to the block of N-type voltage-gated Ca channels (Cav2.2) in dorsal root ganglia (DRG) neurons. The present work aimed to ev...

Dopamine-derived N6-substituents, compared to N6-(2-phenylethyl), in truncated (N)-methanocarba (bicyclo[3.1.0]hexyl) adenosines favored high A3 adenosine receptor (AR) affinity/selectivity, e.g., C2-phenylethynyl analogue 15 (MRS7591, Ki = 10.9/17.8 nM, at human/mouse A3AR). 15 was a partial agonist in vitro (hA3AR, cAMP inhibition, 31% Emax; mA3A...

The A3 adenosine receptor (A3AR) is a G protein-coupled receptor that is involved in a wide variety of physiological and pathological processes, such as cancer. However, the use of compounds pharmacologically targeting this receptor remains limited in clinical practice, despite extensive efforts for compound synthesis. Moreover, the possible occurr...

A side-by-side pharmacological comparison of ribose and (N)-methanocarba (bicyclo[3.1.0]hexane) nucleosides as A3AR agonists indicated that the bicyclic pseudoribose ring constraint provided higher affinity/selectivity at human and mouse A3AR. The mean affinity enhancement for 5 pairs of 5-methylamides was 11-fold at hA3AR and 42-fold at mA3AR. No...

Chemotherapy-induced neuropathic pain (CINP) in both sexes compromises many current chemotherapeutics and lacks a FDA-approved therapy. We recently identified the sphingosine-1-phosphate receptor subtype 1 (S1PR1) and A3 adenosine receptor subtype (A3AR) as novel targets for therapeutic intervention. Our work in male rodents using paclitaxel, oxali...

A1 and A3 adenosine receptors (ARs) belong to the group of GPCRs that primarily couple to Gi/o protein and mediate adenosine’s biological actions. ARs are widely expressed in the body and regulate various metabolic functions. We generated mice lacking two ARs, Adora1-/-; Adora3-/- (double knockout [A1A3DKO]) to enable investigation of the role of G...

P-glycoprotein (P-gp) is a multidrug transporter that is expressed on the luminal surface of epithelial cells in the kidney, intestine, bile-canalicular membrane in the liver, blood-brain barrier, and adrenal gland. This transporter uses energy of ATP hydrolysis to efflux from cells a variety of structurally dissimilar hydrophobic and amphipathic c...

Adenosine receptors (ARs) function in the body’s response to conditions of pathology and stress associated with a functional imbalance, such as in the supply and demand of energy/oxygen/nutrients. Extracellular adenosine concentrations vary widely to raise or lower the basal activation of four subtypes of ARs. Endogenous adenosine can correct an en...

Abstract Recently studies have focused on the anti-hyperalgesic activity of the A3 adenosine receptor (A3AR) in several chronic pain models, but the cellular and molecular basis of this effect is still unknown. Here, we investigated the expression and functional effects of A3AR on the excitability of small-medium sized, capsaicin-sensitive, dorsal...

(N)-Methanocarba ([3.1.0]bicyclohexyl) adenosines and corresponding ribosides were synthesized to identify novel A1 adenosine receptor (A1AR) agonists for CNS or peripheral applications. Human and mouse AR binding was determined to assess the constrained ring system's A1AR compatibility. N⁶-Dicyclobutylmethyl ribose agonist (9, MRS7469, >2000-fold...

While screening off-target effects of rigid (N)-methanocarba-adenosine 5′-methylamides as A3 adenosine receptor (AR) agonists, we discovered μM binding hits at the δ-opioid receptor (DOR) and translocator protein (TSPO). In an effort to increase OR and decrease AR affinity by structure activity analysis of this series, antagonist activity at κ-(K)O...

In the adenosine receptor (AR) subfamily of G protein-coupled receptors (GPCRs), biased agonism has been described for the human A1AR, A2BAR and A3AR. While diverse A3AR agonists have been evaluated for receptor binding and Gi-mediated cAMP signalling, the β-arrestin2 (βarr2) pathway has been left largely unexplored. We screened nineteen diverse ad...

