Clinical Photodynamic Therapy Research Articles

Photoinduced effects of m-tetrahydroxyphenylchlorin loaded lipid nanoemulsions on multicellular tumor spheroids.

BackgroundPhotosensitizers are used in photodynamic therapy (PDT) to destruct tumor cells, however, their limited solubility and specificity hampers routine use, which may be overcome by encapsulation. Several promising novel nanoparticulate drug carriers including liposomes, polymeric nanoparticles, metallic nanoparticles and lipid nanocomposites have been developed. However, many of them contain components that would not meet safety standards of regulatory bodies and due to difficulties of the manufacturing processes, reproducibility and scale up procedures these drugs may eventually not reach the clinics. Recently, we have designed a novel lipid nanostructured carrier, namely Lipidots, consisting of nontoxic and FDA approved ingredients as promising vehicle for the approved photosensitizer m-tetrahydroxyphenylchlorin (mTHPC).ResultsIn this study we tested Lipidots of two different sizes (50 and 120 nm) and assessed their photodynamic potential in 3-dimensional multicellular cancer spheroids. Microscopically, the intracellular accumulation kinetics of mTHPC were retarded after encapsulation. However, after activation mTHPC entrapped into 50 nm particles destroyed cancer spheroids as efficiently as the free drug. Cell death and gene expression studies provide evidence that encapsulation may lead to different cell killing modes in PDT.ConclusionsSince ATP viability assays showed that the carriers were nontoxic and that encapsulation reduced dark toxicity of mTHPC we conclude that our 50 nm photosensitizer carriers may be beneficial for clinical PDT applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-016-0221-x) contains supplementary material, which is available to authorized users.

Functional organic nanoparticles for photodynamic therapy

Abstract In recent years, cancer has been one of the leading causes of death in the world. Much effort has been devoted to developing cancer treatments. Photodynamic therapy (PDT) is a noninvasive therapeutic modality by combining the light of a specific wavelength, a photosensitizer (PS) and oxygen, which has been widely applied for the treatment of cancers. However, the application of PDT in clinic is greatly limited due to lack of tumor selectivity and often causing skin photosensitivity. The use of organic nanoparticles (NPs) as an advanced technology in the field of PDT shows a great promise to overcome these shortcomings. Therefore, in this review, we summarize several functional organic NPs as PS carriers that have been developed to enhance the efficacy of PDT against cancers.

Activatable albumin-photosensitizer nanoassemblies for triple-modal imaging and thermal-modulated photodynamic therapy of cancer

Photodynamic therapy (PDT) is a noninvasive and effective approach for cancer treatment. The main bottlenecks of clinical PDT are poor selectivity of photosensitizer and inadequate oxygen supply resulting in serious side effects and low therapeutic efficiency. Herein, a thermal-modulated reactive oxygen species (ROS) strategy using activatable human serum albumin-chlorin e6 nanoassemblies (HSA-Ce6 NAs) for promoting PDT against cancer is developed. Through intermolecular disulfide bond crosslinking and hydrophobic interaction, Ce6 photosensitizer is effectively loaded into the HSA NAs, and the obtained HSA-Ce6 NAs exhibit excellent reduction response, as well as enhanced tumor accumulation and retention. By the precision control of the overall body temperature instead of local tumor temperature increasing from 37 °C to 43 °C, the photosensitization reaction rate of HSA-Ce6 NAs increases 20%, and the oxygen saturation of tumor tissue raise 52%, significantly enhancing the generation of ROS for promoting PDT. Meanwhile, the intrinsic fluorescence and photoacoustic properties, and the chelating characteristic of porphyrin ring can endow the HSA-Ce6 NAs with fluorescence, photoacoustic and magnetic resonance triple-modal imaging functions. Upon irradiation of low-energy near-infrared laser, the tumors are completely suppressed without tumor recurrence and therapy-induced side effects. The robust thermal-modulated ROS strategy combined with albumin-based activatable nanophotosensitizer is highly potential for multi-modal imaging-guided PDT and clinical translation.

