The acidic tumor microenvironment stands as a major obstacle to the efficient elimination of tumor cells. Norcantharidin (NCTD) is a powerful antitumor agent with multiple bioactivities. However, the effect of NCTD under acidic conditions is still unclear. Here, we report that NCTD can efficiently kill bladder cancer (BC) cells in acidic culture, and more intriguingly, NCTD can induce immunogenic cell death (ICD), thereby promoting antitumor immunity. In NCTD-treated BC cells, the surface-exposed calreticulin (ecto-CALR) was significantly increased. Consistently, co-culture with these cells promoted dendritic cell (DC) maturation. The NCTD-induced ICD is autophagy dependent, as autophagy inhibition completely blocked the NCTD-induced ecto-CALR and DC maturation. In addition, the DC showed a distinct maturation phenotype (CD80^high CD86^low) in acidic culture, as compared to that in physiological pH (CD⁸⁰ high CD86^high). Finally, the NCTD-induced ICD was validated in a mouse model. NCTD treatment significantly increased the tumor-infiltrating T lymphocytes in MB49 bladder cancer mice. Immunizing mice with NCTD-treated MB49 cells significantly increased tumor-free survival as compared to control. These findings demonstrate that NCTD could induce ICD in an acidic environment and suggest the feasibility to combine NCTD with anticancer immunotherapy to treat BC.

中文翻译：

---

去甲斑蝥素通过促进酸性培养中的自噬诱导膀胱癌细胞的免疫原性细胞死亡

酸性肿瘤微环境是有效消除肿瘤细胞的主要障碍。去甲斑蝥素 (NCTD) 是一种强大的抗肿瘤剂，具有多种生物活性。然而，NCTD在酸性条件下的作用仍不清楚。在这里，我们报告了 NCTD 可以有效地杀死酸性培养物中的膀胱癌 (BC) 细胞，更有趣的是，NCTD 可以诱导免疫原性细胞死亡 (ICD)，从而促进抗肿瘤免疫。在 NCTD 处理的 BC 细胞中，表面暴露的钙网蛋白 (ecto-CALR) 显着增加。一致地，与这些细胞共培养促进了树突状细胞 (DC) 的成熟。NCTD 诱导的 ICD 依赖于自噬，因为自噬抑制完全阻断了 NCTD 诱导的 ecto-CALR 和 DC 成熟。此外，DC 表现出明显的成熟表型（CD80^{与生理 pH 值（CD 80}高 CD86^高）相比，酸性培养中的^高CD86^低）。最后，在小鼠模型中验证了 NCTD 诱导的 ICD。NCTD 治疗显着增加了 MB49 膀胱癌小鼠的肿瘤浸润性 T 淋巴细胞。与对照相比，用 NCTD 处理的 MB49 细胞免疫小鼠显着增加了无肿瘤存活率。这些发现表明，NCTD 可以在酸性环境中诱导 ICD，并表明将 NCTD 与抗癌免疫疗法结合治疗 BC 的可行性。