Synergistic Effects of Lenvatinib (E7080) and MEK Inhibitors against Anaplastic Thyroid Cancer in Preclinical Models.

E7080, known as lenvatinib, is an oral multitargeted tyrosine kinase inhibitor that has been shown to improve the survival rate of patients with radioiodine-refractory thyroid cancer. However, a majority of patients do not continue lenvatinib intake due to disease progression or significant toxicity. To improve treatment success rates, we propose the combination of lenvatinib with mitogen-activated protein kinase (MEK) inhibitors. To test this hypothesis, we tested the effects of lenvatinib with the MEK inhibitor U0126 in vitro using two human anaplastic thyroid cancer (ATC) cell lines, 8505C and TCO1, and with another MEK inhibitor, selumetinib (AZD6244), in an ATC mouse model. We found that the combination of lenvatinib with MEK inhibitors enhanced the antitumor effects of monotherapy with either agent in vitro and in vivo, and these effects may be through the AKT (Protein Kinase B) and extracellular signal-regulated kinase (ERK) signaling pathways. Furthermore, the combination does not have significant adverse effects in the ATC mouse models in terms of body weight, blood biochemical parameters, and histopathology. In conclusion, the combination of lenvatinib with an MEK inhibitor is a potentially viable therapeutic approach for ATC treatment.

EphA4-deleted microenvironment regulates cancer development and leukemoid reaction of the isografted 4T1 murine breast cancer via reduction of an IGF1 signal.

UNLABELLED: EphA4 belongs to the largest family of receptor tyrosine kinases (RTKs). Although EphA4 is highly expressed in the central nervous system, EphA4 has also been implicated in cancer progression. Most of the studies focus on the expression and function in tumor cells. It is unknown whether EphA4-deleted microenvironment affects tumor progression. Some of cancers in animals and humans, such as 4T1 cancer cells, are known to produce a large amount of granulocyte colony-stimulating factors (G-CSF/Csf3) which can stimulate myeloproliferation, such as myeloid-derived suppressor cells (MDSCs) leading to a poor recipient prognosis. We isografted 4T1 breast cancer cells into both EphA4-knockout and control wild-type female littermate mice. The results showed that the EphA4-deleted host could inhibit primary tumor growth and tumor metastasis mainly by decreasing the amount of IGF1 synthesis in the circulation and locally tissues. The EphA4-deleted microenvironment and delayed tumor development reduced the production of G-CSF resulting in the decrease of splenomegaly and leukemoid reaction including MDSCs, which in turn inhibit the tumor progression. This inhibition can be reversed by supplying the mice with IGF1. However, an excess of IGF1 supply over demand to the control mice could not further accelerate the tumor growth and metastasis. A better understanding and re-evaluation of the main role of IGF1 in regulating tumor progression could further enhance our cognition of the tumor development niche. Our findings demonstrated that EphA4-deleted microenvironment impairs tumor-supporting conditions. CONCLUSION: Host EphA4 expression regulates cancer development mainly via EphA4-mediated IGF1 synthesis signal. Thus, targeting this signaling pathway may provide a potential therapeutic option for cancer treatment.

Ephrin-A1-mediated dopaminergic neurogenesis and angiogenesis in a rat model of Parkinson's disease.

Cells of the neural stem cell lineage in the adult subventricular zone (SVZ) respond to brain insult by increasing their numbers and migrating through the rostral migratory stream. However, in most areas of the brain other than the SVZ and the subgranular zone of the dentate gyrus, such a regenerative response is extremely weak. Even these two neurogenic regions do not show extensive regenerative responses to repair tissue damage, suggesting the presence of an intrinsic inhibitory microenvironment (niche) for stem cells. In the present study, we assessed the effects of injection of clustered ephrin-A1-Fc into the lateral ventricle of rats with unilateral nigrostriatal dopamine depletion. Ephrin-A1-Fc clustered by anti-IgG(Fc) antibody was injected stereotaxically into the ipsilateral lateral ventricle of rats with unilateral nigrostriatal lesions induced by 6-hydroxydopamine, and histologic analysis and behavioral tests were performed. Clustered ephrin-A1-Fc transformed the subventricular niche, increasing bromodeoxyuridine-positive cells in the subventricular area, and the cells then migrated to the striatum and differentiated to dopaminergic neurons and astrocytes. In addition, clustered ephrin-A1-Fc enhanced angiogenesis in the striatum on the injected side. Along with histologic improvements, behavioral derangement improved dramatically. These findings indicate that the subventricular niche possesses a mechanism for regulating both stem cell and angiogenic responses via an EphA-mediated signal. We conclude that activation of EphA receptor-mediated signaling by clustered ephrin-A1-Fc from within the lateral ventricle could potentially be utilized in the treatment of neurodegenerative diseases such as Parkinson's disease.

