Photodynamic therapy in Barrett's esophagus: results of treatment of 17 patients

Red Blood Cell-Facilitated Photodynamic Therapy for Cancer Treatment

Photodynamic therapy (PDT) is a promising treatment modality for cancer management. So far, most PDT studies have focused on delivery of photosensitizers to tumors. O₂, another essential component of PDT, is not artificially delivered but taken from the biological milieu. However, cancer cells demand a large amount of O₂ to sustain their growth and that often leads to low O₂ levels in tumors. The PDT process may further potentiate the oxygen deficiency, and in turn, adversely affect the PDT efficiency. In the present study, a new technology called red blood cell (RBC)-facilitated PDT, or RBC-PDT, is introduced that can potentially solve the issue. As the name tells, RBC-PDT harnesses erythrocytes, an O₂ transporter, as a carrier for photosensitizers. Because photosensitizers are adjacent to a carry-on O₂ source, RBC-PDT can efficiently produce ¹O₂ even under low oxygen conditions. The treatment also benefits from the long circulation of RBCs, which ensures a high intraluminal concentration of photosensitizers during PDT and hence maximizes damage to tumor blood vessels. When tested in U87MG subcutaneous tumor models, RBC-PDT shows impressive tumor suppression (76.7%) that is attributable to the codelivery of O₂ and photosensitizers. Overall, RBC-PDT is expected to find wide applications in modern oncology.

Endoscopic treatments for Barrett's esophagus: a systematic review of safety and effectiveness compared to esophagectomy

BACKGROUND

Recently, several new endoscopic treatments have been used to treat patients with Barrett's esophagus with high grade dysplasia. This systematic review aimed to determine the safety and effectiveness of these treatments compared with esophagectomy.

METHODS

A comprehensive literature search was undertaken to identify studies of endoscopic treatments for Barrett's esophagus or early stage esophageal cancer. Information from the selected studies was extracted by two independent reviewers. Study quality was assessed and information was tabulated to identify trends or patterns. Results were pooled across studies for each outcome. Safety (occurrence of adverse events) and effectiveness (complete eradication of dysplasia) were compared across different treatments.

RESULTS

The 101 studies that met the selection criteria included 8 endoscopic techniques and esophagectomy; only 12 were comparative studies. The quality of evidence was generally low. Methods and outcomes were inconsistently reported. Protocols, outcomes measured, follow-up times and numbers of treatment sessions varied, making it difficult to calculate pooled estimates.The surgical mortality rate was 1.2%, compared to 0.04% in 2831 patients treated endoscopically (1 death). Adverse events were more severe and frequent with esophagectomy, and included anastomotic leaks (9.4%), wound infections (4.1%) and pulmonary complications (4.1%). Four patients (0.1%) treated endoscopically experienced bleeding requiring transfusions. The stricture rate with esophagectomy (5.3%) was lower than with porfimer sodium photodynamic therapy (18.5%), but higher than aminolevulinic acid (ALA) 60 mg/kg PDT (1.4%). Dysphagia and odynophagia varied in frequency across modalities, with the highest rates reported for multipolar electrocoagulation (MPEC). Photosensitivity, an adverse event that occurs only with photodynamic therapy, was experienced by 26.4% of patients who received porfimer sodium.Some radiofrequency ablation (RFA) or argon plasma coagulation (APC) studies (used in multiple sessions) reported rates of almost 100% for complete eradication of dysplasia. But the study methods and findings were not adequately described. The other studies of endoscopic treatments reported similarly high rates of complete eradication.

CONCLUSIONS

Endoscopic treatments offer safe and effective alternatives to esophagectomy for patients with Barrett's esophagus and high grade dysplasia. Unfortunately, shortcomings in the published studies make it impossible to determine the comparative effectiveness of each of the endoscopic treatments.

Treatment for Barrett's oesophagus

BACKGROUND

Treatments for Barrett's oesophagus, the precursor lesion of adenocarcinoma, are available but whether these therapies effectively prevent the development of adenocarcinoma, and in some cases eradicate the Barrett's oesophagus segment, remains unclear.

OBJECTIVES

To summarise, quantify and compare the efficacy of pharmacological, surgical and endoscopic treatments for the eradication of dysplastic and non-dysplastic Barrett's oesophagus and prevention of these states from progression to adenocarcinoma.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library 2004, issue 4), MEDLINE (1966 to June 2008) and EMBASE (1980 to June 2008).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing medical, endoscopic or non-resectional surgical treatments for Barrett's oesophagus. The primary outcome measures were complete eradication of Barrett's and dysplasia at 12 months, and reduction in the number of patients progressing to cancer at five years or latest time point.

DATA COLLECTION AND ANALYSIS

Three authors independently extracted data and assessed the quality of the trials included in the analysis.

