Intrinsic and acquired resistance to methotrexate in acute leukemia

Dynamic genomic changes in methotrexate-resistant human cancer cell lines beyond DHFR amplification suggest potential new targets for preventing drug resistance

BACKGROUND

Although DHFR gene amplification has long been known as a major mechanism for methotrexate (MTX) resistance in cancer, the early changes and detailed development of the resistance are not yet fully understood.

METHODS

We performed genomic, transcriptional and proteomic analyses of human colon cancer cells with sequentially increasing levels of MTX-resistance.

RESULTS

The genomic amplification evolved in three phases (pre-amplification, homogenously staining region (HSR) and extrachromosomal DNA (ecDNA)). We confirm that genomic amplification and increased expression of DHFR, with formation of HSRs and especially ecDNAs, is the major driver of resistance. However, DHFR did not play a detectable role in the early phase. In the late phase (ecDNA), increase in FAM151B protein level may also have an important role by decreasing sensitivity to MTX. In addition, although MSH3 and ZFYVE16 may be subject to different posttranscriptional regulations and therefore protein expressions are decreased in ecDNA stages compared to HSR stages, they still play important roles in MTX resistance.

CONCLUSION

The study provides a detailed evolutionary trajectory of MTX-resistance and identifies new targets, especially ecDNAs, which could help to prevent drug resistance. It also presents a proof-of-principal approach which could be applied to other cancer drug resistance studies.

Inhibition of mitochondrial folate metabolism drives differentiation through mTORC1 mediated purine sensing

Supporting cell proliferation through nucleotide biosynthesis is an essential requirement for cancer cells. Hence, inhibition of folate-mediated one carbon (1C) metabolism, which is required for nucleotide synthesis, has been successfully exploited in anti-cancer therapy. Here, we reveal that mitochondrial folate metabolism is upregulated in patient-derived leukaemic stem cells (LSCs). We demonstrate that inhibition of mitochondrial 1C metabolism through impairment of de novo purine synthesis has a cytostatic effect on chronic myeloid leukaemia (CML) cells. Consequently, changes in purine nucleotide levels lead to activation of AMPK signalling and suppression of mTORC1 activity. Notably, suppression of mitochondrial 1C metabolism increases expression of erythroid differentiation markers. Moreover, we find that increased differentiation occurs independently of AMPK signalling and can be reversed through reconstitution of purine levels and reactivation of mTORC1. Of clinical relevance, we identify that combination of 1C metabolism inhibition with imatinib, a frontline treatment for CML patients, decreases the number of therapy-resistant CML LSCs in a patient-derived xenograft model. Our results highlight a role for folate metabolism and purine sensing in stem cell fate decisions and leukaemogenesis.

Efficient delivery of methotrexate to MDA-MB-231 breast cancer cells by a pH-responsive ZnO nanocarrier

Methotrexate (MTX), an efficient chemotherapy medication is used in treating various malignancies. However, the breast cancer cell line MDA-MB-231 has developed resistance to it due to low levels of the MTX transport protein, and reduced folate carrier (RFC), making it less effective against these cancer cells. Here we designed a very simple, biocompatible, and non-toxic amine-capped ZnO quantum dots to overcome the MTX resistance on the MDA-MB-231 breast cancer cell line. The QD was characterized by HRTEM, DLS EDX, FT-IR, UV-Vis, and Fluorescence spectroscopy. MTX loading onto the QD was confirmed through fluorescence and UV-Vis spectroscopy. Additionally, extensive confocal microscopic investigations were carried out to determine whether the MTX was successfully released on the MDA-MB-231 cell line. It was discovered that QD is a better pH-responsive delivery system than the previous ones because it successfully delivers MTX to the MDA-MB-231 at a higher rate on an acidic pH than it does at a physiological pH. QD also has anticancer activity and can eradicate cancer cells on its own. These factors make the QD to be an effective pH-responsive delivery system that can improve the efficacy of the medication in therapeutic diagnosis.

Effects of genetic polymorphisms on methotrexate levels and toxicity in Chinese patients with acute lymphoblastic leukemia

Methotrexate (MTX) has an antitumor effect when used for the treatment of acute lymphoblastic leukemia (ALL). This study aims at evaluating the associations between 14 polymorphisms of six genes involved in MTX metabolism with serum MTX concentration and toxicity accompanying high-dose MTX. Polymorphisms in 183 Chinese patients with ALL were analyzed using TaqMan single nucleotide polymorphism genotyping assay. The serum MTX concentration was determined using homogeneous enzyme immunoassay. MTX-related toxicities were also evaluated. Renal toxicity was significantly associated with higher serum MTX concentrations at 24, 48, and 72 hours, and MTX elimination delay (P = 0.001, P < 0.001, P < 0.001, and P < 0.001, respectively), whereas SLCO1B1 rs4149056 was associated with serum MTX concentrations at 48 and 72 hours, and MTX elimination delay in candidate polymorphisms (P = 0.014, P = 0.019, and P = 0.007, respectively). SLC19A1 rs2838958 and rs3788200 were associated with serum MTX concentrations at 24 hours (P = 0.016, P = 0.043, respectively). MTRR rs1801394 was associated with serum MTX concentrations at 72 hours (P = 0.045). Neutropenia was related to SLC19A1 rs4149056 (odds ratio [OR]: 3.172, 95% confidence interval [CI]: 1.310-7.681, P = 0.011). Hepatotoxicity was associated with ABCC2 rs2273697 (OR: 3.494, 95% CI: 1.236-9.873, P = 0.018) and MTRR rs1801394 (OR: 0.231, 95% CI: 0.084-0.632, P = 0.004). Polymorphisms of SLCO1B1, SLC19A1, ABCC2, and MTRR genes help predict higher risk of increased MTX levels or MTX-related toxicities in adult ALL patients.

Insights on Metabolic Reprogramming and Its Therapeutic Potential in Acute Leukemia

Acute leukemias, classified as acute myeloid leukemia and acute lymphoblastic leukemia, represent the most prevalent hematologic tumors in adolescent and young adults. In recent years, new challenges have emerged in order to improve the clinical effectiveness of therapies already in use and reduce their side effects. In particular, in this scenario, metabolic reprogramming plays a key role in tumorigenesis and prognosis, and it contributes to the treatment outcome of acute leukemia. This review summarizes the latest findings regarding the most relevant metabolic pathways contributing to the continuous growth, redox homeostasis, and drug resistance of leukemia cells. We describe the main metabolic deregulations in acute leukemia and evidence vulnerabilities that could be exploited for targeted therapy.

Folate metabolism: a re-emerging therapeutic target in haematological cancers

Folate-mediated one carbon (1C) metabolism supports a series of processes that are essential for the cell. Through a number of interlinked reactions happening in the cytosol and mitochondria of the cell, folate metabolism contributes to de novo purine and thymidylate synthesis, to the methionine cycle and redox defence. Targeting the folate metabolism gave rise to modern chemotherapy, through the introduction of antifolates to treat paediatric leukaemia. Since then, antifolates, such as methotrexate and pralatrexate have been used to treat a series of blood cancers in clinic. However, traditional antifolates have many deleterious side effects in normal proliferating tissue, highlighting the urgent need for novel strategies to more selectively target 1C metabolism. Notably, mitochondrial 1C enzymes have been shown to be significantly upregulated in various cancers, making them attractive targets for the development of new chemotherapeutic agents. In this article, we present a detailed overview of folate-mediated 1C metabolism, its importance on cellular level and discuss how targeting folate metabolism has been exploited in blood cancers. Additionally, we explore possible therapeutic strategies that could overcome the limitations of traditional antifolates.

