Established Subcutaneous Tumors Research Articles

DNA origami-based composite nanosandwich for iteratively potentiated chemo-immunotherapy.

Developing effective nanoplatforms for chemo-immunotherapy to achieve enhanced tumor suppression and systemic antitumor immunity has recently received extensive attention. Herein, we formulated a multifunctional DNA sandwich nanodevice, DSWAC/siPD-L1, based on triangular DNA origami, to implement enhanced cancer chemo-immunotherapy. Taking advantage of the tumor-targeting ability of the AS1411 aptamer, DSWAC/siPD-L1 efficiently delivered doxorubicin (DOX), CpG, and siPD-L1 into tumor cells. Moreover, the sandwich cavity spatially protects siPD-L1 from degradation, and the featured design of the DNA/RNA duplex linkers ensures effective intracellular release of siPD-L1. The pH-responsive release of cytotoxic DOX induces apoptosis and initial mild immunogenic cell death of tumor cells, presenting antigens to enhance the maturation of dendritic cells (DCs) with the assistance of the immune adjuvant CpG, thereby activating cytotoxic T lymphocytes to amplify antitumor immunity. Simultaneously, siPD-L1 downregulated the endogenous expression of PD-L1 to inhibit adaptive tumor immune escape. The functions of DSWAC/siPD-L1 initiated the iterative revolution of the cancer-immunity cycle, leading to the inhibition of primary and metastatic tumors, as demonstrated by DC maturation and T-cell infiltration in established subcutaneous primary tumor model and metastatic lung tumor model. Furthermore, the superior antitumor effect of DSWAC/siPD-L1 resulted in approximately 91 % inhibition of primary tumor growth and 93 % prevention of lung metastasis. Collectively, this study describes a siPD-L1-based sandwich DNA nanodevice functionalized with AS1411/CpG for enhanced cancer chemo-immunotherapy, inspiring the creation of more innovative drug nanocarriers and the exploitation of novel cancer therapies.

Omental Preadipocytes Stimulate Matrix Remodeling and IGF Signaling to Support Ovarian Cancer Metastasis.

Ovarian cancer can metastasize to the omentum, which is associated with a complex tumor microenvironment. Omental stromal cells facilitate ovarian cancer colonization by secreting cytokines and growth factors. An improved understanding of the tumor-supportive functions of specific cell populations in the omentum could identify strategies to prevent and treat ovarian cancer metastasis. Here, we showed that omental preadipocytes enhance the tumor initiation capacity of ovarian cancer cells. Secreted factors from preadipocytes supported cancer cell viability during nutrient and isolation stress and enabled prolonged proliferation. Coculturing with preadipocytes led to the upregulation of genes involved in extracellular matrix (ECM) organization, cellular response to stress, and regulation of insulin-like growth factor (IGF) signaling in ovarian cancer cells. IGF1 induced ECM genes and increased alternative NF-κB signaling by activating RelB. Inhibiting the IGF1 receptor initially increased tumor omental adhesion but decreased the growth of established preadipocyte-induced subcutaneous tumors as well as established intraperitoneal tumors. Together, this study shows that omental preadipocytes support ovarian cancer progression, which has implications for targeting metastasis. Significance: Omental preadipocyte-mediated IGF1 signaling promotes ovarian cancer tumorigenesis and metastasis via extracellular matrix remodeling, revealing a role for preadipocytes in regulating ovarian cancer progression and highlighting potential therapeutic targets for metastatic disease.

RNA with chemotherapeutic base analogues as a dual-functional anti-cancer drug

ABSTRACT Nanoparticles of different sizes formulated with unmodified RNA and Protamine differentially engage Toll-like Receptors (TLRs) and activate innate immune responses in vitro. Here, we report that similar differential immunostimulation that depends on the nanoparticle sizes is induced in vivo in wild type as well as in humanized mice. In addition, we found that the schedule of injections strongly affects the magnitude of the immune response. Immunostimulating 130 nm nanoparticles composed of RNA and Protamine can promote lung metastasis clearance but provides no control of subcutaneous tumors in a CT26 tumor model. We further enhanced the therapeutic capacity of Protamine-RNA nanoparticles by incorporating chemotherapeutic base analogues in the RNA; we coined these immunochemotherapeutic RNAs (icRNAs). Protamine-icRNA nanoparticles were successful at controlling established subcutaneous CT26 and B16 tumors as well as orthotopic glioblastoma. These data indicate that icRNAs are promising cancer therapies, which warrants their further validation for use in the clinic.

Abstract 315: B7H3 is a potential therapeutic target in advanced metastatic prostate cancer

