Localization and efficacy analysis of the phototherapeutic lutetium texaphyrin (PCI-0123) in the murine EMT6 sarcoma model

Trojan Horse-Like Nano-AIE Aggregates Based on Homologous Targeting Strategy and Their Photodynamic Therapy in Anticancer Application

Photodynamic therapy (PDT) has become a promising candidate for cancer theranostics; however, traditional photosensitizers (PSs) usually exhibit weak fluorescence and poor reactive oxygen species (ROS) generation efficiency when aggregated. Recently, aggregation-induced emission (AIE) luminogens have shown great potential in the development of novel PSs owing to their excellent aggregation-induced ROS generation (AIG-ROS) activity. However, there are still concerns that must be addressed. In this study, two near-infrared (NIR) emitters (PI and PTI) are synthesized with AIG-ROS characteristic. PTI exhibit a valuable redder emission with more effective intersystem crossing (ISC) process than PI. The two AIE-active PSs show excellent lipid droplet (LD)-specific targeting ability. The detailed therapeutic mechanism of PDT in LDs specificity is also investigated. The mechanism of oxidation of polyunsaturated fatty acids (PUFAs) in LDs to form toxic lipid peroxides (LPOs) and thereby causing cellular ferroptosis is confirmed first. Homologous targeting is also used to achieve tumor targeting via coating PSs with active cancer cell membranes. Biomimetic aggregates exhibit good targeting ability, and an improved PDT antitumor effect via AIG-ROS activity. These findings offer a clear route to develop advanced PSs with good targeting specificity. A template has also been provided for studying the therapeutic mechanism of AIE-active PSs.

Photodynamic cancer therapy using liposomes as an advanced vesicular photosensitizer delivery system

The multidisciplinary field of photodynamic therapy (PDT) is a combination of photochemistry and photophysics sciences, which has shown tremendous potential for cancer therapy application. PDT employs a photosensitizing agent (PS) and light to form cytotoxic reactive oxygen species and subsequently oxidize light-exposed tissue. Despite numerous advantages of PDT and enormous progress in this field, common PSs are still far from ideal treatment because of their poor permeability, non-specific phototoxicity, side effects, hydrophobicity, weak bioavailability, and tendency to self-aggregation. To circumvent these limitations, PS can be encapsulated in liposomes, an advanced drug delivery system that has demonstrated the ability to enhance drug permeability into biological membranes and loading both hydrophobic and lipophilic agents. Moreover, liposomes can also be coated by targeting agents to improve delivery efficiency. The present review aims to summarize the principles of PDT, various PS generations, PS-loaded nanoparticles, liposomes, and their impact on PDT, then discuss recent photodynamic cancer therapy strategies using liposomes as PS-loaded vectors, and highlight future possibilities and perspectives.

Mechanisms in photodynamic therapy: part two-cellular signaling, cell metabolism and modes of cell death

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In the second of a series of three reviews, we will discuss the mechanisms that operate in PDT on a cellular level. In Part I [Castano AP, Demidova TN, Hamblin MR. Mechanism in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization. Photodiagn Photodyn Ther 2004;1:279-93] it was shown that one of the most important factors governing the outcome of PDT, is how the photosensitizer (PS) interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. PS can localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes. An explosion of investigation and explorations in the field of cell biology have elucidated many of the pathways that mammalian cells undergo when PS are delivered in tissue culture and subsequently illuminated. There is an acute stress response leading to changes in calcium and lipid metabolism and production of cytokines and stress proteins. Enzymes particularly, protein kinases, are activated and transcription factors are expressed. Many of the cellular responses are centered on mitochondria. These effects frequently lead to induction of apoptosis either by the mitochondrial pathway involving caspases and release of cytochrome c, or by pathways involving ceramide or death receptors. However, under certain circumstances cells subjected to PDT die by necrosis. Although there have been many reports of DNA damage caused by PDT, this is not thought to be an important cell-death pathway. This mechanistic research is expected to lead to optimization of PDT as a tumor treatment, and to rational selection of combination therapies that include PDT as a component.

TAT-mediated photochemical internalization results in cell killing by causing the release of calcium into the cytosol of cells

BACKGROUND

Lysis of endocytic organelles is a necessary step in many cellular delivery methodologies. This is achieved efficiently in the photochemical internalization approach but the cell death that accompanies this process remains a problem.

METHODS

We investigate the mechanisms of cell death that accompanies photochemical internalization of the fluorescent peptide TMR-TAT.

RESULTS

TMR-TAT kills cells after endocytosis and light irradiation. The lysis of endocytic organelles by TMR-TAT causes a rapid increase in the concentration of calcium in the cytosol. TMR-TAT co-localizes with endocytic organelles containing calcium prior to irradiation and photochemical internalization leads to the release of the lumenal content of these organelles. Ruthenium red and cyclosporin A, inhibitors of calcium import in mitochondria and of the mitochondria permeability transition pore, inhibit cell death.

CONCLUSIONS

TMR-TAT mediated photochemical internalization leads to a disruption of calcium homeostasis. The subsequent import of calcium in mitochondria is a causative factor of the cell death that accompanies photochemical internalization. General significance Understanding how the lysis of endocytic organelles affects cellular physiology and causes cell death is crucial to the development of optimal delivery methodologies.

