Assessment of renal response in Tunisian patients with proliferative lupus nephritis under three different induction immunosuppressive agents: A prognostic retrospective study.

OBJECTIVE: The aim of our study was to evaluate the renal response (RR) of three immunosuppressive protocols in the induction treatment of proliferative lupus nephritis (PLN) in a Tunisian population. METHODS: We performed a retrospective prognostic cohort study in the Internal Medicine Department of the Habib Thameur University Hospital in Tunis from January 2000 to December 2023, and included kidney biopsy proven proliferative lupus nephritis patients. Three induction treatments were compared: High CYP regimen: glucocorticoids (GC) + IV cyclophosphamide (CYP) in monthly pulses of 0.7 g/m2 for 6 months; Low CYP regimen: GC + IV CYP in biweekly pulses of 500 mg for 3 months; and MMF regimen: GC + oral MMF 1.5 g twice daily for 6 months. The primary endpoint was the incidence of RR (complete and partial remission) at one year post-diagnosis. The additional outcomes were end-stage kidney disease (ESKD), severe adverse events (AEs) and death. RESULTS: Our study included 78 PLN patients (High CYP: 17, Low CYP: 40, MMF: 21). The study found that 94.1% of patients receiving High CYP achieved the primary endpoint, RR, compared to 67.5% of those receiving Low CYP and 61.9% in the MMF group. For the additional outcomes, there were 3 cases of ESKD, all in the Low CYP group, 5 cases of death (4 in the Low CYP group and 1 in the MMF group), and 20 cases of severe AEs, all of which were severe infections (5 in the High CYP group, 12 in the Low CYP group, and 3 in the MMF group). Multivariate analysis showed that the High CYP regimen was more associated with RR than the MMF regimen, with an adjusted OR of 9.846 (95% CI: 1.087-98.210); p = 0.042. Multivariate analysis did not show statistically significant differences between the High CYP regimen and the Low CYP regimen in terms of RR. CONCLUSION: As an induction treatment for PLN, the High CYP regimen was strongly associated with a higher rate of RR than the MMF regimen. There were no statistically significant differences between the High CYP regimen and the Low CYP regimen in terms of RR.

A Novel Lactam and Two Rare Mycophenolic Acid Derivatives from the Fungus Penicillium sclerotiorum JBHL321.

A novel lactam penicillactam (1), two rare mycophenolic acid (MPA) derivatives penimycophens A and B (2 and 3), together with two known biogenetically related MPA derivatives (4 and 5) and a known alkaloid (6) were isolated from the Penicillium sclerotiorum JBHL321. The structures of these compounds were determined by comprehensive spectroscopic analyses. The absolute configuration of 1 was confirmed by electronic circular dichroism (ECD) calculations. Compound 1 represent the rare example of a oxygen bridge-linked lactam from natural products. Structurally, compounds 2 and 3 were rare MPA derivatives featuring a methoxy group at C-3. The inhibitory activity of compounds 1-6 against two phytopathogenic fungi, three phytopathogenic bacteria and four cancer cell lines were evaluated. Compounds 2-5 exhibited significant cytotoxic activity against HeLa, MCF-7, A549 and MGC-803 cells with IC50 values in the low micromolar to nanomolar. Compound 3 exhibited especially cytotoxic activity against four different cell lines with IC50 values ranging from 0.06 to 0.14 µM, compared to IC50 values ranging from 0.62 to 2.51 µM for epirubicin.

Three New Antibacterial Mycophenolic Acid Derivatives from the Marine-Derived Fungus Penicillium sp. HN-66.

Three new mycophenolic acid derivatives, penicacids L-N (1-3), together with four known analogues, were isolated from a fungus Penicillium sp. HN-66 derived from a South China Sea marine sediment. The structures of compounds 1-3 were determined on the basis of HR-ESI-MS, NMR (1H, 13C, HSQC and HMBC) data analyses, and comparison of optical rotations. Antimicrobial activities of 1-7 were tested. The results showed that compounds 1-3 and 5-7 had weak inhibitory effects against E. coli ATCC 25922 with the MIC values of 50 µg/mL.

Impact of Drug Conjugation Site and Corona Chemistry on the Therapeutic Activity of Polymer Nanorod - Drug Conjugates.

