Inhibition of KRAS-Driven Tumorigenicity by Interruption of an Autocrine Cytokine Circuit

Although the roles of mitogen-activated protein kinase ( MAPK) and phosphoinositide 3-kinase (PI3K) signaling in KRAS-driven tumorigenesis are well established, KRAS activates additional pathways required for tumor maintenance, the inhibition of which are likely to be necessary for effective KRAS-directed therapy. Here, we show that the I kappa B kinase (IKK)related kinases Tank-binding kinase-1 (TBK1) and IKK epsilon promote KRAS-driven tumorigenesis by regulating autocrine CCL5 and interleukin(IL)-6 and identify CYT387 as a potent JAK/TBK1/IKK epsilon inhibitor. CYT387 treatment ablates RAS-associated cytokine signaling and impairs Kras-driven murine lung cancer growth. Combined CYT387 treatment and MAPK pathway inhibition induces regression of aggressive murine lung adenocarcinomas driven by Kras mutation and p53 loss. These observations reveal that TBK1/IKKe promote tumor survival by activating CCL5 and IL-6 and identify concurrent inhibition of TBK1/IKKe, Janus-activated kinase (JAK), and MEK signaling as an effective approach to inhibit the actions of oncogenic KRAS. SIGNIFICANCE: In addition to activating MAPK and PI3K, oncogenic KRAS engages cytokine signaling to promote tumorigenesis. CYT387, originally described as a selective JAK inhibitor, is also a potent TBK/ IKKe inhibitor that uniquely disrupts a cytokine circuit involving CCL5, IL-6, and STAT3. The efficacy of CYT387-based treatment in murine Kras-driven lung cancer models uncovers a novel therapeutic approach for these refractory tumors with immediate translational implications. Cancer Discov; 4( 4); 452-65. (c) 2014 AACR.