Purine Nucleoside Phosphorylase Inhibitor Research Articles

N-Phosphonocarbonylpyrrolidine Derivatives of Guanine: A New Class of Bi-Substrate Inhibitors of Human Purine Nucleoside Phosphorylase

A complete series of pyrrolidine nucleotides, (3R)- and (3S)-3-(guanin-9-yl)pyrrolidin-1-N-ylcarbonylphosphonic acids and (3S,4R)-, (3R,4S)-, (3S,4S)-, and (3R,4R)-4-(guanin-9-yl)-3-hydroxypyrrolidin-1-N-ylcarbonylphosphonic acids, were synthesized and evaluated as potential inhibitors of purine nucleoside phosphorylase (PNP) isolated from peripheral blood mononuclear cells (PBMCs) and cell lines of myeloid and lymphoid origin. Two compounds, (S)-3-(guanin-9-yl)pyrrolidin-1-N-ylcarbonylphosphonic acid (2a) and (3S,4R)-4-(guanin-9-yl)-3-hydroxypyrrolidin-1-N-ylcarbonylphosphonic acid (6a), were recognized as nanomolar competitive inhibitors of PNP isolated from cell lines with K(i) values within the ranges of 16-100 and 10-24 nM, respectively. The low (MESG)K(i) and (Pi)K(i) values of both compounds for PNP isolated from PBMCs suggest that these compounds could be bisubstrate inhibitors that occupy both the phosphate and nucleoside binding sites of the enzyme.

Clinical Trials and Treatment of ATL

ATL is a distinct peripheral T-lymphocytic malignancy associated with human T-cell lymphotropic virus type I (HTLV-1). The diversity in clinical features and prognosis of patients with this disease has led to its subtype-classification into four categories, acute, lymphoma, chronic, and smoldering types, defined by organ involvement, and LDH and calcium values. In case of acute, lymphoma, or unfavorable chronic subtypes (aggressive ATL), intensive chemotherapy like the LSG15 regimen (VCAP-AMP-VECP) is usually recommended if outside of clinical trials, based on the results of a phase 3 trial. In case of favorable chronic or smoldering ATL (indolent ATL), watchful waiting until disease progression has been recommended, although the long-term prognosis was inferior to those of, for instance, chronic lymphoid leukemia. Retrospective analysis suggested that the combination of interferon alpha and zidovudine was apparently promising for the treatment of ATL, especially for types with leukemic manifestation. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is also promising for the treatment of aggressive ATL possibly reflecting graft versus ATL effect. Several new agent trials for ATL are ongoing and in preparation, including a defucosylated humanized anti-CC chemokine receptor 4 monoclonal antibody, IL2-fused with diphtheria toxin, histone deacetylase inhibitors, a purine nucleoside phosphorylase inhibitor, a proteasome inhibitor, and lenalidomide.

Some inhibitors of purine nucleoside phosphorylase

Some inhibitors of purine nucleoside phosphorylase

Some inhibitors of purine nucleoside phosphorylase

Purine nucleoside phosphorylase (PNP) catalyzes reversible phosphorolysis of purine deoxy- and ribonucleosides with formation (d)Rib-1-P and corresponding bases. PNP plays a leading role in the cell metabolism of nucleosides and nucleotides, as well as in maintaining the immune status of an organism. The major aim of the majority of studies on the PNP is the detection of highly effective inhibitors of this enzyme, derivatives ofpurine nucleosides used in medicine as immunosuppressors, which are essential for creating selective T-cell immunodeficiency in a human body for organ and tissue transplantation. The present work is devoted to the study of the effects of some synthetic derivatives of purine nucleosides on activity of highly purified PNP from rabbit spleen and also from human healthy and tumor tissues of lung and kidneys. Purine nucleoside analogues modified at various positions of both the heterocyclic base and carbohydrate residues have been investigated. Several compounds, including 8-mercapto-acyclovir, 8-bromo-9-(3,4-hydroxy-butyl)guanine, which demonstrated potent PNP inhibition, could be offered for subsequent study as immunosuppressors during organ and tissue transplantation.