THE USE OF PHOTOD YNAMIC THERAPY IN THE DOMESTIC ONCOLOGY. (REVIEW OF THE LITERA TURE)

In this paper, it has been tasked to demonstrate progress is Russian scientists who are pioneers in the application of clinical photodynamic therapy (PDT) in Europe. In this review current understanding of the mechanisms of action PDT on the tumor and the body, the technical aspects of the application of the laser radiation of varying intensity, particularly its effect on biological tissues. The results of studies on the use of PDT with different photosensitizers in the complex therapeutic measures in patients with cancer. The data on the efficacy and safety of PDT. Given the effectiveness of PDT and ease of use, no adverse reactions, this medical technology can be attributed to one of the most promising trends in oncology. Accumulated a large experience of PDT in oncology testifies to high efficiency of this method in the treatment of various tumors. However, despite the positive results obtained in clinical practice, PDT in oncology is not widely used. It is proposed to implement this knowledge into the educational process at universities. Researchers of the А. Tsyb MRRC and Obninsk Institute for Nuclear Power Engineering (MEPhI) are working under development of educational complex program «Medical physics». This cooperation is expected to improve professional training and education in health physics.

Clinical Photodynamic Therapy Review and the Brazilian Experience

Photodynamic therapy (PDT) is a simple and promising technique indicated for the treatment of non-melanoma skin cancer. Although multicenter research trials have proved its success, PDT is not as much disseminated as surgery andcryotherapy approaches are.A light-activated substance (a photosensitizer) is usually topically administered. By irradiating the sensitized region with specific wavelengths and appropriated light dose, reactive oxygen species take place, which oxidize molecules and destroy tumor cells. This review article presents not only the base principles of PDT, but also a unique experience Brazil-wide, which reached other countries in Latin America. This initiative was funded by the Brazilian government via the Brazilian Development Bank (BNDES), involving private companies and academia in a validation study of the treatment of both pre-malignant and malignant skin cancer lesions.PDT protocol evolution is presented, including details that made the technique highly efficient and placed this experiencein a larger context.

Perfluorocarbon nanoparticles enhance reactive oxygen levels and tumour growth inhibition in photodynamic therapy.

Photodynamic therapy (PDT) kills cancer cells by converting tumour oxygen into reactive singlet oxygen (1O2) using a photosensitizer. However, pre-existing hypoxia in tumours and oxygen consumption during PDT can result in an inadequate oxygen supply, which in turn hampers photodynamic efficacy. Here to overcome this problem, we create oxygen self-enriching photodynamic therapy (Oxy-PDT) by loading a photosensitizer into perfluorocarbon nanodroplets. Because of the higher oxygen capacity and longer 1O2 lifetime of perfluorocarbon, the photodynamic effect of the loaded photosensitizer is significantly enhanced, as demonstrated by the accelerated generation of 1O2 and elevated cytotoxicity. Following direct injection into tumours, in vivo studies reveal tumour growth inhibition in the Oxy-PDT-treated mice. In addition, a single-dose intravenous injection of Oxy-PDT into tumour-bearing mice significantly inhibits tumour growth, whereas traditional PDT has no effect. Oxy-PDT may enable the enhancement of existing clinical PDT and future PDT design.

Monitoring photodynamic therapy with photoacoustic microscopy.

Abstract. We present our work on examining the feasibility of monitoring photodynamic therapy (PDT)-induced vasculature change with acoustic-resolution photoacoustic microscopy (PAM). Verteporfin, an FDA-approved photosensitizer for clinical PDT, was utilized. With a 60-μm-resolution PAM system, we demonstrated the capability of PAM to monitor PDT-induced vasculature variations in a chick chorioallantoic membrane model with topical application and in a rat ear with intravenous injection of the photosensitizer. We also showed oxygen saturation change in target blood vessels due to PDT. Success of the present approach may potentially lead to the application of PAM imaging in evaluating PDT efficacy, guiding treatment, and predicting responders from nonresponders.

A Surgical View of Photodynamic Therapy in Oncology: A Review.

Clinical photodynamic therapy (PDT) has existed for over 30 years, and its scientific basis has been known and investigated for well over 100 years. The scientific foundation of PDT is solid and its application to cancer treatment for many common neoplastic lesions has been the subject of a huge number of clinical trials and observational studies. Yet its acceptance by many clinicians has suffered from its absence from the undergraduate and/or postgraduate education curricula of surgeons, physicians, and oncologists. Surgeons in a variety of specialties many with years of experience who are familiar with PDT bear witness in many thousands of publications to its safety and efficacy as well as to the unique role that it can play in the treatment of cancer with its targeting precision, its lack of collateral damage to healthy structures surrounding the treated lesions, and its usage within minimal access therapy. PDT is closely related to the fluorescence phenomenon used in photodiagnosis. This review aspires both to inform and to present the clinical aspect of PDT as seen by a surgeon.

