Syngeneic Tumor Models Research Articles

Abstract 5322: Discovery of CRD1601, a potent and selective HPK1 inhibitor with robust in vivo anti-cancer activity

Abstract Background: Haematopoietic Progenitor Kinase (HPK-1, MAP4K1) is a member of the STE20 family of serine/threonine kinases, expressed predominantly in hematopoietic cells. HPK-1 functions as a negative regulator of T-cell and B-cell receptor activation by triggering proteasomal degradation and disrupting signalosome complexes downstream of TCR and BCR. HPK1 inhibition is a novel IO strategy that could combine with existing chemotherapies and immunotherapies. Methods: Curadev used a pharmacophore based approach to discover novel small molecule HPK-1 inhibitors using in vitro enzymatic and phenotypic cellular screens using primary cells. CRD1601, the clinical candidate was selected based on its ability to enhance human T-cell proliferation through the induction of IL2 and IFNγ. Syngeneic tumor models were used to assess anti-tumor activity of selected compounds as a monotherapy or combination therapy. Results: CRD1601 is a potent HPK1 inhibitor with a single digit nanomolar IC50 value in enzymatic assay and potent cellular activity in the SLP76 assay. A single dose of CRD1601 in mice treated with an anti-CD3 antibody caused systemic enhancement of pro-inflammatory cytokines such as IL2, IFN gamma and reduced pSLP76 levels in the spleen. Further, CRD1601 reversed the immunosuppressive effect of PGE2 and NECA. CRD1601 demonstrated significant single agent activity in murine tumor models while also synergizing with chemotherapy and immunotherapy. Conclusions: Inhibition of HPK-1 is a promising therapeutic modality that could augment the effects of existing anti-cancer treatments including immunotherapy. CRD1601 is a potent and selective HPK-1 inhibitor with favorable drug like properties that has been selected from a rich portfolio of active compounds and shows promising in vivo activity in tumor models. Citation Format: Monali Banerjee, Ritesh Shrivastava, David Pryde, Sandip Middya, Sabyasachi Debnath, Anindita Middya, Dharmendra Yadav, Nidhi Rawat, Rajib Ghosh, Manisha Padaliya, Sourav Basu, Arjun Surya. Discovery of CRD1601, a potent and selective HPK1 inhibitor with robust in vivo anti-cancer activity [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 5322.

Abstract 3193: Utilizing a pH sensitive peptide (pHLIP) for antigen-directed T cell therapy

Abstract Many targeted therapies, such as antibody drug conjugates (ADCs) and chimeric antigen receptor (CAR) T cell therapies, rely on the identification of an optimal antigen as the cell marker for targeting cancer cells. However, there is a paucity of antigen candidates that are sufficiently specific to epithelial cancers. Therefore, technologies that can mark tumor cells for immune recognition could prove beneficial in the treatment of these solid cancers. pH low insertion peptides (pHLIPs) act as a unique delivery platform that can specifically target the acidic microenvironment of tumors, sparing healthy tissue in the process. We developed a pHLIP-peptide conjugate (pHLIP-SIINFEKL) to deliver the SIINFEKL peptide, an immunogenic fragment of ovalbumin, to investigate antigen delivery and recognition to tumors in vivo. When processed intracellularly, SIINFEKL is presented for immune recognition through the major histocompatibility complex (MHC) class I pathway. We observed selective delivery of pHLIP-SIINFEKL both in vitro and in vivo using fluorescently labeled constructs. In vitro, treatment of melanoma tumor cells with pHLIP-SIINFEKL resulted in recognition by SIINFEKL-specific T cells (OT1), leading to T cell activation and effector function. Mechanistically, we show that this recognition by OT1 cells was abrogated by siRNA knockdown of the β2 microglobulin (β2m) component of MHC class I in the target tumor cells, indicating that an intact antigen processing pathway in the cancer cells is necessary to mediate the effect of pHLIP-directed SIINFEKL delivery. In vivo, pHLIP-SIINFEKL treatment of tumor-bearing mice resulted in recruitment of OT1 T cells and suppression of tumor growth in two syngeneic tumor models in immunocompetent mice, with no effect when mutating either the pHLIP or SIINFEKL components of the conjugate. These results suggest that pHLIP-mediated peptide delivery can provide a novel approach to decorate solid tumors with engineered antigens for enhanced immune recognition and anti-tumor efficacy. Citation Format: Annali M. Yurkevicz, Yanfeng Liu, Peter M. Glazer. Utilizing a pH sensitive peptide (pHLIP) for antigen-directed T cell 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 3193.

Abstract 183: A novel bispecific antibody macrophage engager (BiME) designed for the treatment of solid tumors

