The importance of mTOR signaling in
tumor biology is widely accepted and a number of agents that selectively target mTOR are being developed in
cancer therapy. On the other hand, it has been demonstrated that mTOR can act as an angiogenic agent. Thus, we hypothesized that the mTOR inhibitor-induced anticancer effect is affected by expression of a key
angiogenic factor,
vascular endothelial growth factor (
VEGF) and investigated the anticancer effect underlying mTOR using an in vitro assay. The mTOR inhibitor
rapamycin dose-dependently reduced the cell viability of the
breast cancer cell line, MCF-7, but did not reduce the cell viability of the
colon cancer cell line, HT-29.
Rapamycin reduced the
VEGF expression in the culture medium of MCF-7, while
rapamycin did not contribute
VEGF expression in the culture medium of HT-29.
VEGF stimulated cell viability and
VEGF inhibition reduced cell viability of MCF-7, and
rapamycin dose-dependently restored the cell viability of MCF-7 reduced by
rapamycin. These findings suggest that mTOR acts as a direct
anticancer agent and that the mTOR-inhibitor-induced anticancer effect involved the reduced expression of
VEGF in MCF-7. Our results imply that mTOR regulates the expression of
VEGF and is involved in
breast cancer progression.