De novo purine synthesis inhibition and antileukemic effects of mercaptopurine alone or in combination with methotrexate in vivo

Epigenetic mechanisms and oral mucositis in children with acute lymphoblastic leukaemia

This study aimed to investigate the relationship between epigenetic mechanisms and oral mucositis (OM) in paediatric patients with acute lymphoblastic leukaemia. Oral cells were collected from 76 participants, including 15 healthy individuals, 10 patients with acute lymphoblastic leukaemia but without a history of OM and 51 acute lymphoblastic leukaemia patients with a history of OM (35 with active OM and 16 who had recovered from OM). Global DNA methylation in the miR-9-1 and miR-9-3 genes was performed. Seven polymorphisms rs1801131, rs1801133 (MTHFR), rs2228611 (DNMT1), rs7590760, rs1550117 (DNMT3A), rs6087990, rs2424913 (DNMT3B) were genotyped and an analysis of association with global DNA methylation was performed. The global methylation levels were lower in cancer patients recovered from OM than in the other groups. A higher frequency of unmethylated profile for miR-9-1 and partially methylated profile for miR-9-3 was observed in cancer patients regardless of OM history compared to healthy patients. The GG genotype of the rs2228611 (DNMT1) polymorphism was associated with higher levels of global methylation in cancer patients irrespective of OM. It was concluded that global methylation is associated with mucosal recovery. The effect of DNMT1 genotype on the global DNA methylation profile, as well as the methylation profile of miR-9-1 and miR-9-3 in cancer patients is independent of OM.

Metabolic pathways and antimicrobial peptide resistance in bacteria

Antimicrobial resistance is a pressing concern that poses a significant threat to global public health, necessitating the exploration of alternative strategies to combat drug-resistant microbial infections. Recently, antimicrobial peptides (AMPs) have gained substantial attention as possible replacements for conventional antibiotics. Because of their pharmacodynamics and killing mechanisms, AMPs display a lower risk of bacterial resistance evolution compared with most conventional antibiotics. However, bacteria display different mechanisms to resist AMPs, and the role of metabolic pathways in the resistance mechanism is not fully understood. This review examines the intricate relationship between metabolic genes and AMP resistance, focusing on the impact of metabolic pathways on various aspects of resistance. Metabolic pathways related to guanosine pentaphosphate (pppGpp) and guanosine tetraphosphate (ppGpp) [collectively (p)ppGpp], the tricarboxylic acid (TCA) cycle, haem biosynthesis, purine and pyrimidine biosynthesis, and amino acid and lipid metabolism influence in different ways metabolic adjustments, biofilm formation and energy production that could be involved in AMP resistance. By targeting metabolic pathways and their associated genes, it could be possible to enhance the efficacy of existing antimicrobial therapies and overcome the challenges exhibited by phenotypic (recalcitrance) and genetic resistance toward AMPs. Further research in this area is needed to provide valuable insights into specific mechanisms, uncover novel therapeutic targets, and aid in the fight against antimicrobial resistance.

De novo nucleotide biosynthetic pathway and cancer

De novo nucleotide biosynthetic pathway is a highly conserved and essential biochemical pathway in almost all organisms. Both purine nucleotides and pyrimidine nucleotides are necessary for cell metabolism and proliferation. Thus, the dysregulation of the de novo nucleotide biosynthetic pathway contributes to the development of many human diseases, such as cancer. It has been shown that many enzymes in this pathway are overactivated in different cancers. In this review, we summarize and update the current knowledge on the de novo nucleotide biosynthetic pathway, regulatory mechanisms, its role in tumorigenesis, and potential targeting opportunities.

FOXK2 affects cancer cell response to chemotherapy by promoting nucleotide de novo synthesis

AIMS

Nucleotide de novo synthesis is essential to cell growth and survival, and its dysregulation leads to cancers and drug resistance. However, how this pathway is dysregulated in cancer has not been well clarified. This study aimed to identify the regulatory mechanisms of nucleotide de novo synthesis and drug resistance.

METHODS

By combining the ChIP-Seq data from the Cistrome Data Browser, RNA sequencing (RNA-Seq) and a luciferase-based promoter assay, we identified transcription factor FOXK2 as a regulator of nucleotide de novo synthesis. To explore the biological functions and mechanisms of FOXK2 in cancers, we conducted biochemical and cell biology assays in vitro and in vivo. Finally, we assessed the clinical significance of FOXK2 in hepatocellular carcinoma.

RESULTS

FOXK2 directly regulates the expression of nucleotide synthetic genes, promoting tumor growth and cancer cell resistance to chemotherapy. FOXK2 is SUMOylated by PIAS4, which elicits FOXK2 nuclear translocation, binding to the promoter regions and transcription of nucleotide synthetic genes. FOXK2 SUMOylation is repressed by DNA damage, and elevated FOXK2 SUMOylation promotes nucleotide de novo synthesis which causes resistance to 5-FU in hepatocellular carcinoma. Clinically, elevated expression of FOXK2 in hepatocellular carcinoma patients was associated with increased nucleotide synthetic gene expression and correlated with poor prognoses for patients.

CONCLUSION

Our findings establish FOXK2 as a novel regulator of nucleotide de novo synthesis, with potentially important implications for cancer etiology and drug resistance.

Deletion of MTAP Highly Sensitizes Osteosarcoma Cells to Methionine Restriction With Recombinant Methioninase

BACKGROUND/AIM

Methionine addiction is a fundamental and general hallmark of cancer cells, which require exogenous methionine, despite large amounts of methionine synthesized endogenously. 5-Methylthioadenosine phosphorylase (MTAP) plays a principal role as an enzyme in the methionine-salvage pathway, which produces methionine and adenine from methylthioadenosine and is deleted in 27.5% to 37.5% of osteosarcoma patients.

MATERIALS AND METHODS

Human osteosarcoma cell lines U2OS, SaOS2, MNNG/HOS (HOS) and 143B, were used. The MTAP gene was knocked out in U2OS with CRISPR/Cas9. 143B and HOS have an MTAP deletion and SaOS2 is positive for MTAP. MTAP was determined by western blotting. The four cell lines were compared for sensitivity to recombinant methioninase (rMETase).

RESULTS

MTAP-deleted osteosarcoma cell lines MNNG/HOS and 143B were significantly more sensitive to rMETase than MTAP-positive osteosarcoma cell lines U2OS and SaOS2. In addition, MTAP knock-out U2OS cells were more sensitive to rMETase than the parental MTAP-positive U2OS cells.

CONCLUSION

The present results demonstrated that the absence of MTAP sensitizes osteosarcoma cells to methionine restriction by rMETase, a promising clinical strategy.

Insights into the cellular pharmacokinetics and pharmacodynamics of thiopurine antimetabolites in a model of human intestinal cells

Thiopurines, immunomodulating drugs used in the management of different chronic autoimmune conditions and as anti-leukemic agents, may exert in some cases gastrointestinal toxicity. Moreover, since these agents are administered orally, they are absorbed across the gastrointestinal tract epithelium. On these premises, cellular and molecular events occurring in intestinal cells may be important to understand thiopurine effects. However, quantitative information on the biotransformation of thiopurines in intestinal tissues is still limited. To shed light on biotransformation processes specific of the intestinal tissue, in this study thiopurine metabolites concentrations were analyzed by an in vitro model of human healthy colon, the HCEC cell line, upon exposure to cytotoxic concentrations of azathioprine or mercaptopurine; the investigation was carried out using an innovative mass spectrometry method, that allowed the simultaneous quantification of 11 mono-, di-, and triphosphate thionucleotides. Among the 11 metabolites evaluated, TIMP, TGMP, TGDP, TGTP, MeTIMP, MeTIDP and MeTITP were detectable in HCEC cells treated with azathioprine or mercaptopurine, considering two different incubation times before the addition of the drugs (4 and 48 h). Different associations between metabolites concentrations and cytotoxicity were detected. In particular, the cytotoxicity was dependent on the TGMP, TGDP, TGTP and MeTITP concentrations after the 4 h incubation before the addition of thiopurines. This may be an indication that, to study the association between thiopurine metabolite concentrations and the cytotoxicity activity in vitro, short growth times before treatment should be used. Moreover, for the first time our findings highlight the strong correlation between cytotoxicity and thiopurine pharmacokinetics in HCEC intestinal cells in vitro suggesting that these cells could be a suitable in vitro model for studying thiopurine intestinal cytotoxicity.

Molecular Targeting and Rational Chemotherapy in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a molecularly complex disease with multiple aberrant genetic pathways involved in its pathogenesis. Approximately one-third to one-half of patients with AML would relapse, and no standard therapy is established for relapsing and/or refractory AML (RR-AML) yet. It is unlikely that blockage of only one specific pathway will lead to prolonged remissions and cures in all fractions of the AML patients population. Nowadays, novel therapeutic agents with rational combination are being recognized which improve the cure rate for relapsed AML. These drugs and their metabolites impart unique properties in the interaction with each of the intracellular targets and metabolic enzymes whereby resulting in unique clinical activity. To date, most of the combinations have used a targeted agent combined with standard agents such as anthracyclines, cytarabine, or hypomethylating agents to improve the outcome. Rational combinations of DNA damage-inducing therapies with DNA methyltransferase and histone deacetylase inhibitors synergistically enhance the DNA damage, growth inhibition and apoptosis of myeloid cells. This review makes a thorough look at current antineoplastic agents for AML with emphasis on its genetics and molecular mechanisms of action and the role of combination regimens.

