This difference was reflected mostly in the internalized structure and the size of the internalized substances. Moreover, no microscopic imaging technique is available that can perform the real-time dynamic observation of macropinocytosis around the cell surface, especially macropinocytosis Polydatin (Piceid) in tumor cells with relatively small macropinocytosis structure, which largely limited further studying and understanding the process. major role in the initiation of innate response and specific immune response, as well as in pathogens entering the host cells.2C5 Recently, Commisso et al found that pancreatic cancer cells absorbed extracellular proteins through macropinocytosis for intracellular amino acid metabolism, which suggested that macropinocytosis is used as a mode of nutrition uptake by tumor cells.6 Therefore, it is essential to reveal the differences in macropinocytosis between tumor and other cells. The large size of macropinosome vesicle is the main characteristic differentiating it from clathrin-mediated endocytosis (85C110 nm) and caveolin-mediated endocytosis (55C75 nm).7 Some studies have even found that the size of macropinosomes in macrophages could reac ~5 m. 8 Swanson and Watts identified the whole process of macropinocytosis, from CCND2 ruffle formation, ruffle closure, cup closure to the formation of macropinosome vesicle.9 Commisso et al established a method to observe and quantify the internalized macropinosome vesicles in pancreatic cancer cells.10 Owing to the diffraction limitation of visible light, exploring cells with a spatial resolution higher than for the subcellular level is still powerless for the traditional confocal microscopy. Structured illumination microscopy (SIM) that achieves higher imaging velocity and requires a relatively simple setup has been widely applied in the field of life sciences.11C13 However, the real-time observation of macropinocytosis on the surface of the cell membrane to characterize the strength, duration, and structural features is not yet possible. Due to the complexity of biomolecules, nanoparticles have become an ideal model for studying cell internalization, with the characteristics of controlled and uniform size. Also, as potential drug carriers, it is also significant to reveal about internalization of nanoparticles in tumor cells. The physicochemical properties of nanoparticles could influence the capacity for internalization, including the size, the constituting material, surface chemistry, and so on.14C16 Currently, diverse tools such as flow cytometry, mass spectroscopy, capillary electrophoresis, and Raman spectroscopy are Polydatin (Piceid) used for analysis.17C20 However, they still have some limitations and a visual method which could show the internalization of nanoparticles directly is urgently required. In the present study, by means of the three-dimensional-SIM (3D-SIM) technique, we characterized in situ the dynamic endocytic structures and identified the size of internalized substances on the surface of pancreatic cancer cells with Ras mutation. We established a method for real-time observation of the occurrence of macropinocytosis on the surface of cells for the first time. This method was employed for assessing different-sized silica nanoparticles (SiO2 NPs) as the scale ruler of the internalized substances of macropinocytosis in tumor cells. Materials Polydatin (Piceid) and methods Brief general description First of all, using DNA-single-walled carbon nanotubes (SWCNTs), we observed the differences in modes of macropinocytosis between multiple types of cells; next, based on 3D-SIM, we explored the structural characteristics of macropinocytosis; and finally, applying different sizes of SiO2 NPs, the size range of internalized substances in K-rasG12C MIA PaCa-2 cells was detected. Cell culture The pancreatic adenocarcinoma-derived human KrasG12C MIA PaCa-2 cells (ATCC? CRM-CRL-1420?), Kraswt MIA PaCa-2 cells (ATCC? CRL-1420?), human umbilical vein endothelial cells (HUVECs; ATCC? PCS-100-013?), and mouse macrophage Natural 264.7 cells (ATCC? TIB-71?) were purchased from the American Type Culture Collection (Manassas, VA, USA) and maintained in DMEM (Thermo Fisher Scientific, Waltham, MA, USA), supplemented with 10% heat-inactivated fetal Polydatin (Piceid) bovine serum (Thermo Fisher Scientific), 100 g/mL.