Lipid-based oil-filled nanoparticles (NPs) with a high concentration of surface-chelated nickel (Ni-NPs) were successfully prepared using a Brij 78-NTA-Ni conjugate synthesized with Brij 78 (Polyoxyethylene (20) stearyl ether) and nitrilotriacetic acid (NTA). The facile incorporation of the Brij 78-NTA-Ni conjugate into the NP formulation allowed up to 90% Ni incorporation, which was a significant improvement over the previously used standard agent DOGS-NTA-Ni which led to ~6% Ni incorporation. The Ni-NPs were targeted to the highly epidermal growth factor receptor (EGFR)-overexpressing epidermoid carcinoma cells A431. This was accomplished using a novel high affinity histidine×6-tagged EGFR-binding Z domain (heptameric Z(EGFR) domain). In vitro cell uptake studies showed enhanced internalization (up to 90%) of the targeted Ni-NPs in A431 cells with only ≤10% internalization of the untargeted Ni-NPs. ICP-MS analysis used to quantify the amount of Ni in the cells were in close agreement with flow cytometry studies, which showed a dose dependent increase in the amount of Ni with the targeted Ni-NPs. Cell uptake competition studies showed that internalization of the targeted Ni-NPs within the cells was competed off with free heptameric Z(EGFR) domain at concentrations of 8.75ng/mL or higher. In vivo studies were carried out in nude mice bearing A431 tumors to determine the biodistribution and intracellular delivery. Near Infrared (NIR) optical imaging studies using Alexa750-labeled heptameric Z(EGFR) domain showed localization of 19% of the total detected fluorescence intensity in the tumor tissue, 28% in the liver and 42% in the kidneys 16h post i.v. injection. ICP-MS analysis showed almost a two-fold increase in the amount of intracellular Ni with the targeted Ni-NPs. These new Ni-NPs could be a very useful tool for targeting and drug delivery to a wide range of EGFR positive cancers.
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