Therapeutic drug monitoring of thiopurines: Effect of reduced 6-thioguanine nucleotide target levels in inflammatory bowel disease patients.

AIMS: The effect of the Dutch nationwide adjustment of reducing 6-thioguanine nucleotide (6-TGN) target values (from 600-1200 to 320-630 pmol/8 × 108 red blood cells [RBC]) on toxicity and clinical outcome of thiopurine treatment in patients with inflammatory bowel disease has not yet been established. Therefore, the authors determined the incidence of toxicity-induced discontinuations and efficacy at both target concentrations. METHODS: This retrospective study was performed in inflammatory bowel disease patients treated with azathioprine or mercaptopurine. Two groups were defined: the former target (FT) group with target concentrations of 600-1200 pmol/8 × 108 RBC and the adjusted target (AT) group with target concentrations of 320-630 pmol/8 × 108 RBC. Patients were followed for maximum 52 weeks or until discontinuation of thiopurine therapy. Data were collected from the local hospital electronic health software of Rijnstate Hospital. RESULTS: In total, 151 patients were included, 76 in the FT group and 75 in the AT group. At week 52, 100 out of 151 patients (66%) of the total population discontinued thiopurine therapy. Forty-eight of the discontinuations were due toxicity (48%). The incidence of toxicity induced discontinuations was 35% in the AT group vs. 47% in the FT group (P = .25). No loss of efficacy was seen in the AT group. CONCLUSION: After reduction of the target range, there was a trend towards fewer toxicity-induced discontinuations, albeit not statistically significant. In addition, this study did not find any indication that the reduction of the target range diminished efficacy.

Nanostructure of Functional Larotaxel Liposomes Decorated with Guanine-Rich Quadruplex Nucleotide-Lipid Derivative for Treatment of Resistant Breast Cancer.

Breast cancer is the most common malignant disease in women all over the world and its chemotherapy outcome is restricted by multidrug resistance. Here, a nanostructure by functional larotaxel liposomes decorated with guanine-rich quadruplex nucleotide-lipid derivative for treatment of resistant breast cancer is developed. The studies are performed on the resistant breast cancer cells and the cancer-bearing mice. The nucleotide-lipid derivative (DSPE-PEG2000 -C6 -GT28nt) is synthesized by introducing a hydrophobic hexyl linkage between GT-28nt (containing 17 guanines and 11 thymidines) and DSPE-PEG2000 -NHS, and is incorporated on the functional larotaxel liposomes for specific binding with nucleolin receptor on the resistant cancer cells. The studies demonstrate that the liposomes had long circulatory effect, targeted capability, and significant anticancer efficacy in resistant cancer-bearing mice. The studies further reveal their action mechanism, consisting of blocking depolymerization of microtubules, arresting cell cycle, blocking JAK-STAT signaling pathway, and inhibiting activity of antiapoptotic proteins. In conclusion, the functional larotaxel liposomes can be used for effective treatment of drug-resistant breast cancer, and this study also offers a novel targeted nanomedicine based on nucleotide-lipid derivative.

Review article: opportunities to improve and expand thiopurine therapy for autoimmune hepatitis.

BACKGROUND: Thiopurines in combination with glucocorticoids are used as first-line, second-line and maintenance therapies in autoimmune hepatitis and opportunities exist to improve and expand their use. AIMS: To describe the metabolic pathways and key factors implicated in the efficacy and toxicity of the thiopurine drugs and to indicate the opportunities to improve outcomes by monitoring and manipulating metabolic pathways, individualising dosage and strengthening the response. METHODS: English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. RESULTS: Thiopurine methyltransferase activity and 6-tioguanine (6-thioguanine) nucleotide levels influence drug efficacy and safety, and they can be manipulated to improve treatment response and prevent myelosuppression. Methylated thiopurine metabolites are associated with hepatotoxicity, drug intolerance and nonresponse and their production can be reduced or bypassed. Universal pre-treatment assessment of thiopurine methyltransferase activity and individualisation of dosage to manipulate metabolite thresholds could improve outcomes. Early detection of thiopurine resistance by metabolite testing, accurate estimations of drug onset and strength by surrogate markers and adjunctive use of allopurinol could improve the management of refractory disease. Dose-restricted tioguanine (thioguanine) could expand treatment options by reducing methylated metabolites, increasing the bioavailability of 6-tioguanine nucleotides and ameliorating thiopurine intolerance or resistance. CONCLUSIONS: The efficacy and safety of thiopurines in autoimmune hepatitis can be improved by investigational efforts that establish monitoring strategies that allow individualisation of dosage and prediction of outcome, increase bioavailability of the active metabolites and demonstrate superiority to alternative agents.

