MC38 Cancer Research Articles

Abstract 1546: ADCC enhanced anti-CD25 mAb (TST010) demonstrated antitumor activity via depleting Treg cells and increasing CD8+T/Treg ratio in preclinical tumor models

Abstract Regulatory T (Treg) cells are a distinctive lineage of CD4+ T cells as characterized by expression of FoxP3 and CD25 markers. Treg cells are involved in tumor development and progression by inhibiting antitumor immunity. Accumulation of Treg cells in the tumor microenvironment (TME) is often associated with an adverse prognosis in multiple cancers and also has implication for predicting response to immunotherapy. Treg cell depletion strategy has been explored in preclinical and clinical settings to induce effective antitumor immune responses in TME. CD25, a high-affinity binding subunit alpha of the IL-2 receptor, is constitutively and highly expressed on Treg cells but also transiently upregulated on effector T cells. The high level of CD25 expression on Treg cells could deprive of IL-2 for effector T cells and inhibit their proliferation. Thus, an effective approach to selectively suppress Treg cell function is to deplete Treg cells while avoid blocking IL-2 binding to CD25 for allowing T effect cell proliferation and activation. Using our immune tolerance breaking antibody platform, we generated a humanized IgG1 subtype anti-CD25 monoclonal antibody (TST010). TST010 bound to human CD25 with high affinity and selectivity but did not block IL-2 binding to CD25. No blocking activity to IL-2 signaling on human PBMC was further confirmed by the phosphorylation of Stat5 using FACS analysis. By reducing fucosylation during cell culture process, TST010 mAb gained the enhanced ADCC activity. In an ADCC reporter assay, TST010 showed its sub-nanomolar ADCC activity against CD25-overexpression SU-DHL-1 cell line and human induced Treg cells, but much less to human activated CD8+ T effect cells due to lower CD25 expression. Similarly, in a NK cytotoxicity assay, TST010 selectively killed human induced Treg cells in contrast to activated CD8+ T cells. In vivo antitumor activity of TST010 was evaluated in the syngeneic mouse tumor models. The mouse colon cancer MC38 model was developed on the human CD25 knock-in mice. In the MC38 tumor model, TST010 markedly reduced the Treg (FoxP3+CD4+) population in both peripheral blood and TME. Importantly, the CD8+T/Treg ratio in tumor was increased starting at 2 weeks post TST010 treatment, and it resulted in a significant single agent tumor growth inhibition at a 10 mg/kg dose. Furthermore, in the LLC tumor model which does not respond well to checkpoint inhibitors, the anti-CD25 mAb showed a good combination effect with a PD-L1 inhibitor. In summary, we have discovered a novel therapeutic anti-CD25 mAb that can deplete Treg cells without blocking IL-2 signaling. As demonstrated in our preclinical tumor models, it has a good potential to induce effective antitumor immune responses in TME and tumor growth inhibition especially in combination with PD-1/PD-L1 treatment. Citation Format: Di Sun, Huanhuan Guo, Hongjun Li, Xinlai Yao, Yiqing Xu, Shenjie Zhang, Shijie Zhou, Xiaoli Zi, Lisa Zheng, Yi Gu, Xueming Qian. ADCC enhanced anti-CD25 mAb (TST010) demonstrated antitumor activity via depleting Treg cells and increasing CD8+T/Treg ratio in preclinical tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1546.

Antitumor Effect of Korean Red Ginseng through Blockade of PD-1/PD-L1 Interaction in a Humanized PD-L1 Knock-In MC38 Cancer Mouse Model

Blocking immune checkpoints, programmed death-1 (PD-1) and its ligand PD-L1, has proven a promising anticancer strategy for enhancing cytotoxic T cell activity. Although we previously demonstrated that ginsenoside Rg3, Rh2, and compound K block the interaction of PD-1 and PD-L1, the antitumor effect through blockade of this interaction by Korean Red Ginseng alone is unknown. Therefore, we determined the effects of Korean Red Ginseng extract (RGE) on the PD-1/PD-L1 interaction and its antitumor effects using a humanized PD-1/PD-L1-expressing colorectal cancer (CRC) mouse model. RGE significantly blocked the interaction between human PD-1 and PD-L1 in a competitive ELISA. The CD8+ T cell-mediated tumor cell killing effect of RGE was evaluated using murine hPD-L1-expressing MC38 cells and tumor-infiltrating hPD-1-expressing CD8+ T cells isolated from hPD-L1 MC38 tumor-bearing hPD-1 mice. RGE also reduced the survival of hPD-L1 MC38 cells in a cell co-culture system using tumor-infiltrating CD8+ T cells as effector cells combined with hPD-L1 MC38 target cells. RGE or Keytruda (positive control) treatment markedly suppressed the growth of hPD-L1 MC38 allograft tumors, increased CD8+ T cell infiltration into tumors, and enhanced the production of Granzyme B. RGE exhibits anticancer effects through the PD-1/PD-L1 blockade, which warrants its further development as an immunotherapy.

