An enzyme immunoassay for determining plasma concentrations of didemnin B

Didemnin A was conjugated at the amino terminus of the N‐methylleucine residue, via the linkers N‐succinimidyl‐3‐(2‐pyridyldithio)propionate and trans‐1,4‐maleimidomethylcyclohexane carboxylic acid, to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA). The didemnin‐KLH conjugates were used to hyperimmunize rabbits. The resulting high titer antisera were employed with didemnin‐BSA conjugate‐coated microtiter plate wells to develop an indirect competitive inhibition enzyme immunoassay (CIEIA) that was fully cross reactive with didemnin B. A CIEIA is described that is capable of detecting the drug in plasma from didemnin Btreated patients at concentrations down to 1‐3 ng/ml. This simple, sensitive CIEIA has been employed to demonstrate plasma drug clearance profiles with samples from didemnin B‐treated patients. © 1992 Wiley‐Liss, Inc.