Syngeneic Mice Research Articles

Abstract LB366: KRASG12C inhibition enhances immunogenicity in KRASG12C-mutant colorectal cancer

Abstract RAS mutations are among the most prevalent oncogenic mutations, found in approximately 20% of human cancers. KRAS, the predominantly mutated isoform of RAS, is mutated in 40% of colorectal cancer (CRC) and leads to constitutive activation of the MAPK pathway and other downstream effectors. Despite recent FDA approval for KRASG12C selective inhibitor in non-small cell lung cancer, the response rate in CRC is below 20%, posing a challenge for treatment of these tumors. Several studies have implicated oncogenic KRAS signaling in creating an immunosuppressive tumor microenvironment; therefore, we hypothesized that KRAS inhibitors can enhance anti-tumor immunity, providing a rationale for their combination with immune checkpoint blockade. Using a syngeneic KRASG12C CRC mouse model with knockout of APC, TP53, and SMAD4, we examined tumor cell-intrinsic mechanism of cooperativity between KRAS inhibition and immune response. We found that combining KRASG12C inhibition with anti-PD1 produced a more substantial and sustained reduction in tumor volume compared with KRAS or PD-1 inhibition alone. KRASG12C inhibition led to a significant increase in CD3+CD8+ T cell infiltration compared with vehicle control. Single-cell RNA-sequencing corroborated our observations and revealed increased T cell infiltration in KRASG12C tumors following KRASG12C inhibition. Moreover, these T cells upregulated genes involved in interferon gamma production and T cell activation. Importantly, we observed a significant reduction in the Ras pathway genes, specifically in the tumor cell population, along with enrichment of genes involved in abnormal antigen presentation and MHC Class I peptide loading complex. Mechanistically, we found that KRASG12C inhibition activates the innate immune response, which subsequently induce Type I interferons that activate the expression of T cell-recruiting interferon stimulated genes like CXCL9, CXCL10, IFIT1, IFIT2, and IFIT3. Our data presents a connection between KRAS inhibition and anti-tumor immunity, providing insights into novel combination strategies for KRASG12C colorectal cancers. Citation Format: Parasvi S. Patel, Jun Tian, Ferran Fece de la Cruz, Jacquelyn Curtis, Apekshya Panda, Tomonori Oka, Shadmehr Demehri, Moshe Sade-Feldman, Scott Koptez, Ryan B. Corcoran. KRASG12C inhibition enhances immunogenicity in KRASG12C-mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB366.

IRX4204 Induces Senescence and Cell Death in HER2-positive Breast Cancer and Synergizes with Anti-HER2 Therapy.

Rexinoids, agonists of nuclear retinoid X receptor (RXR), have been used for the treatment of cancers and are well tolerated in both animals and humans. However, the usefulness of rexinoids in treatment of breast cancer remains unknown. This study examines the efficacy of IRX4204, a highly specific rexinoid, in breast cancer cell lines and preclinical models to identify a biomarker for response and potential mechanism of action. IRX4204 effects on breast cancer cell growth and viability were determined using cell lines, syngeneic mouse models, and primary patient-derived xenograft (PDX) tumors. In vitro assays of cell cycle, apoptosis, senescence, and lipid metabolism were used to uncover a potential mechanism of action. Standard anti-HER2 therapies were screened in combination with IRX4204 on a panel of breast cancer cell lines to determine drug synergy. IRX4204 significantly inhibits the growth of HER2-positive breast cancer cell lines, including trastuzumab and lapatinib-resistant JIMT-1 and HCC1954. Treatment with IRX4204 reduced tumor growth rate in the MMTV-ErbB2 mouse and HER2-positive PDX model by 49% and 44%, respectively. Mechanistic studies revealed IRX4204 modulates lipid metabolism and induces senescence of HER2-positive cells. In addition, IRX4204 demonstrates additivity and synergy with HER2-targeted mAbs, tyrosine kinase inhibitors, and antibody-drug conjugates. These findings identify HER2 as a biomarker for IRX4204 treatment response and demonstrate a novel use of RXR agonists to synergize with current anti-HER2 therapies. Furthermore, our results suggest that RXR agonists can be useful for the treatment of anti-HER2 resistant and metastatic HER2-positive breast cancer.

Abstract LB077: CSF-1R inhibition with Pimicotinib (ABSK021) enhanced anti-tumor efficacy of KRASG12C inhibitors in preclinical non-small cell lung cancer mouse models

Abstract Background: KRAS mutations are highly prevalent oncogenic drivers in human cancers and KRASG12C is the most frequent mutations found in KRAS-mutant non-small lung cancer (NSCLC). It is reported that tumor associated macrophages (TAMs) are enriched in KRAS-driven transgenic lung cancer models. Depletion of macrophage results in a significant decrease in tumor burden and increased survival. Sotorasib (AMG510), the first KRASG12C inhibitor approved by FDA, has been found to modulate tumor immunity, impacting the recruitment of macrophages. CSF-1R signaling is critical for macrophage proliferation and survival. CSF-1R inhibition depletes TAMs and reprograms tumor microenvironment (TME), resulting in enhancement of anti-tumor immunity. Therefore, the combination of KRASG12C and CSF-1R inhibitors may synergize to enhance anti-tumor efficacy. Pimicotinib (ABSK021) is a potential best-in-class small molecule inhibitor of CSF-1R in clinical development of multiple indications. Here, we conducted in vivo experiments to explore the combined effects of KRASG12C and CSF-1R inhibitors. Methods: In vivo efficacy studies were performed to evaluate the combined treatment of KRASG12C inhibitors (AMG510 and ABSK071, a next-generation inhibitor targeting KRASG12C with better inhibitory activity) and CSF-1R inhibitor (ABSK021) in NCI-H2122 PBMC humanized mice and LLC syngeneic mice. RNA sequencing was employed to investigate the mechanism of action underlying the synergistic anti-tumor effect. Immunohistochemistry (IHC) was utilized to examine the changes of immune cell populations in TME. Results: The combinatory regimen of ABSK021 and KRASG12C inhibitors showed improved anti-tumor effects than each single agent alone in both mouse NSCLC models. Bioinformatics and follow-up analysis revealed a reduction in immune suppressive TAMs in tumors treated with ABSK021 alone or in combination with KRASG12C inhibitors. Furthermore, modulation of TME related to anti-tumor immunity, such as activated CD4 T, CD8 T and NK cells, was increased, and pro-tumor immunity, such as MDSC, regulatory T cells, was decreased in combination group. IHC results confirmed that ABSK021 addition led to macrophage depletion and more CD8 T cell infiltration in TME. Conclusions: For the first time, we demonstrate that the combined inhibition of KRASG12C and CSF-1R leads to superior therapeutic efficacy in preclinical NSCLC mouse models. This results suggests a potential novel therapeutic regimen that could yield improved clinical benefit to patients. Citation Format: Nannan Zhang, Bin Shen, Shenyan Liu, Cheng Dai, Haiyan Ying, Fushen Guo, Zhixuan Zhu, Wan Shi, Min Tu, Jie Wang, Jie Zhang, Manqi Liu, Qi Zhang, Zhui Chen. CSF-1R inhibition with Pimicotinib (ABSK021) enhanced anti-tumor efficacy of KRASG12C inhibitors in preclinical non-small cell lung cancer mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB077.

