Photoacoustic Imaging of cRGD Targeted Nanoparticles in a Lewis Lung Carcinoma Tumor Model

Photoacoustic (PA) imaging is a biomedical imaging modality that relies on photon adsorption and processing of resultant pressure waves by conventional ultrasound transducers to construct images in 3D real-time high spatial resolution. Through PA imaging, multiple species can be simultaneously imaged; however, these efforts have been greatly limited by the availability of spectrally separable contrast agents that can be used in vivo. Towards this end, we present here the development of a mixed nanoparticle (NP) system for real-time simultaneous in vivo multiplexed PA imaging. Nineteen water-insoluble organic dyes were screened for poly-ethylene glycol (PEG) coated nanoparticle stability, yielding ten with unique separable absorbance profiles, highly tunable optical properties within the near-infrared window, and in vivo compatibility. This new in vivo compatible mixed-NP system with unique separable absorbance profiles enables advanced PA imaging applications with pharmacokinetic implications. Mixed-sample cRGD peptide surface modified NPs and non-modified NPs were simultaneously tracked in real-time in a murine subcutaneous Lewis lung carcinoma tumor model. Simultaneous imaging of non-modified NPs serves to normalize the effects of active-ligand against passive-NP targeting effects with, for example, 25% surface cRGD modified NPs displaying only 9.8 ± 4 fold higher liver to tumor ratio accumulation levels as opposed to 52 ± 22 fold accumulation levels pre-normalization, questioning the effectiveness of NP targeting. As a result, our new nanoparticle contrast agent tools advance the field of PA imaging with in vivo real-time multiplexed imaging capabilities and pharmacokinetic applications.