In vivo biodistribution of PEG coated nanoparticles

All biodistribution animal experiments were performed according to the standards of the University of Missouri Institutional Animal Care and Use committee under Protocol #8390. Clodronate liposomes were acquired from ClodronateLiposomes.org. Organ specimens were weighed and then counted using a calibrated sodium iodide (NaI) well detector to detect the 208 keV (11%) gamma emission from ¹⁷⁷Lu.

Three groups of ten C57BL/6 mice were injected intravenously via the tail vein with [¹⁷⁷Lu]Lu_0.5Gd_0.5(PO₄)@Au@PEG₈₀₀, [¹⁷⁷Lu]Lu_0.5Gd_0.5 (PO₄)@Au@PEG₃₄₀₀, or [¹⁷⁷Lu]Lu_0.5Gd_0.5 (PO₄)@Au@PEG₅₀₀₀, in a suspension of 5 mg/ml of bovine serum albumin (BSA) in PBS. In each case, a small amount of material was observed to settle out in the NP/BSA/PBS solution over time. Prior to injection, the nanoparticles were re-dispersed in solution with simple vortex mixing. In each of the three groups, half of the mice were injected with clodronate liposomes (40 mg/200 μl) intraperitoneally 72 h before nanoconjugate injection in order to suppress the reticuloendothelial system (RES) and increase the blood circulation time of the nanoconjugates.^15,16 The biodistribution was determined at 1 h and 24 h post-injection. A fourth group of 5 control mice was injected with [¹⁷⁷Lu]Lu_0.5Gd_0.5 (PO₄)@Au without any surface modification. Mice were euthanized by intraperitoneal injection of pentobarbital (200 mg/kg).