Therapeutic Considerations and Conjugated Polymer-Based Photosensitizers for Photodynamic Therapy

Photodynamic therapy for cancer: mechanisms, photosensitizers, nanocarriers, and clinical studies

Photodynamic therapy (PDT) is a temporally and spatially precisely controllable, noninvasive, and potentially highly efficient method of phototherapy. The three components of PDT primarily include photosensitizers, oxygen, and light. PDT employs specific wavelengths of light to active photosensitizers at the tumor site, generating reactive oxygen species that are fatal to tumor cells. Nevertheless, traditional photosensitizers have disadvantages such as poor water solubility, severe oxygen-dependency, and low targetability, and the light is difficult to penetrate the deep tumor tissue, which remains the toughest task in the application of PDT in the clinic. Here, we systematically summarize the development and the molecular mechanisms of photosensitizers, and the challenges of PDT in tumor management, highlighting the advantages of nanocarriers-based PDT against cancer. The development of third generation photosensitizers has opened up new horizons in PDT, and the cooperation between nanocarriers and PDT has attained satisfactory achievements. Finally, the clinical studies of PDT are discussed. Overall, we present an overview and our perspective of PDT in the field of tumor management, and we believe this work will provide a new insight into tumor-based PDT.

Near-Infrared Absorbing Para-Azaquinodimethane Conjugated Polymers Synthesized via the Transition-Metal-Free Route toward Efficient Photothermal Conversion

Conjugated polymers with strong absorption in the second near-infrared (NIR-II) window have multiple applications. However, the development of new type of NIR-II conjugated polymers via facile and green methods remains challenging. Herein, this work reports a mild and convenient transition-metal-free method to synthesize near-infrared absorbing quinoidal conjugated polymers containing para-azaquinodimethane (AQM) moieties. The AQM quinoidal conjugated polymers with unique molecular structures and tunable optoelectronic properties can be synthesized by combining the Knoevenagel polycondensation of aromatic dialdehyde monomers with commercially available 1,4-diacetyl-2,5-piperazinedione and the following alkylation reaction. The resultant polymer PQ-DPP shows remarkable NIR-II absorption with a narrow band gap of about 1.08 eV. PQ-DPP nanoparticles exhibit high photothermal conversion efficiency of up to 48% under 1064 nm laser irradiation (1 W cm-2) endowing this polymer with potential in bio-related applications.

Surface photosterilization of implantable silicone biomaterials: structural and functional characterization

Hospital-acquired infections (HAIs) remain one of the major challenges faced by the global healthcare system. The increasing rate of pathogenic resistance against antibiotics suggests that alternative treatments are needed to control recurrent infections. Catheter-associated urinary tract infections (CAUTIs) are the third most common type of HAI worldwide, and this is mainly due to indwelling devices being excellent substrates for bacterial adhesion and growth. Subsequent biofilm formation on the implant surface acts as a constant nidus of bacteria and infection, thereby contributing to increased rates of patient morbidity and mortality. Here, we propose a simple and cost-effective method to sterilize silicone-based implant surfaces and prevent initial bacterial colonization, using Polydimethylsiloxane (PDMS) and an embedded ruthenium photosensitizer (PS). Exposure to LED light triggers potent photokilling action, resulting in significant bactericidal activity as evidenced by the number of adherent bacteria being below the level of detection (<10 CFU/mL) after 24 h. Live/dead staining studies using fluorescence microscopy indicated significant reduction in surface-adhered bacterial growth and biofilm formation. This potent antibacterial activity was verified in vivo, with exposure of contaminated PDMS coupons containing PS to LED prior to implantation resulting in over 99.5% reduction in adherent bacteria compared to controls over the 3-day implantation period. Histological analysis of the implantation site of PDMS+PS samples, in the absence of bacteria, revealed no adverse reactions. This was also confirmed using in vitro cytotoxicity studies. Tensile strength, surface roughness, hydrophobicity, and the development of encrustation of surface-treated groups exhibit comparable or improved properties to bare PDMS.

Self-Doping and Self-Acid-Doping of Conjugated Polymer Bioelectronics: The Case for Accuracy in Nomenclature

Conjugated polymers are enabling the development of flexible bioelectronics, largely driven by their organic nature which facilitates modification and tuning to suit a variety of applications. As organic semiconductors, conjugated polymers require a dopant to exhibit electrical conductivity, which in physiological conditions can result in dopant loss and thereby deterioration in electronic properties. To overcome this challenge, "self-doped" and self-acid-doped conjugated polymers having ionized pendant groups covalently bound to their backbone are being developed. The ionized group in a "self-doped" polymer behaves as the counterion that maintains electroneutrality, while an external dopant is required to induce charge transfer. The ionized group in a self-acid-doped polymer induces charge transfer and behaves as the counterion balancing the charges. Despite their doping processes being different, the two terms, self-doped and self-acid-doped, are often used interchangeably in the literature. Here, the differences are highlighted in the doping mechanisms of self-doped and self-acid-doped polymers, and it is proposed that the term "self-doped" should be replaced by "self-compensated," while reserving the term self-acid-doped for polymers that are intrinsically doped without the need of an external dopant. This is followed by a summary of examples of self-acid-doping in bioelectronics, highlighting their stability in the conductive state under physiological conditions.

