Real-time monitoring of hemodynamic changes in tumor vessels during photoimmunotherapy using optical coherence tomography.

Photoimmunotherapy (PIT) is a cell-specific cancer therapy based on an armed antibody conjugate that induces rapid and highly selective cancer cell necrosis after exposure to near-infrared (NIR) light. The PIT treatment also induces the superenhanced permeability and retention effect, which allows high concentrations of nanoparticles to accumulate in the tumor bed. In our pilot studies, optical coherence tomography (OCT) reveals dramatic hemodynamic changes during PIT. We developed and applied speckle variance analysis, Doppler flow measurement, bulk motion removal, and automatic region of interest selection to quantify vessel diameter and blood velocity within tumors in vivo. OCT imaging reveals that blood velocity in peripheral tumor vessels quickly drops below the detection limit while the vessel lumen remains open (4 vessels from 3 animals). On the other hand, control tumor vessels (receive NIR illumination but no PIT drug) do not show the sustained blood velocity drop (5 vessels from 3 animals). Ultraslow blood velocity could result in a long drug circulation time in tumor. Increase of the blood pool volume within the central tumor (shown in histology) may be the leading cause of the periphery blood velocity drop and could also increase the drug pool volume in tumor vessels.