Therapeutic effects of the euglenoid ichthyotoxin, euglenophycin, in colon cancer

// April B. Cabang 1 , Keya De Mukhopadhyay 1 , Sarah Meyers 2 , Jay Morris 1 , Paul V. Zimba 3 and Michael J. Wargovich 1 1 Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA 2 College of Charleston, Charleston, SC 29424, USA 3 Center for Coastal Studies and Department of Life Sciences, Texas A&M – Corpus Christi, Corpus Christi, TX 78412, USA Correspondence to: Michael J. Wargovich, email: wargovich@uthscsa.edu Keywords: euglenophycin; colon cancer; ichthyotoxin; autophagy; therapy Received: August 16, 2017     Accepted: October 13, 2017     Published: November 01, 2017 ABSTRACT Colorectal cancer (CRC) remains one of the most commonly diagnosed cancers and the 3 rd leading cause of cancer-related mortality. The emergence of drug resistance poses a major challenge in CRC care or treatment. This can be addressed by determining cancer mechanisms, discovery of druggable targets, and development of new drugs. In search for novel agents, aquatic microorganisms offer a vastly untapped pharmacological source that can be developed for cancer therapeutics. In this study, we characterized the anti-colorectal cancer potential of euglenophycin, a microalgal toxin from Euglena sanguinea . The toxin (49.1-114.6 μM) demonstrated cytotoxic, anti-proliferative, anti-clonogenic, and anti-migration effects against HCT116, HT29, and SW620 CRC cells. We identified G1 cell cycle arrest and cell type - dependent modulation of autophagy as mechanisms of growth inhibition. We validated euglenophycin’s anti-tumorigenic activity in vivo using CRL:Nu(NCr)Foxn1nu athymic nude mouse CRC xenograft models. Intraperitoneal toxin administration (100 mg/kg; 5 days) decreased HCT116 and HT29 xenograft tumor volumes (n=10 each). Tumor inhibition was associated with reduced expression of autophagy negative regulator mechanistic target of rapamycin (mTOR) and decreased trend of serum pro-inflammatory cytokines. Together, these results provide compelling evidence that euglenophycin can be a promising anti-colorectal cancer agent targeting multiple cancer-promoting processes. Furthermore, this study supports expanding natural products drug discovery to freshwater niches as prospective sources of anti-cancer compounds.