Comparison of photosensitizer (AIPcS2) quantification techniques: in situ fluorescence microsampling versus tissue chemical extraction

Secure transplantation by tissue purging using photodynamic therapy to eradicate malignant cells

The field of photodynamic therapy (PDT) for treating various malignant neoplasms has been given researchers' attention due to its ability to be a selective and minimally invasive cancer therapy strategy. The possibility of tumor cell infection and hence high recurrence rates in cancer patients tends to restrict autologous transplantation. So, the photodynamic tissue purging process, which consists of selective photoinactivation of the malignant cells in the graft, is defined as a compromising strategy to purify contaminated tissues before transplantation. In this strategy, the direct malignant cells' death results from the reactive oxygen species (ROS) generation through the activation of a photosensitizer (PS) by light exposure in the presence of oxygen. Since new PS generations can effectively penetrate the tissue, PDT could be an ideal ex vivo tissue purging protocol that eradicates cancer cells derived from various malignancies. The challenge is that the applied pharmacologic ex vivo tissue purging should efficiently induce tumor cells with minor influence on normal tissue cells. This review aims to provide an overview of the current status of the most effective PDT strategies and PS development concerning their potential application in ex vivo purging before hematopoietic stem cell or ovarian tissue transplantation.

Photodynamic therapy, priming and optical imaging: Potential co-conspirators in treatment design and optimization - a Thomas Dougherty Award for Excellence in PDT paper

Photodynamic therapy is a photochemistry-based approach, approved for the treatment of several malignant and non-malignant pathologies. It relies on the use of a non-toxic, light activatable chemical, photosensitizer, which preferentially accumulates in tissues/cells and, upon irradiation with the appropriate wavelength of light, confers cytotoxicity by generation of reactive molecular species. The preferential accumulation however is not universal and, depending on the anatomical site, the ratio of tumor to normal tissue may be reversed in favor of normal tissue. Under such circumstances, control of the volume of light illumination provides a second handle of selectivity. Singlet oxygen is the putative favorite reactive molecular species although other entities such as nitric oxide have been credibly implicated. Typically, most photosensitizers in current clinical use have a finite quantum yield of fluorescence which is exploited for surgery guidance and can also be incorporated for monitoring and treatment design. In addition, the photodynamic process alters the cellular, stromal, and/or vascular microenvironment transiently in a process termed photodynamic priming, making it more receptive to subsequent additional therapies including chemo- and immunotherapy. Thus, photodynamic priming may be considered as an enabling technology for the more commonly used frontline treatments. Recently, there has been an increase in the exploitation of the theranostic potential of photodynamic therapy in different preclinical and clinical settings with the use of new photosensitizer formulations and combinatorial therapeutic options. The emergence of nanomedicine has further added to the repertoire of photodynamic therapy's potential and the convergence and co-evolution of these two exciting tools is expected to push the barriers of smart therapies, where such optical approaches might have a special niche. This review provides a perspective on current status of photodynamic therapy in anti-cancer and anti-microbial therapies and it suggests how evolving technologies combined with photochemically-initiated molecular processes may be exploited to become co-conspirators in optimization of treatment outcomes. We also project, at least for the short term, the direction that this modality may be taking in the near future.

Fluorescence Imaging in Vivo: Raster Scanned Point-Source Imaging Provides More Accurate Quantification than Broad Beam Geometries

