MC38 Cancer Research Articles

Engineered protein destabilization reverses intrinsic immune evasion for candidate vaccine pan-strain KSHV and SARS-CoV-2 antigens.

Both Kaposi sarcoma herpesvirus LANA and SARS coronavirus 2 RdRp/nsp12 are highly conserved replication proteins that evade immune processing. By deleting the LANA central repeat 1 domain (LANA ΔCR1 ) or by dividing RdRp into two separated fragments (RdRp Frag ) to maximize nascent protein mis-folding, cis peptide presentation was increased. Native LANA or RdRp SIINFEKL fusion proteins expressed in MC38 cancer cells were not recognized by activated OT-1 CD8 + cells against SIINFEKL but cytotoxic recognition was restored by expression of the corresponding modified proteins. Immunocompetent syngeneic mice injected with LANA- or RdRp-SIINFEKL MC38 cells developed rapidly-growing tumors with short median survival times. Mice injected with LANA ΔCR1 - or RdRp Frag -SIINFEKL had partial tumor regression, slower tumor growth, longer median survival, as well as increased effector-specific tumor-infiltrating lymphocytes. These mice developed robust T cell responses lasting at least 90 days post-injection that recognized native viral protein epitopes. Engineered vaccine candidate antigens can unmask virus-specific CTL responses that are typically suppressed during native viral infection.

ZLN005, a PGC-1α Activator, Protects the Liver against Ischemia-Reperfusion Injury and the Progression of Hepatic Metastases.

Exercise can promote sustainable protection against cold and warm liver ischemia-reperfusion injury (IRI) and tumor metastases. We have shown that this protection is by the induction of hepatic mitochondrial biogenesis pathway. In this study, we hypothesize that ZLN005, a PGC-1α activator, can be utilized as an alternative therapeutic strategy. Eight-week-old mice were pretreated with ZLN005 and subjected to liver warm IRI. To establish a liver metastatic model, MC38 cancer cells (1 × 106) were injected into the spleen, followed by splenectomy and liver IRI. ZLN005-pretreated mice showed a significant decrease in IRI-induced tissue injury as measured by serum ALT/AST/LDH levels and tissue necrosis. ZLN005 pretreatment decreased ROS generation and cell apoptosis at the site of injury, with a significant decrease in serum pro-inflammatory cytokines, innate immune cells infiltration, and intrahepatic neutrophil extracellular trap (NET) formation. Moreover, mitochondrial mass was significantly upregulated in hepatocytes and maintained after IRI. This was confirmed in murine and human hepatocytes treated with ZLN005 in vitro under normoxic and hypoxic conditions. Additionally, ZLN005 preconditioning significantly attenuated tumor burden and increased the percentage of intratumoral cytotoxic T cells. Our study highlights the effective protection of ZLN005 pretreatment as a therapeutic alternative in terms of acute liver injury and tumor metastases.

Abstract LB376: Tirzepatide inhibits tumor growth in mice with diet-induced obesity

Abstract Tirzepatide, a drug used in management of type II diabetes, is an activator of both glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) receptors. Tirzepatide treatment leads to weight loss in murine models of obesity, and clinical trials have shown the drug can achieve ∼ 20% weight loss in obese patients. Obesity has been shown to increase risk and/or to worsen prognosis of certain common cancers, including colon cancer, but the effect of tirzepatide on neoplasia has not been examined in detail. We studied the effects of this drug on mouse weight and energy balance and on the murine MC38 colon cancer model, which was previously shown to exhibit accelerated growth in hosts with diet-induced obesity. Tirzepatide led to substantial reductions in food intake, to reduced adipose tissue mass, and to significant decreases in circulating levels of insulin and leptin. Tirzepatide did not cause tumor regression, but reduced tumor growth rates by ∼ 50%. Tirzepatide had no effect on MC38 cancer cell proliferation in vitro, and the effect of tirzepatide on tumor growth in vivo could be phenocopied in placebo treated mice simply by restricting food intake to the amount consumed mice receiving the drug. This provides evidence that the drug acts indirectly to inhibit tumor growth. Our findings raise the possibility that use of tirzepatide or similar agents may benefit patients with obesity-related cancers. Citation Format: Michael N. Pollak, Jibin Zeng, Linxuan Huang, Ye Wang, Janane Rahbani, Lawrence Kazak. Tirzepatide inhibits tumor growth in mice with diet-induced obesity [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 LB376.

