Aspects of the cellular uptake and retention of hematoporphyrin derivative and their correlation with the biological response to PRT in vitro

pH effect on cellular uptake of Sn(IV) chlorine e6 dichloride trisodium salt by cancer cells in vitro

The effects of pH value and presence of serum in an incubation medium on photosensitizer drug cellular uptake in MCF7 cancer cells have been investigated. The results showed that the presence of serum in an incubation medium reduced the drug cellular uptake at all pH values. It has been found that decreasing on pH values of the incubation medium increased the cellular uptake of the drug, demonstrating selective uptake of the sensitizer. The HepG2 liver cancer cells exhibited more drug cellular uptake than CCD-18CO normal colon cells, which assessed the selectivity uptake of photosensitizer on cancerous cells. The concentration of photosensitizer measured in 10(6) cells showed a good correlation to the incubation time. Fluorescence and absorption spectroscopy been have used to examine the cells.

Drug and light dose responses to focal photodynamic therapy of single blood vessels in vivo

As part of an ongoing program to develop two-photon (2-gamma) photodynamic therapy (PDT) for treatment of wet-form age-related macular degeneration (AMD) and other vascular pathologies, we have evaluated the reciprocity of drug-light doses in focal-PDT. We targeted individual arteries in a murine window chamber model, using primarily the clinical photosensitizer Visudyne/liposomal-verteporfin. Shortly after administration of the photosensitizer, a small region including an arteriole was selected and irradiated with varying light doses. Targeted and nearby vessels were observed for a maximum of 17 to 25 h to assess vascular shutdown, tapering, and dye leakage/occlusion. For a given end-point metric, there was reciprocity between the drug and light doses, i.e., the response correlated with the drug-light product (DLP). These results provide the first quantification of photosensitizer and light dose relationships for localized irradiation of a single blood vessel and are compared to the DLP required for vessel closure between 1-gamma and 2-gamma activation, between focal and broad-beam irradiation, and between verteporfin and a porphyrin dimer with high 2-gamma cross section. Demonstration of reciprocity over a wide range of DLP is important for further development of focal PDT treatments, such as the targeting of feeder vessels in 2-gamma PDT of AMD.

The tyrosine kinase inhibitor imatinib mesylate enhances the efficacy of photodynamic therapy by inhibiting ABCG2

PURPOSE

The ATP-binding cassette protein ABCG2 (breast cancer resistance protein) effluxes some of the photosensitizers used in photodynamic therapy (PDT) and, thus, may confer resistance to this treatment modality. Tyrosine kinase inhibitors (TKI) can block the function of ABCG2. Therefore, we tested the effects of the TKI imatinib mesylate (Gleevec) on photosensitizer accumulation and in vitro and in vivo PDT efficacy.

EXPERIMENTAL DESIGN

Energy-dependent photosensitizer efflux and imatinib mesylate's effects on intracellular accumulation of clinically used second- and first-generation photosensitizers were studied by flow cytometry in murine and human cells with and without ABCG2 expression. Effects of ABCG2 inhibition on PDT were examined in vitro using cell viability assays and in vivo measuring photosensitizer accumulation and time to regrowth in a RIF-1 tumor model.

RESULTS

Energy-dependent efflux of 2-(1-hexyloxethyl)-2-devinyl pyropheophorbide-a (HPPH, Photochlor), endogenous protoporphyrin IX (PpIX) synthesized from 5-aminolevulenic acid, and the benzoporphyrin derivative monoacid ring A (BPD-MA, Verteporfin) was shown in ABCG2+ cell lines, but the first-generation multimeric photosensitizer porfimer sodium (Photofrin) and a novel derivative of HPPH conjugated to galactose were minimally transported. Imatinib mesylate increased accumulation of HPPH, PpIX, and BPD-MA from 1.3- to 6-fold in ABCG2+ cells, but not in ABCG2- cells, and enhanced PDT efficacy both in vitro and in vivo.