Abstract LB237: PVRL2 suppresses antitumor immune responses through PVRIG- and TIGIT-independent pathways

Abstract In recent years, PVRL2 (also known as Nectin-2 or CD112), a member of the Nectin family, has emerged as a crucial regulator of anti-tumor immune responses. PVRL2 interacts with the co-inhibitory receptor PVRIG that is expressed on T cells and NK cells, inhibiting their function. This interaction has thus become the presumed mechanism for PVRL2’s immunoinhibitory function. Therapeutic development targeting the PVRL2 pathway has primarily focused on the receptor PVRIG, with two anti-PVRIG antibodies currently undergoing Phase 1/2 clinical trials (NCT03667716, NCT04570839, NCT05746897). However, to date, very few studies have directly investigated the role of PVRL2, and whether PVRL2 indeed acts through PVRIG hasn’t been formally tested. Our recent work reveals the crucial role of PVRL2 in suppressing anti-tumor immune responses across multiple syngeneic mouse models. CRISPR-directed deletion of PVRL2 robustly reduced tumor growth in an immune-dependent manner, with an even greater effect than seen with the deletion of the prominent checkpoint, PD-L1. Specifically, our findings suggest that PVRL2 functions by suppressing CD8 T and NK cells in the tumor microenvironment. Interestingly, the impact of PVRL2 on tumor growth in our study is certainly much more significant than observed in previous work on PVRIG. To follow up on this interesting finding and determine whether the PVRL2’s impact on immune cells acts through PVRIG, we generated Pvrig KO mice. Surprisingly, we found that PVRL2’s function is largely independent of PVRIG, as it still robustly promotes tumor growth even in the absence of PVRIG, indicating PVRIG-independent mechanisms. We further demonstrate that PVRL2 operates in parallel to the PVR-TIGIT pathway, another important immunoregulatory pathway in the Nectin family. Combined deletion of PVR or PVRIG with PVRL2 loss did not further suppress tumor growth, while combined TIGIT blockade with PVRL2 loss resulted in the most substantial reduction in tumor growth. These findings strongly indicate the existence of additional unknown receptors mediating PVRL2’s function that remain to be discovered. Importantly, our study uncovers PVRL2’s central role in suppressing anti-tumor immune responses through mechanism outside its presumed receptor PVRIG, providing a compelling rationale for directly targeting PVRL2 itself. Combining PVRL2 and TIGIT targeting results in a near-complete block in tumor growth, offering a novel and promising therapeutic approach for cancer immunotherapy through the combinatorial targeting of PVRL2 and TIGIT. Citation Format: Jiuling Yang, Li Wang, James Byrnes, Lisa Kirkemo, Hannah Driks, Cassandra Belair, Oscar Aguilar, Lewis Lanier, Jim Wells, Lawrence Fong, Robert Blelloch. PVRL2 suppresses antitumor immune responses through PVRIG- and TIGIT-independent pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB237.

Abstract LB352: Unraveling therapeutic potentials of mRNA-based cancer vaccine concurrently targeting heterogeneous KRAS mutant cancer

Abstract The utilization of messenger RNA (mRNA)-based cancer vaccines represents a compelling therapeutic strategy, providing distinct advantages over alternative modalities such as peptide vaccines or small-molecule-based cancer therapies. This innovative approach enables the concurrent targeting of heterogeneous cancer populations characterized by multiple mutations while preserving the integrity of normal cells. The Kristen rat sarcoma viral oncogene (KRAS) mutation is prevalent in lung, pancreatic, and colon cancer, and patients harboring KRAS mutations face a particularly dismal prognosis. This study focuses on the optimization of an mRNA-based cancer vaccine designed to target various KRAS mutations, demonstrating its efficacy inducing potent anti-tumor immune responses in both ex vivo immune cell and cancer cell co-culture, as well as in vivo syngeneic mouse cancer models. For the ex vivo evaluation of the multi-targeting capabilities of the vaccine, human peripheral blood mononuclear cells (PBMCs) primed with our mRNA cancer vaccine were subsequently co-incubated with human normal and cancer cell lines harboring KRAS mutations to assess antigen-specific immune responses and the normal cell-sparing effect of the cancer vaccine. Four types of KRAS mutant cancer cells co-cultured with the vaccine-activated PBMCs showed substantially decreased cell viability. We found enrichment of cytotoxic and pro-inflammatory cytokines including ganzyme B, IFNγ, IL-6 and IL-10 in co-culture system with KRAS vaccine transfected monocyte and PBMCs. This suggests that multiple KRAS mutations can be targeted with a single type of mRNA vaccine candidate. In the LL/2 syngeneic model (murine Lewis lung carcinoma, KRAS G12C mutant), the in vivo efficacy of KRAS cancer vaccine candidates was evaluated, revealing a notable reduction in tumor growth in response to the vaccine treatment. Also, during the treatment period, there were no significant clinical symptoms in the mouse between groups indicating the vaccine doses were tolerable. These results indicate that the KRAS vaccine effectively inhibits the growth of an LL/2 tumor which has the immunosuppressive tumor microenvironment. The ability to address the challenges posed by diverse KRAS mutations underscores the promising potential of this multiple-KRAS mutation targeting mRNA-based cancer vaccine in the pursuit of enhanced therapeutic outcomes for patients afflicted with KRAS-mutant cancer. Citation Format: Chang Gyu Lim, Seung-Hyun Shin, Youngjin Han, Yong Ho Heo, Innah Kim, Ji Hee Lee, Miyoung Lee, Seongju Jeong, Yunjae Kim, Jooyun Byun, Daejin Kim, In Young Choi. Unraveling therapeutic potentials of mRNA-based cancer vaccine concurrently targeting heterogeneous KRAS mutant cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB352.

