M9657 Is a Bispecific Tumor-Targeted Anti-CD137 Agonist That Induces MSLN-Dependent Antitumor Immunity without Liver Inflammation

The costimulatory receptor CD137 (also known as TNFRSF9 or 4-1BB) sustains effective cytotoxic T-cell responses. Agonistic anti-CD137 cancer immunotherapies are being investigated in clinical trials. Development of the first-generation CD137-agonist monotherapies utomilumab and urelumab was unsuccessful due to low antitumor efficacy mediated by the epitope recognized on CD137 or hepatotoxicity mediated by Fcγ receptors (FcγR) ligand-dependent CD137 activation, respectively. M9657 was engineered as a tetravalent bispecific antibody (mAb2) in a human IgG1 backbone with LALA mutations to reduce binding to FCγRs. Here, we report that M9657 selectively binds to mesothelin (MSLN) and CD137 with similar affinity in humans and cynomolgus monkeys. In a cellular functional assay, M9657 enhanced CD8+ T cell-mediated cytotoxicity and cytokine release in the presence of tumor cells, which was dependent on both MSLN expression and T-cell receptor/CD3 activation. Both FS122m, a murine surrogate with the same protein structure as M9657, and chimeric M9657, a modified M9657 antibody with the Fab portion replaced with an anti-murine MSLN motif, demonstrated in vivo antitumor efficacy against various tumors in wild-type and human CD137 knock-in mice, and this was accompanied by activated CD8+ T-cell infiltration in the tumor microenvironment. The antitumor immunity of M9657 and FS122m depended on MSLN expression density and the mAb2 structure. Compared with 3H3, a murine surrogate of urelumab, FS122m and chimeric M9657 displayed significantly lower on-target/off-tumor toxicity. Taken together, M9657 exhibits a promising profile for development as a tumor-targeting immune agonist with potent anticancer activity without systemic immune activation and associated hepatotoxicity.

757 M9657, a novel tumor-targeted conditional anti-CD137 agonist displays MSLN-dependent anti-tumor immunity

Background

The costimulatory receptor CD137 (also known as 4-1BB and TNFRSF9) plays an important role in sustaining effective cytotoxic T cell immune responses and its agonism has been investigated as a cancer immunotherapy. In clinical trials, the systemic administration of the 1st generation CD137 agonist monotherapies, utomilumab and urelumab, were suspended due to either low anti-tumor efficacy or hepatotoxicity mediated by recognized epitope on CD137 and FcγR ligand-dependent clustering.

Methods

M9657, a bispecific antibody was engineered a tetravalent bispecific antibody (mAb2) format with the Fab portion binding to the tumor antigen Mesothelin (MSLN) and a modified CH2-CH3 domain as Fc antigen binding (Fcab) portion binding to CD137. M9657 has a human IgG1 backbone with LALA mutations to abrogate the binding to Fcγ receptor. The biological characteristics and activities of M9657 were investigated in a series of in vitro assays and the in vivo efficacy was investigated in syngeneic tumor models with FS122m, a murine-reactive surrogate with the same protein structure of M9657.

Results

M9657 binds efficiently to both human and Cynomolgus CD137 as well as MSLN. In the cellular functional assay, M9657 displayed MSLN- and TCR/CD3 interaction (signal 1)-dependent cytokine release and tumor cell cytotoxicity associated with Bcl-XL activation and immune memory formation. FS122m demonstrated potent MSLN- and dose- dependent in vivo anti-tumor efficacy (figure 1). Comparing with 3H3, a Urelumab surrogate Ab, FS122m displayed an improved therapeutic window with significantly lower for on-target /off-tumor toxicity.

Conclusions

Taken together, M9657 exhibits a promising developability profile as a tumor-targeted immune agonist with potent anti-cancer activity, but without systemic immune activation.

Ethics Approval

All animal experiments were performed in accordance with EMD Serono Research & Development Institute (protocol 17-008, 20-005) and Wuxi AppTec Animal Care and Use Committee (IACUC) guidelines.

Abstract 757 Figure 1

FS122m displayed dose-dependent anti-tumor efficacy

Abstract 964: Induction of immunogenic cell death and interferon signaling by carboplatin and the ATR inhibitor M6620 may contribute to anti-tumor activity of M6620-carboplatin-avelumab triplet combination in MC38 tumor model

Ataxia-telangiectasia mutated and Rad3-related kinase (ATR) is one of the key players in the DNA damage response (DDR) to replication stress. M6620 is a potent and selective ATR inhibitor which has been shown to sensitize cancer cells to the lethal effects of DNA-damaging chemotherapeutic agents. We previously demonstrated that M6620 significantly enhances the anti-tumor efficacy of dual combinations of platinum-based chemotherapy and avelumab, an FDA-approved anti-PD-L1 monoclonal antibody, in syngeneic tumor models in vivo. The purpose of this study was to further elucidate the potential mechanisms of action that drive the therapeutic benefit of this triplet combination therapy.

