Pharmacokinetics of fluorescent polyporphyrin Photofrin II in normal rat tissue and rat bladder tumor

Integrating sphere effect in whole bladder wall photodynamic therapy: I. 532 nm versus 630 nm optical irradiation

The optical absorption, scattering and anisotropy coefficients of piglet bladder, with and without Photofrin, and of diseased human bladder were determined in vitro with a double integrating sphere set-up in the wavelength range 450-800 nm. Monte Carlo simulations were performed in a spherical geometry, representing the bladder, using the optical properties at 532 nm and 630 nm determined in vitro. The calculated fluence rates support the fluence rates that were measured at the bladder wall of a piglet during an in vivo whole bladder wall (WBW) irradiation at 532 nm and 630 nm. Fluence rates calculated and measured in vivo at 630 nm are in agreement with those measured previously in clinical photodynamic therapy (PDT) at 630 nm. WBW-PDT with red light (630 nm) will be technically more advantageous than with green light (532 nm) because of a stronger integrating sphere effect, which reduces the variations of the fluence rate at the bladder wall when the isotropic light source is moved away from the centre of the bladder. Since the optical properties show considerable variations from bladder to bladder, and since as a result the light fluence rate at the bladder wall can vary by a factor of 3 to 4 for the same non-scattered light fluence rate, we conclude that in situ light dosimetry during clinical WBW-PDT is a necessity.

Fluorescence induced with 5-aminolevulinic acid for the endoscopic detection and follow-up of esophageal lesions

BACKGROUND

The aim of this study was to investigate the use of orally administered 5-aminolevulinic acid (ALA) for in vivo photodynamic diagnosis and follow-up of premalignant and malignant esophageal lesions.

METHODS

Twenty-two patients with known or treated malignant and precancerous esophageal lesions were sensitized with orally administered ALA (15 mg/kg). Six patients had Barrett's esophagus, with or without severe dysplasia, 5 squamous cell cancer or early-stage (uT1N0M0) adenocarcinoma, 1 advanced-stage (uT3N1) adenocarcinoma, and 1 patient a lesion with an appearance that suggested esophageal cancer. Nine patients underwent photodynamic diagnosis for follow-up after treatment of esophageal cancer with curative intent; 6 had no macroscopically visible lesion and 3 a barely visible lesion under standard (white-light) endoscopy. Photodynamic diagnosis was conducted 6 to 7 hours after oral administration of ALA by using a special light source capable of delivering either white or violet-blue light. Red fluorescence was detected with a charged coupled device camera attached to a fiberoptic endoscope. Corresponding endoscopic, fluorescence, and microscopic findings were compared.

RESULTS

By using histology as the reference standard (n = 86 biopsies), 85% of the biopsy sites with premalignant or malignant histopathology exhibited red fluorescence, whereas only 25% were detected with white-light endoscopy.

CONCLUSION

ALA-induced fluorescence might be useful for the early endoscopic detection of malignant esophageal lesions and follow-up after treatment of such lesions with curative intent.

Endoscopic photodynamic diagnosis: oral aminolevulinic acid is a marker of GI cancer and dysplastic lesions

BACKGROUND

Dysplasia and early cancer of the upper gastrointestinal (GI) tract often are undetected at white-light endoscopy. We describe oral administration of 5-aminolevulinic acid for the in vivo photodynamic diagnosis of premalignant and malignant lesions during endoscopy.

METHODS

Four patients with known gastric adenoma (n = 1), macroscopically undetected but histologically proven esophageal squamous cell cancer (n = 1), suspected early cancer of the esophagus (n = 1), and multiple duodenal adenomas (n = 1) were sensitized with 5-aminolevulinic acid administered orally (15 mg/kg body weight). Photodynamic diagnosis was conducted after a retention time of 6 to 7 hours with a special light source capable of delivering either white or violet-blue light. Red fluorescence was detected through the gastroscope with an image-intensifying camera.

RESULTS

All malignant lesions exhibited red or bluish fluorescence during photodynamic diagnosis. Fluorescence-negative mucosal areas proved to be histologically benign.

CONCLUSION

Fluorescence induced with 5-aminolevulinic acid might be useful for the endoscopic detection of dysplasia and early carcinoma in the upper GI tract. Further investigations are needed to evaluate the sensitivity and specificity of photodynamic diagnosis for different tumor entities.

