Inhibitor Of Inosine Monophosphate Dehydrogenase Research Articles

The IMPDH cytoophidium couples metabolism and fetal development in mice

The cytoophidium is an evolutionarily conserved subcellular structure formed by filamentous polymers of metabolic enzymes. In vertebrates, inosine monophosphate dehydrogenase (IMPDH), which catalyses the rate-limiting step in guanosine triphosphate (GTP) biosynthesis, is one of the best-known cytoophidium-forming enzymes. Formation of the cytoophidium has been proposed to alleviate the inhibition of IMPDH, thereby facilitating GTP production to support the rapid proliferation of certain cell types such as lymphocytes, cancer cells and pluripotent stem cells (PSCs). However, past studies lacked appropriate models to elucidate the significance of IMPDH cytoophidium under normal physiological conditions. In this study, we demonstrate that the presence of IMPDH cytoophidium in mouse PSCs correlates with their metabolic status rather than pluripotency. By introducing IMPDH2 Y12C point mutation through genome editing, we established mouse embryonic stem cell (ESC) lines incapable of forming IMPDH polymers and the cytoophidium. Our data indicate an important role of IMPDH cytoophidium in sustaining a positive feedback loop that couples nucleotide biosynthesis with upstream metabolic pathways. Additionally, we find that IMPDH2 Y12C mutation leads to decreased cell proliferation and increased DNA damage in teratomas, as well as impaired embryo development following blastocoel injection. Further analysis shows that IMPDH cytoophidium assembly in mouse embryonic development begins after implantation and gradually increases throughout fetal development. These findings provide insights into the regulation of IMPDH polymerisation in embryogenesis and its significance in coordinating cell metabolism and development.

Abstract 1789: Machine learning-based method to analyze metabolic fluxes of patient tumors

Abstract Personalized oncology must overcome the complex challenge of distinct cancer phenotypes in each patient, formed in part in response to unique metabolic crosstalk among cells in the tumor microenvironment which can be a determining factor in therapeutic response. Although isotope tracing sheds light on differences of metabolite enrichments in tumor and normal tissues, quantifying the metabolic fluxes in patients remains elusive. The conventional metabolic flux analysis tools are unable to estimate patient metabolic fluxes because we are limited to a single time point enrichment datapoint from each patient’s in-vivo measurement at isotopic non-steady state. We overcame this challenge by generating training data from the limited patient data and implementing a machine learning model to predict fluxes. To generate training data, we first simulated constrained random fluxes and enrichment patterns at different time points using patient circulating metabolites enrichment via an isotopic non-stationary metabolic flux analysis framework. Using this data, we trained a convolutional neural network to predict flux ratios. To validate our model, we compared predicted flux ratios to the experimental data from mouse models for two different treatments. Our recent findings from a glioblastoma (GBM) mouse model study using conventional metabolic flux analysis revealed higher de novo guanosine monophosphate (GMP) synthesis in GBM than normal cortex. These tumors can be sensitive to mycophenolate mofetil (MMF) which inhibits inosine monophosphate dehydrogenase, but only if the major source of GMP production is de novo synthesis and not salvage. Our machine learning model can discriminate between sources of GMP synthesis in patients, thus enabling prediction of potential responders. Furthermore, we previously showed that serine uptake is higher in GBM than normal cortex, and a serine- and glycine-restricted diet slows tumor growth in mice. While both circulating serine and microenvironment-derived serine could account for serine uptake in GBM, we hypothesized that the circulating serine dependence would better predict response to dietary serine depletion. Hence, we combined patient scRNA-seq and metabolomics data to feed our neural network framework to estimate microenvironmental and circulating serine uptake in six patients with brain cancer. Thus, we have shown that our model can identify patients who will benefit from MMF treatment or a serine- and glycine-restricted diet, enabling administration of highly effective personalized treatments for GBM patients. Citation Format: Baharan Meghdadi, Anjali Mittal, Andrew J. Scott, Sravya Palavalasa, Daniel R. Wahl, Deepak Nagrath. Machine learning-based method to analyze metabolic fluxes of patient tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1789.

Update on monkeypox virus infection: Focusing current treatment and prevention approaches.

