Introduction: Photodynamic therapy (PDT) is a promising method for cancer treatment by using the generated singlet oxygen via irradiation of photosensitizers. To facilitate this technique in biomedical field, there is need for the development of efficient photosensitizers. Here we reported a new lysosome-targeted photosensitizer, which was chemically prepared by using BODIPY modification (Lyso-PDT). It was known that lysosomal photodamage activated the intrinsic apoptotic pathway, but also suppressed autophagic functions. So we anticipated that Lyso-PDT could have higher PDT efficiency than non-targeting photosensitizers.
Materials and Methods: Synthesis of Lyso-PDT. The precursors of Lyso-PDT were prepared by the literature method (J. Med. Chem. 2010, 53, 2865). Lyso-PDT was designed by introducing the tertiary amine substituent (pKa ≈ 10) to BODIPY derivate through an amide linkage, with the expectation that the compound will accumulate in acidic organelles as the protonated form.
Estimation of Lysosomal selectivity. Lyso-PDT was treated at the concentration of 125, 250, 500 nM and treated for 1 h. 100 nM Lysotracker (Blue-DND-22, Invitrogen, ex. 405 nm, em. 420-480 nm) was added for 30 min before imaging. Images were observed using confocal fluorescence microscope (Carl Ziess Observer Z1, 40 x/0.3 EC PlnN Ph1 DIC, ex. 543 nm, em. 560-615 nm).
Cell culture and PDT studies. Cell viability of Lyso-PDT in A549 cells. 1x104 cells were seeded into 96-well plate and incubated for 24 h for cell attachment. LTP was treated for 1 h at the concentration of 0.125, 0.25, 0.5 mM and irradiated with 2 J/cm2 (20 mW/cm2, 1 min 40 sec) using 532 nm CW lawer (n=4). Cell viability was measured through CCK-8 assay after 24 h.
Results and Discussion: The synthetic product was characterized and confirnmed by nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS). To assess whether Lyso-PDT could selectively locate in lysosomes, A549 cells were co-labeled with Lyso-PDT and commertial Lysotracker Blue. We found that the Lyso-PDT and Lysotracker were well merged, meaning that Lyso-PDT was exactly targted to lysosome. Moreover, low concentration of activated Lyso-PDT could significantly kill the cells via laser irradation. These results demonstrated that Lyso-PDT could be useful as a new PDT agent for cancer treatment.
Conclusion: From these study, BODIPY-based photosensitizer having dual modalities could be used for molecular imaging and treatment of cancer.