Long-term outcome of sirolimus rescue in kidney-pancreas transplantation

Mammalian target of rapamycin (mTOR) inhibitors: potential uses and a review of haematological adverse effects

Mammalian target of rapamycin (mTOR) inhibitors (mTORis) constitute a relatively new category of immunosuppressive and antineoplastic drugs. These share a unique mechanism of action that is focused on the inhibition of the mTOR. Their clinical applications have recently expanded significantly to cover a wide spectrum of immune and non-immune-mediated disorders, including, apart from solid organ transplantation, various solid organ and haematological malignancies, rheumatological and auto-immune diseases such as rheumatoid arthritis, systemic lupus erythematosus, fibrotic conditions, e.g. pulmonary and hepatic fibrosis, and even metabolic problems such as diabetes mellitus and obesity. The most challenging and frequent adverse effects of the mTORis are the haematological ones, especially anaemia, leukopenia and thrombocytopenia. A unique characteristic of mTORi-induced anaemia is concurrent marked microcytosis. Recently, mechanisms have been proposed to explain the microcytic appearance of this anaemia; these include globin production defect, erythropoietin resistance, chronic inflammation, dysregulation of cellular iron metabolism and hepcidin-mediated iron homeostasis interference. As the differential diagnosis of microcytic anaemia includes pure iron deficiency, functional iron deficiency and haemoglobinopathies, characterization of the anaemia requires significant investigation, time and costs. Therefore, understanding of the likely interaction between mTORis and patients is valuable in clinical practice. Moreover, this could expand the drugs' therapeutic applications to other disorders, and suggest novel targets for further research.

Mammalian target of rapamycin (mTOR) inhibitors: potential uses and a review of haematological adverse effects

Mammalian target of rapamycin (mTOR) inhibitors (mTORis) constitute a relatively new category of immunosuppressive and antineoplastic drugs. These share a unique mechanism of action that is focused on the inhibition of the mTOR. Their clinical applications have recently expanded significantly to cover a wide spectrum of immune and non-immune-mediated disorders, including, apart from solid organ transplantation, various solid organ and haematological malignancies, rheumatological and auto-immune diseases such as rheumatoid arthritis, systemic lupus erythematosus, fibrotic conditions, e.g. pulmonary and hepatic fibrosis, and even metabolic problems such as diabetes mellitus and obesity. The most challenging and frequent adverse effects of the mTORis are the haematological ones, especially anaemia, leukopenia and thrombocytopenia. A unique characteristic of mTORi-induced anaemia is concurrent marked microcytosis. Recently, mechanisms have been proposed to explain the microcytic appearance of this anaemia; these include globin production defect, erythropoietin resistance, chronic inflammation, dysregulation of cellular iron metabolism and hepcidin-mediated iron homeostasis interference. As the differential diagnosis of microcytic anaemia includes pure iron deficiency, functional iron deficiency and haemoglobinopathies, characterization of the anaemia requires significant investigation, time and costs. Therefore, understanding of the likely interaction between mTORis and patients is valuable in clinical practice. Moreover, this could expand the drugs' therapeutic applications to other disorders, and suggest novel targets for further research.

Conversion to sirolimus in kidney-pancreas and pancreas transplantation

Reports on the use of sirolimus (SRL) in pancreas transplantation are still limited. The aim of this study was to evaluate the outcome of SRL conversion in pancreas transplant patients. Among 247 patients undergoing simultaneous kidney-pancreas or solitary pancreas transplantation, 33 (13%) were converted to SRL. The reasons for conversion were calcineurin inhibitors (CNI) nephrotoxicity (n = 24; 73%), severe neurotoxicity owing to CNI (n = 1; 3%), severe and/or recurrent acute rejection episodes (n = 7; 21%), gastrointestinal (GI) side effects of mycophenolate mofetil (MMF; n = 5; 15%), and hyperglycemia (n = 4; 12%). Before conversion, all patients were maintained on a CNI, MMF, and low-dose steroids. They were gradually converted to SRL associated with either CNI or MMF withdrawal. Sixty-three percent (n = 15) of patients who were converted owing to CNI nephrotoxicity, showed stable or improved renal function. At 12 months after conversion, serum creatinine levels were significantly decreased in this group (2.2 +/- 0.5 vs 1.6 +/- 0.3 mg/dL; P = .001) and C-peptide values increased (2.9 +/- 1.1.1 vs 3.1 +/- 1.3 nmol/L; P = .018). The only patient with leucoencephalopathy showed improved neurologic status after SRL conversion. All patients converted to SRL because of GI side effects of MMF showed improvements, and none of those converted because of hyperglycemia experienced improvement. There were no episodes of acute rejection after conversion. We concluded that conversion to SRL in pancreas transplantation should be considered an important alternative strategy, particularly for CNI nephrotoxicity and neurotoxicity, and in cases of severe diarrhea due to MMF.