While the world is still facing the global pandemic COVID-19, another zoonosis monkeypox (Mpox) has emerged posing a great threat to society. Insight into the pathogenesis, symptoms, and management strategies will aid in the development of potent therapeutics for the treatment of monkeypox virus infection. To get insight into the current treatment and prevention strategies will aid in effectively coping with the disease. For obtaining information regarding the ongoing treatment and prevention strategies and the drugs under pipeline, we referred to Google Scholar, Pub Med, Pub Chem, and WHO official site. There are a few drugs that came out to be effective for the treatment of Mpox. Tecovirimat acts by inhibiting viral replication and viral wrapping. Another drug is cidofovir, which hinders the activity of viral DNA polymerase but has the drawback of nephrotoxicity. To overcome this, a conjugate of cidofovir is being used-known as brincidofovir-which has a similar mechanism as cidofovir but lesser toxicity. Ribavirin acts via inhibiting inosine monophosphate dehydrogenase (IMPDPH) thus disrupting viral translation. It also interferes with helicase activity. Tiazofurin, Adenosine N1 oxide, and HPMPA have shown efficacy in in-vitro studies by inhibiting IMPDH, DNA polymerase, and viral mRNA translation respectively. In-silico studies have proven the effect of nilotinib, simeprevir, and dihydroergotamine for Mpox treatment. They have shown binding affinity for proteins required for the growth and release of MPXV. Vaccines have also been employed for the prevention of Mpox, which includes JYNNEOS, ACAM2000, and VIGIV. This review highlights the pathogenesis of the virus, disease manifestations, drugs, and vaccines that are being used and those under pipeline for the treatment and prevention of Mpox.

Chronic GVHD: review advances in prevention, novel endpoints, and targeted strategies.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy for many malignant and non-malignant hematologic disorders. Chronic graft-versus-host (cGVHD) disease remains a significant hurdle for long-term survival in patients post allo-HCT, and it remains the leading cause of late non-relapse mortality. The risk factors for development of cGVHD include degree of human leukocyte antigen (HLA) disparity, increasing recipient age, use of peripheral blood stem cells as a source, myeloablative conditioning regimens, prior acute GVHD (aGVHD), and female donor to male recipient. Our biological understanding of cGVHD is mostly derived from transplantation mouse models and patient data. There are three distinct phases in the development of cGVHD. Approaches to prevent GVHD include pharmacologic strategies such as calcineurin inhibitors (cyclosporine, tacrolimus) combined with methotrexate or mTOR inhibitors (sirolimus), and IMP dehydrogenase inhibitors (mycophenolate mofetil). Increasingly, posttransplant cyclophosphamide is emerging as a promising strategy for GVCHD prevention especially in a setting of reduced intensity conditioning. Other approaches include serotherapy (ATG, Campath) and graft manipulation strategies. A significant obstacle to evaluating the response of novel GVHD-directed therapies has been standardized response assessments. This has functioned as a barrier to designing and interpreting clinical trials that are structured around the treatment of cGVHD. Novel endpoints including failure-free survival, Graft-versus-host disease-free, relapse-free survival (GRFS), and current GVHD-free, relapse-free survival (CGRFS) may create a clearer picture for post-HCT outcomes. Targeted therapies including Bruton's tyrosine kinase inhibition, JAK1/2 inhibition, and ROCK2 inhibitors have improved cGVHD therapy, especially in the steroid refractory setting. Continued improvement in prophylactic strategies for cGVHD, identification of accurate cGVHD treatment endpoints, and access to novel therapeutic agents are expected to improve cGVHD outcomes.

Mycophenolate mofetil in giant cell arteritis.

Giant cell arteritis (GCA) is a systemic granulomatous vasculitis affecting the large arteries. Abnormal lymphocyte function has been noted as a pathogenic factor in GCA. Mycophenolate mofetil (MMF) inhibits inosine monophosphate dehydrogenase and is therefore a highly lymphocyte-specific immunosuppressive therapy. We aimed to assess the efficacy of MMF for inducing remission in GCA. Seven patients (5 female, 2 male) with GCA under therapy with MMF and who were treated at the outpatient clinic for rare inflammatory systemic diseases at Hannover Medical School between 2010 and 2023 were retrospectively included in the study. All patients underwent duplex sonography, 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET), magnetic resonance imaging (MRI), and/or biopsy to confirm the diagnosis. The primary endpoints were the number of recurrences, CRP levels at 3-6 and 6-12 months, and the period of remission. All patients in this case series showed inflammatory activity of the arterial vessels in at least one of the imaging modalities: duplex sonography (n = 5), 18F-FDG PET (n = 5), MRI (n = 6), and/or biopsy (n = 5). CRP levels of all patients decreased at the measurement time points 3-6 months, and 6-9 months after initiation of therapy with MMF compared with CRP levels before MMF therapy. All patients with GCA in this case series achieved disease remission. The results of the present case series indicate that MMF is an effective therapy in controlling disease activity in GCA, which should be investigated in future randomized controlled trials.

