Monitoring of inosine monophosphate dehydrogenase activity in mononuclear cells of children with acute lymphoblastic leukemia: enzymological and clinical aspects

Therapeutic potential and molecular mechanisms of mycophenolic acid as an anticancer agent

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil (MMF), an immunosuppressive drug approved for the prophylaxis of allograft rejection in transplant recipients. Recent advances in the role of the type II isoform of inosine-5'-monophosphate dehydrogenase (IMPDH2) in the tumorigenesis of various types of cancer have called for a second look of MPA, the first IMPDH2 inhibitor discovered a hundred years ago, to be repurposed as an anticancer agent. Over a half century, a number of in vitro and in vivo experiments have consistently shown anticancer activity of MPA against several cell lines obtained from different malignancies and murine models. However, a few clinical trials have been conducted to investigate its anticancer activity in humans, and most of which have shown unsatisfactory results. Understanding of available evidence and underlying mechanism of action is a key step to be done so as to facilitate further investigations of MPA to reach its full therapeutic potential as an anticancer agent. This article provides a comprehensive review of non-clinical and clinical evidence available to date, with the emphasis on the molecular mechanism of action in which MPA exerts its anticancer activities: induction of apoptosis, induction of cell cycle arrest, and alteration of tumor microenvironment. Future perspective for further development of MPA to be an anticancer agent is extensively discussed, with the aim of translating the anticancer property of MPA from bench to bedside.

Red Blood cell IMPDH activity in adults and children with or without azathioprine: Relationship between thiopurine metabolites, ITPA and TPMT activities

Inosine monophosphate dehydrogenase (IMPDH) is considered as the limiting enzyme of thiopurine metabolism for the formation of 6-thioguanine nucleotides (6-TGN). No data are available on the influence of RBC IMPDH activity on the metabolism of thiopurine drugs in individuals with IBD. The aims of this study were as follows: (a) to carry out a phenotypic study of RBC IMPDH activity in adults and children treated or not with azathioprine (AZA) for autoimmune diseases, and (b) to investigate the relationship between the activities of IMPDH, thiopurine metabolites, inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT). IMPDH activity was determined in 97 adults and 67 children treated or not with AZA. 6-Thioguanine nucleotides (6-TGN), 6-methylmercaptopurine nucleotide (6-MeMPN) levels, and ITPA as well as TPMT activities were measured in RBCs by HPLC. Using the Gaussian mixture model, distribution of IMPDH activity was evaluated. Influence of age, sex and AZA treatment on IMPDH activity was also assessed. A bimodal distribution in IMPDH activity was found with 87% of patients exhibiting normal activity and 13% of patients with high activity. No influence of age, sex and AZA therapy was found. There is no relationship between TPMT, ITPA and IMPDH activities. A negative correlation between IMPDH activity and 6-MeMPN was shown in adults and children (rs = -0.335 P = 0.014 and rs = -0.383 P = 0.012, respectively). Our results suggest that AZA-treated patients exhibiting lower IMPDH activity could have higher Me-6MPN levels with higher risk of hepatotoxicity. We demonstrated that RBC matrix could be an interesting alternative to lymphocyte matrix to monitor thiopurine metabolites and enzyme activity.

Microbial metabolism of thiopurines: A method to measure thioguanine nucleotides

Thiopurines are anti-inflammatory prodrugs. We hypothesised that bacteria may contribute to conversion to active drug. Escherichia coli strain DH5α was evaluated to determine whether it could metabolise the thiopurine drugs, thioguanine or mercaptopurine, to thioguanine nucleotides. A rapid and reliable high performance liquid chromatography (ultraviolet detection) method was developed to quantify indirectly thioguanine nucleotides, by measuring thioguanine nucleoside.

Optimization of immunosuppressive medication upon liver transplantation against HCC recurrence

The introduction of liver transplant listing criteria for hepatocellular cancer (HCC) has significantly improved oncological outcomes and survival. But despite this HCC recurrence is still problematic. There is emerging evidence that the choice of immunosuppression (IS) after transplant for HCC can influence oncological survival and HCC recurrence. The following is a short summary of what has been published on HCC recurrence with the different classes of immunosuppressive agents in present use, concluding with the possible rationalization of the use of these immunosuppressive agents in the post-transplant patient at high risk of recurrence.

