DGKα/ζ inhibition lowers the TCR affinity threshold and potentiates antitumor immunity

Diacylglycerol kinases (DGKs) attenuate diacylglycerol (DAG) signaling by converting DAG to phosphatidic acid, thereby suppressing pathways downstream of T cell receptor signaling. Using a dual DGKα/ζ inhibitor (DGKi), tumor-specific CD8 T cells with different affinities (TRP1high and TRP1low), and altered peptide ligands, we demonstrate that inhibition of DGKα/ζ can lower the signaling threshold for T cell priming. TRP1high and TRP1low CD8 T cells produced more effector cytokines in the presence of cognate antigen and DGKi. Effector TRP1high- and TRP1low-mediated cytolysis of tumor cells with low antigen load required antigen recognition, was mediated by interferon-γ, and augmented by DGKi. Adoptive T cell transfer into mice bearing pancreatic or melanoma tumors synergized with single-agent DGKi or DGKi and antiprogrammed cell death protein 1 (PD-1), with increased expansion of low-affinity T cells and increased cytokine production observed in tumors of treated mice. Collectively, our findings highlight DGKα/ζ as therapeutic targets for augmenting tumor-specific CD8 T cell function.

DGKα/ζ inhibitors combine with PD-1 checkpoint therapy to promote T cell-mediated antitumor immunity

Programmed cell death protein 1 (PD-1) immune checkpoint blockade therapy has revolutionized cancer treatment. Although PD-1 blockade is effective in a subset of patients with cancer, many fail to respond because of either primary or acquired resistance. Thus, next-generation strategies are needed to expand the depth and breadth of clinical responses. Toward this end, we designed a human primary T cell phenotypic high-throughput screening strategy to identify small molecules with distinct and complementary mechanisms of action to PD-1 checkpoint blockade. Through these efforts, we selected and optimized a chemical series that showed robust potentiation of T cell activation and combinatorial activity with αPD-1 blockade. Target identification was facilitated by chemical proteomic profiling with a lipid-based photoaffinity probe, which displayed enhanced binding to diacylglycerol kinase α (DGKα) in the presence of the active compound, a phenomenon that correlated with the translocation of DGKα to the plasma membrane. We further found that optimized leads within this chemical series were potent and selective inhibitors of both DGKα and DGKζ, lipid kinases that constitute an intracellular T cell checkpoint that blunts T cell signaling through diacylglycerol metabolism. We show that dual DGKα/ζ inhibition amplified suboptimal T cell receptor signaling mediated by low-affinity antigen presentation and low major histocompatibility complex class I expression on tumor cells, both hallmarks of resistance to PD-1 blockade. In addition, DGKα/ζ inhibitors combined with αPD-1 therapy to elicit robust tumor regression in syngeneic mouse tumor models. Together, these findings support targeting DGKα/ζ as a next-generation T cell immune checkpoint strategy.

Discovery of Potent, Dual-Inhibitors of Diacylglycerol Kinases Alpha and Zeta Guided by Phenotypic Optimization

We describe a phenotypic screening and optimization strategy to discover compounds that block intracellular checkpoint signaling in T-cells. We identified dual DGKα and ζ inhibitors notwithstanding the modest similarity between α and ζ relative to other DGK isoforms. Optimized compounds produced cytokine release and T-cell proliferation consistent with DGK inhibition and potentiated an immune response in human and mouse T-cells. Additionally, lead inhibitor BMS-502 demonstrated dose-dependent immune stimulation in the mouse OT-1 model, setting the stage for a drug discovery program.

Interrogating the immune-modulating roles of radiation therapy for a rational combination with immune-checkpoint inhibitors in treating pancreatic cancer

BACKGROUND

Radiation therapy (RT) has the potential to enhance the efficacy of immunotherapy, such as checkpoint inhibitors, which has dramatically altered the landscape of treatments for many cancers, but not yet for pancreatic ductal adenocarcinoma (PDAC). Our prior studies demonstrated that PD ligand-1 and indoleamine 2,3-dioxygenase 1 (IDO1) were induced on tumor epithelia of PDACs following neoadjuvant therapy including RT, suggesting RT may prime PDAC for PD-1 blockade antibody (αPD-1) or IDO1 inhibitor (IDO1i) treatments. In this study, we investigated the antitumor efficacy of the combination therapies with radiation and PD-1 blockade or IDO1 inhibition or both.

METHODS

We developed and used a mouse syngeneic orthotopic model of PDAC suitable for hypofractionated RT experiments.

RESULTS

The combination therapy of αPD-1 and RT improved survival. The dual combination of RT/IDO1i and triple combination of RT/αPD-1/IDO1i did not improve survival compared with RT/αPD-1, although all of these combinations offer similar local tumor control. RT/αPD-1 appeared to result in the best systemic interferon-γ response compared with other treatment groups and the highest local expression of immune-activation genes, including Cd28 and Icos.

