Imaging-guided Photodynamic Therapy Research Articles

Stereoisomeric engineering of aggregation-induced emission photosensitizers towards fungal killing

Fungal infection poses and increased risk to human health. Photodynamic therapy (PDT) as an alternative antifungal approach garners much interest due to its minimal side effects and negligible antifungal drug resistance. Herein, we develop stereoisomeric photosensitizers ((Z)- and (E)-TPE-EPy) by harnessing different spatial configurations of one molecule. They possess aggregation-induced emission characteristics and ROS, viz. 1O2 and O2−• generation capabilities that enable image-guided PDT. Also, the cationization of the photosensitizers realizes the targeting of fungal mitochondria for antifungal PDT killing. Particularly, stereoisomeric engineering assisted by supramolecular assembly leads to enhanced fluorescence intensity and ROS generation efficiency of the stereoisomers due to the excited state energy flow from nonradiative decay to the fluorescence pathway and intersystem (ISC) process. As a result, the supramolecular assemblies based on (Z)- and (E)-TPE-EPy show dramatically lowered dark toxicity without sacrificing their significant phototoxicity in the photodynamic antifungal experiments. This study is a demonstration of stereoisomeric engineering of aggregation-induced emission photosensitizers based on (Z)- and (E)-configurations.

Development of Bodipy-Ir complex as an near-infrared photosensitizer for photoacoustic imaging-guided photodynamic therapy

Herein we develop a novel NIR photosensitizer, bodipy-Ir. Under 808 nm excitation, bodipy-Ir could generate significant amount of singlet oxygen. In addition, bodipy-Ir exhibits photoacoustic properties as well. Thus, the photoacoustic imaging-guided photodynamic therapy of bodipy-Ir has been demonstrated.

Special issue on enhanced photodynamic therapy: Part II

Special issue on enhanced photodynamic therapy: Part II

A lipid droplet-targeted multifunctional AIE-active fluorescent probe for hydrogen peroxide detection and imaging-guided photodynamic therapy

Recent developments of activatable photosensitizers (aPSs) invigorate photodynamic therapy by enhancing sensitivity towards cancer cells and avoiding constant phototoxicity. However, the diversity of activatable photosensitizers needs to be developed urgently. Hydrogen peroxide (H2O2), as a typical biomarker which overexpressed in tumor tissue, is an ideal promoter for selectively activating photosensitizers to restore their photosensitivity. Herein, we construct a new H2O2-activated photosensitizer DPP-BPYS based on diketoprrrolopyrrole (DPP), which can rapidly and specifically respond to H2O2 both in vitro and in vivo, and exhibit “turn-on” near-infrared fluorescence emission. The activated DPP-BPYS performs typical aggregation-induced emission (AIE) characteristics, a large Stokes shift (180 nm), strong fluorescence quantum yield and high singlet oxygen (1O2) generating capacity. More importantly, activated DPP-BPYS can target lipid droplets (LDs) in tumor cells to form aggregates, and effectively generate reactive oxygen species under white light irradiation to induce apoptosis of tumor cells. Consequently, this research provides a unique molecular tool for H2O2-activated photodynamic anticancer therapy.

Polymersomes with Red/Near-Infrared Emission and Reactive Oxygen Species Generation.

In photodynamic therapy (PDT), the uses of nanoparticles bearing photosensitizers (PSs) can overcome some of the drawbacks of using a PS alone (e.g., poor water solubility and low tumor selectivity). However, numerous nano-formulations are developed by physical encapsulation of PSs through Van der Waals interactions, which have not only a limited load efficiency but also some in vivo biodistribution problems caused by leakage or burst release. Herein, polymersomes made from an amphiphilic block copolymer, in which a PS with aggregation-induced emission (AIE-PS) is covalently attached to its hydrophobic poly(amino acid) block, are reported. These AIE-PS polymersomes dispersed in aqueous solution have a high AIE-PS load efficiency (up to 46% as a mass fraction), a hydrodynamic diameter of 86nm that is suitable for in vivo applications, and an excellent colloidal stability for at least 1 month. They exhibit a red/near-infrared photoluminescence and ability to generate reactive oxygen species (ROS) under visible light. They are non-cytotoxic in the dark as tested on Hela cells up to concentration of 100µm. Benefiting from colloidal stability, AIE property and ROS generation capability, such a family of polymersomes can be great candidates for image-guided PDT.

