BRIT1已成为同源重组（HR）中的新型关键参与者。它位于8p23，这是肝细胞癌（HCC）中经常缺失的基因座。以前,在我们的小鼠模型中,我们发现BRIT1缺乏引发了基因组不稳定和肿瘤形成.在这里，我们的目标是确定BRIT1畸变是否与HCC有关，如果是,它们是否可用于PARP抑制剂和其他药物的靶向治疗。我们分析了肝癌样本的BRIT1DNA改变，RNA和蛋白质水平。BRIT1在约30％的HCC样品中被发现缺失和/或下调;在HCC中鉴定的BRIT1突变体K659fsX10消除了DNA修复功能。值得注意的是,BRIT1缺失与HCC的低生存率和高复发率相关。为了确定BRIT1缺乏症在增强药物反应中的作用，我们随后产生BRIT1缺陷型肝癌细胞，确定他们的人力资源缺陷，并在体外和小鼠中评估了它们对PARPiolaparib和PI3K抑制剂的反应。BRIT1缺陷型HCC细胞在体外和体内均对单独或与PI3K抑制剂BEZ235组合的奥拉帕尼具有HR缺陷且过敏。奥拉帕尼单独或与BEZ235组合的细胞毒性通过异位BRIT1在很大程度上减轻。我们还发现BEZ235显着增强BRIT1缺陷细胞中聚（ADP-核糖）的产生以及双链断裂（DSB）和单链断裂（SSB）的水平。总之,我们的结果确定BRIT1缺乏是肝癌发展的潜在驱动因素，BRIT1状态对奥拉帕尼和/或BEZ235治疗的敏感性至关重要。PI3K抑制诱导大量DNA损伤，使细胞在BRIT1缺乏的情况下更依赖于PARP活性，因此，BRIT1消耗有助于增强PARP抑制剂和PI3K抑制剂在HCC中的合成致死性。本研究为进一步拓展PARPi在HCC治疗中的应用提供了新的机制基础。
BRIT1 has emerged as a novel key player in homologous recombination (HR). It is located in 8p23, a locus frequently deleted in hepatocellular carcinoma (HCC). Previously, we found that BRIT1-deficiency triggered genomic instability and tumor formation in our mouse model. Here we aim to determine whether BRIT1 aberrations are implicated in HCC and, if so, whether they can be used for targeted therapy with PARP inhibitors and other agents. We analyzed HCC samples for BRIT1 alterations at DNA, RNA and protein levels. BRIT1 was found deleted and/or downregulated in ~30% of HCC samples; BRIT1 mutant K659fsX10 identified in HCC abolished DNA repair function. Notably, BRIT1 deletion was correlated with poor survival and high recurrence of HCC. To determine the role of BRIT1 deficiency in potentiating the drug response, we subsequently generated BRIT1-deficient HCC cells, determined their HR defects, and assessed their response to the PARPi olaparib and PI3K inhibitor in vitro and in mice. BRIT1-deficient HCC cells were HR defective and hypersensitive to olaparib alone or in combination with PI3K inhibitor BEZ235, both in vitro and in vivo. The cytotoxicity of olaparib alone or in combination with BEZ235 was largely alleviated by ectopic BRIT1. We also found that BEZ235 markedly enhanced the production of poly (ADP-ribose) and the level of double-strand breaks (DSB) and single-strand breaks (SSB) in BRIT1-deficient cells. In summary, our results identify BRIT1 deficiency as a potential driver for HCC development, and BRIT1 status is critical to sensitivity to treatment with olaparib and/or BEZ235. PI3K inhibition induces substantial DNA damage and makes cells more dependent on PARP activity in the context of BRIT1 deficiency, thus, BRIT1 depletion facilitates enhancing synthetic lethality of PARP inhibitors and PI3K inhibitors in HCC. This study provides a new mechanistic foundation for significantly expanding the application of PARPi in HCC therapy.
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