Human type I and II IMP dehydrogenases as drug targets

Successful Treatment of Systemic Sclerosis-related Pericarditis with Mycophenolate Mofetil and Low-dose Prednisolone

We herein report a case of systemic sclerosis (SSc)-related pericarditis successfully treated with mycophenolate mofetil (MMF) and low-dose prednisolone (PSL). The patient was a 72-year-old woman with anti-centromere antibody. Her clinical manifestations were Raynaud phenomenon, bilateral pleural effusion, pericardial effusion and skin tightness. Based on the findings of exudative pericardial effusion with the absence of pulmonary arterial hypertension from the results of the cardiac catheter and pericardiocentesis, she was diagnosed with SSc-related pericarditis and treated with PSL10 mg and MMF 1 g per day, leading to the complete resolution of pericarditis. These findings suggested that MMF and low-dose PSL were effective for SSc-related pericarditis.

Pharmacokinetics of mycophenolate mofetil following single-dose intravenous and single- and multiple-dose oral administration and clinicopathologic effects of mycophenolate mofetil following long-term oral administration in healthy horses

OBJECTIVE

To characterize the pharmacokinetics of mycophenolate mofetil (MMF) following single-dose IV or PO administration, characterize the pharmacokinetics of MMF following long-term PO administration, and describe the clinicopathologic effects of long-term MMF administration in horses.

ANIMALS

12 healthy adult horses.

PROCEDURES

In phase 1, 6 horses received a single IV (2.5 mg/kg) or PO (5 mg/kg) dose of MMF in a randomized balanced crossover assessment (≥ 2-week interval between administrations). In phase 2, 6 other horses received MMF for 60 days (5 mg/kg, PO, q 24 h for 30 days and then 5 mg/kg, PO, q 48 h for an additional 30 days).

RESULTS

Following IV (single-dose) or PO (single- or multiple-dose) administration, MMF was rapidly converted to mycophenolic acid. For single-dose PO administration, mean ± SD maximum plasma mycophenolic acid concentration was 1,778.3 ± 441.5 ng/mL at 0.71 ± 0.29 hours. For single-dose IV administration, mean systemic clearance and volume of distribution at steady state were 0.689 ± 0.194 L/h/kg and 1.57 ± 0.626 L/kg, respectively. Following single doses, mean terminal half-life was 3.99 ± 0.865 hours for IV administration and 4.02 ± 1.01 hours for PO administration. The accumulation index following long-term PO administration was 1.0 ± 0.002, and the terminal half-life was 4.59 ± 1.25 hours following the final dose on day 60. None of the horses developed abnormal clinical signs or had any consistently abnormal clinicopathologic findings.

CONCLUSIONS AND CLINICAL RELEVANCE

Further investigation of the clinical efficacy of long-term MMF treatment of horses with autoimmune diseases is warranted.

Treatment of exfoliative cutaneous lupus erythematosus in a German shorthaired pointer dog with mycophenolate mofetil

BACKGROUND

Immune-modulating drugs show limited therapeutic efficacy in canine exfoliative cutaneous lupus erythematosus (ECLE); over half of ECLE dogs are eventually euthanized for their lack of response to therapy.

OBJECTIVE

To describe a case of generalized ECLE in a dog in which mycophenolate mofetil (MMF) treatment achieved complete remission.

ANIMAL

A 3-year-old, male castrated German shorthaired pointer was presented with a three months history of generalized scaling, erythematous macules and plaques, follicular casts and hypotrichosis affecting the head, trunk, ventrum and medial aspects of all limbs. The dog exhibited lameness and stiff gait.

METHODS AND MATERIALS

Complete blood count, serum chemistry profile, urinalysis, serum antinuclear antibody test, histopathological examination and RT-qPCR of skin biopsies.

RESULTS

Histologically, skin biopsy specimens revealed lymphocyte-rich interface dermatitis, infundibular interface mural folliculitis and periglandular lymphocytic infiltrate. The absence of systemic signs and unremarkable laboratory tests excluded concurrent systemic lupus erythematosus. Treatment of ECLE was initiated with oral MMF (22 mg/kg, twice daily). Within three weeks of starting MMF therapy, a marked improvement in lameness and a moderate decrease in erythema and scaling was observed. After four months, erythema, scaling and follicular casts had completely resolved, and at the time of writing the dog's ECLE remains in complete remission with twice daily MMF (10 mg/kg). The lesional skin transcriptome revealed predominant T helper 1 (Th1) lymphocytic inflammatory response with strong upregulation of interferon pathway.

CONCLUSIONS AND CLINICAL IMPORTANCE

To the best of the authors' knowledge, this is the first reported case of successful treatment of ECLE with MMF as a single-agent therapy.

Pragmatic Treatment of Patients With Systemic Lupus Erythematosus With Rituximab: Long-Term Effects on Serum Immunoglobulins

Objective

B cell–depletion therapy based on rituximab is a therapeutic option for refractory disease in patients with systemic lupus erythematosus (SLE). The aim of this observational study was to document long‐term effects on B cell function by following serum immunoglobulin levels in patients with SLE treated with rituximab in routine clinical practice.

Methods

We included 57 consecutive patients with SLE treated with rituximab and concomitant/sequential immunosuppressants and measured serum total IgG, IgM, and IgA and IgG anti‐dsDNA antibodies, over a median of 48 months most recent followup. Flow cytometry was used prospectively to assess B cell phenotypes in 17 of 57 patients.

Results

Twelve patients (21%) had persistent IgM hypogammaglobulinemia (<0.4 gm/liter), and 4 of 57 (5%) had low IgG (<7 gm/liter) at the most recent followup (range 12–144 months). This was not associated with serious adverse events or high anti–double‐stranded DNA (anti‐dsDNA) antibodies (>1,000 IU/ml; normal <50 IU/ml). Factors predictive of low serum IgM included baseline serum IgM ≤0.8 gm/liter (receiver operator curve analysis) and subsequent therapy with mycophenolate mofetil (MMF; odds ratio 6.8, compared with other immunosuppressants). In patients maintaining normal IgM levels (9 of 17), the frequency of circulating IgD+CD27+ B cells was significantly higher (P = 0.05). At 12 months after rituximab, 7 of 30 SLE patients with baseline anti‐dsDNA ≤1,000 IU/ml had lost seropositivity.

Conclusion

Lower baseline serum IgM levels and sequential therapy with MMF were predictive of IgM hypogammaglobulinemia after rituximab in SLE, but this was not associated with higher levels of anti‐dsDNA antibodies or an increased risk of infections. This provides useful directions for clinicians regarding rituximab and sequential immunosuppressive treatment for patients with SLE.

High expression of IMPDH2 is associated with aggressive features and poor prognosis of primary nasopharyngeal carcinoma

Inosine monophosphate dehydrogenase type II (IMPDH2) has been shown to play critical roles in the development and progression of several human cancers. However, little is known about IMPDH2 expression and its clinical significance in nasopharyngeal carcinoma (NPC). Western blotting, qRT-PCR and immunohistochemistry were employed to evaluate IMPDH2 expression in NPC cell lines and tissues. In our study, elevated expression of IMPDH2 was observed at both the protein and mRNA levels in NPC cell lines than in NPEC2 Bmi-1. IMPDH2 protein expression was markedly higher in NPC tissues than in adjacent non-tumorous tissues. Moreover, IMPDH2 expression in NPC correlated with several clinicopathological parameters, including T classification (P = 0.023), TNM stage (P = 0.020), distant metastasis (P = 0.001) and death (P = 0.002). Further Cox regression analysis suggested that IMPDH2 expression was an independent prognostic factor for overall survival (P = 0.001) and disease-free survival (P < 0.001). In addition, stratified survival analysis showed that high expression of IMPDH2 could be a prognostic factor for NPC patients with TNM stage I/II (OS: P = 0.012; DMFS: P = 0.007), TNM stage III/IV (OS: P = 0.028; DMFS: P = 0.020). Our study demonstrates IMPDH2 may be served as an independent prognostic biomarker for NPC patients, in which high IMPDH expression suggests poor prognosis of NPC patients.