Abstract B7H3 is an immunomodulatory protein of the B7 family which inhibits T cell function. B7H3 mRNA is ubiquitously expressed in normal human tissues, but the protein is expressed at low levels, suggesting a tight post-transcriptional regulation. By contrast, B7H3 protein is overexpressed in several solid tumors and often correlates with poor survival, higher tumor grade, and metastasis independently of immune regulation. A few studies also have reported an association between B7H3 overexpression and therapy resistance. Since B7H3 protein is preferentially expressed on cancer cells and tumor vasculature, it is an attractive target for developing novel cancer therapies. Here we analyzed the expression of B7H3 in 26 mCRPC organoid models and examined whether B7H3 can serve as a novel therapeutic target for advanced mPCa patients that fail current treatment regimens. The B7H3 protein expression in PDXOs of various lineages including adenocarcinoma (n=19), double-negative (DNPC, n= 2), and neuroendocrine (NE, n =5) lineages, was analyzed using simple western™ assay, immunofluorescence, and flow cytometry. We tested the ex-vivo drug response of PDXOs and performed PDX preclinical trials using humanized B7H3-ADC armed with a pyrrolobenzodiazepine (PBD) warhead. PBD dimers are DNA interstrand cross-linking agents and are a poor substrate of P-gp drug transporters. Our results showed that B7-H3 was overexpressed in several PDX derived organoids of mPCa. Organoids with adenocarcinoma phenotype (n=19) demonstrated a range of B7H3 protein expression whereas RB1/TP53 mutated small cell neuroendocrine or double negative prostate cancer showed a relatively more uniform and low expression. Nonetheless, PDXOs of neuroendocrine, double negative or adenocarcinoma origin responded with maximum efficacy to B7H3-ADC ex vivo. Adenocarcinoma organoid models (n=19) displayed a wide range of responses, which was only partially correlated with B7H3 protein levels. Genetically-engineered loss of B7-H3 converted a responder to a non-responder phenotype. Our investigation for potential biomarkers of B7H3-PBD sensitivity suggested that RB1-deficiency induced replication stress and/or expression of SLFN11, an interferon pathway transcriptional target, to be the strong predictors of B7H3-PBD response, independent of tumor lineage. We further performed preclinical trials using four PDX models based on their RB1 and SLFN11 status, including a model of advanced adenocarcinoma lineage with low B7H3 expression. B7H3-PBD eradicated large established subcutaneous tumors and metastases and improved long-term overall survival in either RB1 deficient and/or SLFN11HIGH models, but showed no response in RB1+/SLFN11- tumors. In conclusion, B7H3-PBD treatment has potential to produce complete and durable response in appropriately-selected, heavily-pretreated metastatic CRPC and NEPC. Citation Format: Supreet Agarwal, Lei Fang, Juan Juan Yin, Elaine Hurt, Kathleen Kelly. B7H3 is a potential therapeutic target in advanced metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 315.

Mannan-BAM, TLR ligands, and anti-CD40 immunotherapy in established murine pancreatic adenocarcinoma: understanding therapeutic potentials and limitations.

Pancreatic adenocarcinoma is one of the leading causes of cancer-related deaths, and its therapy remains a challenge. Our proposed therapeutic approach is based on the intratumoral injections of mannan-BAM, toll-like receptor ligands, and anti-CD40 antibody (thus termed MBTA therapy), and has shown promising results in the elimination of subcutaneous murine melanoma, pheochromocytoma, colon carcinoma, and smaller pancreatic adenocarcinoma (Panc02). Here, we tested the short- and long-term effects of MBTA therapy in established subcutaneous Panc02 tumors two times larger than in previous study and bilateral Panc02 models as well as the roles of CD4+ and CD8+ T lymphocytes in this therapy. The MBTA therapy resulted in eradication of 67% of Panc02 tumors with the development of long-term memory as evidenced by the rejection of Panc02 cells after subcutaneous and intracranial transplantations. The initial Panc02 tumor elimination is not dependent on the presence of CD4+ T lymphocytes, although these cells seem to be important in long-term survival and resistance against tumor retransplantation. The resistance was revealed to be antigen-specific due to its inability to reject B16-F10 melanoma cells. In the bilateral Panc02 model, MBTA therapy manifested a lower therapeutic response. Despite numerous combinations of MBTA therapy with other therapeutic approaches, our results show that only simultaneous application of MBTA therapy into both tumors has potential for the treatment of the bilateral Panc02 model.

Abstract 5567: In vivo administration of the STING agonist, JNJ-67544412, leads to complete regression of established murine subcutaneous tumors

Abstract STING (Stimulator of Interferon Genes) is an important mediator of innate and adaptive immunity that responds to invading cytosolic bacterial and viral pathogens, and double stranded DNA from transformed cells. Activation of the cGAS-STING pathway leads to pleiotropic cytokine (IFN-α, IFN-β, TNF-α, IL-6) production, maturation and activation of macrophages, and MHC class II expressing dendritic cells (DCs) with generation of CD8+ T cells. JNJ-67544412 (JNJ-4412) is a cyclic dinucleotide (CDN) developed as a STING agonist. JNJ-4412 binds both mouse and human STING and is more potent binding all the major human STING alleles than most other STING CDN agonists. JNJ-4412 phosphorylate STING and IRF3 and induces high levels of IFNβ and other cytokines in M1 and M2 macrophages, dendritic cells, and monocytes. In syngeneic mouse tumor studies, JNJ-4412 was dosed intratumorally (i.t.) on a q3d x 3 or qweekly schedule resulting in significant tumor regression, complete cures and long-lasting antitumor immunity. Body weight loss (<20%) was observed but was transient and recoverable and could be mitigated by utilizing a qweekly schedule with no loss of activity. Proinflammatory cytokines such as IFN-α, IFN-β, IP-10, TNF-α, IL-6 and MCP-1 were detected in tumor and plasma after dosing. Combination studies with anti-PD-1 resulted in enhanced dose-dependent efficacy in treated tumors. In bilateral tumor studies, JNJ-4412 inhibited growth of contralateral un-injected tumors. Pharmacodynamic (PD) and mechanism of action (MOA) studies revealed increased number of CD8+ T cells in the treated tumors; increased apoptosis (cleaved caspase 3); loss of vascularization; decreased tumor cell proliferation and pronounced hemorrhagic necrosis in tumors. Rechallenge of cured mice demonstrated long-lasting antitumor immunity. Thus, in vivo administration of JNJ-4412 potently activates the STING pathway resulting in inflammatory cytokine induction, activation of dendritic cells, proliferation of CD8+ T cells, increased apoptosis and curative antitumor efficacy with immunologic memory. Citation Format: Melissa Smith, Diana Chin, Szeman Chan, Sally Mahady, Liam Campion, Caitlin Morgan, Shefali Patel, Gerald Chu, Anna Hughes, Gilles Bignan, Pete Connolly, Stuart Emanuel, Kathryn Packman, Leopoldo L. Luistro. In vivo administration of the STING agonist, JNJ-67544412, leads to complete regression of established murine subcutaneous tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5567.