Hypoxia-Responsive Photosensitizer Targeting Dual Organelles for Photodynamic Therapy of Tumors.

Developing safe and precise image-guided photodynamic therapy is a challenge. In this study, the hypoxic properties of solid tumors are exploited to construct a hypoxia-responsive photosensitizer, TPA-Azo. Introducing the azo group into the photosensitizer TPA-BN with aggregation-induced emission quenches its fluorescence. When the nonfluorescent TPA-Azo enters hypoxic tumors, it is reduced by the overexpressed azoreductase to generate a fluorescent photosensitizer TPA-BN with an amino group that exhibits fluorescence-activatable image-guided photodynamic therapy with dual-organelle (lipid droplets and lysosomes) targeting. This design strategy provides a basis for the development of fluorescence-activatable photosensitizers.

A Microneedle Patch with Self-Oxygenation and Glutathione Depletion for Repeatable Photodynamic Therapy.

Photodynamic therapy (PDT) has attained extensive attention as a noninvasive tumor treatment modality. However, the hypoxia in solid tumors, skin phototoxicity of "always on" photosensitizers (PSs), and abundant supply of glutathione (GSH) in cancer cells severely hampered the clinical applications of PDT. Herein, a self-oxygenation nanoplatform (denoted as CZCH) with GSH depletion ability was encapsulated into the hyaluronic acid microneedle patch (MN-CZCH) to simultaneously improve the biosafety and therapeutic efficacy of PDT. The Cu2+-doped porous zeolitic imidazolate framework incorporated with catalase (CAT) is capable of efficiently loading PS 2-(1-hexyloxyethyl)-2-divinylpyropheophorbic-a (HPPH). The CZCH intermingled MN patch (MN-CZCH) could effectively penetrate the stratum corneum, topically transport HPPH to the target tumor site, achieve a long tumor retention time, and enhance the efficacy of PDT via the simultaneously synergistic effect of CAT-catalyzed self-supplying O2 and Cu2+-mediated GSH depletion. Using traceable fluorescence (FL) imaging of the released HPPH from CZCH, the FL imaging-guided repeatable PDT can be achieved for enhanced antitumor efficacy. As a result, the MN-CZCH patch exhibited excellent therapeutic efficacy against melanoma with minimal toxicity, which has promising potential for cancer theranostics.

Mitochondria targeted upconversion molecular platform for photodynamic therapy of cancer cells

Increasing interest has been noted in photosensitizer design. Currently, most small molecular photosensitizers have several drawbacks, including limited penetration depth and unsatisfying photostability. For addressing these limitations, Frequency upconversion luminescence (FUCL) small molecule was adopted as a photosensitizer design strategy for its deeper penetration, sensitive imaging, and better photostability. We developed a series of FUCL (NIR-NH2, NIR-NHEt, NIR-NEt2) molecules with rigid structures. Equipped with the most powerful electron donor, NIR-NEt2 exhibits the highest singlet oxygen generation, the strongest upconversion luminescence intensity under 808 nm irradiation and mitochondria-targeted ability. FUCL can be a superior molecular platform for image-guided photodynamic therapy of cancer cells.

