Red and NIR light dosimetry in the human deep brain.

Photobiomodulation (PBM) appears promising to treat the hallmarks of Parkinson's Disease (PD) in cellular or animal models. We measured light propagation in different areas of PD-relevant deep brain tissue during transcranial, transsphenoidal illumination (at 671 and 808 nm) of a cadaver head and modeled optical parameters of human brain tissue using Monte-Carlo simulations. Gray matter, white matter, cerebrospinal fluid, ventricles, thalamus, pons, cerebellum and skull bone were processed into a mesh of the skull (158 × 201 × 211 voxels; voxel side length: 1 mm). Optical parameters were optimized from simulated and measured fluence rate distributions. The estimated µeff for the different tissues was in all cases larger at 671 than at 808 nm, making latter a better choice for light delivery in the deep brain. Absolute values were comparable to those found in the literature or slightly smaller. The effective attenuation in the ventricles was considerably larger than literature values. Optimization yields a new set of optical parameters better reproducing the experimental data. A combination of PBM via the sphenoid sinus and oral cavity could be beneficial. A 20-fold higher efficiency of light delivery to the deep brain was achieved with ventricular instead of transcranial illumination. Our study demonstrates that it is possible to illuminate deep brain tissues transcranially, transsphenoidally and via different application routes. This opens therapeutic options for sufferers of PD or other cerebral diseases necessitating light therapy.

Low dose endoluminal photodynamic therapy improves murine T cell-mediated colitis.

BACKGROUND AND STUDY AIMS: Low dose photodynamic therapy (LDPDT) may modify the mucosal immune response and may thus provide a therapy for Crohn's disease. We evaluated the efficacy and safety of this technique in a murine T cell-mediated colitis model. METHODS: The safety of LDPDT was first tested in BALB/c mice. Naïve T cells were used to induce colitis in mice with severe combined immunodeficiency, which were followed up endoscopically, and a murine endoscopic index of colitis (MEIC) was developed. The efficacy of LDPDT (10 J/cm (2); delta-aminolevulinic acid, 15 mg/kg bodyweight) was then tested on mice with moderate colitis, while a disease control group received no treatment. The MEIC, weight, length, and histology of the colon, cytokine expression indices, number of mucosal CD4 (+) T cells, percentage of apoptotic CD4 (+) T cells, body weight, and systemic side effects were evaluated. RESULTS: LDPDT improved the MEIC ( P = 0.011) and the histological score ( P = 0.025), diminished the expression indices of the proinflammatory cytokines, interleukin-6 ( P = 0.042), interleukin-17 ( P = 0.029), and interferon-gamma ( P = 0.014), decreased the number of mucosal CD4 (+) T cells, and increased the percentage of apoptotic CD4 (+) T cells compared with the disease control group. No local or systemic side effects occurred. CONCLUSION: LDPDT improves murine T cell-mediated colitis, decreases the proinflammatory cytokines interleukin-6, interleukin-17, and interferon-gamma, and decreases the number of CD4 (+) T cells. No adverse events were observed. Therefore, this technique is now being evaluated in patients with inflammatory bowel disease.

[Fluorescence cystoscopy. Perspective in clinical practice and research]. / Fluoreszenzzystoskopie. Perspektiven in Klinik und Forschung.

Many studies confirm the clinical interest of photodynamic diagnostics (PDD) in non-muscle invasive bladder cancer management. PDD or fluorescence cystoscopy is not only of great value in occult urothelial cancer detection, but may have a positive impact on disease-free survival and prognosis. Yet, its specificity is found to be highly variable between studies mainly in relation to different disease profiles. New imaging techniques aimed at enhancing visualization to assess the bladder wall are under development.

Video monitoring of neovessel occlusion induced by photodynamic therapy with verteporfin (Visudyne), in the CAM model.

