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

Unexpected augmentation of mycophenolic acid pharmacokinetics in renal transplant patients receiving tacrolimus and mycophenolate mofetil in combination therapy, and analogous in vitro findings

Mycophenolate mofetil (MMF) a potent immunosuppressive agent, has recently been approved for clinical use (CellCept) in renal transplant patients in combination with cyclosporine (CsA). With the expanded use of tacrolimus (Prograf) as well in renal transplant patients, there is a lack of pharmacokinetic studies clarifying drug interactions between the three agents. A pharmacokinetic study was performed on 18 stable renal transplant patients receiving MMF and tacrolimus together, and four control groups, one receiving tacrolimus alone, two receiving CsA, in combination with MMF (1.0 or 1.5 g bid), and one receiving CsA microemulsion (Neoral). Area-under-the-curve values were calculated for each drug to assess if there was a reciprocal effect on the respective bioavailability of each. In vitro, the immunosuppressive effect of trough level plasma from each patient group was studied using mixed lymphocyte culture (MLC), as well as MLC reactions spiked with various combinations of each drug. There was a minimal effect of MMF on tacrolimus pharmacokinetics. However, patients receiving tacrolimus and MMF displayed significantly higher levels (Cmin and area under the curve) of mycophenolic acid (MPA) than those receiving CsA (Sandimmune or Neoral) and the same dose of MMF (50.2 +/- 16.5 vs 32.1 +/- 16.7 micrograms h/ml AUC, p < 0.02). Equivalent MPA levels could be attained in patients receiving CsA if the MMF dose was increased by 50% (1.5 g bid). There were also significantly lower levels of the glucuronide metabolite of MPA (MPAG) (755 +/- 280 vs 1230 +/- 250 micrograms h/ml AUC, p = 0.02), suggesting a specific inhibition (either direct or indirect) of the conversion of MPA to MPAG in tacrolimus patients, as opposed to those receiving CsA. For each drug combination, there was a positive correlation between the plasma immunosuppressive effect seen in MLC assays and the MMF dose. In addition, trough plasma from patients receiving tacrolimus and MMF was significantly more MLC inhibitory than from those receiving CsA or CsA microemulsion and equivalent-dose MMF. Culture media containing MPA and tacrolimus equal to clinical therapeutic trough concentrations (10 ng/ml) were significantly more MLC inhibitory than CsA at equivalent clinical therapeutic trough concentrations (200 ng/ml) with equivalent MPA levels. These studies in renal transplant patients suggest that tacrolimus in combination with MMF may result in a greater degree of immunosuppression than may be anticipated.

Suppression of acute experimental allergic encephalomyelitis in Lewis rats with a mycophenolic acid derivative

Oral administration of ethyl O-[N-(p-carboxyphenyl-carbamoyl]-mycophenolate (CAM), a derivative of mycophenolic acid (MPA) and an inosine monophosphate dehydrogenase inhibitor, dose-dependently suppressed acute experimental allergic encephalomyelitis in Lewis rats without exerting any serious adverse effects. A daily dose of 50 mg/kg of CAM almost completely abolished both the clinical disease and the inflammation in the CNS. In the CAM-treated rats, a weight loss and fluctuations of peripheral lymphocyte subsets were minimized. The CAM treatment was effective when started at the time of sensitization but ineffective when deferred till day 10. Furthermore, CAM reduced the percentage of CD4+CD45RC- cells in the peripheral blood. The only detectable adverse effect was moderate anemia but it was rapidly improved after withdrawal of the drug. This drug could be a useful adjunct for the long-term immunosuppressive therapy for inflammatory diseases of the CNS.

Review of immunosuppression for lung transplantation. Novel drugs, new uses for conventional immunosuppressants, and alternative strategies

The history, pharmacokinetics, mechanisms of action, and experimental as well as clinical data on the immunosuppressive potential of the novel drugs tacrolimus (FK506), sirolimus (rapamycin), mycophenolic acid (mycophenolate mofetil), and leflunomide (and its malononitriloamide analogues) are provided. Novel approaches with the following conventional immunosuppressants are outlined: methotrexate, aerosolized immunosuppression and the implementation of steroid taper. Total lymphoid irradiation and photopheresis for treatment of recurrent rejection are also discussed.

Prophylaxis post-transplant. The role of monitoring surveillance bronchoscopy and antimicrobials

One of the key areas of successful organ transplantation is the prompt recognition and treatment of problems that otherwise can progress rapidly, leading to morbidity and mortality. Surveillance and prophylaxis are essential in the field of transplant medicine.

Mycophenolate mofetil limits renal damage and prolongs life in murine lupus autoimmune disease

Classical immunosuppressants like cyclophosphamide give excellent results in human lupus nephritis. However, they augment malignancies and viral infections. Here we investigated the effect of the new immunosuppressant agent, mycophenolate mofetil (MMF), in New Zealand Black x New Zealand White (NZBxW) F1 hybrid mice, a model of genetically determined immune complex disease that mimics systemic lupus in humans. MMF has a selective antiproliferative effect on T- and B-lymphocytes, inhibits antibody formation and blocks the glycosylation of lymphocyte glycoproteins involved in the adhesion of leukocytes to endothelial cells. Two groups of NZBxW mice were used: group 1 (N = 20) given daily MMF (60 mg/kg p.o.) and group 2 (N = 15) given daily vehicle alone. Treatment started at three months of age and lasted until the death of the animals. Results showed that percentage of proteinuric mice was significantly reduced by MMF treatment and serum BUN levels were also lower than vehicle. MMF had a suppressive effect on autoantibody production and protected animals from leukopenia and anemia. Life survival of MMF treated lupus mice was significantly improved in respect to untreated animals. Thus, MMF delayed renal function deterioration and prolonged life survival in murine lupus nephritis. MMF has been already recognized as reasonably well tolerated in renal transplant patients and despite its gastrointestinal toxicity its overall safety profile appears superior to azathioprine. Human studies are needed to establish whether MMF may function as a steroid-sparing drug in lupus nephritis.

