Targeting Neurofibromin 1 Inactivation in High-Grade Serous Ovarian Carcinoma
Creators: Yang, Rui Zhe
Publisher: name: University of Alberta Library
Year: 2024

<pre><code>Annually, around 300,000 new cases of ovarian cancer are diagnosed worldwide, with 200,000 deaths. The most common and most deadly form of ovarian cancer, high-grade serous carcinoma (HGSC), accounts for the great majority of those deaths. HGSC almost always presents with peritoneal disease spread that requires the use of systemic therapy in addition to surgical debulking. Even though the majority of HGSC shows initial response to standard-of-care platinum/taxane-based chemotherapy, the disease inevitably progresses over time and there are no effective second-line treatment options. The advent of PARP inhibitor as maintenance therapy has significantly improved progression-free survival as well as overall survival in the half of patients who have homologous recombination deficient (HRD) HGSC. However, the remaining half of patients who have homologous recombination proficient (HRP) HGSC benefit little to none from PARP inhibitor and do not have efficacious therapy options when their disease progresses on platinum/taxane-based chemotherapy. This project seeks to identify precision therapy for the subset patients with HRP HSGC. A potentially targetable molecular alteration is the genomic inactivation of NF1 that is known to occur in a subset of HGSC. Neurofibromin 1, encoded by NF1, is a tumor suppressor protein that suppresses the Ras protein, an oncogenic driver of many cancers. We hypothesize that NF1 loss in HGSC results in the activation of the Ras pathway as well as other pathways that may be targetable by existing pharmacologic inhibitor(s), driving tumor survival and proliferation. Thus, the aims of this project are to: 1) Survey NF1 inactivation/deficiency in HGSC, 2) Identify driver pathways that are activated by NF1 loss, and 3) Selectively target those pathways with inhibitors to identify potential therapeutics to use for HGSC with NF1 loss. Using CRISPR technology, we generated NF1 knockout and wild-type control models from two established HGSC cell lines that included OVCAR3 (a BRCA1/2 wild-type HRP HGSC) and KURAMOCHI (a BRCA2-mutated HRD HGSC). The engineered models were tumorigenic as mouse xenograft models. Through whole transcriptome sequencing-based gene expression profiling and phospho-protein (both global and receptor tyrosine kinase (RTK)-focused) analyses, we have identified that the Ras pathway and certain RTKs are activated in NF1 knockout HGSC xenografted tumors. The KRAS pathway is upregulated in NF1 knockout OVCAR3 cells and cell line-derived xenografts compared to their wild-type counterparts, indicating that targeting both downstream signaling proteins such as MEK and upstream RTKs such as EGFR (epidermal growth factor receptor) may represent a reasonable therapeutic strategy. In the in vitro setting, NF1 knockout OVCAR3 showed greater sensitivity to trametinib (a MEK inhibitor) when compared to wild-type control and parental OVCAR3 cells, with a sensitivity that was comparable to two naturally occurring NF1-deficient BRCA1/2 wild-type HGSC cell lines (FUOV1 and SNU119). In contrast, NF1 knockout KURAMOCHI appeared to be similarly resistant to trametinib when compared to wild-type control and parental KURAMOCHI cells. Combined use of trametinib and erlotinib (EGFR inhibitor) showed additive inhibitory effects on cell viability in OVCAR3 NF1 knockout cells. These findings overall show that NF1-deficient BRCA1/2 wild-type HGSC depends on KRAS pathway activation for cell growth and is sensitive to MEK inhibition. MEK inhibition may be combined with EGFR inhibition if a lower dose of MEK inhibitor is required to reduce toxicity. Validation of these results in in vivo models is needed to establish more robust preclinical evidence. The role of MEK inhibition in the NF1-deficient BRCA1/2 wild-type molecular setting appears to be promising but it warrants further investigation.
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