混合血统激酶3（MLK3）是肿瘤疾病的一个可行靶点，然而，其激活剂或抑制剂是否可以作为抗肿瘤药剂仍不清楚。我们报道了MLK3激酶活性在三阴性（TNBC）人乳腺肿瘤中高于激素受体阳性乳腺肿瘤，其中雌激素抑制了MLK3激酶活性并为ER+乳腺癌细胞提供生存优势。在此，我们展示了在TNBC中，更高的MLK3激酶活性反而促进癌细胞的存活。MLK3的敲降或MLK3抑制剂CEP-1347和URMC-099减弱了TNBC细胞系和患者来源的移植瘤的肿瘤发生。MLK3激酶抑制剂降低了TNBC乳腺移植瘤中MLK3、PAK1和NF-kB蛋白的表达和活化，并引起细胞死亡。RNA-seq分析确定了几个被MLK3抑制剂下调的基因，并且NGF/TrkA MAPK通路在对MLK3抑制剂的生长抑制敏感的肿瘤中显著丰富。对于激酶抑制剂不敏感的TNBC细胞系TrkA显著较低，而TrkA的过表达恢复了对MLK3抑制剂的敏感性。这些结果表明，在TNBC肿瘤中，MLK3的功能取决于表达TrkA的下游靶标，并且MLK3激酶抑制剂可能提供一种新的靶向治疗方法。©2023作者，Springer Nature Limited独家许可。

Mixed Lineage Kinase 3 (MLK3) is a viable target for neoplastic diseases; however, it is unclear whether its activators or inhibitors can act as anti-neoplastic agents. We reported that the MLK3 kinase activity was higher in triple-negative (TNBC) than in hormone receptor-positive human breast tumors, where estrogen inhibited MLK3 kinase activity and provided a survival advantage to ER+ breast cancer cells. Herein, we show that in TNBC, the higher MLK3 kinase activity paradoxically promotes cancer cell survival. Knockdown of MLK3 or MLK3 inhibitors, CEP-1347 and URMC-099, attenuated tumorigenesis of TNBC cell line and Patient-Derived (PDX) xenografts. The MLK3 kinase inhibitors decreased both the expression and activation of MLK3, PAK1, and NF-kB protein and caused cell death in TNBC breast xenografts. RNA-seq analysis identified several genes downregulated by MLK3 inhibition, and the NGF/TrkA MAPK pathway was significantly enriched in tumors sensitive to growth inhibition by MLK3 inhibitors. The TNBC cell line unresponsive to kinase inhibitor had substantially lower TrkA, and overexpression of TrkA restored the sensitivity to MLK3 inhibition. These results suggest that the functions of MLK3 in breast cancer cells depend on downstream targets in TNBC tumors expressing TrkA, and MLK3 kinase inhibition may provide a novel targeted therapy.© 2023. The Author(s), under exclusive licence to Springer Nature Limited.