Purine Nucleoside Phosphorylase Inhibitor Research Articles

Antiproliferative Activity of Purine Nucleoside Phosphorylase Multisubstrate Analogue Inhibitors Containing Difluoromethylene Phosphonic Acid against Leukaemia and Lymphoma Cells

Potent inhibitors of purine nucleoside phosphorylase (PNP) are expected to act as selective agents against T-cell tumours. Five compounds with guanine, three with hypoxanthine, and five with 9-deazaguanine, all connected by a linker with difluoromethylene phosphonic acid, were studied on their inhibitory potential against human and calf PNPs. Antiproliferative activity of these analogues against lymphocytes as well as lymphoma and leukaemia cells has been also investigated. All tested compounds act as multisubstrate analogue inhibitors of PNP with the apparent inhibition constants in the range 5-100 nm, and also show a slight antiproliferative activity. Analogues with 9-deazaguanine aglycone have better anti-leukaemic and anti-lymphoma activities compared to the guanine and hypoxanthine analogues, and applied in the concentration of 100 mum, caused a statistically significant decrease in the cell viability in all human leukaemia and lymphoma cells used. Despite the high PNP inhibitory potential of tested analogues, no differences were observed between the effects on the growth of tumour cells sensible to the inhibition of PNP, such as human adult T-cell leukaemia and lymphoma cells, and other investigated cells. Obtained poor effects on cell proliferation could be explained probably by a poor ability of tested compounds to penetrate cell membranes.

Structural basis for selective inhibition of purine nucleoside phosphorylase from Schistosoma mansoni: Kinetic and structural studies

Selectivity plays a crucial role in the design of enzyme inhibitors as novel antiparasitic agents, particularly in cases where the target enzyme is also present in the human host. Purine nucleoside phosphorylase from Schistosoma mansoni (SmPNP) is an attractive target for the discovery of potential antischistosomal agents. In the present work, kinetic studies were carried out in order to determine the inhibitory potency, mode of action and enzyme selectivity of a series of inhibitors of SmPNP. In addition, crystallographic studies provided important structural insights for rational inhibitor design, revealing consistent structural differences in the binding mode of the inhibitors in the active sites of the SmPNP and human PNP (HsPNP) structures. The molecular information gathered in this work should be useful for future medicinal chemistry efforts in the design of new inhibitors of SmPNP having increased affinity and selectivity.

The Effects of Forodesine in Murine and Human Multiple Myeloma Cells

Multiple myeloma (MM) is the second most commonly diagnosed hematological malignancy, characterized by a monoclonal proliferation of malignant cells in the bone marrow. Despite recent advances in treatment strategies, MM remains incurable and new therapeutical targets are needed. Recently forodesine, a purine nucleoside phosphorylase inhibitor, was found to induce apoptosis in leukemic cells of chronic lymphocytic leukemia patients by increasing the dGTP levels. We therefore tested whether forodesine was able to inhibit proliferation and/or induce apoptosis in both murine and human MM cells through a similar pathway. We found that after 48 hours of treatment with forodesine there was a slight dGTP increase in 5T33MM and RPMI-8226 MM cells associated with partial inhibition of proliferation and a limited induction of apoptosis. When investigating the pathways leading to cell cycle arrest and apoptosis, we observed an upregulation of p27, caspase 3, and BIM. We can conclude that forodesine has some effects on MM cells but not as impressive as the known effects in leukemic cells. Forodesine might be however potentiating towards other established cytotoxic drugs in MM.

Phase II, Single Center Study of Oral Forodesine in Patients with Advanced, Fludarabine-Treated Chronic Lymphocytic Leukemia (CLL).

