Photoacoustic Imaging Quantifies Drug Release from Nanocarriers via Redox Chemistry of Dye‐Labeled Cargo

We report a new approach to monitor drug release from nanocarriers via a paclitaxel–methylene blue conjugate (PTX-MB) with redox activity. This construct is in a photoacoustically silent reduced state inside poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PTX-MB@PLGA NPs). During release, PTX-MB is spontaneously oxidized to produce a concentration-dependent photoacoustic signal. An in vitro drug-release study showed an initial burst release (25 %) between 0–24 h and a sustained release between 24–120 h with a cumulative release of 40.6 % and a 670-fold increase in photoacoustic signal. An in vivo murine drug release showed a photoacoustic signal enhancement of up to 649 % after 10 hours. PTX-MB@PLGA NPs showed an IC50 of 78 μg mL−1 and 44.7±4.8 % decrease of tumor burden in an orthotopic model of colon cancer via luciferase-positive CT26 cells.