Christos Papageorgiou

Calcineurin has a very tight-binding pocket for the side chain of residue 4 of cyclosporin

Abstract Derivatives of cyclosporin A (CsA) at position 4 were synthesised to probe the interaction of the CsA/CypA complex with calcineurin (CaN). Both lipophilic and hydrophilic substituents are detrimental for the immunosuppressive activity, indicating that CaN has a very “tight-binding pocket” for this region.

Design, synthesis, and binding affinity of a nonpeptide mimic of somatostatin

Abstract The tetrasubstituted xylofuranose 4 was synthesized as a potential nonpeptide mimic of somatostatin, based on conformational analysis of the endogenous ligand and molecular modelling studies. It displaced the radioligand [ 125 I-Tyr 3 ]-octreotide with an IC 50 of 23 μM. The tetrasubstituted xylose derivative 4 (Ic 50 =23μM) was synthesised as SRIF mimetic, based on conformational analysis of SRIF and molecular modelling studies.

A non-peptide ligand for the somatostatin receptor having a benzodiazepinone structure

Abstract The 1,3,4-trisubstituted-1,4-benzodiazepin-2-one 2 is a non-peptide mimic of somatostatin 1 . It displaces the radioligand [ 125 I-Tyr 3 ]-octreotide with an IC 50 of 7 μM.

Tolerability profile of sodium mycophenolate (ERL080) and mycophenolate mofetil with and without cyclosporine (Neoral) in the rat

Mycophenolic acid sodium salt (ERL080) is currently in Phase III clinical trials for the prophylaxis of kidney transplant rejection upon coadministration with Neoral (cyclosporin A microemulsion). To assess the relative side effect profile of ERL080 and MMF as drug substances in Lewis rats, a rat strain commonly used in transplantation experiments, a comparative 4-week tolerability study was performed. Escalating doses of ERL080 and MMF were administered orally at 10-30 mg/kg/d (i.e., doses within or above the immunosuppressive range in rats), either in single compound treatment or in combination with cyclosporine (CsA) at a daily oral dose of 7.5 mg/kg. The compounds were well tolerated as documented by body weight monitoring, hematologic parameters, and weight and histology of organs. Major abnormalities observed were a dose-dependent reduction in thymus weight associated with immunosuppression, in some cases villous atrophy in the jejunum, a reduction in white blood cell counts and lymphocyte counts (mean value in distinct treatment groups not exceeding 40-50%), a decrease in red blood cell counts and hemoglobin concentration (at maximum 25-30%), and an increase in platelet counts (in some groups up to doubling). At a given dose, these adverse effects were slightly more pronounced for MMF than for ERL080, and for groups under CsA coadministration compared to both compounds given alone. No significant potentiation effect of CsA on the changes induced by ERL080 or MMF was observed. Moreover, there were no new toxic entities evident upon CsA microemulsion coadministration.

Comparative efficacy of mycophenolate sodium (MPS) and mycophenolate mofetil (MMF) with and without cyclosporine in rat transplantation models.

BACKGROUND ERL is the enteric-coated sodium salt of mycophenolic acid, presently in clinical development. The drug substance mycophenolate sodium (MPS) was evaluated in rat transplantation models and compared with mycophenolate mofetil (MMF) for therapeutic window and synergy with cyclosporine (CsA). METHODS Allotransplantation was performed in the Dark Agouti-to-Lewis (DA-to-Lewis; kidney, heart, and aorta) and Brown Norway-to-Lewis (BN-to-Lewis; kidney) strain combinations, and hamster heart xenotransplantation was performed in athymic and euthymic Lewis rats. The compounds were administered daily orally, starting the day of transplantation. RESULTS In kidney and heart transplantation the minimal efficacious dose of CsA was 5.0 mg/kg/d. For MPS this dose was 10 mg/kg/d in BN-to-Lewis kidney transplantation, 20 mg/kg/d in DA-to-Lewis heart transplantation, and 10 mg/kg/d in hamster-to-athymic rat heart transplantation. At these doses the first signs of adverse effects were evident, indicating a narrow therapeutic window. No window was established for MMF in these models or for MPS in DA-to-Lewis kidney transplantation. There was no potential synergy between CsA and MPS or MMF regarding efficacy, but fewer side effects were noted in efficacious combinations, in particular for MPS. In aorta transplantation, MPS and MMF dose-dependently inhibited intima thickening. The combination of 20 mg/kg/d MPS and 10 mg/kg/d CsA gave long-term survival of hamster-to-rat xenografts. CONCLUSIONS Despite the overall comparable efficacy and narrow therapeutic window of MPS and MMF when given alone, MPS apparently is better tolerated than MMF in some of the transplant models. The combination of these agents with CsA allows fine-tuning between optimal immunosuppression and adverse side effects.