Pharmacological targeting of allergen-specific T lymphocytes

Allergic disorders are the result of a complex pathophysiology, involving major cellular lineages and a multitude of humoral factors of the innate and adaptive immune system, and have the tendency to involve multiple organs. Consequently, even standard pharmacological treatment of allergies is rarely specific but usually targets more than one pathway/cellular system at a time. Accordingly, many of the classic anti-allergic drugs have a critical impact also on T helper cells, which are pivotal not only during the sensitization but also the maintenance phase of allergic diseases. Recent years have seen a dramatic increase of novel drugs with the potency to interfere, more or less specifically, with T lymphocyte function, which might, possibly together with classic anti-allergic drugs, help harnessing one of the central cellular players in allergic responses. A major theme in the years to come will be a thoughtful combination of previously established with recently developed treatment modalities.

Future Immunosuppressive Agents in Solid-Organ Transplantation

Objective

To review the pharmacology, pharmacokinetics, efficacy, and safety of mycophenolate sodium, everolimus, and FTY720.

Study Selection and Data Extraction

Clinical trials and abstracts evaluating mycophenolate sodium, everolimus, and FTY720 in solid-organ transplantation were considered for evaluation. English-language studies and published abstracts were selected for inclusion.

Data Synthesis

Mycophenolate sodium has recently been approved by the Food and Drug Adminstration for marketing in the United States; everolimus and FTY720 are immunosuppressive agents that may soon be available in the United States. These agents have proven efficacy in reducing the incidence of acute rejection in solid-organ transplantation. Clinical trials have shown that these newer agents are relatively well tolerated. The most common adverse events associated with these agents were gastrointestinal and hematologic effects (mycophenolate sodium); hyperlipidemia, increased serum creatinine, and hematologic effects (everolimus); and gastrointestinal effects, headache, and bradycardia (FTY720).

Conclusion

Mycophenolate sodium has been approved in some European countries and the United States. Everolimus has been approved in some European countries and a new drug application has been submitted to the Food and Drug Administration. FTY720 is currently in phase III clinical trials and submission to the Food and Drug Administration for approval is a few years away. The approval of these agents will furnish the transplant practitioner with even more options for immunosuppression.

Enteric-Coated Mycophenolate Sodium

OBJECTIVE:

To review the pharmacology, pharmacokinetics, efficacy, and safety of mycophenolate sodium.

DATA SOURCES:

Primary literature was obtained via a MEDLINE search (1966–June 2003). Abstracts were obtained from the manufacturer and included in the analysis.

STUDY SELECTION AND DATA EXTRACTION:

All studies and abstracts evaluating mycophenolate sodium in solid organ transplantation were considered for inclusion. English-language studies and abstracts were selected for inclusion, but were limited to those consisting of human subjects.

DATA SYNTHESIS:

Mycophenolate sodium, a mycophenolic acid prodrug, is an inhibitor of T-lymphocyte proliferation. Mycophenolic acid reduces the incidence of acute rejection in renal transplantation. Mycophenolate sodium is enteric coated and has been suggested as a potential method to reduce the gastrointestinal adverse events seen with mycophenolate mofetil. Both mycophenolate mofetil and mycophenolate sodium have been shown to be therapeutically equivalent at decreasing the incidence of allograft rejection and loss. The frequency of adverse events is similar between both compounds, with the most common events being diarrhea and leukopenia.

CONCLUSIONS:

Mycophenolate sodium is effective in preventing acute rejection in renal transplant recipients. At doses of 720 mg twice daily, the efficacy and safety profiles are similar to those of mycophenolate mofetil 1000 mg twice daily. Mycophenolate sodium has been approved in Switzerland; approval in the US is pending.

In Vitro Influence of Mycophenolic Acid on Selected Parameters of Stimulated Peripheral Canine Lymphocytes

Mycophenolic acid (MPA) is an active metabolite of mycophenolate mofetil, a new immunosuppressive drug effective in the treatment of canine autoimmune diseases. The impact of MPA on immunity is ambiguous and its influence on the canine immune system is unknown. The aim of the study was to determine markers of changes in stimulated peripheral canine lymphocytes after treatment with MPA in vitro. Twenty nine healthy dogs were studied. Phenotypic and functional analysis of lymphocytes was performed on peripheral blood mononuclear cells cultured with mitogens and different MPA concentrations– 1 μM (10⁻³ mol/m³), 10 μM or 100 μM. Apoptotic cells were detected by Annexin V and 7-aminoactinomycin D (7-AAD). The expression of antigens (CD3, CD4, CD8, CD21, CD25, forkhead box P3 [FoxP3] and proliferating cell nuclear antigen [PCNA]) was assessed with monoclonal antibodies. The proliferation indices were analyzed in carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled cells. All analyses were performed using flow cytometry. The influence of MPA on apoptosis was dependent on the mechanism of cell activation and MPA concentration. MPA caused a decrease in the expression of lymphocyte surface antigens, CD3, CD8 and CD25. Its impact on the expression of CD4 and CD21 was negligible. Its negative influence on the expression of FoxP3 was dependent on cell stimulation. MPA inhibited lymphocyte proliferation. In conclusion, MPA inhibited the activity of stimulated canine lymphocytes by blocking lymphocyte activation and proliferation. The influence of MPA on the development of immune tolerance–expansion of Treg cells and lymphocyte apoptosis–was ambiguous and was dependent on the mechanism of cellular activation. The concentration that MPA reaches in the blood may lead to inhibition of the functions of the canine immune system. The applied panel of markers can be used for evaluation of the effects of immunosuppressive compounds in the dog.

From ribavirin to NAD analogues and back to ribavirin in search for anticancer agents

Ribavirin, a broad-spectrum antiviral agent is used in the clinic alone or in combination with other antivirals and/or interferons. Numerous structural analogues of ribavirin have been developed, among them tiazofurin, which is inactive against viruses but is a potent anticancer drug. Tiazofurin was found to inhibit nicotinamide adenine dinucleotide (NAD)-dependent inosine monophosphate dehydrogenase (IMPDH) after metabolic conversion into tiazofurin adenine dinucleotide (TAD), which binds well but could not serve as IMPDH cofactor. TAD showed high selectivity against human IMPDH vs. other cellular dehydrogenases. Mycophenolic acid (MPA) was even more specific, binding at the cofactor-binding domain of IMPDH. Ribavirin adenine dinucleotide, however, did not show any significant inhibition at the enzymatic level. We synthesized numerous NAD analogues in which natural nicotinamide riboside was replaced by tiazofurin, MPA moiety, or benzamide riboside, and the adenosine moiety as well as the pyrophosphate linker were broadly modified. Some of these compounds were found to be low nanomolar inhibitors of the enzyme and sub-micromolar inhibitors of cancer cell line proliferation. The best were as potent as tyrosine kinase inhibitor gleevec heralded as a ‘magic bullet’ against chronic myelogenous leukemia. In recent years, ribavirin was rediscovered as a potential anticancer agent against number of tumors including leukemia. It was clearly established that its antitumor activity is related to the inhibition of an oncogene, the eukaryotic translation initiation factor (eIF4E).