The aim of the present study was to monitor photodynamic angioocclusion with verteporfin in capillaries. Details of this process were recorded under a microscope in real-time using a high-sensitivity video camera. A procedure was developed based on intravenous (i.v.) injection of a light-activated drug, Visudyne, into the chorioallantoic membrane (CAM) of a 12-day-old chicken embryo. The effect of light activation was probed after 24 h by i.v. injection of a fluorescent dye (FITC dextran), and analysis of its fluorescence distribution. The angioocclusive effect was graded based on the size of the occluded vessels, and these results were compared with clinical observations. The time-resolved thrombus formation taking place in a fraction of the field of view was video recorded using a Peltier-cooled CCD camera. This vessel occlusion in the CAM model was reproducible and, in many ways, similar to that observed in the clinical use of verteporfin. The real-time video recording permitted the monitoring of platelet aggregation and revealed size-selective vascular closure as well as some degree of vasoconstriction. Platelets accumulated at intravascular junctions within seconds after verteporfin light activation, and capillaries were found to be closed 15 min later at the applied conditions. Larger-diameter vessels remained patent. Repetition of these data with a much more sensitive camera revealed occlusion of the treated area after 5 min with doses of verteporfin and light similar to those used clinically. Consequently, newly developed light-activated drugs can now be studied under clinically relevant conditions.

Autofluorescence detection of tumors in the human lung--spectroscopical measurements in situ, in an in vivo model and in vitro.

To detect bronchial carcinoma by autofluorescence, we measured the spectra of tumor and normal tissue in situ, in an in vivo model and in vitro by fiber optic spectrometer and two-dimensional resolved microspectroscopy. The in situ measurements were performed in bronchi of nine patients with squamous cell carcinoma during regular bronchoscopy with autofluorescence assistance. The fluorescence was monitored with a fiber optical spectrometer under blue light excitation (lambda=405nm). In an in vivo model, the resected lobe of a lung was perfused under physiological conditions. Tumorous and normal tissues were examined spectroscopically during perfusion and after blood removal and substitution with formol. In another setup the wavelength dependency of autofluorescence was examined on resected parts of physiological bronchi and central bronchial carcinomas. Under the variation of the excitation from 385 to 465nm the autofluorescence response was monitored with a fiber optic spectrometer. For investigation of the origin of autofluorescence, two-dimensional resolved spectroscopy was performed with the SpectraCube system on several sections of tumor and normal tissues All measurements, performed in vivo, in the in vivo model and in vitro agreed, that the main difference of the autofluorescence between tumor and normal bronchus tissue is the intensity of the fluorescences' main peak at 505nm. The signal on tumor tissue is in all cases significantly lower than that of normal tissue. The shape of the autofluorescence peaks is in healthy and carcinoma tissue approximately the same with two characteristic minima at 540 and 580nm. After the preparation with formaldehyde those minima disappeared from the spectra. A comparison with the absorption spectra of hemoglobin showed, that the variation of the spectra may be due to the blood content in the tissue. Two-dimensional spatially resolved spectroscopy showed, that the lower intensity of fluorescence in tumor tissue is due to the irregular and low-concentrated formation of fluorescent structures, which seen to be the elastic structures of bronchial tissue.

Design of an endoscopic optical reference to be used for autofluorescence bronchoscopy with a commercially available diagnostic autofluorescence endoscopy (DAFE) system.

We present the design of a sterilizable optical reference to characterize and quantify the inter-patient variations in tissue autofluorescence during autofluorescence bronchoscopy with Richard Wolf's diagnostic autofluorescence endoscopy (DAFE) system. The reference was designed to have optical and spectral properties similar to those of the human bronchial wall in spectral conditions corresponding to autofluorescence bronchoscopy conducted with the DAFE system (fluorescence excitation at 390-470 nm and red backscattering light at 590-680 nm). The reference's effective attenuation coefficient and reflectance were measured at 675 nm. In addition, its fluorescence emission spectrum was determined under 430 nm wavelength excitation. The reference is photostable, reproducible, biocompatible and small enough to be easily inserted through the working channel of a conventional bronchofibrescope. This cylindrical (length: 2 mm; diameter: 2 mm) optical reference was validated in a clinical environment.

Photothrombic activity of m-THPC-loaded liposomal formulations: pre-clinical assessment on chick chorioallantoic membrane model.

