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Mouse tumor models have been successfully used to generate preclinical data for numerous clinical programs including immunotherapy. Preclinical in vivo studies are typically carried out using young mice (often less than 2 months old) to generate efficacy data, predictive biomarker and pharmacodynamic markers. In notable contrast, the majority of human cancer occur in adult and older patients. It has become increasingly clear that the immune system of young and old mice is quite different with regards to the relative abundance and functionality of different cell populations. Data generated using young mice could provide a distorted assessment of the potential activity of immuno-oncology drugs in the clinic. Therefore, we tested the activity of GITRL-Fc protein in both young and old mice (>9 months). Previously using extensive young mice experiments, we have shown that GITRL-Fc promoted a robust antitumor immune response and enhanced tumor-specific T-cell responses, particularly of the Th1 type, and also led to a reduction in Treg-mediated immunosuppressive activity. Compared to young mice, tumors grew faster in older mice, and peripheral blood of older tumor-bearing mice has fewer T cells and NK cells. The total MDSC population was increased in the blood and spleen of old tumor-bearing mice, with a significantly higher number of G-MDSCs in the blood. On the other hand, old mice had reduced “antigen-presenting cells” (macrophages/dendritic cells expressing MHCII) in the blood. Furthermore, splenocytes from old mice had impaired production of IL-2. GITRL-Fc significantly inhibited tumor growth in both older and younger mice. However, efficacy was more pronounced in young mice, which frequently exhibited complete tumor regression. There were fewer tumor-infiltrating immune cells with less CD8 T and NK cells in older mice compared to young mice, consistent with faster tumor growth. Interestingly, GITR expression in CD8 T cells in old mice was lower compared with young mice at the tumor site. In old mice, GITRL-Fc (mIgG2a) was still able to deplete Tregs in tumor and increase Tregs in the spleen as has been previously shown with GITRL-Fc in young mice. On the other hand, GITRL-Fc deficient in effector function (mIgG2a (N297A)) did not deplete Tregs in the tumor but did retain some antitumor growth activity, indicating a role for GITR signaling in the mechanism of efficacy by GITLR-Fc. In conclusion, the results demonstrate the potential for the aging of the immune system to impact the efficacy observed with immunotherapy agents and highlight the potential benefits of conducting efficacy studies with both young and older mice. Citation Format: Angie Inkyung Park, Minu K. Srivastava, Rui Yun, Jenny Pokorny, Janice Yu, Fumiko Axelrod, Austin Gurney. Effect of aging on the antitumor activity of GITRL-Fc [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 70.

Meeting abstracts Blocking DLL4, a Notch ligand, effectively inhibits tumor growth by increasing non-functional angiogenesis and decreasing the cancer stem cell (CSC) population. Preclinical studies have demonstrated inhibition of tumor growth by anti-DLL4 treatment and have led us to enter

T-acute lymphoblastic leukemia (T-ALL) is characterized by several genetic alterations and poor prognosis in about 20-25% of patients. Notably, about 60% of T-ALL shows increased Notch1 activity, due to activating NOTCH1 mutations or alterations in the FBW7 gene, which confer to the cell a strong growth advantage. Therapeutic targeting of Notch signaling could be clinically relevant, especially for chemotherapy refractory patients. This study investigated the therapeutic efficacy of a novel anti-Notch1 monoclonal antibody by taking advantage of a collection of pediatric T-ALL engrafted systemically in NOD/SCID mice and genetically characterized with respect to NOTCH1/FBW7 mutations. Anti-Notch1 treatment greatly delayed engraftment of T-ALL cells bearing Notch1 mutations, including samples derived from poor responders or relapsed patients. Notably, the therapeutic efficacy of anti-Notch1 therapy was significantly enhanced in combination with dexamethasone. Anti-Notch1 treatment increased T-ALL cell apoptosis, decreased proliferation and caused strong inhibitory effects on Notch-target genes expression along with complex modulations of gene expression profiles involving cell metabolism. Serial transplantation experiments suggested that anti-Notch1 therapy could compromise leukemia-initiating cell functions. These results show therapeutic efficacy of Notch1 blockade for T-ALL, highlight the potential of combination with dexamethasone and identify surrogate biomarkers of the therapeutic response.