5-Aminolevulinic acid-based photodynamic therapy. Clinical research and future challenges

BACKGROUND

Photodynamic therapy (PDT) for cancer patients has developed into an important new clinical treatment modality in the past 25-years. PDT involves administration of a tumor-localizing photosensitizer or photosensitizer prodrug (5-aminolevulinic acid [ALA], a precursor in the heme biosynthetic pathway) and the subsequent activation of the photosensitizer by light. Although several photosensitizers other than ALA-derived protoprophyrin IX (PpIX) have been used in clinical PDT, ALA-based PDT has been the most active area of clinical PDT research during the past 5 years. Studies have shown that a higher accumulation of ALA-derived PpIX in rapidly proliferating cells may provide a biologic rationale for clinical use of ALA-based PDT and diagnosis. However, no review updating the clinical data has appeared so far.

METHODS

A review of recently published data on clinical ALA-based PDT and diagnosis was conducted.

RESULTS

Several individual studies in which patients with primary nonmelanoma cutaneous tumors received topical ALA-based PDT have reported promising results, including outstanding cosmetic results. However, the modality with present protocols does not in general, appear to be superior to conventional therapies with respect to initial complete response rates and long term recurrence rates, particularly in the treatment of nodular skin tumors. Topical ALA-PDT does have the following advantages over conventional treatments: it is noninvasive; it produces excellent cosmetic results; it is well tolerated by patients; it can be used to treat multiple superficial lesions in short treatment sessions; it can be applied to patients who refuse surgery or have pacemakers and bleeding tendency; it can be used to treat lesions in specific locations, such as the oral mucosa or the genital area; it can be used as a palliative treatment; and it can be applied repeatedly without cumulative toxicity. Topical ALA-PDT also has potential as a treatment for nonneoplastic skin diseases. Systemic administration of ALA does not seem to be severely toxic, but the advantage of using this approach for PDT of superficial lesions of internal hollow organs is still uncertain. The ALA-derived porphyrin fluorescence technique would be useful in the diagnosis of superficial lesions of internal hollow organs.

CONCLUSIONS

Promising results of ALA-based clinical PDT and diagnosis have been obtained. The modality has advantages over conventional treatments. However, some improvements need to be made, such as optimization of parameters of ALA-based PDT and diagnosis; increased tumor selectivity of ALA-derived PpIX; better understanding of light distribution in tissue: improvement of light dosimetry procedure; and development of simpler, cheaper, and more efficient light delivery systems.

In vivo photo-detection of chemically induced premalignant lesions and squamous cell carcinoma of the rat palatal mucosa

Photo-detection using in vivo fluorescence was studied for different stages of chemically induced premalignant lesions and squamous cell carcinoma (SCC) of the Wistar rat palatal mucosa. It was found that the epithelial dysplasia (numerically expressed in the epithelial atypia index (EAI) of the rat palate, induced by repeated application of the carcinogen 4-nitroquinoline 1-oxide (4NQO), showed an increase approximately proportional to the duration of the application period. Photo-detection of the lesions using Photofrin-induced fluorescence was studied with dual-wavelength excitation and the subtraction of images, in an attempt to reduce the autofluorescence. The Photofrin dose was 2.5 mg kg-1. This was based on a dose-response study for normal tissue damage by photodynamic therapy (PDT) in this animal model, because the underlying rationale was to study photo-detection as a method of locating additional (early) malignancies in patients treated by PDT. Fluorescence intensities 24 and 48 h after injection of Photofrin were shown to increase with the duration of 4NQO application and with increasing EAI. For an EAI greater than 15, there was a statistically significant difference (p < 0.01) between the fluorescence signals obtained with and without the injection of Photofrin. Fluorescence signals of these lesions without the use of Photofrin (autofluorescence) also showed an increase with increasing stages of epithelial dysplasia of the rat palate. However, the fluorescence signals obtained with Photofrin were always higher than those of the autofluorescence. From this study, we conclude that photo-detection with Photofrin has potential in distinguishing chemically induced premalignant lesions and squamous cell carcinomas from the normal rat palatal mucosa. Photofrin (2.5 mg per kg of body weight) certainly adds to the sensitivity of photo-detection, but autofluorescence alone also has promising features for detecting premalignant and malignant lesions of the oral mucosa.

The biology of photodynamic therapy

The subcellular, cellular and tissue/tumour interactions with non-toxic photosensitizing chemicals plus non-thermal visible light (photodynamic therapy (PDT) are reviewed. The extent to which endothelium/vasculature is the primary target is discussed, and the biochemical opportunities for manipulating outcome highlighted. The nature of tumour destruction by PDT lends itself to imaging outcome by MRI and PET.

