Mycophenolate mofetil inhibits rat and human mesangial cell proliferation by guanosine depletion.
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BACKGROUND: Mycophenolate mofetil (MMF) is used for immunosuppression after renal transplantation because it reduces lymphocyte proliferation by inhibiting inosine monophosphate dehydrogenase (IMPDH) in lymphocytes and GTP biosynthesis. In the present study we asked if therapeutic concentrations of MMF might interfere with mesangial cell (MC) proliferation which is involved in inflammatory proliferative glomerular diseases. METHODS: Rat and human MCs were growth-arrested by withdrawal of fetal calf serum (FCS) and stimulated by addition of FCS, platelet-derived growth factor (PDGF) or lysophosphatidic acid (LPA). Different concentrations of MMF (0.019-10 microM) were added concomitantly in the presence or absence of guanosine. MC proliferation was determined by [3H]thymidine incorporation. Cell viability was assessed by trypan blue exclusion. Apoptotic nuclei were stained using the Hoechst dye H33258. Cytosolic free Ca2+ concentrations were determined with the fluorescent calcium chelator fura-2-AM. RESULTS: MMF inhibited mitogen-induced rat MC proliferation with an IC50 of 0.45 +/- 0.13 microM. Human MCs proved to be even more sensitive (IC50 0.19 +/- 0.06 microM). Inhibition of MC proliferation was reversible and not accompanied by cellular necrosis or apoptosis. Addition of guanosine prevented the antiproliferative effect of MMF, indicating that inhibition of IMPDH is responsible for decreased MC proliferation. Early signalling events of GTP-binding-protein-coupled receptors, such as changes in intracellular Ca2+ levels were not affected by MMF. CONCLUSIONS: The results show that MMF has a concentration-dependent antiproliferative effect on cultured MCs in the therapeutic range, which might be a rationale for the use of this drug in the treatment of mesangial proliferative glomerulonephritis. (+info)
Crystal structure of human type II inosine monophosphate dehydrogenase: implications for ligand binding and drug design.
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Inosine monophosphate dehydrogenase (IMPDH) controls a key metabolic step in the regulation of cell growth and differentiation. This step is the NAD-dependent oxidation of inosine 5' monophosphate (IMP) to xanthosine 5' monophosphate, the rate-limiting step in the synthesis of the guanine nucleotides. Two isoforms of IMPDH have been identified, one of which (type II) is significantly up- regulated in neoplastic and differentiating cells. As such, it has been identified as a major target in antitumor and immunosuppressive drug design. We present here the 2.9-A structure of a ternary complex of the human type II isoform of IMPDH. The complex contains the substrate analogue 6-chloropurine riboside 5'-monophosphate (6-Cl-IMP) and the NAD analogue selenazole-4-carboxamide adenine dinucleotide, the selenium derivative of the active metabolite of the antitumor drug tiazofurin. The enzyme forms a homotetramer, with the dinucleotide binding at the monomer-monomer interface. The 6 chloro-substituted purine base is dehalogenated, forming a covalent adduct at C6 with Cys-331. The dinucleotide selenazole base is stacked against the 6-Cl-IMP purine ring in an orientation consistent with the B-side stereochemistry of hydride transfer seen with NAD. The adenosine end of the ligand interacts with residues not conserved between the type I and type II isoforms, suggesting strategies for the design of isoform-specific agents. (+info)
Beneficial effect of the inosine monophosphate dehydrogenase inhibitor mycophenolate mofetil on survival and severity of glomerulonephritis in systemic lupus erythematosus (SLE)-prone MRLlpr/lpr mice.