Abstract Background: Anti-CD3-based bispecific T cell engagers (BiTE) showed limited clinical efficacy in solid tumors and caused significant cytokine storm. Similar to BiTE where T cells are activated by CD3 antibody, we constructed a novel bi-specific macrophage engager (BiME) platform where macrophage is activated by anti-SIRPa that is directed to a particular tumor via the targeting of the tumor-associated antigen (TAA), resulting in phagocytosis of the tumor cells. This BiME does not lead to cytokine storm and is particularly applicable for the treatment of solid tumors whose microenvironment contains plenty of macrophages. Tumor-associated macrophages are major component of immune cells in the tumor micro-environment (TME) that express an array of effector molecules leading to the inhibition of anti-tumor immune responses. Signal regulatory protein α (SIRPα) is a myeloid-lineage inhibitory receptor that restricts phagocytosis through engagement of its ligand CD47 expressed on tumors and normal tissues. Compared to anti-CD47 therapeutics, targeting myeloid-restricted SIRPα provides a differential pharmacokinetic, safety, and efficacy profile. Here, we report the construction of a SIRPα antagonist-based bispecific macrophage engager (BiME) platform, a potent tumor-killing bi-specific antibody platform. Methods: We have generated a panel of single domain antibody (sdAb), scFv or Fab antibodies targeting different TAAs and SIRPa. We constructed BiME antibodies using different orientations, ratios, and IgG isotypes of anti-TAA arm and anti-SIRPα arm. These bispecific antibodies were evaluated for homologue binding, and CD47-SIRPα blocking properties by ELISA and FACS. In vitro function activity was determined by phagocytosis assay using human monocyte derived macrophage and mouse bone marrow derived macrophage. In vivo anti-tumor efficacy was tested in a syngeneic tumor model with hSIRPα knock-in mice. The pharmacokinetic (PK) and safety profile were assessed in hSIRPα knock-in mice or cynomolgus monkeys. Results: Through Elpiscience proprietary BiME platform, we have generated a panel of TAA/SIRPα bispecific antibodies with TAA being Claudin18.2, EGFR, PDL1 and DLL-3. The BiME treatment demonstrated strong anti-tumor efficacy in multiple mouse syngeneic tumor models. Mechanistically, both myeloid and T cells were activated and contributed to antitumor activity of BiME bispecific antibody. the BiME bispecific antibodies were well tolerated in non-human primates (NHPs) and there is no hematotoxicity or cytokine release syndrome (CRS) observed after treatment of BiME antibodies. Conclusions: These findings provide novel mechanistic insights into how myeloid and T cells can be uniquely modulated by the bispecific macrophage engagers (BiMEs) and demonstrate the potential and advantage of BiME in future clinical development for solid tumor treatment as compared to BiTE approach. Citation Format: Dawei Sun, Haixia Jiang, Yanan Geng, Yue Wu, Rui Gao, Yefeng Lu, Quan Qiu, Yanfen Hu, Yingchao Liu, Xiaoli Guo, Xiaofeng Niu, Hongtao Lu. A novel bispecific antibody macrophage engager (BiME) designed for the treatment of solid tumors [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 183.

Abstract 2461: Discovery of an orally available and liver-targeted ALPK1 agonist for cancer immunotherapy

Abstract Boosting anti-tumor immune responses can be achieved by activating the innate immune system. Despite the ongoing development of numerous STING and TLR agonists for this purpose, none of them have progressed to late-stage clinical evaluation. Alpha protein kinase-1 (ALPK1) is an intracellular innate immune receptor newly identified for its ability to detect ADP-heptose, a metabolite released during the biosynthesis and degradation of lipopolysaccharides (LPS). Since heptose is not naturally present in mammalian cells, the recognition of heptose metabolites by ALPK1 serves as a reliable mechanism to identify bacterial infections. When ADP-heptose binds to ALPK1, it initiates the phosphorylation of TIFA, thereby triggering a cascade of immune responses. Systemic administration with ADP-heptose induces robust ALPK1-dependent cytokine responses in mice. While high doses of ADP-heptose demonstrate anti-tumor effects, its instability and low in vivo potency hinder its clinical development. Through a SBDD medicinal chemistry effort, a novel, stable, and potent ADP-heptose analog, designated PTT-936, has been discovered and is progressing into clinical evaluation in cancer patients. PTT-936 exhibits remarkable nanomolar potencies for ALPK1 activation in various cellular assays. Notably, in human PBMCs, PTT-936 induces both concentration-dependent release of cytokines and activation of NK and T cells. Consistent with in vitro studies, oral administration of PTT-936 triggered significant cytokine responses in mice at microgram dose levels. However, overt toxicities were observed only at milligram dose levels, indicating a wide therapeutic window for this compound. In syngeneic tumor models, oral administration of PTT-936 induced dose-dependent tumor growth inhibition, which correlated with elevations in several cytokine biomarkers. Mechanistic studies show that PTT-936, working exclusively through the ALPK1 pathway, elicited strong innate and adaptive immune responses, as evidenced by robust cytokine induction and immune cell activation and recruitment. In syngeneic mouse models, the anti-tumor effects of PTT-936 were significantly hindered by either CD8+ T cell depletion or neutralization of select cytokines. Besides monotherapy studies, compelling evidence demonstrates strong synergistic anti-tumor effects when combining PTT-936 with immune checkpoint inhibitors. Intriguingly, PTT-936 exhibits favorable tolerability and a wider therapeutic index compared to certain clinical-stage STING and TLR agonists. Furthermore, PTT-936 does not enhance cytokine elevations induced by checkpoint inhibitors, which have been linked to adverse events (including CRS) observed in clinical combination studies. The dosing frequency of PTT-936 in the upcoming first-in-human clinical trial is carefully designed to prioritize both tolerability and patient compliance. Citation Format: Yupeng Wang, Nana Du, Xiaona Dong, Xuebing Sun, Yuan Hong, Xiaolong Yang, Zhijiang Ji, Qianyu Wang, Yun Lv, Zhichen Shi, Yajuan Gao, Xiaofu Hou, Yaxin Zhang, Juan Wang, Rui Mao, Yinxin Liu, Liang Li, Jingjin Ding, Hexiang Wang, Nan Hu, Counde O’Yang, Zhihong Li, Keith Bley, Feng Shao. Discovery of an orally available and liver-targeted ALPK1 agonist for cancer immunotherapy [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 2461.