Osteoclast Differentiation Is Impaired in a Subgroup of SLE Patients and Correlates Inversely with Mycophenolate Mofetil Treatment

Osteoporosis can arise in systemic lupus erythematosus (SLE) patients secondary to medication and/or chronic inflammation. To analyze if patients with SLE have phenotypically-impaired osteoclastogenesis, we differentiated ex vivo monocytes from 72 SLE patients and 15 healthy individuals into osteoclasts followed by TRAP staining and counting. We identified a subgroup of SLE patients (45%) with a significantly impaired osteoclast differentiation, relative to the other SLE patients or healthy individuals (OR 11.2; 95% CI 1.4–89.9). A review of medication indicated that patients with osteoclast counts equal to healthy donors were significantly more likely to be treated with mycophenolate mofetil (MMF) compared to patients with impaired osteoclastogenesis. We analyzed expression of RANKL and the MMF target genes IMPDH1 and IMPDH2 in osteoclasts by qPCR, but detected no difference. Since MMF might influence interferon-α (IFNα) and -γ (IFNγ) we measured serum IFNα and IFNγ levels. Patients with very low osteoclast counts also had comparably higher IFNα serum levels than patients with normal osteoclast counts. We conclude that in vitro osteoclastogenesis is impaired in a subgroup of SLE patients. This correlates inversely with MMF treatment and high IFNα serum levels. Further observational study will be required to determine whether this translates into a clinically meaningful effect.

Successful Treatment of Lupus Cerebrovascular Disease with Mycophenolate Mofetil

We report a case of neuropsychiatric systemic lupus erythematosus successfully treated with mycophenolate mofetil (MMF). The patient was a 40-year-old female who maintained with 7 mg of prednisolone plus 100 mg of azathioprine (AZ) per day. According to transient ischemic attack that occurred repeatedly and an elevated level of interleukin-6 (IL-6) in spinal fluid, she was diagnosed as having neuropsychiatric systemic lupus erythematosus (NPSLE). Initial increase in doses of prednisolone and AZ to 20 mg and 150 mg per day, respectively, was ineffective. After switching from AZ to MMF, her symptoms of NPSLE completely resolved with marked improvement of the IL-6 level in her spinal fluid, suggesting that MMF was effective.

Descriptive retrospective comparative study between two brands of mycophenolate mofetil used in Uruguay: innovator versus generic (Suprimun)

BACKGROUND

According to our experience, survival of cadaveric renal graft in 5 years increased from 63% as of the introduction of cyclosporine to 73% after azathioprine was substituted with mycophenolate mofetil (MMF) in 1997. Until 2003, the innovator mycophenolate mofetil (IMMF) (Cellcept; Roche) was used. In 2003, Laboratorios Clausen introduced in Uruguay a generic MMF (GMMF) (Suprimun/Micoflavin/Myclausen; Laboratorios Clausen) with previous bioequivalence studies. Since then, every health care provider administers one of these types of MMF available on the market to its renal transplant (RT) patients.

METHODS

We compared the evolution of 2 groups of patients and their grafts, those treated with GMMF or with IMMF. This was a descriptive, retrospective, nonrandomized, comparative study that involved all transplant patients in a center from January 2005 to June 2010 from 2 different health care providers which administered GMMF or IMMF uninterruptedly. Patients were older than 18 years, underwent their first RT and received triple immunosuppressive regime with calcineurin inhibitor (CNI), corticoids, and MMF, and completed ≥6 months of post-RT evolution.

RESULTS

The GMMF group included 29 patients and the IMMF group 23. Patients from both groups had no significant differences (NS) regarding age, sex, diabetes, hepatitis C virus (HCV), recipient hypertension, donor type (living or cadaveric, sex, age, cause of death), or mismatch degree. There were no material differences regarding antibody induction, CNI type, day of diuresis, or function recovery percentage. Statistically different results were reported for time in dialysis (6.1 ± 0.7 y in IMMF vs 3.8 ± 0.5 y in GMMF) and cadaveric donor cold ischemia time (989 ± 205 min vs 851 ± 219 min, respectively). For IMMF and GMMF, respectively, clinical acute rejection was 40.9% and 31% and creatinine over 3, 6, 12, 24, 36, and 48 months, respectively, was (mg%): 1.65 ± 0.12, 1.66 ± 0.15, 1.43 ± 0.10, 1.44 ± 0.12, 1.49 ± 0.18, and 1.41 ± 0.17 and 1.50 ± 0.08, 1.41 ± 0.07, 1.63 ± 0.26, 1.31 ± 0.08, 1.26 ± 0.09, and 1.21 ± 0.10, with 22/28, 22/28, 22/28, 22/26, 19/20, 17/11, and 15/9 patients under follow-up (NS). Patient survival over 3, 6, 12, and 18 months, respectively, was 94%, 94%, 94%, and 94% and 96%, 96%, 96%, and 96%, and graft survival was 94%, 89%, 89%, and 89% and 96%, 93%, 93%, and 93% for IMMF and GMMF, respectively (NS). Dosing adjustment frequency and substitution with mycophenolate sodium was similar for both groups.

CONCLUSIONS

With the results of this preliminary study we can not reach any final conclusion regarding assistance practice. From both groups, which involved similar baseline variables except for time in dialysis and cold ischemia (both greater in IMMF), we could gather a similar graft and patient evolution. New prospective, randomized, double-blind studies involving an adequate number of patients will help to determine the efficacy of GMMF in renal transplantation.

Oxymatrine induces apoptosis in human cervical cancer cells through guanine nucleotide depletion

Oxymatrine is an alkaloid obtained primarily from Sophora roots and has been shown to show anticancer effects in various cancers. However, the cellular and molecular effects of this agent on cervical cancer have been poorly characterized. Here, we investigated the antitumor effect of oxymatrine on a human cervical cancer cell line (HeLa). Our results showed that application of oxymatrine significantly inhibited the cell growth and tumorigenesis in a dose-dependent manner and induced apoptosis through caspase-dependent pathways as determined using flow cytometry and TUNEL staining analysis. To define the proteins potentially related to the mechanisms of action, proteomic analysis was utilized to detect proteins altered by oxymatrine. As the downregulated gene, inosine monophosphate dehydrogenase type II (IMPDH2) was responsible for oxymatrine-induced mitochondrial-related apoptosis. Moreover, oxymatrine depleted intracellular guanosine 5'-triphosphate (GTP) levels by effective IMPDH inhibition. Functional analyses further showed that oxymatrine and tiazofurin, an inhibitor of IMPDH2, sensitized resistant HeLa/DDP cells to cisplatin. In addition, the expression of IMPDH2 in cervical cancer was significantly higher than that in the normal cervical epithelium. Taken together, these findings suggest that targeting of IMPDH2 by potential pharmacological inhibitors, oxymatrine in combination with chemotherapy, might be a promising means of overcoming chemoresistance in cervical cancer with high IMPDH2 expression, and may thus provide new insights into the mechanism of oxyamtrine-induced anticancer effects.

