Abstract
Haematoporphyrin derivatives (HPDs) are potent sensitizers in photodynamic therapy (PDT), associated with prolonged skin photosensitivity. 5-Aminolaevulinic acid (5-ALA), a natural precusor of haem, is converted intracellularly into the photosensitive agent protoporphyrin IX (PPIX), causing direct cytotoxicity after laser light irradiation but limited skin photosensitivity over 1-2 days and higher tumour selectivity. Unfortunately, the use of 5-ALA in PDT has been shown to cause only superficial tissue necrosis. Therefore, a combination of HPD and 5-ALA could be of great clinical value in the treatment of tumours if a synergistic effect of both sensitizers on tumour cell necrosis with less skin photosensitivity could be demonstrated. Human colon adenocarcinoma cells (HT-29) were cultured with either HPD or 5-ALA alone, simultaneously for 24 h with 5-ALA and HPD or in succession with 5-ALA (18 h) followed by HPD (6 h at different concentrations. Intracellular PPIX concentrations were determined by high-performance thin-layer chromatography. Furthermore, PDT was performed with an incoherent light source (lambda = 580-740 nm) using a light dose of 30 J cm(-2) and an output power of 40 mW cm(-2). The intracellular PPIX concentration correlated well with 5-ALA drug dose and incubation time and was highest after single 5-ALA sensitization. In the presence of HPD, either simultaneously or sequentially, PPIX decreased significantly. The PDT effect after simultaneous incubation with both sensitizers for 24 h was not superior to incubation with HPD alone. If 5-ALA incubation (18 h) was followed by HPD (6 h) cytotoxicity after PDT was higher than with either single drug. 5-ALA (80 microg ml(-1)) led to a decrease in tumour cell viability by 40%. A similar effect could be observed when 5-ALA and HPD were sequentially combined allowing for a reduction of the 5-ALA dose from 80 microg ml(-1) in the absence of HPD to 60 microg ml(-1) and 5 microg ml(-1) together with 0.5 microg ml(-1) and 2 microg ml(-1) HPD respectively. We speculate that the enhanced PDT effect after the combined administration of 5-ALA and HPD to cultures of colon carcinoma cells should be even more impressive in the tumour in vivo, since HPD primarily targets the tumour microvasculature and secondarily tumour cells.
Highlights
5,g ml-' together with 0.5,g ml-' and 2,g ml-' HPD respectively
5-Aminolaevulinic acid (5-ALA) is not a sensitizer by itself but represents a naturally occurring precursor for the haem biosynthetic pathway and has been used as a photosensitizing prodrug that is metabolized intracellularly to porphyrins, known to be efficient photosensitizers (Kennedy et al, 1990). 5-ALA has several advantages when compared with other sensitizers in Photodynamic therapy (PDT): 5-ALA-induced porphyrins are rapidly eliminated from the body, limiting skin sensitivity to 1-2 days (Regula et al, 1995)
We wanted to clarify the influence of a haematoporphyrin derivative on the PP IX synthesis after 5-ALA sensitization and whether the PDT effect after 5-ALA sensitization can be enhanced by its combination with low-dose HPD in vitro experiments using cultured human colonic adenocarcinoma cells
Summary
5,g ml-' together with 0.5,g ml-' and 2,g ml-' HPD respectively. We speculate that the enhanced PDT effect after the combined administration of 5-ALA and HPD to cultures of colon carcinoma cells should be even more impressive in the tumour in vivo, since HPD primarily targets the tumour microvasculature and secondarily tumour cells. In addition to tumour cell-directed necrosis induced by PDT, HPD accumulates in endothelial cells (Leunig et al, 1994), allowing destruction of the tumour vascular system (van Geel et al, 1994). The combination of 5-ALA with desferrioxamine, an enzyme inhibitor of ferrochelatase, increased the concentration of PPIX in normal mucosa of the urinary bladder (Chang et al, 1994) This approach led to a better PDT effect upon gastric and colonic carcinoma cells (Tan et al, 1994). We wanted to clarify the influence of a haematoporphyrin derivative on the PP IX synthesis after 5-ALA sensitization and whether the PDT effect after 5-ALA sensitization can be enhanced by its combination with low-dose HPD in vitro experiments using cultured human colonic adenocarcinoma cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
