5-Aminolaevulinic acid-induced photodynamic therapy and photodetection in Barrett's esophagus

Expression levels of PEPT1 and ABCG2 play key roles in 5-aminolevulinic acid (ALA)-induced tumor-specific protoporphyrin IX (PpIX) accumulation in bladder cancer

BACKGROUND

A detection method widely used of late in cancer surgery is 5-aminolevulinic acid-based photodynamic diagnosis (ALA-PDD), which relies on the tumor-specific accumulation of photosensitizing protoporphyrin IX (PpIX) after the administration of ALA. In this regard, we recently reported that peptide transporter PEPT1 and human ATP-binding cassette transporter ABCG2 are key players in regulating intracellular PpIX levels. In the present study, we re-evaluated in vivo the expression of genes involved in the porphyrin biosynthesis pathway.

METHODS

Using quantitative real-time (qRT)-PCR, we measured the mRNA levels in a clinical specimen of bladder cancer from a patient who had been subjected to ALA-PDD.

RESULTS

We confirmed that PEPT1 and ABCG2 are major contributors to the regulation of tumor-specific PpIX accumulation. qRT-PCR analysis revealed a predominantly high level of PEPT1 mRNA and a very low level of ABCG2 mRNA in the bladder cancer, corresponding to the roles of these genes in vitro. These findings were further confirmed by immunohistochemical studies with PEPT1- and ABCG2-specific antibodies.

CONCLUSION

The induction of PEPT1 gene and the suppression of ABCG2 gene expression are among the key molecular mechanisms underlying tumor-specific PpIX accumulation after the administration of ALA in bladder cancer.

Aminolevulinic acid (ALA): photodynamic detection and potential therapeutic applications

Aminolevulinic acid (ALA) is a heme precursor that may have potential applications for photodynamic detection and photodynamic therapy-based treatment of solid tumors in a variety of malignancies. ALA may have a role in other applications in surgical oncology based on its ability to discriminate neoplastic tissue from adjacent normal tissue. In this review, we provide a comprehensive summary of the published studies of ALA in noncutaneous solid malignancies.

Pivotal roles of peptide transporter PEPT1 and ATP-binding cassette (ABC) transporter ABCG2 in 5-aminolevulinic acid (ALA)-based photocytotoxicity of gastric cancer cells in vitro

BACKGROUND

Recently, 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) is being widely used in cancer therapy owing to the tumor-specific accumulation of photosensitizing protoporphyrin IX (PpIX) after the administration of ALA. In the present study, by focusing on genes involved in the porphyrin biosynthesis pathway, we aimed to explore biomarkers that are predictive for the efficacy of ALA-PDT.

METHODS

We used five lines of human gastric cancer cells to measure the ALA-based photocytotoxicity. ALA-induced production of PpIX in cancer cells was quantified by fluorescence spectrophotometry. To examine the potential involvement of PEPT1 and ABCG2 in the ALA-PDT sensitivity, stable cell lines overexpressing PEPT1 were established and ABCG2-specific siRNA used.

RESULTS

We observed that three cell lines were photosensitive, whereas the other two cell lines were resistant to ALA-based photocytotoxicity. The ALA-based photocytotoxicity was found to be well correlated with intracellular PpIX levels, which suggests that certain enzymes and/or transporters involved in ALA-induced PpIX production are critical determinants. We found that high expression of the peptide transporter PEPT1 (ALA influx transporter) and low expression of the ATP-binding cassette transporter ABCG2 (porphyrin efflux transporter) determined ALA-induced PpIX production and cellular photosensitivity in vitro.

CONCLUSION

PEPT1 and ABCG2 are key players in regulating intracellular PpIX levels and determining the efficacy of ALA-based photocytotoxicity against gastric cancer cells in vitro. Evaluation of the expression levels of PEPT1 and ABCG2 genes could be useful to predict the efficacy of ALA-PDT. Primers specific to those target genes are practical and useful biomarkers for predicting the photo-sensitivity to ALA-PDT.

5-Aminolevulinic acid-induced protoporphyrin IX levels in tissue of human malignant brain tumors

