Effects of the pharmacokinetic interaction between orally administered sirolimus and cyclosporine on the synergistic prolongation of heart allograft survival in rats

Cholesterol esterification as a mediator of proliferation of vascular smooth muscle cells and peripheral blood mononuclear cells during atherogenesis

BACKGROUND/AIMS

We determined growth rates, cholesterol esterification and mRNA levels for caveolin-1 (Cav-1), neutral cholesterol esters hydrolase (n-CEH) and ATP-binding cassette transporter (ABCA-1), in quiescent and growth-stimulated peripheral blood mononuclear cells (PBMCs) and intimal vascular smooth muscle cells (VSMCs) from blood and primary atherosclerotic plaques, respectively. These cells were cultured in the presence or absence of the mTOR inhibitor 40-O-(2-hydroxyethyl) rapamycin (RAD).

METHODS

The rate of cell proliferation was determined by 3H-thymidine incorporation into DNA and that of lipid metabolism by utilizing 14C-acetate and 14C-oleate as precursors. Lipid deposit in the vascular cells was evaluated by Oil Red O staining and lipid mass by thin layer chromatography-linked enzymatic assay.

RESULTS

Growth stimulation of PBMCs and VSMCs caused a rapid increase in intracellular cholesterol esterification and an accumulation of cholesterol esters (CEs) accompanied by a reduction of free cholesterol (FC) and Cav-1, ABCA-1 and n-CEH mRNAs. RAD reduced intracellular lipid accumulation in growth-stimulated cells and also increased expression of Cav-1, n-CEH and ABCA-1 genes.

CONCLUSION

Collectively, these data provide evidence that the determination of CEs in PBMCs may be an easy prescreening test to identify subjects at risk for vascular proliferative disease and that FC, CE, Cav-1, n-CEH and ABCA-1 may be suitable targets for antiproliferative therapies.

Influence of Everolimus on Steady-State Pharmacokinetics of Cyclosporine in Maintenance Renal Transplant Patients

To investigate possible interactions of the novel immunosuppressant everolimus with cyclosporine, a multicenter, randomized, double-blind, placebo-controlled, dose-escalating phase I study was performed. Everolimus regimens (0.75-10 mg/d) were administered for 28 days to stable renal allograft recipients receiving the microemulsion form of cyclosporine. Steady-state cyclosporine profiles were assessed at baseline on day 0 (cyclosporine alone) and on day 21 with everolimus on steady state. By day 21, mean dose-normalized cyclosporine AUC0-12 increased by 15% in patients receiving placebo. In everolimus-treated patients, mean increases in cyclosporine AUC0-12 ranged from 7% to 43%, which were not significantly different across all dosing cohorts including placebo. Linear regression of everolimus AUC on day 21 versus the increase in cyclosporine AUC0-12 yielded a slope not significantly different from a horizontal line (P = ns). In conclusion, these results suggest that steady-state everolimus exposure over the wide range assessed in this study did not affect steady-state cyclosporine pharmacokinetics.

Gene expression of P-glycoprotein and cytochrome P450 3A4 in peripheral blood mononuclear cells and correlation with expression in liver

Long-term immunosuppression in renal transplant recipients generally includes calcineurin inhibitors (CNIs), which demonstrate marked interindividual diversity and a narrow therapeutic range. In the clinical setting, it is important to reach therapeutic drug concentrations to prevent allograft rejection. The same immunosuppressant dosage leads to different drug concentrations. Therefore, we investigated factors that influence the metabolism of immunosuppressant agents. The CNIs are substrates of cytochrome P450 (CYP450) and P-glycoprotein. The CYP450 3A genotype significantly influences CNI concentration. Differences in expression of these proteins may explain interindividual pharmacokinetic variations. However, it is risky and impractical to obtain specimens from the liver in renal transplant recipients. Therefore, we investigated the correlation of gene expression between peripheral blood mononuclear cells (PBMCs) and liver parenchyma. We observed that the correlation of relative P-glycoprotein gene expression between PBMCs and liver is not significant (r2=0.03; P=.65). In addition, the correlation of CYP450 3A4 gene expression between PBMCs and liver is not strong (r2=0.23; P=.42). The expression level of CYP450 3A5 is too low to be detected in the sample from PBMCs.

Combination of clopidogrel and everolimus dramatically reduced the development of transplant arteriosclerosis in murine aortic allografts

Our group has shown that platelet inhibition with clopidogrel, an antagonist of the P2Y12 adenosine diphosphate receptor on platelets, reduced the formation of transplant arteriosclerosis. The aim of this study was to investigate whether a combination of cyclosporin or everolimus with clopidogrel has a beneficial effect on the development of transplant arteriosclerosis. Fully MHC mismatched C57Bl/6 (H2(b)) donor aortas were transplanted into CBA.J (H2(k)) recipients and mice received either clopidogrel alone (1 mg/kg/day) or in combination with cyclosporin (2 mg/kg/day) or everolimus (0.05 mg/kg/day). Grafts were analysed by histology and morphometry on day 30 after transplantation. In mice treated with clopidogrel alone, transplant arteriosclerosis was significantly reduced [intima proliferation 56 +/- 11% vs. 81 +/- 7% (control)/n = 7]. Daily application of everolimus reduced the development of transplant arteriosclerosis compared with untreated controls [intima proliferation of 29 +/- 9% vs. 81 +/- 7% (control)/n = 7]. Strikingly, combination of clopidogrel and everolimus almost abolished the formation of transplant arteriosclerosis [intima proliferation: 11 +/- 8% vs. 81 +/- 7% (control)/n = 7]. By contrast, combination of cyclosporin and clopidogrel compared with clopidogrel alone showed no additive effect. These results demonstrate that combination of platelet- and mammalian target of Rapamycin-inhibition can dramatically reduce the development of transplant arteriosclerosis.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.

Proliferation signal inhibitors and cardiac allograft vasculopathy

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is the leading cause of late morbidity and mortality in heart transplant patients and limits long-term survival. Immunosuppression following cardiac transplantation has traditionally comprised a calcineurin inhibitor in combination with mycophenolate mofetil or azathioprine and corticosteroids. This combination provides effective immunosuppression but does not prevent subsequent development of CAV. Proliferation signal inhibitors (such as sirolimus and everolimus), a new class of immunosuppressants, have recently been shown to be effective in attenuating the development of CAV following cardiac transplantation.

RECENT FINDINGS

In addition to immunosuppressive properties, proliferation signal inhibitors have important antiproliferative effects outside the immune system. Several ex-vivo and preclinical studies on animal models have demonstrated control of the vascular manifestations after cardiac transplantation. In clinical trials, proliferation signal inhibitors used as secondary immunosuppressive agents in place of azathioprine or mycophenolate prevented CAV progression and reduced the incidence of clinically significant cardiac events. Proliferation signal inhibitors are also effective as primary immunosuppressants, and, after complete calcineurin inhibitor withdrawal, mitigate the progression of CAV, improve calcineurin inhibitor-induced nephropathy and hypertension.

SUMMARY

Proliferation signal inhibitors are powerful immunosuppressive agents with antiproliferative properties that attenuate CAV and have the potential to improve long-term survival following cardiac transplantation.

Switching from HPLC/UV to MEIA for whole blood sirolimus quantitation: comparison of methods

Sirolimus is a immunosuppressive agent for renal transplant recipients. Monitoring of whole blood sirolimus concentration is necessary in order to improve clinical outcomes. An increasing number of clinical laboratories (4-14% during 2005) are using microparticle enzyme immunoassay (MEIA) for sirolimus quantitation but previous reports indicated a high variability, with a mean difference of 17% for MEIA method vs. high-performance liquid chromatography/ultraviolet (HPLC/UV). This study was aimed at comparing the reliability of MEIA with the HPLC/UV method. Blood samples from transplant patients were processed using both HPLC/UV and MEIA assays. Comparison and Bland-Altman plots, as well as regression analysis and paired t-test were used to compare results of the assays. Concentrations were stratified into three groups and used to investigate whether any observed difference between methods could be influenced by sirolimus concentration. Regression analysis yielded a coefficient of correlation R of 0.9756, the line of best fit being y=0.9832x+0.1976. The statistical analysis showed no difference between the two sets of experimental data. The average percentage difference between the two methods was found to be -0.2+/-19.2%. On the basis of our present results, the tested MEIA assay is able to quantify sirolimus concentration with a clinically acceptable imprecision, similar to that of HPLC/UV method.

