Abstract C105: Gain of function cDNA screen identifies SIK3 activation as a therapeutic strategy for STK11 mutant cancer

Abstract STK11 (also known as LKB1) is a master serine/threonine kinase that regulates a diverse array of cellular functions via phosphorylation of downstream kinases. STK11 is frequently mutated in human cancers, and we hypothesized that reactivation of its downstream effectors could reverse the tumor suppressive role of STK11. Using pooled gain-of-function cDNA screens of known STK11 substrates in a 3D cell culture format, we identified the constitutive activation of the salt-inducible kinases (SIKs) as the top effector molecules driving the progression of STK11 mutant cancers. Follow-up in vivo minipool screens, focusing on the SIK1/2/3 kinases, confirmed that phosphorylation mimetic mutations, which model constitutive activation of the SIK kinases, produced dropout phenotypes comparable to STK11 re-expression. Single gene validation studies further confirmed that expression of a kinase activation mutant form of SIK3 was sufficient to significantly suppress tumor growth of the STK11- mutant A549 xenograft model. In contrast, expression of kinase-dead SIK3 mutant cDNA enhanced tumor growth. Mechanically, tumor RNAseq analysis revealed that genetic activation of SIK3 mimicked the transcriptional effects of STK11 re-expression. Altogether, our functional genomics screen and genetic validation highlight SIK3 activation as a promising therapeutic strategy for STK11-mutant cancers. Citation Format: Teng Teng, James Tepper, Silvia Fenoglio, Samuel R. Meier, Ashley H. Choi, Shangtao Liu, Binzhang Shen, Douglas A. Whittington, Yi Yu, Xuewen Pan, Jannik N. Anderson. Gain of function cDNA screen identifies SIK3 activation as a therapeutic strategy for STK11 mutant cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr C105.