Abstract 3226: Efficacy of PD-1 - PD-L1 pathway disruptors in syngeneic models
Authors: Lagrange Anais , Boidot Romain , Hillairet de Boisferon Marc , Duchamp Olivier , Mirjolet Jean-François , Ghiringhelli François 
Published: July 2016

Abstract
PD-1 - PD-L1 pathway disruptors (e.g. nivolumab, pembrolizumab) are now being approved for treatment of patients with locally evolved or metastatic melanoma and advanced non-small cell lung cancer (NSCLC) who have progressed after first line platinum-based chemotherapy. These drugs have also antitumor efficacy in other tumor types (renal cell carcinoma, bladder, Hodgkin lymphoma, colorectal carcinoma with mismatch-repair deficiency ⋯). However, there is still needs to identify predictive biomarkers of response in order to select patients who will benefit from treatments. PD-L1 expression, mutation numbers, or mismatch repair (MMR) deficiencies were already demonstrated to influence response to PD-1 targeting therapies. However, they did not completely discriminate responders from non-responders or cut off levels are not yet precisely defined.
Syngenic models are one of the only experimental models to evaluate immune system targeting therapies. Eight mouse models (4T1, A20, B16-F10, CT-26, EMT-6, MBT-2, LLC and Renca) were tested for response to PD-1 or PD-L1 targeting antibodies. From them, 3 models were characterized as non-responder (i.e. 4T1, LLC and RenCa) while other 7 models were showing to be sensitive to PD-1 inhibitors. PD-L1 expression (using RT-qPCR, WB and flow cytometry) was analyzed on cell lines at baseline and after 24h incubation with IFNg. At baseline, there is no significant difference between responders and non-responders whatever the level of analysis (mRNA, total PD-L1 protein expression or cell surface PD-L1 expression). However, after incubation with IFNg, there is a trend to segregate between responders and non-responders. Increased level of PD-L1 at the cell surface was evidenced for responders. IFNg signaling pathway used interferon regulatory factors (IRFs). IRF1 have been demonstrated to be responsible for both constitutive PD-L1 expression and early induction of PD-L1 after IFNg stimulation. mRNA expression of IRF1, IRF3, IRF7 and IRF9 were analyzed at baseline and after 24h incubation with IFNg. At baseline or after IFNg stimulation, there is no significant difference for IRF3, IRF7 and IRF9 mRNA expression between responders and non-responders. However, IRF1 mRNA is less expressed at baseline in responders as compared to non-responders. Moreover, increase in IRF1 expression after IFNg stimulation is higher in responders when compared to non-responders, which correlates well with changes in PD-L1 cell surface expression after IFNg stimulation. The total number of genomic variations was also analyzed using whole exome sequencing. Responder cell lines have highest number of variations in comparison to non-responder cell lines.
In depth characterization of these syngeneic models will increase the understanding of how translatable are the results acquired from preclinical mouse studies.
Citation Format: Anais Lagrange, Romain Boidot, Marc Hillairet de Boisferon, Olivier Duchamp, Jean-François Mirjolet, François Ghiringhelli. Efficacy of PD-1 - PD-L1 pathway disruptors in syngeneic models. [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 3226.