Accumulating evidence has suggested that tumors may arise and grow as a result of the formation of a subset cell population termed cancer stem cells (CSC) or tumor initiating cells. Several research reports have indicated that CSCs are relatively resistant to conventional therapies. Thus, therapeutic strategies that specifically target cancer stem cells could have a major impact on cancer patient survival. Patient-derived tumor xenografts (PDX) have played a major role in the development of new cancer therapies. The advantage of PDX over standard cell-line xenograft models is that PDX retain much of the molecular, genetic, and histological heterogeneity of the original tumor and are minimally passed. In addition, self-renewal and lineage differentiation, the hallmarks of cancer stem cells, can be demonstrated through serial transplantation in immunodeficient mice. Our therapeutic approach in cancer stem cell drug discovery has been to target key developmental pathways that have been strongly implicated in cancer including the Notch pathway. We carried out tumorigenicity studies in three SCLC PDX models utilizing naïve cells positively enriched for either Notch2 or Notch3 expression. In two of the three models, Notch2+ and/or Notch3+ cell populations resulted in enhanced tumor formation. In a SCLC tumor that expressed low levels of Notch3, the Notch2+ population resulted in 70% tumor formation compared to CD44+ (10%) or CD133+ (45%) enriched populations. We have developed a monoclonal antibody, tarextumab (OMP-59R5), which selectively inhibits the function of both Notch2 and Notch3. Our preclinical data in PDX models demonstrate that tarextumab was efficacious in inhibiting the growth of various indications with minimal intestinal toxicity. Notably, the sensitivity of tarextumab in combination with gemcitabine or gemcitabine plus nab-paclitaxel in pancreatic tumors was associated with higher levels of Notch3 gene expression. Interference with Notch2/3 signaling by tarextumab delays tumor recurrence, decreases cancer stem cell frequency (as determined by in vivo LDA studies) and modulates the function of tumor vasculature. Our ALPINE Phase 1b clinical trial indicates that tarextumab is generally well-tolerated and shows signs of anti-tumor efficacy and modulation of Notch pathway signaling in the clinic. Furthermore, we observe a higher response rate and longer survival in patients with Notch3 high tumors receiving gemcitabine/nab-paclitaxel/tarextumab combination therapy. Analysis of pre- and post-treatment tumor biopsies showed an inhibition of Notch pathway and CSC gene signatures. Ongoing Phase 2 clinical trials evaluate first-line treatment with tarextumab in metastatic pancreatic cancer (ALPINE) and small cell lung cancer (PINNACLE). Collectively, these results demonstrate the utility of PDX models for discovery and development of anti-cancer stem cell therapeutics, identifying pharmacodynamic endpoints of drug actions, identifying predictive biomarkers for patient stratification, and translating these preclinical findings into clinical trials. Citation Format: Marcus M. Fischer, Wan-Ching Yen, Fumiko Axelrod, Christopher Bond, Jennifer Cain, Belinda Cancilla, Randall Henner, Rene Meisner, Aaron Sato, Jalpa Shaw, Tracy Tang, Breanna Wallace, Min Wang, Chun Zhang, Ann Kapoun, Lei Zhou, Jakob Dupont, John Lewicki, Austin Gurney, Tim Hoey. Use of patient-derived tumor xenografts (PDX) for discovery and development of an anti-Notch2/3 monoclonal antibody targeting cancer stem cells. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr A41.

