Research

Discovery and implementation of transcriptional biomarkers of synthetic LXR agonists in peripheral blood cells

Elizabeth A DiBlasio-Smith¹ , Maya Arai¹ , Elaine M Quinet² , Mark J Evans² , Tad Kornaga¹ , Michael D Basso² , Liang Chen² , Irene Feingold³ , Anita R Halpern² , Qiang-Yuan Liu² , Ponnal Nambi² , Dawn Savio² , Shuguang Wang² , William M Mounts¹ , Jennifer A Isler⁴ , Anna M Slager⁴ , Michael E Burczynski⁴ , Andrew J Dorner¹ and Edward R LaVallie¹

¹  Department of Biological Technologies, Wyeth Research, 35 CambridgePark Drive, Cambridge, MA 02140, USA

²  Department of Cardiovascular and Metabolic Disease, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA

³  Department of Drug Safety and Metabolism, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA

⁴  Department of Clinical Translational Medicine, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA

author email corresponding author email

Journal of Translational Medicine 2008, 6:59doi:10.1186/1479-5876-6-59

Published:	16 October 2008

Abstract

Background

LXRs (Liver X Receptor α and β) are nuclear receptors that act as ligand-activated transcription factors. LXR activation causes upregulation of genes involved in reverse cholesterol transport (RCT), including ABCA1 and ABCG1 transporters, in macrophage and intestine. Anti-atherosclerotic effects of synthetic LXR agonists in murine models suggest clinical utility for such compounds.

Objective

Blood markers of LXR agonist exposure/activity were sought to support clinical development of novel synthetic LXR modulators.

Methods

Transcript levels of LXR target genes ABCA1 and ABCG1 were measured using quantitative reverse transcriptase/polymerase chain reaction assays (qRT-PCR) in peripheral blood from mice and rats (following a single oral dose) and monkeys (following 7 daily oral doses) of synthetic LXR agonists. LXRα, LXRβ, ABCA1, and ABCG1 mRNA were measured by qRT-PCR in human peripheral blood mononuclear cells (PBMC), monocytes, T- and B-cells treated ex vivo with WAY-252623 (LXR-623), and protein levels in human PBMC were measured by Western blotting. ABCA1/G1 transcript levels in whole-blood RNA were measured using analytically validated assays in human subjects participating in a Phase 1 SAD (Single Ascending Dose) clinical study of LXR-623.

Results

A single oral dose of LXR agonists induced ABCA1 and ABCG1 transcription in rodent peripheral blood in a dose- and time-dependent manner. Induction of gene expression in rat peripheral blood correlated with spleen expression, suggesting LXR gene regulation in blood has the potential to function as a marker of tissue gene regulation. Transcriptional response to LXR agonist was confirmed in primates, where peripheral blood ABCA1 and ABCG1 levels increased in a dose-dependent manner following oral treatment with LXR-623. Human PBMC, monocytes, T- and B cells all expressed both LXRα and LXRβ, and all cell types significantly increased ABCA1 and ABCG1 expression upon ex vivo LXR-623 treatment. Peripheral blood from a representative human subject receiving a single oral dose of LXR-623 showed significant time-dependent increases in ABCA1 and ABCG1 transcription.

Conclusion

Peripheral blood cells express LXRα and LXRβ, and respond to LXR agonist treatment by time- and dose-dependently inducing LXR target genes. Transcript levels of LXR target genes in peripheral blood are relevant and useful biological indicators for clinical development of synthetic LXR modulators.