Active and Higher Intracellular Uptake of 5-Aminolevulinic Acid in Tumors may be Inhibited by Glycine

Abstract

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.

δ-Aminolevulinic Acid Transport in Cancer Cells of the Human Extrahepatic Biliary Duct

“…Similarly, for the human adenocarcinoma cell line WiDr transport of ␦-ALA by ␤-amino acid and GABA carriers has been reported (Rud et al, 2000). In amelanotic melanomas uptake of ␦-ALA is inhibited by glycine (Langer et al, 1999). Glycine, however, did not inhibit ␦-ALA transport in the Döring et al (1998) study.…”

Protoporphyrin IX enhancement by 5-aminolaevulinic acid peptide derivatives and the effect of RNA silencing on intracellular metabolism

“…For the ALA prodrugs to exert a pharmacological effect, the derivatives must be able to reach the target sites at a sufficient concentration; this depends on the presence on the target cells of the necessary transport systems able to deliver them into the cytoplasm (Doring et al, 1998;Langer et al, 1999;Novotny et al, 2000;Rud et al, 2000;Irie et al, 2001) and their ability to undergo an efficient enzymatic hydrolysis to liberate ALA for the subsequent conversion to protoporphyrin IX (Peng et al, 1996). A major challenge in ALA-PDT at the present time is the need to achieve a more effective penetration of ALA into target tissues or the cells of pathogenic organisms.…”

Neovascularization of poly(ether ester) block‐copolymer scaffolds in vivo: Long‐term investigations using intravital fluorescent microscopy

“…The dorsal skinfold chamber is a widely used and well-accepted model in microcirculatory research in hamsters and mice. [12][13][14][15][16][17][18] Scaffold manufacturing and characteristics A block-copolymer polymer composed of alternating soft blocks of polyethylene glycol terephthalate (PEGT) and hard blocks of polybutylene terephthalate (PBT) was used. Polymer composition can be modified by varying the weight percentages of PEGT and PBT or by changing the molecular weight (MW) of the PEG.…”