A novel BODIPY-based nano-photosensitizer with aggregation-induced emission for cancer photodynamic therapy

The discovery of aggregation-induced emission (AIE) effect provides opportunities for the rapid development of fluorescence imaging-guided photodynamic therapy (PDT). In this work, a boron dipyrromethene (BODIPY)-based photosensitizer (ET-BDP-O) with AIE characteristics was developed, in which the two linear arms of BODIPY group were linked with triphenylamine to form an electron Donor–Acceptor–Donor (D–A–D) architecture while side chain was equipped with triethylene glycol group. ET-BDP-O was able to directly self-assemble into nanoparticles (NPs) without supplement of any other matrices or stabilizers due to its amphiphilic property. The as-prepared ET-BDP-O NPs had an excellent colloid stability with the size of 125 nm. Benefiting from the AIE property, ET-BDP-O NPs could generate strong fluorescence and reactive oxygen species under light-emitting diode light irradiation (60[Formula: see text]mW/cm[Formula: see text]. After internalized in cancer cells, ET-BDP-O NPs were able to emit bright red fluorescence signal for bioimaging. In addition, the cell viability assay demonstrated that the ET-BDP-O NPs exhibited excellent photo-cytotoxicity against cancer cells, while negligible cytotoxicity under dark environment. Thus, ET-BDP-O NPs might be regarded as a promising photosensitizer for fluorescence imaging-guided PDT in future.

Recent Developments in Heteroatom/Metal-Doped Carbon Dot-Based Image-Guided Photodynamic Therapy for Cancer.

Carbon nanodots (CNDs) are advanced nanomaterials with a size of 2–10 nm and are considered zero-dimensional carbonaceous materials. CNDs have received great attention in the area of cancer theranostics. The majority of review articles have shown the improvement of CNDs for use in cancer therapy and bioimaging applications. However, there is a minimal number of consolidated studies on the currently developed doped CNDs that are used in various ways in cancer therapies. Hence, in this review, we discuss the current developments in different types of heteroatom elements/metal ion-doped CNDs along with their preparations, physicochemical and biological properties, multimodal-imaging, and emerging applications in image-guided photodynamic therapies for cancer.

Structure and functions of Aggregation-Induced Emission-Photosensitizers in anticancer and antimicrobial theranostics.

Photosensitizers with Aggregation-Induced Emission (AIE) can allow the efficient light-mediated generation of Reactive Oxygen Species (ROS) based on their complex molecular structure, while interacting with living cells. They achieve better tissue targeting and allow penetration of different wavelengths of Ultraviolet-Visible-Infrared irradiation. Not surprisingly, they are useful for fluorescence image-guided Photodynamic Therapy (PDT) against cancers of diverse origin. AIE-photosensitizers can also function as broad spectrum antimicrobials, capable of destroying the outer wall of microbes such as bacteria or fungi without the issues of drug resistance, and can also bind to viruses and deactivate them. Often, they exhibit poor solubility and cellular toxicity, which compromise their theranostic efficacy. This could be circumvented by using suitable nanomaterials for improved biological compatibility and cellular targeting. Such dual-function AIE-photosensitizers nanoparticles show unparalleled precision for image-guided detection of tumors as well as generation of ROS for targeted PDT in living systems, even while using low power visible light. In short, the development of AIE-photosensitizer nanoparticles could be a better solution for light-mediated destruction of unwanted eukaryotic cells and selective elimination of prokaryotic pathogens, although, there is a dearth of pre-clinical and clinical data in the literature.

Boron Dipyrromethene-Based Phototheranostics for Near Infrared Fluorescent and Photoacoustic Imaging-Guided Synchronous Photodynamic and Photothermal Therapy of Cancer

The regulation of photochemical properties of phototheranostics, especially the absorption, fluorescence, singlet oxygen (1O2) generation, and photothermal conversion efficiency, is a hot research topic. Here, we designed and synthesized four boron dipyrromethene (BODIPY) derivatives with high absorption coefficients and intense fluorescence in the near-infrared (NIR) region. The substituted electron-donating group significantly improved 1O2 generation and fluorescence of BODIPYs, whereas the electron-withdrawing group boosts photothermal conversion. These hydrophobic BODIPYs were further coated with DSPE-PEG-2000 to form water dispersible nanoparticles (NPs). Among these BODIPY NPs, the B-OMe-NPs with methoxyl substituted at the meso-position showed the highest 1O2 generation, a photothermal conversion efficiency of 66.5%, and an NIR fluorescence peak at 809 nm. In vitro and in vivo experiments demonstrated that B-OMe-NPs might be used for NIR fluorescent and photoacoustic imaging-guided photodynamic and photothermal therapy of cancer.

