Photofrin-induced fluorescence in progressive and regressive murine colonic cancer cells: correlation with cell photosensitivity

A Ratiometric Fluorescence Imaging System for Surgical Guidance

A 3-chip CCD imaging system has been developed for quantitative in vivo fluorescence imaging. This incorporates a ratiometric algorithm to correct for the effects of tissue optical absorption and scattering, imaging “geometry” and tissue autofluorescence background. The performance was characterized, and the algorithm was validated in tissue-simulating optical phantoms for quantitative measurement of the fluorescent molecule protoporphyrin IX (PpIX). The technical feasibility to use this system for fluorescence-guided surgical resection of malignant brain tumor tissue was assessed in an animal model in which PpIX was induced exogenously in the tumor cells by systemic administration of aminolevulinic acid (ALA).

Synthesis, cellular internalization and photodynamic activity of glucoconjugated derivatives of tri and tetra(meta-hydroxyphenyl)chlorins

Glucoconjugated tri and tetra(meta-hydroxyphenyl)chlorins have been synthesized in order to explore how glucoconjugation of the macrocycle affects the photoactivity of the molecule. Internalization processes, photosensitizing efficacy of TPC(m-O-GluOH)(3) and TPC(m-O-GluOH)(4), in HT29 human adenocarcinoma cells have been compared to those of tetra(meta-hydroxyphenyl) chlorin (m-THPC, Foscan). The tetra glucoconjugated chlorin, TPC(m-O-GluOH)(4), was found to be poorly internalized and weakly photoactive. In contrast, the asymmetric and more amphiphilic compound TPC(m-O-GluOH)(3), exhibited superior phototoxicity compared to m-THPC. Drug concentration, temperature and sodium azide effects indicated that TPC(m-O-GluOH)(3) internalization partly proceeds via an active receptor-mediated endocytosis mechanism. Cellular uptake appeared as a saturable process and remained 30% lower than for mTHPC. However, a maximum phototoxicity in HT29 cells (survival fraction of 2+/-0.6%) were observed for concentration as low as 2 microM. A 4-fold higher concentration of m-THPC was necessary to observe the same level of photoactivity. This higher phototoxicity has been correlated to a greater mitochondrial affinity. On the basis of these results, work is in progress to further evaluate the potential of glycosylated chlorins in photodynamic therapy (PDT).

Cellular distribution and phototoxicity of benzoporphyrin derivative and Photofrin

Photodynamic therapy (PDT) induces cell-membrane damage and alterations in cancer-cell adhesiveness, an important parameter in cancer metastasis. These alterations result from cell sensitivity to photosensitizers and the distribution of photosensitizers in cells. The efficacy of photosensitizers depends on their close proximity to targets and thus on their pharmacokinetics at the cellular level. We studied the cellular distribution of photosensitizers with a confocal microspectrofluorimeter by analysing the fluorescence emitted by benzoporphyrin derivative-monoacid ring A (BPD-MA) and Photofrin relative to their cell sensitivity. Two cancer cell lines of colonic origin, but with different metastatic properties, were used: PROb (progressive) and REGb (regressive). For BPD-MA (1.75 microg/ml), maximal fluorescence intensity (8,300 cts) was reached after 2 h for PROb and after 1 h (4,900 cts) for REGb. For Photofrin (10 microg/ml), maximal fluorescence intensity (467 cts) was reached after 5 h for PROb and after 3 h (404 cts) for REGb. Intracellular studies revealed stronger cytoplasmic than nuclear fluorescence for both BPD and Photofrin. Both of the sensitizers induced a dose-dependent phototoxicity; LD50 with BPD-MA was 93.3 ng/ml for PROb and 71.1 ng/ml for REGb, under an irradiation of 10 J/cm2. With Photofrin, LD50 was 1,270 ng/ml for PROb and 1,200 ng/ml for REGb under an irradiation of 25 J/cm2. The photosensitizer effect within PROb and REGb cancer cells was assessed by incorporation kinetics and toxicity-phototoxicity tests. The intracellular concentration of the photosensitive agent was one important factor in the effectiveness of PDT, but not the only one contributing to the photodynamic effect. In conclusion, this study showed that there was a clear difference between sensitizer uptake and phototoxicity, even in cancer cells of the same origin. This could induce cell-killing heterogeneity in clinics.