Abstract 2369Poster Board II-346 Background:The prognosis of fludarabine-refractory patients is poor and the current salvage regimens produce low CR rates and are unlikely to improve long-term survival in this patient population. Forodesine, an analog inhibitor of the enzyme purine nucleoside phosphorylase (PNP), leads to rise in plasma dGuo levels followed by accumulation of dGTP in T-cells,that results in DNA breakdown and cell apoptosis. Forodesine has exhibited promising clinical activity in T cell leukemia with complete inhibition of PNP during therapy (Gandhi et al, Blood 106:4253, 2005). Previous in-vitro studies conducted by our group demonstrated that forodesine induces caspase dependent cell death in primary CLL cells by accumulating high intracellular dGTP in CLL cells (Balakrishnan et al, Blood 108:2392, 2006). This provided the rationale to test forodesine in B-CLL. Aims:i) to investigate the efficacy (CR + PR) of forodesine in treating patients with advanced, fludarabine-treated CLL, ii) to evaluate the toxicity, duration of response, disease-free survival and overall survival associated with treatment with forodesine, and iii) to correlate PK/PD data of forodesine in CLL with its clinical activity. Methods:Patients with primary resistance to fludarabine-based therapy (no CR or PR) or with progressive disease after response to prior fludarabine based regimen were eligible. The forodesine dose was 200 mg oral once daily, administered continuously up to a maximum of 24 weeks. Blood samples were collected on days 1-5 and day 28 and pharmacokinetic and pharmacodynamic parameters were determined. Ex vivo incubation with forodesine and dGuo were also performed in CLL lymphocytes to compare the treatment effects in vivo and ex vivo investigations. Results:8 patients were treated, the median age was 62 years (range 51-68), 7 males, median absolute lymphocyte count 35.85 (range 1.4-156.66) × 109/L, median serum beta 2 microglobulin level was 6.45 (range 3.6-16.3) mg/L. Six patients had Rai stage III-IV disease, the, median number of prior therapy was 5 (range 1-10), 5 patients were fludarabine refractory, 5 were ZAP-70 positive. Seven patients are evaluable for response and toxicity. Two patients had a transient decrease in their absolute lymphocyte count to normal level after the first 4 weeks, but it was short lasting. In the other 5 patients, the WBC counts increased progressively and in 3 patients there was also progression in lymphadenopathies. The toxicities observed were mild and included fatigue, bronchitis, diarrhea and low grade fever. Myelosuppression was transient and included neutropenia thrombocytopenia in 3 patients. One patient had pneumonia.The steady-state level of forodesine, measured on day 2, 3, 4, and 5, ranged between 200-1300 nM (n=8). At these concentrations, PNP inhibition in circulating RBCs, ranged between 57 and 89% (n=8). With this extent of PNP inhibition, steady-state dGuo concentration was a median 1.8 μM (range, 0.56 – 4.4 μM, n=8). The starting level of intracellular dGTP was a median 5 μM (range, 0.9 - 7.8 μM, n = 7) which increased to a median 12.5 μM (range 1.9 - 65 μM, n = 7). The circulating lymphocytes did not show annexin positivity above 10% during the first five days of treatment. To determine if CLL lymphocytes accumulate dGTP at high dGuo (10 and 20 μM) levels, we performed ex vivo incubations. Compared to in vivo, higher levels of dGTP were achieved ex vivo with a 10-50% increase in apoptosis. Conclusion:Oral forodesine showed activity with decrease in peripheral lymphocyte counts in 2 of 7 evaluable patients. However, all patients ultimately progressed while on treatment. Side effects were mild. The ex vivo biologic data and in vivo pharmacodynamic and clinical data suggest that forodesine has biological activity, and that alternative dosing schedules should be explored in future CLL trials. Disclosures:Off Label Use: Forodesine is not approved by FDA for treatment of CLL. Bantia:BioCryst: Employment. Gandhi:Mundipharma: Honoraria, Research Funding; Biocryst: Honoraria, Research Funding. Ravandi:Biocryst: Research Funding.

Transition States

Transition States

Transport of purines and purine salvage pathway inhibitors by the Plasmodium falciparum equilibrative nucleoside transporter PfENT1