Abstract 4035: Lipid-based nanoparticle combination immunotherapy with sitravatinib for the systemic treatment of high-risk neuroblastoma

Abstract We seek to develop a systemic, innate immunomodulatory nanoparticle therapy that combines synergistically with sitravatinib for the treatment of high-risk neuroblastoma, where metastasis is the largest hurdle for current treatment modalities. Here, we utilize a unique lipid-based nanoparticle (LNP) system comprised of co-encapsulated agonists of the Stimulator of Interferon Genes (STING) and Toll-like Receptor 4 (TLR4) pathways (immuno-NPs) that can be safely administered in the systemic blood circulation for delivery to the tumor microenvironment (TME) and uptake by perivascular innate antigen-presenting cells (APCs). STING/TLR4 agonists together promote the synergistic production of Type I interferon β (IFNβ), a key activator of anti-tumor immunity from the TME itself. Here, we also focus on sitravatinib, an investigational drug shown to inhibit receptor tyrosine kinases such as discoidin domain receptor 2 (DDR2), which can inhibit the sustained remodeling of collagen around primary tumors. The inhibition of such is vital to treatment as sustained collagen remodeling can facilitate the metastasis of cancer cells via epithelial-mesenchymal transition (EMT). We hypothesize that the downstream effects of sitravatinib treatment will augment tumor clearance and increase the therapeutic efficacy of immuno-NPs with respect to recruiting APCs. Our early pilot studies in humanized mice bearing orthotopic SH-5YSY tumors show that immuno-NPs are effective at tumor clearance. We found that mice inoculated subcutaneously with syngeneic 9464D-GD2 tumors showed decreased tumor growth when treated with our novel combination therapy in comparison to monotherapy controls. In both humanized and syngeneic tumor models, our ongoing mechanistic studies involve quantification of EMT in primary tumors, systemic nanoparticle deposition at metastatic sites, and the mechanistic impact of combination therapy on IFNβ-promoted elimination of metastasis. Here, we have proposed and tested an immunotherapy with great promise for treating neuroblastoma. However, the impact of nanoparticle-based immunotherapy reaches far beyond neuroblastoma: it has the potential to be a platform for the development of immunotherapies specific to other highly metastatic cancer types. Citation Format: Miranda Diaz-Infante, Griffin Kane, Christina Lusi, Meghan Brassil, Kim Wigglesworth, Christian Alarcon, Jason Shohet, Prabhani Atukorale. Lipid-based nanoparticle combination immunotherapy with sitravatinib for the systemic treatment of high-risk neuroblastoma [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 4035.

Abstract 6537: A novel CCR4 antagonist induces potent anti-tumor response through inhibition of Treg migration into the tumor microenvironment

Abstract Regulatory T cells (Tregs), an immunosuppressive subset of CD4+ T cells, play a vital role in maintaining immune homeostasis by regulating response to self antigens and maintaining tolerance. On the contrary, Tregs infiltrating the tumor microenvironment (TME) impede effective anti-tumor immunity by inhibiting tumor-specific T cell responses and generating a suppressive TME, thus promoting tumor progression. Clinically, Tregs have been proven to play a significant role in resistance to immune checkpoint inhibitors (ICIs) leading to lower response rates. Hence, targeting Tregs would lead to activation of tumor-specific effector T cells and improved long-term anti-tumor immune responses with ICI treatment. CCR4, a chemokine receptor highly expressed on Tregs, spearhead the migration of Tregs and their accumulation in the TME, by responding to the chemokines CCL22 and CCL17 secreted by the inflamed cells in the tumor. CCR4 expression is associated with poor prognosis in various solid tumors. This warrants the therapeutic targeting of CCR4-expressing Tregs to enable effective and durable anti-tumor immune responses. We sought to discover and develop novel small molecule antagonists of CCR4 for use in cancer therapy. Multiple series of CCR4 antagonists were identified by iterative medicinal chemistry efforts and SAR based approach. These compounds were optimized towards attaining required potency, acceptable physicochemical properties, high selectivity and desirable pharmacokinetic profile to achieve anti-tumor activity. Aurigene’s CCR4 antagonists exhibited potent inhibition of CCR4 activity in the reporter-based β-arrestin recruitment assay. This translated well into potent inhibition of CCL22-mediated chemotaxis of CCR4-expressing Tregs in an in vitro cell migration assay. Furthemore, the lead compounds showed desirable drug-like properties and excellent pharmacokinetic exposure in rodents. In an ongoing study in a syngeneic mice tumor model, one of the lead compounds is being evaluated for impact on Treg infiltration, CD8:Treg ratio in the tumor and efficacy. In summary, we have identified novel CCR4 antagonists with desirable drug-like properties that are being evaluated further to identify a clinical candidate. Citation Format: Rashmi Nair, Chandrasekhar Abbineni, Krishna Chaitanya Talluri, Amit A Dhudashiya, Aravind AB, NaveenR Kumar, Ramya R, D Balasubramanyam, Pathur Obanna, Rabin Madhaiyan, DS Samiulla, Girish Daginakatte, Kishore Narayanan, Kavitha Nellore, Shekar Chelur, Susanta Samajdar, Murali Ramachandra. A novel CCR4 antagonist induces potent anti-tumor response through inhibition of Treg migration into 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 6537.

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.

