Self-Reporting Molecular Prodrug for In Situ Quantitative Sensing of Drug Release by Ratiometric Photoacoustic Imaging.

Understanding the pharmacokinetics of prodrugs in vivo necessitates quantitative, noninvasive, and real-time monitoring of drug release, despite its difficulty. Ratiometric photoacoustic (PA) imaging, a promising deep tissue imaging technology with a unique capacity for self-calibration, can aid in solving this problem. Here, for the first time, a methylamino-substituted Aza-BODIPY (BDP-N) and the chemotherapeutic drug camptothecin (CPT) are joined via a disulfide chain to produce the molecular theranostic prodrug (BSC) for real-time tumor mapping and quantitative visualization of intratumoral drug release using ratiometric PA imaging. Intact BSC has an extremely low toxicity, with a maximum absorption at ∼720 nm; however, endogenous glutathione (GSH), which is overexpressed in tumors, will cleave the disulfide bond and liberate CPT (with full toxicity) and BDP-N. This is accompanied by a significant redshift in absorption at ∼800 nm, resulting in the PA800/PA720 ratio. In vitro, a linear relationship is successfully established between PA800/PA720 values and CPT release rates, and subsequent experiments demonstrate that this relationship can also be applied to the quantitative detection of intratumoral CPT release in vivo. Notably, the novel ratiometric strategy eliminates nonresponsive interference and amplifies the multiples of the signal response to significantly improve the imaging contrast and detection precision. Therefore, this research offers a viable alternative for the design of molecular theranostic agents for the clinical diagnosis and treatment of tumors.

A promising strategy for synergistic cancer therapy by integrating a photosensitizer into a hypoxia-activated prodrug.

Herein, we fabricate a multifunctional molecular prodrug BAC where the chemotherapeutical agent camptothecin (CPT) is linked with a boron dipyrromethene (BODIPY)-based photosensitizer by an azobenzene chain which is sensitive to over-expressed azoreductase in hypoxic tumor cells. This prodrug was further loaded into biodegradable monomethoxy poly(ethylene glycol)-b-poly(caprolactone) (mPEG-b-PCL) to improve its solubility and tumor accumulation. The formed BAC nanoparticles (BAC NPs) can destroy aerobic tumor cells with relatively short distance from blood vessels by photodynamic therapy (PDT) under illumination. The PDT action inevitably leads to consumption of O2, and subsequently acute hypoxia which can induce cleavage of azobenzene linkage to boost release of CPT killing the other hypoxic interior tumor cells survived from PDT. Both in vitro and in vivo studies have verified that BAC NPs possess remarkable antitumor activity by a synergistic action of PDT and chemotherapy.

Mitochondria-Targeting Boron Dipyrromethene Based Photosensitizers for Enhanced Photodynamic Therapy: Synthesis, Optical Properties, and in†vitro Biological Activity.

Increasing Investigations show that photosensitizers (PSs) which target mitochondria are useful for enhancing photodynamic therapy (PDT) efficacy. Herein, we carefully designed and synthesized four triphenylphosphonium (TPP)-modified boron dipyrromethene (BDP)-based PSs through Cu(I)-assisted "3+2" cycloaddition reaction. All of them exhibit intense red light absorption with maxima between 659 and 663 nm, considerable fluorescence emission with quantum yields of 0.16-0.23, high singlet oxygen generation efficiency ranging from 0.22 to 0.34, excellent mitochondria-targeting ability, and good biocompatibility. Upon illumination, they induce significant cancer cell death through a mitochondria-related apoptosis pathway. The IC50 values of these BDP dyes against MCF-7 cells were determined to be as low as 0.046-0.113 µM under rather low dosage of light irradiation (1.5 J ⋅ cm-2 ).

A Hypoxia-Activated Prodrug Conjugated with a BODIPY-Based Photothermal Agent for Imaging-Guided Chemo-Photothermal Combination Therapy.