π-Conjugated Polymer Nanoparticles from Design, Synthesis to Biomedical Applications: Sensing, Imaging, and Therapy

In the past decade, π-conjugated polymer nanoparticles (CPNs) have been considered as promising nanomaterials for biomedical applications, and are widely used as probe materials for bioimaging and drug delivery. Due to their distinctive photophysical and physicochemical characteristics, good compatibility, and ease of functionalization, CPNs are gaining popularity and being used in more and more cutting-edge biomedical sectors. Common synthetic techniques can be used to synthesize CPNs with adjustable particle size and dispersion. More importantly, the recent development of CPNs for sensing and imaging applications has rendered them as a promising device for use in healthcare. This review provides a synopsis of the preparation and functionalization of CPNs and summarizes the recent advancements of CPNs for biomedical applications. In particular, we discuss their major role in bioimaging, therapeutics, fluorescence, and electrochemical sensing. As a conclusion, we highlight the challenges and future perspectives of biomedical applications of CPNs.

Drug Delivery Strategies for the Treatment of Pancreatic Cancer

Pancreatic cancer is fast becoming a global menace and it is projected to be the second leading cause of cancer-related death by 2030. Pancreatic adenocarcinomas, which develop in the pancreas' exocrine region, are the predominant type of pancreatic cancer, representing about 95% of total pancreatic tumors. The malignancy progresses asymptomatically, making early diagnosis difficult. It is characterized by excessive production of fibrotic stroma known as desmoplasia, which aids tumor growth and metastatic spread by remodeling the extracellular matrix and releasing tumor growth factors. For decades, immense efforts have been harnessed toward developing more effective drug delivery systems for pancreatic cancer treatment leveraging nanotechnology, immunotherapy, drug conjugates, and combinations of these approaches. However, despite the reported preclinical success of these approaches, no substantial progress has been made clinically and the prognosis for pancreatic cancer is worsening. This review provides insights into challenges associated with the delivery of therapeutics for pancreatic cancer treatment and discusses drug delivery strategies to minimize adverse effects associated with current chemotherapy options and to improve the efficiency of drug treatment.

Conjugated Polymer Nanoparticles for Tumor Theranostics

Water-dispersible conjugated polymer nanoparticles (CPNs) have demonstrated great capabilities in biological applications, such as in vitro cell/subcellular imaging and biosensing, or in vivo tissue imaging and disease treatment. In this review, we summarized the recent advances of CPNs used for tumor imaging and treatment during the past five years. CPNs with different structures, which have been applied to in vivo solid tumor imaging (fluorescence, photoacoustic, and dual-modal) and treatment (phototherapy, drug carriers, and synergistic therapy), are discussed in detail. We also demonstrated the potential of CPNs as cancer theranostic nanoplatforms. Finally, we discussed current challenges and outlooks in this field.

Recent Advances in Hydrogel-Based Phototherapy for Tumor Treatment

Phototherapeutic agent-based phototherapies activated by light have proven to be safe modalities for the treatment of various malignant tumor indications. The two main modalities of phototherapies include photothermal therapy, which causes localized thermal damage to target lesions, and photodynamic therapy, which causes localized chemical damage by generated reactive oxygen species (ROS). Conventional phototherapies suffer a major shortcoming in their clinical application due to their phototoxicity, which primarily arises from the uncontrolled distribution of phototherapeutic agents in vivo. For successful antitumor phototherapy, it is essential to ensure the generation of heat or ROS specifically occurs at the tumor site. To minimize the reverse side effects of phototherapy while improving its therapeutic performance, extensive research has focused on developing hydrogel-based phototherapy for tumor treatment. The utilization of hydrogels as drug carriers allows for the sustained delivery of phototherapeutic agents to tumor sites, thereby limiting their adverse effects. Herein, we summarize the recent advancements in the design of hydrogels for antitumor phototherapy, offer a comprehensive overview of the latest advances in hydrogel-based phototherapy and its combination with other therapeutic modalities for tumor treatment, and discuss the current clinical status of hydrogel-based antitumor phototherapy.

Emerging application of nanotechnology for mankind

Nanotechnology has proven to be the greatest multidisciplinary field in the current years with potential applications in agriculture, pollution remediation, environmental sustainability, as well as most recently in pharmaceutical industries. As a result of its physical, chemical, and biological productivity, resistance, and matricular organization at a larger scale, the potential of nanocomposites revealed different sorts of assembling structures via testing. Biosensors are known some specifically promising inventions whereas carbon nanotube, magnetic nanoparticles (NPs), quantum dots, and gold NPs showed capability to repair damaged cells, molecular docking, drug-delivery, and nano-remediation of toxic elements. PEGylated(Poly ethyl glycol amyl gated) redox-responsive nanoscale COFs drug delivery from AgNPs and AuNPs are known to be sun blockers in sunscreen lotions. The emerging trends and yet more to be discovered to bridge the gaps forming in the field of nanotechnology, especially insights into environmental concerns and health issues most importantly the food web which is connected with the well beings of mankind to perform its tasks giving necessary results. The current review detailed emerging role of nanomaterials in human life.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42247-023-00461-8.

