LJ529 attenuates mast cell-related inflammation via A3R-PKCε-ALDH2 pathway after subarachnoid hemorrhage in rats.

BACKGROUND AND PURPOSE: Mast cells (MCs) has been recognized as an effector of inflammation or a trigger of inflammatory factors during stroke. LJ529 was reported to attenuate inflammation through a Gi protein-coupled Adenosine A3 receptor (A3R) after ischemia. Here, we aim to study the protective effect and its mechanism of LJ529 in subarachnoid hemorrhage (SAH) rat model for mast cell-related inflammation. METHODS: 155 Sprague-Dawley adult male rats were used in experiments. Endovascular perforation was used for SAH model. Intraperitoneal LJ529 was performed 1 h after SAH. Neurological scores were measured 24 h after SAH. Rotarod and morris water maze tests were evaluated for 21 days after SAH. Mast cell degranulation was assessed with Toluidine blue staining and Chymase/Typtase protein expressions. Mast cell-related inflammation was evaluated using IL-6, TNF-α and MCP-1 protein expressions. MRS1523, inhibitor of GPR18 and ε-V1-2, inhibitor of PKCε were respectively given intraperitoneally (i.p.) 1 h and 30 min before SAH for mechanism studies. Pathway related proteins were investigated with western blot and immunofluorescence staining. RESULTS: Expression of A3R, PKCε increased after SAH. LJ529 treatment attenuated mast cell degranulation and inflammation. Meanwhile, both short-term and long-term neurological functions were improved after LJ529 treatment. Administration of LJ529 resulted in increased expressions of A3R, PKCε, ALDH2 proteins and decreased expressions of Chymase, Typtase, IL-6, TNF-α and MCP-1 proteins. MRS1523 abolished the treatment effects of LJ529 on neurobehavior and protein levels. ε-V1-2 also reversed the outcomes of LJ529 administration through reduction in protein expressions downstream of PKCε. CONCLUSIONS: LJ529 attenuated mast cell-related inflammation through inhibiting degranulation via A3R-PKCε-ALDH2 pathway after SAH. LJ529 may serve as a potential treatment strategy to relieve post-SAH brain injury.

NUDT15: A bench to bedside success story.

Recently, the enzyme nudix hydrolase 15 (NUDT15) has been identified as an additional component of the thiopurine metabolism pathway. NUDT15 (also known as MTH2) catalyzes the dephosphorylation of 6-thioguanosine triphosphate (6-TGTP) and 6-thio-deoxyguanosine triphosphate (6-TdGTP), which is the active metabolite of thiopurine medications. Thiopurine compounds, which were first synthesized in the 1950s, are widely used in the treatment of childhood leukemia, inflammatory bowel disease, and autoimmune disorders. For many years, TPMT has been recognized as an enzyme that is involved in thiopurine metabolism, and interindividual variation in TPMT activity has been known to contribute to differences in risk of thiopurine toxicity. Genetic variation that leads to decreased NUDT15 activity has been recognized as an additional contributor, beyond TPMT, to thiopurine toxicity. In some populations, including Asian and Latino populations, NUDT15 genetic variants are more common than TPMT variants, making this a significant biomarker of toxicity. Clinical genetic testing is now available for a subset of NUDT15 variants, representing a remarkably fast translation from bench to bedside. This review will focus on NUDT15 - from discovery to clinical implementation.

Telomere Stress Potentiates STING-Dependent Anti-tumor Immunity.

Telomerase is an attractive target for anti-tumor therapy as it is almost universally expressed in cancer cells. Here, we show that treatment with a telomere-targeting drug, 6-thio-2'-deoxyguanosine (6-thio-dG), leads to tumor regression through innate and adaptive immune-dependent responses in syngeneic and humanized mouse models of telomerase-expressing cancers. 6-thio-dG treatment causes telomere-associated DNA damages that are sensed by dendritic cells (DCs) and activates the host cytosolic DNA sensing STING/interferon I pathway, resulting in enhanced cross-priming capacity of DCs and tumor-specific CD8+ T cell activation. Moreover, 6-thio-dG overcomes resistance to checkpoint blockade in advanced cancer models. Our results unveil how telomere stress increases innate sensing and adaptive anti-tumor immunity and provide strong rationales for combining telomere-targeting therapy with immunotherapy.