Specific inhibitory effects of guanosine on breast cancer cell proliferation

Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer-related death. Drug therapy for breast cancer is currently selected based on the subtype classification; however, many anticancer drugs are highly cytotoxic. Since intracellular levels of GTP are elevated in many cancer cells that undergo a specific cell proliferation cycle, GTP has potential as a target for cancer therapy. The present study focused on nucleosides and nucleotides and examined intracellular GTP-dependent changes in cell proliferation rates in normal (MCF-12A) and cancer (MCF-7) breast cell lines. Decreased cell proliferation due to a reduction in intracellular GTP levels by mycophenolic acid (MPA), an inosine monophosphate dehydrogenase inhibitor, was observed in both cell lines. The inhibitory effects of MPA on cell proliferation were suppressed when it was applied in combination with Guanosine (Guo), a substrate for GTP salvage synthesis, while the single exposure to Guo suppressed the proliferation of MCF-7 cells only. Although the underlying mechanisms remain unclear, since the inhibitory effects of Guo on cell proliferation did not correlate with GTP or ATP intracellular levels or the GTP/ATP ratio, there may be another cause besides GTP metabolism. Guo inhibited the proliferation of MCF-7, a human breast cancer cell line, but not MCF-12A, a human normal breast cell line. Further studies are needed to investigate the potential of applying Guo as a target for the development of a novel cancer treatment system.

Safety and efficacy of mycophenolate in COVID-19: a nonrandomised prospective study in western India.

Antivirals and immunosuppressive agents are used with variable success in the treatment of COVID-19. Mycophenolate, an inhibitor of enzyme inosine monophosphate dehydrogenase, is an immunosuppressant used to prevent allograft rejection and other autoimmune diseases. Few laboratory studies have also reported antiviral properties of mycophenolate. The current study tried to assess the safety and efficacy of mycophenolate in patients hospitalised with COVID-19. This was a prospective non-randomised open label study with the objective to assess the effect of addition of mycophenolate to the standard of care on mortality due to COVID-19 and duration of hospital stay. The target study population was comprised of patients requiring inpatient treatment for COVID-19 during the period from Jan 15-April 15, 2021. The study was registered with Clinical Trial Registry of India (CTRI/2021/01/030477, registered on date-14/01/2021). Adult patients (n=106) requiring hospitalisation for COVID-19 received mycophenolate, 360mg, one tablet daily for one month. Mycophenolate was initiated within 48h of the diagnosis of SARS-CoV-2 infection by RT‒PCR. While patients who did not consent for mycophenolate (n=106), received only standard of care, and were considered as control group. The relevant clinical data including NEWS2 scores and high-resolution computed tomography of the thorax were collected and analysed. The mortality and hospital stay were significantly lower in the study group compared to the control group. Mycophenolate significantly reduced mortality after adjustment for other predictors (adjusted odds ratio: 0.082 with 95% CI: 0.012-0.567). Mycophenolate was an independent predictor of survival in patients hospitalised due to COVID-19. There was also no evidence of secondary bacterial infections and post-COVID complications. Mycophenolate administration is safe in COVID-19. Mycophenolate reduces mortality and duration of hospital stay in patients with COVID-19. Shri Janai Research Foundation, India.

A RARE PRESENTATION OF MYCOPHENOLATE MOFETIL-INDUCED SEGMENTAL COLITIS MASQUERADING AS ISCHEMIC COLITIS

Mycophenolate mofetil (MMOF) is an immunosuppressive pro-drug commonly used to prevent rejection in recipients of solid organ transplants. It is hepatically converted to mycophenolic acid which then acts to reversibly inhibit inosine monophosphate dehydrogenase, thereby preventing B and T lymphocyte proliferation, B cell antibody formation, and leukocyte recruitment to sites of inflammation. Diarrhea is the most common gastrointestinal side effect of MMOF usage with up to 40% of renal transplant patients on MMOF reporting this symptom and colonoscopy not infrequently shows injurious changes that range from edema and erythema to ulcerations and diffuse colitis. Isolated reports note that colonic histopathology from patients on MMOF sometimes mimic graft-versus-host disease, inflammatory bowel disease, or ischemic colitis. However, there are very few cases that describe segmental colitis in MMOF patients. We present a rare case of a renal transplant patient presenting with MMOF-induced segmental colitis after 4 years of medication usage.

