An EPR strategy for bio-responsive fluorescence guided surgery with simulation of the benefit for imaging.

A successful matching of a PEG group size with the EPR effect for an <i>off-to-on</i> responsive NIR-fluorophore conjugate has been accomplished which allows two distinct <i>in vivo</i> tumor imaging periods, the first being the switch on during the initial tumor uptake via enhanced permeability into the ROI (as background is suppressed) and a second, later, due to enhanced retention within the tumor. <div><b>Methods</b>: Software simulation (https://mihaitodor.github.io/particle_simulation/index.html), synthetic chemistry, with <i>in vitro</i> and <i>in vivo</i> imaging have been synergistically employed to identify an optimal PEG conjugate of a bio-responsive NIR-AZA fluorophore for <i>in vivo</i> tumor imaging. </div><div><b>Results</b>: A bio-responsive NIR-AZA fluorophore conjugated to a 10 kDa PEG group has shown excellent <i>in vivo</i> imaging performance with sustained high tumor to background ratios and peak tumor emission within 24 h. Analysis of fluorescence profiles over 7 days has provided evidence for the EPR effect playing a positive role. </div><div><b>Conclusion</b>: Preclinical results show that exploiting the EPR effect by utilizing an optimized PEG substituent on a bio-responsive fluorophore may offer a means for intraoperative tumor margin delineation. The <i>off-to-on</i> responsive nature of the fluorophore makes tumor imaging achievable without waiting for clearance from normal tissue.</div>