Abstract 5023: Synergistic antitumor effects of combinatorial immune checkpoint inhibition with anti-PD-1/PD-L antibodies and the IDO pathway inhibitors NLG-919 and indoximod in the context of active immunotherapy

Combination immunotherapy regimens incorporating agents that target more than a single regulatory pathway or immune inhibitory checkpoint can confer marked enhancement of anti-tumor immune responses when combined with active immunotherapy. We have tested the antitumor effect of the IDO pathway inhibitor NLG-919 (currently in Phase I clinical trial) in combination with indoximod (a different IDO pathway inhibitor currently in Phase II clinical trials), chemotherapy, vaccination and/or PD-1/PD-L1/PD-L2 blockade. Here we show that the highly potent, orally-bioavailable IDO pathway inhibitor NLG-919 is synergistic with blockade of the PD-1/PD-L1/PD-L2 pathway in mouse models of large established tumors. The combination of NLG-919 plus PD-1/PD-L1/PD-L2 blockade showed significantly enhanced anti-tumor effect compared to either agent alone. This synergy was particularly evident in the setting of large established tumors treated with normally ineffective immunotherapy regimens (e.g., a single dose of chemotherapy plus a vaccine against a poorly immunogenic shared-self antigen). In vivo, administration of NLG-919 enhanced anti-tumor vaccine responses against B16F10 melanoma treated with hgp100 vaccine plus resting, non-activated pmel-1 T cells NLG-919 also reduced Treg-mediated suppression in tumor-bearing hosts, and enhanced dendritic cell activation in tumors and TDLNs. In combination with chemotherapy, treatment with NLG-919 allowed effector T cell responses against endogenous tumor antigens released by chemotherapy. By each of the preceding readouts, the in vivo biologic effect of NLG-919 was qualitatively identical to that of indoximod, but the same immunologic effects could be achieved at lower plasma concentrations in vivo. In multiple models, a combination of oral NLG-919 with oral indoximod produced synergistic anti-tumor effects, which was further enhanced by blockade of the PD 1/PD L1/PD-L2 pathway. In a more stringent B16F10 melanoma tumor model that did not involve adoptive transfer of pmel-1 cells, a combination of immune checkpoint inhibition involving NLG-919, indoximod and anti-PD1/PD-L1/PD-L2 antibodies with chemotherapy and hgp100 peptide vaccine was able to achieve a significant antitumor effect. The current preclinical studies suggest a mechanistic rationale for a combining NLG919 with indoximod and with agents targeting the PD 1/PD L1/PD-L2 pathway. Citation Format: Mario R. Mautino, Charles J. Link, Nicholas N. Vahanian, James T. Adams, Clarissa Van Allen, Madhav D. Sharma, Theodore S. Johnson, David Munn. Synergistic antitumor effects of combinatorial immune checkpoint inhibition with anti-PD-1/PD-L antibodies and the IDO pathway inhibitors NLG-919 and indoximod in the context of active immunotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5023. doi:10.1158/1538-7445.AM2014-5023