Texaphyrins: a new approach to drug development

The texaphyrins are prototypical metal-coordinating expanded porphyrins. They represent a burgeoning class of pharmacological agents that show promise for an array of medical applications. Currently, two different water-soluble lanthanide texaphyrins, namely motexafin gadolinium ( Gd-Tex , 1) and motexafin lutetium ( Lu-Tex , 2), are involved in multi-center clinical trials for a variety of indications. The first of these agents, XCYTRIN® (motexafin gadolinium) Injection, is being evaluated as a potential X-ray radiation enhancer in a randomized Phase III clinical trial in patients with brain metastases. The second, in various formulations, is being evaluated as a photosensitizer for use in: (i) the photodynamic treatment of recurrent breast cancer (LUTRIN® Injection; now in Phase IIb clinical trials); (ii) photoangioplastic reduction of atherosclerosis involving peripheral and coronary arteries (ANTRIN® Injection; now in Phase II and Phase I clinical trials, respectively); and (iii) light-based age-related macular degeneration (OPTRIN™ Injection; currently under Phase II clinical evaluation), a vision-threatening disease of the retina. In this article, these developments, along with fundamental aspects of the underlying chemistry are reviewed.

Photosensitization by the Near-IR-absorbing Photosensitizer Lutetium Texaphyrin: Spectroscopic, In Vitro and In Vivo Studies

The spectroscopic and biological properties of the new photosensitizer lutetium texaphyrin (Lu-Tex) were assessed in vitro and in vivo on a C26 colon carcinoma model, in comparison with hematoporphyrin (Hp), photofrin II (PII) and chlorin e 6( Chl ). Strong binding of Lu-Tex to lipid bilayer membranes was observed. The results of confocal fluorescence microscopy on C26 cells showed that Lu-Tex was localized in small vesicles in the cytoplasm, possibly in the lysosomes, while Chl and Hp were distributed in larger cytoplasmic vesicles attributed to mitochondria. Scanning electron microscopy and X-ray microanalysis revealed that photodynamic therapy with Lu-Tex induced only slight damage to the cell membrane, leading to a delayed cell response. Chl and Hp caused significant structural damage to the outer cell membrane, resulting in ionic imbalance and fast cell death. The in vitro quantitative assessment of the relative efficiency per absorbed photon of the sensitizers revealed that Lu-Tex was less effective than Chl and Hp . However, the results of our in vivo study showed that at the same light and drug doses the anti-tumor efficiency of the agents was in the following order: Lu-Tex > Chl > PII . The strong in vivo anti-tumor effect of Lu-Tex can be explained by its higher integrated absorption in the long-wavelength range.

Intracellular sites of photodamage as a factor in apoptotic cell death

The cytotoxic response to photodynamic therapy can involve apoptosis, necrosis or both. Using agents with known patterns of sub-cellular localization, we assessed different sites of photodamage as a determinant of cell death, using murine leukemia cells in vitro. Mitochondrial or mitochondrial + lysosomal photodamage led to a rapid apoptotic response, associated with the release of cytochrome c from mitochondria into the cytosol. This occurred immediately after irradiation of photosensitized cells. When photodamaged cells were warmed to 37 °C, there was a rapid apoptotic response. Lysosomal photodamage led to the immediate release of cathepsins and other proteolytic enzymes. During a subsequent incubation at 37 °C, there was a slow loss of the mitochondrial membrane potential, with cytochrome c appearing in the cytosol within 30 min. These effects derive from proteolytic effects of lysosomal enzymes on mitochondria. The apoptotic response to lysosomal photodamage was both slow and incomplete, with many non-viable cells not exhibiting apoptotic morphology. The latter result was correlated with photodamage to procaspase-3, an effect not observed when mitochondria were the predominant target for photodamage. Depending on the sub-cellular target, photodynamic therapy can either activate or inhibit critical elements of apoptosis.

Regression of the murine LM3 tumor by repeated photodynamic therapy with meso-tetrakis-(4-N,N,N-trimethylanilinium)porphine

Photodynamic therapy (PDT) of cancer is based on the cytotoxicity induced by a photosensitizer (PS) in the presence of oxygen and visible light, with formation of reactive oxygen species which cause cell death and tumor destruction. This work describes the response of the murine mammary adenocarcinoma, LM3, to repeated PDT using meso-tetrakis(4-N,N,N-trimethylanilinium)porphine (TMAP), a PS that has been overlooked for PDT applications. Intradermal LM3 tumors in BALB/c mice (controls) were left untreated, only treated with light, only injected with 0.9% NaCl solution or with TMAP alone (10 μg/0.1 ml). For PDT, the intratumoral PS injection was followed 1 h later by blue-red light irradiation (290 J.cm-2). In all cases, control and PDT treatments were performed on the depilated and glycerol-covered skin which covers the tumor of anesthetized animals, and repeated 4 times (every 2 days). No significant differences were found in the growth rate of all control tumors. PDT-treated tumors showed complete and long-term regression in 4 out of 5 mice, and cure in one animal. The survival of PDT-mice was significantly longer than that of controls (TMAP alone), showing a lower number of tumor-draining lymph node metastasis. The PDT protocol applied in the present work (intratumoral PS injection, repeated photosensitizing treatments, and reduction of tissue light scattering by glycerol) could be a useful strategy in studies on PDT of cancer.