Abstract LB156: Targeting epigenetic activity of beta-catenin/CBP impedes oral cancer progression

Abstract Head and neck cancer is a complex malignancy with its major anatomical subsite, cancer of the oral cavity, ranking among the most deadly and disfiguring cancers. Oral cancer presents primarily as HPV-negative oral squamous cell carcinoma (OSCC) whose etiology is associated with tobacco and alcohol use and for which there are limited treatments. Whereas immunotherapies, such as anti-PD-1 antibodies, have become a promising therapeutic option, only ~20% of head neck cancer patients benefit from anti-PD-1 immunotherapy. We and others have shown that non-mutational epigenetic reprogramming mediated by the β-catenin/CBP complex promotes aggressive cell phenotypes in OSCC by establishing open chromatin at the transcription start sites of genes associated with cancer stemness. Accordingly, pharmacological inhibition of this complex dramatically inhibits OSCC evolution in a syngeneic mouse model of OSCC. Here, we evaluated whether the inhibition of β-catenin/CBP epigenetic activity would enhance the effects of anti-PD-1 immunotherapy. We adapted a syngeneic mouse model of tobacco-associated oral carcinogenesis that utilizes a mouse cell line, 4MOSC1, derived from 4-nitroquinoline-1 oxide- (4NQO)-induced tongue tumors of C57BL/6J mice. After tumors developed for 7 days, mice were blindly separated into treatment cohorts (n=13, each) to receive vehicle control (PBS), monotherapy (either 10 mg/kg anti-PD-1 EOD IP, or 100 mg/kg E7386, a Wnt signaling pathway modulator, QD oral gavage) or combination therapy (anti-PD-1 + E7386). Tumor isografts were harvested 11 days post initiation of treatments and processed for histopathology, immunohistochemistry, and immunofluorescence analyses. Measurements of tumor volumes showed that combination therapy resulted in a statistically significant reduction by ~80% compared to control mice and that it surpassed tumor decrease by either monotherapy. These results were confirmed by histopathology analyses. Evaluation of tumor tissues by immunofluorescence revealed statistically significant decreases in Cbp, H3K4me3, Keratin 14, and Podoplanin expression in response to E7386 alone and in combination with anti PD-1. Collectively our results suggest that a combination therapy comprising anti PD-1 treatment with E7386-targeting β-catenin/CBP epigenetic signaling is likely to impede OSCC evolution to advanced disease. Supported by Eisai, Co Ltd Research Award (MAK), NIH 5R01 DE030350 (MAK, SM, XV) and 5R01 DE031413 (MVB). Citation Format: Emily Fisher, Anthony Spinella, Junji Matsui, Kenichi Nomoto, Xaralabos Varelas, Manish Bais, Maria Kukuruzinska. Targeting epigenetic activity of beta-catenin/CBP impedes oral cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB156.

Iron Oxide Nanoparticles Inhibit Tumor Progression and Suppress Lung Metastases in Mouse Models of Breast Cancer.

Systemic exposure to starch-coated iron oxide nanoparticles (IONPs) can stimulate antitumor T cell responses, even when little IONP is retained within the tumor. Here, we demonstrate in mouse models of metastatic breast cancer that IONPs can alter the host immune landscape, leading to systemic immune-mediated disease suppression. We report that a single intravenous injection of IONPs can inhibit primary tumor growth, suppress metastases, and extend survival. Gene expression analysis revealed the activation of Toll-like receptor (TLR) pathways involving signaling via Toll/Interleukin-1 receptor domain-containing adaptor-inducing IFN-β (TRIF), a TLR pathway adaptor protein. Requisite participation of TRIF in suppressing tumor progression was demonstrated with histopathologic evidence of upregulated IFN-regulatory factor 3 (IRF3), a downstream protein, and confirmed in a TRIF knockout syngeneic mouse model of metastatic breast cancer. Neither starch-coated polystyrene nanoparticles lacking iron, nor iron-containing dextran-coated parenteral iron replacement agent, induced significant antitumor effects, suggesting a dependence on the type of IONP formulation. Analysis of multiple independent clinical databases supports a hypothesis that upregulation of TLR3 and IRF3 correlates with increased overall survival among breast cancer patients. Taken together, these data support a compelling rationale to re-examine IONP formulations as harboring anticancer immune (nano)adjuvant properties to generate a therapeutic benefit without requiring uptake by cancer cells.

