Targeting CD73 with AB680 (Quemliclustat), a Novel and Potent Small-Molecule CD73 Inhibitor, Restores Immune Functionality and Facilitates Antitumor Immunity

T cells play a critical role in the control of cancer. The development of immune checkpoint blockers (ICB) aimed at enhancing antitumor T-cell responses has revolutionized cancer treatment. However, durable clinical benefit is observed in only a subset of patients, prompting research efforts to focus on strategies that target multiple inhibitory signals within the tumor microenvironment (TME) to limit tumor evasion and improve patient outcomes. Adenosine has emerged as a potent immune suppressant within the TME, and CD73 is the major enzyme responsible for its extracellular production. CD73 can be co-opted within the TME to impair T-cell-mediated antitumor immunity and promote tumor growth. To target this pathway and block the formation of adenosine, we designed a novel, selective, and potent class of small-molecule inhibitors of CD73, including AB680 (quemliclustat), which is currently being tested in patients with cancer. AB680 effectively restored T-cell proliferation, cytokine secretion, and cytotoxicity that were dampened by the formation of immunosuppressive adenosine by CD73. Furthermore, in an allogeneic mixed lymphocyte reaction where CD73-derived adenosine had a dominant suppressive effect in the presence of PD-1 blockade, AB680 restored T-cell activation and function. Finally, in a preclinical mouse model of melanoma, AB680 inhibited CD73 in the TME and increased the antitumor activity of PD-1 blockade. Collectively, these data provide a rationale for the inhibition of CD73 with AB680 in combination with ICB, such as anti-PD-1, to improve cancer patient outcomes.

Abstract P206: AB521 potently and selectively inhibits pro-tumorigenic gene transcription by Hypoxia-Inducible Factor (HIF)-2α in vitro and in vivo

Cells in the solid tumor microenvironment are frequently exposed to hypoxic conditions, necessitating molecular adaptations for survival. Of particular importance are transcriptional changes mediated by heterodimeric Hypoxia-Inducible Factor (HIF) proteins that consist of an oxygen-regulated α monomer (either HIF-1α, -2α, and -3α) coupled to a constitutively expressed β monomer (HIF-1β/ARNT). In normal oxygen conditions, HIF-2α is degraded following ubiquitination by the von Hippel-Lindau (pVHL) E3-ubiquitin ligase complex. Exposure to hypoxia, VHL mutation, or epigenetic silencing of pVHL leads to HIF-2α stabilization and transcription of pro-tumorigenic gene sets in both cancer and non-cancer cells. Inhibition of HIF-2α has been shown clinically to be an effective strategy to mitigate tumor growth, particularly in patients suffering from VHL disease or clear cell renal cell carcinoma (ccRCC), a cancer that has a particularly high prevalence of pVHL dysfunction. Applying a pharmacophore mapping and structure-based design approach, we identified a novel and potent small molecule HIF-2α inhibitor, AB521. AB521 avidly binds the HIF-2α PAS-B domain, preventing HIF-2α-mediated gene transcription. AB521 is characterized by a favorable preclinical pharmacokinetic profile and is projected to be suitable for once-daily dosing in humans. When delivered orally in mice, AB521 significantly regressed established 786-O xenograft tumors and decreased pharmacodynamic markers associated with HIF-2α in a dose-dependent manner. In vitro, AB521 potently inhibited HIF-2α-specific luciferase reporter transcription under high-serum conditions, VEGF protein secretion, colony formation in soft agar, and did not exhibit off-target cytotoxicity in 786-O cells. AB521 selectively inhibited HIF-2α-, but not HIF-1α-, mediated gene expression in hypoxic Hep3B hepatocellular carcinoma cells. AB521 also inhibited the transcriptional activity of endogenous HIF-2α in relevant human primary cell types, including endothelial cells and pro-tumorigenic M2-polarized macrophages. Importantly, inhibiting HIF-2α did not impact functionality of activated hypoxic human T cells, suggesting that AB521 would be favorable combination partner for I-O therapeutic agents. Indeed, expression of CD73, the primary enzyme responsible for synthesis of the immunosuppressive metabolite adenosine, was highly correlated with hypoxic signatures across several indications in publicly available bioinformatic datasets, suggesting combinations with adenosine pathway antagonists in ccRCC and beyond. In summary, AB521 is a novel and selective HIF-2α inhibitor with potent anti-tumor activity. Clinical evaluation of this molecule is expected to begin in the latter part of 2021.