Mechanisms of porphyrinoid localization in tumors

The photosensitizing and pharmacokinetic properties of porphyrin-type compounds have been investigated for nearly a century. In the last decade, two porphyrin derivatives were approved in the U.S.A. and in several other countries for the photodynamic treatment of various lesions. An overview of the different mechanisms for preferential porphyrinoid localization in malignant tumors is presented herein. Several uptake pathways are possible for each photosensitizer, which are determined by its structure, mode of delivery and tumor type. Comparisons of the different mechanisms and correlations with the structure of the sensitizer are presented. Current delivery systems for porphyrin sensitizers are described, as well as recent strategies for enhancing their tumor-specificity, including conjugation to a carrier system that selectively targets a tumor-associated receptor or antigen.

Aminolevulinic Acid (ALA) as a Prodrug in Photodynamic Therapy of Cancer

Aminolevulinic acid (ALA) is an endogenous metabolite normally formed in the mitochondria from succinyl-CoA and glycine. Conjugation of eight ALA molecules yields protoporphyrin IX (PpIX) and finally leads to formation of heme. Conversion of PpIX to its downstream substrates requires the activity of a rate-limiting enzyme ferrochelatase. When ALA is administered externally the abundantly produced PpIX cannot be quickly converted to its final product - heme by ferrochelatase and therefore accumulates within cells. Since PpIX is a potent photosensitizer this metabolic pathway can be exploited in photodynamic therapy (PDT). This is an already approved therapeutic strategy making ALA one of the most successful prodrugs used in cancer treatment.

Porphyrin and nonporphyrin photosensitizers in oncology: preclinical and clinical advances in photodynamic therapy

Photodynamic therapy (PDT) is now a well-recognized modality for the treatment of cancer. While PDT has developed progressively over the last century, great advances have been observed in the field in recent years. The concept of dual selectivity of PDT agents is now widely accepted due to the relative specificity and selectivity of PDT along with the absence of harmful side effects often encountered with chemotherapy or radiotherapy. Traditionally, porphyrin-based photosensitizers have dominated the PDT field but these first generation photosensitizers have several disadvantages, with poor light absorption and cutaneous photosensitivity being the predominant side effects. As a result, the requirement for new photosensitizers, including second generation porphyrins and porphyrin derivatives as well as third generation photosensitizers has arisen, with the aim of alleviating the problems encountered with first generation porphyrins and improving the efficacy of PDT. The investigation of nonporphyrin photosensitizers for the development of novel PDT agents has been considerably less extensive than porphyrin-based compounds; however, structural modification of nonporphyrin photosensitizers has allowed for manipulation of the photochemotherapeutic properties. The aim of this review is to provide an insight into PDT photosensitizers clinically approved for application in oncology, as well as those which show significant potential in ongoing preclinical studies.

Motexafin gadolinium: A novel redox active drug for cancer therapy

Motexafin gadolinium (MGd, Xcytrin) is an aromatic macrocycle that has a strong affinity for electrons, i.e., it is easily reduced. In the presence of oxygen, MGd accepts electrons from various cellular reducing metabolites and forms superoxide and other reactive oxygen species (ROS) by redox cycling. The reaction with NADPH is dramatically accelerated by various oxido-reductases including thioredoxin reductase. In vitro studies with various cancer cell lines have shown an increase in ROS and intracellular free zinc in cells treated with MGd. MGd increases cytotoxicity of ionizing radiation and various chemotherapy agents and may be directly cytotoxic to tumor cells under certain conditions. MGd selectively localizes in tumors, perhaps due to their metabolic perturbations. MGd treatment in murine models enhances tumor response to radiation and chemotherapy agents. In controlled, randomized clinical trials, combining MGd treatment with ionizing radiation improves time to neurologic progression in lung cancer patients with brain metastases. The molecular target for MGd appears to be thioredoxin reductase which, when inhibited, results in cellular redox stress, cytotoxicity and an increase in tumor responsiveness to a variety of treatments.

Photodynamic therapy of cerebral glioma – A review Part II – Clinical studies

Photodynamic therapy (PDT) is a binary treatment modality that has been used to treat malignant brain tumours for 25 years. The treatment involves the selective uptake of a photosensitizer (PS) by the tumour cells followed by irradiation of the tumour with light of the appropriate wavelength to excite and activate the PS resulting in selective tumour destruction and is a potentially valuable adjunct to surgical excision and other conventional therapies. PDT has undergone extensive laboratory studies and clinical trials with a variety of PS and tumour models. These are discussed with reference mainly to clinical studies involving the PDT of brain tumours.