CONCLUSION

Our RT model allows examining the immune-modulatory effects of RT alone and in combination with immune-checkpoint inhibitors in the pancreas/local microenvironment. This study highlights the importance of choosing the appropriate immune-modulatory agents to be combined with RT to tip the balance toward antitumor adaptive immune responses.

Prospective prediction of plasma pharmacokinetics of a novel immune-modulating agent in cancer patients after intra-tumoral administration: translation from non-clinical species to humans

Intra-tumoral (I-TUMOUR) delivery is being widely explored for novel anti-cancer agents. This route is anticipated to result in high tumour concentrations leading to better efficacy and safety. Prediction of human systemic pharmacokinetics (PK) from non-clinical species facilitates understanding of pharmacokinetic-pharmacodynamic relationships, efficient dose selection, and risk assessment of novel drugs. However, there is limited knowledge on the predictability of human pharmacokinetics following I-TUMOUR delivery.In this publication, we present a case study wherein human systemic PK of a novel agent administered intra-tumourally was prospectively predicted and compared with observed human PK.Simple allometry was used to project the human clearance (10.5 mL/min/kg) and steady-state volume of distribution (1.4 L/kg) after intravenous (IV) dosing. Using these IV PK parameters and assuming rapid absorption and complete I-TUMOUR bioavailability, human plasma PK profile was simulated. The projected 30 min concentrations and AUC_(0-6h) were within 1.9 to 2.5-fold and 1 to 1.4-fold of the observed PK indicating a reasonable concordance between predicted and observed PK.To our knowledge, this is the first article that prospectively projected human pharmacokinetics after I-TUMOUR dosing. The results from this study indicate that similar approaches can be used to project the human PK of other I-TUMOUR agents.

DGKζ exerts greater control than DGKα over CD8+ T cell activity and tumor inhibition

Two isoforms of diacylglycerol kinases (DGKs), DGKα and DGKζ, are primarily responsible for terminating DAG-mediated activation of Ras and PKCθ pathways in T cells. A direct comparison of tumor growth between mice lacking each isoform has not been undertaken. We evaluated the growth of three syngeneic tumor cell lines in mice lacking either DGKα or DGKζ in the presence or absence of treatment with anti-PD1 and determined that (i) mice deficient in DGKζ conferred enhanced control of tumor relative to mice deficient in DGKα and (ii) deficiency of DGKζ acted additively with anti-PD1 in tumor control. Consistent with this finding, functional and RNA-sequencing analyses revealed greater changes in stimulated DGKζ-deficient T cells compared with DGKα-deficient T cells, which were enhanced relative to wildtype T cells. DGKζ also imparted greater regulation than DGKα in human T cells. Together, these data support targeting the ζ isoform of DGKs to therapeutically enhance T cell anti-tumor activity.

Axl and Mertk Receptors Cooperate to Promote Breast Cancer Progression by Combined Oncogenic Signaling and Evasion of Host Antitumor Immunity

Despite the promising clinical benefit of targeted and immune checkpoint blocking therapeutics, current strategies have limited success in breast cancer, indicating that additional inhibitory pathways are required to complement existing therapeutics. TAM receptors (Tyro-3, Axl, and Mertk) are often correlated with poor prognosis because of their capacities to sustain an immunosuppressive environment. Here, we ablate Axl on tumor cells using CRISPR/Cas9 gene editing, and by targeting Mertk in the tumor microenvironment (TME), we observed distinct functions of TAM as oncogenic kinases, as well as inhibitory immune receptors. Depletion of Axl suppressed cell intrinsic oncogenic properties, decreased tumor growth, reduced the incidence of lung metastasis and increased overall survival of mice when injected into mammary fat pad of syngeneic mice, and demonstrated synergy when combined with anti-PD-1 therapy. Blockade of Mertk function on macrophages decreased efferocytosis, altered the cytokine milieu, and resulted in suppressed macrophage gene expression patterns. Mertk-knockout mice or treatment with anti-Mertk-neutralizing mAb also altered the cellular immune profile, resulting in a more inflamed tumor environment with enhanced T-cell infiltration into tumors and T-cell-mediated cytotoxicity. The antitumor activity from Mertk inhibition was abrogated by depletion of cytotoxic CD8α T cells by using anti-CD8α mAb or by transplantation of tumor cells into B6.CB17-Prkdc SCID mice. Our data indicate that targeting Axl expressed on tumor cells and Mertk in the TME is predicted to have a combinatorial benefit to enhance current immunotherapies and that Axl and Mertk have distinct functional activities that impair host antitumor response. SIGNIFICANCE: This study demonstrates how TAM receptors act both as oncogenic tyrosine kinases and as receptors that mediate immune evasion in cancer progression.