Abstract 5585: RealTVac - a novel strategy to treat advanced, late-stage tumors with real-time tumor vaccination

Abstract Novel anti-cancer immune therapeutic strategies, like various new antibody formats and/or tumor vaccines, show promising results in patients. However, due to the “immune-escape phenomenon” driven by tumor-secreted Transforming Growth Factor-beta (TGF-beta), the host immune system of cancer bearing patients frequently fails to control tumor re-growth. Real-Time Tumor Vaccincation (RealTVac) approach aims at avoiding this “immune-escape phenomenon” by intratumoral inhibition of active TGF-beta isotypes while simultanously and synergistically inducing an efficient immune response by a highly potent combination of immune stimulating factors. The synergistic effects of the proposed combination of a TGF-beta inhibitor with immunostimulating cytokines upon human immune cell activation are demonstrated in in-vitro experiments. Both, immune cell proliferation and tumor cell cytotoxicity were significantly enhanced. Initial experiments in a syngenic B16 melanoma xenograft model in immunocompetent mice indicate that Real-Time Tumor Vaccination of established subcutaneous B16 tumor xenografts reduced local tumor growth compared to untreated controls. To summarize, the goal of the local application of RealTVac is to allow the host immune system to scan in real-time all Tumor Associated Antigens (TAAs) being currently expressed by those tumor cells that are exposed to sufficient TGF-beta inhibition. The repetitive administration of the RealTVac approach is furthermore expected to provide a continuous update of the immune response, reflecting the changing pattern of currently expressed TAAs related to the dynamic intratumoral heterogeneity in malignant tumors. Thus, intratumoral immunization as applied for RealTVac may create a new paradigm for cancer therapy in the future. Citation Format: Piotr Jachimczak, Andreas Mitsch, Achim Aigner. RealTVac - a novel strategy to treat advanced, late-stage tumors with real-time tumor vaccination [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5585.

A Novel GUCY2C-CD3 T-Cell Engaging Bispecific Construct (PF-07062119) for the Treatment of Gastrointestinal Cancers.

Gastrointestinal cancers remain areas of high unmet need despite advances in targeted and immunotherapies. Here, we demonstrate potent, tumor-selective efficacy with PF-07062119, a T-cell engaging CD3 bispecific targeting tumors expressing Guanylyl Cyclase C (GUCY2C), which is expressed widely across colorectal cancer and other gastrointestinal malignancies. In addition, to address immune evasion mechanisms, we explore combinations with immune checkpoint blockade agents and with antiangiogenesis therapy. PF-07062119 activity was evaluated in vitro in multiple tumor cell lines, and in vivo in established subcutaneous and orthotopic human colorectal cancer xenograft tumors with adoptive transfer of human T cells. Efficacy was also evaluated in mouse syngeneic tumors using human CD3ε transgenic mice. IHC and mass cytometry were performed to demonstrate drug biodistribution, recruitment of activated T cells, and to identify markers of immune evasion. Combination studies were performed with anti-PD-1/PD-L1 and anti-VEGF antibodies. Toxicity and pharmacokinetic studies were done in cynomolgus macaque. We demonstrate that GUCY2C-positive tumors can be targeted with an anti-GUCY2C/anti-CD3ε bispecific, with selective drug biodistribution to tumors. PF-07062119 showed potent T-cell-mediated in vitro activity and in vivo efficacy in multiple colorectal cancer human xenograft tumor models, including KRAS- and BRAF-mutant tumors, as well as in the immunocompetent mouse syngeneic tumor model. PF-07062119 activity was further enhanced when combined with anti-PD-1/PD-L1 treatment or in combination with antiangiogenic therapy. Toxicity studies in cynomolgus indicated a monitorable and manageable toxicity profile. These data highlight the potential for PF-07062119 to demonstrate efficacy and improve patient outcomes in colorectal cancer and other gastrointestinal malignancies.

Abstract A16: A GUCY2c-CD3 bispecific engages T cells to induce cytotoxicity in gastrointestinal tumors

