Rational modification of PROTACs for tumor-selective protein degradation.

Proteolysis-targeting chimeras (PROTACs) are heterobifunctional molecules that hijack the ubiquitin-proteasome system to catalytically degrade pathogenic proteins. With the ability to target "undruggable" proteins and exert sustained pharmacological effects, PROTACs hold considerable promise for cancer therapy. However, achieving tumor-selective protein degradation remains a central challenge. This review outlines the application of PROTACs in cancer treatment and systematically summarizes emerging strategies to enhance tumor specificity. These approaches leverage hallmark features of tumors, distinctive surface biomarkers and a unique tumor microenvironment (TME), and are broadly categorized into two classes: active targeting, which employs tumor-selective ligands to enrich PROTACs in malignant cells; and conditionally activated strategies, where TME cues either selectively trigger PROTAC prodrugs or induce structural transformations in nanocarriers to enhance drug accumulation at the tumor site. By elucidating these mechanisms, we aim to bridge medicinal chemistry and intelligent nanomedicine, underpinning the tumor-selective protein degradation strategies and offering perspectives on future research directions to improve the biodistribution, safety, and therapeutic efficacy of next-generation PROTACs.