Semiconducting Polymer Dots for Point-of-Care Biosensing and In Vivo Bioimaging: A Concise Review

In recent years, semiconducting polymer dots (Pdots) have attracted much attention due to their excellent photophysical properties and applicability, such as large absorption cross section, high brightness, tunable fluorescence emission, excellent photostability, good biocompatibility, facile modification and regulation. Therefore, Pdots have been widely used in various types of sensing and imaging in biological medicine. More importantly, the recent development of Pdots for point-of-care biosensing and in vivo imaging has emerged as a promising class of optical diagnostic technologies for clinical applications. In this review, we briefly outline strategies for the preparation and modification of Pdots and summarize the recent progress in the development of Pdots-based optical probes for analytical detection and biomedical imaging. Finally, challenges and future developments of Pdots for biomedical applications are given.

Photoresponsive polymeric microneedles: An innovative way to monitor and treat diseases

Microneedles (MN) technology is an emerging technology for the transdermal delivery of therapeutics. When combined with photoresponsive (PR) materials, MNs can deliver therapeutics precisely and effectively with enhanced efficacy or synergistic effects. This review systematically summarizes the therapeutic applications of PRMNs in cancer therapy, wound healing, diabetes treatment, and diagnostics. Different PR approaches to activate and control the release of therapeutic agents from MNs are also discussed. Overall, PRMNs are a powerful tool for stimuli-responsive controlled-release therapeutic delivery to treat various diseases.

Soft nano and microstructures for the photomodulation of cellular signaling and behavior

Photoresponsive soft materials are everywhere in the nature, from human's retina tissues to plants, and have been the inspiration for engineers in the development of modern biomedical materials. Light as an external stimulus is particularly attractive because it is relatively cheap, noninvasive to superficial biological tissues, can be delivered contactless and offers high spatiotemporal control. In the biomedical field, soft materials that respond to long wavelength or that incorporate a photon upconversion mechanism are desired to overcome the limited UV-visible light penetration into biological tissues. Upon light exposure, photosensitive soft materials respond through mechanisms of isomerization, crosslinking or cleavage, hyperthermia, photoreactions, electrical current generation, among others. In this review, we discuss the most recent applications of photosensitive soft materials in the modulation of cellular behavior, for tissue engineering and regenerative medicine, in drug delivery and for phototherapies.

Semiconducting Polymer Nanoparticles with Surface-Mimicking Protein Secondary Structure as Lysosome-Targeting Chimaeras for Self-Synergistic Cancer Immunotherapy

Immunotherapy has received tremendous attention for tumor treatment, but the efficacy is greatly hindered by insufficient tumor-infiltration of immune cells and immunosuppressive tumor microenvironment. The strategy that can efficiently activate cytotoxic T lymphocytes and inhibit negative immune regulators will greatly amplify immunotherapy outcome, which is however very rare. Herein, a new kind of semiconducting polymer (SP) nanoparticles is developed, featured with surface-mimicking protein secondary structure (SPSS NPs) for self-synergistic cancer immunotherapy by combining immunogenic cell death (ICD) and immune checkpoint blockade therapy. The SPs with excellent photodynamic property are synthesized by rational fluorination, which can massively induce ICD. Additionally, the peptide antagonists are introduced and self-assembled into β-sheet protein secondary structures on the photodynamic NP surface via preparation process optimization, which function as efficient lysosome-targeting chimaeras (LYTACs) to mediate the degradation of programmed cell death ligand-1 (PD-L1) in lysosome. In vivo experiments demonstrate that SPSS NPs can not only elicit strong antitumor immunity to suppress both primary tumor and distant tumor, but also evoke long-term immunological memory against tumor rechallenge. This work introduces a new kind of robust immunotherapy agents by combining well-designed photosensitizer-based ICD induction and protein secondary structures-mediated LYTAC-like multivalence PD-L1 blockade, rendering great promise for synergistic immunotherapy.

Functionalization of Water-Soluble Conjugated Polymers for Bioapplications

Water-soluble conjugated polymers (WS-CPs) have found widespread use in bioapplications ranging from in vitro optical sensing to in vivo phototherapy. Modification of WS-CPs with specific molecular functional units is necessary to enable them to interact with biological targets. These targets include proteins, nucleic acids, antibodies, cells, and intracellular components. WS-CPs have been modified with covalently linked sugars, peptides, nucleic acids, biotin, proteins, and other biorecognition elements. The objective of this article is to comprehensively review the various synthetic chemistries that have been used to covalently link biofunctional groups onto WS-CP platforms. These chemistries include amidation, nucleophilic substitution, Click reactions, and conjugate addition. Different types of WS-CP backbones have been used as platforms including poly(fluorene), poly(phenylene ethynylene), polythiophene, poly(phenylenevinylene), and others. Example applications of biofunctionalized WS-CPs are also reviewed. These include examples of protein sensing, flow cytometry labeling, and cancer therapy. The major challenges and future development of functionalized conjugated polymers are also discussed.