Citation Format: Kelsey E. Sivick Gauthier, Dana Piovesan, Soonweng Cho, Kenneth V. Lawson, Patrick G. Schweickert, Alejandra Lopez, Suan Liu, Timothy Park, Artur Mailyan, Jeremy T. A. Fournier, Joel W. Beatty, Samuel L. Drew, Jarek Kalisiak, Balint Gal, Guillaume Mata, Zhang Wang, Brandon R. Rosen, Clayton Hardman, Matthaw P. Epplin, Kai Yu, Karl T. Haelsig, Lixia Jin, Elaine Ginn, Jennie Au, Cesar A. Meleza, Joel Tencer, Amber Pham, Hyock J. Kwon, Stephen W. Young, Manmohan Leleti, Jay P. Powers, Matthew J. Walters. AB521 potently and selectively inhibits pro-tumorigenic gene transcription by Hypoxia-Inducible Factor (HIF)-2α in vitro and in vivo [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P206.

Design, Synthesis, and Structure-Activity Relationship Optimization of Pyrazolopyrimidine Amide Inhibitors of Phosphoinositide 3-Kinase γ (PI3Kγ)

Phosphoinositide-3-kinase γ (PI3Kγ) is highly expressed in immune cells and promotes the production and migration of inflammatory mediators. The inhibition of PI3Kγ has been shown to repolarize the tumor immune microenvironment to a more inflammatory phenotype, thereby controlling immune suppression in cancer. Herein, we report the structure-based optimization of an early lead series of pyrazolopyrimidine isoindolinones, which culminated in the discovery of highly potent and isoform-selective PI3Kγ inhibitors with favorable drug-like properties. X-ray cocrystal structure analysis, molecular docking studies, and detailed structure-activity relationship investigations resulted in the identification of the optimal amide and isoindolinone substituents to achieve a desirable combination of potency, selectivity, and metabolic stability. Preliminary in vitro studies indicate that inhibition of PI3Kγ with compound 56 results in a significant immune response by increasing pro-inflammatory cytokine gene expression in M1 macrophages.

Abstract 1206: Discovery and characterization of AB521, a novel, potent, and selective hypoxia-inducible factor (HIF)-2α inhibitor

A hypoxic environment is a common characteristic of solid tumors. Cancer cells adapt to hypoxia and become more aggressive by up-regulation of genes associated with metabolism, growth, proliferation, angiogenesis, and erythropoiesis. Hypoxia-inducible factors (HIFs) are the central driving force for the cellular response to hypoxia and regulate a vast array of these genes. HIFs are heterodimers composed of an oxygen-sensitive HIF-α subunit (HIF-1α, HIF-2α, and HIF-3α) and a constitutively expressed HIF-1β subunit. HIF-2α is constitutively synthesized and regulated in an oxygen-dependent manner. Proline residues present in the oxygen-dependent degradation domain of the HIF-2α subunit are hydroxylated and subject to ubiquitination via the von Hippel-Lindau (pVHL) E3 ligase complex for subsequent proteasomal degradation. Under hypoxia or pseudohypoxia, caused by loss of VHL function, this process is inhibited, allowing HIF-2α translocation to the nucleus where, in complex with HIF-1β/ARNT, it promotes transcription of various pro-tumorigenic gene sets. Inhibition of HIF-2α has been demonstrated to be an effective strategy to mitigate tumor growth in the clinic, particularly in clear cell renal cell carcinoma (ccRCC).

Applying a pharmacophore mapping and structure-based design approach, we identified multiple novel series of small molecule HIF-2α inhibitors which avidly bind the HIF-2α PAS-B domain and disrupt dimerization with HIF-1β, preventing HIF-2α-mediated gene transcription. Interrogation of structure activity relationships and pharmacokinetic trends yielded highly optimized inhibitors, including AB521, which potently inhibits HIF-2α reporter transcription and VEGF secretion in a human ccRCC line. AB521 was confirmed to bind HIF-2α via multiple biochemical assays and inhibited HIF-2α-, but not HIF-1α-, mediated gene expression in a hepatocellular carcinoma cell line. Furthermore, AB521 is characterized by a favorable preclinical pharmacokinetic profile with high stability to human hepatocytes and no significant direct or time-dependent inhibition of the major CYP450 drug metabolizing enzymes. AB521 exhibits high bioavailability across preclinical species and is projected to possess a human pharmacokinetic profile suitable for once-daily dosing. In conclusion, we have discovered and extensively characterized a series of novel HIF-2α inhibitors, exemplified by AB521, which potently and selectively inhibits HIF-2α and possesses a favorable preclinical pharmacokinetic profile. The data described herein provides further support for the development of novel HIF-2α inhibitors for cancer therapy.

Citation Format: Kenneth V. Lawson, Kelsey E. Sivick Gauthier, Artur K. Mailyan, Jeremy T. Fournier, Joel W. Beatty, Samuel L. Drew, Jarek Kalisiak, Balint Gal, Guillaume Mata, Zhang Wang, Xuelei Yan, Lixia Jin, Elaine Ginn, Dana Piovesan, Jennifer Au, Cesar A. Meleza, Stephen W. Young, Matthew J. Walters, Manmohan Leleti, Jay P. Powers. Discovery and characterization of AB521, a novel, potent, and selective hypoxia-inducible factor (HIF)-2α inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1206.