CONCLUSIONS

Second-generation clinical photosensitizers are transported out of cells by ABCG2, and this effect can be abrogated by coadministration of imatinib mesylate. By increasing intracellular photosensitizer levels in ABCG2+ tumors, imatinib mesylate or other ABCG2 transport inhibitors may enhance efficacy and selectivity of clinical PDT.

Comparison of the in vivo efficiency of photofrin II-, mTHPC-, mTHPC-PEG- and mTHPCnPEG-mediated PDT in a human xenografted head and neck carcinoma

BACKGROUND AND OBJECTIVE

One of the approaches to enhance the selectivity and efficiency of photodynamic therapy (PDT) was the conjugation of the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC) to the water-soluble polymer polyethylene glycol (PEG). Several studies have demonstrated that mTHPC-PEG has a higher selectivity and a longer circulating half-life than free mTHPC, whereas no in vivo effect of this benefit could be seen.

STUDY DESIGN/MATERIALS AND METHODS

In a model of RAG-2-mice bearing a human oral squamous cell carcinoma xenograft (XF 354), the in vivo efficiency assessed as growth retardation or remission caused by Photofrin II and free mTHPC was compared with mTHPC coupled in two different ways to polyethylene glycol (PEG). One hundred and fourty-nine female RAG-2-mice were randomised into one control group and 13 therapy groups. Treatment parameters were adapted from those routinely applied in animal studies.

RESULTS

Photofrin II-mediated PDT and mTHPC-mediated PDT were both in vivo highly effective, whereas mTHPC induced less scars. The in vivo results after mTHPC-PEG-mediated PDT were disappointing, whereas the effectiveness of mTHPCnPEG-mediated PDT, a newly coupled macromolecular photosensitizer, were promising.

CONCLUSIONS

These results demonstrated the impact of the method of linkage between the photoactive agent mTHPC and polyethylene glycol (PEG) upon the in vivo effectiveness. mTHPC and mTHPCnPEG are promising photosensitizers for the future, especially for the cosmetic treatment needs of head and neck surgery.

Adenoviruses synergize with nuclear localization signals to enhance nuclear delivery and photodynamic action of internalizable conjugates containing chlorin e6

Photosensitizers, molecules that produce active oxygen species upon activation by visible light, are currently being used in photodynamic therapy (PDT) to treat cancer and other conditions, where limitations include normal cells and tissue damage and associated side effects, and the fact that cytotoxic effects are largely restricted to the plasma and other peripheral membranes. In this study, we used insulin-containing conjugates to which variants of the simian-virus-SV40 large-tumor antigen (T-ag) nuclear localization signal (NLS) were linked in order to target the photosensitizer chlorin e6 to the nucleus. NLSs were included either as peptides coupled co-valently to the carrier bovine serum albumin, or within the coding sequence of beta-galactosidase fusion proteins. The most potent photosensitizing conjugate was the NLS-containing T-ag beta-galactosidase fusion protein (P10)-(chlorin e6)-insulin, exhibiting an EC50 more than 2400-fold lower than the value for free chlorin e6, and more than 15-fold lower than that of an NLS-deficient beta-galactosidase-(chlorin e6)-insulin construct, thus demonstrating that NLSs can increase the photosensitizing activity of chlorin e6. Attenuated adenoviruses were used to increase the nuclear delivery of conjugates through its endosomal-membrane-disrupting activity. In the case of the NLS-containing P10-conjugate, co-incubation with adenovirus increased the proportion of cells whose nuclear photosensitizing activity was higher than that in the cytoplasm by 2.5-fold. This use of adenoviruses in conjunction with photosensitizers has clear implications for achieving efficient cell-type-specific PDT.

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.