Pharmacokinetic studies of mycophenolate mofetil in rat kidney allograft recipients

BACKGROUND

A pharmacokinetic estimation of the immunosuppressive activity of mycophenolate mofetil (MPM) was performed in rats with transplanted kidney allografts.

METHODS

Kidney allografts from Brown Norway rats were transplanted into Lewis rats using a microsurgical technique. MPM, at doses of 5, 10, 15 and 25 mg/kg/day, was administered orally every day after transplantation. Pharmacokinetic studies were performed on days 7 and 14, and thereafter every 2 weeks.

RESULTS

After the administration of MPM, the plasma concentration of mycophenolic acid (MPA) increased rapidly, peaking at 15 to 30 minutes, and then decreased biexponentially. The peak concentration of MPA and the area under the plasma MPA concentration versus time curves (AUC) significantly correlated with the dosage. MPM administration at 5 and 10 mg/kg/day significantly prolonged the graft survival time from 7.1 days to 18.5 days and 85.0 days, respectively. The AUC values on day 7 after transplantation were 32.7 micrograms.h/mL and 38.6 micrograms.h/mL in rats receiving 5 and 10 mg/kg/day, respectively. However, in rats receiving 15 mg/kg/day of MPM or more, the AUC value at 7 days was 78.8 micrograms.h/mL, and almost all of these rats died from gastrointestinal toxicity.

CONCLUSION

MPM monotherapy significantly prolonged rat kidney allograft survival, however, high dosages of MPM caused gastrointestinal toxicity. AUC measurements of the MPA concentration are suitable for the pharmacokinetic monitoring of MPM.

Pharmacodynamic monitoring of mycophenolic acid in rabbit heterotopic heart transplant model

Pharmacodynamic (PD) monitoring of immunosuppressive drugs provides a novel approach to optimization of drug therapy in transplant recipients. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. A comparison of the relationship between PD versus drug level monitoring was performed using a heterotopic cardiac transplant in New Zealand white rabbits. The animals were divided into four different treatment groups. Control animals were administered the drug vehicle, the treatment groups were administered mycophenolate mofetil (MMF) at doses of 40, 80, and 160 mg/kg/day. Statistically significant (p < 0.05) prolongation of graft survival was obtained at the 160 mg/kg/day dose group. The mean MPA concentration at this dose was approximately 2.5 mg/l, suggesting that this concentration may provide adequate immunosuppression. An increase in IMPDH activity appeared a few days prior to rejection, suggesting that measurement of enzyme activity may have potential for use as a marker of graft rejection. A significant (p < 0.05) relationship exists between MPA concentration and graft survival and the former with dose of MMF. There was a negative correlation (p = 0.17) between MPA concentration and IMPDH activity, while a trend (p = 0.37) to inverse relationship between graft survival and IMPDH activity was found. The data suggests that the measurement of the biological response may provide a useful adjunct to traditional therapeutic drug monitoring (TDM) for optimization of dosing of immunosuppressive drugs.

RS-61443 prevents microvascular rejection of pancreatic islet xenografts

Inadequate vascularization and microvascular rejection are major limitations for successful free pancreatic islet xenotransplantation. Commonly used immunosuppressive regimens may alter the process of vascularization, and are ineffective at preventing graft rejection. In this study, we investigated, in vivo, the action of the new immunosuppressive agent RS-61443 on angiogenesis and microvascular rejection of rat pancreatic islets after xenogeneic transplantation into the dorsal skinfold of Syrian golden hamsters. In nontreated xenografts, intravital fluorescence microscopy demonstrated a regular process of vascularization during the first 6 days after transplantation. On days 10, 14, and 20, graft rejection was observed, characterized by microvascular leukocyte accumulation (244+/-59 mm(-2)), loss of endothelial integrity, and capillary perfusion failure. Islet xenografts of animals treated with RS-61443 (40 mg/kg per day) demonstrated inhibition of vascularization with the consequence of a markedly reduced size of the grafts' microvascular network (0.05+/-0.007 mm2), when compared with that of nontreated xenografts (0.09+/-0.015 mm2; P< 0.05). However, treatment with RS-61443 effectively prevented microvascular graft rejection, as indicated by the absence of leukocyte accumulation (24+/-9 mm(-2); P<0.01), endothelial damage, and nutritive perfusion failure. Thus, RS-61443 treatment may represent an interesting approach for improving the outcome of pancreatic islet xenotransplantation.