Metabolism of sirolimus in the presence or absence of cyclosporine by genotyped human liver microsomes and recombinant cytochromes P450 3A4 and 3A5

Sirolimus is an immunosuppressive drug currently used alone or in combination with cyclosporine. Both drugs undergo extensive metabolism by the CYP 3A enzymes. This study aimed at comparing the activity of recombinant CYP (rCYP) 3A4 and 3A5 toward sirolimus, investigating the effect of cyclosporine on the metabolic rate of these two cytochromes P450 (P450s), as well as the impact of the CYP 3A5*3 polymorphism on that of human liver microsomes (HLMs). Two distinct approaches were used; i.e., the measurement of (1) hydroxy-sirolimus and desmethyl-sirolimus production, and (2) sirolimus depletion by the in vitro half-life method. rCYP 3A5 exhibited a lower intrinsic clearance (CL(int)) for both hydroxylation (0.11 versus 0.24 microl/pmol P450/min) and depletion of sirolimus (0.64 versus 2.36 microl/pmol P450/min) than rCYP 3A4. Similar CL(int) values for hydroxylation, demethylation, and depletion were found when comparing a pool of HLMs carrying at least one CYP 3A5*1 (active) allele with a pool of HLMs not expressing CYP 3A5. This was further confirmed for sirolimus depletion using individual microsome preparations (p = 0.42). A deeper inhibitory effect of cyclosporine on the CL(int) of sirolimus depletion was found for rCYP 3A4 than for rCYP 3A5 (i.e., -44% versus -8% at 0.62 microM, 750 microg/l cyclosporine), and sirolimus metabolism was slightly less inhibited for HLMs expressing CYP 3A5 than not (-38% versus -56%). In the absence of cyclosporine, the CYP 3A5*3 polymorphism may not influence significantly sirolimus metabolism at the hepatic level. However, strong CYP 3A4 inhibition by cyclosporine could unveil the influence of this polymorphism.

Theoretical basis, experimental design, and computerized simulation of synergism and antagonism in drug combination studies

The median-effect equation derived from the mass-action law principle at equilibrium-steady state via mathematical induction and deduction for different reaction sequences and mechanisms and different types of inhibition has been shown to be the unified theory for the Michaelis-Menten equation, Hill equation, Henderson-Hasselbalch equation, and Scatchard equation. It is shown that dose and effect are interchangeable via defined parameters. This general equation for the single drug effect has been extended to the multiple drug effect equation for n drugs. These equations provide the theoretical basis for the combination index (CI)-isobologram equation that allows quantitative determination of drug interactions, where CI < 1, = 1, and > 1 indicate synergism, additive effect, and antagonism, respectively. Based on these algorithms, computer software has been developed to allow automated simulation of synergism and antagonism at all dose or effect levels. It displays the dose-effect curve, median-effect plot, combination index plot, isobologram, dose-reduction index plot, and polygonogram for in vitro or in vivo studies. This theoretical development, experimental design, and computerized data analysis have facilitated dose-effect analysis for single drug evaluation or carcinogen and radiation risk assessment, as well as for drug or other entity combinations in a vast field of disciplines of biomedical sciences. In this review, selected examples of applications are given, and step-by-step examples of experimental designs and real data analysis are also illustrated. The merging of the mass-action law principle with mathematical induction-deduction has been proven to be a unique and effective scientific method for general theory development. The median-effect principle and its mass-action law based computer software are gaining increased applications in biomedical sciences, from how to effectively evaluate a single compound or entity to how to beneficially use multiple drugs or modalities in combination therapies.

Sirolimus: the evidence for clinical pharmacokinetic monitoring

This review seeks to apply a decision-making algorithm to establish whether clinical pharmacokinetic monitoring (CPM) of sirolimus (rapamycin) in solid organ transplantation is indicated in specific patient populations. The need for CPM of sirolimus, although a regulatory requirement in Europe, has not yet been firmly established in North America and other parts of the world. Sirolimus has demonstrated immunosuppressive efficacy in renal, pancreatic islet cell, liver and heart transplant recipients. The pharmacological response of immunosuppressive therapy with sirolimus cannot be readily evaluated; however, a relationship between trough blood sirolimus concentrations, area under the plasma concentration-time curve (AUC) and the incidence of rejection has been proposed. Furthermore, sirolimus can be measured in whole blood by several assays--high-performance liquid chromatography with detection by tandem mass spectrometry, or with ultraviolet detection, radioreceptor assay or microparticle enzyme immunoassay. Both experimental animal and clinical data suggest that adverse events and their associated severity are correlated with blood concentrations. To prevent rejection and minimise toxicity, a therapeutic range of 4-12 microg/L (measured via chromatographic assays) is recommended when sirolimus is used in conjunction with ciclosporin. If ciclosporin therapy is discontinued, a target trough range of 12-20 microg/L is recommended. Sirolimus pharmacokinetics display large inter- and intrapatient variability, which may change in specific patient populations due to disease states or concurrent immunosuppressants or other interacting drugs. Due to the long half-life of sirolimus, dosage adjustments would ideally be based on trough levels obtained more than 5-7 days after initiation of therapy or dosage change. Once the initial dose titration is complete, monitoring sirolimus trough concentrations weekly for the first month and every 2 weeks for the second month appears to be appropriate. After the first 2 months of dose titration, routine CPM of sirolimus is not necessary in all patients, but may be warranted to achieve target concentrations in certain populations of patients, but the frequency of further monitoring remains to be determined and should be individualised.

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

JAK3 is a cytoplasmic tyrosine kinase with limited tissue expression but is readily found in activated T cells. Patients lacking JAK3 are immune compromised, suggesting that JAK3 represents a therapeutic target for immunosuppression. Herein, we show that a Mannich base, NC1153, blocked IL-2-induced activation of JAK3 and its downstream substrates STAT5a/b more effectively than activation of the closely related prolactin-induced JAK2 or TNF-alpha-driven NF-kappaB. In addition, NC1153 failed to inhibit several other enzymes, including growth factor receptor tyrosine kinases, Src family members, and serine/threonine protein kinases. Although NC1153 inhibited proliferation of normal human T cells challenged with IL-2, IL-4, or IL-7, it did not block T cells void of JAK3. In vivo, a 14-day oral therapy with NC1153 significantly extended survival of MHC/non-MHC mismatched rat kidney allografts, whereas a 90-day therapy induced transplantation tolerance (>200 days). Although NC1153 acted synergistically with cyclosporin A (CsA) to prolong allograft survival, it was not nephrotoxic, myelotoxic, or lipotoxic and did not increase CsA-induced nephrotoxicity. In contrast to CsA, NC1153 was not metabolized by cytochrome P450 3A4. Thus, NC1153 prolongs allograft survival without several toxic effects associated with current immunosuppressive drugs.

Janus kinase 3: a novel target for selective transplant immunosupression

Existing immunosuppressants inhibit lymphocyte activation and T cell cytokine signal transduction pathways, reducing the rate of acute rejection episodes to < 10%. However, the widespread tissue distribution of their molecular targets engenders pleiotropic toxicities. One strategy to address this problem seeks to identify compounds that selectively inhibit a target restricted in distribution to the lymphoid system. Janus kinase (Jak) 3 is such a molecule; it mediates signal transduction via the gamma common chain of lymphokine surface receptors. Disruption of this lymphoid-restricted enzyme would not be predicted to produce collateral damage in other organ systems. Development of selective Jak3 inhibitors has been difficult due to crossreactivity with its homologue, Jak2. In contrast to all other putative antagonists, which are discussed in detail herein, one Jak3 inhibitor, NC1153, shows at least 40-fold greater selective inhibition for Jak3 than for Jak2, is robustly synergistic with calcineurin antagonists, and, either alone or in combination with cyclosporin, produces no adverse effects in rodents preconditioned to be at heightened risk for nephrotoxicity, bone marrow suppression, or altered lipid metabolism.