Biocompatible rod-shaped nanoparticles of controlled length can be produced through the heat-induced "living" seeded crystallization-driven self-assembly (CDSA) of poly(2-isopropyl-2-oxazoline)-containing block copolymers. With a hydrophilic poly(2-methyl-2-oxazine) or poly(2-methyl-2-oxazoline) corona, these nanorods have proven non-cytotoxic, non-hemolytic, and ideal for use as a polymer-based drug delivery system. This study demonstrates a facile, one-pot method for the synthesis of mycophenolic acid (MPA)-conjugated block copolymer "unimers" for use in seeded CDSA. Through altering block order during sequential monomer addition cationic ring-opening polymerization (CROP), MPA is conjugated to either the chain end of the core-forming or corona-forming block. This allows bioactive polymer nanorods to be prepared with MPA positioned at either the periphery of the corona, or at the core-corona interface of the nanorod formed during seeded CDSA. In vitro, these nanorods arrest growth in human T and B lymphocytes, with reduced effect in "off-target" monocytes when compared with unconjugated MPA. Furthermore, the conjugation of MPA to the core-corona interface of the nanorods leads to a slower release and reduced cytostatic effect. This study offers a robust investigation into the effect of steric hindrance and corona chemistry on the therapeutic potential of drug-conjugated CDSA nanorods and demonstrates the potential of poly(2-oxazoline)/poly(2-oxazine)-based CDSA nanomaterials as effective drug delivery platforms.

Mycophenolate Mofetil for the Treatment of Warm Autoimmune Haemolytic Anaemia Post-Rituximab Therapy: A Case Series.

Background: Warm autoimmune haemolytic anaemia (wAIHA) is an acquired haemolytic disorder most commonly treated with a combination of corticosteroids, rituximab and/or splenectomy. Third-line therapies for refractory cases include immunosuppressive agents. Mycophenolate mofetil is frequently used in these scenarios, although its use is supported by small studies and anecdotal evidence rather than large-scale data. Case description: We describe three cases of refractory warm autoimmune haemolytic anaemia successfully treated with mycophenolate mofetil. Case 1: A persistent case of autoimmune haemolytic anaemia in a 56-year-old was ultimately managed with mycophenolate mofetil, leading to successful steroid tapering and stable haemoglobin levels without relapse. Case 2: A woman with a complex oncological history, including lymphoma and breast cancer, achieved remission with mycophenolate therapy, maintaining stability post-steroid treatment. Case 3: Mycophenolate proved effective for a 63-year-old with cirrhosis after recurrent autoimmune anaemia and deep vein thrombosis, enabling cessation of steroids and maintaining remission. Conclusion: Management of this condition can be challenging and balancing the available treatments is crucial to reduce potential complications from long-term therapies that appear to be ineffective. Our case series demonstrates anecdotal experience on successful use of mycophenolate mofetil for complex refractory cases of wAIHA. LEARNING POINTS: Warm autoimmune haemolytic anaemia can be a challenging condition to manage. Refractory cases that are steroid-dependent can benefit from trialling steroid-sparing agents such as mycophenolate.Anti-CD20 agents such as rituximab can be very effective in refractory cases, however there is a small percentage of patients that might not be responsive to this monoclonal antibody.Autoimmune haemolytic anaemias can be frequently complicated by thrombotic events, and part of the backbone treatment is establishing good thromboprophylaxis.

A limited sampling model to estimate the area under the curve of mycophenolic acid in hematopoietic stem cell transplantation recipients.

Relationship between the areas under the curve (AUC) of mycophenolic acid (MPA) and the likelihood of rejection is well-established in solid organ transplantation recipients. In hematopoietic stem cell transplantation (HSCT), MPA AUC is also linked to graft versus host disease. This study aimed to develop a simplified method to estimate MPA AUC0-12 in Chinese patients undergoing allogeneic HSCT (allo-HSCT). Intensive sampling was conducted in 22 patients who were orally administered mycophenolate mofetil. Plasma concentrations of total MPA were measured, and a model predicting AUC0-12 using data from these 22 patients was constructed through regression analysis. The accuracy of the most suitable model was assessed in an additional 20 patients. None of the individual MPA concentrations showed a strong correlation with AUC0-12 (r2 < 0.7). Models utilizing 4 or more concentrations were found to effectively estimate MPA AUC0-12 (r2 > 0.87). The most operationally feasible model demonstrated good predictive performance with a mean absolute percentage error (APE%) < 20%. Single MPA concentrations showed poor correlation with MPA AUC0-12. A model utilizing 4 oral concentrations (0, 0.5, 1, and 4 h postdose) over a 12-h period could effectively estimate MPA AUC0-12 with precise results and minimal bias.