GITRL, (Glucocorticoid-Induced Tumor Necrosis Factor Receptor Ligand, TNFSF18) is a member of the TNF family of ligands and naturally exists as a membrane-anchored type II protein that self assembles as a trimer. GITRL activates the co-stimulatory receptor GITR. A novel single-gene linkerless GITRL trimer was shown to be functional when fused to either the N- or C-terminus of an immunoglobulin Fc domain, offering a flexible strategy that may also be amenable to the production of bispecific agents. GITRL-Fc activated GITR signaling more effectively than prototype GITR agonist antibody DTA-1. GITRL-Fc promoted a robust anti-tumor immune response in several murine tumor graft models, including the apparent total regression of some treated tumors. GITRL-Fc potentiated tumor specific T-cell responses, particularly of the Th1 type, increased antigen-specific CD8 response, and promoted a reduction in Treg-mediated immune-suppressive activity. Citation Format: Fumiko Axelrod, Hyun-Bae Jie, Erin Mayes, Jorge Monteon, Minu Srivastava, Rui Yun, Inkyung Angie Park, Austin Gurney. GITRL-Fc, an immunotherapeutic agent that stimulates T-cell-mediated antitumor immune response. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A058.

Blocking DLL4, a Notch ligand, effectively inhibits tumor growth by increasing non-functional angiogenesis and decreasing the cancer stem cells (CSC) population. We are currently testing an anti-DLL4 antibody, demcizumab, in Phase1B trials in NSCLC, pancreatic, and ovarian cancer. DLL4 is also known to modulate immune responses. In the current study we examine the impact of anti-DLL4 on anti-tumor immune responses as a single agent and in combination with the key immune checkpoint inhibitor Programmed Cell Death Protein 1 (PD1). While the recent clinical success of PD1 inhibitors represents a new and promising cancer immunotherapeutic approach, high initial response rates are often associated by a lack of long-term, durable effects in a significant number of patients. Therefore, we hypothesized that dual blockade of DLL4 and PD1 might further impact tumor growth by further enhancing anti-tumor immune immunity. Our data demonstrates that dual blockade of DLL4 and PD1 using antibodies not only reduces tumor growth, but also led to tumor rejection in ∼50% in CT26WT tumor-bearing mice, similar to those treated with anti-PD1 alone (no tumor rejection was observed with anti-DLL4 alone). Anti-PD1 increased specific CD8+ T cell-mediated IFN-γ production while decreasing IL6. Anti-DLL4 treatment reduced IL17 production. Interestingly, only the dual blockage led to increased production of IL2 by splenocytes. Since IL2 is required for secondary population expansion of CD8+ memory T cells, increased IL2 in the combination group suggests potential for increased T cell activation, maintenance and memory T cell function, as compared to single agent anti-DLL4 and anti-PD1. While anti-PD1 reduced inhibition of CD4+ T cell proliferation by Tregs, the dual blockade significantly reduced Treg-mediated CD8+ T cell suppression. Furthermore, both effector and memory CD8+ T cell frequencies were increased within the total CD8+ T cell population. Interestingly, anti-PD1 decreased granulocytic MDSCs, while anti-DLL4 reduced monocytic MDSCs. Mice cured with single-agent anti-PD1 and anti-DLL4/anti-PD1 combination treatments were protected from series of re-challenge with tumor cells, suggesting the existence of immunologic memory. Interestingly, more mice were protected from tumor re-challenge when both DLL4 and PD1 were blocked, as compared to PD1 alone. Surprisingly, mice previously treated with the anti-DLL4/anti-PD1 combination produced more IL2, clearly indicating the role of DLL4 blockade in enhancing anti-tumor immunity. Therefore, these results show that dual targeting of DLL4 and PD1 may be an effective and durable cancer therapy by increasing anti-tumor immune response and promoting long-term immunological memory. Citation Format: Minu Srivastava, Christopher L. Murriel, Julie Roda, Hyun-Bae Jie, Fumiko Axelrod, Ming-Hong Xie, Rui Yun, Erin Mayes, Trevor Bentley, Belinda Cancilla, Raymond Tam, Tracy Tang, Ann Kapoun, John Lewicki, Tim Hoey, Austin Gurney, Angie Inkyung Park. Dual targeting of Delta-like ligand 4 (DLL4) and programmed death 1(PD1) inhibits tumor growth and generates enhanced long-term immunological memory. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 255. doi:10.1158/1538-7445.AM2015-255

