RS-61443--a phase I clinical trial and pilot rescue study

New immunosuppressive drugs: mechanistic insights and potential therapeutic advances

Together with CsA, the new macrolide immunosuppressants FK506 and rapamycin have proved to be valuable tools in providing new information about key molecular events that underlie lymphocyte activation and degranulation. Studies of their mechanisms of action have pinpointed the phosphatase calcineurin and protein kinases as important signaling mediators in T-cell activation. Other new immunosuppressive drugs, including leflunomide, mycophenolate mofetil, brequinar sodium and deoxyspergualin exhibit diverse inhibitory effects on cells of the immune system and offer considerable promise as adjunctive therapeutic immunosuppressants. FK506 appears to be both a valuable therapeutic alternative to liver or kidney retransplantation and an alternative primary immunosuppressant to CsA in hepatic (especially) and renal transplantation. There is now good evidence that immunosuppressive drugs, both old and new, permit the establishment of donor-derived, multi-lineage cell chimerism following organ transplantation.

Small elevations of glucose concentration redirect and amplify the synthesis of guanosine 5'-triphosphate in rat islets

Recent studies suggest a permissive requirement for guanosine 5'-triphosphate (GTP) in insulin release, based on the use of GTP synthesis inhibitors (such as myocophenolic acid) acting at inosine monophosphate (IMP) dehydrogenase; herein, we examine the glucose dependency of GTP synthesis. Mycophenolic acid inhibited insulin secretion equally well after islet culture at 7.8 or 11.1 mM glucose (51% inhibition) but its effect was dramatically attenuated when provided at < or = 6.4 mM glucose (13% inhibition; P < 0.001). These observations were explicable by a stimulation of islet GTP synthesis derived from IMP since, at high glucose: (a) total GTP content was augmented; (b) a greater decrement in GTP (1.75 vs. 1.05 pmol/islet) was induced by mycophenolic acid; and (c) a smaller "pool" of residual GTP persisted after drug treatment. Glucose also accelerated GTP synthesis from exogenous guanine ("salvage" pathway) and increased content of a pyrimidine, uridine 5'-triphosphate (UTP), suggesting that glucose augments production of a common regulatory intermediate (probably 5-phosphoribosyl-1-pyrophosphate). Pathway-specific radiolabeling studies confirmed that glucose tripled both salvage and de novo synthesis of nucleotides. We conclude that steep changes in the biosynthesis of cytosolic pools of GTP occur at modest changes in glucose concentrations, a finding which may have relevance to the adaptive (patho) physiologic responses of islets to changes in ambient glucose levels.

Effect of mycophenolate mofetil (RS-61443) on cytokine production: inhibition of superantigen-induced cytokines

The effects of the immunosuppressant mycophenolate mofetil (MPAM, RS-61443) on cytokine production at the single cell level were assessed using in vitro activated human mononuclear cells. Cytokine production was studied with UV microscopy of fixed and permeabilized cells stained with cytokine specific monoclonal antibodies (mAbs). The cytokines evaluated included interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10 interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), TNF-beta, and granulocyte macrophage-colony stimulating factor (GM-CSF). MPAM exhibited a marked antiproliferative effect without cytotoxicity in all mononuclear cell cultures. Six to 24 hours after stimulation with the superantigen Staphylococcus aureus enterotoxin A (SEA), most cytokine production was unaffected by MPAM at therapeutic concentrations (10(-6) M), with the exception of GM-CSF. In contrast, by 48 h after antigen activation, MPAM significantly inhibited all studied cytokine production (p < 0.05). Cyclosporin A (CsA), used as a control at a concentration of 100 ng/ml, inhibited production of all studied cytokines, at all time points. Monokine production after lipopolysaccharide (LPS) stimulation was unaffected by MPAM. Similarly, the production of most of the cytokines studied after mitogen stimulation with phorbol ester (PMA) plus calcium ionophore (ionomycin) was not affected by MPAM, in comparison to CsA which demonstrated significant inhibition of all cytokines tested under these conditions. However, a late inhibitory effect on IL-3 production was seen by MPAM at 48 h after mitogenic stimulation. Further observations are required to explain the divergent results on cytokine production by MPAM in superantigen-activated and mitogen-activated human mononuclear cells.