Abstract Background: Guanylyl cyclase C (GUCY2C) is a regulator of intestinal homeostasis and is expressed in more than 90% of colorectal cancer (CRC), as well as in other gastrointestinal malignancies. Target expression in normal tissues is largely restricted to the apical side of intestinal epithelial tight junctions, which could allow for preferential uptake of GUCY2C-targeted biologics by tumors that have disrupted tight junction architecture. Here we demonstrate tumor-selective uptake and potent efficacy with a half-life extended, GUCY2C-CD3 bispecific molecule that recruits CD3-positive T cells to induce cytotoxicity of GUCY2C-expressing tumors in several CRC models in vivo. Additionally, to address immune evasion mechanisms, rational combinations of the bispecific are explored with immune checkpoint blockade agents, as well as by blocking angiogenesis, which has been reported to enhance T-cell infiltration into tumors. Methods: GUCY2C-CD3 mediated activity was evaluated in vivo in several cell line- and patient derived-xenograft models of CRC, using adoptive transfer of human T cells in established subcutaneous and orthotopic tumors. Immunohistochemistry was performed to demonstrate biodistribution of the drug and recruitment of activated T cells in GUCY2C-expressing tumors vs. normal tissues. We also performed CYTOF analyses on GUCY2C-CD3-treated tumors and tumor-infiltrating lymphocytes (TILs) to identify markers of immune evasion. Combination studies with anti PD-1/PD-L1 checkpoint blockade agents and with an anti VEGF-A antibody were performed using the adoptive transfer model. Results: GUCY2C-CD3 bispecific showed preferential biodistribution to GUCY2C-expressing xenograft tumors compared to normal tissue. The drug demonstrated potent dose-dependent efficacy in several CRC models with no signs of toxicity. Bispecific treated tumors not only showed recruitment of activated T cells to the tumor site, but also upregulated checkpoint mechanisms, such as PD-L1 on tumors and exhaustion markers on TILs. Consequently, anti PD-1/PD-L1 checkpoint blocking antibodies provided enhanced efficacy when combined with GUCY2C-CD3. Additionally, significant combination benefit was observed when GUCY2C-CD3 was combined with an anti VEGF-A blocking antibody. Conclusions: Our preclinical data demonstrate that a GUCY2C-CD3 bispecific can selectively target colorectal tumors, including those with KRAS or BRAF mutations, which are difficult to treat with currently approved therapies. This bispecific shows combination benefits with T-cell checkpoint blockade agents, as well as antiangiogenesis agents, indicating that single-agent activity with GUCY2C-CD3 can be further enhanced with mechanisms that address immune evasion. Citation Format: Divya Mathur, Adam Root, Bozena Bugaj-Gaweda, Xingzhi Tan, Wei Fang, Stephanie Bisulco, Jonathan Golas, Jessica Kearney, Eric Upeslacis, Johnny Yao, Edward Rosfjord, Chad Stevens, Lindsay King, Jatin Narula, Kerry Kelleher, Cynthia Rohde, Lioudmila Tchistiakova, Anhco Nguyen, Puja Sapra. A GUCY2c-CD3 bispecific engages T cells to induce cytotoxicity in gastrointestinal tumors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A16.

Immunotherapy of experimental melanoma with ICOS-Fc loaded in biocompatible and biodegradable nanoparticles

Inducible T-cell costimulator (ICOS) upon binding to its ligand (ICOSL) mediates adaptive immunity and antitumor response. Thus, antitumor therapies targeting the ICOS/ICOSL pathway hold great promise for cancer treatment. In this regard, ICOSL triggering by a soluble recombinant form of ICOS (ICOS-Fc) hampered adhesiveness and migration of dendritic, endothelial, and tumor cells in vitro. Furthermore, in vivo treatment with ICOS-Fc previously showed the capability to inhibit lung metastatization of ICOSL+ B16-F10 melanoma cells when injected intravenously in mice, but it failed to block the growth of established subcutaneous B16-F10 murine tumors. Thus, we asked whether passive targeting of solid tumors with ICOS-Fc-loaded biocompatible and biodegradable nanoparticles (NPs) could instead prove effectiveness in reducing tumor growth. Here, ICOS-Fc was loaded in two types of polymer nanoparticles, i.e. cross-linked β-cyclodextrin nanosponges (CDNS) and poly(lactic-co-glycolic acid) (PLGA) NPs and in vitro characterized. In vivo experiments showed that treatment of C57BL6/J mice with ICOS-Fc loaded into the two nanoformulations inhibits the growth of established subcutaneous B16-F10 tumors. This anticancer activity appears to involve both anti-angiogenic and immunoregulatory effects, as shown by decreased tumor vascularization and downmodulation of IL-10 and Foxp3, two markers of regulatory T cells (Tregs). Overall, the substantial in vivo anticancer activity of ICOS-Fc-loaded CDNS and PLGA NPs against different components of the tumor microenvironment makes these nanoformulations attractive candidates for future combination cancer therapy.

In Vivo Efficacy of Anti-CD20-Interferon-Gamma Fusion Protein Against Syngeneic B Cell Lymphoma Is Mediated By Natural Killer Cells