A RARE PRESENTATION OF MYCOPHENOLATE MOFETIL-INDUCED SEGMENTAL COLITIS MASQUERADING AS ISCHEMIC COLITIS

Abstract Mycophenolate mofetil (MMOF) is an immunosuppressive pro-drug commonly used to prevent rejection in recipients of solid organ transplants. It is hepatically converted to mycophenolic acid which then acts to reversibly inhibit inosine monophosphate dehydrogenase, thereby preventing B and T lymphocyte proliferation, B cell antibody formation, and leukocyte recruitment to sites of inflammation. Diarrhea is the most common gastrointestinal side effect of MMOF usage with up to 40% of renal transplant patients on MMOF reporting this symptom and colonoscopy not infrequently shows injurious changes that range from edema and erythema to ulcerations and diffuse colitis. Isolated reports note that colonic histopathology from patients on MMOF sometimes mimic graft-versus-host disease, inflammatory bowel disease, or ischemic colitis. However, there are very few cases that describe segmental colitis in MMOF patients. We present a rare case of a renal transplant patient presenting with MMOF-induced segmental colitis after 4 years of medication usage. A 52-year-old male with a history of native kidney end stage renal disease secondary to diabetic nephrosclerosis status post living unrelated kidney transplant 4 years ago from his wife presented to the emergency room for 1 week of intractable abdominal pain, vomiting, and diarrhea. His current transplant medications included atovaquone, tacrolimus, and mycophenolate mofetil. Lab work showed chronic pancytopenia with hemoglobin 10, MCV 85, platelets 58, BUN:Cr 87:5.6, and tacrolimus level 34.8. His last colonoscopy 7 years ago was unremarkable and the patient had never had an esophagogastroduodenoscopy (EGD) before. EGD while admitted showed significant erosive gastropathy with pathology showing the same. Sigmoidoscopy showed segmental colitis with punctate erythema and loss of vascularity up to the splenic flexure with the distribution of mucosal disruption suggestive of ischemic colitis. Histopathology showed fragments of colonic mucosa with patchy active cryptitis, surface erosion, distorted crypts with concurrent apoptosis and scattered eosinophils in the lamina propria – findings consistent with mycophenolate colitis. Symptomatic care was provided and the patient’s mycophenolate was tapered to cessation with complete resolution of symptoms. He was discharged with appropriate follow-up. Our case highlights a rare presentation of MMOF-induced injury whereby despite, appearance on endoscopy as a segmental ischemic colitis, histopathology was negative for ischemia but notable for MMOF-induced injury which was confirmed by symptom resolution following discontinuation of the immunosuppressive drug.. With early recognition of this pathology by clinicians with subsequent MMOF discontinuation, symptoms and prognosis can be remarkably improved. Colonoscopic image showing segmental colitis with punctate erythema and loss of vascularity. Fragments of colonic mucosa with patchy active cryptitis (star), surface erosion, mildly distorted crypts and apoptosis mainly in crypt bases with scattered eosinophils in the lamina propria, indicative of mycophenolate colitis. 400x magnification.

S-22-3: UNCOVERING NEW GENES, TISSUES AND THERAPEUTIC TARGETS FOR BLOOD PRESSURE THROUGH LARGE-SCALE TRANSCRIPTOME-WIDE ASSOCIATION STUDIES