One of the four G protein-coupled receptors for adenosine, the A1 adenosine receptors (A1AR), is widely distributed in the body and modulates numerous normal and pathological processes, through signaling pathways including those downstream from its coupled Gi protein. It is an attractive drug target for heart failure, arrhythmias, angina, asthma, s...

Numerous structure-activity relationship (SAR) studies of ligands of the A3 adenosine receptor (AR) have generated selective agonists, antagonists, partial agonists, and allosteric modulators. The efficacy of nucleoside agonists may be reduced, while retaining affinity, by successive structural changes. Subnanomolar affinity and selectivity of >10,...

The human dopamine transporter (hDAT) plays a major role in dopamine homeostasis and regulation of neurotransmission by clearing dopamine from the extracellular space using secondary active transport. Dopamine is an essential monoamine chemical messenger that regulates reward seeking behavior, motor control, hormonal release, and emotional response...

Effect of MRS compounds on stability of hDAT. (a) Chemical structures of MRS compounds tested in this study for their effect on hDAT thermostability. (b) Tm of hDAT in complex with various MRS compounds. MRS7292 provides greatest enhancement in Tm. The error bars represent standard errors of mean calculated from triplicate measurements of a represe...

Comparative 12% SDS-PAGE analysis of optimization of purification of hDAT-I248Y. Purification (a) from whole cell solubilization using Talon affinity chromatography, (b) from solubilized membranes using Talon affinity chromatography, (c) using Strep-Tactin affinity chromatography, and (d) using NΔ56 expression construct and Strep-Tactin affinity ch...

Comparison of expression profiles of full length and NΔ56 constructs of hDAT-I248Y. The N-terminal GFP fusion of hDAT-I248Y (red) and NΔ56-hDAT (blue) expression constructs are monitored by FSEC, using detergent solubilized cell lysate from HEK293S cells harvested 36 h post transfection. The NΔ56 expression construct shows smaller void and free GFP...

[3H]Dopamine uptake. The thermostable hDAT-I248Y mutant is uptake active. The uptake counts displayed in the bar graph have been normalized with respect to expression levels of transporter. Also, the uptake was completely inhibited in the presence of MRS7292. The error bars represent standard errors of mean calculated from triplicate measurements o...

On the cover: The cover image, by Kenneth A. Jacobson et al., is based on the Review Article A3 Adenosine Receptors as Modulators of Inflammation: From Medicinal Chemistry to Therapy, https://doi.org/10.1002/med.21456.

The human dopamine transporter (hDAT) plays a major role in dopamine homeostasis and regulation of neurotransmission by clearing dopamine from the extracellular space using secondary active transport. Dopamine is an essential monoamine chemical messenger that regulates reward seeking behavior, motor control, hormonal release, and emotional response...

Development chemotherapy-induced peripheral neuropathic pain (CINP) compromises the use of chemotherapy and greatly impacts thousands of lives. Unfortunately, there are no FDA-approved drugs to prevent or treat CINP. Neuropathological changes within CNS, including neuroinflammation and increased neuronal excitability, are driven by alterations in n...

The human adenosine A3 (hA3) receptor has been suggested as a viable drug target in inflammatory diseases and in cancer. So far, a number of selective hA3 receptor agonists (e.g. IB-MECA and 2-Cl-IB-MECA) inducing anti-inflammatory or anticancer effects are under clinical investigation. Drug-target binding kinetics is increasingly recognized as ano...

A single molecular scaffold can be adapted to interact with diverse targets, either separately or simultaneously. Nucleosides and nucleotides in which ribose is substituted with bicyclo[3.1.0]hexane are an example of a versatile drug-like scaffold for increasing selectivity at their classical targets: kinases, polymerases, adenosine and P2 receptor...

The A3 adenosine receptor (A3 AR) subtype is a novel, promising therapeutic target for inflammatory diseases, such as rheumatoid arthritis (RA) and psoriasis, as well as liver cancer. A3 AR is coupled to inhibition of adenylyl cyclase and regulation of mitogen-activated protein kinase (MAPK) pathways, leading to modulation of transcription. Further...