Tacrolimus rescue therapy for renal allograft rejection--five-year experience

Over the 5 year period from 7/14/1989 until 5/24/1994, we have attempted graft salvage with tacrolimus conversion in a total of 169 patients (median age 33 years, range 2-75 years) with ongoing rejection on baseline CsA immunosuppression after failure of high dose corticosteroids and/or antilymphocyte preparations to reverse rejection. The indications for conversion to tacrolimus were ongoing, biopsy confirmed rejection in all patients. The median interval to tacrolimus conversion was 2 months (range 2 days to 55 months; mean 4.3+/-2.6 months) after transplantation. All patients had failed high dose corticosteroid therapy and 144 (85%) of the 169 patients had received at least one course of an antilymphocyte preparation plus high dose corticosteroid therapy prior to conversion. Twenty-eight patients (17%) were dialysis-dependent at the time of conversion owing to the severity of rejection. With a mean follow-up of 30.0+/-2.4 months (median 36.5 months, range 12-62 months), 125 of 169 patients (74%) have been successfully rescued and still have functioning grafts with a mean serum creatinine (SCR) of 2.3+/-1.1 mg/dl. Of the 144 patients previously treated with antilymphocyte preparations, 117 (81%) were salvaged. Of the 28 patients on dialysis at the time of conversion to tacrolimus, 13 (46%) continue to have functioning grafts (mean SCR 2.15+/-0.37 mg/dl) at a mean follow-up of 37.3+/-16.7 months. In the 125 patients salvaged, prednisone doses have been lowered from 28.0+/-9.0 mg/d (median 32, range 4-60 mg/d) preconversion to 8.5+/-4.1 mg/d (median 12 mg/d, range 2.5-20 mg/d) postconversion. Twenty-eight patients (22.4%) are currently receiving no steroids. This 5 year experience demonstrates that tacrolimus has sustained efficacy as a rescue agent for ongoing renal allograft rejection. Based on these data, we recommend that tacrolimus be used as an alternative to the conventional drugs used for antirejection therapy in renal transplantation.

New immunosuppressive drugs in organ transplantation

An examination of the mechanisms by which four new immunosuppressive drugs--rapamycin, mizoribine, mycophenolate mofetil, and 15-deoxyspergualin--exert their effects reveals three major categories. Rapamycin binds to an intracellular immunophilin. The resulting drug-immunophilin complex inhibits the action of cytokines, thus blocking the activation and proliferation of T cells. Mizoribine and mycophenolate mofetil are antimetabolites that inhibit a key enzyme in the de novo purine biosynthetic pathway. As a result, the proliferation of T cells and B cells is inhibited selectively compared with that of nonlymphoid cells because the salvage pathway is unavailable to lymphocytes. Finally, 15-deoxyspergualin has a unique mechanism of action, which includes suppressive effects on macrophage function, the induction of cytolytic T cells, B-cell reactivity, and antibody responses. The demonstrated synergism among certain immunosuppressants allows reduction in the dose of each agent to minimize the individual toxicities. As more of these new agents become available, it is likely that azathioprine will be replaced, and it may be possible to eliminate the need for long-term maintenance steroid therapy.

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression in renal transplant recipients

The combination of pharmacokinetic and pharmacodynamic monitoring of immunosuppressive drugs provides a novel method for the optimization of drug dosing. We chose to investigate this with the use of mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. The relationship between MPA concentration in plasma, IMPDH activity in whole blood, and nucleotide concentration in lymphocytes was investigated in renal-transplant recipients, who were randomized to receive either mycophenolate mofetil (MMF) (n = 5) or azathioprine (AZA) (n = 7), in combination with cyclosporine and prednisone. Blood samples were collected throughout the dosing interval. Pharmacokinetic analysis revealed substantial variability among the patients in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration of IMPDH activity in whole blood. The peak concentration of MPA achieved at 1 hr after dosing resulted in approximately 40% inhibition of IMPDH activity. As the MPA concentration decreased throughout the dosing interval, there was a gradual restoration of IMPDH activity. The inhibition of IMPDH activity (P < 0.05) in MMF-treated patients as compared with the AZA-treated controls was maintained for approximately 8 hr after dosing. No statistically significant (P > 0.05) difference between the predose and the 12 hr postdose activity was observed. The concentrations of guanine nucleotides, GDP and GMP, were significantly lower than in the AZA-treated group at most of the time points after dosing; however, considerable variability was observed. The measurement of the pharmacodynamic response to immunosuppressive drugs may provide not only a mechanism to predict the most appropriate dosing regimen, but also a viable alternative to traditional therapeutic drug monitoring, by assessing the overall state of immunosuppression.

Mycophenolate mofetil--clinical and experimental experience

Mycophenolate mofetil (MMF) is the first drug approved for the prevention of renal allograft rejection in the United States in the last 10 years. MMF is the morpholinoethyl ester of mycophenolic acid (MPA) and is a selective, reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), an enzyme that is critical for the production of guanine monophosphate. MPA is a potent inhibitor of IMPDH, particularly the type II isoform. Compared with other cell types, lymphocytes appear to be more sensitive to inhibition of the type II isoform of IMPDH. This decreases the metabolism of guanine nucleotides, which are necessary for cell function. MMF is rapidly converted to MPA, which is the pharmacologically active drug. MPA is highly bound to serum albumin, and recent evidence suggests that the pharmacologic activity of MPA is a function of the unbound drug. Recent studies in human clinical transplantation have demonstrated the efficacy of this compound in renal transplantation. A major clinical study with > 1,499 patients demonstrated a 50% reduction in the incidence of acute rejection when compared with azathioprine or placebo control. The primary side effects in these studies were leukopenia, gastrointestinal problems, and cytomegalovirus disease. MMF represents a major advance in immunosuppression for renal transplant recipients. Ongoing studies are being performed in other types of solid organ transplantation.