Background: The interferons, including IFNα/IFNβ (type I) and IFNγ (type II) are essential mediators of anti-cancer immunity. To achieve efficient targeting of IFNs to tumor sites, we have developed antibody (Ab)-IFN fusion protein technology. We previously reported the antigen-specific targeting of IFNα to CD20+ target cells with efficient inhibition of proliferation, induction of apoptosis, and in vivo tumor eradiation dependent upon IFNα receptors on the tumor cell surface (Xuan et al, Blood, 2010). A fusion protein targeting human CD20 (anti-CD20-IFNα) exhibited stronger direct anti-proliferative effects, complement-dependent cytotoxicity (CDC), Ab-dependent cell-mediated cytotoxicity (ADCC), and in vivo potency against B-cell lymphoma xenograft models compared to the parent Ab rituximab (Timmerman et al, Blood 2015). Based on these results, a phase I, first-in-human, dose-escalation trial of anti-CD20-IFNα for B cell non-Hodgkin lymphoma is now underway (NCT02519270). Given the distinct properties of IFNγ from type I IFNs, including upregulation of antigen presentation, control of immune cell trafficking, and activation of T cells, NK cells, and macrophages, we hypothesized that Ab-targeted IFNγ may have anti-tumor effects mechanistically-distinct from those of Ab-IFNα fusions. We now report on the construction and characterization of anti-CD20 fusions containing IFNγ. Methods: The VH and VL regions from antibody 2B8 recognizing human CD20 were engineered in recombinant form with mouse IgG2a constant regions, and fused at the C-terminus with mIFNγ, yielding anti-hCD20-mIFNγ. Tumor cell proliferation in vitro was measured by [3H]-thymidine incorporation, ADCC by LDH release using mouse splenocyte effectors, CDC by propidium iodide (PI) exclusion, and in vivo tumor growth assessed using the huCD20-expressing syngeneic mouse B cell lymphoma 38C13-huCD20. Tumor-infiltrating lymphocytes were measured by flow cytometry. Results: Anti-hCD20-mIFNγ displayed potent IFNγ bioactivity comparable to free recombinant mIFNγ, and suppressed the in vitro proliferation of 38C13-huCD20 lymphoma cells by up to 70% (at 1 nM), though not as potently as anti-hCD20-mIFNα, which inhibited proliferation by 98% (Figure 1). Anti-hCD20-mIFNγ showed enhanced ADCC against lymphoma cells compared with the unfused, parent antibody (16-20% at E:T ratio of 20:1, versus 9-12%, respectively, p=0.0024)(Figure 2), while CDC was identical to unfused antibody. In vivo efficacy was demonstrated in mice bearing established subcutaneous 38C13-huCD20 tumors, with systemic (i.v.) injection of 100 μg anti-hCD20-mIFNγ fusion protein on days 5, 6, 7, or 5, 6, 7, 9 after tumor inoculation resulting in cure of approximately 70-80% of mice in repeated experiments. In contrast, therapy with equimolar doses of unfused, native anti-hCD20 Ab resulted in no cures. Mechanistic studies in anti-hCD20-mIFNγ fusion protein-treated mice showed that depletion of natural killer (NK) cells (using anti-asialo-GM1) significantly abrogated tumor clearance (p=0.01), while depletion of macrophages (clodronate liposomes) had lesser, borderline effects (p= 0.05)(Figure 2), and depletion of complement (cobra venom factor) or T cells (CD4+ or CD8+) had no significant effects on tumor eradication. Subcutaneous mouse B cell lymphomas treated with intratumoral injections of anti-hCD20-mIFNγ displayed increased tumor-infiltrating CD8+ T cells (mean 20.6% versus 5% in PBS-treated controls, p=0.008), and CD4+ T cells (mean 15.3% versus 6.6%). Conclusions: Anti-hCD20-mIFNγ fusion protein has in vitro and in vivo efficacy in a syngeneic, immunocompetent model of B cell lymphoma, with NK cells and possibly macrophages implicated in the mechanism(s) of tumor eradication. Ab-targeted mIFNγ can also promote infiltration of immune cells into the tumor microenvironment. These findings may suggest a novel approach for the immunotherapy of B cell lymphomas and other cancers. Disclosures Vasuthasawat: Qwixel therapeutics LLC: Other: stake;which receives some funding through UCLA. Trinh:Qwixel therapeutics LLC: Other: stake;which receives some funding through UCLA. Morrison:Qwixel therapeutics LLC: Other: stake;which receives some funding through UCLA. Timmerman:ImmunGene: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Other: travel support, Research Funding; Merck: Research Funding; Kite, A Gilead Company: Consultancy, Honoraria, Other: travel support, Research Funding; Spectrum Pharmaceuticals: Research Funding.

Abstract 3719: Systemic and subcutaneous modeling of A20 murine B cell lymphoma in mice: A comparative assessment

Abstract To advance immuno-oncology drug development, there is a need for well-characterized syngeneic tumor models. In addition to subcutaneous modeling, orthotopic models are equally important for preclinical development as they are posited to have improved clinical translatability compared to subcutaneous implantation. To this end, we have generated both subcutaneous and systemic A20 murine B cell lymphoma models. Specific to orthotopic modeling, a luciferase-enabled A20 model (A20-luc) was created to monitor tumor progression by bioluminescence imaging. Systemic parental A20 or A20-luc models show slight differences in median survival (34.5 days and 39 days, respectively) but similar take rates and clinical manifestations, including abdominal distension and metastatic foci in the liver. These data suggest that parental A20 and A20-luc behave similarly in systemic disease. To understand how checkpoint blockade and costimulatory agonists act on A20, anti-mPD-1, anti-mPD-L1, anti-mCD137, and anti-mGITR were evaluated for efficacy against both established subcutaneous and systemic A20 models. Our data indicate that neither anti-mPD-1 nor anti-mGITR demonstrate antitumor activity in either model. Anti-mPD-L1 is inactive in systemic disease but shows some efficacy on A20 subcutaneous tumors with delayed growth observed in 40% of mice. Contrastingly, the costimulatory agonist anti-mCD137 elicits a stronger response, with 50% of established subcutaneous A20 tumors having delayed growth including two complete responses and one tumor free survivor. Similarly, in systemic A20 disease, 50% of animals treated with anti-mCD137 exhibited a profound decrease in luciferase signal. While modestly responsive, both A20 and A20-luc show promise for use in combination strategies. To determine whether this modest activity is due to an infiltration of immunosuppressive cells into the tumor, the composition of immune cells in established subcutaneous A20 tumors was evaluated. Despite modest activity, 50% of total CD45+ infiltrate were T cells and NK cells, 7% were MDSCs and macrophages, and the remaining were dendritic in nature. As high T cell infiltrate is more common in tumors responsive to immunotherapy, these infiltrated T cells are hypothesized to lack signals required for activation or are reactive to non-tumor-associated antigen. Similar assays with metastatic foci resulting from systemic disease are planned. Both subcutaneous and orthotopic A20 models exhibit favorable characteristics for evaluation of investigational agents. Response to immunotherapy is minimal to moderate in both models but are generally aligned. The high infiltrate of T cells in the subcutaneous model have potential for exploitation of this model in development of agents targeting T cells. Taken together, our results indicate that A20 is a favorable syngeneic tumor model for both subcutaneous and orthotopic applications. Citation Format: Sheri R. Barnes, Sumithra Urs, David Draper, Scott Wise, Maryland Rosenfeld Franklin. Systemic and subcutaneous modeling of A20 murine B cell lymphoma in mice: A comparative assessment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3719.

Structural and functional characterization of the membrane-permeabilizing activity of Nicotiana occidentalis defensin NoD173 and protein engineering to enhance oncolysis.

