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Effects of the Vascular Disrupting Agent OXi8006 on Activated Endothelial Cell Signaling and Tumor Growth Delay in a Breast Cancer Mouse Model Treated with the Corresponding Phosphate Prodrug Salt OXi8007
Author(s) -
Odutola Samuel O.,
Strecker Tracy E.,
Taylor Emily A.,
Schwartze Jeffrey,
Gerberich Jeni,
MacDonough Matthew T.,
Chaplin David J.,
Liu Li,
Mason Ralph P.,
Pinney Kevin G.,
Trawick Mary Lynn
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.lb122
Subject(s) - rhoa , focal adhesion , microbiology and biotechnology , rho associated protein kinase , stress fiber , chemistry , microtubule , ptk2 , myosin light chain kinase , kinase , phosphorylation , cancer research , protein kinase a , signal transduction , biology , mitogen activated protein kinase kinase
Tubulin‐binding, small‐molecule vascular disrupting agents (VDAs) are anticancer agents that rapidly depolymerize microtubules in the activated, tumor endothelium causing a pronounced shutdown in blood flow while leaving normal tissues intact. VDAs offer significant therapeutic advantage against solid tumors by selectively targeting pre‐established tumor vasculature and are mechanistically distinct from antiangiogenic agents. The indole‐based tubulin‐binding compound OXi8006 and its phosphate prodrug OXi8007 have shown promise as VDAs although important questions regarding features of their mechanism of action remain. We have shown that OXi8006 and OXi8007 disrupted microtubules in activated human umbilical vein endothelial cells (HUVECs) and caused extensive reorganization of the cytoskeletal network. The pathway involved an increase in phosphorylation of non‐muscle myosin light chain and focal adhesion kinase, resulting in increased actin stress fiber and focal adhesion formation via the intramolecular G protein switch RhoA and RhoA dependent kinase (ROCK) [Strecker et al. Cancer Lett. 369 , 229 (2015)]. An important unresolved question is the connection between microtubule disruption and the downstream effects of VDA treatment. In this study we demonstrated the role of GEF‐H1, a protein that is able to activate RhoA but is inactive when bound to microtubules. GEF‐H1 is released upon microtubule disruption and can activate RhoA. The downstream effects of RhoA activation upon OXi8006 treatment were abrogated by siRNA‐mediated knockdown of GEF‐H1. We also showed the importance of activation of the LIM kinase/cofilin pathway in actin stress fiber formation with VDA treatment. LIM kinase is phosphorylated and activated by RhoA kinase and resulted in phosphorylation of cofilin, thus inhibiting the ability of cofilin to disassemble actin filaments. Treatment of HUVECs with LIM kinase inhibitor significantly diminished the actin stress fiber formation observed with OXi8006 treatment alone. In MDA‐MB‐231 breast cancer cells, OXi8006 treatment reduced cell migration. The water soluble prodrug OXi8007 caused significant tumor growth delay in an MDA‐MB‐231 breast cancer xenograft mouse model. The results of this study elucidated important aspects of the mechanism of tubulin‐binding VDA action, and confirmed the potent anticancer effects of the VDA prodrug OXi8007.