Both Notch/Delta-like ligand 4 (DLL4) and vascular endothelial growth factor (VEGF) pathways play a critical role in angiogenesis and tumor growth. Due to differential regulatory effects of VEGF and DLL4 on the vasculature, inhibition of DLL4 or VEGF inhibits tumor growth by distinct mechanisms: anti-DLL4 treatment induces an abnormal increase of poorly perfused blood vessels, which results in a nonproductive angiogenesis unable to support tumor growth, whereas the anti-VEGF therapy significantly decreases vasculature reducing the blood supply to tumors. We have recently developed a high binding affinity bispecific monoclonal antibody that targets both human DLL4 and human VEGF. In vitro, this antibody exhibited nanomolar affinity to hVEGF and hDLL4, and reduced HUVEC proliferation induced by VEGF. The bispecific antibody demonstrated significant in vivo anti-tumor efficacy in various solid tumors, delayed tumor recurrence following termination of chemotherapy, and decreased the frequency of tumor initiating cells. Analysis of tumor vasculature after treatment with anti-DLL4/VEGF revealed inhibition of vascular gene expression and endothelial cell proliferation, indicating that the anti-VEGF effect on the vasculature is dominant over the anti-DLL4 effect. Notably, at doses where both anti-DLL4 and anti-VEGF alone produced suboptimal anti-tumor effect, dual targeting resulted in additive tumor growth inhibition. These results indicate that our bispecific anti-DLL4/VEGF is broadly efficacious and may be useful for treatment of a variety of solid tumors. Citation Format: Wan-Ching Yen, Fumiko Axelrod, Chris Bond, Jennifer Cain, Cecile Chartier, Marcus Fischer, Shirley Ma, Rene Meisner, Janak Raval, Jalpa Shah, Austin Gurney, John Lewicki, Timothy Hoey. Dual targeting of DLL4 and VEGF signaling by a novel bispecific antibody inhibits tumor growth and reduces cancer stem cell frequency. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 207. doi:10.1158/1538-7445.AM2014-207

Deregulation of the canonical Wnt/beta-catenin signaling pathway has long been associated with cancer. Intracellular components of this pathway, including Axin, APC, and beta-catenin are frequently mutated in a range of human tumors. The identity of specific extracellular ligands that contribute to human cancer development through this signaling axis has remained unclear. Molecular characterization of the secreted beta-catenin signaling activities produced by minimally passaged human tumor xenograft models identified RSPO family members produced by multiple tumor types including ovarian, pancreatic, colon, breast and non-small cell lung cancer. In human tumor xenograft models that had RSPO overexpression, in some instances due to genomic translocation, anti-RSPO treatment markedly inhibited tumor growth. In addition, striking combination activity with standard of care chemotherapy agents resulted in regression of established tumors. These results highlight the potential for therapeutic intervention with this newly appreciated signaling axis. Citation Format: Austin Gurney, Fumiko Axelrod, Chris Bond, Jennifer Cain, Cecile Chartier, Marcus Fischer, May Ji, Chris Murriel, Janak Raval, Jalpa Shah, Min Wang, Wan-Ching Yen, Ann Kapoun, John Lewicki, Timothy Hoey. Inhibition of R-spondin (RSPO) signaling reduces the growth of multiple human tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1764. doi:10.1158/1538-7445.AM2014-1764

