Heart disease remains the primary cause of morbidity and mortality in the industrialized world and continues to incur costs estimated at $30 billion per year, despite detailed understanding of the mechanisms governing cardiac function and contractility. MicroRNAs (miRNAs), a recently discovered family of tiny regulatory RNAs, act as negative regulators of gene expression by inhibiting the translation or promoting the degradation of target mRNAs. Because individual miRNAs often regulate the expression of multiple target genes with related functions, modulating the expression of a single microRNA can, in principle, influence an entire gene network and thereby modify complex disease phenotypes. Recent demonstration of novel roles for miRNAs in the control of diverse aspects of cardiac function and dysfunction provides a wholly new aspect of disease biology to target for therapeutic intervention. Studies by our collaborative group and others have revealed roles for miRNAs in the control of myocyte growth, integrity of the ventricular wall, contractility, maintenance of cardiac rhythm, apoptosis and fibrosis. In particular, our collaborators at miRagen have examined miR-208, a cardiac-specific miRNA that is co-expressed with 1-myosin heavy chain (1MHC). Mice homozygous for the miR-208 deletion are viable and do not display obvious abnormalities in size, shape, or structure of the heart but, significantly, appear resistant to cardiac stress, as shown by a lack of hypertrophy and fibrosis following thoracic aortic banding (TAB). Follow up studies have shown that systemic administration of a locked-nucleic acid (LNA)-modified oligonucleotide (antimiR) binding the mature miR-208 sequence results in significant decreases in cardiac levels of miR-208a. In concordance with the miR-208 knockout mice, antimiR-208 treatment in a rat model for heart failure preserves cardiac function, reduces cardiac remodeling, and increases survival. Where rodent hearts express more 1MHC, monkey hearts, like human hearts, predominantly express 2M HC. Both myosins co-express a miRNA-208 isoform that we will designate as miR- 208a (coming from 1MHC) and miR-208b (coming from 2MHC). Although it is unclear whether miR-208a and miR-208b have overlapping functions, preliminary data in African green monkeys indicate that both isoforms of miR-208 can be specifically targeted in a monkey heart and inducesmiR-208 inhibition lasting for at least 1 month. The current proposal focuses on evaluating the biodistribution, pharmacokinetics and pharmacokinetic/ pharmacodynamics (PK/PD) of antimiR-208a vs. antimiR-208b following systemic delivery in monkeys. Additionally we will induce chronic hypertension to define microRNA changes associated with cardiac remodeling and dysfunction in the setting of congestive heart failure (CHF). Characterization of the pathophysiology will include determination of cardiac tissue expression of miR-208 isoforms, myosin expression, cardiac remodeling and extensive evaluation of functional deficit post-occlusion. Demonstrating hypertrophy and fibrosis in the miR-208 expressing myocardium, coupled with PK/PD data, will permit compelling efficacy assessments in phase II to enable rapid advancement of a miR-208-specific antimiR into IND-enabling toxicology studies and clinical trials.
MicroRNAs, tiny regulators of gene expression and degradation, can regulate cardiac response to injury and our collaborators have demonstrated that cardiac levels of one of these microRNAs, miR-208, is upregulated during cardiac injury and that specific knock down of this with a modified oligonucleotide sequence (antimiR) administered to the bloodstream reduces injury in rodent models of heart failure. We have demonstrated similar knockdown of miR-208 in monkeys by similar antimiR delivery and here propose to determine the pharmacokinetics, pharmacodynamics and biodistribution of antimiRs designed to knock down miR-208 in monkeys to determine optimal dosing. In addition, we will comprehensively characterize miR-208-relevant pathophysiology in a monkey model of congestive heart failure to allow critical pre-clinical efficacy studies to be completed in phase II.