Dual Propionibacterium acnes therapy using skin penetration-enhanced liposomes loaded with a photosensitizer and an antibiotic

Various antibiotics and photosensitizers are used for Propionibacterium acnes therapy. However, the success rate of therapy is limited because of antibiotic resistance, side-effects of photodynamic therapy using photosensitizer and the low skin-penetration efficiency of antibiotics and photosensitizers. In this study, to enhance the skin penetration efficiency, maintain their photodynamic activity and induce dual antibacterial therapeutic effects, we prepare erythromycin and branched polyethyleneimin-hematoporphyrin (bPEI-HPP) conjugates were loaded into liposomes (cationic photosensitizer-erythromycin loaded liposomes, CP-L (bPEI-HPP 10 mg; CP-L 1 and 20 mg; CP-L 2)). The tissue penetration efficiency of CP-Ls was determined by the Franz cell diffusion system and fluorescence microscopy. The penetration efficiency of CP-Ls is greater than that of bPEI-HPP, unloaded cationic photosensitizer and free HPP because CP-Ls comprised phospholipids that are similar to the cell membrane lipid composition. For in vitro antibacterial effects, Propionibacterium acnes (P. acnes) were used. The loss of viability rate of P. acnes by CP-L 2 (95%) from the colony forming unit (CFU) assay, was 2.4-fold higher than erythromycin-loaded liposomes (39%) and 1.9-fold higher than bPEI-HPP-loaded liposomes (50%). Therefore, we suggest that polycationic photosensitizer and antibiotic-loaded liposomes have potential applications in clinical photodynamic anti-bacterial therapy.

Toluidine blue O and porphyrin-mediated photodynamic therapy on three main pathogenic bacteria of periodontitis using portable LED phototherapy device

Photodynamic therapy (PDT) has been commonly used in treating many diseases, such as cancer and infectious diseases. We investigated the different effects of PDT on three main pathogenic bacteria of periodontitis — Prevotella melaninogenica (P.m.), Porphyromonas gingivalis (P.g.) and Aggregatibacter actinomycetemcomitans (A.a.). The portable red light-emitting diode (LED) phototherapy device was used to assess the exogenous PDT effects with different light doses and photosensitizer concentrations (Toluidine blue O, TBO). The portable blue LED phototherapy device was used to assess the endogenous PDT effects with the use of endogenous photosensitizers (porphyrin) under different light doses. We found out that both exogenous and endogenous PDT were able to restrict the growth of all the three bacteria significantly. Moreover, the optimal PDT conditions for these bacteria were obtained through this in vitro screening and could guide the clinical PDT on periodontitis.

Lead Structures for Applications in Photodynamic Therapy. 6. Temoporfin Anti-Inflammatory Conjugates to Target the Tumor Microenvironment for In Vitro PDT.

Due to the ongoing development of clinical photodynamic therapy (PDT), the search continues for optimized photosensitizers that can overcome some of the side effects associated with this type of treatment modality. The main protagonists being: post-treatment photosensitivity, due to only limited cellular selectivity and post-treatment tumor regrowth, due to the up-regulation of pro-inflammatory agents within the tumor microenvironment. A photosensitizer that could overcome one or both of these drawbacks would be highly attractive to those engaged in clinical PDT. Certain non-steroidal anti-inflammatory drugs (NSAIDs) when used in combination with PDT have shown to increase the cytotoxicity of the treatment modality by targeting the tumor microenvironment. Temoporfin (m-THPC), the gold standard chlorin-based photosensitizer (PS) since its discovery in the 1980’s, has successfully been conjugated to non-steroidal anti-inflammatory compounds, in an attempt to address the issue of post-treatment tumor regrowth. Using a modified Steglich esterification reaction, a library of “iPorphyrins” was successfully synthesized and evaluated for their PDT efficacy.

Optical Imaging, Photodynamic Therapy and Optically Triggered Combination Treatments.

Optical imaging is becoming increasingly promising for real-time image-guided resections, and combined with photodynamic therapy (PDT), a photochemistry-based treatment modality, optical approaches can be intrinsically "theranostic." Challenges in PDT include precise light delivery, dosimetry, and photosensitizer tumor localization to establish tumor selectivity, and like all other modalities, incomplete treatment and subsequent activation of molecular escape pathways are often attributable to tumor heterogeneity. Key advances in molecular imaging, target-activatable photosensitizers, and optically active nanoparticles that provide both cytotoxicity and a drug release mechanism have opened exciting avenues to meet these challenges. The focus of the review is optical imaging in the context of PDT, but the general principles presented are applicable to many of the conventional approaches to cancer management. We highlight the role of optical imaging in providing structural, functional, and molecular information regarding photodynamic mechanisms of action, thereby advancing PDT and PDT-based combination therapies of cancer. These advances represent a PDT renaissance with increasing applications of clinical PDT as a frontline cancer therapy working in concert with fluorescence-guided surgery, chemotherapy, and radiation.