Abstract PR004: Older adult-specific microbes correlate with treatment response and markers of T-cell senescence in NSCLC

Abstract The gut microbiome changes with age and affects many aspects of human health, including response to cancer treatments. Cancer survival rates have improved with new treatment options, including immune checkpoint blockade (ICB); however, the objective response rate remains low. Manipulation of the microbiome is a promising approach to improving cancer outcomes, but the effect of age is understudied. Here, we sought to understand whether (1) specific microbes are associated with treatment response in older adults with non-small cell lung cancer (NSCLC) and (2) whether these microbes are the same as for younger adults. Next, we explored the causal effects of the microbiome on ICB response in mouse models and the relationship with blood-based markers of T-cell senescence. We conducted a prospective cohort study of adults ≥60 years with a new diagnosis of NSCLC who received any treatment modality. Stool was collected, and metagenomic whole-genome shotgun sequencing was performed. Blood T-cells were isolated, the RNA purified and then assessed for markers of senescence by nanostring. Response to treatment was determined by RECIST v1.1 criteria. Generalized linear regression was used to relate baseline microbiome abundances to treatment response and non-parametric correlations associated with CDKN2A (p16) expression to microbe abundances. To assess the causal role of the gut microbiome in ICB response, we gavaged gut microbiome samples from responders and non-responders into C57BL/6 mice to create human-microbiome avatar models. The mice were then injected with MC38 cancer cells and treated with anti-PD1 or isotype control antibodies, and tumor volume was measured over time. Biospecimens and best response data at three months were captured from 23 patients, of which five had a complete response, eight had a partial response, eight had stable disease, and two had progressive disease. Over 50 microbes were associated with a response after p-value adjustment. Responder stool was enriched for microbes associated with youth and ICB response (Bifidobacterium adolescentis, p = 2.64e-20). However, microbial taxa associated with response differed from those reported in younger populations (Firmicutes sp. CAG 145, p = 1.58e-20, Oscillibacter sp. 57-20, p = 7.96e-24). Stool from non-responders (NRs) was enriched in taxa previously linked to treatment-related toxicities and shorter progression-free survival (Streptococcus lutetiensis, p = 4.55E-24) but also contained microbes previously linked to response in younger adults (e.g., Roseburia sp. CAG 309, p = 5.16e-15). The T cell senescence marker, p16, correlated with the most enriched taxon in non-responders NRs (Streptococcus thermophilus, r = 0.45, p = 0.02), suggesting a connection between immune aging and the microbiome. Preliminary fecal transplant studies in mice showed improved ICB response in mice engrafted with stool from responders versus non-responders. Together, these data identify potential differences in the gut microbiomes of young and older adult NSCLC patients who respond to ICB. Citation Format: Daniel Spakowicz, Rebecca Hoyd, Caroline E. Wheeler, Nyelia Williams, Amna Bibi, Marium Husain, Srichandhana Rajamouli, Shankar Suman, Joseph Amann, Madison Grogan, Pooja Vibhakar, Dwight H. Owen, David P. Carbone, Ashley Rosko, Christin E. Burd, Carolyn J. Presley. Older adult-specific microbes correlate with treatment response and markers of T-cell senescence in NSCLC [abstract]. In: Proceedings of the AACR Special Conference: Aging and Cancer; 2022 Nov 17-20; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_1):Abstract nr PR004.

Anti-tumor effect of aquaporin 3 monoclonal antibody on syngeneic mouse tumor model

Aquaporin-3 (AQP3), a water channel protein, has been found to be involved in cancer progression via water and small molecule transport function. However, drug development targeting AQP3 has not yet begun.Here, we showed that a recently established anti-AQP3 monoclonal antibody (mAb) suppresses tumor growth in allograft mouse colorectal tumor models produced using CT26 or MC38 cancer cells. Administration of the anti-AQP3 mAb to BALB/c mice with transplanted CT26 cells increased the M1/M2 ratio of tumor-associated macrophages (TAM) and improved the mitochondrial function of T cells in the tumor microenvironment (TME). Administration of anti-AQP3 mAb also restored the TAM-induced decrease in T cell proliferation. Macrophage depletion in wild-type mice counteracted the antitumor effect of anti-AQP3 mAb in the mouse tumor model, suggesting that one of the primary targets of anti-AQP3 mAb is macrophages. In in vitro studies using mice bone marrow monocytes and human monocyte THP-1 cells, anti-AQP3 mAb attenuated carcinoma cell-mediated polarization of monocytes into M2-like TAMs.These data suggest that anti-AQP3 mAb suppresses tumor growth by attenuating immunosuppressive M2-like TAMs, which in turn maintains the antitumor function of T cells in the TME. Thus, the anti-AQP3 mAb is a potential cancer therapy that functions by targeting TAMs.