Hypoxia-activated prodrugs (HAPs) have drawn increasing attention for improving the antitumor effects while minimizing side effects. However, the heterogeneous distribution of the hypoxic region in tumors severely impedes the curative effect of HAPs. Additionally, most HAPs are not amenable to optical imaging, and it is difficult to precisely trace them in tissues. Herein, we carefully designed and synthesized a multifunctional therapeutic BAC prodrug by connecting the chemotherapeutic drug camptothecin (CPT) and the fluorescent photothermal agent boron dipyrromethene (BODIPY) via hypoxia-responsive azobenzene linkers. To enhance the solubility and tumor accumulation, the prepared BAC was further encapsulated into a human serum albumin (HSA)-based drug delivery system to form HSA@BAC nanoparticles. Since the CPT was caged by a BODIPY-based molecule at the active site, the BAC exhibited excellent biosafety. Importantly, the activated CPT could be quickly released from BAC and could perform chemotherapy in hypoxic cancer cells, which was ascribed to the cleavage of the azobenzene linker by overexpressed azoreductase. After irradiation with a 730 nm laser, HSA@BAC can efficiently generate hyperthermia to achieve irreversible cancer cell death by oxygen-independent photothermal therapy. Under fluorescence imaging-guided local irradiation, both in vitro and in vivo studies demonstrated that HSA@BAC exhibited superior antitumor effects with minimal side effects.

Enzyme-Activated Multifunctional Prodrug Combining Site-Specific Chemotherapy with Light-Triggered Photodynamic Therapy.

Combination treatments are more effective than conventional monotherapy in combating cancer. Herein, a multifunctional prodrug BDP-L-CPT was rationally engineered and prepared by the conjugation of a boron dipyrromethene (BDP)-based photosensitizer (PS) to the active site of the chemotherapeutic drug camptothecin (CPT) via a phenyl benzoate group. After modification, the cytotoxicity of CPT was locked. Moreover, the fluorescence emission at 430 nm from the CPT component in the prodrug was substantially inhibited through the intramolecular fluorescence resonance energy transfer process. The phenyl benzoate linker in BDP-L-CPT could be selectively cleaved by exogenous carboxylesterase in phosphate-buffered saline solution and endogenous carboxylesterase overexpressed in cancer cells, which was followed by self-immolation to release free CPT. The drug release process could be monitored by the turn-on of CPT fluorescence in solution and cells. Owing to the combination of site-specific chemotherapy with light-driven photodynamic therapy, the IC50 values of the prodrug BDP-L-CPT against HepG2 human hepatocellular carcinoma and HeLa human cervical carcinoma cells were lower than those of the controls, BDP-COOH and CPT. The combined antitumor effects of the prodrug BDP-L-CPT were also observed in the mice bearing H22 tumors. Furthermore, BDP-L-CPT had a more prolonged blood circulation time in mice than CPT, which is beneficial to persistent therapy. This study may provide a promising strategy for a selective combination cancer treatment by conjugating a prodrug to a PS.

Singlet Oxygen-Responsive Polymeric Nanomedicine for Light-Controlled Drug Release and Image-Guided Photodynamic-Chemo Combination Therapy.

Coencapsulation of chemotherapeutic agents and photosensitizers into nanocarriers can help to achieve a combination of chemotherapy and photodynamic therapy for superior antitumor effects. However, precise on-demand drug release remains a major challenge. In addition, the loaded photosensitizers usually tend to aggregate, which can significantly weaken their fluorescent signals and photodynamic activities. To address these issues, herein, a smart nanocarrier termed as singlet oxygen-responsive nanoparticle (SOR-NP) was constructed by introducing singlet oxygen (1O2)-sensitive aminoacrylate linkers into amphiphilic mPEG-b-PCL copolymers. Boron dipyrromethene (BDP) and paclitaxel (PTX) as model therapeutic agents were coloaded into an 1O2-responsive nanocarrier for realizing light-controlled drug release and combination cancer treatment. This polymeric nanocarrier could substantially relieve the aggregation of encapsulated BDP due to the presence of a long hydrophobic chain. Therefore, the formed SOR-NPBDP/PTX nanodrug could generate bright fluorescent signals and high levels of 1O2, which could mediate cell death via PDT and rupture aminoacrylate linker simultaneously, leading to collapse of SOR-NPBDP/PTX and subsequent PTX release. The light-triggered drug release and combined anticancer effects of SOR-NPBDP/PTX were validated in HepG2 and MCF-7 cancer cells and H22 tumor-bearing mice. This study provides a promising strategy for tumor-specific drug release and selective photodynamic-chemo combination treatment.

