Abstract 1847: Enhancing the efficacy of conventional chemotherapy with novel targeted small molecules to kill Ewing sarcoma cancer stem-like cells
Authors: Roundhill Elizabeth A. , Jeys Lee , Parry Michael , Rankin Kenneth S. , Foster Richard , Bond Jacquelyn , Burchill Susan 
Published: June 2022

Abstract
Since Ewing sarcoma (ES) is a stem cell-like cancer1, improved outcome for some patients will be realised when treatments to eradicate ES stem-like cells (ES-CSCs) are evaluated in clinical trials. Therefore, we have identified small molecules that kill ES-CSCs, and examined their efficacy alone and in combination with chemotherapy.
ES patient-derived cultures and paired ES-CSCs established from treatment-naïve tumors were investigated1. The effect of 1293 small molecules (5µM, 48h) on ES-CSC cell number was examined using high content imaging (Operetta). The effect of the most active small molecules was examined in combination with chemotherapies used to treat ES using high content imaging and CalcuSyn (Biosoft).
ES-CSCs were more resistant to chemotherapy than paired patient derived cells (p&lt;0.05)1. In the drug screen, 6% (75/1293) of small molecules were more effective at killing ES-CSCs than doxorubicin. Eight percent (6/75) of the most effective small molecules targeted the Ras/MAPK pathway, including inhibitors of aurora kinases (n=3) and RAS GTPases (n=3). The efficacy of aurora kinase inhibitors, CCT137690 and CD532, was confirmed in 6 ES-CSCs. Patient-derived cells were more sensitive to aurora kinase inhibitors than ES-CSCs (p&lt;0.0001). In combination with chemotherapy, CCT137690 and CD532 synergistically killed patient-derived ES cells (Table 1).
We have identified small molecules that kill patient-derived ES-CSCs and confirmed they have synergistic activity with classic chemotherapies, supporting our hypothesis that ES-CSC targeted drugs in combination with existing chemotherapies is a promising therapeutic strategy.
1 Roundhill et al. 2021. Cellular Oncology, 44(5):1065-1085
Table 1. Summary of synergy between the aurora kinase inhibitors and chemotherapeutic agents in 4 patient-derived cell cultures (ES1 - ES4). Patient derived cells were treated with increasing concentrations of chemotherapies and small molecules (0.25x, 0.5x, 2x, 4x the EC50). Concentration range of doxorubicin=0.08-6.7µM, vincristine=0.01-1.5µM, etoposide=0.01-33µM, actinomycin-D=0.02-10µM, carboplatin=8.4-135µM, 4-hyperoxyifosfamide=2.6-152µM, CCT137690=0.07-14µM, CD532=0.05-14µM. Where data is available, concentrations did not exceed the maximum achievable concentration in plasma (Liston and Davis. 2017. Clinical Cancer Research, 15(14):3489-3498). Synergy = combination index &lt;0.9. ES1 ES2 ES3 ES4 CCT137690 (EC50, uM) 3 3.6 0.3 0.4 CD532 (EC50, uM) 1.8 3.5 0.2 1.1 Doxorubicin + CCT137690 Synergy Synergy Synergy Synergy Doxorubicin + CD532 Synergy Synergy Vincristine + CCT137690 Synergy Vincristine + CD532 Synergy Synergy Etoposide + CCT137690 Synergy Synergy Etoposide + CD532 Synergy Synergy Actinomycin-D + CCT137690 Synergy Synergy Actinomycin-D + CD532 Synergy Synergy Synergy Carboplatin + CCT137690 Synergy Synergy Carboplatin + CD532 Synergy Synergy 4-Hyperoxyifosfamide + CCT137690 Synergy Synergy 4-Hyperoxyifosfamide + CD532 Synergy
Citation Format: Elizabeth A. Roundhill, Lee Jeys, Michael Parry, Kenneth S. Rankin, Richard Foster, Jacquelyn Bond, Susan Burchill. Enhancing the efficacy of conventional chemotherapy with novel targeted small molecules to kill Ewing sarcoma cancer stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1847.