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.

A Review of the Potential Utility of Mycophenolate Mofetil as a Cancer Therapeutic

Tumor cells adapt to their high metabolic state by increasing energy production. To this end, current efforts in molecular cancer therapeutics have been focused on signaling pathways that modulate cellular metabolism. However, targeting such signaling pathways is challenging due to heterogeneity of tumors and recurrent oncogenic mutations. A critical need remains to develop antitumor drugs that target tumor specific pathways. Here, we discuss an energy metabolic pathway that is preferentially activated in several cancers as a potential target for molecular cancer therapy. In vitro studies have revealed that many cancer cells synthesize guanosine triphosphate (GTP), via the de novo purine nucleotide synthesis pathway by upregulating the rate limiting enzyme of this pathway, inosine monophosphate dehydrogenase (IMPDH). Non-proliferating cells use an alternative purine nucleotide synthesis pathway, the salvage pathway, to synthesize GTP. These observations pose IMPDH as a potential target to suppress tumor cell growth. The IMPDH inhibitor, mycophenolate mofetil (MMF), is an FDA-approved immunosuppressive drug. Accumulating evidence shows that, in addition to its immunosuppressive effects, MMF also has antitumor effects via IMPDH inhibition in vitro and in vivo. Here, we review the literature on IMPDH as related to tumorigenesis and the use of MMF as a potential antitumor drug.

Enhanced expression of IMPDH2 promotes metastasis and advanced tumor progression in patients with prostate cancer

PURPOSE

Our previous study showed the upregulation of inosine 5'-monophosphate dehydrogenase type II (IMPDH2) protein in human prostate cancer (PCa) tissues and sera compared to non-cancerous controls by proteomics and ELISA analyses. However, the clinical significance of IMPDH2 in PCa has not been fully elucidated. Thus, the aim of the current study was to investigate the associations of IMPDH2 upregulation with tumor progression in patients with PCa.

METHODS

IMPDH2 expression at mRNA and protein levels in human PCa and non-cancerous prostate tissues was respectively detected by qRT-PCR, Western blot and immunohistochemistry analyses, which was validated by microarray-based Taylor Data. Then, the association of IMPDH2 expression with clinicopathological features of PCa patients was statistically analyzed.

RESULTS

Compared with non-cancerous prostate tissues, IMPDH2 mRNA and protein expression levels were both significantly upregulated (at mRNA level: 9.22 ± 2.49 vs 5.06 ± 1.45, P < 0.01; at protein level by Western blot: 0.674 ± 0.029 vs 0.418 ± 0.140, P < 0.001; at protein level by immunohistochemistry: 4.97 ± 0.760 vs 3.32 ± 1.66, P < 0.001) in PCa tissues, which were consistent with our previous data. In addition, the enhanced expression of IMPDH2 in PCa tissues was significantly correlated with the advanced clinical stage (for our cohort: P < 0.001; for Taylor data: P = 0.002), the presence of metastasis (for our cohort: P < 0.001; for Taylor data: P = 0.012) and the higher Gleason score (for our cohort: P = 0.002; for Taylor data: P = 0.028).

CONCLUSIONS

These findings suggest for the first time that the enhanced expression of IMPDH2 may promote the tumor metastasis and the advanced tumor progression in patients with PCa.

Rationale of personalized immunosuppressive medication for hepatocellular carcinoma patients after liver transplantation

Liver transplantation is the only potentially curative treatment for hepatocellular carcinoma (HCC) that is not eligible for surgical resection. However, disease recurrence is the main challenge to the success of this treatment. Immunosuppressants that are universally used after transplantation to prevent graft rejection could potentially have a significant impact on HCC recurrence. Nevertheless, current research is exclusively focused on mammalian target of rapamycin inhibitors, which are thought to be the only class of immunosuppressive agents that can reduce HCC recurrence. In fact, substantial evidence from the bench to the bedside indicates that other classes of immunosuppressants may also exert diverse effects; for example, inosine monophosphate dehydrogenase inhibitors potentially have antitumor effects. In this article, we aim to provide a comprehensive overview of the potential effects of different types of immunosuppressants on HCC recurrence and their mechanisms of action from both experimental and clinical perspectives. To ultimately improve the outcomes of HCC patients after transplantation, we propose a concept and approaches for developing personalized immunosuppressive medication to be used either as immunosuppression maintenance or during the prevention/treatment of HCC recurrence.