Treatment with certain chemotherapeutic agents has been reported to promote immunogenic cell death (ICD) in tumor cells. We utilized in vitro assays to test the expression of markers of immunogenic cell death in murine MC38 colorectal carcinoma cells. After 72 hours of treatment, carboplatin and M6620 dual combination treatment significantly increased the levels of Calreticulin, HMGB1, and ATP relative to treatment with either single agent. In addition, gene expression profiling was used to determine pathways differentially induced by the drug treatments. RNA-sequencing (RNA-seq) analysis was performed on MC38 cells treated in vitro with carboplatin, M6620, or dual combination therapy. Comparison of gene expression between treatment groups at 48 hours post-treatment revealed that the dual combination therapy significantly increased expression of genes regulated by type I/II interferons (IFN), including CCl5, CXCL10, CXCL11 and ISG15. RNA-seq gene expression analysis was also performed on MC38 tumor samples from mice treated with carboplatin, M6620, avelumab, carboplatin/avelumab dual therapy, or carboplatin/M6620/avelumab triple combination therapy. Triple combination therapy induced a more robust upregulation of IFN-inducible genes at day 3 compared with monotherapies or carboplatin/avelumab dual combination, consistent with in vitro observations that M6620 and carboplatin dual combination therapy enhanced expression of genes regulated by IFNs.

Taken together, these data suggest that potentiation of immunogenic cell death and induction of pro-inflammatory responses by M6620, in the context of chemotherapy-induced DNA damage, may contribute to the enhanced anti-tumor efficacy observed with carboplatin, M6620, and avelumab triple combination therapy.

Citation Format: Marat Alimzhanov, Ashwin George, Parantu Shah, Astrid Zimmerman, Andreas Schroeder, Martin Falk, Christiane Amendt, Joern-Peter Halle, Andree Blaukat, Frank Zenke, Patricia Soulard. Induction of immunogenic cell death and interferon signaling by carboplatin and the ATR inhibitor M6620 may contribute to anti-tumor activity of M6620-carboplatin-avelumab triplet combination in MC38 tumor model [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 964.

Abstract 2269: ATR inhibitor M6620 enhances anti-tumor efficacy of the combination of the anti-PD-L1 antibody avelumab with platinum-based chemotherapy

Recently, combination of checkpoint inhibitors with chemotherapy demonstrated significant improvement of overall survival (OS) and progression-free survival (PFS) compared with chemotherapy alone in patients with metastatic non-squamous and squamous non-small cell lung cancer (NSCLC). However still a larger number of patients do not benefit of the combination treatment. Ataxia telangiectasia mutated and Rad3 related kinase (ATR) is one of the key players in the DNA damage response (DDR) to replication stress. M6620 is a potent and selective ATR inhibitor currently in Phase I clinical studies in combination with multiple DNA-damaging drugs. M6620 has been shown to sensitize cancer cells to the lethal effects of DNA-damaging chemotherapeutic agents. Here we tested the hypothesis that ATR inhibitor M6620 could further enhance anti-tumor efficacy of chemotherapy combinations with avelumab, an FDA approved human IgG1 anti-PD-L1 monoclonal antibody, in vivo.

We profiled a panel of murine tumor cell lines to identify models sensitive to combination treatment of M6620 with cisplatin, carboplatin or oxaliplatin. Addition of M6620 to the chemotherapeutic agents in vitro potentiated growth inhibition effect and led to the increase in markers of immunogenic cell death (ICD) in the sensitive tumor cell lines. Based on these data we investigated anti-tumor efficacy of carboplatin or cisplatin in combination with M6620 and avelumab in MC38 murine colorectal tumor model. The triple combination regimens demonstrated a statistically significant better control of tumor growth, more frequent tumor regressions and increased overall survival compared to the double combination treatment groups. The triplet combination regimens were well tolerated as assessed by changes in body weight and clinical signs. Animals with complete tumor responses were re-challenged with MC38 tumor cells and were found refractory to the second tumor inoculation, indicating that durable, protective anti-tumor immunity was established in complete responders.

Taken together, robust anti-tumor efficacy and acceptable toxicity of selected triplet combinations in preclinical models provide strong rationale for combining avelumab with M6620 and carboplatin in patients with PARP inhibitor resistant recurrent ovarian cancer.