Skull-Derived Myeloid Cells Augment T Cell Responses and Suppress Glioblastoma Growth

INTRODUCTION: Recent studies have implicated skull marrow as a functional myeloid reservoir in CNS pathology. However, its contribution to malignancy remains unexplored. METHODS: Fluorescently labeled calvarial flaps were transplanted onto syngeneic glioblastoma-bearing mice, followed by flow cytometric profiling of tumor-infiltrative leukocytes. To assay the functional relevance of SDMCs, tumor-bearing C57BL/6 mice were treated with preemptive calvarial ablation (13 Gy irradiation), or conversely intracalvarial AMD3100 to augment myeloid egress from marrow niches. Tumor burden was monitored via survival and bioluminescent imaging. RESULTS: 72 h following CMFDA-stained calvarial transplantation into tumor-bearing Balb/C mice, 40.3% of tumor-infiltrative myeloid cells were fluorescent and thus skull-derived; transplantation in an alternative longitudinal model (GFP+ flaps, C57BL/6) validated that SDMCs were robust and viable at 3 weeks post-operatively. As MHCII+ cells were disproportionately enriched among SDMCs (87.9% vs 67.3%, p = 0.012), we interrogated the immunogenicity of these cells through targeted ablation. Skull-ablated mice had reduced infiltration by antigen-presenting cells than controls (cDCs: 1.1% vs 4.5%, p = 0.002; macrophages: 14.4% vs 36.6%, p < 0.001) and 6-fold greater necrosis (67.7% vs 13.5% apoptotic, p < 0.001), suggesting an impaired ability to mount a controlled, adaptive immune response. The stimulatory role of SDMCs was further demonstrated via intracalvarial AMD3100 administration, which through its promotion of myeloid precursor egress (0.26% vs 0.02%, p < 0.001) and cDC2 infiltration (10.4% vs 3.0%, p = 0.003) yielded robust CD4+ T cell activation and effector memory differentiation. These differences were clinically meaningful, as skull irradiation accelerated tumor growth and attenuated survival compared to controls, while AMD3100 treatment accomplished the opposite (median OS: 17d vs 22d, p < 0.001; 26.5d vs 22d, p = 0.006). CONCLUSIONS: The preferential polarization of SDMCs into immunostimulatory APCs warrants the continued exploration of local marrow-targeting agents (e.g., AMD3100) as therapeutic modalities.

1236 Skull-Derived Myeloid Cells Augment T Cell Responses and Suppress Glioblastoma Growth

INTRODUCTION: Recent studies have implicated skull marrow as a functional myeloid reservoir in CNS pathology. However, its contribution to malignancy remains unexplored. METHODS: Fluorescently labeled calvarial flaps were transplanted onto syngeneic glioblastoma-bearing mice, followed by flow cytometric profiling of tumor-infiltrative leukocytes. To assay SDMC function, tumor-bearing C57BL/6 mice were treated with preemptive calvarial ablation (13 Gy irradiation), or conversely intracalvarial AMD3100 to augment myeloid egress from marrow niches. Tumor burden was monitored via survival and bioluminescent imaging. RESULTS: 72 h following CMFDA-stained calvarial transplantation into tumor-bearing Balb/C mice, 40.3% of tumor-infiltrative myeloid cells were fluorescent and thus skull-derived; transplantation in an alternative longitudinal model (GFP+ flaps, C57BL/6) validated that SDMCs were robust and viable at 3 weeks post-operatively. As MHCII+ cells were disproportionately enriched among SDMCs (87.9% vs 67.3%, p = 0.012), we interrogated the immunogenicity of these cells through targeted ablation. Indeed, skull-ablated mice had reduced aggregate infiltration by antigen-presenting cells than controls (cDCs: 1.1% vs 4.5%, p = 0.002; macrophages: 14.4% vs 36.6%, p < 0.001) and 6-fold greater necrosis (67.7% vs 13.5% apoptotic, p < 0.001), suggesting an impaired ability to mount a controlled, adaptive immune response. The stimulatory role of SDMCs was further demonstrated via intracalvarial AMD3100 administration, which through its promotion of myeloid precursor egress (0.26% vs 0.02%, p < 0.001) and cDC2 infiltration (10.4% vs 3.0%, p = 0.003) yielded robust CD4+ T cell activation and effector memory differentiation. These differences were clinically meaningful, as skull irradiation accelerated tumor growth and attenuated survival compared to controls, while the opposite was observed with AMD3100 treatment (median OS: 17d vs 22d, p < 0.001; 26.5 d vs 22 d, p = 0.006). CONCLUSIONS: The preferential polarization of SDMCs into immunostimulatory APCs warrants the continued exploration of local marrow-targeting agents (e.g., AMD3100) as therapeutic modalities.

PVRL2 Suppresses Antitumor Immunity through PVRIG- and TIGIT-independent Pathways.

Poliovirus receptor-related 2 (PVRL2, also known as nectin-2 or CD112) is believed to act as an immune checkpoint protein in cancer; however, most insight into its role is inferred from studies on its known receptor, poliovirus receptor (PVR)-related immunoglobulin domain protein (PVRIG, also known as CD112R). Here, we study PVRL2 itself. PVRL2 levels were found to be high in tumor cells and tumor-derived exosomes. Deletion of PVRL2 in multiple syngeneic mouse models of cancer showed a dramatic reduction in tumor growth that was immune dependent. This effect was even greater than that seen with deletion of PD-L1. PVRL2 was shown to function by suppressing CD8+ T and natural killer cells in the tumor microenvironment. The loss of PVRL2 suppressed tumor growth even in the absence of PVRIG. In contrast, PVRIG loss showed no additive effect in the absence of PVRL2. T-cell immunoreceptor with Ig and ITIM domains (TIGIT) blockade combined with PVRL2 deletion resulted in a near complete block in tumor growth. This effect was not recapitulated by the combined deletion of PVRL2 with its paralog, PVR, which is the ligand for TIGIT. These data uncover PVRL2 as a distinct inhibitor of the antitumor immune response with functions beyond that of its known receptor PVRIG. Moreover, the data provide a strong rationale for combinatorial targeting of PVRL2 and TIGIT for cancer immunotherapy.

