Selective cytotoxicity of 3-amino-L-tyrosine correlates with peroxidase activity

In the presence of 3-amino-L-tyrosine (3-AT), abundant brown pigment forms in human HL-60 cells, but not in a variety of other cell lines, which are r eported to be lower in mean myeloperoxidase (MPO) content than HL-60. Cells were assessed for peroxidase activity with an ABTS-based colorimetric assa y and compared to values obtained with known amounts of human myeloperoxida se. HL-60 cells were estimated to contain the equivalent of 37.1 ng myelope roxidase/10(6) cells versus 26.1 and 5.0 ng/10(6) cells for human K562 and marine RAW 264.7 cell lines, respectively. HL-60 cells exhibited a nearly 6 0% inhibition of proliferation and > 70% reduction in cell viability after 4 d of culture in the presence of 100 mu g 3-AT per ml. Higher concentratio ns of 3-AT (up to 400 mu g/ml) for 4 d reduced HL-60 proliferation by 80% a nd decreased viability to 1-3%. Comparable levels of cytotoxicity were achi eved in KG-1 cells after 7 d with 200 or 400 mu g 3-AT per ml. K562 cells e xhibited a 40% reduction in cell number after 7 d with 400 mu g 3-AT per ml , but concentrations less than 400 mu g/ml did not significantly affect K56 2 proliferation. K562 viability remained unchanged with doses of 3-AT up to 400 mu g/ml. RAW 264.7 cells exhibited unchanged viability and proliferati on in the presence of 3-AT at concentrations up to 400 mu g 3-AT per ml. K5 62, KG-1, and RAW 264.7 cells exhibited no evidence of brown pigment format ion in the presence of 3-AT and medium containing 10% fetal bovine serum. H owever, RAW 264.7 cells that were converted to protein-free medium and expo sed to 3-AT exhibited intense brown pigment in some cell nuclei. A high per centage of HL-60 cells treated with 3-AT exhibited membrane blebbing, pykno sis, and nuclear fragmentation, which was not observed among other 3-AT-tre ated cell lines. A mechanism involving toxic intermediates of peroxidase-me diated "aminomelanin" formation is hypothesized.