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

Heavy-atom-free BODIPY dendrimer: utilizing the spin-vibronic coupling mechanism for two-photon photodynamic therapy in zebrafish

In this study, the heavy-atom-free BODIPY dendrimer TM4-BDP was synthesized for near-infrared photodynamic therapy, and was composed of a triphenylamine-BODIPY dimer and four 1-(2-morpholinoethyl)-1H-indole-3-ethenyl groups. The TM4-BDP could achieve near-infrared photodynamic therapy through two different photosensitive pathways, which include one-photon excitation at 660 nm and two-photon excitation at 1000 nm. In the one-photon excitation pathway, the TM4-BDP could generate singlet oxygen and superoxide radicals under 660 nm illumination. In addition, the one-photon PDT experiment in human nasopharyngeal carcinoma (CNE-2) cells also indicated that the TM4-BDP could specifically accumulate in lysosomes and show great cell phototoxicity with an IC50 of 22.1 μM. In the two-photon excitation pathway, the two-photon absorption cross-section at 1030 nm of TM4-BDP was determined to be 383 GM, which means that it could generate reactive oxygen species (ROS) under 1000 nm femtosecond laser excitation. Moreover, the two-photon PDT experiment in zebrafish also indicated the TM4-BDP could be used for two-photon fluorescence imaging and two-photon induced ROS generation in biological environments. Furthermore, in terms of the ROS generation mechanism, the TM4-BDP employed a novel spin-vibronic coupling intersystem crossing (SV-ISC) process for the mechanism of ROS generation and the femtosecond transient absorption spectra indicated that this novel SV-ISC mechanism was closely related to its charge transfer state lifetime. These above experiments of TM4-BDP demonstrate that the dendrimer design is an effective strategy for constructing heavy-atom-free BODIPY photosensitizers in the near-infrared region and lay the foundation for two-photon photodynamic therapy in future clinical trials.

Making the Brightest Ones Dim: Maximizing the Photothermal Conversion Efficiency of BODIPY-Based Photothermal Agents

The successful implementation of photothermal therapy (PTT) in cancer treatment hinges on the development of highly effective photothermal agents (PTAs). Boron dipyrromethene (BODIPY) dyes, being well known for their high brightness and quantum efficiencies, are the antithesis of PTAs. Nonetheless, a systematic exploration of the photophysics and photothermal characteristics of a series of π-extended BODIPY dyes with high absorptivity in the near-infrared (NIR) region has achieved superior photothermal conversion efficiencies (>90%), in both monomeric state and nanoparticles after encapsulation in a biocompatible polyethyleneglycol 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy-(polyethylene glycol)-2000]. Optimal PTA candidates combine strong NIR absorption provided by extended donor-acceptor conjugation and an optimization of the electronic and steric effects of meso-substituents to maximize photothermal conversion performance. The PTT-optimized meso-CF3-BODIPY, TCF3PEn exhibits exceptional efficacy in inducing cancer cell apoptosis and in vivo tumor ablation using low-power NIR laser irradiation (0.3 W cm-2, 808 nm) as well as excellent biological safety, underscoring its potential for advancing light-induced cancer therapies.

Liposome encapsulated polydopamine nanoparticles: Enhancing ferroptosis and activating hypoxia prodrug activity

The short lifespan of active oxygen species and depressed O2 level during ferroptosis treatment in tumor cells weaken ferroptosis therapy. How to improve the utilization efficiency of active oxygen species generated in real time is pivotal for anticancer treatment. Herein, the tirapazamine (TPZ) loaded polydopamine-Fe nanoparticles (PDA-Fe-TPZ) was modified with unsaturated liposome (Lip), which was constructed to overcome the drawbacks of traditional ferroptosis therapy. The Lip@PDA-Fe-TPZ nanoliposomes can react with H2O2 to produce •OH by Fenton reaction, which then attacks Lip and transforms into radical intermediate (L•) and phospholipid peroxide radical (LOO•) to avoid the annihilation of •OH. The introduced Lip enhances lipid peroxidation and promotes oxygen consumption, resulting in increased hypoxia at tumor site. The introduced TPZ can be triggered by reductase in tumor cells under hypoxia, which can reduce to transient oxidative free radicals by reductase enzymes and destroy the structure of the surrounding biomacromolecules, thus achieving the synergistic treatment of ferroptosis and chemotherapy. In this work, we organically combined enhanced ferrroptosis with hypoxic activated chemotherapy to achieve efficient and specific tumor killing effect, which can sever as a promising treatment of cancer in the future.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

A Silicon-Rhodamine-Based Heavy-Atom-Free Photosensitizer for Mitochondria-targeted Photodynamic Therapy

