VEGF receptor inhibitor brivanib sensitizes chemotherapy by targeting cGAS to boost antitumor immunity. VEGF receptor inhibitor brivanib sensitizes chemotherapy by targeting cGAS to boost antitumor immunity

Chemoresistance challenges the clinical application of most widely used platinum-based cancer chemotherapeutics which canonically function through inducing DNA damage. The DNA sensor cyclic GMP–AMP synthase (cGAS) connects genome instability to type I IFN response which confers vulnerability to platinum treatment. Here, by using a high throughput small-molecule-microarray-based screening of cGAS interacting compounds, we identified brivanib, known as an inhibitor of the vascular endothelial growth factor receptor (VEGFR), as a novel cGAS agonist. Brivanib markedly enhanced platinum-induced STING-TBK1-type I IFN response in tumor cells indispensable of cGAS. Importantly, brivanib synergizes the effect of cisplatin in restricting the growth of xenografted Lewis Lung Cancer (LLC) cells by boosting CD8+ T cell response in a cGAS-dependent manner. Mechanistically, brivanib enhances the DNA binding affinity of cGAS by directly targeting leucine 495 of cGAS. Moreover, leucine 495 of cGAS is essential for brivanib-mediated promoting effect on cisplatin-mediated type I IFN response and inhibition of tumor growth. Clinically, higher expression of cGAS in tumor renders a more favorable response to platinum-based chemotherapeutic regimens and better prognosis in lung cancer patient. Taken together, our findings discover cGAS as an unprecedented target of brivanib and provide a rationale for the combination of brivanib with platinum-based chemotherapeutics in cancer treatment. Overall design: Total RNA was isolated and used for RNA-seq analysis. cDNA library construction and sequencing were performed by Beijing Genomics Institute using BGISEQ-500 platform. High-quality reads were aligned to the Mus musculus reference genome (UCSC_mm10) using Bowtie2. The expression levels for each of the genes were normalized to fragments per kilobase of exon model per million mapped reads (FPKM) using RNA-seq by Expectation Maximization (RSEM).

化疗耐药制约了多数临床常用铂类抗癌化疗药物的应用，此类药物的经典作用机制为通过诱导DNA损伤发挥抗肿瘤效应。DNA传感器环GMP-AMP合成酶（cyclic GMP–AMP synthase, cGAS）可将基因组不稳定性与I型干扰素应答相关联，而该应答可赋予肿瘤细胞对铂类治疗的敏感性。本研究通过基于高通量小分子微阵列的cGAS相互作用化合物筛选，鉴定出布立凡尼（brivanib）——一种已知的血管内皮生长因子受体（vascular endothelial growth factor receptor, VEGFR）抑制剂——作为新型cGAS激动剂。布立凡尼可在依赖cGAS的肿瘤细胞中显著增强铂类诱导的STING-TBK1-I型干扰素应答。重要的是，布立凡尼可通过cGAS依赖的方式增强CD8+ T细胞应答，从而协同顺铂抑制异种移植Lewis肺癌（Lewis Lung Cancer, LLC）细胞的生长。机制层面，布立凡尼通过直接靶向cGAS的亮氨酸495位点，增强cGAS的DNA结合亲和力。此外，cGAS的亮氨酸495位点对于布立凡尼介导的顺铂诱导I型干扰素应答增强效应以及肿瘤生长抑制作用至关重要。临床数据显示，肿瘤组织中cGAS的高表达可使肺癌患者对铂类化疗方案产生更优应答，并获得更好的预后。综上，本研究发现cGAS是布立凡尼前所未有的作用靶点，为布立凡尼联合铂类化疗药物用于癌症治疗提供了理论依据。

整体实验设计：提取总RNA并用于RNA测序（RNA-seq）分析。由北京基因组研究所（BGI）采用BGISEQ-500平台完成cDNA文库构建及测序。使用Bowtie2将高质量测序读段比对至小鼠参考基因组（UCSC_mm10）。采用期望最大化算法的RNA测序分析工具（RNA-seq by Expectation Maximization, RSEM）将每个基因的表达水平标准化为每百万比对读段的外显子模型每千碱基片段数（fragments per kilobase of exon model per million mapped reads, FPKM）。