Optical properties of human prostate at 732 nm measured in mediated photodynamic therapy

Characterization of the tissue light penetration in prostate photodynamic therapy (PDT) is important to plan the arrangement and weighting of light sources so that sufficient light fluence is delivered to the treatment volume. The optical properties (absorption [mu(a)], transport scattering [mu(s)'] and effective attenuation [mu(eff)] coefficients) of 13 patients with locally recurrent prostate cancer were measured in situ using interstitial isotropic detectors. Measurements were made at 732 nm before and after motexafin lutetium (MLu)-mediated PDT in four quadrants. Optical properties were derived by applying the diffusion theory to the fluence rates measured at several distances (0.5-5 cm) from a point source. mu(a) and mu(s)' varied between 0.07 and 1.62 cm(-1) (mean 0.37 +/- 0.24 cm(-1)) and 1.1 and 44 cm(-1) (mean 14 +/- 11 cm(-1)), respectively. mu(a) was proportional to the concentration of MLu measured by an ex vivo fluorescence assay. We have observed, on average, a reduction of the MLu concentration after PDT, presumably due to the PDT consumption of MLu. mu(eff) varied between 0.91 and 6.7 cm(-1) (mean 2.9 +/- 0.7 cm(-1)), corresponding to an optical penetration depth (delta = 1/micro(eff)) of 0.1-1.1 cm (mean 0.4 +/- 0.1 cm). The mean penetration depth at 732 nm in human prostate is at least two times smaller than that found in normal canine prostates, which can be explained by a four times increase of the mean value of mu(s)' in human prostates. The mean light fluence rate per unit source strength at 0.5 cm from a point source was 1.5 +/- 1.1 cm(-2), excluding situations when bleeding occurs. The total number of measurements was N = 121 for all mean quantities listed above. This study showed significant inter- and intraprostatic differences in the optical properties, suggesting that a real-time dosimetry measurement and feedback system for monitoring light fluences during treatment should be considered for future PDT studies.

Determination of the distribution of light, optical properties, drug concentration, and tissue oxygenation in-vivo in human prostate during motexafin lutetium-mediated photodynamic therapy

It is desirable to quantify the distribution of the light fluence rate, the optical properties, the drug concentration, and the tissue oxygenation for photodynamic therapy (PDT) of prostate cancer. We have developed an integrated system to determine these quantities before and after PDT treatment using motorized probes. The optical properties (absorption (micro(a)), transport scattering (micro(s'), and effective attenuation (micro(eff)) coefficients) of cancerous human prostate were measured in-vivo using interstitial isotropic detectors. Measurements were made at 732 nm before and after motexafin lutetium (MLu) mediated PDT at different locations along each catheter. The light fluence rate distribution was also measured along the catheters during PDT. Diffuse absorption spectroscopy measurement using a white light source allows extrapolation of the distribution of oxygen saturation StO2, total blood volume ([Hb]t), and MLu concentration. The distribution of drug concentration was also studied using fluorescence from a single optical fiber, and was found to be in good agreement with the values determined by absorption spectroscopy. This study shows significant inter- and intra-prostatic variations in the tissue optical properties and MLu drug distribution, suggesting that a real-time dosimetry measurement and feedback system for monitoring these values during treatment should be considered in future PDT studies.

Intracellular signaling mechanisms in photodynamic therapy

In photodynamic therapy (PDT) a sensitizer, light and oxygen are used to induce death of tumor cells and in the treatment of certain noncancerous conditions. Cell death in PDT may occur by apoptosis or by necrosis, depending on the sensitizer, on the PDT dose and on the cell genotype. Some sensitizers that have been used in PDT are accumulated in the mitochondria, and this may explain their efficiency in inducing apoptotic cell death, both in vitro and in vivo. In this review we will focus on the events that characterize apoptotic death in PDT and on the intracellular signaling events that are set in motion in photosensitized cells. Activation of phospholipases, changes in ceramide metabolism, a rise in the cytosolic free Ca2+ concentration, stimulation of nitric oxide synthase (NOS), changes in protein phosphorylation and alterations in the activity of transcription factors and on gene expression have all been observed in PDT-treated cells. Although many of these metabolic reactions contribute to the demise process, some of them may antagonize cell death. Understanding the signaling mechanisms in PDT may provide means to modulate the PDT effects at the molecular level and potentiate its antitumor effectiveness.

Necrosis-like death with plasma membrane damage against cervical cancer cells by photodynamic therapy

In order to elucidate the antitumor effect of photodynamic therapy (PDT) using the photosensitizing agent hematoporphyrin derivative (Photogem) and a diode laser, we evaluated the cell death of uterine cancer cell lines (CaSki, HT3, HeLa, and SKOV-3) and mice transplanted with TC-1 lung cancer cells. Morphological changes, MTT assay, flow cytometry, cytotoxicity, and tumor growth-inhibition study were evaluated at various time intervals after PDT. The results showed that the survival rates of each cell line decreased with time and dose-response after performing PDT. Also, PDT-induced damage of cancer cells was almost entirely confined to necrosis of the tumor cells in the early time courses. The irradiation of CaSki cells in the presence of Photogem induced plasma membrane disruption and cell shrinkage, indicating the plasma membrane as the main target for Photogem. In the experiment in vivo, the time courses of Photogem with irradiation showed significantly longer survival and a significantly smaller tumor size compared to those in the untreated control groups, and resorption of the tumor after PDT treatment was observed. Collectively, our results indicated that Photogem possesses tumor-specific affinity, and necrosis-like death with plasma membrane damage was postulated to be the principal mechanism of the antitumor effect of PDT using Photogem.

