Immunomodulation by regorafenib alone and in combination with anti PD1 antibody on murine models of colorectal cancer

Background: Regorafenib is a small molecule inhibitor of multiple kinases involved in normal cellular functions and in pathologic processes such as oncogenesis, angiogenesis, and tumor immunity. Regorafenib is approved for the treatment of advanced colorectal cancer (CRC) and gastrointestinal stromal tumors. In addition, an overall survival benefit has recently been shown in patients with hepatocellular carcinoma who had previously progressed on sorafenib (RESORCE trial). Immuno-oncology treatment strategies have recently expanded the arsenal of highly effective cancer therapies. In addition to their activity in monotherapy, they are being tested in combination with other therapies, including those inhibiting angiogenesis, to further improve their antitumor activity. We investigated the immunomodulatory effect of regorafenib alone and in combination with a mouse-reactive anti PD1 antibody in mouse models of CRC. Methods: CT26 or MC38 syngeneic tumors were treated with regorafenib alone and in combination with anti PD1. We monitored tumor growth and analyzed the immune status of tumors ex vivo at the end of the study. Immune infiltrates were characterized by flow cytometry, intratumoral cytokines by multiplex ELISA, and expression of immunologically relevant genes by qPCR. Results: Both regorafenib and anti PD1 inhibited the growth of MC38 tumors vs control, and this effect was significantly enhanced by concomitant treatment or when regorafenib was given after anti PD1. Regorafenib treatment most consistently reduced tumor-infiltrating macrophages in both MC38 and CT26 tumors in a dose-dependent manner. Additionally, signs of M1-type macrophage conversion were detected by elevated inducible NO synthase and reduced arginase expression. This may be due to a regorafenib-mediated inhibition of the CSF1 receptor, as shown in vitro in the murine macrophage cell line RAW264.7. Anti PD1 treatment was associated with elevated interferon-g levels, indicative of enhanced T cell activation. Conclusions: These results warrant further exploration of a combination of regorafenib and PD1 for the treatment of colorectal cancer. Legal entity responsible for the study: Bayer AG Funding: Bayer AG Disclosure: S. Hoff, S. Grünewald, L. Röse, D. Zopf: Employees of Bayer AG, and some are shareholders of Bayer AG stocks.