Use of sirolimus in solid organ transplantation

Sirolimus is a mammalian target of rapamycin (mTOR) inhibitor that inhibits cell cycle progression and has proven to be a potent immunosuppressive agent for use in solid organ transplant recipients. The drug was initially studied as an adjunct to ciclosporin (cyclosporine) to prevent acute rejection in kidney transplant recipients. Subsequent studies have shown efficacy when combined with a variety of other immunosuppressive agents. The most common adverse effects of sirolimus are hyperlipidaemia and myelosuppression. The drug has unique antiatherogenic and antineoplastic properties, and may promote immunological tolerance and reduce the incidence of chronic allograft nephropathy. Although sirolimus is relatively non-nephrotoxic when administered as monotherapy, it pharmacodynamically enhances the toxicity of calcineurin inhibitors. Ironically, the drug has been used to facilitate calcineurin inhibitor-free protocols designed to preserve renal function after solid organ transplantation. Whether sirolimus can be used safely over the long term with low doses of calcineurin inhibitors requires further study. The use of sirolimus as a corticosteroid-sparing agent also remains to be proven in controlled trials. Postmarketing studies have revealed a number of unforeseen adverse effects including impaired wound healing and possibly proteinuria, oedema, pneumonitis and thrombotic microangiopathy. Overall, sirolimus is a powerful agent when used judiciously with other available immunosuppressants. As is true for all immunosuppressive drugs available for treatment of solid organ transplant recipients, the efficacy of the drug must be balanced against its considerable adverse effects.

Rapamycin Inhibits Proliferation of Epstein-Barr Virus–Positive B-cell Lymphomas Through Modulation of Cell-Cycle Protein Expression

BACKGROUND

Posttransplant lymphoproliferative disease (PTLD) is a serious complication of solid organ and bone marrow transplantation and is closely associated with Epstein-Barr virus (EBV) infection. We have previously shown that rapamycin (RAPA) directly inhibits the in vitro and in vivo proliferation of EBV-infected B lymphoblastoid cell lines (SLCL), derived from patients with PTLD, by arresting cells in the G1 phase of the cell cycle. The aim of this study is to elucidate the mechanism by which RAPA causes cell cycle arrest in EBV+ B cells.

METHODS

SLCL were cultured without or with RAPA (10 ng/ml) and G1-associated cell cycle proteins were analyzed by immunoblot and densitometric analysis. CDK complexes were immunoprecipitated and incubated with retinoblastoma protein (Rb) substrate. Kinase activity of the complex was determined by Western blot with anti-phospho-Rb antibodies.

RESULTS

We show that RAPA decreased both Cyclin D2 and Cyclin D3 protein levels. Furthermore, RAPA decreased the protein levels of cyclin dependent kinase 4 (CDK4) and increased the expression of the CDK inhibitor p27. In contrast, expression of the CDK inhibitor p21 was markedly inhibited by RAPA in the SLCL. Finally, in vitro kinase assays revealed that downstream hyperphosphorylation of Rb by CDK complexes was also decreased by RAPA.

CONCLUSION

The results presented here elucidate key targets of RAPA-induced cell cycle arrest, provide insight into the growth pathways of EBV+ B-cell lymphomas, and demonstrate the potential for RAPA as a therapeutic option in the treatment of PTLD and other EBV+ lymphomas.

Evaluation of the cost effectiveness of sirolimus versus tacrolimus for immunosuppression following renal transplantation in the UK

INTRODUCTION

Immunosuppressive therapy is required to prevent graft rejection. Calcineurin inhibitors such as tacrolimus are paradoxically toxic to the kidney, whereas sirolimus (rapamycin; Rapamune) is not generally associated with the nephrotoxicity of CNIs. The purpose of this study was to evaluate the relative cost utility of sirolimus versus tacrolimus for the primary prevention of graft rejection in renal transplant recipients in the UK.

METHODS

A stochastic simulation model was constructed using clinical trial and observational data comparing the two treatments. Time duration was up to 20 years. Costs were from a UK NHS perspective, valued at 2003 prices and discounted at 6%. Benefits were discounted at 1.5%. Simulated events included patient and graft survival, haemodialysis, peritoneal dialysis, re-transplants and acute rejection. Costs were summed for events and various maintenance therapies. Utility was differentially accredited depending upon survival and using the alternative renal replacement therapies. Outcome was predicted using post-transplant creatinine levels up to 3 years. Extensive statistical economic and sensitivity analyses were undertaken.

RESULTS

Over the 10-year horizon, sirolimus gained 0.72 years (discounted) of functioning graft over tacrolimus, resulting in an incremental cost per year of functioning graft that was dominant. Over a 20-year time horizon, the cost effectiveness of sirolimus over tacrolimus further improved with an average discounted gain in years of a functioning graft of 1.8 years, resulting in an incremental cost-utility ratio that was also dominant. The number of haemodialysis events was 48,243 for sirolimus recipients versus 127,829 for those receiving tacrolimus and peritoneal dialysis events 40,872 versus 105,249, respectively. Similar values were obtained when real-life observational data on tacrolimus use in Cardiff, Wales were entered into the model. Using data from Cardiff, sirolimus remained dominant over tacrolimus under all scenarios.

CONCLUSION

Our study suggests that sirolimus may be more cost effective than tacrolimus for the primary prevention of graft rejection in renal transplant recipients in the UK. Sirolimus was economically 'dominant' under almost all scenarios investigated. This finding was robust using statistical economic analysis and univariate sensitivity analysis.