Adult T-cell leukemia–lymphoma: current treatment strategies and novel immunological approaches

Adult T-cell leukemia–lymphoma (ATL) is a peripheral T-cell malignancy, closely associated with human T-cell lymphotropic virus type I infection. Clinically, ATL is classified into four subtypes: acute, lymphoma, chronic and smoldering type. Although the prognosis of chronic and smoldering-type ATL is relatively good, that of patients with acute- or lymphoma-type ATL still remains extremely poor. Zidovudine/IFN-α therapy seems to be promising, although its efficacy has not yet been confirmed in well-designed prospective studies. High-dose chemotherapy with the support of autologous transplantation does not improve outcome. Allogeneic stem cell transplantation is promising and approximately 40% of aggressive ATL patients are expected to survive long-term, although transplantation-related mortality is as high as 40–50%. Stem cell transplantation using reduced-intensity conditioning is also effective and safer, with graft-versus-ATL and graft-versus-human T-cell lymphotropic virus type I effects observed after transplantation. Novel approaches including new agents such as purine nucleoside phosphorylase inhibitors and histone deacetylase inhibitors, or targeted immunotherapy using antichemokine receptor-4 antibody or dendritic cell/peptide vaccine are also warranted.

Phase I Study of Forodesine (BCX1777), An Oral PNP Inhibitor In Patients with Relapsed or Refractory T/NK Malignancies.

AbstractAbstract 1796 Background:Forodesine is a rationally designed potent inhibitor of purine nucleoside phosphorylase (PNP) that leads to elevation of plasma deoxyguanosine (dGuo) and intracellular accumulation of dGTP levels and then apoptosis mainly in T cells. Oral forodesine has shown clinical activity in patients with cutaneous T-cell lymphoma (CTCL) (M. Duvic et al, ASH 2007). The objective of this phase I study was to evaluate the safety, PK profile, and efficacy of oral forodesine in patients with recurrent or refractory T/NK malignancies in Japan. Methods:An open-label dose-escalation study of forodesine, 100 to 300 mg/body qd for 4 weeks, was conducted to evaluate safety profile (dose-limiting toxicities, DLT), tolerability and PK profile as primary endpoints. Forodesine was administered until disease progression or unacceptable toxicity is observed. Relapsed or refractory T/NK malignancies with PS 0 to 1 and without major organ dysfunction were eligible. Results:Overall, 13 Japanese patients, 8 males and 5 females, with a median age of 69 (range 30–77) years were enrolled in the study: 5 patients in the 100mg cohort, 3 in the 200mg cohort and 5 in the 300mg cohort. Patients' histopathologic subtypes were as follows: peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) (6 patients), anaplastic large cell lymphoma (ALCL) (3), primary cutaneous ALCL (C-ALCL) (2) and mycosis fungoides (MF) (2). Median stage and prior treatment regimen were IIIA (range IA-IVA) and 2 (range 1, 8), respectively.No DLT was observed and a maximum tolerated dose was never defined. The most common toxicities of grade 2 or less were constipation (39 %), rash (31%), lymphopenia (31 %), neutropenia (23 %), nausea (23 %), peripheral edema (23 %), LDH elevation (23 %) and leukopenia (23 %). The toxicities of grade 3 or greater were lymphopenia (62 %), anemia (15 %), leukopenia (8 %), thrombocytopenia (8 %) and viral infection (8 %). Median baseline, nadir, and last visit lymphocytes counts (1,000/μL) were 0.69 (95% CI: 0.56, 1.18), 0.35 (95% CI: 0.14, 0.60) and 0.60 (95% CI: 0.24, 0.95), respectively.Plasma levels for forodesine showed less than dose-proportional increase in exposure as mean AUC at Day 1 was 1,948 (ng·h/mL) in the 100mg cohort, 4,608 (ng·h/mL) in the 200mg cohort, and 4,596 (ng·h/mL) in the 300mg cohort. The levels for dGuo displayed a similar trend, with mean AUC at Day 1 4,023 (ng·h/mL) in the 100mg cohort, 5,705 (ng·h/mL) in the 200mg cohort, and 6,074 (ng·h/mL) in the 300mg cohort.One patient with ALCL reached complete response (CR) in the 100mg cohort and 2 patients with MF reached partial response in the 200mg cohort. In addition, 4 patients with stable disease (SD) were observed: 1 patient with PTCL-NOS in the 100mg cohort, 1 with C-ALCL in the 200mg cohort and 2 with C-ALCL and PTCL-NOS in the 300mg cohort. As of Aug, 2010, 2 patients with ALCL (CR patient in the 100mg cohort) and PTCL-NOS (SD patient in the 300mg cohort) have continued the treatment for more than 510 days and 290 days, respectively.Conclusion: Oral forodesine was well tolerated at all the dose levels tested with similar PK findings to those in the CTCL study in USA, demonstrating potential efficacy against relapsed or refractory T/NK lymphomas including PTCL for the first time. Based on these promising data, we are planning a phase I /II study of forodesine in patients with relapsed or refractory PTCL. Disclosures:No relevant conflicts of interest to declare.

