Immunomodulatory effects of a dipeptidyl peptidase inhibitor, ARI-4175, and NK cell activation in a colon cancer model.

Abstract

3058 Background: A possible mechanism of the antitumor effect of therapeutic antibodies is antibody-dependent cellular cytotoxicity (ADCC). We reported that an inhibitor of dipeptidyl peptidase (DPP)4-like serine proteases, Ari-4175, significantly slowed the growth of KRAS-mutated HCT-116 xenografts in nude mice, either as a single agent or with cetuximab (Ctx). Ari-4175 is not cytotoxic in vitro, and since it was able to overcome the resistance to Ctx due to the KRAS mutation in the HCT-116 line, we hypothesized that the antitumor activity involves the activation of NK cells and enhancement of ADCC. Methods: Ari-4175 was administered orally to nude 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. Natural cytotoxicity and ADCC were assayed using HCT116 cells and Ctx using a flow based assay. Cytokines were measured using Luminex assays. Results: Ari-4175 induced upregulation of CD69 on NK cells on day 2, followed by upregulation of CD16 on day 7. Coordinate with these changes in peripheral blood, splenocytes from treated mice exhibited significantly increased in vitro cytotoxicity toward the HCT116 cells. Increased serum levels of inflammatory cytokines, including IL-1b, IL-6, MCP-1, GCSF, and IL-2 were seen. 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 was also seen after one week of treatment. Conclusions: Ari-4175 showed dramatic anti-tumor effect in KRAS-mutant CRC xengrafts when given alone or in combination with Ctx. In vitro data suggest that the therapeutic effect of 4175 might partially be due to the augmentation of ADCC through elevated 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.