Mitochondria-targeting BODIPY-loaded micelles as novel class of photosensitizer for photodynamic therapy

Fe-HCOF-PEG2000 as a Hypoxia-Tolerant Photosensitizer to Trigger Ferroptosis and Enhance ROS-Based Cancer Therapy

Background

The hypoxic tumor microenvironment and single mechanisms severely limit the photodynamic therapy (PDT) efficiency of covalent organic framework (COF) nanoparticles in cancer treatment.

Purpose

Here, we propose an iron-loaded, hydrophilic 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG2000)-modified hollow covalent organic framework (HCOF), Fe-HCOF-PEG2000, for use in hypoxic PDT and ferroptosis therapy owing to its type I and II photodynamic ability and iron nanoparticle loading property.

Results

Fe-HCOF-PEG2000 nanoparticles (Fe-HCOFs-PEG2000) with semiconducting polymers and microporous skeletons allow efficient photophysical properties. Moreover, the iron nanoparticles on Fe-HCOF-PEG2000 caused ferroptosis and further enhanced tumor elimination under normoxic and hypoxic conditions. DSPE-PEG2000 endowed Fe-HCOF-PEG2000 with hydrophilicity, allowing it to circulate and accumulate in organs rich in blood supply, especially tumors. 808 nm NIR activated Fe-HCOF-PEG2000 aggregated in tumors and significantly inhibited tumor growth under hypoxia.

Conclusion

To our knowledge, Fe-HCOF-PEG2000 is the leading combination of type I/II PDT and ferroptosis. The strong antitumor effects of this nanomaterial suggest prospects for clinical translation as a tumor nanotherapy drug.

Anti-Seizure and Neuronal Protective Effects of Irisin in Kainic Acid-Induced Chronic Epilepsy Model with Spontaneous Seizures

An increased level of reactive oxygen species is a key factor in neuronal apoptosis and epileptic seizures. Irisin reportedly attenuates the apoptosis and injury induced by oxidative stress. Therefore, we evaluated the effects of exogenous irisin in a kainic acid (KA)-induced chronic spontaneous epilepsy rat model. The results indicated that exogenous irisin significantly attenuated the KA-induced neuronal injury, learning and memory defects, and seizures. Irisin treatment also increased the levels of brain-derived neurotrophic factor (BDNF) and uncoupling protein 2 (UCP2), which were initially reduced following KA administration. Furthermore, the specific inhibitor of UCP2 (genipin) was administered to evaluate the possible protective mechanism of irisin. The reduced apoptosis, neurodegeneration, and spontaneous seizures in rats treated with irisin were significantly reversed by genipin administration. Our findings indicated that neuronal injury in KA-induced chronic epilepsy might be related to reduced levels of BDNF and UCP2. Moreover, our results confirmed the inhibition of neuronal injury and epileptic seizures by exogenous irisin. The protective effects of irisin may be mediated through the BDNF-mediated UCP2 level. Our results thus highlight irisin as a valuable therapeutic strategy against neuronal injury and epileptic seizures.

Aggregation behavior and spectroscopic properties of red-emitting distyryl-BODIPY in aqueous solution, Langmuir-Schaefer films and Pluoronic® F127 micelles

Red-emitting distyryl substituted BODIPY dyes are among the most promising luminophors for bioimaging and optics applications. However, the practical application of BODIPYs is limited due to their high hydrophobicity and tendency to aggregate in aqueous organic solutions and solid phase. In this article, we propose an elegant solution to this problem. To this end, we carried out the detailed experimental and quantum-chemical study of the structural and spectral features of BF₂-ms-phenyl-5,5'-bis(4-dimethylaminostyryl)-3,3'-dimethyl-2,2'-dipyrromethene (distyryl-BDP). The particular attention was paid to analysis of high sensitivity of the distyryl-BDP spectral characteristics to the solvent properties, and also the aggregation behavior features both in water-organic media and in mono- and multilayer Langmuir-Schaefer films. We selected the best conditions to obtain the hydrophilic micellar structures of distyryl-BDP with Pluronic® F127 having a high efficiency of dye solubilization. This method increasing the solubility improves the distyryl-BDP transport efficiency in physiological aqueous media. The aqueous solutions of distyryl-BDP-Pl micelles show the intense fluorescence in the phototherapy window region (λ_fl = 739 nm).

