Development of Drugs Acting at Adenosine Receptors

National Institute Of Diabetes And Digestive And Kidney Diseases

Investigators

Linked publications, trials & patents

Abstract

We showed that our recent A3AR molecular model, obtained using AlphaFold, is essential identical to the recently determined structure. Our novel selective A3AR agonists and antagonists containing a methanocarba (bicyclo3.1.0hexane) ribose-ring substitution constrained in the receptor-preferred North (N) conformation have enhanced pharmacological profiles. Also, at the A1AR, (N)-methanocarba nucleosides were truncated to eliminate 5-CH2OH with partial or full retention of agonism. Truncated derivatives have more drug-like physical properties; this approach is appealing for preclinical development of nucleoside analogues. Our ongoing program to develop selective A3AR agonists has resulted in advanced clinical trials of two nucleosides, and early stage trials of a third. Therapeutic interests related to selective ligands for the A3AR are anti-inflammatory, anti-ischemic (e.g. in the heart, brain, lungs, and skeletal muscle) and anticancer, by molecular mechanisms that entail modulation of the Wnt and the NF-kB signal transduction pathways. The A3AR is overexpressed in inflammatory and cancer cells, while low expression is found in normal cells, rendering the A3AR as a potential therapeutic target. Currently, A3AR agonists discovered in our lab (IB-MECA and Cl-IB-MECA) are already in Phase 3 clinical trials. Another AR agonist, MRS4322 (a (N)-methanocarba nucleoside), recently entered a Phase 2 clinical trial for concussion, and is also intended for stroke/traumatic brain injury. If successful, it would fill an unmet medical need. We are studying the inhibition of ABC transporters by A3 agonists and synthesizing nucleosides that are selective for transporters. We designed a masked, photocleavable derivative of A3 agonist MRS5698 that can be used as a light-activated prodrug for skin conditions. When administered systemically, it was protective in a mouse model of IL-23 induced psoriasis, but only when the lesion area was irradiated with blue light. This is one of the first examples of light-directed delivery of a potent GPCR ligand selectively to the skin to act as an anti-inflammatory agent. Sterically constrained ((N)-methanocarba) adenosine derivatives were nanomolar full agonists of the A3AR and highly selective (>3000-fold). Combined 2-arylethynyl-N6-3-chlorobenzyl substitutions preserved A3AR affinity/selectivity (e.g., 3,4-difluorophenylethynyl full agonist MRS5698). We discovered rationally designed macrocyclic derivatives of small molecular GPCR agonists, i.e. closing a ring as predicted by molecular modeling to preserve high A3 agonist affinity. There were differences between Cl-IB-MECA and the macrocycles in the spectrum of signaling pathways. In collaboration with Daniela Salvemini, we have shown potent protection by A3AR agonists in models of chronic neuropathic pain, including visceral pain. Surprisingly, functional A3AR also occurs on mitochondria. A3AR agonists suppress or prevent the development of chronic neuropathic pain in mice following chronic constriction injury or cancer chemotherapeutic agents (by both central and peripheral mechanisms). Highly selective A3 agonists MRS5698 and MRS5980 were more potent and efficacious than morphine. If used therapeutically, A3 agonists could facilitate the life-saving use of cancer chemotherapy, which often has to be limited or discontinued because of severe side effects such as pain. A3 agonists in combination with opioids reduce opioid side effects to tolerance, withdrawal and opioid-induced hyperalgesia. In collaboration with Laura Lucarini, we identified a new beneficial A3AR agonist activity in a mouse model of lung fibrosis. Another promising application of AR ligands is the use of A3AR antagonists for topical application in the treatment of glaucoma. Certain A3AR antagonists from our lab and outside collaborations are licensed for development as antiglaucoma agents. Blocking A2A and or A2B receptors with antagonists is being explored to boost cancer immunotherapy. Our collaboration with Lak Shin Jeong demonstrated that a thiophene modification at the C8 position in the common adenine scaffold converted an A2AAR agonist into an antagonist, useful for reducing cancer cell and tumor proliferation. We discovered that protein kinase C (PKC) both enhances and activates the A2B adenosine receptor. Thus, anticancer A2B antagonists may act in two ways, blocking the effects of local adenosine and PKC (also an anticancer target for inhibitors). A means of lowering adenosine in the tumor microenvironment is to inhibit the enzyme CD73, and we have discovered novel nucleotide inhibitors of CD73. We have discovered positive allosteric modulators (PAMs) of the A3AR that magnify the beneficial effects of the endogenous adenosine released during stress conditions. These effects of the PAMs would be event-specific within the body, i.e. the PAM would have no biological effect on its own unless adenosine was locally elevated. In collaboration with John Auchampach (Med. Coll. Wisconsin), we recently expanded the range of heterocyclic PAMs of the A3AR and demonstrated that they have an unexpected site of action: on the intracellular side of the receptor. We are introducing varied functionality on the amine-terminal chains that interact with anionic phospholipids on the inner leaflet of the plasma membrane. A1 agonists are cerebroprotective and anticonvulsant agents. Most known A1 receptor agonists display unacceptable cardiovascular side effects due to their peripheral action. However, MRS5474, a mixed A3/A1 agonist is efficacious without these side effects. The compound is on a translational path.