We have previously shown that CdSe/ZnS core/shell luminescent semiconductor nanocrystals or QDs (quantum dots) coated with PEG [poly(ethylene glycol)]-appended DHLA (dihydrolipoic acid) can bind AcWG(Pal)VKIKKP9GGH6 (Palm1) through the histidine residues. The coating on the QD provides colloidal stability and this peptide complex uniquely allows the QDs to be taken up by cultured cells and readily exit the endosome into the soma. We now show that use of a polyampholyte coating [in which the neutral PEG is replaced by the negatively heterocharged CL4 (compact ligand)], results in the specific targeting of the palmitoylated peptide to neurons in mature rat hippocampal slice cultures. There was no noticeable uptake by astrocytes, oligodendrocytes or microglia (identified by immunocytochemistry), demonstrating neuronal specificity to the overall negatively charged CL4 coating. In addition, EM (electron microscopy) images confirm the endosomal egress ability of the Palm1 peptide by showing a much more disperse cytosolic distribution of the CL4 QDs conjugated to Palm1 compared with CL4 QDs alone. This suggests a novel and robust way of delivering neurotherapeutics to neurons.
Keywords: cell targeting, drug delivery, nanoparticle, neuronal uptake, pyramidal neuron, quantum dot
Abbreviations: CL4, compact ligand; CNS, central nervous system; CPP, cell-penetrating peptide; DAPI, 4′,6-diamidino-2-phenylindole; DHLA, dihydrolipoic acid; EM, electron microscopy; ER, endoplasmic reticulum; GFAP, glial fibrillary acidic protein; HEK-293, human embryonic kidney 293 cell; NeuN, neuron-specific nuclear protein; PEG, polyethylene glycol; PPT1, palmitoyl:protein thioesterase 1; QD, quantum dot