Regulation of ephexin1, a guanine nucleotide exchange factor of Rho family GTPases, by fibroblast growth factor receptor-mediated tyrosine phosphorylation.

Fibroblast growth factor (FGF) signal is implicated in not only cell proliferation, but cell migration and morphological changes. Several different Rho family GTPases downstream of the Ras/ERK pathway are postulated to mediate the latter functions. However, none have been recognized to be directly coupled to FGF receptors (FGFRs). We have previously reported that EphA4 and FGFRs hetero-oligomerize through their cytoplasmic domains, trans-activate each other, and transduce a signal for cell proliferation through a docking protein, FRS2alpha (Yokote, H., Fujita, K., Jing, X., Sawada, T., Liang, S., Yao, L., Yan, X., Zhang, Y., Schlessinger, J., and Sakaguchi, K. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 18866-18871). Here, we have found that ephexin1, a guanine nucleotide exchange factor for Rho family GTPases, constitutes another downstream component of the receptor complex. Ephexin1 directly binds to the kinase domain of FGFR mainly through its DH and PH domains. The binding appears to become weaker and limited to the DH domain when FGFRs become activated. FGFR-mediated phosphorylation of ephexin1 enhances the guanine nucleotide exchange activity toward RhoA without affecting the activity to Rac1 or Cdc42. The FGFR-mediated tyrosine phosphorylation includes, but is not limited to, the residue (Tyr-87) phosphorylated by Src family kinase, which is known to be activated following EphA4 activation. The Tyr-to-Asp mutations that mimic the tyrosine phosphorylation in some of the putative FGFR-mediated phosphorylation sites increase the nucleotide exchange activity for RhoA without changing the activity for Rac1 or Cdc42. From these results, we conclude that ephexin1 is located immediately downstream of the EphA4-FGFR complex and the function is altered by the FGFR-mediated tyrosine phosphorylation at multiple sites.

Trans-activation of EphA4 and FGF receptors mediated by direct interactions between their cytoplasmic domains.

A yeast two-hybrid analysis has shown that the juxtamembrane region of FGF receptor 3 (FGFR3) interacts with the cytoplasmic domain of EphA4, which is a member of the largest family of receptor tyrosine kinases. Complex formation between the two receptors was shown to be mediated by direct interactions between the juxtamembrane domain of FGFR1, FGFR2, FGFR3, or FGFR4 and the N-terminal portion of the tyrosine kinase domain of EphA4. Activation of FGFR1 in transfected cells resulted in tyrosine phosphorylation of a kinase-negative EphA4 mutant and activation of EphA4 led to tyrosine phosphorylation of a kinase-negative FGFR1 mutant. Moreover, both receptors stimulate tyrosine phosphorylation of the docking protein FRS2alpha and induce mitogen-activated protein kinase stimulation with a time course and intensity that depends on the ligand that is applied. We also demonstrate that FGF-receptor-mediated mitogen-activated protein kinase stimulation is potentiated in cells costimulated with ephrin-A1. The direct interaction between EphA4 and FGFRs and the potentiation of FGF response that is induced by ephrin-A1 stimulation may modulate the biological responses that are mediated by these receptor families in cells or tissues in which the two receptors are coexpressed.

Fibroblast growth factor 23 reduces expression of type IIa Na+/Pi co-transporter by signaling through a receptor functionally distinct from the known FGFRs in opossum kidney cells.

Fibroblast growth factor (FGF) 23 is an important phosphaturic factor that inhibits inorganic phosphate (Pi) reabsorption from the renal proximal tubule. Its overproduction and proteolysis-resistant mutation such as R179Q cause tumor-induced osteomalacia and autosomal dominant hypophosphatemic rickets, respectively. To clarify the signaling mechanisms of FGF23 that mediate the reduction of Pi reabsorption, we inhibited the function of the known FGFRs in opossum kidney (OK-E) cells by expressing a dominant-negative (DN) form of FGFR. OK-E cells, which represent the renal proximal tubular cells, expressed all four known FGFRs. FGF23(R179Q) bound to and activated FGFR2, a prominent FGFR expressed in OK-E cells. The activated receptor transmitted a signal to increase the expression of type IIa Na(+)/Pi co-transporter and the Pi uptake. Expression of FGFR2(DN), which suppresses the major FGFR-mediated signal through the FRS2alpha-ERK pathway, reversed the function of FGF23(R179Q). When FGF23(R179Q) was applied to the basolateral side of polarized OK-E cells, regardless of the FGFR2(DN) expression, the apical Pi uptake decreased significantly. The apical application of FGF23(R179Q) in the polarized cells did not show such decrease but increase. The exogenously expressed FGFR2 was detectable only at the apical membrane. These results suggest that an FGF23 receptor, which is functionally distinct from the known FGFRs, is expressed at the basolateral membrane of OK-E cells.