Biodistribution of
photosensitizer (PS) in
photodynamic therapy (
PDT) can be assessed by fluorescence imaging that visualizes the accumulation of PS in malignant tissue prior to
PDT. At the same time, excitation of the PS during an assessment of its biodistribution results in premature photobleaching and can cause toxicity to healthy tissues. Combination of PS with a separate fluorescent moiety, which can be excited apart from PS activation, provides a possibility for fluorescence imaging (FI) guided delivery of PS to
cancer site, followed by
PDT.
RESULTS: In this work, we report nanoformulations (NFs) of core-shell polymeric nanoparticles (NPs) co-loaded with PS [2-(1-hexyloxyethyl)-2-devinyl
pyropheophorbide-a,
HPPH] and near infrared fluorescent organic
dyes (NIRFDs) that can be excited in the first or second near-infrared windows of tissue optical transparency (NIR-I, ~ 700-950 nm and NIR-II, ~ 1000-1350 nm), where
HPPH does not absorb and emit. After addition to nanoparticle
suspensions, PS and NIRFDs are entrapped by the nanoparticle shell of co-
polymer of
N-isopropylacrylamide and acrylamide [
poly(NIPAM-co-AA)], while do not bind with the
polystyrene (polySt) core alone. Loading of the NIRFD and PS to the NPs shell precludes aggregation of these hydrophobic molecules in water, preventing fluorescence quenching and reduction of
singlet oxygen generation. Moreover, shift of the absorption of NIRFD to longer wavelengths was found to strongly reduce an efficiency of the electronic excitation energy transfer between PS and NIRFD, increasing the efficacy of
PDT with PS-NIRFD combination. As a result, use of the NFs of PS and NIR-II NIRFD enables fluorescence imaging guided
PDT, as it was shown by confocal microscopy and
PDT of the
cancer cells in vitro. In vivo studies with subcutaneously tumored mice demonstrated a possibility to image biodistribution of
tumor targeted NFs both using
HPPH fluorescence with conventional imaging camera sensitive in visible and NIR-I ranges (~ 400-750 nm) and imaging camera for short-wave infrared (SWIR) region (~ 1000-1700 nm), which was recently shown to be beneficial for in vivo optical imaging.
CONCLUSIONS: A combination of PS with fluorescence in visible and NIR-I spectral ranges and, NIR-II
fluorescent dye allowed us to obtain PS nanoformulation promising for see-and-treat
PDT guided with visible-NIR-SWIR fluorescence imaging.