In vivo quantification of chromophore concentration using fluorescence differential path length spectroscopy

We present an optical method based on fluorescence spectroscopy for measuring chromophore concentrations in vivo. Fluorescence differential path length spectroscopy (FPDS) determines chromophore concentration based on the fluorescence intensity corrected for absorption. The concentration of the photosensitizer m-THPC (Foscan) was studied in vivo in normal rat liver, which is highly vascularized and therefore highly absorbing. Concentration estimates of m-THPC measured by FDPS on the liver are compared with chemical extraction. Twenty-five rats were injected with 0.3 mg kg m-THPC. In vivo optical concentration measurements were performed on tissue 3, 24, 48, and 96 h after m-THPC administration to yield a 10-fold variation in tissue concentration. After the optical measurements, the liver was harvested for chemical extraction. FDPS showed good correlation with chemical extraction. FDPS also showed a correlation between m-THPC fluorescence and blood volume fraction at the two shortest drug-light intervals. This suggests different compartmental localization of m-THPC for different drug-light intervals that can be resolved using fluorescence spectroscopy. Differences in measured m-THPC concentration between FDPS and chemical extraction are related to the interrogation volume of each technique; approximately 0.2 mm(3) and approximately 10(2) mm(3), respectively. This indicates intra-animal variation in m-THPC distribution in the liver on the scale of the FDPS sampling volume.

Fluorescence Anisotropy Imaging Reveals Localization of meso-Tetrahydroxyphenyl Chlorin in the Nuclear Envelope

We have measured the intrinsic fluorescence anisotropies of six photosensitizers in homogeneous solution, and we have imaged the anisotropies of these sensitizers in tumor cell monolayers using polarization-sensitive laser-scanning confocal microscopy. The intrinsic anisotropies are unremarkable and are within the approximate range of 0.2-0.27. In cells, however, very interesting behavior is exhibited by meso-tetrahydroxyphenyl chlorin (mTHPC). Polarization-sensitive images of mTHPC's fluorescence show a pronounced banding of alternating high and low anisotropy consistent with an ordering of the sensitizer in the nuclear envelope, indicating that this structure is a target of photodynamic damage with this sensitizer. None of the other sensitizers exhibits localization to the nuclear envelope. The frequency distributions of the intracellular anisotropies of the sensitizers exhibit variable peaks and widths. An unusual case is that of Photofrin, with a peak in its anisotropy frequency distribution of -0.12. The change from a positive intrinsic anisotropy in homogeneous solution to a negative value in cells suggests an environmentally induced change in the relative orientations of the absorption and emission dipole moments.

HPLC-electrospray mass spectrometry for the analysis of temoporfin-poly(ethylene glycol) conjugates

The photodynamic therapeutic agent temoporfin, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (m-THPC) conjugated with poly(ethylene glycol) 2000 (PEG), has been analysed by high performance liquid chromatography (HPLC), linked to electrospray ionisation mass spectrometry (ESI-MS). Sufficient separation of m-THPC-PEG 2000 oligomers was achieved, enabling determination of molecular mass. The use of ESI-MS alone could not achieve this, because of too great a complexity in the mass spectrum, resulting from the presence of four PEG 2000 side chains with a wide molecular mass distribution. The technique is applicable to similar PEG conjugated compounds.

Sensitive isocratic liquid chromatographic assay for the determination of 5,10,15,20-tetra(m-hydroxyphenyl)chlorin in plasma and tissue with electrochemical detection

A simple extraction procedure and a sensitive high-performance liquid chromatographic (HPLC) method are described for the determination of the photodynamic therapeutic agent 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC) in plasma and tumour tissue. Reversed-phase high-performance liquid chromatography was performed on a C18 column (70 x 4.6 mm I.D.) with a mobile phase of 0.01 M potassium dihydrogenphosphate buffer, pH 2.5-acetonitrile (55:45, v/v) and a coulometric detection (+0.80 V). The mean recoveries of mTHPC in the concentration ranges (5-2000 and 10-1000 ng/ml) were 90 and 89% for plasma and tumour samples, respectively. The procedure for plasma and tissue preparation involved solvent precipitation using methanol combined with ammonia solution and dimethyl sulphoxide (4, 0.2, 0.1, v/v/v) and (2, 0.1, 0.1, v/v/v) for plasma and tissue, respectively. For mTHPC at concentrations ranging from 5 to 2000 ng/ml, the within-day relative standard deviations, based on triplicate determinations were less than 8% and the between-day relative standard deviations calculated by performing extraction procedure of plasma samples on three different days ranged from 3 to 18%. This highly sensitive method, 5 and 10 ng/ml for plasma and tissue respectively, was applied successfully to the determination of mTHPC in mouse tumours for pharmacokinetic studies.