Abstract 3739: Different combination regimens for OX40 agonists and PD-1 inhibitors exert different antitumor effects in OX40 humanized mice

Abstract OX40, also known as CD134 or TNFRSF4, is a member of the tumor necrosis factor receptor (TNFR) superfamily which mainly expressed on the surface of activated T cells including Treg cells. Engagement of OX40 with its ligand, TNFSF4, leads to effector T cell expansion and cytokine release, inhibits activation-induced cell death (AICD) and promotes the survival of antigen-specific memory T cells. In contrast to the massive hit of immune checkpoint inhibitors like PD-1 and PD-L1, the benefit of agonistic antibodies in clinical trials has not been completely demonstrated to date. On one hand, higher doses could leads to T cell exhaustion or AICD, paradoxically, with no efficacy improvement. Another hand, the limited understanding of the biology of immune checkpoints underlying “accelerator and brake” should account for the slow clinical progress of OX40-targeted biologics. It seems that the dosing sequence or timing of anti-OX40 and anti-PD-1 is an important consideration in combination therapies. Given this, we firstly evaluated the antitumor effects of two different anti-human OX40 agonists in syngeneic MC38 and Pan02 tumor models, respectively, in hOX40 knockin mice. We observed tumor regressions upon treatment of OX40 agonistic Ab1 in a dose-dependence way in the homozygous hOX40 knockin mice engrafted with MC38 tumors. The anti-hOX40 Ab1 at high-dose (10 mg/kg) led to ~60% TGI, but no response at very low dose (0.1 mg/kg). Furthermore, the homozygous hOX40 knockin mice inoculated with Pan02 pancreatic tumors were treated with a novel strong anti-hOX40 agonist (Ab2) and surrogate anti-mPD-1. Notably, Anit-hOX40 (Ab2) alone at low dose (1 mg/kg, Q3D*9 doses) exerted strong anti-tumor potency (TGI=59.3%, p< 0.005) and no statistical significant antitumor difference was observed between high-dose group (at 5mg/kg) and low-dose group (at 1 mpk) as monotherapy, though anti-hOX40 (Ab2) at 5mg/kg showed the best therapeutic response (TGI=72%, p=0.0002) among all treatment groups. In contrast, the second therapeutic response was observed in the combo group treated with first dosing of 5mg/kg anti-hOX40 (Ab2) combining delayed dosing of 10mg/kg anti-mPD-1 (TGI=64%, p< 0.005) and the concurrent dosing group of Ab2 (5 mg/kg, Q3D × 9 doses) plus anti-mPD-1 (2 mg/kg, Q3D × 9 doses) (TGI=62.3%, p= 0.001). In conclusion, different human-specific OX40 agonists displayed different anti-tumor activity as monotherapy, and different dose led to different antitumor potency for the same agonist. In terms of different combination regimens, although no advanced benefit was observed for the combination of anti-mPD-1/anti-OX40 (Ab2) in comparison to strong anti-OX40 agonist (Ab2) alone, it demonstrated that the dosing timing and sequence of either anti-PD-1 or anti-hOX40 did has impact on the therapeutic outcome. Citation Format: Yi Li, Yanlei Zhang, Xiaolei Qiu, Dongxiao Feng, Ruilin Sun, Daniel X. He. Different combination regimens for OX40 agonists and PD-1 inhibitors exert different antitumor effects in OX40 humanized mice [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 3739.

An IRF2-Expressing Oncolytic Virus Changes the Susceptibility of Tumor Cells to Antitumor T Cells and Promotes Tumor Clearance.

IFN regulatory factor 1 (IRF1) can promote antitumor immunity. However, we have shown previously that in the tumor cell, IRF1 can promote tumor growth, and IRF1-deficient tumor cells exhibit severely restricted tumor growth in several syngeneic mouse tumor models. Here, we investigate the potential of functionally modulating IRF1 to reduce tumor progression and prolong survival. Using inducible IRF1 expression, we established that it is possible to regulate IRF1 expression to modulate tumor progression in established B16-F10 tumors. Expression of IRF2, which is a functional antagonist of IRF1, downregulated IFNγ-induced expression of inhibitory ligands, upregulated MHC-related molecules, and slowed tumor growth and extended survival. We characterized the functional domain(s) of IRF2 needed for this antitumor activity, showing that a full-length IRF2 was required for its antitumor functions. Finally, using an oncolytic vaccinia virus as a delivery platform, we showed that IRF2-expressing vaccinia virus suppressed tumor progression and prolonged survival in multiple tumor models. These results suggest the potency of targeting IRF1 and using IRF2 to modulate immunotherapy.

Abstract 2474: Antitumoral efficacy of ASKG812, a Smartkine® based bifunctional PD-1-eIL-2 molecule, through enhancing T effector cis agonism

Abstract Cytokines are potent molecules, yet their broad application as therapeutics has been significantly hampered due to short PK, severe systemic toxicity, and narrow therapeutic window. To improve the developability of cytokines, AskGene has invented a proprietary cytokine platform (Smartkine®) to achieve its overarching objective of modulating immune reactions at a disease site in a selective and controlled manner. Several antibody-cytokine fusion molecules using the SmartKine® platform have been moving into preclinical and clinical development. ASKG812 is a unique fusion molecule composed of anti-PD-1 antibody and engineered IL-2 (eIL-2). The eIL-2 moiety also comprises a specific mask such that the eIL-2 molecule binding biases towards PD-1+ T effector cells in a cis agonism manner for improved efficacy and therapeutic window. In ex vivo human PBMC assays, we demonstrated that ASKG812 significantly reduced activity in PD-1− T and NK cells, and enhanced activity in PD-1+ T cells judged by levels of pSTAT5, Ki67 and Granzyme B. In a cytotoxicity assay, ASKG812 can efficiently induce PBMC-mediated killing of MDA-MB-231 tumor cells in a dose-dependent manner. Moreover, in both anti-PD-1 therapy responsive and non-responsive syngeneic mouse tumor models, ASKG812 showed robust efficacy; without noticeable toxicity compared to a reference anti-PD-1-IL-2v fusion molecule. In conclusion, these findings provide the basis for the development of this new generation of PD-1 cis-targeted IL-2R agonists with enhanced therapeutic potential for the clinical treatment of cancer. Citation Format: Chunxiao Yu, Kurt Shanebeck, Shiguang Yu, Jeanine Ruiz, Shichang Li, Stone D.-H Shi, Hong Ma, Yuefeng Lu. Antitumoral efficacy of ASKG812, a Smartkine® based bifunctional PD-1-eIL-2 molecule, through enhancing T effector cis agonism [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 2474.

