Mutations in genes of the RAS family are preset on about 20% of human cancers, making RAS proteins prime potential targets for cancer therapy. Direct targeting of RAS proteins has not so far been productive, but two papers published in this issue offer the prospect of alternative targets in a signalling pathway downstream of RAS. Using a synthetic lethality RNAi screen, Barbie et al. identify TBK1 as a kinase in the NF-κB signalling pathway that is essential for the survival of KRAS-transformed cells. TBK1 induces anti-apoptotic signals and may be a therapeutic cancer target. And in an elegant mouse model for lung cancer driven by Kras mutation and loss of p53, Meylan et al. show that NF-κB signalling is activated by the concerted actions of these two alterations and required for tumour initiation and tumour maintenance. KRAS is a proto-oncogene that is mutated in a wide variety of human cancers. Although this makes KRAS an obvious candidate for the development of targeted therapies, it has so far remained refractory to this approach. Systematic RNA interference is now used to detect synthetic lethal partners of oncogenic KRAS, revealing that TBK1 and NF-κB signalling are essential in KRAS mutant tumours. This may provide an alternative approach for targeting KRAS therapeutically. The proto-oncogene KRAS is mutated in a wide array of human cancers, most of which are aggressive and respond poorly to standard therapies. Although the identification of specific oncogenes has led to the development of clinically effective, molecularly targeted therapies in some cases, KRAS has remained refractory to this approach. A complementary strategy for targeting KRAS is to identify gene products that, when inhibited, result in cell death only in the presence of an oncogenic allele1,2. Here we have used systematic RNA interference to detect synthetic lethal partners of oncogenic KRAS and found that the non-canonical IκB kinase TBK1 was selectively essential in cells that contain mutant KRAS. Suppression of TBK1 induced apoptosis specifically in human cancer cell lines that depend on oncogenic KRAS expression. In these cells, TBK1 activated NF-κB anti-apoptotic signals involving c-Rel and BCL-XL (also known as BCL2L1) that were essential for survival, providing mechanistic insights into this synthetic lethal interaction. These observations indicate that TBK1 and NF-κB signalling are essential in KRAS mutant tumours, and establish a general approach for the rational identification of co-dependent pathways in cancer.

Systematic RNA interference reveals that oncogenic KRAS-driven cancers require TBK1