Human Nanoplatelets as Living Vehicles for Tumor-Targeted Endocytosis In Vitro and Imaging In Vivo.

Recent studies have shown human platelets can access the tumor microenvironment by passive diffusion across capillaries or via activated immune cells. In a previous study, we exploited this affinity of platelets for tumor cells as part of a new approach to target tumors with modified platelets. Therefore, the engineering of human nanoplatelets as living vehicles for in vivo tumor-targeted near-infra-red fluorescence (NIRF) imaging and the delivery of cytotoxins to tumor cells by endocytosis are described in this study. Nanoplatelets with an average diameter of 200 nm were prepared by mild sonication of kabiramide C (KabC)-loaded human platelets. The sealed plasma membrane of the nanoplatelets allows them to accumulate and retain membrane-permeable chemicals, such as epidoxorubicin (EPI) and KabC. Tumor-targeted imaging functionalities were engineered on the nanoplatelets by surface-coupling transferrin, Cy5 and Cy7. High-resolution fluorescence imaging and flow cytometry analyses showed that the nanoplatelets loaded with EPI and Cy5 targeted human myeloma cells (RPMI8226 cells) that over-expressed the transferrin receptor. The endocytosis of the nanoplatelets by RPMI8226 cells was transferrin-dependent and induced apoptosis. The test results also showed that the nanoplatelets functionalized with transferrin and Cy7 and injected in mice bearing RPMI8226 cells-derived myeloma xenotransplants accumulated in the tumor tissue and could be used for high-contrast in vivo NIRF imaging of early-stage tumors. Nanoplatelets represent a new class of living nano-vehicles that may efficiently target and deliver therapeutic agents and imaging probes to diseased tissues including tumors.