Evaluation of Nanoparticle Penetration in the Tumor Spheroid Using Two-Photon Microscopy

Mesoporous silica nanoparticles (MSNs) have emerged as a prominent nanomedicine platform, especially for tumor-related nanocarrier systems. However, there is increasing concern about the ability of nanoparticles (NPs) to penetrate solid tumors, resulting in compromised antitumor efficacy. Because the physicochemical properties of NPs play a significant role in their penetration and accumulation in solid tumors, it is essential to systematically study their relationship in a model system. Here, we report a multihierarchical assessment of the accumulation and penetration of fluorescence-labeled MSNs with nine different physicochemical properties in tumor spheroids using two-photon microscopy. Our results indicated that individual physicochemical parameters separately could not define the MSNs' ability to accumulate in a deeper tumor region; their features are entangled. We observed that the MSNs' stability determined their success in reaching the hypoxia region. Moreover, the change in the MSNs' penetration behavior postprotein crowning was associated with both the original properties of NPs and proteins on their surfaces.