An amphiphilic tetraphenylethylene-based photosensitizer for cancer cell ablation and bacteria killing

Bacterial infections are closely related to the initiation of cancer, and the killing of cancer-related bacteria can greatly improve the therapeutic effect of cancer. Image-guided photodynamic therapy (PDT) can solve bacterial drug resistance, which has attracted wide attention as a non-invasive and safe cancer treatment method. In this study, we design and synthesis a new amphiphilic tetraphenylethylene-based photosensitizer TPETP-TG, and its compared compound TPETP-Me, for cancer cell ablation and bacteria killing. TPETP-TG bears the hydrophilic triethylene glycol (TG) tail and a positive pyridinium salt with a strong electron push–pull effect. It self-assembles nano-aggregation in aqueous solution, and emits a typical AIE characteristics fluorescence at 635 nm. The TPETP-TG aggregations show a good photostability and biocompatibility, and also a high reactive oxygen species (ROS) generation under the white light irradiation, which is superior to the control photosensitizer TPETP-Me. TPETP-TG selectively targets mitochondria in cancer cells, and makes it ablation under the white light irradiation. In addition, TPETP-TG is also successfully used for photodynamic killing E. coli and S. aureus at low working concentrations. Furthermore, the therapeutic experiments with bacterial-infected zebrafish imply that TPETP-TG effectively eliminates the bacteria and improves their survival rate under light irradiation.

Acceptor-donor-acceptor structured phototheranostics for near-infrared II fluorescent and photoacoustic imaging-guided photodynamic and photothermal synergistic therapy

Multi-modal imaging-guided synergistic photodynamic therapy (PDT) and photothermal therapy (PTT) show great benefits in cancer treatment. The phototheranostics with near-infrared (NIR) absorption, high reactive oxygen species (ROS) generation and photothermal conversion efficiency is highly desirable. Here, we designed and synthesized an “acceptor-donor-acceptor” (A-D-A) structured molecule named IDCIC, with strong absorbance in the NIR region. We further prepared IDCIC into water-soluble nanoparticles (NPs) by wrapping with 1,2-distearoylsn-glycero-3-phosphoethanolamine-N-[(polyethylene glycol)-2000]-amine (DSPE-PEG2000-NH2). The obtained IDCIC NPs show an NIR absorption peak at 760 nm and an NIR-II fluorescence spectrum peak at ∼1000 nm with a fluorescent quantum yield of 1.2%, enabling them excellent photoacoustic and NIR-II fluorescent imaging capabilities. Moreover, IDCIC NPs could simultaneously generate singlet oxygen (with a quantum yield of 9.1%), hydroxyl radicals (·OH) and heat (with a photothermal conversion efficiency of 78.9%) under 808-nm laser irradiation. Based on the above-mentioned properties, IDCIC NPs were used for dual-modal imagingguided synergistic photodynamic/photothermal therapy of cancer.

Novel selenium-containing photosensitizers for near-infrared fluorescence imaging-guided photodynamic therapy.

Benzopyran nitrile dyes cannot be used as qualified photosensitizers due to the low quantum yield of triplet state. The benzopyran derivatives containing selenium instead of oxygen atom based on the heavy atom effect are expected to become potential agents for photodynamic therapy. In this paper, a series of selenium-containing photosensitizers (PSX) were prepared according to this strategy. PSX can effectively produce both singlet oxygen and superoxide anions upon laser irradiation. PSX exhibited the emission wavelength at 500-800nm and near-infrared (NIR) fluorescence imaging in HeLa cells. Excellent biocompatibility and phototoxicity further indicated that PSX could be used as efficient photosensitizers for NIR fluorescence imaging and photodynamic therapy.

