Cyclosporins

Example Miller and Rich investigated the conformational consequences of substitution s on an amino acid in cyclosporin A. an importan t iininunosnppressive dnig. One of th e ammo acids iii this cyclic iin decapeptide is (2.v, ir. 4r, 5f )-3-nydroxy-4-methyl-2-(methylamino)-6-octenoic acid (MeBmtli. It is essential for biological activitv. 

Miller an d Rich assumed th at cyclosporin A an d its MeHrn t an alogs share a common hioactive con formation. fheir molecular mech an ics calculation s found such a conformation, fh e Boltzmann population of th e proposed hioactive conformation correlates with the immunosuppressive activities of the compounds. 

Price S L, R J Harrison and M F Guest 1989. An Ab Initio Distributed Multipole Study of the Electrostatic Potential Around an Undecapeptide Cyclosporin Derivative and a Comparison with Point Charge Electrostatic Models. Journal of Computational Chemistry 10 552-567. 

Yun-Yu S, W Lu and W F van Gunsteren 1988. On the Approximation of Solvent Effects on Conformation and Dynamics of Cyclosporin A by Stochastic Dynamics Simulation Teclmiqi Molecular Simulation 1 369-383. 

Miller, KE. Rich, D.H. Molecular Mechanics Calculations of Cyclosporin A Analogues. Effect of Chirality and Degree of Substitution on the Side-Chain Conformations of (2s, 3r, 4r, 6e)-3-Hydroxy-4-methyl-2-(methylamino)-6-octenoic Acid and Related Derivatives. 

Nonspecific immunosuppressive therapy in an adult patient is usually through cyclosporin (35), started intravenously at the time of transplantation, and given orally once feeding is tolerated. Typically, methylprednisone is started also at the time of transplantation, then reduced to a maintenance dose. A athioprine (31) may also be used in conjunction with the prednisone to achieve adequate immunosuppression. Whereas the objective of immunosuppression is to protect the transplant, general or excessive immunosuppression may lead to undesirable compHcations, eg, opportunistic infections and potential malignancies. These adverse effects could be avoided if selective immunosuppression could be achieved. Suspected rejection episodes are treated with intravenous corticosteroids. Steroid-resistant rejection may be treated with monoclonal antibodies (78,79) such as Muromonab-CD3, specific for the T3-receptor on human T-ceUs. Alternatively, antithymocyte globulin (ATG) may be used against both B- and T-ceUs. 

A number of fungal immunosuppressives have been isolated from fermentation broths and demonstrated to have immunotherapeutic efficacy. Other than cyclosporin (35), two fungal metaboHtes, sirolimus (36), previously known as rapamycin (80), and FK-506 (37) (81) are in various stages of development (see Antibiotics, macrolides). 

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. 

Bleomycin and cyclosporine are the two economically most important streptomycete peptide antibiotics used as antitumor agents and immunomodulators, although dactinomycin is important medically for several tumors (see Chemotherapeutics, anticancer Immunotherapeutic agents). 

Fig. 14. Structure of cyclosporin A where MeBmt = 4-(2-butenyl)-4, A-dimethylthreonine Sar = sarcosine MeLeu = A-methylleucine ...

The first human kidney and bone marrow transplants using cyclosporine were reported in 1978. Oral or intravenous cyclosporine is an immunosuppressant for transplantation of these and other organs and investigations are underway for its possible use in a variety of autoimmune diseases including rheumatoid arthritis, severe psoriasis, and Crohn s disease. Dose-dependent nephrotoxicity (261—264) remains the primary limitation of the dmg and necessitates close monitoring of patients, including measurement of dmg levels in blood. Cyclosporine research has been reviewed (265—274). 

Cyclosporin A forms white prismatic crystals from acetone and is only slightly soluble in water and saturated hydrocarbons, but is very soluble in methanol, ethanol, acetone, and diethyl ether. Optical and nmr data on cyclosporins and x-ray crystallographic data on cyclosporin A and an io do derivative have been reviewed (273,275). 

R. Schindler, ed.. Cyclosporin in Autoimmune Diseases, Springer-Vedag, Berlin, 1985. 

Kallen, J., et al. Structure of human cyclophilin and its binding site for cyclosporin A determined by x-ray crystallography and NMR spectroscopy. Nature 353 276-279, 1991. 

Takahashi, N., Hayano, T., Suzuki, M. Peptidyl-prolyl cis-trans isomerase is the cyclosporin A binding protein cyclophilin. Nature 337 473-475, 1989. 

Structural determination of macrocyclic peptides cyclosporins by mass spectrometry 97CLY2. 

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