Objective: Transcriptome-wide association study (TWAS) leverages information from reference panels of human tissues to predict the genetically determined component of expression in much larger datasets for thousands of genes and explore their association with a phenotype/disease of interest in thousands of individuals. Using TWAS, we sought to 1) define contributors to blood pressure (BP) regulation across a panel of 49 human cell-types/tissues 2) detect new kidney genes associated with BP in human kidney samples and 3) identify new pharmacological opportunities for hypertension through TWAS-informed drug repurposing. Design and method: We performed TWAS using PrediXcan across 49 human tissues/cell-types from The Genotype-Tissue Expression project and ranked the overall relevance of tissue of BP according to three independent metrics defining the strength of uncovered tissue-trait associations. We then trained predictors of gene expression from 478 samples from the Human Kidney Tissue Resource by applying a new predictive model which utilises epigenetic and three-dimensional genomic information to prioritise essential genetic variants. The subsequent BP kidney TWAS was conducted in up to ∼750k individuals from UK Biobank and International Consortium for Blood Pressure. Finally, we combined the input from BP kidney TWAS with Connectivity Map to identify drugs capable of inducing or reversing the identified gene expression signatures. Results: We found that fibroblasts, kidney cortex, lymphocytes, brain, thyroid, adrenal glands, aorta and spleen showed the overall strongest associations with BP across 49 human tissues/cell-types. Through TWAS of systolic blood pressure/diastolic blood pressure/pulse pressure we identified 997 kidney genes associated with at least one BP trait. Of these, 562 (56%) have not been reported before. Our computational druggability analysis re-affirmed the potential of several known BP inducers (glucocorticoid receptor agonists, calcineurin inhibitors) to increase BP and uncovered adenylate cyclase system activators to reverse the BP-related changes in the transcriptome. We also found purinergic receptor as a potential gene target for drug repurposing in hypertension. Finally, we found that use of topoisomerase inhibitors, cyclin-dependent kinase inhibitors, inosine monophosphate dehydrogenase inhibitors, and histone deacetylase inhibitors may be associated with hypotension. Conclusion: Our data provided evidence for the role of the kidney as an organ of the key relevance to hypertension and highlighted the importance of immune system in BP regulation. We also identified 997 kidney genes robustly associated with BP. Through TWAS-informed drug repurposing analysis, we uncovered novel targets for drug development in hypertension and highlighted BP drop as a potential side effect of several existing therapeutics.

Repurposing immunosuppressants for antileukemia therapy.

Drug repurposing, the strategy to identify new therapeutic use for clinically approved drugs has attracted much attention in recent years. This strategy offers various advantages over traditional approaches to develop new drugs, including shorter development timelines, low cost, and reduced risk of failure. In this issue of EMBO Molecular Medicine, Liu etal show that inosine monophosphate dehydrogenase (IMPDH) inhibitors, the well-known immunosuppressants have a potent therapeutic effect on the aggressive blood cancer, acute myeloid leukemia with MLL rearrangements. Intriguingly, the antileukemia effect of IMPDH inhibitors is mediated, at least in part through the overactivation of TLR signaling and Vcam1 upregulation. The robust antileukemia effect of IMPDH inhibitors, both invitro and invivo, together with their mechanistic findings provides a rational basis for repurposing IMPDH inhibitors for antileukemia therapy.

Individualization of Mycophenolic Acid Therapy through Pharmacogenetic, Pharmacokinetic and Pharmacodynamic Testing.

Mycophenolic acid (MPA) is a widely used immunosuppressive agent and exerts its effect by inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH), the main regulating enzyme of purine metabolism. However, significant unexplained differences in the efficacy and tolerability of MPA therapy pose a clinical challenge. Therefore, broad pharmacogenetic, pharmacokinetic, and pharmacodynamic approaches are needed to individualize MPA therapy. In this prospective cohort study including 277 renal transplant recipients, IMPDH2 rs11706052 SNP status was assessed by genetic sequencing, and plasma MPA trough levels were determined by HPLC and IMPDH enzyme activity in peripheral blood mononuclear cells (PBMCs) by liquid chromatography-mass spectrometry. Among the 277 patients, 84 were identified with episodes of biopsy-proven rejection (BPR). No association was found between rs11706052 SNP status and graft rejection (OR 1.808, and 95% CI, 0.939 to 3.479; p = 0.076). Furthermore, there was no association between MPA plasma levels and BPR (p = 0.69). However, the patients with graft rejection had a significantly higher predose IMPDH activity in PBMCs compared to the controls without rejection at the time of biopsy (110.1 ± 50.2 vs. 95.2 ± 45.4 pmol/h; p = 0.001), and relative to the baseline IMPDH activity before transplantation (p = 0.042). Our results suggest that individualization of MPA therapy, particularly through pharmacodynamic monitoring of IMPDH activity in PBMCs, has the potential to improve the clinical outcomes of transplant patients.

