Abstract
Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood. About 25% of RMS expresses fusion oncoproteins such as PAX3/PAX7-FOXO1 (fusion-positive, FP) while fusion-negative (FN)-RMS harbors RAS mutations. Radiotherapy (RT) plays a crucial role in local control but metastatic RMS is often radio-resistant. HDAC inhibitors (HDACi) radio-sensitize different cancer cells types. Thus, we evaluated MS-275 (Entinostat), a Class I and IV HDACi, in combination with RT on RMS cells in vitro and in vivo. MS-275 reversibly hampered cell survival in vitro in FN-RMS RD (RASmut) and irreversibly in FP-RMS RH30 cell lines down-regulating cyclin A, B, and D1, up-regulating p21 and p27 and reducing ERKs activity, and c-Myc expression in RD and PI3K/Akt/mTOR activity and N-Myc expression in RH30 cells. Further, MS-275 and RT combination reduced colony formation ability of RH30 cells. In both cell lines, co-treatment increased DNA damage repair inhibition and reactive oxygen species formation, down-regulated NRF2, SOD, CAT and GPx4 anti-oxidant genes and improved RT ability to induce G2 growth arrest. MS-275 inhibited in vivo growth of RH30 cells and completely prevented the growth of RT-unresponsive RH30 xenografts when combined with radiation. Thus, MS-275 could be considered as a radio-sensitizing agent for the treatment of intrinsically radio-resistant PAX3-FOXO1 RMS.
Highlights
Rhabdomyosarcoma (RMS), a highly aggressive form of cancer deriving from mesenchymal cells failing to differentiate into skeletal muscle, represents the most frequent soft tissue sarcoma in children and adolescents [1]
We investigated the on effects of MS−275 on cell performing In both cell lines, MS-275 treatment resulted in a progressive reduction of the cell percentage in the flow cytometry on RD and RH30 cells at 1, 2, 4 and 6 days post-treatment
We investigated the potential of MS-275 (Entinostat), a potent class I and IV–selective histone deacetylases (HDACs) inhibitors (HDACi) [43], in sensitizing RMS cells to RT
Summary
Rhabdomyosarcoma (RMS), a highly aggressive form of cancer deriving from mesenchymal cells failing to differentiate into skeletal muscle, represents the most frequent soft tissue sarcoma in children and adolescents [1]. The two major RMS histological subtypes are the ‘alveolar’ (ARMS) and ‘embryonal’ (ERMS) variants. ARMS is frequently characterized by the expression of the PAX3- or PAX7-FOXO1 oncogenic “fusion proteins”. ERMS, the most frequent subtype, is devoid of any fusion gene (fusion-negative, FN) but has specific mutations of the RAS and RTK pathways [1]. Both FN-RMS and FP-RMS are developmentalderived tumors and, are characterized by an epigenetic imbalance that affects core gene regulatory architecture and sustains the transformed phenotype [2,3,4,5,6,7,8]. First-line treatment of RMS includes surgery to eradicate the primary tumor, radiation therapy (RT)
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