Enhancement of photodynamic therapy with 5-aminolaevulinic acid-induced porphyrin photosensitisation in normal rat colon by threshold and light fractionation studies

5-Aminolaevulinic acid (ALA)-induced prophyrin photosensitisation is an attractive option for photodynamic therapy (PDT) since skin photosensitivity is limited to 1-2 days. However, early clinical results on colon tumours using the maximum tolerated oral dose of 60 mg kg-1 showed only superficial necrosis, presumably owing to insufficient intratumoral porphyrin levels, although inadequate light dosimetry may also be a factor. We undertook experiments using ALA, 25-400 mg kg-1 intravenously, to establish the threshold doses required for a PDT effect. Laser light at 630 nm (100 mW, 10-200 J) was delivered to a single site in the colon of photosensitised normal Wistar rats at laparotomy. The animals were killed 3 days later and the area of PDT-induced necrosis measured. No lesion was seen with 25 mg kg-1. The lesion size increased with larger ALA doses and with the light dose but little benefit was seen from increasing the ALA dose above 200 mg kg-1 or the light dose above 100 J. Thus there is a fairly narrow window for optimum doses of drug and light. Further experiments showed that the PDT effect can be markedly enhanced by fractionating the light dose. A series of animals was sensitized with 200 mg kg-1 ALA and then treated with 25 J. With continuous irradiation, the lesion area was 13 mm2, but with a single interruption of 150 s the area rose to 94 mm2 with the same total energy. Results were basically similar for different intervals between fractions (10-900 s) and different numbers of fractions (2-25). This suggests that a single short interruption in the light irradiation may dramatically reduce the net light dose required to achieve extensive necrosis.

Clinical applications of photodynamic therapy

This is a review of photodynamic therapy, which is a classic binary system involving the use of a photosensitizer and light of very specific wavelength, consistent with the absorption characteristics of that sensitizer. As a binary system, its effects are almost entirely limited to tumour cells, but the major drawback is its limited penetration because it utilizes physical light within the visible spectrum. For Photofrin II, which is the only approved sensitizer for clinical use in this country, the effects are limited to approximately 0.5 cm or less, depending on the tissue and the amount of blood, etc. Newer sensitizers offer more penetration and the opportunity to repeat treatments, because the newer sensitizers do not have the very long (up to 10 weeks) period of enhanced skin sensitivity to sunlight. A summary of the results of photodynamic therapy by individual sites is included. The use of newer sensitizers, which represent much purer substances than Photofrin II, should give an opportunity for repeated treatments, which should eventually make this form of treatment far more important than it has been up to now.

Relation of early Photofrin uptake to photodynamically induced phototoxicity and changes of cell volume in different cell lines

For efficacy of photodynamic therapy, selective uptake and retention of photoactive substances has been postulated. Therefore, measurements were performed to find out whether the photosensitiser Photofrin is taken up differently in malignant and non-malignant cells in vitro. In addition, the sensitivity of malignant cells and non-malignant cells to photodynamic exposure was investigated, by quantifying viability and volume alterations of the cells. Bovine aortic endothelial cells, mouse fibroblasts and amelanotic hamster melanoma cells were suspended in a specially designed incubation chamber under controlled conditions (e.g. pH, pO2, pCO2 and temperature). After establishing constant baseline conditions, the cellular fluorescence intensity per cell volume, indicative of the uptake of Photofrin, and cell volume were assessed by flow cytometry, and cell viability was quantified by the trypan blue exclusion test. Photodynamic exposure of cells was performed using an argon-pumped dye laser system via a 600 microns optical fibre at energy density of 4 Joules at the cell surface (40 mW/cm2, 100 s). In comparison to endothelial and fibroblast cells, the melanoma cells exhibited no increased uptake of Photofrin, and no enhanced sensitivity to photodynamic therapy (PDT). However, the fluorescence intensity/volume of endothelial cells was two to three times higher at each concentration of the photosensitiser. Following PDT, reduction in cell viability was dependent on the concentration of Photofrin, and directly correlated with fluorescence intensity per cell volume. In addition, the cells of all three lines, treated by PDT, revealed dose-dependent changes in cell volume. Melanoma cells exhibited the most excessive increase. It is suggested that selective uptake of photosensitiser in vitro is not characteristic for tumour cells. The high uptake of Photofrin by endothelial cells may indicate that the vascular endothelium is a major target for PDT, leading to cessation of tumour blood flow and subsequent destruction of tumour tissue. In addition, PDT-induced swelling of tumour cells might represent and effect synergistically impairing tumour perfusion, and thereby promoting tumour death.