Abstract 6673: Tumor microbial burden is regulated by mast cells and determines immunotherapy responses

Abstract Immune checkpoint inhibitors (ICI) have notably improved overall survival rates across various cancers, particularly in cases of mismatch repair deficient cancer (MMRd). However, numerous factors influence patient response following ICI treatment. Beyond genetic factors, mutations, and levels of immune cell infiltration, several studies highlight the correlation between the gut microbiome and treatment response rates. Furthermore, specific bacterial compositions have been observed to shift during therapeutic interventions. Notably, studies have demonstrated that patients who used antibiotics before and during ICI treatment exhibited lower progression-free survival and overall survival, serving as evidence for this association. Our previous investigations elucidated the impact of distinct tumor microbial burdens on modulating immune activation. Consequently, our hypothesis posits the substantive involvement of the interplay between tumor microbial burden and the immune system response to ICI treatment. We evaluated the presence of intra-tumoral microbes within Colorectal cancers (CRC) by examining TCGA data. Patients with elevated microbial levels demonstrated heightened immune activity and better survival rates. Using cybersport analysis, we validated increased mast cell infiltration in CRC patients with abundant microbes. Quantification involved assessing bacterial burden through 16s rRNA via FISH staining and mast cell counts using tryptase via IHC staining. Reducing bacterial load in MC38 cancer model, achieved by locally administering antibiotics, led to a diminished immune response when PD-1 was introduced to these mice. Cross-referencing TCGA data, we identified upregulated genes in CRC patients with high microbial burden and downregulated genes in mice receiving local antibiotics after MC38 cell implantation. The common genes were associated with immune responses, suggesting a strong correlation between bacterial burden and immune activity in CRCs. In conclusion, the high burden of bacteria in CRC improves immune response to ICI and increases the infiltration of mast cells, which all contribute to better survival rates. Citation Format: Hajar Rajaei, Jeong-Hoon Jang, Haoyue Liu, Erika Y. Faraoni, Olivia Le Roux, Vidhi Chandra, Virginia Tahan, Le Li, Erick Riquelme, James Robert White, Luis A. Diaz Jr., Florencia McAllister. Tumor microbial burden is regulated by mast cells and determines immunotherapy responses [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 6673.

Abstract 5316: SM2256: A bispecific conditional CD40 and 4-1BB dual agonist for enhanced solid tumor immune response

Abstract Background: Monoclonal antibodies targeting the co-stimulatory receptors CD137 (4-1BB) and CD40 have displayed encouraging activity against a wide range of solid tumors in preclinical animal models. However, their clinical development as monotherapy has been hindered by dose-related liver toxicity, leading to limited efficacy at safe doses. To address this challenge and bolster tumor-specific immunity by orchestrating the interaction between dendritic cells (DCs) and cytotoxic T cells, we introduce SM2256 - a bispecific conditional CD40 and 4-1BB dual agonist. SM2256 physically bridges DCs and T cells, enhancing T cell priming and reactivation. In preclinical animal studies, SM2256 exhibited both excellent tolerability and potent anti-tumor activity. Methods: SM2256 was engineered by fusing high-affinity, non-ligand-blocking VHH domains targeting 4-1BB and CD40 to a silenced IgG1 Fc backbone. This fusion resulted in a tetravalent bispecific antibody capable of conditionally activating CD40 and 4-1BB upon mutual receptor binding. We assessed the binding specificity and affinity of SM2256 to human CD40 and 4-1BB using ELISA and flow cytometry. The target-dependent activation of CD40 and 4-1BB was confirmed via reporter assays and co-culture systems using primary DCs and T cells. In vivo safety and anti-tumor efficacy were evaluated in a syngeneic transplantation model using the MC38 cancer cell line in B-h41BB/B-hCD40 double humanized mice. Results: SM2256 exhibited sub-nanomolar binding affinity to recombinant human and cynomolgus monkey CD40 and 4-1BB, activating 4-1BB-NFκB-luc and CD40-NFκB-luc reporter cell lines at picomolar concentrations in a strictly target-dependent manner. Furthermore, SM2256 physically facilitated the interaction between DCs and T cells, leading to increased expression of DC co-stimulatory ligands and elevated secretion of cytokines by T cells in mixed lymphocyte cultures. In a syngeneic tumor transplantation model, SM2256 significantly restrained the growth of MC38 tumors in B-h41BB/B-hCD40 double humanized mice. Conclusions: SM2256 is a novel conditional CD40 and 4-1BB dual agonist that demonstrates promising preclinical efficacy against solid tumors while boasting an improved safety profile when compared to existing monoclonal antibodies. Citation Format: Wenjing Song, Simin Yang, Yi Wei, Shihao Lu, Huiqin Geng, Xiaodan Liu, Hong Zhou, Siyao Xie, Xing Zhang, Sheila Zhou, Yanbin Liang. SM2256: A bispecific conditional CD40 and 4-1BB dual agonist for enhanced solid tumor immune response [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 5316.