Plasmodium falciparum is a purine auxotroph. The transport of purine nucleosides and nucleobases from the host erythrocyte to the parasite cytoplasm is essential to support parasite growth. P. falciparum equilibrative nucleoside transporter 1 (PfENT1) is a major route for purine transport across the parasite plasma membrane. Malarial parasites are sensitive to inhibitors of purine salvage pathway enzymes. The immucillin class of purine nucleoside phosphorylase inhibitors and the adenosine analog, tubercidin, block growth of P. falciparum under in vitro culture conditions. We sought to determine whether these inhibitors utilize PfENT1 to gain access to the parasite cytosol. There is considerable controversy in the literature regarding the Km and/or Ki for purine transport by PfENT1 in the Xenopus oocyte expression system. We show that oocytes metabolize adenosine but not hypoxanthine. For adenosine, metabolism is the rate limiting step in oocyte uptake assays, making hypoxanthine the preferred substrate for PfENT1 transport studies in oocytes. We demonstrate that the Ki for PfENT1 transport of hypoxanthine and adenosine is in the 300–700μM range. Effects of substrate metabolism on uptake studies may explain conflicting results in the literature regarding the PfENT1 adenosine transport Km. PfENT1 transports the tubercidin class of compounds. None of the immucillin compounds tested inhibited PfENT1 transport of [3H]hypoxanthine or [3H]adenosine. Although nucleobases are transported, modifications of the ribose ring in corresponding nucleoside analogs affect substrate recognition by PfENT1. These results provide new insights into PfENT1 and the mechanism by which purine salvage pathway inhibitors are transported into the parasite cytoplasm.

Development of a Practical Synthesis of a Purine Nucleoside Phosphorylase Inhibitor: BCX-4208

A practical synthesis of the purine nucleoside phosphorylase (PNP) inhibitor BCX-4208 (1) was accomplished in three telescoped steps. Mannich condensation of the 4-benzyloxy-9-deazahypoxanthine with (3R,4R)-3-hydroxy-4-(hydroxymethyl)pyrrolidine and formaldehyde followed by removal of the protecting group and crystallization furnished the desired product as a hydrochloride salt in 85% overall yield and 99.8% purity. A scalable synthesis of 9-deazahypoxanthine is also reported.

Alternative route towards the convergent synthesis of a human purine nucleoside phosphorylase inhibitor—forodesine HCl

Forodesine HCl is being investigated as a potential target for the control of T-cell proliferation. Herein we present an alternative route for the synthesis of the target molecule with addition of lactam to the lithiated deazahypoxanthine (generated in situ). The lactam was synthesized in five steps starting from l-pyroglutamic acid.

Mechanism of Thiol-Supported Arsenate Reduction Mediated by Phosphorolytic-Arsenolytic Enzymes

Enzymes catalyzing the phosphorolytic cleavage of their substrates can reduce arsenate (AsV) to the more toxic arsenite (AsIII) via the arsenolytic substrate cleavage in presence of a reductant, as glutathione or dithiotreitol (DTT). We have shown this for purine nucleoside phosphorylase (PNP), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glycogen phosphorylase-a (GPa), and phosphotransacetylase (PTA). Using a multidisciplinary approach, we explored the mechanism whereby these enzymes mediate AsV reduction. It is known that PNP cleaves inosine with AsV into hypoxanthine and ribose-1-arsenate. In presence of inosine, AsV and DTT, PNP mediates AsIII formation. In this study, we incubated PNP first with inosine and AsV, allowing the arsenolytic reaction to run, then blocked this reaction with the PNP inhibitor BCX-1777, added DTT and continued the incubation. Despite inhibition of PNP, large amount of AsIII was formed in these incubations, indicating that PNP does not reduce AsV directly but forms a product (i.e., ribose-1-arsenate) that is reduced to AsIII by DTT. Similar studies with the other arsenolytic enzymes (GPa, GAPDH, and PTA) yielded similar results. Various thiols that differentially supported AsV reduction when present during PNP-catalyzed arsenolysis (DTT approximately dimercaptopropane-1-sulfonic acid > mercaptoethanol > DMSA > GSH) similarly supported AsV reduction when added only after a transient PNP-catalyzed arsenolysis, which preformed ribose-1-arsenate. Experiments with progressively delayed addition of DTT after BCX-1777 indicated that ribose-1-arsenate is short-lived with a half-life of 4 min. In conclusion, phosphorolytic enzymes, such as PNP, GAPDH, GPa, and PTA, promote thiol-dependent AsV reduction because they convert AsV into arsenylated products reducible by thiols more readily than AsV. In support of this view, reactivity studies using conceptual density functional theory reactivity descriptors (local softness, nucleofugality) indicate that reduction by thiols of the arsenylated metabolites is favored over AsV.