Citation Format: Marat Alimzhanov, Patricia Soulard, Astrid Zimmermann, Andreas Schroeder, Keyvan Tadjalli Mehr, Christiane Amendt, Geok Choo Sim, Andree Blaukat, Joern-Peter Halle, Frank T. Zenke. ATR inhibitor M6620 enhances anti-tumor efficacy of the combination of the anti-PD-L1 antibody avelumab with platinum-based chemotherapy [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 2269.

Inhibition of ALK1 signaling with dalantercept combined with VEGFR TKI leads to tumor stasis in renal cell carcinoma

Treatment of metastatic renal cell carcinoma (mRCC) with agents that block signaling through vascular endothelial growth factor receptor 2 (VEGFR2) induces disease regression or stabilization in some patients; however, these responses tend to be short-lived. Therefore, development of combination therapies that can extend the efficacy of VEGFR antagonists in mRCC remains a priority.

We studied murine xenograft models of RCC that become refractory to treatment with the VEGFR tyrosine kinase inhibitor (TKI) sunitinib. Dalantercept is a novel antagonist of Activin receptor-like kinase 1 (ALK1)/Bone morphogenetic protein (BMP) 9 signaling. Dalantercept inhibited growth in the murine A498 xenograft model which correlated with hyperdilation of the tumor vasculature and an increase in tumor hypoxia. When combined with sunitinib, dalantercept induced tumor necrosis and prevented tumor regrowth and revascularization typically seen with sunitinib monotherapy in two RCC models. Combination therapy led to significant downregulation of angiogenic genes as well as downregulation of endothelial specific gene expression particularly of the Notch signaling pathway.

We demonstrate that simultaneous targeting of molecules that control distinct phases of angiogenesis, such as ALK1 and VEGFR, is a valid strategy for treatment of mRCC. At the molecular level, combination therapy leads to downregulation of Notch signaling.

Potent and Selective CK2 Kinase Inhibitors with Effects on Wnt Pathway Signaling in Vivo

The Wnt pathway is an evolutionarily conserved and tightly regulated signaling network with important roles in embryonic development and adult tissue regeneration. Impaired Wnt pathway regulation, arising from mutations in Wnt signaling components, such as Axin, APC, and β-catenin, results in uncontrolled cell growth and triggers oncogenesis. To explore the reported link between CK2 kinase activity and Wnt pathway signaling, we sought to identify a potent, selective inhibitor of CK2 suitable for proof of concept studies in vivo. Starting from a pyrazolo[1,5-a]pyrimidine lead (2), we identified compound 7h, a potent CK2 inhibitor with picomolar affinity that is highly selectivity against other kinase family enzymes and inhibits Wnt pathway signaling (IC50 = 50 nM) in DLD-1 cells. In addition, compound 7h has physicochemical properties that are suitable for formulation as an intravenous solution, has demonstrated good pharmacokinetics in preclinical species, and exhibits a high level of activity as a monotherapy in HCT-116 and SW-620 xenografts.

Identification of azabenzimidazoles as potent JAK1 selective inhibitors

We have identified a class of azabenzimidazoles as potent and selective JAK1 inhibitors. Investigations into the SAR are presented along with the structural features required to achieve selectivity for JAK1 versus other JAK family members. An example from the series demonstrated highly selective inhibition of JAK1 versus JAK2 and JAK3, along with inhibition of pSTAT3 in vivo, enabling it to serve as a JAK1 selective tool compound to further probe the biology of JAK1 selective inhibitors.

Identification and Characterization of MEDI4736, an Antagonistic Anti-PD-L1 Monoclonal Antibody

Programmed cell-death 1 ligand 1 (PD-L1) is a member of the B7/CD28 family of proteins that control T-cell activation. Many tumors can upregulate expression of PD-L1, inhibiting antitumor T-cell responses and avoiding immune surveillance and elimination. We have identified and characterized MEDI4736, a human IgG1 monoclonal antibody that binds with high affinity and specificity to PD-L1 and is uniquely engineered to prevent antibody-dependent cell-mediated cytotoxicity. In vitro assays demonstrate that MEDI4736 is a potent antagonist of PD-L1 function, blocking interaction with PD-1 and CD80 to overcome inhibition of primary human T-cell activation. In vivo MEDI4736 significantly inhibits the growth of human tumors in a novel xenograft model containing coimplanted human T cells. This activity is entirely dependent on the presence of transplanted T cells, supporting the immunological mechanism of action for MEDI4736. To further determine the utility of PD-L1 blockade, an anti-mouse PD-L1 antibody was investigated in immunocompetent mice. Here, anti-mouse PD-L1 significantly improved survival of mice implanted with CT26 colorectal cancer cells. The antitumor activity of anti-PD-L1 was enhanced by combination with oxaliplatin, which resulted in increased release of HMGB1 within CT26 tumors. Taken together, our results demonstrate that inhibition of PD-L1 function can have potent antitumor activity when used as monotherapy or in combination in preclinical models, and suggest it may be a promising therapeutic approach for the treatment of cancer. MEDI4736 is currently in several clinical trials both alone and in combination with other agents, including anti-CTLA-4, anti-PD-1, and inhibitors of IDO, MEK, BRAF, and EGFR.

