Authors:
E. Kulikowski1, S. Wasiak1, D. Gilham1, L. Tsujikawa1, C. Halliday1, M. Sweeney2, J. Johansson2, N.C.W. Wong1, 1Resverlogix Corp. - Calgary - Canada, 2Resverlogix Corp. - San Francisco - United States of America,

Background: Apabetalone (RVX-208) is an inhibitor of the epigenetic regulators bromodomain and extraterminal (BET) proteins, currently in a phase 3 outcomes trial in patients with cardiovascular disease (CVD) and diabetes mellitus (DM). BET proteins control recruitment of transcriptional machinery to coordinate gene transcription. BET inhibition by apabetalone has been shown to modulate gene expression of pathways that underlie CVD including reverse cholesterol transport, vascular inflammation, coagulation and complement. Patients with acute coronary syndrome (ACS) have increased post-infarction plasma levels of C5b-9 and levels of C3 and C4 correlate with CVD risk, indicating a role of the complement system in the pathogenesis of CVD.

Purpose: To investigate the effect of BET inhibition on the abundance and function of the complement cascade in clinical samples and cultured cells.

Methods: To assess apabetalone induced changes in levels of circulating complement proteins, plasma from the phase IIb trial ASSURE (n=47) was used to perform a SOMAscan proteomic analysis (measure of ∼1300 analytes). SOMAscan uses aptamers (short DNA sequences with “protein-like” side chains), each of which is highly specific for its cognate protein. Function of the complement cascade was determined in CH50 and AH50 hemolytic assays (n=11). Primary human hepatocytes (PHH) exposed to apabetalone were surveyed by microarray, mRNA assay and complement protein secretion.

Results: Complement is one of the top pathways downregulated in CVD patients receiving apabetalone as assessed by the bioinformatic analysis of the serum proteome. Numerous circulating complement proteins were reduced from 10–20% versus baseline (p-value<0.05) including C5, C6, C8, C9, and MBL2 (−12%, −14%, −10%, −18%, −15%, respectively). This translated into a reduction in the function of the complement cascade by 26% in both the CH50 and AH50 hemolytic assays after 26 weeks of apabetalone treatment (p<0.01). This modulation of complement activity did not increase the rate of infections in the phase 2b trials. Widespread effects of BET inhibition on complement genes and proteins were further confirmed in PHH exposed to apabetalone, where basal and inflammatory stimuli induced mRNA and secretion of complement components C3, C4, C5 and C9 were decreased by 20–100%.

Conclusions: The role of the complement pathway in the pathogenesis of ACS represents a novel target for therapeutic intervention. BET inhibition by apabetalone decreases abundance and function of the complement cascade in CVD patients. By modulating innate immune pathways which impact disease, apabetalone may lower the incidence of MACE in patients with high residual CVD risk.