Oncogenic KRAS mutations are encountered in more than 90% of pancreatic ductal adenocarcinomas. MEK inhibition has failed to procure any clinical benefits in mutant RAS-driven cancers including pancreatic ductal adenocarcinoma (PDAC). To identify potential resistance mechanisms underlying MEK inhibitor (MEKi) resistance in PDAC, we investigated lysosomal drug accumulation in PDAC models both in vitro and in vivo. Mouse PDAC models and human PDAC cell lines as well as human PDAC xenografts treated with the MEK inhibitor trametinib or refametinib led to an enhanced expression of lysosomal markers and enrichment of lysosomal gene sets. A time-dependent, increase in lysosomal content was observed upon MEK inhibition. Strikingly, there was a strong activation of lysosomal biogenesis in cell lines of the classical compared to the basal-like molecular subtype. Increase in lysosomal content was associated with nuclear translocation of the Transcription Factor EB (TFEB) and upregulation of TFEB target genes. siRNA-mediated depletion of TFEB led to a decreased lysosomal biogenesis upon MEK inhibition and potentiated sensitivity. Using LC-MS, we show accumulation of MEKi in the lysosomes of treated cells. Therefore, MEK inhibition triggers lysosomal biogenesis and subsequent drug sequestration. Combined targeting of MEK and lysosomal function may improve sensitivity to MEK inhibition in PDAC.

超过 90% 的胰腺导管腺癌都存在致癌KRAS突变。MEK 抑制未能在突变 RAS 驱动的癌症（包括胰腺导管腺癌 (PDAC)）中获得任何临床益处。为了确定 PDAC 中 MEK 抑制剂 (MEKi) 耐药性的潜在耐药机制，我们在体外和体内研究了 PDAC 模型中溶酶体药物的积累。用 MEK 抑制剂曲美替尼或瑞法美替尼处理的小鼠 PDAC 模型和人 PDAC 细胞系以及人 PDAC 异种移植物导致溶酶体标记物表达增强和溶酶体基因集富集。MEK 抑制后观察到溶酶体含量呈时间依赖性增加。引人注目的是，与基底样分子亚型相比，经典细胞系中的溶酶体生物发生被强烈激活。溶酶体含量的增加与转录因子 EB ( TFEB ) 的核转位和TFEB靶基因的上调有关。siRNA 介导的TFEB消耗导致 MEK 抑制后溶酶体生物发生减少并增强敏感性。使用 LC-MS，我们显示了 MEKi 在处理细胞的溶酶体中的积累。因此，MEK 抑制会触发溶酶体生物发生和随后的药物隔离。MEK 和溶酶体功能的联合靶向可能会提高 PDAC 对 MEK 抑制的敏感性。