Protoporphyrin IX (PpIX) produced from exogenous, orally administered 5-aminolevulinic acid (ALA) displays high tumor-selective uptake and is being successfully employed for fluorescence-guided resection (FGR) of human malignant gliomas. Furthermore, the phototoxicity of PpIX can be utilized for photodynamic therapy (PDT) of brain tumors, which has been shown previously. Here, the absolute PpIX concentration in human brain tissue was investigated following oral ALA administration (20 mg kg(-1) b.w.). An extraction procedure was used to quantify PpIX in macroscopic tissue samples, weighing 0.013-0.214 g, obtained during FGR. The PpIX concentration was significantly higher in vital grade IV tumors (5.8 ± 4.8 μm, mean ± SD, range 0-28.2 μm, n = 8) as compared with grade III tumors (0.2 ± 0.4 μm, mean ± SD, range 0-0.9 μm, n = 4). There was also a large heterogeneity within grade IV tumors with PpIX displaying significantly lower levels in infiltration zones and necrotic regions as compared with vital tumor parts. The average PpIX concentration in vital grade IV tumor parts was in the range previously shown sufficient for PDT-induced tissue damage following irradiation. However, the feasibility of PDT for grade III brain tumors and for grade IV brain tumors displaying mainly necrotic tissue areas without solid tumor parts needs to be further investigated.

Photobleaching-based dosimetry predicts deposited dose in ALA-PpIX PDT of rodent esophagus

An improved method to estimate dose to esophageal tissue was investigated in the setting of photodynamic therapy with aminolevulinic acid-induced protoporphyrin IX (PpIX) treatment. A model of treatment-induced edema in the esophagus mucosa proved to be a well controlled and useful way to test the dosimetry model, and the light from the treatment laser together with the PpIX fluorescence intensity could be quantified reliably in real time. Dosimetry calculations based upon the detected fluorescence and bleaching kinetics were used to calculate the "effective" dose to the tissue, and a correlation was shown to exist between this metric and the edema induced in the esophagus. The difference between animals with no detectable treatment effect and those with significant edema was predictable based upon the dose calculation. The underlying assumption in the interpretation of the data is that rapid photobleaching of PpIX occurs when there is ample oxygen supply, and this bleaching is not present when oxygen is limited. This leads to the prediction that integration of the light and drug dose, in intervals where appreciable photobleaching occurs, should provide a prediction of the relative dose of singlet oxygen produced. This detection system and rodent model can be used for prospective dosimetry studies that focus on optimization of esophageal PDT.

Optical properties of adenocarcinoma and squamous cell carcinoma of the gastroesophageal junction

Photodynamic therapy (PDT) is an alternative to radical surgical resection for T1a or nonresectable carcinomas of the gastroesophageal junction. Besides the concentration of the photosensitizer, the light distribution in tissue is responsible for tumor destruction. For this reason, knowledge about the behavior of light in healthy and dysplastic tissue is of great interest for careful irradiation scheduling. The aim of this study is to determine the optical parameters (OP) of healthy and carcinomatous tissue of the gastroesophageal junction in vitro to provide reproducible parameters for optimal dosimetry when applying PDT. A total of 36 tissue samples [adenocarcinoma tissue (n=21), squamous cell tissue (n=15)] are obtained from patients with carcinomas of the gastroesophageal junction. The optical parameters are measured in 10-nm steps using new integrating sphere spectrometers in the PDT-relevant wavelength range of 300 to 1140 nm and evaluated by inverse Monte-Carlo simulation. Additional examinations are done in healthy tissue from the surgical safety margin. In the wavelength range of frequently applied photosensitizers at 330, 630, and 650 nm, the absorption coefficient in tumor tissue (adenocarcinoma 1.22, 0.16, and 0.15 mm(-1); squamous cell carcinoma 1.48, 0.13, and 0.11 mm(-1)) is significantly lower than in healthy tissue (stomach 3.34, 0.26, and 0.20 mm(-1); esophagus 2.47, 0.21, and 0.18 mm(-1)). The scattering coefficient of all tissues decreases continuously with increasing wavelength (adenocarcinoma 22.8, 12.99, and 12.52 mm(-1); squamous cell carcinoma 19.44, 9.35, and 8.98 mm(-1); stomach 20.55, 13.96, and 13.94 mm(-1); esophagus 20.34, 12.56, and 12.22 mm(-1). All tissues show an anisotropy factor between 0.80 and 0.94 over the entire spectrum. The maximum optical penetration depth for all tissues is achieved in the range of 800 to 1100 nm. At the wavelength range of 330, 630, and 650 nm, the optical penetration depth is significantly higher in carcinoma tissue (adenocarcinoma 0.27, 1.54, and 1.66 mm; squamous cell carcinoma 0.23, 1.71, and 1.84 mm) than in healthy tissue (stomach 0.16, 1.10, and 1.26 mm; esophagus 0.17, 1.47, and 1.65 mm; p<0.05). Above 1000 nm, a higher absorption coefficient of tumor tissue results in a lower optical penetration depth than in healthy tissue (p<0.05). The higher absorption and scattering of the tumor tissue in the wavelength range of available photosensitizer is associated with a low optical penetration depth. This necessitates higher energy doses and long application times or repeated applications to effectively treat large tumor volumes. Photosensitizers optimized for larger wavelength range need to be developed to increase the efficacy of PDT.