Single-walled carbon nanohorns-based smart nanotheranostic: From phototherapy to enzyme-activated fluorescence imaging-guided photodynamic therapy

Phototheranostics, a local non-invasive approach that integrates light-based diagnostics and therapeutics, enables precise treatment using nanotheranostic agents with minimal damage to normal tissues. However, ensuring high-efficiency ablation of cancer cells using phototheranostics for one time irradiation is highly challenging. Herein, we designed and synthesized a single-walled carbon nanohorns-based nanotheranostic agent, HA-IR808-SWNHs, by loading IR808, a photosensitizer, conjugated hyaluronic acid (HA) with an amide bond on the surface of single-walled carbon nanohorns (SWNHs) through noncovalent π−π interaction by the sonication method. The HA in HA-IR808-SWNHs improves the water dispersibility of SWNHs and endows SWNHs with targeting capabilities. Importantly, overexpressed endogenous hyaluronidase in cancer cells actively disassembles HA-IR808-SWNHs, forming small HA-IR808 fragments. The fragments exhibit a strong fluorescence signal and can be used to guide programmed photodynamic therapy for sequentially eliminating the residual living cancer cells. The current study confirms that HA-IR808-SWNHs is an endogenous enzyme-responsive nanotheranostic agent that can be employed to precisely track and ablate residual cancer cells in a spatiotemporal manner. The results strengthen the understanding of SWNH functionalization and expand its potential biomedical application, especially in cancer theranostics.

NRNC-8, a novel mitochondria-immobilization superoxide radical generator for photodynamic therapy

Mitochondria play an important role in carcinogenesis, and alterations in mitochondrial activity are frequently associated with cancer formation. Mitochondria have become attractive targets for cancer therapy, with mitochondria-targeted photodynamic therapy (PDT) being one of the most prominent fields. However, significant limitations remain, such as low spectroscopic absorption, short photosensitizer absorption wavelengths, and organelle targeting stability deterioration during phototherapy. In this work, we synthesized an Aza-Nile red-structured near-infrared photosensitizer NRNC-8 based on side-chain engineering for the first time. NRNC-8 can be successfully immobilized on mitochondria in a reaction-free way by linking C8 alkyl chain on the N atom. This reaction-free immobilization approach efficiently prevents irreversible damage to mitochondrial structure and potential effects on mitochondrial function, as well as photosensitizer leaking from mitochondria during phototherapy. Superoxide anion (O2•-) can be created efficiently under red LED irradiation, which directly damages mitochondria and causes cell death, boosting PDT efficiency. A series of studies demonstrated the great potential of NRNC-8 dyes as efficient mitochondria-targeted imaging-guided photodynamic therapy agents, further highlighting the potential value of the “reaction-free mitochondrion-immobilized” strategy in the design of mitochondria-targeted photosensitizers for more efficient photodynamic therapy.

An advanced multifunctional prodrug combining photodynamic therapy with chemotherapy for highly efficient and precise tumor ablation

It is urgently required to develop the molecular agents with high therapeutic efficacy and low side effects for precise cancer therapy. Herein, an advanced multifunctional prodrug B-BDP-CL-CPT, consisting of a glutathione (GSH)-responsive boron dipyrromethene (BDP)-based photosensitizer, a chemo drug camptothecin (CPT), a reactive oxygen species (ROS)-sensitive chain linking BDP with CPT, and a biotin fragment with specific affinity to biotin-receptor, was designed and synthesized. Owing to the introduction of 2,4-dinitrobenzenesulfonate (DNBS) as the quencher into BDP core and chemical modification of CPT at the active site, B-BDP-CL-CPT is non-cytotoxic. Having biotin as the targeting ligand, the prodrug can be efficiently internalized by biotin-acceptor positive cancer cells, and then activated to generate substantial light-induced ROS through removal of the stopper DNBS by intracellular GSH which is abundant in cancer cells. The resulting ROS can not only serve for photodynamic therapy (PDT) but also further cleave thioketal linkage causing the release of CPT, to achieve dual PDT and chemotherapy. And the combination of preferential accumulation with specific activation in tumor tissues for this prodrug is conducive to improving the dual therapeutic outcome meanwhile greatly reducing the photo-damage and the release of CPT in adjacent healthy tissues. In addition, the activated B-BDP-CL-CPT can give bright fluorescence signals which are favor for imaging-guided PDT and real-time tracking the release of therapeutic agent. The in vitro and in vivo investigations have been performed to demonstrate the targeted and combined anticancer activities of this prodrug against HepG2 and HeLa cancer cells, and the mice with H22 tumors. This study proposes a new tactics for highly efficient and precise cancer treatment.

