Determination of heroin hapten densities in protein conjugates: comparison of MALDI-TOF MS, TNBS and indirect Ellman assay

One strategy for treating drug addiction is the development of vaccines directed against drugs of abuse. Vaccines induce antibodies which bind to the drug in the blood, preventing it from crossing the blood-brain barrier, thereby, blocking the euphoria and addictive effects. Drugs of abuse are small molecules which do not induce antibodies. To induce antibodies, a surrogate drug (MorHapten) is attached to a carrier protein. Evaluation of the number of haptens attached to the carrier is a vaccine characterization requirement. Evaluation was done using indirect methods, trinitrobenzenesulfonic acid (TNBS) to measure amines, and indirect (modified) Ellman assay to measure linkers, and a direct method, High Mass (HM) MALDI TOF MS. The goal of this study is to compare indirect methods to MALDI-TOF MS.