SLC43A3 Is a Biomarker of Sensitivity to the Telomeric DNA Damage Mediator 6-Thio-2'-Deoxyguanosine.

Cell membrane transporters facilitate the passage of nucleobases and nucleosides for nucleotide synthesis and metabolism, and are important for the delivery of nucleoside analogues used in anticancer drug therapy. Here, we investigated if cell membrane transporters are involved in the cellular uptake of the nucleoside analogue DNA damage mediator 6-thio-2'-deoxyguanosine (6-thio-dG). A large panel of non-small cell lung cancer (NSCLC) cell lines (73 of 77) were sensitive to 6-thio-dG; only four NSCLC lines were resistant to 6-thio-dG. When analyzed by microarray and RNA sequencing, the resistant NSCLC cell lines clustered together, providing a molecular signature for patients that may not respond to 6-thio-dG. Significant downregulation of solute carrier family 43 A3 (SLC43A3), an equilibrative nucleobase transporter, was identified as a candidate in this molecular resistance signature. High levels of SLC43A3 mRNA predicted sensitivity to 6-thio-dG and therefore SLC43A3 could serve as a promising biomarker for 6-thio-dG sensitivity in patients with NSCLC. SIGNIFICANCE: These findings identify a biomarker of resistance to the telomeric DNA damage mediator 6-thio-2'-deoxyguanosine.

The state of the art on treatment of Crohn's disease.

Crohn's disease (CD) is a chronic, progressive, and destructive disease of the gastrointestinal tract. Although its incidence appears to be stable or decreasing in most countries in the North America and Europe, the incidence is rising rapidly in Asian countries. Immunomodulators and biologics are increasingly used to avoid long-term bowel damage and subsequent disability. Therapeutic drug monitoring facilitates optimizing thiopurines and anti-TNFs use. New biologic agents targeting various pathological pathways of CD are blooming in recent years, and the high cost of biologics and expiration of patents for several biologic agents have driven the utility of biosimilars for CD treatment. Here, the literature regarding the efficacy, safety, and withdrawal of the drugs, as well as the evolution of therapeutic targets will be reviewed.

American Gastroenterological Association Institute Technical Review on the Role of Therapeutic Drug Monitoring in the Management of Inflammatory Bowel Diseases.

Therapeutic drug monitoring (TDM), which involves measurement of drug or active metabolite levels and anti-drug antibodies, is a promising strategy that can be used to optimize inflammatory bowel disease therapeutics. It is based on the premise that there is a relationship between drug exposure and outcomes, and that considerable inter-individual variability exists in how patients metabolize the drug (pharmacokinetics) and the magnitude and duration of response to therapy (pharmacodynamics). Therefore, the American Gastroenterological Association has prioritized clinical guidelines on the role of TDM in the management of inflammatory bowel disease. To inform these clinical guidelines, this technical review was developed in accordance with the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) framework for interventional and prognostic studies, and focused on the application of TDM for biologic therapy, specifically anti-tumor necrosis factor-α agents, and for thiopurines. Focused questions address the benefits and risks of a strategy of reactive TDM (in patients with active inflammatory bowel disease) to guide treatment changes compared with empiric treatment changes, and the benefits and risks of a strategy of routine proactive TDM (during routine clinical care in patients with quiescent disease) compared with no routine TDM. Additionally, the review addresses the benefits and risks of routine measurement of thiopurine methyltransferase enzyme activity or genotype before starting thiopurine therapy compared with empiric weight-based dosing and explores the performance of different trough drug concentrations for anti-tumor necrosis factor agents and thiopurines to inform clinical decision making when applying TDM in a reactive setting. Due to a paucity of data, this review does not address the role of TDM for more recently approved biologic agents, such as vedolizumab or ustekinumab.

Combination therapy with infliximab and thiopurine compared to infliximab monotherapy in maintaining remission of postoperative Crohn's disease.

