Development and Mechanistic Evaluation of Cathepsin B‐Activatable Peptide‐Drug Conjugate PROTACs for Targeted Protein Degradation in Malignant Tumors: Advancing Precision Protein Degradation Therapeutics in Oncology

Since the advent of proteolysis targeting chimeras (PROTACs), both small molecule PROTACs and peptide-based PROTACs have exhibited distinct advantages. However, PROTACs still exist issues such as poor membrane permeability, low bioavailability, and potential off-target effects. The development of novel PROTACs represents an innovative approach to addressing these challenges. Here, a class of novel PDC-PROTACs is designed and modified with cell-penetrating peptides and tumor-targeting peptides, which incorporate a Cathepsin B-sensitive sequence to enhance the targeting of PROTACs to tumor cells and ensure their controlled release within these cells. Subsequent verification employing HPLC-MRM-MS technology confirms that the utilization of functional peptides and enzyme-sensitive linkers significantly augments the intracellular concentration of PDC-PROTACs, demonstrating improved transmembrane delivery efficiency. Compared to HIF-S or HIF-IMA, the enzyme-responsive PDC-PROTACs Cyclo-A7R-RRR-GFLG-HIF-S and Cyclo-C9C-R-GFLG-HIF-IMA demonstrate enhanced anti-proliferation activity, target protein degradation, and pro-apoptotic effects. In vivo studies indicate that Cyclo-A7R-RRR-GFLG-HIF-S exhibits favorable therapeutic efficacy and safety profile in the U87MG xenograft mouse model. In summary, this research culminates in the creation of novel enzyme-responsive PDC-PROTACs, which leverage the elevated expression of specific enzymes in tumor cells to promote their release, thus enabling the degradation of target proteins. The innovative enzyme-responsive PDC-PROTACs hold considerable promise for tumor therapy.