The selective autophagy pathway of nanodiamond‐SSEA‐1 antibody in GBM cells

Nanodiamond (ND) is a biocompatible carbon‐based nanomaterial that has been developed for cellular labeling and detection. Previously, we found that Ub (ubiquitin)‐coated nanodiamonds bind to autophagy receptors, including SQSTM1 (sequestosome 1), OPTN (optineurin), and CALCOCO2/NDP52 (calcium binding and coiled‐coil domain 2) and the LC3 (microtubule‐associated protein 1 light chain 3) for entry into the selective autophagy pathway, to deliver the cargos to lysosomes. In this study, we further reported that ND conjugated to a specific SSEA‐1 antibody (Ab) that can specifically bind to SSEA‐1, which is the marker of glioblastoma multiforme stem cells, and enter the selective autophagy pathway. ND‐SSEA‐1 Ab could bind to the SSEA‐1 proteins and increased the uptake ability of NDs in S1R1 (SSEA‐1 positive) cells but not in the GBM8901 (SSEA‐1 negative) cells. The ND‐SSEA‐1 Ab could bind with SSEA‐1 proteins by protein G beads using immunoprecipitation assays and observed under confocal microscope. Interestingly, the NDs were coated with Ub and then recognized by autophagy receptors to transport to the lysosomes in the S1R1 cells after treatment with ND‐SSEA‐1. We suggest that ND‐SSEA‐1 can specifically recognize the SSEA‐1 proteins on the GBM cells and delivered to lysosome through the selective autophagy pathway. These findings provide that the delivery pathway of antibody‐conjugated nanoparticles, which may develop biomedical applications including cancer stem cell labeling and tracking.