Triiodothyronine-stimulated dendritic cell vaccination boosts antitumor immunity against murine colon cancer

Given the ability of dendritic cells (DCs) to modulate other immune players, their manipulation holds great potential for inducing efficient antitumor immunity. However, DC vaccine manufacturing deserve optimization since tumor cell cargo and DC functional state induced by maturation signals influence their in vivo immunogenic potential. We reported that triiodothyronine (T3) stimulates mice DCs’ maturation and their ability to promote pro-inflammatory and cytotoxic T-cell responses. This study aimed to evaluate the efficacy of T3-conditioned DC vaccination in a murine model of colon carcinoma, deciphering the molecular players involved; and to examine the effects of T3 on the maturation and activation of human DCs (huDCs). Bone marrow-derived DCs were exposed to T3 and MC38 cancer cells that underwent cell death (MC38-Apo/Nec) by UVB irradiation. Our results showed that MC38-Apo/Nec cells are efficiently uptaken by DCs and that T3 upregulates CD86 expression with increased production of the pro-inflammatory cytokines IL-12, IL-6 and TGF-β. In a colon cancer model, vaccination with T3-stimulated and tumor antigen-loaded DCs inhibited tumor growth in wild type mice, an effect that was eliminated in IL-17-deficient animals. Notably, secretion of high levels of IFN-γ and IL-17, induction of Th1, Th17 and tumor-specific cytotoxic T lymphocytes characterized the antitumor response upon vaccination. Moreover, our initial findings demonstrated a significant increase in CD86 expression and IL-12 production by huDCs induced by T3. Overall, these results reinforce the adjuvant properties of T3-conditioned DCs to potentiate T-cell-mediated antitumor immunity and support promising advances in the translation process to human oncotherapy.

Abstract SY18-02: Beyond tumor antigen immunogenicity: Determinants of protective immunity induced by therapeutic cancer vaccines

Abstract Cancer-specific mutations can generate neoantigens that are recognized as foreign by the immune system and elicit potent T cell responses against cancer. The identification of neoantigens as drivers of effective anti-tumor immunity has promoted the development of neoantigen-based therapeutic strategies, including vaccines and cell-based therapies. One challenge for these approaches is to accurately predict neoantigens. Most mutations are unique to each patient and only a fraction are immunogenic. The generation of large-scale mass spectrometry-based immunopeptidomics training data for the development of deep learning models has resulted in significantly improved computational methods for prediction of neoantigen presentation on HLA. In addition, on-going efforts to characterize antigen determinants involved in TCR recognition may also contribute to further improving immunogenicity prediction. However, induction of neoantigen-specific T cells may not be sufficient for efficacy. We used the MC38 cancer model to characterize the factors associated with effective neoantigen-specific T cell responses after vaccination. We designed two RNA-LPX vaccines (Deca-1 and Deca-2), each encoding 10 MC38 neoantigens. The two vaccines elicited T cell responses with comparable magnitude and functionality. Prophylactic vaccination with either vaccine prevented establishment of MC38 tumors, confirming that vaccine-induced T cells can recognize and kill tumor cells. Surprisingly, while vaccination with Deca-2 was protective in therapeutic settings, vaccination with Deca-1 was unable to reverse growth of established tumors. Neoantigen-specific CD8 T cell migration to the tumor was comparable between the two vaccines, but the phenotypes of the T cells were significantly different. Gene expression analysis revealed specific activation states of T cells that differed according to their antigenic specificity and clonal expansion, suggesting intrinsic differences across different T cell specificities. Remarkably, T cells elicited by Deca-1 exhibited a gene signature of reduced functionality at the tumor site and also in the spleen, the primary site of vaccine activity. Our study has important implications for the development of neoantigen therapies, as it suggests that the properties of the neoantigen/TCR pairs influence the phenotype of vaccine-induced T cells at the tumor site and therapeutic outcome. Furthermore, our results indicate that the tumor may influence the phenotype of vaccine-induced T cells outside the tumor microenvironment. Additional experiments are on-going to further define the exact nature of these determinants. Citation Format: Lelia Delamarre. Beyond tumor antigen immunogenicity: Determinants of protective immunity induced by therapeutic cancer vaccines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr SY18-02.

Abstract 1643: B-hIL12A/hIL12B/hIL12RB1/hIL12RB2: A novel animal model for generation of IL12 therapies