Abstract 5926: YB-1 inhibition as an effective approach for the treatment of osteosarcoma

Abstract Background: Osteosarcoma (OS) is a bone cancer primarily affecting adolescents and young adults, with about 20% of patients having detectable metastatic disease at the time of diagnosis. Despite a large number of clinical trial efforts, metastatic sarcoma remains a lethal disease, and there have been no meaningful advances in therapy or improvements in patient outcomes for decades. Y-box binding protein 1 (YB-1) is a multifunctional cold-shock protein that translationally activates diverse stress response factors with pro-metastatic activities in many cancer types. Importantly, YB-1 is strongly associated with poor outcomes in sarcoma patients and is a major metastatic driver in high-risk sarcomas. Methods: We recently described a novel compound, CET056, that inhibits cancer progression via YB-1 inhibition. We hypothesized that CET056 had the potential to suppress the progression of OS and could provide a new treatment for this disease. We screened osteosarcoma human and mouse cell lines for YB-1 protein expression. OS cells were functionally characterized for responses to CET056 in vitro and in vivo. Results: YB-1 expression was seen in nearly all cell lines tested. CET056 treatment of OS cells resulted in reduced cell viability and YB-1 protein expression in a dose- and time- dependent manner, as well as reduced formation of colonies and spheroids. In vivo efficacy studies, which employed a syngeneic subcutaneous tumor model, revealed that CET056 effectively inhibited tumor progression and enhanced overall survival in contrast to vehicle treated control mice. Conclusion: These results support our hypothesis and illustrate that YB-1 inhibition by CET056 is a promising candidate for further development as a therapy for OS. Citation Format: Kirsten Stefan, Arpit Dheeraj, Dhanir Tailor, Lara E. Davis, Sanjay V. Malhotra. YB-1 inhibition as an effective approach for the treatment of osteosarcoma [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 5926.

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 5562: Altered tumor microenvironment in animal model of concomitant GBM and Alzheimer's pathology

Abstract Glioblastoma (GBM) and Alzheimer’s disease (AD) are two devastating central nervous system diagnoses with no known cure. Both diseases are associated with advanced age. The majority of GBM tumors form in the frontal and temporal lobes, two of the brain regions most impacted by amyloid and tau pathology in AD. Females have a higher risk of AD, while males have a higher risk of GBM. Several large case series have established epidemiological evidence that the two diseases are inversely correlated. Nevertheless, it remains unknown whether presence of subclinical amyloid or tau pathology antagonizes the establishment or progression of GBM. The present study sought to characterize GBM growth, progression, and immune response in the setting of concomitant AD pathology using the syngeneic murine GL261 tumor model. To further understand the tumor cell changes that occur in the presence or absence of AD pathology, we engineered GL261 with a dual-tagged vector consisting of RiboTag (to allow for full-length mRNA profiling) and TurboID (to allow for proteomic profiling). GL261 cells were injected intracranially into APPNL-G-F/NL-G-F - MAPThuman/human, APPNL-G-F/+ - MAPThuman/+, and wildtype C57BL/6J mice. Tumors in both wildtype and AD conditions contained ~50% intratumoral myeloid cells (Iba+, P2RY12-). Differential activation of intratumoral myeloid cells will be assessed with immunohistochemistry. Microgliosis (IBA1, P2RY12) and astrogliosis (GFAP) around the tumor in the setting of Alzheimer’s pathology versus normal conditions will be compared. Invasiveness, proliferation, DNA damage (pH2AX), and apoptosis (cleaved PARP, cleaved Caspase 3) will be compared. Tumor cell-specific changes unique to tumors in the AD microenvironment will be assessed transcriptionally with RiboTag profiling as well as proteomically with TurboID purifications. Our preliminary data suggests that the presence of concomitant AD pathology affects GBM growth and progression as well as the immune response to the tumor, and warrants further investigation. Citation Format: David Nascari, Ryan Eghlimi, Angad Beniwal, Drake Alton, John Fryer, Nhan L. Tran. Altered tumor microenvironment in animal model of concomitant GBM and Alzheimer's pathology [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 5562.

Abstract 5735: Efficient and safe delivery of doxorubicin by DNA fragments: A full preclinical study

