Experimental tests of the feasibility of singlet oxygen luminescence monitoring in vivo during photodynamic therapy

Singlet oxygen lifetime changes in dying glioblastoma cells

Time-resolved phosphorescence detection was employed to determine the lifetime of singlet oxygen in live cells. Using hypericin as a photosensitizer, singlet oxygen was generated in U87MG glioblastoma cells. The phosphorescence of singlet oxygen was detected in aqueous cell suspensions following pulsed laser excitation. Our goal was to eliminate or reduce the problems associated with lifetime measurements in water-based cell suspensions. The apparatus enabled simultaneous singlet oxygen phosphorescence and transient absorption measurements, reducing uncertainty in lifetime estimation. The changes in singlet oxygen lifetime were observed during early and late apoptosis induced by photodynamic action. Our findings show that the effective lifetime of singlet oxygen in the intracellular space of the studied glioblastoma cells is 0.4 μs and increases to 1.5 μs as apoptosis progresses. Another group of hypericin, presumably located in the membrane blebs and the plasma membrane of apoptotic cells, generates singlet oxygen with a lifetime of 1.9 μs.

Singlet Molecular Oxygen: from COIL Lasers to Photodynamic Cancer Therapy

Translation of experimental techniques from one scientific discipline to another is often difficult but rewarding. Knowledge gained from the new area can lead to long lasting and fruitful collaborations with concomitant development of new ideas and studies. In this Review Article, we describe how early work on the chemically pumped atomic iodine laser (COIL) led to the development of a key diagnostic for a promising cancer treatment known as photodynamic therapy (PDT). The highly metastable excited state of molecular oxygen, a1Δg, also known as singlet oxygen, is the link between these disparate fields. It powers the COIL laser and is the active species that kills cancer cells during PDT. We describe the fundamentals of both COIL and PDT and trace the development path of an ultrasensitive dosimeter for singlet oxygen. The path from COIL lasers to cancer research was relatively long and required medical and engineering expertise from numerous collaborations. As we show below, the knowledge gained in the COIL research, combined with these extensive collaborations, has resulted in our being able to show a strong correlation between cancer cell death and the singlet oxygen measured during PDT treatments of mice. This progress is a key step in the eventual development of a singlet oxygen dosimeter that could be used to guide PDT treatments and improve outcomes.

A portable NIR fluorimeter directly quantifies singlet oxygen generated by nanostructures for Photodynamic Therapy

This paper reports on the setting up and calibration of a portable NIR fluorimeter specifically developed for quantitative direct detection of the highly reactive singlet oxygen (¹O₂) chemical specie, of great importance in Photodynamic therapies. This quantification relies on the measurement of fluorescence emission of ¹O₂, which is peaked in the near-infrared (NIR) at λ=1270nm. In recent years, several nanostructures capable of generating reactive oxygen species (ROS) when activated by penetrating radiation (X-rays, NIR light) have been developed to apply Photodynamic Therapy (PDT) to tumours in deep tissue, where visible light cannot penetrate. A bottleneck in the characterization of these nanostructures is the lack of a fast and reliable technique to quantitatively assess their performances in generating ROS, and in particular ¹O₂. For instance, the widely used PDT "Singlet Oxygen Sensor Green" kit suffers from self-activation under X-ray irradiation. To solve this difficulty, we propose here direct detection of ¹O₂ by spectroscopic means, using an apparatus developed by us around a recent thermoelectrically-cooled InGaAs single photon avalanche photodiode (SPAD). The SPAD is coupled to a custom-made integrating sphere designed for use under irradiation with high-energy X-ray beams from clinical Radiotherapy sources. We determine the detection threshold for our apparatus, which turns to be ∼9·10⁸¹O₂ in realistic experimental condition and for measurements extending to 1 min of integration. After calibrations on standard photosensitizers, we demonstrate the potentiality of this instrument characterizing some photosensitizing nanostructures developed by us.

Detection of singlet oxygen luminescence for experimental corneal rose bengal photodynamic antimicrobial therapy

Rose bengal photodynamic antimicrobial therapy (RB-PDAT) treats corneal infection by activating rose bengal (RB) with green light to produce singlet oxygen (¹O₂). Singlet oxygen dosimetry can help optimize treatment parameters. We present a ¹O₂ dosimeter for detection of ¹O₂ generated during experimental RB-PDAT. The system uses a 520 nm laser and an InGaAs photoreceiver with bandpass filters to detect ¹O₂ luminescence during irradiation. The system was validated in RB solutions and ex vivo in human donor eyes. The results demonstrate the feasibility of ¹O₂ dosimetry in an experimental model of RB-PDAT in the cornea.

