Investigator
University Of Pittsburgh
Targeting Therapeutic Resistance and Multinucleate Giant Cells in CCNE1-Amplified HR-Proficient Ovarian Cancer
Abstract Approximately 20% of high-grade serous ovarian cancers (HGSOC) have CCNE1 amplification. CCNE1-amplified tumors are homologous recombination (HR) proficient and resistant to standard therapies. Therapy resistance is associated with increased numbers of polyploid giant cancer cells (PGCC). We sought to identify new therapeutic approaches for patients with CCNE1-amplified tumors. Using TCGA data, we find that the mTOR, HR, and DNA checkpoint pathways are enriched in CCNE1-amplified ovarian cancers. Furthermore, Interactome Mapping Analysis linked the mTOR activity with upregulation of HR and DNA checkpoint pathways. Indeed, we find that mTOR inhibitors (mTORi) downregulate HR/checkpoint genes in CCNE1-amplified tumors. As CCNE1-amplified tumors are dependent on the HR pathway for viability, mTORi proved selectively effective in CCNE1-amplified tumors. Similarly, via downregulation of HR genes, mTORi increased CCNE1-amplifed HGSOC response to PARPi. In contrast, overexpression of HR/checkpoint proteins (RAD51 or ATR), induced resistance to mTORi. In vivo, mTORi alone potently reduced CCNE1-amplified tumor growth and the combination of mTORi and PARPi increased response and tumor eradication. Tumors treated with mTORi demonstrated a significant reduction in ALDH+ PGCCs. Finally, as a proof of principle, we identified three patients with CCNE1 amplified tumors who were treated with an mTORi. All three obtained clinical benefits from the therapy. Our studies and clinical experience indicate mTORi are a potential therapeutic approach for patients with CCNE1-amplified tumors.
EGFL6 is a novel HER3 ligand, inducing HER3/integrin heterodimers to induce pERK centrosomal deposition and therapeutic resistance
EGF-like domain multiple-6 (EGFL6) is a secreted tumor growth/migration factor linked with poor outcomes in many tumor types. While EGFL6 is known to signal, in part, via its integrin-binding RGD domain, little else is known about EGFL6 receptors. We evaluated putative EGFL6 receptors and found that EGFL6 treatment of ovarian cancer cells leads to both transient phosphorylation of EGFR and prolonged phosphorylation of HER2 and HER3 and subsequent phosphorylation of ERK (pERK). We found that EGFL6 directly binds HER3. However, EGFL6-driven prolonged activation of HER3 is dependent on an intact EGFL6 integrin-binding RGD domain. Immunoprecipitation and proximity ligation assays confirmed that EGFL6 treatment of cancer cells induces HER2/3-integrin-β3 heterocomplexes. Suggesting EGFL6 could play a role in resistance to HER targeting therapies, EGFL6 is upregulated in EGFR/HER receptor inhibitor-resistant cells, and EGFL6 treatment increases resistance to EGFR/HER inhibitors in vitro. Interestingly, we found that, in EGFL6-treated ovarian cancer cells undergoing mitosis, pERK localizes to the centrosome. Both EGFL6-neutralizing antibodies and HER protein-targeted inhibitors resulted in aberrant pERK centrosomal localization with associated altered mitotic spindle alignment and mitotic catastrophe. Furthermore, combination anti-EGFL6 therapy with the pan-EGFR receptor inhibitor neratinib, compared to either therapy alone, led to an increase in aberrant pERK localization and cancer cell death in vitro and significant restricted tumor growth in vivo. Combined, our data suggests that EGFL6 is a new ligand for HER3 and that dual targeting of the EGFL6/HER signaling axis, via altered pERK localization, may be an effective therapeutic strategy in ovarian cancer. SIGNIFICANCE: This work reveals that EGFL6 is a previously unrecognized ligand for HER3 which can increase resistance to HER family-targeted therapy. We also reveal a novel function of pERK downstream of pHER3 at the centrosome in mitosis. Importantly, we show that EGFL6 is an important therapeutic target to enhance the efficacy of EGFR/HER-targeted therapy.
