Linear and high-molecular-weight poly-porphyrins for efficient photodynamic therapy

Enhanced Photodynamic Therapy by Improved Light Energy Capture Efficiency of Porphyrin Photosensitizers

OPINION STATEMENT

Photodynamic therapy (PDT) has garnered increasing attention in cancer treatment because of its advantages such as minimal invasiveness and selective destruction. With the development of PDT, impressive progress has been made in the preparation of photosensitizers, particularly porphyrin photosensitizers. However, the limited tissue penetration of the activating light wavelengths and relatively low light energy capture efficiency of porphyrin photosensitizers are two major disadvantages in conventional photosensitizers. Therefore, tissue penetration needs to be enhanced and the light energy capture efficiency of porphyrin photosensitizers improved through structural modifications. The indirect excitation of porphyrin photosensitizers using fluorescent donors (fluorescence resonance energy transfer) has been successfully used to address these issues. In this review, the enhancement of the light energy capture efficiency of porphyrins is discussed.

Polymeric Phthalocyanine-Based Nanosensitizers for Enhanced Photodynamic and Sonodynamic Therapies

Photodynamic therapy and sonodynamic therapy are two highly promising modalities for cancer treatment. The latter holds an additional advantage in deep-tumor therapy owing to the deep penetration of the ultrasonic radiation. The therapeutic efficacy depends highly on the photo/ultrasound-responsive properties of the sensitizers as well as their tumor-localization property and pharmacokinetics. A novel nanosensitizer system based on a polymeric phthalocyanine (pPC-TK) is reported herein in which the phthalocyanine units are connected with cleavable thioketal linkers. Such polymer could self-assemble in water forming nanoparticles with a hydrodynamic diameter of 48 nm. The degradable and flexible thioketal linkers could effectively inhibit the π-π stacking of the phthalocyanine units, rendering the resulting nanoparticles an efficient generator of reactive oxygen species upon light or ultrasonic irradiation. The nanosensitizer could be internalized into cancer cells readily, inducing cell death by efficient photodynamic and sonodynamic effects. The potency is significantly higher than that of the monomeric phthalocyanine (PC-4COOH). The nanosensitizer could also effectively inhibit the growth of tumor in liver tumor-bearing mice by these two therapies without causing noticeable side effects. More importantly, it could also retard the growth of a deep-located orthotopic liver tumor in vivo by sonodynamic therapy.

Secondary Structure in Overcoming Photosensitizers' Aggregation: α-Helical Polypeptides for Enhanced Photodynamic Therapy

Aggregation caused quenching (ACQ) effect can severely inhibit the application of hydrophobic photosensitizers (PSs) bearing planar and rigid structures. Most of the reported cases utilized random-coiled polymers for the in vivo delivery of PSs, which would inevitably aggravate ACQ effect due to the flexible chains. In this work, the role of polymers' secondary structures (especially α-helical conformation) in overcoming the PSs' aggregation is systemically investigated based on the design of α-helical polypeptides bearing tetraphenylporphyrin (TPP) side chains. Atomistic molecular dynamics simulation, fluorescence quantum yield, and reactive oxygen species (ROS) generation yield are evaluated to demonstrate that α-helical polypeptide backbones can significantly boost both fluorescence quantum yield and ROS by suppressing the π-π stacking interaction between TPP units. The enhanced in vitro and in vivo phototoxicity for helical polypeptides also reveal functions of secondary structures in inhibiting ACQ and improving the membrane activity. Successful in vivo photodynamic therapy (PDT) results in mice bearing H22 tumors showed great potentials for further clinical applications.

Photodynamic Therapy: From the Basics to the Current Progress of N-Heterocyclic-Bearing Dyes as Effective Photosensitizers

Photodynamic therapy, an alternative that has gained weight and popularity compared to current conventional therapies in the treatment of cancer, is a minimally invasive therapeutic strategy that generally results from the simultaneous action of three factors: a molecule with high sensitivity to light, the photosensitizer, molecular oxygen in the triplet state, and light energy. There is much to be said about each of these three elements; however, the efficacy of the photosensitizer is the most determining factor for the success of this therapeutic modality. Porphyrins, chlorins, phthalocyanines, boron-dipyrromethenes, and cyanines are some of the N-heterocycle-bearing dyes' classes with high biological promise. In this review, a concise approach is taken to these and other families of potential photosensitizers and the molecular modifications that have recently appeared in the literature within the scope of their photodynamic application, as well as how these compounds and their formulations may eventually overcome the deficiencies of the molecules currently clinically used and revolutionize the therapies to eradicate or delay the growth of tumor cells.

A pectin-based photoactivated bactericide nanosystem for achieving an improved utilization rate, photostability and targeted delivery of hematoporphyrin

Photoactivated pesticides have many advantages, such as high activity, low toxicity, and no drug resistance. However, poor photostability and a low utilization rate limit their practical application. Herein, the photosensitizer hematoporphyrin (HP) was used as a photoactivated pesticide, covalently linked with pectin (PEC) via ester bonds, to prepare an amphiphilic polymer pro-bactericide, and subsequently self-assembled in aqueous solutions to obtain an esterase-triggered nanobactericide delivery system. The fluorescence quenching effect due to the aggregation of HP in nanoparticles (NPs) enabled the inhibition of photodegradation of HP in this system. Esterase stimulation could trigger HP release and increase its photodynamic activity. Antibacterial assays have shown that the NPs had potent antibacterial capacity, almost completely inactivating bacteria after 60 min of exposure to light. The NPs had good adherence to the leaves. Safety assessment indicated that the NPs have no obvious toxic effects on plants. Antibacterial studies on plants have shown that the NPs have excellent antibacterial effects on infected plants. These results provide a new strategy for obtaining a photoactivated bactericide nanosystem with a high utilization rate and good photostability and targeting ability.