Defensins are an extensive family of host defense peptides found ubiquitously across plant and animal species. In addition to protecting against infection by pathogenic microorganisms, some defensins are selectively cytotoxic toward tumor cells. As such, defensins have attracted interest as potential antimicrobial and anticancer therapeutics. The mechanism of defensin action against microbes and tumor cells appears to be conserved and involves the targeting and disruption of cellular membranes. This has been best defined for plant defensins, which upon binding specific phospholipids, such as phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidic acid, form defensin-lipid oligomeric complexes that destabilize membranes, leading to cell lysis. In this study, to further define the anticancer and therapeutic properties of plant defensins, we have characterized a novel plant defensin, Nicotiana occidentalis defensin 173 (NoD173), from N. occidentalis. NoD173 at low micromolar concentrations selectively killed a panel of tumor cell lines over normal primary cells. To improve the anticancer activity of NoD173, we explored increasing cationicity by mutation, with NoD173 with the substitution of Q22 with lysine [NoD173(Q22K)], increasing the antitumor cell activity by 2-fold. NoD173 and the NoD173(Q22K) mutant exhibited only low levels of hemolytic activity, and both maintained activity against tumor cells in serum. The ability of NoD173 to inhibit solid tumor growth in vivo was tested in a mouse B16-F1 model, whereby injection of NoD173 into established subcutaneous tumors significantly inhibited tumor growth. Finally, we showed that NoD173 specifically targets PIP2 and determined by X-ray crystallography that a high-resolution structure of NoD173, which forms a conserved family-defining cysteine-stabilized-αβ motif with a dimeric lipid-binding conformation, configured into an arch-shaped oligomer of 4 dimers. These data provide insights into the mechanism of how defensins target membranes to kill tumor cells and provide proof of concept that defensins are able to inhibit tumor growth in vivo.-Lay, F. T., Ryan, G. F., Caria, S., Phan, T. K., Veneer, P. K., White, J. A., Kvansakul, M., Hulett M. D. Structural and functional characterization of the membrane-permeabilizing activity of Nicotiana occidentalis defensin NoD173 and protein engineering to enhance oncolysis.

Abstract A050: Intratumoral delivery of a novel STING agonist synergizes with checkpoint blockade to regress multifocal pancreatic cancer

Abstract Immunosuppressive myeloid populations including tumor-associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) are abundant within pancreatic adenocarcinoma (PDAC) tumors and play critical roles in constraining cytotoxic T-cell function in the tumor microenvironment. We hypothesized that intratumoral engagement of innate pathogen recognition receptors such as Stimulator of Interferon Genes (STING) could induce proinflammatory polarization of the myeloid stroma and liberate the antitumor T-cell response to regress refractory PDAC tumors in the presence of checkpoint blockade.We developed and characterized a novel cyclic dinucleotide (CDN) STING agonist IACS-8803, and found that 8803 activates downstream STING signaling in both human (THP-1) and murine (J774) myeloid reporter cells with over 10-fold greater potency than ML-RR-S2-CDA, the first-in-class CDN currently undergoing clinical evaluation (NCT02675439, NCT03172936). Intratumoral delivery of 8803 into subcutaneous B16 melanoma and PDAC tumors additionally revealed a greater capacity to induce tumor regression relative to ML-RR-S2-CDA. In order to evaluate the specific effects of 8803 on the phenotype and function of suppressive myeloid populations, we generated in vitro polarized human M2 macrophages and murine bone marrow-derived MDSC. Upon exposure to 8803, we observe downregulation of M2 markers CD163, LAP/TGF-β, and Arginase on human M2 macrophages, concomitant with upregulation of M1 markers CD86, CD80, and IL-6. Additionally, 8803-stimulated murine MDSC exhibit reduced T-cell suppressive capacity compared to unstimulated MDSC. In these studies, we consistently observe that the magnitude of phenotypic and functional repolarization by 8803 is superior to that of ML-RR-S2-CDA as well as other known CDN, 2’3’-cGAMP and c-di-GMP. Therefore, we describe IACS-8803 as a novel, highly potent STING agonist with the capacity to induce inflammatory repolarization in suppressive myeloid cells of both human and murine origin. We next investigated the capacity for intratumoral delivery of IACS-8803 to sensitize murine pancreatic cancer to checkpoint blockade and to mobilize systemic immunity against disseminated lesions. We utilized mT4-2D, a novel pancreatic cancer cell line from Kras+/LSL-G12D Tp53+/LSL-R172H Pdx1-Cre tumor organoids. We isolateda single cell clone of mT4-2D with reduced in vivo growth kinetics (termed mT4-LS), as well as a clone that maintains the aggressive nature of the parental line (termed mT4-LA). Mice bearing 10-day established orthotopic and subcutaneous mT4-LS tumors received standard regimens of αCTLA-4, αPD-1, or combined αCTLA-4/αPD-1 in the presence or absence of 8803 CDN injected into the orthotopic pancreatic tumor. We find single-agent treatment with 8803, αCTLA-4, αPD-1, or αCTLA-4/αPD-1 can cure 40-60% of mice of both orthotopic and subcutaneous tumors in this system; however, combining 8803 with checkpoint blockade completely eradicates both injected and distal mT4-LS tumors in all mice. We replicated these studies using the highly aggressive and refractory mT4-LA model, and found that combination therapy with intra-pancreatic 8803 and systemic αCTLA-4/αPD-1 significantly extends survival compared to 8803 or αCTLA-4/αPD-1 alone (p=0.001, p=0.0086, respectively). Analysis of treated mT4-LA tumors by flow cytometry reveals that combination therapy enhances the cytotoxic potential of CD8 T-cells at both injected and uninjected lesions, and promotes dendritic cell proliferation within the pancreatic milieu. These studies provide a preclinical rationale for pursuing the use of STING-activating CDN as a localized approach to sensitize refractory PDAC tumors to checkpoint blockade immunotherapy. Citation Format: Casey R. Ager, Maria E. Di Francesco, Philip Jones, Michael A. Curran. Intratumoral delivery of a novel STING agonist synergizes with checkpoint blockade to regress multifocal pancreatic cancer [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A050.

