Abstract
Low-Grade Serous Ovarian Cancer (LGSOC) is a distinct subtype of epithelial ovarian cancer (OC), accounting for 5-10% of Serous OC diagnoses and disproportionally affecting younger women. Effective treatment options are urgently required for LGSOC due to its poor response to standard of care chemotherapy and high recurrence rate. Recent studies report ~50% of LGSOC cases harbour mutations within the MAPK signalling pathway. While clinical trials with the MEK inhibitor Trametinib show promise, the majority of patients have few evidence-based treatment opportunities.
This project investigated the molecular landscape and functionality of the Human epidermal growth factor receptor (HER) family in a panel of LGSOC cell lines, due to their known ability to signal through MAPK. EGFR, HER2 and HER3 protein expression was quantified using western blot and immunofluorescent cytostaining alongside mRNA expression analysis. EGFR and HER3 protein expression were detected in 5/5 LGSOC cell lines examined. Low HER2 protein levels corroborated a degree of mutual exclusivity for ERBB2 and EGFR gene expression in LGSOC (p-value 0.052).
We investigated the functionality of EGFR in LGSOC cell lines by stimulation with EGF ligand and by inhibition using EGFR-targeting small-molecule inhibitors (SMIs). Time constraints permitted one assay. Whilst EGF stimulation increased proliferation in 1/3 LGSOC cell lines, proliferation remained highest in full serum. VOA4627 cells, chosen due to having the highest EGFR expression, were confirmed resistant to Trametinib (IC50 80nM). Sensitivity to Gefitinib (EGFR-selective) and Sapitinib (broad-spectrum HER-selective) were analysed alone and in combination with 80nM Trametinib. VOA4627 was sensitive to Gefitinib at higher doses (>0.5µM) and had slight synergy with Trametinib at ≥1µM. However, Sapitinib was ineffective in VOA4627 cells, alone and in combination with Trametinib.
LGSOC cell line morphology displayed low cell-cell cohesion as 2D monolayers, some appearing mesenchymal. Loss of CDH1 protein expression by immunofluorescent cytostaining was associated with mesenchymal presentation in VOA1056. This observation was consistent with CDH1 mRNA expression loss in LGSOC cell lines, revealing novel therapeutic opportunities to explore in LGSOC.
Our data suggests investigation of sensitivity to SMIs is warranted, in parallel with studies to define functional pathways stimulated by receptor tyrosine kinases (RTKs) to define more robust therapeutic combinations.