BACKGROUND AND AIMS: Infliximab is an efficacious agent used for the induction and maintenance of remission in Crohn's disease (CD), and recent studies suggested that it may also prevent the recurrence of this disease after surgery. The present study was performed to assess the efficacy and safety of infliximab in the postoperative setting, and to identify whether combination treatment with thiopurines had any additional beneficial effect as compared to mono-therapy. METHODS: We performed a retrospective cohort study to compare the efficacy of infliximab mono-therapy and combination treatment with a thiopurine in preventing recurrence after surgery. RESULTS: Forty-one patients who received infliximab as maintenance treatment following surgery from May 2002 to April 2010 were identified. Twenty-four were naive to infliximab, and 17 who underwent surgery during infliximab treatment were continued on it following surgery. The median follow-up period was 27 months (range 12-66 months). All patients continued infliximab as maintenance treatment, but 10 required dose intensification due to clinical recurrence. Kaplan-Meier analysis demonstrated that the use of concomitant thiopurine was correlated with the continuation of infliximab treatment at an 8-week interval (log-rank test p = 0.018). The rate of adverse event was 9.8% with no patient experiencing severe adverse reactions. CONCLUSION: Infliximab appears to be safe and it prevented clinical recurrence after surgery. Concomitant thiopurine use predicted response toward continuation of therapy at an 8-week interval. Prospective controlled studies to assess the efficacy of combination treatment in the postoperative setting are warranted.

Addressing current treatment challenges in Crohn's disease in real life: a physician's survey.

BACKGROUND: In recent years several trials have addressed treatment challenges in Crohn's disease. Clinical trials however, represent a very special situation. AIMS: To perform a cross-sectional survey among gastroenterologists on the current clinical real life therapeutic approach focussing on the use of biologics. METHODS: A survey including six main questions on clinical management of loss of response, diagnostic evaluation prior to major treatment changes, preference for anti-tumour necrosis factor (TNF) agent, (de-)escalation strategies as well as a basic section regarding personal information was sent by mail to all gastroenterologists in Switzerland (n=318). RESULTS: In total, 120 questionnaires were analysed (response rate 37.7%). 90% of gastroenterologists in Switzerland use a thiopurine as the first step-up strategy (anti-TNF alone 7.5%, combination 2.5%). To address loss of response, most physicians prefer shortening the interval of anti-TNF administration followed by dose increase, switching the biologic and adding a thiopurine. In case of prolonged remission on combination therapy, the thiopurine is stopped first (52.6%) after a mean treatment duration of 15.7 months (biologic first in 41.4%). CONCLUSIONS: Everyday clinical practice in Crohn's disease patients appears to be incongruent with clinical data derived from major trials. Studies investigating reasons underlying these discrepancies are of need to optimize and harmonize treatment.

5'-Methylthioadenosine attenuates ischemia reperfusion injury after liver transplantation in rats.

5'-Methylthioadenosine (MTA) is a nucleoside generated from S-adenosylmethionine (SAM) during polyamine synthesis. Previous study has indicated that MTA regulated the production of inflammatory mediators by modulating the activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signal pathway. The objective of this study was to determine whether MTA possessed anti-inflammatory properties during rat liver transplantation. Sprague Dawley (SD) to SD rat orthotropic liver transplantation was performed according to the Kamada's technique. Donors in MTA group were given a single dose of MTA (96 µmol/kg, intraperitoneal) 30 min before surgery (n = 36), and the control group were given the same volume of normal saline (n = 36) intraperitoneally. The histopathologic change in the liver was analyzed. The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), tumor necrosis factor alpha (TNF-α), inhibitors of kappa B alpha (IκBα) degradation, NF-κB transcriptional activity, and MAPK activation were determined at 3, 6, and 24 h after reperfusion. Pretreatment with MTA significantly improved liver function, attenuated hepatic ischemia-reperfusion injury (IRI) by downregulating TNF-α level and suppressing inflammatory reaction after liver transplantation. Moreover, MTA also inhibited the IκBα degradation, NF-κB transcriptional activity, and the activation of MAPK signal. MTA protected against hepatic IRI by suppressing inflammatory reaction following liver transplantation. The mechanism for this effect of MTA is mediated, at least in part, by inhibiting the activation of NF-κB and MAPK signal pathway.

Differential neuroprotective effects of 5'-deoxy-5'-methylthioadenosine.

