Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype with the worst prognosis and few effective therapies. Here we identified MS023, an inhibitor of type I protein arginine methyltransferases (PRMTs), which has antitumor growth activity in TNBC. Pathway analysis of TNBC cell lines indicates that the activation of interferon responses before and after MS023 treatment is a functional biomarker and determinant of response, and these observations extend to a panel of human-derived organoids. Inhibition of type I PRMT triggers an interferon response through the antiviral defense pathway with the induction of double-stranded RNA, which is derived, at least in part, from inverted repeat Alu elements. Together, our results represent a shift in understanding the antitumor mechanism of type I PRMT inhibitors and provide a rationale and biomarker approach for the clinical development of type I PRMT inhibitors.

Selective protein degradation platforms have opened novel avenues in therapeutic development and biological inquiry. Antibody‐based lysosome‐targeting chimeras (LYTACs) have emerged as a promising technology that extends the scope of targeted protein degradation to extracellular targets. Aptamers offer an advantageous alternative owing to their potential for modification and manipulation toward a multivalent state. In this study, a chemically engineered platform of multivalent aptamer‐based LYTACs (AptLYTACs) is established for the targeted degradation of either single or dual protein targets. Leveraging the biotin‐streptavidin system as a molecular scaffold, this investigation reveals that trivalently mono‐targeted AptLYTACs demonstrate optimum efficiency in degrading membrane proteins. The development of this multivalent AptLYTACs platform provides a principle of concept for mono‐/dual‐targets degradation, expanding the possibilities of targeted protein degradation.

Despite the well-established significance of transcription factors (TFs) in pathogenesis, their utilization as pharmacological targets has been limited by the inherent challenges in modulating their protein interactions. The lack of defined small-molecule binding pockets and the nuclear localization of TFs do not favor the use of traditional tools. Aptamers possess large molecular weights, expansive blocking surfaces and efficient cellular internalization, making them compelling tools for modulating TF interactions. Here, we report a structure-guided design strategy called Blocker-SELEX to develop inhibitory aptamers (iAptamers) that selectively block TF interactions. Our approach leads to the discovery of iAptamers that cooperatively disrupt SCAF4/SCAF8-RNAP2 interactions, dysregulating RNAP2-dependent gene expression, which impairs cell proliferation. This approach is further applied to develop iAptamers blocking WDR5-MYC interactions. Overall, our study highlights the potential of iAptamers in disrupting pathogenic TF interactions, implicating their potential utility in studying the biological functions of TF interactions and in nucleic acids drug discovery.

Cell surface proteins are key disease biomarkers and therapeutic targets, yet high-throughput methods for aptamer discovery targeting these proteins in situ remain limited. We introduce single-cell perturbation-driven aptamer recognition and kinetics sequencing (SPARK-seq), a high-throughput platform integrating single-cell messenger RNA and aptamer sequencing with CRISPR-based surface protein perturbation. In a single experiment, SPARK-seq simultaneously mapped 5535 distinct aptamers to eight surface proteins, capturing interactions across more than two orders of magnitude in protein abundance and spanning diverse biophysical classes. The method discriminated closely related paralogous proteins with no detectable cross-reactivity and provided kinetic information that enabled the prioritization of aptamers with slow dissociation rates. Leveraging this kinetic diversity, we engineered variants with improved off-rate properties. SPARK-seq establishes a platform for high-efficiency discovery and rational variant design of aptamers and functional nucleic acids, unlocking possibilities in diagnostics and therapeutics.