Targeting intracellular cancer proteins with tumor-microenvironment-responsive bispecific nanobody-PROTACs for enhanced therapeutic efficacy

Proteolysis targeting chimeras (PROTACs) are pivotal in cancer therapy for their ability to degrade specific proteins. However, their non-specificity can lead to systemic toxicity due to protein degradation in normal cells. To address this, we have integrated a nanobody into the PROTACs framework and leveraged the tumor microenvironment to enhance drug specificity. In this study, we engineered BumPeD, a novel bispecific nanobody-targeted PROTACs-like platform, by fusing two nanobodies with a Furin protease cleavage site (RVRR) and a degron sequence (ALAPYIP or KIGLGRQKPPKATK), enabling the tumor microenvironment to direct the degradation of intracellular proteins. We utilized KN035 and Nb4A to target PD-L1 (programmed death ligand 1) on the cell surface and intracellular Survivin, respectively. In vitro experiments showed that BumPeD triggers Survivin degradation via the ubiquitin-proteasome pathway, inducing tumor apoptosis and suppressing bladder tumor cell proliferation and migration. In vivo experiments further confirmed BumPeD's robust anti-tumor efficacy, underscoring its potential as a precise protein degradation strategy for cancer therapy. Our platform provides a systematic approach to developing effective and practical protein degraders, offering a targeted theoretical basis and experimental support for the development of novel degradative drugs, as well as new directions for cancer therapy.