Arginase activity in human breast cancer cell lines: N-omega-hydroxy-L-arginine selectively inhibits cell proliferation and induces apoptosis in MDA-MB-468 cells

L-Arginine is the common substrate for two enzymes, arginase and nitric oxi de synthase (NOS), Arginase converts L-arginine to L-ornithine, which is th e precursor of polyamines, which are essential components of cell prolifera tion. NOS converts L-arginine to produce NO, which inhibits proliferation o f many cell lines. Various human breast cancer cell lines were initially sc reened for the presence of arginase and NOS, Two cell lines, BT-474 and MDA -MB-468, were found to have relatively high arginase activity and very low NOS activity, Another cell line, ZR-75-30, had the highest NOS activity and comparatively low arginase activity. The basal proliferation rates of MDA- MB-468 and BT-474 were found to be higher than the ZR-75-30 cell line. N-Hy droxy-L-arginine (NOHA), a stable intermediate product formed during conver sion of L-arginine to NO, inhibited proliferation of the high arginase-expr essing MDA-MB-468 cells and induced apoptosis after 48 h, NOHA arrested the se cells in the S phase, increased the expression of p21, and reduced sperm ine content. These effects of NOHA were not observed in the ZR-75-30 cell l ine, which expresses high NOS and relatively low arginase, The effects of N OHA were antagonized in the presence of L-ornithine (500 mu M), which sugge sts that in MDA-MB-468 cell line, the arginase pathway is very important fo r cell proliferation. Inhibition of the arginase pathway led to depletion o f intracellular spermine and apoptosis as observed by terminal deoxynucleot idyl transferase (Tdt)-mediated nick end labeling assay and induction of ca spase 3, In contrast, the ZR-75-30 cell line maintained its viability and i ts L-ornithine and spermine levels in the presence of NOHA, We conclude tha t NOHA has antiproliferative and apoptotic actions on arginase-expressing h uman breast cancer cells that are independent of NO.