Altered Enthalpy−Entropy Compensation in Picomolar Transition State Analogues of Human Purine Nucleoside Phosphorylase

Human purine nucleoside phosphorylase (PNP) belongs to the trimeric class of PNPs and is essential for catabolism of deoxyguanosine. Genetic deficiency of PNP in humans causes a specific T-cell immune deficiency, and transition state analogue inhibitors of PNP are in development for treatment of T-cell cancers and autoimmune disorders. Four generations of Immucillins have been developed, each of which contains inhibitors binding with picomolar affinity to human PNP. Full inhibition of PNP occurs upon binding to the first of three subunits, and binding to subsequent sites occurs with negative cooperativity. In contrast, substrate analogue and product bind without cooperativity. Titrations of human PNP using isothermal calorimetry indicate that binding of a structurally rigid first-generation Immucillin (K(d) = 56 pM) is driven by large negative enthalpy values (DeltaH = -21.2 kcal/mol) with a substantial entropic (-TDeltaS) penalty. The tightest-binding inhibitors (K(d) = 5-9 pM) have increased conformational flexibility. Despite their conformational freedom in solution, flexible inhibitors bind with high affinity because of reduced entropic penalties. Entropic penalties are proposed to arise from conformational freezing of the PNP.inhibitor complex with the entropy term dominated by protein dynamics. The conformationally flexible Immucillins reduce the system entropic penalty. Disrupting the ribosyl 5'-hydroxyl interaction of transition state analogues with PNP causes favorable entropy of binding. Tight binding of the 17 Immucillins is characterized by large enthalpic contributions, emphasizing their similarity to the transition state. Via introduction of flexibility into the inhibitor structure, the enthalpy-entropy compensation pattern is altered to permit tighter binding.

Long-term treatment of CTCL with the oral PNP inhibitor, forodesine

8552 Background: Forodesine is a potent inhibitor of purine nucleoside phosphorylase (PNP) that leads to T-cell selective intracellular accumulation of dGTP, resulting in apoptosis. Methods: An open-label dose escalation study of oral forodesine (40–320 mg/m2 daily) for 4 wks with extended therapy was performed to determine the maximum tolerated and/or optimal biologic dose (OBD). Additional subjects were accrued at an OBD (80 mg/m2) to further assess safety and clinical efficacy. Subjects with refractory CTCL, stages IB-IV were eligible. The primary efficacy endpoint (objective response rate [ORR]) was defined as ≥ 50% improvement by a severity-weighted assessment tool (mSWAT). Results: The overall intent to treat response rate was 17 of 64 (27%) subjects or 14 of 36 (39%) at the OBD. As of October 2008, nine of 64 subjects (14%) have received forodesine treatment for >12 months. This cohort of 9 subjects is further examined. Six discontinued treatment (median time on treatment 440 days): 4 for progressive disease, 1 withdrew consent, and 1 due to an adverse event (Diffuse Large B-cell Lymphoma). Three are continuing on therapy for 416, 710, and 863 days. Median age was 68 years (range 42, 81), and all but one was ≥ stage III. They had received a median of 3 prior systemic therapies including 8 of 9 with prior bexarotene. Five of 9 subjects had a response (2 with complete response, 3 with partial response, and 4 with stable disease). Related AEs were experienced by 7 of 9 subjects. The most frequent were nausea (44%), fatigue, peripheral edema, dyspnea, and urinary casts (all 22%). Grade 3 or higher related AEs were experienced by 2 of 9 subjects (Diffuse Large B-Cell Lymphoma as previously mentioned and peripheral edema). There were no hematologic or infection AEs related to forodesine. Grade 3 lymphopenia and CD4 count < 200 were noted in 8 of 9 and 4 of 9 subjects respectively. The risk of any infection AE regardless of cause in these 9 subjects was 15 per 100 person-months of forodesine exposure compared to 59 in all other subjects (n=55). Conclusions: Forodesine has an acceptable safety profile and efficacy in these CTCL subjects treated for 12 months or longer. [Table: see text]

Synthesis of analogs of forodesine HCl, a human purine nucleoside phosphorylase inhibitor—Part I

Forodesine HCl is being investigated as a potential therapeutic target for the control of T-cell proliferation. During our ongoing process development work on forodesine HCl several novel compounds were identified as possible impurities in the process. Herein we present the synthesis of three novel compounds ( 2– 4).

