Abstract 4141: EWS-FLI regulates mitotic kinesins in Ewing sarcoma family of tumors

Abstract

Abstract The current situation faced by children and young adults diagnosed with Ewing sarcoma family of tumors (ESFT), the second most common pediatric bone malignancy in the U.S., is bleak. Although the oncogenic phenotype and master regulator of ESFT is driven by an underlying pathognomonic chromosomal translocation (EWS-Ets), therapeutic targeting of this molecular Achilles' heel has been notoriously challenging. For pediatric patients with progressive (refractory) or recurrent ESFT, the overall survival continues to remain poor. To date, no established second-line (salvage) treatment regimen exists for these pediatric sarcoma patients. The failure to improve the overall survival for these patients highlights the need to better understand the molecular points of vulnerability of these diseases, which can be translated into novel treatment strategies. To address this challenge, we have identified KIF11, KIF15 and TPX2, part of the cellular mitotic machinery, as druggable downstream targets of EWS-Ets in ESFT. Our recent studies sought to identify drugs that reverse a gene expression profile similar to the pattern obtained by the silencing of EWS/FLI1 via RNAi approaches (siEWS/FLI1) (Pessetto et al., 2017). This work identified KIF15 (gene rank #1, p=0.00005) and its potential binding partner TPX2 (gene rank #14, p=0.01830) as significantly downregulated genes within this signature. These genes encode KIF15 and TPX2, which are postulated to play a compensatory role in resistance to KIF11 inhibitors in the clinic. We found that KIF11, KIF15 and TPX2 proteins are abundantly expressed in ESFT cell lines as compared with benign controls (7.7-, 5.5-, and 8.5-fold, respectively). We also discovered that RNAi-mediated downregulation of KIF15 increases sensitivity of ESFT cell lines to treatment with KIF11 inhibitors (KIF11i). We have for the first time, shown that silencing EWS-FLI1 (the most common EWS-Ets translocation), in ESFT cells decreases KIF11, KIF15 and TPX2 promoter activity by 99%, 97%, and 87%, respectively. We propose that this activity is a function of EWS-FLI1-mediated E2Fs; EWS-FLI1 disrupts the E2F-regulated proliferation balance such that the suppressive E2F4 transcription factor is displaced by the activating E2F3. Our data show that E2F3 is enriched at KIF15 (8.9-fold) and TPX2 (2.9-fold) promoters. Further, when EWS-FLI1 is siRNA depleted, enrichment at the KIF15 and TPX2 promoters is lost (3.9-fold or 2.6-fold decrease, respectively). These data strongly suggest that aberrant expression of the genes encoding these proteins is controlled by oncogenic EWS-FLI1. Taken together, we have demonstrated that KIF11, KIF15 and TPX2 are aberrantly expressed in ESFT and are putative therapeutic targets. Our ongoing work includes development of KIF11/KIF11/TPX2 axis-targeting compounds toward the goal of implementing pharmacologic approaches to provide new therapies for children diagnosed with these deadly diseases. Citation Format: Rebecca J. Wates, Yan Ma, Jennifer Crow, Glenson Samuel, Andrew K. Godwin. EWS-FLI regulates mitotic kinesins in Ewing sarcoma family of tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4141.