Liposome-Based Nanoencapsulation of a Mitochondria-Stapling Photosensitizer for Efficient Photodynamic Therapy

Recent advances in nanomedicine design strategies for targeting subcellular structures

The current state of cancer treatment has encountered limitations, with each method having its own drawbacks. The emergence of nanotechnology in recent years has highlighted its potential in overcoming these limitations. Nanomedicine offers various drug delivery mechanisms, including passive, active, and endogenous targeting, with the advantage of modifiability and shapability. This flexibility enables researchers to develop tailored treatments for different types of tumors and populations. As nanodrug technology evolves from first to third generation, the focus is now on achieving precise drug delivery by targeting subcellular structures within tumors. This review summarizes the progress made in subcellular structure-targeted nanodrugs over the past 5 years, highlighting design strategies for targeting mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus, and cytoskeleton. The review also addresses the current status, limitations, and future directions about the research of nanodrugs.

Recent Advances in Thermally Activated Delayed Fluorescent Materials in Type II Photodynamic Therapy

Photodynamic therapy (PDT) represents a novel, dual-stage cancer treatment approach that combines light energy and photosensitizers to destroy cancerous and precancerous cells through the generation of radicals (Type I) or singlet oxygen (Type II). Since the early 2010s, PDT has advanced significantly, with the focus shifting toward the exploration of molecules capable of thermally activated delayed fluorescence (TADF) as viable alternatives to traditional metallic complexes and organometallic compounds for producing the necessary active species. TADF molecules exhibit higher energy conversion efficiency, long-lived triplet excitons, tunable photophysical properties, and a small singlet-triplet energy gap, facilitating efficient intersystem crossing and enhanced singlet oxygen generation. As metal-free luminophores, they offer benefits such as reduced health risks, high structural flexibility, and biocompatibility, which can significantly enhance PDT treatment efficacy. Notably, in 2019, a pivotal shift occurred, with researchers concentrating their efforts on identifying and investing in potential molecules specifically for Type II PDT applications. This review presents the innovative use of materials characterized by closely spaced S1 and T1 orbitals, crucial for the efficient generation of singlet oxygen in PDT. Exploring these materials opens new avenues for enhancing the efficacy and specificity of PDT, offering promising for future cancer treatments.

Advancements in nano drug delivery system for liver cancer therapy based on mitochondria-targeting

Based on poor efficacy and non-specific toxic side effects of conventional drug therapy for liver cancer, nano-based drug delivery system (NDDS) offers the advantage of drug targeting delivery. Subcellular targeting of nanomedicines on this basis enables more precise and effective termination of tumor cells. Mitochondria, as the crucial cell powerhouse, possesses distinctive physical and chemical properties in hepatoma cells different from that in hepatic cells, and controls apoptosis, tumor metastasis, and cellular drug resistance in hepatoma cells through metabolism and dynamics, which serves as a good choice for drug targeting delivery. Thus, mitochondria-targeting NDDS have become a recent research focus, showcasing the design of cationic nanoparticles, metal nanoparticles, mitochondrial peptide modification and so on. Although many studies have shown good results regarding anti-tumor efficacy, it is a long way to go before the successful translation of clinical application. Based on these, we summarized the specificity and importance of mitochondria in hepatoma cells, and reviewed the current mitochondria-targeting NDDS for liver cancer therapy, aiming to provide a better understanding for current development process, strengths and weaknesses of mitochondria-targeting NDDS as well as informing subsequent improvements and developments.

Chimeric Antigen-LgDNA Nanoparticles Attenuate Airway Th2 Polarization

Introduction

The therapeutic efficacy for airway allergies needs to be improved. Th2 polarization is a primary pathological feature of airway allergies. We constructed chimeric antigen-LgDNA (Lactobacillus rhamnosus DNA) nanoparticles (CAP-NPs). The effects of CAP-NPs on reconciling airway Th2 polarization were tested.

Methods

In this study, disulfide bond-linked antigen-major histocompatibility complex II (MHC II)-LgDNA nanoparticles (NPs) were constructed and designated CAP-NPs. An airway Th2 polarization mouse model was established to test the effects of CAP-NPs on suppressing the Th2 response.