Functionalization of Photosensitized Silica Nanoparticles for Advanced Photodynamic Therapy of Cancer

BODIPY dyes have recently attracted attention as potential photosensitizers. In this work, commercial and novel photosensitizers (PSs) based on BODIPY chromophores (haloBODIPYs and orthogonal dimers strategically designed with intense bands in the blue, green or red region of the visible spectra and high singlet oxygen production) were covalently linked to mesoporous silica nanoparticles (MSNs) further functionalized with PEG and folic acid (FA). MSNs approximately 50 nm in size with different functional groups were synthesized to allow multiple alternatives of PS-PEG-FA decoration of their external surface. Different combinations varying the type of PS (commercial Rose Bengal, Thionine and Chlorine e6 or custom-made BODIPY-based), the linkage design, and the length of PEG are detailed. All the nanosystems were physicochemically characterized (morphology, diameter, size distribution and PS loaded amount) and photophysically studied (absorption capacity, fluorescence efficiency, and singlet oxygen production) in suspension. For the most promising PS-PEG-FA silica nanoplatforms, the biocompatibility in dark conditions and the phototoxicity under suitable irradiation wavelengths (blue, green, or red) at regulated light doses (10-15 J/cm2) were compared with PSs free in solution in HeLa cells in vitro.

BODIPY-based monofunctional Pt (II) complexes for specific photocytotoxicity against cancer cells

Photodynamic therapy (PDT) has attracted extensive attention in cancer treatment because of its minimum trauma, less side effects, and so on. Photosensitizers, as one of the core elements of PDT, usually have to face problems such as poor water solubility and light stability, lack of targeting, and other problems, which seriously affect the therapeutic effect. In this work, two BODIPY (boron-dipyrromethene)-based monofunctional Pt (II) complexes, 1a and 2a, were designed and synthesized, and their PDT effect was studied. The Pt atom improved the singlet oxygen quantum yield (0.19 for 1a and 0.14 for 2a, respectively), which effectively improves the efficiency of PDT. MTT assay confirmed that the short time photo-irradiation distinctly promoted antitumor cytotoxicity of Pt (II) compounds against different cell lines. For 1a under irradiation, the IC₅₀ value of cancer cell lines were 13.1 μM for HeLa cells and 7.6 μM for MCF-7 cells, while those of normal cell lines were 32.4 μM for HBL-100 cells and 48.6 μM for L02 cells. The results demonstrated that 1a showed specific phototoxicity to cancer cells. This specific selectivity could be attributed to the synergistic effect of increased cellular uptake (determined by ICP-MS) and higher ROS generation (detected by Cell ROX Deep Red) in cancer cells after irradiation. This study laid the foundation for the future design and synthesis of effective PDT photosensitizers.

Mitocanic Di- and Triterpenoid Rhodamine B Conjugates

The combination of the “correct” triterpenoid, the “correct” spacer and rhodamine B (RhoB) seems to be decisive for the ability of the conjugate to accumulate in mitochondria. So far, several triterpenoid rhodamine B conjugates have been prepared and screened for their cytotoxic activity. To obtain cytotoxic compounds with EC₅₀ values in a low nano-molar range combined with good tumor/non-tumor selectivity, the Rho B unit has to be attached via an amine spacer to the terpenoid skeleton. To avoid spirolactamization, secondary amines have to be used. First results indicate that a homopiperazinyl spacer is superior to a piperazinyl spacer. Hybrids derived from maslinic acid or tormentic acid are superior to those from oleanolic, ursolic, glycyrrhetinic or euscaphic acid. Thus, a tormentic acid-derived RhoB conjugate 32, holding a homopiperazinyl spacer can be regarded, at present, as the most promising candidate for further biological studies.