Synthesis of analogs of forodesine HCl, a human purine nucleoside phosphorylase inhibitor—Part II

Forodesine HCl is being investigated as a potential therapeutic target for the control of T-cell proliferation. During the filing process for a New Drug Application (NDA) it became evident that there was a need to synthesize some stereo-isomers of forodesine HCl. Herein we present the synthesis of these three novel compounds ( 2– 4).

Synthesis of labeled BCX‐4208, a potent inhibitor of purine nucleoside phosphorylase

BCX-4208, a novel inhibitor of the enzyme purine nucleoside phosphorylase, mimics the charged ribosyl oxocarbenium ion formed during the transition state of the enzyme-catalyzed C-N bond cleavage of nucleosides. A slow-onset, tight-binding inhibitor with a Ki(*) of 16 +/- 1.4 pM, BCX-4208 is one of the most potent inhibitors known for the enzyme. In support of our BCX-4208 clinical program, a mass spectrometric assay has been developed that required labeled BCX-4208 as an internal standard. The synthesis of [(2)H](2)-BCX-4208 and [(13)C]-BCX-4208 is described in this report.

Third-Generation Immucillins: Syntheses and Bioactivities of Acyclic Immucillin Inhibitors of Human Purine Nucleoside Phosphorylase

ImmH (1) and DADMe-ImmH (2) are potent inhibitors of human purine nucleoside phoshorylase (PNP), developed by us and currently in clinical trials for the treatment of a variety of T-cell related diseases. Compounds 1 and 2 were used as templates for the design and synthesis of a series of acyclic immucillin analogues (8-38) in order to identify simplified alternatives to 1 and 2. SerMe-ImmG (8) and DATMe-ImmG (9) displayed the lowest inhibition constants of 2.1 and 3.4 pM, respectively, vs PNP. It was postulated that the flexible natures of 8 and 9 enabled them to adopt conformations resembling those of 1 and 2 within the active site of PNP and that the positioning of two hydroxyl groups was critical for picomolar activity. SerMe-ImmH (10, K(d) = 5.2 pM) was shown to be orally available in mice with a long biological residence time on blood PNP.

Novel Therapies for Cutaneous T-Cell Lymphomas

Cutaneous T-cell lymphomas (CTCLs) are a group of uncommon mature T-cell lymphomas presenting primarily or exclusively in the skin. The most common subtype, mycosis fungoides and its leukemic variant Sézary syndrome, frequently behave as a chronic lymphoma with good prognosis for early-stage disease and shortened survival only for patients in advanced stages. Historically, these patients have experienced excessive toxicity from chemotherapy without durable benefit, leading to current conservative treatment strategies. An increasing number of novel therapies are available or in development. These newer therapies often have unique mechanisms of action and different toxicities with less myelosuppression than traditional cytotoxic chemotherapy. Among these novel systemic therapies are so-called biologic therapies such as retinoids like bexarotene, the fusion toxin denileukin diftitox, lenalidomide, and toll-like receptor agonists. Other important novel or emerging agents include the histone deacetylase inhibitors; a novel antifolate, pralatrexate; the proteasome inhibitor bortezomib; and the purine nucleoside phosphorylase inhibitor forodesine. Even agents considered to be conventional chemotherapy, such as gemcitabine or pegylated liposomal doxorubicin, have demonstrated activity in CTCL at relatively lower doses with less myelosuppression. The mechanisms of action of the novel agents are reviewed as well as available clinical data. As the role of these new agents is better understood, particularly with regard to nonoverlapping toxicities, combination strategies might emerge. Evaluation through carefully designed clinical trials should lead to better, safer, and more effective treatment strategies in the future.