Results

The CAP-NP components of ovalbumin (OVA), major histocompatibility complex II (MHC II), and LgDNA were confirmed in a series of laboratory tests. The CAP-NPs remained stable at pH7.2 for at least 96 h. In in vitro experiments, CAP-NPs bound to the surface of OVA-specific CD4+ T cells, which resulted in apoptosis of the antigen-specific CD4+ T cells. Removal of any of the three components from the NPs abolished the induction of apoptosis of antigen specific CD4+ T cells. CAP-NPs increased the expression of lysine-specific demethylase 5A (KDM5A) in CD4+ T cells. Histone H3K9 and the gene promoter of caspase 8 were demethylated by KDM5A, which led to transcription and expression of the caspase 8 gene. Administration of CAP-NPs significantly alleviated experimental airway Th2 polarization through activating the caspase 8-apoptosis signaling pathway.

Discussion

In this paper, we constructed CAP-NPs that could induce antigen-specific CD4+ T cell apoptosis. Administration of CAP-NPs efficiently alleviated experimental airway Th2 polarization.

Synthesis, Photo-Characterizations, and Pre-Clinical Studies on Advanced Cellular and Animal Models of Zinc(II) and Platinum(II) Sulfonyl-Substituted Phthalocyanines for Enhanced Vascular-Targeted Photodynamic Therapy

Two phthalocyanine derivatives tetra-peripherally substituted with tert-butylsulfonyl groups and coordinating either zinc(II) or platinum(II) ions have been synthesized and subsequently investigated in terms of their optical and photochemical properties, as well as biological activity in cellular, tissue-engineered, and animal models. Our research has revealed that both synthesized phthalocyanines are effective generators of reactive oxygen species (ROS). PtSO2tBu demonstrated an outstanding ability to generate singlet oxygen (ΦΔ = 0.87-0.99), while ZnSO2tBu in addition to 1O2 (ΦΔ = 0.45-0.48) generated efficiently other ROS, in particular ·OH. Considering future biomedical applications, the affinity of the tested phthalocyanines for biological membranes (partition coefficient; log Pow) and their primary interaction with serum albumin were also determined. To facilitate their biological administration, a water-dispersible formulation of these phthalocyanines was developed using Pluronic triblock copolymers to prevent self-aggregation and improve their delivery to cancer cells and tissues. The results showed a significant increase in cellular uptake and phototoxicity when phthalocyanines were incorporated into the customizable polymeric micelles. Moreover, the improved distribution in the body and photodynamic efficacy of the encapsulated phthalocyanines were investigated in hiPSC-delivered organoids and BALB/c mice bearing CT26 tumors. Both photosensitizers exhibit strong antitumor activity. Notably, vascular-targeted photodynamic therapy (V-PDT) led to complete tumor eradication in 84% of ZnSO2tBu and 100% of PtSO2tBu-treated mice, and no recurrence has so far been observed for up to five months after treatment. In the case of PtSO2tBu, the effect was significantly stronger, offering a wider range of light doses suitable for achieving effective PDT.

NIR-Absorbing Tetraphenylethene-Containing bisBODIPY Nanoplatforms Demonstrate Effective Lysosome-Targeting and Combinational Phototherapy

Photosensitizer-based phototherapies, including photodynamic therapy (PDT) and photothermal therapy (PTT), offer safe treatment modalities for tumor ablation with spatiotemporal precision. After photons are absorbed, PDT creates localized chemical damage by generating reactive oxygen species (ROS), while PTT induces localized thermal damage. However, PDT still faces hypoxic tumor challenges, while PTT encounters issues related to heat resistance and potential overheating. The combination of PDT and PTT shows great potential as an effective anticancer strategy. By targeting lysosomes with carefully designed phototherapeutic reagents for combined phototherapy, rapid dysfunction and cell death in cancer cells can be induced, showing promise for cancer treatment. Herein, two α-α-linked bisBODIPYs with tetraphenylethene (TPE) moieties are designed and synthesized. These TPE-substituted bisBODIPYs expand the absorption into NIR range (λmaxabs/λmaxem ∼ 740/810 nm) and confer aggregation-induced emission (AIE) activity (λmaxem ∼ 912 nm). Moreover, these bisBODIPYs self-assemble with surfactant F-127 into nanoparticles (NPs), which efficiently generate ROS (1O2 and •OH) in both solution and cellular environments and demonstrate superior photothermal conversion efficiencies (η ∼ 68.3%) along with exceptional photothermal stability. More importantly, these NPs showed lysosomal targeting and remarkable tumor ablation in cellular and murine models, indicating their potential in precision tumor therapy.