Side effects of brequinar and brequinar analogues, in combination with cyclosporine, in the rat

Brequinar is an immunosuppressant with the potential to be combined with cyclosporine in synergistic combination therapy. The drug tends to accumulate when given daily per os, and pharmacokinetic interaction with cyclosporine appears to enhance toxicity. Analogues with similar immunosuppressive activity have been identified at Du Pont Merck Pharmaceutical Co., that do not accumulate upon daily oral dosing in rats, and hence could have an improved potential in combination treatment with cyclosporine. We performed a toxicity study with brequinar and two brequinar analogues, administered orally once daily for 4 weeks, either alone or in combination with cyclosporine (Neoral, Novartis Pharma AG). In a first study relatively high doses were evaluated with cyclosporine at non-toxic doses of 5 and 10 mg/kg/d. The maximum tolerated dose of brequinar alone was estimated between 5 and 10 mg/kg/d; that of the analogues was estimated between 10 and 20 mg/kg/d, and above 20 mg/kg/d, respectively. In combination with cyclosporine at 5 and 10 mg/kg/d, approximately a 2-fold reduction in the maximum tolerated dose was observed. In a second study lower doses were evaluated in combination with cyclosporine at 2.5 and 5 mg/kg/d. Also this study revealed increased toxicity of brequinar (analogues) when given in combination with cyclosporine. The side effects observed were typical for drugs in the brequinar class and included leukocytopenia and thrombocytopenia, reduced body weight gain or body weight loss, thymic atrophy, cellular depletion of bone marrow and splenic white pulp, and villous atrophy in jejunum. Concentrations of brequinar (analogues) were determined in blood sampled 4 h after administration at day 1, 14 and 21-28 of the experiment. There was a tendency for drug accumulation in some groups treated with brequinar and cyclosporine. For one of the analogues at a low dose, higher concentrations were measured in groups treated with combinations of this compound and cyclosporine. We conclude that a potential synergism in immunosuppression using combinations of brequinar (analogues) and cyclosporine can be complicated by enhanced toxicity of the compounds. This indicates the need for a careful evaluation of the therapeutic window in a combined treatment together with detailed pharmacokinetics.

Cell permeability as a parameter for lead generation in the protein Tyrosine kinase inhibition field

Based on the inverse relationship between polar surface area and cell permeability and capitalizing on the properties of pyrrolopyrimidines 1 as protein tyrosine kinase inhibitors, pyrrolopyridones 2 were designed and synthesized as potential leads for the development of novel inhibitors with improved cell permeability properties.

Conformational control of cyclosporin through substitution of the N-5 position. A new class of cyclosporin antagonists

Cyclosporin A (CsA) can be regiospecifically alkylated at the NH of Val-5 with reactive bromides in the presence of phosphazene-base P4-t-Bu to yield derivatives 2-5. These are devoid of immunosuppressive activity in vitro but they have binding affinity for cyclophilin A (CypA) similar to that of CsA and thus represent a new class of cyclosporin antagonists. 1H NMR (DMSO-d6) studies have shown that the compounds exist in a single, all trans conformation. A comparison of this NMR data with X-ray crystallographic analysis of a CypA/CsA derivative complex demonstrates that the solution structure does not correspond to the bioactive conformation.

Isoxazolylthioamides as potential immunosuppressants a combinatorial chemistry approach

A library of thioamide derivatives of leflunomide 1a and of its bioactive metabolite 1b has been synthesised on solid phase. Thus, para-substituted phenylacetic acids were coupled to TentaGel and were subsequently reacted with aromatic isothiocyanates. Treatment of the resulting enaminothioamides with hydroxylamine led to their simultaneous cyclisation and cleavage from the resin affording 2-25. Their in vitro profiling demonstrated that the amide-thioamide isologous substitution was detrimental of the biological activity.

Mycophenolate sodium: tolerability and efficacy in transplantation in the rat

Inhibition of inosine monophosphate dehydrogenase by mycophenolate compounds results in potent immunosuppression, as demonstrated by the efficacy of the marketed prodrug mycophenolate mofetil (MMF) in clinical allotransplantation. Side effects are well-known and include bone marrow depression and gastrointestinal intolerability. Mycophenolate sodium (MPS) is in clinical development as an enteric-coated formulation to alleviate this gastrointestinal adverse effect. Accompanying this development, MPS and MMF were evaluated in a tolerability study in rats and in efficacy studies in rat allo- and xenotransplantation models. The compounds were given either singly or in combination with cyclosporine A and were efficacious in the prevention of allo- or xeno-graft rejection, but with a rather narrow window between optimal immunosuppression and adverse side effects. For instance, the minimal effective dose to prevent rejection of a kidney or heart allograft or a hamster heart xenograft is a daily dose of 10-20 mg/kg MPS, at which dose the first adverse side effects can be observed: the compound at 40 mg/kg is not tolerated. This window is even narrower for MMF than for MPS, and in most models, a minimal effective MMF dose could not be established. The window between optimal immunosuppression and adverse side effects is larger when the compounds are given in combination with cyclosporine A: in all models investigated combinations were established yielding long-term survival without histologic signs of rejection and without signs of side effects. Thus, the combination of an IMPDH inhibitor (MPS, MMF) and a calcineurin inhibitor (cyclosporine A) enables fine-tuning in achieving optimal immunosuppression avoiding drug side effects.