Impact of system L amino acid transporter 1 (LAT1) on proliferation of human ovarian cancer cells: A possible target for combination therapy with anti-proliferative aminopeptidase inhibitors

Amino acids activate nutrient signaling via the mammalian target of rapamycin (mTOR), we therefore evaluated the relationship between amino acid transporter gene expression and proliferation in human ovarian cancer cell lines. Expression of three cancer-associated amino acid transporter genes, LAT1, ASCT2 and SN2, was measured by qRT-PCR and Western blot. The effects of silencing the LAT1 gene and its inhibitor BCH on cell growth were evaluated by means of cell proliferation and colony formation assays. The system L amino acid transporter LAT1 was up-regulated in human ovarian cancer SKOV3, IGROV1, A2780, and OVCAR3 cells, compared to normal ovarian epithelial IOSE397 cells, whereas ASCT2 and SN2 were not. BCH reduced phosphorylation of p70S6K, a down-stream effector of mTOR, in SKOV3 and IGROV1 cells, and decreased their proliferation by 30% and 28%, respectively. Although proliferation of SKOV3 (S1) or IGROV1 (I10) cells was unaffected by LAT1-knockdown, plating efficiency in colony formation assays was significantly reduced in SKOV3(S1) and IGROV1(I10) cells to 21% and 52% of the respective plasmid transfected control cells, SKOV3(SC) and IGROV(IC), suggesting that LAT1 affects anchorage-independent cell proliferation. Finally, BCH caused 10.5- and 4.3-fold decrease in the IC₅₀ value of bestatin, an anti-proliferative aminopeptidase inhibitor, in IGROV1 and A2780 cells, respectively, suggesting that the combined therapy is synergistic. Our findings indicate that LAT1 expression is increased in human ovarian cancer cell lines; LAT1 may be a target for combination therapy with anti-proliferative aminopeptidase inhibitors to combat ovarian cancer.