Triphenylphosphonium-functionalized dimeric BODIPY-based nanoparticles for mitochondria-targeting photodynamic therapy

The dimerization of boron dipyrromethene (BODIPY) moieties is an appealing molecular design approach for developing heavy-atom-free triplet photosensitizers (PSs). However, BODIPY dimer-based PSs generally lack target specificity, which limits their clinical use for photodynamic therapy. This study reports the synthesis of two mitochondria-targeting triphenylphosphonium (TPP)-functionalized meso-β directly linked BODIPY dimers (BTPP and BeTPP). Both BODIPY dimers exhibited solvent-polarity-dependent singlet oxygen (1O2) quantum yields, with maximum values of 0.84 and 0.55 for BTPP and BeTPP, respectively, in tetrahydrofuran. The compact orthogonal geometry of the BODIPY dimers facilitated the generation of triplet excited states via photoinduced charge separation (CS) and subsequent spin-orbit charge-transfer intersystem crossing (SOCT-ISC) processes and their rates were dependent on the energetic configuration between the frontier molecular orbitals of the two BODIPY subunits. The as-synthesized compounds were amphiphilic and hence formed stable nanoparticles (∼36 nm in diameter) in aqueous solutions, with a zeta potential of ∼33 mV beneficial for mitochondrial targeting. In vitro experiments with MCF-7 and HeLa cancer cells indicated the effective localization of BTPP and BeTPP within cancer-cell mitochondria. Under light irradiation, BTPP and BeTPP exhibited robust photo-induced therapeutic effects in both cell lines, with half-maximal inhibitory concentration (IC50) values of ∼30 and ∼55 nM, respectively.

Red fluorescent BODIPY-based nanoparticles for targeted cancer imaging-guided photodynamic therapy

Imaging-guided diagnosis and treatment of cancer hold potential to significantly improve therapeutic accuracies and efficacies. Central to this theragnostic approach has been the use of multicomponent-based multimodal nanoparticles (NPs). Apart from this conventional approach, here we propose a design strategy for the simple and straightforward formulation of NPs based on boron dipyrromethene (BODIPY) derivatives, LaB-X (X = H, Et, and Br). Specifically, the conjugation of lactose to the inherently hydrophobic BODIPY promoted the formation of LaB-X NPs in water. Furthermore, the BODIPY backbone was subjected to distyrylation, dibromination, and diethylation to tailor the optical window and the balance between fluorescence and singlet oxygen generation capabilities. We demonstrate that while the photoinduced anticancer activities of LaB-H and LaB-Et NPs were trivial, LaB-Br NPs effectively induced the apoptotic death of hepatocellular carcinoma cells under red light irradiation while allowing fluorescence cell imaging in the phototherapeutic window. This dual fluorescence photosensitizing activity of LaB-Br NPs could be switched off and on, so that both fluorescence and singlet oxygen generation were paused during NP formation in an aqueous solution, while both processes resumed after cellular uptake, likely due to NP disassembly.

Synthesis and Photophysical Properties of Tumor-Targeted Water-Soluble BODIPY Photosensitizers for Photodynamic Therapy

The synthesis of three water-soluble lactose-modified 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based photosensitizers with tumor-targeting capabilities is reported, including an investigation into their photodynamic therapeutic activity on three distinct cancer cell lines (human hepatoma Huh7, cervical cancer HeLa, and breast cancer MCF-7 cell lines). The halogenated BODIPY dyes exhibited a decreased fluorescence quantum yield compared to their non-halogenated counterpart, and facilitated the efficient generation of singlet oxygen species. The synthesized dyes exhibited low cytotoxicities in the dark and high photodynamic therapeutic capabilities against the treated cancer cell lines following irradiation at 530 nm. Moreover, the incorporation of lactose moieties led to an enhanced cellular uptake of the BODIPY dyes. Collectively, the results presented herein provide promising insights for the development of photodynamic therapeutic agents for cancer treatment.