The objective of this study was to evaluate the ability of meso-tetra(hydroxyphenyl)chlorin (m-THPC) encapsulated into liposomal formulations to occlude neovascularization. Two m-THPC formulations including conventional or plain liposomes (Foslip) based on dipalmitoylphosphatidylcholine (DPPC) and the corresponding long-circulating poly(ethylene glycol) (PEG)-modified liposomes (PEGylated liposomes: Fospeg) were evaluated as delivery systems. Using the chick chorioallantoic membrane (CAM) as in vivo model, the fluorescence pharmacokinetic behaviour of encapsulated m-THPC reflecting the rate of the extravasation of the dye from the CAM vasculature and its photothrombic effectiveness were determined. This study was focused on the influence of the drug and/or light doses on the mean retention time of m-THPC within the CAM blood vessels after intravenous injection, and its photothrombic efficacy. Irrespective of the formulations tested and the drug doses injected, similar fluorescence pharmacokinetic profiles were obtained. The fluorescence contrast reached a steady state 30 s after injection. Constant positive values of the fluorescence contrast suggest that m-THPC is confined into the intravascular compartment during the experimental time (500 s). However, the photodynamic therapy assays showed that Foslip appears to be less potent than Fospeg in terms of photothrombic activities on the CAM model. For instance, the light dose necessary to induce the desired vascular damage with Foslip was twice (100 J/cm2) higher than with Fospeg (50 J/cm2). It can be inferred that this pre-clinical study showed that the formulation based on PEGylated liposomes technology offers a suitable delivery system for the treatment of choroidal neovascularization associated with age-related macular degeneration.

Preclinical evaluation of a novel water-soluble chlorin E6 derivative (BLC 1010) as photosensitizer for the closure of the neovessels.

In the present study, photodynamic activity of a novel photosensitizer (PS), Chlorin e(6)-2.5 N-methyl-d-glucamine (BLC 1010), was evaluated using the chorioallantoic membrane (CAM) as an in vivo model. After intravenous (i.v.) injection of BLC 1010 into the CAM vasculature, the applicability of this drug for photodynamic therapy (PDT) was assessed in terms of fluorescence pharmacokinetics, i.e. leakage from the CAM vessels, and photothrombic activity. The influence of different PDT parameters including drug and light doses on the photodynamic activity of BLC 1010 has been investigated. It was found that, irrespective of drug dose, an identical continuous decrease in fluorescence contrast between the drug inside and outside the blood vessels was observed. The optimal treatment conditions leading to desired vascular damage were obtained by varying drug and light doses. Indeed, observable damage was achieved when irradiation was performed at light doses up to 5 J/cm(2) 1 min after i.v. injection of drug doses up to 0.5 mg/kg body weight(b.w.). However, when irradiation with light doses of more than 10 J/cm(2) was performed 1 min after injection of drug doses up to 2 mg/kg body weight, this led to occlusion of large blood vessels. It has been demonstrated that it is possible to obtain the desired vascular occlusion and stasis with BLC 1010 for different combinations of drug and/or light doses.

Photodynamic therapy and endoscopic mucosal resection as minimally invasive approaches for the treatment of early esophageal tumors: Pre-clinical and clinical experience in Lausanne.

Esophageal cancer, when detected at an early stage, has a very good probability of being eradicated by surgery or radiotherapy. However, less aggressive treatments also tend to provide high rates of cure without the side effects of radical surgery or radiotherapy. Among them, photodynamic therapy and endoscopic mucosal resection have been experienced as alternative techniques for mucosal ablation in patients with superficial squamous-cell carcinoma (SCC) of the esophagus, or high-grade dysplasia and early stage adenocarcinoma arising in Barrett's esophagus. We report on the results of our clinical experience with photodynamic therapy and discuss about its advantages and limitations. We also present a pre-clinical study, which had evaluated the feasibility, efficacy, and safety of a promising new method of endoscopic mucosal resection (EMR) based on the use of a modified rigid esophagoscope. The animal model chosen was the sheep because of its similarities with humans regarding the thickness and histologic structure of the esophagus. This new resection modality offers a promising approach in comparison with other options currently available, namely EMRs performed with flexible gastroscopes. It appears to be superior in terms of the size of the resected specimen, the precision and regularity of the resection depth, and the accuracy of histological diagnosis with safety margins.

Selectivity of the photosensitiser Tookad for photodynamic therapy evaluated in the Syrian golden hamster cheek pouch tumour model.