BACKGROUND: 5'-deoxy-5'-methylthioadenosine (MTA) is an endogenous compound produced through the metabolism of polyamines. The therapeutic potential of MTA has been assayed mainly in liver diseases and, more recently, in animal models of multiple sclerosis. The aim of this study was to determine the neuroprotective effect of this molecule in vitro and to assess whether MTA can cross the blood brain barrier (BBB) in order to also analyze its potential neuroprotective efficacy in vivo. METHODS: Neuroprotection was assessed in vitro using models of excitotoxicity in primary neurons, mixed astrocyte-neuron and primary oligodendrocyte cultures. The capacity of MTA to cross the BBB was measured in an artificial membrane assay and using an in vitro cell model. Finally, in vivo tests were performed in models of hypoxic brain damage, Parkinson's disease and epilepsy. RESULTS: MTA displays a wide array of neuroprotective activities against different insults in vitro. While the data from the two complementary approaches adopted indicate that MTA is likely to cross the BBB, the in vivo data showed that MTA may provide therapeutic benefits in specific circumstances. Whereas MTA reduced the neuronal cell death in pilocarpine-induced status epilepticus and the size of the lesion in global but not focal ischemic brain damage, it was ineffective in preserving dopaminergic neurons of the substantia nigra in the 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP)-mice model. However, in this model of Parkinson's disease the combined administration of MTA and an A2A adenosine receptor antagonist did produce significant neuroprotection in this brain region. CONCLUSION: MTA may potentially offer therapeutic neuroprotection.

Role of thiopurine metabolite testing and thiopurine methyltransferase determination in pediatric IBD.

Thiopurines have been used in inflammatory bowel disease (IBD) for >30 years, and measurements of both thiopurine methyltransferase (TPMT) and thiopurine (TP) metabolites, 6-thioguanine nucleotides (6-TGN) and 6-methylmercaptopurine (6-MMP), have been readily available. The North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) Committee on Inflammatory Bowel Disease thought it appropriate to review the present indications for use of TPMT and TP metabolite testing. Substantial evidence demonstrates that TP therapy is useful for both Crohn disease and ulcerative colitis. Review of the existing data yielded the following recommendations. TPMT testing is recommended before initiation of TPs to identify individuals who are homozygote recessive or have extremely low TPMT activity, with the latter having more reliability than the former. Individuals who are homozygous recessive or have extremely low TPMT activity should avoid the use of TPs because of concerns for significant leukopenia. TMPT testing does not predict all cases of leukopenia and has no value to predict hypersensitivity adverse effects such as pancreatitis. Any potential value to reduce the risk of malignancy has not been studied. All individuals taking TPs should have routine monitoring with complete blood cell count and white blood cell count differential to evaluate for leukopenia regardless of TPMT testing results. Metabolite testing can be used to determine adherence with TP therapy. Metabolite testing can be used to guide dose increases or modifications in patients with active disease. Consideration would include either increasing the dose, changing therapy or for those with elevated transaminases or an elevated 6-MMP, using adjunctive allopurinol to help raise 6-thioguanine metabolites and suppress formation of 6-MMP. Routine and repetitive metabolite testing has little or no role in patients who are doing well and taking an acceptable dose of a TP.

A2A adenosine receptor agonists reduce both high-palatability and low-palatability food intake in female rats.

The present study examined the effect of two A(2A) adenosine receptor (AR) agonists, CGS 21680 and VT 7, on high-palatability food (HPF) intake in a model of binge eating in sated rats and on low-palatability food (LPF) intake in food-deprived rats. Binge eating was induced in female rats by three 8-day cycles of food restriction/refeeding, followed by acute stress. Two groups of rats were used: NR+NS rats normally fed and not stressed and R+S rats exposed to cycles of food restriction/refeeding and then stressed. R+S rats had higher intake of HPF than the NR+NS controls. The two A(2A)AR agonists were tested at doses of 0.1 and 0.05 mg/kg intraperitoneally; VT 7 did not modify locomotor activity at either dose, whereas CGS 21680 only slightly reduced it at the higher dose tested. The injection of 0.1 mg/kg of both agonists markedly reduced HPF intake both in R+S and in NR+NS rats. The dose of 0.05 mg/kg was inactive. CGS 21680 and VT 7, 0.1 mg/kg, also reduced the standard LPF intake in 24 h food-deprived rats; however, they did not reduce water intake, indicating that their effect on food intake is selective. The dose of 0.05 mg/kg was inactive. Thus, A(2A)AR agonists exert a rather general effect on food intake, inhibiting both HPF intake in sated rats and LPF intake in food-deprived rats. They may potentially be useful pharmacological agents to control binge-related eating disorders and to reduce food overconsumption associated with obesity.

Methylthioadenosine reverses brain autoimmune disease.

