Photochemical internalization enhances cytosolic release of antibiotic and increases its efficacy against staphylococcal infection

Harnessing light-activated gallium porphyrins to combat intracellular Staphylococcus aureus using an in vitro keratinocyte infection model

Staphylococcus aureus (S. aureus) can survive inside nonprofessional phagocytes such as keratinocytes, enabling it to evade antibiotics and cause recurrent infections once treatment stops. New antibacterial strategies to eliminate intracellular, multidrug-resistant bacteria are needed. This study used a keratinocyte model infected with methicillin-resistant S. aureus (MRSA) to test light-activated compounds, specifically heme-mimetic gallium (III) porphyrin (Ga3+CHP) and visible light, known as antimicrobial photodynamic inactivation (aPDI), for eliminating intracellular MRSA. Ga3+CHP was found to accumulate more in infected cells, particularly within lysosomal structures where MRSA resides. Flow cytometry and fluorescence microscopy revealed significant colocalization of MRSA and Ga3+CHP. Under aPDI, MRSA showed reduced adhesion to host cells and a 70% reduction in the GFP signal from intracellular bacteria. Additionally, light-activated Ga3+CHP significantly decreased the number of extracellular bacteria, reducing the potential for further infection. This study is the first to analyze aPDI toxicity in real time within an infection model, demonstrating that this method is neither cytotoxic nor phototoxic.

Non-antibiotic strategies for prevention and treatment of internalized Staphylococcus aureus

Staphylococcus aureus (S. aureus) infections are often difficult to cure completely. One of the main reasons for this difficulty is that S. aureus can be internalized into cells after infecting tissue. Because conventional antibiotics and immune cells have difficulty entering cells, the bacteria can survive long enough to cause recurrent infections, which poses a serious burden in healthcare settings because repeated infections drastically increase treatment costs. Therefore, preventing and treating S. aureus internalization is becoming a research hotspot. S. aureus internalization can essentially be divided into three phases: (1) S. aureus binds to the extracellular matrix (ECM), (2) fibronectin (Fn) receptors mediate S. aureus internalization into cells, and (3) intracellular S. aureus and persistence into cells. Different phases require different treatments. Many studies have reported on different treatments at different phases of bacterial infection. In the first and second phases, the latest research results show that the cell wall-anchored protein vaccine and some microbial agents can inhibit the adhesion of S. aureus to host cells. In the third phase, nanoparticles, photochemical internalization (PCI), cell-penetrating peptides (CPPs), antimicrobial peptides (AMPs), and bacteriophage therapy can effectively eliminate bacteria from cells. In this paper, the recent progress in the infection process and the prevention and treatment of S. aureus internalization is summarized by reviewing a large number of studies.

Photosubstitution in a trisheteroleptic ruthenium complex inhibits conjunctival melanoma growth in a zebrafish orthotopic xenograft model

