University of British Columbia, 4500 Oak St., Room. C234, Vancouver, BC V6H 3N1, Canada.
Mol Cancer Res. 2013 Oct;11(10):1179-92. doi: 10.1158/1541-7786.MCR-12-0575. Epub 2013 Aug 2.
Rhabdomyosarcoma is the most common soft tissue sarcoma in children. Metastatic rhabdomyosarcoma in children has a 5-year event-free survival rate of <30%, and a recent clinical trial with irinotecan, a topoisomerase I inhibitor, failed to improve outcome. Therefore, it was surmised that failure of irinotecan may be the result of overexpression of the DNA repair enzyme tyrosyl-DNA phosphodiesterase (TDP1), which processes topoisomerase I-DNA complexes resulting from topoisomerase I inhibitor treatment. Using human tissue microarrays and gene expression arrays, a marked overexpression of TDP1 protein and mRNA in RMS tumors was observed. Critically, knockdown of TDP1 or inhibition of poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme in the same complex as TDP1, sensitized rhabdomyosarcoma cell lines to analogues of irinotecan. Interestingly, BRCA1/2 mutations or altered expression was not detectable in rhabdomyosarcoma cells; however, TDP1 knockdown and PARP-1 inhibition alone were cytotoxic to a subset of rhabdomyosarcoma cells, suggesting that they harbor genetic lesions in DNA repair components that have synthetic lethal interactions with loss of TDP1 or PARP1 function. Furthermore, culturing embryonal rhabdomyosarcoma cells in serum/nutrient-restricted medium increased cellular cytotoxicity upon PARP-1 inhibition and was intrinsically cytotoxic to alveolar, though not embryonal rhabdomyosarcoma cells. The results of these studies suggest a compensatory role for TDP1 in rhabdomyosarcoma after topoisomerase-I based therapy and further demonstrate that TDP1 knockdown, PARP-1 inhibition, and dietary restriction have therapeutic validity.
Selective targeting of TDP1 and/or PARP-1 in rhabdomyosarcoma induces cytotoxicity and sensitizes to DNA damaging agents.
横纹肌肉瘤是儿童中最常见的软组织肉瘤。转移性横纹肌肉瘤患儿的 5 年无事件生存率<30%，最近一项伊立替康（拓扑异构酶 I 抑制剂）临床试验未能改善预后。因此，人们推测伊立替康失败可能是由于 DNA 修复酶酪氨酰-DNA 磷酸二酯酶（TDP1）的过度表达所致，该酶处理拓扑异构酶 I-DNA 复合物，导致拓扑异构酶 I 抑制剂治疗的结果。使用人体组织微阵列和基因表达阵列，观察到 RMS 肿瘤中 TDP1 蛋白和 mRNA 的显著过度表达。至关重要的是，TDP1 的敲低或多聚（ADP-核糖）聚合酶-1（PARP-1）的抑制，与 TDP1 相同的复合物中的一种酶，使横纹肌肉瘤细胞系对伊立替康类似物敏感。有趣的是，BRCA1/2 突变或表达改变在横纹肌肉瘤细胞中不可检测；然而，TDP1 的敲低和 PARP-1 的抑制单独对横纹肌肉瘤细胞的亚群具有细胞毒性，表明它们具有遗传缺陷，这些缺陷与 TDP1 或 PARP1 功能的丧失具有合成致死性相互作用。此外，在血清/营养受限的培养基中培养胚胎性横纹肌肉瘤细胞，在 PARP-1 抑制时增加细胞毒性，并对肺泡性横纹肌肉瘤细胞固有地具有细胞毒性，但对胚胎性横纹肌肉瘤细胞则不然。这些研究结果表明，TDP1 在基于拓扑异构酶 I 的治疗后在横纹肌肉瘤中起代偿作用，并且进一步证明 TDP1 的敲低、PARP-1 的抑制和饮食限制具有治疗有效性。
在横纹肌肉瘤中选择性靶向 TDP1 和/或 PARP1 可诱导细胞毒性并对 DNA 损伤剂敏感。