The response to photodynamic therapy (PDT) with the photosensitiser (PS) Tookad was measured in the Syrian hamster cheek pouch model on normal mucosae and chemically induced squamous cell carcinoma. This PS is a palladium-bacteriopheophorbide presenting absorption peaks at 538 and 762 nm. The light dose, drug dose and drug injection-light irradiation times (DLI), ranging between 100 and 300 J cm(-2), 1-5 mg kg(-1) and 10-240 min respectively, were varied and the response to PDT was analysed by staging the macroscopic response and by the histological examination of the sections of the irradiated cheek pouch. A fast time decay of the tissular response with drug dose of 1-5 mg kg(-1) was observed for DLI ranging from 10 to 240 min and for light doses of 100-300 J cm(-2) delivered at a light dose rate of 150 mW cm(-2). A significantly higher level of tissular response was observed for squamous cell carcinoma compared to normal tissue. Nevertheless, the threshold level of the drug-light dose for a detectable response was not significantly different in the tumoral vs normal tissue. The highest response at the shortest DLIs and the absence of measurable response at DLI larger than 240 min at light dose of 300 J cm(-2) and drug dose of 5 mg kg(-1) reveals the predominantly vascular effect of Tookad. This observation suggests that Tookad could be effective in PDT of vascularised lesions.

Endoscopic fluorescence detection of intraepithelial neoplasia in Barrett's esophagus after oral administration of aminolevulinic acid.

BACKGROUND AND STUDY AIMS: Barrett's esophagus is strongly associated with adenocarcinoma. Early malignant transformation of the Barrett's mucosa is often not visible endoscopically and may remain undetected until the invasive adenocarcinoma stage. Endoscopic surveillance is currently carried out on random four-quadrant biopsies at 1-2 cm intervals. Endoscopic fluorescence detection of protoporphyrin IX induced by 5-aminolevulinic acid can identify premalignant lesions. This study evaluates endoscopic fluorescence detection in patients having Barrett's esophagus and compares the results to those of standard endoscopy with random four-quadrant biopsies. PATIENTS AND METHODS: The study included 30 examinations in 28 patients (22 men, 6 women; age range 37-78 years, mean age 60 years,), with five patients having known intraepithelial neoplasia. A dose of 20 mg/kg of 5-aminolevulinic acid was given orally 5 hours before examination. Random four-quadrant biopsies were performed 4-6 weeks before endoscopic fluorescence detection. RESULTS: Of the biopsies taken during the endoscopic fluorescence detection procedure, 28 % (23/81) were true positives. More than one-third of the false-positive results were due to inflammation. None of the 97 control biopsies taken on nonfluorescing areas during endoscopic fluorescence detection were dysplastic. Endoscopic fluorescence detection showed low-grade intraepithelial neoplasia in five patients which was not diagnosed with random four-quadrant biopsies, while random four-quadrant biopsies alone showed three low-grade intraepithelial neoplasias that were invisible during endoscopic fluorescence detection. All high-grade intraepithelial neoplasias or adenocarcinomas (2/2) were detected with both methods. CONCLUSIONS: Fluorescence detection achieved a similar performance when compared with four-quadrant random biopsy, but resulted in fewer biopsies (81 for endoscopic fluorescence detection vs 531 for random four-quadrant biopsies).

Photodynamic diagnosis of ovarian cancer using hexaminolaevulinate: a preclinical study.

The unfailing detection of micrometastases during surgery of patients suffering from ovarian cancer is mandatory for the optimal management of this disease. Thus, the present study aimed at determining the feasibility of detecting micrometastases in an ovarian cancer model using the intraperitoneal administration of the photosensitiser precursor hexaminolaevulinate (HAL). For this purpose, HAL was applied intraperitoneally at different concentrations (4-12 mM) to immunocompetent Fischer 344 rats bearing a syngeneic epithelial ovarian carcinoma. The tumours were visualised laparoscopically using both white and blue light (D-light, Karl Storz, Tuttlingen, Germany), and the number of peritoneal micrometastases detected through HAL-induced photodiagnosis (PD) was compared to standard white light visualisation. Fluorescence spectra were recorded with an optical fibre-based spectrofluorometer and the fluorescence intensities were compared to the protoporphyrin IX (PpIX) fluorescence induced by 5-aminolevulinic acid under similar conditions. The number of metastases detected by the PD blue light mode was higher than when using standard white light abdominal inspection for all applied concentrations. Twice as many cancer lesions were detected by fluorescence than by white light inspection. The hexyl-ester derivative produced higher PpIX fluorescence than its parent substance aminolevulinic acid at the same concentration and application time. Fluorescence contrast between healthy and cancerous tissue was excellent for both compounds. To overcome poor diagnostic efficiency and to detect peritoneal ovarian carcinoma foci in the large surface area of the human peritoneal cavity, HAL fluorescence-based visualisation techniques may acquire importance in future and lead to a more correct staging of early ovarian cancer.