Investigation of copper-cysteamine nanoparticles as a new photosensitizer for anti-hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a primary malignancy of the liver and occurs predominantly in patients with underlying chronic liver disease and cirrhosis. HCC is now the third leading cause of cancer deaths worldwide, with over 500,000 people affected. However, there is no complete effective (ideal) treatment for liver cancer yet, and the new methods are expected to be discovered. Herein, for the first time, we report the anti-HCC effects of copper-cysteamine nanoparticles (Cu-Cy NPs), a new type of photosensitizers. An in vitro 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay shows that Cu-Cy NPs could significantly reduce the activity of HepG2 cells at a very low dose after a short time of ultraviolet radiation. In addition, we found that cell death was induced by Cu-Cy NPs, which is associated with cellular apoptosis. This implied that apoptosis might be the main mechanism of the Cu-Cy's anti-HCC activity. Furthermore, we found that Cu-Cy NPs obviously inhibited the tumor growth in vivo. More interestingly, we found that the soluble Cu-Cy NPs were able to enter exosomes which were secreted by tumor cells, and exosomes could be used to deliver Cu-Cy NPs to target tumor cells. All these observations suggest that Cu-Cy NPs have a good potential for cancer treatment.

Measurement of Cyanine Dye Photobleaching in Photosensitizer Cyanine Dye Conjugates Could Help in Optimizing Light Dosimetry for Improved Photodynamic Therapy of Cancer

Photodynamic therapy (PDT) of cancer is dependent on three primary components: photosensitizer (PS), light and oxygen. Because these components are interdependent and vary during the dynamic process of PDT, assessing PDT efficacy may not be trivial. Therefore, it has become necessary to develop pre-treatment planning, on-line monitoring and dosimetry strategies during PDT, which become more critical for two or more chromophore systems, for example, PS-CD (Photosensitizer-Cyanine dye) conjugates developed in our laboratory for fluorescence-imaging and PDT of cancer. In this study, we observed a significant impact of variable light dosimetry; (i) high light fluence and fluence rate (light dose: 135 J/cm², fluence rate: 75 mW/cm²) and (ii) low light fluence and fluence rate (128 J/cm² and 14 mW/cm² and 128 J/cm² and 7 mW/cm²) in photobleaching of the individual chromophores of PS-CD conjugates and their long-term tumor response. The fluorescence at the near-infrared (NIR) region of the PS-NIR fluorophore conjugate was assessed intermittently via fluorescence imaging. The loss of fluorescence, photobleaching, caused by singlet oxygen from the PS was mapped continuously during PDT. The tumor responses (BALB/c mice bearing Colon26 tumors) were assessed after PDT by measuring tumor sizes daily. Our results showed distinctive photobleaching kinetics rates between the PS and CD. Interestingly, compared to higher light fluence, the tumors exposed at low light fluence showed reduced photobleaching and enhanced long-term PDT efficacy. The presence of NIR fluorophore in PS-CD conjugates provides an opportunity of fluorescence imaging and monitoring the photobleaching rate of the CD moiety for large and deeply seated tumors and assessing PDT tumor response in real-time.

Photophysicochemical behaviour and antimicrobial properties of monocarboxy Mg (II) and Al (III) phthalocyanine-magnetite conjugates

Asymmetric Mg (II) or Al (III) phthalocyanine (containing a COOH group and 3-pyridylsulfanyl units) was conjugated via an amide bond to amino functionalized magnetic nanoparticle (AIMN) to form MgPc-AIMN or AlPc-AIMN conjugate, and characterized. The photophysicochemical behaviour of the phthalocyanine-AIMN conjugates was investigated and compared to the asymmetric Pcs and to the simple mixture of Pc with AIMNs without a chemical bond, (MPc-AIMN (mixed)). The directed covalent linkage of AIMNs to the asymmetrical metallopthalocyanines afforded improvements in the singlet oxygen (Ф_Δ) and triplet state quantum yield (Ф_T) as well as singlet oxygen lifetimes for the MPcs-AIMN-linked conjugates compared to MPc-AIMN (mixed) and MPcs alone. The asymmetric phthalocyanines and their conjugates showed effective antimicrobial activity against Escherichia coli bacteria under illumination.

