Abstract 6053: Characterizing plasticity of chemotherapy-tolerant persister cells in rhabdomyosarcoma

Abstract

Abstract Rhabdomyosarcoma (RMS) is a rare pediatric soft tissue sarcoma (250-300 cases a year in the US). The prognosis for patients with relapsed and metastatic disease remains poor with less than 30% overall survival rate. Current treatment regimens are ineffective against relapsed disease of RMS. There remains the urgent to need to identify more effective therapy options. While some studies have demonstrated up-regulation of multi-drug resistance genes and abnormal activity of selected signaling pathways in chemotherapy-resistant RMS tumors, the cellular and molecular mechanisms underlying adaptive cell changes leading to persistent survival of treatment-resistant RMS cells remain poorly understood. The stem cell-like tumor propagating cells (TPCs) have the capacity for self-renewal and are thought to be responsible for initiating treatment-resistant relapse and metastasis of some cancer types. The drug-tolerant persister (DTP) cell population with stem-cell like features has been shown in some cancer types to exhibit plasticity in cell state and dynamic changes in chromatin and transcriptional activity. A better understanding of how the cellular plasticity of the DTPs is regulated is critical for developing therapies to overcome treatment resistance in RMS. We have shown that initial treatment of RMS cells with standard-of-care cytotoxic agent, vincristine, selects for a DTP that is enriched with CD133+ stem-like cells. By gene expression studies, MYC and YBX1 driven-gene networks are upregulated in CD133+ cells. Targeted disruption of MYC and YBX1 by CRISPR/Cas9 reduces self-renewal capacity of RMS cells, and overexpression of MYC and YBX1 confers tolerance on RMS cells to vincristine. RMS cells treated in long-term culture with incremental increase in vincristine dose gives rise to late DTP with a distinct transcriptional profile including up-regulation of many genes regulated by the myogenic regulatory factor, MYOD1. MYC binds to the promoters of YBX1 and MYOD1. The findings suggest dynamic transcriptional changes and cell state plasticity of the DTPs in RMS. Our ongoing work includes characterizing the mechanisms by which MYC and MYOD1 regulate cell state plasticity and transcriptional adaptation of the DTP, assess inter- and intra-tumoral transcriptional heterogeneity of treatment-refractory RMS tumors and determine prognostic significance of functional network modules of MYC, MYOD and their downstream genes. Our ultimate goal is to translate our findings into more effective therapies for treatment-refractory RMS patients. Citation Format: Weiliang Tang, Madeline Fritzke, Spencer Stinson, Eleanor Chen. Characterizing plasticity of chemotherapy-tolerant persister cells in rhabdomyosarcoma [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 6053.