Photosensitizer-antibiotic conjugates: a novel class of antibacterial molecules

Platelet-mimetic nano-sensor for combating postoperative recurrence and wound infection of triple-negative breast cancer

Tumor recurrence mainly triggered by tumor residual cells significantly contributes to mortality following breast tumor resection, and meanwhile post-surgical bacterial wound infections may accelerate tumor recurrence due to a series of infection-related complications. In this study, a nano-sensor system, Van-ICG@PLT, is constructed by a membrane camouflage and small molecule drug self-assembly strategy. This nano-sensor harnesses the innate tropism of platelets (PLT) to deliver vancomycin (Van) and indocyanine green (ICG) to surgical incisions, effectively eliminating both residual tumor cells and bacterial infections. Our findings demonstrate that Van-ICG@PLT preferentially accumulates at surgical wound. Under near-infrared (NIR) laser irradiation, Van-ICG@PLT exhibits significant cytotoxicity against 4T1 cells. Additionally, it is found to significantly promote ROS production thus inhibiting Staphylococcus aureus (S. aureus) growth, underscoring the synergistic benefits of phototherapy in combination with antibiotic treatment. In the 4T1 post-surgery recurrence mice model, Van-ICG@PLT is shown to efficiently ablate tumors in tumor-bearing mice (tumor inhibition rate of about 83%), and it demonstrates an excellent anti-infective effect in mice abscess models. Taken together, Van-ICG@PLT represents a promising paradigm in post-surgical adjuvant therapy (PAT). Its dual benefit in inhibiting cancer growth and promoting antibacterial activity makes Van-ICG@PLT a valuable addition to the existing arsenal of therapeutic options available for breast cancer patients.

Photosensitizers combination approach to enhance photodynamic inactivation of planktonic and biofilm bacteria

To improve bacterial photodynamic inactivation (PDI), this work analyzes the photodynamic effect caused by the combination of photosensitizers (PSs) on two bacterial models and different growth mode. Simultaneous administration of PSs from different families, zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc4+), 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin (TMAP4+), meso-tetrakis(9-ethyl-9-methyl-3-carbazoyl)chlorin (TEMCC4+) and 5,10,15,20-tetrakis[4-(3-N,N-dimethylaminopropoxy)phenyl] chlorin (TAPC) was investigated against Staphylococcus aureus and Escherichia coli, in planktonic form, biofilm and growth curve. Various PSs combinations showed greater inactivation compared to when used separately under the same conditions but at twice the concentration. However, differences were found in the effectiveness of the PSs combinations on Gram positive and negative bacteria, as well as in planktonic or biofilm form. Likewise, the combination of three PSs completely stopped E. coli growth under optimal nutritional conditions. PSs combination allows extending the range of light absorption by agents that absorb in different areas of the visible spectrum. Therefore, PDI with combined PSs increases its antimicrobial capacity using agents' concentrations and light fluences lower than those necessary to cause the same effect as single PS. These advances represent a starting point for future research on the potentiation of PDI promoted by the combined use of PSs.

Increasing the Selectivity of Light-Active Antimicrobial Agents - Or How To Get a Photosensitizer to the Desired Target

Photosensitizers combine the inherent reactivity of reactive oxygen species with the sophisticated reaction control of light. Through selective targeting, these light-active molecules have the potential to overcome certain limitations in drug discovery. Ongoing advances in the synthesis and evaluation of photosensitizer conjugates with biomolecules such as antibodies, peptides, or small-molecule drugs are leading to increasingly powerful agents for the eradication of a growing number of microbial species. This review article, therefore, summarizes challenges and opportunities in the development of selective photosensitizers and their conjugates described in recent literature. This provides adequate insight for newcomers and those interested in this field.

Breaking the Rebellion: Photodynamic Inactivation against Erwinia amylovora Resistant to Streptomycin

Global crop production depends on strategies to counteract the ever-increasing spread of plant pathogens. Antibiotics are often used for large-scale treatments. As a result, Erwinia amylovora, causal agent of the contagious fire blight disease, has already evolved resistance to streptomycin (Sm). Photodynamic Inactivation (PDI) of microorganisms has been introduced as innovative method for plant protection. The aim of this study is to demonstrate that E. amylovora resistant to Sm (E. amylovora^SmR) can be killed by PDI. Two photosensitizers, the synthetic B17-0024, and the natural derived anionic sodium magnesium chlorophyllin (Chl) with cell-wall-permeabilizing agents are compared in terms of their photo-killing efficiency in liquid culture with or without 100 µg/mL Sm. In vitro experiments were performed at photosensitizer concentrations of 1, 10 or 100 µM and 5 or 30 min incubation in the dark, followed by illumination at 395 nm (radiant exposure 26.6 J/cm²). The highest inactivation of seven log steps was achieved at 100 µM B17-0024 after 30 min incubation. Shorter incubation (5 min), likely to represent field conditions, reduced the photo-killing to 5 log steps. Chlorophyllin at 100 µM in combination with 1.2% polyaspartic acid (PASA) reduced the number of bacteria by 6 log steps. While PASA itself caused some light independent toxicity, an antibacterial effect (3 log reduction) was achieved only in combination with Chl, even at concentrations as low as 10 µM. Addition of 100 µg/mL Sm to media did not significantly increase the efficacy of the photodynamic treatment. This study proves principle that PDI can be used to treat plant diseases even if causative bacteria are resistant to conventional treatment. Therefore, PDI based on natural photosensitizers might represent an eco-friendly treatment strategy especially in organic farming.