Pharmacokinetics of mycophenolate mofetil, a new immunosuppressant, in rats

Mycophenolate mofetil (MPM), a new immunosuppressant, is the morpholinoethyl ester of mycophenolic acid (MPA). The distribution in blood and pharmacokinetics of MPA after administration of MPM were examined. The plasma to erythrocyte concentration ratio was low (0.10-0.15). MPA existed in rat plasma as the highly bound form (bound fraction was 9.79 +/- 0.57%). MPA disappeared from the systemic circulation with biexponential decay. After i.v. administration of MPM at the doses of 8.3, 16.7, and 33.3 mg/kg, the total clearance of MPA was 0.241 +/- 0.056, 0.321 +/- 0.126, and 0.317 +/- 0.092 L/h/kg, respectively. The terminal elimination half-live were 5.17 +/- 1.44, 8.89 +/- 2.76, and 7.94 +/- 2.94 h, respectively. After i.d. administration of MPM at the doses of 8.3, 16.7, 33.3, and 50.0 mg/kg, the terminal elimination half-live were 6.41 +/- 4.16, 4.49 +/- 2.20, 7.58 +/- 3.72, and 8.18 +/- 1.32 h, respectively. The mean peak times were within 30 min. The systemic availability of MPA after i.d. administration of MPM (at 8.3, 16.7, and 33.3 mg/kg) was calculated using the corresponding mean AUCiv, and the values were 84.3 +/- 35.0%, 69.9 +/- 25.7%, and 63.6 +/- 8.8%, respectively.

Use of combination of low-dose cyclosporine and RS-61443 in a rat hindlimb model of composite tissue allotransplantation

Despite technical feasibility, composite tissue allotransplantation has not been applied clinically because of immunosuppressive toxicity associated with these highly antigenic allografts. Combination immunosuppression therapy can help overcome this obstacle by allowing lower doses of individual drugs and minimizing toxicity. RS-61443 (mycophenolate mofetil), an effective immunosuppressant that inhibits lymphocyte proliferation, was tested at subtherapeutic doses in combination with cyclosporine (CsA) in a rat hindlimb allotransplantation model with a major antigenic mismatch at the MHC. Five groups were studied: untreated autograft controls (n=4), untreated allograft controls (n=6), allografts receiving low-dose CsA 1.5 mg/kg/day (n=11), allografts receiving low-dose RS-61443 15 mg/kg/day (n=17), and allografts receiving combination low-dose CsA 1.5 mg/kg/day + RS-61443 15 mg/kg/day (n=18). The autograft controls survived indefinitely, while untreated allograft control animals developed severe rejection within 12 days. Subtherapeutic CsA and RS-61443 monotherapy groups developed acute rejection in 64% and 100% of rats, respectively. In contrast, only 11% of rats receiving combination therapy with CsA + RS-61443 at these same subtherapeutic doses developed acute rejection (P < or = 0.0013). Bone marrow toxicity, manifested primarily by anemia and measured objectively by hematocrits, was reduced significantly (P=0.04) in animals receiving low-dose RS-61443 therapy when compared with high-dose controls. These results confirm that subtherapeutic RS-61443 + CsA combination therapy is efficacious in preventing rejection while minimizing toxicity.

Mycophenolate mofetil. A review of its pharmacodynamic and pharmacokinetic properties and clinical efficacy in renal transplantation

Mycophenolate mofetil is an ester prodrug of the active immunosuppressant mycophenolic acid. It is a noncompetitive, selective and reversible inhibitor of inosine monophosphate dehydrogenase, an important enzyme in the de novo synthesis of guanosine nucleotides in T and B lymphocytes. Mycophenolate mofetil and/or mycophenolic acid inhibit the proliferation of lymphocytes and the production of antibodies induced by a variety of mitogens and antigens. Mycophenolate mofetil is also active in several animal models of transplantation and has produced effects in animals that indicate that it may inhibit the chronic rejection process. Mycophenolate mofetil has been compared with azathioprine or placebo in 3 large, randomised, double-blind, multicentre trials as part of combination immunosuppression therapy with cyclosporin and corticosteroids. Compared with either placebo or azathioprine (1 to 2 mg/kg/day or 100 to 150 mg/day), mycophenolate mofetil 2 or 3 g/day was associated with a significantly lower proportion of patients experiencing acute rejection or treatment failure during the first 6 months after transplantation. Mycophenolate mofetil also tended to be associated with a lower proportion of patients who required a full course of antirejection therapy. However, the proportion of patients who died or who had graft loss was similar between all of the treatment groups. There are currently no data regarding the effects of mycophenolate mofetil on long term patient or graft survival, which are important clinical outcomes in assessing its place in the management of renal transplantation. Clinical trials are also needed to evaluate mycophenolate mofetil in specific patient populations (e.g. repeat renal transplant patients or highly sensitised patients), to determine its efficacy in alternative immunosuppressive protocols and to investigate its use in the transplantation of other solid organs. In summary, mycophenolate mofetil appears to be an attractive new agent in the prevention of graft rejection in renal transplant recipients that has shown superior efficacy to azathioprine. Although long term clinical outcome data are required, mycophenolate is a potentially important advance in transplant immunosuppression.