Synthesis and Biological Evaluation of Novel Anti-leukemia Proteolysis-Targeting Chimeras in Degradating Inosine Monophosphate Dehydrogenase.

Proteolysis-targeting chimera (PROTAC) is a bifunctional molecule comprising a ligand to recognize the targeted protein to be degraded. To use the advantages of the PROTAC technique, we have synthesized novel compounds to degrade inosine monophosphate dehydrogenase (IMPDH) by the proteasome system. We describe the synthesis of new PROTACs based on a combination of mycophenolic acid (MPA) as the potent IMPDH inhibitor and pomalidomide as a ligand of E3 ubiquitin ligase via linkers formed from Cu(I)-catalyzed cycloaddition reaction. All synthesized compounds were investigated against Jurkat cells as acute T-cell leukemia and were potent apoptosis inducers at 50 nM. The effect of compound 2 in 0.05 μM on IMPDH degradation can be almost prevented by competition with bortezomib as the proteasome inhibitor at 0.1 and 0.5 μM.

Metabolomics reveals inosine 5′-monophosphate is increased during mice adipocyte browning

Adipocyte browning is one of the potential strategies for the prevention of obesity-related metabolic syndromes, but it is a complex process. Although previous studies make it increasingly clear that several transcription factors and enzymes are essential to induce browning, it is unclear what dynamic and metabolic changes occur in induction of browning. Here, we analyzed the effect of a beta-adrenergic receptor agonist (CL316243, accelerator of browning) on metabolic change in mice adipose tissue and plasma using metabolome analysis and speculated that browning is regulated partly by inosine 5′-monophosphate (IMP) metabolism. To test this hypothesis, we investigated whether Ucp-1, a functional marker of browning, mRNA expression is influenced by IMP metabolism using immortalized adipocytes. Our study showed that mycophenolic acid, an IMP dehydrogenase inhibitor, increases the mRNA expression of Ucp-1 in immortalized adipocytes. Furthermore, we performed a single administration of mycophenolate mofetil, a prodrug of mycophenolic acid, to mice and demonstrated that mycophenolate mofetil induces adipocyte browning and miniaturization of adipocyte size, leading to adipose tissue weight loss. These findings showed that IMP metabolism has a significant effect on adipocyte browning, suggesting that the regulator of IMP metabolism has the potential to prevent obesity.

Inosine monophosphate dehydrogenase activity and mycophenolate pharmacokinetics in children with nephrotic syndrome treated with mycophenolate mofetil

Some studies have shown that the area under the concentration-time curve (AUC) of mycophenolic acid (MPA) should be higher for children with nephrotic syndrome (NS) than after renal transplantation. The pharmacodynamic aspect of MPA, the activity of inosine monophosphate dehydrogenase (IMPDH), has not been studied in children with NS. The study included 21 children (4-16 years old) with NS treated with mycophenolate mofetil. MPA and its glucuronide plasma concentrations were determined using validated high-performance liquid chromatography-ultraviolet (HPLC-UV). The separate HPLC-UV method was applied for IMPDH activity determination. The variability was expressed by the coefficient of variation (CV). IMPDH activity and MPA concentration (Ctrough ) before the morning dose amounted to 29.95 μmol s-1 mol-1 adenosine monophosphate (AMP) (range, 6.71-98.60 μmol s-1 mol-1 AMP) and 1.72 μg/mL (range, 0.39-4.34 μg/mL), respectively, whereas the area under the effect-time curve from 0 to 4h and MPA AUC0-4 were 130.36 μmol s-1 mol-1 AMP × h (range, 23.58-306.57 μmol s-1 mol-1 AMP × h) and 24.63 μg h/mL (range, 12.21-67.48 μg h/mL), respectively. IMPDH activity decreased concomitantly with MPA concentration increase, however, the variability of the pharmacodynamic parameters was greater than of the pharmacokinetics. The median degree of maximum IMPDH inhibition was 61%. MPA Ctrough and predicted AUC were lower than in our previous study. Only a few MPA pharmacokinetic parameters correlated with the pharmacodynamics. IMPDH activity did not correlate with the children's age and did not differ between boys and girls. MPA clearance was the highest in younger children (median, 10.54 L/m2 /h) and cholesterol correlated negatively with the children's age (r=-0.659, P=0.003). IMPDH minimum activity and the degree of maximum IMPDH inhibition were similar to those obtained in renal transplant recipients. IMPDH activity does not undergo developmental or gender-specific regulation in children with NS. MPA underexposure might be more frequent in younger children, especially with high cholesterol and triglycerides levels because of high MPA clearance.