CEDIA® Sirolimus Assay Compared With HPLC-MS/MS and HPLC-UV in Transplant Recipient Specimens

The role of the therapeutic drug monitoring laboratory in support of immunosuppressant drug therapy is well established, and the introduction of sirolimus (SRL) is a new direction in this field. The lack of an immunoassay for several years has restricted the availability of SRL assay services. The recent availability of a CEDIA SRL assay has the potential to improve this situation. The present communication has compared the CEDIA SRL method with 2 established chromatographic methods, HPLC-UV and HPLC-MS/MS. The CEDIA method, run on a Hitachi 917 analyzer, showed acceptable validation criteria with within-assay precision of 9.1% and 3.3%, and bias of 17.1% and 5.8%, at SRL concentrations of 5.0 microg/L and 20 microg/L, respectively. The corresponding between-run precision values were 11.5% and 3.3% and bias of 7.1% and 2.9% at 5.0 microg/L and 20 microg/L, respectively. The lower limit of quantification was found to be 3.0 microg/L. A series of 96 EDTA whole-blood samples predominantly from renal transplant recipients were assayed by the 3 methods for comparison. It was found that the CEDIA method showed a Deming regression line of CEDIA=1.20xHPLC-MS/MS-0.07 (r=0.934, SEE=.47), with a mean bias of 20.4%. Serial blood samples from 8 patients included in this evaluation showed that the CEDIA method reflected the clinical fluctuations in the chromatographic methods, albeit with the variable bias noted. The CEDIA method on the H917 analyzer is therefore a useful adjunct to SRL dosage individualization in renal transplant recipients.

Selectin blockade plus therapy with low-dose sirolimus and cyclosporin a prevent brain death-induced renal allograft dysfunction

Both antigen-dependent and -independent factors influence long-term organ allograft function and survival. Brain death (BD), a significant antigen-independent, donor-related injury upregulates a variety of inflammatory mediators in peripheral organs. One of the earliest responses to such an insult is the expression of selectins by endothelial cells of the transplanted tissues; these in turn trigger a cascade of nonspecific events, that enhance host alloresponses and which may be worsened by toxic effects of long-term immunosuppression. Using a rat model in which donor BD accentuates subsequent renal allograft injury, we have tested the effects of therapy with recombinant P-selectin glycoprotein ligand (rPSGL-Ig) alone, or in combination with sirolimus (SRL) and cyclosporin A. We found that in contrast to the effects of standard doses of SRL or cyclosporine, rPSGL-Ig decreased inflammation in the early posttransplant period such that lower doses of maintenance immunosuppression were sufficient to maintain long-term graft function.

Benefit-Risk Assessment of Sirolimus in Renal Transplantation

Sirolimus (rapamycin) is a macrocyclic lactone isolated from a strain of Streptomyces hygroscopicus that inhibits the mammalian target of rapamycin (mTOR)-mediated signal-transduction pathways, resulting in the arrest of cell cycle of various cell types, including T- and B-lymphocytes. Sirolimus has been demonstrated to prolong graft survival in various animal models of transplantation, ranging from rodents to primates for both heterotopic, as well as orthotopic organ grafting, bone marrow transplantation and islet cell grafting. In human clinical renal transplantation, sirolimus in combination with ciclosporin (cyclosporine) efficiently reduces the incidence of acute allograft rejection. Because of the synergistic effect of sirolimus on ciclosporin-induced nephrotoxicity, a prolonged combination of the two drugs inevitably leads to progressive irreversible renal allograft damage. Early elimination of calcineurin inhibitor therapy or complete avoidance of the latter by using sirolimus therapy is the optimal strategy for this drug. Prospective randomised phase II and III clinical studies have confirmed this approach, at least for recipients with a low to moderate immunological risk. For patients with a high immunological risk or recipients exposed to delayed graft function, sirolimus might not constitute the best therapeutic choice--despite its ability to enable calcineurin inhibitor sparing in the latter situation--because of its anti-proliferative effects on recovering renal tubular cells. Whether lower doses of sirolimus or a combination with a reduced dose of tacrolimus would be advantageous in these high risk situations remains to be determined. Clinically relevant adverse effects of sirolimus that require a specific therapeutic response or can potentially influence short- and long-term patient morbidity and mortality as well as graft survival include hypercholesterolaemia, hypertriglyceridaemia, infectious and non-infectious pneumonia, anaemia, lymphocele formation and impaired wound healing. These drug-related adverse effects are important determinants in the choice of a tailor-made immunosuppressive drug regimen that complies with the individual patient risk profile. Equally important in the latter decision is the lack of severe intrinsic nephrotoxicity associated with sirolimus and its advantageous effects on arterial hypertension, post-transplantation diabetes mellitus and esthetic changes induced by calcineurin inhibitors. Mild and transient thrombocytopenia, leukopenia, gastrointestinal adverse effects and mucosal ulcerations are all minor complications of sirolimus therapy that have less impact on the decision for choosing this drug as the basis for tailor-made immunosuppressive therapy. It is clear that sirolimus has gained a proper place in the present-day immunosuppressive armament used in renal transplantation and will contribute to the development of a tailor-made immunosuppressive therapy aimed at fulfilling the requirements outlined by the individual patient profile.

Sirolimus increases transforming growth factor-beta1 expression and potentiates chronic cyclosporine nephrotoxicity

BACKGROUND

Sirolimus (SRL) is increasingly being used to decrease cyclosporine (CsA) exposure. SRL is not known to be nephrotoxic and has a mechanism of action distinct from CsA. We investigated the effect of combining CsA and SRL on renal structure and function and on transforming growth factor-beta1 (TGF-beta1) and extracellular matrix (ECM) proteins in a model of chronic CsA nephrotoxicity.

METHODS

Rats treated with vehicle, SRL 0.3 mg/kg/day, CsA 5 or 10 mg/kg/day, or CsA5+SRL were sacrificed at 7 or 28 days. Physiologic and histologic changes were studied in addition to TGF-beta1 mRNA and protein expressions, and mRNA expression of plasminogen activator inhibitor-1 (PAI-1) and ECM proteins biglycan and types I and IV collagen.

RESULTS

While SRL alone did not alter renal function and structure, it potentiated the nephrotoxic actions of CsA when used in combination with low-dose CsA5 and resulted in significant changes similar to high-dose CsA10. In addition, SRL alone increased TGF-beta1 by 44% to 49% (P < 0.05 vs. VH). When used in combination with low-dose CsA5, SRL potentiated TGF-beta1 mRNA and protein by 121% and 176%, respectively (P < 0.05 vs. VH and CsA5), to levels achieved with high-dose CsA10. The expression of the ECM proteins followed that of TGF-beta1; a similar effect was observed with PAI-1, suggesting a decrease in ECM degradation.

CONCLUSION

Because SRL augments nephrotoxicity, caution should be exercised when it is used in combination with CsA. More studies are needed to determine the long-term clinical impact of SRL on nephrotoxicity and allograft function.

Therapeutic drug monitoring of sirolimus: effect of concomitant immunosuppressive therapy and optimization of drug dosing

Sirolimus (SRL) is a new immunosuppressant which shares a common metabolic pathway with several other immunosuppressive agents. This leads to potential pharmacokinetic interactions that might affect SRL blood levels with relevant clinical consequences. As a validated laboratory, 2658 SRL trough samples (corresponding to 495 kidney transplant recipients treated with different immunosuppressive regimens) from more than 40 Italian Transplant Units were analyzed. We found that dose-normalized SRL trough levels were significantly higher in patients treated with cyclosporine (CsA) and SRL (4.15 +/- 2.23 ng/mL/mg SRL), compared with patients treated with mycophenolate mofetil (MMF) and SRL (3.26 +/- 1.86 ng/mL/mg SRL; p < 0.01) or with MMF, steroids and SRL (2.52 +/- 1.73 ng/mL/mg SRL; p < 0.01). Mean intra- and interpatient variabilities were 19% and 47%, respectively. Both parameters are significantly affected by the time postsurgery, with the first week post transplantation being associated with the greatest variability. As additional analysis, a simple dose-adjustment formula has been proposed as a useful tool to guide SRL dose changes. The proposed equation has been able to predict SRL concentration after a dose change in 73% of the tested samples. These findings suggest that different immunosuppressants significantly interfere with SRL bioavailability. Strategies aimed at reducing variability in SRL exposure may have a positive clinical impact.

