pyrimidinones and Leukemia-Lymphoma--Adult-T-Cell

The most common subtype of T-/natural killer (NK) cell lymphoma in Japan is adult T-cell leukemia-lymphoma (ATL), which is associated with the human T-cell lymphotropic virus type I (HTLV-1). The investigators in Japan have conducted several clinical trials on multi-agent chemotherapy and stem cell transplantation for patients with ATL. They have also initiated several new clinical trials with a number of agents: an anti-CCR4 antibody, KW-0761; forodesine, a purine nucleoside phosphorylase inhibitor; and lenalidomide, an immunomodulatory agent. Clinical trials with pralatrexate, a folate analog, and denileukin diftitox, an immunoconjugate, are under discussion for patients with ATL and peripheral T-cell lymphoma (PTCL).

Topics: Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antineoplastic Combined Chemotherapy Protocols; Clinical Trials as Topic; Combined Modality Therapy; Drugs, Investigational; Hematopoietic Stem Cell Transplantation; Humans; Immunologic Factors; Japan; Lenalidomide; Leukemia-Lymphoma, Adult T-Cell; Multicenter Studies as Topic; Purine Nucleosides; Pyrimidinones; Thalidomide; Treatment Outcome

Purine nucleoside phosphorylase (PNP) deficiency is a rare, inherited immunodeficiency disorder in which the specific molecular defect was identified. Clinically, a lack of PNP manifests as profound T-cell deficiency with minor or variable changes in the humoral system. Biochemically, the absence of PNP results in an increase in plasma deoxyguanosine (dGuo) and a T-cell-specific increase in intracellular deoxyguanosine triphosphate (dGTP). This observation has been the impetus for the search for either inhibitors of the enzyme or PNP-resistant dGuo analogues as potential anti-T-cell-lineage agents over the past 30 years. Forodesine (an inhibitor of PNP) and nelarabine (a PNP-resistant dGuo analogue) proved to be T-cell selective when tested in clinic. This review summarises the preclinical, clinical and pharmacokinetic investigations with these novel agents.

Topics: Adult; Animals; Antimetabolites, Antineoplastic; Arabinonucleosides; Child; Clinical Trials, Phase I as Topic; Clinical Trials, Phase II as Topic; Deoxyguanosine; Drug Design; Drug Screening Assays, Antitumor; Drugs, Investigational; Humans; Leukemia-Lymphoma, Adult T-Cell; Leukemia, Experimental; Lymphoma, T-Cell; Mice; Neoplasm Proteins; Purine Nucleosides; Purine-Nucleoside Phosphorylase; Pyrimidinones; Pyrroles; T-Lymphocytes

Purine nucleoside phosphorylase (PNP) deficiency in humans produces a relatively selective depletion of T cells. BCX-1777 is a potent inhibitor of PNP. BCX-1777 in the presence of deoxyguanosine (dGuo) inhibits the proliferation of CEM-SS [T-acute lymphoblastic leukemia (T-ALL)] cells with an IC(50)=0.015 microM. This inhibition by BCX-1777 and dGuo is accompanied by elevation of dGTP (154-fold) and dATP (8-fold). Deoxycytidine (dCyt) completely and lamivudine (3TC) partially reverse this inhibition caused by BCX-1777 and dGuo. dNTP analysis of these samples indicates that, in the presence of dCyt, where complete reversal of inhibition is observed, dGTP and dATP pools revert back to the control levels. In samples containing 3TC, where partial reversal of inhibition was observed, dGTP decreased from 154-fold to 38-fold and dATP levels further increased from 8-fold to 30-fold compared to the control sample. In CEM-SS cells, inhibition of proliferation by BCX-1777 and dGuo is not due to accumulation of dATP because in the presence of 3TC, where reversal of inhibition is observed, dATP levels are further increased. These studies clearly indicate that inhibition of T cells is due to accumulation of dGTP resulting in cell death with characteristics of apoptosis. The half-life of dGTP in CEM-SS cells is 18 h, which is longer than that observed in human lymphocytes (4 h), suggesting that the nucleotidase level in CEM-SS cells is lower than in human lymphocytes. A 154-fold accumulation of dGTP in CEM-SS cells in the presence of BCX-1777 and dGuo compared to a 15-fold accumulation of dGTP in human lymphocytes suggests that kinase level is higher in CEM-SS cells compared to human lymphocytes. High kinase and low nucleotidase levels make CEM-SS cells more sensitive to inhibition by BCX-1777 and dGuo than human lymphocytes. Currently, BCX-1777 is in phase I/II clinical trial for the treatment of T cell malignancies.

Topics: Apoptosis; Cell Division; Cell Line; Culture Media; Half-Life; HIV Reverse Transcriptase; Humans; Lamivudine; Leukemia-Lymphoma, Adult T-Cell; Lymphocytes; Purine Nucleosides; Purine-Nucleoside Phosphorylase; Pyrimidinones; Pyrroles; Reverse Transcriptase Inhibitors; Stavudine