Abstract 1533: Characterizing tumor-immune surveillance in Li-Fraumeni syndrome

Abstract Li-Fraumeni Syndrome (LFS) is a cancer predisposition syndrome associated with germline TP53 mutations and increased lifetime risk of developing multiple cancers. p53, the protein encoded by TP53, plays a role in regulating various aspects of immune cell biology. Accordingly, inactivation of p53 in tumor cells shapes interactions with the immune system and influences the anti-tumor immune response. Mutation or deletion of p53 in immune cells also favors tumor development and progression. However, to date, a comprehensive study of immune cell populations and the anti-tumor immune response has not been undertaken in the context of LFS. We hypothesized that germline TP53 mutation carriers possess dysfunctional immune cells and/or immune responses, supporting LFS-associated tumor progression. Our preliminary data indicate a profound defect in tumor-immune surveillance in an LFS murine model. We observed that MC38 cancer cells develop significantly faster into tumors when injected into LFS mice (harboring a gain-of-function mutation Trp53R172H/WT) compared to wildtype (WT) control mice. Importantly, we identified significant alterations in immune cell compositions and phenotypes within the tumor microenvironment as well as immune organs using flow cytometry. We are currently using ex vivo proliferation assays and cytotoxicity assays to investigate the impact of mutant p53 on the tumor-killing ability of immune effector cells. Altogether, an improved understanding of anti-tumor immune dysfunction in the context of germline TP53 mutation may reveal the potential for innovative therapies to target different facets of the immune system to intercept cancer progression in LFS patients. Citation Format: Camilla Giovino, Nicholas Fischer, Noel Ong, Ashby Kissoondoyal, Ran Kafri, David Malkin. Characterizing tumor-immune surveillance in Li-Fraumeni syndrome [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 1533.

Abstract 1350: KD6001: A promising new anti-CTLA-4 human monoclonal antibody for cancer therapy

Abstract Cytotoxic T lymphocyte antigen-4 (CTLA-4) is a crucial immune checkpoint that negatively regulates T cell activation. Inhibiting this negative regulation through CTLA-4 blockade has emerged as a promising therapeutic strategy against cancer. Herein, we present the preclinical pharmacology study of KD6001, a novel anti-CTLA-4 IgG1 kappa human monoclonal antibody with superior properties compared to ipilimumab, a currently approved anti-CTLA-4 mAb. Surface plasmon resonance (SPR) analysis revealed that KD6001 exhibits a higher affinity for CTLA-4 compared to ipilimumab (KD = 0.57 nM vs 1.20 nM). Competition ELISA experiments demonstrated that KD6001 is significantly more potent than ipilimumab in disrupting CTLA-4 interactions with CD80 (IC50 = 16 ng/mL vs 93 ng/mL) and CD86. Further, amino acid point mutation analysis indicated that two specific residues following the CD80/CD86 binding site (99MYPPPY104) are critical for ipilimumab binding, whereas mutation of the two residues had minimal impact on KD6001's CTLA-4 binding activity. These findings suggest that KD6001 and ipilimumab bind distinct epitopes on CTLA-4. In vitro experiments demonstrated that KD6001 enhances the production of IL-2 and IFNγ in PHA-activated human lymphocytes and exhibits synergistic anti-tumor effects when combined with anti-PD-1/L1 antibodies. Moreover, in vivo studies utilizing syngeneic murine tumor models established in human CTLA-4 gene knock-in mice revealed that KD6001 effectively inhibits or delays tumor growth in colon cancer MC38, melanoma B16, and hepatocellular carcinoma Hepa1-6 models. Additionally, KD6001 demonstrated synergistic anti-tumor effects when combined with a mouse anti-PD-1 antibody or ibuprofen. Toxicity evaluation in cynomolgus monkeys revealed that KD6001 was generally well-tolerated at doses ranging from 1 mg/kg to 10 mg/kg administered intravenously once weekly for four weeks. The primary pathological changes observed were lymphocyte/monocyte infiltration or increased lymphocyte/monocyte infiltration in several organs, consistent with KD6001's mechanism of action. Notably, the similar affinity of KD6001 for human and cynomolgus monkey CTLA-4 suggests that the toxicity profile observed in monkeys accurately reflects the dose-toxicity relationship in human. The promising preclinical data presented herein support the further clinical development of KD6001 as a potential therapeutic agent for cancer treatment. Currently, clinical trials evaluating KD6001 in patients with advanced melanoma are ongoing. Citation Format: Yi Chen, Peng Li, Guobo Fang, Heng Wu, Chi Zhang, Zeling Cai. KD6001: A promising new anti-CTLA-4 human monoclonal antibody for cancer therapy [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 1350.

Abstract 125: Development of humanized VEGFA models to assess preclinical efficacy of novel therapeutics in vivo