Laser-induced fluorescence studies of meso-tetra(hydroxyphenyl)chlorin in malignant and normal tissues in rats

meso-Tetra(hydroxyphenyl)chlorin (mTHPC) is an attractive second-generation dihydroporphyrin photosensitiser for use in photodynamic therapy. In this study, 1.3 mg kg-1 body weight mTHPC was administered intravenously, and laser-induced fluorescence was used to characterise and compare its localisation and retention in different rat tissues, including an induced experimental adenocarcinoma, 24 h and 48 h post injection. These studies were performed in an attempt to predict the anatomical locations where mTHPC PDT might be most effective and suggest suitable injection--irradiation intervals in each case. Of particular interest were the intra-abdominal and intrathoracic tissues. The fluorescence was induced at 405 nm and the fluorescence spectrum in the region 450-750 nm was analysed. All collected spectra were dominated by the fluorescence signature of mTHPC with its peak at 652 nm, and all values in this study are in terms of background-free drug-specific fluorescence intensity at that wavelength. The photosensitiser accumulated in high concentrations in the tumour and the reticuloendothelial system. Muscular organs, such as the heart and the abdominal wall, were characterised by a low drug fluorescence signature.

Determination of 5,10,15,20-tetra-(m-hydroxyphenyl)chlorin in tissues by high performance liquid chromatography

A procedure for the extraction and high performance liquid chromatographic (HPLC) determination of the photodynamic therapeutic agent 5,10,15,20-tetra(m-hydroxyphenyl)chlorin in human, rat and mouse tissues following intravenous administration of the drug is described. The tissue (tumour, skin, muscle and liver) was homogenized and extracted into a mixture of methanol:dimethyl sulphoxide:water (32:8:1 by vol.) containing, 5,10,15,20-tetra(p-hydroxyphenyl)chlorin as the internal standard. The precipitated proteins were removed by centrifugation and the supernatant was separated by reversed phase HPLC on a Hypersil-ODS column with 77% (v/v) acetonitrile in 0.1% trifluoroacetic acid as the mobile phase. The solute was detected with high sensitivity and specificity by a UV-VIS detector set at 423 nm.

Model for the porphyrin-DNA binding site: ENDOR investigations of Cu-porphyrins binding to DNA

Proton ENDOR has been observed from frozen solutions (ca. 38K degrees) of copper meso-(4-N-tetra-methylpyridyl)porphyrin (CuTMpyP(4)) complexed with Salmon sperm DNA in water and D2O. Lines from exchangeable protons of the DNA bases have been observed in these ENDOR spectra. Analyses of these ENDOR data show that the separations of these DNA protons from the copper atom are between 3.76 and 3.84 A with angles of 19.5 to 22.5 degrees between the Cu-H vectors and the gz axis. A distant ENDOR response has also been observed from phosphorous nuclei in the DNA backbone. We estimate that the phosphorous atoms producing this ENDOR signal are 7.5-10 A from the copper center of the porphyrin. These ENDOR data combined with results from an earlier NMR investigation have been used to construct a computer simulated model of the binding site in which the porphyrin is partially intercalated and extends into the major groove of DNA. The two GC base pairs at this site are slightly inequivalent. For each, the G imino proton and one of the C amino protons are at appropriate positions to account for the ENDOR signals arising from exchangeable protons. It is unlikely that this inequivalence would persist at room temperature where dynamic processes would give an apparently symmetric interaction. Although the model accounts for all reported experimental data involving tetracationic porphyrin species which have been suggested to be intercalators, it is not a unique solution.

High-performance liquid chromatographic analysis of porphyrins in clinical materials

Methods for the isolation of porphyrins as their methyl esters from porphyric urine and faeces as well as other biological materials are described. Quantitative analyses can be carried out by high-performance liquid chromatography (HPLC), using appropriate internal standards; hence excretion patterns in the various types of porphyria can be obtained which may facilitate clinical diagnosis more effectively than the earlier qualitative thin-layer chromatographic methods. Use of the newer microparticulate column packing materials has improved the efficiency of the HPLC analyses, and enables the more convenient isochratic elution techniques to be used (rather than gradient elution). Separations of some porphyrin isomers on these columns are also described.