Forodesine, a Purine Nucleoside Phosphorylase (PNP) Inhibitor, Shows Clinical Activity In a Phase 2 Trial In Patients with Previously Treated Chronic Lymphocytic Leukemia (CLL) – Interim Analysis

AbstractAbstract 1397 Introduction:Forodesine is a potent, specific transition-state inhibitor of the purine salvage pathway enzyme PNP. It induces apoptosis in primary CLL cells through accumulation of deoxyguanosine triphosphate. Unlike other nucleoside analogues, forodesine is not phosphorylated, is not incorporated into DNA and is not cytotoxic. Previous phase 1 and 2 studies showed clinical activity in T-cell acute lymphoblastic leukemia (i.v. forodesine) and cutaneous T-cell lymphoma (i.v. and oral). In a single institute exploratory study 5 of 13 (38%) CLL patients demonstrated anti-leukemic effects (decrease in peripheral blood malignant lymphocyte counts) with oral forodesine (200mg QD). However none of the patients achieved remission. Forodesine is absorbed via a saturable mechanism, and in a clinical pharmacology study in normal subjects, 200mg twice-daily (BID) dosing was found to partially overcome the exposure limits from once daily dosing; the 200mg BID regimen was used in the current study. Methods and Results:This is a multicenter phase II open label study. Eligible CLL patients had either failed at least 1 prior therapy (progressive disease [PD] or refractory) or were treatment-naïve provided age was >65 or ECOG 2 or 3, or unable to tolerate standard therapy. Among the 26 patients enrolled 1 was deemed ineligible (Waldenstrom's). The median age was 70 (48-92) years, 65% male and 77% had Rai Stage III/IV disease. The median duration from time to CLL diagnosis was 92.7 (8.4-243.5) months. Features of high-risk disease were del (17p) (n=6), ZAP70+ (n=13), and CD38+ (n=15). All patients had relapsed or refractory CLL with a median of 2 (1-21) prior therapies including fludarabine (76%), alkylating agents (72%), anti-CD20 monoclonal antibodies (72%) and experimental agents (36%). Interim analysis was conducted when 13 patients had been observed for ≥ 6 months: maximum duration of continuous BID forodesine therapy was 364 days. At the date of data cut-off, 20 were evaluable for response (5 were not evaluable because they had received < 8 weeks of therapy), and 12 were still on study. The revised NCI-WG (1996) criteria were used for response assessment. Partial remission was noted in 3 (15%) patients. Additionally 12 (48%) patients demonstrated stabilization of disease. PR onset was noted at 2, 6 and 6 months of therapy. Three patients discontinued due to adverse events (AEs). Serious AEs were reported in 18 patients. Individual SAEs reports included 7 cases of febrile neutropenia, 7 cases of non-neutropenic infections, pneumonia in 4, and herpes zoster in 1. Conclusion:Oral forodesine 200mg BID given continuously was generally safe and well-tolerated in previously-treated CLL patients. The overall response rate was 15%. These safety and efficacy results are particularly intriguing given the relapsed / refractory CLL population studied, which included elderly and poor performance status patients. Furthermore, we observed that, despite being a purine analog, forodesine was well tolerated with continuous daily dosing. This is particularly of interest when considering combination regimens with this new agent. Further studies of optimized dosing regimens of PNP inhibitors in CLL are warranted. These studies could include evaluation of forodesine in combination with other antileukemic agents with different mechanisms of action, in patients intolerant of or ineligible for aggressive conventional chemotherapeutic regimens, or maintenance treatment after conventional therapy. Updated results including ≥6 months follow up for all patients in the Phase II study will be presented at the meeting. Disclosures:Lyman:BioCryst Pharmaceuticals, Inc.: Employment, Equity Ownership. Cantey-Kiser:PharPoint Research, Inc.: Employment. Sheridan:BioCryst Pharmaceuticals, Inc.: Employment, Equity Ownership.

