CYCLOSPORINE METABOLITE CROSS-REACTIVITY IN DIFFERENT CYCLOSPORINE ASSAYS

Objectives: There is a controversy regarding the role of cyclosporine (CsA) metabolites in both immunosuppression and toxicity, and measurem ent of the parent drug is commonly recommended. High performance liqui d chromatography (HPLC) is the method commonly used for specific measu rement of the parent drug, but is very time consuming. Antibody techni ques are available but vary in specificity. Mixed lymphocyte culture a ssay (MLC) is a functional bioassay for the measurement of CsA which m easures both parent drug and active metabolites. Because it is time co nsuming and labor intensive, it is not practical to use the MLC to mon itor patient's CsA levels. The objective of this study is to evaluate the degree of cross-reactivity or interference among two different CsA immunoassays [(Immunoassay: CYCLO-Trac-RIA, Monoclonal-TDX; and two r adioreceptor assays (RRA) (52 kDa immunophilin and cyclophilin)] with seven cyclosporine metabolites (AM19, AM1c9, AM4n9, AM1, AM9, AM1c, AM 4n). The results are compared with a previously published MLC assay fo r the same metabolites. Methods: 500 ng/mL of each of the CsA metaboli tes was assayed in spiked blood samples with both RRA using 52 kDa imm unophilin and commercial cyclophilin and two commonly used commercial immunoassay procedures. The results were compared to those obtained wi th the previously published MLC assay. Results and Conclusion: The CYC LO-Trac-radioimmunoassay showed minimal cross-reactivity with all of t he seven CsA metabolites tested and is more specific to parent CsA tha n the current Abbott monoclonal procedure for the measurement of CsA. However the cross-reactivity of the seven metabolites using the Abbott monoclonal assay matched closely with their pharmacological potency a s measured in the MLC assay. The RRAs showed greater cross-reactivity for most of the CsA metabolites tested than that found in the immunoas say procedures. Copyright (C) 1998 The Canadian Society of Clinical Ch emists.