3D mesoscopic fluorescence tomography for imaging micro‐distribution of antibody‐photon absorber conjugates during near infrared photoimmunotherapy in vivo

ABSTRACT As a novel low‐side‐effect cancer therapy, photo‐immunotherapy (PIT) is based on conjugating monoclonal antibody (mAb) with a near‐infrared (NIR) phthalocyanine dye IRDye700DX (IR 700). IR700 is not only fluorescent to be used as an imaging agent, but also phototoxic. When illuminating with NIR light, PIT can induce highly‐selective cancer cell death while leaving most of tumor blood vessels unharmed, leading to an effect termed super‐enhanced permeability and retention (SUPR), which can significantly improve the effectiveness of anti‐cancer drug. Currently, the therapeutic effects of PIT are monitored using 2D macroscopic fluorescence reflectance imager, which lacks the resolution and depth information to reveal the 3D distribution of mAb‐IR700. In the study, we applied a multi‐modal optical imaging approach including high‐resolution optical coherence tomography (OCT) and high‐sensitivity fluorescence laminar optical tomography (FLOT), to provide 3D tumor micro‐structure and micro‐distribution of mAb‐IR700 in the tumor simultaneously during PIT in situ and in vivo. The multi‐wavelength FLOT can also provide the blood vessels morphology of the tumor. Thus, the 3D FLOT reconstructed images allow us to evaluate the IR700 fluorescence distribution change with respect to the blood vessels and at different tumor locations/depths non‐invasively, thereby enabling evaluation of the therapeutic effects in vivo and optimization of treatment regimens accordingly. The mAb‐IR700 can access more tumor areas after PIT treatment, which can be explained by increased vascular permeability immediately after NIR‐PIT. Two‐photon microscopy was also used to record the mAb‐IR700 on the tumor surface near the blood vessels to verify the results.