Clinical pharmacokinetics of everolimus

Everolimus is an immunosuppressive macrolide bearing a stable 2-hydroxyethyl chain substitution at position 40 on the sirolimus (rapamycin) structure. Everolimus, which has greater polarity than sirolimus, was developed in an attempt to improve the pharmacokinetic characteristics of sirolimus, particularly to increase its oral bioavailability. Everolimus has a mechanism of action similar to that of sirolimus. It blocks growth-driven transduction signals in the T-cell response to alloantigen and thus acts at a later stage than the calcineurin inhibitors ciclosporin and tacrolimus. Everolimus and ciclosporin show synergism in immunosuppression both in vitro and in vivo and therefore the drugs are intended to be given in combination after solid organ transplantation. The synergistic effect allows a dosage reduction that decreases adverse effects. For the quantification of the pharmacokinetics of everolimus, nine different assays using high performance liquid chromatography coupled to an electrospray mass spectrometer, and one enzyme-linked immunosorbent assay, have been developed. Oral everolimus is absorbed rapidly, and reaches peak concentration after 1.3-1.8 hours. Steady state is reached within 7 days, and steady-state peak and trough concentrations, and area under the concentration-time curve (AUC), are proportional to dosage. In adults, everolimus pharmacokinetic characteristics do not differ according to age, weight or sex, but bodyweight-adjusted dosages are necessary in children. The interindividual pharmacokinetic variability of everolimus can be explained by different activities of the drug efflux pump P-glycoprotein and of metabolism by cytochrome P450 (CYP) 3A4, 3A5 and 2C8. The critical role of the CYP3A4 system for everolimus biotransformation leads to drug-drug interactions with other drugs metabolised by this cytochrome system. In patients with hepatic impairment, the apparent clearance of everolimus is significantly lower than in healthy volunteers, and therefore the dosage of everolimus should be reduced by half in these patients. The advantage of everolimus seems to be its lower nephrotoxicity in comparison with the standard immunosuppressants ciclosporin and tacrolimus. Observed adverse effects with everolimus include hypertriglyceridaemia, hypercholesterolaemia, opportunistic infections, thrombocytopenia and leucocytopenia. Because of the variable oral bioavailability and narrow therapeutic index of everolimus, blood concentration monitoring seems to be important. The excellent correlation between steady-state trough concentration and AUC makes the former a simple and reliable index for monitoring everolimus exposure. The target trough concentration of everolimus should range between 3 and 15 microg/L in combination therapy with ciclosporin (trough concentration 100-300 microg/L) and prednisone.

Synergistic effects of RAD and Neoral in inhibition of host-vs.-graft and graft-vs.-host immune responses in rat small-bowel transplantation

The combined effects of RAD and Neoral were tested in a rat orthotopic small-bowel transplantation model. Seven groups (n = 6) were involved in this study, and each one was included in three rejection models for the evaluation of host-vs.-graft disease (HVG) (LBN-F1 to LEW), graft-vs.-host disease (GVH) (LEW to LBN-F1), and combined HVG and GVH immune responses (BN to LEW). Both drugs were administered orally throughout the study. Low doses of RAD (1.0-2.5 mg/kg/day) combined with Neoral (2.0-5.0 mg/kg/day) produced strong synergistic effects in the prolongation of small-bowel graft survival in HVG (combination index, CI = 0.095, 0.1212), GVH (CI = 0.027, 0.020), and combined HVG and GVH immune responses (CI = 0.070, 0.301). The combination therapy of RAD and Neoral produces a strong synergistic effect toward the inhibition of HVG, GVH, and combined HVG and GVH immune responses in a rat small-bowel transplantation model.

Specific inhibition of Stat5a/b promotes apoptosis of IL-2-responsive primary and tumor-derived lymphoid cells

Stat5a/b exhibits 96% homology and are required for normal immune function. The present studies examined Stat5a/b function in lymphoid cells by specific and simultaneous disruption of both proteins using novel phosphorothioate-2'-O-methoxyethyl antisense oligodeoxynucleotides (asODN). Efficient delivery was confirmed by the presence of fluorescent TAMRA-labeled ODN in >or=55 and 95% in human primary and tumor cell lines, respectively. Acute asODN administration reduced levels of Stat5a (90%) in 6 h, whereas Stat5b required nearly 48 h to attain the same inhibition, suggesting that the apparent turnover rate for Stat5a was 8-fold higher than that for Stat5b. Expression of the closely related Stat3 protein was unchanged after asODN treatment, however. Molecular ablation of Stat5a/b promoted apoptotic cell death in a significant population of primary PHA-activated T cells (72%) and lymphoid tumor cell line (e.g., YT; 74%) within 24 h, as assessed by 1) visualization of karyolytic nuclear degeneration and other generalized cytoarchitectural alterations, 2) enzymatic detection of TdT-positive DNA degradation, and 3) automated cytometric detection of annexin V translocation. Contrary to findings from Stat5a/b-null mice, cell cycle progression did not appear to be significantly affected. Interestingly, IL-2-insensitive and unprimed T cells and Jurkat cells remained mostly unaffected. Finally, evidence is provided that the cytotoxicity associated with Stat5a/b ablation may derive from activation of caspase-8, an initiator protease that contributes to apoptotic cell commitment. We propose that in lymphoid cells competent to activate Stat5a and Stat5b, both proteins preferentially mediate an antiapoptotic survival influence.

Sirolimus delays recovery of rat kidney transplants after ischemia-reperfusion injury

BACKGROUND

Sirolimus (SRL) seems to impair renal recovery from ischemic injury in animal models and delayed graft function after clinical renal transplantation. This study determined the impact of SRL on renal recovery after ischemia-reperfusion injury in a rat kidney transplant model.

METHODS

Syngeneic kidneys were preserved in University of Wisconsin solution before transplantation into bilaterally nephrectomized rats. Recipients received vehicle or SRL targeting for whole-blood trough levels of 10 to 20 ng/mL as measured by high-performance liquid chromatography. Renal function was assessed by animal survival or daily serum creatinine. Tissue samples were collected for histologic examination.

RESULTS

Median SRL whole-blood concentrations were 16.6 +/- 1.6 ng/mL on postoperative day (POD) 1 and 12.0 +/- 0.9 ng/mL on POD 3. Transplantation of kidneys after 39 hr of cold storage resulted in 30% survival in the SRL-treated group compared with 100% survival in the control group (P=0.002). Transplantation of kidneys after 24 hr of cold storage resulted in no survival differences, but there were significant differences in renal function. Daily serum creatinine (PODs 1-4) was higher in the SRL-treated group compared with the control group (P<0.05 at all time points). Grafts from SRL-treated animals showed more severe tubular necrosis compared with control animals.

CONCLUSIONS

When given at therapeutic immunosuppressive doses, SRL compromises renal function after ischemia-reperfusion injury in a rat kidney transplant model. The antiproliferative effect of SRL may translate into impairment of tubular repair and regeneration necessary for recovery after such injury.

Steroid-refractory graft-vs.-host disease: past, present and future

Despite current standard preventive strategies that include optimizing donor selection and the combination of methorexate and a calcineurine inhibitor, acute and chronic GVHD remains a major barrier to successful hematopoietic cell transplantation for a sizeable proportion of patients. When acute and chronic GVHD become manifest a standard primary therapy approach has been the addition of glucocorticoid therapy to a background of calcineurine inhibition. When this approach fails patients with GVHD require secondary therapy. Ideally, second-line agents should promote transplantation tolerance so that the morbidity associated with prolonged use of glucocorticoids and other immunosuppressive agents can be minimized. Promising new agents or strategies which warrant further controlled clinical trials include: mycophenolate mofetil, sirolimus, humanized or chimeric monoclonal antibodies such as visilizumab, daclizumab and infliximab, and extracorporeal photopheresis. Co-operative studies are necessary to hasten the process of evaluating novel treatment strategies for acute and chronic GVHD.

Synergistic effects of malononitrilamides (FK778, FK779) with tacrolimus (FK506) in prevention of acute heart and kidney allograft rejection and reversal of ongoing heart allograft rejection in the rat

BACKGROUND

The effects of tacrolimus (FK506) and malononitrilamides (MNA) (FK778 and FK779) monotherapy and combination therapy were examined in prevention of acute heart and kidney allograft rejection and reversal of ongoing acute heart allograft rejection in the rat.

METHODS

Brown Norway (RT1n)-to-Lewis (RT11) and ACI (RT1a)-to-Lewis (RT11) combinations were used, respectively, for heart and kidney transplantation models. Immunosuppressants were administered orally from day 1 to day 14 for preventing acute rejection and from day 4 to day 34 after transplantation for the reversal of ongoing acute rejection.

