Regorafenib is an oral multi-kinase inhibitor which has recently been reported to extend overall survival in a Phase III trial in patients with metastatic colorectal tumors who have failed standard therapies (CORRECT trial) when given with best supportive care (BSC) vs placebo plus BSC. It is also examined in a Phase III trial for the treatment of patients with metastatic and/or unresectable gastrointestinal stromal tumors who have failed imatinib and sunitinib therapy (GRID trial). Regorafenib deactivates tumors across three dimensions (angiogenesis, oncogenesis, and stromatogenesis) by inhibition of angiogenic receptor tyrosine kinases (RTK) (e.g., VEGFR1-3, TIE2), oncogenic (e.g., KIT, RET) and stromal RTKs (e.g., PDGFR, FGFR). In preclinical studies it was previously shown that regorafenib inhibits a broad spectrum of different tumor types including colorectal cancer (CRC) models. Regorafenib was efficacious as a single agent and in combination with irinotecan in CRC models and demonstrated anti-metastatic activities in preclinical models of breast cancer. VEGFR-3, a member of the VEGF receptor family, is thought to play an important role in tumor lymphangiogenesis and metastasis. Regorafenib potently inhibited (4-8 nM) VEGF-C stimulated VEGFR-3 receptor autophosphorylation in human dermal lymphatic endothelial cells (LECs) and inhibited VEGF-C stimulated LEC cell migration in a scratch assay at concentrations below 100 nM. In vivo regorafenib's antimetastatic potential was examined in a syngeneic CRC liver metastasis model. In this model murine MC38 CRC cells were injected into the mouse spleen with following ablation of the organ. Significant survival of mice treated orally at a daily dose of 10 mg/kg regorafenib was observed compared to vehicle-treated control mice. Liver weights, which were used as read-out for the degree of metastases formation, was reduced in mice treated with regorafenib for thirteen days vs vehicle treated animals. This was accompanied by significantly reduced number of metastases observed outside the liver. Finally, the direct effects of regorafenib in CRC cell lines was evaluated in vitro in a panel of 25 different human CRC cell lines where it inhibited the proliferation of 19 cell lines with IC50 values between 1 and 10µM and no correlation with mutated KRAS or BRAF was observed. Effects of regorafenib on intracellular MAPK signalling in CRC cell lines was analyzed by western blotting. Regorafenib, which also inhibits Raf kinases, reduced pERK by 50% at concentrations of about 500-2000 nM in HT29, HCT116 and Colo-205 CRC cell lines. In summary, these results suggest that regorafenib may exert its anti-tumor activity in colorectal cancer by inhibition of multiple kinases across its three dimensions within the tumor environment. Additional analyses in particular of clinical tumor samples are necessary to more clearly understand regorafenib's molecular mechanisms of action. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2337. doi:1538-7445.AM2012-2337