Therapeutic effect of N-acetylcysteine on chemotherapy-induced liver injury

BACKGROUND

N-acetylcysteine (NAC) may be useful in the management of chemotherapy-induced liver injury.

AIMS

The present study evaluates the possible therapeutic effects of NAC on chemotherapy-induced hepatotoxicity.

METHODS

A total of 102 patients' files who were diagnosed with cancer between 2015 and 2019 were evaluated retrospectively. Two patient groups with and without NAC were selected. NAC was administered in a 3-μg/kg IV dose in a 24-h infusion to 70 patients when any alanine aminotransferase (ALT) or gamma-glutamyl transferase (GGT) values reached three times the normal levels. The other group consisted of 32 patients who were not treated with NAC. Alanine aminotransferase and GGT values were recorded at pretreatment, and on the 1st, 3rd, 5th, and 7th days in both the NAC and non-NAC groups from files.

RESULTS

In the NAC group, ALT and GGT values on day 1, 3, 5, and 7 differed from each other, decreasing from day 1 to day 7. A statistically significant difference was noted between the values in the NAC group (p < 0.001). In the non-NAC group, the ALT values on day 7 were lower than the ALT values on day 1. A comparison of the ALT and GGT values in the NAC and non-NAC groups found that the values in the NAC group decreased earlier than in the non-NAC group.

CONCLUSIONS

This study shows that NAC has a therapeutic effect on hepatotoxicity in children being treated with chemotherapeutic agents due to underlying malign diseases. The early reduction in the results of liver function tests is important for the continuation of chemotherapy.

Results of a phase II clinical trial of 6-mercaptopurine (6MP) and methotrexate in patients with BRCA-defective tumours

BACKGROUND

Tumour cells with BRCA1/2 gene mutations demonstrate increased sensitivity to platinum and poly (ADP-ribose) polymerase (PARP) inhibitors. 6-mercaptopurine (6MP) was found to selectively kill BRCA-defective cells in a xenograft model as effectively as the PARP inhibitor AG014699, even after these cells acquired resistance to a PARP inhibitor or cisplatin.

METHODS

This phase II single-arm trial investigated the activity of 6MP 55-75 mg/m2 per day, and methotrexate 15-20 mg/m2 per week in advanced breast or platinum-resistant ovarian cancer patients with a BRCA1/2 germline mutation, who had progressed after ≥1 previous line of chemotherapy. The primary outcome was objective response including stable disease (SD) as an assessment of clinical benefit rate (CBR), at 8 weeks, by RECIST v1.1. Secondary outcomes included overall survival (OS) and progression-free survival (PFS).

RESULTS

In total, 67 evaluable patients were recruited; 55 ovarian and 11 breast cancer patients. In total, 21 patients had SD (31%), one had a partial response (1.5%); CBR was 33% at 8 weeks. In total, 12/67 patients (18%) had SD at 16 weeks. In total, five ovarian cancer patients had SD for over 200 days. Median OS was 10.3 months (95% CI 6.9-14.5), median PFS 1.9 months (1.7-2.8).

CONCLUSIONS

The overall activity of 6MP and methotrexate in these patients was low; however, there was a small group of patients who appeared to derive longer-term clinical benefit.

TRIAL REGISTRATION

NCT01432145 http://www.ClinicalTrials.gov.

Analytical methodologies for determination of methotrexate and its metabolites in pharmaceutical, biological and environmental samples

Methotrexate (MTX) is a folate antagonist drug used for several diseases, such as cancers, various malignancies, rheumatoid arthritis (RA) and inflammatory bowel disease. Due to its structural features, including the presence of two carboxylic acid groups and its low native fluorescence, there are some challenges to develop analytical methods for its determination. MTX is metabolized to 7-hydroxymethotrexate (7-OH-MTX), 2,4-diamino-N10-methylpteroic acid (DAMPA), and the active MTX polyglutamates (MTXPGs) in the liver, intestine, and red blood cells (RBCs), respectively. Additionally, the drug has a narrow therapeutic range; hence, its therapeutic drug monitoring (TDM) is necessary to regulate the pharmacokinetics of the drug and to decrease the risk of toxicity. Due to environmental toxicity of MTX; its sensitive, fast and low cost determination in workplace environments is of great interest. A large number of methodologies including high performance liquid chromatography equipped with UV-visible, fluorescence, or electrochemical detection, liquid chromatography-mass spectroscopy, capillary electrophoresis, UV-visible spectrophotometry, and electrochemical methods have been developed for the quantitation of MTX and its metabolites in pharmaceutical, biological, and environmental samples. This paper will attempt to review several published methodologies and the instrumental conditions, which have been applied to measure MTX and its metabolites within the last decade.

Evaluation of the susceptibility of neurons and neural stem/progenitor cells derived from human induced pluripotent stem cells to anticancer drugs

Various chemicals, including pharmaceuticals, can induce acute or delayed neurotoxicity in humans. Because isolation of human primary neurons is extremely difficult, toxicity tests for these agents have been performed using in vivo or in vitro models. Human induced pluripotent stem cells (hiPSCs) can be used to establish hiPSC-derived neural stem/progenitor cells (hiPSC-NSPCs), which can then be used to obtain hiPSC-neurons. In this study, we differentiated hiPSC-NSPCs into neurons and evaluated the susceptibility of hiPSC-neurons and parental hiPSC-NSPCs to anticancer drugs in vitro by ATP assay and immunocytostaining. The hiPSC-neurons were more resistant to anticancer drugs than the parental hiPSC-NSPCs. In the toxicity tests, high-dose cisplatin reduced the levels of ELAVL3/4, a neuronal marker, in the hiPSC-neurons. These results suggest that our methodology is potentially applicable for efficient determination of the toxicity of any drug to hiPSC-neurons.

New methods to assess 6-thiopurine toxicity and expanding its therapeutic application to pancreatic cancer via small molecule potentiators

6-Thiopurine (6TP) is a potent cytotoxic agent that is a clinically prescribed anti-metabolite employed in the treatment of numerous blood cancers since 1952. However, its reported severe toxicities limit its general usage in the clinic. We previously have undertaken investigations into identifying the mode of toxicity for 6TP, and have found that the oxidative metabolites of 6TP, specifically 6-thiouric acid (6TU), is responsible for the in vitro inhibition of UDP-glucose dehydrogenase (UDPGDH) in a UV-vis method. In this method, inhibition was quantified through the quantification of NADH production, however, purines absorb at the same wavelength and thereby can interfere with the NADH detection. Herein, we report a HPLC method that allows for direct quantification of UDP-glucuronic acid, product from UDPGDH, for the assessment of inhibition towards UDPGDH with no interference from purines. In this method it was revealed that 6TP possesses a greater inhibitory properties than previously observed; 111 vs. 288 μM. Building upon the data collected from a previously performed rat hepatocyte study, which correlated our in vitro to in vivo inhibition theories about UDPGDH, we have developed a bio-mimic in vitro assay to aid in the inhibitory assessment of 6TP and analogs. In our efforts to expand the use of 6TP, and analogs constructed, our laboratory has undertaken a screening campaign to identify small molecule potentiators that work in synergy with 6TP in other types of cancers. Three chalcone-based compounds have been discovered through our total synthesis campaign of uvaretin, and it has been found that 11c has strong synergism with 6TP in the pancreatic cancer cell line MIA PaCa-2. Through the work presented herein, we reveal new methods to assess toxicity of 6TP and future analogs and new small molecules that work in synergy to expand the therapeutic applications of this neglected cytotoxic agent.

The immunosuppressant drug azathioprine restrains adipogenesis of muscle Fibro/Adipogenic Progenitors from dystrophic mice by affecting AKT signaling

Fibro/Adipogenic Progenitors (FAPs) define a stem cell population playing a pro-regenerative role after muscle damage. When removed from their natural niche, FAPs readily differentiate into adipocytes or fibroblasts. This digressive differentiation potential, which is kept under tight control in the healthy muscle niche, contributes to fat and scar infiltrations in degenerative myopathies, such as in Duchenne Muscular Dystrophy (DMD). Controlling FAP differentiation by means of small molecules may contribute to delay the adverse consequences of the progressive pathological degeneration while offering, at the same time, a wider temporal window for gene therapy and cell-based strategies. In a high content phenotypic screening, we identified the immunosuppressant, azathioprine (AZA) as a negative modulator of FAP adipogenesis. We show here that AZA negatively affects the adipogenic propensity of FAPs purified from wild type and mdx mice by impairing the expression of the master adipogenic regulator, peroxisome proliferator-activated receptor γ (PPARγ). We show that this inhibition correlates with a decline in the activation of the AKT-mTOR axis, the main pathway that transduces the pro-adipogenic stimulus triggered by insulin. In addition, AZA exerts a cytostatic effect that has a negative impact on the mitotic clonal process that is required for the terminal differentiation of the preadipocyte-committed cells.