Forodesine (Immucillin H, BCX-1777) Shows Activity on Mantle Cell Lymphoma Primary Cells

Mantle cell lymphoma (MCL) represents a subtype of B-cell lymphoma associated with a very unfavourable clinical outcome. Currently no therapy can be considered as standard, and new therapeutic approaches are needed. Forodesine is a potent inhibitor of purine nucleoside phosphorylase (PNP), whose major role is to catalyze the cleavage of inosine, deoxyinosine guanosine, and deoxyguanosine (dGuo) to their corresponding base and sugar 1-phosphate by phosphorolysis. In the presence of deoxycytidine kinase, PNP inhibition leads to an increase in the concentration of dGuo triphosphate (dGTP), followed by inhibition of DNA synthesis and cell death by apoptosis. When combined with dGuo, forodesine has been shown to have in vitro cytotoxic activity on T-cell (T-ALL, T-PLL) and on B-cell malignancies (CLL, B-ALL), and Phase I/II trials are on going in CLL and CTCL patients. Here, we report the first data on in vitro activity of forodesine in MCL. Primary MCL cells, derived from six patients, were exposed to forodesine (0, 2, 20 μM) in combination with dGuo (0, 10, 20 μM), for 48 hrs. Cells were cultured in X-VIVO 10 medium (Cambrex) with 10% FBS. Cell viability was assessed by flow cytometry with the Annexin V - propidium iodide assay. Four patient samples (67%) showed an increase in the number of Annexin V positive cells ranging from 1.9 to 5.3 times compared to untreated cells. The effect was larger for 20 μM forodesine compared with 2 μM. There was no effect of dGuo alone and only a minimal effect of increasing dGuo concentration from 10 μM to 20 μM. Cell lines did not appear to be ideal models to evaluate the efficacy of forodesine in vitro. Three established MCL cell lines (Granta-519, Rec, JeKo1) were treated with escalating doses of forodesine, but the results were not reproducible, while the same cells showed expected IC50 values between 25–30 μM when exposed to bendamustine for 72 hrs. In conclusion, the in vitro data reported here with 4/6 MCL patients primary samples sensitive to forodesine and the results from various groups on other T- and B-cell malignancies suggest that clinical trials of forodesine in MCL may be warranted.

BCX-4208 (RO5092888), a Purine Nucleoside Phosphorylase (PNP) Inhibitor, Is a Novel, Potent Orally Active Anti-T-Cell and B-Cell Agent.

The profound suppression of T-cell immunity seen in patients with an inherited PNP deficiency supports the potential application of inhibitors of this purine salvage enzyme in the therapy of T-cell malignancies and T-cell mediated autoimmune diseases. About thirty percent of PNP deficient patients also show evidence of B-cell dysfunction. BCX-4208 is a novel potent transition state analog inhibitor of PNP (IC50 ~ 0.0005 μM) and in the presence of 10 μM deoxyguanosine (dGuo), inhibits human lymphocyte proliferation induced by MLR, IL-2 or Con-A with IC50s of 0.159, 0.26 and 0.73 μM, respectively. The IC50 for dGuo in the same assays in the presence of 1 μM BCX-4208 ranges from 1–3 μM. Neither BCX-4208 alone nor dGuo alone inhibits proliferation of lymphocytes. In the presence of PNP inhibitor, dGuo is converted to dGMP and then to dGTP. Accumulation of dGTP results in the alteration of deoxynucleotide (dNTP) pools, causing death of cells via a mechanism characteristic of apoptosis. In vitro data demonstrates that following exposure to BCX-4208 and dGuo, dGTP in human lymphocytes is elevated and a 5–8 fold increase in dGTP results in 50% inhibition of lymphocyte proliferation. Flow cytometric analyses of human lymphocytes using annexin-V staining reveal that BCX-4208 in the presence of dGuo induces cellular apoptosis not only in T cells (CD3+), but also in B cells (CD20+; CD19+) (Table 1). BCX-4208 is orally bioavailable in mice, can achieve maximal inhibition of PNP, and elevates plasma dGuo levels to 3–5 μM (predose levels < 0.004 μM), which is similar to levels seen in PNP deficient patients and to levels needed to cause apoptosis in T and B-cells. These data support the evaluation of BCX-4208 in the treatment of not only T-cell mediated diseases but also B-cell mediated diseases. BCX- 4208 is currently undergoing early clinical investigation in patients with psoriasis.Table 1.Cell subsets% Apoptotic cells mean ± SEM (n = 4–7)VehicleTreatment groupCD3+7.2 ± 0.918.3 ± 3.7*CD20+24.0 ± 3.641.8 ± 6.2*CD19+25.0 ± 3.151.6 ± 7.4**p ≤ 0.01 compared to vehicle