Abstract 1692: Dalantercept, an ALK1 inhibitor of angiogenesis, in combination with cisplatin inhibits tumor growth in a xenograft model of squamous cell carcinoma of the head and neck

Activin receptor-like kinase 1 (ALK1) is a key regulator of angiogenesis and vascular morphogenesis. ALK1 and its co-receptor endoglin are selectively expressed on the surface of activated endothelial cells during angiogenesis. Bone morphogenetic proteins (BMP) 9 and 10 are ligands that bind to ALK1 and induce activation of the heteromeric receptor complex, phosphorylation of SMAD1/5/8, and upregulation of specific genes involved in the maturation stage of angiogenesis, such as Id-1 and TMEM100. In particular, BMP9 expression is upregulated in a majority of squamous cell carcinomas of the head and neck (SCCHN).

Dalantercept is an ALK1 extracellular domain-Fc fusion protein that binds BMP9 and BMP10 with high affinity and antagonizes ALK1 signaling in vivo resulting in defective vascular maturation and inhibition of tumor growth in preclinical models. In a completed Phase 1 trial in patients with advanced, refractory solid tumors dalantercept demonstrated signs of clinical activity in a variety of patients, including two of three patients with SCCHN who achieved either an objective response or prolonged stable disease. A Phase 2 trial of dalantercept as monotherapy in recurrent/metastatic SCCHN patients who have had prior platinum-based chemotherapy is currently ongoing.

Based upon the single agent activity of both dalantercept and cisplatin in SCCHN, we tested the feasibility of the combination of cisplatin plus dalantercept in a mouse model of SCCHN. Combination treatment of dalantercept plus cisplatin showed significant tumor growth inhibition (TGI) in the RPMI2650 xenograft model (59% TGI on day 30) which was significantly better than either cisplatin (35% TGI, p= 0.0077) or dalantercept (32% TGI, p=0.0002) alone. No additional toxicity was observed in the combination treatment group compared to cisplatin monotherapy group.

These data suggest that combination of dalantercept plus cisplatin may result in enhanced clinical activity and supports prospective evaluation in patients with SCCHN.

Citation Format: Marat Alimzhanov, Michael Lee, Nicolas Solban, Scott Pearsall, Susan Pandya, Matthew L. Sherman, Ravindra Kumar. Dalantercept, an ALK1 inhibitor of angiogenesis, in combination with cisplatin inhibits tumor growth in a xenograft model of squamous cell carcinoma of the head and neck. [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 1692. doi:10.1158/1538-7445.AM2014-1692

Discovery of 1-methyl-1H-imidazole derivatives as potent Jak2 inhibitors

Structure based design, synthesis, and biological evaluation of a novel series of 1-methyl-1H-imidazole, as potent Jak2 inhibitors to modulate the Jak/STAT pathway, are described. Using the C-ring fragment from our first clinical candidate AZD1480 (24), optimization of the series led to the discovery of compound 19a, a potent, orally bioavailable Jak2 inhibitor. Compound 19a displayed a high level of cellular activity in hematopoietic cell lines harboring the V617F mutation and in murine BaF3 TEL-Jak2 cells. Compound 19a demonstrated significant tumor growth inhibition in a UKE-1 xenograft model within a well-tolerated dose range.

Structure and Property Based Design of Pyrazolo[1,5-a]pyrimidine Inhibitors of CK2 Kinase with Activity in Vivo

In this letter, we describe the design, synthesis, and structure-activity relationship of 5-anilinopyrazolo[1,5-a]pyrimidine inhibitors of CK2 kinase. Property-based optimization of early leads using the 7-oxetan-3-yl amino group led to a series of matched molecular pairs with lower lipophilicity, decreased affinity for human plasma proteins, and reduced binding to the hERG ion channel. Agents in this study were shown to modulate pAKT(S129), a direct substrate of CK2, in vitro and in vivo, and exhibited tumor growth inhibition when administered orally in a murine DLD-1 xenograft.