Deubiquitinase USP4 suppresses antitumor immunity by inhibiting IRF3 activation and tumor cell-intrinsic interferon response in colorectal cancer

Despite the approval of immune checkpoint blockade (ICB) therapy for various tumor types, its effectiveness is limited to only approximately 15% of patients with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR) colorectal cancer (CRC). Approximately 80%–85% of CRC patients have a microsatellite stability (MSS) phenotype, which features a rare T-cell infiltration. Thus, elucidating the mechanisms underlying resistance to ICB in patients with MSS CRC is imperative. In this study, we demonstrate that ubiquitin-specific peptidase 4 (USP4) is upregulated in MSS CRC tumors and negatively regulates the immune response against tumors in CRC. Additionally, USP4 represses the cellular interferon (IFN) response and antigen presentation and impairs PRR signaling-mediated cell death. Mechanistically, USP4 impedes the nuclear localization of interferon regulator Factor 3 (IRF3) by deubiquitinating the K63-polyubiquitin chain of TRAF6 and IRF3. Knockdown of USP4 enhances the infiltration of T cells in CRC tumors and overcomes ICB resistance in an MC38 syngeneic mouse model. Moreover, published datasets revealed that patients showing higher USP4 expression exhibited decreased responsiveness to anti-PD-L1 therapy. These findings highlight an essential role of USP4 in the suppression of antitumor immunity in CRC.

Gemcitabine elaidate and ONC201 combination therapy for inhibiting pancreatic cancer in a KRAS mutated syngeneic mouse model

Approximately 90% of pancreatic cancer (PC) contain KRAS mutations. Mutated KRAS activates the downstream oncogenic PI3K/AKT and MEK signaling pathways and induces drug resistance. However, targeting both pathways with different drugs can also lead to excessive toxicity. ONC201 is a dual PI3K/AKT and MEK pathway inhibitor with an excellent safety profile that targets death receptor 5 (DR5) to induce apoptosis. Gemcitabine (GEM) is a first-line chemotherapy in PC, but it is metabolically unstable and can be stabilized by a prodrug approach. In this study, phospho-Akt, phospho-mTOR, and phospho-ERK protein expressions were evaluated in patient PDAC-tissues (n = 10). We used lipid-gemcitabine (L_GEM) conjugate, which is more stable and enters the cells by passive diffusion. Further, we evaluated the efficacy of L_GEM and ONC201 in PC cells and “KrasLSL-G12D; p53LoxP; Pdx1-CreER (KPC) triple mutant xenograft tumor-bearing mice. PDAC patient tissues showed significantly higher levels of p-AKT (Ser473), p-ERK (T202/T204), and p-mTOR compared to surrounding non-cancerous tissues. ONC201 in combination with L_GEM, showed a superior inhibitory effect on the growth of MIA PaCa-2 cells. In our in-vivo study, we found that ONC201 and L_GEM combination prevented neoplastic proliferation via AKT/ERK blockade to overcome chemoresistance and increased T-cell tumor surveillance. Simultaneous inhibition of the PI3K/AKT and MEK pathways with ONC201 is an attractive approach to potentiate the effect of GEM. Our findings provide insight into rational-directed precision chemo and immunotherapy therapy in PDAC.

Dynamic Proteomic Changes in Tumor and Immune Organs Reveal Systemic Immune Response to Tumor Development

In orthotopic mouse tumor models, tumor progression is a complex process, involving interactions among tumor cells, host cell-derived stromal cells, and immune cells. Much attention has been focused on the tumor and its tumor microenvironment, while the host’s macroenvironment including immune organs in response to tumorigenesis is poorly understood. Here, we report a temporal proteomic analysis on a subcutaneous tumor and three immune organs (LN, MLN, and spleen) collected on Days 0, 3, 7, 10, 14, and 21 after inoculation of mouse forestomach cancer cells in a syngeneic mouse model. Bioinformatics analysis identified key biological processes during distinct tumor development phases, including an initial acute immune response, the attack by the host immune system, followed by the adaptive immune activation, and the build-up of extracellular matrix. Proteomic changes in LN and spleen largely recapitulated the dynamics of the immune response in the tumor, consistent with an acute defense response on D3, adaptive immune response on D10, and immune evasion by D21. In contrast, the immune response in MLN showed a gradual and sustained activation, suggesting a delayed response from a distal immune organ. Combined analyses of tumors and host immune organs allowed the identification of potential therapeutic targets. A proof-of-concept experiment demonstrated that significant growth reduction can be achieved by dual inhibition of MEK and DDR2. Together, our temporal proteomic dataset of tumors and immune organs provides a useful resource for understanding the interaction between tumors and the immune system and has the potential for identifying new therapeutic targets for cancer treatment.

Swine pseudorabies virus attenuated vaccine reprograms the kidney cancer tumor microenvironment and synergizes with PD-1 blockade.

The global incidence rate of kidney cancer (KC) has been steadily increasing over the past 30 years. With the aging global population, kidney cancer has become an escalating concern that necessitates vigilant surveillance. Nowadays, surgical intervention remains the optimal therapeutic approach for kidney cancer, while the availability of efficacious treatments for advanced tumors remains limited. Oncolytic viruses, an emerging form of immunotherapy, have demonstrated encouraging anti-neoplastic properties and are progressively garnering public acceptance. However, research on oncolytic viruses in kidney cancer is relatively limited. Furthermore, given the high complexity and heterogeneity of kidney cancer, it is crucial to identify an optimal oncolytic virus agent that is better suited for its treatment. The present study investigates the oncolytic activity of the Pseudorabies virus live attenuated vaccine (PRV-LAV) against KC. The findings clearly demonstrate that PRV-LAV exhibits robust oncolytic activity targeting KC cell lines. Furthermore, the therapeutic efficacy of PRV-LAV was confirmed in both a subcutaneous tumor-bearing nude mouse model and a syngeneic mouse model of KC. Combined RNA-seq analysis and flow cytometry revealed that PRV-LAV treatment substantially enhances the infiltration of a diverse range of lymphocytes, including T cells, B cells, macrophages, and NK cells. Additionally, PRV-LAV treatment enhances T cell activation and exerts antitumor effects. Importantly, the combination of PRV-LAV with anti-PD-1 antibodies, an approved drug for KC treatment, synergistically enhances the efficacy against KC. Overall, the discovery of PRV-LAV as an effective oncolytic virus holds significant importance for improving the treatment efficacy and survival rates of KC patients.