External Validation of a Limited Sampling Strategy for the Estimation of Mycophenolic Acid Exposure Between Different Assay Methods: PETINIA and HPLC Methods.

INTRODUCTION: A limited sampling strategy (LSS) for estimating the area under the plasma concentration-time curve (AUC0-12) of the immunosuppressant mycophenolic acid (MPA) is used for therapeutic drug monitoring (TDM) in clinical practice. Our study delves into the applicability of the MPA AUC0-12 LSS, originally developed using particle-enhanced turbidimetric inhibition immunoassay (PETINIA) measurements, to those obtained via high-performance liquid chromatography with ultraviolet detection (HPLC-UV). METHODS: We developed an LSS for estimating MPA AUC0-12 based on PETINIA measurements in 32 adult kidney transplant patients who were receiving mycophenolate mofetil. Validation of this strategy was conducted in an additional 14 adult kidney transplant patients (validation sets) through measurements obtained by both PETINIA and HPLC-UV. Predictive performance was assessed using mean absolute error (MAE), root mean squared error (RMSE), and "good guess" defined as predicted AUC within observed AUC ± 15%. RESULTS: The three time point equation (0, 2, and 6 h) emerged as optimal for estimating MPA AUC0-12, balancing predictive performance and usefulness in clinical settings. In validation sets, the coefficient of determination for observed versus predicted AUC0-12 was consistent between PETINIA (0.978) and HPLC-UV (0.958) measurements. Comparable MAE, RMSE, and "good guess" outcomes were observed for PETINIA (6.4%, 8.1%, and 85.7%, respectively) and HPLC-UV (7.6%, 9.4%, and 85.7%, respectively) measurements. CONCLUSION: Our findings support the application of the MPA AUC0-12 LSS, originally developed using PETINIA measurements, to those obtained via HPLC-UV.

An integrated sampling strategy for therapeutic mycophenolic acid monitoring in lung transplant recipients.

BACKGROUND: Mycophenolic Acid (MPA) is the most used anti-proliferative in lung transplantation, but its pharmacokinetic (PK) variability has precluded therapeutic drug monitoring. Both genetic and clinical factors have been implicated in MPA variability. This study aimed to integrate genetic and clinical factors with PK measurements to quantify MPA exposure. METHODS: We performed 12-hour pharmacokinetic analysis on 60 adult lung transplant recipients maintained on MPA for immunosuppression. We genotyped a SLCO1B3 polymorphisms previously associated MPA metabolism and collected relevant clinical data. We calculated area under the curve (AUC0-12) and performed univariate linear regression analysis to evaluate its association with genetic, clinical, and pharmacokinetic variables. We performed lasso regression analysis to create final AUC estimation tools. RESULTS: PK-only measurements obtained 2, 3, and 8 hours after MPA administration (C2, C3, and C8) were strongly associated with MPA AUC0-12 (R267%, 67% and 68% respectively). Clinical and genetic factors associated with MPA AUC0-12 included the MPA dose (p = 0.001), transplant diagnosis (p = 0.015), SLCO1B3 genotype (p = 0.049), and body surface area (p = 0.050). The best integrated single-sampling strategy included C2 and achieved an R2 value of 80%. The best integrated limited-sampling strategy included C0, C0.25, and C2 and achieved an R2 value of 90%. CONCLUSIONS: An integrated limited sampling strategy (LSS) for MPA allows increased accuracy in prediction of MPA AUC0-12 compared to PK-only modeling. Validation of this model will allow for clinically feasible MPA therapeutic drug monitoring and help advance precision management of MPA.

Pharmacokinetic-based Dosing Individualization of Mycophenolate Mofetil in Solid Organ Transplanted Patients.

Mycophenolate mofetil (MMF) is an immunosuppressant drug approved for prophylaxis of transplant rejection in patients undergoing solid organ transplantation and is further employed in management of various autoimmune disorders. MMF exhibits notable pharmacokinetic inter- and intraindividual variability necessitating tailored therapeutic approaches to achieve optimal therapeutic outcomes while mitigating risks of adverse effects. The objective of this review was to summarize factors that influence the pharmacokinetics of MMF and its active metabolite mycophenolic acid in order to deduce recommendations for personalized treatment strategies. Presumed predictors were analysed in relation to each of the four pharmacokinetic phases, providing tools and targets for MMF dosing optimization amenable to clinical implementation.