Abstract The pro-inflammatory cytokine, interleukin 12 (IL12), is primarily responsible for cell-mediated immunity and is chiefly produced by antigen presenting cells. Prior preclinical studies elucidated a promising role for IL12 mediating anti-tumor effects, however, clinical studies using cancer patients showed disappointing efficacy results, as well as severe adverse effects, with administration of systemic IL12 therapies. Intriguingly, progress in targeted delivery to the tumor microenvironment renewed high expectations on IL12 as a promising anti-tumor drug either alone or in combination due to its ability to inhibit and/or reprogram immunosuppressive cell subsets. Therefore, to evaluate the efficacy of IL12 and IL12 analogs in preclinical studies, Biocytogen has successfully generated a novel hIL12A/hIL12B/hIL12RB1/hIL12RB2 knock-in mouse strain. In this mouse model, the full coding sequences (CDS) of the mouse Il12a or Il12b gene were replaced by their human counterpart IL12A or IL12B gene sequences respectively. In addition, chimeric CDS, composed of human IL12RB1 or IL12RB2 extracellular region plus mouse Il12rb1 or Il12rb2 cytoplasmic region, was inserted into the mouse endogenous gene locus in in these animals, to express an IL12 receptor (IL12R) capable of recognizing human IL12 signaling. Expression analysis by RT-PCR detected human IL12A/IL12B/IL12RB1/IL12RB2 mRNA in humanized mice but not in wild-type mice. Additionally, human IL12 p70 was successfully detected in the serum of humanized mice by ELISA. The immune cell subpopulations in spleen, blood, and lymph node did not differ between humanized mice and wild-type mice suggesting no impact on cell differentiation and maturation. Anti-tumor activity of a modified human IL12 was assessed in humanized mice bearing colon cancer MC38 cells and showed tumor inhibitory effects. Moreover, the tumor growth recovered when the administration of the drug was stopped. Altogether, B-hIL12A/hIL12B/hIL12RB1/hIL12RB2 humanized mice provide a promising preclinical efficacy model for human IL12 therapy alone or in combination. Keywords: IL12, humanized mice, antibody efficacy Citation Format: Linlin Wang, Chang Liu, Veronika Chromikova, Ruili Lyu, Tianquan Jin, Mari Kuraguchi. B-hIL12A/hIL12B/hIL12RB1/hIL12RB2: A novel animal model for generation of IL12 therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1643.

Combined analysis of T cell activation and T cell-mediated cytotoxicity by imaging cytometry

Immunotherapies for the treatment of cancer have spurred the development of new drugs that seek to harness the ability of T cells to recognize and kill malignant cells. There is a substantial need to evaluate how these experimental drugs influence T cell functional outputs in co-culture systems that contain cancerous cells. We describe an imaging cytometry-based platform that can simultaneously quantify activated T cells and the capacity of these T cells to kill cancer cells. Our platform was developed using the Nur77-GFP reporter system because GFP expression provides a direct readout of T cell activation that is induced by T cell antigen receptor (TCR) signaling. We combined the Nur77-GFP reporter system with a cancer cell line that displays a TCR-specific antigen and evaluated the relationship between T cell activation and cancer cell death. We demonstrate that imaging cytometry can be used to quantify the number of activated cytotoxic CD8+ T cells (CTLs) and the capacity of these CTLs to recognize and kill adherent MC38 cancer cells. We tested whether this platform could evaluate heterogenous lymphocyte populations by quantifying the proportion of antigen-specific activated T cells in co-cultures that contain unresponsive lymphocytes. The effects of a SRC family kinase inhibitor on CTL activation and MC38 cell death were also determined. Our findings demonstrate that the Nur77-GFP reporter system can be used to evaluate the effects of diverse treatment conditions on T cell-cancer co-cultures in a microtiter plate-based format by imaging cytometry. We anticipate the combined analysis of T cell activation with T cell-mediated cancer cell death can be used to rapidly assess immuno-oncology drug candidates and T cell-based therapeutics.

Bioactive cytomembrane@poly(citrate-peptide)-miRNA365 nanoplatform with immune escape and homologous targeting for colon cancer therapy.

Colon cancer is one of the most common gastrointestinal tumors in the world. Currently, the commonly used methods such as radiotherapy, chemotherapy and drug treatments are often ineffective and have significant side effects. Here we developed a safe and efficient biomaterials based anti-tumor nanoplatform (M@NPs/miR365), which was formed with poly (citrate-peptide) (PCP), miRNA365 mimic and MC38 cancer cell membrane (M). PCP could efficiently deliver miR365 mimic into MC38 cancer cells, promote the apoptosis of MC38 tumor cells and regulate the expression of Bcl2 and Ki67 in vitro. Tumor cell membranes were prepared by a fast and convenient sonication method. This tumor cell membrane-coated drug delivery system M@NPs can effectively reduce macrophage uptake and increase the stability of NPs. And the MC38 tumor model mice experiment showed that M@NPs/miR365 via caudal vein injection effectively inhibit tumor development. Based on the immune escape and homologous targeting of cancer cells and efficient gene transfection ability of NPs, this “Trojan horse” like “Pseudotumor cell” carries the target gene miR365 mimic to the tumor site and realizes cancer therapy. Noteworthy, the drug delivery system has good biocompatibility. Thus, this safe drug delivery strategy mediated by cancer cell membrane and gene therapy may have a certain significance for reducing the gap between nanoplatform and tumor clinical treatment.

