Navigating CYP1A Induction and Arylhydrocarbon Receptor Agonism in Drug Discovery. A Case History with S1P1 Agonists.

This article describes the finding of substantial upregulation of mRNA and enzymes of the cytochrome P450 1A family during a lead optimization campaign for small molecule S1P1 agonists. Fold changes in mRNA up to 10,000-fold for CYP1A1 in vivo in rat and cynomolgus monkey and up to 45-fold for CYP1A1 and CYP1A2 in vitro in rat and human hepatocytes were observed. Challenges observed with correlating induction in vitro and induction in vivo resulted in the implementation of a short, 4 day in vivo screening study in the rat which successfully identified noninducers. Subtle structure-activity relationships in this series of S1P1 agonists are described extending beyond planarity and lipophilicity, and the impact and considerations of AhR and CYP1A induction in the context of drug development are discussed.

Nephrotoxicity of hexachloro-1:3-butadiene in the male Hanover Wistar rat; correlation of minimal histopathological changes with biomarkers of renal injury.

Hexachloro-1:3-butadiene (HCBD) causes damage specifically to the renal proximal tubule in rats. In the present study, injury to the nephron of male Hanover Wistar rats was characterized at 24 h following dosing with HCBD in the range 5-90 mg kg⁻¹ to determine the most sensitive biomarkers of damage, that is, the biomarkers demonstrating significant changes at the lowest dose of HCBD, using a range of measurements in serum and urine, renal histopathology, and renal and hepatic gene expression. Histologically, kidney degeneration was noted at doses as low as 10 mg kg⁻¹ HCBD. Significant changes in the hepatic and renal gene expression categories of xenobiotic metabolism and oxidative stress were observed at 5 mg kg⁻¹ HCBD, and in the kidney alone, evidence of inflammation at 90 mg kg⁻¹ HCBD. Increases in the urinary excretion of α-glutathione S-transferase (α-GST) and kidney injury molecule-1 (KIM-1) were seen at 10 mg kg⁻¹ HCBD, and increases in urinary excretion of albumin and total protein were evident at 15 mg kg⁻¹ HCBD. The most sensitive, noninvasive biomarkers of HCBD-induced renal toxicity in Hanover Wistar rats were urinary α-GST and KIM-1. Urinary albumin measurement is also recommended as, although it is not the most sensitive biomarker, together with α-GST, albumin showed the largest relative increase of all the biomarkers investigated, and the protein is easily measured.