Abstract 647: FDA approved library screen revealed Ewing and clear cell sarcomas have increased sensitivity to filanesib over other cancer types

Abstract There is a compelling need for the development of more effective and less toxic therapies for patients with Ewing Sarcoma (ES) and Clear Cell Sarcoma (CCS). ES and CCS are characterized by chromosomal translocations which result in two distinct fusion proteins: EWS-ATF1 (t (12;22) (q13;q12) ) in CCS and EWS-FLI1 (t (11;22) (q24;q12) ) in ES. There is a strong premise that targeting the fusion proteins or their key downstream signaling pathways will be disease modifying and improve outcomes for patients. Preliminary high throughput screening studies using an FDA approved small molecule compound library identified filanesib, a kinesin spindle protein (KIF11) inhibitor, as having potent anti-proliferative activity in ES and CCS cells over other cancer subtypes. The mechanism linking the fusion proteins with KIF11 and the tumorigenic role of KIF11 in ES and CCS has yet to be described. Previous studies have shown that the EWS-ATF1 fusion protein forms a heterodimer with transcription factors to target the promoters of its downstream genes. In breast cancer, the knockdown of KIF11 has been shown to significantly reduce the phosphorylation of these transcription factors. Additionally, KIF11 has been shown to directly interact with p300/CBP-associated factor (PCAF), a histone acetyltransferase (HAT). HATs are necessary for EWS-FLI1-induced chromatin remodeling. We hypothesize that the fusion proteins, EWS-FLI1 and EWS-ATF1, form a complex with KIF11 that regulates the activity of co-transcription factors during chromatin remodeling. The target of filanesib, KIF11, has essential roles in maintaining cell cycle progression through mitosis and its inhibition results in mitotic arrest and subsequent cell death. We used ImageStream to assess the effects of filanesib on the cell cycle. ImageStream allows both a quantitative and qualitative analysis of the cell cycle by measuring the population of cells that are positive for a given marker as well as imaging each cell by microscopy. Results demonstrate that filanesib promotes an increase in cells arrested in prophase with dramatically altered spindle formation. We are currently addressing the role of KIF11 in regulating the expression levels of the fusion proteins’ associated transcriptional coactivators and downstream target genes. By completing these studies, we aim to, i) outline the mechanism underpinning the relationship between KIF11 and the oncogenic fusion proteins in ES and CCS cells, and ii) gain an understanding of why ES and CCS cells are particularly vulnerable to KIF11 inhibition. This work has been supported in part by the Flow Cytometry and the Molecular Genomics Cores at the H. Lee Moffitt Cancer Center Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 647.