Dual-acidity-labile polysaccharide-di-drugs conjugate for targeted cancer chemotherapy

Polymer-drug conjugates synthesized by binding therapeutic agents to functional polymers have long been a mainstay of prodrugs, while the slow drug release, insufficient efficacy of a single drug, and low selectivity hamper the clinical translation. By rational prodrug design, a targeted dual-acidity-labile polysaccharide-di-drugs conjugate was synthesized by one-pot simultaneous Schiff base and boronic esterification reactions between oxidized dextran (Dex-CHO) and cyclo-(Arg-Gly-Asp-D-Phe-Lys) (c(RGDfK)), doxorubicin (DOX), and bortezomib (BTZ). The polysaccharide-di-drugs conjugate (Dex-g-(DOX+BTZ)/cRGD) self-assembled into micelle with a diameter at around 80 nm and released the drugs simultaneously triggered by the acidic conditions. Dex-g-(DOX+BTZ)/cRGD specifically recognized and entered the cancer cells through the RGD-α_vβ₃ integrin interplay, selectively released DOX and BTZ in the acidic intracellular microenvironment, and efficiently inhibited the cell proliferation in vitro. More importantly, Dex-DOX/BTZ/cRGD showed higher intratumoral accumulation and better antitumor efficacy in vivo compared with free drugs and non-targeted control prodrug Dex-g-(DOX+BTZ). The findings indicated that this study provided a facile strategy to develop smart polymer-multi-drugs conjugates for targeted cancer chemotherapy.

Sequential-targeting nanocarriers with pH-controlled charge reversal for enhanced mitochondria-located photodynamic-immunotherapy of cancer

Targeting delivery of photosensitizers to mitochondria as the most sensitive cellular organelles to reactive oxygen species (ROS) by positively charged polymeric nanocarriers (NCs) is one of the useful methods for efficient photodynamic therapy (PDT). However, the NCs with positively charged mitochondria-targeting moieties are easily cleaned during circulation, restricting their in vivo applications. Herein, to address this issue and enhance in vivo PDT efficacy, we developed a sequential-targeting delivery system consisting of mitochondria-targeting micelles as the core prepared from the cationic amphiphilic copolymer for loading chlorin e6 (Ce6) and a tumor-targeting pH-dependent charge transformational layer as the shell obtained from 2,3-dimethylmaleic anhydride modified Biotin-PEG₄₀₀₀-NH₂ (BioPEGDMA) via electrostatic interaction. Concealed by the anionic shell, the as-prepared NCs showed longer retention within the first stage of tumor-targeting. Then, the accumulated NCs conversed to positive charge in tumor extracellular microenvironment (pH ∼ 6.5), which could be more effectively internalized by tumor cells, and the re-exposed triphenylphosphonium (TPP) groups endowed their second-stage targetability to the mitochondria. In vivo experiments revealed that the Ce6-loaded NCs exhibited remarkable tumor inhibition rates of 84.1% and 93.2% on BALB/c nude mice and Kunming mice, respectively, under 660 nm NIR irradiation, and stimulated immune responses with upregulated expression of IFN-γ, TNF-α and CD3⁺ in tumor tissues, and enhanced activation of CD3⁺/CD4⁺, CD3⁺/CD8⁺ T lymphocytes and DCs in both tumor tissues and lymph glands. This work provided a new pathway for the development of smart drug delivery system with advanced PDT efficacy. STATEMENT OF SIGNIFICANCE: Although the existing targeting delivery of photosensitizers to mitochondria by positively charged nanocarriers (NCs) have efficiently enhanced photodynamic therapy (PDT), their positive charges caused rapid clearance during circulation, which has restricted their in vivo applications. Therefore, we fabricated a novel sequential-targeting NC to solve the problem. The tumor accumulated NCs conversed to positive charge in tumor extracellular microenvironment, and the re-exposed triphenylphosphonium groups initiated second-stage targetability to mitochondria. This system exhibited remarkable tumor inhibition efficiency both in vitro and in vivo. Moreover, as we hypothesized, mitochondria-located PDT could promote immune response, resulting in improvement of PDT. The strategy of sequential targeting-based PDT in combination with augmented immune response showed a novel pathway for the development of smart drug delivery system with advanced PDT.

Tetraphenylporphine-Modified Polymeric Nanoparticles Containing NIR Photosensitizer for Mitochondria-Targeting and Imaging-Guided Photodynamic Therapy

Near-infrared (NIR) photodynamic therapy (PDT) is a promising antitumor strategy under NIR light irradiation to kill cancer cells. Mitochondria has a critical function in sustaining cellular viability and death, which is the ideal organelle for PDT. Here, we reported a tetraphenylporphine (TPP)-conjugated amphiphilic copolymer and an iodinated boron dipyrromethene photosensitizer (BDPI) with high singlet oxygen yield to form nanoparticles (PBDPI-TPP), which could realize mitochondria-targeting and improve the NIR imaging-guided PDT. The as-prepared mitochondria-targeting nanoplatform could show effective subcellular localization and bring about significant irreversible mitochondrial injury for enhanced PDT. Both in vitro and in vivo experiments revealed that the mitochondria-targeting PDT system could achieve a remarkable therapeutic effect, indicating that it is a promising nanoplatform for NIR imaging-guided PDT in cancer therapeutics.