Efforts in redesigning the antileukemic drug 6-thiopurine: decreasing toxic side effects while maintaining efficacy

6-Thiopurine (6TP) is a currently prescribed drug in the treatment of diseases ranging from Crohn's disease to acute lymphocytic leukemia. While its potent mode of action is through incorporation into DNA as a thiol mimic of deoxyguanosine, severe toxicities are associated with its administration which hinder the potential therapeutic application. We have previously reported in vitro that the oxidative metabolites of 6TP, specifically 6-thiouric acid (6TU, K _i 7 μM), are potent inhibitors of UDP-glucose dehydrogenase (UDPGDH), an enzyme that is responsible for the formation of UDP-glucuronic acid (UDPGA), an essential substrate that is used in detoxification processes in the liver. An in vivo investigation was undertaken to probe if 6TU inhibits UDPGDH in rat hepatocytes, and it was observed that 6TU does greatly suppress the conjugation of bilirubin with UDPGA. The failed excretion of bilirubin is linked to a majority of the reported toxicities associated with 6TP administration. Efforts were undertaken for the construction of 6TP analogs, substituted at the C8 position, to reduce inhibition of UDPGDH while retaining therapeutic efficacy. Three new 6TP analogs bearing a halogen (Br, Cl, and F) at the C8 position have been achieved over five-synthetic steps in overall yields of 16 to 32%. Each of these analogs were shown to have reduced inhibition towards UDPGDH, with K _i values of 192, 163, 215 μM, respectively. In addition, the bromine, chlorine, and fluorine analogs were shown to possess cytotoxicity towards the REH cell line (acute lymphocytic leukemia) having IC₅₀ values of 9.54 μM (±0.97), 3.95 μM (±1.94), and 4.71 μM (±1.40), respectively. These three new 6TP analogs represent the first steps in the redesign of this potent anticancer agent into a better drug that possesses reduced toxic side effects while retaining therapeutic potency.

Immune Response-Dependent Assembly of IMP Dehydrogenase Filaments

Inosine monophosphate dehydrogenase (IMPDH) catalyzes the conversion of IMP to xanthosine monophosphate, the rate-limiting step in de novo guanosine monophosphate (GMP) synthesis. In cultured cells, IMPDH polymerizes into micron-scale filamentous structures when GMP synthesis is inhibited by depletion of purine precursors or by various drugs, including mycophenolic acid, ribavirin, and methotrexate. IMPDH filaments also spontaneously form in undifferentiated mouse embryonic stem cells and induced pluripotent stem cells, hinting they might function in various highly proliferative cell types. Therefore, we investigated IMPDH filament formation in human and murine T cells, which rely heavily on de novo guanine nucleotide synthesis to rapidly proliferate in response to antigenic challenge. We discovered extensive in vivo IMPDH filament formation in mature T cells, B cells, and other proliferating splenocytes of normal, adult B6 mice. Both cortical and medullary thymocytes in young and old mice also showed considerable assembly of IMPDH filaments. We then stimulated primary human peripheral blood mononuclear cells ex vivo with T cell mitogens phytohemagglutinin (PHA), concanavalin A (ConA), or antibodies to CD3 and CD28 for 72 h. We detected IMPDH filaments in 40–60% of T cells after activation compared to 0–10% of unstimulated T cells. Staining of activated T cells for the proliferation marker Ki-67 also showed an association between IMPDH filament formation and proliferation. Additionally, we transferred ovalbumin-specific CD4⁺ T cells from B6.OT-II mice into B6.Ly5a recipient mice, challenged these mice with ovalbumin, and harvested spleens 6 days later. In these spleens, we identified abundant IMPDH filaments in transferred T cells by immunofluorescence, indicating that IMPDH also polymerizes during in vivo antigen-specific T cell activation. Overall, our data indicate that IMPDH filament formation is a novel aspect of T cell activation and proliferation, and that filaments might be useful morphological markers for T cell activation. The data also suggest that in vivo IMPDH filament formation could be occurring in a variety of proliferating cell types throughout the body. We propose that T cell activation will be a valuable model for future experiments probing the molecular mechanisms that drive IMPDH polymerization, as well as how IMPDH filament formation affects cell function.

Association of C3435T, C1236T and C4125A Polymorphisms of the MDR-1 Gene in Egyptian Children with Acute Lymphoblastic Leukaemia

Background:

P-glycoprotein (P-gp), a membrane transporter encoded by the multidrug resistance-1 (MDR1) gene, influences pharmacokinetics and metabolism of anticancer drugs and contributes to multidrug resistance phenotype in acute lymphoblastic leukemia (ALL). Genetic variation ofMDR1 in ALL patients is increasingly recognized as a factor influencing response to treatment.

Aim:

To investigate the possible role of MDR-1 gene polymorphisms (C3435T, C1236T and C4125A) as risk factors for the development and clinical outcome of ALL in Egyptian children.

Materials and Methods:

Genotyping of MDR-1 C3435T, C1236T and C4125A single nucleotide polymorphisms (SNPs) was accomplished using a polymerase chain reaction–restriction fragment length polymorphism (RFLP-PCR) assay with 120 childhood ALL patients and 100 healthy controls.

Results:

Homozygous T with the C3435T SNP showed a protective effect as compared to homozygous C (OR=0.748) while heterozygous CT correlated with a poor outcome (high risk, drug unresponsiveness, relapse and high percentage of death). Additionally, the T allele of the C1236T SNP showed a significant relation with ALL risk (OR=1.6). However, there were no significant differences in the genotype and allele frequencies of MDR-1 SNPs between patients and controls. Only one genotype (CC) and one allele of MDR-1 (C4125A) were seen. Neither CA/AA genotypes nor A alleles were present in ALL patients and normal controls. TC was the predominant haplotype in both groups, while CT proved to be minor. The cumulative incidence of relapse was higher with the CC genotype of C1236T as compared with TT.

Conclusion:

From our preliminary data, the CT genotype of C3435T is associated with a poor ALL outcome while the CC genotype of C1236T is related with an increased incidence of relapse. Although our results provide assistance for oncologist choice of individual therapeutic strategy taking the patient genetic repertoire into consideration, further investigations with larger sample size should be conducted to validate our results.

Photochemical relaxation pathways of S6-methylthioinosine and O6-methylguanosine in solution

S6-Methylthioinosine and O6-methylguanosine are byproducts resulting from the enzymatic reactions of sulfur-substituted prodrugs in cells and from the interaction of alkylating agents with cellular DNA, respectively. Their photochemistry has not been investigated, and it is currently unknown whether light absorption by these byproducts may pose any threat to the cell. In this contribution, their photoinduced processes upon absorption of UVB radiation are reported using broadband transient absorption spectroscopy. Plausible electronic relaxation mechanisms are proposed for both biological molecules, which are supported by steady-state absorption and emission measurements, and by singlet and triplet vertical excitation energies performed on a large subset of ground-state optimized conformational isomers in solution. The results are compared to the body of knowledge gathered in the scientific literature about the light-induced processes in the sulfur-substituted and canonical purine monomers. In particular, it is shown that S6-methylation decreases the rate to populate the lowest-energy triplet state and blueshifts the ground-state absorption spectrum compared to those for the sulfur-substituted prodrugs and for the 6-thioguanosine metabolite. Similarly, O6-methylation decreases the rate of internal conversion to the ground state observed in the guanine monomers by more than 10-fold in acetonitrile and 40-fold in aqueous solution, while it redshifts the ground-state absorption spectrum. Collectively, this investigation provides relevant new insights about the relationship between structural modifications of the purine chromophore and the electronic relaxation mechanisms in this important group of biological molecules.

6-mercaptopurine promotes energetic failure in proliferating T cells

The anticancer drug 6-mercaptopurine (6-MP) inhibits de novo purine synthesis and acts as an antiproliferative agent by interfering with protein, DNA and RNA synthesis and promoting apoptosis. Metabolic reprogramming is crucial for tumor progression to foster cancer cells growth and proliferation, and is regulated by mechanistic target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) as well as the oncogenes Myc and hypoxia inducible factor 1α (HIF-1α). We hypothesized that 6-MP impacts metabolic remodeling through its action on nucleotide synthesis. The aim of our study is to provide a comprehensive characterization of the metabolic changes induced by 6-MP in leukemic T cells. Our results indicate that exposition to 6-MP rapidly reduces intracellular ATP concentration, leading to the activation of AMPK. In turn, mTOR, an AMPK target, was inhibited, and the expression of HIF-1α and Myc was reduced upon 6-MP incubation. As a consequence of these inhibitions, glucose and glutamine fluxes were strongly decreased. Notably, no difference was observed on glucose uptake upon exposition to 6-MP. In conclusion, our findings provide new insights into how 6-MP profoundly impacts cellular energetic metabolism by reducing ATP production and decreasing glycolytic and glutaminolytic fluxes, and how 6-MP modifies human leukemic T cells metabolism with potential antiproliferative effects.