Clinical pharmacokinetic studies of photofrin by fluorescence spectroscopy in the oral cavity, the esophagus, and the bronchi

BACKGROUND

To optimize photodynamic therapy (PDT) and photodetection of cancer, two important variables that must be considered are the uptake of the dye and the dye contrast between normal and neoplastic tissue after injection.

METHODS

To study these variables in a clinical context, an apparatus based on a noninvasive optical fiber that detects the dye by light-induced fluorescence (LIF) was constructed.

RESULTS

Studies on the pharmacokinetics of the fluorescent fraction of Photofrin in patients with early squamous cell carcinoma in the oral cavity, esophagus or bronchi show a signal contrast ranging from 1.5 to 3.5 a short time after intravenous injection that rapidly decreases and tends to unity (one) about 12 hours later. The magnitude of this contrast appears to correlate with the staging of the cancer, the more invasive tumors showing the highest contrast. The more invasive tumors also show the highest uptake. The oral cavity pharmacokinetics are similar to those found in the esophagus and the bronchi.

CONCLUSIONS

The oral cavity appears to be a good model, with easy access for optimizing photodetection and PDT in the esophagus and the bronchi. These pharmacokinetics can be used directly for optimizing photodetection. However, complementary information on the detailed localization of the drug by fluorescence microscopy and a correlation of these data with tumor necrosis efficacy are necessary to optimize PDT timing and therapeutic gain.

Fluorescence photodetection of neoplastic urothelial lesions following intravesical instillation of 5-aminolevulinic acid

OBJECTIVES

Tiny papillary tumors and flat urothelial lesions such as dysplasia or carcinoma in situ can easily be missed during routine cystoscopy. Various methods for in vivo detection of fluorescing agents (preferentially localized in malignant tissue) have been developed. Most of them are based on systemically administered synthetic porphyrin compounds and require sensitive detection devices and image processing units for fluorescence visualization. The usefulness of intracellularly accumulated endogenous protoporphyrin IX (PPIX), induced by 5-aminolevulinic acid (ALA), for diagnosis of early bladder cancer and the correlation with cystoscopic, microscopic, and fluorescence findings was investigated.

METHODS

ALA was instilled intravesically in 68 patients, followed by fluorescence cystoscopy with violet light from a krypton ion laser that produced fluorescence excitation. There were 299 biopsies obtained from fluorescing and nonfluorescing areas of the bladder.

RESULTS

ALA-induced fluorescence could be easily observed with the naked eye during cystoscopy under violet light illumination. All tumor lesions were sharply marked with brightly shining red fluorescence. Correlation of fluorescence and microscopic findings gave a sensitivity of 100% and a specificity of 68.5%. There were 26 malignant or precancerous lesions that were missed during routine cystoscopy but were detected only by ALA-induced fluorescence.

CONCLUSIONS

Labeling of urothelial lesions by PPIX fluorescence induced by intravesically instilled ALA seems to be a promising diagnostic procedure for malignant lesions that are difficult to visualize with standard cystoscopy.

Functional and histological bladder damage in mice after photodynamic therapy: the influence of sensitiser dose and time of administration

The bladders of anaesthetised mice were illuminated with red laser light (630 nm) at intervals of 1 day to 4 weeks after i.p. administration of Photofrin. Light was delivered intravesically by inserting a fibre optic, with a diffusing bulb tip, into the centre of fluid filled bladders. A single light dose of 11.3 J cm-2 applies 1 day after 10 mg kg-1 Photofrin caused a severe acute response, with increased urination frequency (five to seven times control) and hematuria. Recovery was good, however, and by 10 weeks only a mild (approximately two-fold) increase in frequency remained. There was no reduction in the amount of acute bladder damage or in the rate of healing when the interval between Photofrin and light was increased from 1 to 7 days but a 2 to 3 week interval lead to a significant reduction in damage. For an interval of 4 weeks there was only a mild (less than two-fold) increase in urination frequency during the first week. A drug dose of 2.5 mg kg-1 given 1 day before illumination caused transient haematuria but no increase in urination frequency. Doses of 5, 7.5 or 10 mg kg-1 all caused photosensitisation and the amount of bladder damage was drug dose dependent. The bladder seems to be well able to recover from severe acute damage induced by PDT. Occasional incidences of pyelonephritis were seen, however, suggesting that urinary tract infection during the acute period may lead to permanent renal damage.