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Due to micrometastatic spread, radical surgery alone rarely results in cure. Introduction of combination chemotherapy in the 1970s, however, dramatically increased overall survival rates from 20% to approximately 70%. Unfortunately, large clinical trials aiming to intensify treatment in the past decades have failed to achieve higher cure rates. In this review, we revisit how the heterogenous nature of osteosarcoma as well as acquired and intrinsic resistance to chemotherapy can account for stagnation in therapy improvement. We summarise current osteosarcoma treatment strategies focusing on molecular determinants of treatment susceptibility and resistance. Understanding therapy susceptibility and resistance provides a basis for rational therapy betterment for both identifying patients that might be cured with less toxic interventions and targeting resistance mechanisms to sensitise resistant osteosarcoma to conventional therapies.

Histone deacetylase inhibition enhances the therapeutic effects of methotrexate on primary central nervous system lymphoma

Background

Polyglutamylation is a reversible protein modification that commonly occurs in tumor cells. Methotrexate (MTX) in tumor cells is polyglutamylated and strongly binds to dihydrofolate reductase (DHFR) without competitive inhibition by leucovorin. Therefore, tumor cells with high polyglutamylation levels are supposed to be selectively killed, whereas normal cells with lower polyglutamylation are rescued by leucovorin. This study investigated the combined effects of MTX plus histone deacetylase inhibitors (HDACIs), which upregulate MTX polyglutamylation, in primary central nervous system lymphoma (PCNSL).

Methods

We evaluated cell viability after MTX treatment and leucovorin rescue and compared the expression of folylpolyglutamate synthetase (FPGS), γ-glutamyl hydrolase (GGH), and DHFR in 2 human PCNSL-derived cell lines (HKBML and TK) and a human Burkitt lymphoma cell line (TL-1). Combination treatments were created using 4 HDACIs: panobinostat, vorinostat, sodium butyrate, and valproic acid. The expression of DHFR was examined as well as ratios of FPGS/GGH expression. The combined effects of MTX plus HDACIs were evaluated using a cell viability assay, mass spectroscopy imaging, and subcutaneous and intracranial xenograft models.

Results

HDACIs upregulated the ratio of FPGS/GGH expression resulting in increased polyglutamylation of MTX, but also downregulated expression of the target molecule of MTX: DHFR. The combination of MTX and vorinostat decreased cell viability in vitro (P < .05) and tumor volumes in a subcutaneous model (P < .0001), and prolonged survival in an intracranial model (P < .01), relative to controls.

Conclusion

HDACIs enhanced the therapeutic effect of MTX through increased polyglutamylation of MTX and concomitant downregulation of DHFR expression.

GSEA-assisted gene signatures valid for combinations of prognostic markers in PCNSL

Primary central nervous system lymphoma (PCNSL) is a brain malignant non-Hodgkin’s B-cell lymphoma. The standard treatments are high-dose methotrexate (MTX)-based chemotherapies and deferred whole brain radiotherapy. However, MTX resistance-dependent global expression and signaling pathway changes and their relationship with prognoses have not yet been elucidated. Here, we conducted a global expression analysis with next-generation sequencing and gene set enrichment analysis (GSEA) in MTX-resistant PCNSL cell lines (HKBML-MTX and TK-MTX) and PCNSL tissues. In rank scores, genes listed in HKBML-MTX and TK-MTX were enriched in PCNSL with poor prognoses. In fold changes, a part of differentially-expressed genes in PCNSL tissues were also detected in HKBML-MTX and TK-MTX cells; FOXD2-AS1 and MMP19 were commonly expressed in both HKBML-MTX and TK-MTX, FABP5 and CD70 were HKBML-MTX-specifically expressed, and CLCN2, HOXB9, INE1, and LRP5L were TK-MTX-specifically expressed, which may provide a combination of prognostic markers on MTX-sensitivities in PCNSL. Additionally, PCNSL subgroups, divided with hierarchical clustering and Kaplan-Meier methods, included twenty commonly expressed genes in both HKBML-MTX and TK-MTX, ten HKBML-MTX-specifically expressed genes, and two TK-MTX-specifically expressed genes. These results suggest that the GSEA-assisted gene signatures can provide a combination for prognostic markers in recurrent PCNSL with MTX resistances.

A Case/Control Study: AGBL1 Polymorphism Related to Lung Cancer Risk in Chinese Nonsmoking Females

ATP/GTP binding protein like 1 (AGBL1) plays a role in controlling the length of polyglutamate side chains. Polymorphism rs4513061 in AGBL1 is suspected to influence the risk of lung cancer. A case/control study was performed involving 556 cases and 563 controls from a hospital participating in donation. The relationship between rs4513061 and the risk of lung cancer and the interaction between rs4513061 and environmental exposure were determined by the chi-square tests, logistic regression analysis, and crossover analysis. The survival analysis was conducted by Cox proportional hazard regression. The results showed that rs4513061 polymorphism is associated with the risk of lung cancer. The stratified analysis suggested the protective effect of rs4513061 to different histological types of lung cancer, including lung adenocarcinoma (AA vs. GG: odds ratio [OR] = 0.505, 95% confidence interval [CI] = 0.337-0.756, p < 0.001), squamous cell lung cancer (AG vs. GG: OR = 0.488, 95% CI = 0.269-0.883, p = 0.018), and small-cell lung cancer (AA vs. GG: OR = 0.421, 95% CI = 0.216-0.819, p = 0.011). Nevertheless, there was no significant interaction between rs4513061 and cooking oil fume. Significant impact was not observed between the rs4513061 polymorphism and survival time of lung cancer. Our study indicated that rs4513061 in AGBL1 decreases the risk of lung cancer in nonsmoking females from northeast China.

Cell-type-specific sensitivity of bortezomib in the methotrexate-resistant primary central nervous system lymphoma cells

BACKGROUND

Methotrexate (MTX) is used in first-line treatment of primary central nervous system lymphoma (PCNSL), but most cases result in relapse-acquired resistance to MTX. However, only few studies have reported on internal changes and chemotherapies in PCNSL.

METHODS

In this study, we generated two MTX-resistant PCNSL cell lines, designated MTX-HKBML and MTX-TK, in addition to a MTX-resistant Burkitt lymphoma cell line, designated MTX-RAJI. We examined gene expression changes and drug sensitivity to a proteasome inhibitor, bortezomib, in these cells.

RESULTS

Cytotoxic tests revealed that the 50% inhibitory concentration for MTX in MTX-HKBML is markedly higher than that in the other two cell lines. Expression of the genes in MTX and folate metabolisms, including gamma-glutamyl hydrolase and dihydrofolate reductase, are upregulated in both MTX-HKBML and MTX-TK, whereas the gene expression of folylpolyglutamate synthetase, thymidylate synthase, and methylenetetrahydrofolate dehydrogenase 1 were upregulated and downregulated in MTX-HKBML and MTX-TK, respectively, on the other hand, bortezomib sensitivity was observed in MTX-TK, as compared with control TK, but not in MTX-HKBML.

