Cholesterol depletion sensitizes gallbladder cancer to cisplatin by impairing DNA damage response

Gallbladder cancer (GBC) is the common malignancy of the bile tract system with extremely poor clinical outcomes, owing to its metastatic property and intrinsic resistance to the first-line drugs. Although it is well-established that cholesterol abnormity contributes to gallstone formation, a leading risk factor for GBC, the link of cholesterol homeostasis with GBC has not been investigated. The present study systematically examined the genes implicated in cholesterol homeostasis, and revealed altered gene expressions of <i>de novo</i> cholesterol biosynthesis and sterol sulfonation (SULT2B1), reduced bile acid synthesis (CYP7B1 and CYP39A1) and impaired sterol efflux (ABCA1, ABCG5, LCAT, and CETP) in GBC tissues. Suppression of cholesterol biosynthesis by lovastatin inhibited GBC cell proliferation possibly through attenuating the DNA repair process. Further investigation revealed lovastatin sensitized GBC cells to cisplatin-induced apoptosis and suppressed the activation of CHK1, CHK2, and H2AX during DNA damage response. By using chemically distinct statins, HMGCR depletion or supplementing mevalonate, the product of HMGCR, we showed the inhibitory effects on DNA repair process of lovastatin were due to the blockage of the mevalonate pathway. Subcutaneous xenograft mice model suggested lovastatin promoted the therapeutic efficacy of cisplatin, and significantly prolonged the survival times of tumor-bearing mice. Moreover, HMGCR ablation repressed tumor growth <i>in vivo</i>, which can be rescued partially by restored expression of HMGCR, suggesting the on-target effects of lovastatin. Therefore, our study provides the clinical relevance of cholesterol homeostasis with GBC progression, and highlights a novel intervention of combined use of lovastatin and cisplatin for GBC.

胆囊癌（Gallbladder cancer, GBC）是胆道系统常见的恶性肿瘤，因其侵袭转移特性及对一线药物的固有耐药性，临床预后极差。尽管学界已证实胆固醇异常可诱发胆结石形成——而胆结石是胆囊癌的首要危险因素——但胆固醇稳态与胆囊癌之间的关联尚未得到系统研究。本研究对参与胆固醇稳态调控的基因进行了系统性检测，发现胆囊癌组织中存在胆固醇从头（de novo）生物合成及固醇磺化（SULT2B1）相关基因的表达异常，胆汁酸合成相关基因（CYP7B1、CYP39A1）表达下调，同时固醇外流相关基因（ABCA1、ABCG5、LCAT及CETP）功能受损。洛伐他汀对胆固醇生物合成的抑制作用，可通过减弱DNA修复过程，进而抑制胆囊癌细胞的增殖。进一步研究显示，洛伐他汀可增强胆囊癌细胞对顺铂诱导凋亡的敏感性，并在DNA损伤应答过程中抑制CHK1、CHK2及H2AX的激活。通过采用化学结构各异的他汀类药物、敲低羟甲基戊二酰辅酶A还原酶（HMGCR）或补充HMGCR的代谢产物甲羟戊酸，本研究证实洛伐他汀对DNA修复过程的抑制效应，源于甲羟戊酸通路的阻断。皮下移植瘤小鼠模型实验表明，洛伐他汀可增强顺铂的治疗效果，并显著延长荷瘤小鼠的生存时长。此外，敲除HMGCR可在体内（in vivo）抑制肿瘤生长，该效应可通过恢复HMGCR的表达得到部分逆转，提示洛伐他汀发挥了靶向作用。综上，本研究明确了胆固醇稳态与胆囊癌进展的临床相关性，并提出了联合使用洛伐他汀与顺铂治疗胆囊癌的新型干预策略。