Sunday, May 18, 2025
5/18/2025
Pharmacodynamic Biomarker of Myotonic Dystrophy - ABSTRACT. Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are dominantly-inherited degenerative disorders that cause muscle weakness and multi-systemic symptoms. Both disorders involve RNA toxicity, a novel gain-of-function mechanism, triggered by expression of RNAs that have thousands of CUG- or CCUG- repeats (DM1 or DM2, respectively). Key proteins that regulate RNA alternative splicing, that have high affinity for CUG- and CCUG-repeats, become trapped on repetitive RNA, causing mis-regulated splicing of transcripts encoding critical components of skeletal muscle. In mouse models we have used a variety of approaches, including oligonucleotides, gene therapy vectors, and small molecules, to show that reduction of RNA toxicity causes normalization of RNA splicing and muscle function, suggesting that DM is at least partly reversible. We also reported that targeted RNAseq analysis of misregulated splice events is reliable and sensitive for monitoring therapeutic impact in mice, providing a near-real-time assessment of target engagement. These developments, and prospects for conducting biomarker-driven trials, have spurred many drug development programs for DM, including some that are now advancing to IND-enabling studies or early-phase trials. To prepare for these studies we developed human targeted RNAseq similar to that employed in mouse studies. Building on comprehensive discovery by deep RNAseq of more than 90 muscle samples, we identified transcripts that show splicing dysregulation, and then developed targeted RNAseq to evaluate 22 splice events that show large effects in DM1. We then determined a composite splicing index for each sample. The splicing index stratifies the population in a large cohort of DM1 patients, correlates with the extent of muscle weakness, shows acceptable test-retest agreement of splicing defects over 2-3 months, and provides a serviceable pharmacodynamic biomarker. However, as the field advances and we gain more experience, important limitations have emerged, particularly in the method for obtaining muscle samples and the selection of splice events for targeted RNAseq – two aspects that are closely linked. Here we seek to optimize and show feasibility for a new sampling method, called myoaspiration, that enables multi-sampling. i.e. sampling of more muscles on more occasions. In parallel, we seek to optimize and validate a new targeted RNAseq assay, applicable to both DM1 and DM2, designed to accommodate myoaspirate samples, and providing greater precision and stronger inferences about target engagement in muscle fibers. Performance of the assay will be initially evaluated using previously collected samples in our BioBank, and then proceed to prospective evaluation of newly-collected myoaspirate samples from DM1 and DM2 patients, focusing on the muscles that are selectively affected or relatively spared. Upon completion, the project is expected to provide a simple yet effective pharmacodynamic biomarker for therapeutic trials leading to drug approval, and for post-approval studies to compare the effectiveness of different agents, regimens, and combinations.
HHS’ Tracking Accountability in Government Grants System (TAGGS) website provides access to detailed descriptions of grants, loans, aggregated direct payments and other types of financial assistance awarded by the HHS Operating Divisions (OPDIVs) and the Office of the Secretary Staff Divisions (STAFFDIVs).