Uptake and localisation of mTHPC (Foscan) and its 14C-labelled form in normal and tumour tissues of the hamster squamous cell carcinoma model: a comparative study.

The aim of this study was to evaluate the pharmacokinetics of meta(tetrahydroxyphenyl)chlorin (mTHPC) on different tissues of interest in a hamster tumour model and to confirm our earlier animal studies on semi-quantitative fluorescence microscopy. The results obtained by three different evaluation methods were compared: in vivo spectrofluorometry, ex vivo fluorescence microscopy and chemical extraction of (14)C-labelled mTHPC. Following intracardiac injection of 0.5 mg kg(-1) mTHPC, groups of five tumour-bearing animals were used for in situ light-induced fluorescence spectroscopy. Afterwards, the biopsies were taken and snap frozen for fluorescence microscopy. The presence of radioactivity in serum and tissues was determined after chemical digestion in scintillation fluid using a scintillation counter. For each analysed tissue, a good correlation was observed between the three evaluation methods. The highest fluorescence intensity and quantities of mTHPC were observed between 12 and 24 h in liver, kidney, serum, vascular endothelium and advanced neoplasia. The majority of mTHPC was found at around 48 h in smooth muscle and at 96 h in healthy cheek pouch mucosa and early malignant lesions. The lowest level of mTHPC was noted in striated muscle at all times. No selectivity in dye localisation was observed between early squamous cell carcinoma and healthy mucosa. Soon after the injection, a significant selectivity was noted for advanced squamous cell carcinoma as compared to healthy cheek pouch mucosa or striated muscle. A significant difference in mTHPC localisation and quantity was also observed between striated and smooth muscle during the first 48 h following the injection. Finally, this study demonstrated the usefulness of non-invasive in situ spectroscopic measurements to be performed systematically prior to photodynamic therapy as a real-time monitoring for each treated patient in order to individualise and adapt the light dosimetry and avoid over or under treatments.

Optimization of the diameter of a radial irradiation device for photodynamic therapy in the esophagus.

BACKGROUND AND STUDY AIMS: Photodynamic therapy (PDT) is a local therapeutic technique based on the photosensitization of lesions using a dye prior to light-induced tissue destruction. PDT of intraepithelial neoplasia in Barrett's esophagus, or of early squamous-cell carcinoma of the esophagus, requires light application devices that allow homogeneous and well-defined illumination of the tissue surface. Such devices must be large enough to induce complete unfolding of the esophagus in spite of esophageal motility and elasticity. The aim of this study was therefore to determine the optimal diameter of a cylindrical illumination device for PDT in this organ. PATIENTS AND METHODS: The study included nine patients (aged 49-72 years) who underwent panendoscopy. Flexible transparent hollow tubes with diameters ranging from 13 to 19 mm were successively introduced into the esophagus, and the esophageal wall was viewed from the inside through the tube using a flexible small-diameter endoscope. The number of folds was counted. Observations of the upper, middle, and lower thirds of the esophagus were recorded. The radial location of the folds was also recorded, and defined as follows: anterior wall (up), posterior wall (down), side walls (right, left). RESULTS: No significant difference in the number of folds between the lower and middle parts of the esophagus was noticed. However, the upper third had significantly fewer folds (about 30 %) than the other two parts. For diameters above 17 mm, this difference was less dramatic. The number of such folds was shown to decrease with the increasing diameter of the device. CONCLUSIONS: It appears that 18 mm or more is the optimal diameter for a fixed-geometry cylindrical photodynamic therapy irradiating device for the patient category considered in this study. It was also observed that most folds were located on the side walls of the esophagus.

Localization of tetra(m-hydroxyphenyl)chlorin (Foscan) in human healthy tissues and squamous cell carcinomas of the upper aero-digestive tract, the esophagus and the bronchi: a fluorescence microscopy study.