Enhanced cytotoxic CD8+ T cell (CTL) antigen recognition by LCK activation

Abstract The anti-tumor response of cytotoxic T cells requires detection of tumor-derived antigenic peptide-MHC complex (pMHC) by the T cell antigen receptor (TCR). Strategies that boost TCR signaling caused by weak pMHC could augment the recognition of poorly immunogenic tumors by T cells. Because LCK kinase phosphorylates the TCR complex and the recruited ZAP-70 kinase, increased LCK activity has been shown to increase TCR signaling in naïve T cells. Our previous study demonstrated that a small molecule inhibitor of CSK kinase, a negative regulator of LCK, increased LCK kinase activity and sensitized naïve T cells such that they became activated by weak antigens ex vivo. Our goal was to determine whether CD8+ cytotoxic T cells (CTL) could also be sensitized to detect weak antigens, and evaluate whether their capacity to recognize and kill cancer cells could be augmented. Because the Nur77-GFP reporter system responds to TCR-mediated signaling, we used it to determine that LCK activation sensitized OT-1 TCR transgenic CTLs to detect weak (low affinity) antigens displayed by splenocytes. We also observed increased phosphorylation of ZAP-70 and other signaling mediators upon TCR stimulation. We will next evaluate whether CTL-mediated effector functions can be enhanced by monitoring killing of MC38 cancer cells that display a weak antigen. Our findings will inform whether LCK kinase can be targeted to improve the recognition of cancer by T cells.

YPD-30, a prodrug of YPD-29B, is an oral small-molecule inhibitor targeting PD-L1 for the treatment of human cancer

PD-1 and PD-L1 antibodies have brought about extraordinary clinical benefits for cancer patients, and their indications are expanding incessantly. Currently, most PD-1/PD-L1 agents are administered intravenously, which may be uncomfortable for some cancer patients. Herein, we develop a novel oral-delivered small molecular, YPD-29B, which specifically targets human PD-L1. Our data suggested that YPD-29B could potently and selectively block the interaction between PD-L1 and PD-1, but did not inhibit any other immune checkpoints. Mechanistically, YPD-29B induced human PD-L1 dimerization and internalization, which subsequently activated T lymphocytes and therefore overcomes immunity tolerance in vitro. YDP-29B was modified as the YPD-30 prodrug to improve druggability. Using humanized mice with human PD-1 xenografts of human PD-L1 knock-in mouse MC38 cancer cells, we demonstrated that YPD-30 exhibited significant antitumor activity and was well tolerated in vivo. Taken together, our results indicate that YPD-30 serves as a promising therapeutic candidate for anti-human PD-L1 cancer immunotherapy.

In vitro and in vivo degradation of programmed cell death ligand 1 (PD-L1) by a proteolysis targeting chimera (PROTAC)

Immunotherapy via immune checkpoints blockade has aroused the attention of researchers worldwide. Inhibition of the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) interaction has been one of the most promising immunotherapy strategies. Several neutralizing antibodies targeting this interaction have been developed, which have already achieved considerable clinical success. Additionally, numerous pharmaceutical companies have been committed to develop small molecules which could block the interaction between PD-1 and PD-L1. In this study, a novel PROTAC molecule 21a was developed, and effectively induced the degradation of PD-L1 protein in various malignant cells in a proteasome-dependent manner. Moreover, compound 21a could significantly reduce PD-L1 protein levels of MC-38 cancer cells in vivo, by which promoted the invasion of CD8+ T cells and inhibited the growth of MC-38 in vivo. This PROTAC molecule could be used as a novel and alternative strategy for cancer immunotherapy.

Single-Domain Antibody Nuclear Imaging Allows Noninvasive Quantification of LAG-3 Expression by Tumor-Infiltrating Leukocytes and Predicts Response of Immune Checkpoint Blockade.

Recent advances in the field of immune-oncology led to the discovery of next-generation immune checkpoints (ICPs). Lymphocyte activation gene-3 (LAG-3), being the most widely studied among them, is being explored as a target for the treatment of cancer patients. Several antagonistic anti-LAG-3 antibodies are being developed and are prime candidates for clinical application. Furthermore, validated therapies targeting cytotoxic T-lymphocyte-associated protein-4, programmed cell-death protein-1, or programmed cell-death ligand-1 showed that only subsets of patients respond. This finding highlights the need for better tools for patient selection and monitoring. The potential of molecular imaging to detect ICPs noninvasively in cancer is supported by several preclinical and clinical studies. Here, we report on a single-domain antibody to evaluate whole-body LAG-3 expression in various syngeneic mouse cancer models using nuclear imaging. Methods: SPECT/CT scans of tumor-bearing mice were performed 1 h after injection with radiolabeled single-domain antibody. Organs and tumors of mice were isolated and evaluated for the presence of the radiolabeled tracer and LAG-3-expressing immune cells using a γ-counter and flow cytometry respectively. PD-1/LAG-3-blocking antibodies were injected in MC38-bearing mice. Results: The radiolabeled single-domain antibody detected LAG-3 expression on tumor-infiltrating lymphocytes (TILs) as soon as 1 h after injection in MC38, MO4, and TC-1 cancer models. The single-domain antibody tracer visualized a compensatory upregulation of LAG-3 on TILs in MC38 tumors of mice treated with PD-1-blocking antibodies. When PD-1 blockade was combined with LAG-3 blockade, a synergistic effect on tumor growth delay was observed. Conclusion: These findings consolidate LAG-3 as a next-generation ICP and support the use of single-domain antibodies as tools to noninvasively monitor the dynamic evolution of LAG-3 expression by TILs, which could be exploited to predict therapy outcome.

