Affinity targeting is used to deliver nanoparticles to cells and tissues. For efficient targeting, it is critical to consider the expression and accessibility of the relevant receptors in the target cells. Here, we describe isotopically barcoded
silver nanoparticles (AgNPs) as a tool for auditing affinity
ligand receptors in cells.
Tumor penetrating
peptide RPARPAR (receptor: NRP-1) and
tumor homing
peptide GKRK (receptor: p32) were used as affinity
ligands on the AgNPs. The binding and uptake of the
peptide-functionalized AgNPs by cultured PPC-1
prostate cancer and M21
melanoma cells was dependent on the cell surface expression of the cognate
peptide receptors. Barcoded
peptide-functionalized AgNPs were synthesized from
silver and
palladium isotopes. The cells were incubated with a cocktail of the barcoded nanoparticles [RPARPAR (R), GKRK (K), and control], and cellular binding and internalization of each type of nanoparticle was assessed by inductively coupled plasma mass spectrometry. The results of isotopic analysis were in agreement with data obtained using optical methods. Using ratiometric measurements, we were able to classify the PPC-1 cell line as mainly NRP-1-positive, with 75 ± 5% R-AgNP uptake, and the M21 cell line as only p32-positive, with 89 ± 9% K-AgNP uptake. The isotopically barcoded multiplexed AgNPs are useful as an in vitro ratiometric phenotyping tool and have potential uses in functional evaluation of the expression of accessible homing
peptide receptors in vivo.