RESULTS

In the prevention of acute heart rejection model, recipient rats treated with monotherapy of tacrolimus or MNA (FK778, FK779) showed a dose-related prolongation of mean survival time (MST) compared with naive control rats (P<0.01). The mean survival time in combination therapy of tacrolimus (FK506) and FK778 indicated that an additive to synergistic interaction was produced when compared with the respective monotherapies (combination index [CI]=0.631-1.022). These results were reproducible with tacrolimus and FK779 combination therapy (CI=0.572-0.846). Furthermore, similar results were also found in the prevention of acute kidney allograft rejection in the rat (CI=0.137-0.516). In the reversal of ongoing acute heart allograft rejection, combination therapy of tacrolimus and FK778 demonstrated a strong synergistic interaction (CI=0.166-0.970) compared with monotherapy of tacrolimus or FK778.

CONCLUSIONS

Combination therapy of tacrolimus and MNA (FK778, FK779) produces synergistic effects in prevention of acute heart and kidney rejection and reversal of ongoing heart allograft rejection in the rat.

Sirolimus: its discovery, biological properties, and mechanism of action

Sirolimus is the USAN-assigned generic name for the natural product rapamycin. Sirolimus is produced by a strain of Streptomyces hygroscopicus, isolated from a soil sample collected from Rapa Nui commonly known as Easter Island. Although sirolimus was isolated as an antifungal agent with potent anticandida activity, subsequent studies revealed impressive antitumor and immunosuppressive activities. Sirolimus demonstrates activity against several murine tumors, such as B16 43 melanocarcinoma, Colon 26 tumor, EM ependymoblastoma, and mammary and colon 38 solid tumors. Sirolimus is a potent inhibitor of antigen-induced proliferation of T cells, B cells, and antibody production. Demonstration of the potent immunosuppressive activity of sirolimus in animal models of organ transplantation led to clinical trials and subsequent approval by regulatory authorities for prophylaxis of renal graft rejection. Interest in sirolimus as an immunosuppressive therapy in organ transplantation derives from its unique mechanism of action, its unique side-effect profile, and its ability to synergize with other immunosuppressive agents. The molecular mechanism underlying the antifungal, antiproliferative, and immunosuppressive activities of sirolimus is the same. Sirolimus forms an immunosuppressive complex with intracellular protein, FKBP12. This complex blocks the activation of the cell-cycle-specific kinase, TOR. The downstream events that follow the inactivation of TOR result in the blockage of cell-cycle progression at the juncture of G1 and S phase.

Preclinical results of sirolimus treatment in transplant models

Sirolimus (SRL; rapamycin) is a macrolide antibiotic, which modest anticandidal and tumoricidal activities were superseded by its immunosuppressive potential to block allograft rejection. The most intriguing biological characteristic of SRL emerged after demonstration of its potent synergism with cyclosporine (CsA). Naïve T cells, residing in the G(0) phase of the cell cycle, become activated by three signals. Signal 1 (T cell antigen receptor/alloantigen) and Signal 2 (CD28/B7) progress T cell to the early G(1) phase inducing production of interleukin-2 (IL-2) and other T cell growth factors (TGFs). Signal 3 (cytokine/cytokine receptor) initiate cell division and differentiation in the late G(1)/S phase. Whereas CsA binding to calcineurin blocks Signal 1/2, SRL binding to mammalian target of rapamycin (mTOR) blocks Signal 3. Our preclinical studies have established the in vivo principles of the effects exhibited by SRL alone on allograft survival, synergism between SRL and CsA as well as two drugs pharmacokinetic and pharmacodynamic interactions. In our experimental model, a 14-day i.v. continuous infusion of SRL by osmotic pump into rat recipients extended the survivals of heart allografts in a dose-dependent fashion. In comparison to untreated controls (MST of 6.3 +/- 0.5 days), 0.08 mg/kg SRL extended MST to 34.4 +/- 12.1 days, and 0.8 mg/kg to 74.1 +/- 20.2 days, with 6/18 allografts surviving for more than 100 days. Since almost identical results were produced by 10-fold higher SRL doses delivered by oral gavage, we estimated its bioavailability at 10%. Similarly, SRL prolonged the survivals of kidney, pancreas, and small bowel allografts in rats. At the same time large animal models cautioned about potential toxicities, namely intestinal vasculitis. The synergistic interactions of CsA and SRL may be explained by sequential effects in the early G(0)/G(1) versus late G1/S phases of cell cycle progression, respectively. The in vivo interaction of SRL with other immunosuppressive drugs was evaluated by the median effect analysis and the combination index (CI) values (CI = 1 shows additive, CI < 1, synergistic, and CI > 1, antagonistic, interactions). Oral SRL proved to be synergistic in both CsA-resistant mouse (CI = 0.4-1.5) and CsA-sensitive rat (CI = 0.3-0.6) models. The pharmacokinetic interactions of SRL and/or CsA were evaluated in rats for i.v. and oral formulations. Although low CsA and SRL i.v. doses did not affect each other levels, potent interaction was observed after oral gavage: CsA increased SRL levels by 2-11 folds; and, SRL increased CsA levels by 2-3-folds. Our results suggested that both pharmacodynamic and pharmacokinetic interactions contribute to the synergism between SRL and CsA. We also estimated the impact of CsA/SRL interaction on renal dysfunction, myelosuppression, and hyperlipidemia. Salt-depleted rats treated with SRL (0.4-6.4 mg/kg) and/or CsA (2.5-20 mg/kg) were examined for glomerular filtration rates (GFR), lipid levels, and bone marrow cellularity. CsA-induced kidney function deficiency was exacerbated by SRL. This exacerbation of renal dysfunction correlated with increased CsA levels in kidneys when combined with SRL. Furthermore, CsA potentiated SRL-mediated toxicities, namely myelosuppression and increased cholesterol. In conclusion, SRL therapy is synergistic with CsA but both drug levels should be carefully monitored to avoid toxic effects.

Sirolimus oral absorption in rats is increased by ketoconazole but is not affected by D-alpha-tocopheryl poly(ethylene glycol 1000) succinate

The contributions of cytochrome P450 3A (CYP3A) and P-glycoprotein to sirolimus oral bioavailability in rats were evaluated by coadministration of sirolimus (Rapamune) with the CYP3A inhibitor ketoconazole or the P-glycoprotein inhibitor D-alpha-tocopheryl poly(ethylene glycol 1000) succinate (TPGS). Groups of six male Sprague-Dawley rats (250-300 g) were administered Rapamune (1 mg/kg) by oral gavage, alone and with ketoconazole (30 mg/kg) or TPGS (50 mg/kg). Sirolimus levels were measured in whole blood over a 6-h time course. Sirolimus C(max) (6.6 +/- 1.6 versus 26 +/- 7 ng/ml) and area under the concentration versus time curve from 0 to 6 h (AUC(0-6)) (22 +/- 7 versus 105 +/- 27 ng. h/ml) were increased 3- to 5-fold by ketoconazole. Median T(max) (1.5-2 h) was unchanged. TPGS had no effect on sirolimus absorption. The interaction of sirolimus with P-glycoprotein was also evaluated in vitro using HCT-8 and Caco-2 cell monolayers. Consistent with published reports, sirolimus was a good inhibitor of P-glycoprotein, inhibiting polarized basolateral-to-apical flux of rhodamine 123 with an IC(50) of 0.625 to 1.25 microM (cyclosporine caused >80% inhibition at 5 microM). Sirolimus did not demonstrate significant polarized flux in either direction using the same monolayers (basolateral-to-apical flux was <2 times the apical-to-basolateral). Moreover, sirolimus flux was not impacted by cyclosporine, suggesting that it does not undergo P-glycoprotein-mediated transport in this system. The lack of significant sirolimus transport by P-glycoprotein may, in part, explain the lack of a TPGS effect on sirolimus absorption in rats.