Polymer Dots with Delayed Fluorescence and Tunable Cellular Uptake for Photodynamic Therapy and Time-Gated Imaging

By combining bioimaging and photodynamic therapy (PDT), it is possible to treat cancer through a theranostic approach with targeted action for minimum invasiveness and side effects. Thermally activated delayed fluorescence (TADF) probes have gained recent interest in theranostics due to their ability to generate singlet oxygen (1O2) while providing delayed emission that can be used in time-gated imaging. However, it is still challenging to design systems that simultaneously show (1) high contrast for imaging, (2) low dark toxicity but high phototoxicity and (3) tunable biological uptake. Here, we circumvent shortcomings of TADF systems by designing block copolymers and their corresponding semiconducting polymer dots (Pdots) that encapsulate a TADF dye in the core and expose an additional boron-dipyrromethene (BODIPY) oxygen sensitizer in the corona. This architecture provides orange-red luminescent particles (ΦPL up to 18 %) that can efficiently promote PDT (1O2 QY=42 %) of HeLa cells with very low photosensitizer loading (IC50 ~0.05-0.13 μg/mL after 30 min). Additionally, we design Pdots with tunable cellular uptake but similar PDT efficiencies using either polyethylene glycol or guanidinium-based coronas. Finally, we demonstrate that these Pdots can be used for time-gated imaging to effectively filter out background fluorescence from biological samples and improve image contrast.

Mitochondrial-Targeting Nanotrapper Captured Copper Ions to Alleviate Tumor Hypoxia for Amplified Photoimmunotherapy in Breast Cancer

Hypoxia is a pervasive feature of solid tumors, which significantly limits the therapeutic effect of photodynamic therapy (PDT) and further influences the immunotherapy efficiency in breast cancer. However, the transient alleviation of tumor hypoxia fails to address the underlying issue of increased oxygen consumption, resulting from the rapid proliferation of tumor cells. At present, studies have found that the reduction of the oxygen consumption rate (OCR) by cytochrome C oxidase (COX) inhibition that induced oxidative phosphorylation (OXHPOS) suppression was able to solve the proposed problem. Herein, we developed a specific mitochondrial-targeting nanotrapper (I@MSN-Im-PEG), which exhibited good copper chelating ability to inhibit COX for reducing the OCR. The results proved that the nanotrapper significantly alleviated the hypoxic tumor microenvironment by copper chelation in mitochondria and enhanced the PDT effect in vitro and in vivo. Meanwhile, the nanotrapper improved photoimmunotherapy through both enhancing PDT-induced immunogenetic cell death (ICD) effects and reversing Treg-mediated immune suppression on 4T1 tumor-bearing mice. The mitochondrial-targeting nanotrapper provided a novel and efficacious strategy to enhance the PDT effect and amplify photoimmunotherapy in breast cancer.

Nanomaterials for Disease Treatment by Modulating the Pyroptosis Pathway

Pyroptosis differs significantly from apoptosis and cell necrosis as an alternative mode of programmed cell death. Its occurrence is mediated by the gasdermin protein, leading to characteristic outcomes including cell swelling, membrane perforation, and release of cell contents. Research underscores the role of pyroptosis in the etiology and progression of many diseases, making it a focus of research intervention as scientists explore ways to regulate pyroptosis pathways in disease management. Despite numerous reviews detailing the relationship between pyroptosis and disease mechanisms, few delve into recent advancements in nanomaterials as a mechanism for modulating the pyroptosis pathway to mitigate disease effects. Therefore, there is an urgent need to fill this gap and elucidate the path for the use of this promising technology in the field of disease treatment. This review article delves into recent developments in nanomaterials for disease management through pyroptosis modulation, details the mechanisms by which drugs interact with pyroptosis pathways, and highlights the promise that nanomaterial research holds in driving forward disease treatment.