Abstract B138: Cancer immunotherapy with APOBEC3B-induced heteroclitic library tumor cell vaccines and immune checkpoint blockade

Abstract We have previously shown that a vesicular stomatitis virus-based cDNA library expressing xenogeneic altered self-epitopes led to T-cell mediated rejection of prostate cancer, glioma and melanoma. The use of a library of altered self-peptides which reflects the transcriptome of the tumor circumvents the necessity for a priori knowledge of which antigens may be immunogenic in a patient, and primes a polyclonal T-cell response that provides strong cumulative antitumor selective pressure. We have expanded this concept of altered-self library vaccination using tumor vaccines modified by the overexpression of APOBEC3B, a cytosine deaminase that generates C to T transition mutations. A freeze-thawed whole tumor cell vaccine prepared from B16 melanoma cells stably overexpressing human APOBEC3B treated established subcutaneous parental B16 tumors and, when combined with PD-1 checkpoint blockade, cured between 75%-100% of mice. T-cells from mice treated with the vaccine and anti-PD1 produced high levels of IFN-γ when restimulated with parental unmodified B16 melanoma cells in vitro. Whole-genome sequencing of B16APOBEC3B overexpressing cells identified 301 C to T or G to A missense mutations unique to the APOBEC3B line. Using an in silico MHC binding affinity algorithm, we identified and experimentally validated a short list of 10 APOBEC3B- induced heteroclitic peptides. We have also shown that this approach can be extended to an orthotopic brainstem model of high grade glioma. GL261 tumors stereotactically implanted into the brainstem were significantly responsive to treatment with an APOBEC3B- modified GL261 vaccine in combination with anti-PD-1 checkpoint blockade. In summary, when overexpressed in tumor cells, APOBEC3B generates a library of heteroclitic sequences that primes both CD4 and CD8 T-cells that have escaped central tolerance and that recognize both newly mutated antigens from the vaccine, and the corresponding unaltered self epitopes expressed on the tumor cells. Citation Format: Richard Vile, Laura Evgin, Timothy Kottke, Matthew Schuelke, Christopher B. Driscoll, Amanda L. Huff, Jill Thompson, Amy Molan, Reuben S. Harris, Jose S. Pulido, Phonphimon Wongthida. Cancer immunotherapy with APOBEC3B-induced heteroclitic library tumor cell vaccines and immune checkpoint blockade [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B138.

Abstract 3878: Drug-loaded microparticles as a treatment approach for pancreatic cancer

Abstract Pancreatic cancer is the fourth leading cause of cancer death in the United States with only 7% of diagnosed patients surviving 5 years. Most pancreatic cancer patients are not surgical candidates due to advanced stage at diagnosis. Also, current systemic chemotherapies have not been very effective at decreasing tumor burden. Poly(lactic-co-glycolic acid)-based (PLGA) microparticles (MPs) are a promising tool for localized drug delivery within the tumor due to their biocompatibility, flexibility in drug encapsulation and extended drug release. The present study investigated whether gemcitabine-loaded microparticles (GMPs), paclitaxel-loaded microparticles (PMPs) or sequential treatment of both, in comparison with blank (no drug) MPs, systemic treatments and no treatment control, are able to promote cancer cell killing effects and modulate drug resistance in vitro and in vivo. We previously showed in vitro studies with PANC-1 cells and we were able to complete the MPs studies with a second human pancreatic cancer cell line, MIAPaCa-2. In both cases, we tested the effect of single and combination treatments on two well-known resistance markers for gemcitabine, ribonucleotide reductase catalytic subunit M1 and cytidine deaminase, as well as on the promotion of cell death measuring cleaved caspase-3 (CC3). When treated with GMPs alone, both markers went up suggesting an increase in resistance against gemcitabine. Interestingly, both cell lines treated with PMPs alone showed an increase in CC3 expression and a significant decrease in the expression of both markers. Subsequently, we tested the in vivo efficacy of MPs by direct injection into established subcutaneous MIAPaCa-2 tumors in nude mice. Following four weeks of treatment, the tumors were excised, biopsied for protein analysis and frozen in OCT to allow visualization of fluorescent MPs and detect apoptosis by immunofluorescence. We also want to evaluate reactive oxygen species production; where we expect to see an increase in the MPs treated groups. This analysis is in progress. In conclusion, we observed a decrease in cell viability and drug resistance proteins in vitro using the drug-loaded microparticles in two grade 3 (or high grade) pancreatic cancer cell lines. The described drug delivery method has the potential to be a more efficient treatment modality than systemic gemcitabine and paclitaxel against early stage and locally advanced pancreatic cancer. Citation Format: Maria Munoz-Sagastibelza, Oluwafeyikemi Okome, Jenny E. Paredes Sanchez, Albert Palileo, Catherine Burkhart, Laura Martello-Rooney. Drug-loaded microparticles as a treatment approach for pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3878.