Targeting CD73 with flavonoids inhibits cancer stem cells and increases lymphocyte infiltration in a triple-negative breast cancer mouse model.

Chemotherapy remains the mainstay treatment for triple-negative breast cancer (TNBC) due to the lack of specific targets. Given a modest response of immune checkpoint inhibitors in TNBC patients, improving immunotherapy is an urgent and crucial task in this field. CD73 has emerged as a novel immunotherapeutic target, given its elevated expression on tumor, stromal, and specific immune cells, and its established role in inhibiting anti-cancer immunity. CD73-generated adenosine suppresses immunity by attenuating tumor-infiltrating T- and NK-cell activation, while amplifying regulatory T cell activation. Chemotherapy often leads to increased CD73 expression and activity, further suppressing anti-tumor immunity. While debulking the tumor mass, chemotherapy also enriches heterogenous cancer stem cells (CSC), potentially leading to tumor relapse. Therefore, drugs targeting both CD73, and CSCs hold promise for enhancing chemotherapy efficacy, overcoming treatment resistance, and improving clinical outcomes. However, safe and effective inhibitors of CD73 have not been developed as of now. We used in silico docking to screen compounds that may be repurposed for inhibiting CD73. The efficacy of these compounds was investigated through flow cytometry, RT-qPCR, CD73 activity, cell viability, tumorsphere formation, and other in vitro functional assays. For assessment of clinical translatability, TNBC patient-derived xenograft organotypic cultures were utilized. We also employed the ovalbumin-expressing AT3 TNBC mouse model to evaluate tumor-specific lymphocyte responses. We identified quercetin and luteolin, currently used as over-the-counter supplements, to have high in silico complementarity with CD73. When quercetin and luteolin were combined with the chemotherapeutic paclitaxel in a triple-drug regimen, we found an effective downregulation in paclitaxel-enhanced CD73 and CSC-promoting pathways YAP and Wnt. We found that CD73 expression was required for the maintenance of CD44highCD24low CSCs, and co-targeting CD73, YAP, and Wnt effectively suppressed the growth of human TNBC cell lines and patient-derived xenograft organotypic cultures. Furthermore, triple-drug combination inhibited paclitaxel-enriched CSCs and simultaneously improved lymphocyte infiltration in syngeneic TNBC mouse tumors. Conclusively, our findings elucidate the significance of CSCs in impairing anti-tumor immunity. The high efficacy of our triple-drug regimen in clinically relevant platforms not only underscores the importance for further mechanistic investigations but also paves the way for potential development of new, safe, and cost-effective therapeutic strategies for TNBC.

Abstract 162: Fatty acid synthesis blockade synergizes with immune checkpoint blockade by repolarizing macrophages and enhancing anti-tumor cytotoxicity in gastric cancer

Abstract Background: Immune checkpoint blockade (ICB), which unleashes potent CD8+ T cell-based anti-tumor responses, has emerged as a promising therapeutic option for several cancer types. However, response rates stay limited in gastric cancer (GC) patients, indicating the necessity of combinational strategies to overcome other immunosuppressive factors. Fatty acid synthesis (FAS) is an indispensable metabolic pathway proven to support cancer cell survival. The rate-limiting enzyme of FAS, FASN, is upregulated in several cancers and could contribute to cancer immune escape. Though some investigations propose that specific gene alterations can cause FASN upregulation under the GC setting, the immunoregulatory role and therapeutic value of FASN in the tumor microenvironment (TME) of GC have not been fully elucidated. Methods: FASN expression was measured by Western Blotting and flow cytometry. Bioinformatic analysis was conducted via an online website (www.camoip.net). The syngeneic GC mouse model was established by subcutaneous inoculation of MFC cells in 615-line mice, treated by vehicles, FASN inhibitor (FASNi), anti-PD-1 antibodies, or FASNi+anti-PD-1 antibodies. TAM and CD8+ T cell depletion was implemented by anti-CSF1R and anti-CD8α antibodies. Bone marrow-derived macrophages (BMDMs) were extracted from the femurs of 615-line mice, induced by M-CSF and stimulated by LPS or IL-4. The proportions and functional status of immune cells were identified by flow cytometry. Results: FASN was upregulated in GC tissues and GC human cell lines. Bioinformatic analyses demonstrated that FASN expression was related to poor infiltration of cytotoxic lymphocytes, as well as the downregulation of pathways related to anti-cancer immune responses. FASNi inhibited tumor growth in a syngeneic GC mouse model, with elevated PD-1 and IFN-γ expression in CD8+ T cells and increased NK cell infiltration, suggesting the enhancement in anti-cancer cytotoxicity. Meanwhile, FASNi induced a shift from M2-like to M1-like in tumor-associated macrophages (TAM). We detected that M2-like TAM and CD8+ T cells harbored higher FASN expression than other immune cells in GC mouse tissues, and tumor-suppressing effects of FASN inhibition could be reversed by TAM and CD8+ T cell depletion, which corroborated the key role of TAM and CD8+ T cells in shaping FASN-mediated tumor regulation. FASNi could also repolarize BMDMs from M1-like to M2-like in vitro. Finally, FASNi exhibited synergistic tumor control with anti-PD-1 therapy in GC and melanoma mouse models. Conclusion: This work sheds light on the impact of FASN on TME modulation of GC. We proved that FASNi could repolarize M2-like TAM to M1 phenotypes and promote cytotoxic lymphocyte-mediated anti-tumor immunity. Our results propose FASN inhibition as a potential therapeutic strategy to sensitize ICB therapy in GC. Citation Format: Hanbing Wang, Tao Shi, Yue Wang, Yuting Luo, Yunfeng Pan, Xiaoyu Zhou, Yue Zhang, Baorui Liu, Jia Wei. Fatty acid synthesis blockade synergizes with immune checkpoint blockade by repolarizing macrophages and enhancing anti-tumor cytotoxicity in gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 162.