Inhibition of UDP-glucose dehydrogenase by 6-thiopurine and its oxidative metabolites: Possible mechanism for its interaction within the bilirubin excretion pathway and 6TP associated liver toxicity

6-Thiopurine (6TP) is an actively prescribed drug in the treatment of various diseases ranging from Crohn's disease and other inflammatory diseases to acute lymphocytic leukemia and non-Hodgkin's leukemia. While 6TP has beneficial therapeutic uses, severe toxicities are also reported with its use, such as jaundice and liver toxicity. While numerous investigations into the mode in which toxicity originates has been undertaken. None have investigated the effects of inhibition towards UDP-Glucose Dehydrogenase (UDPGDH), an oxidative enzyme responsible for UDP-glucuronic acid (UDPGA) formation or UDP-Glucuronosyl transferase (UGT1A1), which is responsible for the conjugation of bilirubin with UDPGA for excretion. Failure to excrete bilirubin leads to jaundice and liver toxicity. We proposed that either 6TP or its primary oxidative excretion metabolites inhibit one or both of these enzymes, resulting in the observed toxicity from 6TP administration. Inhibition analysis of these purines revealed that 6-thiopurine has weak to no inhibition towards UDPGDH with a K_i of 288 μM with regard to varying UDP-glucose, but 6-thiouric (primary end metabolite, fully oxidized at carbon 2 and 8, and highly retained by the body) has a near six-fold increased inhibition towards UDPGDH with a K_i of 7 μM. Inhibition was also observed by 6-thioxanthine (oxidized at carbon 2) and 8-OH-6TP with K_i values of 54 and 14 μM, respectively. Neither 6-thiopurine or its excretion metabolites were shown to inhibit UGT1A1. Our results show that the C2 and C8 positions of 6TP are pivotal in said inhibition towards UDPGDH and have no effect upon UGT1A1, and that blocking C8 could lead to new analogs with reduced, if not eliminated jaundice and liver toxicities.

Oxidatively-generated damage to DNA and proteins mediated by photosensitized UVA

UVA accounts for about 95% of the solar ultraviolet (UV) radiation that reaches Earth and most likely contributes to human skin cancer risk. In contrast to UVB, which comprises the remaining 5% and is absorbed by DNA nucleobases to cause direct photodamage, UVA damages DNA indirectly. It does this largely through its interactions with cellular chromophores that act as photosensitisers to generate reactive oxygen species. Exogenously supplied chemicals, including some widely-prescribed medicines, may also act as photosensitisers and these drugs are associated with an increased risk of sun-related cancer. Because they amplify the effects of UVA on cells, they provide a means to investigate the mechanisms and effects of UVA-induced photodamage. Here, we describe some of the major lesions induced by two groups of UVA photosensitisers, the DNA thionucleotides and the fluoroquinolone antibiotics. In thionucleotides, replacement of the oxygen atoms of canonical nucleobases by sulfur converts them into strong UVA chromophores that can be incorporated into DNA. The fluoroquinolones are also UVA chromophores. They are not incorporated into DNA and induce a different range of DNA damages. We also draw attention to the potentially important contribution of photochemical protein damage to the cellular effects of photosensitised UVA. Proteins targeted for oxidation damage include DNA repair factors and we suggest that UVA-mediated protein damage may contribute to sunlight-induced cancer risk.

DNA-thioguanine nucleotide concentration and relapse-free survival during maintenance therapy of childhood acute lymphoblastic leukaemia (NOPHO ALL2008): a prospective substudy of a phase 3 trial

BACKGROUND

Adjustment of mercaptopurine and methotrexate maintenance therapy of acute lymphoblastic leukaemia by leucocyte count is confounded by natural variations. Cytotoxicity is primarily mediated by DNA-incorporated thioguanine nucleotides (DNA-TGN). The aim of this study was to establish whether DNA-TGN concentrations in blood leucocytes during maintenance therapy are associated with relapse-free survival.

METHODS

In this substudy of the NOPHO ALL2008 phase 3 trial done in 23 hospitals in seven European countries (Denmark, Estonia, Finland, Iceland, Lithuania, Norway, and Sweden), we analysed data from centralised and blinded analyses of 6-mercaptopurine and methotrexate metabolites in blood samples from patients with non-high-risk childhood acute lymphoblastic leukaemia. Eligible patients were aged 1·0-17·9 years; had been diagnosed with non-high-risk precursor B-cell or T-cell leukaemia; had been treated according to the Nordic Society of Pediatric Hematology and Oncology ALL2008 protocol; and had reached maintenance therapy in first remission. Maintenance therapy was (mercaptopurine 75 mg/m² once per day and methotrexate 20 mg/m² once per week, targeted to a leucocyte count of 1·5-3·0 × 10⁹ cells per L). We measured DNA-TGN and erythrocyte concentrations of TGN nucleotides, methylated mercaptopurine metabolites, and methotrexate polyglutamates. The primary objective was the association of DNA-TGN concentrations and 6-mercaptopurine and methotrexate metabolites with relapse-free survival. The secondary endpoint was the assessment of DNA-TGN concentration and 6-mercaptopurine and methotrexate metabolites during maintenance therapy phase 2.

FINDINGS

Between Nov 26, 2008 and June 14, 2016, 1509 patients from the NOPHO ALL2008 study were assessed for eligibility in the DNA-TGN substudy, of which 918 (89%) of 1026 eligible patients had at least one DNA-TGN measurement and were included in the analyses. Median follow-up was 4·6 years (IQR 3·1-6·1). Relapse-free survival was significantly associated with DNA-TGN concentration (adjusted hazard ratio 0·81 per 100 fmol/μg DNA increase, 95% CI 0·67-0·98; p=0·029). In patients with at least five blood samples, erythrocyte concentrations of TGN, methylated mercaptopurine metabolites, and methotrexate polyglutamates were associated with DNA-TGN concentration (all p<0·0001).

INTERPRETATION

Our results suggest the need for intervention trials to identify clinically applicable strategies for individualised drug dosing to increase DNA-TGN concentration, and randomised studies to investigate whether such strategies improve cure rates compared with current dose adjustments based on white blood cell counts.

FUNDING

Danish Cancer Society, Childhood Cancer Foundation (Denmark), Childhood Cancer Foundation (Sweden), Nordic Cancer Union, Otto Christensen Foundation, University Hospital Rigshospitalet, and Novo Nordic Foundation.

Association of erythrocyte methotrexate-polyglutamate levels with the efficacy and hepatotoxicity of methotrexate in patients with rheumatoid arthritis: a 76-week prospective study

Objective

To assess the utility of erythrocyte methotrexate-polyglutamate (MTX-PG) concentrations in determining the safety and efficacy of MTX in patients with rheumatoid arthritis (RA).

Methods

79 MTX-naïve patients with RA were enrolled in this prospective 76-week cohort study. MTX was initiated, and a predefined dose-escalation protocol was followed. Erythrocyte MTX-PG concentrations were measured using liquid chromatography. The associations of MTX-PG concentrations with disease activity and adverse events were analysed.

Results

Dose escalation of MTX resulted in increased MTX-PG concentrations and a decrease in the mean Disease Activity Score in 28 joints (DAS28). A significant association was observed between total MTX-PG concentrations and ΔDAS28 at week 12 (β=−0.013, p=0.003) and at week 24 (β=−0.014, p=0.003). The maximum MTX-PG levels were significantly higher in patients presenting with elevated transaminases (≥100 IU/L) than in those without (146 vs 106 nmol/L, p=0.009). Receiver operating characteristic curve analysis revealed that a total MTX-PG concentrations of 83 nmol/L at week 12 was the threshold for a DAS28 improvement of ≥1.2 at week 24, and 105 nmol/L was the threshold for transaminases of ≥50 IU/L and 131 nmol/L for transaminases of ≥100 IU/L. MTX-PG concentrations were strongly influenced by body mass index and a serum albumin level.

Conclusions

MTX-PG concentrations are a useful biomarker in MTX therapy, in terms of efficacy and safety.

Colonic microbiota can promote rapid local improvement of murine colitis by thioguanine independently of T lymphocytes and host metabolism

OBJECTIVE

Mercaptopurine (MP) and pro-drug azathioprine are 'first-line' oral therapies for maintaining remission in IBD. It is believed that their pharmacodynamic action is due to a slow cumulative decrease in activated lymphocytes homing to inflamed gut. We examined the role of host metabolism, lymphocytes and microbiome for the amelioration of colitis by the related thioguanine (TG).

DESIGN

C57Bl/6 mice with or without specific genes altered to elucidate mechanisms responsible for TG's actions were treated daily with oral or intrarectal TG, MP or water. Disease activity was scored daily. At sacrifice, colonic histology, cytokine message, caecal luminal and mucosal microbiomes were analysed.