Pharmacologic Screening Identifies Metabolic Vulnerabilities of CD8+ T Cells.

Metabolic constraints in the tumor microenvironment constitute a barrier to effective antitumor immunity and similarities in the metabolic properties of T cells and cancer cells impede the specific therapeutic targeting of metabolism in either population. To identify distinct metabolic vulnerabilities of CD8+ T cells and cancer cells, we developed a high-throughput in vitro pharmacologic screening platform and used it to measure the cell type-specific sensitivities of activated CD8+ T cells and B16 melanoma cells to a wide array of metabolic perturbations during antigen-specific killing of cancer cells by CD8+ T cells. We illustrated the applicability of this screening platform by showing that CD8+ T cells were more sensitive to ferroptosis induction by inhibitors of glutathione peroxidase 4 (GPX4) than B16 and MC38 cancer cells. Overexpression of ferroptosis suppressor protein 1 (FSP1) or cytosolic GPX4 yielded ferroptosis-resistant CD8+ T cells without compromising their function, while genetic deletion of the ferroptosis sensitivity-promoting enzyme acyl-CoA synthetase long-chain family member 4 (ACSL4) protected CD8+ T cells from ferroptosis but impaired antitumor CD8+ T-cell responses. Our screen also revealed high T cell-specific vulnerabilities for compounds targeting NAD+ metabolism or autophagy and endoplasmic reticulum (ER) stress pathways. We focused the current screening effort on metabolic agents. However, this in vitro screening platform may also be valuable for rapid testing of other types of compounds to identify regulators of antitumor CD8+ T-cell function and potential therapeutic targets.

Arginine Deiminase Induces Immunogenic Cell Death and Is Enhanced by N-acetylcysteine in Murine MC38 Colorectal Cancer Cells and MDA-MB-231 Human Breast Cancer Cells In Vitro.

The use of arginine deiminase (ADI) for arginine depletion therapy is an attractive anticancer approach. Combination strategies are needed to overcome the resistance of severe types of cancer cells to this monotherapy. In the current study, we report, for the first time, that the antioxidant N-acetylcysteine (NAC), which has been used in therapeutic practices for several decades, is a potent enhancer for targeted therapy that utilizes arginine deiminase. We demonstrated that pegylated arginine deiminase (ADI-PEG 20) induces apoptosis and G0/G1 phase arrest in murine MC38 colorectal cancer cells; ADI-PEG 20 induces Ca2+ overload and decreases the mitochondrial membrane potential in MC38 cells. ADI-PEG 20 induced the most important immunogenic cell death (ICD)-associated feature: cell surface exposure of calreticulin (CRT). The antioxidant NAC enhanced the antitumor activity of ADI-PEG 20 and strengthened its ICD-associated features including the secretion of high mobility group box 1 (HMGB1) and adenosine triphosphate (ATP). In addition, these regimens resulted in phagocytosis of treated MC38 cancer cells by bone marrow-derived dendritic cells (BMDCs). In conclusion, we describe, for the first time, that NAC in combination with ADI-PEG 20 not only possesses unique cytotoxic anticancer properties but also triggers the hallmarks of immunogenic cell death. Hence, ADI-PEG 20 in combination with NAC may represent a promising approach to treat ADI-sensitive tumors while preventing relapse and metastasis.

Abstract 3317: Discovery of novel STING agonists with robust anti-tumor activity

Abstract Introduction: Stimulator of interferon genes (STING) is an endoplasmic reticulum (ER) membrane signaling protein, which plays a key role in the sensing of cytoplasmic DNA arising from bacterial and viral infection, as well as self-DNA. Several studies have shown that STING signaling is essential for antitumor immunity by inducing the production of type I IFN and activating both innate and adaptive immunity. Therefore, activation of STING pathway in the tumor microenvironment could be a potential effective approach for cancer immunotherapy. Here, we present the characterization of novel STING agonists in a variety of in vitro cell lines and in vivo murine models. Methods: THP-1 monocyte cells and HEK 293-derived cells transfected with STING variants were used for cellular potency evaluation. Multiple murine tumor models were used for evaluation of in vivo efficacy. Tumor cells were inoculated into C57BL/6 mice and compounds were injected intratumorally three times at every three days when tumors reached a mean volume of approximately 100 mm3. Compounds-treated mice free from tumor for 30 days were re-challenged with MC38 tumor cells in MC38 murine model. Results: Several lead compounds CS-1018, CS-1020 and CS-1010 activate mouse and human STING variants in vitro with much better potency than natural ligand cGAMP and reference compound X. CS-1018 demonstrated dose dependent robust antitumor activity in B16F10 and MC38 mouse models. 3 out of 8 mice achieve complete responses at the dose of 100 ug in B16F10, 25% or 75% of mice were tumor free when treated with 5 ug or 25 ug of compound respectively in MC38. The survival mice from 5 ug and 25 ug groups remained tumor-free after re-challenged with another inoculation of MC38 cancer cells. The antitumor activity of compound CS-1020 and CS-1010 was also demonstrated in MC38 mouse model. When CS-1020 was dosed at 5 ug or 25 ug, complete responses were observed in 63% or 88% of mice respectively. In the case of CS-1010, the dose of 5 ug provides complete responses in 100% of treated mice. Similarly, both compounds induced immune-mediated tumor rejection when re-challenged with the same cancer cells. Conclusions: We have identified several STING agonists, which demonstrated better cellular potency to mouse and human STING alleles compared to natural ligand cGAMP and reference compound. All compounds showed dose dependent antitumor activity in MC38 or B16F10 syngeneic models, in addition, tumor-free mice after treatment of compounds developed tumor specific immunologic memory response in MC38 murine model. Combination studies of identified STING agonists with other IO agents are currently ongoing. The results will be discussed. Citation Format: Anrong Li, Yuntao Song, Chen Dong, Xiaoqi Chen, Junbao Yang. Discovery of novel STING agonists with robust anti-tumor activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3317.

