Abstract TMIM-079: INHIBITION OF TUMOR MICROENVIRONMENT CYTOKINE SIGNALING SENSITIZES OVARIAN CANCER CELLS TO ANTIESTROGEN THERAPY
Authors: Tan Lijun , Prince Victoria , Erba Jake , McLean Karen 
Published: June 2021

OBJECTIVE: Ovarian cancer tumor cell estrogen receptor (ER) expression alone is a poor predictor of response to antiestrogen therapy and some patients with ER-negative cancers still demonstrate clinical response to therapy, suggesting modifiers of response that can potentially be targeted to improve outcomes. We have demonstrated that IL6 and LIF cytokine signaling from carcinoma-associated mesenchymal stem cells (CA-MSC) in the tumor microenvironment promotes tumorigenesis and hypothesize that this cytokine signaling also engages in crosstalk with estrogen signaling pathways. Furthermore, we propose that blocking both cytokine and estrogen signaling will improve anti-cancer effects.

METHODS: High grade serous ovarian cancer (HGSOC) cell lines were treated with CA-MSC conditioned media or recombinant cytokines IL6 and/or LIF. Ovarian cancer cells were then assessed for (i) activation of estrogen response element (ERE)-driven luciferase reporter constructs (SABiosciences), (ii) changes in levels of reported ER target genes by qRT-PCR, and (iii) ER-alpha expression levels by immunoblotting. ER-alpha expression in CA-MSC was assessed by immunoblotting. We then assessed the effect of treating cells with ruxolitinib, the FDA-approved inhibitor of the Janus-associated kinase (JAK) protein that is downstream of IL6/LIF signaling. Tumor cells in the absence or presence of CA-MSC conditioned media were treated with ruxolitinib without or with anti-estrogen therapy. Anti-estrogens studied include the selective estrogen receptor modulator tamoxifen, the selective estrogen receptor downregulator fulvestrant, and the aromatase inhibitor letrozole. Following drug treatment, cell viability was assessed with the MTT assay and colony forming assays, and signaling cascade protein expression determined by immunoblotting. Synergy was calculated by the Chou-Talalay method using CompuSyn software.

RESULTS: IL6 and LIF induce ERE reporter construct activation in HGSOC cell lines to a similar extent as control estradiol treatment and increase the expression of known ER target genes. Additionally, IL6 and LIF increase ER-alpha levels in HGSOC cell lines as detected by immunoblotting. The treatment of HGSOC cells with both ruxolitinib and antiestrogen therapy results in a synergistic decrease in cell viability. Variable effects are noted depending on the specific antiestrogen used and the cell line studied, indicating subtle mechanistic differences between cell lines. CA-MSC express ER-alpha, suggesting antiestrogens may exert their effects at least in part through changes in stromal signaling. Further studies are underway, including characterization of effects in both primary tumor cells and animal models.

CONCLUSIONS: IL6 and LIF signaling from the tumor microenvironment promotes ovarian cancer cell estrogen signaling. The combination of inhibiting IL6/LIF signaling with ruxolitinib and antiestrogen therapy results in a synergistic decrease in ovarian cancer tumor cell viability. Given the clinical tolerability of antiestrogen therapy with a low side effect profile, strategies such as ruxolitinib treatment to sensitize tumor cells to antiestrogens are an exciting area that warrant further study.

Citation Format: Lijun Tan, Victoria Prince, Jake Erba, Karen McLean. INHIBITION OF TUMOR MICROENVIRONMENT CYTOKINE SIGNALING SENSITIZES OVARIAN CANCER CELLS TO ANTIESTROGEN THERAPY [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-079.