MAIN RESULTS

Sixteen studies, including 1074 patients, were included. The mean number of participants in the studies was small (n = 49; range 8 to 208). Most studies did not report on the primary outcomes. Medical and surgical interventions to reduce symptoms and sequelae of gastro-oesophageal reflux disease (GORD) did not induce significant eradication of Barrett's oesophagus or dysplasia. Endoscopic therapies (photodynamic therapy (PDT with aminolevulinic acid or porfimer sodium), argon plasma coagulation (APC) and radiofrequency ablation (RFA)) all induced regression of Barrett's oesophagus and dysplasia. The data for photodynamic therapy were heterogeneous with a mean eradication rate of 51% for Barrett's oesophagus and between 56% and 100% for dysplasia, depending on the treatment regimens. The variation in photodynamic therapy eradication rates for dysplasia was dependent on the drug, source and dose of light. Radiofrequency ablation resulted in eradication rates of 82% and 94% for Barrett's oesophagus and dysplasia respectively, compared to a sham treatment. Endoscopic treatments were generally well tolerated, however all were associated with some buried glands, particularly following argon plasma coagulation and photodynamic therapy, as well as photosensitivity and strictures induced by porfimer sodium based photodynamic therapy in particular.

AUTHORS' CONCLUSIONS

Despite their failure to eradicate Barrett's oesophagus, the role of medical and surgical interventions to reduce the troubling symptoms and sequelae of GORD is not questioned. Whether therapies for GORD reduce the cancer risk is not yet known. Ablative therapies have an increasing role in the management of dysplasia within Barrett's and current data would favour the use of radiofrequency ablation compared with photodynamic therapy. Radiofrequency ablation has been shown to yield significantly fewer complications than photodynamic therapy and is very efficacious at eradicating both dysplasia and Barrett's itself. However, long-term follow-up data are still needed before radiofrequency ablation can be used in routine clinical care without the need for very careful post-treatment surveillance. More clinical trial data and in particular randomised controlled trials are required to assess whether or not the cancer risk is reduced in routine clinical practice.

Advances in photodynamic therapy for gastrointestinal tumors and its propect

This paper reviews the photodynamic therapy for gastrointestinal tumors and its mechanisms, and describes the authors' experience with it. It is feasible and reasonable to use photodynamic therapy for gastrointestinal tumors. It is not in contradiction with PDT and traditional surgical treatment, chemotherapy, radiation and immune therapy, etc. The main mechanisms of photodynamic therapy for gastrointestinal tumors are to damage tumor microvasculature, induce cancer cell apoptosis, injure cancer cell membrane, and trigger immune reactions.

Columnar lined (Barrett's) esophagus: future perspectives

Columnar lined esophagus (CLE) or Barrett's esophagus is the precursor for esophageal adenocarcinoma. Future advances in understanding and management of this condition as well as improving the quality of care of CLE patients depends on answering essential questions. It is important to standardize the criteria for CLE definition. The rapid increase in incidence of CLE and adenocarcinoma raises serious concerns that the current management of gastroesophageal reflux disease (GERD) needs reassessment. The risk factors that determine who will and will not develop CLE are as yet undetermined. There is a need to develop a clinical risk stratification tool, which will help in determining who should be screened. The impact of elimination of GERD on the natural history of CLE is one important area for future research. The benefit of surveillance strategies remains unproven and the ideal endoscopic frequency, protocols and markers of cancer risk are unknown. Dysplasia may not provide the gold standard marker of cancer risk because of some inherited problems. A better technique than the current endoscopic pinch biopsy protocol is needed. To overcome the limitations of histological markers, many other markers of cancer risk needs to be developed and validated. The key question as to whether cancer risk is actually reduced by the new ablation modalities remains unanswered. The natural history of dysplasia and its management needs to be clarified. Although many questions have to be answered, it seems, however, that at least some answers exist, and these and proposals for answering some of these questions are underlined throughout this review.

Synthesis and biological in vitro evaluation of novel PEG-psoralen conjugates

Psoralens are well-known photosensitizers, and 8-methoxypsoralen and 4,5',8-trimethylpsoralen are widely used in photomedicine as "psoralens plus UVA therapy" (PUVA), in photopheresis, and in sterilization of blood preparations. In an attempt to improve the therapeutic efficiency of PUVA therapy and photopheresis, four poly(ethylene glycol) (PEG)-psoralen conjugates were synthesized to promote tumor targeting by the enhanced permeability and retention (EPR) effect. Peptide linkers were used to exploit specific enzymatic cleavage by lysosomal proteases. A new psoralen, 4-hydroxymethyl-4',8-dimethylpsoralen (6), suitable for polymer conjugation was synthesized. The hydroxy group allowed exploring different strategies for PEG conjugation, and linkages with different stability such ester or urethanes were obtained. PEG (5 kDa) was covalently conjugated to the new psoralen derivative using four different linkages, namely, (i) direct ester bond (7), (ii) ester linkage with a peptide spacer (8), (iii) a carbamic linker (9), and (iv) a carbamic linker with a peptide spacer (12). The stability of these new conjugates was assessed at different pHs, in plasma and following incubation with cathepsin B. Conjugates 7 and 8 were rapidly hydrolyzed in plasma, while 9 was stable in buffer and in the presence of cathepsin B. As expected, only the conjugates containing the peptide linker released the drug in presence of cathepsin B. In vitro evaluation of the cytotoxic activity in the presence and absence of light was carried out in two cell lines (MCF-7 and A375 cells). Conjugates 7 and 8 displayed a similar activity to the free drug (probably due to the low stability of the ester linkage). Interestingly, the conjugates containing the carbamate linkage (9 and 12) were completely inactive in the dark (IC50 > 100 microM in both cell lines). However, antiproliferative activity become apparent after UV irradiation. Conjugate 12 appears to be the most promising for future in vivo evaluation, since it was relatively stable in plasma, which should allow tumor targeting and drug release to occur by cathepsin B-mediated hydrolysis.