The probability of local tumor control after radiotherapy (RT) remains still miserably poor in pediatric rhabdomyosarcoma (RMS). Thus, understanding the molecular mechanisms responsible of tumor relapse is essential to identify personalized RT-based strategies. Contrary to what has been done so far, a correct characterization of cellular radioresistance should be performed comparing radioresistant and radiosensitive cells with the same isogenic background. Clinically relevant radioresistant (RR) embryonal (RD) and alveolar (RH30) RMS cell lines have been developed by irradiating them with clinical-like hypo-fractionated schedule. RMS-RR cells were compared to parental isogenic counterpart (RMS-PR) and studied following the radiobiological concept of the “6Rs”, which stand for repair, redistribution, repopulation, reoxygenation, intrinsic radioresistance and radio-immuno-biology. RMS-RR cell lines, characterized by a more aggressive and in vitro pro-metastatic phenotype, showed a higher ability to i) detoxify from reactive oxygen species; ii) repair DNA damage by differently activating non-homologous end joining and homologous recombination pathways; iii) counteract RT-induced G2/M cell cycle arrest by re-starting growth and repopulating after irradiation; iv) express cancer stem-like profile. Bioinformatic analyses, performed to assess the role of 41 cytokines after RT exposure and their network interactions, suggested TGF-β, MIF, CCL2, CXCL5, CXCL8 and CXCL12 as master regulators of cancer immune escape in RMS tumors. These results suggest that RMS could sustain intrinsic and acquire radioresistance by different mechanisms and indicate potential targets for future combined radiosensitizing strategies.

中文翻译：

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临床相关的抗辐射横纹肌肉瘤细胞系：功能、分子和免疫相关特征。

小儿横纹肌肉瘤（RMS）放疗（RT）后局部肿瘤控制的可能性仍然很低。因此，了解肿瘤复发的分子机制对于确定个性化的基于放疗的策略至关重要。与迄今为止所做的相反，应该通过比较具有相同同基因背景的放射抗性和放射敏感细胞来对细胞放射抗性进行正确的表征。临床相关的抗辐射 (RR) 胚胎 (RD) 和肺泡 (RH30) RMS 细胞系是通过采用类似临床的大分割方案进行照射而开发出来的。将 RMS-RR 细胞与亲本同基因对应细胞 (RMS-PR) 进行比较，并按照“6R”的放射生物学概念进行研究，“6R”代表修复、再分布、再增殖、再氧合、内在放射抗性和放射免疫生物学。RMS-RR 细胞系的特点是更具侵袭性和体外促转移表型，表现出更高的能力：i) 活性氧的解毒能力；ii) 通过不同地激活非同源末端连接和同源重组途径来修复 DNA 损伤；iii) 通过在照射后重新开始生长和重新增殖来抵消 RT 诱导的 G2/M 细胞周期停滞；iv) 表达癌症干细胞样特征。为评估 RT 暴露后 41 种细胞因子的作用及其网络相互作用而进行的生物信息学分析表明，TGF-β、MIF、CCL2、CXCL5、CXCL8 和 CXCL12 是 RMS 肿瘤中癌症免疫逃逸的主要调节因子。这些结果表明 RMS 可以通过不同的机制维持内在的并获得放射抗性，并为未来组合放射增敏策略指明了潜在的目标。