A randomized, placebo-controlled study to evaluate safety and pharmacokinetics of inhaled ribavirin.

Ribavirin is an inosine monophosphate dehydrogenase inhibitor. Studies suggest ribavirin aerosol could be a safe and efficacious treatment option in the fight against coronaviruses. However, current treatment is long (12–18 h per day, 3–7 days), limiting clinical utility. A reduction in treatment time would reduce treatment burden. We aimed to evaluate safety and pharmacokinetics (PK) of four, single‐dose regimens of ribavirin aerosol in healthy volunteers. Thirty‐two subjects were randomized, to four cohorts of aerosolized ribavirin (active) or placebo. Cohort 1 received 50 mg/ml ribavirin/placebo (10 ml total volume); cohort 2, 50 mg/ml ribavirin/placebo (20 ml total volume); cohort 3, 100 mg/ml ribavirin/placebo (10 ml total volume); and cohort 4, 100 mg/ml ribavirin/placebo (20 ml total volume). Intense safety monitoring and PK sampling took place on days 1, 2, 3, and 40. Subjects were (mean ± SD, active vs. placebo) aged 57 ± 4.5 vs. 60 ± 2.5 years; 83% vs. 88% were female; and 75% vs. 50% were Caucasian. Some 12.5% (3/24) and 25% (2/8) experienced at least one treatment‐emergent adverse event (TEAE) (two moderate; five mild) in the active and placebo groups, respectively. No clinically significant safety concerns were reported. Mean maximum observed concentration (C max) and area under the curve (AUC) values were higher in cohort 4, whereas cohorts 2 and 3 showed similar PK values. Ribavirin absorption reached C max within 2 h across cohorts. Four single‐dose regimens of ribavirin aerosol demonstrated systemic exposure with minimal systemic effects. Results support continued clinical development of ribavirin aerosol as a treatment option in patients with coronaviruses.

Inosine triphosphate pyrophosphatase from Trypanosoma brucei cleanses cytosolic pools from deaminated nucleotides

Inosine triphosphate pyrophosphatases (ITPases) are ubiquitous house-cleaning enzymes that specifically recognize deaminated purine nucleotides and catalyze their hydrolytic cleavage. In this work, we have characterized the Trypanosoma brucei ITPase ortholog (TbITPA). Recombinant TbITPA efficiently hydrolyzes (deoxy)ITP and XTP nucleotides into their respective monophosphate form. Immunolocalization analysis performed in bloodstream forms suggests that the primary role of TbITPA is the exclusion of deaminated purines from the cytosolic nucleoside triphosphate pools. Even though ITPA-knockout bloodstream parasites are viable, they are more sensitive to inhibition of IMP dehydrogenase with mycophenolic acid, likely due to an expansion of IMP, the ITP precursor. On the other hand, TbITPA can also hydrolyze the activated form of the antiviral ribavirin although in this case, the absence of ITPase activity in the cell confers protection against this nucleoside analog. This unexpected phenotype is dependant on purine availability and can be explained by the fact that ribavirin monophosphate, the reaction product generated by TbITPA, is a potent inhibitor of trypanosomal IMP dehydrogenase and GMP reductase. In summary, the present study constitutes the first report on a protozoan inosine triphosphate pyrophosphatase involved in the removal of harmful deaminated nucleotides from the cytosolic pool.

Comparative efficacy and safety of mizoribine and mycophenolate mofetil for treating systemic lupus erythematosus: a retrospective cohort study.

