Early Detection of Growth Hormone Secretagogue Receptor Antagonists Exploiting Their Atypical Behavior in Competitive Assays.

We report the proof-of-concept of a bioaffinity format designed for the early detection of growth hormone secretagogue receptor (GHS-R1a) antagonists in urine samples. We exploit here their atypical behavior in competitive experiments with labeled ghrelin (GHR), namely, the strong promoting effect on the GHR/GHS-R1a interaction at low molar ratios GHR/antagonist. The antagonists potentiate the GHR/GHS-R1a interaction, and they display the same effect on the interaction of GHS-R1a with other agonists listed as doping agents. The developed assay allows the estimation of affinity constants of ligand/receptor and antagonist/receptor binding and is amenable to optical, electrochemical, and mass-sensitive detection. The estimated affinity constants for GHR/GHS-R1a and antagonist/GHS-R1a in the absence of G proteins are in good agreement with recently reported data.

Identification of Novel Pathways in Idelalisib Metabolism and Bioactivation.

Idelalisib (ILB) is a selective phosphatidylinositol-3-kinase delta inhibitor approved for the treatment of hematological malignancies. However, ILB frequently causes hepatotoxicity, and the exact mechanism remains unclear. The current study profiled the metabolites of ILB in mouse liver, urine, and feces. The major metabolites found in the liver were oxidized metabolite GS-563117 (M1) and ILB-glutathione (GSH) adduct (M2). These metabolic pathways were confirmed by analysis of urine and feces from mice treated with ILB. Identification of ILB-GSH adduct (M2) suggests the formation of reactive metabolites of ILB. We also found that M1 can produce reactive metabolites and form M1-GSH adducts. The GSH-conjugates identified in mouse liver were also found in the incubations of ILB and M1 with human liver microsomes. Furthermore, we illustrated that CYP3A4 and 2C9 are the key enzymes contributing to the bioactivation pathway of ILB and M1. In summary, our work revealed that both ILB and its major metabolite M1 can undergo bioactivation to produce reactive metabolites in the liver. Further studies are required to determine whether these metabolic pathways contribute to ILB hepatotoxicity.