Recent Progress in Mitochondria-Targeted Drug and Drug-Free Agents for Cancer Therapy

The mitochondrion is a dynamic eukaryotic organelle that controls lethal and vital functions of the cell. Being a critical center of metabolic activities and involved in many diseases, mitochondria have been attracting attention as a potential target for therapeutics, especially for cancer treatment. Structural and functional differences between healthy and cancerous mitochondria, such as membrane potential, respiratory rate, energy production pathway, and gene mutations, could be employed for the design of selective targeting systems for cancer mitochondria. A number of mitochondria-targeting compounds, including mitochondria-directed conventional drugs, mitochondrial proteins/metabolism-inhibiting agents, and mitochondria-targeted photosensitizers, have been discussed. Recently, certain drug-free approaches have been introduced as an alternative to induce selective cancer mitochondria dysfunction, such as intramitochondrial aggregation, self-assembly, and biomineralization. In this review, we discuss the recent progress in mitochondria-targeted cancer therapy from the conventional approach of drug/cytotoxic agent conjugates to advanced drug-free approaches.

Tumor microenvironment-activated nanosystems with selenophenol substituted BODIPYs as photosensitizers for photodynamic therapy

NIR-light-absorbing photosensitizers with the capability of selective localization and activation in tumor regions are of great importance for practical photodynamic therapy (PDT). Here, selenophenol substituted BODIPYs were designed and synthesized as new photosensitizers for PDT. One of these obtained BODIPYs, IBSeOV, possesses an intense and low energy absorption with a high singlet oxygen quantum yield (Φ_Δ = 60%). Considering manganese dioxide (MnO₂) nanosheets as versatile nanocarriers in cancer theranostics, nanosystem IBSeOV/MnO₂ was then fabricated to furnish tumor environment selective activation. Such designed nanoplatform allowed for GSH-controllable ¹O₂ production and exhibited low cytotoxicity in dark but good photocytotoxicity to cancer cells. The in vivo antitumor outcome suggested the high treatment efficiency of IBSeOV/MnO₂ for tumor therapy.

Mitochondria-Targeting Selenophene-Modified BODIPY-Based Photosensitizers for the Treatment of Hypoxic Cancer Cells

Two red-absorbing, water-soluble and mitochondria (MT)-targeting selenophene-substituted BODIPY-based photosensitizers (PSs) were realized (BOD-Se, BOD-Se-I), and their potential as photodynamic therapy (PDT) agents were evaluated. BOD-Se-I showed higher ¹ O₂ generation yield thanks to the enhanced heavy-atom effect, and this derivative was further tested in detail in cell culture studies under both normoxic and hypoxic conditions. BOD-Se-I not only effectively functioned under hypoxic conditions, but also showed highly selective photocytotoxicity towards cancer cells. The selectivity is believed to arise from differences in mitochondrial membrane potentials of healthy and cancerous cells. To the best of our knowledge, this marks the first example of a MT-targeted BODIPY PS that functions under hypoxic conditions. Remarkably, thanks to the design strategy, all these properties where realized by a compound that was synthesized in only five steps with 32 % overall yield. Hence, this material holds great promise for the realization of next-generation PDT drugs for the treatment of hypoxic solid tumors.

Activatable near-infrared emission-guided on-demand administration of photodynamic anticancer therapy with a theranostic nanoprobe

Development of theranostic probes that can be used to identify tumors and direct the on-demand drug administration to cancers is ongoing but remains challenging. Herein, we report a theranostic platform composed of a H2S-activated imaging probe and a light-sensitive drug. The designed probe affords advantages of H2S-activated NIR emission light-up and efficient 1O2 generation, enabling the selective visualization of H2S-rich cancers and the subsequent imaging-directed on-demand light exposure to the detected cancers while leaving normal tissues untouched. Such controllable administration of photodynamic anticancer therapy maximizes the therapeutic efficiency and minimizes side effects. This work should facilitate significant advances toward precise diagnosis and treatment of cancer.