Abstract 5923: CD133-targeted oncolytic adenovirus exhibits anti-tumor effect in colorectal cancers, and its combination with irradiation inhibits liver metastasis

Abstract Colorectal cancer (CRC) is the third most common cancer in the world, and about 50% of patients relapse after treatment. Cancer stem cells (CSCs) have contribution to recurrence, metastasis and chemotherapy resistant of CRC. CD133 (Prominin-1), a member of the transmembrane glycoprotein family, is a marker of CSCs in several cancers including CRC: its expression correlates with recurrence, metastases and chemotherapy resistance, as well as poor prognosis in CRC. It is therefore reasonable to develop a CSC-directed CRC therapeutic strategy by employing CD133as a target molecule. Recently, we have established a method for isolating transductionally-targeted infectivity-selective adenovirus by high-throughput screening. Using this adenovirus library screening system, we isolated the CD133-specific Oncolytic Adenovirus (OAd) and tested the oncolytic activity of CD133-targeted OAd (CD133-OAd) in both in vitro and in vivo, with and without irradiation which induces CD133 expression. The infectivity-selective OAd (ISOAd) with CD133-targeting motif (TYML motif) selectively infected CD133+ CRC cell lines and lysed them efficiently. In the context of modulation of stemness, CD133-OAd inhibited colony formation in vitro. In tumor formation assay in nude mice, treatment with CD133-OAd prior to tumor inoculation inhibited the establishment of tumor of CD133+ CRC cell lines. Intra-tumor (i.t.) administration of CD133-OAd into established subcutaneous tumor exhibited significantly stronger antitumor effect compared to OAd without targeting. We have reported that the irradiation increases CD133 expression in CRC cells, and the replication of CD133-OAd increased significantly after irradiation. In athymic nude mice, treatment of irradiated cells with CD133-OAd abolished tumor-forming capacity, compared to cells without irradiated and cells treated with radiation alone (5% vs 94% and 5% vs 73% respectively, p<0.0001). When the antitumor effect of CD133-OAd was analyzed on subcutaneously established tumors, treatment with radiation and CD133-OAd significantly reduced tumor growth compared to no treatment and treatment with radiation only (both p<0.0001). In addition to the effect on the main tumor, CD133-OAd suppressed liver metastasis of CRC. The mice injected with human CRC cells pretreated with CD133-OAd combined with irradiation had significantly lower incidence of liver metastasis compared with the untreated control group or the groups received irradiation or CD133-OAd treatment alone. Our CD133-targeted ISOAd is effective for cytotoxic killing, reduces tumor formation, and mitigates tumor growth in radiation resistant CRC cells. This targeted OAd therapy may be applicable to address therapeutic resistance and prevent the establishment of recurrent colorectal cancer. Citation Format: Jing Li Huang, Mizuho Sato-Dahlman, Kari Jacobsen, Masato Yamamoto. CD133-targeted oncolytic adenovirus exhibits anti-tumor effect in colorectal cancers, and its combination with irradiation inhibits liver metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5923.

Tumor Regression and Cure Depends on Sustained Th1 Responses.

While immunomodulatory monoclonal antibodies (mAbs) have therapeutic efficacy against many tumors, few patients are cured. Attempting to improve their therapeutic efficacy we have applied the TC1 mouse lung carcinoma model and injected established subcutaneous tumors intratumorally with 3 weekly doses of various combinations of mAbs. Combinations of mAbs to CTLA4/PD1/CD137 (the 3 mAb combination) and to CTLA4/PD1/CD137/CD19 (the 4 mAb combination) were most efficacious to induce complete regression of both the injected tumor and an untreated tumor in the same mouse. Tumor cure was consistently associated with shifting a Th2 to a Th1 response in tumor-draining lymph nodes and spleen and it involved epitope specific and long-lived memory T cells as well as M1 macrophages. This shift and accompanying tumor rejection was harder to achieve as the treated tumors increased in size. Relapse of tumors which had initially regressed following treatment with immunomodulatory mAbs was associated with return of a Th2 microenvironment in tumors, tumor-draining lymph nodes and spleens rather than the emergence of immune-resistant tumor cells. While mAbs to CTLA4 plus PD-1 were therapeutically ineffective, combining the 2 of them with intraperitoneal cisplatin, 10 mg/kg, induced long-term complete tumor regression in most mice with small TC1 tumors and the therapeutic efficacy against larger tumors improved by administrating cisplatin together with the 3 or 4 mAb combination.

Enrichment and Characterization of the Tumor Immune and Non-immune Microenvironments in Established Subcutaneous Murine Tumors

Enrichment and Characterization of the Tumor Immune and Non-immune Microenvironments in Established Subcutaneous Murine Tumors

Enrichment and Characterization of the Tumor Immune and Non-immune Microenvironments in Established Subcutaneous Murine Tumors.

The tumor immune microenvironment (TIME) has recently been recognized as a critical mediator of treatment response in solid tumors, especially for immunotherapies. Recent clinical advances in immunotherapy highlight the need for reproducible methods to accurately and thoroughly characterize the tumor and its associated immune infiltrate. Tumor enzymatic digestion and flow cytometric analysis allow broad characterization of numerous immune cell subsets and phenotypes; however, depth of analysis is often limited by fluorophore restrictions on panel design and the need to acquire large tumor samples to observe rare immune populations of interest. Thus, we have developed an effective and high throughput method for separating and enriching the tumor immune infiltrate from the non-immune tumor components. The described tumor digestion and centrifugal density-based separation technique allows separate characterization of tumor and tumor immune infiltrate fractions and preserves cellular viability, and thus, provides a broad characterization of the tumor immunologic state. This method was used to characterize the extensive spatial immune heterogeneity in solid tumors, which further demonstrates the need for consistent whole tumor immunologic profiling techniques. Overall, this method provides an effective and adaptable technique for the immunologic characterization of subcutaneous solid murine tumors; as such, this tool can be used to better characterize the tumoral immunologic features and in the preclinical evaluation of novel immunotherapeutic strategies.