Two fluorescence imaging systems were compared for their ability to quantify mean fluorescence intensity from surface-weighted imaging of tissue. A broad beam CCD camera system was compared to a point sampling system that raster scans to create the image. The effects of absorption and scattering in the background tissue volume were shown to be similar in their effect upon the signal, but the effect of the three-dimensional shape of the tissue was shown to be a significant distortion upon the signal. Spherical phantoms with Intralipid and blood for absorber and scatterer were used with a fixed concentration of aluminum phthalocyanine fluorophore to illustrate that the mean intensity observed with the broad beam system increased with size, while the mean intensity observed with the raster scanned system was not as significantly affected. Similar results were observed in vivo with mice injected with the fluorophore and imaged multiple times to observe the pharmacokinetics of the drug. The fluorescence in the tumor observed with the broad beam system was higher than that observed with the raster scanned system. Based upon the phantom and animal observations in this study, it should be concluded that using broad beam fluorescence imaging systems to quantify fluorescence in vivo may be problematic when comparing tissues with different three dimensional characteristics. In particular, the ratio of fluorescence from tumor to normal tissue can yield inaccurate results when the tumor is large. However, similar measurements with a narrow beam system that is raster scanned to create the images are not as significantly affected by the three dimensional shape of the tissue. Raster scanned imaging appears to provide a more uniform and accurate way to quantify fluorescence signals from distributed tissues in vivo.

Photosensitizer fluorescence and singlet oxygen luminescence as dosimetric predictors of topical 5-aminolevulinic acid photodynamic therapy induced clinical erythema

The need for patient-specific photodynamic therapy (PDT) in dermatologic and oncologic applications has triggered several studies that explore the utility of surrogate parameters as predictive reporters of treatment outcome. Although photosensitizer (PS) fluorescence, a widely used parameter, can be viewed as emission from several fluorescent states of the PS (e.g., minimally aggregated and monomeric), we suggest that singlet oxygen luminescence (SOL) indicates only the active PS component responsible for the PDT. Here, the ability of discrete PS fluorescence-based metrics (absolute and percent PS photobleaching and PS re-accumulation post-PDT) to predict the clinical phototoxic response (erythema) resulting from 5-aminolevulinic acid PDT was compared with discrete SOL (DSOL)-based metrics (DSOL counts pre-PDT and change in DSOL counts pre/post-PDT) in healthy human skin. Receiver operating characteristic curve (ROC) analyses demonstrated that absolute fluorescence photobleaching metric (AFPM) exhibited the highest area under the curve (AUC) of all tested parameters, including DSOL based metrics. The combination of dose-metrics did not yield better AUC than AFPM alone. Although sophisticated real-time SOL measurements may improve the clinical utility of SOL-based dosimetry, discrete PS fluorescence-based metrics are easy to implement, and our results suggest that AFPM may sufficiently predict the PDT outcomes and identify treatment nonresponders with high specificity in clinical contexts.

Vitamin D Combined with Aminolevulinate (ALA)-Mediated Photodynamic Therapy (PDT) for Human Psoriasis: A Proof-of-Principle Study

We previously showed that select agents (methotrexate or Vitamin D), when administered as a preconditioning regimen, are capable of promoting cellular differentiation of epithelial cancer cells while simultaneously enhancing the efficacy of 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT). In solid tumors, pretreatment with Vitamin D simultaneously promotes cellular differentiation and leads to selective accumulation of target porphyrins (mainly protoporphyrin IX, PpIX) within diseased tissue. However, questions of whether or not the effects upon cellular differentiation are inexorably linked to PpIX accumulation, and whether these effects might occur in hyperproliferative noncancerous tissues, have remained unanswered. In this paper, we reasoned that psoriasis, a human skin disease in which abnormal cellular proliferation and differentiation plays a major role, could serve as a useful model to test the effects of pro-differentiating agents upon PpIX levels in a non-neoplastic setting. In particular, Vitamin D, a treatment for psoriasis that restores (increases) differentiation, might increase PpIX levels in psoriatic lesions and facilitate their responsiveness to ALA-PDT. This concept was tested in a pilot study of 7 patients with bilaterally-matched psoriatic plaques. A regimen in which calcipotriol 0.005% ointment was applied for 3 days prior to ALA-PDT with blue light, led to preferential increases in PpIX (~130%), and reductions in thickness, redness, scaling, and itching in the pretreated plaques. The results suggest that a larger clinical trial is warranted to confirm a role for combination treatments with Vitamin D and ALA-PDT for psoriasis.

