Intracellular Localization is a Cofactor for the Phototoxicity of Protoporphyrin IX in the Gastrointestinal Tract: In Vitro Study¶†

Photodynamic Therapy and Immunological View in Gastrointestinal Tumors

Gastrointestinal cancers are a specific group of oncological diseases in which the location and nature of growth are of key importance for clinical symptoms and prognosis. At the same time, as research shows, they pose a serious threat to a patient's life, especially at an advanced stage of development. The type of therapy used depends on the anatomical location of the cancer, its type, and the degree of progression. One of the modern forms of therapy used to treat gastrointestinal cancers is PDT, which has been approved for the treatment of esophageal cancer in the United States. Despite the increasingly rapid clinical use of this treatment method, the exact immunological mechanisms it induces in cancer cells has not yet been fully elucidated. This article presents a review of the current understanding of the mode of action of photodynamic therapy on cells of various gastrointestinal cancers with an emphasis on colorectal cancer. The types of cell death induced by PDT include apoptosis, necrosis, and pyroptosis. Anticancer effects are also a result of the destruction of tumor vasculature and activation of the immune system. Many reports exist that concern the mechanism of apoptosis induction, of which the mitochondrial pathway is most often emphasized. Photodynamic therapy may also have a beneficial effect on such aspects of cancer as the ability to develop metastases or contribute to reducing resistance to known pharmacological agents.

Chimeric Mouse With Humanized Liver Is an Appropriate Animal Model to Investigate Mode of Action for Porphyria-Mediated Hepatocytotoxicity

Porphyrinogenic compounds are known to induce porphyria-mediated hepatocellular injury and subsequent regenerative proliferation in rodents, ultimately leading to hepatocellular tumor induction. However, an appropriate in vivo experimental model to evaluate an effect of porphyrinogenic compounds on human liver has not been fully established. Recently, the chimeric mouse with humanized liver (PXB mice) became widely used as a humanized model in which human hepatocytes are transplanted. In the present study, we examined the utility of PXB mice as an in vivo experimental model to evaluate the key events of the porphyria-mediated cytotoxicity mode of action (MOA) in humans. The treatment of PXB mice with 5-aminolevulinic acid, a representative porphyrinogenic compound, for 28 days caused protoporphyrin IX accumulation, followed by hepatocyte necrosis, increased mitosis, and an increase in replicative DNA synthesis in human hepatocytes, indicative of cellular injury and regenerative proliferation, similar to findings in patients with porphyria or experimental porphyria models and corresponding to the key events of the MOA for porphyria-mediated hepatocellular carcinogenesis. We conclude that the PXB mouse is a useful model to evaluate the key events of the porphyria-mediated cytotoxicity MOA in humans and suggest the utility of PXB mice for clarifying the human relevancy of findings in mice.

In vivo photobleaching kinetics and epithelial biodistribution of hexylaminolevulinate-induced protoporphyrin IX in rat bladder cancer

In a previous paper, we showed that rat bladder instillations with 8 or 16 mM of hexyl aminolevulinate (hALA) result in diametrically opposed photodynamic therapy efficiency. Although the same fluorescent intensities were detected spectroscopically and by fluorescent microscopy in both conditions, while a given light dose resulted in tumor necrosis with an intact bladder wall after 8 mM hALA, bladders instilled with 16 mM showed total wall necrosis without impact on the tumor. The current study investigated the photobleaching and localization pattern of protoporphyrin IX (PpIX) after both hALA intravesical instillations in tumor-bearing rat bladders. The total PpIX content was evaluated by the extraction of postmortem whole bladders. Photobleaching was evaluated in vivo by fluorescent spectroscopy. Cryosections of bladders were subjected to fluorescent microscopy for cellular localization of the photosensitizer. PpIX extraction showed identical amounts of photosensitizer in tumor-bearing bladders at both concentrations. Photobleaching experiments revealed mono-exponential decay curves in both situations but with a two times faster decay constant in 16 mM bladders. Fluorescent microscopy showed an identical fluorescent pattern for normal bladders at both concentrations and tumor bladders at 8 mM with bright spots. Tumor bladders at 16 mM exhibited a more diffuse cytoplasmatic fluorescent distribution. The different response to photodynamic therapy with regard to the initial pro-drug concentration can thus be attributed to the different cellular localizations.