Phase II study of dalantercept, a novel inhibitor of ALK1-mediated angiogenesis, in patients with recurrent or metastatic squamous cell carcinoma of the head and neck

TPS6098

Background: Despite advances in the treatment of recurrent or metastatic squamous cell carcinoma of the head and neck (SCCHN), the prognosis remains poor with a need to develop novel therapeutic strategies. Targeting angiogenesis in SCCHN is an active area of clinical research. Activin receptor-like kinase 1 (ALK1) is a type 1 receptor in the TGF-ß superfamily which is selectively expressed on activated endothelial cells. ALK1 binds bone morphogenetic proteins (BMP) 9 and 10 (ligands for ALK1) and is primarily involved in the maturation stage of angiogenesis. Dalantercept is a human ALK1-Fc receptor fusion protein that binds BMP9/10 and acts as a ligand trap. In preclinical tumor models, dalantercept demonstrated a decrease in tumor vascularization and delayed tumor growth. In a completed phase I study, dalantercept demonstrated anti-tumor activity in patients with advanced solid tumors including SCCHN. Methods: An open label, multi-center, multiple dose, phase II study to evaluate dalantercept in patients with advanced SCCHN is ongoing. Dalantercept is being administered every three weeks via SC injection in a total of 45 patients to assess safety, tolerability, and efficacy. 13 patients were enrolled at the 0.6 mg/kg dose level. To date, 6 out of 30 planned patients have received dalantercept at the 1.2 mg/kg dose level. Key inclusion criteria are tumors arising from the oral cavity, oropharynx, hypopharynx, or larynx, at least one prior platinum-containing regimen, ECOG performance status </= 1, and measurable disease. Exclusion criteria include prior anti-angiogenesis therapy, significant pulmonary, cardiovascular, or bleeding risk. The primary efficacy endpoint is RR. Secondary endpoints include PFS, OS, TTP, DOR, DCR, and PD biomarkers on tumor and serum specimens including BMP9/10 and ALK1 expression. Clinical trial information: NCT01458392.

Abstract 5080: Inhibiting the ALK1/BMP9 signaling pathway with dalantercept as an antiangiogenic therapy

Activin receptor-like kinase 1 (ALK1) is an endothelial cell-specific receptor for bone morphogenetic proteins (BMP) 9 and 10, and is a key regulator of angiogenesis and vascular morphogenesis. Preclinical data suggest that the BMP9/ALK1 pathway is operating in the resolution and maturation stage of angiogenesis, which is distinct from the VEGF/VEGFR pathway which drives the initiation stage of angiogenesis. Dalantercept is an ALK1 extracellular domain-Fc fusion protein that inhibits the BMP9/ALK1 pathway. Thus, dalantercept may prove useful either as a monotherapy to inhibit tumor angiogenesis or in combination with VEGFR inhibitors to target different phases of vascular network formation and potentially to overcome acquired resistance to anti-VEGF therapy.

To test this hypothesis, the A498 renal cell carcinoma xenograft model was used to test dalantercept efficacy either alone or in combination with sunitinib. In this model, tumor progression was defined as a 2 mm increase in tumor length. In the placebo group, mean (± SD) tumor progression was 5.8 ±0.6 days. Treatment with dalantercept delayed tumor progression to 10.8 ± 1.7 days (p&lt;0.01 vs placebo) and sunitinib delayed tumor progression to 13.8 ± 2.5 days (p&lt;0.01 vs placebo). The combination treatment of dalantercept plus sunitinib had a greater beneficial effect with a delay in tumor progression to 35 ± 12.6 days (p=0.01 vs sunitinib).

We used immunohistochemistry (IHC) analysis to evaluate effects of dalantercept on tumor vasculature and to look for potential biomarkers of response to treatment in A498 tumors. Id1 is a transcription factor expressed in endothelial cells and is known to be regulated via the BMP9/ALK1/SMAD pathway. We observed a decrease in Id1 protein expression in endothelial cells of A498 xenografts treated with dalantercept, consistent with our previous experiments. Because BMP9 is one of the main target ligands of dalantercept, IHC analysis of archived human tumor samples was performed to determine BMP9 expression levels in various tumor types. In squamous cell carcinoma of the head and neck it was shown that out of 28 tumor samples 79% had high or medium levels of BMP9 staining, with little to no staining in normal tissues. Data from BMP9 expression in renal cell carcinoma and hepatocellular carcinoma will also be presented.

