PII-049 - IDENTIFYING FUNCTIONAL REGULATORY SNPS THAT REGULATE CYP2C9 EXPRESSION TO OPTIMIZE CYP2C9 BIOMARKER PANELS.

A. Montalvo¹, J. Collins¹, D. Wang²; ¹University of Florida College of Pharmacy, FL, United States, ²University of Florida College of Pharmacy, University of Florida - Gainesville, FL, USA.

Background: CYP2C9 metabolizes ~25% of clinically administered drugs. Several non-synonymous single nucleotide polymorphisms (SNPs) of CYP2C9 (e.g *2, *3, *8, etc.) are used as biomarkers to predict CYP2C9 activity, but large variability in CYP2C9 expression remains unexplained. An additional distal non-coding SNP, rs12777823, was identified in a GWAS study as being associated with decreased warfarin dose requirements in African Americans. The Clinical Pharmacogenetics Implementation Consortium recommends the use of rs12777823 as a biomarker for warfarin dose adjustment in African Americans. Evidence suggests that rs12777823 is not functional by itself and its association with warfarin dose may be caused by high LD with a functional SNP. This study aims to identify and characterize the functional SNP underlying the association between rs12777823 and warfarin.

Methods: We measured allelic expression imbalance (AEI) of CYP2C9 in 156 liver samples derived from African American donors and used targeted long-read sequencing to scan the entire CYP2C locus in AEI positive (n=7) and AEI negative (n=9) samples. Lab generated 4C and ATAC-seq data as well as publicly available data bases were used to select targets for CRISPR interference (CRISPRi) assays in a hepatic cell line (Huh7 cells).

Results: Long-read sequencing revealed >10K SNPs per sample across ~600 kb of the CYP2C locus. Correlating AEI status with SNP heterozygosity identified 117 potential candidate SNPs. Using 4C and ATAC-seq data with publicly available functional genomic data, we identified 25 potential enhancer regions for CYP2C9. Alignment of the locations of 117 candidate SNPs with the 25 potential enhancer regions narrowed the list to 29 SNPs and 14 potential enhancers. By screening several CYP2C9 CRISPRi validated enhancers, we identified one SNP (MAF=0.12 in African Americans) that was significantly associated with hepatic CYP2C9 expression (p – value= 0.004).

Conclusion: We identified a SNP in a distal enhancer that is associated with the expression of CYP2C9. The clinical impact of the identified functional SNP will be tested for association with stable warfarin doses in patients taking warfarin. The identified functional SNP is expected to improve the CYP2C9 biomarker panels for not only warfarin but for any drug metabolized by CYP2C9 across different populations.