Inhibition of tumor angiogenesis by blockading the vascular endothelial growth factor (VEGF) signaling pathway is a promising therapeutic strategy for thyroid cancer. Lenvatinib mesilate (lenvatinib) is a potent inhibitor of VEGF receptors (VEGFR1–3) and other prooncogenic and prooncogenic receptor tyrosine kinases, including fibroblast growth factor receptors (FGFR1–4), platelet derived growth factor receptor α (PDGFRα), KIT, and RET. We examined the antitumor activity of lenvatinib against human thyroid cancer xenograft models in nude mice. Orally administered lenvatinib showed significant antitumor activity in 5 differentiated thyroid cancer (DTC), 5 anaplastic thyroid cancer (ATC), and 1 medullary thyroid cancer (MTC) xenograft models. Lenvatinib also showed antiangiogenesis activity against 5 DTC and 5 ATC xenografts, while lenvatinib showed in vitro antiproliferative activity against only 2 of 11 thyroid cancer cell lines: that is, RO82-W-1 and TT cells. Western blot analysis showed that cultured RO82-W-1 cells overexpressed FGFR1 and that lenvatinib inhibited the phosphorylation of FGFR1 and its downstream effector FRS2. Lenvatinib also inhibited the phosphorylation of RET with the activated mutation C634W in TT cells. These data demonstrate that lenvatinib provides antitumor activity mainly via angiogenesis inhibition but also inhibits FGFR and RET signaling pathway in preclinical human thyroid cancer models.

Angiogenesis, the formation of new blood vessels from pre-existing vessels, occurs physiologically during embryonal development, tissue injury and inflammation. It is also well known to play an important role in several pathological conditions, such as cancer, diabetic retinopathy, rheumatoid arthritis and atherosclerosis.1) An understanding of the angiogenic process may lead to new therapies for the above diseases, and some angiogenesis inhibitors are already under clinical study as anti-cancer drugs.2)The formation of new capillaries is a complex biological process whose regulatory mechanisms are incompletely understood. The initiation of angiogenesis involves focal reduction of intercellular interactions and of interactions between endothelial cells and the surrounding extracellular matrix (ECM). Cell migration, proliferation and capillary tube formation then follow. It is clear that complex orchestration of many processes, some overlapping, is required in order for angiogenesis to proceed. Various types of angiogenic growth factors such as vascular endothelial growth factor (VEGF), 3) basic fibroblast growth factor (bFGF), 4) platelet-derived growth factor (PDGF) 5) and hepatocyte growth factor (HGF) 6) stimulate both the endothelial cells and mesenchymal cells. ECM-degrading proteolytic enzymes, including matrix metalloprotease (MMP) and plasminogen activator (PA), are secreted by endothelial cells in response to angiogenic factors and/or cytokines. 7) Cell adhesion molecules such as integrins, cadherin and PECAM also regulate the angiogenic process.8) There are some reports on the interactions of the angiogenic factors mentioned above; for example, bFGF up-regulates VEGF production 9); the production of proteolytic enzymes and integrin alpha subunits is induced by VEGF, 10) bFGF 11) and PDGF 12); MMP-2 associates with integrin avb3 and growth factor receptor.13) Therefore, an in vitro model of angiogenesis should retain, as far as possible, the in vivo interactions of angiogenic factors and the regulatory mechanisms.Fragments of rat thoracic aorta within type I collagen gel provide a good model of the overall angiogenic process, including cell migration, proliferation and capillary tube formation, for 1 to 2 weeks. The aortic fragments contain several types of cells, such as endothelial cells, smooth muscle cells and fibroblasts, which co-ordinate to form capillary vessels in the collagen gel. It was reported that aortic fragments endogenously produce bFGF, 14) and exogenous growth factors such as PDGF, insulin-like growth fator (IGF) and VEGF enhance capillary formation. 15)In this report, we show that VEGF, its receptor and proteolytic enzymes (MMP, PA) are endogenously expressed in the rat aorta model and gradually increase during the process of angiogenesis. When the action of these endogenous factors was blocked by inhibitors, capillary tube formation was clearly inhibited, demonstrating that these endogenous factors play key roles in angiogenesis in this model. Interestingly, the formed capillaries a...