Abstract 494: Immunomodulatory effects of a small molecule dipeptidyl peptidase inhibitor, Ari-4175, are mediated through NK cell activation in a colorectal cancer model.

Abstract

Abstract Introduction: A possible mechanism of the antitumor effect of many therapeutic monoclonal antibodies is antibody-dependent cellular cytotoxicity (ADCC) mediated by NK cells. We recently observed that an inhibitor of dipeptidyl peptidase (DPP)4-like serine proteases, Ari-4175, significantly slowed the growth of K-RAS mutated HCT-116 tumor xenografts in nude mice, either as a single agent or in combination with cetuximab. Ari-4175 is not directly cytotoxic in vitro, and since it was able to overcome, in vivo, the resistance to blockade of the epidermal growth factor receptor engendered by the KRAS mutation in the HCT-116 colorectal cancer (CRC) cell line, we tested the hypothesis that the mechanism of the antitumor activity involves the activation of NK cells, resulting in the enhancement of ADCC. Methods: Ari-4175 was administered orally to C57Bl/6 mice at 200 μg q.d. x5 days/week. Peripheral blood or spleens were assayed for immune parameters, ex vivo, at various time points. Expression of surface markers on myeloid and NK cells were monitored by flow cytometry. Natural cytotoxicity and ADCC were assayed using HCT116 cells and cetuximab using a flow cytometry-based assay. Cytokines were measured in mouse serum using Luminex assays. Results: Treatment of mice with Ari-4175 induced up-regulation of the activation marker CD69 on NK cells on day 2, followed by up-regulated expression of FcRIIIA (CD16, which mediates ADCC) on day 7. Coordinate with these changes in surface markers detected in peripheral blood samples, splenocytes from Ari-4175-treated mice exhibited significantly increased in vitro natural cytotoxicity responses toward the HCT116 colon cancer cell line. The treated mice exhibited increased serum levels of inflammatory cytokines, including IL-1, IL-6, MCP-1, GCSF, and IL-2. In addition to the impacts on NK cells, we also observed a significant expansion of a distinct CD45+CD14+Gr-1+MHC-II−CDllb+CD11cvariable myeloid cell population in both peripheral blood and spleens of mice after one week of treatment with Ari-4175. Conclusion: The prolyl peptidase inhibitor, Ari-4175, showed dramatic anti-tumor effect in KRAS mutant colorectal cancer xengrafts when given alone or in combination with cetuximab. In vitro data suggest that the therapeutic effect of 4175 might partially be due to the augmentation of ADCC through elevating expression of CD16 on NK cells. In addition, Ari-4175 appears, in vivo, to expand a unique myeloid cell population, which may be responsible for an inflammatory cytokine response and subsequent activation of NK cells. Our study provides a mechanistic rationale for testing Ari-4175 in a clinical trial and possible biomarker endpoints for evaluation in peripheral blood samples. Citation Format: Alexander W. MacFarlane, Jiping Zhang, Barry Jones, William Bachovchin, Kerry Campbell, Hossein Borghaei. Immunomodulatory effects of a small molecule dipeptidyl peptidase inhibitor, Ari-4175, are mediated through NK cell activation in a colorectal cancer model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 494. doi:10.1158/1538-7445.AM2013-494