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

Abstract

Although the roles of mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3K) signaling in KRAS-driven tumorigenesis are well established, KRAS activates additional pathways required for tumor maintenance, inhibition of which are likely to be necessary for effective KRAS-directed therapy. Here we show that the IKK-related kinases TBK1 and IKKε promote KRAS-driven tumorigenesis by regulating autocrine CCL5 and IL-6 and identify CYT387 as a potent JAK/TBK1/IKKε inhibitor. CYT387 treatment ablates RAS-associated cytokine signaling and impairs Kras-driven murine lung cancer growth. Combined CYT387 and MEK inhibitor therapy induces regression of aggressive murine lung adenocarcinomas driven by Kras mutation and p53 loss. These observations reveal that TBK1/IKKε promote tumor survival by activating CCL5 and IL-6 and identify concurrent inhibition of TBK1/IKKε, JAK, and MEK signaling as an effective approach to inhibit the actions of oncogenic KRAS.

Targeting cytokine networks in KRAS-driven tumorigenesis

“…The direct requirement for NF-kB signaling in KRAS-driven tumorigenesis has also been solidified by multiple recent studies in oncogenic Kras lung genetically engineered mouse models [13,14]. Mechanistically, IL-1 promotes activation of the noncanonical IkB kinases (IKKs) TBK1/IKKe downstream of oncogenic KRAS [10], enhancing the expression of both IL-6 and CCL5. IL-1 also engages canonical IKK signaling, likely contributing to the expression of other cytokines and chemokines that foster KRAS-induced tumorigenesis.…”

“…IL-8 attracts inflammatory and endothelial cells expressing its receptor CXCR2, and blockade of this signaling also impairs Kras-induced lung tumorigenesis in mice [4,8]. While multiple other cytokines and chemokines have been incriminated in tumor-promoting inflammation, recent work has uncovered a major role for the chemokine CCL5 [9,10]. Secretion of CCL5 in oncogenic RAS-expressing cells is enhanced by interactions with the tumor microenvironment and acts in concert with IL-6 to promote RAS-mediated transformation, migration and metastatic behavior.…”

“…STAT3 and NF-kB not only cooperate as transcription factors, but STAT3-activating cytokines such as IL-6 are also NF-kB target genes. KRAS directly engages TBK1 via its downstream effector RALB, which further promotes NF-kB activation and drives CCL5 and IL-6 production together with IKKe [10,15,16]. IL-6 and STAT3 signaling also stimulate the expression of IKKe, unique among family members as an inducible IKK [17], which reinforces NF-kB activation and cytokine signaling downstream of KRAS.…”

“…In this regard, drugs that suppress signaling more broadly by targeting IKK ubiquitination [18], or by inhibiting multiple kinases at once, may be more active than selective inhibitors. Indeed, BAY11-7082, which inhibits the E3 ligase linear ubiquitin assembly complex that activates both canonical and non-canonical IKKs [14,18], and momelotinib (previously known as CYT387), a multitargeted JAK/TBK1/ IKKe kinase inhibitor [10], are each potent suppressors of cytokine signaling and exhibit single agent activity in mouse models of Kras-driven lung cancer. Although treatment regimens that included either inhibitor resulted in robust activity and prolonged responses in aggressive Kras-p53 mutated murine lung cancer, resistance was found to emerge, highlighting further the ability of tumors to compensate through potential bypass pathways that reengage cytokine expression or render them cytokine-independent.…”

“…Accelerated pharmacologic development of a variety of JAK inhibitors has been motivated in part by the discovery of activating JAK2 mutations in myeloproliferative neoplasms [19], and indeed the JAK1/2 inhibitor ruxolitinib is US FDA approved for the treatment of myelofibrosis, Momelotinib is currently being compared with ruxolitinib in Phase III studies for myelofibrosis and may even show superior activity in terms of reducing transfusion dependence [20]. As described above, the impressive activity of momelotinib in murine Kras-driven lung cancer, particularly when combined with MEK inhibition [10], suggests that incorporating the potent suppression of cytokine networks via multitargeted JAK/TBK1/IKKe inhibition holds significant promise for these treatment refractory solid tumors. Clinical trials utilizing ruxolitinib or momelotinib together with cytotoxic chemotherapy or other targeted agents will help to answer this question and define certain subpopulations of KRAS mutated tumors that may benefit the most.…”