We have repurposed (N)-methanocarba adenosine derivatives (A3 adenosine receptor (AR) agonists) to enhance radioligand binding allosterically at the human dopamine (DA) transporter (DAT) and inhibit DA uptake. We extended the structure–activity relationship of this series with small N⁶-alkyl substitution, 5′-esters, deaza modifications of adenine,...

Adenosine derivatives developed to activate adenosine receptors (ARs) revealed micromolar activity at serotonin 5HT2B and 5HT2C receptors (5HTRs). We explored the structure-activity relationship at 5HT2Rs and modeled receptor interactions in order to optimize affinity and simultaneously reduce AR affinity. Depending on N(6) substitution, small 5'-a...

Small mammals have the ability to enter torpor, a hypothermic, hypometabolic state, allowing impressive energy conservation. Administration of adenosine or adenosine 5'-monophosphate (AMP) can trigger a hypothermic, torpor-like state. We investigated the mechanisms for hypothermia using telemetric monitoring of body temperature in wild type and rec...

Biased agonism at G protein-coupled receptors (GPCRs) has significant implications for current drug discovery, but molecular determinants that govern ligand bias remain largely unknown. The adenosine A3 GPCR (A3AR) is a potential therapeutic target for various conditions, including cancer, inflammation and ischemia, but for which biased agonism rem...

Mitochondrial dysfunction is emerging as a common mechanism of a variety of neurodegenerative diseases, including chemotherapy‐induced neuropathic pain. We have recently found that administration of selective agonists to the G protein‐coupled, adenosine A 3 receptor (A 3 AR) prevents the development of chemotherapy‐induced mitochondrial dysfunction...

Purine (N)-methanocarba-5'-N-alkyluronamidoriboside A3 adenosine receptor (A3AR) agonists lacking an exocyclic amine resulted from an unexpected reaction during a Sonogashira coupling and subsequent aminolysis. Because the initial C6-Me and C6-styryl derivatives had unexpectedly high A3AR affinity, other rigid nucleoside analogues lacking an exocyc...

Thirty two congeneric rigid adenine nucleoside derivatives containing a (N)-methanocarba ribose substitution and a 2-arylethynyl group either enhanced (up to 760% of control) or inhibited [(125)I]RTI-55 binding at the human dopamine (DA) transporter (DAT) and inhibited DA uptake. Several nucleosides also enhanced [(3)H]mazindol binding to DAT. The...

We establish structure activity relationships of extracellular nucleosides and nucleotides at G protein-coupled receptors (GPCRs), e.g. adenosine receptors (ARs) and P2Y receptors (P2YRs), respectively. We synthesize selective agents for use as pharmacological probes and potential therapeutic agents (e.g. A3AR agonists for neuropathic pain). Detail...

Adenosine can induce hypothermia, as previously demonstrated for adenosine A1 receptor (A1AR) agonists. Here we use the potent, specific A3AR agonists MRS5698, MRS5841, and MRS5980 to show that adenosine also induces hypothermia via the A3AR. The hypothermic effect of A3AR agonists is independent of A1AR activation, as it was fully intact in mice l...

Major depressive disorder is among the most commonly diagnosed disabling mental diseases. Several non-pharmacological treatments of depression upregulate adenosine concentration and/or adenosine A1 receptors (A1R) in the brain. To test whether enhanced A1R signaling mediates antidepressant effects, we generated a transgenic mouse with enhanced doxy...

(1S,2R,3S,4R,5S)-4-(2-((5-Chlorothiophen-2-yl) ethynyl)-6-(methylamino)-9H-purin-9-yl)-2,3-dihydroxy-N-methylbicyclo[3.1.0]hexane-1-carboxamide (MRS5980) is an A3AR selective agonist containing multiple receptor affinity- and selectivity-enhancing modifications and a therapeutic candidate drug for many metabolic diseases. Metabolism-related poor ph...

