Therapeutic inhibition of oncogenic miR-181a processing for cancer therapy

Background: Oncogenic microRNA-181a (miR-181a) is a master regulator of tumor pathogenesis, driving cancer initiation, progression, metastasis, and immune evasion across diverse cancer lineages by suppressing critical pathways such as STING, WNT, and TGFbeta signaling. While genetic ablation of miR-181a is potently anti-tumorigenic and well tolerated, no therapies currently exist targeting miR-181a, presenting a critical therapeutic gap. Targeting miR-181a offers a promising strategy as it regulates multiple oncogenic pathways simultaneously, unlike existing therapies that act on a single target. Nucleotide-based miRNA-targeting therapies have made significant advances with more than 1,300 clinical trials having been conducted to target miRNAs; yet challenges remain in bioavailability, stability, and effective delivery. Therefore, a small molecule pharmacological strategy targeting miR-181a processing represents an attractive alternative with superior pharmacokinetic properties, improved stability, and enhanced delivery potential. Here, we report the discovery and characterization of SMIR-181s (Small Molecule Inhibitors of miR-181a), a novel class of compounds that alter miR-181a biogenesis and suppress cancer properties. Results: Using a high-throughput biosensor-based screening platform in miR-181a dependent cancer lines, we identified a novel small molecule inhibitor of miR-181a biogenesis. Screening identified a class of seven SMIR-181s, that impair miR-181a maturation, resulting in the accumulation of precursor miR-181a accumulation and depletion of mature. Mechanistic studies reveal that SMIR-181s mediate this depletion by inducing degradation of TARBP2 (Trans-Activating Responsive Binding Protein 2), an RNA-binding protein that acts as a rheostat for stress-induced miRNAs such as miR-181a. Importantly, SMIR-181s display broad cytotoxicity across the NCI-60 cancer cell line panel, with enhanced efficacy in miR-181a high tumor cells while sparing normal cells. Furthermore, these compounds trigger apoptosis and exhibit a novel mechanism of action distinct from all known agents in the NCI-60 database. Conclusions: Collectively, this work emphasizes miR-181a's potential as a predictive biomarker, establishes proof-of-concept for small molecules that target miRNA processing, and nominates the SMIR-181 class as first-in-class candidates for the treatment of a broad spectrum of miR-181a-driven malignancies.