P99 Evaluation of Inhibitory Potential of SRD005825 on Human CYP Enzymes

Zhen Lou , Shire, Lexington, MA
Sara Leitz , Drug Metabolism and Disposition, Covance Laboratories Inc., Madison, WI
Devin Welty , Shire, Lexington, MA
Jody Wanta , Drug Metabolism and Disposition, Covance Laboratories Inc., Madison, WI
Daniel Albaugh , Drug Metabolism and Disposition, Covance Laboratories Inc., Madison, WI
Amy Nehmer , Drug Metabolism and Disposition, Covance Laboratories Inc., Madison, WI
Serene Josiah , Shire, Lexington, MA
Donald McKenzie , Drug Metabolism and Disposition, Covance Laboratories Inc., Madison, WI
Gang Luo , Drug Metabolism and Disposition, Covance Laboratories Inc., Madison, WI
SRD005825 (also known as SHP630) is a drug candidate developed for the treatment of autosomal dominant retinitis pigmentosa. In this current study, the in vitro inhibitory potential of SRD005825 on the activities of the major human hepatic cytochrome P450 (CYP) enzymes was characterized. The CYP enzymes included CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5. A single CYP-selective substrate concentration was used, approximating the concentration of the substrate that gives half the maximum reaction velocity (Km) for human hepatic microsomes for each cytochrome P450 assay. For reversible inhibition, assays were performed in the absence and presence of SRD005825 (0.02187, 0.0729, 0.243, 0.81, 2.7, 9, 30, and 100 µM). For metabolism-dependent inhibition, SRD005825 (0.02187, 9, and 100 µM) was incubated in the absence and presence of nicotinamide adenine dinucleotide phosphate (reduced form, NADPH, 1 mM) with 10-fold concentrated suspensions of pooled human hepatic microsomes at 37°C for 30 minutes. CYP activities were then determined subsequent to the pre-incubation step by diluting the microsomal protein samples 10-fold with assay buffer containing 1 mM NADPH to achieve the final protein concentration. The extent of metabolism-dependent inhibitory potential was determined by comparing activities from microsomes pre-incubated with SRD005825 in the presence and absence of NADPH. Positive controls for both reversible and metabolism-dependent inhibition were included. SRD005825 showed weak reversible inhibition on CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP3A4/5, but not CYP2D6. The IC50 value for CYP2C8 inhibition was 43.2 µM. The IC50 values of SRD005825 were not calculated for other CYP enzymes, but were estimated to be >100 µM. In addition, SRD005825 showed no metabolism-dependent inhibition of CYP enzymes tested. In summary, SRD005825 is a weak inhibitor of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP3A4/5, but not CYP2D6.