Photodynamic therapy of bladder cancer--uptake and phototoxicity of photosan in vitro

The uptake of photosan and the intracellular sites of photoradiation-induced damage were investigated in vitro in bladder carcinoma cells and in normal bladder cells. Cells were examined by phase contrast, fluorescence and electron microscopy. The concentration of photosan, measured in microgram/10(6) cells, showed a good correlation to the incubation time. At all incubation times, control cells showed a lower uptake when compared with tumor cells. Following photodynamic therapy (PDT), phase-contrast microscopy revealed marked changes in tumor cells, whereas only minor effects could be detected at the cell membrane of the control cells. Following PDT, most of the investigated cells showed changes of the mitochondria and cytoplasma. These changes consisted of dissolution of the cristae, predominantly in the central part of the mitochondria. Twenty-four hours after PDT the shape of the mitochondria had changed markedly and the cristae were found to be completely destroyed. Moreover, the cystoplasma showed numerous vacuoles, and the number of mitochondria was decreased compared to non-treated cells.

Cellular delivery and retention of Photofrin II: the effects of interaction with human plasma proteins

The absorbance and fluorescence spectra of Photofrin II (PII) in the presence of albumin, globulins and lipoproteins from human plasma show that all of these proteins induce a degree of disaggregation of PII material. In addition, there are substantial rearrangements in the distribution of different fractions contained in PII and their binding to the protein. It is shown that these rearrangements have considerable impact on the uptake of PII by cultured cells and the ensuing retention of the drug in the cells. The information on the contribution of fluorescing and non-fluorescing components of PII in the cells was obtained by measuring first the PII fluorescence in suspensions of live cells, followed by chemical extraction of porphyrin material from the same cells. The interaction of PII with low density lipoproteins resulted in markedly lower levels of PII material retained in the cells, compared to protein-free drug exposure. Somewhat better but still inferior PII retention was observed with high density lipoproteins. The samples with very low density lipoproteins showed increased uptake of PII, but the subsequent retention of the drug was low, so that the remaining amount of the drug was not much different than in protein-free samples. The strongest inhibition of PII uptake was seen with albumin, with ensuing retention of PII not significantly different than in protein-free samples. The best retention of PII was observed with globulins, with approx. 25% higher total drug content retained in the cells after long-term clearance relative to protein-free samples.

Cellular uptake and relative efficiency in cell inactivation by photoactivated sulfonated meso-tetraphenylporphines

The cellular uptake, relative fluorescence quantum yields and photosensitizing efficiencies of meso-tetraphenylporphines sulfonated to different degrees (TPPSn) have been investigated using the human carcinoma cell line NHIK 3025. The efficiencies of these dyes in photoinactivation of cells were highly dependent on the number of sulfonate groups on the derivatives. These differences in phototoxicity were primarily due to different abilities to be taken up by cells, but were also dependent upon the cellular localization of the dyes. TPPS1 and TPPS2a were more efficiently taken up by the cells than TPPS2o and TPPS4. Plasma membrane associated TPPS4 was less efficient in cell inactivation per quantum of fluorescence emitted than intracellularly located dye. This was also to some extent the case for TPPS1 but not for TPPS2a and TPPS2o. The results presented here indicate that TPPS2a and TPPS1 are the most promising of the TPPSns for possible future use in photodynamic therapy.