A Phase II Study of the Purine Nucleoside Phosphorylase (PNP) Inhibitor RO5092888 (BCX-4208) in Patients with Moderate to Severe Chronic Plaque Psoriasis: Safety, Tolerability and Lymphocyte Effects

Introduction: PNP is a purine-metabolizing enzyme that catalyzes the phosphorolysis of 2′-deoxyguanosine [dGuo] to guanine and deoxyribose-1-phosphate. In T-cells, PNP inhibition leads to accumulation of deoxyguanosine triphosphate (dGTP), triggering apoptotic cell death. Chronic-plaque type psoriasis (psoriasis) is an autoimmune disorder, in which T-cells contribute, at least in part, to the manifestations and maintenance of the disease. Therefore, targeting T-cells may be a beneficial treatment strategy. Since for chronic inflammatory diseases the safety of potential immunosuppressive drugs is a major consideration, we conducted this study to investigate safety and tolerability of oral RO5092888 (BCX-4208) in patients with moderate to severe chronic plaque psoriasis.Methods: This was a randomized, double-blind, placebo-controlled, dose-ranging study. Sixty-six patients 18 to 70 years old were randomized into one of three groups: placebo, 20mg/d or 120mg/d. The study was conducted from August 2007 to June 2008. Patients received study drug over six weeks and were observed over an additional 4 weeks. Assessments for safety included tracking of adverse events (AEs) including infections; vital signs; ECGs; chemistry panel; LFTs; hematologic parameters including peripheral blood (PB) lymphocyte subsets CD3+, CD4+, CD8+, CD56+, CD20+; and urinalysis.Results: 65 of the 66 enrolled patients were analyzed. One serious AE was observed in the 20mg/d group, a deep vein thrombosis (DVT) in a patient with a history of DVTs, and was considered unrelated to study drug. The percentage of patients experiencing at least one adverse event (AE) of any grade was placebo: 33% (7/21), 20mg: 41% (9/22), and 120mg: 59% (13/22). During treatment, two infections occurred in the placebo group (influenza and sinusitis), one in the 20mg group (nasopharyngitis), and 4 in the 120mg group (2-upper respiratory tract infections, 1 bronchitis, and 1 otitis externa). Reductions in PB lymphocytes and subsets were observed (Table 1). Nine patients showed decreased levels of CD4+ lymphocytes, below 350 cells/μL (20mg/d, 3; 120mg/d, 6).Conclusion: Daily oral administration of 20 mg or 120 mg of RO5092888 for up to 6 weeks demonstrated adequate safety and tolerability. Reductions in PB T cells, T cell subsets and B cells were observed. Further investigation of RO5092888 is warranted in both T-cell and B-cell diseases.Lymphocyte subpopulationMean Nadir (% change from baseline)Placebo (n=21)20 mg (n=22)120 mg (n=22)CD3+24.030.647.5CD4+23.628.944.9CD8+26.131.853.9CD20+37.542.664.2CD56+40.147.772.6Table 1

9-Deazaguanine derivatives: synthesis and inhibitory properties as multi-substrate analogue inhibitors of mammalian PNPs

9-(5',5'-Difluoro-5'-phosphonopentyl)-9-deazaguanine (DFPP-DG) and its related analogues were designed as multi-substrate analogue inhibitors of purine nucleoside phosphorylase (PNP) on the basis of the X-ray crystallographic data obtained for the binary complex of 9-(5',5'-difluoro-5'-phosphonopentyl)guanine (DFPP-G) with calf spleen PNP. One of these analogues, homo-DFPP-DG was found to be a very potent PNP inhibitor at an intracellular (approximately 1 mM) phosphate concentration.