Red light triggered photodynamic-chemo combination therapy using a prodrug caged by photosensitizer.

Development of the drug with high therapeutic efficacy and low toxicity is crucial to cancer ablation. In this study, we have demonstrated a red light-responsive prodrug BDP-TK-CPT by connecting the chemotherapeutic agent camptothecin with a boron dipyrromethene (BDP)-based photosensitizer via a reactive oxygen species (ROS)-labile thioketal chain. Since camptothecin is modified by a BDP-based macrocycle at the active site, the formed prodrug displays an extremely low toxicity in dark. However, upon illumination by red light, it can efficiently generate ROS leading to cell death by photodynamic therapy. Meanwhile, the ROS generated can destroy thioketal group to release free camptothecin which further results in local cell death by chemotherapy. The combined antitumor effects of the prodrug have been verified in HepG2, EC109, and HeLa cancer cells and mice bearing H22 tumors. This study may provide an alternative strategy for stimuli-responsive combination treatment of tumors by conjugation of ROS-activatable prodrugs with photosensitizing agents.

A glutathione-responsive photosensitizer with fluorescence resonance energy transfer characteristics for imaging-guided targeting photodynamic therapy.

Here, we have synthesized and characterized a novel activatable photosensitizer (PS) 8a in which two well-designed boron dipyrromethene (BODIPY) derivatives are utilized as the photosensitizing fluorophore and quencher respectively, which are connected by a disulfide linker via two successive Cu (І) catalyzed click reactions. The fluorescence emission and singlet oxygen production of 8a are suppressed via intramolecular fluorescence resonance energy transfer (FRET) from the excited BODIPY-based PS part to quencher unit, but both of them can be simultaneously switched on by cancer-related biothiol glutathione (GSH) in phosphate buffered saline (PBS) solution with 0.05% Tween 80 as a result of cleavage of disulfide. Also, 8a exhibits a bright fluorescence image and a substantial ROS production in A549 human lung adenocarcinoma, HeLa human cervical carcinoma and H22 mouse hepatoma cells having a relatively high concentration of GSH, thereby leading to a significant photocytotoxicity, with IC50 values as low as 0.44 µM, 0.67 µM and 0.48 µM, respectively. In addition, the photosensitizer can be effectively activated and imaged in H22 transplanted hepatoma tumors of mice and shows a strong inhibition on tumor growth. All these results suggest that such a GSH-responsive photosensitizer based on FRET mechanism may provide a new strategy for tumor-targeted and fluorescence imaging-guided cancer therapy.

A H2O2-Responsive Boron Dipyrromethene-Based Photosensitizer for Imaging-Guided Photodynamic Therapy.

In this study, we demonstrate a novel H2O2 activatable photosensitizer (compound 7) which contains a diiodo distyryl boron dipyrromethene (BODIPY) core and an arylboronate group that quenches the excited state of the BODIPY dye by photoinduced electron transfer (PET). The BODIPY-based photosensitizer is highly soluble and remains nonaggregated in dimethyl sulfoxide (DMSO) as shown by the intense and sharp Q-band absorption (707 nm). As expected, compound 7 exhibits negligible fluorescence emission and singlet oxygen generation efficiency. However, upon interaction with H2O2, both the fluorescence emission and singlet oxygen production of the photosensitizer can be restored in phosphate buffered saline (PBS) solution and PBS buffer solution containing 20% DMSO as a result of the cleavage of the arylboronate group. Due to the higher concentration of H2O2 in cancer cells, compound 7 even with low concentration is particularly sensitive to human cervical carcinoma (HeLa) cells (IC50 = 0.95 µM) but hardly damage human embryonic lung fibroblast (HELF) cells. The results above suggest that this novel BODIPY derivative is a promising candidate for fluorescence imaging-guided photodynamic cancer therapy.