Abstract 86: Deep immuno-profiling of syngeneic tumor mouse models for preclinical studies

Abstract The identification of the major cellular players involved in the progression of a type of cancer is a key step for the success of new immunotherapies for personalized medicine. Immune cells play critical functions in cancer, and mice with intact immune systems are vital to understanding tumor immunology. It is however a daunting challenge as complex relationships interplay between tumor cells and the immune system. Each component of innate immunity or adaptive immunity, such as T lymphocytes, macrophages or neutrophils, may be directed to a pro- or anti-tumor function. In order to cope with the complexity of the tumor microenvironment, it is necessary to use an experimental approach capable of characterizing the heterogeneity of the cell types present in the tumor, the evolution of their relative proportion and their fine-tuned functional specificity. This approach leads to the identification of new cellular biomarkers of different stages of tumor progression in order to identify new targets for therapeutic time-window of and improve cancer diagnosis To decipher the impact of immunotherapy treatments involved in the anti-tumor response, cellular phenotyping of leukocytes infiltrating a tumor but also those present in peripheral organs is necessary. Essentially based on extracellular labeling, this primary screen aims to quantify the different cell populations present in a syngenic tumor models on B6/N or BalbC genetical backgrounds. In order to increase our understanding in the precise mode of action of anti-PD1 treatment at the cellular level in sensitive and unsensitive models, we investigated immunophenotypes and responses to immune checkpoint inhibitor (ICI) of several hallmark syngeneic tumor models (MC38, CT26, B16F10, B16-OVA, RENCA, EMT6) in immunocompetent mouse models by flow and mass cytometry. We compared growth kinetics and profiled the immune cell composition of tumor microenvironment (TME), draining lymph node (dLN) and blood in order to establish immune-phenotypic cell signatures that correlates with treatment efficacy. Supervised, unsupervised and integrative data analysis as well as visualization tools are used to identify significant changes across different experimental settings. Our results indicate that each model possesses a unique tumor-immune infiltrate profile that can be modulated with immunotherapies. Overall, these studies provide an important resource of highly-characterized syngeneic tumor model and highlight the importance of tumor immune landscape variance across models that will drive selecting the most appropriate model to test novel immunotherapeutic agents and enhance our translation of knowledge from syngeneic models to human tumors. Citation Format: Anais Joachim, Emilie Maturin, Marielle Mello, Lilia Hadjem, Magali Grange, Olivier Deas, Ana Zarubica, Bernard Malissen, Hervé Luche, François Romagne, Stéphanie Blanchin. Deep immuno-profiling of syngeneic tumor mouse models for preclinical studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 86.

Abstract 4457: Skeletal muscle-infiltrating CD8 T cells exacerbate muscle atrophy in a syngeneic lung cancer cachexia mouse model

Abstract Cancer-associated cachexia (CAC) is a devastating syndrome of irreversible body weight loss and muscle wasting. CAC has been reported to often lead to poor outcomes of immune checkpoint inhibitors (ICIs), emerging as a standard treatment for various types of cancer. Previously, we have demonstrated that KRAS-mutant lung tumor tissues display an immunosuppressive microenvironment with decreased CD8 T cells and increased regulatory T cells (Tregs). In this orthotopic lung cancer mouse model, treatment with an anti-PD-L1 antibody, a representative ICI, reduced tumor burden, whereas accelerated loss of body weight and skeletal muscle mass. We thus assumed that CD8 T cells could facilitate skeletal muscle wasting in lung tumor-bearing mice, a key feature of CAC. First, we established a syngeneic CAC mouse model through orthotopic transplantation of murine lung cancer cells. At 7 weeks post-injection, these mice developed CAC, displaying over 20 % body weight loss, almost total loss of epididymal fats, and profound skeletal muscle wasting. In line with our assumption, CAC mice showed an increased number of CD8 T cells but a reduced number of Tregs in skeletal muscles, compared to tumor-free control mice. We then investigated whether skeletal muscle-infiltrating CD8 T cells directly induce muscle atrophy indeed. In CAC mice, CD8 neutralization led to restoration of muscle mass and downregulation of muscle atrophy markers, but was not able to significantly affect lung tumor burden. Moreover, direct co-culture with splenic CD8 T cells exacerbated C2C12 myotube atrophy in a conditioned medium from lung cancer cells, further supporting the involvement of CD8 T cells in CAC. To elucidate its underlying mechanism, RNA sequencing analysis was conducted in both skeletal muscles and lung tumors of CAC mice. Based on the differently expressed gene analysis, Cxcl13 was upregulated in skeletal muscles of CAC mice, while downregulated in lung tumors. It is well documented that CXCL13 can mediate recruitment of CD8 T cells. In this regard, CXCL13 might be a plausible regulator in CD8 T cell-induced skeletal muscle atrophy, which requires further investigation to fully understand the molecular mechanism. Citation Format: Se-Young Park, Bomi Kim, Myunggyo Lee, Haeseung Lee, Na-Young Song. Skeletal muscle-infiltrating CD8 T cells exacerbate muscle atrophy in a syngeneic lung cancer cachexia mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4457.