CONCLUSION

These results indicate the cell-type-specific changes downstream of metabolic pathways for MTX and folate, bortezomib sensitivity, and purine and pyrimidine syntheses, in each PCNSL cell line. The MTX-resistant lymphoma cell lines established may be useful for in vitro relapse models for MTX and development of salvage chemotherapy and drug discovery.

Overexpression of dihydrofolate reductase is a factor of poor survival in acute lymphoblastic leukemia

Dihydrofolate reductase (DHFR) has an important function in DNA synthesis and is a target of methotrexate, which is a crucial treatment option for acute lymphoblastic leukemia (ALL). However, the number of studies conducted to date on DHFR expression in childhood ALL is limited. The aim of the present study was to determine whether the expression of DHFR is associated with survival in childhood ALL. The expression of DHFR in 96 children with ALL and 100 control individuals was determined using reverse transcription-quantitative polymerase chain reaction. The results of the present study demonstrated that the expression of DHFR mRNA in children with ALL was significantly increased (P<0.001), compared with that in the control group. In addition, increased levels of DHFR mRNA were observed in patients with B-cell lineage, compared with patients with T-cell lineage ALL (P<0.05). The Kaplan-Meier estimator analysis revealed that children with ALL who exhibited increased levels of DHFR mRNA had a decreased overall survival time (P<0.05). It was observed that certain patient prognostic features (including age, sex, white blood cell count and high DHFR expression), are associated with poor survival (log-rank test, P<0.05). Therefore, the results of the present study indicated that DHFR upregulation is a factor for poor survival in ALL.

Clinical significance of polyglutamylation in primary central nervous system lymphoma

The therapeutic response to high-dose methotrexate (HD-MTX) therapy for primary central nervous system lymphoma (PCNSL) varies. Polyglutamylation is a reversible protein modification with a high occurrence rate in tumor cells. MTX incorporated into cells is polyglutamylated and strongly binds to dihydrofolate reductase without competitive inhibition by leucovorin (LV). Tumor cells with high polyglutamylation levels are selectively killed, whereas normal cells with lower polyglutamylation are rescued by LV. We hypothesized that the extent of polyglutamylation in tumor cells determines treatment resistance. Here, we investigated the therapeutic response of PCNSL to HD-MTX therapy with LV rescue based on polyglutamylation status. Among 113 consecutive PCNSL patients who underwent HD-MTX therapy in our department between 2001 and 2014, polyglutamylation was evaluated by immunostaining in 82 cases, with relationships between polyglutamylation and therapeutic response retrospectively examined. Human malignant lymphoma lines were used for in vitro experiments, and folpolyglutamate synthetase (FPGS), which induces polyglutamylation, was knocked down with short-hairpin RNA, and a stable cell line with a low rate of polyglutamylation was established. Cell viability after MTX treatment with LV rescue was evaluated using sodium butyrate (NaBu), a histone-deacetylase inhibitor that induces polyglutamylation by elevating FPGS expression. The complete response rate was significantly higher in the group with polyglutamylation than in the non-polyglutamylation group [58.1% (25/43) and 33.3% (13/39), respectively] (p < 0.05), and progression-free survival was also significantly increased in the group with polyglutamylation (p < 0.01). In vitro, the relief effect of LV after MTX administration was significantly enhanced after FPGS knockdown in al cell lines, whereas enhancement of FPGS expression by NaBu treatment significantly reduced this relief effect. These findings suggested that polyglutamylation could be a predictor of therapeutic response to HD-MTX therapy with LV rescue in PCNSL. Combination therapy with HD-MTX and polyglutamylation-inducing agents might represent a promising strategy for PCNSL treatment.

Role of topical interferon alpha-2b in 'mitomycin-C-resistant' ocular surface squamous neoplasia: our preliminary findings

PURPOSE

To report the clinical presentation of mitomycin-C (MMC)-resistant ocular surface squamous neoplasia (OSSN) and its treatment outcome with topical interferon alpha-2b (IFNα-2b).

METHODS

A prospective, non-randomised, pilot study enrolling clinically diagnosed OSSN patients. The inclusion criterion was resistance of OSSN to standard topical MMC (0.02%) chemotherapy. The resistance was defined as 'no clinical response' in the terms of reduction in tumour size, extension and vascularity after minimum 6 weeks 'on-cycles' of MMC. Any previous surgical intervention or recurrent OSSN lesions were excluded. Topical MMC was stopped in all, and topical IFNα-2b (1million IU/ml) eyedrops were prescribed to each patient. At first presentation, the clinical features and side-effect profile of MMC was noted and therapeutic effect of IFNα-2b was clinically monitored at each follow-up. Topical immunotherapy was continued for 24 weeks and a minimum follow-up of 12 weeks was observed after stopping IFNα-2b.

RESULTS

Six patients with a mean age of 62 years met the inclusion criteria. At presentation, all had unilateral, circumscribed, sessile and unifocal lesions with mean dimensions of 7.67 × 5.17 mm. Four patients had temporal lesions while surface keratin, pigmentation and corneal involvement were noted in three lesions, separately. All lesions had dilated and tortuous feeder vessels. All six tumours resolved completely over a mean tumour resolution time of 16 weeks while the total duration of IFNα-2b treatment was 24 weeks. After stopping immunotherapy, a mean of 14.5 weeks follow-up was observed. None showed any recurrence. The approximate cost of total therapy session was 8400 Indian rupees.

CONCLUSION

The OSSN lesions showing 'less or no response' to topical MMC may be shifted to topical recombinant IFNα-2b before proceeding for a surgical excision.

Association between a microRNA binding site polymorphism in SLCO1A2 and the risk of delayed methotrexate elimination in Chinese children with acute lymphoblastic leukemia

Organic anion-transporting polypeptide 1A2 (OATP1A2) is involved in the cellular uptake of methotrexate (MTX). Genetic variation in solute carrier organic anion transporter family member 1A2 (SLCO1A2, the coding gene of OATP1A2) has important implications for the elimination of MTX. We investigated the association between a microRNA (miRNA) binding site polymorphism (rs4149009 G > A) in the 3'-untranslated region (3'-UTR) of SLCO1A2 with the serum MTX concentrations in Chinese children with acute lymphoblastic leukemia (ALL). Genotyping for SLCO1A2 rs4149009 G > A in 141 children with ALL was performed using the Sequenom MassARRAY system. Serum MTX concentrations were determined by fluorescence polarization immunoassay. The percentages of MTX level ≥1 μmol/L at 42 h were compared among the AA, GA, and GG genotypes. The minor allele frequency observed in this study (33.0%) was significantly lower than that in the African samples reported in the 1000 Genomes Project (57.4%, P = 0.00). The incidence rate of delayed MTX elimination was significantly higher in patients with the GG genotype (23.1%) compared with the AA genotype (0.0%, P = 0.03). Bioinformatics tools predicted that the rs4149009 A allele would disrupt the putative binding sites of hsa-miR-324-3p and hsa-miR-1913. These results indicate that the rs4149009 G > A polymorphism might affect MTX pharmacokinetics by interfering with the function of miRNAs.

Influence of chemotherapeutic drug-related gene polymorphisms on toxicity and survival of early breast cancer patients receiving adjuvant chemotherapy

BACKGROUND

We investigated whether GSTT1 ("null" allele), GSTM1 ("null"allele), GSTP1 (A313G), RFC1 (G80A), MTHFR (C677T), TS (2R/3R) polymorphisms were associated with toxicity and survival in patients with early breast cancer (EBC) treated with adjuvant chemotherapy (CT).