RESULTS

Oral and intrarectal TG but not MP rapidly ameliorated spontaneous chronic colitis in Winnie mice (point mutation in Muc2 secretory mucin). TG ameliorated dextran sodium sulfate-induced chronic colitis in wild-type (WT) mice and in mice lacking T and B lymphocytes. Remarkably, colitis improved without immunosuppressive effects in the absence of host hypoxanthine (guanine) phosphoribosyltransferase (Hprt)-mediated conversion of TG to active drug, the thioguanine nucleotides (TGN). Colonic bacteria converted TG and less so MP to TGN, consistent with intestinal bacterial conversion of TG to so reduce inflammation in the mice lacking host Hprt. TG rapidly induced autophagic flux in epithelial, macrophage and WT but not Hprt^-/- fibroblast cell lines and augmented epithelial intracellular bacterial killing.

CONCLUSIONS

Treatment by TG is not necessarily dependent on the adaptive immune system. TG is a more efficacious treatment than MP in Winnie spontaneous colitis. Rapid local bacterial conversion of TG correlated with decreased intestinal inflammation and immune activation.

Avidin inhibits PHA-induced human peripheral blood mononuclear cell proliferation

Background: Cell proliferation occurs not only in normal but also in cancer cells. Most of cell proliferation inhibition can be done by inhibiting the DNA synthesis, notably by intervening the formation of purine or pyrimidine. In purine de novo synthesis, it was assumed that biotin plays a role as a coenzyme in carboxylation reaction, one of the pivotal steps in the purine de novo pathways. The aim of this study was to see the avidin potency to bind biotin and inhibit mitosis.Methods: Peripheral blood mononuclear cell (PBMC) was cultured in RPMI-1640 medium and stimulated by phytohemagglutinin (PHA) in the presence or absence of interleukin-2 (IL-2), with or without avidin. The effect of avidin addition was observed at 24, 48, and 72 hours for cell proliferation, viability, and cell cycle. Statistical analysis was done by one-way ANOVA.Results: Avidin inhibited cell proliferation and viability in culture under stimulation by PHA with and without IL-2. Cell cycle analysis showed that avidin arrested the progression of PBMC after 72 hours of culture. Most cells were found in G0/G1 phase.Conclusion: Inhibition of biotin utilization by avidin binding can halt cell proliferation.

Assessment of mercaptopurine (6MP) metabolites and 6MP metabolic key-enzymes in childhood acute lymphoblastic leukemia

Pediatric acute lymphoblastic leukemia (ALL) is treated with combination chemotherapy including mercaptopurine (6MP) as an important component. Upon its uptake, 6MP undergoes a complex metabolism involving many enzymes and active products. The prognostic value of all the factors engaged in this pathway still remains unclear. This study attempted to determine which components of 6MP metabolism in leukemic blasts and red blood cells are important for 6MP's sensitivity and toxicity. In addition, changes in the enzymatic activities and metabolite levels during the treatment were analyzed. In a cohort (N=236) of pediatric ALL patients enrolled in the Dutch ALL-9 protocol, we studied the enzymes inosine-5'-monophosphate dehydrogenase (IMPDH), thiopurine S-methyltransferase (TPMT), hypoxanthine guanine phosphoribosyl transferase (HGPRT), and purine nucleoside phosphorylase (PNP) as well as thioguanine nucleotides (TGN) and methylthioinosine nucleotides (meTINs). Activities of selected enzymes and levels of 6MP derivatives were measured at various time points during the course of therapy. The data obtained and the toxicity related parameters available for these patients were correlated with each other. We found several interesting relations, including high concentrations of two active forms of 6MP--TGN and meTIN--showing a trend toward association with better in vitro antileukemic effect of 6MP. High concentrations of TGN and elevated activity of HGPRT were found to be significantly associated with grade III/IV leucopenia. However, a lot of data of enzymatic activities and metabolite concentrations as well as clinical toxicity were missing, thereby limiting the number of assessed relations. Therefore, although a complex study of 6MP metabolism in ALL patients is feasible, it warrants more robust and strict data collection in order to be able to draw more reliable conclusions.

Implementation of TPMT testing

The activity of the enzyme thiopurine methyltransferase (TPMT) is regulated by a common genetic polymorphism. One in 300 individuals lack enzyme activity and 11% are heterozygous for a variant low activity allele and have an intermediate activity. The thiopurine drugs azathioprine, mercaptopurine and thioguanine are substrates for TPMT; these drugs exhibit well documented myelosuppressive effects on haematopoietic cells and have a track record of idiosyncratic drug reactions. The development of severe bone marrow toxicity, in patients taking standard doses of thiopurine drugs, is associated with TPMT deficiency whilst the TPMT heterozygote is at an increased risk of developing myelosuppression. Factors influencing TPMT enzyme activity, as measured in the surrogate red blood cell, are discussed in this review to enable an appreciation of why concordance between TPMT genotype and phenotype is not 100%. This is particularly important for lower/intermediate TPMT activities to avoid misclassification of TPMT status. TPMT testing is now widely available in routine service laboratories. The British National Formulary suggests TPMT testing before starting thiopurine drugs. Dermatologists were quick to adopt routine TPMT testing whilst gastroenterologists do not specifically recommend TPMT screening. TPMT testing is mandatory prior to the use of mercaptopurine in childhood leukaemia. Thiopurine drug dose and other treatment related influences on cell counts explain some of the differing recommendations between clinical specialities. TPMT testing is cost-effective and the major role is in the identification of the TPMT deficient individual prior to the start of thiopurine drugs.

Independent validation of a model using cell line chemosensitivity to predict response to therapy

BACKGROUND

Methods using cell line microarray and drug sensitivity data to predict patients' chemotherapy response are appealing, but groups may be reluctant to release details to preserve intellectual property. Here we describe a case study to validate predictions while treating the methods as a "black box."

METHODS

Medical Prognosis Institute (MPI) constructed cell-line-derived sensitivity scores (SSs) and combined scores (CSs) that incorporate clinical variables. MD Anderson researchers evaluated their predictions. We searched the Gene Expression Omnibus (GEO) to identify validation datasets, and we performed statistical evaluation of the agreement between prediction and clinical observation.

RESULTS

We identified 3 suitable datasets: GSE16446 (n = 120; binary outcome), GSE17920 (n = 130; binary outcome), and GSE10255 (n = 161; continuous and time-to-event outcomes). The SS was statistically significantly associated with primary treatment responses for all studies (GSE16446: P = .02; GSE17920: P = .02; GSE10255: P = .02). Dichotomized SSs performed no better than chance for GSE16446 and GSE17920, and categorized SSs did not predict disease-free survival (GSE10255). SSs sometimes improved on predictions using clinical variables (GSE16446: P = .05; GSE17920: P = .31; GSE10255: P = .045), but gains were limited (95% confidence intervals for GSE16446 and GSE17920 include 0). The CS did not predict treatment response for GSE16446 (P = .55), but it did for GSE17920 (P < .001). Coefficients of clinical variables provided by MPI for CSs agree with estimates for GSE17920 better than estimates for GSE16446.

CONCLUSIONS

Model predictions were better than chance in all three datasets. However, these scores added little to existing clinical predictors; statistically significant contributions were likely to be too small to change clinical practice. These findings suggest that discovering better predictors will require both cell line data and a clinical training dataset of patient samples.

Mathematical modeling of folate metabolism

Folate metabolism is a complex biological process that is influenced by many variables including transporters, cofactors, and enzymes. Mathematical models provide a useful tool to evaluate this complex system and to elucidate hypotheses that would be otherwise untenable to test in vitro or in vivo. Forty years of model development and refinement along with enhancements in technology have led to systematic improvement in our biological understanding of these models. However, increased complexity does not always lead to increased understanding, and a balanced approach to modeling the system is often advantageous. This approach should address questions about sensitivity of the model to variation and incorporate genomic data. The folate model is a useful platform for investigating the effects of antifolates on the folate pathway. The utility of the model is demonstrated through interrogation of drug resistance, drug-drug interactions, drug selectivity, and drug doses and schedules. Mathematics can be used to create models with the ability to design and improve rationale therapeutic interventions.

Methotrexate binds to recombinant thiopurine S-methyltransferase and inhibits enzyme activity after high-dose infusions in childhood leukaemia

PURPOSE

Important drugs in the treatment of childhood acute lymphoblastic leukaemia (ALL) are 6-mercaptopurine (6-MP) and methotrexate (MTX). Thiopurine methyltransferase (TPMT) is a polymorphic enzyme causing variability in 6-MP response and toxicity. The aim of this study was to investigate the fluctuation in TPMT enzyme activity over time and the effect of high-dose MTX infusions on TPMT enzyme activity and 6-MP metabolites in paediatric ALL patients.

METHODS

Fifty-three children with ALL treated according to the NOPHO-ALL 2000 protocol were included in the study. TPMT enzyme activity was measured at six different times starting from diagnosis until after the end of maintenance treatment. TPMT and 6-MP metabolites were measured before the initiation of high-dose MTX (HD-MTX) infusions and at 66 h post-infusion. The interaction between MTX and TPMT was investigated in vitro using recombinant TPMT protein and a leukaemic cell line.

RESULTS

Forty percent of TPMT wild-type individuals had deceptively low TPMT enzyme activity according to genotype at the time of diagnosis. TPMT activity had decreased significantly 66 h after the start of HD-MTX infusions (-9.2 %; p = 0.013). MTX bound to recombinant TPMT protein severely inhibiting TPMT enzyme activity (remaining activity 16 %).