Photodynamic efficiency of hypericin compared with chlorin and hematoporphyrin derivatives in HEp-2 and Vero epithelial cell lines

Hypericin (HY) is a photoactive aromatic dianthraquinone that is considered a potent photodynamic agent. In this study, hypericin and two other photosensitizers, a hematoporphyrin derivative (Photogem(®); PG) and a chlorin derivative (Photodithazine(®); PZ), were compared in terms of their phototoxicity toward two cell lines, HEp-2 and Vero. The median inhibitory concentration (IC(50)) of each of the photosensitizers was obtained after a 16.2J cm(-2) dose of irradiation at 630 ± 10 nm. The IC(50) values were 0.07 ± 0.01 (HY), 1.0 ± 0.2 (PZ), and 9 ± 1 μgmL(-1) (PG) in HEp-2 cells and 0.3 ± 0.1 (HY), 1.6 ± 0.2 (PZ) and 11 ± 1 μgmL(-1) (PG) in Vero cells, showing that HY is more phototoxic than the others when irradiated at 630 nm. If these results are analyzed, simultaneously, with the first-order constant for BSA tryptophan photooxidation, obtained by fluorescence decay (λ(excitation)=280 nm), which are 11×10(-3) min(-1)±1. 10(-3) min(-1) (HY), 10 × 10(-3) min(-1)±1 × 10(-3) min(-1) (PZ), and 6 × 10(-3)min(-1) ± 1×10(-3)min(-1) (PG), it is possible to infer that the photodynamic efficiency alone is not sufficient to explain the higher HY phototoxicity. The lipophilicity is also an important factor for an efficient target cell accumulation and was assessed for all sensitizers through the octanol-water partition coefficient (log P): 1.20 ± 0.02 (HY), -0.62 ± 0.03 (PZ), and -0.9 ± 0.2 (PG). The higher value for HY correlates well with its observed superior efficiency to promote damage at low concentrations and doses. As HY is used for the long-term treatment of mild depression, it is considered safe for humans. This fact and the present results reinforce the great potential of this photosensitizer to replace porphyrin derivatives, with the advantages that mean it could be used as photosensitizer in clinical photodynamic therapy.

Correction for tissue optical properties enables quantitative skin fluorescence measurements using multi-diameter single fiber reflectance spectroscopy

Background and objectiveFluorescence measurements in the skin are very much affected by absorption and scattering but existing methods to correct for this are not applicable to superficial skin measurements. Study design/materials and methodsThe first use of multiple-diameter single fiber reflectance (MDSFR) and single fiber fluorescence (SFF) spectroscopy in human skin was investigated. MDSFR spectroscopy allows a quantification of the full optical properties in superficial skin (μa, μs′ and γ), which can next be used to retrieve the corrected – intrinsic – fluorescence of a fluorophore Qμa,xf. Our goal was to investigate the importance of such correction for individual patients. We studied this in 22 patients undergoing photodynamic therapy (PDT) for actinic keratosis. ResultsThe magnitude of correction of fluorescence was around 4 (for both autofluorescence and protoporphyrin IX). Moreover, it was variable between patients, but also within patients over the course of fractionated aminolevulinic acid PDT (range 2.7–7.5). Patients also varied in the amount of protoporphyrin IX synthesis, photobleaching percentages and resynthesis (>100× difference between the lowest and highest PpIX synthesis). The autofluorescence was lower in actinic keratosis than contralateral normal skin (0.0032 versus 0.0052; P<0.0005). ConclusionsOur results clearly demonstrate the importance of correcting the measured fluorescence for optical properties, because these vary considerably between individual patients and also during PDT. Protoporphyrin IX synthesis and photobleaching kinetics allow monitoring clinical PDT which facilitates individual-based PDT dosing and improvement of clinical treatment protocols. Furthermore, the skin autofluorescence can be relevant for diagnostic use in the skin, but it may also be interesting because of its association with several internal diseases.