In a Phase 1 study in patients with advanced, refractory solid tumors, dalantercept was generally well tolerated and exhibited signs of clinical activity including patients with objective response and prolonged stable disease. Dalantercept is currently being tested in several Phase 2 oncology studies, including a study of dalantercept in combination with the anti-VEGFR TKI axitinib in second-line advanced renal cell carcinoma.

Citation Format: Marat Alimzhanov, Nicolas Solban, Michael Lee, Phaethon Philbrook, Xiaoen Wang, Lin Wei, Jiaxi Song, Sabina Signoretti, R. Scott Pearsall, Matthew L. Sherman, Ravindra Kumar, Rupal S. Bhatt. Inhibiting the ALK1/BMP9 signaling pathway with dalantercept as an antiangiogenic therapy. [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 5080. doi:10.1158/1538-7445.AM2013-5080

Inhibition of tumor growth in a VEGFR TKI-resistant model of renal cell carcinoma using dalantercept combined with sunitinib

370

Background: Antagonists of VEGF/VEGFR pathway have demonstrated clinical utility in patients with metastatic renal cell carcinoma (RCC); however, the therapeutic responses tend to be short-lived. Thus, there is a need for new treatments to overcome the acquired resistance to the current standards of care. Methods: We have used a murine xenograft model of RCC to study the relationship of the bone morphogenetic protein (BMP)/transforming growth factor-β (TGF-β) superfamily pathways and the VEGF pathways. Additionally, we have studied the effects of BMP9/10 inhibition on RCC tumor growth and performed MRI based tumor blood flow analyses to study antiangiogenic activity of the treatments. To explore the role of BMP9/10/ALK1 signaling in resistance to VEGFR inhibition, we used dalantercept (human ALK1-Fc fusion protein) as a ligand trap for BMP9 and 10. Results: We have found evidence of upregulation of BMP10 in A498 RCC xenograft tumors that have developed resistance to sunitinib. In tumors that had developed resistance to sunitinib, addition of ALK1-Fc to sunitinib led to prolonged tumor stabilization compared to either agent alone. Imaging of tumors revealed that addition of ALK1-Fc to sunitinib prevented the resumption in blood flow that is generally seen with continued sunitinib. Conclusions: These murine xenograft model data demonstrate that inhibition of ALK1 receptor pathway in combination with inhibition of VEGFR pathway may be a useful strategy for the treatment of RCC. A phase II randomized study of dalantercept in combination with axitinib in patients with metastatic RCC after progression on VEGFR/TKI therapy is ongoing.

Intersection of Complement C4 and Interferon Alpha pathways in B cell tolerance (171.32)

Humoral autoimmunity is an important hallmark of autoimmune diseases like lupus. Factors that allow self-reactive B cells to escape negative selection stages and become activated remain poorly defined. Using a novel B cell receptor knock-in mouse strain 564Igi, we define a complement-dependent pathway by which B cell tolerance is upheld. Interestingly, the 564-autoantibody could bind SSB/La, a common lupus antigen, establishing the physiological relevance of this model. Deficiency in complement C4 caused a breakdown in the elimination of autoreactive B cell clones at the transitional stage, as demonstrated by their continued maturation, their ability to respond to a range of stimuli, entry into follicles (lack of follicular exclusion) and formation of germinal centers with a higher propensity. All results taken together indicate that the complement system must be intact for B cell tolerance to be upheld. Strikingly, the dysregulation of autoreactive B cells in C4-deficient mice was not B cell intrinsic, as a C4-sufficient myeloid compartment could re-establish efficient B cell selection. Our current model holds that poor clearance of apoptotic debris in the absence of C4 chronically activates myeloid cells to release cytokines, like IFNα, in excess and reduce the stringency of tolerance at the transitional stage. In support of our hypothesis, IFNα receptor blockade was found to restore negative selection of B cells in C4-deficient 564Igi mice.

Abstract 3770: PK/PD/Efficacy characterization of AZ285, a selective CK2 kinase inhibitor

Casein Kinase 2 (CK2) is an abundant, highly conserved protein serine/threonine kinase with numerous physiological targets and participates in the maintenance of cell viability with a role in cell growth and proliferation. While the expression level of CK2 in normal cells is tightly regulated, there is an increasing body of evidence demonstrating it's over expression in cancerous cells, thereby making inhibition a viable chemotherapeutic target. Here we will describe a mathematical tumor growth inhibition model describing the relationship between systemic exposure to a potent inhibitor of CK2 (AZ285) and efficacy in the HCT116 xenograft model. Furthermore, a PK/PD model describing the onset, intensity, and duration of the pAKT and cleaved caspase 3 response as function of concentration and time is described and linked to pre-clinical xenograft efficacy outcomes.