In vivo data are rare but essential for establishing the clinical potential of ruthenium-based photoactivated chemotherapy (PACT) compounds, a new family of phototherapeutic drugs that are activated via ligand photosubstitution. Here a novel trisheteroleptic ruthenium complex [Ru(dpp)(bpy)(mtmp)](PF₆)₂ ([2](PF₆)₂, dpp = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, mtmp = 2-methylthiomethylpyridine) was synthesized and its light-activated anticancer properties were validated in cancer cell monolayers, 3D tumor spheroids, and in embryonic zebrafish cancer models. Upon green light irradiation, the non-toxic mtmp ligand is selectively cleaved off, thereby releasing a phototoxic ruthenium-based photoproduct capable notably of binding to nuclear DNA and triggering DNA damage and apoptosis within 24–48 h. In vitro, fifteen minutes of green light irradiation (21 mW cm⁻², 19 J cm⁻², 520 nm) were sufficient to generate high phototherapeutic indexes (PI) for this compound in a range of cancer cell lines including lung (A549), prostate (PC3Pro4), conjunctival melanoma (CRMM1, CRMM2, CM2005.1) and uveal melanoma (OMM1, OMM2.5, Mel270) cancer cell lines. The therapeutic potential of [2](PF₆)₂ was further evaluated in zebrafish embryo ectopic (PC3Pro4) or orthotopic (CRMM1, CRMM2) tumour models. The ectopic model consisted of red fluorescent PC3Pro4-mCherry cells injected intravenously (IV) into zebrafish, that formed perivascular metastatic lesions at the posterior ventral end of caudal hematopoietic tissue (CHT). By contrast, in the orthotopic model, CRMM1- and CRMM2-mCherry cells were injected behind the eye where they developed primary lesions. The maximally-tolerated dose (MTD) of [2](PF₆)₂ was first determined for three different modes of compound administration: (i) incubating the fish in prodrug-containing water (WA); (ii) injecting the prodrug intravenously (IV) into the fish; or (iii) injecting the prodrug retro-orbitally (RO) into the fish. To test the anticancer efficiency of [2](PF₆)₂, the embryos were treated 24 h after engraftment at the MTD. Optimally, four consecutive PACT treatments were performed on engrafted embryos using 60 min drug-to-light intervals and 90 min green light irradiation (21 mW cm⁻², 114 J cm⁻², 520 nm). Most importantly, this PACT protocol was not toxic to the zebrafish. In the ectopic prostate tumour models, where [2](PF₆)₂ showed the highest photoindex in vitro (PI > 31), the PACT treatment did not significantly diminish the growth of primary lesions, while in both conjunctival melanoma orthotopic tumour models, where [2](PF₆)₂ showed more modest photoindexes (PI ∼ 9), retro-orbitally administered PACT treatment significantly inhibited growth of the engrafted tumors. Overall, this study represents the first demonstration in zebrafish cancer models of the clinical potential of ruthenium-based PACT, here against conjunctival melanoma.

A new tris-heteroleptic photoactivated chemotherapy ruthenium complex induces apoptosis upon green light activation in a zebrafish orthothopic conjunctival melanoma xenograft model.

Photochemical Internalization as a New Strategy to Enhance Efficacy of Antimicrobial Agents Against Intracellular Infections

Pathogens such as Staphylococcus aureus are able to survive in many types of host cells including phagocytes such as neutrophils and macrophages, thereby resulting in intracellular infections. Treatment of intracellular infections by conventional antimicrobials (e.g., antibiotics) is often ineffective due to low intracellular efficacy of the drugs. Thus, novel techniques which can enhance the activity of antimicrobials within cells are highly demanded. Our recent studies have shown that photochemical internalization (PCI) is a promising approach for improving the efficacy of antibiotics such as gentamicin against intracellular staphylococcal infection. In this chapter, we describe the protocols aiming to study the potential of PCI-antibiotic treatment for intracellular infections in vitro and in vivo using a RAW 264.7 cell infection model and a zebrafish embryo infection model. Proof of concept of this approach is demonstrated. The protocols are expected to prompt further development of PCI-antimicrobial based novel therapies for clinically challenging infectious diseases associated with intracellular survival of pathogens.

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.

Zebrafish: An Attractive Model to Study Staphylococcus aureus Infection and Its Use as a Drug Discovery Tool

Non-mammalian in vivo disease models are particularly popular in early drug discovery. Zebrafish (Danio rerio) is an attractive vertebrate model, the success of which is driven by several advantages, such as the optical transparency of larvae, the small and completely sequenced genome, the small size of embryos and larvae enabling high-throughput screening, and low costs. In this review, we highlight zebrafish models of Staphyloccoccus aureus infection, which are used in drug discovery and for studying disease pathogenesis and virulence. Further, these infection models are discussed in the context of other relevant zebrafish models for pharmacological and toxicological studies as part of early drug profiling. In addition, we examine key differences to commonly applied models of S.aureus infection based on invertebrate organisms, and we compare their frequency of use in academic research covering the period of January 2011 to January 2021.

