Calcium-dependent photodynamic action of di- and tetrasulphonated aluminium phthalocyanine on normal and tumour-derived rat pancreatic exocrine cells

Photodynamic therapy for pancreatic cancer

OBJECTIVES

This study examined the status of photodynamic therapy (PDT) in the treatment of cancers of the pancreas.

METHODS

Original and review articles, editorials, and case reports published primarily in English and listed in Medline/ISI up to October 2006 or identified by a manual search have been reviewed in an attempt to provide a comprehensive overview of the mechanisms of PDT action and clinical application of PDT in the treatment of pancreatic cancers.

RESULTS

Photodynamic therapy represents a novel treatment of pancreatic malignancy; it produces local necrosis of tissue with light after administration of a photosensitizing agent. Evidences from in vivo and in vitro results have shown that PDT significantly decreases pancreatic cancer cell growth, destroys pancreatic carcinoma, and prolongs the survival of patients with unresectable pancreatic malignancy, and also show that PDT has disadvantages and limitations for the treatment of pancreatic cancer.

CONCLUSIONS

Photodynamic therapy can be an effective treatment of patients with pancreatic cancer, but more extensive preclinical and clinical trials are needed for further improvement in the clinical application of PDT, especially in avoidance of complications during PDT.

Photodynamic inactivation of isolated crayfish neuron requires protein kinase C, PI 3-kinase and Ca2+

Involvement of some signalling pathways in response to photodynamic therapy (PDT) of sulfonated aluminium phthalocyanine Photosens has been studied in isolated nerve cell. Neurone photosensitisation with 10(-7) M Photosens gradually inhibited firing and irreversibly abolished neuronal activity. Activation of protein kinase C (PKC) by phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) precipitated PDT-induced abolition of neurone activity and caused nucleus swelling and impairment of the nucleus border. Elevation of cytosolic Ca(2+) concentration by ionomycin or thapsigargin also reduced neurone lifetime. In contrast, the PKC inhibitors staurosporine, hypericin or chelerythrine as well as the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitors wortmannin or LY294002 increased neurone lifetime. These results showed that PKC, PI 3-kinase and Ca(2+) are involved in PDT-induced neurone inactivation and following death.

Intracellular calcium dynamics during photolysis

The objective of this investigation was to gain a deeper understanding of the intracellular events that precede photolysis of cells. A model system, consisting of malignant melanoma cells pretreated with the calcium sensitive fluorescent dye, Fluo-3, was used to examine the intracellular calcium dynamics in single-cell photolysis experiments. Exposure of the cells to 632 nm laser light in the presence of photosensitizer, tin chlorin e6, resulted in a rise in intracellular calcium. The increase in intracellular calcium was blocked using a variety of calcium channel blocking agents, including verapamil, nifedipine, and nickel. Treatment with the channel blockers was also effective in either decreasing or eliminating cell death despite the presence of lethal doses of photosensitizer and irradiation. These results show that intracellular calcium rises prior to plasma membrane lysis, and that this early rise in intracellular calcium is necessary for membrane rupture.

Photodynamic triggering of calcium oscillation in the isolated rat pancreatic acini

1. Photodynamic agents, due to their photon-dependent selective activation, can selectively activate a number of physiological processes and may directly modulate signal transduction in a number of cells including pancreatic acinar cells. 2. Activation of the photodynamic agent sulphonated aluminium phthalocyanine (SALPC) triggered recurrent cytosolic calcium ([Ca2+]i) spiking in pancreatic acinar cells. 3. The photodynamically triggered calcium spiking could be blocked by phosphatidylinositol-specific phospholipase C (PI-PLC) inhibitor U73122, but not by phosphatidylcholine-specific phospholipase C inhibitor D609. 4. Removal of extracellular Ca2+ abolished spiking, as did 2-aminoethoxydiphenylborate (2-APB), an inhibitory modulator of IP3-mediated Ca2+ release from intracellular stores. 5. These data suggest that SALPC photodynamic action may permanently fix PI-PLC in an active conformation, and this produced recurrent [Ca2+]i spiking.