Intracellular localization of sulfonated meso-tetraphenylporphines in a human carcinoma cell line

The intracellular localization of meso-tetraphenylporphines sulfonated to different degrees (TPPSn), in a human cervix carcinoma cell line (NHIK 3025), was studied by fluorescence microscopy and fluorescence spectroscopy. After an 18 h incubation, TPPS4, TPPS2a and TPPS2o were localized in extranuclear granules. Studies of cells stained with both TPPS4, and acridine orange, which is known to fluoresce red in lysosomes, indicated that these granules were lysosomes. In addition, a fraction of the cellbound TPPS4, TPPS2a and TPPS2o seems to be associated with the plasma membrane. Fluorescence quenching studies of cells doublestained with acridine orange and TPPS4 indicated that TPPS4 is also localized in the nucleus and in the extralysosomal cytoplasm. The intracellular location of TPPS1 differed from that of the other TPPSns studied: In 6 out of 9 experiments fluorescing extranuclear granules were found. A diffuse fluorescence extending from the perinuclear area was also observed.

A practical test for in vitro evaluation of photosensitization: assessment with hematoporphyrin derivative (HPD)

A simple procedure is described for the determination of the photosensitizing potency of drugs, using three leukemic cell lines, two of lymphocytic origin, L1210 and P388 and one of erythroid type, Friend-745. The procedure allows one to investigate several aspects of the photosensitization properties of tested compounds such as cellular localization and direct (trypan blue exclusion) or delayed (clonogenicity) photomediated toxicities. The method was assessed using crude hematoporphyrin derivative (HPD) as well as dihematoporphyrin ether (DHE) or commercially available Photofrin II. Results were compared to those obtained with normal cells, e.g spleen lymphocytes and erythropoietic stem cells (CFU-e), and discussed in the light of the relative response of normal versus transformed cells.

Equilibrium among hematoporphyrin derivative components--II. Effect of esterase activity

Photofrin II is the hematoporphyrin-derivative fraction enriched in covalently-linked oligomers, characterized by a high degree of folding. Interaction with hydrophobic structures, such as biomolecules and cell structures, results in a modification of the equilibria among the different species, as a consequence of an unfolding effect exerted towards the electrostatic aggregates. The effect of esterase activity was evaluated, taking into account the nature suggested for the covalent linkage of the oligomers (ether and/or ester). The study was performed in Photofrin II aqueous solution by means of absorption and fluorescence spectral analysis. The results showed that the esterase is active only towards the unfold oligomers: that is, in Photofrin II solution supplemented with albumin. In these conditions, spectral analysis revealed the presence of a monomerization process, which is clearly evident during the first four hours of incubation. The monomerization effect induced by the enzyme was also proven by both equilibrium-dialysis measurements and zinc ion complexation. Zinc ion complexes with high affinity for monomeric species, giving rise to a very distinct emission band at 580 nm. The amount of ester linkage shown in the oligomers through enzyme hydrolysis appeared to be less than might have been expected, owing to the inhibiting effect of the monomer produced on the enzyme. The results are a step toward clarifying the intracellular and intratissue turnover of the drug observed after administration.

Photodynamic therapy--new approaches

Photodynamic therapy (PDT) requires a photosensitizer within a target tissue and activation by proper-wavelength radiation at appropriate energy level to achieve complete eradication of that tissue. Whereas the first clinical results were reported nearly a decade ago, only in the past few years has the necessary technology been available for development of phase III controlled clinical trials. Photofrin II, the trade name for a mixture of oligomeric porphyrins, is effective in treatment of a wide variety of malignant tumors and is the subject of Phase III controlled trials in bladder and lung. New photosensitizers are being developed that may be both more efficient and less likely to cause the generalized cutaneous photosensitivity associated with Photofrin II. Further advances in light sources and delivery systems portend an even broader acceptance of PDT in medical and biological science.

Cell uptake, distribution and response to aluminium chloro sulphonated phthalocyanine, a potential anti-tumour photosensitizer