Chronic graft-versus-host disease and late effects after hematopoietic stem cell transplantation

Late effects following HSCT are related to either the transplant process or to the transplant preparative regimen. Problems related to the transplant process include delayed recovery of the immune system and chronic GVHD. Chronic GVHD presents between 3-14 months post-HSCT in approximately 20% of matched sibling transplants and 40% of matched unrelated donor recipients. Most commonly involved sites are skin, mouth, liver, gastrointestinal tract, and eye. Patients with platelet count < 100,000/ml and receiving cortocosteroid therapy at day 80 with any clinical manifestations of chronic GVHD require prolonged immune suppressive therapy with prednisone, cyclosporine +/- other agents. Treatment should be administered until all clinical and pathological signs and symptoms of chronic GVHD have resolved which may take one to several years. Problems related to the transplant preparative regimen include those involving the endocrine system, eyes, lungs, bone, and development of secondary malignancies. Endocrine deficiencies include growth failure with growth hormone (GH) deficiency, overt hypothyroidism, primary gonadal failure, Type 1 or Type 2 diabetes, and exocrine pancreatic insufficiency. These problems develop at any time post-HSCT, but usually occur within the first few years and should be treated with appropriate hormone supplementation. Eye problems are primarily related to development of cateracts secondary to total body irradiation (TBI) or prolonged corticosteroid use. Cateracts developing after fractionated frequently do not require removal. Pulmonary problems may be due to bronchiolitis obliterans (BO) or to restrictive lung disease. BO may be associated with chronic GVHD and may respond to chronic GVHD therapy. Restrictive lung disease does not occur for many years after HSCT. There is not therapy for this problem. Development of decreased bone mineral density (BMD) is related to GH deficiency and/or corticosteroid therapy. Treatment includes withdrawal of corticosteroids, administration of GH and calcium, Vitamin D and antiresorptive agents. All malignant disease survivors are at risk for development of secondary malignancies, including survivors of HSCT. Recipients of TBI are at highest risk as are children. All pediatric and adult survivors of HSCT should be followed for their life-time for development of delayed effects of transplantation.

Simultaneous quantification of sirolimus, everolimus, tacrolimus and cyclosporine by liquid chromatography-mass spectrometry (LC-MS)

We developed a universal liquid chromatography-mass spectrometry (LC-MS) assay with automated online extraction to quantify simultaneously the immunosuppressants sirolimus, everolimus, tacrolimus, and cyclosporine. Whole blood (300 microl) plus 6 microl 32-desmethoxyrapamycin (1 ng/microl) as internal standard was treated with 600 microl methanol/0.2 M ZnSO4 (80/20 v/v). After vortexing (30 s) and centrifugation (20000 g, 5 min) 50 microl of the supernatant were loaded on an extraction column, were washed by 0.35 ml/min water for 3 min and, after activation of a column-switching valve, were back-flushed by 0.25 ml/min methanol/ water (90/10 v/v) onto a C18 analytical column. After 22 min the extraction column was washed for 2 min with methanol and for 3 min with water before starting the next run. Column temperatures were kept at 33 degrees C. Sodium adduct ions [M+Na]+ ions were detected in the selected ion mode. For sirolimus, everolimus and tacrolimus the assay was linear from 0.3 to 200 microg/l and for cyclosporine from 5 to 1000 microg/l (all r2>0.999). Recovery of all immunosuppressants and the internal standard was >90% and in general, inter-day and intraday precision was <10%. The simultaneous quantification of blood levels by LC-MS seems to be the method of choice in transplanted patients receiving multiple immunosuppressants.

Update on pharmacokinetic/pharmacodynamic studies with FTY720 and sirolimus

Expanding the cytokine paradigm beyond the use of calcineurin inhibitors as baseline therapy provides new strategies in immunosuppression. Drugs such as FTY720 alter the sensitivity of lymphocytes to homing chemokines, and agents such as sirolimus (SRL) disrupt downstream cytokine signal transduction. Confirming studies in rodents and nonhuman primates, administration of either FTY720 or both of these drugs afford synergistic interactions with cyclosporine to renal transplant patients to rapidly and dramatically deplete peripheral blood lymphocytes (PBL) but neither granulocytes nor monocytes. Present information suggests that FTY720 facilitates lymphocyte homing mechanisms, leading to T and B cell sequestration in secondary lymphoid structures. Interestingly, FTY720 displays pharmacokinetic characteristics suggesting that therapeutic drug monitoring (TDM) will not be essential for clinical applications. In contrast, SRL is a critical-dose drug that requires TDM. SRL disrupts costimulatory and cytokine-stimulated T cell activation by inhibiting a multifunctional kinase, mammalian target of sirolimus (mTOR). Two pivotal trials including more than 1,300 patients demonstrated that addition of SRL to a CsA-based regimen reduces the incidence, time to onset, and severity of acute rejection episodes. When used alone, SRL seems therapeutically equivalent to CsA. In the coming decade, SRL is likely to be used in a variety of drug combination regimens both simultaneously and sequentially, not only to avert acute rejection episodes, but also to forestall chronic nephropathic processes. These two new agents are likely to usher in a new era of transplant therapy.

Selective inhibitor of Janus tyrosine kinase 3, PNU156804, prolongs allograft survival and acts synergistically with cyclosporine but additively with rapamycin

Janus kinase 3 (Jak3) is a cytoplasmic tyrosine (Tyr) kinase associated with the interleukin-2 (IL-2) receptor common gamma chain (gamma(c)) that is activated by multiple T-cell growth factors (TCGFs) such as IL-2, -4, and -7. Using human T cells, it was found that a recently discovered variant of the undecylprodigiosin family of antibiotics, PNU156804, previously shown to inhibit IL-2-induced cell proliferation, also blocks IL-2-mediated Jak3 auto-tyrosine phosphorylation, activation of Jak3 substrates signal transducers and activators of transcription (Stat) 5a and Stat5b, and extracellular regulated kinase 1 (Erk1) and Erk2 (p44/p42). Although PNU156804 displayed similar efficacy in blocking Jak3-dependent T-cell proliferation by IL-2, -4, -7, or -15, it was more than 2-fold less effective in blocking Jak2-mediated cell growth, its most homologous Jak family member. A 14-day alternate-day oral gavage with 40 to 120 mg/kg PNU156804 extended the survival of heart allografts in a dose-dependent fashion. In vivo, PNU156804 acted synergistically with the signal 1 inhibitor cyclosporine A (CsA) and additively with the signal 3 inhibitor rapamycin to block allograft rejection. It is concluded that inhibition of signal 3 alone by targeting Jak3 in combination with a signal 1 inhibitor provides a unique strategy to achieve potent immunosuppression.

Clinical pharmacokinetics of sirolimus

Sirolimus (previously known as rapamycin), a macrocyclic lactone, is a potent immunosuppressive agent. Sirolimus was recently approved by the US Food and Drug Administration, on the basis of 2 large, double-blind, prospective clinical trials, for use in kidney transplant recipients at a fixed dosage of 2 or 5 mg/day in addition to full dosages of cyclosporin and prednisone. However, despite the fixed dosage regimens used in these pivotal trials, pharmacokinetic and clinical data show that sirolimus is a critical-dose drug requiring therapeutic drug monitoring to minimise drug-related toxicities and maximise efficacy. Assays using high performance liquid chromatography coupled to mass spectrometry, although cumbersome, are the gold standard for evaluating other commonly used assays, such as liquid chromatography with ultraviolet detection, radioreceptor assay and microparticle enzyme immunoassay. Sirolimus is available in oral solution and tablet form. It has poor oral absorption and distributes widely in tissues, displaying not only a wide inter- and intrapatient variability in drug clearance, but also less than optimal correlations between whole blood concentrations and drug dose, demographic features or patient characteristics. Furthermore, the critical role of the cytochrome P450 3A4 system for sirolimus biotransformation leads to extensive drug-drug interactions, among which are increases in cyclosporin concentrations. Thus, sirolimus is now being used to reduce or eliminate exposure to cyclosporin or corticosteroids. The long elimination half-life of sirolimus necessitates a loading dose but allows once daily administration, which is more convenient and thereby could help to improve patient compliance. This review emphasises the importance of blood concentration monitoring in optimising the use of sirolimus. The excellent correlation between steady-state trough concentration (at least 4 days after inception of, or change in, therapy) and area under the concentration-time curve makes the former a simple and reliable index for monitoring sirolimus exposure. Target trough concentration ranges depend on the concomitant immunosuppressive regimen, but a range of 5 to 15 microg/L is appropriate if cyclosporin is being used at trough concentrations of 75 to 150 microg/L. Weekly monitoring is recommended for the first month and bi-weekly for the next month; thereafter,concentration measurements are necessary only if warranted clinically.

Selective inhibition of IL-2 gene expression by IL-2 antisense oligonucleotides blocks heart allograft rejection

PURPOSE

We tested the effects of selective inhibition of interleukin (IL)-2 gene expression by IL-2 antisense oligonucleotide (oligo) with phosphorothioate (PS)/phosphodiester (PD)/2'-methoxyethyl (ME) modifications (17359) on T-cell function and the survival of heart allografts in mice.