Forodesine: review of preclinical and clinical data.

Purine nucleoside phosphorylase (PNP) is an important catalytic enzyme in the purine salvage pathway; its deficiency is associated with T-cell lymphopenia and with humoral deficiency. This clinical observation led to the investigation of PNP inhibitors and their possible clinical application in the management of hematologic malignancies, notably those of T-cell lineage. Forodesine is the most potent of the PNP inhibitors. Its effect appears to be linked to increased 2 -deoxyguanosine levels in plasma, which in turn is converted to 2 -deoxyguanosine triphosphate in target cells and disrupts DNA synthesis. Several preclinical studies have shown forodesine's effect against lymphocytes in vitro and in vivo, and these findings have led to several Phase I/II studies in patients with lymphoid neoplasms. Early clinical trials show that forodesine has promise as a single agent for the treatment of relapsed/refractory hematologic malignancies, and combination therapies might be warranted to improve clinical results.

Influence of bone marrow stromal microenvironment on forodesine-induced responses in CLL primary cells

AbstractForodesine, a purine nucleoside phosphorylase inhibitor, displays in vitro activity in chronic lymphocytic leukemia (CLL) cells in presence of dGuo, which is the basis for an ongoing clinical trial in patients with fludarabine-refractory CLL. Initial clinical data indicate forodesine has significant activity on circulating CLL cells, but less activity in clearing CLL cells from tissues such as marrow. In tissue microenvironments, lymphocytes interact with accessory stromal cells that provide survival and drug-resistance signals, which may account for residual disease. Therefore, we investigated the impact of marrow stromal cells (MSCs) on forodesine-induced response in CLL lymphocytes. We demonstrate that spontaneous and forodesine-induced apoptosis of CLL cells was significantly inhibited by human and murine MSCs. Forodesine-promoted dGuo triphosphate (dGTP) accumulation and GTP and ATP depletion in CLL cells was inhibited by MSCs, providing a mechanism for resistance. Also, MSCs rescued CLL cells from forodesine-induced RNA- and protein-synthesis inhibition and stabilized and increased Mcl-1 transcript and protein levels. Conversely, MSC viability was not affected by forodesine and dGuo. Collectively, MSC-induced biochemical changes antagonized forodesine-induced CLL cell apoptosis. This provides a biochemical mechanism for MSC-derived resistance to forodesine and emphasizes the need to move toward combinations with agents that interfere with the microenvironment's protective role for improving current therapeutic efforts.

