Active and higher intracellular uptake of 5-aminolevulinic acid in tumors may be inhibited by glycine.
Topical 5-aminolevulinic acid is used for the fluorescence-based diagnosis and photodynamic treatment of superficial precancerous and cancerous lesions of the skin. Thus, we investigated the kinetics of 5-aminolevulinic acid-induced fluorescence and the mechanisms responsible for the selective formation of porphyrins in tumors in vivo. Using amelanotic melanomas (A-Mel-3) grown in dorsal skinfold chambers of Syrian golden hamsters fluorescence kinetics were measured up to 24 h after topical application of 5-aminolevulinic acid (1%, 3%, or 10%) for 1 h, 4 h, or 8 h by intravital microscopy (n = 54). Maximal fluorescence intensity in tumors after 1 h application (3% 5-aminolevulinic acid) occurred 150 min and after 4 h application (3% 5-aminolevulinic acid) directly thereafter. Increasing either concentration of 5-aminolevulinic acid or application time did not yield a higher fluorescence intensity. The selectivity of the fluorescence in tumors decreased with increasing application time. Fluorescence spectra indicated the formation of protoporphyrin IX (3% 5-aminolevulinic acid, 4 h; n = 3). The simultaneous application of 5-aminolevulinic acid (3%, 4 h) and glycine (20 microM or 200 microM; n = 10) reduced fluorescence in tumor and surrounding host tissue significantly. In contrast, neither decreasing iron concentration by desferrioxamine (1% and 3%; n = 10) nor inducing tetrapyrrole accumulation using 1, 10-phenanthroline (7.5 mM; n = 5) increased fluorescence in tumors. The saturation and faster increase of fluorescence in the tumor together with a reduction of fluorescence by the application of glycine suggests an active and higher intracellular uptake of 5-aminolevulinic acid in tumor as compared with the surrounding tissue. Shorter application (1 h) yields a better contrast between tumor and surrounding tissue for fluorescence diagnosis. The additional topical application of modifiers of the heme biosynthesis, desferrioxamine or 1,10-phenanthroline, however, is unlikely to enhance the efficacy of topical 5-aminolevulinic acid-photodynamic therapy at least in our model.
Langer
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S
Institute for Surgical Research, Klinikum Grosshadern, Ludwig-Maximilians-University, Munich, Germany.
Abels
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Botzlar
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Pahernik
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Rick
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Szeimies
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Goetz
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D000622:Aminolevulinic Acid / Q000493:pharmacokinetics*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D006224:Cricetinae; D003676:Deferoxamine / Q000494:pharmacology; D015194:Diffusion Chambers, Culture; D005998:Glycine / Q000494:pharmacology*; D008297:Male; D018328:Melanoma, Amelanotic / Q000378:metabolism*; D008647:Mesocricetus; D009368:Neoplasm Transplantation; D010618:Phenanthrolines / Q000494:pharmacology; D011524:Protoporphyrins / Q000096:biosynthesis; D012878:Skin Neoplasms / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D010618:Phenanthrolines; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; D003676:Deferoxamine; D005998:Glycine; C025205:1,10-phenanthroline