Design of RGD-functionalized GSH-responsive pegylated polymeric protacs for selective BRD4 degradation and EndMT-driven cardiac fibrosis inhibition

Endothelial cells (ECs) of endothelial-to-mesenchymal transition (EndMT) are drivers of cardiac fibrosis. BRD4 has recently been identified as an epigenetic regulator of EndMT. Proteolysis-targeting chimera (PROTAC) technology has revolutionized targeted protein degradation, offering unprecedented opportunities for BRD4 modulation in diverse pathological contexts. Nevertheless, the non-selective cellular targeting profile of PROTACs poses significant limitations for their therapeutic application in cardiac fibrosis management. To address these limitations, we developed a GSH-responsive nanoscale PROTAC (RGD-PEG-MZ1) that targets activated platelets, leveraging their chemotactic properties to precisely degrade BRD4 in ECs. RGD-PEG-MZ1 exhibits selectivity for ECs and inhibition of EndMT, which can prevent the progression of cardiac fibrosis. The RNA-seq analysis revealed an attenuation of the MAPK signaling pathway following RGD-PEG-MZ1 treatment. The interaction between BRD4 and the MAPK signaling was analyzed through AlphaFold3 and immunoprecipitation assays. The experimental data showed that BRD4 directly interacts with RAF1, a critical effector in MAPK signaling, which suggested that RGD-PEG-MZ1 modulates MAPK signaling by disrupting the BRD4-RAF1 interaction. This innovative GSH-activated PROTAC strategy not only offers a novel therapeutic approach for cardiac fibrosis but also provides insights into the functional role of BRD4 in the disease pathogenesis of cardiac fibrosis.