Imaging technologies such as Ultrasound, OCT, MRI and CT are useful for diagnostics and tomographic assessment of therapy response. Fluorescence imaging with its high sensitivity is a promising approach and is extensively used for lesion localization, surgical guidance and monitoring response to therapies. While conjugating fluorophores to antibodies improves specificity, further conjugation of drugs provides a dual function, where fluorescence monitoring may simultaneously reveal drug pharmacokinetics. Fluorescence imaging, however, is limited by low penetration of light, which can be partially overcome by photoacoustic imaging (PAI). In this study, by conjugating a fluorophore and photoacoustic molecule to an antibody (Dual Function Antibody Conjugate (DFAC)), we evaluate whether PAI can significantly improve deep-tissue imaging.
To provide a systematic comparison of these imaging modalities we developed a DFAC, comprising of Cetuximab (anti-EGFR antibody) conjugated with a fluorophore (AF647) and a photoacoustic dye (IRDye800) in a 1:2:2 ratio. We hypothesize that, conjugating quantifiable probes to an antibody, would provide information about different depths within the confines of optical approaches. Such quantification is particularly important in photodynamic therapy, for determination of tissue concentration of photosensitizers and in chemotherapy for quantification of drug concentrations non-invasively. The relationship between the photoacoustic and fluorescence signals from the DFAC is demonstrated through spectroscopic techniques and their EGFR specificity along with deep tissue photoacoustic quantification is established using EGFR positive/negative cell lines and tissue mimicking phantoms.
The DFAC, presented in this study, demonstrates a combination of two complimentary imaging modalities for non-invasive determination of pharmacokinetics and in vivo drug quantification.