Abstract P146: Loss of HS2ST1 cooperates with MAPK inhibition to impair growth of mesenchymal KRAS mutant NSCLC
Authors: Ahronian Leanne G. , Fenoglio Silvia , Das Nikitha , Aird Daniel , Guerin David , Whittington Douglas , Jahic Haris , Brophy Erin , McCarren Patrick , McMillan Brian , Tepper James , Mentzer Michaela , Li Fang , Zhang Hongxiang , Pan Xuewen , Maxwell John , Andersen Jannik , Huang Alan , Sjin Robert Tjin Tham 
Published: December 2021

Abstract
Activating mutations in the KRAS oncogene occur in approximately 30% of non-small cell lung cancers (NSCLC). Hence, multiple therapeutic strategies have been explored to block RAS including inhibition of downstream effector molecules in the MAPK pathway and direct pharmacological inhibition of the KRAS G12C mutant protein. However, inhibition of the RAS-RAF-MEK-ERK cascade with MEK inhibitor monotherapy has been insufficient to induce robust clinical responses. To identify novel drug targets that are synthetic lethal with MEK inhibition, CRISPR screens were conducted in multiple KRAS mutant NSCLC cell lines with or without trametinib treatment. Consistent with previous reports, several known MAPK-pathway genes, including KRAS, MEK, ERK, and FGFR1, were identified as top sensitizers validating our functional genomics approach. Interestingly, several novel targets were ranked among these top hits, including several members of the heparan sulfate biosynthesis pathway, such as the heparan sulfate 2-O-sulfotransferase (HS2ST1). In cells, HS2ST1 is responsible for transferring a sulfate from PAPS (3-phosphoadenosine-5’-phosphosulfate) to the 2-O position of a growing heparan sulfate chain. These chains partner with receptor tyrosine kinases at the cell surface to facilitate their interactions with growth factors. In this case, the interaction of FGF2 and FGFR1 has been shown to require HS2ST1-mediated 2-O sulfation, making HS2ST1 a novel druggable target in a well-validated FGFR-MAPK adaptive signaling axis. Here, we report that HS2ST1 is required for the feedback activation of the MAPK pathway that occurs downstream and in response to MEK or KRAS G12C inhibition via genetic validations studies. Knockout of HS2ST1 results in reduced feedback activation via FGFR1 and reduced MAPK pathway signaling. This reduced signaling leads to a reduction in cell growth in the presence of a MEK inhibitor, such as trametinib or selumetinib, or a KRAS G12C inhibitor like sotorasib. Our screen results reiterate the findings of others which indicate that effective MAPK suppression is key to inhibiting KRAS-mutant NSCLC cell growth. We find that HS2ST1 blockade would aid in maintaining the suppression of MAPK pathway signaling in KRAS-mutant NSCLC, leading to reduced cell viability and growth suppression. While others have described pairing receptor tyrosine kinase inhibitors with MAPK pathway inhibitors, this would be a novel approach to reducing upstream MAPK pathway feedback that may lead to reduced toxicity in patients.
Citation Format: Leanne G. Ahronian, Silvia Fenoglio, Nikitha Das, Daniel Aird, David Guerin, Douglas Whittington, Haris Jahic, Erin Brophy, Patrick McCarren, Brian McMillan, James Tepper, Michaela Mentzer, Fang Li, Hongxiang Zhang, Xuewen Pan, John Maxwell, Jannik Andersen, Alan Huang, Robert Tjin Tham Sjin. Loss of HS2ST1 cooperates with MAPK inhibition to impair growth of mesenchymal KRAS mutant NSCLC [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P146.