Long wavelength absorbing cationic Zn(II)-phthalocyanines as fluorescent contrast agents for B16 pigmented melanoma

Three cationic zinc phthalocyanines ( ZnPcs ), tetrakis-(3-methylpyridyloxy)-, tetrakis-(3-hexyl-pyridyloxy)-, and tetrakis-(3-dodecylpyridyloxy)phthalocyaninezinc ( ZnPc Me, ZnPc He and ZnPc Do) have been studied as advanced fluorescent contrast agents for pigmented melanoma tumor. UV-vis spectroscopic properties of the monomers were investigated. Their photophysical behavior as a substantial part of dye-induced fluorescence was evaluated. The selective accumulation and labeling capacity towards B16F0 pigmented melanoma tumor were determined. Melanin containing cells were isolated and incubated with ZnPcs at several time intervals (1, 1.5 and 6 h) following the kinetics of cellular uptake. The highest accumulation was found for ZnPcHe . A lower uptake was detected for the more lipophilic ZnPcDo and more hydrophilic ZnPcMe . The fluorescence diagnostic potential of ZnPcs towards pigmented melanoma by using an argon-dye laser detection set-up was demonstrated.

Semi-empirical model of the effect of scattering on single fiber fluorescence intensity measured on a turbid medium

Quantitative determination of fluorophore content from fluorescence measurements in turbid media, such as tissue, is complicated by the influence of scattering properties on the collected signal. This study utilizes a Monte Carlo model to characterize the relationship between the fluorescence intensity collected by a single fiber optic probe (F(SF)) and the scattering properties. Simulations investigate a wide range of biologically relevant scattering properties specified independently at excitation (λ(x)) and emission (λ(m)) wavelengths, including reduced scattering coefficients in the range μ'(s)(λ(x)) ∈ [0.1 - 8]mm(-1) and μ'(s)(λ(m)) ∈ [0.25 - 1] × μ'(s)(λ(x)). Investigated scattering phase functions (P(θ)) include both Henyey-Greenstein and Modified Henyey-Greenstein forms, and a wide range of fiber diameters (d(f) ∈ [0.2 - 1.0] mm) was simulated. A semi-empirical model is developed to estimate the collected F(SF) as the product of an effective sampling volume, and the effective excitation fluence and the effective escape probability within the effective sampling volume. The model accurately estimates F(SF) intensities (r=0.999) over the investigated range of μ'(s)(λ(x)) and μ'(s)(λ(m)), is insensitive to the form of the P(θ), and provides novel insight into a dimensionless relationship linking F(SF) measured by different d(f).

In vivo study of photosensitizer pharmacokinetics by fluorescence transillumination imaging

The possibility of in vivo investigation of the pharmacokinetics of photosensitizers by means of fluorescence transillumination imaging is demonstrated. An animal is scanned in the transilluminative configuration by a single source and detector pair. Transillumination is chosen as an alternative approach to reflection imaging. In comparison with the traditional back-reflection technique, transillumination is preferable for photosensitizer detection due to its higher sensitivity to deep-seated fluorophores. The experiments are performed on transplantable mouse cervical carcinomas using three drugs: photosens, alasens, and fotoditazin. For quantitative evaluation of the photosensitizer concentration in tumor tissue the fluorescence signal is calibrated using tissue phantoms. We show that the kinetics of photosensitizer tumor uptake obtained by transillumination imaging in vivo agree with data of standard ex vivo methods. The described approach enables rapid and cost-effective study of newly developed photosensitizers in small animals.

Protoporphyrin IX fluorescence photobleaching increases with the use of fractionated irradiation in the esophagus

Fluorescence measurements have been used to track the dosimetry of photodynamic therapy (PDT) for many years, and this approach can be especially important for treatments with aminolevulinic-acid-induced protoporphyrin IX (ALA-PpIX). PpIX photobleaches rapidly, and the bleaching is known to be oxygen dependent, and at the same time, fractionation or reduced irradiance treatments have been shown to significantly increase efficacy. Thus, in vivo measurement of either the bleaching rate and/or the total bleaching yield could be used to track the deposited dose in tissue and determine the optimal treatment plans. Fluorescence in rat esophagus and human Barrett's esophagus are measured during PDT in both continuous and fractionated light delivery treatment, and the bleaching is quantified. Reducing the optical irradiance from 50 to 25 mWcm did not significantly alter photobleaching in rat esophagus, but fractionation of the light at 1-min on and off intervals did increase photobleaching up to 10% more (p value=0.02) and up to 25% more in the human Barrett's tissue (p value<0.001). While two different tissues and two different dosimetry systems are used, the data support the overall hypothesis that light fractionation in ALA-PpIX PDT esophageal treatments should have a beneficial effect on the total treatment effect.

