Inhibitors of apoptosis proteins (IAPs) are intracellular proteins, with important roles in regulating cell death, inflammation, and immunity. Here, we examined the clinical and therapeutic relevance of IAPs in colorectal cancer. We found that elevated expression of cIAP1 and cIAP2 (but not XIAP) significantly correlated with poor prognosis in patients with microsatellite stable (MSS) stage III colorectal cancer treated with 5-fluorouracil (5FU)–based adjuvant chemotherapy, suggesting their involvement in promoting chemoresistance. A novel IAP antagonist tolinapant (ASTX660) potently and rapidly downregulated cIAP1 in colorectal cancer models, demonstrating its robust on-target efficacy. In cells co-cultured with TNFα to mimic an inflammatory tumor microenvironment, tolinapant induced caspase-8–dependent apoptosis in colorectal cancer cell line models; however, the extent of apoptosis was limited because of inhibition by the caspase-8 paralogs FLIP and, unexpectedly, caspase-10. Importantly, tolinapant-induced apoptosis was augmented by FOLFOX in human colorectal cancer and murine organoid models in vitro and in vivo , due (at least in part) to FOLFOX-induced downregulation of class I histone deacetylases (HDAC), leading to acetylation of the FLIP-binding partner Ku70 and downregulation of FLIP. Moreover, the effects of FOLFOX could be phenocopied using the clinically relevant class I HDAC inhibitor, entinostat, which also induced acetylation of Ku70 and FLIP downregulation. Further analyses revealed that caspase-8 knockout RIPK3-positive colorectal cancer models were sensitive to tolinapant-induced necroptosis, an effect that could be exploited in caspase-8–proficient models using the clinically relevant caspase inhibitor emricasan. Our study provides evidence for immediate clinical exploration of tolinapant in combination with FOLFOX in poor prognosis MSS colorectal cancer with elevated cIAP1/2 expression.

中文翻译：

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IAP 拮抗剂 Tolinapant (ASTX660) 在结直肠癌中的临床定位

凋亡蛋白抑制剂 (IAPs) 是细胞内蛋白，在调节细胞死亡、炎症和免疫方面具有重要作用。在这里，我们检查了 IAP 在结直肠癌中的临床和治疗相关性。我们发现，在接受基于 5-氟尿嘧啶 (5FU) 的辅助化疗的微卫星稳定 (MSS) III 期结直肠癌患者中，cIAP1 和 cIAP2（但不是 XIAP）的表达升高与预后不良显着相关，这表明它们参与促进化疗耐药. 一种新型 IAP 拮抗剂 tolinapant (ASTX660) 在结直肠癌模型中有效且快速地下调 cIAP1，证明了其强大的靶向功效。在与 TNFα 共培养以模拟炎性肿瘤微环境的细胞中，tolinapant 在结直肠癌细胞系模型中诱导 caspase-8 依赖性细胞凋亡；然而，由于 caspase-8 旁系同源物 FLIP 和意外的 caspase-10 的抑制作用，细胞凋亡的程度受到限制。重要的是，FOLFOX 在人结肠直肠癌和体外和体内小鼠类器官模型中增强了 tolinapant 诱导的细胞凋亡，这至少部分是由于 FOLFOX 诱导的 I 类组蛋白去乙酰化酶 (HDAC) 的下调，导致乙酰化FLIP 结合伙伴 Ku70 和 FLIP 的下调。此外，FOLFOX 的作用可以通过临床相关的 I 类 HDAC 抑制剂 entinostat 进行表型复制，该抑制剂还诱导 Ku70 的乙酰化和 FLIP 下调。进一步的分析表明，caspase-8 敲除 RIPK3 阳性结直肠癌模型对 tolinapant 诱导的坏死性凋亡很敏感，这种效应可以在 caspase-8 熟练模型中使用临床相关的 caspase 抑制剂 emricasan 加以利用。我们的研究为在 cIAP1/2 表达升高的预后不良的 MSS 结直肠癌中立即临床探索 tolinapant 联合 FOLFOX 提供了证据。