Recent advances in noble metal complex based photodynamic therapy

Photodynamic therapy (PDT) utilizes light-activated photosensitizers (PSs) to generate toxic species for therapeutics. It has become an emerging solution for cancer treatment because of its specific spatiotemporal selectivity and minimal invasiveness. Noble metal (Ru, Ir and Pt) complexes are of increasing interest as photosensitizers for their excellent photophysical, photochemical, and photobiological properties. In this review, we highlight recent advancements in the development of noble metal complex photosensitizers for PDT during the last 5 years. We will summarize the design strategies of noble metal complexes for efficient and precise PDT, including increasing the light penetration depth, reducing the oxygen-dependent nature and improving target ability. Finally, we summarize recent efforts for the development of noble-based PSs and discuss the limitations of such PSs in clinical application and future perspectives in this field, such as the combination of PDT with other treatment modalities.

Oxygen self-supplied enzyme nanogels for tumor targeting with amplified synergistic starvation and photodynamic therapy

Tumor tissues need vast supply of nutrients and energy to sustain the rapid proliferation of cancer cells. Cutting off the glucose supply represents a promising cancer therapy approach. Herein, a tumor tissue-targeted enzyme nanogel (rGCP nanogel) with self-supply oxygen capability was developed. The enzyme nanogel synergistically enhanced starvation therapy and photodynamic therapy (PDT) to mitigate the rapid proliferation of cancer cells. The rGCP nanogel was fabricated by copolymerizing two monomers, porphyrin and cancer cells-targeted, Arg-Gly-Asp (RGD), onto the glucose oxidase (GOX) and catalase (CAT) surfaces. The cascade reaction within the rGCP nanogel could efficiently consume intracellular glucose catalyzed by GOX. Concurrently, CAT safely decomposed the produced H₂O₂ with systemic toxicity to promote oxygen generation and achieved low toxicity starvation therapy. The produced oxygen subsequently facilitated the glucose oxidation reaction and significantly enhanced the generation of cytotoxic singlet oxygen (¹O₂) in the presence of 660 nm light irradiation. Combining starvation therapy and PDT, the designed enzyme nanogel system presented an amplified synergic cancer therapy effect. This approach potentially paved a new way to fabricate a combinatorial therapy approach by employing cascaded catalytic nanomedicines with good tumor selectivity and efficient anti-cancer effect. STATEMENT OF SIGNIFICANCE: The performance of starvation and photodynamic therapy (PDT) is usually suppressed by intrinsic tumorous hypoxia. Herein, an oxygen self-supplied and tumor tissue-targeted enzyme nanogel was created by copolymerization of two monomers, porphyrin and cancer cell-targeted Arg-Gly-Asp (RGD), onto the surface of glucose oxidase (GOX) and catalase (CAT), which synergistically enhanced starvation therapy and PDT. Moreover, the enzyme nanogels possessed high stability and could be synthesized straightforwardly. This anti-cancer system provides an approach for constructing a combinatorial therapy approach by employing cascaded catalytic nanomedicine with good tumor selectivity and therapeutic efficacy.

Strategies to Improve Photodynamic Therapy Efficacy of Metal-Free Semiconducting Conjugated Polymers

Photodynamic therapy (PDT) is a noninvasive therapy for cancer and bacterial infection. Metal-free semiconducting conjugated polymers (SCPS) with good stability and optical and electrical properties are promising photosensitizers (PSs) for PDT compared with traditional small-molecule PSs. This review analyzes the latest progress of strategies to improve PDT effect of linear, planar, and three-dimensional SCPS, including improving solubility, adjusting conjugated structure, enhancing PS-doped SCPs, and combining therapies. Moreover, the current issues, such as hypoxia, low penetration, targeting and biosafety of SCPS, and corresponding strategies, are discussed. Furthermore, the challenges and potential opportunities on further improvement of PDT for SCPs are presented.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

Current Strategies for Tumor Photodynamic Therapy Combined With Immunotherapy

Photodynamic therapy (PDT) is a low invasive antitumor therapy with fewer side effects. On the other hand, immunotherapy also has significant clinical applications in the treatment of cancer. Both therapies, on their own, have some limitations and are incapable of meeting the demands of the current cancer treatment. The efficacy of PDT and immunotherapy against tumor metastasis and tumor recurrence may be improved by combination strategies. In this review, we discussed the possibility that PDT could be used to activate immune responses by inducing immunogenic cell death or generating cancer vaccines. Furthermore, we explored the latest advances in PDT antitumor therapy in combination with some immunotherapy such as immune adjuvants, inhibitors of immune suppression, and immune checkpoint blockade.

Molecular Design of Monochromophore-Based Bifunctional Photosensitizers for Simultaneous Ratiometric Oxygen Reporting and Photodynamic Cancer Therapy

Monitoring the tumor oxygen level when implementing photodynamic therapy (PDT) on malignant cancer has vital significance but remains challenging yet. Herein, by structurally manipulating a 2,4-dimethylpyrrole-engineered asymmetric BODIPY scaffold with different kinds, numbers, and positions of halogen atoms, we rationally designed several monochromophore-based bifunctional photosensitizers, named BDPs (BDP-I, BDP-II, and BDP-III), with self-sensitized photooxidation characteristics for accurate oxygen reporting and photodynamic tumor ablation. We show that different ways of halogen regulation allow available tuning of BDPs' oxygen-dependent ratiometric fluorescence turn-ons upon light irradiation as well as type-II PDT efficiencies before and after self-sensitized photooxidation. Encouragingly, measuring the specific ratiometric signals of the most promising BDP-II enabled the direct observation of initial oxygen concentration in both living 4T1 cells and a tumor-bearing mice model, affording an alternative way for evaluating oxygen supplementation strategies. Meanwhile, the "always on" PDT effect of BDP-II ensured efficient tumor ablation via apoptosis. Our research was thus believed to be of instructive significance for future application of oxygen-related auxiliary strategies and the design of unimolecular multifunctional PDT agents for cancer precision therapy.

