Development of Prodrugs for PDT-Based Combination Therapy Using a Singlet-Oxygen-Sensitive Linker and Quantitative Systems Pharmacology

Enhancing Precision in Photodynamic Therapy: Innovations in Light-Driven and Bioorthogonal Activation

Over the past few decades, photodynamic therapy (PDT) has evolved as a minimally invasive treatment modality offering precise control over cancer and various other diseases. To address inherent challenges associated with PDT, researchers have been exploring two promising avenues: the development of intelligent photosensitizers activated through light-induced energy transfers, charges, or electron transfers, and the disruption of photosensitive bonds. Moreover, there is a growing emphasis on the bioorthogonal delivery or activation of photosensitizers within tumors, enabling targeted deployment and activation of these intelligent photosensitive systems in specific tissues, thus achieving highly precise PDT. This concise review highlights advancements made over the last decade in the realm of light-activated or bioorthogonal photosensitizers, comparing their efficacy and shaping future directions in the advancement of photodynamic therapy.

Evaluation of a photodynamic therapy agent using a canine prostate cancer model

BACKGROUND

Male dogs can develop spontaneous prostate cancer, which is similar physiologically to human disease. Recently, Tweedle and coworkers have developed an orthotopic canine prostate model allowing implanted tumors and therapeutic agents to be tested in a more translational large animal model. We used the canine model to evaluate prostate-specific membrane antigen (PSMA)-targeted gold nanoparticles as a theranostic approach for fluorescence (FL) imaging and photodynamic therapy (PDT) of early stage prostate cancer.

METHODS

Dogs (four in total) were immunosuppressed with a cyclosporine-based immunosuppressant regimen and their prostate glands were injected with Ace-1-hPSMA cells using transabdominal ultrasound (US) guidance. Intraprostatic tumors grew in 4-5 weeks and were monitored by ultrasound (US). When tumors reached an appropriate size, dogs were injected intravenously (iv) with PSMA-targeted nano agents (AuNPs-Pc158) and underwent surgery 24 h later to expose the prostate tumors for FL imaging and PDT. Ex vivo FL imaging and histopathological studies were performed to confirm PDT efficacy.

RESULTS

All dogs had tumor growth in the prostate gland as revealed by US. Twenty-four hours after injection of PSMA-targeted nano agents (AuNPs-Pc158), the tumors were imaged using a Curadel FL imaging device. While normal prostate tissue had minimal fluorescent signal, the prostate tumors had significantly increased FL. PDT was activated by irradiating specific fluorescent tumor areas with laser light (672 nm). PDT bleached the FL signal, while fluorescent signals from the other unexposed tumor tissues were unaffected. Histological analysis of tumors and adjacent prostate revealed that PDT damaged the irradiated areas to a depth of 1-2 mms with the presence of necrosis, hemorrhage, secondary inflammation, and occasional focal thrombosis. The nonirradiated areas showed no visible damages by PDT.

CONCLUSION

We have successfully established a PSMA-expressing canine orthotopic prostate tumor model and used the model to evaluate the PSMA-targeted nano agents (AuNPs-Pc158) in the application of FL imaging and PDT. It was demonstrated that the nano agents allowed visualization of the cancer cells and enabled their destruction when they were irradiated with a specific wavelength of light.

Visible light-activated prodrug system with a novel heavy-atom-free photosensitizer

The use of light to activate prodrugs offers a promising method for the precise control of drug release, reducing drug-related side effects, and enhancing therapeutic effectiveness. We have created a novel prodrug system that utilizes a unique, heavy-atom-free photosensitizer to produce singlet oxygen, which then triggers the conversion of the prodrug into its active form. This system has been successfully demonstrated through the creation of "photo-unclick" prodrugs of paclitaxel (PTX), combretastatin A-4 (CA-4), and 10-hydroxy-7-ethylcamptothecin (SN-38). These prodrugs show decreased toxicity in the absence of light, but exhibit increased toxicity when exposed to red light.

Pathway network-based quantitative modeling of the time-dependent and dose-response anti-inflammatory effect of Reduning Injection

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) has extensive healing effects on inflammatory diseases with few side effects. Reduning injection (RDNI), a TCM prescription composed of Lonicera japonica Thunb., Gardenia jasminoides Ellis. and Artemisia annua L., is wildly used for treating inflammatory diseases. However, the mechanism of action of RDNI, like most TCM prescriptions, is unclear due to the complexity of relationships between components and their curative effects.

AIM OF THE STUDY

To develop a universal systems pharmacology protocol for mechanism modeling of TCM and apply it to reveal the real-time anti-inflammatory effect of Reduning Injection.

MATERIALS AND METHODS

Combined with database mining and references, a regulatory mechanism network of inflammation was constructed. A quantitative model was established afterwards by integrating pharmacokinetic data and two network parameters, namely Network Efficiency and Network Flux. The time-dependent and dose-response relationship of RDNI on the regulation of inflammation was then quantitatively evaluated. ELISA tests were performed to verify the reliability of the model.

RESULTS

Three cytokines, namely IL-1β, IL-6 and TNF-α were screened out to be markers for evaluation of the anti-inflammatory effect of RDNI. An HPLC method for the simultaneous determination of 10 RDNI compounds in SD rat plasma was established and then applied to pharmacokinetic studies. Based on compound activity and pharmacokinetic data, the time-dependent effect of RDNI were quantitatively predicted by the pathway network-based modeling procedure.