Therapeutic effect of photodynamic therapy using PAD-S31 and diode laser on human liver cancer cells

BACKGROUND/AIMS

Photodynamic therapy (PDT) is an effective local cancer treatment which a photosensitizer is administered and the tumor is irradiated with light. We examined the effect of PDT using PAD-S31 as the photosensitizer, and the 670 nm diode laser on human hepatocellular carcinomas (HCCs).

METHODS

Huh-7, HepG2 and Hep3B cell lines were used in the all experiments. Cell viability was determined by a modified MTT assay. Two methods were used for the determination of apoptosis: terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling assay and detection of fragmented mono- and oligo-nucleosomes by enzyme-linked immunosorbent assay. The caspase activity was measured by fluorometric assay. Cytochrome c in cytosolic fraction was determined using a human cytochrome c immunoassay. Xenografts of human oral HCC cells were generated in KSN S1c nude mice.

RESULTS

In vitro PDT showed excellent cytotoxicity that was a function of laser energy, drug concentration and time to the hepatoma cell lines. The combined use of PAD-S31 and laser irradiation showed excellent anti-tumor activity without severe side-effect against human hepatoma xenografts in nude mice. PDT-mediated cell death occurred predominantly by apoptosis in vitro and in vivo. Furthermore, this treatment initiates early cytochrome c release, followed by late caspase-3 and -9 activation.

CONCLUSION

Our study demonstrates that PDT using PAD-S31 and the diode laser induces apoptosis that is mediated by cytochrome c release and caspase activation in human liver cancer cell lines. It is expected that this therapy will be clinically useful for the treatment of patients with HCC.

Photodynamic therapy for human oral squamous cell carcinoma and xenografts using a new photosensitizer, PAD-S31

BACKGROUND AND OBJECTIVES

Photodynamic therapy (PDT) is a novel and promising cancer treatment that employs a combination of photosensitizer and visible light. We examined the effect of PDT using a new photosensitizer, PAD-S31, and the 670-nm diode laser in human oral squamous cell carcinomas (SCC).

STUDY DESIGN/MATERIALS AND METHODS

SAS and HSC-4 cell lines were used in all the experiments. Cell viability was determined by a modified MTT assay. Two methods were used for the determination of apoptosis in human oral SCC cells: TUNEL assay and detection of fragmented mono- and oligo-nucleosomes by ELISA. Xenografts of human oral SCC cells were generated in KSN S1c nude mice.

RESULTS

In vitro PDT using PAD-S31 and the 670-nm diode laser showed cytotoxicity that was a function of laser energy, drug concentration, and time to the SAS and HSC-4 cell lines. On the other hand, PAD-S31 without irradiation had no effect on cell viability. The combinated use of PAD-S31 and the laser irradiation showed excellent anti-tumor activity against tumor xenografts without severe side effects. PDT-mediated cell death occurred predominantly by apoptosis in vitro and in vivo.

CONCLUSIONS

The present study demonstrates that PAD-S31 may serve as a potent photosensitizer for PDT. Furthermore, it is expected that this therapy will be clinically useful for the treatment of patients with oral carcinoma.

Liposomal photofrin enhances therapeutic efficacy of photodynamic therapy against the human gastric cancer

Photodynamic therapy (PDT) has been established as a potent and less invasive treatment for gastrointestinal tumors. The aim of the present study was to investigate whether or not liposomalization of the photosensitizer enhanced the therapeutic efficacy of PDT. Photofrin (PF) was entrapped in multilammelar liposomes. Mice implanted with a human gastric cancer xenograft, were divided into a PF group and a liposomal photofrin (LPF) group and intravenously administered 10 mg/kg of PF or LPF (as a dose of PF), respectively. At 8 h after injection PF level in tumor tissue in the LPF group was significantly higher level by 2.4-fold of that in the PF group, whereas the PF levels in the skin were almost equal. Irradiation was performed with the excimer dye laser at 150 mW/cm(2), total dose 40 J, at 8 h after PF or LPF administration. The results revealed that the volume of necrotic tumor tissue was significantly higher in the LPF group than in the PF group. The apoptotic index of the tumor was also significantly higher in the LPF group. In conclusion, the liposomalization of the photosensitizer increased its tumor accumulation, with a resulting enhancement of the therapeutic effect of PDT.

Kinetics of the superficial perfusion and temperature in connection with photodynamic therapy of basal cell carcinomas using esterified and non-esterified 5-aminolaevulinic acid

BACKGROUND

Photodynamic therapy (PDT) is a local treatment modality with increasing indications for various malignant and non malignant diseases. The treatment parameters have not yet been optimized as there is a need for a better understanding of the process. The skin is an important target and serves as a good model for monitoring and evaluating the interaction of light with biological tissue.

OBJECTIVES

The tissue perfusion and the temperature of basal cell carcinomas were measured in connection with PDT in order to investigate the biological mechanisms involved.