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.

Photodynamic and antibiotic therapy in combination against bacterial infections: efficacy, determinants, mechanisms, and future perspectives

Antibiotic treatment, the mainstay for the control of bacterial infections, is greatly hampered by the global prevalence of multidrug-resistant (MDR) bacteria. Photodynamic therapy (PDT) is effective against MDR infections, but PDT-induced bacterial inactivation is often incomplete, causing the relapse of infections. Combination of PDT and antibiotics is a promising strategy to overcome the limitation of both antibiotic treatment and PDT, exerting increased disinfection efficacy on MDR bacterial pathogens versus either of the monotherapies alone. In this review, we present an overview of the therapeutic effects of PDT/antibiotic combinations that have been developed. We further summarize the influencing factors and the governing molecular mechanisms of the therapeutic outcomes of PDT/antibiotic combinations. In the end, we provide concluding remarks on the strengths, limitations, and future research directions of PDT/antibiotic combination therapy to guide its appropriate usage and further development.

A porphycene-gentamicin conjugate for enhanced photodynamic inactivation of bacteria

A novel photoantimicrobial agent, namely 2-aminothiazolo[4,5-c]-2,7,12,17-tetrakis(methoxyethyl)porphycene (ATAZTMPo-gentamicin) conjugate, has been prepared by a click reaction between the red-light absorbing 9-isothiocyanate-2,7,12,17-tetrakis(methoxyethyl)porphycene (9-ITMPo) and the antibiotic gentamicin. The conjugate exhibits submicromolar activity in vitro against both Gram-positive and Gram-negative bacteria (Staphylococcus aureus and Escherichia coli, respectively) upon exposure to red light and is devoid of any cytotoxicity in the dark. The conjugate outperforms the two components delivered separately, which may be used to enhance the therapeutic index of gentamicin, broaden the spectrum of pathogens against which it is effective and reduce its side effects. Additionally, we report a novel straightforward synthesis of 2,7,12,17-tetrakis(methoxyethyl) porphycene (TMPo) that decreases the number of steps from nine to six.

Polymyxin-based photosensitizer for the potent and selective killing of Gram-negative bacteria

The methylene blue-polymyxin conjugate demonstrated high selectivity, sensitivity and phototoxicity against Gram-negative bacteria, including in early biofilm models.

Effect of Photodynamic Antibacterial Chemotherapy Combined with Antibiotics on Gram-Positive and Gram-Negative Bacteria

The well-known and rapidly growing phenomenon of bacterial resistance to antibiotics is caused by uncontrolled, excessive and inappropriate use of antibiotics. One of alternatives to antibiotics is Photodynamic Antibacterial Chemotherapy (PACT). In the present study, the effect of PACT using a photosensitizer Rose Bengal alone and in combination with antibiotics including methicillin and derivatives of sulfanilamide synthesized by us was tested against antibiotic-sensitive and antibiotic-resistant clinical isolates of Gram-positive S. aureus and Gram-negative P. aeruginosa. Antibiotic-sensitive and resistant strains of P. aeruginosa were eradicated by Rose Bengal under illumination and by sulfanilamide but were not inhibited by new sulfanilamide derivatives. No increase in sensitivity of P. aeruginosa cells to sulfanilamide was observed upon a combination of Rose Bengal and sulfanilamide under illumination. All tested S. aureus strains (MSSA and MRSA) were effectively inhibited by PACT. When treated with sub-MIC concentrations of Rose Bengal under illumination, the minimum inhibitory concentrations (MIC) of methicillin decreased significantly for MSSA and MRSA strains. In some cases, antibiotic sensitivity of resistant strains can be restored by combining antibiotics with PACT.

Combined Antimicrobial Activity of Photodynamic Inactivation and Antimicrobials-State of the Art

Antimicrobial photodynamic inactivation (aPDI) is a promising tool for the eradication of life-threatening pathogens with different profiles of resistance. This study presents the state-of-the-art published studies that have been dedicated to analyzing the bactericidal effects of combining aPDI and routinely applied antibiotics in in vitro (using biofilm and planktonic cultures) and in vivo experiments. Furthermore, the current paper reviews the methodology used to obtain the published data that describes the synergy between these antimicrobial approaches. The authors are convinced that even though the combined efficacy of aPDI and antimicrobials could be investigated with the wide range of methods, the use of a unified experimental methodology that is in agreement with antimicrobial susceptibility testing (AST) is required to investigate possible synergistic cooperation between aPDI and antimicrobials. Conclusions concerning the possible synergistic activity between the two treatments can be drawn only when appropriate assays are employed. It must be noticed that some of the described papers were just aimed at determination if combined treatments exert enhanced antibacterial outcome, without following the standard methodology to evaluate the synergistic effect, but in most of them (18 out of 27) authors indicated the existence of synergy between described antibacterial approaches. In general, the increase in bacterial inactivation was observed when both therapies were used in combination.

