Abstract 41: XI-006 induces potent p53-independent apoptosis in Ewing sarcoma

Despite aggressive multi-modal treatment strategies, limited improvement in overall survival rates for patients diagnosed with Ewing sarcoma, the second most prevalent solid bone tumor observed in children and young adolescents, has been achieved over the past thirty years. As such, new targeted therapies are urgently required particularly for those sarcoma patients with recurrent or metastatic disease. Overexpression of MDM4, a major transcriptional regulator of the TP53 tumour suppressor has been documented in a substantial proportion of Ewing, Synovial and Osteosarcomas (>30%). For this reason, we have examined the molecular and cellular responses of cultured Ewing and Osteosarcoma cell lines following treatment with XI-006 (NSC207895), a small molecule 4-nitrobenzofuroxan derivative MDM4 transcriptional inhibitor. XI-0006 treatment of Ewing and osteosarcoma cell lines (n=11) resulted in rapid and potent apoptosis at low nano-molar concentrations specifically in Ewing sarcoma cell lines (48hr IC50: 0.098-1.61µM). Importantly, the viability of normal human fibroblasts (IMR90) remained unaffected at these low nano-molar concentrations (48hr IC50: 6.80µM). Unexpectedly, apoptotic response was not dependent on MDMX mRNA and protein levels or TP53 status. Alkaline/neutral comet and γH2AX immunofluorescence assays revealed that the cytotoxic effects of XI-006 at low nano-molar concentrations could not be attributed to the induction of DNA damage. RNA expression analysis of XI-006 treated cell lines revealed that the mechanism of action of XI-006 could be attributed to the inhibition of cell division and cycle regulators such as KIF20A and GPSM2. XI-006 was also shown to synergise with current Ewing sarcoma chemotherapeutic protocols, Doxorubicin, Etoposide and Actinomycin D in vitro. Furthermore, combinatorial treatment with Olaparib led to a maximum 56.3% increase in apoptosis compared to XI-006 alone, due to the down-regulation of Mre11. Our pre-clinical findings suggest that XI-006 represents a novel therapeutic intervention for the treatment of Ewing sarcoma, and warrants further pharmacokinetic and pharmacodynamic investigations of XI-006 in vivo. Citation Format: Kathleen Pishas, Susan Neuhaus, Mark Clayer, Gelareh Farshid, Alexander Staudacher, David Callen. XI-006 induces potent p53-independent apoptosis in Ewing sarcoma. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr 41.