Experience with mycophenolate mofetil (RS61443) in renal transplantation at a single center

OBJECTIVE

Mycophenolate mofetil (MM) is a new immunosuppressive agent that reversibly inhibits guanine nucleotide synthesis and DNA replication. Its activity is highly selective for T and B lymphocytes. Two open-label multicenter trials of MM in renal transplantation have been performed. This report summarizes the results from one center involved in these two trials.

METHODS AND RESULTS

The initial trial of MM was an open-label dose-ranging trial in primary cadaveric renal transplantation. Mycophenolate mofetil was included in the maintenance immunosuppression regimen from the day after transplantation. Of the 21 patients enrolled in this trial, one (5%) was withdrawn for side effects. There was one graft loss due to recurrent renal disease and two patients were withdrawn for difficulty with follow-up. Mean follow-up is 26 months, and patient and graft survival at 2 years are 100 and 95% respectively. The second trial was designed to study the efficacy of mycophenolate in reversing refractory renal allograft rejection. Patients enrolled in the trial had biopsy-proven acute rejection and had previously received at least one course of high-dose corticosteroids and/or OKT3. Of the 26 patients enrolled in this trial, one (4%) was withdrawn for side effects. There were two deaths. Mean follow-up is 20 months, and patient and graft survival at 12 months was 91 and 54%. The incidence of infections in the two groups was 38% and there were no deaths in either group attributable to infection.

CONCLUSIONS

The results of these two studies indicate that mycophenolate mofetil could be administered safely to renal allograft recipients for periods up to 2 years. It appears to be effective in reversing acute rejection in a high percentage of patients refractory to other forms of therapy.

Inhibition of PHA induced mononuclear cell proliferation by FK506 in combination with cyclosporine, methylprednisolone, 6-mercaptopurine and mycophenolic acid

In vitro inhibition of human peripheral blood mononuclear cell (PBMC) proliferation by immunosuppressive drugs has been shown to correlate with clinical outcomes in kidney transplant patients. The aim of our study was to analyse the degree of variability of in vitro interactions of FK506 (FK) with combinations of cyclosporin A (CyA), methylprednisolone (MP), 6-mercaptopurine (6ME), and mycophenolic acid (MPA) using phytohaemagglutinin (PHA) stimulated PBMCs. Our hypotheses were: that a wide range of interindividual variation would be detected; and that certain combinations of drugs would have a synergistic inhibitory effect on PHA stimulated PBMCs. Cells were cultured in supplemented RPMI 1640 for 65 hours at 37 degrees C in humidified 5% CO2 - 95% air and proliferative responses measured by 3H-thymidine incorporation over a further 24 hours. Inhibition of PBMC proliferation was assessed over 10 FK concentrations ranging from 1 x 10(-8) to 10 micrograms/ml using both volunteer controls (n = 51) and dialysis patients (n = 23). A wide range of interindividual variability of FK inhibition occurred throughout the range of FK concentrations tested, becoming less variable at the higher concentrations. The interactions of FK with CyA, MP, 6ME and MPA were assessed using PBMCs from 12 volunteer controls. For FK at 1 x 10(-8) micrograms/ml; CyA, MP, 6ME and MPA were used at 0.01 microgram/ml. For FK at 1 x 10(-7) micrograms/ml; CyA, MP, 6ME and MPA were used at 0.1 microgram/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of combined administration of FK 506 and the purine biosynthesis inhibitors mizoribine or mycophenolic acid on lymphocyte DNA synthesis and T cell activation molecule expression in human mixed lymphocyte cultures

Our objective was to obtain new information on the in vitro antilymphocytic action of the cytokine synthesis inhibitor FK 506 and the purine biosynthesis inhibitors mycophenolic acid (MPA; the active moiety of RS61443) and mizoribine (MZB) when used alone or in combination. When added at the initiation of six-day human mixed lymphocyte cultures (MLC), FK 506, MPA or MZB exhibited dose-dependent inhibition of T-lymphocyte DNA synthesis. FK 506, however, was 100-fold more potent than MPA, and 10,000-fold more potent than MZB. Combination of FK 506 with either MPA or MZB, each at suboptional concentrations, produced no more than additive inhibitory effects on 3H thymidine incorporation. Two-colour flow cytometric analysis of lymphocytes revealed that none of the drugs affected cell surface activation molecule expression (CD25 = IL-2R 55 kD alpha-chain, HLA-DR or CD71 = transferrin receptor [TR]) on allostimulated CD4+ or CD8+ cells harvested at three days of culture. By day six, however, all three agents, at levels which markedly inhibited proliferation, suppressed the expression of activation markers on both CD4+ and CD8+ cells. Also at day six, inhibition of activation molecule expression on CD4+ cells was achieved with the combination of FK 506 and either MPA or MZB at concentrations which, on their own, were ineffective. These data provide new, additional information on the in vitro antilymphocytic action of FK 506, MPA and MZB when used alone and in combination.