Model-informed dose optimization of mycophenolic acid in pediatric kidney transplant patients.

PURPOSE: We aimed to develop and evaluate a population PK model of mycophenolic acid (MPA) in pediatric kidney transplant patients to aid MPA dose optimization. METHODS: Data were collected from pediatric kidney transplant recipients from a Dutch academic hospital (Radboudumc, the Netherlands). Pharmacokinetic model-building and model-validation analyses were performed using NONMEM. Subsequently, we externally evaluated the final model using data from another academic hospital. The final model was used to develop an optimized dosing regimen. RESULTS: Thirty pediatric patients were included of whom 266 measured MPA plasma concentrations, including 20 full pharmacokinetic (PK) curves and 24 limited sampling curves, were available. A two-compartment model with a transition compartment for Erlang-type absorption best described the data. The final population PK parameter estimates were Ktr (1.48 h-1; 95% CI, 1.15-1.84), CL/F (16.0 L h-1; 95% CI, 10.3-20.4), Vc/F (24.9 L; 95% CI, 93.0-6.71E25), Vp/F (1590 L; 95% CI, 651-2994), and Q/F (36.2 L h-1; 95% CI, 9.63-74.7). The performance of the PK model in the external population was adequate. An optimized initial dose scheme based on bodyweight was developed. With the licensed initial dose, 35% of patients were predicted to achieve the target AUC, compared to 42% using the optimized scheme. CONCLUSION: We have successfully developed a pharmacokinetic model for MPA in pediatric renal transplant patients. The optimized dosing regimen is expected to result in better target attainment early in treatment. It can be used in combination with model-informed follow-up dosing to further individualize the dose when PK samples become available.

Structural basis for substrate flexibility of the O-methyltransferase MpaG' involved in mycophenolic acid biosynthesis.

MpaG' is an S-adenosyl-L-methionine (SAM)-dependent methyltransferase involved in the compartmentalized biosynthesis of mycophenolic acid (MPA), a first-line immunosuppressive drug for organ transplantations and autoimmune diseases. MpaG' catalyzes the 5-O-methylation of three precursors in MPA biosynthesis including demethylmycophenolic acid (DMMPA), 4-farnesyl-3,5-dihydroxy-6-methylphthalide (FDHMP), and an intermediate containing three fewer carbon atoms compared to FDHMP (FDHMP-3C) with different catalytic efficiencies. Here, we report the crystal structures of S-adenosyl-L-homocysteine (SAH)/DMMPA-bound MpaG', SAH/FDHMP-3C-bound MpaG', and SAH/FDHMP-bound MpaG' to understand the catalytic mechanism of MpaG' and structural basis for its substrate flexibility. Structural and biochemical analyses reveal that MpaG' utilizes the catalytic dyad H306-E362 to deprotonate the C5 hydroxyl group of the substrates for the following methylation. The three substrates with differently modified farnesyl moieties are well accommodated in a large semi-open substrate binding pocket with the orientation of their phthalide moiety almost identical. Based on the structure-directed mutagenesis, a single mutant MpaG'Q267A is engineered with significantly improved catalytic efficiency for all three substrates. This study expands the mechanistic understanding and the pocket engineering strategy for O-methyltransferases involved in fungal natural product biosynthesis. Our research also highlights the potential of O-methyltransferases to modify diverse substrates by protein design and engineering.

Treatment of moderate-to-severe canine atopic dermatitis with modified-release mycophenolate (OKV-1001): A pilot open-label, single-arm multicentric clinical trial.