METHODS

The PS- (17328) or PS/PD/ME- (17359) IL-2 oligo was electroporated to mouse T cell lymphoma cells (TIB 155) stimulated with concanavalin A (Con A). Expression of IL-2 was analyzed by an ELISA spot assay and a reverse transcript polymerase chain reaction method. C3H (H-2k) mice transplanted with BALB/c (H-2d) heart grafts were treated i.v. with a 7-day osmotic pump with 20 mg/kg 17359 alone or in combination with sirolimus (SRL).

RESULTS

In comparison with untreated controls, 500 to 2000 nM 17328 inhibited IL-2 protein production by 21.8% to 47.2%, whereas 500 to 2000 nM 17359 did so by 35.5% to 83.5% (both P<0.001). In vivo, 20 mg/kg 17359 prolonged survivals to a mean survival time (MST) of 18.3+/-2.6 days (P<0.001) in comparison with only 8.2+/-0.8 days in untreated controls. Although 0.2 mg/kg SRL alone produced a MST of 18.8+/-6.0 days (P<0.01), addition of 20 mg/kg 17539 synergistically extended survivals to 54.3+/-12.1 days (P<0.001). As expected, IL-2 mRNA, but not IL-7, IL-9, or IL-15 mRNA, was reduced in allografts from recipients treated with 17359 compared with untreated controls. Lymph node cells from the same recipients displayed reduction in proliferative response to donor alloantigen and in generation of alloantigen-specific cytotoxic T cells.

CONCLUSION

Selective inhibition of IL-2 mRNA in vivo inhibits T-cell function and extends allograft survival.

Sirolimus, but not the structurally related RAD (everolimus), enhances the negative effects of cyclosporine on mitochondrial metabolism in the rat brain

Clinical studies have shown enhancement of cyclosporine toxicity when co-administered with the immunosuppressant sirolimus. We evaluated the biochemical mechanisms underlying the sirolimus/cyclosporine interaction on rat brain metabolism using magnetic resonance spectroscopy (MRS) and compared the effects of sirolimus with those of the structurally related RAD. Two-week-old rats (25 g) were allocated to the following treatment groups (all n=6): I. control, II. cyclosporine (10 mg kg(-1) d(-1)), III. sirolimus (3 mg kg(-1) d(-1)), IV. RAD (3 mg kg(-1) d(-1)), V. cyclosporine+sirolimus and VI. cyclosporine+RAD. Drugs were administered by oral gavage for 6 days. Twelve hours after the last dose, metabolic changes were assessed in brain tissue extracts using multinuclear MRS. Cyclosporine significantly inhibited mitochondrial glucose metabolism (glutamate: 78+/-6% of control; GABA: 67+/-12%; NAD(+): 76+/-3%; P<0.05), but increased lactate production. Sirolimus and RAD inhibited cytosolic glucose metabolism via lactate production (sirolimus: 81+/-3% of control, RAD: 69+/-2%; P<0.02). Sirolimus enhanced cyclosporine-induced inhibition of mitochondrial glucose metabolism (glutamate: 60+/-4%; GABA: 59+/-8%; NAD(+): 45+/-5%; P<0.02 versus cyclosporine alone). Lactate production was significantly reduced. In contrast, RAD antagonized the effects of cyclosporine (glutamate, GABA, and NAD(+), not significantly different from controls). The results can partially be explained by pharmacokinetic interactions: co-administration increased the distribution of cyclosporine and sirolimus into brain tissue, while co-administration with RAD decreased cyclosporine brain tissue concentrations. In addition RAD, but not sirolimus, distributed into brain mitochondria. The combination of cyclosporine/RAD compares favourably to cyclosporine/sirolimus in regards to their effects on brain high-energy metabolism and tissue distribution in the rat.

Effect of low dose cyclosporine and sirolimus on hepatic drug metabolism in the rat1

BACKGROUND

We examined the effect cyclosporine (CsA) and sirolimus (SRL) alone and in combination on hepatic cytochrome P450-mediated metabolism in rats.

METHODS

Rats were given 1 mg/kg of CsA or 0.4 mg/kg of SRL alone or in combination via constant intravenous infusion. Renal function was evaluated at the end of treatment. Blood samples were obtained to estimate CsA and SRL concentrations. Hepatic microsomes were prepared for immunoblotting and catalytic assays.

RESULTS

CsA alone did not alter serum creatinine levels. SRL given alone or in combination with CsA produced a significant increase in urine output without changes in fluid balance. Although CsA and SRL administered alone caused damage to renal proximal tubules, the two-drug combination dramatically increased the renal structural damage. CsA alone suppressed cytochrome P450 (CYP) 3A2 protein levels by 39% (P=0.012) and catalytic activity by 30% (P=0.042). SRL alone reduced catalytic activity by 38% (P=0.012). Combination therapy reduced both CYP3A2 levels by 55% (P<0.001) and catalytic activity by 55% (P=0.001). CYP2C11 protein expression or catalytic activity were not changed in any group. CYP2A1 protein expression and catalytic activity were both significantly reduced in rats given CsA or/and SRL. Steady-state CsA levels were increased during concurrent SRL dosing, however, SRL concentrations were not changed by CsA coadministration.

CONCLUSIONS

Concurrent SRL dosing increases CsA concentrations due to inhibition of hepatic CYP3A2 protein expression. Nephrotoxicity caused by combination therapy is due to CsA elevating levels of SRL or by SRL itself. Concurrent administration of CsA and SRL in transplant patients should be performed with caution.

A calcineurin antagonist-free induction strategy for immunosuppression in cadaveric kidney transplant recipients at risk for delayed graft function

BACKGROUND

Avoidance of calcineurin antagonists for a prolonged period de novo after cadaver donor renal transplantation may facilitate recovery from delayed graft function. The present study examined the benefit of prolonging the calcineurin antagonist-free interval by administering sirolimus (SRL) in combination with chimeric (c-) anti-interleukin-2 receptor (IL-2R) monoclonal antibodies (mAb).

METHODS

Three contemporaneous but nonrandomized cohorts were compared for acute rejection episodes, patient and graft survival rates, renal function, and adverse reaction profiles for 12 months. Patients with delayed graft function were treated with either SRL/c-IL-2R mAb/prednisone (Pred) with inception of cyclosporine (CsA) once the serum creatinine value was < or =2.5 mg/dl (n=43; group 1) or anti-lymphocyte preparations/Pred/delayed CsA for 7 to 14 days (n=18; group 3). A third cohort displayed immediate function and was treated de novo with CsA/c-IL-2R mAb/Pred (n=21; group 2).

RESULTS

The incidence of acute rejection episodes was significantly lower among group 1 (16%) compared with groups 2 (52%, P=0.004) or 3 (39%, P=0.05). Among the seven rejection episodes in group 1, six of seven occurred among African-American or retransplant recipients, and a separate cluster of six of seven occurred among patients who displayed SRL trough concentrations < or =9 ng/ml. Furthermore, additional antilymphocyte antibody treatment was required to reverse either steroid-resistant or Banff grades II or III acute rejection episodes among 14%, 55% (P=0.08), and 71% (P=0.03) of patients in each group, respectively. Patient and graft survival rates, as well as mean serum creatinine values, were similar at 12 months among the three groups. However, group 1 patients displayed higher serum cholesterol and triglyceride values, as well as lower hemoglobin, platelet, and leukocyte values compared with the other two groups.

CONCLUSION

This pilot study suggests that a SRL/c-IL-2R mAb/Pred induction regimen provides excellent acute rejection prophylaxis.