Variability of apoptosis and response in N1-S1 rodent hepatomas to benzamide riboside and correlation to early changes in water apparent diffusion coefficient and sodium MR imaging

PURPOSE

This pilot trial assesses variability of apoptosis and response 1 day after hepatic intraarterial (IA) benzamide riboside (BR) in rodent hepatomas and its correlation to water apparent diffusion coefficient (ADC) and single-quantum (SQ) and triple-quantum-filtered (TQF) sodium-23 ((23)Na) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Sprague-Dawley rats (n = 8) were inoculated with 10(6) N1-S1 cells. IA BR (20 mg/kg) was infused after 14 days. Animals were killed 1 day (n = 4) or 21 days (n = 4) after therapy. Imaging was performed 1 day before and after treatment. Volume was assessed over 2 weeks. Percentage apoptosis was counted from terminal deoxynucleotidyl transferase dUTP nick-end labeling-stained slides at 400×magnification. Kruskal-Wallis tests were used to compare apoptosis, and Wilcoxon signed-rank tests were used to compare MR signal intensity (SI).

RESULTS

Apoptosis was marginally greater in tumor than in nontumor (6.7% vs 1.3%; P = .08), varying from 2% to 10%. Before treatment, MR SI was greater in tumor than in nontumor (ADC, 1.18 vs 0.76 [P = .0078]; SQ, 1.20 vs 1.04 [P = .03]; TQF, 0.55 vs 0.34 [P = .03]). After treatment, tumors increased in volume (0.62 vs 0.33; P = .016) variably over 2 weeks. MR SI remained greater in tumor than in nontumor (ADC, 1.20 vs 0.77 [P = .0078]; SQ, 1.76 vs 1.15 [P = .016]; TQF, 0.84 vs 0.49 [P = .03]). SQ and TQF SI increased by 47% (P = .016) and 53% (P = .016) in tumors, whereas ADC did not change.

CONCLUSIONS

Apoptosis was marginal and varied from 2% to 10%. Water ADC, SQ, and TQF MR imaging distinguished tumor from nontumor. Changes in water ADC and sodium MR imaging correlated to apoptosis and volume in select cases, but additional animals are needed to validate this trend against tumor growth.

Evaluation of potential interactions between mycophenolic acid derivatives and proton pump inhibitors

OBJECTIVE

To evaluate the incidence of gastrointestinal (GI) complications in solid organ transplant (SOT) recipients, impact of the complications on transplant outcomes, and the potential interactions between mycophenolic acid (MPA) derivatives and proton pump inhibitors (PPIs).

DATA SOURCES

An unrestricted literature search (1980-January 2012) was performed with MEDLINE and EMBASE using the following key words: drug-drug interaction, enteric-coated mycophenolic acid, GI complications, mycophenolate mofetil, solid organ transplant, and proton pump inhibitor, including individual agents within the class. Abstracts from scientific meetings were also evaluated. Additionally, reference citations from identified publications were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Relevant English-language, original research articles and review articles were evaluated if they focused on any of the topics identified in the search or included substantial content addressing GI complications in SOT recipients or drug interactions.

DATA SYNTHESIS

GI complications are frequent among SOT recipients, with some studies showing prevalence rates as high as 70%. Transplant outcomes among renal transplant recipients are significantly impacted by GI complications, especially in patients requiring immunosuppressant dosage reductions or premature discontinuation. To this end, PPI use among patients receiving transplants is common. Recent data demonstrate that PPIs significantly reduce the overall exposure to MPA after oral administration of mycophenolate mofetil. Similar studies show this interaction does not exist between PPIs and enteric-coated mycophenolic acid (EC-MPA). Unfortunately, most of the available data evaluating this interaction are pharmacokinetic analyses that do not investigate the clinical impact of this interaction.

CONCLUSIONS

A significant interaction exists between PPIs and mycophenolate mofetil secondary to reduced dissolution of mycophenolate mofetil in higher pH environments. EC-MPA is not absorbed in the stomach; therefore, low intragastric acidity does not impact EC-MPA and bioavailability is maintained with this formulation during PPI coadministration. The clinical impact of this interaction is unknown, yet one can theorize that reduced exposure to MPA in SOT recipients can increase the risk of allograft rejection and/or failure.

Opportunistic infections in myasthenia gravis treated with mycophenolate mofetil

Mycophenolate mofetil (MMF) is used for immunosuppression in myasthenia gravis (MG). Although there are numerous data on associated infection and prophylaxis in transplant patients who are on MMF, data in MG remains lacking. We report two elderly seropositive MG patients who developed cytomegalovirus (CMV) enteritis and Epstein-Barr virus (EBV) encephalitis while on MMF for 5months and 1year, respectively. Chronic MMF therapy in MG patients may trigger life-threatening infections including CMV and EBV diseases, especially in the elderly. Similar to the practice in transplant patients, viral serology testing and appropriate prophylactic regimen with antiviral agents should be considered, particularly in older MG patients.

Tumor response and apoptosis of N1-S1 rodent hepatomas in response to intra-arterial and intravenous benzamide riboside

PURPOSE

Benzamide riboside (BR) induces tumor apoptosis in multiple cell lines and animals. This pilot study compares apoptosis and tumor response in rat hepatomas treated with hepatic arterial BR (IA) or intravenous (IV) BR.

METHODS

A total of 10(6) N1-S1 cells were placed in the left hepatic lobes of 15 Sprague-Dawley rats. After 2 weeks, BR (20 mg/kg) was infused IA (n=5) or IV (n=5). One animal in each group was excluded for technical factors, which prevented a full dose administration (1 IA and 1 IV). Five rats received saline (3 IA and 2 IV). Animals were killed after 3 weeks. Tumor volumes after IA and IV treatments were analyzed by Wilcoxon rank sum test. The percentage of tumor and normal liver apoptosis was counted by using 10 fields of TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling)-stained slides at 40× magnification. The percentage of apoptosis was compared between IV and IA administrations and with saline sham-treated rats by the Wilcoxon rank sum test.

RESULTS

Tumors were smaller after IA treatment, but this did not reach statistical significance (0.14 IA vs. 0.57 IV; P=0.138). There was much variability in percentage of apoptosis and no significant difference between IA and IV BR (44.49 vs. 1.52%; P=0.18); IA BR and saline (44.49 vs. 33.83%; P=0.66); or IV BR and saline (1.52 vs. 193%; P=0.18).

CONCLUSIONS

Although differences in tumor volumes did not reach statistical significance, there was a trend toward smaller tumors after IA BR than IV BR in this small pilot study. Comparisons of these treatment methods will require a larger sample size and repeat experimentation.

Overexpression of inosine 5'-monophosphate dehydrogenase type II mediates chemoresistance to human osteosarcoma cells

Background

Chemoresistance is the principal reason for poor survival and disease recurrence in osteosarcoma patients. Inosine 5′-monophosphate dehydrogenase type II (IMPDH2) encodes the rate-limiting enzyme in the de novo guanine nucleotide biosynthesis and has been linked to cell growth, differentiation, and malignant transformation. In a previous study we identified IMPDH2 as an independent prognostic factor and observed frequent IMPDH2 overexpression in osteosarcoma patients with poor response to chemotherapy. The aim of this study was to provide evidence for direct involvement of IMPDH2 in the development of chemoresistance.

Methodology/Principal Findings

Stable cell lines overexpressing IMPDH2 and IMPDH2 knock-down cells were generated using the osteosarcoma cell line Saos-2 as parental cell line. Chemosensitivity, proliferation, and the expression of apoptosis-related proteins were analyzed by flow cytometry, WST-1-assay, and western blot analysis. Overexpression of IMPDH2 in Saos-2 cells induced strong chemoresistance against cisplatin and methotrexate. The observed chemoresistance was mediated at least in part by increased expression of the anti-apoptotic proteins Bcl-2, Mcl-1, and XIAP, reduced activation of caspase-9, and, consequently, reduced cleavage of the caspase substrate PARP. Pharmacological inhibition of IMPDH induced a moderate reduction of cell viability and a strong decrease of cell proliferation, but no increase in chemosensitivity. However, chemoresistant IMPDH2-overexpressing cells could be resensitized by RNA interference-mediated downregulation of IMPDH2.