METHODS

This prospective trial included patients with stage I-III BC subjected to CT with CMF or FEC regimens. PCR-RFLP was performed for MTHFR, RFC1 and GSTP1, while PCR for TS, GSTT1 and GSTM1 genes.

RESULTS

Among the 244 patients consecutively enrolled, 48.7% were treated with FEC and 51.3% with CMF. Patients with TS2R/3R genotype showed less frequently severe neutropenia (G3/G4) than those with TS2R/2R and 3R/3R genotype (p = 0.038). Patients with MTHFRCT genotype had a higher probability of developing severe neutropenia than those with MTHFR CC genotype (p = 0.043). Patients with RFC1GG or GSTT1-null genotype or their combination (GSTT1-null/RFC1GG) were significantly associated with a shorter disease free survival (DFS) (p = 0.009, p = 0.053, p = 0.003, respectively) and overall survival (OS) (p = 0.036, p = 0.015, p = 0.005, respectively). Multivariate analysis confirmed the association of RFC1GG genotype with a shorter DFS (p = 0.018) and of GSTT1-null genotype of a worse OS (p = 0.003), as well as for the combined genotypes GSTT1-null/RFC1GG, (DFS: p = 0.004 and OS: p = 0.003).

CONCLUSIONS

Our data suggest that TS2R/2R and 3R/3R or MTHFR CT genotypes have a potential role in identifying patients with greater risk of toxicity to CMF/FEC and that RFC1 GG and GSTT1-null genotypes alone or in combination could be important markers in predicting clinical outcome in EBC patients.

mTORC1 Inhibition Induces Resistance to Methotrexate and 6-Mercaptopurine in Ph+ and Ph-like B-ALL

Elevated activity of mTOR is associated with poor prognosis and higher incidence of relapse in B-cell acute lymphoblastic leukemia (B-ALL). Thus, ongoing clinical trials are testing mTOR inhibitors in combination with chemotherapy in B-ALL. However, the combination of mTOR inhibitors with standard of care chemotherapy drugs has not been studied extensively in high-risk B-ALL subtypes. Therefore, we tested whether mTOR inhibition can augment the efficacy of current chemotherapy agents in Ph⁺ and Ph-like B-ALL models. Surprisingly, inhibiting mTOR complex 1 (mTORC1) protected B-ALL cells from killing by methotrexate and 6-mercaptopurine, two antimetabolite drugs used in maintenance chemotherapy. The cytoprotective effects correlated with decreased cell-cycle progression and were recapitulated using cell-cycle inhibitors, palbociclib or aphidicolin. Dasatinib, a tyrosine kinase inhibitor currently used in Ph⁺ patients, inhibits ABL kinase upstream of mTOR. Dasatinib resistance is mainly caused by ABL kinase mutations, but is also observed in a subset of ABL unmutated cases. We identified dasatinib-resistant Ph+ cell lines and patient samples in which dasatinib can effectively reduce ABL kinase activity and mTORC1 signaling without causing cell death. In these cases, dasatinib protected leukemia cells from killing by 6-mercaptopurine. Using xenograft models, we observed that mTOR inhibition or dasatinib increased the numbers of leukemia cells that emerge after cessation of chemotherapy treatment. These results demonstrate that inhibitors targeting mTOR or upstream signaling nodes should be used with caution when combined with chemotherapeutic agents that rely on cell-cycle progression to kill B-ALL cells. Mol Cancer Ther; 16(9); 1942-53. ©2017 AACR.

MTHFR polymorphisms in childhood acute lymphoblastic leukemia: influence on methotrexate therapy

Methotrexate (MTX) is an important component in the therapy used to treat childhood acute lymphoblastic leukemia (ALL). Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme for MTX pharmacokinetics. Two single-nucleotide polymorphisms in MTHFR gene, C677T and A1298C, affecting MTHFR activity, have been widely studied as potential markers of MTX toxicity and/or outcome in pediatric ALL. In this review, we show that the majority of published reports do not find association or present opposite effect. Therefore, MTHFR C677T and A1298C polymorphisms do not seem to be good markers of MTX-related toxicity and/or outcome in pediatric ALL. The efforts should be focused on other genes, such as transporter genes or microRNA-related genes.

Genome Analysis of Osteosarcoma Progression Samples Identifies FGFR1 Overexpression as a Potential Treatment Target and CHM as a Candidate Tumor Suppressor Gene

Osteosarcoma (OS) is the most common primary malignant tumor of bone, showing complex chromosomal rearrangements but with few known consistent changes. Deeper biological understanding is crucial to find new therapies to improve patient survival. We have sequenced the whole exome of two primary tumors (before and after chemotherapy), one metastatic tumor and a matched normal sample from two OS patients, to identify mutations involved in cancer biology. The metastatic samples were also RNA sequenced. By RNA sequencing we identified dysregulated expression levels of drug resistance- and apoptosis-related genes. Two fusion transcripts were identified in one patient (OS111); the first resulted in p53 inactivation by fusing the first exon of TP53 to the fifth exon of FAM45A. The second fusion joined the two first exons of FGFR1 to the second exon of ZNF343. Furthermore, FGFR1 was amplified and highly expressed, representing a potential treatment target in this patient. Whole exome sequencing revealed large intertumor heterogeneity, with surprisingly few shared mutations. Careful evaluation and validation of the data sets revealed a number of artefacts, but one recurrent mutation was validated, a nonsense mutation in CHM (patient OS106), which also was the mutation with the highest expression frequency (53%). The second patient (OS111) had wild-type CHM, but a downregulated expression level. In a panel of 71 clinical samples, we confirmed significant low expression of CHM compared to the controls (p = 0.003). Furthermore, by analyzing public datasets, we identified a significant association between low expression and poor survival in two other cancer types. Together, these results suggest CHM as a candidate tumor suppressor gene that warrants further investigation.

Preliminary study for predicting better methotrexate efficacy in Japanese patients with rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by systemic inflammatory status, joint destruction, disability, and pain. Methotrexate (MTX) has been confirmed to reduce disease activity and delay or stabilize the development of bone erosions. However, major drawbacks are that patients show great interindividual variability in response to MTX and the unpredictable occurrence of side effects. A strategy for personalized MTX treatment to predict its efficacy and toxicity has not yet been determined. To establish personalized MTX therapy in Japanese patients with rheumatoid arthritis, we performed a preliminary study for predicting better methotrexate efficacy including single-nucleotide polymorphisms (SNPs) for MTX-related transporters/enzymes.

METHODS

Disease control status (good or poor) was judged by the number of Disease Activity Scores (DAS28) of <2 for 6-12 months. The response index R was calculated by the improved area under the curve (AUC) of the DAS28 score for 0-3 or 0-6 months by dividing the cumulative dose of MTX during 0-3 or 0-6 months, respectively. Genotyping of alleles of RFC1 80G > A, RFC1 -43 T > C, FPGS 1994G > A, GGH 401C > T, MTHFR 1298A > C, and TYMS 3'-UTR (-6/+6) was performed using the real-time PCR system.

