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Design of Novel Pro-drugs for the Treatment of Cystinosis Dr D. Cairns Institute of Pharmacy and Chemistry University of Sunderland, Sunderland, UK
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Nephropathic cystinosis n Rare autosomal recessive metabolic disease n Characterized by elevated levels of intracellular cystine n Caused by defect in lysosomal transporter mechanism for cystine n CTNS gene described
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Cystinosis - symptoms n Renal Fanconi syndrome (impairment in proximal tubular function) n Polyuria (excessive urination) n Polydipsia (excessive thirst) n Hypokalaemia (low levels K + ) n Hypophosphataemia (low levels PO 4 - )
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Cystinosis - symptoms n Crystals of cystine present in lysosomes, bone marrow aspirates, leukocytes, cornea and conjunctiva n Photophobia, headaches, burning/itching of eyes n Growth retardation, rickets, muscle myopathy n CNS involvement, hypothyroidism n Hepatic and GI complications
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Cystinosis - Treatment n Administration of electrolytes, glucose etc. to address imbalance n Renal dialysis, transplant n Eye drops, corneal transplant
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Drug Treatment n Cysteamine (mercaptamine) n Cystagon (mercaptamine bitartrate)
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Cysteamine - problems n Poor patient compliance due to offensive taste and smell n Excretion in breath and sweat leads to halitosis and body odour n Release in GI tract can cause nausea, vomiting, irritation etc. n Reformulate - sustained release, coated pellets
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Pro-drugs of Cysteamine n Pharmacologically inactive molecule metabolically activated in vivo to yield active compound. n Release of cysteamine is intra-cellular n Avoids GI related side-effects n Minimises odour problems n Increased lipophilicity improves uptake into cells, better PK and PD profiles
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Glutamyl Transpeptidase Glutamyl Transpeptidase n Provides mechanism for energy-driven transport of amino acids (AA) into cells GT situated on external cell membrane. High levels present in kidney cells GT situated on external cell membrane. High levels present in kidney cells n Accepts amino acids (Cys and Met) Transfers Glu from GSH to external amino acid Transfers Glu from GSH to external amino acid Glu-AA complex transported into cell Glu-AA complex transported into cell
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Cell culture Pro-drugs added to CHO Cell lines genetically modified to express GT. Pro-drugs added to CHO Cell lines genetically modified to express GT. n Cytotoxicity and LD 50 determined (SRB) n Cells lysed with Triton X 100 and breakdown of compound followed by hplc-m/s Histochemical detection of GT using Histochemical detection of GT using L- - glutamyl-p-nitroanilide and measurement of absorbance at 530 nm
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Results n Pro-drugs synthesized in good yield and fully characterised spectroscopically Pro-drugs taken up into CHO cells expressing -GT and detected by hplc Pro-drugs taken up into CHO cells expressing -GT and detected by hplc n Levels of pro-drug fall wrt time but….. n Unable to detect release of cysteamine using hplc-m/s
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Conclusions -glutamylcysteamine prodrugs can be readily synthesized in significant quantities n n These prodrugs are almost entirely non-toxic to cells and are taken up successfully into CHO cells in vitro The receptor enzyme -glutamyl transpeptidase is a valid vehicle for targetting cysteamine to the cells that most require it.
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Acknowledgements n Wendy Cardwell and Dr Roz Anderson, University of Sunderland (synthesis) n Prof. Geoff Rowley and Dr Berwyn Owen, University of Sunderland (formulation) n Dr Malcolm Coulthard, RVI, Newcastle n Dr Andy Hall, University of Newcastle (cell culture) n Northern Region NHS for funding support
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