Online

Lenahan, Sean Michael

Cellular, Molecular, and Biomedical Sciences Graduate Program

2023

Ph. D.

The high mortality rate for lung cancer is largely attributed to the fact that nearly half of patients present at an advanced stage, resulting in a 5-year relative survival rate of 7%. While treatment strategies for advanced stage lung cancer patients have led to successful tumor regression and prolonged survival for subsets of patients, many remain unresponsive leading to a poor prognosis. KRAS-driven lung adenocarcinoma (LUAD) patients with concomitant loss of Serine/Threonine Kinase 11 (STK11) exhibit a dramatic decrease in therapeutic efficacy and lowered overall survival relative to tumors harboring intact STK11. Clinical observations associate STK11 loss in KRAS-driven LUAD with lack of response to immune checkpoint inhibitors (ICIs), a first line treatment for advance stage LUAD. However, the tumor-intrinsic molecular mechanisms underlying this correlation remain ill-defined. The work presented here characterizes STK11-dependent pathways that regulate tumor-intrinsic cytokine expression with the goal of identifying targetable vulnerabilities in KRAS-driven STK11 null LUAD. Using human KRAS-driven LUAD cell lines, our work demonstrates that STK11 loss results in altered cytokine expression upon glutamine depletion. Pathway enrichment analyses suggest the altered cytokine transcript levels downstream of STK11 loss are mediated by the Hippo and NF-[kappa]B signaling networks. Both pathways are reported to regulate expression of cytokines involved with immune suppression in the tumor microenvironment (TME). Further, these pathways have previously been linked to STK11-mediated negative regulation. To explore whether targeting these pathways altered cytokine expression in STK11-null KRAS-driven LUAD cells, we attempted to disrupt each network utilizing pharmacologic inhibition and genetic ablation. Intriguingly, perturbations of the Hippo pathway in STK11-null KRAS-driven LUAD cell lines via inhibition or ablation of YAP1 successfully blunted expression of target cytokines, restoring a transcriptional profile similar to KRAS-driven LUADs with intact STK11 alleles. Targeting the NF-[kappa]B pathway resulted in partial transcriptional profile restoration, and in combination with YAP1 inhibition, led to synergistic suppression of critical cytokines, notably CXCL8, postulated to promote immune evasion and therapeutic resistance. To determine whether our cell culture-based observations regarding STK11-dependent transcriptional impacts held in vivo we development an inducible KRAS-driven LUAD mouse model with conditional STK11 alleles. As expected, STK11-loss was associated with differences in tumor progression, tumor-intrinsic and serum cytokine levels, TME immune cell composition, and enhanced onset of cancer cachexia, all contributing to decreased overall survival. Analogous to our human cell line data, transcriptomic analyses revealed a STK11-loss dependent dysregulation of the Hippo and NF- [kappa]B signaling networks. Together, our data support the conceptual targeting of either the Hippo or NF-[kappa]B pathways as an avenue to restore STK11-loss dependent transcriptional alterations in KRAS-driven LUAD. Furthermore, we speculate that by restoring the transcriptional profiles of STK11-null tumors to mimic those of STK11 WT tumors we could potentially restore effectiveness of ICIs.