Abstract The clinical uses of anthracyclines (e.g., doxorubicin) are hampered especially by dose-dependent cardiac toxicity, resulting in a narrow therapeutic window. Doxorubicin formulations have marginally improved its therapeutic efficacy while suffering from difficult and costly manufacturing, poor characterization and quality control, limited scalability in production, and disappointingly low drug loading. This study employs DNA fragments extracted from the salmon sperm cells, which is known for high biocompatibility in various biomedical application, to self-assemble via intercalation by doxorubicin. DNA/DOX nanocomplexes are easy in manufacturing, high scalability, straightforward characterization and quantification, and efficiency in drug loading. Doxorubicin and DNA fragments were dissolved in water and mixed at the optimized 1:6 weight ratio, followed by stirring and incubation for 30 min. DNA/DOX nanocomplexes were characterized for doxorubicin loading and release, size, surface charge, and morphology by UV/fluorescence spectroscopy, stable isotope tracer ultrafiltration assay (SITUA), dynamic light scattering particle analysis, and transmission electron microscopy. The anticancer efficacy of the DNA/DOX nanocomplexes were tested in vitro and in vivo using syngeneic and PDX tumor models. Along with PD/PK studies, DNA/DOX nanocomplexes were also evaluated for their systemic and cardiac toxicity. Characterization and quantification studies revealed DNA/DOX nanocomplexes to be relatively monodisperse with a size of 40 nm in diameter, efficient for drug encapsulation (~100%) and drug loading (14.3%, w/w), and stable for storage while readily releasing doxorubicin in a cell. The self-assembled nanocomplexes were formed when doxorubicin inter- and intra-molecularly chelated DNA fragments. DNA/DOX nanocomplexes were more efficient in killing cancer cells in vitro than both doxorubicin and the liposomal doxorubicin Doxil. PD/PK studies demonstrated that DNA/DOX nanocomplexes circulated longer with less accumulation in the heart than doxorubicin, which altogether lower toxicity. A repeated administration of the DNA/DOX nanocomplexes to Sprague-Dawley rats exhibited a substantially lower cardiotoxicity score than that of doxorubicin. The improved anti-tumor efficacy of the DNA/DOX nanocomplexes were finally confirmed using a syngeneic lymphoma mouse model and PDX mouse models of triple-negative breast and ovarian cancers. Complexing doxorubicin with DNA fragments addresses the current technological challenges in achieving an efficient and safe therapy for a broad range of cancers. DNA/DOX nanocomplexes are amenable to rigorous chemistry, manufacturing, and controls (CMC) evaluation with proven anti-cancer efficacy and improved safety profiles. Clinical trials on DNA/DOX nanocomplexes for cancer chemotherapy are warranted to fully validate their clinical utilities. Citation Format: Minhyeong Park, Youngwoo Kim, Hyunchu Cho, Saad Mohammad, Yeon Su Choi, Hyunjoo Lee, Seonah Lee, Edward Cedrone, Barry Neun, Maria Dobrovolskaia, David Fruman, Juwan Kim, Young Jik Kwon. Efficient and safe delivery of doxorubicin by DNA fragments: A full preclinical study [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 5735.

Abstract 2357: T cell receptor beta chain-directed Tri-specific antibody molecules retarget V-beta T cell subsets to tumors to promote potent and durable antitumor activity

Abstract Background We have previously shown that novel bifunctional “STAR” antibody-fusion molecules comprising germline β chain TCR-targeting antibodies fused to costimulatory cytokines co-engage the TCR and T cell cytokine receptors, thereby promoting activation and expansion of subsets of T cells expressing distinct germline variable β (Vβ) chain TCRs. Here we describe a new class of T cell engager (TriSTAR) that utilizes a tri-specific format comprising the STAR TCR β chain antibody-IL-2 fusion with an additional Fab arm targeting tumor-associated antigens (TAA). By design, TriSTAR molecules promote the activation and expansion of Vβ T cell subsets that adopt a novel memory phenotype and are subsequently re-targeted to tumors expressing specific TAAs. TriSTAR molecules induce potent and durable anti-tumor activity which in refractory murine solid tumor models appear to be superior to established anti-CD3 T cell engager (TCE) formats. Methods Using the gp75 (Tryp1) melanoma antigen as a model TAA, gp75-targeting TriSTARs were tested in vivo in the B16F10 syngeneic mouse tumor model, compared with a conventional gp75-targeting CD3 bispecific TCE. Cured mice were re-challenged with tumors to assess the potential of TriSTARs to induce immunological memory responses. The pharmacodynamics and pharmacokinetics of gp75-targeting TriSTARs and anti-CD3 TCEs were assessed in blood and tumor using flow cytometry, NanoString and other immunoassays. This work was further extended to testing human TAA-targeting TriSTARs using in vitro human cytotoxicity assays and a transgenic MC38 model. Results In the B16F10 murine melanoma model, gp75-targeting TriSTARs induced potent anti-tumor responses that were superior to control constructs and gp75-targeting CD3 TCEs. The superior anti-tumor activity of the gp75-targeting TriSTARs was attributed to a significant increase and accumulation of CD8+, CD25+ and Granzyme B+ T cells in tumors that was due to the expansion of the target Vβ T cell subset. Further immune profiling by flow cytometry and NanoString in tumors and blood isolated from treated B16F10 mice highlighted significant remodeling of tumor-infiltrating lymphocytes (TILs) and other immunological changes associated with immune activation. These observations with murine gp75-targeting TriSTAR molecules were broadly confirmed with TriSTARs targeting human TAAs in both human in vitro studies and human TAA transgenic mouse tumor models. Conclusions Vβ TCR-targeting TriSTAR molecules represent a new class of T cell engager with the potential to deliver improved anti-tumor activity compared with existing anti-CD3 T cell engagers in immunologically “cold” solid tumors with low levels of T cell infiltration and antigen presentation and may therefore offer a new therapeutic approach for the treatment of patients with refractory solid tumors. Citation Format: Madan Katragadda, Jacques Moisan, Gurkan Guntas, Manuel Sequeria, Roya Servattalab, Jessica Lowry, Robert Ruidera, Kent Nybakken, Erik Gerson, Ke Liu, Kevin Chin, Zhen Su, Andrew Bayliffe. T cell receptor beta chain-directed Tri-specific antibody molecules retarget V-beta T cell subsets to tumors to promote potent and durable antitumor activity [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 2357.

