Lanthanide-doped upconversion nanoparticles (UCNPs) are considered promising novel near-infrared (NIR) bioimaging agents with the characteristics of high contrast and high penetration depth. However, the interactions between charged UCNPs and mammalian cells have not been thoroughly studied, and the corresponding intracellular uptake pathways remain unclear. Herein, our research work involved the use of a hydrothermal method to synthesize polyvinylpyrrolidone-coated UCNPs (UCNP-PVP), and then a ligand exchange reaction was performed on UCNP-PVP, with the help of polyethylenimine (PEI) and poly(acrylic acid) (PAA), to generate UCNP-PEI and UCNP-PAA. These polymer-coated UCNPs demonstrated good dispersibility in aqueous medium, had the same elemental composition and crystal phase, shared similar TEM and dynamic light scattering (DLS) size distribution, and exhibited similar upconversion luminescence efficiency. However, the positively charged UCNP-PEI evinced greatly enhanced cellular uptake in comparison with its neutral or negative counterparts, as shown by multiphoton confocal microscopy and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Meanwhile, we found that cationic UCNP-PEI can be effectively internalized mainly through the clathrin endocytic mechanism, as revealed by colocalization, chemical, and genetic inhibitor studies. This study elucidates the role of the surface polymer coatings in governing UCNP-cell interactions, and it is the first report on the endocytic mechanism of positively charged lanthanide-doped UCNPs. Furthermore, this study provides important guidance for the development of UCNPs as specific intracellular nanoprobes, allowing us to control the UCNP-cell interactions by tuning surface properties.

Biomimetic nanoparticles (NPs) combine the flexibility and reproducibility of synthetic materials with the functionality of biological materials. Here, we developed and characterized biomimetic poly­(lactic-co-glycolic acid) (PLGA) NPs coated with human cancer cell membrane fractions (CCMFs) to form CCMF-coated PLGA (CCMF-PLGA) NPs. We evaluated the ability of these CCMF-PLGA NPs to disrupt cancer cell–stromal cell interactions and to induce an immune response. Western blot analysis verified the plasma membrane purity of CCMFs. Confocal fluorescence microscopy and flow cytometry confirmed the presence of intact membrane-associated proteins including CXCR4 and CD44 following membrane derivation and coating. CCMFs and CCMF-PLGA NPs were capable of inhibiting cancer cell migration toward human mammary fibroblasts. Intravenous injection of CCMF-PLGA NPs significantly reduced experimental metastasis in vivo. Following immunization of Balb/c mice, near-infrared fluorescence imaging confirmed the migration of NPs to proximal draining lymph nodes (LNs). A higher percentage of CD8+ and CD4+ cytotoxic T-lymphocyte populations was observed in spleens and LNs of CCMF-PLGA NP-immunized mice. Splenocytes isolated from CCMF-PLGA NP-immunized mice had the highest number of interferon gamma-producing T-cells as detected by the ELISpot assay. CCMF-PLGA NPs hold promise for disrupting cancer cell–stromal cell interactions and for priming the immune system in cancer immunotherapy.

Nanoparticles (NPs) camouflaged in cell membranes represent novel biomimetic platforms that can mimic some of the membrane functions of the cells from which these membranes are derived, in biological systems. Studies using cell membrane coated NPs cover a large repertoire of membranes derived from cells such as red blood cells, immune cells, macrophages, and cancer cells. Cancer cell membrane coated nanoparticles (CCMCNPs) typically consist of a NP core with a cancer cell plasma membrane coat that can carry tumor-specific receptors and antigens for cancer targeting. The NP core can serve as a vehicle to carry imaging and therapeutic moieties. As a result, these CCMCNPs are being investigated for multiple purposes including cancer theranostics. Here we have discussed the key steps and major issues in the synthesis and characterization of CCMCNPs. We have highlighted the homologous binding mechanisms of CCMCNPs that are being investigated for cancer targeting, and have presented our data that identify BT474 CCMCNPs as binding to multiple cancer cell lines. Current preclinical applications of CCMCNPs for cancer theranostics and their advantages and limitations are discussed.

Triple-negative breast cancer (TNBC) is one of the most lethal subtypes of breast cancer that has limited treatment options. Its high rates of recurrence and metastasis have been associated, in part, with a subpopulation of breast cancer stem-like cells that are resistant to conventional therapies. A compendium of markers such as CD44high/CD24low, and increased expression of the ABCG2 transporter and increased aldehyde dehydrogenase (ALDH1), have been associated with these cells. We developed a CD44-targeted monoclonal antibody photosensitizer conjugate for combined fluorescent detection and photoimmunotherapy (PIT) of CD44 expressing cells in TNBC. The CD44-targeted conjugate demonstrated acute cell killing of breast cancer cells with high CD44 expression. This cell death process was dependent upon CD44-specific cell membrane binding combined with near-infrared irradiation. The conjugate selectively accumulated in CD44-positive tumors and caused dramatic tumor shrinkage and efficient elimination of CD44-positive cell populations following irradiation. This novel phototheranostic strategy provides a promising opportunity for the destruction of CD44-positive populations that include cancer stem-like cells, in locally advanced primary and metastatic TNBC.