Evasion of apoptosis is a hallmark of cancer, which is frequently mediated by upregulation of the antiapoptotic BCL-2 family proteins. In colorectal cancer (CRC), previous work has highlighted differential antiapoptotic protein dependencies determined by the stage of the disease. While intestinal stem cells (ISCs) require BCL-2 for adenoma outgrowth and survival during transformation, ISC-specific MCL1 deletion results in disturbed intestinal homeostasis, eventually contributing to tumorigenesis. Colon cancer stem cells (CSCs), however, no longer require BCL-2 and depend mainly on BCL-XL for their survival. We therefore hypothesized that a shift in antiapoptotic protein reliance occurs in ISCs as the disease progresses from normal to adenoma to carcinoma. By targeting antiapoptotic proteins with specific BH3 mimetics in organoid models of CRC progression, we found that BCL-2 is essential only during ISC transformation while MCL1 inhibition did not affect adenoma outgrowth. BCL-XL, on the other hand, was crucial for stem cell survival throughout the adenoma-to-carcinoma sequence. Furthermore, we identified that the limited window of BCL-2 reliance is a result of its downregulation by miR-17-5p, a microRNA that is upregulated upon APC-mutation driven transformation. Here we show that BCL-XL inhibition effectively impairs adenoma outgrowth in vivo and enhances the efficacy of chemotherapy. In line with this dependency, expression of BCL-XL, but not BCL-2 or MCL1, directly correlated to the outcome of chemotherapy-treated CRC patients. Our results provide insights to enable the rational use of BH3 mimetics in CRC management, particularly underlining the therapeutic potential of BCL-XL targeting mimetics in both early and late-stage disease.

逃避细胞凋亡是癌症的一个标志，这通常是由抗细胞凋亡 BCL-2 家族蛋白的上调介导的。在结直肠癌（CRC）中，之前的工作强调了由疾病阶段决定的不同抗凋亡蛋白依赖性。虽然肠道干细胞 (ISC) 在转化过程中需要 BCL-2 来实现腺瘤的生长和存活，但 ISC 特异性MCL1缺失会导致肠道稳态紊乱，最终导致肿瘤发生。然而，结肠癌干细胞 (CSC) 不再需要 BCL-2，而是主要依赖 BCL-XL 生存。因此，我们假设，随着疾病从正常进展到腺瘤再到癌，ISC 中抗凋亡蛋白依赖性发生转变。通过在 CRC 进展的类器官模型中用特定的 BH3 模拟物靶向抗凋亡蛋白，我们发现 BCL-2 仅在 ISC 转化过程中至关重要，而 MCL1 抑制并不影响腺瘤的生长。另一方面，BCL-XL 在整个腺瘤到癌的过程中对于干细胞的存活至关重要。此外，我们发现 BCL-2 依赖的有限窗口是 miR-17-5p 下调的结果，miR-17-5p 是一种在APC突变驱动的转化后上调的 microRNA。在这里，我们证明 BCL-XL 抑制有效地削弱体内腺瘤的生长并增强化疗的疗效。与这种依赖性一致， BCL-XL的表达（而不是BCL-2或MCL1 ）与化疗治疗的 CRC 患者的结果直接相关。 我们的结果为在 CRC 治疗中合理使用 BH3 模拟物提供了见解，特别强调了 BCL-XL 靶向模拟物在早期和晚期疾病中的治疗潜力。