The use of therapeutic drug monitoring to optimise immunosuppressive therapy

Most experience of the therapeutic drug monitoring of immunosuppressive agents has been acquired in the field of solid organ transplantation; however, agents such as cyclosporin (cyclosporin A) are being increasingly utilised for the management of autoimmune diseases. Cyclosporin is the most widely studied immunosuppressant, but in spite of this many controversies still exist as to the optimum strategy for monitoring this drug. Owing to its widely variable pharmacokinetics and metabolism, and the absence of a simple method to measure therapeutic effectiveness, many factors should be considered. In most circumstances, measuring whole blood through concentrations of cyclosporin with a specific assay methodology is warranted. In addition, knowledge of other factors that may alter the pharmacokinetics (such as liver function, concomitant food or medications, gastrointestinal status, and time since transplantation) should be taken into account so that therapy can be appropriately adjusted. Other methods of monitoring have been investigated, such as AUC (area under the concentration-time curve) monitoring and immunological monitoring. However, further refinement of these techniques and greater experience with their efficacy must be accumulated before their role in the monitoring of cyclosporin can be defined. Tacrolimus, like cyclosporin, shares many of the difficulties in monitoring for efficacy and toxicity due largely to the variable pharmacokinetics; similarly to cyclosporin, whole blood through concentration monitoring should be utilised in combination with knowledge of the factors that may affect the pharmacokinetics. Muromonab CD3 (OKT3) is a monoclonal antibody used for the treatment and prophylaxis of acute allograft rejection. Several immunological monitoring techniques have been investigated for this agent. Monitoring CD3+ levels can assist clinicians in determining therapeutic efficacy, while measuring antimuromonab CD3 antibody titres can help determine if xenosensitisation has occurred, causing therapeutic ineffectiveness. The clinical monitoring of azathioprine, one of the first immunosuppressive agents used in transplantation, has historically been limited to monitoring complete blood counts for bone marrow suppression. However, newer techniques measuring intracellular DNA nucleotides appear to be promising. The new immunosuppressants on the horizon include mycophenolate mofetil and rapamycin. The clinical experience with therapeutic drug monitoring of these 2 compounds is scant in the literature; however, both agents have demonstrated efficacy in preventing or treating allograft rejection while maintaining a relatively well tolerated toxicity profile in recent clinical trials. Routine monitoring does not appear to be warranted for immunosuppressive therapy in autoimmune diseases.

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression by measurement of inosine monophosphate dehydrogenase activity in a canine model

The combination of pharmacokinetic and pharmacodynamic (measurement of the biological effect) monitoring of immunosuppressive drugs provides a method for the optimization of drug dosing. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. Using an assay developed for measurement of IMPDH activity in whole blood, the concentration required for 50% inhibition of IMPDH activity was approximately 200 mg/L (58 +/- 8.3% for whole blood [n = 6] and 55 +/- 10.0% for isolated lymphocytes). To ascertain the relationship between MPA concentration and IMPDH inhibition in vivo, dogs were administered a single dose of mycophenolate mofetil, the pro-drug of MPA, at 20 or 40 mg/kg orally. Pharmacokinetic analysis revealed that the Cmax of the 40-mg/kg group was statistically greater than that of the 20-mg/kg group (P < 0.05). There were no statistical differences in the other parameters investigated (area under the curve, beta half-life, mean residence time, volume of distribution at steady state, and clearance) between the two treatment groups. The half-life was calculated at approximately 8 hr for both dose groups. There was also substantial variability among the dogs in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration and IMPDH. Maximal inhibition of IMPDH activity of 30-40% occurs approximately 2-4 hr after dosing, followed by a gradual restoration in enzyme activity. After 24 hr, there is an increase in IMPDH activity that exceeds the pre-dosing levels in some cases by 3-fold. Evaluation of the pharmacokinetic and the pharmacodynamic responses to MPA in the canine model suggests that the drug should be administered ever 8 hr to optimize its immunosuppressive efficacy. This combined approach can be used for optimization of doses of this and other immunosuppressive drugs.

Mycophenolate mofetil (MMF, RS-61443) inhibits inflammation and smooth muscle cell proliferation in rat aortic allografts

To investigate the impact of mycophenolate mofetil (MMF) on allograft arteriosclerosis (chronic rejection) in rat aortic allograft model, we administrated MMF 20 mg/kg/day from the day of transplantation and sacrificed the rats at 1-12 months afterwards. MMF significantly suppressed all major histological manifestations of allograft arteriosclerosis, i.e. adventitial inflammation, media necrosis and intimal thickening and cellularity. There was a significant decrease in the replication rate (3H-thymidine incorporation) of inflammatory cells in the adventitia and of smooth muscle cells (SMC) in the media. MMF did not have any major effect on mRNA expression of several growth factors, (determined by polymerase chain reaction with inbuilt glyceraldehyde-3-phosphate dehydrogenase control), which have previously been demonstrated to be elevated in nonimmunosuppressed allografts. Immunoperoxidase staining showed a 40% reduction in the number of adventitial interleukin-2 receptors expressing lymphoid cells in MMF-treated allografts. The intensity of SMC alpha-actin staining was also significantly reduced. As the results suggested that MMF may have a direct antiproliferative effect on SMC, this possibility was investigated in primary SMC cultures in vitro and using the carotid denudation model in vivo. Both approaches showed inhibition of SMC proliferation by MMF. Our results indicate that MMF inhibits histopathological changes of chronic rejection by reducing the immune response and possible replication of SMC.