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.

Photodynamic therapy of cerebral glioma – A review Part I – A biological basis

Photodynamic therapy (PDT) has been investigated extensively in the laboratory for decades, and for over 25 years in the clinical environment, establishing it as a useful adjuvant to standard treatments for many cancers. A combination of both photochemical and photobiological processes occur that lead to the eventual selective destruction of the tumour cells. It is a potentially valuable adjuvant therapy that can be used in conjunction with other conventional therapies for the treatment of cerebral glioma. PDT has undergone extensive laboratory studies and clinical trials with a variety of photosensitizers (PS) and tumour models of cerebral glioma. Many environmental and genetically based factors influence the outcome of the PDT response. The biological basis of PDT is discussed with reference to laboratory and preclinical studies.

Spectroscopy and fluorescence in esophageal diseases

Malignant tumors of the esophagus continue to be a major health issue associated with high mortality primarily because most present with symptoms of dysphagia or anaemia. The disease at that stage is advanced and not likely curable. The big issue for squamous dysplasia and that associated with BE is that only a small proportion are discovered in surveillance programs when they are asymptomatic, either because the patient lives in a high-incidence geographical area, has a family history, previously diagnosed head and neck cancer or chronic reflux, as in Barrett's. Current endoscopic methods are hampered by the endoscopist's inability to recognize subtle topographic clues of dysplasia, sampling errors related to biopsy protocols, and confounding inflammation-induced artifacts both for the endoscopist and pathologist. What is desperately needed would be a biomarker (e.g. serological, fecal, urinary) that selects patients for endoscopy. However, such a test is not yet on the horizon. This article examines the current status in practice and research of novel optically based 'bioendoscopic' devices (i.e. fluorescence spectroscopy and imaging, confocal fluorescence microendoscopy (CFM), light scattering spectroscopy (LSS), Raman spectroscopy (RS), and immunophotodiagnostic endoscopy) which may enhance the diagnosis of dysplasia in all patients undergoing conventional white light endoscopy. Perhaps these new technologies will lead to more cost-effective diagnosis, mapping (e.g. surface), and staging (e.g. depth) of dysplasia, thereby allowing timely cure by endoscopic means (e.g. EMR and/or PDT), biological interventions (e.g. Cox-2 inhibitors) rather than esophajectomy.

Endoscopic therapy for Barrett's esophagus

With the increase in the rate of esophageal adenocarcinoma in the United States and the Western world matched with the high morbidity and mortality of esophagectomy, there is an increasing need for new and effective techniques to treat and prevent esophageal adenocarcinoma. A wide variety of endoscopic mucosal ablative techniques have been developed for early esophageal neoplasia. However, long-term control of neoplasic risk has not been demonstrated. Most studies show that specialized intestinal metaplasia may persist underneath neo-squamous mucosa, posing a risk for subsequent neoplastic progression. In this article we review current published literature on endoscopic therapies for the management of Barrett's esophagus.

Porphyrin-related photosensitizers for cancer imaging and therapeutic applications

A photosensitizer is defined as a chemical entity, which upon absorption of light induces a chemical or physical alteration of another chemical entity. Some photosensitizers are utilized therapeutically such as in photodynamic therapy (PDT) and for diagnosis of cancer (fluorescence diagnosis, FD). PDT is approved for several cancer indications and FD has recently been approved for diagnosis of bladder cancer. The photosensitizers used are in most cases based on the porphyrin structure. These photosensitizers generally accumulate in cancer tissues to a higher extent than in the surrounding tissues and their fluorescing properties may be utilized for cancer detection. The photosensitizers may be chemically synthesized or induced endogenously by an intermediate in heme synthesis, 5-aminolevulinic acid (5-ALA) or 5-ALA esters. The therapeutic effect is based on the formation of reactive oxygen species (ROS) upon activation of the photosensitizer by light. Singlet oxygen is assumed to be the most important ROS for the therapeutic outcome. The fluorescing properties of the photosensitizers can be used to evaluate their intracellular localization and treatment effects. Some photosensitizers localize intracellularly in endocytic vesicles and upon light exposure induce a release of the contents of these vesicles, including externally added macromolecules, into the cytosol. This is the basis for a novel method for macromolecule activation, named photochemical internalization (PCI). PCI has been shown to potentiate the biological activity of a large variety of macromolecules and other molecules that do not readily penetrate the plasma membrane, including type I ribosome-inactivating proteins, immunotoxins, gene-encoding plasmids, adenovirus, peptide-nucleic acids and the chemotherapeutic drug bleomycin. The background and present status of PDT, FD and PCI are reviewed.