Systematic Review and Meta-Analysis of In Vitro Anti-Human Cancer Experiments Investigating the Use of 5-Aminolevulinic Acid (5-ALA) for Photodynamic Therapy

5-Aminolevulinic acid (5-ALA) is an amino acid derivative and a precursor of protoporphyrin IX (PpIX). The photophysical feature of PpIX is clinically used in photodynamic diagnosis (PDD) and photodynamic therapy (PDT). These clinical applications are potentially based on in vitro cell culture experiments. Thus, conducting a systematic review and meta-analysis of in vitro 5-ALA PDT experiments is meaningful and may provide opportunities to consider future perspectives in this field. We conducted a systematic literature search in PubMed to summarize the in vitro 5-ALA PDT experiments and calculated the effectiveness of 5-ALA PDT for several cancer cell types. In total, 412 articles were identified, and 77 were extracted based on our inclusion criteria. The calculated effectiveness of 5-ALA PDT was statistically analyzed, which revealed a tendency of cancer-classification-dependent sensitivity to 5-ALA PDT, and stomach cancer was significantly more sensitive to 5-ALA PDT compared with cancers of different origins. Based on our analysis, we suggest a standardized in vitro experimental protocol for 5-ALA PDT.

Uptake and phototoxicity of meso-tetrahydroxyphenyl chlorine are highly variable in human biliary tract cancer cell lines and correlate with markers of differentiation and proliferation

Photodynamic therapy (PDT) using Photofrin and, recently, Foscan has gained broad acceptance for palliative treatment of non-resectable cholangiocarcinoma (CC). No information, however, is available whether the phenotype of CC tumour cells has an effect on the efficiency of the treatment. Using a well-characterised set of n = 9 biliary tract cancer cell lines this study investigated the uptake, phototoxicity, and release of meso-tetrahydroxyphenyl chlorine (mTHPC, Foscan) after incubation with 200 or 400 ng ml(-1) mTHPC. For uptake of mTHPC we found great variations between the individual cell lines (up to a factor 2), resulting in even more pronounced differences in phototoxicity. Based on statistical classification by hierarchical cluster analysis, two groups of cell lines can be distinguished which are characterised by either high or low susceptibility towards mTHPC-based photodynamic treatment. Correlation analysis with previously established immunochemical parameters showed that cells with a low cytokeratin-19 (ductal differentiation), high vimentin (mesenchymal marker), and high proliferative phenotype preferentially show higher uptake of mTHPC and subsequent phototoxicity. These results demonstrate high variability of biliary tract cancer cells when subjected to mTHPC-based photodynamic treatment and identify possible markers that could be used in the clinical setting in order to predict the efficiency of PDT and adjust the dose for complete tumour elimination.

Photodynamic ultradeformable liposomes: Design and characterization

Hydrophobic ([tetrakis(2,4-dimetil-3-pentyloxi)-phthalocyaninate]zinc(II)) (ZnPc) and hydrophilic ([tetrakis(N,N,N-trimethylammoniumetoxi)-phthalocyaninate]zinc(II) tetraiodide) (ZnPcMet) phthalocyanines were synthesized and loaded in ultradeformable liposomes (UDL) of soybean phosphatidylcholine and sodium cholate (6:1, w/w, ratio), resulting 100 nm mean size vesicles of negative Zeta potential, with encapsulation efficiencies of 85 and 53%, enthalpy of phase transition of 5.33 and 158 J/mmol for ZnPc and ZnPcMet, respectively, indicating their deep and moderate partition into UD matrices. Matrix elasticity of UDL-phthalocyanines resulted 28-fold greater than that of non-UDL, leaking only 25% of its inner aqueous content after passage through a nanoporous barrier versus 100% leakage for non-UDL. UDL-ZnPc made ZnPc soluble in aqueous buffer while kept the monomeric state, rendering singlet oxygen quantum yield (Phi(Delta)) similar to that obtained in ethanol (0.61), whereas UDL-ZnPcMet had a four-fold higher Phi(Delta) than that of free ZnPcMet (0.21). Free phthalocyanines were non-toxic at 1 and 10 microM, both in dark or upon irradiation at 15 J/cm2 on Vero and J-774 cells (MTT assay). Only liposomal ZnPc at 10 microM was toxic for J-774 cells under both conditions. Additionally, endo-lysosomal confinement of the HPTS dye was kept after irradiation at 15 J/cm2 in the presence of UDL-phtalocyanines. This could lead to improve effects of singlet oxygen against intra-vesicular pathogen targets inside the endo-lysosomal system.

Identification of a mammalian mitochondrial porphyrin transporter

The movement of anionic porphyrins (for example, haem) across intracellular membranes is crucial to many biological processes, but their mitochondrial translocation and coordination with haem biosynthesis is not understood. Transport of porphyrins into isolated mitochondria is energy-dependent, as expected for the movement of anions into a negatively charged environment. ATP-binding cassette transporters actively facilitate the transmembrane movement of substances. We found that the mitochondrial ATP-binding cassette transporter ABCB6 is upregulated (messenger RNA and protein in human and mouse cells) by elevation of cellular porphyrins and postulated that ABCB6 has a function in porphyrin transport. We also predicted that ABCB6 is functionally linked to haem biosynthesis, because its mRNA is found in both human bone marrow and CD71+ early erythroid cells (by database searching), and because our results show that ABCB6 is highly expressed in human fetal liver, and Abcb6 in mouse embryonic liver. Here we demonstrate that ABCB6 is uniquely located in the outer mitochondrial membrane and is required for mitochondrial porphyrin uptake. After ABCB6 is upregulated in response to increased intracellular porphyrin, mitochondrial porphyrin uptake activates de novo porphyrin biosynthesis. This process is blocked when the Abcb6 gene is silenced. Our results challenge previous assumptions about the intracellular movement of porphyrins and the factors controlling haem biosynthesis.

