Preclinical models of diffuse-type gastric cancer (DGC) that reliably predict clinical activity of novel compounds are lacking. To overcome the problem of poor tumor cellularity in DGC, we used cells from malignant ascites to establish DGC patient-derived xenograft (PDX) models that recapitulate the primary cancer. Cells in PDX model GAGA6 with FGFR2 amplification were sensitive to AZD4547, a potent FGFR inhibitor that is being clinically evaluated for FGFR-aberrant cancer types. Intermittent in vivo treatment of GAGA6 tumors with AZD4547 gave rise to PDX tumors with acquired resistance to AZD4547, GAGA6-R. Surprisingly, there were no mutations in the FGFR2 gene in GAGA6-R, negating gatekeeper mutations as a mechanism of drug resistance. Phosphorylation of FGFR2 and downstream signaling molecules AKT/PKB and MAPK/ERK remained inhibited by AZD4547. Further analysis of signaling pathways identified AKT-independent phosphorylation and inhibition of GSK3β as a mechanism of drug resistance in GAGA6-R cells. Treatment of GAGA6-R cells with protein kinase C (PKC) inhibitor H7 in combination with AZD4547 led to dephosphorylation and activation of GSK3β with concomitant downregulation of MCL-1 and BCL-XL. Combined treatment with AZD4547 and H7 in vitro synergistically enhanced cell death in GAGA6-R but not GAGA6 cells. Furthermore, midostaurin, a multikinase inhibitor with PKC-inhibiting activity, in part reversed resistance of GAGA6-R tumor to AZD4547 in vivo. Our results suggest that upon challenge with FGFR inhibitors, FGFR2-amplified tumors that are highly dependent on FGFR2 signaling for survival rapidly develop resistance by switching to a PKC-mediated inhibition of GSK3β to gain a survival advantage. Mol Cancer Ther; 17(1); 232–42. ©2017 AACR.

中文翻译：

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通过不依赖 AKT 的 PKC 介导的 GSK3β 磷酸化在弥漫型胃癌中获得对 FGFR 抑制剂的抗性

缺乏能够可靠预测新化合物临床活性的弥漫型胃癌 (DGC) 的临床前模型。为了克服 DGC 中肿瘤细胞结构差的问题，我们使用来自恶性腹水的细胞来建立 DGC 患者来源的异种移植 (PDX) 模型，以重现原发癌。具有 FGFR2 扩增的 PDX 模型 GAGA6 中的细胞对 AZD4547 敏感，AZD4547 是一种有效的 FGFR 抑制剂，正在临床评估 FGFR 异常癌症类型。用 AZD4547 对 GAGA6 肿瘤的间歇性体内治疗产生了对 AZD4547、GAGA6-R 具有获得性抗性的 PDX 肿瘤。令人惊讶的是，GAGA6-R 中的 FGFR2 基因没有突变，否定了作为耐药机制的看门人突变。FGFR2 和下游信号分子 AKT/PKB 和 MAPK/ERK 的磷酸化仍然被 AZD4547 抑制。对信号通路的进一步分析发现，AKT 非依赖性磷酸化和 GSK3β 的抑制是 GAGA6-R 细胞耐药的一种机制。用蛋白激酶 C (PKC) 抑制剂 H7 和 AZD4547 联合处理 GAGA6-R 细胞导致 GSK3β 去磷酸化和激活，同时下调 MCL-1 和 BCL-XL。AZD4547 和 H7 的体外联合治疗协同增强了 GAGA6-R 中的细胞死亡，但不是 GAGA6 细胞。此外，midostaurin，一种具有 PKC 抑制活性的多激酶抑制剂，在体内部分逆转了 GAGA6-R 肿瘤对 AZD4547 的耐药性。我们的结果表明，在使用 FGFR 抑制剂进行挑战时，高度依赖 FGFR2 信号的 FGFR2 扩增肿瘤通过切换到 PKC 介导的 GSK3β 抑制来获得生存优势，从而迅速产生耐药性。摩尔癌症治疗; 17(1); 232-42。©2017 AACR。