Photodynamic Inactivation Potentiates the Susceptibility of Antifungal Agents against the Planktonic and Biofilm Cells of Candida albicans

Photodynamic inactivation (PDI) has been shown to be a potential treatment modality against Candida infection. However, limited light penetration might leave some cells alive and undergoing regrowth. In this study, we explored the possibility of combining PDI and antifungal agents to enhance the therapeutic efficacy of Candida albicans and drug-resistant clinical isolates. We found that planktonic cells that had survived toluidine blue O (TBO)-mediated PDI were significantly susceptible to fluconazole within the first 2 h post PDI. Following PDI, the killing efficacy of antifungal agents relates to the PDI dose in wild-type and drug-resistant clinical isolates. However, only a 3-log reduction was found in the biofilm cells, suggesting limited therapeutic efficacy under the combined treatment of PDI and azole antifungal drugs. Using confocal microscopic analysis, we showed that TBO-mediated PDI could partially remove the extracellular polymeric substance (EPS) of biofilm. Finally, we showed that a combination of PDI with caspofungin could result in the complete killing of biofilms compared to those treated with caspofungin or PDI alone. These results clearly indicate that the combination of PDI and antifungal agents could be a promising treatment against C. albicans infections.

Evaluation of photodynamic therapy effect along with colistin on pandrug-resistant Acinetobacter baumannii

BACKGROUND AND AIMS

Pandrug-resistant Acinetobacter baumannii (PDRAB) are including colistin resistant starins (CoRAB) which cause infections potentially untreatable infections. Recently, incidence of these strains are increasing worldwide. Therefore, new approaches, methods and strategies are urgently needed for treatment and eradication of infections due to PDRAB. So the aim of this study was to evaluate the efficacy of photodynamic therapy (PDT) in combination treatment with colistin against PDRAB.

MATERIALS AND METHODS

PDRAB which was isolated from burn patients was used as a test strain. PDT carried out in which toluidine blue O (TBO) and light-emitting diode (LED) were used as photosensitizer and radiation source, respectively. Then, the effect of PDT plus colistin was evaluated on CoRAB and the colony-forming units of each tested groups calculated. Finally, confirmation of antibacterial activity of combination therapy was carried out using scanning electron microscope.

RESULTS

PDT declined bacterial count in comparing with control group by 83.7% of killing percentage, in other words, less than one log reduction. While PDT in combination with colistin showed high synergetic effect against A. baumannii in all concentrations of colistin tested by 100% of killing percentage with 9-log reduction.

CONCLUSIONS

According to our results, PDT alone couldn't eliminate all of the treated bacterial cells. But when combined with colistin, it killed all of the treated bacterial cells in all tested concentrations. Also PDT decreased the minimal inhibitory concentration of colistin against PDRAB by more than 11 fold.

Photodynamic and Antibiotic Therapy in Combination to Fight Biofilms and Resistant Surface Bacterial Infections

Although photodynamic therapy (PDT), a therapeutic approach that involves a photosensitizer, light and O₂, has been principally considered for the treatment of specific types of cancers, other applications exist, including the treatment of infections. Unfortunately, PDT does not always guarantee full success since it exerts lethal effects only in cells that have taken up a sufficient amount of photosensitizer and have been exposed to adequate light doses, conditions that are not always achieved. Based on our previous experience on the combination PDT/chemotherapy, we have explored the possibility of fighting bacteria that commonly crowd infected surfaces by combining PDT with an antibiotic, which normally does not harm the strain at low concentrations. To this purpose, we employed 5-aminolevulinic acid (5-ALA), a pro-drug that, once absorbed by proliferating bacteria, is converted into the natural photosensitizer Protoporphyrin IX (PpIX), followed by Gentamicin. Photoactivation generates reactive oxygen species (ROS) which damage or kill the cell, while Gentamicin, even at low doses, ends the work. Our experiments, in combination, have been highly successful against biofilms produced by several Gram positive bacteria (i.e., Staphylococcus aureus, Staphylococcus epidermidis, etc.). This original approach points to potentially new and wide applications in the therapy of infections of superficial wounds and sores.

Photosensitization reactions in vitro and in vivo

This review of Photochemistry and Photobiology summarizes articles published in 2010, and highlights progress in the area of photosensitization. The synthesis of conjugated photosensitizers is an area of interest where increasing water solubility has been a goal. Targeting infrared sensitizer absorption has been another goal, and relates to the practical need of deep tissue absorption of light. Photodynamic techniques for inactivating microbes and destroying tumors have been particularly successful. Biologically, singlet oxygen [(1)O(2)((1)Δ(g))] is an integral species in many of these reactions, although photosensitized oxidations tuned to electron and hydrogen transfer (Type I) give rise to other reactive species, such as superoxide and hydrogen peroxide. How photoprotection against yellowing, oxygenation and degradation occurs was also an area of topical interest.