Silicon-xanthene derivatives (SiXs) have gained popularity in the field of bioimaging due to their advantageous far-red to near-infrared (NIR) absorption and emission wavelengths, notable brightness (ε × Φ), inherent mitochondrial targeting properties and high photo-stability, making them an excellent candidate for photodynamic therapy (PDT). Nevertheless, the utilization of SiXs as photosensitizers (PSs) for PDT in cancer treatment remains largely unexplored, primarily due to their limited capacity to generate cytotoxic reactive oxygen species (ROS). However, the potential of SiXs in PDT warrants further investigation. In this study, utilizing the spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) mechanism, we reported one novel heavy-atom-free, mitochondria-targeted, silicon-rhodamine-based photosensitizer (SiR-PXZ), which demonstrated excellent biocompatibility, minimal dark toxicity, favorable water-solubility and stability, and considerable singlet oxygen quantum yield under 660 nm light irradiation (ΦΔ = 0.16 in air-saturated PBS). Moreover, SiR-PXZ could be rapidly taken up by the mitochondria and efficiently induced apoptosis of cancer cells with an IC50 value of 1.2 μM. The in vivo studies showed that SiR-PXZ exhibited excellent anti-tumor effects, making it potentially valuable for clinical application. This study offers a source of ideas for the construction of SiXs-based photosensitizers for photodynamic cancer treatment in the future.

Multifunctional Nanoplatform for Single NIR Laser-Regulated Efficient PDT/PTT/Chemotherapy

The combination of phototherapy and chemotherapy with superior advantages is a promising strategy for cancer therapy. However, combination therapy is generally regulated by two different wavelengths of light or other stimuli, which results in complex operations and inevitable systemic side effects, even affecting therapeutic efficacy. Herein, we design a signal NIR light-regulated nanoplatform via the self-assembly process of reactive oxygen species (ROS)-sensitive prodrug (DTD), human serum albumin (HSA), and IR780 for combined photothermal/photodynamic therapy and chemotherapy. Upon 808 nm laser irradiation, IR780 in nanoparticles generates abundant ROS and a significant photothermal effect to achieve photothermal/photodynamic therapy. Meanwhile, the generating ROS further cleans up the thioketal link to release DOX for chemotherapy. Hence, signal NIR light can effectively control the process of combination therapy. In vivo and in vitro experiment results demonstrate that the multifunctional nanoparticles exhibit excellent antitumor efficacy via the combination of phototherapy and chemotherapy controlled by a signal NIR laser. Overall, the signal NIR light-regulated nanoparticles with combination therapy performance provide a versatile platform for enhancing antitumor efficacy.

Camptothecin-based prodrug nanomedicines for cancer therapy

Camptothecin (CPT) is a cytotoxic alkaloid that attenuates the replication of cancer cells via blocking DNA topoisomerase 1. Despite its encouraging and wide-spectrum antitumour activity, its application is significantly restricted owing to its instability, low solubility, significant toxicity, and acquired tumour cell resistance. This has resulted in the development of many CPT-based therapeutic agents, especially CPT-based nanomedicines, with improved pharmacokinetic and pharmacodynamic profiles. Specifically, smart CPT-based prodrug nanomedicines with stimuli-responsive release capacity have been extensively explored owing to the advantages such as high drug loading, improved stability, and decreased potential toxicity caused by the carrier materials in comparison with normal nanodrugs and traditional delivery systems. In this review, the potential strategies and applications of CPT-based nanoprodrugs for enhanced CPT delivery toward cancer cells are summarized. We appraise in detail the chemical structures and release mechanisms of these nanoprodrugs and guide materials chemists to develop more powerful nanomedicines that have real clinical therapeutic capacities.

A type I and II compatible vinyl-pyridine modified BODIPY dimer photosensitizer for photodynamic therapy in A-549 cells

In this paper, the vinyl-pyridine group was used to modify the BODIPY dimer photosensitizer (T-BDP2) to obtain a VP-BDP2 photosensitizer. Compared with the T-BDP2 photosensitizer, the VP-BDP2 photosensitizer could work under pure water conditions, the singlet oxygen yield was increased from 9.38% to 22.2%, the charge transfer rate was increased from about 30 ps to about 10 ps, and the red emission was enhanced in fluorescence imaging. In addition, the VP-BDP2 photosensitizer could also generate the superoxide radical (O2˙-) under pure water conditions. The ROS generation mechanism of the VP-BDP2 photosensitizer was considered to be the spin-orbit charge-transfer intersystem crossing (SOCT-ISC) mechanism, which was verified by fs-transient absorption spectra and theoretical calculation. In the photodynamic therapy of A-549 cells, the VP-BDP2 photosensitizers could generate singlet oxygen and superoxide radicals (O2˙-) under biological conditions, and showed high phototoxicity with the IC50 value at 12.1 μM under light at 525 nm. Additionally, the multiple dipolar configuration meant that the VP-BDP2 photosensitizer could be used in two-photon fluorescence zebrafish imaging under 800 nm excitation, which sets the stage for future two-photon photodynamic therapy.