Exploration of Thermally Activated Delayed Fluorescence (TADF)-Based Photoredox Catalyst To Establish the Mechanisms of Action for Photodynamic Therapy

The mechanisms of action (MoA) have been proposed to further reduce the O2 dependence of photodynamic therapy (PDT) significantly. However, the triplet states of traditional photosensitizers are relatively short and also are easily deactivated by the quenching of H2O or O2. This is not conducive for the electron transfer in the photocatalytic process and poses a great obstacle to establish the MoA. Therefore, we selected and synthesized a zirconium(IV) complex (Zr(MesPDPPh)2) reported by Milsmann to address this issue. The specific symmetric and intact geometry endowed Zr(MesPDPPh)2 NPs with long-lived triplet excited state (τ = 350 μs), desired sensitized ability, and improved anti-interfering performance on O2, which was matched with the requirements of photoredox catalyst significantly. The results showed that while PDT (I) and PDT (II) could be achieved simultaneously by leveraging Zr(MesPDPPh)2 NPs, it also could be served as a rare example of thermally activated delayed fluorescence (TADF)-based photoredox catalyst to implement the MoA of PDT. It involved the oxidation of NADH and the establishment of catalytic cycle collaborating by O2 and cytochrome c (cyt c) in normoxia and hypoxia, respectively. As a result, the oxygen-free PDT and tumor-growth inhibition was realized.

Self-Assembly Induced Photosensitization of Long-Tailed Heavy-Atom-Free BODIPY Derivatives for Photodynamic Therapy

Type I photosensitizers (PSs) are a promising approach for photodynamic therapy (PDT) since they can generate radicals that are tolerant to hypoxia. Thus, the development of highly efficient type I PSs is essential. Self-assembly is a promising strategy for developing novel PSs with desirable properties. Here, a simple and effective approach is developed to create heavy-atom-free PSs for PDT by self-assembling long-tailed boron dipyrromethene dyes (BODIPYs). The resulting aggregates BY-I16 and BY-I18 can efficiently convert their excited energy to the triplet state, producing reactive oxygen species that are essential for PDT. Furthermore, the aggregation and PDT performance can be regulated by adjusting the length of the tailed alkyl chains. As proof of concept, the efficacy of these heavy-atom-free PSs both in vitro and in vivo under both normoxic and hypoxic conditions is demonstrated.

Radio- and Photosensitizing Os(II)-Based Nanocage for Combined Radio-/Chemo-/X-ray-Induced Photodynamic Therapies, NIR Imaging, and Drug Delivery

Integration of clinical imaging and collaborative multimodal therapies into a single nanomaterial for multipurpose diagnosis and treatment is of great interest to theranostic nanomedicine. Here, we report a rational design of a discrete Os-based metal-organic nanocage Pd6(OsL3)828+ (MOC-43) as a versatile theranostic nanoplatform to meet the following demands simultaneously: (1) synergistic treatments of radio-, chemo-, and X-ray-induced photodynamic therapies (X-PDT) for breast cancer, (2) NIR imaging for cancer cell tracking and tumor-targeting, and (3) anticancer drug transport through a host-guest strategy. The nanoscale MOC-43 incorporates high-Z Os-element to interact with X-ray irradiation for dual radiosensitization and photosensitization, showing efficient energy transfer to endogenous oxygen in cancer cells to enhance X-PDT efficacy. It also features intrinsic NIR emission originating from metal-to-ligand charge transfer (MLCT) as an excellent imaging probe. Meanwhile, its 12 pockets can capture and concentrate low-water-soluble molecules for anticancer drug delivery. These multifunctions are implemented and demonstrated by micellization of coumarin-loaded cages with DSPE-PEG2000 into coumarin ⊂ MOC-43 nanoparticles (CMNPs) for efficient subcellular endocytosis and uptake. The cancer treatments in vitro/in vivo show promising antitumor performance, providing a conceptual protocol to combine cage-cargo drug transport with diagnosis and treatment for collaborative cancer theranostics by virtue of multifunction synergism on a single-nanomaterial platform.

