The morphology of hydroxyapatite nanoparticles regulates clathrin-mediated endocytosis in melanoma cells and resultant anti-tumor efficiency

Clathrin-mediated endocytosis plays a critical role for hydroxyapatite nanoparticles (HANPs) to enter tumor cells, induce mitochondrial apoptosis, and inhibit tumor growth. This study was aimed to investigate how the morphology of HANPs impacts the endocytosis of the particles in melanoma cells, and their anti-tumor effect by using in vitro cell experiments and in vivo tumor animal model. Three shapes of HANPs, including granular HANPs (G-HANPs), rod-like HANPs (R-HANPs), and needle-like HANPs (N-HANPs), were successfully prepared by wet chemical method. All the three HANPs could be internalized into A375 melanoma cells as indicated by cellular transmission electron microscopy images. Among these HANPs, only G-HANPs induced morphological change of mitochondria and loss of mitochondrial membrane potential (Δψ_m), and exhibited the greatest intracellular internalization efficiency in the tumor cells. Furthermore, the results of immunofluorescence staining and western blotting indicated that the level of adaptin-2 (AP2) protein was up-regulated by all the HANPs, and highest in G-HANPs treated A375 cells. Moreover, in the tumor-bearing mouse model, we found that tumor growth was delayed by all the three HANPs, of which, G-HANPs delayed tumor growth most efficiently and presented a highest expression level of AP2 protein in tumor tissues. Therefore, this study suggested that the morphology of HANPs regulated their endocytosis efficiency and their effect to inhibit tumor growth. This work facilitates to direct the rational design of nano-materials for tumor therapy.