BACKGROUND: Mycophenolate is an immunomodulating agent successfully used for the treatment of moderate-to-severe atopic dermatitis (AD) in people. Mycophenolate is an effective steroid-sparing treatment option for use in dogs with inflammatory skin diseases. OBJECTIVE: To evaluate whether once-daily modified-release mycophenolate (OKV-1001) is safe and effective for treating moderate-to-severe canine AD. ANIMALS: Client-owned atopic dogs (n = 9) were enrolled. MATERIALS AND METHODS: In an open-label multicentre pilot study, OKV-1001 (30 mg/kg every 24 h) was given orally for ≤84 days. Concomitant tapering doses of glucocorticoids were administered up to Day (D)28. Clinicians assessed Canine Atopic Dermatitis Extent and Severity Index, 4th iteration (CADESI-04) on D0, D14, D28, D56 and D84. Body weight and clinical pathological parameters were measured at baseline and at the end of the study. RESULTS: Treatment with OKV-1001 combined with glucocorticoids significantly reduced the severity of AD within two weeks in seven of nine (77.8%) dogs. The mean percentage change from baseline in the CADESI-04 score was 29% (p = 0.009) at D14 (n = 9), 39% (p = 0.008) at D28 (n = 9) and 49% (p = 0.03) at D56 (n = 7) at which point glucocorticoids had been withdrawn. In two dogs the improvement in CADESI-04 was 62% and 23% (respectively) on D84. No significant adverse events including clinical pathological findings were reported. CONCLUSIONS AND CLINICAL RELEVANCE: Modified-release mycophenolate (OKV-1001) may represent a promising alternative treatment option for dogs with moderate-to-severe AD. The safety and efficacy profile of OKV-1001 will need to be established in larger, placebo-controlled clinical trials.

Exposure to Mycophenolic Acid and Its Clinical Response in an Indian Pediatric Population with Nephrotic Syndrome.

Background: Children with nephrotic syndrome experience many side effects and frequent relapses when treated with steroids and other drugs. Mycophenolic acid (MPA) is one of the effective and least toxic drug for the treatment of nephrotic syndrome. This drug needs to be monitored for maximal efficacy and minimal toxicity. The therapeutic reference range for this drug is not established for the aforementioned patient population of Indian origin. Materials and Methods: In this observational study, children with nephrotic syndrome on mycophenolate mofetil were followed up for a minimum duration of three months. Following this, their clinical status (relapse/remission) was determined and the mycophenolate exposure was measured for over 12 hours. Results: A total of 34 participants were included, with 17 (50%) in relapse. Median MPA Area under the curve over 12 hours (AUC0-12h) (36.5 µg·h/ml) in the remission group differed significantly compared to that in the relapse group (17.2 µg·h/ml). Conclusion: Higher exposure to MPA AUC0-12h is associated with clinical remission of pediatric nephrotic syndrome.

Development of an HPLC method using relative molar sensitivity for the measurement of blood concentrations of nine pharmaceutical compounds.

We developed a reliable high-performance liquid chromatographic analysis method using a relative molar sensitivity (RMS) technique that does not require an authentic, identical reference analyte material to quantify blood serum carbamazepine, phenytoin, voriconazole, lamotrigine, meropenem, mycophenolic acid, linezolid, vancomycin, and caffeine levels for routine blood concentration measurements. Carbamazepine and caffeine were also used as non-analyte reference materials to calculate the RMS of each analyte. The RMS was calculated from the ratio of the slope of the calibration equation (analyte/non-analyte reference material), then used to quantify analytes in control serum samples spiked with carbamazepine, phenytoin, voriconazole, meropenem, mycophenolic acid, linezolid or vancomycin. In addition, the concentrations of these six drugs in control serum samples determined by the proposed RMS method agreed well with that obtained using a conventional method. The proposed RMS method is a promising tool for the clinical determination of nine drugs, given the accuracy, precision, and efficiency of quantifying these analytes.

Gut microbiota biotransformation of drug glucuronides leading to gastrointestinal toxicity: Therapeutic potential of bacterial ß-glucuronidase inhibition in mycophenolate-induced enteropathy.

