The
vascular endothelial growth factor (
VEGF) is a central mediator of
tumor-induced angiogenesis.
Everolimus, a
mammalian target of rapamycin (mTOR) inhibitor, decreases
VEGF-secretion of
cancer cells.
Vatalanib is a selective inhibitor of
VEGF receptors 1-3. In the present study it was hypothesized that dual inhibition of
VEGF signaling by inhibition of
VEGF production and
VEGF receptor signaling leads to synergistic anti-
tumor effects. In vitro, effects of
vatalanib and
everolimus on cell proliferation, cell cycle, apoptosis and signal transduction were examined in three
gastric cancer cell lines. Effects on angiogenesis were assessed using tube formation assays of cultured human umbilical vein endothelial cells (HUVECs). In vivo, the antitumor effect of compounds was studied using a
gastric cancer xenograft nude mouse model.
VEGF of murine origin (mVEGF) and human
cancer cell-derived
VEGF (hVEGF) were studied separately by specific ELISAs.
Tumor vascularization and proliferation were quantified by immunohistochemistry. In vitro,
everolimus but not
vatalanib decreased
gastric cancer proliferation without inducing apoptosis.
Vatalanib abolished endothelial cell tube formation, whereas inhibition of tube formation by
everolimus was incomplete. In vivo, the combination of
vatalanib with
everolimus was superior to single agent treatments and reduced
tumor size by about 50% relative to
everolimus monotherapy (p < 0.005). Pharmacodynamic analysis of
VEGF plasma level showed a decrease of hVEGF by
everolimus and indicated a trend towards lower mVEGF level only in the combination group. In line, there was a tendency for lower vascular density and proliferation for combination treatment. We conclude that in a preclinical model of
gastric cancer the antitumor activity of
vatalanib can be augmented by
everolimus.