The uptake, retention and effects of aluminium chloro sulphonated phthalocyanine (AlSPc) were measured in two cell lines, UV-2237 a murine fibrosarcoma and the non-tumorigenic NIH/3T3 fibroblast line. The behaviour of cells treated with AlSPc was compared with that of those treated with haematoporphyrin derivative (HpD), a photosensitizer often used in photodynamic therapy (PDT) of cancer. AlSPc absorbs light strongly in the red region, is taken up by cells in a dose dependent fashion and is retained in vitro over a period of days (5 days after exposure greater than 40% remains cell-associated versus less than 25% of HpD). Additionally AlSPc was less cytotoxic to cells, maintained in darkness or exposed to room light, compared to HpD (100% viability versus 0% viability 3 days after 60 min exposure to room light). However red light (approximately 600-700 nm) caused greater toxicity in AlSPc-treated cells (100%) than in similarly exposed HpD-treated cells (less than 60%). No significant differences were detected between the responses of the fibrosarcoma and the fibroblast cell lines. These characteristics of AlSPc suggest that it may prove to be a useful photosensitizer for PDT of cancer and this possibility is discussed.

Photosensitization of malignant tumors

Photodynamic therapy is a new, experimental method of treating malignant tumors by utilizing the relatively selective retention of the photosensitizer (hematoporphyrin derivative or dihematoporphyrin ether) and its ability to elicit an efficient photodynamic reaction upon activation with penetrating viable light. Application of this therapy to tumors in the bronchus, bladder, skin, and several other sites has demonstrated both safety and efficacy, even in advanced cases. Eradication of early stage tumors in the bronchus and bladder has been demonstrated. Selective retention of the photosensitizers in tumors is apparently related to the relatively large size of the aggregates of these materials causing phagocytosis by reticuloendothelial cells as well as preventing rapid clearance from tumor interstitial fluid and subsequent uptake in lipophylic components of cells. Upon light activation, generally delivered from lasers via fiber optics, the sensitizers generate singlet oxygen, the apparent cytotoxic agent, causing both vascular damage and injury to tumor cells.

Phototoxic effects of hematoporphyrin derivative and its chromatographic fractions on hormone-producing human malignant trophoblast cells in vitro

The in vitro phototoxicity of HPD on malignant cells relative to normal cells has been examined. Two human malignant cell lines were studied: the BeWo line of choriocarcinoma cells, which secrete the tumor marker human chorionic gonadotropin (hCG) and its alpha-subunit; and the CaSki line of human cervical carcinoma cells, which secrete hCG and its beta-subunit. Trophoblast-derived, hCG-secreting cells from human amniotic fluid were used as normal controls. In all experiments with HPD plus light, a close correlation was found 24 h after light between cell number and RIA-detectable marker concentration in the medium. Phototoxicity was greater when HPD was introduced in serum-free rather than serum-containing medium. No toxicity was observed in light and dark controls. Cells in Leighton tubes were incubated 1 h with HPD (25 micrograms/ml) in serum-free medium, then rinsed and incubated with medium containing 10% serum. At 2 and 3 days after contact with HPD, flasks were exposed to cool white fluorescent light (1 mW/cm2) for 5 min. Viable cell counts taken 1 day after the light dose indicated that HPD is significantly more phototoxic to BeWo than to CaSki cells; and that both malignant cell types are more photosensitive than amniotic fluid cells, presumably because the latter retain HPD less effectively. In another aspect of this work BeWo cells were used as a model system for comparing the phototoxic effects of the fast (F) and slow (S) eluting fractions of HPD obtained by Bio-Gel P-10 chromatography. Cells in light-shielded tubes were sensitized by incubating with porphyrins for 20 h in media containing 10% calf serum. At 2, 3, or 4 days after removal of porphyrin, with daily replacement of serum-containing medium, flasks were irradiated (see above), and then incubated in the dark for 2 to 4 additional days. Daily culture fluids were analyzed for hormone levels (hCG alpha), and cell counts were performed 2 or 3 days after the light dose. HPD-S (25 micrograms/ml) had no effect on either hormone secretion or cell viability in any of the flasks, whether exposed to light or not. HPD-F at low concentrations (0.25 or 2.5 micrograms/ml) had no detectable effect on cell count or hormone secretion in irradiated flasks. At 10 micrograms/ml, HPD-F was innocuous in dark controls, but caused a large decrease in cell count and hormone output in irradiated flasks.(ABSTRACT TRUNCATED AT 400 WORDS)