Immunoassays exhibiting reduced cross-reactivity with hydrophobic drug analyte metabolites
The present disclosure provides among other things immunoassays exhibiting reduced cross-reactivity with analyte metabolites. Additionally, the present disclosure provides diagnostic immunoassays to determine the concentration or level in a test sample of a hydrophobic drug that metabolizes in vivo or in vitro to form cross-reacting metabolites wherein cross-reactivity with such metabolites of the drug analyte is reduced. In particular, the disclosure provides such immunoassays where the hydrophobic drug is an immunosuppressant drug such as cyclosporine A.
1. An immunoassay for assessing the amount of an analyte of interest in a test sample, wherein the analyte is a hydrophobic drug that metabolizes to form one or more cross-reacting metabolites, the immunoassay comprising the steps of:
(a) contacting the test sample with one or more pretreatment reagents to form a first mixture, wherein the one or more pretreatment reagents lyse any cells and solubilize any analyte and cross-reacting metabolites present in the test sample;
(b) contacting the first mixture with an antibody specific for the analyte to form a second mixture comprising a complex of the antibody with either analyte or metabolite, wherein the amount of antibody with which the first mixture is contacted is from about 0.1% to about 10% of the amount of analyte in the test sample;
(c) washing the second mixture to remove any analyte and any metabolite not complexed with the antibody and to form a third mixture in which the analyte concentration is decreased to near the equilibrium dissociation constant (K D ) of the antibody for analyte wherein the analyte and metabolite concentrations are decreased in the third mixture from about 10-fold to about 500-fold as compared to in the test sample;
(d) contacting the third mixture with a specific binding partner of the antibody labeled with a detectable label (“tracer”) to form a fourth mixture comprising a complex of the antibody with tracer (“antibody-tracer complex”);
(e) washing the fourth mixture to remove any tracer not complexed with antibody; and
(f) detecting the antibody-tracer complex as measure of the amount of analyte present in the test sample, wherein the immunoassay has less than about 10% cross-reactivity with any one or more cross-reacting metabolites present in the sample.
2. The immunoassay of claim 1 , wherein the immunoassay has less than about 5% cross-reactivity with any one or more cross-reacting metabolites present in the sample.
3. The immunoassay of claim 1 , wherein the antibody specific for the analyte is immobilized on a solid phase.
4. The immunoassay of claim 1 , wherein the one or more pretreatment reagents precipitate in step (a) any analyte binding protein present in the sample.
5. The immunoassay of claim 4 , which further comprises removing any analyte binding protein from the first mixture.
6. The immunoassay of claim 1 , wherein in step (d) the amount of analyte
present in a complex with antibody ranges from about 1.0 and about 10.0 nM, and the tracer is present in an amount from between about 0.1 to about 1.0 nM.
7. The immunoassay of claim 1 , wherein the test sample is whole blood.
8. The immunoassay of claim 1 , wherein the hydrophobic drug is soluble in detergent or organic solvent.
9. The immunoassay of claim 1 , wherein the hydrophobic drug is an immunosuppressive.
10. The immunoassay of claim 9 , wherein the immunosuppressive is selected from the group consisting of tacrolimus, sirolimus and cyclosporine.
11. The immunoassay of claim 10 , wherein
(a) the immunosuppressive is tacrolimus and the metabolite is selected from the group consisting of M-I, M-II, M-III, and combinations thereof;
(b) the immunosuppressive is cyclosporine and the metabolite is selected from the group consisting of M1, M8, M9, M13, M17, M18, M21 and combinations thereof; or
(c) the immunosuppressive is sirolimus and the metabolite is selected from the group consisting of 11-Hydroxy-sirolimus, 41-O-demethyl-sirolimus, 7-O-demethylsirolimus, 41-O-demethyl-hydroxy-sirolimus and combinations thereof.
12. The immunoassay of claim 9 , wherein the immunosuppressive is cyclosporine and the metabolites are AM1 and AM9.
13. The immunoassay of claim 1 , wherein the antibody is selected from the
group consisting of a polyclonal antibody, a monoclonal antibody, a humanized antibody, a F(ab)′2, a chimeric antibody, a human antibody, and an affinity maturated antibody.
14. The immunoassay of claim 1 , wherein the solid phase is selected from the group consisting of a magnetic particle, bead, test tube, microtiter plate, cuvette, membrane, a scaffolding molecule, film, filter paper, disc, and chip.
15. The immunoassay of claim 1 , wherein the detectable label is selected from the group consisting of a radioactive label, an enzymatic label, a chemiluminescent label, a fluorescent label, a thermometric label, and an immunopolymerase chain reaction label.
16. The immunoassay of claim 1 , wherein the tracer comprises multiple binding partners.
17. The immunoassay of claim 1 , wherein the one or more pretreatment reagents comprise saponin, methanol, ethylene glycol, and zinc sulfate.
18. The immunoassay of claim 1 , wherein the second mixture further comprises an assay diluent.
19. The immunoassay of claim 18 , wherein the assay diluent comprises a buffer, salt, detergent, solvent, or combinations thereof.
20. The immunoassay of claim 1 , wherein the fourth mixture in step (d) further comprises a detergent.
21. The immunoassay of claim 20 , wherein the detergent is reduced Triton® X-100.
22. The immunoassay of claim 1 , wherein the analyte is cyclosporine and the tracer comprises cyclosporine labeled with acridinium.
23. The immunoassay of claim 1 , wherein the antibody in step (b) has a K D for cross-reacting metabolite that is between about 10-fold and about 1000-fold higher than for analyte.
24. The immunoassay of claim 1 , wherein the immunoassay relates an amount of the antibody-tracer complex formed to the amount of the analyte in the test sample either by use of a standard curve for the analyte, or by comparison to a reference standard.
25. The immunoassay of claim 1 , further comprising:
(i) incubating the first mixture in step (a) for a first incubation period;
(ii) incubating the second mixture in step (b) for a second incubation period; and
(iii) incubating the fourth mixture in step (d) for a third incubation period.
26. The immunoassay of claim 25 , wherein the first incubation period comprises a period of from about 2 minutes to about 60 minutes.
27. The immunoassay of claim 25 , wherein the second incubation period comprises a period of from about 2 minutes to about 30 minutes.
28. The immunoassay of claim 25 , wherein the third incubation period comprises a period of from about 2 minutes to about 30 minutes.