AIMS: Drug-induced enteropathy is often associated with the therapeutic use of certain glucuronidated drugs. One such drug is mycophenolic acid (MPA), a well-established immunosuppressant of which gastrointestinal adverse effects are a major concern. The role of bacterial ß-glucuronidase (ß-G) from the gut microbiota in MPA-induced enteropathy has recently been discovered. Bacterial ß-G hydrolyzes MPAG, the glucuronide metabolite of MPA excreted in the bile, leading to the digestive accumulation of MPA that would favor in turn these adverse events. We therefore hypothesized that taming bacterial ß-G activity might reduce MPA digestive exposure and prevent its toxicity. MAIN METHODS: By using a multiscale approach, we evaluated the effect of increasing concentrations of MPA on intestinal epithelial cells (Caco-2 cell line) viability, proliferation, and migration. Then, we investigated the inhibitory properties of amoxapine, a previously described bacterial ß-G inhibitor, by using molecular dynamics simulations, and evaluated its efficiency in blocking MPAG hydrolysis in an Escherichia coli-based ß-G activity assay. The pharmacological effect of amoxapine was evaluated in a mouse model. KEY FINDINGS: We observed that MPA impairs intestinal epithelial cell homeostasis. Amoxapine efficiently blocks the hydrolysis of MPAG to MPA and significantly reduces digestive exposure to MPA in mice. As a result, administration of amoxapine in MPA-treated mice significantly attenuated gastrointestinal lesions. SIGNIFICANCE: Collectively, these results suggest that the digestive accumulation of MPA is involved in the pathophysiology of MPA-gastrointestinal adverse effects. This study provides a proof-of-concept of the therapeutic potential of bacterial ß-G inhibitors in glucuronidated drug-induced enteropathy.

Influence of genetic polymorphisms on pharmacokinetics and treatment response of mycophenolic acid: a scoping review.

This scoping review explores the impact of genetic polymorphisms on the pharmacokinetics and treatment responses of mycophenolic acid (MPA), an immunosuppressant. The study includes 83 articles from 1226 original studies, focusing on transplantation (n = 80) and autoimmune disorders (n = 3). Genetic variants in uridine 5'-diphospho-glucuronosyltransferase (UGT1A9, UGT1A8 and UGT2B7) and transmembrane transporters (ABCC2, SLCO1B1, SLCO1B3 and ABCB1) significantly affected MPA's pharmacokinetics and susceptibility to its adverse effect. Whereas variants in several genes including UGT1A9, UGT2B7, IMPDH1 and IMPDH2 have been associated with a higher risk of transplant rejection. However, there is a lack of studies on MPA's impact on autoimmune disorders and limited research on the Asian population. The findings underscore the need for further research on MPA's impact across different populations and diseases, particularly among other Asian ethnic groups, to advance personalized medicine in MPA therapy.

[Box: see text].

IMPDH Inhibition Decreases TERT Expression and Synergizes the Cytotoxic Effect of Chemotherapeutic Agents in Glioblastoma Cells.

IMP dehydrogenase (IMPDH) inhibition has emerged as a new target therapy for glioblastoma multiforme (GBM), which remains one of the most refractory tumors to date. TCGA analyses revealed distinct expression profiles of IMPDH isoenzymes in various subtypes of GBM and low-grade glioma (LGG). To dissect the mechanism(s) underlying the anti-tumor effect of IMPDH inhibition in adult GBM, we investigated how mycophenolic acid (MPA, an IMPDH inhibitor) treatment affected key oncogenic drivers in glioblastoma cells. Our results showed that MPA decreased the expression of telomerase reverse transcriptase (TERT) in both U87 and U251 cells, and the expression of O6-methylguanine-DNA methyltransferase (MGMT) in U251 cells. In support, MPA treatment reduced the amount of telomere repeats in U87 and U251 cells. TERT downregulation by MPA was associated with a significant decrease in c-Myc (a TERT transcription activator) in U87 but not U251 cells, and a dose-dependent increase in p53 and CCCTC-binding factor (CTCF) (TERT repressors) in both U87 and U251 cells. In U251 cells, MPA displayed strong cytotoxic synergy with BCNU and moderate synergy with irinotecan, oxaliplatin, paclitaxel, or temozolomide (TMZ). In U87 cells, MPA displayed strong cytotoxic synergy with all except TMZ, acting primarily through the apoptotic pathway. Our work expands the mechanistic potential of IMPDH inhibition to TERT/telomere regulation and reveals a synthetic lethality between MPA and anti-GBM drugs.

Live-cell analysis of IMPDH protein levels during yeast colony growth provides insights into the regulation of GTP synthesis.