Integration of fluorescence differential path-length spectroscopy to photodynamic therapy of the head and neck tumors is useful in monitoring clinical outcome

The use of fluorescence differential pathlength spectroscopy (FDPS) has the potential to provide real-time information on photosensitiser pharmacokinetics, vascular physiology and photosensitizer photobleaching based dosimetry of tumors in the oral cavity receiving m-tetrahydroxyphenylchlorin (mTHPC) photodynamic therapy (PDT). Reflectance spectra can be used provide quantitative values of oxygen saturation, blood volume fraction, blood vessel diameter, and to determine the local optical properties that can be used to correct raw fluorescence for tissue absorption. Patients and methods: Twenty-seven lesions in the oral cavity, either dysplasias or cancer were interrogated using FDPS, before and immediately after the therapeutic illumination. The average tumor center to normal mucosa ratio of fluorescence was 1.50 ± 0.66. mTHPC photobleaching was observed in 24 of the lesions treated. The average extent of photobleaching was 81% ± 17%. Information from FDPS spectroscopy coupled with the clinical results of the treatment identified 3 types of correctable errors in the application of mTHPC-PDT: Two patients exhibited very low concentrations of photosensitizer in tumour center, indicating an ineffective i.v. injection of photosensitiser or an erroneous systemic distribution of mTHPC. In one in tumor we observed no photobleaching accompanied by a high blood volume fraction in the illuminated tissue, suggesting that the presence of blood prevented therapeutic light reaching the target tissue. All 3 of the these lesions had no clinical response to PDT. In four patients we observed less than 50% photobleaching at the tumor margins , suggesting a possible geographic miss. One patient in this group had a recurrence within 2 months after PDT even though the initial response was good. The integration of FDPS to clinical PDT yields data on tissue physiology, photosensitiser content and photobleaching that can help identify treatment errors that can potentially be corrected.

Study on nanocomposite construction based on the multi-functional biotemplate self-assembled by the recombinant TMGMV coat protein for potential biomedical applications.

Nowadays there is a growing interest in bio-scaffolded nanoarchitectures. Rapid progress in nanobiotechnology and molecular biology has allowed the engineering of inorganic-binding peptides termed as genetically engineered polypeptides for inorganics (GEPIs) into self-assembling biological structures to facilitate the design of novel biomedical or bioimaging devices. Here we introduce a novel nanocomposite comprising a self-assembled protein scaffold based on a recombinant tobacco mild green mosaic tobamovirus (TMGMV) coat protein (CP) and the photocatalytic TiO2 nanoparticles attached to it, which may provide a generic method for materials engineering. A template containing a modified TMGMV CP (mCP) gene, with the first six C-terminal amino acid residues deleted to accommodate more foreign peptides and expressing a site-directed mutation of A123C for bioconjugation utility, and two genetically engineered mutants, Escherichia coli-based P-mCP-Ti7 containing a C-terminal TiO2 GEPI sequence of seven peptides (Ti7) and Hi5 insect cells-derived E-CP-Ti7-His6 C-terminally fused with Ti7+His6 tag were created. Expression vectors and protocols for enriching of the two CP variants were established and the resultant proteins were identified by western blot analysis. Their RNA-free self-assembling structures were analyzed by transmission electron microscopy (TEM) and immuno-gold labeling TEM analysis. Adherence of nanoparticles to the P-mCP-Ti7 induced protein scaffold was visualized by TEM analysis. Also discussed is the Cysteine thiol reactivity in bioconjugation reactions with the maleimide-functionalized porphyrin photosensitizers which can function as clinical photodynamic therapy agents. This study introduced a novel approach to producing an assembly-competent recombinant TMGMV CP, examined its ability to serve as a novel platform for the multivalent display of surface ligands and demonstrated an alternative method for nanodevice synthesis for nanobiotechnological applications by combining GEPIs-mediated immobilization with the controllability of self-assembling recombinant TMGMV CP.

H2O2-activatable and O2-evolving nanoparticles for highly efficient and selective photodynamic therapy against hypoxic tumor cells.