Hepatic allograft rejection: new developments in terminology, diagnosis, prevention, and treatment

Hepatic allograft rejection remains a major cause of morbidity related to the need for increased immunosuppression and continues to be a principal cause of late failure of the graft. Hepatic allograft rejection is defined on the basis of morphologic findings; cellular rejection is defined as portal or periportal hepatitis with nonsuppurative cholangitis or endotheliitis (or both), and ductopenic rejection is defined as loss of interlobular and septal bile ducts, typically in at least 50% of the portal tracts. The overall incidence of episodes of cellular rejection, which usually occur within the first 2 weeks after liver transplantation, varies from 50 to 100%. Ductopenic rejection occurs in approximately 8% of patients who undergo initial liver transplantation and is usually diagnosed between 6 weeks and 6 months after transplantation. Induction and maintenance immunosuppression with triple-drug (cyclosporine, prednisone, and azathioprine) therapy and other combinations that include antilymphocyte preparations, however, has decreased the incidence of both cellular and ductopenic rejection. In patients experiencing episodes of cellular rejection, high-dose intravenously administered corticosteroid therapy yields the best response and is associated with a lower incidence of ductopenic rejection than is low-dose and orally administered corticosteroid therapy. The correlation between degree of biochemical liver dysfunction and presence of histologic rejection is minimal early after transplantation. Histologic severity of rejection, however, suggests which patients will require more immunosuppression and which patients may need antilymphocyte therapy for controlling the rejection episode. With the availability of new immunosuppressive agents, distinguishing patients at high risk for rejection is important. The goals for use of new immunosuppressive agents and regimens are to improve graft and patient survival, to decrease the incidence of cellular and ductopenic rejection, and to minimize side effects and complications.

RS-61443 (mycophenolate mofetil). A multicenter study for refractory kidney transplant rejection

RS-61443 (mycophenolate mofetil) inhibits a key enzyme of the de novo synthesis of purine nucleotides in T and B lymphocytes. The purpose of this study was to evaluate the efficacy of RS-61443 in patients with refractory renal allograft rejection. Patients eligible for the study had previously undergone anti-rejection therapy with high-dose steroids or OKT3 monoclonal antibody. All rejection episodes were proven by renal biopsy. Successful rescue was achieved in 52 (69%) patients. Rescue was more successful when patients were entered with a creatinine of 4 mg/dL or lower (79%), versus a 52% rescue rate in patients entered with a creatinine of 4 mg/dL or above. Major side effects were predominantly gastrointestinal, but there was no overt nephrotoxicity, hepatotoxicity, or bone marrow suppression. The overall infection rate was 40%, with the spectrum of infections characteristic for the highly immunocompromised patient. The conclude that this pilot study suggests that RS-61443 is effective in refractory kidney allograft rejection. Based on this study, prospectively randomized multi-center trails have been planned and are in progress.

Immunosuppressive therapy

Although Cyclosporin A has improved transplant outcome, its use has serious limitations due to its narrow therapeutic window. New approaches to broaden this window exploit alternative drug formulations, pharmacokinetic profiling and new immunosuppressive agents, such as Rapamycin and Brequinar, which act in a synergistic fashion. There is no evidence to suggest that the pharmacological alternative to Cyclosporin A, FK-506, displays a broader therapeutic window, although it may be tenfold more potent. Similarly, despite the specificity of the IgG2a mouse anti-human CD3 monoclonal antibody, it displays a significant range of clinical side effects, delayed therapeutic action and frequently stimulates generation of human anti-mouse monoclonal antibodies. Recent advances in monoclonal antibody technology seek not only to produce antibodies against determinants involved in alloactivation, but also to 'humanize' the antibodies for reduced side effects. The availability of this array of potential agents highlights the need to develop guidelines for clinical trial methodologies to address the unique needs and demands of organ transplantation.