Phase 2 and pharmacodynamic study of oral forodesine in patients with advanced, fludarabine-treated chronic lymphocytic leukemia

AbstractForodesine is a new and potent purine nucleoside phosphorylase (PNP) inhibitor. Patients with chronic lymphocytic leukemia (CLL) with primary resistance to fludarabine-based therapy or with progressive disease were eligible for oral forodesine (200 mg/d) for up to 24 weeks. Eight patients with median lymphocyte count of 35.9 × 109/L and median serum β2 microglobulin level of 6.45 mg/L were treated. Six had Rai stage III to IV and were previously heavily treated (median prior therapy = 5). Two had transient decrease in lymphocyte count to normal, whereas in 5, disease progressed. Adverse events were mild. Steady-state level of forodesine ranged from 200 to 1300nM and did not reach desired 2µM level. PNP inhibition ranged from 57% to 89% and steady-state 2′-deoxyguanosine (dGuo) concentration median was 1.8µM. Intracellular deoxyguanosine triphosphate (dGTP) increase was very modest, from median of 6µM to 10µM. Compared with in vivo, in vitro incubations of CLL lymphocytes with 10 or 20µM dGuo and forodesine (2µM) resulted in accumulation of higher levels of dGTP (40-250µM) which resulted in increase in apoptosis. Forodesine has biologic activity in CLL; pharmacodynamic parameters suggest that an alternate dosing schedule and/or higher doses to achieve greater intracellular dGTP may be beneficial in this patient population. This study is registered at www.clinicaltrials.gov as #NCT00289549.

ChemInform Abstract: Certain 3,9-Dideazapurines as Inhibitors of Purine Nucleoside Phosphorylase.

Abstract The synthesis of four 3,9-dideazapurines is described. In order to achieve the desired substitution pattern, a new approach to the pyrrolo[2, 3-c]pyridine ring system was devised utilizing the Gassman reaction as the key step for its construction. The four target heterocycles were all evaluated for their ability to inhibit human erythrocytic purine nucleoside phosphorylase.

ChemInform Abstract: Synthesis of Transition State Analogue Inhibitors for Purine Nucleoside Phosphorylase and N-Riboside Hydrolases.

Abstract Syntheses of the ‘Immucillins’, potent aza-C-nucleoside inhibitors of purine nucleoside phosphorylase are reported as well as those of 5-deoxy-, 5-deoxyfluoro- and 2-deoxy- analogues and others having modified bases.

ChemInform Abstract: Synthesis and Biological Activity of a Novel Class of Purine Nucleoside Phosphorylase Inhibitors.

Abstract Purine nucleoside phosphorylase.(PNP, EC. 2.4.2.1) functions as a salvage enzyme in the purine and is important in the T-cell portion of the immune system As such, PNP is an important therapeutic target for diseases which are T-cell mediated. The biochemical basis for using PNP inhibitors as well as the various classes of inhibitors developed has been recently reviewed. Using X-ray crystallography we have designed and synthesized a series of 7-substituted 2-amino-1,5-dihydroHpyrrolo[3,2-djpyrimidin-4-ones which are potent PNP inhibitors .2-5 The 3-(pyridinylmethyl) derivative 1 (BCX-34, peldesine, IC50 = 0.036 ± 0.003 μM) is in clinical trials for the treatment of cutaneous T-cell Ivqphoma. acute lymphoblastic leukemia and HIV infections.

Targeting Plasmodium Falciparum Purine Salvage Enzymes: A Look At Structure-Based Drug Development

New antimalarials are needed due to the rapid development of resistance to currently deployed drugs. Because Plasmodium species are unable to synthesize purines, purine salvage pathways have been proposed as novel anti-malarial targets. The purine salvage pathway in Plasmodium is streamlined with adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) and hypoxanthine-xanthine-guanine-phosphoribosyltransferase (HXGPRT) representing the major pathway for purine acquisition. Plasmodium falciparum enzymes PfADA and PfPNP have unique dual specificity that enable them to act upon methylthiopurines resulting from polyamine synthesis. Thus Plasmodium ADA and PNP function in both purine salvage and purine recycling. Genetic studies have confirmed the importance of Plasmodium PNP for viability of malaria parasites. Immucillins, powerful picomolar transition state inhibitors of PNP, are active against cultured Plasmodium falciparum and inhibit all Plasmodium PNPs tested. Several immucillins have undergone human clinical trials, and these compounds represent a new class of compounds with potential activity against human malarias.

