Timur Zhiyentayev

Photodynamic therapy for methicillin-resistant Staphylococcus aureus infection in a mouse skin abrasion model.

Methicillin‐resistant Staphylococcus aureus (MRSA) skin infections are now known to be a common and important problem in the Unites States. The objective of this study was to investigate the efficacy of photodynamic therapy (PDT) for the treatment of MRSA infection in skin abrasion wounds using a mouse model.

Type I and Type II mechanisms of antimicrobial photodynamic therapy: An in vitro study on gram-negative and gram-positive bacteria

Antimicrobial photodynamic therapy (APDT) employs a non‐toxic photosensitizer (PS) and visible light, which in the presence of oxygen produce reactive oxygen species (ROS), such as singlet oxygen (1O2, produced via Type II mechanism) and hydroxyl radical (HO., produced via Type I mechanism). This study examined the relative contributions of 1O2 and HO. to APDT killing of Gram‐positive and Gram‐negative bacteria.

Photodynamic Therapy for Acinetobacter baumannii Burn Infections in Mice

ABSTRACT Multidrug-resistant Acinetobacter baumannii infections represent a growing problem, especially in traumatic wounds and burns suffered by military personnel injured in Middle Eastern conflicts. Effective treatment with traditional antibiotics can be extremely difficult, and new antimicrobial approaches are being investigated. One of these alternatives to antimicrobials could be the combination of nontoxic photosensitizers (PSs) and visible light, known as photodynamic therapy (PDT). We report on the establishment of a new mouse model of full-thickness thermal burns infected with a bioluminescent derivative of a clinical Iraqi isolate of A. baumannii and its PDT treatment by topical application of a PS produced by the covalent conjugation of chlorin(e6) to polyethylenimine, followed by illumination of the burn surface with red light. Application of 108A. baumannii cells to the surface of 10-s burns made on the dorsal surface of shaved female BALB/c mice led to chronic infections that lasted, on average, 22 days and that were characterized by a remarkably stable bacterial bioluminescence. PDT carried out on day 0 soon after application of the bacteria gave over 3 log units of loss of bacterial luminescence in a light exposure-dependent manner, while PDT carried out on day 1 and day 2 gave an approximately 1.7-log reduction. The application of PS dissolved in 10% or 20% dimethyl sulfoxide without light gave only a modest reduction in the bacterial luminescence from mouse burns. Some bacterial regrowth in the treated burn was observed but was generally modest. It was also found that PDT did not lead to the inhibition of wound healing. The data suggest that PDT may be an effective new treatment for multidrug-resistant localized A. baumannii infections.

Innovative cationic fullerenes as broad-spectrum light-activated antimicrobials

UNLABELLED Photodynamic inactivation is a rapidly developing antimicrobial technology that combines a nontoxic photoactivatable dye or photosensitizer in combination with harmless visible light of the correct wavelength to excite the dye to its reactive-triplet state that will then generate reactive oxygen species that are highly toxic to cells. Buckminsterfullerenes are closed-cage molecules entirely composed of sp2-hybridized carbon atoms, and although their main absorption is in the UV, they also absorb visible light and have a long-lived triplet state. When C(60) fullerene is derivatized with cationic functional groups it forms molecules that are more water-soluble and can mediate photodynamic therapy efficiently upon illumination; moreover, cationic fullerenes can selectively bind to microbial cells. In this report we describe the synthesis and characterization of several new cationic fullerenes. Their relative effectiveness as broad-spectrum antimicrobial photosensitizers against gram-positive and gram-negative bacteria, and a fungal yeast was determined by quantitative structure-function relationships. FROM THE CLINICAL EDITOR Photodynamic inactivation (PDI) is a rapidly developing antimicrobial technology in which a non-toxic photoactivatable dye or photosensitizer is excited with harmless visible light to its reactive state, where it will generate highly toxic reactive oxygen species. Buckminsterfullerenes derivatized with cationic functional groups form molecules that are water-soluble and mediate PDI efficiently. These fullerenes can also selectively bind to microbial cells. Several new cationic fullerenes are presented in this paper, and their efficacy against Gram-positive, Gram-negative bacteria, and a fungal yeast is also demonstrated.

