Photodynamic therapy (PDT) for Actinic Kertoses (AK) using aminoluvelinic acid (ALA) is an FDA-approved treatment,
which is generally effective, yet response rates vary. The origin of the variability is not well characterized, but may be
related to inter-patient variability in the production of protoporphyrin IX (PpIX). While fiber-based point probe systems
provide a method for measuring PpIX production, these measurements have demonstrated large spatial and inter-operator
variability. Thus, in an effort to improve patient-specific dosimetry and treatment it is important to develop a robust system
that accounts for spatial variability and reduces the chance of operator errors. To address this need, a wide-field
multispectral imaging system was developed that is capable of quantifying maps of PpIX in both liquid phantoms and in
vivo experiments, focusing on high sensitivity light signals. The system uses both red and blue excitation to elicit a
fluorescent response at varying skin depths. A ten-position filter wheel with bandpass filters ranging from 635nm to 710nm
are used to capture images along the emission band. A linear least-square spectral fitting algorithm provides the ability to
decouple background autofluorescence from PpIX fluorescence, which has improved the system sensitivity by an order of
magnitude, detecting nanomolar PpIX concentrations in liquid phantoms in the presence of 2% whole blood and 2%
intralipid.
The key to fluorescence guided surgical oncology is the ability to create specific contrast between normal and glioma tissue. The blood brain barrier that limits the delivery of substances to the normal brain is broken in tumors, allowing accumulation of agents in the tumor interior. However, for a clinical success, imaging agents should be in the infiltrative edges to minimize the resection of normal brain while enable the removal of tumor. The aberrant overexpression and/or activation of EGFR is associated with many types of cancers, including glioblastoma and the injection of a fluorescent molecule targeted to these receptors would improve tumor contrast during fluorescence guided surgery. Affibody molecules have intentional medium affinity and high potential specificity, which are the desirable features of a good surgical imaging agent. The aim of this study was evaluate the brain/glioma uptake of ABY029 labeled with near-infrared dye IRDye800CW after intravenous injection. Rats were either inoculated with orthotopic implantations of U251 human glioma cell line or PBS (shams control) in the brain. The tumors were allowed to grow for 2–3 weeks before carrying out fluorescent tracer experiments. Fluorescent imaging of ex vivo brain slices from rats was acquired at different time points after infection of fluorescently labeled EGFR-specific affibody to verify which time provided maximal contrast tumor to normal brain. Although the tumor was most clearly visualized after 1h of IRDye800CW-labeled ABY029 injection, the tumor location could be identified from the background after 48h. These results suggest that the NIR-labeled affibody examined shows excellent potential to increase surgical visualization for confirmed EGFR positive tumors.
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