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Modulating the Luminescence, Photosensitizing Properties, and Mitochondria-Targeting Ability of D-π-A-Structured Dihydrodibenzo[a,c]phenazines

Herein, pyridinium and 4-vinylpyridinium groups are introduced into the VIE-active N,N'-disubstituted-dihydrodibenzo[a,c]phenazines (DPAC) framework to afford a series of D-π-A-structured dihydrodibenzo[a,c]phenazines in consideration of the aggregation-benefited performance of the DPAC module and the potential mitochondria-targeting capability of the resultant pyridinium-decorated DPACs (DPAC-PyPF6 and DPAC-D-PyPF6). To modulate the properties and elucidate the structure-property relationship, the corresponding pyridinyl/4-vinylpyridinyl-substituted DPACs, i.e., DPAC-Py and DPAC-D-Py, are designed and studied as controls. It is found that the strong intramolecular charge transfer (ICT) effect enables the effective separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of DPAC-PyPF6 and DPAC-D-PyPF6, which is conducive to the generation of ROS. By adjusting the electron-accepting group and the π-bridge, the excitation, absorption, luminescence, photosensitizing properties as well as the mitochondria-targeting ability can be finely tuned. Both DPAC-PyPF6 and DPAC-D-PyPF6 display large Stokes shifts (70-222 nm), solvent-dependent absorptions and emissions, aggregation-induced emission (AIE), red fluorescence in the aggregated state (λem = 600-650 nm), aggregation-promoted photosensitizing ability with the relative singlet-oxygen quantum yields higher than 1.10, and a mitochondria-targeting ability with the Pearson coefficients larger than 0.85. DPAC-D-PyPF6 shows absorption maximum at a longer wavelength, slightly redder fluorescence and better photosensitivity as compared to DPAC-PyPF6, which consequently leads to the higher photocytotoxicity under the irradiation of white light as a result of the larger π-conjugation.

Constructing lipid droplet-targeting photosensitizers based on coumarins with NIR emission

The development of photosensitizers (PSs) with subcellular targeting capability has raised interest for photodynamic therapy (PDT) research. In this work, two coumarin-based photosensitizers (C-S-2 and C-S-3) were designed and synthesized via expanding their π-conjugation, introducing strong electron-donor and acceptor groups, and adopting sulfur substitution strategy. These sulfured-coumarins exhibited near-infrared emission (greater than 650 nm), lipid droplet-targeting ability and obvious photocytotoxicity under laser irradiation. In particular, C-S-3 exhibited better photostability, superior lipid droplet-targeting capability, and stronger photodynamic effect on cancer cells than C-S-2.

Enzyme-triggered deep tumor penetration of a dual-drug nanomedicine enables an enhanced cancer combination therapy

Cancer cells could be eradicated by promoting generation of excessive intracellular reactive oxygen species (ROS) via emerging nanomedicines. However, tumor heterogeneity and poor penetration of nanomedicines often lead to diverse levels of ROS production in the tumor site, and ROS at a low level promote tumor cell growth, thus diminishing the therapeutic effect of these nanomedicines. Herein, we construct an amphiphilic and block polymer-dendron conjugate-derived nanomedicine (Lap@pOEGMA-b-p(GFLG-Dendron-Ppa), GFLG-DP/Lap NPs) that incorporates a photosensitizer, Pyropheophorbide a (Ppa), for ROS therapy and Lapatinib (Lap) for molecular targeted therapy. Lap, an epidermal growth factor receptor (EGFR) inhibitor that plays a role in inhibiting cell growth and proliferation, is hypothesized to synergize with ROS therapy for effectively killing cancer cells. Our results suggest that the enzyme-sensitive polymeric conjugate, pOEGMA-b-p(GFLG-Dendron-Ppa) (GFLG-DP), releases in response to cathepsin B (CTSB) after entering the tumor tissue. Dendritic-Ppa has a strong adsorption capacity to tumor cell membranes, which promotes efficient penetration and long-term retention. Lap can also be efficiently delivered to internal tumor cells to play its role due to the increased vesicle activity. Laser irradiation of Ppa-containing tumor cells results in production of intracellular ROS that is sufficient for inducing cell apoptosis. Meanwhile, Lap efficiently inhibits proliferation of remaining viable cells even in deep tumor regions, thus generating a significant synergistic anti-tumor therapeutic effect. This novel strategy can be extended to the development of efficient membrane lipid-based therapies to effectively combat tumors.