Stable Synthetic Cationic Bacteriochlorins as Selective Antimicrobial Photosensitizers

ABSTRACT Photodynamic inactivation is a rapidly developing antimicrobial treatment that employs a nontoxic photoactivatable dye or photosensitizer in combination with harmless visible light to generate reactive oxygen species that are toxic to cells. Tetrapyrroles (e.g., porphyrins, chlorins, bacteriochlorins) are a class of photosensitizers that exhibit promising characteristics to serve as broad-spectrum antimicrobials. In order to bind to and efficiently penetrate into all classes of microbial cells, tetrapyrroles should have structures that contain (i) one or more cationic charge(s) or (ii) a basic group. In this report, we investigate the use of new stable synthetic bacteriochlorins that have a strong absorption band in the range 720 to 740 nm, which is in the near-infrared spectral region. Four bacteriochlorins with 2, 4, or 6 quaternized ammonium groups or 2 basic amine groups were compared for light-mediated killing against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli), and a dimorphic fungal yeast (Candida albicans). Selectivity was assessed by determining phototoxicity against human HeLa cancer cells under the same conditions. All four compounds were highly active (6 logs of killing at 1 μM or less) against S. aureus and showed selectivity for bacteria over human cells. Increasing the cationic charge increased activity against E. coli. Only the compound with basic groups was highly active against C. albicans. Supporting photochemical and theoretical characterization studies indicate that (i) the four bacteriochlorins have comparable photophysical features in homogeneous solution and (ii) the anticipated redox characteristics do not correlate with cell-killing ability. These results support the interpretation that the disparate biological activities observed stem from cellular binding and localization effects rather than intrinsic electronic properties. These findings further establish cationic bacteriochlorins as extremely active and selective near-infrared activated antimicrobial photosensitizers, and the results provide fundamental information on structure-activity relationships for antimicrobial photosensitizers.

Stable synthetic bacteriochlorins overcome the resistance of melanoma to photodynamic therapy

Cutaneous malignant melanoma remains a therapeutic challenge, and patients with advanced disease have limited survival. Photodynamic therapy (PDT) has been successfully used to treat many malignancies, and it may show promise as an antimelanoma modality. However, high melanin levels in melanomas can adversely affect PDT effectiveness. Herein the extent of melanin contribution to melanoma resistance to PDT was investigated in a set of melanoma cell lines that markedly differ in the levels of pigmentation;3 new bacteriochlorins successfully overcame the resistance. Cell killing studies determined that bacteriochlorins are superior at (LD50≈0.1 µM) when compared with controls such as the FDA‐approved Photofrin (LD50≈10 µM) and clinically tested LuTex (LD50≈=1 µM). The melanin content affects PDT effectiveness, but the degree of reduction is significantly lower for bacteriochlorins than for Photofrin. Microscopy reveals that the least effective bacteriochlorin localizes predominantly in lysosomes, while the most effective one preferentially accumulates in mitochondria. Interestingly all bacteriochlorins accumulate in melanosomes, and subsequent illumination leads to melanosomal damage shown by electron microscopy. Fluorescent probes show that the most effective bacteriochlorin produces significantly higher levels of hydroxyl radicals, and this is consistent with the redox properties suggested by molecular‐orbital calculations. The best in vitro performing bacteriochlorin was tested in vivo in a mouse melanoma model using spectrally resolved fluorescence imaging and provided significant survival advantage with 20% of cures (P<0.01).—Mroz, P., Huang, Y.‐Y., Szokalska, A., Zhiyentayev, T., Janjua, S., Nifli, A.‐P., Sherwood, M. E., Ruzié, C., Borbas, K. E., Fan, D., Krayer, M., Balasubramanian, T., Yang, E., Kee, H. L., Kirmaier, C., Diers, J. R., Bocian, D. F., Holten, D., Lindsey, J. S., Hamblin, M. R. Stable synthetic bacteriochlorins overcome the resistance of melanoma to photodynamic therapy. FASEB J. 24, 3160–3170 (2010). www.fasebj.org

In Vitro Photodynamic Therapy and Quantitative Structure–Activity Relationship Studies with Stable Synthetic Near-Infrared-Absorbing Bacteriochlorin Photosensitizers

