Abstract

The orally active microtubule disrupting agent CYT997, previously reported by us, is potently cytotoxic to a variety of cancer cell lines in vitro and shows anti-tumor activity in vivo. In addition to its cytotoxic activity, CYT997 possesses antivascular effects on tumor vasculature. To further characterise 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 using a variety of techniques. In vitro, CYT997 is shown to potently inhibit proliferation of VEGF stimulated HUVEC cells (IC₅₀ 3.7 ± 1.8 nM) and to cause significant morphological changes at 100 nM including membrane blebbing. Using the method of corrosion casting visualised with scanning electron microscopy, a single dose of CYT997 (7.5mg/kg, i.p.) in a metastatic cancer model is shown to cause destruction of tumor microvasculature in metastatic lesions. Furthermore, repeat dosing of CYT997 at 10 mg/kg and above (i.p., b.i.d.) is shown to effectively inhibit development of liver metastases. The time and dose-dependence of the anti-vascular effects is studied in a DLD-1 colon adenocarcinoma xenograft model using the fluorescent dye Hoechst 33342. CYT997 demonstrates rapid and dose-dependent vascular shutdown which persists for greater than 24 h after a single oral dose. Together the data demonstrate that CYT997 possesses potent anti-vascular activity and supports continuing development of this promising compound.