Background:Mizoribine (MZR) is an immunosuppressive agent that selectively inhibits inosine monophosphate dehydrogenase; its actions are considerably similar to those of mycophenolate mofetil (MMF). This study aimed to clarify whether MZR can be a good treatment option for systemic lupus erythematosus (SLE) and to compare the efficacy and safety of MZR and MMF in patients with active SLE.Methods:We retrospectively compared the efficacy, continuation rate, and safety of MZR (52 patients) and MMF (31 patients) after adjusting for stabilized inverse probability of treatment weighting based on propensity scores. The efficacy endpoints were as follows: cumulative incidence of lupus low disease activity state (LLDAS) or remission attainment and flares and change in prednisolone dose over 2 years. Drug continuation rates were defined as the time from drug initiation to discontinuation for any cause, owing to the lack of efficacy, or owing to adverse events. The safety endpoint was the frequency of adverse events.Results:Overall, 25 (48.1%) and 13 (25.0%) patients in the MZR group and 18 (58.1%) and 15 (48.3%) in the MMF group achieved LLDAS and remission during the follow-up period, respectively; thus, the cumulative incidence of LLDAS and remission attainment of the two groups was similar after adjustment. Prednisolone dose was steadily reduced in both the groups, and the change in prednisolone dose was nearly identical between the two groups. Drug discontinuation rate due to adverse events and the frequency of all adverse events and infections were higher in the MMF group than in the MZR group, albeit without significance after adjustment.Conclusion:MZR is as effective as MMF in controlling SLE activity. The adverse events of MZR, whose profile differs from MMF, are comparable to or less than those of MMF. MZR may be a valuable option as an immunosuppressive agent for SLE, as well as MMF.

Mechanism of Action and Efficacy of Immunosupressors in Lupus Nephritis.

Approximately 70% of the patients with systemic lupus erythematosus will have clinical evidence of kidney damage during their evolution. Patients with impaired renal function at onset and those with recurrent flares have a poor prognosis. Understanding the mechanism of action of immunosuppressants is essential for proper prescription. Steroids inhibit the DNA sequence that promotes the release of inflammatory cytokines. Phosphoramide mustard, metabolite of cyclophosphamide, cross-link with the DNA, causing the aggregation of an alkyl group, causing cell death. Mycophenolate inhibits inosine monophosphate dehydrogenase, prevents de novo synthesis of guanine, inducing cell arrest in S phase. Azathioprine blocks the synthesis of purines and induces apoptosis. Calcineurin inhibitors prevent the dephosphorylation of NFAT and reduce the production of interleukin 2. Antimalarials alter the enzymatic release of lysosomes by increasing intravesicular pH. The mechanism of action of rituximab is related to complement-dependent cytotoxicity and the elimination of anti-CD20-labeled B cells. Progress in the knowledge and management of low doses of steroids may change the current paradigm and reduce the frequency of related adverse events. Mycophenolate seems to be a better choice than cyclophosphamide for induction, it is also preferred over azathioprine as a maintenance immunosuppressive agent, although azathioprine is preferred in women with a desire for conception, those pregnant, or with low resources. For treatment-resistant cases, tacrolimus, rituximab or belimumab may be effective. Ongoing clinical trials with new drugs offer promising results.

A broad influenza virus inhibitor acting via IMP dehydrogenase and in synergism with ribavirin

To suppress serious influenza infections in persons showing insufficient protection from the vaccines, antiviral drugs are of vital importance. There is a need for novel agents with broad activity against influenza A (IAV) and B (IBV) viruses and with targets that differ from those of the current antivirals. We here report a new small molecule influenza virus inhibitor referred to as CPD A (chemical name: N-(pyridin-3-yl)thiophene-2-carboxamide). In an influenza virus minigenome assay, this non-nucleoside compound inhibited RNA synthesis of IAV and IBV with EC50 values of 2.3 μM and 2.6 μM, respectively. Robust in vitro activity was noted against a broad panel of IAV (H1N1 and H3N2) and IBV strains, with a median EC50 value of 0.20 μM, which is 185-fold below the 50% cytotoxic concentration. The action point in the viral replication cycle was located between 1 and 5 h p.i., showing a similar profile as ribavirin. Like this nucleoside analogue, CPD A was shown to cause strong depletion of the cellular GTP pool and, accordingly, its antiviral activity was antagonized when this pool was restored with exogenous guanosine. This aligns with the observed inhibition in a cell-based IMP dehydrogenase (IMPDH) assay, which seems to require metabolic activation of CPD A since no direct inhibition was seen in an enzymatic IMPDH assay. The combination of CPD A with ribavirin, another IMPDH inhibitor, proved strongly synergistic. To conclude, we established CPD A as a new inhibitor of influenza A and B virus replication and RNA synthesis, and support the potential of IMPDH inhibitors for influenza therapy with acceptable safety profile.