Spectrum of toxicities of amino acid methyl esters for myeloid cells is determined by distinct metabolic pathways.
L-leucine methyl ester (Leu-OMe), Leu-Leu-OMe, Phe-OMe, and Glu-(OMe)2 are toxic to mononuclear phagocytes (M phi) and neutrophils. In the present studies, the mechanism of this toxicity was examined. A concentration of NH4Cl known to neutralize lysosomal pH and to block conversion of Leu-OMe to the dipeptide condensation product Leu-Leu-OMe inhibited Leu-OMe- or Glu-(OMe)2- but not Leu-Leu-OMe-mediated M phi toxicity. Leu-OMe-, Glu-(OMe)2-, or Leu-Leu-OMe-mediated killing of M phi was prevented by Gly-Phe-CHN2, a specific inhibitor of the thiol protease, dipeptidyl peptidase I (DPPI). Neither NH4Cl nor Gly-Phe-CHN2 prevented Phe-OMe-mediated M phi toxicity. In contrast, inhibition of M phi serine esterase activity prevented Phe-OMe- but not Leu-OMe- or Glu-(OMe)2-mediated killing of M phi. The myeloid tumor lines U937, HL60, and THP-1 were found to be uniformly enriched in DPPI and susceptible to Leu-Leu-OMe but not Leu-OMe toxicity. Whereas HL60 were resistant to Phe-OMe, THP-1 cells were killed by this agent. Incubation of peripheral blood mononuclear cells with Leu-OMe resulted in loss of natural killer (NK) functions and cytotoxic T lymphocytes (CTL) precursors, a process that requires the DPPI-dependent generation of membranolytic polymerization products. Phe-OMe had no toxic effects on NK cells or CTL precursors. These results indicate that Leu-OMe and Glu-(OMe)2 toxicity for M phi is related to the production of higher molecular weight hydrophobic polymerization products via the sequential action of two nonserine esterase lysosomal enzymes. In contrast, Phe-OMe toxicity for myeloid cells was found to correlate with serine esterase-mediated intracellular trapping of high concentrations of the free amino acid Phe. These distinct enzymatic mechanisms may provide a unique means of targeting agents capable of selectively deleting cells of myeloid lineage.
Thiele
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DL
Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-8887.
Lipsky
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PE
D000328:Adult; D000643:Ammonium Chloride / Q000494:pharmacology; D020789:Cathepsin C; D016923:Cell Death / Q000187:drug effects*; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004950:Esterases / Q000378:metabolism; D005971:Glutamates / Q000494:pharmacology*; D006098:Granulocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007694:Killer Cells, Natural / Q000187:drug effects / Q000378:metabolism; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D007951:Leukemia, Myeloid / Q000473:pathology; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D010586:Phagocytes / Q000187:drug effects; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000378:metabolism; D014407:Tumor Cells, Cultured
D005971:Glutamates; D000643:Ammonium Chloride; C034515:phenylalanine methyl ester; C030365:leucine methyl ester; D010649:Phenylalanine; C035873:glutamic acid dimethyl ester; D004950:Esterases; C022635:serine esterase; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D020789:Cathepsin C; D007930:Leucine