METHODS

An infrared camera was used during the treatment to measure skin temperature and a laser Doppler perfusion imaging device was used to image the superficial perfusion before and after treatment. Six hours after topical application of 5-aminolaevulinic acid (ALA) or methyl esterified ALA (ALA-ME), 38 basal cell carcinomas were treated using light from a diode laser at 633 nm.

RESULTS

In the lesions, the perfusion immediately after PDT was similar to that before PDT. One hour after the treatment the perfusion in the lesion was increased 50% compared with before PDT. However, in the skin surrounding the lesions the perfusion was doubled immediately after PDT and was still increasing 1 h after treatment. A temperature increase in the lesions of about 1-3 degrees C was observed for light fluence rates of 100-150 mW cm-2. In all patients treated, a diffuse temperature increase was visible outside the lesions. In some of the patients, the outlines of the blood vessels surrounding the treated lesions became visible in the thermal images. Measurements of temperature on healthy volunteers not administered photosensitizer, but illuminated with light of the same fluence rate, showed a similar increase in temperature in the illuminated spots. However, no temperature increase was observed outside the illuminated area. No statistically significant differences were found between the measurements on patients treated with ALA and ALA-ME.

CONCLUSIONS

The increased perfusion in the area surrounding the lesions after PDT, as seen by perfusion and temperature measurements, is the result of an inflammatory reaction to the PDT process. However, directly after PDT the perfusion in the lesions was the same as before irradiation. The combination of these observations suggests the presence of local blood stasis during and immediately after the treatment. The temperature measurements showed that the increased temperature was well below the temperature limit of hyperthermal damage. Furthermore, the measurements indicate that the increase in temperature was primarily a consequence of the heat absorbed in the tissue.

Correlation of subcellular compartmentalization of HPMA copolymer-Mce6 conjugates with chemotherapeutic activity in human ovarian carcinoma cells

PURPOSE

Intracellular targets sensitive to oxidized damage generated by photodynamic therapy (PDT) utilizing N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-mesochlorin e6 monoethylenediamine (Mce6) conjugates was explored to aid in the design of second generation PDT delivery systems.

METHODS

Low temperature, metabolic inhibitor, and nuclear localization sequences (NLS(FITC)) were used to achieve desired subcellular localization that was evaluated by confocal analysis and subcellular fractionation. Mce6 was bound to HPMA copolymer conjugates via non-degradable dipeptide linkers (P-GG-Mce6, P-NLS(FITC)-GG-Mce6) or lysosomally degradable tetrapeptide spacers (P-GFLG-Mce6, P-NLS(FITC)-GFLG-Mce6). Chemotherapeutic efficacy was assessed by the concentration that inhibited growth by 50% (IC50), cell associated drug concentration (CAD) and confocal microscopy.

RESULTS

P-GFLG-Mce6 possessed enhanced chemotherapeutic activ ity compared to P-GG-Mce6 indicating enzymatically released Mce6 was more active than copolymer-bound Mce6. Lysosomes appeared less sensitive to photodamage as observed by a higher IC50. Nuclear-directed HPMA copolymer-Mce6 conjugates (P-NLS(FITC)-GG-Mce6, P-NLS(FITC)-GFLG-Mce6) possessed enhanced chemotherapeutic activity. However, control cationic HPMA copolymer-Mce6 conjugates containing a scrambled NLS (P-scNLS(FITC)-GG-Mce6) or amino groups (P-NH2-GG-Mce6) also displayed increased chemotherapeutic activity.

CONCLUSIONS

Nuclear delivery was observed for P-NLS(FITC)-GG-Mce6 and P-NLS(FITC)-GFLG-Mce6 indicating NLS was a feasible approach for nuclear delivery. Due to the cationic nature of NLS, increased membrane binding of PDT systems incorporating cationic nuclear targeting moieties must be addressed.

Correlation of in vivo photosensitizer fluorescence and photodynamic-therapy-induced depth of necrosis in a murine tumor model

We compared light-induced fluorescence (LIF) to nominal injected drug dose for predicting the depth of necrosis response to photodynamic therapy (PDT) in a murine tumor model. Mice were implanted with radiation-induced fibrosarcoma (RIF) and were injected with 0, 5, or 10 mg/kg Photofrin. 630-nm light (30 J/cm(2), 75 mW/cm(2)) was delivered to the tumor after 24 hours. Fluorescence emission (lambda(excitation)=545 nm, lambda( emission)=628 nm) from the tumor was measured. The LIF data had less scatter than injected drug dose, and was found to be at least as good as an injected drug dose for predicting the depth of necrosis after PDT. Our observations provide further evidence that fluorescence spectroscopy can be used to quantify tissue photosensitizer uptake and to predict PDT tissue damage.