Photodynamic therapy (PDT) is a rapidly developing approach to treating cancer that combines harmless visible and near-infrared light with a nontoxic photoactivatable dye, which upon encounter with molecular oxygen generates the reactive oxygen species that are toxic to cancer cells. Bacteriochlorins are tetrapyrrole compounds with two reduced pyrrole rings in the macrocycle. These molecules are characterized by strong absorption features from 700 to >800 nm, which enable deep penetration into tissue. This report describes testing of 12 new stable synthetic bacteriochlorins for PDT activity. The 12 compounds possess a variety of peripheral substituents and are very potent in killing cancer cells in vitro after illumination. Quantitative structure-activity relationships were derived, and subcellular localization was determined. The most active compounds have both low dark toxicity and high phototoxicity. This combination together with near-infrared absorption gives these bacteriochlorins great potential as photosensitizers for treatment of cancer.

Antimicrobial Photodynamic Therapy with Functionalized Fullerenes: Quantitative Structure-activity Relationships

Photosensitive dyes or photo sensitizers (PS) in combination with visible light and oxygen produce reactive oxygen species that kill cells in the process known as photodynamic therapy (PDT). Antimicrobial PDT employs PS that is selective for microbial cells and is a new treatment for infections. Most antimicrobial PS is based on tetrapyrrole or phenothiazinium structures that have been synthesized to carry quaternary cationic charges or basic amino groups. However we recently showed that cationic-substituted fullerene derivative were highly effective in killing a broad spectrum of microbial cells after illumination with white light. In the present report we compared a new group of synthetic fullerene derivatives that possessed either basic or quaternary amino groups as antimicrobial PS against Gram-positive (Staphylococcus aureus), Gram-negative bacteria (Escherichia coli) and fungi (Candida albicans). Quantitative structure-function relationships were derived with LogP and hydrophilic lipophilic balance parameters. Compounds with non-quaternary amino groups tended to form nanoaggregates in water and were only effective against S. aureus. The most important determinant of effectiveness was an increased number of quaternary cationic groups that were widely dispersed around the fullerene cage to minimize aggregation. S. aureus was most susceptible; E. coli was intermediate, while C. albicans was the most resistant species tested. The high effectiveness of antimicrobial PDT with quaternized fullerenes suggest they may have applications in treatment of superficial infections (for instance in wounds and burns) where light penetration into tissue is not problematic.

Intraperitoneal photodynamic therapy mediated by a fullerene in a mouse model of abdominal dissemination of colon adenocarcinoma

UNLABELLED Functionalized fullerenes represent a new class of photosensitizer (PS) that is being investigated for photodynamic therapy (PDT) of various diseases, including cancer. We tested the hypothesis that fullerenes could be used to mediate PDT of intraperitoneal (IP) carcinomatosis in a mouse model. In humans this form of cancer responds poorly to standard treatment and manifests as a thin covering of tumor nodules on intestines and on other abdominal organs. We used a colon adenocarcinoma cell line (CT26) stably expressing luciferase to allow monitoring of IP tumor burden in BALB/c mice by noninvasive real-time optical imaging using a sensitive low-light camera. IP injection of a preparation of N-methylpyrrolidinium-fullerene formulated in Cremophor-EL micelles, followed by white-light illumination delivered through the peritoneal wall (after creation of a skin flap), produced a statistically significant reduction in bioluminescence and a survival advantage in mice. FROM THE CLINICAL EDITOR This team of investigators report on functionalized fullerenes, to be used as photosensitizer for photodynamic therapy and demonstrate the efficacy of this method in an intraperitoneal carcinomatosis mouse model.

Photodynamic inactivation of bacteria using polyethylenimine–chlorin(e6) conjugates: Effect of polymer molecular weight, substitution ratio of chlorin(e6) and pH

Antimicrobial photodynamic therapy (APDT) is a novel technique to treat local infections. Previously we reported that the attachment of chlorin(e6) to polyethylenimine (PEI) polymers to form PEI‐ce6 conjugates is an effective way to improve ce6 PDT activity against bacteria. The aim of this work was to explore how the polymer molecular weight, substitution ratio (SR) of ce6 and pH value affect the PDT efficacy.