To date, little is known about precise time-dependent distribution and histological localization of tetra(m-hydroxyphenyl)chlorin (mTHPC) in human healthy tissues and squamous cell malignancies in the upper aero-digestive tract. A fluorescence microscopy study was performed on 50 healthy tissue biopsies and on 13 tumors (graded from Tis to T1 SCC) from 30 patients. Tissue samples were taken between 4 h and 11 days following injection of 0.15 mg/kg mTHPC. A fairly comparable distribution pattern in various tissues was observed over time in different patients. Vascular localization of mTHPC fluorescence predominates at a short delay, whereas the dye is essentially located in the tumoral and healthy mucosa after longer delays. A much lower uptake and retention of mTHPC fluorescence was noted in striated muscle and cartilage as compared to neoplastic lesions. No significant selectivity was found between healthy and tumoral mucosa. The obtained data are important to confirm drug-light interval that have been selected for effective PDT for early SCC malignancies while minimizing the risks of over- or under-treatment. The low fluorescence level in striated muscle provides the opportunity to develop interstitial PDT as a treatment modality for invasive SCC of unfavorable locations in the oral cavity or pharynx, such as the base of the tongue.

In vivo autofluorescence spectroscopy of human bronchial tissue to optimize the detection and imaging of early cancers.

We are developing an imaging system to detect pre-/early cancers in the tracheo-bronchial tree. Autofluorescence might be useful but many features remain suboptimal. We have studied the autofluorescence of human healthy, metaplastic and dysplastic/CIS bronchial tissue, covering excitation wavelengths from 350 to 480 nm. These measurements are performed with a spectrofluorometer whose distal end is designed to simulate the spectroscopic response of an imaging system using routine bronchoscopes. Our data provide information about the excitation and emission spectral ranges to be used in a dual range detection imaging system to maximize the tumor vs healthy and the tumor vs. inflammatory/metaplastic contrast in detecting pre-/early malignant lesions. We find that the excitation wavelengths yielding the highest contrasts are between 400 and 480 nm with a peak at 405 nm. We also find that the shape of the spectra of healthy tissue is similar to that of its inflammatory/metaplastic counterpart. Finally we find that, when the spectra are normalized, the region of divergence between the tumor and the nontumor spectra is consistently between 600 and 800 nm and that the transition wavelength between the two spectral regions is around 590 nm for all the spectra regardless of the excitation wavelength, thus suggesting that there might be one absorber or one fluorophore. The use of backscattered red light enhances the autofluorescence contrast.

A new drug-screening procedure for photosensitizing agents used in photodynamic therapy for CNV.

PURPOSE: Because vascular occlusion has been observed as a consequence of photodynamic therapy (PDT), this method has been successfully used for the treatment of choroidal neovascularization (CNV) in age-related macular degeneration (AMD). However, most conventional photosensitizers, primarily developed for tumor PDT, lack selectivity for the targeting of neovascularization. An experimental model has been developed for drug screening of new photosensitizers for the treatment of CNV associated with AMD. It consists of intravenous (IV) injection of photosensitizers and fluorescent dyes into the chick's chorioallantoic membrane (CAM), followed by measurement of fluorescence pharmacokinetics, leakage from the vascular system, and photothrombic efficacy. METHODS: Fertilized chicken eggs were placed under a fluorescence microscope. After intravenous injection of different dyes, time-dependent fluorescence angiography was performed. The effect of PDT parameters was assessed by fluorescence angiography 24 hours after PDT. RESULTS: Although fluorescence of lipophilic benzoporphyrin derivative monoacid ring A (BPD-MA) remained intravascular during 2 hours, hydrophilic dyes tended to leak through the fenestrated neovascularization. By variation of PDT parameters, vascular damage could be directed toward closure of vessels with a diameter smaller than 10 microm, as measured 24 hours after PDT. High photosensitizer concentrations and high light doses resulted in blood flow stasis within 60 minutes, confirmed by fluorescence angiography. CONCLUSIONS: Fluorescence angiography and PDT after IV injection into the CAM showed strong similarities to results obtained in clinical tests of PDT in CNV associated with AMD. Thus, this model can provide valuable information about PDT mechanisms and can be used for drug-screening purposes in development of improved sensitizers for the PDT of CNV.

Absolute autofluorescence spectra of human healthy, metaplastic, and early cancerous bronchial tissue in vivo.