RESULTS

Seven of 21 patients were judged as good responders in terms of disease control, and the remainder as poor responders. For 0-3 months after starting MTX administration, the median cumulative dose and improved DAS28 AUC in the good and poor response groups were 96.0 mg and 25.4 and 118.0 mg and 23.4, respectively. For 0-6 months, the median cumulative dose and improved DAS28 AUC in the good and poor response groups were 192.0 mg and 51.0 and 214.0 mg and 47.6, respectively. Statistically significant differences between the 2 groups in the 0-6-month period were observed in DAS28 AUC improvement and index R. A slight tendency for a correlation between G/G genotypes and A allele genotypes in RFC1 80 genotypes was observed, although it did not reach statistical significance.

CONCLUSION

This study suggested that aggressive RA treatment with MTX from the early period of administration is necessary to obtain a good response after 6 months, although no SNPs predicting a better treatment response to MTX were identified.

Influence of genetic polymorphisms in the folate pathway on toxicity after high-dose methotrexate treatment in pediatric osteosarcoma

BACKGROUND

Methotrexate (MTX), one of the main drugs used to treat osteosarcoma, is a representative folic acid antagonist. Polymorphisms of various enzymes involved in the metabolism of MTX could contribute to differences in response to MTX in pediatric osteosarcoma patients.

METHODS

Blood and tissue samples were obtained from 37 pediatric osteosarcoma patients who were treated with high-dose MTX therapy. The following 4 single nucleotide polymorphisms (SNPs) were analyzed: ATIC 347C>G, MTHFR 677C>T, MTHFR 1298A>C and SLC19A1 80G>A. Serial plasma MTX concentrations after high-dose MTX therapy and MTX-induced toxicities were evaluated. Correlations among polymorphisms, MTX concentrations and treatment-induced toxicities were assessed.

RESULTS

Plasma MTX levels at 48 hours after high-dose MTX infusion were significantly associated with SLC19A1 80G>A (P=0.031). Higher plasma levels of MTX at 48 and 72 hours were significantly associated with MTX-induced mucositis (P=0.007 and P=0.046) and renal toxicity (P=0.002), respectively. SNP of SLC19A1 gene was associated with development of severe mucositis (P=0.026).

CONCLUSION

This study suggests that plasma levels of MTX are associated with GI and renal toxicities after high-dose MTX therapy, and genetic polymorphisms that affect the metabolism of MTX may influence drug concentrations and development of significant side effects in pediatric patients treated with high-dose MTX.

Mechanisms of Drug Resistance in Veterinary Oncology- A Review with an Emphasis on Canine Lymphoma

Drug resistance (DR) is the major limiting factor in the successful treatment of systemic neoplasia with cytotoxic chemotherapy. DR can be either intrinsic or acquired, and although the development and clinical implications are different, the underlying mechanisms are likely to be similar. Most causes for DR are pharmacodynamic in nature, result from adaptations within the tumor cell and include reduced drug uptake, increased drug efflux, changes in drug metabolism or drug target, increased capacity to repair drug-induced DNA damage or increased resistance to apoptosis. The role of active drug efflux transporters, and those of the ABC-transporter family in particular, have been studied extensively in human oncology and to a lesser extent in veterinary medicine. Methods reported to assess ABC-transporter status include detection of the actual protein (Western blot, immunohistochemistry), mRNA or ABC-transporter function. The three major ABC-transporters associated with DR in human oncology are ABCB1 or P-gp, ABCC1 or MRP1, and ABCG2 or BCRP, and have been demonstrated in canine cell lines, healthy dogs and dogs with cancer. Although this supports a causative role for these ABC-transporters in DR cytotoxic agents in the dog, the relative contribution to the clinical phenotype of DR in canine cancer remains an area of debate and requires further prospective studies.

Influence of SLCO1B1 polymorphism on maintenance therapy for childhood leukemia

BACKGROUND

Management of the adverse effects of chemotherapy is essential to improve outcome of children with leukemia. Some genetic polymorphisms can predict treatment-related toxicity, and be used individually in dose modification of 6-mercaptopurine (6-MP) and methotrexate (MTX) in maintenance therapy for childhood acute lymphoblastic leukemia (ALL). We investigated associations between clinical course and candidate gene polymorphisms less evaluated in Japanese patients.

METHODS

Fifty-three children who received maintenance chemotherapy were enrolled in this study. The scheduled dose of oral 6-MP was 40 mg/m(2) daily and that of oral MTX was 25 mg/m(2) weekly. The doses were adjusted according to white blood cell count (target range, 2.5-3.5 × 10(9) /L) and aspartate aminotransferase and alanine aminotransferase level (< 750 IU/L). Eight polymorphisms in six candidate genes, TPMT, ITPA, MRP4, MTHFR, RFC1, and SLCO1B1, were genotyped using the Taqman PCR method. Clinical course was reviewed retrospectively from medical records.

RESULTS

The average dose of 6-MP was lower in the patients with at least one variant allele at SLCO1B1 c.521 T > C than in the patients with wild homozygous genotype. The other analyzed polymorphisms were not associated with toxicity, 6-MP, or MTX dose.

CONCLUSIONS

Polymorphism of SLCO1B1 c.521 T > C could be a strong predictor of 6-MP dose reduction in maintenance chemotherapy in childhood ALL.

Methotrexate-conjugated quantum dots: synthesis, characterisation and cytotoxicity in drug resistant cancer cells

Methotrexate (MTX), a folic acid derivative, is a potent anticancer used for treatment of different malignancies, but possible initiation of drug resistance to MTX by cancer cells has limited its applications. Nanoconjugates (NCs) of MTX to quantum dots (QDs) may favour the cellular uptake via folate receptors (FRs)-mediated endocytosis that circumvents the efflux functions of cancer cells. We synthesised MTX-conjugated l-cysteine capped CdSe QDs (MTX-QD nanoconjugates) and evaluated their internalisation and cytotoxicity in the KB cells with/without resistancy to MTX. The NCs were fully characterised by high resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and optical spectroscopy. Upon conjugation with MTX, the photoluminescence (PL) properties of QDs altered, while an obvious quenching in PL of QDs was observed after physical mixing. The MTX-QD nanoconjugates efficiently internalised into the cancer cells, and induced markedly high cytotoxicity (IC50, 12.0 µg/mL) in the MTX-resistant KB cells as compared to the free MTX molecules (IC50,105.0 µg/mL), whereas, these values were respectively about 7.0 and 0.6 µg/mL in the MTX-sensitive KB cells. Based on these findings, the MTX-QD nanoconjugates are proposed for the targeted therapy of MTX-resistant cancers, which may provide an improved outcome in the relapsed FR-overexpressing cancers.

Effects of silymarin on methotrexate-induced nephrotoxicity in rats

Methotrexate (MTX) is widely used in the treatment of various malignancies and nononcological diseases but its use has been limited by its nephrotoxicity. Silymarin (SLY), a natural flavonoid, has been reported to have antioxidant, anti-inflammatory and anti-apoptotic effects. This study was carried out to determine whether SLY exerts a protective effect against MTX-induced nephrotoxicity. Rats were divided into six groups: Group 1 (saline, i.p., single injection), Group 2 (0.5% carboxymethyl cellulose (CMC), by gavage once daily for five consecutive days), Group 3 (SLY, 300 mg/kg per day, i.p. for five consecutive days), Group 4 (MTX, 20 mg/kg, i.p., single injection), Group 5 (MTX + CMC similarly as groups 2 and 4) and Group 6 (MTX + CMC + SLY similarly as groups 2, 3 and 4). Histopathologic alterations including apoptotic changes of the kidney were evaluated. MTX injection exhibited dilated Bowman's space, inflammatory cell infiltration, glomerular and peritubular vascular congestion and swelling of renal tubular epithelium cells. Apoptotic cell death was also markedly increased in renal tubules after MTX administration. SLY treatment resulted in statistically significant amelioration in the histological alterations and reduced the number of TUNEL-positive cells as compared with the MTX treated rats (p < 0.05). In conclusion, SLY treatment leads to a reduction on MTX-induced renal damage in rats. Since SLY is safe and acceptable for human consumption, further studies to define the exact mechanism of the protecting effect of SLY on MTX-induced nephrotoxicity and the optimum dosage of this compound would be useful.