Thiopurines in inflammatory bowel disease: pharmacogenetics, therapeutic drug monitoring and clinical recommendations.

There is a growing interest in the use of thiopurines (azathioprine, 6-mercaptopurine and 6-thioguanine) for the management of inflammatory bowel disease. The genetically controlled thiopurine (S)-methyltransferase enzyme is involved in the metabolism of these agents and is hypothesised to determine the clinical response to thiopurines. Diminished activity of this enzyme decreases the methylation of thiopurines, theoretically resulting in potential overdosing, while high thiopurine (S)-methyltransferase status leads to overproduction of toxic metabolites and ineffectiveness of azathioprine and 6-mercaptopurine. In practice, controversies exist regarding the utility of standard thiopurine (S)-methyltransferase pheno- and genotyping. Current pharmacogenetic insights suggest that another enzyme system may participate in the efficacy and toxicity of thiopurines; inosine triphosphate pyrophosphatase. Other topics discussed in this review are the utilisation of therapeutic drug monitoring and the experimental use of 6-thioguanine in the treatment of inflammatory bowel disease. 6-Thioguanine has a less genetically controlled metabolism and skips genetically determined metabolic steps. On theoretical basis, 6-thioguanine might therefore have a more predictable profile than azathioprine and 6-mercaptopurine. However, the use of 6-thioguanine has been associated with an increased risk of nodular regenerative hyperplasia of the liver and veno-occlusive disease. Further research is warranted before 6-thioguanine can be considered as a treatment option for inflammatory bowel disease.

Intracerebroventricular guanine-based purines protect against seizures induced by quinolinic acid in mice.

Acute and chronic administration of the nucleoside guanosine have been shown to prevent quinolinic acid (QA) and alpha-dendrotoxin-induced seizures, as well as to impair memory and anxiety in rats and mice. In this study, we investigated the effect of i.c.v. administration of guanine-based purines (GTP, GDP, GMP, and guanosine) against seizures induced by the NMDA agonist and glutamate releaser quinolinic acid in mice. We also aimed to study the effects of the poorly hydrolysable analogs of GTP (GppNHp and GTPgammaS) and GDP (GDPbetaS) in this seizure model. QA produced seizures in 100% of mice, an effect partially prevented by guanine-based purines. In contrast to GTP (480 nmol), GDP (320-640 nmol), GMP (320-480 nmol) and guanosine (300-400 nmol), the poorly hydrolysable analogs of GTP and GDP did not affect QA-induced seizures. Thus, the protective effects of guanine nucleotides seem to be due to their conversion to guanosine. Altogether, these findings suggest a potential role of guanine-based purines for treating diseases involving glutamatergic excitotoxicity.

Synthesis and biological properties of purine and pyrimidine 5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl analogues of AMP, GMP, IMP, and CMP.

Methyl 2,3-O-isopropylidene-D-ribofuranoside (1) was converted to 1-O-acetyl-5-bromo-5-deoxy-2,3-di-O-benzoyl-D-ribofuranose (6) in five steps with good yield. The Arbuzov condensation of compound 6 with triethyl phosphite resulted in the synthesis of 1-O-acetyl-2,3-di-O-benzoyl-5-deoxy-5-(diethoxyphosphinyl)-D-ribofuranos e (7). Compound 7 was used for direct glycosylation of both purine and pyrimidine bases. The glycosylation was accomplished with the dry silylated heterocyclic base in the presence of trimethylsilyl triflate. Deblocking of the glycosylation products gave exclusively the beta anomer of the 5'-phosphonate analogues of 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]adenine (13), 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]guanosin e (16), 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]hypoxant hine (17), and 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]cytosine (15), described here for the first time. The target compounds as well as their intermediates showed no in vitro antiviral or antitumor activity, although phosphorylation of 15 and 16 to di- and triphosphate analogues was demonstrated with use of isolated cellular enzymes.