Peptide-Induced Inflammatory Increase in Vascular Permeability Improves Photosensitizer Delivery and Intersubject Photodynamic Treatment Efficacy

Photodynamic therapy (PDT) treatment can exhibit high intersubject variability due to the inherent differences in drug delivery within the tissue to be treated. In this study, the increased perfusion of the lipid-associated photosensitizer verteporfin was studied using substance P, a peptide known to increase vascular permeability. The transvascular permeability coefficient was quantified before and after administration of substance P, and the mean value increased from 0.026 to 0.043 microm/s with the induced inflammation. Correspondingly, there was a 40-50% increase in uptake of verteporfin in the tumor parenchyma in tumors injected with substance P compared to those without. This increased drug uptake resulted in a modest increase in tumor doubling time from 4 days with regular PDT to 6.2 days with substance P and PDT. There was also a significant reduction in the interindividual variability in with substance P plus PDT from 64% to 13%. The resulting treatment was therefore more effective and there was less variability in dose between subjects.

Noninvasive and nondestructive optical spectroscopic measurement of motexafin gadolinium in mouse tissues: comparison to high-performance liquid chromatography

Efficient design of anti-cancer treatments involving radiation- and photo-sensitizing therapeutics requires knowledge of tissue-specific drug concentrations. This study investigates the use of the optical pharmacokinetic system (OPS) to measure concentrations of the anti-cancer agent motexafin gadolinium (MGd) in mouse tissues noninvasively and nondestructively using elastic-scattering spectroscopy. The magnitude of MGd absorbance was quantitated by integration of the MGd peak absorbance area, and MGd concentrations were estimated by comparison with standard curves that were validated by high performance liquid chromatography (HPLC). In tissue-simulating phantoms in vitro, MGd peak absorbance area correlated with MGd concentration. Female C.B-17 SCID mice, bearing subcutaneous MDA-MB-231 human breast cancer xenografts, were dosed with 23 mg/kg MGd i.v. At specific times between 5 min and 24h after dosing, noninvasive OPS measurements were made on skin overlaying the subcutaneous tumor and skin on the opposite flank in vivo, and following exsanguination, nondestructive measurements were made on tumor, skin, and internal tissues in situ. OPS measurements on tissues in vivo detected MGd present in both tissue and blood perfusing the tissue. Both the OPS and the HPLC detected selective localization of MGd in malignant tissues compared with surrounding non-malignant tissues, and neither technique detected MGd in brain tissue. Comparison of MGd concentrations measured by HPLC and OPS is complicated by mismatch between measured tissue volumes, heterogeneous spatial distribution of MGd in tissues, and blood-localized MGd at early time points. Tumor-specific MGd concentrations measured by HPLC correlated with those measured by OPS in vivo and in situ. Best fit lines to the concentration estimates (forced through zero) had slopes of 0.900 and 1.185, respectively; however, the variability was significant (r(2)=0.477 and 0.269). The clinical utility of the OPS to quantitate MGd concentrations remains to be validated.