Pharmacogenetics predictive of response and toxicity in acute lymphoblastic leukemia therapy

Acute lymphoblastic leukemia (ALL) is a relatively rare disease in adults accounting for no more than 20% of all cases of acute leukemia. By contrast with the pediatric population, in whom significant improvements in long term survival and even cure have been achieved over the last 30years, adult ALL remains a significant challenge. Overall survival in this group remains a relatively poor 20-40%. Modern research has focused on improved pharmacokinetics, novel pharmacogenetics and personalized principles to optimize the efficacy of the treatment while reducing toxicity. Here we review the pharmacogenetics of medications used in the management of patients with ALL, including l-asparaginase, glucocorticoids, 6-mercaptopurine, methotrexate, vincristine and tyrosine kinase inhibitors. Incorporating recent pharmacogenetic data, mainly from pediatric ALL, will provide novel perspective of predicting response and toxicity in both pediatric and adult ALL therapies.

Pharmacogenetics of childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the major pediatric cancer in developed countries. Although treatment outcome has improved owing to advances in chemotherapy, there is still a group of patients for which therapy fails while some patients experience severe toxicity. In the last few years, several pharmacogenetic studies have been performed to search for markers of outcome and toxicity in pediatric ALL. However, to date, TPMT is the only pharmacogenetic marker in ALL with clinical guidelines for drug dosing. In this article, we will provide an overview of the most important findings carried out in pharmacogenetics for pediatric ALL, such as the interest drawn by methotrexate transporters in the context of methotrexate treatment. Even if most of the studies are centered on coding genes, we will also point to new approaches focusing on noncoding regions and epigenetic variation that could be interesting for consideration in the near future.

Influence of genetic polymorphisms of FPGS, GGH, and MTHFR on serum methotrexate levels in Chinese children with acute lymphoblastic leukemia

PURPOSE

To investigate the correlation between common genetic polymorphisms of folylpolyglutamate synthase (FPGS), gamma-glutamyl hydrolase (GGH), and methylenetetrahydrofolate reductase (MTHFR) and serum levels of methotrexate (MTX) in Chinese children with acute lymphoblastic leukemia (ALL).

METHODS

Ninety-one children with ALL who received high-dose MTX were recruited. The polymorphisms FPGS (rs1544105 G>A), GGH (rs3758149 C>T), and MTHFR (rs1801133 C>T) were genotyped through polymerase chain reaction-restriction fragment length polymorphism analysis. Serum MTX was measured by fluorescence polarization immunoassay. The association between targeted polymorphisms and MTX concentration-to-dose (C/D) ratios was assessed, and between targeted polymorphisms and the percent of MTX above the therapeutic threshold (40 µmol/L).

RESULTS

The minor allele frequencies of rs1544105 G (34.1%), rs3758149 T (19.2%), and rs1801133 C (48.4%) observed in our population were significantly lower than those reported for European populations (64.2, 30.8, and 69.0%, respectively). The association between the GGH rs3758149 polymorphism and MTX C/D was gender-specific; in girls, the MTX C/D at 24 h of GGH rs3758149 CC carriers (12.09 μmol/L per g/m(2)) was significantly lower than that of CT or TT carriers (16.80 μmol/L per g/m(2)). The percent of serum MTX above the therapeutic threshold in GGH rs3758149 CC carriers (18.3%) was significantly lower than that of CT and TT carriers (38.7%). The MTX C/D ratios at 24 h and the percent of MTX >40 µmol/L for the A-T-T (three variant alleles) haplotype were significantly higher than those for other haplotypes combined (P < 0.05).

CONCLUSIONS

These data indicate that FPGS rs1544105, GGH rs3758149, and MTHFR rs1801133 polymorphisms contribute to the variability of MTX pharmacokinetics, and their genotyping may be useful to reduce toxicities associated with MTX therapy.

Polymorphisms in genes involved in the mechanism of action of methotrexate: are they associated with outcome in rheumatoid arthritis patients?

Background: Methotrexate (MTX) is the first-line treatment option for newly diagnosed rheumatoid arthritis (RA) patients. However, 50–70% of the patients respond to treatment and 30% suffer toxicity. Aim: To identify pharmacogenetic markers of outcome in RA patients treated with MTX. Patients & methods: We analyzed 27 genetic variants in DHFR, TYMS, MTHFR, ATIC and CCND1 genes. Results: We included 124 RA patients treated with MTX monotherapy. In multivariate analyses two variants in the MTHFR gene were associated with response, rs17421511 (p = 0.024) and rs1476413 (p = 0.0086), as well as one in the DHFR gene, rs1643650 (p = 0.026). The ATIC rs16853826 variant was associated with toxicity (p = 0.039). Conclusion: MTHFR, DHFR and ATIC genetic variants can be considered as pharmacogenetic markers of outcome in RA patients under MTX monotherapy.

Original submitted 10 January 2014; Revision submitted 28 March 2014

Treatment of acute lymphoblastic leukemia from traditional chinese medicine

Acute lymphoblastic leukemia (ALL) is a cancer that immature white blood cells continuously overproduce in the bone marrow. These cells crowd out normal cells in the bone marrow bringing damage and death. Methotrexate (MTX) is a drug used in the treatment of various cancer and autoimmune diseases. In particular, for the treatment of childhood acute lymphoblastic leukemia, it had significant effect. MTX competitively inhibits dihydrofolate reductase (DHFR), an enzyme that participates in the tetrahydrofolate synthesis so as to inhibit purine synthesis. In addition, its downstream metabolite methotrexate polyglutamates (MTX-PGs) inhibit the thymidylate synthase (TS). Therefore, MTX can inhibit the synthesis of DNA. However, MTX has cytotoxicity and neurotoxin may cause multiple organ injury and is potentially lethal. Thus, the lower toxicity drugs are necessary to be developed. Recently, diseases treatments with Traditional Chinese Medicine (TCM) as complements are getting more and more attention. In this study, we attempted to discover the compounds with drug-like potential for ALL treatment from the components in TCM. We applied virtual screen and QSAR models based on structure-based and ligand-based studies to identify the potential TCM component compounds. Our results show that the TCM compounds adenosine triphosphate, manninotriose, raffinose, and stachyose could have potential to improve the side effects of MTX for ALL treatment.

Uptake carriers and oncology drug safety

Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics in multiple tissues. Many of these transporters are highly expressed in the gastrointestinal tract, liver, and kidney and are considered to be of particular importance in governing drug absorption, elimination, and cellular sensitivity of specific organs to a wide variety of oncology drugs. Although the majority of studies on the interaction of oncology drugs with SLC have been restricted to the use of exploratory in vitro model systems, emerging evidence suggests that several SLCs, including OCT2 and OATP1B1, contribute to clinically important phenotypes associated with those agents. Recent literature has indicated that modulation of SLC activity may result in drug-drug interactions, and genetic polymorphisms in SLC genes have been described that can affect the handling of substrates. Alteration of SLC function by either of these mechanisms has been demonstrated to contribute to interindividual variability in the pharmacokinetics and toxicity associated with several oncology drugs. In this report, we provide an update on this rapidly emerging field.

