Forodesine hydrochloride is the salt of the synthetic high-affinity transition-state analog forodesine (BCX-1777, immucillin-H), a substrate designed to mimic the properties or the geometry of the transition state of reaction. It is an anticancer drug that has been developed for the treatment of different hematologic malignancies. In December 2006, orphan designation (EU/3/06/421) was granted by the European Commission to Napp Pharmaceuticals Research Limited, United Kingdom, for forodesine hydrochloride for the treatment of acute lymphoblastic leukemia. Forodesine hydrochloride has been evaluated in Phase I/Phase II clinical trials for several cancer types including chronic lymphocytic leukemia (CLL), B-Cell acute lymphoblastic leukemia and refractory cutaneous T-cell lymphoma (CTCL). Forodesine is a potent purine nucleoside phosphorylase (PNP) inhibitor that acts by elevating plasma 2'-deoxyguanosine (dGuo) and intracellular deoxyguanosine triphosphate, which in turn affects deoxynucleotide-triphosphate pools and induces cell death by apoptosis. Forodesine in the presence of dGuo inhibited the proliferation of CEM-SS (T-acute lymphoblastic leukemia) cells with an IC50 of 0.015 uM. This inhibition by forodesine and dGuo was accompanied by a 154-fold and 8-fold elevation of endogenous dGuo triphosphate (dGTP) and deoxyadenosine triphosphate (dATP) pools, respectively. Cytotoxic activity of forodesine in the presence of dGuo was selective to T lymphocytes. It is a 10- to 100-fold more potent inhibitor of human lymphocyte proliferation than other known PNP inhibitors such as PD141955 and BCX-34.8

Allopurinol riboside is a metabolite of allopurinol, a xanthine oxidase inhibitor indicated for the management of patients with leukemia, lymphoma, and solid tumor malignancies who are receiving cancer therapy which causes elevations of serum and urinary uric acid levels and who cannot tolerate oral therapy. Allopurinol riboside is not an inhibitor of xanthine oxidase. Allopurinol riboside is commonly thought to be directly synthesized by purine nucleoside phosphorylase (PNP) in vivo. Allopurinol riboside competitively inhibits the action of PNP on inosine in vitro. Allopurinol riboside potently inhibits growth in vitro of promastigotes of Leishmania species. Patients with American cutaneous leishmaniasis who received allopurinol riboside had clinical improvement. In addition, allopurinol riboside demonstrated some effectivity against Trypanosoma cruzi infections in animals.

Deoxyguanosine is a nucleoside consisting of the base guanine and the sugar deoxyribose. It is like guanosine, but with one oxygen atom removed. It is a nucleoside component of DNA. Deoxyguanosine can be converted to 8-hydroxy-deoxyguanosine (8-OHdG) due to hydroxyl radical attack at the C8 of guanine. 8-OHdG is a sensitive marker of the DNA damage This damage, if left unrepaired, has been proposed to contribute to mutagenicity and cancer promotion. Deoxyguanosine has long been recognized as a potent cytotoxic agent to cultured mammalian cells. This toxicity or inhibition of DNA synthesis by deoxyguanosine appears to be mediated by deoxyguanosine triphosphate-mediated inhibition of the enzyme ribonucleotide reductase. Purine nucleoside phosphorylase deficiency is thought to cause T-lymphocyte depletion by accumulation of deoxyguanosine and deoxyguanosine triphosphate, resulting in feedback inhibition of ribonucleotide reductase and hence DNA synthesis. Deoxyguanosine nucleoside analogs are potent antiviral agents.

Forodesine hydrochloride is the salt of the synthetic high-affinity transition-state analog forodesine (BCX-1777, immucillin-H), a substrate designed to mimic the properties or the geometry of the transition state of reaction. It is an anticancer drug that has been developed for the treatment of different hematologic malignancies. In December 2006, orphan designation (EU/3/06/421) was granted by the European Commission to Napp Pharmaceuticals Research Limited, United Kingdom, for forodesine hydrochloride for the treatment of acute lymphoblastic leukemia. Forodesine hydrochloride has been evaluated in Phase I/Phase II clinical trials for several cancer types including chronic lymphocytic leukemia (CLL), B-Cell acute lymphoblastic leukemia and refractory cutaneous T-cell lymphoma (CTCL). Forodesine is a potent purine nucleoside phosphorylase (PNP) inhibitor that acts by elevating plasma 2'-deoxyguanosine (dGuo) and intracellular deoxyguanosine triphosphate, which in turn affects deoxynucleotide-triphosphate pools and induces cell death by apoptosis. Forodesine in the presence of dGuo inhibited the proliferation of CEM-SS (T-acute lymphoblastic leukemia) cells with an IC50 of 0.015 uM. This inhibition by forodesine and dGuo was accompanied by a 154-fold and 8-fold elevation of endogenous dGuo triphosphate (dGTP) and deoxyadenosine triphosphate (dATP) pools, respectively. Cytotoxic activity of forodesine in the presence of dGuo was selective to T lymphocytes. It is a 10- to 100-fold more potent inhibitor of human lymphocyte proliferation than other known PNP inhibitors such as PD141955 and BCX-34.8