Immunosuppressive agents sirolimus

Easter Island (Rapa Nui) first discovered and characterized by Sehgal in 1975 (38), Initially identified as an antifungal agent, the compound was subsequently found to posses potent immunosuppressive activities, initially demonstrated through its ability to prevent adjuvant-induced arthritis and experimental allergic encephalomyelitis in rodent models. As a potent immunosuppressive agent, sirolimus has been developed and marketed by Wyeth Pharmaceuticals for the prevention of renal transplant rejection (Rapamune ) (39). 

Immunosuppression induced by sirolimus (36) appears to be mediated by a mechanism distincdy different from that of either cyclosporin or FK-506. Sirolimus markedly suppresses IL-2 or IL-4-driven T-ceU proliferation. The preclinical studies suggest that sirolimus is a potent immunosuppressive agent in transplantation and autoimmune disease models. The clinical potential of this agent depends on its toxicity profile (80). 

FK-506 (37) interferes with IL-2 synthesis and release and has a cyclosporin-like profile, but is considerably more potent in vitro. IC q values are approximately 100-fold lower. This neutral macroHde suppresses the mixed lymphocyte reaction T-ceU proliferation generation of cytotoxic T-ceUs production of T-ceU derived soluble mediators, such as IL-2, IL-3, and y-IFN and IL-2 receptor expression (83). StmcturaHy, FK-506 is similar to sirolimus. Mycophenolate mofetil (33), brequinar (34), and deoxyspergualin are in various phases of clinical evaluation. Identification of therapeutic efficacy and safety are important factors in the deterrnination of their utiUty as immunosuppressive agents. 

Sirolimus is a potent immunosuppressive agent. To prevent thrombocytopenia and hypercholesterolemia, optimize efficacy, and reduce organ rejection, assays were developed to monitor concentrations of sirolimus in the whole blood of patients under treatment.40"12 Wallemacq et al.43 developed and validated a simple high-throughput HPLC-MS/MS method to routinely monitor sirolimus... 

Pharmacology Sirolimus, a macrolide immunosuppressive agent, inhibits both T-lymphocyte activation and proliferation that occurs in response to antigenic and cytokine (interleukin-2, -4, and -15) stimulation and also inhibits antibody production. In cells, sirolimus binds to the immunophilin, FK binding protein-12 (FKBP-12), to generate an immunosuppressive complex. 

Concurrent immunosuppressants Sirolimus has been administered concurrently with cyclosporine and corticosteroids. The efficacy and safety of the use of sirolimus in combination with other immunosuppressive agents have not been determined. Renai function impairment Mean serum creatinine was increased and mean glomerular filtration rate was decreased in patients treated with sirolimus and cyclosporine compared with those treated with cyclosporine and placebo or azathioprine controls. Monitor renal function during the administration of maintenance immunosuppression regimens including sirolimus in combination with cyclosporine, and consider appropriate adjustment of the immunosuppression... 

Selective immunosuppressive agents mycophenolate mofetil sirolimus tacrolimus... 

A new class of immunosuppressive agents called proliferation-signal inhibitors (PSIs) includes sirolimus (rapamycin) and its derivative everolimus. The mechanism of action of PSIs differs from that of the calcineurin inhibitors. PSIs bind the circulating immunophilin FK506-binding protein 12, resulting in an active complex that blocks the molecular target of rapamycin (mTOR). 

Sirolimus (Rapamycin, Rapamune ), a natural macrocyclic lactone, is a potent immunosuppressive agent. It was developed by Wyeth-Ayerst Laboratories (Philadelphia, Pennsylvania, U.S.A.) and approved by the Food and Drug Administration for the prophylaxis of renal transplant rejection in 1999 (28,29). Sirolimus has its roots in Easter Island, where an actinomycete streptomyces hygroscopicus was found that produced a novel macrolide antibiotic with potent antibiotic, potent antifungal, immunosuppressive, and antimitotic activities. 

The first two DES to be commercialized incorporated sirolimus (rapamycin Rapamune , Wyeth Pharmaceuticals, Inc, Collegeville, Pennsylvania, U.S.A.), an immunosuppressive agent used for the prevention of transplanted organ rejection, or paclitaxel (Taxol , Bristol-Myers Squibb, Princeton, New Jersey, U.S.A.) an agent with an extensive history as an anti-cancer therapy. 

For a number of overt, broad spectrum immunosuppressive xenobiotics (e.g., azathioprine) there is sufficient clinical experience to indicate the types of neoplasms for which there is an increased risk. These tumor types are listed in Table 27.1. Also listed are the tumors that occur in the unfortunate experiment of nature, namely patients infected with human immunodeficiency virus type 1 (HIV-1) and the tumors that may occur at higher incidence with more selective yet strong immunosuppressants (e.g., cyclosporin, sirolimus, and tacrolimus). Compared to the broad spectrum immunosuppressive agents listed above, most IMBPs express a highly selective regulatory influence on the immune system modulating the activity of host defense systems rather than mediating frank immunosuppression. 

The advent of potent non-nephrotoxic immunosuppressive agents might make the replacement of CsA or the decrease to it exposure in drugs protocols more feasible. At the moment, mofetil mycophenolate and sirolimus are the only commercially available new... 

It has been estimated that well over 300,000 secondary metabolites exist, and it s thought that their primary function is to increase the likelihood of an organism s survival by repelling or attracting other organisms. Alkaloids, such as morphine antibiotics, such as erythromycin and the penicillins and immunosuppressive agents, such as rapamycin (sirolimus) prescribed for liver transplant recipients, are examples. 

Sirolimus is currently the only FDA-approved ToR inhibitor. One of its derivatives, everolimus, is in phase III clinical trials and has been approved for use in some European countries.30 Sirolimus is a macrolide antibiotic that has no effect on cal-cineurin phosphatase.11,31,32 Sirolimus inhibits T cell activation and proliferation by binding to and inhibiting the activation of the mammalian ToR, which suppresses cellular response to IL-2 and other cytokines (i.e., IL-4 and IL-15J.11,31 Studies have shown that sirolimus may be used safely and effectively with either cyclosporine or tacrolimus as a replacement for either azathioprine or mycophenolate mofetil.33 However, when using both sirolimus and cyclosporine as part of a patient s immunosuppressant therapy, because of a drug interaction between the two resulting in a marked increase in sirolimus concentrations, it is recommended to separate the sirolimus and cyclosporine doses by at least 4 hours. Sirolimus also can be used as an alternative agent for patients who do not tolerate calcineurin inhibitors due to nephrotoxicity or other adverse events.34... 

Sirolimus (Rapamune) is structurally related to tacrolimus. It is approved for use as an adjunctive agent in combination with cyclosporine for prevention of acute renal allograft rejection. It blocks IL-2-dependent T-cell proliferation by inhibiting a cytoplasmic serine-threonine kinase. This mechanism of action is different from those of tacrolimus and cyclosporine. This allows sirolimus to augment the immunosuppressive effects of these drugs. 

Immunosuppressive drugs can be divided into five basic categories. Corticosteroids such as methylprednisolone and prednisone are a part of virtually all immunosuppressive drug regimens. Corticosteroids block the production of IL-1 and have potent anti-inflammatory effects. Calcineurin inhibitors such as cyclosporine and tacrolimus are also used in a majority of immunosuppressive drug regimens. Calcineurin inhibitors inhibit the production and secretion of IL-2. IL-2 is involved with T-lymphocyte activation and proliferation. Antiproliferative agents such as azathioprine, mycophenolate mofetil, and sirolimus block T-lymphocyte... 

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