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The aim of the present study was to evaluate the therapeutic effect of mycophenolate mofetil (MMF) on the course of disease in SLE-prone MRLlpr/lpr mice. Three-months-old mice displaying clinical symptoms of glomerulonephritis were given MMF (100 mg/kg per day) orally via the drinking water. Control mice received i.p. injections of cyclophosphamide (CYC) (1.8 mg/mouse per week) or saline. Survival, albuminuria and haematuria, immunoglobulin levels and anti-dsDNA antibodies in serum, frequencies of immunoglobulin-producing B lymphocytes and glomerular deposits of immunoglobulin and C3 were analysed. The results showed that MMF treatment significantly prolonged survival and reduced the occurrence of albuminuria and haematuria in MRLlpr/lpr mice. In addition, the number of immunoglobulin-producing B cells and serum levels of IgG and IgG anti-dsDNA antibodies were reduced after MMF and CYC treatment. MMF treatment significantly reduced the extent of deposition of C3 in glomeruli. We conclude that the reduced severity of glomerulonephritis following treatment of lupus-prone mice with MMF was as efficacious as that of CYC. These results warrant clinical trials of MMF in SLE patients with glomerulonephritis. (+info)
The apparent inhibition of inosine monophosphate dehydrogenase by mycophenolic acid glucuronide is attributable to the presence of trace quantities of mycophenolic acid.
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BACKGROUND: Mycophenolic acid glucuronide, the primary metabolite of the immunosuppressive agent mycophenolic acid, affords weak inhibition of proliferating and resting lymphocytes and recombinant human inosine monophosphate dehydrogenase in comparison to the active drug. We evaluated the hypothesis that mycophenolic acid is a trace contaminant of the glucuronide metabolite preparation and that this accounts for the observed effects of mycophenolic acid glucuronide on human inosine monophosphate dehydrogenase catalytic activity both in lymphocytes and the pure enzyme. METHODS: We used negative ion electrospray HPLC-mass spectrometry (HPLC-MS) and HPLC-tandem MS (HPLC-MS-MS) to identify mycophenolic acid as a contaminant of mycophenolic acid glucuronide. Quantification of the mycophenolic acid contaminant was achieved using a negative ion electrospray HPLC-MS method in the selected-ion monitoring mode. RESULTS: Trace amounts of mycophenolic acid were detected and definitively identified in the mycophenolic acid glucuronide preparation by the HPLC-MS-MS analysis. In addition to having identical HPLC retention times, pure mycophenolic acid and the contaminant produced the following major fragments upon HPLC-MS-MS analysis: deprotonated molecular ion, m/z 319; and fragment ions, m/z 275, 243, 205, and 191 (the most abundant fragment ion). Using the negative ion electrospray HPLC-MS procedure in the selected-ion monitoring mode, the quantity of the contaminant mycophenolic acid was determined to be 0.312% +/- 0.0184% on a molar basis. CONCLUSION: These data provide strong support for the proposal that the apparent inhibition of the target enzyme inosine monophosphate dehydrogenase by mycophenolic acid glucuronide is attributable to the presence of trace amounts of contaminant mycophenolic acid. (+info)
Benzamide riboside induces apoptosis independent of Cdc25A expression in human ovarian carcinoma N.1 cells.
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One of the mechanisms of action of a new oncolytic agent, benzamide riboside (BR) is by inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH) which catalyzes the formation of xanthine 5'-monophosphate from inosine 5'-monophosphate and nicotinamide adenine dinucleotide, thereby restricting the biosynthesis of guanylates. In the present study BR (10 - 20 microM) induced apoptosis in a human ovarian carcinoma N.1 cell line (a monoclonal derivative of its heterogenous parent line HOC-7). This was ascertained by DNA fragmentation, TUNEL assay, [poly(ADP)ribose polymerase]-cleavage and alteration in cell morphology. Apoptosis was accompanied by sustained c-Myc expression, concurrent down-regulation of cdc25A mRNA and protein, and by inhibition of Cdk2 activity. Both Cdk2 and cdc25A are G1 phase specific genes and Cdk2 is the target of Cdc25A. These studies demonstrate that BR exhibits dual mechanisms of action, first by inhibiting IMPDH, and second by inducing apoptosis, which is associated with repression of components of the cell cycle that are downstream of constitutive c-Myc expression. (+info)
The SHAPES strategy: an NMR-based approach for lead generation in drug discovery.