Both Notch/Delta-like ligand 4 (DLL4) and vascular endothelial growth factor (VEGF) pathways play a critical role in angiogenesis and tumor growth. Due to differential regulatory effects of VEGF and DLL4 on the vasculature, blockage of DLL4 or VEGF inhibits tumor growth by distinct mechanisms: anti-DLL4 treatment induces an abnormal increase of poorly perfused blood vessels, which results in a nonproductive angiogenesis unable to support tumor growth, whereas the anti-VEGF therapy significantly decreases vasculature reducing the blood supply to tumors. In our study, we have developed a bispecific monoclonal antibody that targets both human DLL4 (hDLL4) and human VEGF (hVEGF). In vitro, this antibody demonstrated nanomolar affinity to hVEGF and hDLL4, and reduced HUVEC proliferation induced by VEGF (EC50 0.86 ug/ml). To test the activity of this bispecific antibody in vivo, we developed a human skin graft model in NOD/SCID mice, and implanted human tumor specimen-derived colon cancer cells intradermally into these skin transplants. The tumor model was selected based on its sensitivity to both the anti-human DLL4 antibody, OMP-21M18, and to the human VEGF inhibitor bevacizumab. The skin graft model provides a suitable human microenvironment for evaluating anti-tumor efficacy and anti-angiogenesis of the bispecific antibody directed against the human component of DLL4 and VEGF and allows a comparison to OMP-21M18 and also to bevacizumab. Each of these treatments was administered to mice intraperitoneally at a dose of 25 mg/Kg weekly. The bispecific antibody caused a significant inhibition of tumor growth (87% TGI) compared to control antibody (p=0.00001), and this effect was superior to either OMP-21M18 (45% TGI) or bevacizumab (70%TGI). The inhibition of tumor growth by the bispecific antibody was consistently associated with increased blood vessels, up-regulated VEGFA and VEGFR2, and enhanced hypoxia and these effects were more pronounced compared to OMP-21M18. As expected, in this model bevacizumab caused a significant decrease of blood vessels, down-regulated VEGFR2, and increased hypoxia. In separate experiments with mice bearing subcutaneous human colon tumors, the bispecific antibody delayed tumor recurrence following termination of chemotherapy and impacted tumorigenicity by decreasing the frequency of tumor initiating cells. These results suggest that our bispecific anti-DLL4 and anti-VEGF antibody is a potential candidate in the treatment of tumors driven by both VEGF and Notch/DLL4 signaling pathways. Citation Format: Lucia Beviglia, Pete Yeung, Wang-Ching Yen, Belinda Cancilla, Sato Aaron, Chris Bond, Janak Raval, Fumiko Axelrod, Cecile Chartier, Shirley Ma, Austin Gurney, John Lewicki, Ann M. Kapoun, Timothy Hoey. In vivo evaluation of anti-tumor activity by an anti-VEGF and anti-DLL4 bispecific antibody in a humanized model of skin graft. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4330. doi:10.1158/1538-7445.AM2013-4330

The Wnt/beta-catenin pathway, which signals through the Frizzled (Fzd) receptor family and several co-receptors, is known to play a critical role in several major cancer types. Mutations in the signalling pathway occur in most cases of human colon cancer, and activation of Wnt signalling through various mechanisms has been reported in multiple major tumor types. We have developed a novel Wnt pathway antagonist antibody, OMP-18R5 which was initially identified by binding to Frizzled7, and subsequently found to also bind several other human FZDs through a conserved epitope within the extracellular domain. OMP-18R5 blocks Wnt binding and canonical signalling induced by multiple Wnt family members. In xenograft studies with minimally passaged human tumors, OMP-18R5 inhibited the growth of a broad range of tumor types and has been found to be particularly active in breast cancer. OMP-18R5 treatment reduced tumor growth and the frequency of tumor initiating cells in combination with pacilitaxel. Furthermore, we found that OMP-18R5 treatment can restore chemosensitivity in drug resistant breast tumors. Molecular analyses indicated OMP-18R5 inhibits the expression of EMT markers in breast tumors, thus providing additional evidence linking EMT with resistance to chemotherapy and cancer stem cells. In addition to combination activity with paclitaxel, OMP-18R5 treatment also resulted in increased anti-tumor activity in combination with trastuzumab in a Her2+ breast cancer model. These data suggest that OMP-18R5, which has recently entered Phase 1 clinical testing, may be useful in the treatment of various types of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3356. doi:1538-7445.AM2012-3356