Amplifying the reactivity of BODIPY photoremovable protecting groups

Conjugated polymer nanoparticles (CPNs or Pdots) are used to sensitize the photorelease reaction of a BODIPY photoremovable protecting group. Sensitization yields effective values of ε_λΦ_pr - the product of the extinction coefficient at the irradiation wavelength and the photorelease quantum yield - that are more than 60-fold greater than those measured upon direct excitation.

Innovative strategies for enhanced tumor photodynamic therapy

Photodynamic therapy (PDT) is an approved and promising treatment approach that utilizes a photosensitizer (PS) to produce cytotoxic reactive oxygen species (ROS) through irradiation to achieve tumor noninvasive therapy. However, the limited singlet oxygen generation, the nonspecific uptake of PS in normal cells, and tumor hypoxia have become major challenges in conventional PDT, impeding its development and further clinical application. This review summarizes an overview of recent advances for the enhanced PDT. The development of PDT with innovative strategies, including molecular engineering and heavy atom-free photosensitizers is presented and future directions in this promising field are also provided. This review aims to highlight the recent advances in PDT and discuss the potential strategies that show promise in overcoming the challenges of PDT.

Property Regulation of Conjugated Oligoelectrolytes with Polyisocyanide to Achieve Efficient Photodynamic Antibacterial Biomimetic Hydrogels

Fabricating antibacterial hydrogels with antimicrobial drugs and synthetic biocompatible biomimetic hydrogels is a promising strategy for practical medical applications. Here, we report a bicomponent hydrogel composed of a biomimetic polyisocyanopetide (PIC) hydrogel and a photodynamic antibacterial membrane-intercalating conjugated oligoelectrolyte (COE). The aggregation behavior and aggregate size of the COEs in water can be regulated using the PIC hydrogel, which could induce COEs with higher reactive oxygen species (ROS) production efficiency and increased association of COEs toward bacteria, therefore enhancing the antibacterial efficiency. This strategy provides a facile method for developing biomimetic hydrogels with high antibacterial capability.

Theranostic Near-Infrared-Active Conjugated Polymer Nanoparticles

Conjugated polymer nanoparticles (CPNs) based on a common solar cell material (PTB7) have been prepared, and their potential in theranostic applications based on bioimaging and photosensitizing capabilities has been evaluated. The main absorption and emission bands of the prepared CPNs both fell within the NIR-I (650-950 nm) transparency window, allowing facile and efficient implementation of our CPNs as bioimaging agents, as demonstrated in this work for A549 human lung cancer cell cultures. The prepared CPN samples were also shown to produce reactive oxygen species (ROS) upon photoexcitation in the near-infrared or ultraviolet spectral regions, both in aqueous solutions and in HaCaT keratinocyte cell cultures. Importantly, we show that the photosensitizing ability of our CPNs was largely determined by the nature of the stabilizing shell: coating the CPNs with a Pluronic F-127 copolymer led to an improvement of photoinitiated ROS production, while using poly[styrene-co-maleic anhydride] instead completely quenched said process. This work therefore demonstrates that the photosensitizing capability of CPNs can be modulated via an appropriate selection of stabilizing material and highlights the significance of this parameter for the on-demand design of theranostic probes based on CPNs.

Conjugated Polymers with Aggregation-Induced Emission Characteristics for Fluorescence Imaging and Photodynamic Therapy

Accurate diagnosis and treatment have been extensively developed in the field of biomedicine, which put forward higher requirements for the development of biomedical materials with high efficiency and selectivity. Among them, conjugated polymers featuring aggregation-induced emission (AIE) characteristics (AIE conjugated polymers) have stood out in recent years owing to their unique properties, such as intense solid emission, high light-harvesting ability, efficient energy transfer, and high ¹ O₂ generation ability, which empower them with effective biomedical functions in fluorescence imaging (FLI), photodynamic therapy (PDT), FLI-guided PDT, two-photon excited photodynamic therapy (2PE-PDT), etc. In this review, we highlight recent progress in AIE conjugated polymers and their applications in anticancer and antibacterial areas based on FLI and PDT, and summarize the mechanism of color-tuned fluorescence emission and efficient ¹ O₂ generation ability. The challenges and perspectives for the future development of AIE conjugated polymers are also discussed.