Porphyrin sensitization and intracellular calcium changes in the prokaryote Propionibacterium acnes

Photosensitization induces intracellular free calcium changes ([Ca2+]i) in some eukaryotic cell systems which either contribute to or protect against cell inactivation. We have investigated whether or not similar changes can be induced in prokaryotes. The skin bacterium Propionibacterium acnes was sensitized using protoporphyrin IX (PP IX) or 5-aminolevulinic acid (ALA). Exogenous ALA resulted in either a preferential accumulation of protoporphyrin (ALA-PP) or of coproporphyrin and/or uroporphyrin (ALA-CP/UP) in P. acnes. For PP IX or ALA-PP sensitization, exposure to broad-band red light resulted in an increase in [Ca2+]i. For ALA-PP sensitization, this increase was transient and [Ca2+]i returned to basal levels within 5-10 min after irradiation. However, the elevated [Ca2+]i levels obtained after PP IX sensitization were maintained for at least 1 h after irradiation. In both cases, the reduction in the external calcium concentration led to an enhancement in the cell survival, indicating that induced [Ca2+]i changes may participate in photoinactivation. Sensitization by hydrophilic coproporphyrin and/or uroporphyrin (ALA-CP/UP) did not affect the [Ca2+]i levels, but higher levels of cell inactivation were obtained. It therefore appears that damage to membrane-associated components is at least partly responsible for [Ca2+]i alterations after photosensitization.

A novel aspect of photodynamic action: induction of recurrent spikes in cytosolic calcium concentration

Effects of photodynamic action of gadolinium porphyrin-like macrocycle B (PLMGdB) on cytosolic Ca2+ concentration, [Ca2+]c, was investigated in isolated rat pancreatic acini. The PLMGdB alone or light alone (2 min) had no effect on [Ca2+]c. Cell-bound PLMGdB upon brief (0.5-2.0 min) light activation triggered recurrent spikes in [Ca2+]c. At lower PLMGdB concentration (100 nM) the spikes continued during the whole period of monitoring [Ca2+]c. At a higher concentration of 500 nM, the spikes continued for the first 40 min, followed by a gradual increase in basal [Ca2+]c upon which smaller spikes were superimposed. At 1 microM, the spikes continued for the first 20 min, after that spiking gradually degenerated into a plateau phase. In many aspects, photodynamically triggered spikes resembled spikes generated by physiological concentrations of cholecystokinin. The spikes triggered by photodynamic action were likely to be the result of the ignition of a physiological "chain reaction", because functional inositol-1,4,5-trisphosphate (IP3) receptors were required for spiking to occur. Two-aminoethoxydiphenylborate, an inhibitory modulator of IP3-triggered Ca2+ release from intracellular stores, effectively inhibited photodynamically generated spikes. Therefore photodynamic action appears to be able to permanently transfix a physiological process, leading to long-lasting pharmacological or therapeutic effects.

Influence of topical photodynamic therapy with 5-aminolevulinic acid on porphyrin metabolism

Photodynamic therapy (PDT) with topically applied 5-aminolaevulinic acid (5-ALA) is increasingly used for treating tumours. The efficacy of topical PDT is limited to superficial and initial tumours. The topically applied doses of 5-ALA vary from 0.02 to 7.0 g per session according to the type of lesion. There are no studies on the influence of topically applied 5-ALA on the systemic accumulation of porphyrins or porphyrin precursors. A group of 20 patients with actinic keratoses (AK) and basal cell carcinomas (BCC) were treated by topical PDT with 5-ALA. Prior to and 6 and 24 h after PDT, 5-ALA and total porphyrin concentrations were determined in red blood cells and plasma, respectively. In addition, before and after 5-ALA treatment, 24-h urine samples were collected and porphyrins and porphyrin precursors were measured. There was no significant alteration in porphyrin metabolism. In some patients, a slight but insignificant increase in erythrocyte and plasma porphyrins was found 6 h after 5-ALA PDT. This investigation confirms clearly the safety of this treatment modality and demonstrates that 5-ALA application (up to 7 g) in the course of PDT has no influence on the concentrations of porphyrins and porphyrin precursors measured in various compartments.

Cytotoxic, nuclear, and growth inhibitory effects of photodynamic drugs on pancreatic carcinoma cells

The light-activated drugs AlPcS4 and T4MPyP were studied in a pancreatic carcinoma cell line for their effects on DNA integrity, cell division, proliferation, and survival. The micronucleus assay measured nuclear changes and also the number of actively dividing cells while, under similar conditions, the MTT assay measured cell survival. When tumour cells were exposed to light, pre-treatment with AlPcS4 induced more micronuclei than did T4MPyP at the same levels of cell division and survival. Both drugs showed a correlation between phototoxicity and changes to DNA integrity so establishing micronuclei formation as an important indicator of photodynamic drug action on tumour cells.