Photodynamic Therapy

Photodynamic therapy is a clinical technique for the treatment of cancers, microbial infections and other medical conditions by means of light-induced generation of reactive oxygen species using photosensitising drugs. The intrinsic fluorescence of many such drugs make them potential theranostic agents for simultaneous diagnosis and therapy. This chapter reviews the basic chemical and biological aspects of photodynamic therapy with an emphasis on its applications in theranostics. The roles of nanotechnology is highlighted, as well as emerging trends such as photoimmunotherapy, image-guided surgery and light- and singlet-oxygen dosimetry.

Photodynamic inactivation of Escherichia coli - Correlation of singlet oxygen kinetics and phototoxicity

Photodynamic inactivation (PDI) of bacteria may play a major role in facing the challenge of the ever expanding antibiotic resistances. Here we report about the direct correlation of singlet oxygen luminescence kinetics and phototoxicity in E. coli cell suspension under PDI using the widely applied cationic photosensitizer TMPyP. Through direct access to the microenvironment, the time resolved investigation of singlet oxygen luminescence plays a key role in understanding the photosensitization mechanism and inactivation pathway. Using the homemade set-up for highly sensitive time resolved singlet oxygen luminescence detection, we show that the cationic TMPyP is localized predominantly outside the bacterial cells but in their immediate vicinity prior to photodynamic inactivation. Throughout following light exposure, a clear change in singlet oxygen kinetics indicates a redistribution of photosensitizer molecules to at least one additional microenvironment. We found the signal kinetics mirrored in cell viability measurements of equally treated samples from same overnight cultures conducted in parallel: A significant drop in cell viability of the illuminated samples and stationary viability of dark controls. Thus, for the system investigated in this work - a Gram-negative model bacteria and a well-known PS for its PDI - singlet oxygen kinetics correlates with phototoxicity. This finding suggests that it is well possible to evaluate PDI efficiency directly via time resolved singlet oxygen detection.

On the in vivo photochemical rate parameters for PDT reactive oxygen species modeling

Photosensitizer photochemical parameters are crucial data in accurate dosimetry for photodynamic therapy (PDT) based on photochemical modeling. Progress has been made in the last few decades in determining the photochemical properties of commonly used photosensitizers (PS), but mostly in solution or in vitro. Recent developments allow for the estimation of some of these photochemical parameters in vivo. This review will cover the currently available in vivo photochemical properties of photosensitizers as well as the techniques for measuring those parameters. Furthermore, photochemical parameters that are independent of environmental factors or are universal for different photosensitizers will be examined. Most photosensitizers discussed in this review are of the type II (singlet oxygen) photooxidation category, although type I photosensitizers that involve other reactive oxygen species (ROS) will be discussed as well. The compilation of these parameters will be essential for ROS modeling of PDT.

Photophysical behavior and photodynamic therapy activity of conjugates of zinc monocarboxyphenoxy phthalocyanine with human serum albumin and chitosan

Zinc monocarboxyphenoxy phthalocyanine (ZnMCPPc) was linked to human serum albumin (HSA) and chitosan via amide bond formation. The photophysical behavior and photodynamic therapy (PDT) activity (against human breast adenocarcinoma cell line (MCF-7 cells) of ZnMCPPc alone and its conjugates were investigated. The conjugates showed improved fluorescence, triplet and singlet oxygen quantum yields when compared to ZnMCPPc alone. The in vitro dark cytotoxicity and PDT studies were carried out at a dose of 3.6μg/mL to 57.1μg/mL. The in vitro dark cytotoxicity studies of ZnMCPPc showed cell viability <50% at 28.6μg/mL and 57.1μg/mL, while the conjugates showed > 50% in all their tested concentrations (3.6 to 57.1) μg/mL. Thus, conjugation of ZnMCPPc to HSA and chitosan improves its dark cytotoxicity, an important criteria for molecules meant for photodynamic therapy. Complex 1 showed the most efficacious PDT activity with cell viability <50% at concentration range of (14.3 to 57.1) μg/mL in comparison to the conjugates which only showed <50% cell viability at 28.6μg/mL and 57.1μg/mL for 1-HSA and 57.1μg/mL for 1-Chitosan.