Triclosan-based supramolecular hydrogels as nanoantibiotics for enhanced antibacterial activity

With the emergence of drug-resistant bacteria, conventional antibiotics are becoming increasingly ineffective for the treatment of bacterial infections. Nanomaterial-modified antibiotics, denoted as "nanoantibiotics", can usually circumvent most of the shortcomings of conventional antibiotics, thus improving antibacterial activities. Here, we developed triclosan-based supramolecular hydrogel nanoantibiotics by conjugating small molecule antibiotic triclosan (TCS) to self-assembling peptides. The resultant nanoantibiotics presented many beneficial characteristics: (i) a stable three-dimensional nanofiber structure; (ii) increased TCS solubility by 850-fold; (iii) acid-responsive TCS release; (iv) favorable biocompatibility. In consequence, the nanoantibiotics showed potent in vitro broad-spectrum antibacterial activities against both Gram-positive and Gram-negative bacteria based on the cooperative effect of antibiotic TCS and the nanostructure-induced bacterial membrane disruption. Furthermore, the TCS-based supramolecular hydrogel nanoantibiotics exhibited enhanced antibacterial activities with low side effects, according to the in vivo antibacterial evaluation at the macro and micro level. Therefore, the simple and effective hydrogel nanoantibiotics developed here hold great potential for the treatment of intractable bacterial infections.

Photochemical Internalization for Intracellular Drug Delivery. From Basic Mechanisms to Clinical Research

Photochemical internalisation (PCI) is a unique intervention which involves the release of endocytosed macromolecules into the cytoplasmic matrix. PCI is based on the use of photosensitizers placed in endocytic vesicles that, following light activation, lead to rupture of the endocytic vesicles and the release of the macromolecules into the cytoplasmic matrix. This technology has been shown to improve the biological activity of a number of macromolecules that do not readily penetrate the plasma membrane, including type I ribosome-inactivating proteins (RIPs), gene-encoding plasmids, adenovirus and oligonucleotides and certain chemotherapeutics, such as bleomycin. This new intervention has also been found appealing for intracellular delivery of drugs incorporated into nanocarriers and for cancer vaccination. PCI is currently being evaluated in clinical trials. Data from the first-in-human phase I clinical trial as well as an update on the development of the PCI technology towards clinical practice is presented here.

Recommendations for design and conduct of preclinical in vivo studies of orthopedic device-related infection

Orthopedic device-related infection (ODRI), including both fracture-related infection (FRI) and periprosthetic joint infection (PJI), remain among the most challenging complications in orthopedic and musculoskeletal trauma surgery. ODRI has been convincingly shown to delay healing, worsen functional outcome and incur significant socio-economic costs. To address this clinical problem, ever more sophisticated technologies targeting the prevention and/or treatment of ODRI are being developed and tested in vitro and in vivo. Among the most commonly described innovations are antimicrobial-coated orthopedic devices, antimicrobial-loaded bone cements and void fillers, and dual osteo-inductive/antimicrobial biomaterials. Unfortunately, translation of these technologies to the clinic has been limited, at least partially due to the challenging and still evolving regulatory environment for antimicrobial drug-device combination products, and a lack of clarity in the burden of proof required in preclinical studies. Preclinical in vivo testing (i.e. animal studies) represents a critical phase of the multidisciplinary effort to design, produce and reliably test both safety and efficacy of any new antimicrobial device. Nonetheless, current in vivo testing protocols, procedures, models, and assessments are highly disparate, irregularly conducted and reported, and without standardization and validation. The purpose of the present opinion piece is to discuss best practices in preclinical in vivo testing of antimicrobial interventions targeting ODRI. By sharing these experience-driven views, we aim to aid others in conducting such studies both for fundamental biomedical research, but also for regulatory and clinical evaluation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:271-287, 2019.