Targeting of sebocytes by aminolevulinic acid-dependent photosensitization

Photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX has been developed as a very useful therapeutic modality. Recently, several authors have reported on the efficacy of this procedure for acne. This approach is based on the fact that 5-aminolevulinic acid-induced protoporphyrin IX has strong selectivity for sebaceous glands. We used the immortalized human sebaceous gland cell line SZ95 to investigate cellular mechanisms of photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX. Quantification of induced protoporphyrin IX production showed dependence on the applied 5-aminolevulinic acid dose. When SZ95 sebocytes were differentiated by arachidonic acid treatment, there was no difference between them and the control cells with respect to both the amount of 5-aminolevulinic acid-induced protoporphyrin IX and the phototoxic effects. We altered protoporphyrin IX formation rates by growing cells scattered as single cells in the culture dishes. Single cells produced significantly lower protoporphyrin IX levels than those grown with intercellular contacts. Intracellular localization of protoporphyrin IX was imaged using confocal laser scanning microscopy. The differentiation-specific lipid droplets were virtually excluded from protoporphyrin IX fluorescence. In addition to weak mitochondrial and strong membrane fluorescence, distinctive spots with strong fluorescence were observed. These did not colocalize with fluorescent probes for mitochondria, lysosomes or the Golgi apparati.

The pH-dependent conformational transition of β-lactoglobulin modulates the binding of protoporphyrin IX

We have investigated the interaction between PPIX and beta-lactoglobulin (beta-lg) as a function of the pH of the solution. beta-lg is a small globular protein (MW approximately 18 kDa) with a very well characterized structure that reveals several possible binding sites for ligands. The interaction with beta-lg affects the photophysical properties of PPIX. The shift of PPIX emission maximum, excitation maximum and the increase of the fluorescence intensity is an indicator that binding between the porphyrin and beta-lg occurs. The binding constant appears to be modulated by the pH of the solution. Spectroscopic measurements do not reveal any significant energy transfer between the Trp residues of beta-lg and PPIX, however, fluorescence anisotropy decay measurements confirm the binding and the modulation introduced by the pH of the solution. Since beta-lg has been shown to be stable within the range of pH adopted in our experiments (5.0-9.0), the results suggest that PPIX binds a site affected by the pH of the solution. Because of the crystallographic evidence an obvious site is near the aperture of the interior beta-barrel however an alternative (or concurrent) binding site may still be present.

RNA expression profiling of normal and tumor cells following photodynamic therapy with 5-aminolevulinic acid-induced protoporphyrin IX in vitro

Photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX synthesis as a photosensitizing reagent is an encouraging modality for cancer treatment. Understanding the mechanism of tumor phototoxicity is important to provide a basis for combinatory therapy regimens. A normal cell line (UROtsa, urothelial) and two tumor cell lines (RT4, urothelial; HT29, colonic) were treated with cell line-specific LD50 doses of light after exposure to 5-aminolevulinic acid (100 microg/mL), and harvested for RNA extraction 0, 10, and 30 minutes after irradiation. The RNA was hybridized to the metg001A Affymetrix GeneChip containing 2,800 genes, focusing on cancer-related and growth regulatory targets. Comparing the gene expression profiles between the different samples, 40 genes (e.g., SOD2, LUC7A, CASP8, and DUSP1) were identified as significantly altered in comparison with the control samples, and grouped according to their gene ontology. We selected caspase-8 (CASP8) and dual specificity phosphatase 1 (DUSP1) for further validation of the array findings, and compared their expression with the expression of the immediate early gene FOS by quantitative reverse transcription-PCR. RNA expression of CASP8 stayed unchanged whereas DUSP1 RNA was up-regulated in normal and tumor cells starting 30 minutes after irradiation. In contrast, FOS RNA was found continuously up-regulated over time in all three cell lines. Induction of DUSP1 protein expression was clearly shown after 1 hour using Western blot analysis. Interestingly, no changes of caspase-8 protein expression but activation of catalytic activity was detected only in UROtsa cells starting 1 hour after photodynamic therapy, whereas no changes were seen in both tumor cell lines. According to caspase-8, the active caspase 3 fragment was found only in the normal urothelial cell line (UROtsa) 1 hour after photodynamic therapy. Combined data analysis suggests that photodynamic therapy in vitro (LD50) leads to apoptosis in UROtsa and to necrosis in the tumor cell lines, respectively. RNA expression profiling of normal and tumor cell lines following photodynamic therapy with 5-aminolevulinic acid gave insight into the major molecular mechanisms induced by photodynamic therapy.