Functionalized Fluorescent Nanodiamonds Reveal Therapeutic Protein Clearance Through ENDOTAC Linked to AUTOTAC

Targeted protein degradation has emerged as a transformative therapeutic modality in cancer therapy, enabling the elimination of undruggable proteins and overcoming conventional small-molecule resistance. Therapeutic approaches such as endocytosis-targeting chimera (ENDOTAC) and autophagy-targeting chimera (AUTOTAC) facilitate undruggable protein elimination. Here, functionalized fluorescent nanodiamond-targeting chimera (FND-TAC) reveals therapeutic protein clearance and tumor suppression through ENDOTAC linked to AUTOTAC networks. SQSTM1 is a key autophagy receptor mediating ENDOTAC linked to AUTOTAC for targeting protein degradation and cancer therapy. FND is a nanocarrier with stable fluorescence, enabling real-time tracking of protein degradation and tumorigenesis. Pull-down proteomics and STRING network analyses identified SQSTM1 as a central mediator linking Rab5/Rab7-mediated FND endocytosis through ENDOTAC to AUTOTAC. Rab5/Rab7 ubiquitination, coordinated activation of the SQSTM1 PB1, LIR, and UBA domains, and SQSTM1 S403 phosphorylation through AUTOTAC enabled FND nanoparticulosome formation and subsequent nanoparticulophagy. Moreover, SQSTM1-mediated LAMP1/2 organization linked AUTOTAC to LYTAC for lysosomal targeting. Functionalization with the therapeutic PD-L1 monoclonal antibody atezolizumab (ATZ) to form FND-ATZ demonstrated that ATZ-targeted PD-L1 was delivered to lysosomes for clearance and cancer cell death. Furthermore, FND-ATZ highlighted therapeutic PD-L1 clearance and tumor suppression through ENDOTAC linked to AUTOTAC networks. Real-time observation of FND-TAC reveals that ENDOTAC-AUTOTAC networks mediate therapeutic protein clearance and tumor inhibition.