Integrating mechanisms of response and resistance against the tubulin binding agent Eribulin in preclinical models of osteosarcoma

// Valerie B. Sampson 1 , Nancy S. Vetter 1 , Wendong Zhang 2 , Pratima U. Patil 3 , Robert W. Mason 3 , Erika George 4 , Richard Gorlick 2 , Edward A. Kolb 1 1 Cancer Therapeutics Laboratory, Nemours Center for Cancer and Blood Disorders, Nemours/A.I. duPont Hospital for Children, Wilmington, DE, USA 2 Department of Pediatrics - Hematology and Oncology, The Children's Hospital at Montefiore, The Albert Einstein College of Medicine, Bronx, NY, USA 3 Nemours Center for Childhood Cancer Research, Alfred I. duPont Hospital for Children, Wilmington, DE, USA 4 Department of Biological Sciences, University of Delaware, Newark, DE, USA Correspondence to: Valerie B. Sampson, email: vsampson@nemours.org Keywords: eribulin, microtubule destabilization, G2/M arrest, mitotic catastrophe, cell death Received: March 22, 2016      Accepted: October 29, 2016      Published: November 15, 2016 ABSTRACT Osteosarcoma is the most frequently occurring bone cancer in children and adolescents. Unfortunately, treatment failures are common. Eribulin is a synthetic microtubule inhibitor that has demonstrated activity in preclinical osteosarcoma models. The effects of eribulin were evaluated in two human osteosarcoma cell lines as well as in eribulin-sensitive and -resistant osteosarcoma xenograft tumors of the Pediatric Preclinical Testing Program (PPTP) by characterizing cell viability, microtubule destabilization, mitotic arrest and mechanism of cell death. Eribulin demonstrated cytotoxic activity in vitro , through promotion of microtubule dynamic instability, arrest of cells in the G2/M phase, mitotic catastrophe and cell death. The microtubule-destabilizing protein stathmin-1 (STMN1) was coimmunoprecipitated with the cyclin-dependent kinase inhibitor p27 indicating that these cytoplasmic complexes can protect cells from the microtubule destabilizing effect of eribulin. Increased tumoral expression of P-glycoprotein (P-gp) and TUBB3 were also associated with lower drug sensitivity. In summary, eribulin successfully blocked cells in G2/M phase but interfered with mitochondria activity to inhibit proteins involved in apoptosis. Understanding the complex and inter-related mechanisms involved in the overall drug response to eribulin may help in the design of therapeutic strategies that enhance drug activity and improve benefits of eribulin in pediatric patients with osteosarcoma.