Abstract 6535: Targeting estrogen receptor signaling in tumor associated myeloid cells to enhance anti-tumor immunity

Abstract Immune checkpoint inhibitors (ICB) have significantly improved outcomes across the spectrum of cancers, especially in patients with metastatic melanoma or non-small cell lung cancer (NSCLC). Despite encouraging efficacy in some patients, the development of primary and acquired resistance and severe toxicity associated with these treatment regimens, together with the overall low response rates, have limited their widespread use. Mining publicly available transcriptomic datasets, we have demonstrated that the response to ICB in patients with melanoma is influenced by the functionality of tumor associated macrophages (TAMs). Thus, it is of significance that we have demonstrated that 17-β estradiol (E2), working through myeloid cell intrinsic estrogen receptor alpha (ERα), promotes tumor growth in preclinical mouse models by polarizing tumor associated macrophages towards an immune-suppressive state in a manner that suppresses CD8+T cell functionality and limits ICB efficacy independent of gender. Transcriptomic analysis of tumor infiltrating myeloid cells isolated from E2-treated syngeneic tumors revealed that the type I interferon (IFN) signaling pathway was suppressed and that this activity could be reversed by the addition of fulvestrant a Selective Estrogen Receptor Downregulator. The importance of type I IFN signaling in E2-regulated tumor growth was confirmed in syngeneic mouse tumor models (B16F10-melanoma and LLC1-NSCLC cells) by showing that inhibiting type I interferon receptor (IFNAR) activity using blocking antibodies reversed the protective effects of E2 deprivation (ovariectomy) on tumor growth. Further, using in vitro cultures of macrophages from mouse bone marrow or peripheral blood mononuclear cells from deidentified human donors, we demonstrated that E2-dependent inhibition of type I IFN signaling could be attributed to increased efferocytosis by myeloid cells. These findings were recapitulated in vivo using an IFN reporter mouse (Mx1-egfp) implanted with labelled tumor cells (mCherry-Spectrin labelled LLC1), where we demonstrated that E2 mediated-suppression of myeloid cell intrinsic interferon signaling within the tumor microenvironment is contingent upon their engulfment of apoptotic cancer cells. Mechanistically, this enhanced efferocytosis was attributed to increased expression of the fractalkine receptor (CX3CR1) in E2-treated myeloid cells- as either genetic or pharmacological depletion of CX3CR1 in mouse reversed E2-mediated tumor growth (B16F10 and LLC1), myeloid cell polarization (from immunosuppressive to proinflammatory), myeloid cell intrinsic type I IFN signaling and reinvigorated CD8+T cell function. Taken together, our results highlight the potential clinical utility of targeting the E2/ER-CX3CR1 pathway as a means to enhance response to ICBs. Citation Format: Binita Chakraborty, Michael Brown, Prabuddha Chakraborty, Aditi Goyal, Ching Yi Chang, Donald McDonnell. Targeting estrogen receptor signaling in tumor associated myeloid cells to enhance anti-tumor immunity [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 6535.

Abstract 5534: Needle biopsy induces pro-metastatic progression and systemic dissemination of estrogen receptor-positive breast cancer cells through the COX-2/PGE2 cascade

Abstract Breast cancer is the most commonly diagnosed malignancy in the U.S. and over two-thirds of invasive breast cancer cases are diagnosed early stage. However, 15-year survival rates for early-stage breast cancer remain in the range of 70-77%. Mounting evidence showed an increased risk of disease progression and mortality among early-stage breast cancer patients whose surgery was delayed over 60 days after the diagnostic biopsy. Yet, the mechanism(s) underlying the rapidly increased mortality due to delay of surgery after diagnosis remains unknown. Our cohort analyses of early-stage breast cancer patients reveal the emergence of a significantly rising mortality risk when the biopsy-to-surgery interval was extended beyond 53 days. Additionally, histology of post-biopsy tumors shows prolonged retention of a metastasis-permissive wound stroma dominated by M2-like macrophages capable of promoting cancer cell epithelial-to-mesenchymal transition and angiogenesis by secretion of transforming growth factor beta 1 (TGF-β1) and vascular endothelial growth factor (VEGF). We show that needle biopsy promotes systemic dissemination of cancer cells through a mechanism of sustained activation of the cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) cascade, which favors M2-polarization and its associated pro-metastatic changes, but are abrogated by oral treatment with COX-2 inhibitors in estrogen receptor-positive (ER+) syngeneic mouse tumor models. Therefore, we conclude that needle biopsy of ER+ breast cancer provokes progressive pro-metastatic changes, which may explain the mortality risk posed by surgery delay after diagnosis. Also, our data may provide a rationale for a pharmacologic strategy to inhibit the COX-2/PGE2 cascade in cases when delay of surgery is unavoidable. Citation Format: Hiroyasu Kameyama, Macall Leslie, Reese Simmons, Yunguang Sun, Misung Yi, Priya Dondapati, John F. Langenheim, Kar-Ming Fung, Inna Chervoneva, Hallgeir Rui, Takemi Tanaka. Needle biopsy induces pro-metastatic progression and systemic dissemination of estrogen receptor-positive breast cancer cells through the COX-2/PGE2 cascade [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 5534.

Abstract 4081: rhIL-7-hyFc (efineptakin-alfa, NT-I7) increases tumor-specific CD8+ T cells despite FOLFOX cytotoxicity effect

