Abstract A103: Cell-autonomous activation of the interferon/STAT1 pathway in response to genotoxic treatment
Authors: Gaston Julie , Cheradame Laura , Legrier Marie-Emmanuelle , Déas Olivier , Lassalle Myriam , Le Ven Enora , Judde Jean-Gabriel , Goffin Vincent , Cairo Stefano 
Published: May 2016

Abstract
Identification of the mechanisms of tumor resistance remains an unmet need in oncology. Among the reasons for this challenging issue is the lack of reliable preclinical models that represent inter and intra-patient tumor heterogeneity observed in the clinic. Patient-derived xenografts (PDXs) consist in grafting human cancer samples into immunocompromised mice directly after patient surgery. Since each PDX faithfully recapitulates patient's tumor genetics, these preclinical models well represent the intrinsic heterogeneity of cancer. We took advantage of the large collection of breast cancer PDXs held at XenTech to address the mechanisms of tumor response to treatment vs tumor recurrence. Upon receiving chemotherapy, some breast cancer PDXs (the 'responders') undergo tumor shrinkage, whereas others continue to grow (the 'non-responders'). Comparative transcriptomic profiling of laser-microdissected cancer cells showed that the reduction of tumor volume in responders was closely associated to the over-expression of genes related to the interferon (IFN)/signal transducer and activator of transcription 1 (STAT1) pathway.
Using mouse versus human cytokine arrays we observed that activation of this pathway was associated with the secretion of ligands of human origin (cancer) rather than with ligands secreted from the nude mice residual immune system. Next, we screened a large number of cell lines to identify in vitro cell models able to mimic cell-autonomous induction of the IFN/STAT1 signature after genotoxic treatment. Both an immortalized cell line and a primary culture dissociated from a responder PDX were shown to activate the IFN/STAT1 pathway and to express the cognate gene signature after treatment with mafosfamide (the active metabolite of cyclophosphamide used in the clinic). Expression analyses (qPCR) confirmed induction of IFN type I elements by cell models. Conditioned medium collected from mafosfamide-treated cancer cells was able to activate luciferase reporter genes harboring ISRE (interferon stimulated response elements) and GAS (gamma interferon activated sequence) response elements, meaning that active ligands of the IFN/STAT1 pathways were secreted. Accordingly, STAT1 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 the over-expression of the IFN/STAT1 pathway may ultimately have protective effect on cancer cell viability.
In conclusion, this study supports that cell-autonomous activation of the IFN/STAT1 pathway is a surrogate biomarker of initial tumor shrinkage in response to genotoxics, and suggests that it may play a role in tumor resistance to treatment.
Citation Format: Julie Gaston, Laura Cheradame, Marie-Emmanuelle Legrier, Olivier Déas, Myriam Lassalle, Enora Le Ven, Jean-Gabriel Judde, Vincent Goffin, Stefano Cairo. Cell-autonomous activation of the interferon/STAT1 pathway in response to genotoxic treatment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A103.