Application of phototherapeutic-based nanoparticles in colorectal cancer

Colorectal cancer (CRC) is the third most commonly diagnosed malignancy and the second leading cause of cancer death, which accounts for approximately 10% of all new cancer cases worldwide. Surgery is the main method for treatment of early-stage CRC. However, it is not effective for most metastatic tumors, and new treatment and diagnosis strategies need to be developed. Photosensitizers (PSs) play an important role in the treatment of CRC. Phototherapy also has a broad prospect in the treatment of CRC because of its low invasiveness and low toxicity. However, most PSs are associated with limitations including poor solubility, poor selectivity and high toxicity. The application of nanomaterials in PSs has added many advantages, including increased solubility, bioavailability, targeting, stability and low toxicity. In this review, based on phototherapy, we discuss the characteristics and development progress of PSs, the targeting of PSs at organ, cell and molecular levels, and the current methods of optimizing PSs, especially the application of nanoparticles as carriers in CRC. We introduce the photosensitizer (PS) targeting process in photodynamic therapy (PDT), the damage mechanism of PDT, and the application of classic PS in CRC. The action process and damage mechanism of photothermal therapy (PTT) and the types of ablation agents. In addition, we present the imaging examination and the application of PDT / PTT in tumor, including (fluorescence imaging, photoacoustic imaging, nuclear magnetic resonance imaging, nuclear imaging) to provide the basis for the early diagnosis of CRC. Notably, single phototherapy has several limitations in vivo, especially for deep tumors. Here, we discuss the advantages of the combination therapy of PDT and PTT compared with the single therapy. At the same time, this review summarizes the clinical application of PS in CRC. Although a variety of nanomaterials are in the research and development stage, few of them are actually on the market, they will show great advantages in the treatment of CRC in the near future.

Interrogating biological systems using visible-light-powered catalysis

Light-powered catalysis has found broad utility as a chemical transformation strategy, with widespread impact on energy, environment, drug discovery and human health. A noteworthy application impacting human health is light-induced sensitization of cofactors for photodynamic therapy in cancer treatment. The clinical adoption of this photosensitization approach has inspired the search for other photochemical methods, such as photoredox catalysis, to influence biological discovery. Over the past decade, light-mediated catalysis has enabled the discovery of valuable synthetic transformations, propelling it to become a highly utilized chemical synthesis strategy. The reaction components required to achieve a photoredox reaction are identical to photosensitization (catalyst, light source and substrate), making it ideally suited for probing biological environments. In this Review, we discuss the therapeutic application of photosensitization and advancements made in developing next-generation catalysts. We then highlight emerging uses of photoredox catalytic methods for protein bioconjugation and probing complex cellular environments in living cells.

ROS-Responsive and active targeted drug delivery based on conjugated polymer nanoparticles for synergistic chemo-/photodynamic therapy

Stimuli-responsive and active targeted drug release is highly significant and challenging for precise and effective cancer therapy. Herein, a reactive oxygen species (ROS)-responsive drug delivery system iRGD-BDOX@CPNs with active targeting for chemo-/photodynamic (PDT) synergistic therapy has been reported. This nanocarrier iRGD-BDOX@CPNs is constructed by the self-assembly of conjugated polymer poly(fluorene-co-vinylene) (PFV), prodrug BDOX (doxorubicin modified with a phenylboronic acid ester group) and an amphiphilic polymer (DSPE-PEG) modified with internalized RGD (DSPE-PEG-iRGD). The hydrophobic inner cores formed by PFV main chains tightly enclose BDOX. Due to PFV generating many ROS by light triggering, the BDOX prodrug can be in situ activated, resulting in the highly efficient drug release. In addition, the remarkable fluorescence recovery could be used for real-time monitoring of drug delivery and guiding antitumor therapy. Contributing to the specific recognition between iRGD and integrin αvβ3 receptors over-expressed on the surface of tumor cells, the active targeting and uptake of iRGD-BDOX@CPNs in tumor cells are greatly enhanced. The prominent anti-cancer effect of iRGD-BDOX@CPNs is realized by targeted drug delivery and synergistic therapeutic effects of PDT/chemotherapy. This study illustrates that the development of ROS-responsive and targeted drug delivery nanocarriers iRGD-BDOX@CPNs provides a new insight for controllable drug release and tumor precision therapy.

New Approach in the Application of Conjugated Polymers: The Light-Activated Source of Versatile Singlet Oxygen Molecule

For many years, the research on conjugated polymers (CPs) has been mainly focused on their application in organic electronics. Recent works, however, show that due to the unique optical and photophysical properties of CPs, such as high absorption in UV–Vis or even near-infrared (NIR) region and efficient intra-/intermolecular energy transfer, which can be relatively easily optimized, CPs can be considered as an effective light-activated source of versatile and highly reactive singlet oxygen for medical or catalytic use. The aim of this short review is to present the novel possibilities that lie dormant in those exceptional polymers with the extended system of π-conjugated bonds.

New Hybrid Copper Nanoparticles/Conjugated Polyelectrolyte Composite with Antibacterial Activity

In the search for new materials to fight against antibiotic-resistant bacteria, a hybrid composite from metallic copper nanoparticles (CuNPs) and a novel cationic π-conjugated polyelectrolyte (CPE) were designed, synthesized, and characterized. The CuNPs were prepared by chemical reduction in the presence of CPE, which acts as a stabilizing agent. Spectroscopic analysis and electron microscopy showed the distinctive band of the metallic CuNP surface plasmon and their random distribution on the CPE laminar surface, respectively. Theoretical calculations on CuNP/CPE deposits suggest that the interaction between both materials occurs through polyelectrolyte side chains, with a small contribution of its backbone electron density. The CuNP/CPE composite showed antibacterial activity against Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Escherichia coli and Salmonella enteritidis) bacteria, mainly attributed to the CuNPs’ effect and, to a lesser extent, to the cationic CPE.