A compact fiber-optic probe-based singlet oxygen luminescence detection system

This paper presents a novel compact fiberoptic based singlet oxygen near-infrared luminescence probe coupled to an InGaAs/InP single photon avalanche diode (SPAD) detector. Patterned time gating of the single-photon detector is used to limit unwanted dark counts and eliminate the strong photosensitizer luminescence background. Singlet oxygen luminescence detection at 1270 nm is confirmed through spectral filtering and lifetime fitting for Rose Bengal in water, and Photofrin in methanol as model photosensitizers. The overall performance, measured by the signal-to-noise ratio, improves by a factor of 50 over a previous system that used a fiberoptic-coupled superconducting nanowire single-photon detector. The effect of adding light scattering to the photosensitizer is also examined as a first step towards applications in tissue in vivo.

Photophysical properties of tetraphenylporphyrinsubphthalocyanine conjugates

Novel tetraphenylporphyrin-subphthalocyanine conjugates have been prepared and characterized. An analysis of their optical spectroscopy and electronic structures using fluorescence emission and magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations, demonstrates that the two chromophores do not interact to any significant extent.

Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success

Photodynamic therapy (PDT) can be a highly complex treatment, with many parameters influencing treatment efficacy. The extent to which dosimetry is used to monitor and standardize treatment delivery varies widely, ranging from measurement of a single surrogate marker to comprehensive approaches that aim to measure or estimate as many relevant parameters as possible. Today, most clinical PDT treatments are still administered with little more than application of a prescribed drug dose and timed light delivery, and thus the role of patient-specific dosimetry has not reached widespread clinical adoption. This disconnect is at least partly due to the inherent conflict between the need to measure and understand multiple parameters in vivo in order to optimize treatment, and the need for expedience in the clinic and in the regulatory and commercialization process. Thus, a methodical approach to selecting primary dosimetry metrics is required at each stage of translation of a treatment procedure, moving from complex measurements to understand PDT mechanisms in pre-clinical and early phase I trials, towards the identification and application of essential dose-limiting and/or surrogate measurements in phase II/III trials. If successful, identifying the essential and/or reliable surrogate dosimetry measurements should help facilitate increased adoption of clinical PDT. In this paper, examples of essential dosimetry points and surrogate dosimetry tools that may be implemented in phase II/III trials are discussed. For example, the treatment efficacy as limited by light penetration in interstitial PDT may be predicted by the amount of contrast uptake in CT, and so this could be utilized as a surrogate dosimetry measurement to prescribe light doses based upon pre-treatment contrast. Success of clinical ALA-based skin lesion treatment is predicted almost uniquely by the explicit or implicit measurements of photosensitizer and photobleaching, yet the individualization of treatment based upon each patients measured bleaching needs to be attempted. In the case of ALA, lack of PpIX is more likely an indicator that alternative PpIX production methods must be implemented. Parsimonious dosimetry, using surrogate measurements that are clinically acceptable, might strategically help to advance PDT in a medical world that is increasingly cost and time sensitive. Careful attention to methodologies that can identify and advance the most critical dosimetric measurements, either direct or surrogate, are needed to ensure successful incorporation of PDT into niche clinical procedures.

A feasibility study of singlet oxygen explicit dosmietry (SOED) of PDT by intercomparison with a singlet oxygen luminescence dosimetry (SOLD) system

An explicit dosimetry model has been developed to calculate the apparent reacted 1O2 concentration ([1O2]rx) in an in-vivo model. In the model, a macroscopic quantity, g, is introduced to account for oxygen perfusion to the medium during PDT. In this study, the SOED model is extended for PDT treatment in phantom conditions where vasculature is not present; the oxygen perfusion is achieved through the air-phantom interface instead. The solution of the SOED model is obtained by solving the coupled photochemical rate equations incorporating oxygen perfusion through the air-liquid interface. Experiments were performed for two photosensitizers (PS), Rose Bengal (RB) and Photofrin (PH), in solution, using SOED and SOLD measurements to determine both the instantaneous [1O2] as well as cumulative [1O2]rx concentrations, where [1O2] rx = (1/τΔ) · ∫[1O2]dt. The PS concentrations varied between 10 and 100 mM for RB and ~200 mM for Photofrin. The resulting magnitudes of [1O2] were compared between SOED and SOLD.