Abstract VEGFA is an essential growth factor required for angiogenesis in the context of normal wound healing as well as malignant tissue growth, ultimately facilitating the delivery of oxygen and nutrients to fuel cellular survival, expansion, and repair. VEGFA signaling has also been reported to exert effects on cancer cells and immune cells directly, with evidence suggesting that the pathway can both support tumor growth and inhibit immune surveillance. Thus, targeting VEGFA has been intensely explored as a therapeutic strategy for several cancer indications. Here, we generated a novel humanized VEGFA model (B-hVEGFA mice) to explore the ability of novel VEGFA-targeting therapeutics to curb cancer cell growth and angiogenesis in vivo. This was achieved by replacing the murine Vegfa gene with the corresponding human VEGFA coding region. We confirmed exclusive expression of human VEGF in lung homogenates of the humanized model at levels comparable to murine VEGF quantified in wild-type C57BL/6 mice. Immunohistochemical analysis at 8 weeks of age demonstrates no significant difference in the CD31+ area in several organs of the humanized mice when compared to wild-type C57BL/6 mice, including kidney, heart, liver, and eye. To assess the functional utility of this model in evaluating VEGFA modulators, tumor studies were conducted: murine colon cancer MC38 cells that were also engineered to express VEGFA in a similar manner (B-hVEGFA MC38 cells) were subcutaneously implanted into homozygous B-hVEGFA mice. Treatment with bevacizumab analog essentially abolished tumor growth in the humanized mice, while control tumors continued to expand over the 3 week study. To further evaluate the role of novel combination therapies or bispecific antibodies targeting VEGFA and PD-1, we also generated a triple humanized model expressing human VEGF, PD-1, and PD-L1 (B-hPD-1/hPD-L1/hVEGFA mice) by crossing B-hVEGFA mice with our B-hPD-1/hPD-L1 mice model, which expresses the extracellular domains of human PD-1 and PD-L1. Flow cytometric analysis of this model is currently underway to validate the model for further efficacy testing. Together, these humanized VEGF models provide robust in vivo platforms to evaluate novel VEGFA therapeutic candidates. Citation Format: Shujin Zhang, Chonghui Liu, Jin Guo, Zhiyuan Shen, James Jin, Bahetiyaer Huwatibieke, Yang Shen. Development of humanized VEGFA models to assess preclinical efficacy of novel therapeutics in vivo [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 125.

Abstract 5617: Combined inhibition of ATR and ATM with tuvusertib and lartesertib (M4076) impacts the tumor microenvironment

Abstract Ataxia telangiectasia and Rad3-related protein (ATR) and ataxia telangiectasia mutated (ATM) are two of the main kinases of the DNA damage response (DDR). Recent work has demonstrated that the addition of ATM inhibitors enhances the cytotoxicity and in vivo anti-tumor efficacy of ATR inhibitors by abrogating the ATR inhibitor mediated G1 cell cycle arrest and enhancing chromosomal damage.1 Prior to causing cell death, damaged chromosome fragments can end up in the cytosol where they are detected by cytosolic nucleic acid sensors such as cGAS, resulting in the induction of inflammatory signaling pathways and an anti-tumor immune response. This suggests that the mode of action of DDR inhibitors may involve the tumor microenvironment (TME). We therefore aimed to assess the influence of combined pharmacological ATR and ATM inhibition on the TME to better understand how this could be exploited therapeutically. In line with published results in human tumor models, the treatment of murine colon cancer MC-38 cells in vitro with a combination of ATR inhibitor tuvusertib and ATM inhibitor lartesertib led to cell death. Further analysis revealed an activation of the cGAS-STING signaling pathway, an upregulation of PD-L1 and the release of inflammatory cytokines. These results confirmed the activation of immune signaling pathways upon combined inhibition of ATR and ATM. To analyze the stimulation of an anti-tumor immune response upon tuvusertib + lartesertib treatment in vivo, MC-38 cells were transplanted into immunocompetent C57BL/6J mice. Immunoprofiling by flow cytometry and immunohistochemistry staining confirmed that treatment with tuvusertib + lartesertib indeed altered the TME in this setting. In line with the in vitro findings, a significant upregulation of PD-L1 on immune and tumor cells could be observed after 24, 48, and 72 h of treatment even though MC-38 cells expressed high levels of PD-L1 already. Immunoprofiling did not reveal any changes in the TME immune cell content at these early time points. Interestingly, PD-L1 expression as well as tumor immune population changed after prolonged (23 days) treatment. PD-L1 was still expressed on tumor cells but to a significantly lesser extent and a depletion of CD8+ T-cells was observed. However, a significant increase in NK cells could be detected. In summary, we show that inhibition of the DDR through a combination of ATR and ATM inhibitors influences the TME in the MC-38 tumor model. These findings suggest an additional mode of action beyond direct cancer cell cytotoxicity. Further studies on how this may be leveraged therapeutically, for example through a combination with immune checkpoint inhibitors, are warranted. 1. Turchick A, Zimmermann A, et al. Mol Cancer Ther 2023;22(7):859-872. Citation Format: Karin Laaber, Audrey Turchick, Julia Jabs, Brian Elenbaas, Lyubomir T. Vassilev, Astrid Zimmermann. Combined inhibition of ATR and ATM with tuvusertib and lartesertib (M4076) impacts the tumor microenvironment [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 5617.

