Purpose: Combination strategies leveraging chemotherapeutic agents and immunotherapy have held the promise as a method to improve benefit for patients with cancer. However, most chemotherapies have detrimental effects on immune homeostasis and differ in their ability to induce immunogenic cell death (ICD). The approval of pemetrexed and carboplatin with anti-PD-1 (pembrolizumab) for treatment of non-small cell lung cancer represents the first approved chemotherapy and immunotherapy combination. Although the clinical data suggest a positive interaction between pemetrexed-based chemotherapy and immunotherapy, the underlying mechanism remains unknown.Experimental Design: Mouse tumor models (MC38, Colon26) and high-content biomarker studies (flow cytometry, Quantigene Plex, and nCounter gene expression analysis) were deployed to obtain insights into the mechanistic rationale behind the efficacy observed with pemetrexed/anti-PD-L1 combination. ICD in tumor cell lines was assessed by calreticulin and HMGB-1 immunoassays, and metabolic function of primary T cells was evaluated by Seahorse analysis.Results: Pemetrexed treatment alone increased T-cell activation in mouse tumors in vivo, robustly induced ICD in mouse tumor cells and exerted T-cell-intrinsic effects exemplified by augmented mitochondrial function and enhanced T-cell activation in vitro. Increased antitumor efficacy and pronounced inflamed/immune activation were observed when pemetrexed was combined with anti-PD-L1.Conclusions: Pemetrexed augments systemic intratumor immune responses through tumor intrinsic mechanisms including immunogenic cell death, T-cell-intrinsic mechanisms enhancing mitochondrial biogenesis leading to increased T-cell infiltration/activation along with modulation of innate immune pathways, which are significantly enhanced in combination with PD-1 pathway blockade.See related commentary by Buque et al., p. 6890

Background-The process of arteriogenesis after occlusion of a major artery is poorly understood. We have used high-resolution microcomputed tomography (-CT) imaging to define the arteriogenic response in the mouse model of hindlimb ischemia and to examine the effect of placental growth factor-1 (PlGF-1) on this process. Methods and Results-After common femoral artery ligation, -CT imaging demonstrated formation of collateral vessels originating near the ligation site in the upper limb and connecting to the ischemic calf muscle region. Three-dimensional -CT and quantitative image analysis revealed changes in the number of segments and the segmental volume of vessels, ranging from 8 to 160 m in diameter. The medium-size vessels (48 to 160 m) comprising 85% of the vascular volume were the major contributor (188%) to the change in vascular volume in response to ischemia. Intramuscular injections of Ad-PlGF-1 significantly increased Sca1 ϩ cells in the circulation, ␣-actin-stained vessels, and perfusion of the ischemic hindlimb. These effects were predominantly associated with an increase in vascular volume contributed by the medium-size (96 to 144 m) vessels as determined by -CT. Conclusions-High-resolution -CT delineated the formation of medium-size collaterals representing a major vascular change that contributed to the restoration of vascular volume after ischemia. This effect is selectively potentiated by PlGF-1. Such selective enhancement of arteriogenesis by therapeutically administered PlGF-1 demonstrates a desirable biological activity for promoting the growth of functionally relevant vasculature.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-dependent enzyme that catalyzes the initial and rate-limiting step of tryptophan catabolism resulting in the local depletion of tryptophan and the concomitant production of kynurenine, both of which are immunosuppressive. Targeting IDO1 in combination with PD-1/PD-L1-targeted antibodies has shown promise in early phase clinical trials in several cancers and strongly suggests that, in some patients, IDO1 expression restrains PD-1/PD-L1-targeted checkpoint therapies. While some cancers extrinsically express IDO1 in response to IFN-γ produced from an ongoing, yet ineffective immune response, others select for the intrinsic expression of IDO1, independent of an immune response. We identified several cancer cell lines that intrinsically expressed either IDO1 or the related isozyme TDO2. Using these cell lines, we discovered LY3381916, a potent and selective inhibitor of cell-based IDO1 activity (IDO1 7 nM; TDO2 >20 µM). Using a variety of techniques, we demonstrated that LY3381916 binds to newly synthesized apo-IDO1 lacking heme, but does not inhibit mature heme-bound IDO1. Protein x-ray crystallography confirmed that LY3381916 binds to apo-IDO1 where it occupies the heme-binding pocket of IDO1. As a result of this novel mechanism of action, substantial inhibition of IDO1 in tumors requires the turn-over of mature heme-bound IDO1. Modeling of the pre-clinical PK/PD relationship suggests QD dosing of LY3381916 will maintain greater than 90% inhibition over 24 hours. In addition, due to the favorable properties of the drug, significant central nervous system (CNS) penetration has been measured for LY3381916 (rodent kp,uu 0.26). Kynurenine-mediated agonism of the aryl hydrocarbon receptor (AHR) is immunosuppressive in the tumor microenvironment. Inhibition of IDO1 and the subsequent reduction of kynurenine can relieve this immunosuppression. However, several heme-binding IDO1 inhibitors have been shown to replace kynurenine as an AHR agonist potentially limiting their ability to relieve this IDO1-dependent immunosuppressive mechanism. LY3381916 shows no confounding agonism of AHR up to 100 µM. Additionally, we characterized LY3381916 in pre-clinical tumor models and demonstrated that it was able to enhance LY3300054, anti-PD-L1 antibody (LY3300054) activity, which was associated with an enhanced T cell response. Based on these characteristics, LY3381916 is currently being investigated in a Phase I clinical trial. These data suggest further development of LY3381916 may be warranted. Citation Format: Frank C. Dorsey, Karim A. Benhadji, Lillian L. Sams, Debra A. Young, John F. Schindler, Karen L. Huss, Alexander Nikolayev, Carmine Carpenito, David Clawson, Bonita Jones, Andrew L. Faber, James E. Thomas, Steven A. Haney, Gaiying Zhao, William T. McMillen, Tod Smeal, Daniel J. Sall, Michael D. Kalos, Sandaruwan Geeganage, James R. Henry. Identification and characterization of the IDO1 inhibitor LY3381916 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5245.

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Pharmacological inhibition of CHK1 in the absence of p53 functionality leads to abrogation of the S and G2/M DNA damage checkpoints. We report the preclinical therapeutic activity of LY2603618 (CHK1 inhibitor) at inhibiting CHK1 activation by gemcitabine and enhancing in vivo efficacy. The in vivo biochemical effects of CHK1 inhibition in the absence or presence of DNA damage were measured in human tumor xenograft models. Colon, lung and pancreatic xenografts models were treated with gemcitabine, LY2603618, or gemcitabine plus LY2603618. Gemcitabine treatment alone induced a significant increase in CHK1 autophosphorylation over untreated tumors. Co-administration of LY2603618 with gemcitabine showed a clear inhibition of CHK1 autophosphorylation for at least 24 h. Combining LY2603618 with gemcitabine resulted in an increase in H2AX serine 139 phosphorylation, indicating a corresponding increase in damaged DNA in the tumors. LY2603618 abrogated the S-phase DNA damage checkpoint in Calu-6 xenograft tumors treated with gemcitabine but did not significantly alter the G2/M checkpoint. Combining gemcitabine with LY2603618 resulted in a significant increase in tumor growth inhibition in Calu-6, HT-29 and PAXF 1869 xenografts over gemcitabine treatment alone. The best combination efficacy occurred when LY2603618 was given 24 h following dosing with gemcitabine. LY2603618 worked effectively to remove the S-phase DNA damage checkpoint and increase the DNA damage and the antitumor activity of gemcitabine treatment.