A comparative study of the cellular uptake, localization and phototoxicity of meta-tetra(hydroxyphenyl) chlorin encapsulated in surface-modified submicronic oil/water carriers in HT29 tumor cells

The poor selectivity of photosensitizers for tumor tissue remains a drawback in photodynamic therapy (PDT) and could be improved by adapted formulations. The cellular uptake, localization and phototoxicity of meta-tetra(hydroxyphenyl)chlorin (mTHPC) encapsulated in submicronic colloidal carriers have been studied in macrophage-like J774 cells and HT 29 human adenocarcinoma cells. Nanocapsules with an external layer made of poly(D,L lactic acid) (PLA NCs), PLA grafted with polyethylene glycol (PLA-PEG NCs), PLA coated with poloxamer 188 (polox PLA NCs) and oil/water nanoemulsion (NE) have been examined. The cellular uptake by J774, as determined by microspectroflorimetry, is reduced with mTHPC encapsulated into surface-modified NCs--PLA-PEG and polox PLA--compared with naked PLA, indicating a possible limitation of the clearance of such carriers by the reticuloendothelial system. Encapsulation also modifies the interaction between mTHPC and HT29 cells. Compared with the manufacturer's solution (PEG, ethanol, water), the cellular uptake is strongly reduced. However, the HT29 phototoxicity is much less affected and a protecting effect against plasma proteins is observed. Fluorescence microscopy reveals a specific punctate fluorescence pattern with PLA-PEG and polox PLA NCs in contrast to a more diffuse distribution with NE and solution, indicating that photodamage targeting could be different. These findings suggest that photosensitizers encapsulated into surface-modified nanocapsules could be a promising approach for improving PDT efficacy and this has to be confirmed in vivo.

A new UV-visible confocal laser scanning microspectrofluorometer designed for spectral cellular imaging

With the aim to perform spectroscopic studies and spectral images inside living cells, a microspectrofluorometer has been designed for two-dimensional spectral imaging in the visible and in the near-UV region. The main advantage of the device relies on its ability to scan the laser beam along one direction of the sample. This scanning is optically coupled with one direction of a bidimensional detector, allowing an instantaneous recording of a one-dimensional spectral image. The overall scanning of the sample is achieved by means of submicrometric displacements of the stage in the perpendicular direction. The main characteristics and performances of the microspectrofluorometer in terms of sensitivity (detection of a few molecules), spatial resolution (0.5 x 0.5 x 1 microm), and spectral resolution (1 nm) are presented. Finally, applications of this new apparatus concerning in situ localization and spectral characterization of two dyes are shown with Drosophila salivary glands (ethidium bromide) and T47D tumor cells (Hoechst 33342).

Fungicidal properties of meso-arylglycosylporphyrins: influence of sugar substituents on photoinduced damage in the yeast Saccharomyces cerevisiae

A series of neutral meso-arylglycosylporphyrins has been tested in order to evaluate their potency as antifungal agents against the yeast Saccharomyces cerevisiae. Photodynamic activity of these molecules results in intracellular damage as evidenced by the loss of clonogenicity and DNA fragmentation. The ability of these photosensitizers to permeate yeast cells is determined by microspectrofluorimetry and is correlated with their antifungal potency. Amphiphilic porphyrin derivatives are shown to exhibit the more pronounced photoactivity.

Photodynamic therapy in neurosurgery: a review

Photodynamic therapy (PDT) has been investigated extensively, both experimentally and clinically, as an adjunctive treatment in the neuro-oncological field. It is based on the more selective accumulation of a photosensitizer in malignant than normal tissue with low systemic toxicity. Subsequent light activation induces photo-oxidation, followed by selective tumour destruction via vascular and direct cellular mechanisms. Malignant brain tumours carry a lethal prognosis with a median survival of 15 months despite surgery, radiotherapy and chemotherapy. PDT is therefore a logical therapeutic concept for brain tumours infiltrating into normal brain. In this review, all the available data on patients treated with haematoporphyrin derivative-mediated PDT are critically analysed. Over 310 patients have been reported in the literature suffering from primary or recurrent malignant brain tumours which were treated with PDT following tumour resection in open clinical phase I/II trials. This number includes 58 patients treated at our own institution. Variations in the treatment protocols make evaluation scientifically difficult; however, there is a clear trend of increased median survival after surgical resection and one single photodynamic treatment. PDT is generally well tolerated and side effects consist of moderate increased intracranial pressure and prolonged skin sensitivity to direct sunlight. The current available data indicate that PDT is a safe treatment, which is well tolerated by the patients and yields an improvement in survival of those with malignant brain tumours. Conclusive information can be expected from controlled clinical trials which are currently being designed. The results raise the hope that PDT will be a valuable addition to the armamentarium for the treatment of cerebral malignancies.