Potent orally bioavailable purine nucleoside phosphorylase inhibitor BCX-4208 induces apoptosis in B- and T-lymphocytes—A novel treatment approach for autoimmune diseases, organ transplantation and hematologic malignancies

The profound suppression of T-cell immunity seen in purine nucleoside phosphorylase (PNP; EC 2.4.2.1) deficient patients supports potential application of inhibitors of PNP in the therapy of T-cell mediated diseases. BCX-4208 is a novel potent transition state analog inhibitor of human PNP with an IC 50 of 0.5 nM. PNP inhibition leads to elevation of dGuo which is converted to dGTP mainly in lymphocytes causing imbalance in deoxynucleotide (dNTP) pools and cell apoptosis. In in vitro studies, neither BCX-4208 nor dGuo alone inhibits proliferation of lymphocytes. BCX-4208 in the presence of 10 µM deoxyguanosine (dGuo) inhibits lymphocyte proliferation induced by MLR, IL-2 or Con A with IC 50s of 0.159, 0.26 and 0.73 µM, respectively. The IC 50 for dGuo in the presence of 1 µM BCX-4208 for the IL-2 stimulated lymphocytes was 3.12 µM. dGTP in human lymphocytes is elevated and a 3–5 fold increase in dGTP results in 50% inhibition after in vitro exposure to BCX-4208 and dGuo. Flow cytometric analyses of human lymphocytes using annexin V staining reveal that BCX-4208 in the presence of dGuo induces cellular apoptosis in T-cells (CD3+), B-cells (CD20+, CD19+) and NK (CD56+) cells. BCX-4208 is orally bioavailable in mice and elevates plasma dGuo levels to 3.7 µM (predose levels < 0.004 µM), similar to levels seen in PNP-deficient patients and levels needed to cause apoptosis in T and B-cells. These data support the evaluation of BCX-4208 in the treatment of T-cell and B-cell mediated diseases. BCX-4208 is currently undergoing early clinical investigation in psoriasis and gout.

Clinical Trials for Human T-Cell Lymphotropic Virus Type I–Associated Peripheral T-Cell Lymphoma in Japan

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).

Novel Agents in Development for Peripheral T-Cell Lymphoma

Though peripheral T-cell lymphoma (PTCL) is an area of significant unmet therapeutic need, a number of new treatment options are available for patients, especially those with relapsed or refractory disease. A plethora of drugs are now in development for PTCL, but drugs that truly target novel disease biology are noticeably absent. Combinations of T-cell centric agents could produce novel platforms of therapy to replace the relatively ineffective CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone)-based regimens. Among agents with T-cell activity are the folate analog pralatrexate, histone deacetylase inhibitors (HDACi) like romidepsin, the proteasome inhibitor bortezomib, the immunomodulatory agent lenalidomide, the purine nucleoside phosphorylase (PNP) inhibitor forodesine, the nucleoside analog gemcitabine, and BH3-only mimetics like ABT-263 and ABT-737.

9‐Deazaguanine derivatives connected by a linker to difluoromethylene phosphonic acid are slow‐binding picomolar inhibitors of trimeric purine nucleoside phosphorylase