Pharmacokinetic interactions augment toxicities of sirolimus/cyclosporine combinations

This study correlated the dynamic effects of sirolimus (rapamycin; RAPA) and cyclosporine (CsA) alone versus in combination to produce renal dysfunction, myelosuppression, or hyperlipidemia, with their corresponding blood and tissue concentrations. After salt-depleted rats were treated with RAPA (0.4 to 6.4 mg/kg per d) and/or CsA (2.5 to 20.0 mg/kg per d) for 14 d, the GFR, lipid levels, bone marrow cellularity, and CsA/RAPA concentrations in whole blood versus liver or renal tissues were measured, and the median effect model was used to discern the type of drug interactions. Compared with vehicle controls (1.98 +/- 0.34 ml/min), GFR values were reduced only by large doses of drug monotherapy, namely RAPA (3.2 mg/kg per d = 1.2 +/- 0.02 ml/min or 6.4 mg/kg per d = 1.3 +/- 0.2 ml/min; both P < 0.01) or CsA (10.0 mg/kg per d = 1.2 +/- 0.1 ml/min or 20.0 mg/kg per d = 0.8 +/- 0.4 ml/min; both P < 0.01). In contrast, hosts that were treated with smaller doses of CsA/RAPA combinations showed more pronounced effects in reduction of GFR values: 2.5/0.4 mg/kg per d, modestly (1.5 +/- 0.5 ml/min; P < 0.01); 5.0/0.8 mg/kg per d, moderately (0.23 +/- 0.01 ml/min; P < 0.001); and higher-dose groups, markedly. The exacerbation of renal dysfunction seemed to be due to a pharmacokinetic interaction of RAPA to greatly increase CsA concentrations in whole blood and, particularly, in kidney tissue. In contrast, the pharmacodynamic effects of CsA to potentiate two RAPA-mediated toxicities-myelosuppression and increased serum cholesterol/low-density lipoprotein cholesterol-occurred independently of pharmacokinetic interactions. RAPA aggravates CsA-induced renal dysfunction owing to a pharmacokinetic interaction, whereas CsA produces a pharmacodynamic effect that augments RAPA-induced myelosuppression and hyperlipidemia.

Concomitant inhibition of Janus kinase 3 and calcineurin-dependent signaling pathways synergistically prolongs the survival of rat heart allografts

The cytoplasmic localized Janus tyrosine kinase 3 (Jak3) is activated by multiple cytokines, including IL-2, IL-4, and IL-7, through engagement of the IL-2R common gamma-chain. Genetic inactivation of Jak3 is manifested as SCID in humans and mice. These findings have suggested that Jak3 represents a pharmacological target to control certain lymphoid-derived diseases. Using the rat T cell line Nb2-11c, we document that tyrphostin AG-490 blocked in vitro IL-2-induced cell proliferation (IC(50) approximately 20 microM), Jak3 autophosphorylation, and activation of its key substrates, Stat5a and Stat5b, as measured by tyrosine/serine phosphorylation analysis and DNA-binding experiments. To test the notion that inhibition of Jak3 provides immunosuppressive potential, a 7-day course of i.v. therapy with 5-20 mg/kg AG-490 was used to inhibit rejection of heterotopically transplanted Lewis (RT1(l)) heart allografts in ACI (RT1(a)) recipients. In this study, we report that AG-490 significantly prolonged allograft survival, but also acted synergistically when used in combination with the signal 1 inhibitor cyclosporin A, but not the signal 3 inhibitor, rapamycin. Finally, AG-490 treatment reduced graft infiltration of mononuclear cells and Stat5a/b DNA binding of ex vivo IL-2-stimulated graft infiltrating of mononuclear cells, but failed to affect IL2R alpha expression, as judged by RNase protection assays. Thus, inhibition of Jak3 prolongs allograft survival and also potentiates the immunosuppressive effects of cyclosporin A, but not rapamycin.

Automated, fast and sensitive quantification of drugs in blood by liquid chromatography-mass spectrometry with on-line extraction: immunosuppressants

We developed a universal LC-mass spectrometry assay with automated online extraction (LC/LC-MS) to quantify the immunosuppressants cyclosporine, tacrolimus, sirolimus and SDZ-RAD alone or in combination in whole blood. After protein precipitation, samples were loaded on a C18 extraction column, were washed and, after activation of the column-switching valve, were backflushed onto the C8 analytical column. [M+Na]+ ions were detected in the selected ion mode. For tacrolimus, sirolimus and SDZ-RAD, the assay was linear from 0.25 to 100 microg/l and for cyclosporine from 7.5 to 1250 microg/l (all r2>0.99). Analytical recovery was >85% and, in general, inter-day, intra-day variability for precision and accuracy were <10%.

Toxicity and efficacy of sirolimus: relationship to whole-blood concentrations

BACKGROUND

Sirolimus is a novel macrolide immunosuppressive drug with a mechanism of action distinct from that of both cyclosporine and tacrolimus. Recent clinical studies have demonstrated a decrease in acute rejection episodes in renal transplant patients receiving sirolimus compared with controls. The major toxicities associated with sirolimus treatment are thrombocytopenia and hyperlipidemia. In addition, concern has been raised by the higher serum creatinine levels noted in patients receiving sirolimus and cyclosporine compared with controls receiving cyclosporine and azathioprine.

OBJECTIVE

The objective of the present review is to summarize the efficacy and toxicity data for sirolimus. Special consideration is given to evidence that links these effects to dose or whole-blood concentrations of sirolimus.

RESULTS

The literature indicates that trough concentrations of sirolimus >15 ng/mL appear to be associated with a greater risk of both thrombocytopenia and hyperlipidemia, whereas trough sirolimus concentrations <6 ng/mL have been associated with an increased incidence of acute rejection.

CONCLUSION

The evidence to date supports target trough sirolimus concentrations of 6 to 15 ng/mL in most patients. In higher-risk groups and patients receiving cyclosporine-sparing regimens, higher concentrations may be necessary to achieve similar efficacy.

The quantification of sirolimus by high-performance liquid chromatography-tandem mass spectrometry and microparticle enzyme immunoassay in renal transplant recipients

BACKGROUND

Sirolimus, an immunosuppressive agent, is undergoing clinical trials in the prophylaxis of organ rejection.

OBJECTIVES

The aim of this study was to compare the performance of the semi-automated prototype (mode IA) microparticle enzyme immunoassay (MEIA) against a validated high-performance liquid chromatography-mass spectrometry (HPLC-MS) method for measuring sirolimus concentrations. A secondary objective was to identify potential factors that may influence sirolimus measurement.

METHODS

The comparison was based on predose samples (n = 841) from 74 renal transplant patients receiving sirolimus therapy. Samples were collected up to 12 months after transplantation.

RESULTS

The mean (+/- SD) overestimation by MEIA was 42.5%+/-16.9%. Several variables were investigated to determine potential contributors to the observed overestimation. Stratification of the data based on the mean sirolimus concentrations determined by both assays yielded no statistically significant differences in bias between concentration subgroups within the clinically relevant range. Multiple linear regression analysis identified HPLC-MS sirolimus concentration (P = 0.03), hemoglobin concentration (P < 0.001), and time after transplantation (P < 0.001) as significant variables in the prediction of overestimation by MEIA. Analysis of the effect of time after transplantation on overestimation yielded a statistically significant difference up to 6 months after transplantation (35.6% to 46.4%) compared with 9 (23.9%) and 12 months (24.4%). A relationship between hemoglobin concentration and time after transplantation may explain the reduction in bias observed after 6 months.

CONCLUSION

The MEIA overestimates sirolimus concentrations in renal transplant patients compared with HPLC-MS. The clinical importance of this observed overestimation requires further investigation.

Inhibition of C-raf expression by antisense oligonucleotides extends heart allograft survival in rats

BACKGROUND

C-raf is a well-characterized serine/ threonine (Ser/Thr) protein kinase that is involved in the transduction of multiple signals of T cells. We demonstrate that the inhibition of C-raf mRNA expression prolongs heart allograft survival.

METHODS

Three 20-mer C-raf antisense oligonucleotides, each with identical sequences, were synthesized with different chemical modifications: one as a uniform phosphorothioate oligodeoxynucleotide (PS oligo), a second with a PS backbone and 2'-methoxyethyl (ME) substitutions at the 2'-sugar positions in the first and last five nucleotides, and a third with a mixed PS and phosphodiester (PD) backbone and ME modifications on the first and last five nucleotides.

RESULTS

Both ME-modified C-raf antisense oligos were at least 5-fold more effective than the PS C-raf antisense oligo in blocking C-raf mRNA expression in two cell lines. Similarly, each of the ME C-raf antisense oligos produced better heart allograft survival rates than did PS C-raf oligo. Furthermore, although the combination of PS C-raf antisense oligo with sirolimus (SRL) acted synergistically to extend heart allograft survival, the effect was potentiated by either of the ME-modified oligos.

CONCLUSIONS

C-raf inhibition extends heart allograft survival, and ME-modification potentiates antisense activity.