Development of a Human Photoacoustic Imaging Reporter Gene Using the Clinical Dye Indocyanine Green

Purpose: To develop a photoacoustic imaging (PAI) reporter gene that has high translational potential. Previous research has shown that human organic anion–transporting polypeptide 1b3 (OATP1B3) promotes the uptake of the near-infrared fluorescent dye indo- cyanine green (ICG). In this study, the authors have established OATP1B3 and ICG as a reporter gene–probe pair for in vivo PAI. Materials and Methods: Human breast cancer cells were engineered to express OATP1B3. Control cells (not expressing OATP1B3) or OATP1B3-expressing cells were incubated with or without ICG, placed in a breast-mimicking phantom, and imaged with PAI. Control (n = 6) or OATP1B3-expressing (n = 5) cells were then implanted orthotopically into female mice. Full-spectrum PAI was performed before and 24 hours after ICG administration. One-way analysis of variance was performed, followed by Tukey posthoc multiple comparisons, to assess statistical significance. Results: OATP1B3-expressing cells incubated with ICG exhibited a 2.7-fold increase in contrast-to-noise ratio relative to all other con- trols in vitro (P , .05). In mice, PAI signals after ICG administration were increased 2.3-fold in OATP1B3 tumors relative to those in controls (P , .05). Conclusion: OATP1B3 operates as an in vivo PAI reporter gene based on its ability to promote the cellular uptake of ICG. Benefits include the human derivation of OATP1B3, combined with the use of wavelengths in the near-infrared region, high extinction coef- ficient, low quantum yield, and clinical approval of ICG. The authors posit that this system will be useful for localized monitoring of emerging gene- and cell-based therapies in clinical applications.