The low selectivity of currently available photosensitizers, which causes the treatment-related toxicity and side effects on adjacent normal tissues, is a major limitation for clinical photodynamic therapy (PDT) against cancer. Moreover, since PDT process is strongly oxygen dependent, its therapeutic effect is seriously hindered in hypoxic tumor cells. To overcome these problems, a cell-specific, H(2)O(2)-activatable, and O(2)-evolving PDT nanoparticle (HAOP NP) is developed for highly selective and efficient cancer treatment. The nanoparticle is composed of photosensitizer and catalase in the aqueous core, black hole quencher in the polymeric shell, and functionalized with a tumor targeting ligand c(RGDfK). Once HAOP NP is selectively taken up by α(v)β(3) integrin-rich tumor cells, the intracellular H(2)O(2) penetrates the shell into the core and is catalyzed by catalase to generate O(2), leading to the shell rupture and release of photosensitizer. Under irradiation, the released photosensitizer induces the formation of cytotoxic singlet oxygen ((1)O(2)) in the presence of O(2) to kill cancer cells. The cell-specific and H(2)O(2)-activatable generation of (1)O(2) selectively destroys cancer cells and prevents the damage to normal cells. More significantly, HAOP NP continuously generates O(2) in PDT process, which greatly improves the PDT efficacy in hypoxic tumor. Therefore, this work presents a new paradigm for H(2)O(2)-triggered PDT against cancer cells and provides a new avenue for overcoming hypoxia to achieve effective treatment of solid tumors.

Light emitting fabric technologies for photodynamic therapy

Photodynamic therapy (PDT) is considered to be a promising method for treating various types of cancer. A homogeneous and reproducible illumination during clinical PDT plays a determinant role in preventing under- or over-treatment. The development of flexible light sources would considerably improve the homogeneity of light delivery. The integration of optical fiber into flexible structures could offer an interesting alternative. This paper aims to describe different methods proposed to develop Side Emitting Optical Fibers (SEOF), and how these SEOF can be integrated in a flexible structure to improve light illumination of the skin during PDT. Four main techniques can be described: (i) light blanket integrating side-glowing optical fibers, (ii) light emitting panel composed of SEOF obtained by micro-perforations of the cladding, (iii) embroidery-based light emitting fabric, and (iv) woven-based light emitting fabric. Woven-based light emitting fabrics give the best performances: higher fluence rate, best homogeneity of light delivery, good flexibility.

Hydrophobic IR780 encapsulated in biodegradable human serum albumin nanoparticles for photothermal and photodynamic therapy

It has been reported that IR780 iodide, a near-infrared dye, can be applied for cancer imaging, photodynamic therapy (PDT) and photothermal therapy (PTT). However, the hydrophobicity and toxicity of IR780 severely limit its further clinical applications. In this study, human serum albumin was used to load IR780 to form nanoparticles (HSA-IR780 NPs) by protein self-assembly. Compared to free IR-780, the solubility of HSA-IR780 NPs was greatly increased (1000-fold) while the toxicity was decreased (from 2.5mgkg−1 to 25mgkg−1). Moreover, both PTT and PDT could be observed in HSA-IR780 NPs, as determined by increased temperature and enhanced generation of singlet oxygen after laser irradiation at a wavelength of 808nm. In vivo studies also showed a great tumor inhibition by the injection of HSA-IR780 NPs into tumor-bearing mice. Therefore, HSA-IR780 NPs may serve as a promising substitute for IR780 in further clinical PDT and PTT.

Low-level light therapy potentiates NPe6-mediated photodynamic therapy in a human osteosarcoma cell line via increased ATP

BackgroundLow-level light therapy (LLLT) is used to stimulate healing, reduce pain and inflammation, and preserve tissue from dying. LLLT has been shown to protect cells in culture from dying after various cytotoxic insults, and LLLT is known to increase the cellular ATP content. Previous studies have demonstrated that maintaining a sufficiently high ATP level is necessary for the efficient induction and execution of apoptosis steps after photodynamic therapy (PDT). MethodsWe asked whether LLLT would protect cells from cytotoxicity due to PDT, or conversely whether LLLT would enhance the efficacy of PDT mediated by mono-l-aspartyl chlorin(e6) (NPe6). Increased ATP could lead to enhanced cell uptake of NPe6 by the energy dependent process of endocytosis, and also to more efficient apoptosis. In this study, human osteosarcoma cell line MG-63 was subjected to 1.5J/cm2 of 810nm near infrared radiation (NIR) followed by addition of 10μM NPe6 and after 2h incubation by 1.5J/cm2 of 652nm red light for PDT. ResultsPDT combined with LLLT led to higher cell death and increased intracellular reactive oxygen species compared to PDT alone. The uptake of NPe6 was moderately increased by LLLT, and cellular ATP was increased. The mitochondrial respiratory chain inhibitor antimycin A abrogated the LLLT-induced increase in cytotoxicity. ConclusionsTaken together, these results demonstrate that LLLT potentiates NPe6-mediated PDT via increased ATP synthesis and is a potentially promising strategy that could be applied in clinical PDT.