Inhibition of experimental autoimmune uveoretinitis by mycophenolate mofetil, an inhibitor of purine metabolism

Mycophenolate mofetil (MM), an inhibitor of purine metabolism, was found to effectively inhibit the development of experimental autoimmune uveoretinitis (EAU) induced by S-antigen (SAg) in Lewis rats. MM completely inhibited EAU development in the majority of rats when administered daily, on days 0-13, at a dose of 30 mg kg-1 day-1. The drug was less effective, however, when given on days 7-20: minimal disease inhibition was achieved with the drug at 30 mg kg-1 day-1, although at 60 mg kg-1 day-1 the drug inhibited EAU development in most treated rats during the period of its administration. MM also completely inhibited in most treated rats the development of EAU adoptively transferred by SAg-sensitized lymphocytes, thus depicting its capacity to inhibit the efferent limb of the immune response. Treatment with MM also suppressed the cellular and humoral immune responses against SAg, with a good correlation being observed between the inhibition of these responses and suppression of EAU in the different groups of rats. MM is currently being examined for its immunosuppressive effects in humans and the data recorded here thus suggest this compound may be useful in treatment of immune-mediated uveitic conditions.

Stability and pharmacokinetic studies of a new immunosuppressant, mycophenolate mofetil (RS-61443), in rats

Mycophenolate mofetil (MPM), a new immunosuppressant, is a morpholinoethyl ester of mycophenolic acid (MPA). The enzymatic and non-enzymatic hydrolysis was studied in an artificial digestive fluid, rat plasma, and tissue homogenates. MPM was chemically stable in the artificial digestive fluid. In rat tissue homogenates and plasma, MPM was rapidly hydrolysed to MPA. The conversion rate of MPM to MPA in various rat tissue homogenates was in the order of liver > kidney > plasma > small-intestine epithelial cells. After the intravenous injection of MPM at 16.7 mg kg-1, the terminal elimination half-life, t1/2 beta, was 4.74 +/- 0.33 (mean +/- SD)h, and the area under the plasma concentration versus time curve, AUC, was 48.78 +/- 6.01 micrograms h mL-1. After intraduodenal (ID) administration of MPM at 16.7 mg kg-1, t1/2 beta was 3.92 +/- 1.05 h, and the AUC was 38.08 +/- 8.30 micrograms h mL-1. The systemic availability of MPA after ID MPM dosing was 1.52 times higher than that after ID administration of MPA. This result supports the usefulness of MPM as an oral prodrug of MPA as a new oral immunosuppressant.

Immunobiology and immunopharmacology of organ allograft rejection

Much has been learned regarding immunobiological mechanisms responsible for the rejection of histoincompatible allografts. There has also been considerable progress in our understanding of mechanisms responsible for tolerance. The new knowledge gained regarding graft destructive alloimmunity process and the mechanisms of action of immunosuppressants have resulted in solid organ graft survival rates that are in excess of 80% at one year posttransplantation. The principles of tolerance mechanism are yet to be successfully applied in the clinic. In this review, molecular and cellular mechanisms of action of clinically useful immunosuppressive drugs are reviewed from the perspective of regulation of the anti-allograft repertory.

Optimizing the use of cyclosporine in renal transplantation

OBJECTIVE

To review the existing data on the use of cyclosporine (CsA) in kidney transplantation, particularly with respect to therapeutic drug monitoring.

DATA SOURCES

A literature search was conducted of applicable articles related to therapeutic drug monitoring of cyclosporine in renal transplantation. Previous consensus guidelines were examined. Discussions on issues related to this topic convened in Toronto, ON, on June 15-16, 1994.

DATA SYNTHESIS

The literature was analyzed to examine patient factors and drug interactions affecting CsA concentrations, the effect of CsA concentrations on patient outcome, current methods of analysis, pharmacodynamic monitoring, and new immunosuppressants.

CONCLUSIONS

CsA has improved the success of kidney transplantation, reducing the incidence and severity of acute rejection and improving short-term patient and graft survival. The rate of graft loss after the first year (primarily due to chronic rejection) has remained largely unchanged. Sandimmune Neoral offers promise due to its better bioavailability and limited dependence on bile flow for absorption. Long-term studies are underway to determine its effectiveness and safety. Indications for therapeutic drug monitoring for CsA are provided.

Progress in renal transplantation. A single center study of 3359 patients over 25 years

OBJECTIVE

The study analyzed 3359 consecutive renal transplant operations for patient and graft survival, including living related, cadaveric, and living unrelated patients. The analysis was separated into three groups according to immunosuppression and date of transplant.

SUMMARY BACKGROUND DATA

Improvements in renal transplantation in the past 25 years have been the result of better immunosuppression, organ preservation, and patient selection.

METHODS

A single transplant center's experience over a 25-year period was analyzed regarding patient and graft survival. Potential risk factors included patient demographics, tissue typing, donor characteristics, number of transplants, acute and chronic rejection, acute tubular necrosis, primary disease, and malignancy.

RESULTS

The primary cause of graft loss was rejection. Improvement in cadaveric graft survival since 1987 with quadruple therapy was not apparent in living donor patients. Race continued to be a negative factor in graft survival. Avoiding previous mismatched antigens and the use of flow cytometry improved allograft survival. The leading cause of death in the past 7 years in cadaveric recipients was cardiac (52%).

CONCLUSIONS

Improved graft survival in the past 25 years was related to 1) advances in immunosuppression, 2) better methods of cytotoxic antibody detection, and 3) human lymphocyte antigen match.