Subcellular localization of Photofrin determines the death phenotype of human epidermoid carcinoma A431 cells triggered by photodynamic therapy: when plasma membranes are the main targets

Photodynamic therapy (PDT) is a kind of photochemo-therapeutic treatment that exerts its effect mainly through the induction of cell death. Distinct types of cell death may be elicited by different PDT regimes. In this study, the mechanisms involved in the death of human epidermoid carcinoma A431 cells triggered by PDT with Photofrin (a clinically approved photosensitizer) were characterized. Photofrin distributes dynamically in A431 cells; the plasma membranes and Golgi complex are the main target sites of Photofrin after a brief (3 h) and prolonged (24 h) incubation, respectively. Cells with differentially localized Photofrin displayed distinct death phenotypes in response to PDT. The effects of PDT on cells with plasma membrane-localized Photofrin were further studied in details. Cells stopped proliferating post PDT at Photofrin dose >7 micro g/ml, and at higher dose (28 micro g/ml) plasma membrane disruption and cell swelling were observed immediately after PDT. Dramatic alterations of several important signaling events were detected in A431 cells post Photofrin-PDT, including (i) immediate formation of reactive oxygen species (ROS), (ii) rapid activation of c-Jun N-terminal kinase, (iii) delayed activation of caspase-3 and cleavage of polyADP-ribose polymerase and p21-activated kinase 2, and (iv) loss of mitochondrial membrane potential. Intriguingly, the characteristics of typical apoptosis such as phosphatidylserine externalization and DNA fragmentation were not detected in the cell death process caused by this PDT regime. In conclusion, our results show that when plasma membranes are the main targets, Photofrin-PDT can lead to instant ROS formation and subsequent activation of downstream signaling events similar to those elicited by many apoptotic stimuli, but the damage of plasma membranes renders the death phenotype more necrosis like.

In vivo optical properties of normal canine prostate at 732 nm using motexafin lutetium-mediated photodynamic therapy

The optical properties (absorption [mu(a)], transport scattering [mu('s)] and effective attenuation [mu(eff)] coefficients) of normal canine prostate were measured in vivo using interstitial isotropic detectors. Measurements were made at 732 nm before, during and after motexafin lutetium (MLu)-mediated photodynamic therapy (PDT). They were derived by applying the diffusion theory to the in vivo peak fluence rates measured at several distances (3, 6, 9, 12 and 15 mm) from the central axis of a 2.5 cm cylindrical diffusing fiber (CDF). Mu(a) and mu('s) varied between 0.03-0.58 and 1.0-20 cm(-1), respectively. Mu(a) was proportional to the concentration of MLu.Mu(eff) varied between 0.33 and 4.9 cm(-1) (mean 1.3 +/- 1.1 cm(-1)), corresponding to an optical penetration depth (8 = 1/(mu(eff)) of 0.5-3 cm (mean 1.3 +/- 0.8 cm). The mean light fluence rate at 0.5 cm from the CDF was 126 +/- 48 mW/cm2 (N = 22) when the total power from the fiber was 375 mW (150 mW/cm). This study showed significant inter- and intraprostatic differences in the optical properties, suggesting that a real-time dosimetry measurement and feedback system for monitoring light fluences during treatment should be advocated for future PDT studies. However, no significant changes were observed before, during and after PDT within a single treatment site.

Quantitation of motexafin lutetium in human plasma by liquid chromatography-tandem mass spectrometry and inductively coupled plasma-atomic emission spectroscopy

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) methods were developed and validated for the evaluation of motexafin lutetium (MLu, lutetium texaphyrin, PCI-0123) pharmacokinetics in human plasma. The LC-MS/MS method was specific for MLu, whereas the ICP-AES method measured total elemental lutetium. Both methods were fast, simple, precise, and accurate. For the LC-MS/MS method, a closely related analogue (PCI-0353) was used as the internal standard (IS). MLu and the IS were extracted from plasma by protein precipitation and injected into an LC-MS/MS system configured with a C18 column and an electrospray interface. The lower limit of quantitation was 0.05 microg MLu mL(-1), with a signal-to-noise ratio of 15:1. The response was linear from 0.05 to 5.0 microg MLu mL(-1). For the ICP-AES method, indium was used as the IS. The sample was digested with nitric acid, diluted, filtered, and then injected into the ICP-AES system. Two standard curve ranges were validated to meet the expected range of sample concentrations: 0.5 to 50, and 0.1 to 10 microg Lu mL(-1). The LC-MS/MS and ICP-AES methods were validated to establish accuracy, precision, analyte stability, and assay robustness. Interday precision and accuracy of quality control samples were < or =6.3% coefficient of variation (CV) and within 2.2% relative error (RE) for the LC-MS/MS method, and < or =8.7% CV and within 4.9% RE for the ICP-AES method. Plasma samples from a subset of patients in a clinical study were analyzed using both methods. For a representative patient, over 90% of the elemental lutetium in plasma could be ascribed to intact MLu at early time points. This percentage decreased to 59% at 48 hours after dosing, suggesting that some degradation and/or metabolism of the drug may have occurred.

A comparison of protoporphyrin IX and protoporphyrin IX dimethyl ester as a photosensitizer in poorly differentiated human nasopharyngeal carcinoma cells

Protoporphyrin IX dimethyl ester (PME), a dimethyl esterification of protoporphyrin IX (PpIX), exhibits higher intracellular uptake into NPC/CNE2 cells, a poorly differentiated human nasopharyngeal carcinoma, than does PpIX. Phototoxicity studies reveal PME to be a more potent photosensitizer than is PpIX, at the early and late incubation time points. Correlating phototoxicity with subcellular localization indicates that PME is a more potent photosensitizer when its primary target of photodamage is mitochondria. Also, additional targeting of lysosome enhances phototoxicity.