Oxydextran-based photodynamic antibacterial nanoplatform with broad-Spectrum antibacterial activity

The compounding of polysaccharide macromolecules and antibacterial agents always has been the preferred strategy to prepare antibacterial products, attracting increasing interest. Herein, a novel acid-responsive oxidized dextran-based nanoplatform (OTP NP) has been fabricated for photodynamic antibacterial therapy by combing photosensitizer monoaminoporphyrin (TPP-NH₂) with oxidized dextran (ODex) via the Schiff Base reaction. OTP NP of about 100 nm is composed of an inner hydrophobic core of 30 nm and peripheral polysaccharide macromolecules. The OTP NP killed 99.9 % of E. coli and S. aureus within 1.5 light cycles at a concentration of 200 μg/mL. Concurrently, OTP NP exhibited excellent cytocompatibility at a concentration of 1 mg/mL (about 5 folds bactericidal concentration). Particularly, except for the recognized antibacterial mechanism of photodynamic therapy, a novel mechanism of bacterial membrane damage was discovered: the bacterial cell membrane was peeled off and formed spherical particles that aggregated around the bacteria to accelerate bacterial apoptosis under the combined action of ROS and nanomaterials. Moreover, the slightly soluble drug levofloxacin (Lev) as a model drug was loaded into OTP NP to test its carrier function, providing a practicable strategy to design multifunctional polysaccharide-based photodynamic antibacterial materials.

pH-responsive dynamically cross-linked nanogels with effective endo-lysosomal escape for synergetic cancer therapy based on intracellular co-delivery of photosensitizers and proteins

Co-delivery of photosensitizers (PSs) and protein drugs represents great potentiality for enhancing the efficiency of synergistic cancer therapy. However, the intricate tumor-microenvironment and the lack of nanoplatforms to co-deliver both into cancer cells and activate their functions significantly hinder the clinical translation of this combined approach for cancer treatment. Herein, a chlorine e6 (Ce6)-functionalized and pH-responsive dynamically cross-linked nanogel (Ce6@NG) is fabricated by formation of benzoic imine linkages between Ce6-modified methoxy poly (ethyleneglycol)-block-poly (diethylenetriamine)-L-glutamate-Ce6 [MPEG-b-P(Deta)LG-Ce6] and terephthalaldehyde as cross-linkers for effective intracellular co-delivery of Ce6 and cytochrome c (CC), which could form a novel combination therapy system (CC/Ce6@NGs). The pH-sensitive benzoic imine bonds in the CC/Ce6@NGs endow them with excellent systemic stability under normal physiological environment while this nanosystem can be further cationized to enhance cell uptake in acidic extracellular environment. Upon cellular internalization, CC/Ce6@NGs can rapidly escape from the endo/lysosomal compartments and subsequently activate Ce6 to generate cytotoxic singlet oxygen upon laser irradiation and release of CC to induce programmed cell death by complete cleavage of benzoic imines at more acidic intracellular environments. Importantly, the catalase-like activity of CC can decompose H₂O₂ to produce O₂ for hypoxia alleviation and improvement of the photodynamic therapy (PDT) of cancer. Moreover, this enhanced synergistic anticancer activity is confirmed both in vitro and in vivo. In view of the versatile chemical conjugation, this research offers a promising and smart nanosystem for intracellular co-delivery of PSs and therapeutic proteins.

Graphene quantum dots-porphyrins/phthalocyanines multifunctional hybrid systems: from interfacial dialogue to applications

Engineered well-ordered hybrid nanomaterials are at a symbolically pivotal point, just ahead of a long-anticipated human race transformation. Incorporating newer carbon nanomaterials like graphene quantum dots (GQDs) with tetrapyrrolic porphyrins...

Component-optimized chemo-dynamic nanoagent for enhanced tumour cell-selective chemo-dynamic therapy with minimal side effect in glioma mouse model

Although CuO-deposited bovine serum albumin (CuO-BSA) and glucose oxidase (Gox) were combined to achieve H2O2 self-supplied chemo-dynamic therapy (CDT) and glucose consumption-based starvation therapy, the uses of copper and Gox...

Codelivery of High-Molecular-Weight Poly-porphyrins and HIF-1α Inhibitors for In Vivo Synergistic Anticancer Therapy

Photodynamic therapy (PDT) is showing great potential in the treatment of cancer diseases, and photosensitizers play crucial roles in absorbing the energy of light and generating reactive oxygen species (ROS) during PDT. Most of the photosensitizers bearing macrocyclic structures have strong hydrophobicity and suffer from the π-π interaction and undesired aggregation caused quenching (ACQ), which severely limit the PDT efficacy. Moreover, the continuous oxygen consumption during PDT also leads to the upregulated expression of hypoxia-inducible factor-1α (HIF-1α), which can aggravate the growth of tumors. To overcome the abovementioned problems, polymerized photosensitizers repelled by flexible thioketal linkers were designed and synthesized using a multicomponent polymerization (MCP) method to afford the poly-porphyrins with high molecular weight (M_w > 20 000 g/mol) under room temperature. The ACQ effect could be significantly inhibited by introducing flexible chains and increasing M_w, leading to the improvement in the singlet oxygen quantum yield and phototoxicity simultaneously. An HIF-1α inhibitor, Lificiguat (YC-1) was synthesized as a chemodrug and codelivered with poly-porphyrins to decrease the expression of HIF-1α and inhibit tumor growth under hypoxia. With the synergistic PDT and chemotherapy, poly-porphyrin/YC-1 micelles showed excellent therapeutic antitumor efficacy both in vitro and in vivo.