Genetic deficiency of purine nucleoside phosphorylase (PNP; EC 2.4.2.1) activity leads to a severe selective disorder of T-cell function. Therefore, potent inhibitors of mammalian PNP are expected to act as selective immunosuppressive agents against, for example, T-cell cancers and some autoimmune diseases. 9-(5',5'-difluoro-5'-phosphonopentyl)-9-deazaguanine (DFPP-DG) was found to be a slow- and tight-binding inhibitor of mammalian PNP. The inhibition constant at equilibrium (1 mm phosphate concentration) with calf spleen PNP was shown to be = 85 +/- 13 pm (pH 7.0, 25 degrees C), whereas the apparent inhibition constant determined by classical methods was two orders of magnitude higher ( = 4.4 +/- 0.6 nm). The rate constant for formation of the enzyme/inhibitor reversible complex is (8.4 +/- 0.5) x 10(5) m(-1).s(-1), which is a value that is too low to be diffusion-controlled. The picomolar binding of DFPP-DG was confirmed by fluorimetric titration, which led to a dissociation constant of 254 pm (68% confidence interval is 147-389 pm). Stopped-flow experiments, together with the above data, are most consistent with a two-step binding mechanism: E + I <--> (EI) <--> (EI)*. The rate constants for reversible enzyme/inhibitor complex formation (EI), and for the conformational change (EI) <--> (EI)*, are k(on1) = (17.46 +/- 0.05) x 10(5) m(-1).s(-1), k(off1) = (0.021 +/- 0.003) s(-1), k(on2) = (1.22 +/- 0.08) s(-1) and k(off2) = (0.024 +/- 0.005) s(-1), respectively. This leads to inhibition constants for the first (EI) and second (EI)* complexes of K(i) = 12.1 nM (68% confidence interval is 8.7-15.5 nm) and = 237 pm (68% confidence interval is 123-401 pm), respectively. At a concentration of 10(-4) m, DFPP-DG exhibits weak, but statistically significant, inhibition of the growth of cell lines sensible to inhibition of PNP activity, such as human adult T-cell leukaemia and lymphoma (Jurkat, HuT78 and CCRF-CEM). Similar inhibitory activities of the tested compound were noted on the growth of lymphocytes collected from patients with Hashimoto's thyroiditis and Graves' disease. The observed weak cytotoxicity may be a result of poor membrane permeability.

Current and Emerging Treatment Strategies for Cutaneous T-cell Lymphoma

Cutaneous T-cell lymphomas (CTCLs) are a rare group of mature T-cell lymphomas presenting primarily in the skin. The most common subtypes of CTCL are mycosis fungoides and its leukaemic variant Sézary's syndrome. Patients with early-stage disease frequently have an indolent clinical course; however, those with advanced stages have a shortened survival. For the treating physician, the question of how to choose a particular therapy in the management of CTCL is important. These diseases span the disciplines of dermatology, medical oncology and radiation oncology. Other than an allogeneic stem cell transplant, there are no curative therapies for this disease. Hence, many treatment modalities need to be offered to the patient over the course of their life. An accepted treatment approach has been to delay traditional chemotherapy, which can cause excessive toxicity without durable benefit. More conservative treatment strategies in the initial management of CTCL have led to the development of newer biological and targeted therapies. These therapies include biological immune enhancers such as interferon alpha and extracorporeal photopheresis that exert their effect by stimulating an immune response to the tumour cells. Retinoids such as bexarotene have been shown to be effective and well tolerated with predictable adverse effects. The fusion toxin denileukin diftitox targets the interleukin-2 receptor expressed on malignant T cells. Histone deacetylase inhibitors such as vorinostat and romidepsin (depsipeptide) may reverse the epigenetic states associated with cancer. Forodesine is a novel inhibitor of purine nucleoside phosphorylase and leads to apoptosis of malignant T cells. Pralatrexate is a novel targeted antifolate that targets the reduced folate carrier in cancer cells. Lastly, systemic chemotherapy including transplantation is used when rapid disease control is needed or if all other biological therapies have failed. As response rates to most of the biological agents used to treat CTCL are 25-30%, it is also reasonable to consider clinical trials with novel agents if one or two front-line therapies have failed, especially before considering chemotherapy. CTCL is largely an incurable disease with significant morbidity and more active agents are needed.

Synthesis of Purine Nucleoside Phosphorylase Inhibitor BCX-4208

BCX-4208 is an inhibitor of purine nucleoside phosphorylase (PNP). It is currently undergoing clinical trials for the treatment of ­relapsed/resistant T-cell leukemia. The synthesis depicted in the scheme provided 25 kg batches of the drug.