Conclusions

IMPDH2 is directly involved in the development of chemoresistance in osteosarcoma cells, suggesting that targeting of IMPDH2 by RNAi or more effective pharmacological inhibitors in combination with chemotherapy might be a promising means of overcoming chemoresistance in osteosarcomas with high IMPDH2 expression.

Triple molecular target approach to selective melanoma cytotoxicity

Phenylalanine-linked pyrrolo[1,2-a]benzimidazoles were successfully designed to target melanoma cells in vitro. Our design utilised three molecular targets: a phenylalanine pump, the reducing enzyme DT-diaphorase, and IMP dehydrogenase. We describe the synthesis of these compounds as well as the results of in vitro, in vivo, and QSAR studies.

Inosine monophosphate dehydrogenase messenger RNA expression is correlated to clinical outcomes in mycophenolate mofetil-treated kidney transplant patients, whereas inosine monophosphate dehydrogenase activity is not

Measurement of the pharmacodynamic biomarker inosine monophosphate dehydrogenase (IMPDH) activity in renal transplant recipients has been proposed to reflect the biological effect better than using pharmacokinetic parameters to monitor mycophenolate mofetil therapy. The IMPDH assays are however labor intensive and this complicates implementation into patient care. Quantification of IMPDH messenger RNA (mRNA) could form an attractive alternative. This study was designed to correlate IMPDH mRNA levels with IMPDH activity and clinical outcome in renal transplant recipients. From a cohort of 101 renal transplant patients, blood samples were drawn pre transplantation and at 4 times after transplantation. IMPDH activity, IMPDH type 1 and type 2 mRNA levels, and mycophenolic acid concentrations were measured and correlated to clinical outcomes. No correlation was found between IMPDH type 1 and type 2 mRNA levels and IMPDH activity in pre- and posttransplant samples. A significant increase in IMPDH mRNA levels was found between day 6 and day 140 after transplantation. IMPDH type 1 and type 2 mRNA levels before transplant showed a trend toward statistically significant higher levels in patients with an acute rejection (P = 0.052 and P = 0.058). After transplant, the IMPDH type 1 and type 2 mRNA levels were significantly lower in patients with an acute rejection (P = 0.026 and P = 0.007). We conclude that IMPDH mRNA levels do not correlate with IMPDH activity but are nevertheless correlated with acute rejections. Furthermore, although the regulation of the expression of the 2 isoforms is presumed to be different, in this study, the changes in the expression of type 1 mRNA closely paralleled those of type 2.

Interpatient variability in IMPDH activity in MMF-treated renal transplant patients is correlated with IMPDH type II 3757T > C polymorphism

OBJECTIVES

The active metabolite of mycophenolate mofetil (MMF), mycophenolic acid, inhibits the activity of the target enzyme inosine monophosphate dehydrogenase (IMPDH). The aim of this study was to correlate eight different single nucleotide polymorphisms of the IMPDH type II gene to the activity of the IMPDH enzyme to explain between-patient differences in IMPDH activity.

METHODS AND RESULTS

In a prospective study, we measured IMPDH activity, mycophenolic acid plasma concentrations, and eight polymorphisms of IMPDH type II in de novo kidney transplant recipients, 6 days posttransplantation while on MMF treatment. Polymorphisms in the IMPDH type II gene were only observed for the IMPDH type II 3757T > C (rs11706052) single nucleotide polymorphism. Ten of 101 patients (10%) were heterozygous and two of 101 patients (2%) homozygous for IMPDH type II 3757T > C. The allele frequency was 6.9%. The IMPDH activity over 12 h (AUC(act)) was 49% higher for patients with an IMPDH type II 3757C variant [n = 12 vs. n = 68; 336 (95% confidence interval: 216-521) vs. 227 (95% confidence interval: 198-260) hmicromol/s/mol adenosine monophosphate; P = 0.04]. The IMPDH activity measured before transplantation (Act(pre-Tx)) was not significantly different between IMPDH type II 3757TT wild-type and variant carrier patients (P = 0.99).

CONCLUSION

We report that the IMPDH type II 3757T > C polymorphism is associated with an increased IMPDH activity in MMF-treated renal transplant patients. This polymorphism explains 8.0% of the interpatient variability in IMPDH activity.

Interpopulation variation frequency of human inosine 5'-monophosphate dehydrogenase type II (IMPDH2) genetic polymorphisms

Inosine monophosphate dehydrogenase type II (IMPDH2) is the target for immunosuppression by mycophenolic acid and has been linked to resistance of tumor cells to chemotherapy. Determining the frequency of IMPDH2 genetic polymorphisms can inform the design of clinical studies investigating the impact of IMPDH2 genetic variability on both cancer therapy and immunosuppression. Frequencies of three IMPDH2 polymorphisms (rs4974081, rs5848860, and rs11557540) in >400 DNA samples from four different racial/ethnic groups (Caucasian, African American, Hispanic, and Asian populations) were characterized by the pyrosequencing genotyping method. For rs5848860 1591 CTT/- (500 G/EG) and rs11557540 1345 A/G (418 D/G), we did not observe any variant alleles in all DNA samples from these populations, which suggests that these variants could simply be sequencing errors rather than real polymorphisms. The observed frequency of the 5'-upstream single-nucleotide polymorphism (SNP) rs4974081 A/G was similar to that previously reported in the NCBI databank (dbSNP). An in silico functional analysis using FASTSNP predicts that this promoter SNP rs4974081 (-3624 A/G) could be a potential transcription factor binding site. This finding suggests that rs4974081 could be a good candidate SNP for association studies with immunosuppressive and chemotherapeutic therapy outcomes.

Expression of inosine monophosphate dehydrogenase type I and type II after mycophenolate mofetil treatment: a 2-year follow-up in kidney transplantation

The objective of the study was to evaluate the effect of mycophenolate mofetil (MMF) on the regulation of inosine monophosphate dehydrogenase (IMPDH) during the first 2 years after renal transplantation. Twelve patients were enrolled, and 10-h time-course evaluations of the effects of MMF were regularly performed during the study. IMPDH activity and gene expression were measured in whole blood and in mononuclear cells, respectively. Type I IMPDH (IMPDH-I) mRNA was increased during the first 3 months following transplantation and reached its maximal level during acute rejection episodes, whereas type II IMPDH mRNA was stable. Furthermore, although no alteration in the predose samples was observed, patients with prolonged MMF treatment exhibited an increase in the induction potency of both IMPDH activity and gene expression. In vitro experiments confirmed that IMPDH-I is inducible, but preferentially in monocytes than in lymphocytes. This finding suggests that the measurement of IMPDH mRNAs may provide reliable information to predict acute rejection.

IMPDH activity in thiopurine-treated patients with inflammatory bowel disease - relation to TPMT activity and metabolite concentrations

AIMS

Azathioprine and 6-mercaptopurine are steroid-sparing drugs used in inflammatory bowel disease (IBD). The polymorphic enzyme thiopurine S-methyltransferase (TPMT) is of importance for thiopurine metabolism and occurrence of adverse events. The role of other thiopurine-metabolizing enzymes is less well known. This study investigated the role of inosine-5'-monophosphate dehydrogenase (IMPDH), which is a key enzyme in the de novo synthesis of guanine nucleotides and also strategically positioned in the metabolic pathway of thiopurines.

