Inducing Mitotic Catastrophe as a Therapeutic Approach to Improve Outcomes in Ewing Sarcoma

SIMPLE SUMMARY: Ewing sarcoma (EWS) is a rare pediatric sarcoma affecting children and adolescents, with median diagnosis around the age of 15. Despite an intensive therapeutic regimen, including chemotherapy, surgery/radiation patients with recurrent (10–15%) and metastatic disease (<30%) have poor overall survival rates. Moreover, standard chemotherapy is intense and is often associated with systemic toxicity and secondary malignancies. Hence, it is critical to find new treatments to improve outcomes in EWS patients. We identified a combination of mitotic inhibitors targeting KIF11 (SB-743921) and AURKA (VIC-1911) that are effective in inhibiting EWS tumor growth at physiologically relevant nanomolar doses. This drug combination inhibited EWS cell viability in vitro by promoting cell cycle arrest followed by cell death. In vivo, this treatment regimen led to significantly delayed tumor growth and improved overall survival in xenograft EWS mouse models. Overall, these preclinical data provide encouragement to consider a future clinical trial for patients with this deadly disease. ABSTRACT: Ewing sarcoma (EWS) is an aggressive pediatric malignancy of the bone and soft tissues in need of novel therapeutic options. To identify potential therapeutic targets, we focused on essential biological pathways that are upregulated by EWS-FLI1, the primary oncogenic driver of EWS, including mitotic proteins such as Aurora kinase A (AURKA) and kinesin family member 15 (KIF15) and its binding partner, targeting protein for Xklp2 (TPX2). KIF15/TPX2 cooperates with KIF11, a key mitotic kinesin essential for mitotic spindle orientation. Given the lack of clinical-grade KIF15/TPX2 inhibitors, we chose to target KIF11 (using SB-743921) in combination with AURKA (using VIC-1911) given that phosphorylation of KIF15(S1169) by Aurora A is required for its targeting to the spindle. In vitro, the drug combination demonstrated strong synergy (Bliss score ≥ 10) at nanomolar doses. Colony formation assay revealed significant reduction in plating efficiency (1–3%) and increased percentage accumulation of cells in the G2/M phase with the combination treatment (45–52%) upon cell cycle analysis, indicating mitotic arrest. In vivo studies in EWS xenograft mouse models showed significant tumor reduction and overall effectiveness: drug combination vs. vehicle control (p ≤ 0.01), SB-743921 (p ≤ 0.01) and VIC-1911 (p ≤ 0.05). Kaplan–Meier curves demonstrated superior overall survival with the combination compared to vehicle or monotherapy arms (p ≤ 0.0001).