Abstract rhIL-7-hyFc (efineptakin-alfa; NT-I7) is a potent T cell amplifier, comprised of two molecules of interleukin-7 (IL-7) fused to the hybrid Fc domain of IgD/IgG4 immunoglobulin. NT-I7 safely, significantly, and persistently increases the absolute lymphocyte counts (ALC) in humans in a dose-proportional manner. Importantly, this increase is primarily due to an increase in T cells (1). Previous studies have shown that NT-I7 not only significantly increases the number of CD8+ T cells in peripheral blood but also dramatically boosts the presence of tumor-infiltrating CD8+ T cells, including both tumor-specific (p15E+PD-1+) and tumor non-specific (PD-1-) CD8+ T cells in mice (2). FOLFOX is a chemotherapy regimen composed of 5-fluorouracil, leucovorin, and oxaliplatin that inhibits DNA duplication and eradicates rapidly dividing cells (3). Although the mechanism of FOLFOX results in direct tumor killing, it also has the potential to kill newly dividing lymphocytes during NT-I7 treatment (4-6). Therefore, in this study, we aimed to evaluate the feasibility of combining FOLFOX with NT-I7 in a syngeneic MC38 mouse tumor model. Our results show that NT-I7 improves the efficacy of FOLFOX, irrespective of the timing of NT-I7 administration: simultaneous administration or delayed 3 hours, or 2 days after FOLFOX administration. This improvement persists despite a significant decrease in ALC for the first 6 days, which was significantly lower than the ALC observed with FOLFOX alone. FOLFOX decreases the absolute numbers of tumor non-specific CD8+ T cells. However, adding FOLFOX does not affect the NT-I7-driven increase of tumor-specific CD8+ T cells within the tumor. Taken together, our data demonstrate that FOLFOX does not compromise NT-I7’s ability to increase tumor-specific T cells within the tumor and the combination enhances the anti-tumor response irrespective of the timing of NT-I7 administration. Citation Format: Soung-Min Lee, Miyoung Kim, Sara Ferrando-Martínez, Sun-Kyoung Im, Mankyu Ji, Donghoon Choi. rhIL-7-hyFc (efineptakin-alfa, NT-I7) increases tumor-specific CD8+ T cells despite FOLFOX cytotoxicity effect [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 4081.

Abstract 3971: Progesterone impacts regulatory T cell activity to promote immunosuppression in the mammary gland

Abstract Estrogen and progesterone signaling together drive hormone-receptor positive breast cancer growth and progression. However, there have been limited studies on the independent role that progesterone and its receptor, the progesterone receptor (PR), play in the development of breast cancer. Studies in the Hagan lab have shown that progesterone signaling promotes mammary tumor growth and changes the immune landscape of the mammary gland towards immunosuppression. Regulatory T-cells (Tregs) are immune cells known to promote immunosuppression in the tumor microenvironment. The data from our lab shows that among hormone receptor positive breast cancers, higher levels of PR expression correlates to higher levels of Tregs in the tumor microenvironment. To determine if progesterone signaling increases the number of Tregs in the tumor-bearing mammary gland, we used a syngeneic orthotopic murine tumor model, E0771 cells, engineered to express mouse PR or control empty vector. Mice were treated with progesterone or placebo for 7 days before implantation of the modified E0771 cells. The results of this study show that progesterone promoted tumor growth, and flow cytometry analysis at tumor endpoint showed that PR-positive tumors treated with progesterone harbored more Tregs than mice treated with placebo. Additionally, initial studies using flow cytometry and RNA-seq indicate increased Treg activity following progesterone treatment in PR+ tumor-bearing mice. As progesterone treatment promoted tumor growth and Treg recruitment in progesterone receptor-positive tumors, these data imply that progesterone treatment may promote the release of secreted factors impacting the immune cells in the mammary microenvironment. To determine if progesterone treatment results in cytokine or chemokine changes that may affect Treg recruitment, cytokine arrays and enzyme-linked immunosorbent assays (ELISAs) were performed using cell culture supernatant from murine mammary tumor cells expressing progesterone receptor (E0771-PR) treated with progesterone (0-72 hours). E0771-PR cells treated with progesterone showed higher levels of cytokines and chemokines that have been linked to Treg recruitment and differentiation, such as MCSF. Our findings demonstrate that progesterone signaling promotes an immune suppressed microenvironment in the mammary gland through an increase in Tregs. This evidence provides rationale to investigate the use of anti-progestins as a mechanism to overcome the immune-cold tumor microenvironment seen in progesterone receptor positive breast tumors. Citation Format: Eilidh I. Chowanec, Lauryn R. Werner, Christy R. Hagan. Progesterone impacts regulatory T cell activity to promote immunosuppression in the mammary gland [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 3971.

Abstract 6592: Deciphering the effects of age on T cell immunity and immunotherapy

Abstract Aging induces profound alterations in host biology and correlates with unfavorable clinical outcomes in age-related diseases such as cancer. While the pivotal role of the immune system in regulating tumor progression is well-acknowledged, the precise mechanisms through which aging influences anti-tumor T cell immunity and responsiveness to immune checkpoint blockade (ICB) remain elusive. In this study, we employed syngeneic murine tumor models (B16, MC38, and E0771) in young (2-4 months) and aged (20-24 months) cohorts to elucidate the early impacts of aging on tumor development and T cell responses. Our findings demonstrate that aged mice exhibit accelerated tumor growth across various models. In-depth analysis of tumor-infiltrating lymphocytes (TILs) uncovered distinct alterations in the CD8+ T cell population, characterized by decreased activation status and diminished tumor specificity in aged mice. Correspondingly, aged mice exhibited resistance to anti-PD-1 immunotherapy. To unravel the underlying environmental factors contributing to compromised anti-tumor T cell responses and ICB resistance, we characterized the immune and metabolic landscapes of the aged tumor-draining lymph nodes and tumors. Furthermore, we established a genetically engineered mouse model of lung adenocarcinoma in both young and aged mice, unveiling novel functions and mechanisms associated with age-related T cells actively impeding effective tumor control. In the context of increasing average life expectancy, comprehending the intricate interplay between age-related T cell dysfunction and cancer assumes paramount importance. Such insights hold the key to the development of innovative therapeutic strategies tailored for the growing population of older patients. Citation Format: SeongJun Han, Peter Georgiev, Jaime Schneider, Amy Huang, Zhanel Nugmanova, Thao H. Nguyen, Conghui Yao, Sheila Johnson, Shakchhi Joshi, Ishita Dhiman, Jefte M. Drijvers, Megan Fung, Jared H. Rowe, Brian C. Miller, Gordon J. Freeman, Alison E. Ringel, Marcia C. Haigis, Arlene H. Sharpe. Deciphering the effects of age on T cell immunity and immunotherapy [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 6592.