A zwitterionic red-emitting water-soluble conjugated polymer with high resistance to nonspecific binding for two-photon cell imaging and good singlet oxygen production capability

A zwitterionic red-emitting water-soluble conjugated polymer exhibited better two-photon cell imaging and singlet oxygen production capability than its cationic analogue.

Photodynamic Inactivation of ESKAPE Group Bacterial Pathogens in Planktonic and Biofilm Cultures Using Metallated Porphyrin-Doped Conjugated Polymer Nanoparticles

Photodynamic inactivation (PDI) protocols using photoactive metallated porphyrin-doped conjugated polymer nanoparticles (CPNs) and blue light were developed to eliminate multidrug-resistant pathogens. CPNs-PDI protocols using varying particle concentrations and irradiation doses were tested against nine pathogenic bacterial strains including antibiotic-resistant bacteria of the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens group. The bactericidal effect was achieved in methicillin-resistant Staphylococus aureus (S. aureus) strains using low light doses (9.6-14.4 J/cm²), while Gram-negative bacteria required a higher light dose (28.8 J/cm²). The bacteria-CPN interaction was studied through flow cytometry, taking advantage of the intrinsic CPN fluorescence, demonstrating that CPNs efficiently bind to the bacterial envelope. Finally, the performance of CPNs-PDI was explored in biofilms; good antibiofilm ability and almost complete eradication were observed for S. aureus and Escherichia coli biofilms, respectively, using confocal microscopy. Overall, we demonstrated that CPNs-PDI is an efficient tool not only to kill superbugs as sessile cells but also to disrupt and eradicate biofilms of highly relevant pathogenic bacterial species.

Molecular Design of Conjugated Small Molecule Nanoparticles for Synergistically Enhanced PTT/PDT

Simultaneous photothermal therapy (PTT) and photodynamic therapy (PDT) is beneficial for enhanced cancer therapy due to the synergistic effect. Conventional materials developed for synergistic PTT/PDT are generally multicomponent agents that need complicated preparation procedures and be activated by multiple laser sources. The emerging monocomponent diketopyrrolopyrrole (DPP)-based conjugated small molecular agents enable dual PTT/PDT under a single laser irradiation, but suffer from low singlet oxygen quantum yield, which severely restricts the therapeutic efficacy. Herein, we report acceptor-oriented molecular design of a donor-acceptor-donor (D-A-D) conjugated small molecule (IID-ThTPA)-based phototheranostic agent, with isoindigo (IID) as selective acceptor and triphenylamine (TPA) as donor. The strong D-A strength and narrow singlet-triplet energy gap endow IID-ThTPA nanoparticles (IID-ThTPA NPs) high mass extinction coefficient (18.2 L g^-1 cm^-1), competitive photothermal conversion efficiency (35.4%), and a dramatically enhanced singlet oxygen quantum yield (84.0%) comparing with previously reported monocomponent PTT/PDT agents. Such a high PTT/PDT performance of IID-ThTPA NPs achieved superior tumor cooperative eradicating capability in vitro and in vivo.

Development of A Thermo-Responsive Conjugated Polymer with Photobleaching-Resistance Property and Tunable Photosensitizing Performance

A thermo-responsive conjugated polymer, PFBT-gPA is synthesized by grafting the poly(N-isopropylacrylamide) (PNIPAAm) to the side chains of a conjugated polyfluorene derivative through atom transfer radical polymerization (ATRP). PFBT-gPA undergoes a reversible phase transition in water below and above the lower critical solution temperature (LCST) and the process is studied by differential scanning calorimetry (DSC) analysis and UV/vis absorption spectra. PFBT-gPA shows a good photostability under UV light irradiation especially above the LCST. Moreover, the photosensitizing performance of PFBT-gPA could be tuned simply by changing temperature. The unique properties of PFBT-gPA promise its potential applications in sensing and photodynamic therapy.

Rational design of semiconducting polymer brushes as cancer theranostics

Photonic theranostics (PTs) generally contain optical agents for the optical sensing of biomolecules and therapeutic components for converting light into heat or chemical energy. Semiconducting polymer nanoparticles (SPNs) as advanced PTs possessing good biocompatibility, stable photophysical properties, and sensitive and tunable optical responses from the ultraviolet to near-infrared (NIR) II window (300-1700 nm) have recently aroused great interest. Although semiconducting polymers (SPs) with various building blocks have been synthesized and developed to meet the demands of biophotonic applications, most of the SPNs were made by a nanoprecipitation method that used amphiphilic surfactants to encapsulate SPs. Such binary SP micelles usually exhibit weakened photophysical properties of SPs and undergo dissociation in vivo. SP brushes (SPBs) are products of functional post-modification of SP backbones, which endows unique features to SPNs (e.g. enhanced optical properties and multiple chemical reaction sites for the conjunction of organic/inorganic imaging agents and therapeutics). Furthermore, the SPB-based SPNs can be highly stable due to supramolecular self-assembly and/or chemical crosslinking. In this review, we highlight the recent progress in the development of SPBs for advanced theranostics.