We reported that 2-(3,4-difluorophenylethynyl)-N 6-3-chlorobenzyl (N)-methanocarba adenosine derivative 1 (MRS5698) binds selectively to human and mouse A3 adenosine receptors (A3ARs, K i 3 nM). It is becoming an important pharmacological tool for defining A3AR effects and is orally active in a chronic neuropathic pain model. Here, we introduce a n...

Substitution of rigidified A3 adenosine receptor (AR) agonists with a 2-((5-chlorothiophen-2-yl)ethynyl) or a 2-(4-(5-chlorothiophen-2-yl)-1H-1,2,3-triazol-1-yl) group provides prolonged protection in a model of chronic neuropathic pain. These agonists contain a bicyclo[3.1.0]hexane ((N)-methanocarba) ring system in place of ribose, which adopts a...

More than 1.5 billion people worldwide suffer from chronic pain, yet current treatment strategies often lack efficacy or have deleterious side effects in patients. Adenosine is an inhibitory neuromodulator that was previously thought to mediate antinociception through the A1 and A2A receptor subtypes. We have since demonstrated that A3AR agonists h...

2-Arylethynyl derivatives of (N)-methanocarba adenosine 5′-uronamides are selective A3AR (adenosine receptor) agonists. Here we substitute a 1,2,3-triazol-1-yl linker in place of the rigid, linear ethynyl group to eliminate its potential metabolic liability. Docking of nucleosides containing possible short linker moieties at the adenine C2 position...

(N)-Methanocarba adenosine 5'-methyluronamides containing 2-arylethynyl groups were synthesized as A3 adenosine receptor (AR) agonists and screened in vivo (po) for reduction of neuropathic pain. A small N(6)-methyl group maintained binding affinity, with human > mouse A3AR and MW < 500 and other favorable physicochemical properties. Emax (maximal...

Chronic pain is a global burden that promotes disability and unnecessary suffering. To date, efficacious treatment of chronic pain has not been achieved. Thus, new therapeutic targets are needed. Here, we demonstrate that increasing endogenous adenosine levels through selective adenosine kinase inhibition produces powerful analgesic effects in rode...

Chemotherapy-induced peripheral neuropathy (CIPN) accompanied by chronic neuropathic pain is the major dose-limiting toxicity of several anticancer agents including the taxane paclitaxel (Taxol(®)). A critical mechanism underlying paclitaxel-induced neuropathic pain is the increased production of peroxynitrite (PN) in spinal cord generated in respo...

Many commonly used chemotherapeutics including oxaliplatin are associated with the development of a painful chemotherapy-induced peripheral neuropathy (CIPN). This dose-limiting complication can appear long after the completion of therapy causing a significant reduction in quality-of-life and impeding cancer treatment. We recently reported that act...

2-Arylethynyl-(N)-methanocarba adenosine 5'-methyluronamides containing rigid N(6)-(trans-2-phenylcyclopropyl) and 2-phenylethynyl groups were synthesized as agonists for probing structural features of the A3 adenosine receptor (AR). Radioligand binding confirmed A3AR selectivity and N(6)-1S,2R stereoselectivity for one diastereomeric pair. The env...

We studied patterns of off-target receptor interactions, mostly at G protein-coupled receptors (GPCRs) in the µM range, of nucleoside derivatives that are highly engineered for nM interaction with adenosine receptors (ARs). Because of the considerable interest of using AR ligands for treating diseases of the CNS, we used the Psychoactive Drug Scree...

Chronic pain is a global burden that promotes disability and unnecessary suffering. To date, efficacious treatment of chronic pain has not been achieved. Thus, new therapeutic targets are needed. Here, we demonstrate that increasing endogenous adenosine levels through selective adenosine kinase inhibition produces powerful analgesic effects in rode...

(N)-Methanocarba (bicyclo[3.1.0]hexane)-adenosine derivatives were probed for sites of charged sulfonate substitution, which precludes diffusion across biological membranes, e.g. blood brain barrier. Molecular modeling predicted that sulfonate groups on C2-phenylethynyl substituents would provide high affinity at both mouse (m) and human (h) A3 ade...