Bioorthogonal Glycoengineering-Mediated Multifunctional Liquid Metal Nanoprobes for Highly Efficient Photoacoustic Imaging-Guided Photothermal/Chemotherapy of Tumor

The development of a multifunctional cancer diagnosis and treatment platform offers excellent prospects for the effective eradication of malignant solid tumors. Herein, a doxorubicin hydrochloride (DOX)-loaded tannic acid (TA)-coated liquid metal (LM) multifunctional nanoprobe was synthesized and applied as a highly efficient platform for the photoacoustic (PA) imaging-guided photothermal/chemotherapy of tumor. The multifunctional nanoprobes exhibited strong near-infrared absorption, a remarkable photothermal conversion efficiency (PCE) of 55%, and high DOX loading capacity. Combined with the large intrinsic thermal expansion coefficient of LM, highly efficient PA imaging and effective drug release were realized. The LM-based multifunctional nanoprobes were specifically adsorbed into the cancer cells and tumor tissues via glycoengineering biorthogonal chemistry. The in vitro and in vivo photothermal/chemo-anticancer activity confirmed their promising potential in cancer treatment. The subcutaneous breast tumor-bearing mice completely recovered in 5 days under light illumination with clear PA imaging presentation, which showed better antitumor outcomes than single-mode chemotherapy or photothermal therapy (PTT), while keeping side effects at a minimum. Such an LM-based PA imaging-guided photothermal/chemotherapy strategy provided a valuable platform for resistant cancer precise treatment and intelligent biomedicine.

Application of tumor pH/hypoxia-responsive nanoparticles for combined photodynamic therapy and hypoxia-activated chemotherapy

Introduction: Cancer selectivity, including targeted internalization and accelerated drug release in tumor cells, remains a major challenge for designing novel stimuli-responsive nanocarriers to promote therapeutic efficacy. The hypoxic microenvironment created by photodynamic therapy (PDT) is believed to play a critical role in chemoresistance. Methods: We construct dual-responsive carriers (^DANP_CT) that encapsulate the photosensitizer chlorin e6 (Ce6) and hypoxia-activated prodrug tirapazamine (TPZ) to enable efficient PDT and PDT-boosted hypoxia-activated chemotherapy. Results and discussion: Due to TAT masking, ^DANP_CT prolonged payload circulation in the bloodstream, and selective tumor cell uptake occurred via acidity-triggered TAT presentation. PDT was performed with a spatially controlled 660-nm laser to enable precise cell killing and exacerbate hypoxia. Hypoxia-responsive conversion of the hydrophobic NI moiety led to the disassembly of ^DANP_CT, facilitating TPZ release. TPZ was reduced to cytotoxic radicals under hypoxic conditions, contributing to the chemotherapeutic cascade. This work offers a sophisticated strategy for programmed chemo-PDT.

Dual-Activated Nano-Prodrug for Chemo-Photodynamic Combination Therapy of Breast Cancer

Herein, we developed a dual-activated prodrug, BTC, that contains three functional components: a glutathione (GSH)-responsive BODIPY-based photosensitizer with a photoinduced electron transfer (PET) effect between BODIPY and the 2,4-dinitrobenzenesulfonate (DNBS) group, and an ROS-responsive thioketal linker connecting BODIPY and the chemotherapeutic agent camptothecin (CPT). Interestingly, CPT displayed low toxicity because the active site of CPT was modified by the BODIPY-based macrocycle. Additionally, BTC was encapsulated with the amphiphilic polymer DSPE-mPEG₂₀₀₀ to improve drug solubility and tumor selectivity. The resulting nano-prodrug passively targeted tumor cells through enhanced permeability and retention (EPR) effects, and then the photosensitizing ability of the BODIPY dye was restored by removing the DNBS group with the high concentration of GSH in tumor cells. Light-triggered ROS from activated BODIPY can not only induce apoptosis or necrosis of tumor cells but also sever the thioketal linker to release CPT, achieving the combination treatment of selective photodynamic therapy and chemotherapy. The antitumor activity of the prodrug has been demonstrated in mouse mammary carcinoma 4T1 and human breast cancer MCF-7 cell lines and 4T1 tumor-bearing mice.