The precise mechanism about drug resistance of cancer stem cells (CSCs) has not yet been completely understood. Based on the expression of CD44 and CD133, two well-recognized cell surface markers for CSC identification, we tried to separate HCT8 colorectal cancer cells into different subpopulations and then investigated how the expression of CD44 and CD133 associated with doxorubicin (DXR) resistance. Interestingly, DXR resistance was observed in CD44⁺CD133⁺ (vs. all other subpopulations), but not in CD44⁺CD133^- cells. CD44⁺CD133⁺ cells also showed an enhanced expression of ABCB1 and drug efflux ability (vs. all other subpopulations), but verapamil, an inhibitor of ABCB1, only partially mitigated the DXR resistance. Independent on the accumulation of DXR, lower level of reactive oxygen species and higher expression of Nrf2 were detected in CD44⁺CD133⁺ than CD44⁺CD133^- cells (). Unexpectedly, silencing CD133 by siRNA only partially enhanced the cytotoxicity of DXR, but did not obviously change the expression of ABCB1 and the accumulation of DXR in CD44⁺CD133⁺ cells. Complex mechanisms, including drug excretion and redox regulation, are likely involved in the DXR resistance of CD133-positive cells, suggesting the difficulty of drug resistance problem in cancer chemotherapy.

中文翻译：

---

CD133阳性癌症干细胞中ABCB1和Nrf2的增强表达与阿霉素抗性相关。

关于癌症干细胞（CSCs）耐药性的确切机制尚未完全了解。基于CD44和CD133的表达，这是两种公认的CSC识别细胞表面标记，我们试图将HCT8大肠癌细胞分为不同的亚群，然后研究CD44和CD133的表达如何与阿霉素（DXR）耐药相关。有趣的是，在CD44 ⁺ CD133 ⁺（与所有其他亚群），但不是在CD44 ⁺ CD133 ^-细胞。CD44 ⁺ CD133 ⁺细胞还显示出增强的ABCB1表达和药物外排能力（与所有其他亚群相比），但维拉帕米（ABCB1的抑制剂）仅部分缓解了DXR耐药性。独立于DXR的积累，活性氧和Nrf2的更高的表达水平较低的CD44中检测到⁺ CD133 ⁺比CD44 ⁺ CD133 ^-细胞（）。出乎意料的是，通过siRNA沉默CD133只能部分增强DXR的细胞毒性，但并没有明显改变CD44 ⁺ CD133 ⁺细胞中ABCB1的表达和DXR的积累。CD133阳性细胞的DXR耐药性可能涉及复杂的机制，包括药物排泄和氧化还原调节，这表明在癌症化疗中存在耐药性问题的难度。