Novel Blood Protein Modification Assay for Retrospective Detection of Drug Exposure - Development and Validation

As submitted by the proposer: Detection and confirmation of drug exposure typically relies on measurement of parent compounds or metabolites in blood or urine. This approach, however, has significant drawbacks with regard to the useful time frame for drug detection since most drugs and their metabolites are cleared from the body within a week. Consequently, such measurements alone cannot provide data on past episodic or repeated exposure. Nevertheless, longer windows of detection are valuable for measurement of drug compliance or abstinence, such as in pain drug management, drug addiction rehabilitation programs, and probation/parole criminal justice situations. Currently, retrospective assessment of drug use is limited to analysis of hair. While clearly important for this purpose, hair analysis does have certain technical and interpretive challenges. Another potential technology for longer-term drug monitoring involves measurement of the products of covalent modification (i.e., “adducts”) of the blood proteins hemoglobin (Hb) and serum albumin (SA) by reactive drug metabolites (RM). Since they persist for the life of the protein, such modifications can provide a considerably longer window of detection than is possible with parent drugs or metabolites. While widely used in exposure assessment for environmental and occupational chemicals, applications of protein adducts as markers of illicit drug exposure are virtually nonexistent. The aim of this proposed project is to expand upon our successful proof-of-concept studies for retrospective detection of drugs of abuse by measuring stable drug protein adducts. The researchers propose three steps to accomplish these goals: 1) The researchers will characterize thiol modifications of human Hb and SA by RM of 16 selected drugs following in vitro incubation to assess specificity of thiol modification at 34Cys in SA and 93Cys in Hb. 2) The researchers will then explore approaches to maximize sensitivity and selectivity of protein adduct detection by pre-enrichment of adducted Hb and SA and the use of targeted MRM analysis of adducted tryptic peptides by LC-QqQ-MS/MS, along with determination of LODs. 3) Finally, the researchers will screen for drug-specific SA and Hb adducts by targeted MRM analysis of a set of authentic whole blood specimens from subjects enrolled in addiction treatment programs, and compare results with those obtained from standard drug/metabolite screening analysis. The researchers will also assess adduct stability in stored blood specimens and in vivo in serial blood specimens. This work will support the researchers long-term goal of validating a protein adduct-based screening and confirmatory assay for abused drugs to be used in conjunction with, or as an alternative to, hair analysis. Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14). ca/ncf