Bacterial targeted AIE photosensitizers synergistically promote chemotherapy for the treatment of inflammatory cancer

Tumor-associated components, especially extratumoral bacteria (EB) in the form of biofilms, could exacerbate cancer progression and hinder the effectiveness of antitumor drugs by covering the interstitial tumor space. Although photodynamic therapy (PDT) is a promising modality to kill cancer cells and bacteria with high spatiotemporal precision, the low penetration of light limits its potential in deep tumor therapy. Furthermore, current 2D culture-based preclinical in vitro models failed to reflect the complexity of the tumor microenvironment. Here, we developed an unprecedented “1 + 1 > 2″ combinatorial strategy of PDT and chemotherapy by co-delivering a bacterial-targeted photosensitizer with aggregation-induced emission (AIE) property and an anticancer drug, doxorubicin. The theranostic system could selectively visualize and rapidly kill EB, using a microfluidic-based 3D bladder cancer model. The effect of combinatorial therapy was synergistic, resulting in improved efficacy, as evidenced by at least a 2.5-fold reduction in the half-maximal inhibitory concentration of doxorubicin. Validation using a fish wound infection model further demonstrated the feasibility of AIE photosensitizers for efficient fluorescence imaging-guided PDT in vivo. Overall, we proposed a robust AIE PDT/chemotherapy strategy that shows great potential for rapid and concurrent treatment of bacterially infected cancer patients.

Tuning long-term mitochondrial imaging and photodynamic therapy capabilities through rational design of aggregation-induced emission luminogens

Many aggregation-induced emission luminogens (AIEgens) not only act as photosensitizers to generate cytotoxic reactive oxygen species under the irradiation of appropriate light, but also emit bright fluorescence for positioning and tracking, realizing image-guided photodynamic therapy. However, few AIEgens can achieve long-term near-infrared bioimaging, and the design of AIEgens rarely involves multi-faceted functional optimization and the combined use of different AIE groups. In this study, a series of low-toxic salicylaldehyde-based Schiff base AIEgens (NPy-AIE, NNPy-AIE, TPy-AIE and TTPy-AIE) are rational designed from multiple aspects to study structure-function relationships, which all exhibit excellent long-term bioimaging capability. Starting from NPy-AIE, its water solubility is enhanced by increasing the number of cations and constructing hydrophilic groups to obtain NNPy-AIE. Dimethylaniline groups of NPy-AIE are replaced with triphenylamine groups to acquire TPy-AIE with enhanced AIE activity. Thiophene groups are introduced in TPy-AIE to obtain TTPy-AIE with larger conjugation structure and electron donor-acceptor strength. The first two red-emitting AIEgens have better long-term mitochondrial targeting capability. NNPy-AIE has better water solubility and mitochondrial membrane potential detection capabilities. In particular, the latter two near-infrared emitting AIEgens can not only achieve long-term in vivo and in vitro near-infrared imaging, but also generate singlet oxygen under white light irradiation, which increases the level of intracellular reactive oxygen species and the proportion of apoptotic cells, showing potential as photosensitizers for image-guided photodynamic therapy. In vivo photodynamic therapy experiment of TTPy-AIE in 4T1 tumor-bearing mice has confirmed its excellent biocompatibility and photodynamic therapy ability.