Mitochondria-Targeting Upconversion Nanoparticles@MOF for Multiple-Enhanced Photodynamic Therapy in Hypoxic Tumor

The effect of photodynamic therapy (PDT) is severely limited by tumor hypoxia and the short half-life of reactive oxygen species (ROS). Herein, we constructed a near-infrared (NIR) light-regulated PDT nanoplatform (TPP-UCNPs@MOF-Pt) consisting of an upconversion nanoparticle (UCNP) core and porphyrin-based metal-organic framework (MOF) shell with platinum nanoparticles (PtNPs) and a mitochondria-targeting triphenylphosphine (TPP) group on the surface. TPP-UCNPs@MOF-Pt could effectively relieve the tumor hypoxia by converting intracellular H₂O₂ to oxygen (O₂) and elevated the ROS level to enhance PDT efficacy under NIR light irradiation. In addition, the mitochondria-targeting TPP-UCNPs@MOF-Pt was localized on the mitochondria, leading to severe depolarization of the mitochondrial membrane and activation of the apoptotic pathway, further amplifying the therapeutic efficacy. In vitro and in vivo experiments demonstrated that the greatly enhanced photodynamic therapeutic efficacy of TPP-UCNPs@MOF-Pt was achieved by combining relief of tumor hypoxia with mitochondrial targeting and NIR activation. This study provides a promising strategy for construction of an MOF-based multifunctional nanoplatform to address the current limitations of PDT treatment for hypoxic tumors.

Biomimetic Nanovesicle with Mitochondria-Synthesized Sonosensitizer and Mitophagy Inhibition for Cancer Sono-Immunotherapy

Mitochondria are crucial for both sonodynamic therapy and antitumor immunity. However, how to accurately damage mitochondria and meanwhile prevent the mitophagy and immune checkpoint inhibition is still a great challenge. Herein, hexyl 5-aminolevulinate hydrochloride (HAL) and 3-methyladenine (3MA) are loaded into the tumor cell-derived microparticle (X-MP), which can direct the target delivery of the prepared HAL/3MA@X-MP to the tumor cells. HAL induces the confined biosynthesis and accumulation of sonosensitizer PpIX in mitochondria, leading to the localized generation of reactive oxygen species (ROS) upon ultrasound irradiation and, thus, the efficient mitochondrial damage. Meanwhile, 3MA not only inhibits mitophagy but also down-regulates the PD-L1 expression, promoting the immunogenic cell death (ICD) while blocking the immune checkpoint recognition. The smart synergism of precise mitochondrial damage, mitophagy inhibition and antitumor immunity results in potent therapeutic efficacy without obvious side effects.

Near-Infrared Dyes: Towards Broad-Spectrum Antivirals

Broad antiviral activity in vitro is known for many organic photosensitizers generating reactive oxygen species under irradiation with visible light. Low tissue penetration of visible light prevents further development of antiviral therapeutics based on these compounds. One possible solution to this problem is the development of photosensitizers with near-infrared absorption (NIR dyes). These compounds found diverse applications in the photodynamic therapy of tumors and bacterial infections, but they are scarcely mentioned as antivirals. In this account, we aimed to evaluate the therapeutic prospects of various NIR-absorbing and singlet oxygen-generating chromophores for the development of broad-spectrum photosensitizing antivirals.