CONCLUSIONS

The quantitative model established in this work was successfully applied to predict a TCM prescription's real-time dynamic healing effect after administration. It is qualified to provide novel insights into the time-dependent and dose-effect relationship of drugs in an intricate biological system and new strategies for investigating the detailed molecular mechanisms of TCM.

Synthesis and Design of Purpurin-18-Loaded Solid Lipid Nanoparticles for Improved Anticancer Efficiency of Photodynamic Therapy

Purpurin-18 (P18) is one of the essential photosensitizers used in photodynamic therapy (PDT), but its hydrophobicity causes easy coalescence and poor bioavailability. This study aimed to synthesize P18 and design P18-loaded solid lipid nanoparticles (SLNs) to improve its bioavailability. The characteristics of the synthesized P18 and SLNs were evaluated by particle characteristics and release studies. The effects of P18 were evaluated using the 1,3-diphenylisobenzofuran (DPBF) assay as a nonbiological assay and a phototoxicity assay against HeLa and A549 cell lines as a biological assay. The mean particle size and zeta potential of the SLNs were 164.70–762.53 nm and −16.77–25.54 mV, respectively. These results indicate that P18-loaded SLNs are suitable for an enhanced permeability and retention effect as a passive targeting anti-cancer strategy. The formulations exhibited a burst and sustained release based on their stability. The DPBF assay indicated that the PDT effect of P18 improved when it was entrapped in the SLNs. The photocytotoxicity assay indicated that P18-loaded SLNs possessed light cytotoxicity but no dark cytotoxicity. In addition, the PDT activity of the formulations was cell type- and size-dependent. These results suggest that the designed P18-loaded SLNs are a promising tool for anticancer treatment using PDT.

Mitochondria-Targeting and ROS-Responsive Nanocarriers via Amphiphilic TPP-PEG-TK-Ce6 for Nanoenabled Photodynamic Therapy

Designing targeted-delivering and stimuli-responsive nanocarriers for photodynamic therapy (PDT) is an appealing method, especially, targeting delivery of photosensitizers to mitochondria as the most sensitive cellular organelles to reactive oxygen species (ROS) could significantly enhance the therapeutic efficacy of PDT. In this study, we synthesized triphenylphosphonium bonded PEG-NH2 (TPP-PEG-NH2) and bridged to chlorin e6 (Ce6) via thioketal (TK) linkage to obtain red light-triggered, amphiphilic copolymer (TPP-PEG-TK-Ce6), which could self-assemble into micelles with an average size of 160 nm and zeta potential of +20.1 mV. The in vitro release behavior of TPP-PEG-TK-Ce6 nanocarriers showed a light-activated way and was dependent on the H2O2 concentration. TPP-PEG-TK-Ce6 nanocarriers exhibited high cytotoxicity against C6 cells with illumination. Confocal laser scanning microscopy observation indicated that TPP-PEG-TK-Ce6 nanocarriers were efficiently internalized into the mitochondrion of C6 cells, released Ce6 via light activated. By contrast, in the case of TPP-PEG-NH2 directly bonded Ce6 (TPP-PEG-Ce6) nanocarriers, little Ce6 was found in the mitochondrion. The stronger fluorescence in the mitochondrion of TPP-PEG-TK-Ce6 nanocarriers originated from the mitochondrial-targeting capability of TPP and the cleavage of TK linkages activated by light irradiation, which greatly improved the cellular uptake of TPP-PEG-TK-Ce6 nanocarriers and released more Ce6 in the mitochondrion. This work provided a facile strategy to improve PDT efficacy.

Targeted Chemoradiotherapy of Prostate Cancer Using Gold Nanoclusters with Protease Activatable Monomethyl Auristatin E

Combined radiotherapy (RT) and chemotherapy are prescribed to patients with advanced prostate cancer (PCa) to increase their survival; however, radiation-related side effects and systematic toxicity caused by chemotherapeutic drugs are unavoidable. To improve the precision and efficacy of concurrent RT and chemotherapy, we have developed a PCa-targeted gold nanocluster radiosensitizer conjugated with a highly potent cytotoxin, monomethyl auristatin E, PSMA-AuNC-MMAE, for RT and chemotherapy of PCa. This approach resulted in enhanced uptake of NCs by PSMA-positive cancer cells, targeted chemotherapy, and increased efficacy of RT both in vitro and in vivo. In addition, the combination of gold and MMAE further increased the efficacy of either of the agents delivered alone or simultaneously but not covalently linked. The PSMA-AuNC-MMAE conjugates improve the specificity and efficacy of radiation and chemotherapy, potentially reducing the toxicity of each therapy and making this an attractive avenue for clinical treatment of advanced PCa.

Preparation of porphyrin and phthalocyanine conjugates for biomedical applications

The aim of this review is to offer a succinct overview of the main synthetic techniques used in the preparation of conjugates containing porphyrins, including chlorins and bacteriochlorins and phthalocyanines for biomedical applications and photodynamic therapy (PDT). To illustrate the conjugation techniques representative examples from the literature will be presented.

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.