Abstract 939: Evaluating anti-PD-1/4-1BB combination therapy: In vivo efficacy with humanized double knock-in mice

Abstract The transmembrane protein receptor 4-1BB is a member of the tumor necrosis factor (TNF) receptor super family and is involved in the co-stimulation of immune cells. 4-1BB is expressed in activated CD4 helper T cells, B cells, natural killer cells, natural killer T cells, dendritic cells, and activated endothelium. Most regulatory T cells (Tregs) also express 4-1BB, but it remains unclear that whether agonistic antibody treatment exerts pro- or anti-suppressive effect on these cells. 4-1BB enhances tumor rejection because it is upregulated on T cells following activation as its engagement increases T cell proliferation and pro-inflammatory cytokine production. Despite of the toxicity of 4-1BB-targeting drugs associated with overt immune activation, new therapeutic modalities using 4-1BB targeting aptamers, as well as combination therapies with other immuno-modulatory and traditional anti-cancer treatments, have revived excitement for the use of 4-1BB agonists in the clinic. Biocytogen has developed a double humanized B-hPD-1/h4-1BB mouse model to unlock the tremendous potential of combination therapy involving 4-1BB agonists and anti-PD-1 antibodies. In such model, mouse PD-1 gene exon 2, and 4-1BB gene exons 2-7 were replaced with their human counterparts. Murine colon cancer MC38 cells, humanized PD-L1 in MC38 cells, humanized PD-L1 in murine melanoma B16F10 cells, and murine lymphoma EL4 cells were subcutaneously implanted into homozygous B-hPD-1/h4-1BB mice. Combination treatment of Urelumab (anti-4-1BB) and Pembrolizumab (anti-PD-1) has shown enhanced inhibitory effects compared to single antibody treatments using the B-hPD-1/h4-1BB mice models. Based on these findings, it could be concluded that the B-hPD-1/h4-1BB double-humanized mouse model is a validated tool for in vivo evaluation of hPD-1 and h4-1BB antibody combination therapy. Citation Format: Tian Gan, Xiaofei Zhou, Yuting Hu, Chengzhang Shang, Gary Ng. Evaluating anti-PD-1/4-1BB combination therapy: In vivo efficacy with humanized double knock-in mice [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 939.

Abstract 589: Immune biomarker profiling and safety evaluation response to 4-1BB antibody (Urelumab) in humanized 4-1BB mice

Abstract 4-1BB (CD137) belongs to the TNFR superfamily and is expressed by activated CD4 helper T cells, B cells, natural killer cells, natural killer T cells, dendritic cells and Treg cells. 4-1BB is a potential therapeutic target as it enhances tumor rejection by upregulating T cells following activation and its engagement increases T cell proliferation and pro-inflammatory cytokine production. However, the liver toxicity associated with over immune activation has obstructed the clinical development of 4-1BB targeting therapies. To address the issue, Biocytogen has developed humanized B-h4-1BB mice as an efficient platform of both in vivo MOA and safety studies of 4-1BB antibody. In B-h4-1BB mice, murine colon cancer MC38 cells were subcutaneously implanted. Biomarkers, such as, mCD45, mCD3, mCD4, mCD8, mNK, mFoxp3, mCD11b, and etc., were profiled after the treatment with an 4-1BB antibody (Urelumab). FACS, IHC, and IF data showed that Urelumab have increased the ratio of CD8+ T cell, but on the other hand decreased Treg cell, the PD-1 and Tim3 (T cell exhausted marker) upon treatment. Toxicity have also been with the treatment of Urelumab using this model. The blood chemistry assays showed that the high dose Urelumab had toxicity effects compared with the control group and WT C57BL/6 mice. Based on these findings, we conclude that the B-h4-1BB humanized mouse model is a powerful platform for both MOA (biomarker) discovery and safety evaluation of 4-1BB antibody. Citation Format: Jie Xiang, Dirui Li, Hao Yang, Gary Ng, Yuelei Shen. Immune biomarker profiling and safety evaluation response to 4-1BB antibody (Urelumab) in humanized 4-1BB mice [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 589.

