The orally active microtubule-disrupting agent (S)-1-ethyl-3-(2-methoxy-4-(5-methyl-4-((1-(pyridin-3-yl)butyl)amino)pyrimidin-2-yl)phenyl)urea (
CYT997), reported previously by us (Bioorg Med Chem Lett 19:4639-4642, 2009; Mol
Cancer Ther 8:3036-3045, 2009), is potently cytotoxic to a variety of
cancer cell lines in vitro and shows antitumor activity in vivo. In addition to its cytotoxic activity,
CYT997 possesses antivascular effects on
tumor vasculature. To further characterize the vascular disrupting activity of
CYT997 in terms of dose and temporal effects, we studied the activity of the compound on endothelial cells in vitro and on
tumor blood flow in vivo by using a variety of techniques. In vitro,
CYT997 is shown to potently inhibit the proliferation of
vascular endothelial growth factor-stimulated human umbilical vein endothelial cells (IC(50) 3.7 ± 1.8 nM) and cause significant morphological changes at 100 nM, including membrane blebbing. Using the method of corrosion casting visualized with scanning electron microscopy, a single dose of
CYT997 (7.5 mg/kg i.p.) in a metastatic
cancer model was shown to cause destruction of
tumor microvasculature in metastatic lesions. Furthermore, repeat dosing of
CYT997 at 10 mg/kg and above (intraperitoneally, b.i.d.) was shown to effectively inhibit development of liver
metastases. The time and dose dependence of the antivascular effects were studied in a DLD-1
colon adenocarcinoma xenograft model using the
fluorescent dye Hoechst 33342.
CYT997 demonstrated rapid and dose-dependent vascular shutdown, which persists for more than 24 h after a single oral dose. Together, the data demonstrate that
CYT997 possesses potent antivascular activity and support continuing development of this promising compound.