Photodynamic therapy: applications in atherosclerotic vascular disease with motexafin lutetium

Photodynamic therapy (PDT) has been approved as a tissue-specific light-activated cytotoxic therapy for many diseases. The ability of PDT to destroy target tissues selectively is especially appealing for atherosclerotic plaque. Biotechnology has developed a new generation of selective photosensitizers and catheter-based technological advances in light delivery have allowed the introduction of PDT into the vasculature. The largest experience to date is with motexafin lutetium (MLu, Antrin), an expanded porphyrin (texaphyrin) that accumulates in plaque. The combination of the motexafin lutetium and endovascular illumination, or Antrin phototherapy, has been shown to reduce plaque in animal models. Antrin phototherapy generates cytotoxic singlet oxygen that has been shown to induce apoptosis in macrophages and smooth muscle cells. The safety, tolerability, and preliminary efficacy of Antrin phototherapy has been assessed in a phase 1 dose-ranging clinical trial in subjects with peripheral artery disease and is currently being examined in a phase 1 study in subjects with lesions of the native coronary arteries undergoing stent implantation. The preliminary results suggest that Antrin phototherapy is safe, well tolerated, and nontraumatic.

Release of cytochrome c and activation of pro-caspase-9 following lysosomal photodamage involves Bid cleavage

Photodynamic therapy (PDT) protocols employing lysosomal sensitizers induce apoptosis via a mechanism that causes cytochrome c release prior to loss of mitochondrial membrane potential (DeltaPsi(m)). The current study was designed to determine how lysosomal photodamage initiates mitochondrial-mediated apoptosis in murine hepatoma 1c1c7 cells. Fluorescence microscopy demonstrated that the photosensitizer N-aspartyl chlorin e6 (NPe6) localized to the lysosomes. Irradiation of cultures preloaded with NPe6 induced the rapid destruction of lysosomes, and subsequent cleavage/activation of Bid, pro-caspases-9 and -3. Pro-caspase-8 was not activated. Release of cytochrome c occurred at about the time of Bid cleavage and preceded the loss of DeltaPsi(m). Extracts of purified lysosomes catalyzed the in vitro cleavage of cytosolic Bid, but not pro-caspase-3 activation. Pharmacological inhibition of cathepsin B, L and D activities did not suppress Bid cleavage or pro-caspases-9 and -3 activation. These studies demonstrate that photodamaged lysosomes trigger the mitochondrial apoptotic pathway by releasing proteases that activate Bid.

Photodynamic therapy for choroidal neovascularization: a review

PURPOSE

To review the biophysical basis and current state of therapy for photodynamic closure of subfoveal choroidal neovascularization in the eye.

METHODS

A review of the literature is included, which encompasses the chemical structure, biophysical mechanism of action, range of available agents, status of clinical trials, clinical indications, results of treatments, complications, and future directions.

RESULTS

Photodynamic therapy has been shown to be effective in closing both experimental choroidal neovascularization in animal models as well as subfoveal choroidal neovascularization in humans. The therapy results in temporary closure of choroidal new vessels for a period of approximately 1 to 4 weeks. By 12 weeks, most patients have reperfusion or reproliferation of choroidal new vessels resulting in the need for retreatment to achieve continued closure and visual stabilization. Differences exist in the quantum yield, clinical efficiency, and light and sensitizer dose requirements between different classes of agents. Further clinical trials will be required to determine the optimal form of therapy, with verteporfin (Visudyne) as the only currently approved agent. Other agents, including tin etiopurpurin (Purlytin) and motexafin lutetium (Optrin), are currently undergoing phase III, and phase II trials, respectively.

CONCLUSIONS

Photodynamic therapy is a promising treatment modality shown to be effective in achieving closure and stabilization of vision loss compared with placebo control in eyes with subfoveal choroidal neovascularization.

Photodynamic therapy with pyropheophorbide-a methyl ester in human lung carcinoma cancer cell: efficacy, localization and apoptosis

Pyropheophorbide-a methyl ester (MPPa) is a semisynthetic photosensitizer derived from chlorophyll a. The absorption peak of MPPa in organic solvent and in cells was at 667 and 674 nm, respectively. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay showed that MPPa had no dark cytotoxicity. In vitro photodynamic activity was extensively evaluated using a human lung carcinoma cancer cell line (NCI-h446). MPPa exhibited no genotoxicity, as assayed by single-cell gel electrophoresis. Using confocal laser scanning microscopy and organelle-specific fluorescent probes, MPPa was found to localize in the intracellular membrane system, namely the endoplasmic reticulum, Golgi apparatus, lysosomes and mitochondria, in the NCI-h446 cells. Furthermore, nuclear staining and DNA gel electrophoresis revealed that DNA condensation and fragmentation occurred post-photodynamic therapy, indicating the cell death was in the apoptotic mode.