Selectively Targeting Activated Myofibroblasts by ABT-263 Reverses Radiation-Induced Intestinal Fibrosis in Mice

Abstract

<h3>Purpose/Objective(s)</h3> Radiation induced intestinal fibrosis (RIF) is an irreversible and severe late effect of abdominal and pelvic radiation therapy. The goal of this study was to determine whether clearance of activated fibroblasts with ABT-263, a BCL2/xl inhibitor that can selectively kill myofibroblasts, can reverse RIF. <h3>Materials/Methods</h3> C57BL/6J mice were exposed to a single dose of 12 Gy irradiation on the whole abdomen. The intestinal wall thickness of mice was monitored by MRI at 0, 8^th, 12^th and 18^th week. Eighteen weeks after IR, mice were given 2 cycles of vehicle or ABT-263 treatment by gavage (50 mg/kg per day, 5 days per cycle). Two weeks after last treatment, intestinal sections were harvested for evaluation the effect of ABT-263 on irradiation induced activation of fibroblasts and extracellular matrix deposition by immunohistochemistry and Masson staining. The expression of TGF-β1, α-SMA, BCL-2/BCL-w proteins and phosphorylation of STAT3 in intestinal homogenate were analyzed by western blot analysis. Human and murine fibroblasts were cultured to evaluate the effects of ABT-263 on irradiation or classical TGF-β1-induced (5 ng/ml) activation of fibroblasts. <h3>Results</h3> At 18 weeks after 12Gy abdominal irradiation, C57BL/6J mice developed a significant thickness of the irradiated intestinal wall, with increased number of a-SMA⁺ fibroblasts (activated fibroblasts). Treatment of the RIF mice with ABT-263 after developed RIF could reverse the disease by specific clearance of activated fibroblasts. In vitro, inhibition of Bcl-2 and Bcl-xL by the small molecule BH3 mimetic, ABT-263, or Bcl-xL-specific small interfering RNA induced apoptosis in TGFb1 or irradiation-activated fibroblasts, but not in quiescent fibroblasts. <h3>Conclusion</h3> To our knowledge, this is the first study to demonstrate that RIF can be reversed by a specific myofibroblasts depletion drug ABT-263. ABT-263 has the potential to be developed as a new treatment for RIF.