Overexpression of CK20, MAP3K8 and EIF5A correlates with poor prognosis in early-onset colorectal cancer patients

PURPOSE

Due to ethnic, genetic and environmental factors, the clinical and molecular characteristics of Turkish colorectal cancer (CRC) patients are different from those of Western populations. The aim of this study was to clarify the relevant alterations of gene expression associated with colorectal carcinogenesis in early-onset patients and to identify specific biomarkers that could provide novel therapeutic molecular targets in this population.

METHODS

The expression profiles of 114 different genes were evaluated using mRNA PCR arrays in 39 tumors and 20 surgical margin tissue samples from 39 sporadic CRC patients diagnosed at less than 50 years of age.

RESULTS

The expression levels of IMPDH2, CK20, MAP3K8 and EIF5A were strongly up-regulated in CRC tissues compared with normal colorectal tissues (p < 0.05). The highly significant expression ratios of CK20, MAP3K8 and EIF5A observed in the colorectal tumors of patients predicted recurrence (p < 0.05). The expression of IMPDH2, CK20, MAP3K8 and EIF5A was significantly higher in the tumors of patients with short median survival (log-rank p value < 0.05). Progression-free survival was also significantly increased in patients with low expression of the EIF5A gene compared with those who exhibited high expression of this gene (log-rank p value < 0.05).

CONCLUSION

We demonstrated that high CK20, MAP3K8 and EIF5A expression levels were significant prognostic factors for poor overall survival in CRC patients. Further studies and validations are required; these genes may provide novel therapeutic molecular targets for CRC treatment, as well as new directions for the development of anticancer drugs.

A preclinical and clinical study of mycophenolate mofetil in pancreatic cancer

A high throughput screening for anticancer activity of FDA approved drugs identified mycophenolic acid (MPA), an inhibitor of inositol monophosphate dehydrogenase (IMPDH) as an active agent with an antiangiogenesis mode of action. Exposure of pancreatic cancer cell lines to MPA resulted in growth inhibition and reduced the expression of VEGF that was reversed by supplementing the media with guanosine supporting and IMPDH-dependant mechanism. In preclinical in vivo study, MPA showed a moderate inhibition of tumor growth in a panel of 6 human derived pancreatic cancer xenografts but reduced the expression of VEGF. To investigate the effects of MPA in human pancreatic cancer, a total of 12 patients with resectable pancreatic cancer (PDA) received increasing doses of mycophenolate mofetil (MMF) in cohorts of 6 patients each from 5-15 days prior to surgical resection. Treatment was well tolerated with one episode of grade 1 muscle pain, one episode of grade 2 lymphopenia (2 gr/day dose) and one episode of grade 2 elevantion in LFT (all in the 2 gr./day dose). Patients recovered from surgery uneventfully with no increased post-operative complications. Assessment of CD31, VEGF, and TUNEL in resected specimens compared to a non treated control of 6 patients showed no significant variations in any of the study endpoints. In conclusion, this study shows the feasibility of translating a preclinical observation to the clinical setting and to explore a drug mechanism of action in patients. MPA, however, did not show any hints of antiangiogenesis of anticancer clinical activity questioning if this agent should be further developed in PDA.

Inosine 5'-monophosphate dehydrogenase activity as a biomarker in the field of transplantation

Inosine 5'monophosphate dehydrogenase (IMPDH) is the rate limiting enzyme in the de novo synthesis of guanine nucleotides. The direct determination of target enzyme activity as a biomarker of mycophenolic acid (MPA) may help to estimate better the individual response to the immunosuppressant. However, the assessment of the clinical utility of this approach is limited by the diversity of the assay systems, which has not yet allowed the prospective assessment of this enzyme in larger patient cohorts. A recently validated and standardized assay allows the investigation of IMPDH activity in larger clinical studies. Although descriptive results from observational studies hold promise for a more individualized therapy in transplant medicine, more studies are needed to prospectively validate this approach.