CONCLUSIONS

Our results show that TPMT genotyping should be performed in children with ALL, since 40 % of the children in our study who carried the wild-type TPMT gene were at risk of initial underdosing of 6-MP in cases where only TPMT enzyme activity was determined. MTX inhibits the TPMT enzyme activity after HD-MTX infusions due to protein binding.

Gene-gene interactions in folate and adenosine biosynthesis pathways affect methotrexate efficacy and tolerability in rheumatoid arthritis

OBJECTIVE

As no single nucleotide polymorphism has emerged as pivotal to predict the lack of efficacy and dose-limiting toxicities to methotrexate (MTX), we evaluated the contribution of gene-gene interactions to the effects of this prodrug in rheumatoid arthritis.

METHODS

A total of 255 patients treated with MTX for at least 3 months were evaluated with efficacy assessed using the European League Against Rheumatism response criteria or a physician's assessment of patient's response to MTX visual analog scale. Gastrointestinal and neurological idiosyncrasies were recorded in 158 patients. Fourteen single nucleotide polymorphisms in folate and adenosine biosynthesis pathways were measured and detection of gene-gene interactions was performed using multifactor-dimensionality reduction, a method that reduces high-dimensional genetic data into a single dimension of predisposing or risk-genotype combinations.

RESULTS

Efficacy to MTX (53% responders) was associated with high-order epistasis among variants in inosine-triphosphate pyrophosphatase, aminoimidazole-carboxamide ribonucleotide transformylase, and reduced folate carrier genes. In the absence of predisposing genotype combinations, a 3.8-fold lower likelihood of efficacy was observed (vs. in their presence, 95% confidence interval: 2.2-6.4; P<0.001). Increasing MTX polyglutamate concentrations tended to partially overcome this selective disadvantage. Idiosyncrasies occurred in 29% of patients. In the presence of risk-genotype combinations among variants in methylene tetrahydrofolate reductase, γ-glutamyl-hydrolase, thymidylate synthase, serine hydroxymethyltransferase, and inosine-triphosphate pyrophosphatase genes, an 8.9-fold higher likelihood to exhibit toxicities was observed (vs. in their absence, 95% confidence interval: 3.6-21.9; P<0.001). False-positive report probabilities were below 0.2, thereby indicating that true signals were likely detected in this cohort.

CONCLUSION

These data indicate that gene-gene interactions impact MTX efficacy and tolerability in rheumatoid arthritis.

Oxidation-mediated DNA cross-linking contributes to the toxicity of 6-thioguanine in human cells

The thiopurines azathioprine and 6-mercaptopurine have been extensively prescribed as immunosuppressant and anticancer agents for several decades. A third member of the thiopurine family, 6-thioguanine (6-TG), has been used less widely. Although known to be partly dependent on DNA mismatch repair (MMR), the cytotoxicity of 6-TG remains incompletely understood. Here, we describe a novel MMR-independent pathway of 6-TG toxicity. Cell killing depended on two properties of 6-TG: its incorporation into DNA and its ability to act as a source of reactive oxygen species (ROS). ROS targeted DNA 6-TG to generate potentially lethal replication-arresting DNA lesions including interstrand cross-links. These triggered processing by the Fanconi anemia and homologous recombination DNA repair pathways. Allopurinol protected against 6-TG toxicity by acting as a ROS scavenger and preventing DNA damage. Together, our findings provide mechanistic evidence to support the proposed use of thiopurines to treat HR-defective tumors and for the coadministration of 6-TG and allopurinol as an immunomodulation strategy in inflammatory disorders.

Multiple forms of DNA damage caused by UVA photoactivation of DNA 6-thioguanine

Thiopurines are prescribed frequently as medication for cancer and for inflammatory disorders. One of them, azathioprine, has been the immunosuppressant of choice for organ transplant recipients for many years. Thiopurine use is associated with elevated sun sensitivity and skin cancer risk. Skin sensitization is selective for UVA. 6-TG integrates into DNA and unlike the canonical DNA bases, it is a strong UVA chromophore with an absorbance maximum at 342 nm. DNA 6-TG is a photosensitizer and a source of reactive oxygen species. Reactive oxygen that is generated from the photochemical activation of DNA 6-TG causes extensive damage to DNA and proteins. This damage is mutagenic and extremely toxic to cultured human cells. Here we describe some of the lesions that are known to be generated from UVA irradiation of DNA 6-TG. We discuss how this photochemical damage might contribute to the toxic effect of thiopurine/UVA treatment on cultured cells and to the high risk of skin cancer in thiopurine-treated patients.

Patterns of interaction between genetic and nongenetic attributes and methotrexate efficacy in rheumatoid arthritis

OBJECTIVE

The contribution of low-penetrance single nucleotide polymorphisms to methotrexate efficacy in rheumatoid arthritis (RA) is inconsistent between studies. We sought to elucidate architecture of methotrexate response in three cohorts of patients with RA treated with methotrexate.

METHODS

Single nucleotide polymorphism frequencies in genes from folate, purine, and pyrimidine pathways were measured to develop a model of gene-gene interactions using multifactor dimensionality reduction in 439 patients who received methotrexate in the USA and The Netherlands. A third cohort of 530 patients with RA from Sweden was used to replicate the findings. Methotrexate efficacy was assessed using the European League Against Rheumatism criteria in the majority of patients.

RESULTS

Nonlinear patterns of gene-gene interactions between variants in aminoimidazole carboxamide ribonucleotide transformylase (C347G), reduced-folate carrier (G80A) and inosine-triphosphate pyrophosphatase (C94A) revealed a predisposing genetic attribute significantly associated with methotrexate response in the USA and Dutch cohorts [odds ratio (OR)=2.9, 95% confidence interval (CI): 1.9-4.2; P<0.001]. Although the finding was not replicated in the Swedish cohort (OR=0.9; 95% CI: 0.64-1.37; P=0.74) a multifactor dimensionality reduction analysis superimposing the predisposing genetic attribute with patient's age, sex, and anticitrullinated peptide antibodies positivity (ACPA) revealed a pattern of interaction significant in all three cohorts (OR=2.2, 95% CI: 1.6-2.9; P<0.01). The selective advantage toward response in the presence of the predisposing genetic attribute was lost in females and ACPA-positive patients, whereas older and male ACPA-negative patients tended to exhibit a greater likelihood of response in the absence of the predisposing genetic attribute.

CONCLUSION

Gene-gene interactions together with nongenetic attributes may contribute to methotrexate efficacy in RA.

Adherence to oral chemotherapy in childhood acute lymphoblastic leukemia: an evolutionary concept analysis

PURPOSE/OBJECTIVES

To clarify the concept of adherence to daily oral chemotherapy in children with acute lymphoblastic leukemia (ALL), to examine its implications for clinical practice, and to provide a foundation for further research and knowledge development.

DATA SOURCES

Published literature identified through the MEDLINE®, CINAHL®, PsycINFO, and ERIC databases.

DATA SYNTHESIS

Identified attributes of adherence to oral chemotherapy in childhood ALL included motivation, persistence, collaboration, mindfulness, cognitive capacity, flexibility, active participation, and identification of key participants in the process. Identified antecedents included a diagnosis of leukemia, the perceived value of adherence, and patient, family, and healthcare system-related factors. Identified consequences included the potential for maintaining optimal drug levels and improving disease outcome, as well as increased patient and caregiver esteem through active participation in the process. Adherence in the context of childhood ALL is defined as the active self-care behavior of taking (or having the responsibility for administering) daily oral chemotherapy, in collaboration with and according to the instructions of the healthcare provider over a defined, prolonged treatment period.

CONCLUSIONS

Adherence to oral chemotherapy in childhood ALL is a complex, multidimensional behavior that involves not only a willingness to follow the prescribed regimen over a prolonged period, but also the cognitive capacity and psychomotor skills to carry out the process.

IMPLICATIONS FOR NURSING

Nurses should recognize the importance of clear communication of medication instructions, reinforcement of adherence-related behaviors, and assistance with common issues such as pill-swallowing skills and reminder systems in caring for children with ALL.

Gene polymorphisms and pharmacogenetics in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic, chronic and inflammatory disease of unknown etiology with genetic predisposition. The advent of new biological agents, as well as the more traditional disease-modifying antirheumatic drugs, has resulted in highly efficient therapies for reducing the symptoms and signs of RA; however, not all patients show the same level of response in disease progression to these therapies. These variations suggest that RA patients may have different genetic regulatory mechanisms. The extensive polymorphisms revealed in non-coding gene-regulatory regions in the immune system, as well as genetic variations in drug-metabolizing enzymes, suggest that this type of variation is of functional and evolutionary importance and may provide clues for developing new therapeutic strategies. Pharmacogenetics is a rapidly advancing area of research that holds the promise that therapies will soon be tailored to an individual patient’s genetic profile.

Shortening infusion time for high-dose methotrexate alters antileukemic effects: a randomized prospective clinical trial

PURPOSE

To determine whether shortening the infusion duration of high-dose methotrexate (HDMTX; 1 g/m(2)) affects the in vivo accumulation of active methotrexate polyglutamates (MTXPG(1-7)) in leukemia cells and whether this differs among major acute lymphoblastic leukemia (ALL) subtypes.

