Uridine triacetate (formally PN401) is an acetylated prodrug of uridine. Following oral administration, uridine triacetate is deacetylated by nonspecific esterases present throughout the body, yielding uridine in the circulation. Uridine triacetate under VISTOGARD trade name is a uridine replacement agent approved for the emergency treatment of fluorouracil or capecitabine overdose (regardless of the presence of symptoms) or early-onset severe or life-threatening cardiac or central nervous system (CNS) toxicity and/or early-onset unusually severe adverse reactions (eg, gastrointestinal [GI] toxicity and/or neutropenia) within 96 hours following the end of fluorouracil or capecitabine administration in adult and pediatric patients. Uridine competitively inhibits cell damage and cell death caused by fluorouracil. Fluorouracil is a cytotoxic antimetabolite that interferes with nucleic acid metabolism in normal and cancer cells. Cells anabolize fluorouracil to the cytotoxic intermediates 5-fluoro-2’-deoxyuridine-5’- monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP). FdUMP inhibits thymidylate synthase, blocking thymidine synthesis. Thymidine is required for DNA replication and repair. Uridine is not found in DNA. The second source of fluorouracil cytotoxicity is the incorporation of its metabolite, FUTP, into RNA. This incorporation of FUTP into RNA is proportional to systemic fluorouracil exposure. Excess circulating uridine derived from VISTOGARD is converted into uridine triphosphate (UTP), which competes with FUTP for incorporation into RNA. Uridine triacetate is also approved for the treatment of hereditary orotic aciduria under XURIDEN trade name. Uridine triacetate provides uridine in the systemic circulation of patients with hereditary orotic aciduria who cannot synthesize adequate quantities of uridine due to a genetic defect in uridine nucleotide synthesis.

Cladribine is used for the treatment of hairy cell leukemia and multiple sclerosis (MS). As a purine analog, it is a synthetic anti-cancer agent that also suppresses the immune system. Chemically, it mimics the nucleoside adenosine and thus inhibits the enzyme adenosine deaminase, which interferes with the cell's ability to process DNA. It can be distinguished from other chemotherapeutic agents affecting purine metabolism in that it is cytotoxic to both actively dividing and quiescent lymphocytes and monocytes, inhibiting both DNA synthesis and repair. Cladribine injection is a potent antineoplastic agent with potentially significant toxic side effects. In MS, the novel mechanism of action of cladribine is expected to reduce inflammation, autoimmune effects and autoreactive cell damage, thereby improving the integrity of the blood–brain barrier. Thus, the effects of cladribine may target some of the key events that are central to the pathophysiology of MS.

Binodenoson, a selective adenosine A(2A) receptor agonist, was being developed as a short-acting coronary vasodilator as an adjunct to radiotracers for use in myocardial stress imaging. Binodenoson for injection under the brand name CorVue was developed for use in patients with or at risk for coronary artery disease (CAD) who are unable to perform a cardiac exercise stress test. CorVue was designed to minimize side effects such as dyspnea, flushing, heart block, and chest pain. Binodenoson did not achieve FDA approval in 2009 due to concerns over equivalence of its efficacy with adenosine.

Piclidenoson (CF101), generically known as IB-MECA (methyl 1-[N6-(3-iodobenzyl)-adenin-9-yl]-b-D-ribofuronamide), is an oral small molecule drug formulated in a tablet. The activity of CF101 as an anti-inflammatory agent has been tested in a number of different experimental models including adjuvant and collagen induced arthritis and inflammatory bowel disease. CF101 is a highly specific agonist at the A3AR known to induce a robust anti-inflammatory effect in different experimental animal models. The CF101 mechanism of action entails down-regulation of the NF-κB-TNF-α signaling pathway, resulting in inhibition of pro-inflammatory cytokine production and apoptosis of inflammatory cells. Piclidenoson is currently being developed for the treatment of autoimmune inflammatory diseases like RA and psoriasis, hoping to replace the current standard of care, methotrexate (MTX). Can-Fite has tested CF101 in a number of Phase II studies in different diseases. A Phase II study in Psoriasis successfully met its primary endpoint showing that CF101 effectively ameliorated disease symptoms. In an interim analysis of the Phase II/III study the data justified full enrollment of the study. Phase II studies in Rheumatoid Arthritis (RA) demonstrated efficacy of CF101 given as a monotherapy. Moreover, a direct correlation between A3AR at baseline and patients’ response to CF101, suggesting its utilization as a predictive biomarker. Piclidenoson is headed into Phase 3 trials for RA and psoriasis.

8-chloroadenosine (8-Cl-Ado) is a ribonucleoside analog. The mechanism of its action remains poorly understood, however, it is known that the drug inhibits RNA synthesis. It has significant cytotoxic activity against lymphoid and myeloid malignant cells. The nucleoside analog 8-Cl-Ado is phosphorylated into its cytotoxic triphosphate 8-Cl-ATP. The accumulation of the cytotoxic metabolite results in a parallel decrease of the ATP cellular pools. 8-Cl-Ado gets incorporated into RNA during transcription, hindering this process. In addition, this triphosphate inhibits ATP-dependent poly(A) tail synthesis, and, as a consequence, mRNA processing is inhibited, resulting in vitro cytotoxicity in several solid and hematological malignancies. This agent is currently in clinical trials for the treatment of chronic lymphocytic leukemia and acute myeloid leukemia.