Abstract B046: Addition of anti-VEGF overcomes the anti-PD-L1 refractoriness in a OV2944-HM-1 tumor model
Authors: Ishikura Nobuyuki , Yorozu Keigo , Kurasawa Mitsue , Sugimoto Masamichi , Kondoh Osamu 
Published: March 2020

Abstract
Background: Efficacy of combination therapy with atezolizumab plus bevacizumab was shown in the IMpower150 trial. In this study, we use the anti-PD-L1 sensitive Colon 38 mouse tumor model and the anti-PD-L1 insensitive OV2944-HM-1 (HM-1) mouse tumor model to investigate the efficacy and the mechanisms of this combination. Methods: Colon 38 and HM-1 tumor cells were subcutaneously inoculated into the right flank of C57BL/6J and B6C3F1 mice, respectively. Mice with established tumors were randomized into treatment groups (day1). Anti-PD-L1 mAb (anti-PD-L1, clone 6E11) or mouse IgG was administrated intraperitoneally to the mice at a dose of 5 mg/kg twice a week from day 1. Anti-VEGF mAb (anti-VEGF, clone B20-4.1.1) or mouse IgG was administrated intraperitoneally at a dose of 10 mg/kg weekly from day 1. Anti-CD8 mAb (anti-CD8, clone 116-13.1) was intraperitoneally administered at a dose of 100 µg/head twice a week from day -10. Anti-CXCR3 mAb (anti-CXCR3, clone CXCR3-173) was intraperitoneally administered at a dose of 100 µg/head twice a week from day 1. Tumor volume was measured twice a week. The tumors were sampled on day 1 and were subjected to immunohistochemical staining using the anti-CD8 mAb (anti-CD8, clone KT15) and anti-B7-H1/PD-L1 polyclonal antibody. The tumors were sampled on day 4 or 8 and were subjected to flow cytometry analysis using the antibody for CD8 and Granzyme B, and ELISA analysis for CXCL9. Results: HM-1 tumors showed lower PD-L1 expression under conditions where Colon 38 tumors were partially PD-L1 positive. CD8+ T cells were hardly observed in HM-1 tumors, while CD8+ T cells were prominently observed in Colon 38 tumors. In the Colon 38 model, combination treatment with anti-PD-L1 plus anti-VEGF significantly inhibited the tumor growth compared with the single agent treatments which themselves significantly inhibited the tumor growth compared with control treatment. In the HM-1 model, combination treatment with anti-PD-L1 plus anti-VEGF significantly inhibited the tumor growth compared with the anti-VEGF treatment which itself significantly inhibited the tumor growth compared with control treatment. In the HM-l model, significantly larger number of CD8+ T cells and Granzyme B+CD8+ T cells and a significantly higher level of CXCL9 were observed in tumor tissue with anti-PD-L1 treatment compared with control treatment on day 4. However, these statuses were not maintained on day 8. On the other hand, these statuses were observed in tumor tissue with combination treatment both on day 4 and day 8. Anti-CD8 canceled the potentiation of the antitumor effect in combination treatment to the level of anti-VEGF treatment. Anti-CXCR3 canceled the increased number of intratumoral CD8+ T cells in combination treatment to the level of control treatment. Conclusions: This is the first study to show that the combination treatment of anti-PD-L1 plus anti-VEGF exhibits more potent anti-tumor activity compared with single agent treatments, not only in an anti-PD-L1 sensitive model but also in an anti-PD-L1 insensitive model with PD-L1 low and immune desert like properties. At least in the anti-PD-L1 insensitive model, this can be mainly explained by the maintained increase of intratumoral CXCL9 leading to the increased infiltration of activated effector CD8+ T cells into tumor tissue. Conflict of interest: The authors are employees of Chugai Pharmaceutical Co., Ltd.
Citation Format: Nobuyuki Ishikura, Keigo Yorozu, Mitsue Kurasawa, Masamichi Sugimoto, Osamu Kondoh. Addition of anti-VEGF overcomes the anti-PD-L1 refractoriness in a OV2944-HM-1 tumor model [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B046. doi:10.1158/1535-7163.TARG-19-B046