Abstract 2511: ErbB2 receptor levels in patient-derived spheroids vs. solid tumors reveal high ovarian cancer cell plasticity

Although ErbB receptors are often expressed in primary ovarian tumors, targeted therapy against these receptors has been minimally successful. Since therapies typically target EGFR or ErbB2 that are present in 25-35% of cases, variability in receptor expression among patients may mask effects. ErbB3 and ErbB4 are more ubiquitous, but targeting these receptors is less common. The timing of treatment with targeted therapies may also be crucial. Clinical trials test these therapies in recurrent platinum-resistant disease, but they might be more effective at preventing recurrence after surgery by eliminating free-floating cancer spheroids that give rise to new solid tumors. Since cancer spheroids are not routinely characterized in ovarian cancer, we isolated spheroids from the malignant ascites of 22 ovarian cancer patients undergoing cytoreductive surgery and analyzed their ErbB receptor signatures by immunofluorescence. Surprisingly, cancer spheroids from nearly all samples (85%) were positive for ErbB2. This differs markedly from the 35% of primary ovarian cancer tumors that were ErbB2 positive in our previous study. NSG mice injected intraperitoneally with cancer spheroids to model disseminated disease developed a combination of solid tumors and malignant ascites. Spheroids obtained from these patient-derived xenograft (PDX) models were also ErbB2 positive. However, solid tumors from the PDX models showed little to no ErbB2 labeling. This altered receptor expression demonstrates the plasticity of ovarian cancer cells as they transition from free-floating spheroids to solid tumors. In the ErbB receptor family, this change may be ErbB2-specific. Analysis of ErbB3 receptor status found no change between spheroids and solid tumors. One implication of this finding is that ErbB2 targeted therapies may be effective in ovarian cancer cases where patients are optimally debulked with only microscopic residual disease. Because spheroids are ErbB2 positive, while solid tumors tend to be ErbB4 and/or ErbB3 positive, we explored the effect of a pan-ErbB inhibitor, afatinib, on tumor burden in our mouse models. Cells were inoculated into the peritoneal cavity and tumors were allowed to develop before treatment. To measure tumor burden in PDX models, anti-HLA-ABC antibody was conjugated to CF750 near-infrared dye and injected IP 24 hours prior to imaging. Tumor burden of fluorescently labeled tumors was measured on the IVIS Spectrum using fluorescence tomography. A decrease in tumor burden and a reduction in ascites was seen in groups treated with afatinib or paclitaxel alone, but particularly with the combined treatment of afatinib and paclitaxel. Supplementing current first-line treatments with ErbB targeted therapies could potentially destroy chemoresistant cells while limiting increased toxicity. Citation Format: Mara P. Steinkamp, Ashley Remy, Irina Lagutina, Carolyn Y. Muller, Diane S. Lidke, Bridget S. Wilson. ErbB2 receptor levels in patient-derived spheroids vs. solid tumors reveal high ovarian cancer cell plasticity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2511.