N6-methyladenosine levels in peripheral blood RNA: a potential diagnostic biomarker for colorectal cancer

BackgroundN6-methyladenosine (m6A) is dysregulated in various cancers, including colorectal cancer (CRC). Herein, we assess the diagnostic potential of peripheral blood (PB) m6A levels in CRC.MethodsWe collected PB from healthy controls (HCs) and patients with CRC, analyzed PB RNA m6A levels and the expression of m6A-related demethylase genes FTO and ALKBH5, cocultured CRC cells with PB mononuclear cells (PBMCs), and constructed an MC38 cancer model.ResultsPB RNA m6A levels were higher in the CRC than that in HCs. The area under the curve (AUC) of m6A levels (0.886) in the CRC was significantly larger compared with carbohydrate antigen 199 (CA199; 0.666) and carcinoembryonic antigen (CEA; 0.834). The combination of CEA and CA199 with PB RNA m6A led to an increase in the AUC (0.935). Compared with HCs, the expression of FTO and ALKBH5 was decreased in the CRC. After coculturing with CRC cells, the PBMCs RNA m6A were significantly increased, whereas the expression of FTO and ALKBH5 decreased. Furthermore, m6A RNA levels in the PB of MC38 cancer models were upregulated, whereas the expression of FTO and ALKBH5 decreased.ConclusionsPB RNA m6A levels are a potential diagnostic biomarker for patients with CRC.

In situ production and secretion of proteins endow therapeutic benefit against psoriasiform dermatitis and melanoma.

Genetic medicines have the potential to treat various diseases; however, certain ailments including inflammatory diseases and cancer would benefit from control over extracellular localization of therapeutic proteins. A critical gap therefore remains the need to develop and incorporate methodologies that allow for posttranslational control over expression dynamics, localization, and stability of nucleic acid-generated protein therapeutics. To address this, we explored how the body's endogenous machinery controls protein localization through signal peptides (SPs), including how these motifs could be incorporated modularly into therapeutics. SPs serve as a virtual zip code for mRNA transcripts that direct the cell where to send completed proteins within the cell and the body. Utilizing this signaling biology, we incorporated secretory SP sequences upstream of mRNA transcripts coding for reporter, natural, and therapeutic proteins to induce secretion of the proteins into systemic circulation. SP sequences generated secretion of various engineered proteins into the bloodstream following intravenous, intramuscular, and subcutaneous SP mRNA delivery by lipid, polymer, and ionizable phospholipid delivery carriers. SP-engineered etanercept/TNF-α inhibitor proteins demonstrated therapeutic efficacy in an imiquimod-induced psoriasis model by reducing hyperkeratosis and inflammation. An SP-engineered anti-PD-L1 construct mediated mRNA encoded proteins with longer serum half-lives that reduced tumor burden and extended survival in MC38 and B16F10 cancer models. The modular nature of SP platform should enable intracellular and extracellular localization control of various functional proteins for diverse therapeutic applications.

Abstract B004: Neoantigen adenoviral cancer vaccine generates improved CD8+ T-cell responses compared to adjuvanted peptide vaccine

Abstract Development of large, functional CD8+ T cell responses is crucial for successful cancer vaccine therapeutics. Neoantigens have demonstrated their potential as cancer vaccine immunogens, but improvements in delivery method are still necessary. In this work, we characterized five candidate Adenovirus Serotype 26 (Ad26) cancer vaccines for prophylactic efficacy in the MC-38 cancer model. All five single shot vaccines generated cellular immune responses at a higher level than prime boost peptide vaccination. The vaccines generated varying degrees of protection against tumor growth. The best Ad26 vaccine candidates showed improved protection compared to long synthetic peptide vaccines containing the same immunogens, the current standard in the field. Ad26 expressing seven neoantigens conjugated to the Herpes Viral Protein 22 (VP22) (Ad26.VP22.7Epi) was found to reduce tumor growth the most. Ad26.VP227Epi was compared to peptide vaccination in immune recall post challenge studies, in both the spleen and the tumor. Both Ad26.VP22.7Epi and Peptide showed a clear recall response after challenge in the spleen. This response was primarily focused on the Adpgk neoantigen but Ad26.VP22.7Epi additionally induced responses to the Irgq neoantigen while the peptide vaccine had stronger responses against the Reps1 neoantigen. The Ad26.VP227Epi vaccine generated increased numbers of infiltrating CD8+ T-cells, IFN+ CD8+ T-cells, and CD107a+ CD8+ T-cells, which all correlated with reduced tumor growth. We used single cell RNA-seq (scRNA-seq) to characterize tumor infiltrating lymphocyte populations (defined as CD45+) generated by the two platforms. We found that both Ad26.VP22.7Epi and Peptide induced higher numbers of infiltrating CD8+ T-cells within the tumor as compared to Sham. Single-cell analysis also showed higher numbers of tumor infiltrating Tregs in peptide vaccinated mice. Higher numbers of CD8+ T-cells correlated with protection as expected but interestingly increased numbers of Tregs positively correlated with tumor volume only among vaccinated mice, which could further explain differences between Ad vector and peptide vaccination. Differential gene expression analysis of CD8+ T-cells showed an upregulation of Th1 pathways and general T cell activation when comparing Ad vector vaccinated mice to peptide vaccinated. Peptide vaccinated CD8+ T-cells showed upregulation in the IL-10 pathway, potentially caused by an increased Tregs. Further investigation of these differences among CD8+ T cell and Treg populations could further elucidate potential mechanisms explaining the differences in platform efficacy. Citation Format: Gabriel Dagotto, Alessandro Colarusso, Robert Patio, David Li, Tochi Anioke, Victoria Giffin, Malika Aid, Dan Barouch. Neoantigen adenoviral cancer vaccine generates improved CD8+ T-cell responses compared to adjuvanted peptide vaccine [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B004.