OBJECTIVE: To assess the immunomodulatory activity of methylthioadenosine (MTA) in rodent experimental autoimmune encephalomyelitis (EAE) and in patients with multiple sclerosis. METHODS: We studied the effect of intraperitoneal MTA in the acute and chronic EAE model by quantifying clinical and histological scores and by performing immunohistochemistry stains of the brain. We studied the immunomodulatory effect of MTA in lymphocytes from EAE animals and in peripheral blood mononuclear cells from healthy control subjects and multiple sclerosis patients by assessing cell proliferation and cytokine gene expression, by real-time polymerase chain reaction, and by nuclear factor-kappaB modulation by Western blot. RESULTS: We found that MTA prevents acute EAE and, more importantly, reverses chronic-relapsing EAE. MTA treatment markedly inhibited brain inflammation and reduced brain damage. Administration of MTA suppressed T-cell activation in vivo and in vitro, likely through a blockade in T-cell signaling resulting in the prevention of inhibitor of kappa B (IkappaB-alpha) degradation and in the impaired activation transcription factor nuclear factor-kappaB. Indeed, MTA suppressed the production of proinflammatory genes and cytokines (interferon-gamma, tumor necrosis factor-alpha, and inducible nitric oxide synthase) and increased the production of antiinflammatory cytokines (interleukin-10). INTERPRETATION: MTA has a remarkable immunomodulatory activity and may be beneficial for multiple sclerosis and other autoimmune diseases.

The antitumor effect of LJ-529, a novel agonist to A3 adenosine receptor, in both estrogen receptor-positive and estrogen receptor-negative human breast cancers.

Agonists to A3 adenosine receptor (A3AR) have been reported to inhibit cell growth and/or induce apoptosis in various tumors. We tested the effect of a novel A3AR agonist generically known as LJ-529 in breast cancer cells. Anchorage-dependent cell growth and in vivo tumor growth were attenuated by LJ-529, independently of its estrogen receptor (ER) alpha status. In addition, apoptosis was induced as evidenced by the activation of caspase-3 and c-poly(ADP)ribose polymerase. Furthermore, the Wnt signaling pathway was down-regulated and p27(kip) was induced by LJ-529. In ER-positive cells, the expression of ER was down-regulated by LJ-529, which might have additionally contributed to attenuated cell proliferation. In ER-negative, c-ErbB2-overexpressing SK-BR-3 cells, the expression of c-ErbB2 and its downstream extracellular signal-regulated kinase pathway were down-regulated by LJ-529. However, such effect of LJ-529 acted independently of its receptor because no A3AR was detected by reverse transcription-PCR in all four cell lines tested. In conclusion, our novel findings open the possibility of LJ-529 as an effective therapeutic agent against both ER-positive and ER-negative breast cancers, particularly against the more aggressive ER-negative, c-ErbB2-overexpressing types.

EFA (9-beta-D-erythrofuranosyladenine) is an effective salvage agent for methylthioadenosine phosphorylase-selective therapy of T-cell acute lymphoblastic leukemia with L-alanosine.

The deficiency of methylthioadenosine phosphorylase (MTAP) in T-cell acute lymphoblastic leukemia (T-ALL) and other cancers, while constitutively expressed in normal cells, allows for selective therapy using L-alanosine, an inhibitor of de novo AMP synthesis. We demonstrate that MTAP- T-ALL cells obtained at relapse are as sensitive to L-alanosine toxicity as diagnosis samples. The therapeutic index of L-alanosine can be increased by the use of a MTAP substrate, which protects MTAP+ normal cells. Since MTAP substrates MTA and 5'deoxyadenosine are prone to toxicities associated with adenosine, we synthesized and evaluated a potentially nontoxic MTAP substrate, 9-beta-D-erythrofuranosyladenine (EFA). The cytotoxicity of EFA to hematopoietic progenitors erythroid burst-forming units (BFU-Es) and granulocyte-macrophage colony-forming units (CFU-GMs) was at least 26- to 41-fold less than that of MTA. In addition, EFA selectively rescued MTAP+ MOLT-4 cells from L-alanosine toxicity at 25 microM with negligible toxicity even at 100 microM. As for MTA, significant, albeit incomplete, rescue was achieved at 12.5 microM, but higher concentrations were toxic. EFA at 20 microM or less rescued primary MTAP+ T-ALL cells and normal lymphocytes from L-alanosine toxicity. Collectively, these data indicate that EFA is an effective agent for salvaging MTAP+ cells from L-alanosine toxicity and is superior to MTA due to lower cytotoxicity.