Abstract 585: Regorafenib antitumor immune response is enhanced by a novel drug combination in CRC syngeneic model

Abstract Purpose: In the United States, colorectal cancer (CRC) is the second leading cause of cancer mortality. Metastatic CRC (mCRC) refractory to traditional chemotherapy is managed with regorafenib, a multiple-kinase inhibitor. However, patients show only a modest improvement in overall survival but experience high drug toxicity, adverse side effects, and poor tolerability. Thus, to reduce regorafenib-induced toxicity and to enhance antitumor activity, we combined it with a hybrid/dual JAK/HDAC small-molecule inhibitor (JAK/HDACi) to leverage the advantages of both JAK and HDAC inhibition in a single agent. With syngeneic mice, the efficacy and impact on immunomodulation of this drug combination was assessed. Methods: To assess effects of the agents, C57BL/6 immunocompetent mice were injected with MC38 murine CRC cells and treated with regorafenib (6mg/kg body wt) or JAK/HDACi (30mg/kg body wt), and their combination every third day for 21 days. Upon completion of the experiment, the tumors were harvested and processed for RNA and protein expression profiles. The effect of drug treatment on immune response was analyzed by nCounter Gene Expression assays (NanoString Technologies). Cytokines were measured in serum using the MesoScale Discovery mouse V-Plex Proinflammatory Panel kit. For pharmacokinetic studies, plasma samples were assayed from C57BL/6 treated with drugs after 1, 7, 21, and 48 hrs of treatment. Results: The combination treatment significantly reduced tumor growth (volume and weight),relative to the vehicle control or single treatments. Gene expression showed higher CD45 abundance score in the combination treatment. This is an exciting observation, as CD45 has phosphatase activity and dephosphorylates key targets of the drugs used in the study. Additionally, after treatment with the combination, there was higher expression of Gzmb and Gzme and lower expression of Cx3cr1, indicating enhanced immuno modulation relative to regorafenib alone. We confirmed these findings by immunoprofiling of tumors. Higher CD45 staining, noted in tumors of mice treated with the combination, corroborated the gene expression results. Pronounced CD8 T lymphocytes infiltration was observed in combination, compared to regorafenib alone. Reduction of proinflammatory cytokine, TNF-α was noted in the combination group. This is an interesting observation as CD45 negatively regulates TNF, and combination treated mice had highest number of CD45 positive cells. Pharmacokinetic studies showed that the bioavailability of regorafenib was elevated after combination treatment relative to single-agent treatment. Conclusions: Relative to the single agents, the combination of regorafenib with JAK/HDACi was more effective, with an elevated antitumor immune response and with sustained inhibition of tumor growth. A clinical trial to evaluate this combination for the treatment of mCRCs is warranted. Citation Format: Prachi Bajpai, Farrukh Afaq, Sameer Al Diffalha, Sumit Agarwal, Hyung Gyoon Kim, Dennis Otali, Sooryanarayana Varambally, Ashish Manne, Ravi Paluri, Moh’d Khushman, Upender Manne. Regorafenib antitumor immune response is enhanced by a novel drug combination in CRC syngeneic model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 585.

Abstract 5301: Tumor-targeted activation of CD137 using Bicycles: New insights into mechanism of action and discovery of BT7455, a clinical candidate for the treatment of EphA2-expressing cancers

Abstract Introduction: Clinical studies in cancer patients have validated CD137 agonism as an activator of the immune system to enable tumor rejection. We have demonstrated that small, chemically synthetic bicyclic peptides can drive tumor-localized agonism of CD137 and anti-tumor immunity in mouse models. Here, we report the next stage of our work - delving into the mechanism of action of these novel agents and extending our program to serve patients whose tumors express EphA2. Experimental Procedures: MultiOmyx™ hyperplexed immunofluorescence assay was used to evaluate the expression of CD137 and EphA2 in head and neck squamous cell carcinoma samples. Human PBMC/tumor cell co-culture assays were used to assess CD137 Bicycle TICA™ in vitro bioactivity and syngeneic mouse tumor models were used to evaluate CD137 Bicycle TICA anti-tumor activity as mono- or combination therapies. Pharmacodynamic activity was evaluated by transcriptional profiling using NanoString assays or single cell RNA sequencing. Summary of the Data: Studies utilizing a syngeneic mouse model and deep RNA sequencing of tumors from CD137 Bicycle TICA-treated mice implicated intratumoral dendritic cells in addition to T cells as early responders to localized CD137 agonism and potential contributors to the anti-tumor response. Furthermore, a mouse efficacy model demonstrated synergy with checkpoint inhibitor therapy. Multiplex imaging revealed that EphA2 and CD137 are co-expressed in human tumors of high unmet medical need and therefore, using our highly modular Bicycle platform, we discovered BT7455, a Bicycle TICA that engages EphA2 and CD137 with high affinity, resulting in potent EphA2-dependent activity in vitro and robust anti-tumor activity in vivo with intermittent dosing in mouse models. Gene expression profiling of tumors revealed that BT7455 led to increased production of cytokines and chemokines known to drive T cell infiltration, the extent of which differentiated it from both a checkpoint inhibitor and an anti-CD137 monoclonal antibody agonist. BT7455 was well tolerated in preclinical species and liver function tests indicated no evidence of hepatic toxicity. Statement of Conclusions: In summary, we have identified EphA2 as a promising target to pair with a CD137 agonist. In addition to CD8+ T cells, tumor-resident dendritic cells are a likely contributor to anti-tumor immunity following treatment with Bicycle® TICAs, supporting utility for Bicycle® tumor-targeted CD137 agonists in solid tumors beyond those that are highly T cell-infiltrated. We have advanced a clinical development candidate, BT7455, to realize this potential for patients with EphA2-expressing cancers. Citation Format: Johanna Lahdenranta, Kristen Hurov, Heather Cohen, Lia Luus, Cara Bray, Peter Brown, Anna Devlen, Carly Campbell, Matthew Gray, Mike Kelly, Gemma Mudd, Punit Upadhyaya, Sailaja Battula, Kelvin Zhang, Anne-Sophie Dugast, Kevin McDonnell, Phil Brandish, Nicholas Keen. Tumor-targeted activation of CD137 using Bicycles: New insights into mechanism of action and discovery of BT7455, a clinical candidate for the treatment of EphA2-expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5301.