Abstract 2620: Selecting the right chemotherapy partner for checkpoint inhibitors: an in vivo comparison of different drugs and dosages
Authors: Orecchioni Stefania , Talarico Giovanna , Labanca Valentina , Mancuso Patrizia , Bertolini Francesco 
Published: July 2017

Abstract
Anti-PD-1 and anti-PD-L1 monoclonal antibodies (checkpoint inhibitors, CIs) have shown a remarkable clinical activity in a variety of types of solid cancers and hematological malignancies. However, complete and/or long-lasting clinical responses have been observed only in a minority of patients. The clinical response to CIs depends on a complex balance between tumor-associated and circulating CD3+CD4+ and CD3+CD8+ T, regulatory, B, NK and myeloid/suppressor cell subsets. We have used immunocompetent mice to generate orthotopic models of breast cancer (BC, injecting 4T1 triple negative murine cells) and of non-Hodgkin’s lymphoma (NHL, injecting A20 murine malignant B cells). In these models and in cancer-free mice we studied by 10-color flow cytometry the effect of different doses of 3 widely-used, orally-active chemotherapy drugs (cyclophosphamide, CTX; capecitabine, 5FU; and vinorelbine, VNR) over a variety of immune cell subsets including CD3+CD4+ and CD3+CD8+ T cells, CD56+ NKs, CD19+ B cells, CD3+CD4+CD25++CD127low/neg Tregs, GR1-CD11b+CD11c+ monocytes, SSClowCD11b+GR1+ total Myeloid-Derived Suppressor Cells (t-MDSC, monocytic and polymorphonuclear), SSChighCD11b+GR1+ granulocytes and CD11c+CD11b-GR1- antigen-presenting cells (APCs). Chemotherapy drugs were given alone or in combination with murine anti-PD-1 or anti PD-L1 monoclonal antibodies (Bioxcell clones J43 and 10F.9G2, respectively). For every type of chemotherapy drugs, we selected 3 dosages representative of clinical low-dose metronomic (LDM), medium (M), or maximum tolerable (MT) dosages. Mice were treated for 3 weeks, blood cell subsets were measured weekly. CTX and 5FU, at M and MT dosages, reduced significantly the number of T, B, and NK cells and of t-MDSC. CTX, but not 5FU, reduced Tregs and APCs. 5FU, but not CTX, reduced t-MDSC. At variance, VNR at LDM, M and MT doses did not reduce T, NK and t-MDSC. At M and MT doses, VNR reduced Tregs, B and SSChighCD11b+GR1+ granulocytes. Considering these data, we designed preclinical protocols in both BC and NHL models associating CTX, 5FU and VNR with CIs. Cumulative and unbearable toxicities were observed in mice treated with 2 or more chemotherapy drugs at MT doses plus CIs. In both models, anti-PD-L1 plus M or LDM combinatory doses of CTX and VNR were the most effective therapies for reducing local and metastatic neoplastic growth. Our data indicate that chemotherapy drugs have relevant effects on immune cell subsets involved in the anti-neoplastic activity of CIs, and that the type and the dosage of chemotherapy are crucial to obtain synergy with CIs. Further studies are ongoing to find the right chemotherapy/CI balance to a) maintain an adequate T, APC and NK cell activity, b) reduce Tregs and myeloid suppressors, c) avoid toxicity, and d) target cancer cells.
Citation Format: Stefania Orecchioni, Giovanna Talarico, Valentina Labanca, Patrizia Mancuso, Francesco Bertolini. Selecting the right chemotherapy partner for checkpoint inhibitors: an in vivo comparison of different drugs and dosages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2620. doi:10.1158/1538-7445.AM2017-2620