Recent advances in 4'-thionucleosides as potential antiviral and antitumor agents.

The classical 4'-oxonucleoside analogs exhibit interesting biological activities such as antibiotic, antiviral and antitumor, which are believed to be the result of inhibition of the viral or cellular DNA or RNA polymerase after being converted to their corresponding 5'-triphosphates. However, the activity of 4'-oxonucleosides were limited by their susceptibility to degradation by nucleoside phosphorylases or acid hydrolysis. This aspect called for the chemical modification of the carbohydrate portion. This compulsion led to two kinds of strategies; (1) replacement of the 4'-oxygen by the methylene group - carbocyclic nucleosides; (2) replacement of the 4' oxygen by sulphur-4'-thionucleosides. This group has also conferred the resistance to the nucleoside cleavage. Although, there were some pioneering work on 4'-thionucleosides in 1960s and 1970s, the interest in this group of compounds was rekindled by the antiviral activities of 2'-deoxy-4'-thionucleosides reported independently by Secrist et al. and Walker et al. Subsequent contributions by the other authors, enhanced its standing as an important class of antiviral agents. Following is a reasonably exhaustive account of this class of compounds reported after 1990.

In vivo efficacies of 5'-methylthioadenosine analogs as trypanocides.

5'-Deoxy-5'-(methylthio)adenosine (MTA), a key by-product of polyamine biosynthesis, is cleaved by MTA phosphorylase and is salvaged as adenine and, through conversion of the ribose moiety, methionine. An analog of MTA, 5'-deoxy-5'-(hydroxyethylthio)adenosine (HETA), is a substrate for trypanosome MTA phosphorylase and is active in vitro and in vivo against Trypanosoma brucei brucei, an agent of bovine trypanosomiasis. In this study, HETA and three O-acylated HETA derivatives were examined for their activities against model infections of T. b. brucei and Trypanosoma brucei rhodesiense, the agent of East African sleeping sickness. HETA was curative (>60%) for infections caused by 5 of 11 clinical isolates of T. b. rhodesiense when it was given to mice at 200 mg/kg of body weight for 7 days as a continuous infusion in osmotic pumps. HETA at 150 to 200 mg/kg also extended the life spans of the mice infected with four additional isolates two- to fivefold. Di- and tri-O-acetylated derivatives of HETA also proved curative for the infections, while a tri-O-propionyl derivative, although also curative, was not as effective. This study indicates that substrate analogs of MTA should be given important consideration for development as novel chemotherapies against African trypanosomiasis.

Methylthioadenosine phosphorylase deficiency in human non-small cell lung cancers.

Methylthioadenosine (MeSAdo) phosphorylase, a purine metabolic enzyme, is present in all normal mammalian tissues. A deficiency of this enzyme has been reported in some human leukemias and lymphomas and in a few solid tumors. In the present study, a specific immunoassay was used to assess the enzyme levels in human non-small cell lung cancer cell lines and primary tumors. We also tested the effects of MeSAdo phosphorylase-selective chemotherapy on the in vitro growth of enzyme-positive and enzyme-negative lung cancer cell lines. Of 29 non-small cell lung cancers, 9 (6 cell lines and 3 primary tumors, 31%) lacked detectable immunoreactive enzyme protein. Both 5,10-dideazatetrahydrofolate, an inhibitor of de novo purine synthesis, and methionine depletion, combined with MeSAdo, prevented the growth of the enzyme-negative non-small cell lung cancer cells under conditions in which enzyme-positive cells utilized MeSAdo to endogenously synthesize purine nucleotides and methionine. Our data suggest that MeSAdo phosphorylase deficiency is frequently found in non-small cell lung cancers and can be exploited in designing enzyme-selective chemotherapy.

Synthesis and biological activity of 2'-deoxy-4'-thio pyrimidine nucleosides.

2'-Deoxy-4'-thiocytidine (7 beta), 2'-deoxy-4'-thiouridine (9), and 4'-thiothymidine (10) have been synthesized and evaluated for cytotoxicity in vitro. All these compounds were cytotoxic to L1210, H-Ep-2, and CCRF-CEM cell lines. 4'-Thiothymidine was also active against herpes simplex 1 and human cytomegalovirus in cell culture.