Modulatory effects of supplementation of Lentinula edodes mycelia extract and l-arginine on the therapeutic efficacy of immunogenic chemotherapy in colon cancer-bearing mice.

Some chemotherapeutic drugs can induce cancer cell death and enhance antitumor T-cell immunity in cancer-bearing hosts. Immunomodulatory reagents could augment such chemotherapy-induced effects. We previously reported that oral digestion of Lentinula edodes mycelia (L.E.M.) extract or l-arginine supplementation can augment antitumor T-cell responses in cancer-bearing mice. In this study, the effects of L.E.M. extract with or without l-arginine on the therapeutic efficacy of immunogenic chemotherapy by 5-fluorouracil (5-FU)/oxaliplatin (L-OHP) and/or cyclophosphamide (CP) are examined using two mouse colon cancer models. In MC38 and CT26 cancer models, therapy with 5-FU/L-OHP/CP significantly suppressed tumor growth, and supplementation with L.E.M. extract halved the tumor volumes. However, the modulatory effect of L.E.M. extract was not significant. In the CT26 cancer model, supplementation with L.E.M. extract and l-arginine had no clear effect on tumor growth. In contrast, their addition to chemotherapy halved the tumor volumes, although the effect was not significant. There was no difference in the cytotoxicity of tumor-specific cytotoxic T cells generated from CT26-cured mice treated by chemotherapy alone versus chemotherapy combined with L.E.M. extract/ l-arginine. These results indicate that the antitumor effects of immunogenic chemotherapy were too strong to ascertain the effects of supplementation of L.E.M. extract and l-arginine, but these reagents nonetheless have immunomodulatory effects on the therapeutic efficacy of immunogenic chemotherapy in colon cancer-bearing mice.

Carm1 Inhibition Potentiates Irradiation-Induced Antitumor Immunity via Tumor Intrinsic STING Pathway Activation

Radiotherapy is commonly applied in multiple cancer types. Besides irradiation induced direct cell death, radiotherapy stimulated significant immune responses for tumor control. Intact and functional cGAS-STING pathway in both tumor cells and host cells is indispensable for efficient irradiation-induced anti-tumor effects. Coactivator-associated arginine methyltransferase 1 (Carm1) is emerging as an attractive therapeutic target and a biomarker for prognosis in various types of cancer. It has been reported that Carm1 inhibition could improve immunotherapy induced anti-tumor effects. However, it remains unclear how tumor cell intrinsic Carm1 affects irradiation-induced anti-tumor immunity. Carm1 deficient cell lines were established in MC38 and B16F10 murine cancer cells using the CRISPR/Cas9 technology. To verify the effects of tumor `subcutaneous tumor mouse models were established and one fraction of 15Gy was administrated when the tumor volume reached 200mm3, followed by flow cytometry assays. Transcriptome sequencing, protein mass spectrometry, single-cell sequencing, Digital Spatial Profiling (DSP), real-time qPCR, western blotting, immunofluorescence and co-immunoprecipitation were carried out to explore and verify possible molecular mechanisms. Here we found Carm1 deficiency in tumor cells dramatically enhanced irradiation-induced anti-tumor immune responses. Transcriptome sequencing of irradiated tumor cells and further experiments then validated that cGAS-STING pathway was significantly activated after irradiation in the absence of Carm1 in tumor cells, which contributed to enhance anti-tumor immunity after irradiation. Mechanistically, Carm1 deficiency in tumor cells attenuated autophagy, resulting in increased cytoplasmic mtDNA enrichment and enhanced cGAS-STING pathway activation. On the other hand, we also found that Carm1 caused asymmetric arginine methylation (ADMA) modification of TBK1 with reduced phosphorylation level, and Carm1 deficiency could activate cGAS-STING pathway by reducing AMDA modification and enhancing phosphorylation of TBK1. Finally, Carm1 inhibitor EZM2302 was applied in combination with radiotherapy in vitro, and it's indicated that combination therapy resulted in intensive anti-tumor immunity and prominent abscopal effects. In this study, we identified that Carm1 ablation in tumor cells could promote irradiation-induced antitumor immunity through tumor cell intrinsic STING pathway activation. Mechanically, Carm1 deficiency directly activated the cGAS-STING pathway by interacting with TBK1 and increased mtDNA accumulation in cytoplasm by inhibiting autophagy. These findings provided new strategies for targeting Carm1 to boost the efficacy of radiotherapy.

