Abstract
TBK1 (TANK-binding kinase 1) is a noncanonical IκB protein kinase that phosphorylates and activates downstream targets such as IRF3 and c-Rel and, mediates NF-κB activation in cancer. Previous reports demonstrated synthetic lethality of TBK1 with mutant KRAS in non-small cell lung cancer (NSCLC); thus, TBK1 could be a novel target for treatment of KRAS-mutant NSCLC. Here, the effect of TBK1 on proliferation in a panel of cancer cells by both genetic and pharmacologic approaches was evaluated. In KRAS-mutant cancer cells, reduction of TBK1 activity by knockdown or treatment with TBK1 inhibitors did not correlate with reduced proliferation in a two-dimensional viability assay. Verification of target engagement via reduced phosphorylation of S386 of IRF3 (pIRF3(S386)) was difficult to assess in NSCLC cells due to low protein expression. However, several cell lines were identified with high pIRF3(S386) levels after screening a large panel of cell lines, many of which also harbor KRAS mutations. Specifically, a large subset of KRAS-mutant pancreatic cancer cell lines was uncovered with high constitutive pIRF3(S386) levels, which correlated with high levels of phosphorylated S172 of TBK1 (pTBK1(S172)). Finally, TBK1 inhibitors dose-dependently inhibited pIRF3(S386) in these cell lines, but this did not correlate with inhibition of cell growth. Taken together, these data demonstrate that the regulation of pathways important for cell proliferation in some NSCLC, pancreatic, and colorectal cell lines is not solely dependent on TBK1 activity. TBK1 has therapeutic potential under certain contexts and phosphorylation of its downstream target IRF3 is a biomarker of TBK1 activity.
Highlights
TBK1 (TANK-binding kinase 1) is a noncanonical IkB kinase, which shares 65% similarity to IKKe and is highly expressed in lung, breast, pancreatic, and colon cancers [1]
We evaluated the role of TBK1 in KRAS-mutant non–small cell lung cancer (NSCLC) cell lines further using both genetic and pharmacologic approaches
ShTBK1-T15 (30UTR), which showed a very strong level of TBK1 knockdown, had no impact on cell growth in both of these NSCLC cell lines as well as in 7 cell lines tested from pancreatic ductal adenocarcinoma cell lines (PDAC) and colorectal cancer cell line panels, including both KRAS-mutant (G12A, G12C, G12D, G12S, and Q61H) and KRAS-wt genotypic profiles (Table 1)
Summary
TBK1 (TANK-binding kinase 1) is a noncanonical IkB kinase, which shares 65% similarity to IKKe and is highly expressed in lung, breast, pancreatic, and colon cancers [1]. Besides its key role in innate immune response, increasing evidence indicates that the activation of TBK1 and its close homolog IKKe is associated with the development of human cancers [2,3,4,5,6,7,8,9,10]. TBK1 is an NF-kB–activating kinase, which is constitu-. Tively expressed in many normal tissues, including immune cells, brain, lungs, gastrointestinal tract, and reproductive organs [11, 12]. TBK1-deficent mice exhibit embryonic lethality due to widespread hepatic apoptosis [13, 14]
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