Abstract 2138: Functional evaluation of interferon/STAT1 pathway activation in response to genotoxic treatment
Authors: Gaston Julie , Cheradame Laura , Legrier Marie-Emmanuelle , Deas Olivier , Judde Jean Gabriel , Goffin Vincent , Cairo Stefano 
Published: July 2016

Abstract
Triple negative breast cancer (TNBC) accounts for approximately 15-25% of breast cancers at diagnosis, and is one of the most aggressive subtypes, with around 70% of patients that live free of disease 5 years post-diagnosis. One of the most reliable predictive markers of patient outcome is the pathological complete response (pCR), with no tumor cells detectable at histopathological level after neoadjuvant chemotherapy.
As pCR is observed in only about 20-30% of TNBC, it is mandatory to identify new therapeutic options to improve pCR rate upon neoadjuvant chemotherapy. The mechanisms of tumor resistance remain an unmet need in oncology. In a recent study, we used our breast cancer PDXs collection to tackle this question, and address the mechanisms of tumor response to treatment vs tumor recurrence. To do this we analyzed the gene expression profile of laser-microdissected residual tumor nodules interspersed in the murine stroma upon very efficient tumor response to Adriamycin/Cyclophosphamide (AC). When doing so, we identified several genes of the IFN/STAT1 pathway that were strongly over-expressed when compared to pre-treatment tumors. In this study, we investigated the mechanisms leading to IFN/STAT1 pathway activation following chemotherapy in tumor cells and we evaluated the functional involvement of the IFN/STAT1 signature as a whole or at single target gene level in residual tumor cell resistance to chemotherapy after genotoxic treatment.
To this aim, we set up an ex-vivo/in vitro assay to mimic induction of the IFN/STAT1 signature in tumor cells after genotoxic treatment. We identified cell lines and primary cultures from a patient-derived xenograft (PDX) that mimicked the in vivo situation, as only the cell lines that respond to genotoxic stress in vivo activated IFN/STAT1 pathway in response to genotoxic treatment in vitro. When exposed to conditioned medium collected from mafosfamide-treated cancer cells, these cells activated luciferase reporter genes harboring ISRE (interferon stimulated response elements) and GAS (gamma interferon activated sequence) response elements, suggesting active ligands of the IFN/STAT1 pathways were secreted. STAT1 or IFNAR1 gene silencing (siRNA) resulted in markedly attenuated gene signature expression after mafosfamide treatment. The addition of conditioned medium significantly reduced mafosfamide-induced cancer cell death suggesting that IFN/STAT1-related genes over-expression may ultimately have protective effect on cancer cell viability. Accordingly, the inhibition of several genes of the IFN/STAT pathway, or DNA sensors acting upstream, increased cell mortality when combined with genotoxic treatment and delayed colony formation.
Overall, this study supports the functional implication of IFN/STAT1-related genes in tumor resistance to genotoxic treatment.
Citation Format: Julie Gaston, Laura Cheradame, Marie-Emmanuelle Legrier, Olivier Deas, Jean Gabriel Judde, Vincent Goffin, Stefano Cairo. Functional evaluation of interferon/STAT1 pathway activation in response to genotoxic treatment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2138.