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

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.

Real-time monitoring of microdistribution of antibody-photon absorber conjugates during photoimmunotherapy in vivo.

Photoimmunotherapy (PIT) is an emerging low side effect cancer therapy based on a monoclonal antibody (mAb) conjugated with a near-infrared (NIR) phthalocyanine dye IRDye 700DX. IR700 is fluorescent, can be used as an imaging agent, and also is phototoxic. It induces rapid cell death after exposure to NIR light. PIT induces highly selective cancer cell death, while leaving most of tumor blood vessels unharmed, leading to an effect called super-enhanced permeability and retention (SUPR). SUPR significantly improves the effectiveness of the anticancer drug. Currently, the therapeutic effects of PIT are monitored using the IR700 fluorescent signal based on macroscopic fluorescence reflectance imagery. This technique, however, lacks the resolution and depth information to reveal the intratumor heterogeneity of mAb-IR700 distribution. We applied a minimally invasive two-channel fluorescence fiber imaging system by combining the traditional fluorescence imaging microscope with two imaging fiber bundles (~0.85mm). This method monitored mAb-IR700 distribution and therapeutic effects during PIT at different intratumor locations (e.g., tumor surface vs. deep tumor) in situ and in real time simultaneously. This enabled evaluation of the therapeutic effects in vivo and treatment regimens. The average IR700 fluorescence intensity recovery after PIT to the tumor surface is 91.50%, while it is 100.63% in deep tumors. To verify the results, two-photon microscopy combined with a microprism was also used to record the mAb-IR700 distribution and fluorescence intensity of green fluorescent protein (GFP) at different tumor depths during PIT. After PIT treatment, there was significantly higher IR700 fluorescence recovery in deep tumor than in the tumor surface. This phenomenon can be explained by increased vascular permeability immediately after NIR-PIT. Fluorescence intensity of GFP at the tumor surface decreased significantly more compared to that of deep tumor and in controls (no PIT).

In Vivo Voltage-Sensitive Dye Imaging of Subcortical Brain Function.

The whisker system of rodents is an excellent model to study peripherally evoked neural activity in the brain. Discrete neural modules represent each whisker in the somatosensory cortex ("barrels"), thalamus ("barreloids"), and brain stem ("barrelettes"). Stimulation of a single whisker evokes neural activity sequentially in its corresponding barrelette, barreloid, and barrel. Conventional optical imaging of functional activation in the brain is limited to surface structures such as the cerebral cortex. To access subcortical structures and image sensory-evoked neural activity, we designed a needle-based optical system using gradient-index (GRIN) rod lens. We performed voltage-sensitive dye imaging (VSDi) with GRIN rod lens to visualize neural activity evoked in the thalamic barreloids by deflection of whiskers in vivo. We stimulated several whiskers together to determine the sensitivity of our approach in differentiating between different barreloid responses. We also carried out stimulation of different whiskers at different times. Finally, we used muscimol in the barrel cortex to silence the corticothalamic inputs while imaging in the thalamus. Our results show that it is possible to obtain functional maps of the sensory periphery in deep brain structures such as the thalamic barreloids. Our approach can be broadly applicable to functional imaging of other core brain structures.