Recognition of various biomolecules by the environment-sensitive spectral responses of hypocrellin B

In this work, the spectral responses of hypocrellin B (HB) to the microenvironments of various biomolecules were studied, with human serum albumin (HSA), bovine serum albumin (BSA) and ovalbumin (OVA) used as the models for proteins, sodium alginate (SOA) and hyaluronan (HYA) for polysaccharides and liposomes for lipid membranes. Generally, compared to those in aqueous solution, the absorbance and fluorescence of HB were all strengthened in the model systems except for the fluorescence in HYA. Specially, according to the spectral responses of HB, the microenvironments in biomolecules and liposomes could be set in a sequence of hydrophobic grades, i.e., liposomes > proteins > polysaccharides. Further, R(F/A), a parameter defined as the ratio of the fluorescence intensity to the absorbance, was proposed to identify the microenvironment quantitatively. It was found that the R(F/A) could not only distinguish various types of biomolecules but also identify specific binding from nonspecific binding to proteins or polysaccharides.

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.

Pretreatment photosensitizer dosimetry reduces variation in tumor response

PURPOSE

To compensate for photosensitizer uptake variation in photodynamic therapy (PDT), via control of delivered light dose through photodynamic dose calculation based on online dosimetry of photosensitizer in tissue before treatment.

METHODS AND MATERIALS

Photosensitizer verteporfin was quantified via multiple fluorescence microprobe measurements immediately before treatment. To compensate individual PDT treatments, photodynamic doses were calculated on an individual animal basis, by matching the light delivered to provide an equal photosensitizer dose multiplied by light dose. This was completed for the lower quartile, median, and upper quartile of the photosensitizer distribution. PDT-induced tumor responses were evaluated by the tumor regrowth assay.

RESULTS

Verteporfin uptake varied considerably among tumors and within a tumor. The coefficient of variation in the surviving fraction was found significantly decreased in groups compensated to the lower quartile (CL-PDT), the median (CM-PDT), and the upper quartile (CU-PDT) of photosensitizer distribution. The CL-PDT group was significantly less effective compared with NC-PDT (Noncompensated PDT), CM-PDT, and CU-PDT treatments. No significant difference in effectiveness was observed between NC-PDT, CM-PDT, and CU-PDT treatment groups.

CONCLUSIONS

This research suggests that accurate quantification of tissue photosensitizer levels and subsequent adjustment of light dose will allow for reduced subject variation and improved treatment consistency.

Light dosimetry measurements during ALA-PDT of Barrett's oesophagus

A fibre optic probe and compact light detection system has been used to monitor the fluence-rate at the tissue surface during 5-aminolaevulinic acid based photodynamic therapy (PDT) of Barrett's oesophagous. The contributions from three specific wavelengths were recorded, corresponding to the combination of therapeutic laser light and fluorescence emission from protoporphyrin IX (635nm), the fluorescence from an oxidation product of the photosensitiser (670nm), and the protoporphyrin IX fluorescence alone (705nm). We have found that light scattering results in an enhancement of the therapeutic fluence-rate, and hence light dose, by approximately 70%. At the onset of therapy the fluorescence provides a 10% contribution to the overall fluence-rate at 635nm. The dynamics of photosensitiser bleaching could be extracted from the depletion in light signals. By defining a bleaching dose as the 635nm light fluence delivered over the period during which the photosensitiser fluorescence decays to 1/e(3) of its initial value, we find that the average ratio of bleaching to total dose is 33%. Further, the fluorescence contributes approximately 5% of the bleaching light dose. These results suggest that the prescribed period of therapeutic light exposure may be reduced with no loss in clinical efficacy, but with a consequent improvement in patient tolerance to this therapy.

Analysis of sampling volume and tissue heterogeneity on the in vivo detection of fluorescence

The effect of sampling region size and tissue heterogeneity is examined using fluorescence histogram assessment in a rat prostate tumor model with benzoporphyrin derivative fluorophore. Spatial heterogeneity in the fluorescence signal occurs on both macroscopic and microscopic scales. The periphery of the tumor is more fluorescent than the center. Fluorescence is also highest nearest the blood vessels immediately after injection, but over time this fluorescence becomes uniform through the tumor tissue. Using microscopy analysis, the fluorescence intensity histogram distributions follow a normal distribution, yet as the sampling area is increased from the micron scale to the millimeter scale, the variance of the distribution decreases. The mean fluorescence intensity is accurately measured with a millimeter size scale, but this cannot provide accurate measurements of the microscopic variance of drug in tissue. Fiber probe measurements taken in vivo are used to confirm that the variance observed is smaller than would be expected with microscopic sampling, but that the average fluorescence can be measured with fibers. Sampling tissue with fibers smaller than the intercapillary spacing could provide a way to estimate the spatial variance more accurately. In summary, sampling fiber size affects the fluorescence intensities detected and use of multiple region microscopic sampling could provide better information about the distribution of values that occur.