Basic aspects of neuroimmunology as they relate to immunotherapeutic targets: present and future prospects

The neurological diseases with definite or putative immune pathogenesis include myasthenia gravis; Lambert-Eaton myasthenic syndrome; IgM monoclonal anti-myelin-associated glycoprotein-associated demyelinating polyneuropathy; Guillain-Barré syndrome; chronic inflammatory demyelinating polyneuropathy; multifocal motor neuropathy with or without GM1 antibodies; multiple sclerosis; inflammatory myopathies; stiff-man syndrome; autoimmune neuromyotonia; paraneoplastic neuronopathies and cerebellar degeneration; and neurological diseases associated with systemic autoimmune conditions, vasculitis, or viral infections. The events that lead to these autoimmune diseases are not clear but the following sequential steps are critical: (a) the breaking of tolerance, a process in which cytokines, molecular mimicry, or superantigens may play a role in rendering previously anergic T cells to recognize neural autoantigens; (b) antigen recognition by the T-cell receptor complex and processing of the antigen via the major histocompatibility complex class I or II; (c) costimulatory factors especially B7 and B7-binding proteins (CD28, CTLA-4) and intercellular adhesion molecule (ICAM)-1 and its leukocyte function-associated (LFA)-1 ligand; (d) traffic of the activated T cells across the blood-brain or blood-nerve barrier via a series of adhesion molecules that include selectins, leukocyte integrins (LFA-1, Mac-1, very late activating antigen [VLA]-4) and their counterreceptors (ICAM-1, vascular cell adhesion molecule [VCAM]) on the endothelial cells; and (e) tissue injury when the activated T cells, macrophages, or specific autoantibodies find their antigenic targets on glial cells, myelin, axon, calcium channels, or muscle. In designing specific immunotherapy, the main players involved in every step of the immune response need to be considered. Targets for specific therapy in neurological diseases include agents that (a) interfere or compete with antigen recognition or stimulation, (b) inhibit costimulatory signals or cytokines, (c) inhibit the traffic of the activated cells to tissues, and (d) intervene at the antigen recognition sites in the targeted organ. The various immunomodulating procedures and immunosuppressive drugs currently used for nonselective neuroimmunotherapy are discussed in the context of their interference with the above-described immune mediators.

FK506 in pediatric kidney transplantation--primary and rescue experience

Between 14 December 1989 and 17 December 1993, 43 patients undergoing kidney transplantation alone at the Children's Hospital of Pittsburgh received FK506 as the primary immunosuppressive agent. The mean recipient age was 10.2 +/- 4.8 years (range 0.7-17.4 years), with 7 (16%) children under 5 years of age and 2 (5%) under 2 years of age. Fifteen (35%) children underwent retransplantation, and 5 (12%) had a panel-reactive antibody level greater than 40%. Twenty-two (51%) transplants were with cadaveric donors and 21 (49%) were with living donors. The mean follow-up was 25 +/- 14 months; there were no deaths; 1- and 3-year actuarial graft survival was 98% and 85%. The mean serum creatinine and blood urea nitrogen were 1.2 +/- 0.6 mg/dl and 26 +/- 11 mg/dl; the calculated creatinine clearance was 75 +/- 23 ml/min per 1.73 m2. Twenty-four (62%) patients have been successfully withdrawn from steroids and 24 (62%) require no anti-hypertensive medication. Improved growth was seen, particularly in pre-adolescent children off steroids. Between 28 July 1990 and 2 December 1993, 24 children were referred for rescue therapy with FK506, 14.6 +/- 16.4 months (range 1.1-53.2 months) after transplantation. Nineteen (79%) were referred because of resistant rejection; 4 (17%) were referred because of proteinuria; 1 (4%) was switched because of steroid-related obesity. There were no deaths; 1- and 2-year graft survival was 75% and 68%; 17 (71%) patients were successfully rescued, including 1 of 2 patients who arrived on dialysis; 4 (24%) of the successfully rescued patients were weaned off steroids.(ABSTRACT TRUNCATED AT 250 WORDS)

Which way for drug-mediated immunosuppression?

The basic immunosuppressive protocol involves the use of multiple drugs, each directed at a discrete site in the T-cell activation cascade. The prevailing paradigm regarding the mechanisms of action of immunosuppressants is that they function to prevent allograft rejection by preventing cell activation, proliferation and/or cytokine production. A new hypothesis is that some of the immunosuppressants might function by stimulating the expression of immunosuppressive molecules and/or cells.

Monitoring of kidney and simultaneous pancreas-kidney transplantation rejection by release of donor-specific, soluble HLA class I

Using an HLA-A2-specific ELISA we monitored daily pretransplantation and posttransplantation sera from five kidney and eight simultaneous pancreas-kidney HLA-A2-negative recipients of HLA-A2-positive transplants during hospitalization. We found that, unlike liver transplants, neither kidney nor simultaneous pancreas-kidney transplants continuously secreted donor HLA proteins. However, three of four rejection episodes in kidney recipients and seven of seven rejection episodes in simultaneous pancreas-kidney recipients were accompanied by elevated serum levels of donor sHLA-A2 (> 5 ng/ml). In only one kidney patient was there a release of donor antigen without evidence of rejection, but in the simultaneous pancreas-kidney group most patients had at least one time point of detectable sHLA-A2 without strong evidence of kidney rejection. While total sHLA levels were also elevated during rejection, the rise in donor-specific sHLA was more dramatic when compared to pretransplantation background levels. We hypothesized that the release of donor sHLA class I proteins by transplanted organs might be a systemic indication of rejection in both pancreas and kidney allografts. The detection of donor sHLA in recipient sera could be an important noninvasive monitor of rejection, especially in the pancreas, which is currently difficult to monitor as a single-organ transplant.