The purine nucleotides ATP and GTP are made from the common precursor inosine monophosphate (IMP). Maintaining the correct balance of these nucleotides for optimal cell growth is controlled in part by the enzyme IMP dehydrogenase (IMPDH), which catalyzes the first dedicated step of GTP biosynthesis. The regulation of IMPDH mRNA and protein levels in the yeast S. cerevisiae grown in liquid culture has been studied in some detail, but regulation of IMPDH protein under conditions of cellular crowding on a solid substrate has not been examined. Here, we report real-time, live-cell analysis of the accumulation of the Imd2 isoform of IMPDH in yeast cells forming a monolayer colony in a microfluidic device over a 50-hour time course. We observe two distinct phases of increased Imd2 accumulation: a guanine-insensitive phase early in outgrowth and a guanine-sensitive phase later, when cells become crowded. We show that the IMPDH inhibitor mycophenolic acid enhances both phases of increase. Deletion of a transcription attenuator upstream of the mRNA start site that decreases Imd2 mRNA synthesis in the presence of high GTP increases the baseline level of Imd2 protein 10-fold and abolishes guanine-sensitive but not guanine-insensitive induction. Our results suggest that at least two mechanisms of yeast Imd2 regulation exist, the known GTP-dependent attenuation of RNA polymerase II elongation and a GTP concentration-independent pathway that may be controlled by cell growth state. Live-cell analysis of IMPDH protein levels in a growing yeast colony confirms a known mechanism of regulation and provides evidence for an additional mode of regulation. IMPORTANCE: This study used live-cell microscopy to track changes in the level of a key enzyme in GTP nucleotide biosynthesis, inosine monophosphate dehydrogenase (IMPDH), during growth of a brewers yeast colony over 2 days in a microfluidic device. The results show that feedback regulation via transcription attenuation allows cells to adapt to nutrient limitation in the crowded environs of a yeast colony. They also identify a novel mode of regulation of IMPDH level that is not driven by guanine nucleotide availability.

Therapeutic drug monitoring in kidney and liver transplantation: current advances and future directions.

INTRODUCTION: Immunosuppressive drugs (ISD) present a narrow therapeutic window and extremely high inter- and intra-individual pharmacokinetic variability, which complicates their use in solid organ transplant recipients. In order to find a narrow appropriate equilibrium for each patient with the aim of maintaining clinical efficacy and reducing the risk of adverse drug reactions, a complex both clinical and biological monitoring is required, in particular through the use of therapeutic drug monitoring (TDM). AREA COVERED: This review provides an overview of the available information on the relationship between exposure to immunosuppressive drugs and their efficacy and/or toxicity in kidney and liver transplantation. The aim of the review is to describe the pharmacodynamic/pharmacokinetic relationship that exists for immunosuppressive drugs, to summarize the studies that assess the value of TDM for these drugs in clinical practice, and to present the target and monitoring strategies aimed at optimizing patient immunosuppression, which could help to take a step forward in the field of solid organ transplant patient care. EXPERT OPINION: To improve the care of transplant patients, several TDM innovations can be pursued by investigators. Among these, the development of microsampling methods for TDM or the combination of pharmacodynamic biomarkers with ISD exposure measurements appear to be relevant strategies.

Optimal exposure of mycophenolic acid for induction therapy of childhood lupus nephritis patients: an observational cohort study.

OBJECTIVES: Mycophenolic acid (MPA) is recommended for lupus nephritis (LN) treatment, but with large inter-individual variability in pharmacokinetics (PK). The aim of this study is to reveal the relationship between MPA exposure and disease response and adverse drug reactions in pediatric LN patients. METHOD: This was a population-based observational cohort study. A total of 86 pediatric LN patients treated with mycophenolate mofetil (MMF) for induction therapy were enrolled. The area-under the concentration-time curve (AUC) was calculated using MPA concentrations according to a limited sampling strategy. Receiver operating characteristic analysis was performed to assess the MPA-AUC threshold values. The cumulative incidence of renal remission and inactive systemic lupus erythematosus (SLE) over time was evaluated by Kaplan-Meier's analysis. RESULTS: MPA-AUC was identified as an independent factor associated with renal remission and lupus activity at 6 and 12 months after MMF treatment, and the improved renal remission rates were correlated with higher MPA-AUC, with thresholds of 29.81 and 30.63 µg·h·mL-1 at 6 months and 12 months, respectively. Furthermore, the thresholds for maintaining the hypoactive state of LN were 30.96 and 31.19 µg·h·mL-1at 6 months and 12 months, respectively. Patients reaching target thresholds for MPA-AUC achieved renal response or stable disease earlier. In addition, the MPA-AUC threshold for decreasing MMF-related adverse reactions was 50.80 µg·h·mL-1. CONCLUSION: The initial and long-term treatments of pediatric LN patients with MMF should be individualized according to the MPA-AUC, and the recommended MPA exposure is 31.19-50.80 µg·h·mL-1.