METHODS

IMPDH was measured in 100 healthy blood donors. IMPDH, TPMT and metabolite concentrations were studied in 50 patients with IBD on stable thiopurine therapy. IMPDH activity was measured in peripheral blood mononuclear cells. TPMT activity, 6-methylthioinosine 5'-monophosphate (meTIMP) and 6-thioguanine nucleotide (6-TGN) concentrations were measured in red blood cells, which is the current practice in clinical monitoring of thiopurines. Enzyme activities were related to metabolite concentrations and clinical characteristics.

RESULTS

A wide range of IMPDH activity was observed both in healthy blood donors (median 13.1, range 4.7-24.2 nmol mg(-1) protein h(-1)) and IBD patients (median 14.0, range 7.0-21.7). There was a negative correlation between IMPDH activity and dose-normalized meTIMP concentrations (r(s) = -0.31, P = 0.03), but no evident correlation to 6-TGN concentration or the meTIMP/6-TGN ratio. There were no significant correlations between TPMT activity and metabolite concentrations.

CONCLUSION

Even though the meTIMP concentrations correlated inversely to the IMPDH activity, the role of IMPDH in balancing the formation of methylated and phosphorylated metabolites was not evident. Taken together, the results give cause to question established opinions about thiopurine metabolism.

Mycophenolate mofetil in organ transplantation: focus on metabolism, safety and tolerability

Mycophenolate mofetil (MMF) received its first approval for the prevention of renal allograft rejection in 1995 and has now become the most frequently used antiproliferative agent in maintenance immunosuppressive therapy for kidney, pancreas, liver and heart transplantation. In addition, its use for the treatment of autoimmune diseases steadily increases. This review focuses on the miscellaneous pharmacodynamic properties of the drug, its pharmacokinetics in healthy subjects, recipients of different organ transplants and combination therapy with other pharmaceuticals, as well as its safety profile. The immunosuppressive activity of MMF is thought to derive mainly from the potent and selective inhibition of purine synthesis in both T and B lymphocytes. In contrast to other immunosuppressants on the market, it is metabolised primarily by glucuronidation and lacks nephrotoxicity, cardiovascular toxicity or diabetogenic potential, thus making it a suitable candidate for combination regimens. The most important side effects under MMF include gastrointestinal disorders, of which the underlying mechanisms are not yet fully understood, but seem to be complex and related to both effects of mycophenolic acid and its acyl glucuronide, as well as to decreased -immunity due to general immunosuppression after transplantation.

Mycophenolate mofetil (Cellcept)

Mycophenolate mofetil (MMF) is a new immunosuppressive drug designed to inhibit inosine monophosphate dehydrogenase (IMPDH). IMPDH is a key enzyme in the purine synthesis pathway of lymphocytes. IMPDH is crucially important for the proliferative responses of human T- and B-lymphocytes. Therefore, inhibition of IMPDH leads to selective lymphocyte suppression. Following successful testing in different in vitro and animal models, MMF entered clinical trials, where it has been used in combination with cyclosporin and steroids. MMF has rapid and complete absorption following oral administration. Pilot studies suggested a significant reduction in the incidence of rejection at doses of 1-3 g/day. These data led to the initiation of 3 pivotal trials, in which MMF was compared against different standard immunosuppressive protocols. Nearly 1500 patients were enrolled in these 3 randomised, double-blind, multicentre studies of the addition of MMF to standard immunosuppressive protocols for the prevention of acute renal allograft rejection. After six months, the rate of biopsy-proven rejection was significantly reduced. The adverse event profile resembles that of triple therapy with azathioprine: primarily involving the gastrointestinal (GI) tract, the haematopoietic system and the occurrence of opportunistic infections. MMF affords improved immunosuppressive therapy following renal, and probably other solid organ, transplantation. It is licensed for the prevention of acute renal allograft rejection in most countries around the world.

Future immunosuppressive agents in solid-organ transplantation

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of mycophenolate sodium, everolimus, and FTY720.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials and abstracts evaluating mycophenolate sodium, everolimus, and FTY720 in solid-organ transplantation were considered for evaluation. English-language studies and published abstracts were selected for inclusion.

DATA SYNTHESIS

Mycophenolate sodium has recently been approved by the Food and Drug Adminstration for marketing in the United States; everolimus and FTY720 are immunosuppressive agents that may soon be available in the United States. These agents have proven efficacy in reducing the incidence of acute rejection in solid-organ transplantation. Clinical trials have shown that these newer agents are relatively well tolerated. The most common adverse events associated with these agents were gastrointestinal and hematologic effects (mycophenolate sodium); hyperlipidemia, increased serum creatinine, and hematologic effects (everolimus): and gastrointestinal effects, headache, and bradycardia (FTY720).

CONCLUSION

Mycophenolate sodium has been approved in some European countries and the United States. Everolimus has been approved in some European countries and a new drug application has been submitted to the Food and Drug Administration. FTY720 is currently in phase III clinical trials and submission to the Food and Drug Administration for approval is a few years away. The approval of these agents will furnish the transplant practitioner with even more options for immunosuppression.

Mycophenolate mofetil in solid-organ transplantation

This review focuses on the use of mycophenolate mofetil (MMF) as an immunosuppressive agent in solid-organ transplantation. MMF, a non-competitive inhibitor of inosine monophosphate dehydrogenase, blocks de novo purine synthesis in T and B lymphocytes, resulting in the selective inhibition of proliferation of these cells in response to antigenic stimuli. MMF may also promote apoptosis of these cells. The immunosuppressive ability of MMF is thought to derive mainly from the inhibition of inosine monophosphate dehydrogenase. The other effects of MMF include suppression of antibody synthesis by B lymphocytes, inhibition of proliferation of smooth muscle cells in culture and impaired glycosylation of adhesion molecules. MMF may exhibit anti-inflammatory effects resulting from decreased activity of the inducible form of nitric oxide synthase, a consequence of depletion of tetrahydrobiopterin, which leads to decreased generation of peroxynitrite, a pro-inflammatory molecule. The pharmacokinetics, pharmacodynamics and principles underlying therapeutic drug monitoring of MMF are reviewed. The results of the pivotal clinical trials of MMF in kidney and heart transplantation are discussed and a summary of the major studies demonstrating a positive effect of MMF on renal transplantation outcomes is presented. The use of MMF in the context of ABO-incompatible renal transplantation, renal transplantation in highly sensitised and cross-match positive recipients, humoral rejection of renal allografts, chronic allograft nephropathy and steroid/calcineurin inhibitor minimisation in renal transplantation are also discussed.

Mycophenolate mofetil inhibits differentiation, maturation and allostimulatory function of human monocyte-derived dendritic cells

We have studied the effect of mycophenolate mofetil (MMF), a new drug used in prevention of transplant rejection, on differentiation, maturation and allostimulatory activity of human monocyte-derived dendritic cells (MDDC). MDDC were generated in vitro with granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin (IL)-4 in the presence or absence of MMF. MMF reduced the number of immature MDDC in culture, dose-dependently, by inducing apoptosis and inhibited their stimulatory activity on allogeneic lymphocytes. These changes correlated with down-regulation of co-stimulatory and adhesion molecules such as CD40, CD54, CD80 and CD86. No differences were observed in mannose receptor (MR)-mediated endocytosis, measured by the uptake of fluorescein isothiocyanate (FITC)-dextran. MDDC differentiated in the presence of MMF showed significantly reduced maturation upon stimulation with lipopolysaccharide, as judged by lower expresson of CD83 and co-stimulatory molecules, lower production of tumour necrosis factor (TNF)-alpha, IL-10, IL-12 and IL-18 as well as lower stimulation of alloreactive T cells including naive CD4+ CD45RA+ T cells. In contrast, MDDC matured in the presence of MMF showed a more marked decrease in the FITC-dextran uptake than mature MDDC cultivated without MMF and the phenomenon correlated with down-regulation of the MR expression. These results suggest that MMF impairs differentiation, maturation and function of human MDDC in vitro, which is an additional mechanism of its immunosuppressive effect.