Developmental pharmacogenetics of immunosuppressants in pediatric organ transplantation

Cyclosporine, tacrolimus, sirolimus, and mycophenolate mofetil are the primary immunosuppressants used on pediatric organ transplantation. Therapeutic drug monitoring is used in daily practice, because their clinical use is hampered by a narrow therapeutic index and large variability. Tailoring immunosuppressive therapy to the individual patient to optimize efficacy and minimize toxicity is therefore essential. Because research in pharmacogenetics already identified polymorphisms impacting their pharmacokinetic parameters in adults, developmental pharmacogenetics of immunosuppressants holds promises for optimizing dosage regimens and improving clinical outcome in children. In this review, we focus on the impact of age and pharmacogenetics on these immunosuppressants in children undergoing organ transplantation.

Identification of IMPDH2 as a tumor-associated antigen in colorectal cancer using immunoproteomics analysis

BACKGROUND AND AIMS

Sera from cancer patients contain tumor-specific autoantibodies directly against antigenic proteins. The identification of tumor autoantigens may have utility in cancer diagnosis, prognosis, and therapy. In this study, we used immunoproteomics analysis to identify tumor proteins that elicit humoral response in colorectal cancer (CRC).

MATERIALS AND METHODS

The CRC cell line HCT116 was used as a source of proteins for two-dimensional polyacrylamide gel electrophoresis and subsequent Western blot analysis in which individual serum from patients with CRC was analyzed for autoantibodies. Proteins that specifically react with sera from cancer patients were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis. In addition, the selected protein expression in tumor tissues collected from 40 patients with CRC were assessed by immunohistochemistry.

RESULTS

An autoantibody against inosine monophosphate dehydrogenase II (IMPDH2) identified by mass spectrometry was detected in eight out of 25 patients with CRC. However, none of the 15 healthy controls demonstrated autoantibody to IMPDH2.The expression of IMPDH2 in tumor tissue was significantly higher in patients with CRC than that in healthy subjects.

CONCLUSIONS

The result confirmed that the immunoproteomics analysis holds considerable promise for the discovery of tumor-associated antigens. IMPDH2 may be a protein biomarker and novel therapeutic target in CRC.

IMP dehydrogenase basal activity in MOLT-4 human leukaemia cells is altered by mycophenolic acid and 6-thioguanosine

OBJECTIVE

Depletion of guanine and deoxyguanine nucleotides by inhibition of inosine 5'-monophosphate dehydrogenase (IMPDH, EC 1.1.1.205) or introduction of 6-thioguanine nucleotide antimetabolites are two principles of retarding cell proliferation by interference with the cellular purine nucleotide pool. IMPDH activity may be a promising pharmacodynamic biomarker during immunosuppressive and anticancer pharmacotherapy. The aim of the study was to investigate the impact of mycophenolic acid (MPA) and 6-thioguanosine (tGuO) on IMPDH basal activity.

MATERIAL AND METHODS

We studied the IMPDH basal activity (i.e. the enzyme activity following inhibitor exposure, but measured in absence of the inhibitor) in response to increasing concentrations of the IMPDH inhibitor MPA and the antimetabolite tGuO in MOLT-4 human leukaemia cells. In parallel, IMPDH gene expression and cellular purine nucleotide concentrations were examined.

RESULTS

A biphasic concentration-dependent influence of MPA on the IMPDH basal activity was observed. At concentrations < or =IC50, MPA increased the IMPDH basal activity. The increase was associated with elevated expression of IMPDH2. Despite increased expression, the basal enzyme activity decreased following exposure to high MPA concentrations. The IMPDH2 expression increased modestly in response to tGuO exposure. However, the IMPDH basal activity decreased when the cells were exposed to a proliferation-blocking tGuO concentration.

CONCLUSIONS

These findings demonstrate that IMPDH basal activity is influenced by MPA and tGuO, and suggest that reduced IMPDH basal activity is related to the proliferation-blocking effects of these agents.