Anti-tumor activity of mycophenolate mofetil against human and mouse tumors in vivo

Cultured tumor cell lines, tumor xenografts grown in athymic nude mice, and a murine experimental metastasis model were used to assess the in vitro and in vivo anti-tumor activity of the potent IMP dehydrogenase (IMPDH) inhibitor, mycophenolic acid (MPA), and its morpholinoethyl ester pro-drug, mycophenolate mofetil (MM). The growth of all the cell lines tested was inhibited by MPA in vitro, with EC50 values ranging from less than 0.1 microM to 3.9 microM. Mice were monitored for s.c. tumor outgrowth in the case of human tumor xenograft models or survival time for the murine experimental metastasis model. Treatment with MM p.o. was started 24 hr after tumor challenge or after tumors became palpable. Treatment of athymic nude mice bearing A3.01 (T-lymphoblast), Molt-4 (T-cell leukemia), CaPan-2 (pancreatic adenocarcinoma), CaLu-3 (non-small-cell lung adenocarcinoma), LS174T and T84 (colon adenocarcinoma), and Daudi (B-cell lymphoma) human tumor xenografts with MM significantly inhibited s.c. tumor growth. Treatment of BALB/c mice with MM after i.v. injection of murine RAW117-H10 lymphoma cells in an experimental metastasis assay resulted in increased survival time for treated animals. No significant inhibitory effect on s.c. tumor outgrowth was seen with MM treatment of SK-Hep-1, a human hepatic endothelioma, or Hep-3B, a liver adenocarcinoma, at any of the doses tested.

The interaction of immunosuppressive compounds in tandem stimulated peripheral human lymphocytes

We have developed an in vitro system to model the interactions of drugs used to treat transplant rejection. This system consists of stimulation of human lymphocytes with a primary mitogen (anti-T-cell receptor complex antibodies (OKT3 or wt31)) and treatment with a primary immunosuppressive drug (ISD) (Cyclosporine A (CsA) or FK-506)). This is later followed by stimulation with a secondary mitogen (Interleukin-2 or anti-CD28), and treatment with a second ISD. This system allows a variety of concentrations and compounds to be rapidly tested. We have used this system to study the effect of various compounds when used as either primary or secondary ISDs. Our results show that when CsA is used as the primary ISD, further proliferation can be inhibited by rapamycin, mycophenolic acid, or suramin. When FK-506 is the primary ISD, inhibition of proliferation by rapamycin is variable depending on the primary and secondary mitogens. If rapamycin is the primary ISD, both CsA and FK-506 show antagonistic interactions. These results suggest that the order in which combinations of ISDs are administered in transplantation may have significant effects on the clinical outcome.

Developments and dilemmas in renal transplantation

The number of patients waiting for a kidney transplant is about three times greater than the number of transplants performed each year. This article highlights current immunosuppression protocols and the newer immunosuppressive drugs under investigation in a number of multicenter trials. These hold out the promise of reducing the frequency of acute rejection and of prolonging graft survival. They are divided into three groups. The first, like cyclosporine, interferes with the action of interleukin 2. The second, like azathioprine, are antimetabolites; and the third, new monoclonal antibodies. The use of antibody-induction therapy is compared with standard regimens. There are risks related to prednisone withdrawal protocols and inadequate cyclosporine dosing that may lead to accelerated graft loss. Cardiovascular disease is a significant problem in older diabetic patients for whom coronary angiography is recommended. A defined set of risk factors is outlined that predicts which younger diabetic patients should have a cardiovascular evaluation. Chronic liver disease is a growing problem and rational strategies are emerging from studies of patients with biopsy-proven active hepatitis. The presence of hepatic inflammation is associated with progressive liver disease and patients must be made aware of this risk when seeking transplantation. A large number of studies of various prophylactic regimens are starting to provide data on the cost-effective reduction of cytomegalovirus disease in transplant recipients. It is recommended that patients receiving antibody therapy also receive preemptive gangciclovir. The issue of chronic allograft rejection is discussed briefly. The most important predictors of chronic allograft rejection are the frequency of acute rejection, inadequate immunosuppression, and infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of a new immunosuppressant, mycophenolate mofetil, and its active metabolite, mycophenolic acid, in rat and human body fluids by high-performance liquid chromatography

Mycophenolate mofetil, a new immunosuppressant, is a morpholinoethyl ester of mycophenolic acid. A new selective, sensitive and simple high-performance liquid chromatographic method was developed for the determination of mycophenolic acid and mycophenolate mofetil in biological samples. The preparation of samples was based on liquid-liquid extraction. The compounds were separated on a CN column using acetonitrile-0.01 M phosphate buffer (1:4, v/v) as the mobile phase. UV detection was used at wavelengths 215 and 304 nm. The detection limit was 5 ng per injection volume. This method enabled pharmacokinetic and pharmacodynamic studies in humans and rats.

Effect of mycophenolic acid on Epstein-Barr virus infection of human B lymphocytes

The effect of mycophenolic acid (MPA) on the growth of Epstein-Barr virus (EBV)-transformed B cells and on EBV lytic-cycle gene expression was investigated. MPA inhibited the proliferation of newly infected or established EBV-transformed B-cell lines but was not able to block cell growth transformation or the viral lytic cycle. These results suggest that MPA might reduce transformed-cell proliferation in transplant patients and possibly decrease the risk of development of EBV-related lymphoproliferative disorders.