Photodynamic antimicrobial chemotherapy activity of (5,10,15,20-tetrakis(4-(4-carboxyphenycarbonoimidoyl)phenyl)porphyrinato) chloro gallium(III)

(5,10,15,20-Tetrakis(4-(4-carboxyphenycarbonoimidoyl)phenyl)porphyrinato) chloro gallium(III) (complex 1) was conjugated to platinum nanoparticles (PtNPs) (represented as 1-PtNPs). The resulting conjugate showed 18 nm red shift in the Soret band when compared to 1 alone. Complex 1 and 1-PtNPs showed promising photodynamic antimicrobial chemotherapy (PACT) activity against Staphylococcus aureus, Escherichia coli and Candida albicans in solution where the log reductions obtained were 4.92, 3.76, and 3.95, respectively for 1-PtNPs. The singlet oxygen quantum yields obtained were higher at 0.56 for 1-PtNPs in DMF while that of 1 was 0.52 in the same solvent. This resulted in improved PACT activity for 1-PtNPs compared to 1 alone.

Reactive oxygen species: Reactions and detection from photosynthetic tissues

Reactive oxygen species (ROS) have long been recognized as compounds with dual roles. They cause cellular damage by reacting with biomolecules but they also function as agents of cellular signaling. Several different oxygen-containing compounds are classified as ROS because they react, at least with certain partners, more rapidly than ground-state molecular oxygen or because they are known to have biological effects. The present review describes the typical reactions of the most important ROS. The reactions are the basis for both the detection methods and for prediction of reactions between ROS and biomolecules. Chemical and physical methods used for detection, visualization and quantification of ROS from plants, algae and cyanobacteria will be reviewed. The main focus will be on photosynthetic tissues, and limitations of the methods will be discussed.

The effect of ascorbic acid on the photophysical properties and photodynamic therapy activities of zinc phthalocyanine-single walled carbon nanotube conjugate on MCF-7 cancer cells

Zinc mono carboxy phenoxy phthalocyanine (1) was chemical modified with ascorbic acid via an ester bond to give ZnMCPPc-AA (2). Complexes 2 and 1 were coordinated to single walled carbon nanotubes via π-π interaction to give ZnMCPPc-AA-SWCNT (3) and ZnMCPPc-SWCNT (4) respectively. Complexes 2, 3 and 4 showed better photophysical properties: with improved triplet lifetimes and quantum yields, and singlet oxygen quantum yields when compared to 1 alone. The photodynamic therapy activities of complexes 1, 2, 3 and 4 were tested in vitro on MCF-7 breast cancer cells. Ascorbic acid suppresses the photodynamic therapy effect of 1, due to its ability to reduce oxidative DNA damage as a result of its potent reducing properties. The highest phototoxicity was observed for 4 which resulted in 77% decrease in cell viability, followed by 3 which resulted in 67% decrease in cell viability. This shows the importance of combination therapy, where the phthalocyanines are the photodynamic therapy agents and single walled carbon nanotubes are the photothermal therapy agents.

Photophysical properties of zinc phthalocyanine-uridine single walled carbon nanotube--conjugates

The photophysical properties of the conjugate of uridine and zinc mono carboxy phenoxy phthalocyanine (ZnMCPPc-uridine, 4) are reported in this work. The conjugate was also adsorbed onto single walled carbon nanotubes (ZnMCPPc-uridine-SWCNT, 5). The X-ray photoelectron spectroscopy of 4 showed three N 1s peaks while that of 5 showed four N 1s peak, a new peak at 399.4 eV of 5 was assigned to pyrrolidonic nitrogen, due to the interaction of the pyrrolic nitrogen of 4 with the oxygen moiety of SWCNT-COOH in 5. The triplet lifetime, triplet and singlet oxygen quantum yields of the zinc mono carboxy phenoxy phthalocyanine increased by over 40% in the presence of uridine. SWCNTs resulted in only a small quenching of the triplet state parameters of 4.

Photophysical studies of newly derivatized mono substituted phthalocyanines grafted onto silica nanoparticles via click chemistry

This work reports on the synthesis, characterization and photophysical studies of newly derived phthalocyanine complexes and the phthalocyanine-silica nanoparticles conjugates. The derived phthalocyanine complexes have one terminal alkyne group. The derived phthalocyanine complexes showed improved photophysical properties (ФF, ФT, ΦΔ and τT) compared to the respective phthalocyanine complexes from which they were derived. The derived phthalocyanine complexes were conjugated to the surface of an azide functionalized silica nanoparticles via copper (1) catalyzed cyclo-addition reaction. All the conjugates showed lower triplet quantum yields ranging from 0.37 to 0.44 compared to the free phthalocyanine complexes. The triplet lifetimes ranged from 352 to 484 μs for the conjugates and from 341 to 366 μs for the free phthalocyanine complexes.