Pharmacogenetics of methotrexate in acute lymphoblastic leukaemia: why still at the bench level?

PURPOSE

The antifolate drug methotrexate (MTX) was introduced into clinical practice about 60 years ago and remains an important component of different acute lymphoblastic leukemia (ALL) treatment protocols. It acts by inhibiting several enzymes in the folate pathway, thereby resulting in the disruption of folate homeostasis. To date, treatment regimens have not been personalized despite there being experimental evidence that gene polymorphisms of folate metabolizing enzymes affect MTX response. The aim of this review was to evaluate the influence of genetic polymorphisms of the enzymes involved in the MTX pathway on ALL treatment outcomes and identify factors underlining the failure to personalize MTX therapy.

METHODS

We conducted a literature search in PUBMED and Google Scholar using the following key words: methotrexate, polymorphism, acute lymphoblastic leukemia, pharmacogenetics, pharmacogenomics and personalized medicine.

RESULTS

The reasons for the failure to personalize MTX therapy may be due to (1) most studies involving single-center, small-sized cohorts, (2) differences in MTX dose across different protocols, (3) failure to consider minimal residual disease as a risk factor for post-induction treatment, (4) differences in outcome criteria between studies and (5) failure to consider the folate levels of a patient before initiation of MTX therapy. Although high-throughput techniques allow the mapping of thousands of genetic polymorphisms in a single run, it remains a major challenge to dissect out folate-metabolizing enzymes which have a high impact on the efficacy and toxicity of MTX and which, therefore, could be the targets for intervention.

CONCLUSIONS

Prospective pharmacogenetic studies which consider all of the above-mentioned factors should be undertaken to facilitate the design of personalized MTX treatment for ALL patients.

Methotrexate analogues display enhanced inhibition of TNF-α production in whole blood from RA patients

OBJECTIVES

Although methotrexate (MTX) is the anchor drug in the treatment of rheumatoid arthritis (RA), patients experience clinical resistance to MTX upon prolonged treatment. We explored whether new-generation antifolates elicit superior anti-inflammatory properties when compared to MTX, based on their capacity to inhibit tumour necrosis factor (TNF)-α production.

METHOD

T cells in whole blood from 18 RA patients (including MTX-naïve, MTX- responsive, and MTX non-responsive patients) and seven healthy volunteers were stimulated with αCD3/αCD28 antibodies and incubated ex vivo for 72 h with MTX and eight novel antifolate drugs with potentially favourable biochemical and pharmacological properties. Drug concentrations exerting 50% inhibition (IC-50) of TNF-α production (by enzyme-linked immunosorbent assay, ELISA) were determined as an estimate for their anti-inflammatory capacity. In addition, induction of T-cell apoptosis was evaluated by flow cytometry.

RESULTS

The new-generation antifolates PT523, PT644, raltitrexed, and GW1843 proved to be potent inhibitors of TNF-α production in activated T cells from all three groups of RA patients and from healthy volunteers. Based on IC-50 values, these antifolates were up to 10.3 times more potent than MTX. The anti-inflammatory effects were observed at drug concentrations that provoked suppression of T-cell activation and induction of apoptosis in 20-40% of activated T cells.

CONCLUSION

In an ex-vivo setting, novel antifolates elicited marked inhibition of TNF-α production in activated T cells from RA patients. Further clinical evaluation is warranted to investigate whether a low dosage of these antifolates can elicit immunosuppressive effects equivalent to MTX, and whether they are superior to MTX in patients who fail to respond to MTX.

Germline genetic variations in methotrexate candidate genes are associated with pharmacokinetics, toxicity, and outcome in childhood acute lymphoblastic leukemia

The pharmacogenetics of methotrexate (MTX) was investigated in a large cohort of pediatric patients with acute lymphoblastic leukemia (ALL). Four hundred ninety-nine children with ALL from the ALL-BFM (Berlin-Frankfurt-Münster) 2000 trial who received 1996 courses of MTX at 5 g/m(2) were genotyped for 8 single nucleotide polymorphisms in 5 candidate genes of the MTX/folate pathway. Patients' MTX pharmacokinetics, MTX toxicities, and outcomes were correlated with the genotypes. The interindividual variability in MTX kinetics had a substantial genetic component between 68% and 75%. The SLCO1B1 rs4149056 variant was significantly associated with MTX kinetics. In a multiple regression model, MTX area under the concentration time curve (AUC)0-48h increased by 26% (P < .001) per SLCO1B1 rs4149056 C allele. MTX AUC0-48h was a significant predictor of overall toxic adverse events during MTX courses (R(2) = 0.043; P < .001), whereas the thymidylate synthase rs34743033 tandem repeat polymorphism was predictive of stomatitis (R(2) = 0.018; P = .009), a frequent side effect of high-dose MTX. Multiple Cox regression analyses revealed an association of minimal residual disease (hazard ratio 7.3; P < .001) and methylenetetrahydrofolate reductase rs1801131 (hazard ratio 3.1; P = .015) with event-free survival in the ALL-BFM 2000 study population. Genetic variations substantially influence the kinetics and response to high-dose MTX therapy in childhood ALL.

Enhanced degradation of dihydrofolate reductase through inhibition of NAD kinase by nicotinamide analogs

Dihydrofolate reductase (DHFR), because of its essential role in DNA synthesis, has been targeted for the treatment of a wide variety of human diseases, including cancer, autoimmune diseases, and infectious diseases. Methotrexate (MTX), a tight binding inhibitor of DHFR, is one of the most widely used drugs in cancer treatment and is especially effective in the treatment of acute lymphocytic leukemia, non-Hodgkin's lymphoma, and osteosarcoma. Limitations to its use in cancer include natural resistance and acquired resistance due to decreased cellular uptake and decreased retention due to impaired polyglutamylate formation and toxicity at higher doses. Here, we describe a novel mechanism to induce DHFR degradation through cofactor depletion in neoplastic cells by inhibition of NAD kinase, the only enzyme responsible for generating NADP, which is rapidly converted to NADPH by dehydrogenases/reductases. We identified an inhibitor of NAD kinase, thionicotinamide adenine dinucleotide phosphate (NADPS), which led to accelerated degradation of DHFR and to inhibition of cancer cell growth. Of importance, combination treatment of NADPS with MTX displayed significant synergy in a metastatic colon cancer cell line and was effective in a MTX-transport resistant leukemic cell line. We suggest that NAD kinase is a valid target for further inhibitor development for cancer treatment.

