Immunochemical approach using monoclonal antibody against Δ(9)-tetrahydrocannabinolic acid (THCA) to discern cannabis plants and to investigate new drug candidates.

A monoclonal antibody (MAb-4A4) against Δ9- tetrahydrocannabinolic acid (THCA) showing extensive cross-reactivity against various cannabinoids was prepared. Using this antibody, a competitive enzyme-linked immunoassay (ELISA) was developed to detect Δ9-THCA in the range of 1 to 100 mg/ml. Various cannabinoids including Δ9-THC (Δ9-tetrahydrocannabinolic acid), Δ8-THCA (Δ8-tetrahydrocannabinolic acid), Δ8-THC (Δ8-tetrahydrocannabinol), CBD (cannabidiol), and CBN (cannabinol) were recognized by MAb-4A4, and their cross-reactivities were 55-1600% compared with Δ9-THCA (100%). This novel characteristic of this MAb enabled detection of marijuana residues in biological samples by detection of residual cannabinoids. The ELISA using MAb-4A4 was found to be applicable even for withered samples which contained only trace amounts of Δ9-THCA and Δ9-THC. In addition, this method using MAb-4A4 could be useful in forensic analysis since the MAb-4A4 also shows cross-reactivities against cannabinoid metabolites in body fluids. As well as forensic applications using this MAb, an investigation of new drug candidates focusing on cannabinoid metabolites arising from biotransformation in plant tissue was performed using immunochemical screening. The resulting new drug candidates were cannabinoid glycosides biotransformed by Pinellia ternata whose bioactivity is as yet unidentified. Our results indicate the utility of the application of ELISA using MAb-4A4 for further experiments involving marijuana and cannabinoids not only in the forensic field but also in the context of drug discovery.