Self-assembled peptide-dye nanostructures for in vivo tumor imaging and photodynamic toxicity

We report noncovalent assemblies of iRGD peptides and methylene blue dyes via electrostatic and hydrophobic stacking. These resulting nanomaterials could bind to cancer cells, image them with photoacoustic signal, and then treat them via photodynamic therapy. We first assessed the optical properties and physical properties of the materials. We then evaluated their utility for live cell targeting, in vivo imaging, and in vivo photodynamic toxicity. We tuned the performance of iRGD by adding aspartic acid (DD) or tryptophan doublets (WW) to the peptide to promote electrostatic or hydrophobic stacking with methylene blue, respectively. The iRGD-DD led to 150-nm branched nanoparticles, but iRGD-WW produced 200-nm nano spheres. The branched particles had an absorbance peak that was redshifted to 720 nm suitable for photoacoustic signal. The nanospheres had a peak at 680 nm similar to monomeric methylene blue. Upon continuous irradiation, the nanospheres and branched nanoparticles led to a 116.62% and 94.82% increase in reactive oxygen species in SKOV-3 cells relative to free methylene blue at isomolar concentrations suggesting photodynamic toxicity. Targeted uptake was validated via competitive inhibition. Finally, we used in vivo bioluminescent signal to monitor tumor burden and the effect of for photodynamic therapy: The nanospheres had little impact versus controls (p = 0.089), but the branched nanoparticles slowed SKOV-3 tumor burden by 75.9% (p < 0.05).