Quantification of fluorophore concentration in vivo using two simple fluorescence-based measurement techniques

The effect of photodynamic therapy treatments depends on the concentration of photosensitizer at the treatment site; thus a simple method to quantify concentration is desirable. This study compares the concentration of a fluorophore and sensitizer, aluminum phthalocyanine tetrasulfonate (AlPcS4), measured by two simple fluorescence-based techniques in vivo to post mortem chemical extraction and fluorometric assay of those tissues: skin, muscle, fascia, liver, and kidney (cortex and medulla). Fluorescence was excited and detected by a single optical fiber, or by an instrument that measured the ratio of the fluorescence and excitation reflectance. The in vivo measurements were compared to calibration measurements made in tissue-simulating phantoms to estimate the tissue concentrations. Reasonable agreement was observed between the concentration estimates of the two instruments in the lighter colored tissues (skin, muscle, and fascia). The in vivo measurements also agreed with the chemical extractions at low (< 0.6 microg/g) tissue concentrations, but underestimated higher tissue concentrations. Measurements of fluorescence lifetime in vivo demonstrated that AlPcS4 retains its mono-exponential decay in skin, muscle, and fascia tissues with a lifetime similar to that measured in aqueous tissue-simulating phantoms. In liver and kidney an additional short lifetime component was evident.

Assessment of photosensitizer dosimetry and tissue damage assay for photodynamic therapy in advanced-stage tumors

Photodynamic therapy (PDT) efficacy is a complex function of tissue sensitivity, photosensitizer (PS) uptake, tissue oxygen concentration, delivered light dose and some other parameters. To better understand the mechanisms and optimization of PDT treatment, we assessed two techniques for quantifying tissue PS concentration and two methods for quantifying pathological tumor damage. The two methods used to determine tissue PS concentration kinetic were in vivo fluorescence probe and ex vivo chemical extraction. Both methods show that the highest tumor to normal tissue PS uptake ratio appears 4 h after PS administration. Two different histopathologic techniques were used to quantify tumor and normal tissue damage. A planimetry assessment of regional tumor necrosis demonstrated a linear relationship with increasing light dose. However, in large murine tumors this finding was complicated by the presence of significant spontaneous necrosis. A second method (densitometry) assessed cell death by nuclear size and density. With some exceptions the densitometry method generally supported the planimetry results. Although the densitometry method is potentially more accurate, it has greater potential subjectivity. Finally, our research suggests that the tools or methods we are studying for quantifying PS levels and tissue damage are necessary for the understanding of PDT effect and therapeutic ratio in experimental in vivo tumor research.

Measurement of fluorophore concentrations and fluorescence quantum yield in tissue-simulating phantoms using three diffusion models of steady-state spatially resolved fluorescence