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BACKGROUND: Recently, it has been shown that nuclear magnetic resonance (NMR) may be used to identify ligands that bind to low molecular weight protein drug targets. Recognizing the utility of NMR as a very sensitive method for detecting binding, we have focused on developing alternative approaches that are applicable to larger molecular weight drug targets and do not require isotopic labeling. RESULTS: A new method for lead generation (SHAPES) is described that uses NMR to detect binding of a limited but diverse library of small molecules to a potential drug target. The compound scaffolds are derived from shapes most commonly found in known therapeutic agents. NMR detection of low (microM-mM) affinity binding is achieved using either differential line broadening or transferred NOE (nuclear Overhauser effect) NMR techniques. CONCLUSIONS: The SHAPES method for lead generation by NMR is useful for identifying potential lead classes of drugs early in a drug design program, and is easily integrated with other discovery tools such as virtual screening, high-throughput screening and combinatorial chemistry. (+info)
Theoretical studies of the conformational properties of ribavirin.
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One of the factors required for the antiviral activity of the synthetic nucleoside, ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), is the ability of the molecule to adopt the substrate conformation specified by the enzyme for which it is a competitive inhibitor, inosine 5'-phosphate dehydrogenase (IMP:NAD+ oxidoreductase, EC 1.2.1.14). The calculated glycosidic minimum for ribavirin is the high syn conformation, which is in agreement with experimental determinations of the molecule's solution conformation. The similarity in solution between the conformation of the active ribavirin molecule and the conformation of its inactive 5-methyl and 5-chloro derivatives indicate that some other substrate conformation is specified by the enzyme. The high anti conformation, found by these calculations to be close in energy to the high syn minimum, is postulated to be the active conformation required by the enzyme. The inactivity of the 5-methyl and 5-chloro derivatives is attributed to the much greater stability of these derivatives in the inactive high syn conformation. (+info)
Broad-spectrum antiviral activity of the IMP dehydrogenase inhibitor VX-497: a comparison with ribavirin and demonstration of antiviral additivity with alpha interferon.
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The enzyme IMP dehydrogenase (IMPDH) catalyzes an essential step in the de novo biosynthesis of guanine nucleotides, namely, the conversion of IMP to XMP. The major event occurring in cells exposed to competitive IMPDH inhibitors such as ribavirin or uncompetitive inhibitors such as mycophenolic acid (MPA) is a depletion of the intracellular GTP and dGTP pools. Ribavirin is approved as an inhaled antiviral agent for treatment of respiratory syncytial virus (RSV) infection and orally, in combination with alpha interferon (IFN-alpha), for the treatment of chronic hepatitis C virus (HCV) infection. VX-497 is a potent, reversible uncompetitive IMPDH inhibitor which is structurally unrelated to other known IMPDH inhibitors. Studies were performed to compare VX-497 and ribavirin in terms of their cytotoxicities and their efficacies against a variety of viruses. They included DNA viruses (hepatitis B virus [HBV], human cytomegalovirus [HCMV], and herpes simplex virus type 1 [HSV-1]) and RNA viruses (respiratory syncytial virus [RSV], parainfluenza-3 virus, bovine viral diarrhea virus, Venezuelan equine encephalomyelitis virus [VEEV], dengue virus, yellow fever virus, coxsackie B3 virus, encephalomyocarditis virus [EMCV], and influenza A virus). VX-497 was 17- to 186-fold more potent than ribavirin against HBV, HCMV, RSV, HSV-1, parainfluenza-3 virus, EMCV, and VEEV infections in cultured cells. The therapeutic index of VX-497 was significantly better than that of ribavirin for HBV and HCMV (14- and 39-fold, respectively). Finally, the antiviral effect of VX-497 in combination with IFN-alpha was compared to that of ribavirin with IFN-alpha in the EMCV replication system. Both VX-497 and ribavirin demonstrated additivity when coapplied with IFN-alpha, with VX-497 again being the more potent in this combination. These data are supportive of the hypothesis that VX-497, like ribavirin, is a broad-spectrum antiviral agent. (+info)