Discovery of Anti-CD47 Peptides as Innate Immune Checkpoint Inhibitors.

Cancer immunotherapy targeting adaptive immune cells has been attracting considerable interest due to its great success in treating multiple cancers. Recently, there is also increasing interest in agents that can stimulate innate immune cell activities. Immune checkpoint inhibitors targeting innate immune cells can block inhibitory interactions ('don't eat me' signals) between tumor cells and phagocytes. CD47 is a transmembrane protein overexpressed in various cancers and acts as a potent 'do not eat me' signal that contributes to the immune evasion of cancer cells. Anti-CD47 peptides that can bind to CD47 and block CD47/SIRPα interaction were discovered using a novel phage display biopanning strategy. Anti-CD47 peptides enhanced the macrophage-mediated phagocytosis of NCI-H82 tumor cells in vitro. Unlike anti-CD47 antibodies, these peptides do not induce the agglutination of RBCs. Moreover, anti-CD47 peptides exhibit high specificity for MC-38 cancer cells expressing CD47. CMP-22 peptide showed the ability to increase the antitumor activity of doxorubicin and extends the survival of CT26 tumor-bearing mice. The discovered anti-CD47 peptides can be considered potential candidates for cancer immunotherapy by blocking the CD47/SIRPα interaction, especially in combination with chemotherapy, to elicit synergistic effects.

Enhancing therapeutic effects of murine cancer vaccine by reshaping gut microbiota with Lactobacillus rhamnosus GG and jujube powder.

Cancer vaccines have gained widespread attention in recent years as an emerging treatment for tumors. However, most therapeutic cancer vaccines have failed in phase III clinical trials due to faint clinical benefits. In this study, we funded that a specific synbiotic composing Lactobacillus rhamnosus GG (LGG) and jujube powder significantly enhanced the therapeutic effects of whole cells cancer vaccine in MC38 cancer cells bearing-mouse. The utilization of LGG increased the abundance of Muribaculaceae, which is conductive to an enhanced anti-tumor effect, but reduced microbial α-diversity. The use of jujube nursed probiotic microorganisms in Lachnospiaceae and enriched microbial diversity, as indicated by increased Shannon and Chao index. The reshaped gut microbiota by this synbiotic improved lipid metabolism conductive to intensified infiltration of CD8+ T cells in the tumor microenvironment and enhanced the potency of above-mentioned cancer vaccine. These encouraging findings are helpful for further efforts towards enhancing the therapeutic effects of cancer vaccines through nutritional intervention.

A bionic "Trojan horse"-like gene delivery system hybridized with tumor and macrophage cell membrane for cancer therapy.

MiRNA-based gene therapy as a novel targeted therapy has yielded promising results in experimental cancer treatment, however, the inefficient delivery of miRNA to target tissues has limited its application in vivo. Here a unique dual-membrane-camouflaged miRNA21 antagomir delivery nanoplatform (M@NPs/miR21) with immune escape and homologous targeting properties was constructed by cancer cell membrane and macrophage membrane. Different from the single-cell membrane camouflage strategy, the dual-membrane camouflage miRNA21 antagomir delivery nanoplatform based on modification of CD47 protein with immune escape signal and galectin-3 protein with tumor cell aggregation enables efficient, safe and targeted therapy for colon cancer and lung metastases. Camouflaged with the dual-cell membrane, the "Trojan horse" like "pseudo-tumor cell" and/or "pseudo-macrophage" (M@NPs/miR21) carried the target gene miR21 antagomir to the tumor site and showed significant anti-tumor properties at the periphery and the core of subcutaneous tumor tissues. In addition, M@NPs/miR21 was more likely to penetrate dense tumor tissues and function within the tumor mass than NPs/miR21 without membrane coating. M@NPs/miR21 can deliver miR21 antagomir into MC38 cancer cells and tumor tissues, promote tumor apoptosis, and regulate the expression of Bcl2 and Ki67. Moreover, the M@NPs/miR21 gene delivery system not only can effectively inhibit the progression of subcutaneous tumors and lung metastases, but also showed minimal toxicity and good biosafety, making this delivery system particularly attractive for future translational research.

IL-22BP controls the progression of liver metastasis in colorectal cancer.

The immune system plays a pivotal role in cancer progression. Interleukin 22 binding protein (IL-22BP), a natural antagonist of the cytokine interleukin 22 (IL-22) has been shown to control the progression of colorectal cancer (CRC). However, the role of IL-22BP in the process of metastasis formation remains unknown. We used two different murine in vivo metastasis models using the MC38 and LLC cancer cell lines and studied lung and liver metastasis formation after intracaecal or intrasplenic injection of cancer cells. Furthermore, IL22BP expression was measured in a clinical cohort of CRC patients and correlated with metastatic tumor stages. Our data indicate that low levels of IL-22BP are associated with advanced (metastatic) tumor stages in colorectal cancer. Using two different murine in vivo models we show that IL-22BP indeed controls the progression of liver but not lung metastasis in mice. We here demonstrate a crucial role of IL-22BP in controlling metastasis progression. Thus, IL-22 might represent a future therapeutic target against the progression of metastatic CRC.