Role of heat shock factor 1 (HSF1) on activation-induced metabolic reprogramming of T cells

Abstract Heat Shock Factor 1 (HSF1) is transcriptionally activated in response to a variety of environmental stressors. Data from our laboratory indicates that genetic inactivation of HSF1 significantly delays tumorigenesis in various tumor models. Increasing evidence supports the paradigm that modulating the metabolic bioenergetics of T cells i.e., inhibiting glycolytic flux or enforcing fatty acid oxidation, enhances the formation of more efficient anti tumor CD8+ T-cells. Since, HSF1 is involved in cellular metabolism, in this study, we explored the strategies to manipulate (or reprogram) the metabolic pathways used by the immune system to improve anti-tumor immunity. We observed that deletion of HSF1 profoundly affects the metabolic reprogramming of naive CD8+ T cells upon anti-CD3/CD28 stimulation in vitro. Furthermore, HSF1-deficient T cells show reduced oxygen consumption rate and extracellular acidification rate upon activation. These effects correspond to delayed T-cell receptor signaling and slower activation of naive T cells preventing them from moving towards early exhaustion stage resulting in improved longevity. In addition, we detected delayed initiation of colon cancer MC38 tumors that was implanted into a T-cell specific HSF1 deficient mice compared to wild-type mice. Finally, we confirmed that the delay in tumorigenesis is mediated through CD8 response since treatment of above tumor bearing mice with anti-CD8 antibody reversed the suppressive effects of HSF1 deficient CD8 T cells on tumor growth. Taken together, HSF1 can be a potential therapeutic target to overcome the limitations with existing cancer therapies and further studies will be directed towards exploring impact of HSF1 on checkpoint blockade.

Abstract B043: Identification of secreted PD-L1 variants as a decoy of PD-L1 blockade antibody mediating the therapeutic resistance

Abstract Immune checkpoint blockade therapy targeting PD-L1/PD-1 have been widely used and shown remarkable clinical response in various cancers. However, therapeutic resistance after initial response is increasingly observed and the detailed mechanisms of resistance have yet to be fully understood. Recently, several mechanisms including loss-of-function alteration in genes related to antigen presentation and interferon-receptor signaling have been suggested to induce the resistance to PD-1 blockade treatment, yet few studies have focused on anti-PD-L1 (aPD-L1) blockade therapy. In current study, we performed whole exome sequencing and RNA-sequencing analysis in two non-small cell lung cancer (NSCLC) patients who were refractory during aPD-L1 therapy. We have identified the mutations in RNA splicing related gene, TARDBP/TDP-43, which were uncovered as hot spot mutations in Amyotrophic lateral sclerosis (ALS), and found two unique secreted PD-L1 variants, which lacked the transmembrane domain by aberrant RNA splicing. These secreted PD-L1 variants were shown to be stable by pulse chase assay, and worked as “decoys” of aPD-L1 antibody in the HLA-matched coculture system of iPSC-derived CD8 T cells and cancer cells. Moreover, expression of secreted mPD-L1 variant in mouse MC38 cancer cells conferred the resistance to PD-L1 blockade therapy, and soluble PD-L1 were time dependently accumulated in plasma using the MC38 syngeneic mice model. To further investigate the presence of secreted PD-L1 splicing variants in patients, we additionally analyzed 15 specimen who were resistant to anti-PD-L1 treatment by RNA-seq. We revealed that approximately 20% of therapeutic resistant patients harbored secreted PD-L1 variants and several new mutations in JAK1/2, the key mediator of interferon-receptor signaling, were found in a part of patients as well. Furthermore, we also identified the presence of secreted PD-L1 variants in the surgical specimens of squamous NSCLC patients without prior chemotherapy, targeted therapy, and /or immune-checkpoint inhibitor therapy. Consistent to the data, the plasma level of soluble PD-L1 in patients with secreted PD-L1 variants were high than those without the variants. Collectively, our results elucidated a novel resistant mechanism of PD-L1 blockade antibody mediated by secreted PD-L1 variants. The presence of sPD-L1 splicing variants or the level of soluble PD-L1 in plasma or pleural effusion may work as a biomarker to predict a patient’s response to PD-L1 blockade therapy. Citation Format: Bo Gong, Kazuma Kiyotani, Seiji Sakata, Ken Takahashi, Seiji Nagano, Shun Kumehara, Satoko Baba, Benjamin Besse, Noriko Yanagitani, Luc Friboulet, Makoto Nishio, Kengo Takeuchi, Hiroshi Kawamoto, Naoya Fujita, Ryohei Katayama. Identification of secreted PD-L1 variants as a decoy of PD-L1 blockade antibody mediating the therapeutic resistance [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B043. doi:10.1158/1535-7163.TARG-19-B043