AZD2171 is a potent inhibitor of vascular endothelial growth factor (VEGF) signaling, inhibiting VEGF receptor-2 (VEGFR-2) phosphorylation with an IC50 of 0.5 nM and VEGF driven proliferation with an IC50 of 0.4 nM in human umbilical vein endothelial cells. Once-daily oral administration of AZD2171 inhibited the growth of histologically distinct established human tumor xenografts dose-dependently, consistent with potent inhibition of VEGF signaling and angiogenesis. The purpose of this study was to examine the antitumor activity of AZD2171 and its mode of action in gastric cancer. We examined the growth inhibitory effect of AZD2171 in seven gastric cancer cell lines in vitro with an MTT assay. AZD2171 inhibited the proliferation of KATOIII gastric cancer cells with an IC50 of 150 nM (300 fold higher than the concentration required for comparable inhibition of VEGF-induced HUVEC proliferation) and only inhibited the proliferation of other gastric cell lines at concentrations of >5μM. Only the KATOIII cells overexpress an active form of K-SAM/FGFR2 with a C-terminal truncation, and they do not express VEGFR-2 or -3. Therefore, we hypothesized that the variant K-SAM could be an alternative target for AZD2171. The inhibition of K-SAM phosphorylation by AZD2171 was examined by immunoblotting. Untreated KATOIII cells showed phosphorylation of K-SAM in the absence of ligand stimulation. AZD2171 inhibited K-SAM phosphorylation in these cells at a concentration of 100 nM. Phosphorylation of AKT and MAPK was also inhibited by AZD2171 in these cells. An in vitro kinetic assay revealed that the variant K-SAM is constitutively active and can be inhibited by AZD2171 (Ki 50nM). These results suggest that AZD2171 can inhibit K-SAM in gastric cells that overexpress K-SAM with a C-terminal truncation, but only at comparatively high concentrations. The potential relevance of this finding is being explored in vivo.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]