Abstract 5136: Surgical stress promotes long-lasting protumorigenic changes in bone marrow derived progenitor cells

Abstract Introduction: Surgery is a crucial intervention for cancer patients. However, the perioperative period is characterized by an increased risk for accelerated growth of metastatic disease. Our recent work shows that the protumorigenic systemic inflammatory changes and the formation of neutrophil extracellular traps (NETs) persist months after surgery in both mice and humans, and parallel micrometastatic tumor growth and recurrence. Here we hypothesized that surgery may induce long-term sustained epigenetic and transcriptomic changes in bone marrow derived granulocytes-monocytes progenitor cells (GMPs) leading to functional reprogramming of mature neutrophils and persistent systemic release of these protumorigenic NET-forming neutrophils. Methods: Eight-week-old mice were subjected to non-lethal surgical stress (laparotomy) for 30 mins. Seven days after, mice were inoculated with 1x106 MC38 (murine colorectal cancer cells) subcutaneously. For bone marrow (BM) transplant model, a group of B6 congenic (CD45.1) mice were subjected to laparotomy. BM derived cells were harvested 7 days after the procedure and orthotopically transplanted into B6 CD45.2 irradiated (1000 rads) mice. After the establishment of hematopoiesis (6 weeks), MC38 cancer cells were implanted into the recipient mice. Results: Mice that underwent laparotomy had significantly increased tumor volume at 3 weeks compared to control mice, that only underwent anesthesia (Laparotomy vs control **p<0.01). While the intratumoral flowcytometry analysis showed no difference in the frequency of infiltrating immune cells, quantitative (q) PCR analysis revealed significant plasticity in the tumor infiltrating neutrophils (TANs) observed by an increase in the expression of genes (MCP1, Arg1) associated with pro-inflammatory (N2) type neutrophils compared to control. A persistent increased level of NETs was also observed within the tumors and circulation of mice several weeks after laparotomy. ATAC-seq and Bulk-RNA-seq analysis further revealed major epigenetic and transcriptomic changes in TANs, circulating neutrophils and GMPs. To substantiate long-lasting surgical effects, tumor burden was assessed in the BM recipient mice and showed to be significantly increased in mice that had received BM cells from laparotomy mice versus BM cells from sham group. Conclusion: Surgery promotes long-term rewiring of the bone marrow derived cells resulting in increased tumor growth. Understanding the underlying molecular mechanism may help with therapeutic interventions to prevent protumorigenic surgical effects and improve patient outcomes. Citation Format: Hamza O. Yazdani, Tony Haykal, Ruiqi Yang, Celine Tohme, David A. Geller, Samer Tohme. Surgical stress promotes long-lasting protumorigenic changes in bone marrow derived progenitor cells. [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 5136.

Abstract 5982: A potent and selective CDK8 inhibitor ABM-3249 with excellent efficacies in multiple in vivo cancer models

Abstract CDK8 is a member of the CDK family in which belongs to the serine/threonine protein kinase. It binds with cyclin C to regulate the transcription. By modulation of various gene expression programs, CDK8 associated with the mediator complex to sustain proliferation and viability of cancer cells. CDK8 has been identified as an important factor in cancer occurrence and development. It also involves in the regulation of cancer cell stress response to radiotherapy and chemotherapy, assists tumor cell invasion, metastasis and drug resistance. Therefore inhibition of CDK8 is regarded as a promising target for cancer therapy. ABM-3249 was discovered as a potent and selective CDK8 inhibitor with a novel chemical structure. It inhibited CDK8 kinase activity in biochemical assay and cellular binding assay, with IC50 values of 1.4 nM and 19nM respectively. ABM-3249 displayed good kinase selectivity: <50% inhibition on all other CDK family members at 1uM. Consistently, ABM-3249 reduced STAT1-S727 phosphorylation with an IC50 of less than 100nM. ABM-3249 showed good ADME properties with high oral bioavailability (~90%) in rodents. In efficacy studies, ABM-3249 exhibited excellent anti-tumor activities in multiple in vivo models. In an AML MV4-11 xenograft model at 25mpk oral dosing ABM-3249 achieved complete remission in all mice within 17 days and no tumor recurrence within one month after drug withdrawal. ABM-3249 showed good efficacies as a single agent, as well as a synergetic effect with anti-PD1 combination in a murine colon cancer MC38 model. It also showed an efficacy in a murine colon cancer B16F10 metastasis model. In addition, ABM-3249 displayed a good safety margin in a preliminary tox screen in rodents. Citation Format: Chen Chen, Charles Huang, Min Xu, Xiuquan Chen, Xiaobing Lv, Chen Yang, Lanjiao Zhao, YouQin Chen, Jizhi Li, Li Zhao. A potent and selective CDK8 inhibitor ABM-3249 with excellent efficacies in multiple in vivo cancer 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 5982.