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 3770. doi:1538-7445.AM2012-3770

Abstract 3907: Discovery and characterization of AZ285 as a potent and selective inhibitor of CK2 kinase

Casein Kinase 2 (CK2) is a highly conserved and ubiquitously expressed serine/threonine kinase that regulates several key oncogenic signaling pathways, including PI3K/AKT, and NFkB and Wnt, and whose targeted overexpression in transgenic animal models results in neoplastic growth. Herein we describe the identification of AZ285, a potent pyrazolo[1,5-a]pyrimidine-derived inhibitor of CK2 with a high degree of kinase selectivity. AZ285 depletes levels of the CK2 substrates pAKTS129 and PTENS370 and induces apoptosis in cells in a concentration-dependent manner. Optimization of early leads was aided in part by cell wash-out experiments and X-ray cocrystallography with huCK2a and resulted in an agent with physical properties and DMPK characteristics suitable for evaluation in disease model studies.

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 3907. doi:1538-7445.AM2012-3907

Abstract LB-158: MEDI4736: Delivering effective blockade of immunosupression to enhance tumour rejection: Monoclonal antibody discovery and preclinical development

Cancerous cells emerge within the body following accumulation of deleterious genetic mutations. These mutations alter the phenotype of a cancer cell marking it as distinct from the surrounding host; an immunological state termed “altered self”. These cells, like other non-self entities such as viruses and bacteria, are recognised by the immune system and marked for destruction, a process known as “immune surveillance”. B7-H1 expression by tumour cells is believed to aid tumours in evading detection and elimination by the immune system. B7-H1 functions in this respect via several alternative mechanisms including driving exhaustion and anergy of tumour infiltrating T lymphocytes, stimulating secretion of immune repressive cytokines into the tumour micro-environment, stimulating repressive regulatory T cell function and protecting B7-H1 expressing tumour cells from lysis by tumour cell specific cytotoxic T cells.

Using hybridoma technology and high throughput screening MedImmune has identified a series of fully human antibodies specific for human B7-H1. Further characterisation of these antibodies led to the identification of a single high affinity antibody, MEDI 4736, with the ability to relieve B7-H1 mediated suppression of T cell activation in vitro and to enhance sub-optimal T cell activation in a mixed lymphocyte reaction. In vitro testing shows that MEDI 4736 does not trigger non-specific cytokine release in whole blood, and is only able to activate T cells in the context of an active T cell receptor signal.

A surrogate anti-mouse B7-H1 antibody shows significant anti-tumour activity in a syngeneic model when dosed in combination with chemotherapy. Similarly MEDI 4736 is able to inhibit tumour growth in a novel in vivo xenograft model, via a mechanism that is dependent on the presence of tumour specific human T cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-158. doi:10.1158/1538-7445.AM2011-LB-158

Abstract 5196: The discovery of small molecule inhibitors of Tankyrases 1 and 2, which modulate Axin homeostasis and inhibit Wnt signaling in vivo

Deregulated Wnt signaling has been implicated in a wide range of cancer types, both through truncating mutations in the tumor suppressor protein Adenomatous Polyposis Coli (APC), most prevalent in colorectal cancer, as well as overexpression of Wnt ligands and receptors. Canonical Wnt signaling involves the regulated degradation of the beta catenin protein. In the absence of Wnt signaling, cytosolic beta catenin levels are maintained at low levels, as a result of its phosphorylation-dependent ubiquitination and subsequent proteasomal degradation. This degradation is mediated by the ‘destruction complex’, whose constituents include Glycogen Synthase Kinase 3 (GSK3β), Casein Kinase 1 (CK1) and the scaffolding proteins Axin and APC. The efficient assembly of this complex depends upon the steady state levels of its components, such as Axin, which when overexpressed has been shown to decrease beta catenin levels and inhibit Wnt signaling. Recent reports suggest that the poly-ADP-ribosylating Tankyrase enzymes can bind to and regulate Axin levels, hence providing promising targets for treating Wnt-dependent tumors.

We have identified potent, low nM small molecule inhibitors of the Wnt pathway, which inhibit Tankyrases 1 and 2, stabilize Axin, deplete beta catenin protein levels and modulate a set of Wnt-regulated genes in colorectal cell lines in a similar manner as seen when using siRNA to beta catenin. Furthermore, using siRNAs to Tankyrase 1 and 2 we have shown that co-depletion of both enzymes is required for Axin stabilization and Wnt pathway inhibition. We have also successfully demonstrated that our lead molecules cause prolonged Axin stabilization and Wnt pathway inhibition in vivo following oral BID dosing in colon xenografts carrying APC mutations.