T cell immunostimulation by methyl inosine 5'-monophosphate: application to infectious diseases

Methyl inosine 5'-monophosphate (MIMP) was designed and synthesized in an endeavor to generate compounds with immunostimulatory activity based on the precedent of purines, particularly inosine playing a central role in the development and function of the immune system. This review will summarize the immune-enhancing effects of MIMP on a variety of immunological responses both in vitro and in vivo. Among these studies, MIMP displays protective effects in several in vivo models of infectious disease following administration by one of several routes including oral. Furthermore, MIMP enhanced responses to Hepatitis B and influenza vaccines. Vaccination represents an extremely powerful tool for combating a variety of diseases, perhaps even cancer. However, to date, vaccines have been limited by their inability to produce cell-mediated responses and by the low immunogenicity of soluble/subunit antigens. In addition, there are difficulties in eliciting sufficient responses in immunocompromised individuals, which includes the elderly, due to the natural immunosenescence that occurs with aging. The data described here suggest that MIMP could be used to overcome some of these limitations. The application of MIMP as an adjuvant to the influenza vaccine, focusing on the elderly, at-risk populations will be discussed in more detail; however, several other bacterial and viral vaccine and/or disease targets merit further consideration.

Cytotoxicity and cellular differentiation activity of methylenebis(phosphonate) analogs of tiazofurin and mycophenolic acid adenine dinucleotide in human cancer cell lines

Mycophenolic acid (MPA) is a fungally-derived inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH). MPA binds IMPDH at the nicotinamide sub-site of the NAD cofactor binding domain leaving the adenosine sub-site empty. In order to improve the binding affinity we synthesized MPA analogs by linking adenosine 5'-methylenebis(phosphonate) with mycophenolic alcohols containing 2-, 4-, and 6-carbon atoms in their aliphatic side chain. Adenine dinucleotide analogs of tiazofurin, selenazofurin and benzamide riboside were synthesized as P1, P2-disubstituted pyrophosphates. Cytotoxicity of each analog was examined in human colon adenocarcinoma HT-29 and erythroleukemia K562 cells, and induction of differentiation in K562 cells by these agents was determined. Mycophenolic acid is currently used as an immunosuppressant but its anticancer action is limited by inactivation due to rapid glucuronidation. The new analogs show resistance to metabolism to inactive species and exhibit enhanced cytotoxicity in tumor cell lines, and therefore could be useful as anticancer agents.

How pharmacokinetic and pharmacodynamic drug monitoring can improve outcome in solid organ transplant recipients

Within the field of solid organ transplantation there is an unprecedented interest in therapeutic drug monitoring of immunosuppressive drugs. Ideally therapeutic drug monitoring should cost-effectively lead to improved efficacy of the drug and to a reduction in side effects. Therapeutic drug monitoring will be most effective if there is a large interpatient variability and a small intrapatient variability. Therapeutic drug monitoring in transplantation is largely based on correlations between drug concentrations and toxicity or between drug concentrations and efficacy. Pharmacodynamic monitoring of immunosuppressive drugs has not reached the stage of widespread clinical application. In part this is caused by the fact that most of the pharmacodynamic assays are time-consuming, costly and in some cases only give a result after several days of incubation. Another reason for the limited interest in pharmacodynamic monitoring is the lack of data showing improved outcome if dose adjustment is based on pharmacodynamics rather than pharmacokinetics. On the other hand, such data are also lacking for pharmacokinetic monitoring. Prospective investigations on the contribution of therapeutic drug monitoring may result in further improvement of the safety and efficacy of our immunosuppressive regimens and more refined methods for therapeutic drug monitoring. There is no contest between pharmacokinetic and pharmacodynamic monitoring. Most likely the results of both ways of monitoring will be complementary.

Adverse gastrointestinal effects of mycophenolate mofetil: aetiology, incidence and management

Mycophenolate mofetil (MMF) is a relatively new immunosuppressive drug. It inhibits inosine monophosphate dehydrogenase, a key enzyme in the de novo pathway of purine synthesis, and thus causes lymphocyte-selective immunosuppression. Large clinical trials have revealed the efficacy of MMF in the prevention of allograft rejection when administered together with cyclosporin or tacrolimus and corticosteroids. Although the adverse effect profile of MMF is comparatively benign, gastrointestinal adverse effects are a major concern. These effects are partially explained by the increased immune suppression, by the mode of action and by interactions, particularly with other immunosuppressants. The aetiology of the rarest gastrointestinal adverse effects is still not completely clear. Therapy depends upon the clinical gravity of the adverse effects and is therefore a case of waiting and ob- serving. An adjustment of dosage of immunosuppressants according to the clinical situation and, particularly in the case of MMF, spreading the total dosage over more than 2 daily doses are often sufficient. Should adverse effects persist for a longer period of time and be of a more serious nature, a comprehensive invasive diagnostic process is necessary, including endoscopy and biopsy and the search for opportunistic infections. In this case, dosage reduction or the complete withdrawal of MMF seems to be unavoidable. Severe gastrointestinal complications with MMF are rare, but when they do occur they may require extensive diagnosis and treatment. In the future, therapeutic drug monitoring and, where necessary, pharmacological modifications of MMF could lead to a further reduction of adverse effects with an equal or even increased efficacy.

Specific inhibition of type II inosine monophosphate dehydrogenase activity of Tmolt4 T cell human leukaemia cells by 3-methoxy and di-benzohydroxamic acids, maleic hydrazide and malonic acids

Small-molecular-weight benzohydroxamic and malonic acids and maleic hydrazide proved to be potent inhibitors of the activity of human Tmolt4 leukaemia Type II IMP (inosine monophosphate) dehydrogenase (IMPDH) activity. They were competitive inhibitors with respect to IMPDH demonstrating Ki values in the range 2.57-41.3 microM, less than half the values of the IC50 (microM) for the inhibition of Type II IMPDH. The IC50 microM values positively correlated with the ability of each compound to inhibit crude IMPDH activity, de-novo purine and DNA syntheses and growth of the T leukaemia cell line. Compounds were not inhibitors of Type I IMPDH. Type I IMPDH predominates in normal resting cells compared with Type II which is found in rapidly proliferating cells. Discovery of agents which would selectivity target IMPDH found in proliferating cells should eliminate any antineoplastic therapeutic toxic effects in normal cells of the body.

Mycophenolate mofetil: suggested guidelines for use in kidney transplantation

Mycophenolate mofetil (MMF) is an immunosuppressive drug designed to inhibit inosine monophosphate dehydrogenase (IMPDH). IMPDH is a key enzyme in the de novo purine synthesis of lymphocytes. It is crucially important for proliferative responses of human T and B lymphocytes. The inhibition of IMPDH thus leads to selective lymphocyte suppression. After successful use in various in vitro and animal models, MMF was brought to clinical trial in patients undergoing transplantation. The drug is rapidly and completely absorbed following oral administration. Pilot studies of administration with cyclosporin and corticosteroids suggested a significant reduction in the incidence of organ rejection at dosages of 1 to 3 g/day. As a result of these studies, 3 pivotal randomised double-blind multicentre trials, involving nearly 1500 patients, were designed to investigate the effects of addition of MMF to different standard immunosuppressive protocols on the prevention of acute renal allograft rejection. After 6 months, the rates of biopsy-proven rejection were significantly reduced in patients receiving MMF. In combination with cyclosporin and corticosteroids, the adverse effect profile resembled that of azathioprine. Most adverse effects were associated with the gastrointestinal tract, the blood system and opportunistic infections. MMF offers improved immunosuppressive therapy following renal and probably other solid organ transplantation. MMF has been licensed since 1995 for the prevention of acute renal allograft rejection in most countries. It has been used in different combinations of immunosuppressive drugs and in various dosages and regimens.