A comparative photophysicochemical study of mono substituted phthalocyanines grafted onto silica nanoparticles

In this study, we report on the covalent linking of carboxylic acid functionalized silica nanoparticles with zinc phthalocyanine mono-substituted non-peripherally and peripherally with either a 4-amino phenoxy (1, peripheral and 2, non-peripheral) or an amino group (3 peripheral). The grafting is achieved via the formation of an amide bond between the carboxylic acid of the silica nanoparticles and the amino group of the phthalocyanine complexes. The hybrid nanoparticles retained the amorphous nature of silica nanoparticles after conjugation. A slight decrease in fluorescence and a general improvement in triplet quantum yields compared to free Pcs were observed. Triplet lifetimes for 2- SiNPs and 3- SiNPs also improved when compared to the free phthalocyanine. The changes in singlet oxygen quantum yields upon conjugation were minimal.

Photophysicochemical behavior and antimicrobial activity of dihydroxosilicon tris(diaquaplatinum)octacarboxyphthalocyanine

Platination of dihydroxosilicon octacarboxyphthalocyanine (OH)2SiOCPc was successfully carried out to give dihydroxosilicon tris(diaquaplatinum)octacarboxyphthalocyanine (OH)2SiOCPc(Pt)3 conjugate. Slight blue shifting of the absorption spectrum of (OH)2SiOCPc(Pt)3 was observed on conjugation with platinum. Comparative photophysicochemical behavior and antimicrobial photo-activities of (OH)2SiOCPc(Pt)3 conjugate with (OH)2SiOCPc or Pt nanoparticles revealed that the heavy atom, Pt on the periphery of the phthalocyanine significantly enhanced its singlet oxygen generation with a quantum yield of 0.56 obtained for the (OH)2SiOCPc(Pt)3 conjugate. The (OH)2SiOCPc(Pt)3 conjugate showed highest antimicrobial activity towards Candida albicans and Escherichia coli compared to (OH)2SiOCPc and Pt nanoparticles alone under illumination.

Effect of bovine serum albumin and single walled carbon nanotube on the photophysical properties of zinc octacarboxy phthalocyanine

This work reports on the photophysical parameters of the conjugate between zinc octacarboxy phthalocyanine (ZnOCPc) and bovine serum albumin (BSA) represented as ZnOCPc-BSA (1) which was further adsorbed onto single walled carbon nanotubes (SWCNT) represented as (ZnOCPc-BSA-SWCNT 2). ZnOCPc (without BSA) was also adsorbed on SWCNT represented as ZnOCPc-SWCNT (3). The presence of BSA resulted in the increase in singlet oxygen quantum yield (ΦΔ) for 1 (at ΦΔ=0.44) and 2 (at ΦΔ=0.41) compared to ΦΔ=0.21 for ZnOCPc alone. For complex 3 which did not contain BSA singlet oxygen quantum yield decreased.

IMPROVEMENT OF THE PHOTOPHYSICAL PARAMETERS OF ZINC OCTACARBOXY PHTHALOCYANINE UPON CONJUGATION TO MAGNETIC NANOPARTICLES

Magnetic nanoparticles (MNPs) comprising magnetite (Fe3O4) were functionalized with 3-aminopropyl-triethoxysilane forming amino functionalized magnetite nanoparticles (AMNPs). The amino group allows for conjugation with zinc octacarboxyphthalocyanine ( ZnOCPc ) via the carboxyl group to form an amide bond. Transmission electron microscopy showed a change in morphology after conjugation. The covalent linkage of AMNPs to ZnOCPc has shown improvements in the photophysical behavior of the Pc in the presence of the MNP, increasing the triplet quantum yield (ΦT), singlet oxygen quantum yield (ΦΔ), triplet lifetime (τT) and singlet oxygen lifetime (τΔ) of the ZnOCPc and thus improving the efficiency of the ZnOCPc as a photosensitizer.