Boto R, Ferreira D, R. Fernandes J, Almeida P, F. V. Ferreira L, Silva AM, V. Reis L. Red and Near-Infrared Absorbing DicyanomethyleneSquaraine Cyanine Dyes: PhotophysicochemicalProperties and Anti-Tumor Photosensitizing Effects

Photodynamic therapy is a medical modality developed for the treatment of several diseases of oncological and non-oncological etiology that requires the presence of a photosensitizer, light and molecular oxygen, which combined will trigger physicochemical reactions responsible for reactive oxygen species production. Given the scarcity of photosensitizers that exhibit desirable characteristics for its potential application in this therapeutic strategy, the main aims of this work were the study of the photophysical and photochemical properties and the photobiological activity of several dicyanomethylene squaraine cyanine dyes. Thus, herein, the study of their aggregation character, photobleaching and singlet oxygen production ability, and the further application of the previously synthesized dyes in Caco-2 and HepG2 cancer cell lines, to evaluate their phototherapeutic effects, are described. Dicyanomethylene squaraine dyes exhibited moderate light-stability and, despite the low singlet oxygen quantum yields, were a core of dyes that exhibited relevant in vitro photodynamic activity, as there was an evident increase in the toxicity of some of the tested dyes exclusive to radiation treatments.

Oligonucleotide-Polymer Conjugates: From Molecular Basics to Practical Application

DNA exhibits many attractive properties, such as programmability, precise self-assembly, sequence-coded biomedical functions, and good biocompatibility; therefore, DNA has been used extensively as a building block to construct novel nanomaterials. Recently, studies on oligonucleotide-polymer conjugates (OPCs) have attracted increasing attention. As hybrid molecules, OPCs exhibit novel properties, e.g., sophisticated self-assembly behaviors, which are distinct from the simple combination of the functions of DNA and polymer, making OPCs interesting and useful. The synthesis and applications of OPCs are highly dependent on the choice of the polymer block, but a systematic summary of OPCs based on their molecular structures is still lacking. In order to design OPCs for further applications, it is necessary to thoroughly understand the structure-function relationship of OPCs. In this review, we carefully categorize recently developed OPCs by the structures of the polymer blocks, and discuss the synthesis, purification, and applications for each category. Finally, we will comment on future prospects for OPCs.

Self-assembly of luminescent triblock bottlebrush copolymers in solution

Self-assembly presents bottom-up strategies for the construction of complex micelles from luminescent bottlebrush copolymers.

Tailor-Made Polymer Nano-Assembly with Switchable Function and Amplified Anti-Tumor Therapy

The difficulty in killing tumor cells due to the tendency to metastasis and drug resistance are outstanding and urgent problems for the treatment of cancer. It is imperative to figure out an effective therapy strategy to break the treatment dilemmas. Nano self-assembly has the characteristics of flexible regulation, biological compatibility, and easy access. Herein, an albumin-polymer nano-assembly with switchable cytotoxicity and reactive oxygen species (ROS) amplification capability is developed for anti-tumor therapy. The nano-assembly (PFFBT@HSA) is comprised of conjugated polymer PFFBT and natural protein human serum albumin (HSA) via the hydrophobic and electrostatic interactions. The innovative switchable strategy is proposed and realized by HSA turning off the cytotoxicity of PFFBT and then turning on and enhancing the cytotoxicity by generating massive ROS upon light irradiation. The combination of HSA provides more stable microenvironment to benefit the generation of highly effective anti-tumor model of "0+1>1". These results display that the nanostructured self-assembly and the proposed anti-tumor regulation strategy are effective, which will contribute to the diversified treatment of cancer.

Rational design of near-infrared platinum(ii)-acetylide conjugated polymers for photoacoustic imaging-guided synergistic phototherapy under 808 nm irradiation

We have developed a novel near-infrared Pt-acetylide conjugated polymer CP3 with highly efficient photoconversion behaviors for synergistic cancer phototherapy.

Size-Dependent Photophysical Behavior of Low Bandgap Semiconducting Polymer Particles

The photophysics of water and propan-1-ol suspensions of poly [N-9"-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'- benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles has been studied by ultrafast spectroscopy. High molar mass polymer (HMM > 20 kg/mol) forms nanoparticles with around 50 nm diameter via mini-emulsion post-polymerization, while low molar mass (LMM < 5 kg/mol) polymer prepared by dispersion polymerization results in particles with a diameter of almost one order of magnitude larger (450 ± 50 nm). In this study, the presence of excited-states and charge separated species was identified through UV pump and visible/near-infrared probe femtosecond transient absorption spectroscopy. A different behavior for the HMM nanoparticles has been identified compared to the LMM mesoparticles. The nanoparticles exhibit typical features of an energetically disordered conjugated polymer with a broad density of states, allowing for delayed spectral relaxation of excited states, while the mesoparticles show a J-aggregate-like behavior where interchain interactions are less efficient. Stimulated emission in the red-near infrared region has been found in the mesoparticles which indicates that they present a more energetically ordered system.