Abstract B08: C-C chemokine receptor 4 (CCR4) antagonism enhances the effectiveness of checkpoint Inhibition in mouse tumor models
Authors: Li Shijie “Chris” , Campbell James J. , Ertl Linda S. , Miao Zhenhua , Chhina Vicky , Kumamoto Alice , Yau Simon , Dang Ton , Zhang Penglie , Schall Thomas J. , Singh Rajinder 
Published: June 2021

Abstract
Introduction: Chemokines and their receptors influence many of the hallmark processes in cancer: they act not only on infiltrating leukocytes, but also on fibroblasts, endothelial cells, and directly on some types of tumor cells. C-C chemokine receptor 4 (CCR4) and its ligands have been found to be highly expressed in multiple types of human tumors and are associated with poor prognosis. CCR4 antagonism has been demonstrated to reduce tumor growth in various mouse tumor models. Here we assess small-molecule inhibition of CCR4 as a therapeutic agent to potentiate the effects of checkpoint inhibitors in the CT26 and KCM tumor models.
Methods: The subcutaneous CT26 colon cancer model and the orthotopic KCM pancreatic cancer model were used to assess the effects of a CCR4 inhibitor, CCX6239, in combination with anti-CTLA-4 antibody. CT26 cells were implanted into the flanks of 9wk female Balb/c mice. Mice were randomized into study groups based on the tumor sizes on day 6, and dosing of both CCX6239 and anti-CTLA-4 started on day 7. For the orthotopic pancreatic cancer model, KCM cells were implanted directly into the pancreas, and dosing of CCX6239 and anti-CTLA-4 also began on day 7. CCX6239 was dosed orally twice daily at 30mg/kg, and anti-CTLA-4 was dosed IP on days 7, 11 and 15 at 100μg/mouse.
Results: Blockade of CCR4 appreciably enhanced the therapeutic effects of anti-CTLA-4 in both models. Combined anti-CTLA-4/CCR4 inhibitor significantly decreased tumor size and increased the proportion of long-term survivors in the CT26 model. The antitumor response was CT26-specific; long-term survivors were resistant to reinoculation with CT26 cells (without further dosing of either drug), but 4T1 breast tumors grew well upon challenge of CT26 survivors. Mice with tumor regression exhibited a high proportion of CD8 T cells that recognized a CT26-specific neoantigen, as illustrated by AH1 peptide-MHC tetramer staining. Although long-term survival has not yet been examined in the KCM model, CCX6239 alone significantly reduced tumor burden in 3 independent studies. Anti-CTLA-4 alone provided substantial inhibition of tumor growth in this model, which was further enhanced by CCX6239.
Summary: A specific CCR4 small-molecule inhibitor enhanced the effectiveness of anti-CTLA-4 in 2 preclinical models, suggesting that targeting CCR4 may be a viable clinical approach for combinatorial treatment with checkpoint blockers.
Citation Format: Shijie “Chris” Li, James J. Campbell, Linda S. Ertl, Zhenhua Miao, Vicky Chhina, Alice Kumamoto, Simon Yau, Ton Dang, Penglie Zhang, Thomas J. Schall, Rajinder Singh. C-C chemokine receptor 4 (CCR4) antagonism enhances the effectiveness of checkpoint Inhibition in mouse tumor models [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B08.