Steady-state diffusion theory models of fluorescence in tissue have been investigated for recovering fluorophore concentrations and fluorescence quantum yield. Spatially resolved fluorescence, excitation and emission reflectance Carlo simulations, and measured using a multi-fibre probe on tissue-simulating phantoms containing either aluminium phthalocyanine tetrasulfonate (AlPcS4), Photofrin meso-tetra-(4-sulfonatophenyl)-porphine dihydrochloride The accuracy of the fluorophore concentration and fluorescence quantum yield recovered by three different models of spatially resolved fluorescence were compared. The models were based on: (a) weighted difference of the excitation and emission reflectance, (b) fluorescence due to a point excitation source or (c) fluorescence due to a pencil beam excitation source. When literature values for the fluorescence quantum yield were used for each of the fluorophores, the fluorophore absorption coefficient (and hence concentration) at the excitation wavelength (mu(a,x,f)) was recovered with a root-mean-square accuracy of 11.4% using the point source model of fluorescence and 8.0% using the more complicated pencil beam excitation model. The accuracy was calculated over a broad range of optical properties and fluorophore concentrations. The weighted difference of reflectance model performed poorly, with a root-mean-square error in concentration of about 50%. Monte Carlo simulations suggest that there are some situations where the weighted difference of reflectance is as accurate as the other two models, although this was not confirmed experimentally. Estimates of the fluorescence quantum yield in multiple scattering media were also made by determining mu(a,x,f) independently from the fitted absorption spectrum and applying the various diffusion theory models. The fluorescence quantum yields for AlPcS4 and TPPS4 were calculated to be 0.59 +/- 0.03 and 0.121 +/- 0.001 respectively using the point source model, and 0.63 +/- 0.03 and 0.129 +/- 0.002 using the pencil beam excitation model. These results are consistent with published values.

Quantification of fluorophore concentration in tissue-simulating media by fluorescence measurements with a single optical fiber

Quantifying fluorescent compounds in turbid media such as tissue is made difficult by the effects of multiple scattering and absorption of the excitation and emission light. The approach that we used was to measure fluorescence using a single 200-microm optical fiber as both the illumination source and the detector. Fluorescence of aluminum phthalocyanine tetrasulfonate (AlPcS4) was measured over a wide range of fluorophore concentrations and optical properties in tissue-simulating phantoms. A root-mean-square accuracy of 10.6% in AlPcS4 concentration was attainable when fluorescence was measured either interstitially or at the phantom surface. The individual effects of scattering, absorption, and the scattering phase function on the fluorescence signal were also studied by experiments and Monte Carlo simulations.

Spatial heterogeneity and temporal kinetics of photosensitizer (AlPcS2) concentration in murine tumors RIF-1 and MTG-B

In this study we compared the photosensitizer concentration in two experimental murine tumors using an in situ fluorescence detection instrument to examine temporal and spatial variations, after intravenous versus intratumor injection. Also, the variations in the estimate as detected by large area sampling and micro-region sampling are compared, in order to determine what the inter-tissue and inter-animal variations are, and how the method of sampling affects this estimate. The latter study was carried out ex vivo in the same tumors, which had been harvested and frozen after in vivo measurements were made. The photosensitizer, disulphonated aluminum phthalocyanine (AlPcS2) was injected either intravenously (IV) or directly into the tumor (ITu), using two murine models, MTG-B (mammary adenocarcinoma) and RIF-1 (radiation-induced fibrosarcoma) grown subcutaneously on the flank. An in situ microsampling fluorescence probe was used to assess photosensitizer concentration, through real-time measurement of the remitted intensity. The photosensitizer concentration was evaluated at 8 time endpoints between 15 min and 48 h post-injection. Inter-tumor and intra-tumor variations were assessed by repeated samples from the tumor tissues. The average photosensitizer level reaches a peak between 3 to 6 h in both tumor and normal tissues using IV administration, but peaks within 1 h following ITu administration. MTG-B tumors demonstrated a factor of 2 higher uptake than RIF-1 tumors. The pharmacokinetic uptake rates of the RIF-1 tumor were 3 times faster than for MTG-B, while there was no statistical difference in their clearance rates. Preferential uptake of AlPcS2 by both tumors compared to contra-lateral flank subcutaneous normal tissue was documented, with ITu injection exceeding IV injection by a factor of 10 in the tumor to normal tissue ratio. Inter-animal standard deviation in the mean fluorescence was near 76% for both routes of administration, but estimates of the variation within tumor were near 16% standard deviation when a large sampling volume was used. In contrast, microscopic intra-tumor standard deviation in the mean estimate was near 76%, with IV injection, indicating that high heterogeneity exists in the photosensitizer concentration on a smaller distance scale. The inter-tumor variation was reduced by ITu injection, but at the expense of increasing intra-tumor variation.

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.