Sun Zhuang, Shi Mengyuan, Xia Jinhong, Li Xin, Chen Nan, Wang Hanyang, Gao Zhaoya, Jia Jinying, Yang Peng, Ji Dengbo, Gu Jin
Key laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Gastrointestinal Surgery III, Peking University Cancer Hospital & Institute, Beijing, China.
Peking University Shougang Hospital, Beijing, China.
J Immunother Cancer. 2025 Jan 11;13(1):e010460. doi: 10.1136/jitc-2024-010460.
B-Raf proto-oncogene, serine/threonine kinase (BRAF)-mutant microsatellite stable (MSS) colorectal cancer (CRC) constitutes a distinct CRC subgroup, traditionally perceived as minimally responsive to standard therapies. Recent clinical attempts, such as BRAF inhibitors (BRAFi) monotherapy and combining BRAFi with other inhibitors, have yielded unsatisfactory efficacy. This study aims to identify a novel therapeutic strategy for this challenging subgroup.
We first performed a large-scale drug screening using patient-derived organoid models and cell lines to pinpoint potential therapies. Subsequently, we investigated the synergistic effects of identified effective inhibitors and probed their cooperative mechanisms. Concurrently, we explored the immune characteristics of BRAF MSS CRC using RNA sequencing and multiplex immunohistochemistry. Finally, we established a CT26 BRAF mouse cell line and validated the efficacy of combining these inhibitors and programmed death 1 (PD-1) blockades in immunocompetent mice.
Drug screening identified histone deacetylase (HDAC) inhibitor and mitogen-activated protein kinase kinase (MEK) inhibitor as significantly effective against BRAF MSS CRC. Further research revealed that these two inhibitors have superior synergistic effects by comprehensively inhibiting the activation of the epidermal growth factor receptor, mitogen-activated protein kinase, and phosphoinositide 3-kinase-protein kinase B pathways and suppressing the key target homeobox C6 (HOXC6). HOXC6, overexpressed in BRAF MSS CRC, regulates the MYC gene and contributes to treatment resistance, tumor growth, and metastasis. Moreover, the combination therapy demonstrated the ability to enhance antitumor immunity by synergistically upregulating the expression of immune activation-related genes, activating the cyclic guanosine monophosphate-adenosine monophosphate synthase/stimulator of interferon genes (cGAS/STING) pathway, and diminishing the tumor cells' DNA mismatch repair capacity. Notably, BRAF MSS CRC was identified to exhibit a distinct immune microenvironment with increased PD-1 cell infiltration and potential responsiveness to immunotherapy. Echoing the above findings, in vivo, HDAC and MEK inhibitors significantly improved PD-1 blockade efficacy, accompanied by increased CD8 T-cell infiltration.
Our findings indicate that combining HDAC inhibitor, MEK inhibitor, and PD-1 blockade is a potential strategy for treating BRAF-mutant MSS CRC, warranting further investigation in clinical settings.
B-Raf原癌基因丝氨酸/苏氨酸激酶（BRAF）突变的微卫星稳定（MSS）结直肠癌（CRC）构成了一个独特的CRC亚组，传统上认为其对标准疗法反应甚微。最近的临床尝试，如BRAF抑制剂（BRAFi）单药治疗以及BRAFi与其他抑制剂联合使用，疗效均不尽人意。本研究旨在为这一具有挑战性的亚组确定一种新的治疗策略。
我们首先使用患者来源的类器官模型和细胞系进行大规模药物筛选，以确定潜在的治疗方法。随后，我们研究了已确定的有效抑制剂的协同作用，并探究其协同机制。同时，我们使用RNA测序和多重免疫组化技术探索BRAF MSS CRC的免疫特征。最后，我们建立了CT26 BRAF小鼠细胞系，并在具有免疫活性的小鼠中验证了这些抑制剂与程序性死亡1（PD-1）阻断剂联合使用的疗效。
药物筛选确定组蛋白去乙酰化酶（HDAC）抑制剂和丝裂原活化蛋白激酶激酶（MEK）抑制剂对BRAF MSS CRC具有显著疗效。进一步研究表明，这两种抑制剂通过全面抑制表皮生长因子受体、丝裂原活化蛋白激酶和磷酸肌醇3激酶-蛋白激酶B通路的激活以及抑制关键靶点同源盒C6（HOXC6），具有卓越的协同作用。HOXC6在BRAF MSS CRC中过表达，调节MYC基因，并导致治疗耐药、肿瘤生长和转移。此外，联合治疗通过协同上调免疫激活相关基因的表达、激活环磷酸鸟苷-磷酸腺苷合酶/干扰素基因刺激因子（cGAS/STING）通路以及降低肿瘤细胞的DNA错配修复能力，显示出增强抗肿瘤免疫的能力。值得注意的是，BRAF MSS CRC被确定表现出独特的免疫微环境，PD-1细胞浸润增加，且对免疫治疗具有潜在反应性。与上述发现一致，在体内，HDAC和MEK抑制剂显著提高了PD-1阻断疗效，同时伴有CD8 T细胞浸润增加。
我们的研究结果表明，联合使用HDAC抑制剂、MEK抑制剂和PD-1阻断是治疗BRAF突变MSS CRC的一种潜在策略，值得在临床环境中进一步研究。