Identification of transporters associated with Etoposide sensitivity of stomach cancer cell lines and methotrexate sensitivity of breast cancer cell lines by quantitative targeted absolute proteomics

Membrane transporter proteins may influence the sensitivity of cancer cells to anticancer drugs that can be recognized as substrates. The purpose of this study was to identify proteins that play a key role in the drug sensitivity of stomach and breast cancer cell lines by measuring the absolute protein expression levels of multiple transporters and other membrane proteins and examining their correlation to drug sensitivity. Absolute protein expression levels of 90 membrane proteins were examined by quantitative targeted absolute proteomics using liquid chromatography-linked tandem mass spectrometry. Among them, 11 and 14 membrane proteins, including transporters, were present in quantifiable amounts in membrane fraction of stomach cancer and breast cancer cell lines, respectively. In stomach cancer cell lines, the protein expression level of multidrug resistance-associated protein 1 (MRP1) was inversely correlated with etoposide sensitivity. MK571, an MRP inhibitor, increased both the cell-to-medium ratio of etoposide and the etoposide sensitivity of MRP1-expressing stomach cancer cell lines. In breast cancer cell lines, the protein expression level of reduced folate carrier 1 (RFC1) was directly correlated with methotrexate (MTX) sensitivity. Initial uptake rate and steady-state cell-to-medium ratio of [(3)H]MTX were correlated with both RFC1 expression level and MTX sensitivity. These results suggest that MRP1 modulates the etoposide sensitivity of stomach cancer cell lines and RFC1 modulates the MTX sensitivity of breast cancer cell lines. Our results indicate that absolute quantification of multiple membrane proteins could be a useful strategy for identification of candidate proteins involved in drug sensitivity.

A systematic review and meta-analysis of MTHFR polymorphisms in methotrexate toxicity prediction in pediatric acute lymphoblastic leukemia

Methotrexate (MTX) is an important component of therapy used to treat childhood acute lymphoblastic leukemia (ALL). Two single-nucleotide polymorphisms (SNPs) in the methylenetetrahydrofolate reductase (MTHFR) gene, C677T and A1298C, affect MTHFR activity. A large body of studies has investigated the potential role of MTHFR SNPs in MTX toxicity in pediatric ALL. However, the results are controversial. In this review and meta-analysis, we critically evaluate the relationship between the C677T and A1298C polymorphisms of MTHFR and MTX toxicity in pediatric ALL. The majority of published reports do not find associations between MTHFR polymorphisms and toxicity in pediatric ALL. When associations are reported, often the results are contradictory to each other. The meta-analysis confirms a lack of association. In conclusion, MTHFR, C677T and A1298C polymorphisms do not seem to be good markers of MTX-related toxicity in pediatric ALL.

A second target of benzamide riboside: dihydrofolate reductase

Dihydrofolate reductase (DHFR) is an essential enzyme involved in de novo purine and thymidine biosynthesis. For several decades, selective inhibition of DHFR has proven to be a potent therapeutic approach in the treatment of various cancers including acute lymphoblastic leukemia, non-Hodgkin's lymphoma, osteogenic sarcoma, carcinoma of the breast, and head and neck cancer. Therapeutic success with DHFR inhibitor methotrexate (MTX) has been compromised in the clinic, which limits the success of MTX treatment by both acquired and intrinsic resistance mechanisms. We report that benzamide riboside (BR), via anabolism to benzamide adenine dinucleotide (BAD) known to potently inhibit inosine monophosphate dehydrogenase (IMPDH), also inhibits cell growth through a mechanism involving downregulation of DHFR protein. Evidence to support this second site of action of BR includes the finding that CCRF-CEM/R human T-cell lymphoblasic leukemia cells, resistant to MTX as a consequence of gene amplification and overexpression of DHFR, are more resistant to BR than are parental cells. Studies of the mechanism by which BR lowers DHFR showed that BR, through its metabolite BAD, reduced NADP and NADPH cellular levels by inhibiting nicotinamide adenine dinucleotide kinase (NADK). As consequence of the lack of NADPH, DHFR was shown to be destabilized. We suggest that, inhibition of NADK is a new approach to downregulate DHFR and to inhibit cell growth.

ABCB1 C3435T genetic polymorphism on population pharmacokinetics of methotrexate after hematopoietic stem cell transplantation in Korean patients: a prospective analysis

BACKGROUND

Methotrexate (MTX) is often used to prevent graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). However, MTX has great pharmacokinetic variability and its use can result in fatal complications and/or infections after HSCT.

OBJECTIVES

The purposes of this study were to build a population pharmacokinetic model of MTX treatment in Korean patients who have undergone HSCT and to identify covariates, including genetic polymorphisms, that affect the pharmacokinetic properties of MTX.

METHODS

Clinical characteristics and MTX concentration data for 20 post-HSCT patients were collected. For each patient, ABCB1, ABCC2, ATIC, GGH, MTHFR, and TYMS genotyping was performed. Population pharmacokinetic analysis was performed using the NONMEM program. Analysis of MTX pharmacokinetic properties was accomplished using a 2-compartment pharmacokinetic model that incorporated first-order conditional estimation methods with interaction. The effects of a variety of demographic and genetic factors on MTX disposition were investigated.

RESULTS

The study population consisted of 12 men (60%) and 8 women (40%). Median age and body weight were 28 years (range, 18-49 years) and 55.6 kg (range, 44.8-80.8 kg), respectively. Within the study population, the estimated mean MTX clearance (CL) was 7.08 L/h, whereas the mean central compartment volume (V(1)) of MTX distribution was 19.4 L. MTX CL was significantly affected by glomerular filtration rate (GFR), penicillin use, and the ABCB1 3435 genotype. Interindividual variabilities for CL and V(1) were 21.6% and 73.3%. A 10-mL/min GFR increase was associated with a 32% increase in mean MTX CL, whereas penicillin use was associated with a decrease in MTX CL of 61%. MTX CL was significantly greater (by ∼21%) in patients with the ABCB1 3435 CC and CT genotype than in those with the ABCB1 3435 TT genotype (P < 0.001).

CONCLUSIONS

There was great interindividual variation in MTX pharmacokinetic properties in patients who had undergone HSCT. GFR, concurrent penicillin use, and the presence of the ABCB1 3435 C<T genotypes significantly affected MTX CL. The MTX population pharmacokinetic model developed here may provide useful information for individualizing MTX therapy after HSCT.

Methotrexate (MTX)-cIBR conjugate for targeting MTX to leukocytes: conjugate stability and in vivo efficacy in suppressing rheumatoid arthritis

Methotrexate (MTX) has been used to treat rheumatoid arthritis at low doses and leukemia at high doses; however, this drug can produce severe side effects. Our hypothesis is that MTX side effects can be attenuated by directing the drug to the target cells (i.e., leukocytes) using (cyclo(1,12)PenPRGGSVLVTGC) peptide (cIBR). To test this hypothesis, MTX was conjugated to the N-terminus of cIBR peptide to give MTX-cIBR conjugate. MTX-cIBR (5.0 mg/kg) suppressed joint arthritis in adjuvant arthritis rats and prevented periarticular inflammation and bone resorption of the limb joints. In vitro, the toxicity of MTX-cIBR peptide against Molt-3 T cells was inhibited by anti-lymphocyte function-associated antigen-1 (LFA-1) antibody and cIBR peptide in a concentration-dependent manner, suggesting that the uptake of MTX-cIBR was partially mediated by LFA-1. Chemical stability studies indicated that MTX-cIBR was most stable at pH 6.0. The MTX portion of MTX-cIBR was unstable under acidic conditions, whereas the cIBR portion was unstable under basic conditions. In biological media, MTX-cIBR had short half lives in rat plasma (44 min) and homogenized rat heart tissue (38 min). This low plasma stability may contribute to the low in vivo efficacy of MTX-cIBR; therefore, there is a need to design a more stable conjugate to improve the in vivo efficacy.