METHODS

From June 2000 through October 2007, 356 children with ALL were randomly assigned to receive initial single-agent treatment with HDMTX (1 g/m(2)) as either a 24-hour infusion or a 4-hour infusion at two pediatric hospitals in the United States. The primary outcome measures were the accumulation of MTXPG(1-7) in leukemia cells and the antileukemic effects (eg, inhibition of de novo purine synthesis in bone marrow ALL cells, and decrease in circulating ALL cells).

RESULTS

The 24-hour infusion resulted in significantly higher amounts of MTXPG(1-7) in bone marrow leukemia cells (median: 1,695 v 1,150 pmol/10(9) cells, P = .0059), and better antileukemic effects. The 24-hour infusion had the greatest effect on MTXPG(1-7) accumulation in hyperdiploid ALL (median: 3,919 v 2,417 pmol/10(9) cells, P = .0038); T-cell ALL exhibited smaller differences in MTXPG(1-7) but greater antileukemic effects with the longer infusion (median decrease in leukemia cells: 88.4% v 51.8%, P = .0075). In contrast, infusion duration had no significant impact on MTXPG(1-7) accumulation or antileukemic effects in ALL with the t(12;21)/(ETV6-RUNX1) chromosomal translocation.

CONCLUSION

Shortening the infusion time of HDMTX reduces accumulation of active methotrexate in leukemia cells and decreases antileukemic effects, with differing consequences among major ALL subtypes.

Modeling mechanisms of in vivo variability in methotrexate accumulation and folate pathway inhibition in acute lymphoblastic leukemia cells

Methotrexate (MTX) is widely used for the treatment of childhood acute lymphoblastic leukemia (ALL). The accumulation of MTX and its active metabolites, methotrexate polyglutamates (MTXPG), in ALL cells is an important determinant of its antileukemic effects. We studied 194 of 356 patients enrolled on St. Jude Total XV protocol for newly diagnosed ALL with the goal of characterizing the intracellular pharmacokinetics of MTXPG in leukemia cells; relating these pharmacokinetics to ALL lineage, ploidy and molecular subtype; and using a folate pathway model to simulate optimal treatment strategies. Serial MTX concentrations were measured in plasma and intracellular MTXPG concentrations were measured in circulating leukemia cells. A pharmacokinetic model was developed which accounted for the plasma disposition of MTX along with the transport and metabolism of MTXPG. In addition, a folate pathway model was adapted to simulate the effects of treatment strategies on the inhibition of de novo purine synthesis (DNPS). The intracellular MTXPG pharmacokinetic model parameters differed significantly by lineage, ploidy, and molecular subtypes of ALL. Folylpolyglutamate synthetase (FPGS) activity was higher in B vs T lineage ALL (p<0.005), MTX influx and FPGS activity were higher in hyperdiploid vs non-hyperdiploid ALL (p<0.03), MTX influx and FPGS activity were lower in the t(12;21) (ETV6-RUNX1) subtype (p<0.05), and the ratio of FPGS to γ-glutamyl hydrolase (GGH) activity was lower in the t(1;19) (TCF3-PBX1) subtype (p<0.03) than other genetic subtypes. In addition, the folate pathway model showed differential inhibition of DNPS relative to MTXPG accumulation, MTX dose, and schedule. This study has provided new insights into the intracellular disposition of MTX in leukemia cells and how it affects treatment efficacy.

One of the primary agents used in the treatment of childhood acute lymphoblastic leukemia (ALL) is methotrexate (MTX). By better understanding its intracellular disposition, we are able to better design treatments that circumvent drug resistance and thus help improve ALL cure rates. In this study, we develop a system of mathematical models that describe the intracellular disposition of MTX along with its inhibition of important biosynthetic pathways necessary for cell division. First, we used the models to describe the disposition of intracellular MTX in a cohort of 194 patients enrolled on St. Jude Total XV protocol for newly diagnosed ALL. The results of this modeling allowed us to determine mechanisms of in vivo variability in MTX accumulation. These mechanisms related to both the influx and efflux of the drug along with the enzymes related to its metabolism. Next, we used model simulations to show the effects of changes in MTX dose and schedule on its efficacy. The results of these simulations show that longer infusions yield better efficacy and that higher MTX doses can circumvent resistance observed in ALL subtypes with lower intracellular MTX accumulate. The results from this study provide new insights into the design of more effective therapy for pediatric ALL.

Red blood cell methotrexate polyglutamates emerge as a function of dosage intensity and route of administration during pulse methotrexate therapy in rheumatoid arthritis

OBJECTIVE

MTX is a prodrug producing anti-arthritic effects through a folylpolyglutamate synthase-mediated activation to MTX polyglutamates (MTXPGs). Our objective was to characterize the pharmacokinetics of intracellular MTXPGs and the factors associated with their accumulation in adult RA patients treated with MTX weekly.

METHODS

MTX pharmacokinetics were evaluated in 47 MTX-naïve patients enrolled in an MTX dose-escalation study for an average of 20 weeks and 223 patients enrolled in a cross-sectional study under long-term MTX therapy. Short-chain (MTXPG1-2), long-chain (MTXPG3) and very long-chain (MTXPG4-5) concentrations were measured in circulating red blood cells using liquid chromatography. Statistical analyses consisted of non-linear mixed models, multivariate regression analyses and Wilcoxon signed-rank test.

RESULTS

The accumulation of MTXPG1-5 was sigmoidal and steady-state concentrations were achieved after 7 weeks of therapy. However, additional exposure and MTX dosage escalation produced a selective redistribution towards longer chain MTXPGs at the expense of shorter chain MTXPGs. Age, glomerular filtration rate and route of MTX administration were the most important predictors of MTXPG accumulation. In 10 patients, a switch from oral to parenteral MTX was associated with a 37% increase in long-chain MTXPGs, a 132% increase in very long-chain MTXPGs and a concomitant 31% reduction in disease activity (P<0.02).

CONCLUSION

The selective emergence of long-chain MTXPGs is function of dose, time of exposure and hence dosage intensity. Switching from oral to parenteral MTX produces a selective accumulation of longer chain MTXPGs that are known to be more potent inhibitors of de novo purine biosynthesis than shorter chain MTXPGs.

The impact of high-dose methotrexate on intracellular 6-mercaptopurine disposition during interval therapy of childhood acute lymphoblastic leukemia

PURPOSE

Low-dose methotrexate (MTX) therapy is the cornerstone treatment of acute lymphoblastic leukemia (ALL) and may enhance the activation of 6-mercaptopurine (6-MP) to 6-thioguanine nucleotides (6-TGN). Yet, data have established that high-dose MTX (HDMTX) hampers the accumulation of 6-TGN in red blood cells (RBC) and lymphoblasts.

METHODS

To clarify the pharmacokinetic interactions between these two antimetabolites, we serially measured RBC 6-TGN and MTX polyglutamates (MTXPG) levels following repeated courses of HDMTX (5 g/m(2) over 24 h) with daily oral 6-MP (25 mg/m(2)) during interval therapy in 20 children with ALL.

RESULTS

HDMTX produced a rapid reduction in RBC 6-TGN 24 h after the start of MTX, and this effect was sustained at least by the third day (median decrease -21%; P < 0.001). However, a return to pre-infusion of 6-TGN levels was observed by the time of the following HDMTX course 14 days later (P < 0.001). RBC MTX polyglutamates accumulation followed Michaelis-Menten kinetics but was not associated with the change in pre-infusion 6-TGN levels which remained stable during the interval period.

CONCLUSION

HDMTX does not appear to enhance 6-MP activation to 6-TGN. Moreover, given that the deleterious effect of HDMTX on intracellular 6-MP disposition has been shown to be several folds greater in lymphoblasts than in RBC. Our data warrant additional studies elucidating the optimal MTX dose synergizing with 6-MP.

Thiopurine methyltransferase genetics is not a major risk factor for secondary malignant neoplasms after treatment of childhood acute lymphoblastic leukemia on Berlin-Frankfurt-Münster protocols

Thiopurine methyltransferase (TPMT)is involved in the metabolism of thiopurines such as 6-mercaptopurine and 6-thioguanine. TPMT activity is significantly altered by genetics, and heterozygous and even more homozygous variant people reveal substiantially decreased TPMT activity. Treatment for childhood acute lymphoblastic leukemia (ALL) regularly includes the use of thiopurine drugs. Importantly, childhood ALL patients with low TPMT activity have been considered to be at increased risk of developing therapy-associated acute myeloid leukemia and brain tumors. In the present study, we genotyped 105 of 129 patients who developed a secondary malignant neoplasm after ALL treatment on 7 consecutive German Berlin-Frankfurt-Münster trials for all functionally relevant TPMT variants. Frequencies of TPMT variants were similarly distributed in secondary malignant neoplasm patients and the overall ALL patient population of 814 patients. Thus, TPMT does not play a major role in the etiology of secondary malignant neoplasm after treatment for childhood ALL, according to Berlin-Frankfurt-Münster strategies.