Cancer cell-selective in vivo near infrared photoimmunotherapy targeting specific membrane molecules

Three major modes of cancer therapies, surgery, radiation and chemotherapy, have been the mainstay of modern oncologic therapy. To minimize side effects, molecular targeted cancer therapies including armed antibody therapy have been developed with limited success. In this study, we developed a new type of molecular targeted cancer therapy, photoimmunotherapy (PIT), employing a target-specific photosensitizer based on a near infrared (NIR) phthalocyanine dye, IR700, conjugated to monoclonal antibodies (MAb) targeting epidermal growth factor receptors (EGFR). Cell death was induced immediately only upon irradiating, MAb-IR700 bound, target cells with NIR light. In vivo tumor shrinkage after irradiation with NIR light was observed only in target EGFR-expressing cells. The MAb-IR700 conjugates were most effective when bound to the cell membrane, producing no phototoxicity when not bound, suggesting a different mechanism for PIT compared with conventional photodynamic therapies. Target selective PIT enables treatment of cancer based on MAb binding on the cell membrane.

Measurement of singlet-oxygen in vivo: progress and pitfalls

This article is a highlight of the paper by Jarvi et al. in this issue of Photochemistry and Photobiology as well as a brief overview of the state of the field of singlet-oxygen ((1) O(2) ) detection in vivo. The in vivo detection of (1) O(2) using its characteristic 1270 nm phosphorescence is technically challenging. Nevertheless, substantial progress has been made in this area. Major advances have included the commercial development of photomultiplier tubes sensitive to 1270 nm light, techniques for spatially resolving the location of (1) O(2) at a subcellular level and more complex mathematical models for interpreting the kinetics of (1) O(2) emission from living cells. It is now recognized that oxygen consumption, photosensitizer bleaching, oxidation of biological molecules and diffusion of (1) O(2) can significantly change the kinetics of (1) O(2) emission from living cells.

Repetition rate dependency of reactive oxygen species formation during femtosecond laser-based cell surgery

Femtosecond (fs) laser-based cell surgery is typically done in two different regimes, at kHz or MHz repetition rate. Formation of reactive oxygen species (ROS) is an often predicted effect due to illumination with short laser pulses in biological tissue. We present our study on ROS formation in single cells in response to irradiation with fs laser pulses depending on the repetition rate while focusing into the cell nucleus. We observed a significant increase of ROS concentration directly after manipulation followed by a decrease in both regimes at kHz and MHz repetition rate. In addition, effects of consecutive exposures at MHz and kHz repetition rate and vice versa on ROS production were studied. Irradiation with a MHz pulse train followed by a kHz pulse train resulted in a significantly higher increase of ROS concentration than in the reversed case and often caused cell death. In the presence of the antioxidant ascorbic acid, accumulation of ROS and cell death were strongly reduced. Therefore, addition of antioxidants during fs laser-based cell surgery experiments could be advantageous in terms of suppressing photochemical damage to the cell.

The use of magnetic field effects on photosensitizer luminescence as a novel probe for optical monitoring of oxygen in photodynamic therapy

The effect of a magnetic field on the steady-state and time-resolved optical emission of a custom fullerene-linked photosensitizer (PS) in liposome cell phantoms was studied at various oxygen concentrations (0.19-190 microM). Zeeman splitting of the triplet state and hyperfine coupling, which control intersystem crossing between singlet and triplet states, are altered in the presence of low magnetic fields (B < 320 mT), perturbing the luminescence intensity and lifetime as compared to the triplet state at B = 0. Measurements of the luminescence intensity and lifetime were performed using a time-domain apparatus integrated with a magnet. We propose that by probing magnet-affected optical emissions, one can monitor the state of oxygenation throughout the course of photodynamic therapy. Since the magnetic field effect (MFE) operates primarily by affecting the radical ion pairs related to type I photodynamic action, the enhancement or suppression of the MFE can be used as a measure of the dynamic equilibrium between the type I and II photodynamic pathways. The unique photo-initiated charge-transfer properties of the PS used in this study allow it to serve as both cytotoxic agent and oxygen probe that can provide in situ dosimetric information at close to real time.

Pulsed diode laser-based monitor for singlet molecular oxygen

Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photosensitizers to be selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in the metastable singlet delta state O2(1Delta) are believed to be the species that destroys cancerous cells during PDT. Monitoring singlet oxygen produced by PDT may lead to more precise and effective PDT treatments. Our approach uses a pulsed diode laser-based monitor with optical fibers and a fast data acquisition system to monitor singlet oxygen during PDT. We present results of in vitro singlet oxygen detection in solutions and in a rat prostate cancer cell line as well as PDT mechanism modeling.