Autofluorescence is emerging as a useful tool for the detection of early cancers in the bronchi. It has already produced interesting results, which have been implemented in commercial imaging devices. Their design relies on the spectroscopy of the tissues of interest. However, a large majority of these autofluorescence spectroscopy studies have been presented in arbitrary units. This is a drawback for, in particular, the designing of imaging devices based on autofluorescence. Using correction factors and a spectral sensitivity correction curve, we determined the absolute spectral distribution of the tissue autofluorescence in vivo. These measurements were performed on healthy, metaplastic, and dysplastic bronchial tissues at several excitation wavelengths ranging from 350 to 495 nm. Moreover, we measured at a fixed distance between the tissue and the probe to avoid geometric distortions of the spectra that are due to the optical characteristics of tissue. We found that the order of magnitude of the autofluorescence brightness was stable as the excitation wavelengths varied (on the order of 5 pW/muW x nm at the maximum of the fluorescence emission spectra).

Pharmacokinetics and pharmacodynamics of tetra(m-hydroxyphenyl)chlorin in the hamster cheek pouch tumor model: comparison with clinical measurements.

The pharmacokinetics (PK) of the photosensitizer tetra(m-hydroxyphenyl)chlorin (mTHPC) was measured by optical fiber-based light-induced fluorescence spectroscopy (LIFS) in the normal and tumoral cheek pouch mucosa of 29 Golden Syrian hamsters with chemically induced squamous cell carcinoma. Similar measurements were carried out on the normal oral cavity mucosa of five patients up to 30 days after injection. The drug doses were between 0.15 and 0.3 mg per kg of body weight (mg/kg), and the mTHPC fluorescence in the tissue was excited at 420 nm. The PK in both human and hamster exhibited similar behavior although the PK in the hamster mucosa was slightly delayed in comparison with that of its human counterpart. The mTHPC fluorescence signal of the hamster mucosa was smaller than that of the human mucosa by a factor of about 3 for the same injected drug dose. A linear correlation was found between the fluorescence signal and the mTHPC dose in the range from 0.075 to 0.5 mg/kg at times between 8 and 96 h after injection. No significant selectivity in mTHPC fluorescence between the tumoral and normal mucosa of the hamsters was found at any of the applied conditions. The sensitivity of the normal and tumoral hamster cheek pouch mucosa to mTHPC photodynamic therapy as a function of the light dose was determined by light irradiation at 650 nm and 150 mW/cm2, 4 days after the injection of a drug dose of 0.15 mg/kg. These results were compared with irradiations of the normal oral and normal and tumoral bronchial mucosa of 37 patients under the same conditions. The reaction to PDT of both types of human mucosae was considerably stronger than that of the hamster cheek pouch mucosa. The sensitivity to PDT became comparable between hamster and human mucosa when the drug dose for the hamster was increased to 0.5 mg/kg. A significant therapeutic selectivity between the normal and neoplastic hamster cheek pouch was observed. Less selectivity was found following irradiations of normal mucosa and early carcinomas in the human bronchi. The pharmacodynamic behavior of mTHPC was determined by test irradiations of the normal mucosa of hamsters and patients between 6 h and 8 days after injection of 0.5 and 0.15 mg/kg in the hamsters and the patients, respectively. The normal hamster cheek pouch showed a maximum response to irradiation 6 h after injection and then decreased continuously to no observable reaction at 8 days after injection. The reaction of the normal human oral mucosa, however, showed an increasing sensitivity to the applied light between 6 h and 4 days after mTHPC injection and then decreased again at 8 days. The hamster model with the chemically induced early squamous cell cancer in the cheek pouch thus showed some similarity to the early squamous cell cancer of the human oral mucosa considering the PK. However, a quantitative difference in fluorescence signal for identical mTHPC doses as well as a significant difference in pharmacodynamic behavior were also observed. The suitability of this animal model for the optimization of PDT parameters in the clinic is therefore limited. Hence great care must be taken in screening new dyes for PDT of early squamous cell cancer of the upper aerodigestive tract based upon observables in the hamster cheek pouch model.

Photodynamic therapy of early squamous cell cancers of the esophagus.

The conventional treatment for the cure of esophageal cancer is surgical resection. Esophageal cancer, when detected at an early stage, has a very good probability of being eradicated by less aggressive procedures, and photodynamic therapy has proven to be a safe and effective treatment modality in some carefully selected patients. The indications, outcomes, and future considerations regarding the use of photodynamic therapy for the treatment of superficial squamous cell carcinomas of the esophagus are discussed in this article.