[Effect of guanyl nucleotides and hyperbaric oxygenation on the adenylate cyclase activity of the heart in rabbits with myocardial hypertrophy]. / Vliianie guanilovykh nukleotidov i giperbaricheskoi oksigenatsii na aktivnost' adenilattsiklazy serdtsa krolikov pri gipertrofii miokarda.

The authors studied the role of guanyl nucleotides and hyperbaric oxygenation (HBO) in desensitization and resensitization of adenylate cyclase of the heart during hypertrophy which was induced by aorta stenosing. The basal activity of the enzyme and the rate of its activation with adrenaline and guanyl nucleotides were discovered to be reduced. In the presence of guanyl nucleotides, HBO gave rise to the recovery of enzyme sensitivity to the hormone. The data obtained indicate that during myocardial hypertrophy, guanyl nucleotides participate both in densensitization of adenylate cyclase to hormonal exposure and in the enzyme resensitization during HBO therapy.

Synthesis and anti-DNA -virus activity of the 5'-monophosphate and the cyclic 3',5'-monophosphate of 9-(beta-D-xylofuranosyl) guanine.

9-(beta-TD-xylofuranosyl)guanine (xylo-G) was converted chemically to the 9-(beta-D-xylofuranosyl)guanine 5'-monophosphate (xylo-GMP) and 9-(beta-D-xylofuranosyl)guanine cyclic 3',5'-monophosphate (c-xylo-GMP). These compounds were tested against a variety of DNA viruses in tissue culture in parallel with 9-(beta-D-arabinofuranosyl)adenine (ara-A). This evaluation revealed that xylo-G, xylo-GMP, and c-xylo-GMP were all moderately active but less effective than ara-A. When the four compounds were administered intracerebrally as a treatment for herpes virus, type 1 induced encephalitis in mice, c-xylo-GMP exhibited superior activity to that shown by the other three. When administered intraperitoneally, c-xylo-GMP was found to have a therapeutic index of about 4, which is less than that for ara-A (approximately 30) in the same system.

Biochemical approaches to the combination chemotherapy of colon cancer.

The employment of biochemical concepts to select drugs for use in the treatment of colorectal cancer is advocated. It is stressed that new drug mixtures, even those employing agents inactive alone, with unique mechanisms of action may be fashioned through biochemical design. Following delineation of activity in animal model systems, these drug combinations then become candidates for use in man. It is emphasized that 6-thioguanine is a particularly attractive agent for consideration as a component of new combinations of drugs to be used in patients with cancer. The desirability of this agent derives from (a) the known, albeit weak, activity of 6-thioguanine against colorectal neoplasms of man, thereby providing some inherent activity to be joined by additional materials; (b) a knowledge of several major biochemical and pharmacologic determinants of tissue susceptibility to its cytotoxic action, possibly allowing the ultimate selection of patients with a high probability of response; and (c) the availability of four different agents or classes of agents which synergistically interact with 6-thioguanine to inhibit the growth of malignant cells by diverse biochemical mechanisms.

Synthesis and biological activity of some 8-substituted selenoguanosine cyclic 3',5'-phosphates and related compounds.

8-Bromoguanosine cyclic 3',5'-monophosphate, 8-bromoguanosine 5'-monophosphate, and 8-bromoguanosine served as intermediates for the chemical synthesis of a series of 8-substituted seleno cyclic nucleotides, nucleotides, and their nucleosides. Selenourea was found to be a useful reagent in synthesizing these seleno-substituted nucleoside, nucleotide, and cyclic nucleotide. A nucleic acid analyzer was used to study the hydrolysis of these cyclic nucleotides by phosphodiesterase. It was found that all of the 8-substituted selenoguanosine cyclic 3',5'-phosphates synthesized, except 8-MeSe-cGMP, were resistant to hydrolyze by phosphodiesterase. These 8-substituted seleno cyclic GMP derivatives showed some antitumor activities against murine leukemic cells (L5178Y) in vitro and in vivo.