Use of Pharmacogenetics, Enzymatic Phenotyping, and Metabolite Monitoring to Guide Treatment with Azathioprine in Patients with Systemic Lupus Erythematosus

Objective.

Individualized therapy based on genetic background and monitoring of metabolites can optimize drug safety and efficacy. Such an approach is available for azathioprine (AZA), the thiopurine antimetabolite. AZA exerts therapeutic effects when metabolized to the active thiopurine nucleotide, 6-thioguanine (6-TGN). In inflammatory bowel disease (IBD), 6-TGN levels in the target range of 235–400 pmol/8 ×108 red blood cells (RBC) are associated with a high likelihood of response. Our objective was to evaluate whether drug escalation based on metabolite levels improves efficacy and maintains safety in patients with systemic lupus erythematosus (SLE).

Methods.

We conducted a 6-month open-label dose-escalation clinical study of patients with active SLE treated with azathioprine dosed by body weight and metabolite levels. The primary endpoint was ≥50% improvement in any one parameter of disease activity, or 50% decrease in glucocorticoid dose.

Results.

Of 50 patients enrolled in the study, 21 achieved clinical responses, 13 of whom had 6-TGN < 235 pmol/8 ×108 RBC. Ten patients had no clinical response at 6 months, yet achieved either therapeutic IBD 6-TGN levels (> 235, n = 4) or received maximum AZA dose ≥3.5 mg/kg (n = 6). In 19 patients the drug was discontinued prematurely due to side effects or SLE activity. For those patients in whom either liver function test or white blood cell count abnormalities were encountered, metabolites guided attribution to drug or disease activity.

Conclusion.

Clinical responses in SLE can occur at levels of 6-TGN lower than the target range established for IBD. During followup, measurements of AZA metabolites may provide a rational approach to safety.

Genetic polymorphism of inosine triphosphate pyrophosphatase is a determinant of mercaptopurine metabolism and toxicity during treatment for acute lymphoblastic leukemia

The influence of genetic polymorphism in inosine triphosphate pyrophosphatase (ITPA) on thiopurine-induced adverse events has not been investigated in the context of combination chemotherapy for acute lymphoblastic leukemia (ALL). This study investigated the effects of a common ITPA variant allele (rs41320251) on mercaptopurine metabolism and toxicity during treatment of children with ALL. Significantly higher concentrations of methyl mercaptopurine nucleotides were found in patients with the nonfunctional ITPA allele. Moreover, there was a significantly higher probability of severe febrile neutropenia in patients with a variant ITPA allele among patients whose dose of mercaptopurine had been adjusted for TPMT genotype. In a cohort of patients whose mercaptopurine dose was not adjusted for TPMT phenotype, the TPMT genotype had a greater effect than the ITPA genotype. In conclusion, genetic polymorphism of ITPA is a significant determinant of mercaptopurine metabolism and of severe febrile neutropenia, after combination chemotherapy for ALL in which mercaptopurine doses are individualized on the basis of TPMT genotype.

Modulatory effects of 6-carboxymethylthiopurine on activated murine macrophages

The immunological activity of macrophages against pathogens in hosts includes the phagocytosis and the production of nitric oxide. We report herein the investigation of the effect of 6-carboxymethylthiopurine on nitric oxide production by murine macrophages as well as its effect on the cell viability and proliferation after stimulus with Mycobacterium bovis bacille Calmette-Guérin, interferon-gamma or a combination of both. J774A.1 macrophages stimulated or not by bacille Calmette-Guérin (20 microg/mL), interferon-gamma or both, were cultured in the presence of 6-carboxymethylthiopurine (125, 250 and 500 microm). Nitric oxide production was measured by the Griess method and cell viability/proliferation by the diphenyltetrazolium assay [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide]. We observed an increase of J774A.1 cell proliferation after stimulus with bacille Calmette-Guérin at 125, 250 and 500 microm (69.1, 124.0 and 89.7%, respectively) and with interferon-gamma at 125 and 250 microm (64.8% and 61.7%, respectively) (p < 0.05). In all cultures treated with 6-carboxymethylthiopurine, interferon-gamma-activated nitric oxide production by J774A.1 cells decreased as well as when subjected to interferon-gamma plus bacille Calmette-Guérin stimuli at 500 microm (p < 0.05). Altogether these data point to an anti-inflammatory effect of 6-carboxymethylthiopurine on stimulated macrophages.

In vivo response to methotrexate forecasts outcome of acute lymphoblastic leukemia and has a distinct gene expression profile

BACKGROUND

Childhood acute lymphoblastic leukemia (ALL) is the most common cancer in children, and can now be cured in approximately 80% of patients. Nevertheless, drug resistance is the major cause of treatment failure in children with ALL. The drug methotrexate (MTX), which is widely used to treat many human cancers, is used in essentially all treatment protocols worldwide for newly diagnosed ALL. Although MTX has been extensively studied for many years, relatively little is known about mechanisms of de novo resistance in primary cancer cells, including leukemia cells. This lack of knowledge is due in part to the fact that existing in vitro methods are not sufficiently reliable to permit assessment of MTX resistance in primary ALL cells. Therefore, we measured the in vivo antileukemic effects of MTX and identified genes whose expression differed significantly in patients with a good versus poor response to MTX.

METHODS AND FINDINGS

We utilized measures of decreased circulating leukemia cells of 293 newly diagnosed children after initial "up-front" in vivo MTX treatment (1 g/m(2)) to elucidate interpatient differences in the antileukemic effects of MTX. To identify genomic determinants of these effects, we performed a genome-wide assessment of gene expression in primary ALL cells from 161 of these newly diagnosed children (1-18 y). We identified 48 genes and two cDNA clones whose expression was significantly related to the reduction of circulating leukemia cells after initial in vivo treatment with MTX. This finding was validated in an independent cohort of children with ALL. Furthermore, this measure of initial MTX in vivo response and the associated gene expression pattern were predictive of long-term disease-free survival (p < 0.001, p = 0.02).

CONCLUSIONS

Together, these data provide new insights into the genomic basis of MTX resistance and interpatient differences in MTX response, pointing to new strategies to overcome MTX resistance in childhood ALL.

TRIAL REGISTRATIONS

Total XV, Therapy for Newly Diagnosed Patients With Acute Lymphoblastic Leukemia, http://www.ClinicalTrials.gov (NCT00137111); Total XIIIBH, Phase III Randomized Study of Antimetabolite-Based Induction plus High-Dose MTX Consolidation for Newly Diagnosed Pediatric Acute Lymphocytic Leukemia at Intermediate or High Risk of Treatment Failure (NCI-T93-0101D); Total XIIIBL, Phase III Randomized Study of Antimetabolite-Based Induction plus High-Dose MTX Consolidation for Newly Diagnosed Pediatric Acute Lymphocytic Leukemia at Lower Risk of Treatment Failure (NCI-T93-0103D).

Thiopurines in current medical practice: molecular mechanisms and contributions to therapy-related cancer

Thiopurines have diverse clinical applications and their long-term use as anti-rejection drugs in transplant patients has been associated with a significantly increased risk of various types of cancer. Although they are slowly being replaced by a new generation of non-thiopurine immunosuppressants, it is anticipated that their use in the management of inflammatory and autoimmune diseases will continue to increase. Therapy-related cancer will remain a potential consequence of prolonged treatment for these generally non-life-threatening conditions. Understanding how thiopurines contribute to the development of cancer will facilitate clinical decisions about the potential risks to patients of long-term treatment for chronic inflammatory disorders.

Methotrexate Conjugated to Gold Nanoparticles Inhibits Tumor Growth in a Syngeneic Lung Tumor Model

Methotrexate (MTX), a stoichiometric inhibitor of dihydrofolate reductase, is a chemotherapeutic agent for treating a variety of neoplasms. Impairment of drug import into cells and increase in drug export from cells may render cells resistant to MTX. MTX, when locally administered in a soluble form, is rapidly absorbed through capillaries into the circulatory system, which may also account for therapeutic failure in patients. To retain MTX within tumor cells for longer duration and alter its pharmacokinetic behavior, we proposed a new formulation of MTX bound to the gold nanoparticle (AuNP) that serves as drug carriers. In this study, we developed the MTX-AuNP conjugate and examined its cytotoxic effect in vitro and antitumor effect in vivo. Spectroscopic examinations revealed that MTX can be directly bound onto AuNP via the carboxyl group (-COOH) to form the MTX-AuNP complex and kinetically released from the nanoparticles. The accumulation of MTX is faster and higher in tumor cells treated with MTX-AuNP than that treated with free MTX. Notably, MTX-AuNP shows higher cytotoxic effects on several tumor cell lines compared with an equal dose of free MTX. This can be attributed to the "concentrated effect" of MTX-AuNP. Administration of MTX-AuNP suppresses tumor growth in a mouse ascites model of Lewis lung carcinoma (LL2), whereas an equal dose of free MTX had no antitumor effect. In conclusion, these results suggest that by combining nanomaterials with anticancer drugs MTX-AuNP may be more effective than free MTX for cancer treatment.