Treatment of systemic lupus erythematosus with mycophenolate mofetil

Mycophenolate mofetil is an immunosuppressive drug that is of established efficacy in renal transplantation. It inhibits the de novo pathway of purine synthesis and therefore lymphocyte proliferation. Mycophenylate mofetil has been shown to ameliorate the severity of renal injury in murine models of lupus nephritis. Recent studies suggest that it may also be effective in the treatment of patients with lupus nephritis when used in conjunction with steroids. These observations need to be confirmed in adequately sized randomised-controlled studies.

Targeting of human Tmolt4 leukemic type II IMP dehydrogenase by cyclic imide related derivatives

2,3-Dihydrophthalazine-1,4-diones, indazolones, 3-imino-1-oxoisodolines, homophthalimides, napthalidimides, diphenamides, and 6,7-dihydro-5H-dibenz[c,e]azepines proved to be potent inhibitors of the activity of human Tmolt4 T cell leukemia Type II IMP dehydrogenase (IMPDH). This inhibition was competitive, yielding Ki values in the range of 1.96 to 48.9 microM. The inhibition of Type II IMPDH correlated positively with the inhibition of the growth of Tmolt4 cells, the syntheses of DNA and purine, and the activity of crude IMPDH. The Type II IMPDH isoform is found in rapidly proliferating cells. The isoform present in normal resting cells, Type I IMPDH, was elevated by the compounds at 100 microM. In addition, Compound 5 significantly increased the Type I enzyme activity in a concentration and time dependent manner. The selectivity of these derivatives towards Type II IMPDH will allow for the separation of cellular effects, which should reduce clinical toxicity when treating with antimetabolite IMPDH inhibitors.

Tmolt4 leukemic type II isoform of IMP dehydrogenase as a target for 1,2,4-triazolidine-3,5-diones, 1-(1-(3-methylphenyl)ethylidineamino)-4,4-diethyl-3,5-azetidinediones, 3,5-isoxazolidinediones, and 4,4-disubstituted-3,5-pyrazolidinediones

The 1,2,4-triazolidine-3,5-diones, 1-(1-(3-methylphenyl)ethylidineamino)-4,4-diethyl-3,5-azetidinediones, and 4,4-disubstituted-3,5-pyrazolidinediones proved to be potent competitive inhibitors of human Tmolt4 leukemia Type II IMP dehydrogenase [IMPDH] activity, an enzyme isoform which is induced in highly proliferating cells. On the other hand, the 3,5-isoxazolidinediones were shown to be uncompetitive inhibitors of Type II IMPDH activity. The correlation between inhibition of Type II IMPDH activity with the agents' ability to suppress DNA and purine syntheses in these Tmolt4 leukemia cell was positive. Type I IMPDH (i.e., the isoform that is present in normal cells) was not inhibited by these compounds suggesting that these agents would be less toxic to normal cells and have selective inhibition towards proliferating cells.

The structure of inosine 5'-monophosphate dehydrogenase and the design of novel inhibitors

The enzyme IMPDH is a homotetramer of approximately 55 kDa subunits and consists of a (beta/alpha)(8) barrel core domain and a smaller subdomain. The active site has binding pockets for the two substrates IMP and NAD. The enzymatic reaction of oxidation of IMP to XMP proceeds through a covalent mechanism involving an active site cysteine residue. This enzyme is a target for immunosuppressive agents because it catalyzes a key step in purine nucleotide biosynthesis which is important for the proliferation of lymphocytes. Several X-ray structures of inhibitors bound to IMPDH have been published. The uncompetitive IMPDH inhibitor MPA is the active metabolite of the immunosuppressive agent mycophenolate mofetil (CellCept(R)) which is approved for the prevention of acute rejection after kidney and heart transplantation. The bicyclic ring system of MPA packs underneath the hypoxanthine ring of XMP*, thereby trapping this covalent intermediate of the enzymatic reaction. Ribavirin monophosphate, the active metabolite of the antiviral agent ribavirin, is a substrate mimic of IMP. The structure of the two inhibitors 6-Cl-IMP and SAD binding in the IMP and NAD pockets of IMPDH, respectively, gives information for the binding mode of the di-nucleotide cofactor to the enzyme. At Vertex Pharmaceuticals a structure-based drug design program for the design of IMPDH inhibitors was initiated. Several new lead compound classes unrelated to other IMPDH inhibitors were found. Integrating structural information into an iterative drug-design process led to the design of VX-497. VX-497 is a potent uncompetitive enzyme inhibitor of IMPDH. The phenyl-oxazole moiety of the molecule packs underneath XMP*, analogous to MPA. VX-497 also makes several new interactions that are not observed in the binding of MPA. VX-497 is a potent immunosuppressive agent in vitro and in vivo. A Phase I clinical trial has been successfully concluded and the compound is currently in Phase II trials in psoriasis and hepatitis C. The rapid progress from initiation of the drug design program to a compound entering clinical trials illustrates the power of structure-based drug design to accelerate the drug discovery process. The structural information on IMPDH has also significantly increased our knowledge about the mechanistic details of this fascinating enzyme.

The use of mycophenolate mofetil in transplant recipients

With the development of new immunosuppressive agents, the focus of anti-rejection therapy has shifted from prevention of acute allograft rejection to an emphasis on sufficient immunosuppression with minimal toxicity. Mycophenolate mofetil (MMF) is a recently developed immunosuppressive drug, which acts to inhibit T and B cell proliferation by blocking the production of guanosine nucleotides required for DNA synthesis. It also prevents the glycosylation of adhesion molecules that are involved in attachment of lymphocytes to endothelium and potentially in leukocyte infiltration of an allograft during an immune response. High-quality randomized clinical trials have demonstrated that MMF, when used with cyclosporine (CsA) and steroids, reduces the frequency and severity of acute rejection episodes in kidney and heart transplants, improves patient and graft survival in heart allograft recipients and increases renal allograft survival at 3 years. It has also been effective in reversing acute and resistant rejection episodes in heart, kidney and liver recipients. The ability of MMF to facilitate sparing of other immunosuppressive agents, particularly in CsA-related nephrotoxicity, is also promising. By permitting reduction in CsA doses, MMF may stabilize or improve renal graft function in patients with CsA-related nephrotoxicity or chronic allograft nephropathy. Early results of phase I and II trials evaluating MMF therapy in liver and combined pancreas/kidney transplant recipients are encouraging. The main adverse effects associated with oral or intravenous MMF are gastrointestinal and hematologic in nature. Although the direct costs of using MMF vs. azathioprine (AZA) are higher, the decreased incidence and treatment of acute rejection in patients treated with MMF supports its use as a cost-effective option during the first year following transplantation.Thus, MMF has become an important therapeutic tool in the transplant clinician's armamentarium. Ongoing issues to be resolved in clinical trials include the role of MMF in the absence of other potent agents, e.g., as monotherapy or with a steroid but without calcineurin inhibitor; whether MMF will have an impact on chronic allograft dysfunction; and the cost-effectiveness of treatment following the first year of transplantation.