The arrest sequence, FXXXXWIXXXXGIRAGP, of E. coli SecM interacts with the ribosomal exit tunnel, thereby interfering with translation elongation. Here, we studied this elongation arrest in vitro using purified translation components. While a simplest scenario would be that elongation is arrested beyond Pro166, the last arrest-essential amino acid, and that the Pro166 codon is positioned at the P site of the ribosomal peptidyl transferase center (PTC), our toeprint analyses revealed that the ribosome actually stalls when the Pro166 codon is positioned at the A site. Northern hybridization identification of the polypeptide bound tRNA and mass determination showed that the last amino acid of the arrested peptidyl-tRNA is Gly165, which is only inefficiently transferred to Pro166. Also, puromycin does not effectively release the arrested peptidyl-tRNA under the conditions of A site occupancy by Pro166-tRNA. These results reveal that secM-encoded Pro166-tRNA functions as a nonpolypeptide element in fulfilling SecM's role as a secretion monitor.
Almost all cancers show intrinsic and/or evasive resistance to vascular endothelial growth factor (VEGF) inhibitors by multiple mechanisms. Serum angiopoietin-2 (Ang2) level has been proposed as a potential biomarker of VEGF inhibitor response in several cancers. From these clinical observations, the Ang2 and Tie2 (its receptor) axis has been focused on as a promising target. Here, we show a novel strategy to circumvent the resistance by combining multi-tyrosine kinase inhibitors lenvatinib (VEGF receptor, fibroblast growth factor receptor, and RET inhibitor) and golvatinib (E7050; c-Met, Tie2, and EphB4 inhibitor). Tie2 identifies a highly pro-angiogenic macrophage subset, Tie2-expressing macrophages (TEM). Angi-Tie2 and EphB4-EphrinB2 signaling plays critical roles in pericyte-mediated vessel stabilization. In vitro analyses suggested that golvatinib combined with lenvatinib inhibited pericyte-mediated vessel stabilization and TEM differentiation. In thyroid and endometrial cancer models, golvatinib and lenvatinib inhibited pericyte network development and TEM infiltration, resulting in severe perfusion disorder and massive apoptosis. Body weight loss was tolerable, and no macroscopic change was observed. These preclinical studies suggest that modulation of the tumor microenvironment by a strategic and well-tolerated combination of multi-targeting tyrosine kinase inhibitors may sensitize cancer to VEGF inhibitors.
Although vascular endothelial growth factor (VEGF) inhibitors provide significant clinical benefit, they often require dose reductions or even withdrawals due to their severe toxicities. Furthermore, almost all cancers show intrinsic and/or evasive resistance to VEGF inhibitors by multiple mechanisms. Serum angiopoietin-2 (Ang2) level has been proposed as a potential biomarker of VEGF inhibitor response in several cancers. Response to lenvatinib (E7080; VEGFR1-3 inhibitor) is also reported to correlate with low Ang2 level in differentiated thyroid cancer and endometrial cancer. From these clinical observations, Ang2 and its receptor Tie2 has been focused as promising targets. Here, we demonstrated mechanisms of resistance induced by Ang2 and a novel strategy to circumvent the resistance by combination of multi-tyrosine kinase inhibitors (TKIs), lenvatinib and golvatinib (E7050; c-Met, Tie2, EphB4 inhibitor). Tie2 defines a highly pro-angiogenic macrophage subset, Tie2-expressing macrophage (TEM). Ang-Tie2 and EphB4-EphrinB2 signaling play critical roles in pericyte-mediated vessel stabilization. Ectopic expression of Ang2 in thyroid cancer conferred resistance to lenvatinib and enhanced pericyte-associated endothelial network development and TEM infiltration. In vitro analyses suggested that golvatinib/lenvatinib combination inhibited pericyte-mediated vessel stabilization and TEM differentiation. In thyroid and endometrial cancer models, golvatinib/lenvatinib combination inhibited pericyte network development and TEM infiltration, resulting in severe perfusion disorder and massive apoptosis. Body weight loss was tolerable in mice, and no macroscopic change was observed. These results suggest that modulation of tumor microenvironment by strategic and well-tolerated combination of multi-targeting TKIs sensitizes cancer to VEGF inhibitors, which warrants further clinical investigation to determine the clinical benefit of anti-angiogenesis cancer therapy.
Citation Format: Youya Nakazawa, Satoshi Kawano, Junji Matsui, Yasuhiro Funahashi, Osamu Tohyama, Hiroki Muto, Takayuki Nakagawa, Tomohiro Matsushima. Maximizing the efficacy of anti-angiogenesis cancer therapy: A multi-targeting strategy by tyrosine kinase inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2980. doi:10.1158/1538-7445.AM2014-2980
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