However, in contrast to previous reports, using molecular tools and our lead compounds (e.g. inducible Axin cell lines, compound rescue experiments using siRNAs to Axin 1/2), we have shown that Axin stabilization has no effect on the viability/proliferation of APC mutant colorectal cell lines, under conditions where siRNA to beta catenin was able to cause significant growth inhibition. Some potential mechanistic rationales for this lack of phenotypic effect will be presented.

Understanding the consequences of Tankyrase inhibition in vivo in relevant disease models will be important to establish the clinical utility of these molecules in colorectal cancer and beyond.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5196. doi:10.1158/1538-7445.AM2011-5196

Discovery of 5-chloro-N2-[(1S)-1-(5-fluoropyrimidin-2-yl)ethyl]-N4-(5-methyl-1H-pyrazol-3-yl)pyrimidine-2,4-diamine (AZD1480) as a novel inhibitor of the Jak/Stat pathway

The myeloproliferative neoplasms, polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis are a heterogeneous but related group of hematological malignancies characterized by clonal expansion of one or more myeloid lineages. The discovery of the Jak2 V617F gain of function mutation highlighted Jak2 as a potential therapeutic target in the MPNs. Herein, we disclose the discovery of a series of pyrazol-3-yl pyrimidin-4-amines and the identification of 9e (AZD1480) as a potent Jak2 inhibitor. 9e inhibits signaling and proliferation of Jak2 V617F cell lines in vitro, demonstrates in vivo efficacy in a TEL-Jak2 model, has excellent physical properties and preclinical pharmacokinetics, and is currently being evaluated in Phase I clinical trials.

The JAK2 inhibitor AZD1480 potently blocks Stat3 signaling and oncogenesis in solid tumors

Persistent activation of Stat3 is oncogenic and is prevalent in a wide variety of human cancers. Chronic cytokine stimulation is associated with Stat3 activation in some tumors, implicating cytokine receptor-associated Jak family kinases. Using Jak2 inhibitors, we demonstrate a central role of Jaks in modulating basal and cytokine-induced Stat3 activation in human solid tumor cell lines. Inhibition of Jak2 activity is associated with abrogation of Stat3 nuclear translocation and tumorigenesis. The Jak2 inhibitor AZD1480 suppresses the growth of human solid tumor xenografts harboring persistent Stat3 activity. We demonstrate the essential role of Stat3 downstream of Jaks by inhibition of tumor growth using short hairpin RNA targeting Stat3. Our data support a key role of Jak kinase activity in Stat3-dependent tumorigenesis.

B cell-specific deletion of protein-tyrosine phosphatase Shp1 promotes B-1a cell development and causes systemic autoimmunity

Spontaneous loss-of-function mutations in the protein-tyrosine phosphatase Shp1 cause the motheaten phenotype, characterized by widespread inflammation and autoimmunity. Because Shp1 is expressed in all hematopoietic cells, it has been unclear which aspects of the motheaten phenotypes are primary effects of Shp1 deficiency. We generated mice (Ptpn6(f/f);CD19-cre) that delete Shp1 specifically in B cells. Analysis of these mice indicates that the increase in B-1a cells in motheaten mice is a cell-autonomous consequence of Shp1 deficiency. Shp1-deficient B-1a cells could be derived from adult bone marrow and had N-nucleotide additions, consistent with an adult origin. Shp1 deficiency altered calcium response evoked by B cell antigen receptors and impaired CD40-evoked proliferation. Young Ptpn6(f/f);CD19-cre mice exhibited elevated serum immunoglobulins and impaired antibody responses to immunization, whereas older Ptpn6(f/f);CD19-cre mice developed systemic autoimmunity, characterized by DNA antibodies and immune complex glomerulonephritis. Thus, Shp1 deficiency in B cells alone perturbs B cell development and causes autoimmune disease.

B cell receptor signal strength determines B cell fate

B cell receptor (BCR)-mediated antigen recognition is thought to regulate B cell differentiation. BCR signal strength may also influence B cell fate decisions. Here, we used the Epstein-Barr virus protein LMP2A as a constitutively active BCR surrogate to study the contribution of BCR signal strength in B cell differentiation. Mice carrying a targeted replacement of Igh by LMP2A leading to high or low expression of the LMP2A protein developed B-1 or follicular and marginal zone B cells, respectively. These data indicate that BCR signal strength, rather than antigen specificity, determines mature B cell fate. Furthermore, spontaneous germinal centers developed in gut-associated lymphoid tissue of LMP2A mice, indicating that microbial antigens can promote germinal centers independently of BCR-mediated antigen recognition.