Discovery of Potent and Selective Methylenephosphonic Acid CD73 Inhibitors

Solid tumors are often associated with high levels of extracellular ATP. Ectonucleotidases catalyze the sequential hydrolysis of ATP to adenosine, which potently suppresses T-cell and NK-cell functions via the adenosine receptors (A_2a and A_2b). The ectonucleotidase CD73 catalyzes the conversion of AMP to adenosine. Thus, increased CD73 enzymatic activity in the tumor microenvironment is a potential mechanism for tumor immune evasion and has been associated with poor prognosis in the clinic. CD73 inhibition is anticipated to restore immune function by skirting this major mechanism of adenosine generation. We have developed a series of potent and selective methylenephosphonic acid CD73 inhibitors via a structure-based design. Key binding interactions of the known inhibitor adenosine-5'-(α,β-methylene)diphosphate (AMPCP) with hCD73 provided the foundation for our early designs. The structure-activity relationship study guided by this structure-based design led to the discovery of 4a, which exhibits excellent potency against CD73, exquisite selectivity against related ectonucleotidases, and a favorable pharmacokinetic profile.

Discovery of Potent and Selective 7-Azaindole Isoindolinone-Based PI3Kγ Inhibitors

The successful application of immunotherapy in the treatment of cancer relies on effective engagement of immune cells in the tumor microenvironment. Phosphoinositide 3-kinase γ (PI3Kγ) is highly expressed in tumor-associated macrophages, and its expression levels are associated with tumor immunosuppression and growth. Selective inhibition of PI3Kγ offers a promising strategy in immuno-oncology, which has led to the development of numerous potent PI3Kγ inhibitors with variable selectivity profiles. To facilitate further investigation of the therapeutic potential of PI3Kγ inhibition, we required a potent and PI3Kγ-selective tool compound with sufficient metabolic stability for use in future in vivo studies. Herein, we describe some of our efforts to realize this goal through the systematic study of SARs within a series of 7-azaindole-based PI3Kγ inhibitors. The large volume of data generated from this study helped guide our subsequent lead optimization efforts and will inform further development of PI3Kγ-selective inhibitors for use in immunomodulation.

Discovery of Potent and Selective PI3Kγ Inhibitors

The selective inhibition of the lipid signaling enzyme PI3Kγ constitutes an opportunity to mediate immunosuppression and inflammation within the tumor microenvironment but is difficult to achieve due to the high sequence homology across the class I PI3K isoforms. Here, we describe the design of a novel series of potent PI3Kγ inhibitors that attain high isoform selectivity through the divergent projection of substituents into both the "selectivity" and "alkyl-induced" pockets within the adenosine triphosphate (ATP) binding site of PI3Kγ. These efforts have culminated in the discovery of 5-[2-amino-3-(1-methyl-1H-pyrazol-4-yl)pyrazolo[1,5-a]pyrimidin-5-yl]-2-[(1S)-1-cyclopropylethyl]-7-(trifluoromethyl)-2,3-dihydro-1H-isoindol-1-one (4, IC₅₀ = 0.064 μM, THP-1 cells), which displays >600-fold selectivity for PI3Kγ over the other class I isoforms and is a promising step toward the identification of a clinical development candidate. The structure-activity relationships identified throughout this campaign demonstrate that greater γ-selectivity can be achieved by inhibitors that occupy an "alkyl-induced" pocket and possess bicyclic hinge-binding motifs capable of forming more than one hydrogen bond to the hinge region of PI3Kγ.

Targeting Metabolism of Extracellular Nucleotides via Inhibition of Ectonucleotidases CD73 and CD39

In the tumor microenvironment, unusually high concentrations of extracellular adenosine promote tumor proliferation through various immunosuppressive mechanisms. Blocking adenosine production by inhibiting nucleotide-metabolizing enzymes, such as ectonucleotidases CD73 and CD39, represents a promising therapeutic strategy that may synergize with other immuno-oncology mechanisms and chemotherapies. Emerging small-molecule ectonucleotidase inhibitors have recently entered clinical trials. This Perspective will outline challenges, strategies, and recent advancements in targeting this class with small-molecule inhibitors, including AB680, the first small-molecule CD73 inhibitor to enter clinical development. Specific case studies, including structure-based drug design and lead optimization, will be outlined. Preclinical data on these molecules and their ability to enhance antitumor immunity will be discussed.

Abstract A10: The dual A2aR/A2bR antagonist AB928 reverses adenosine-mediated immune suppression and inhibits tumor growth in vivo

Introduction: High levels of immunosuppressive adenosine are found in the tumor microenvironment, reaching 50-100 μM in experimental models. Adenosine exerts its effects on immune cells primarily through the adenosine receptors A2aR/A2bR, which increase intracellular levels of cyclic AMP, leading to CREB phosphorylation (pCREB). We have previously shown that the dual A2aR/A2bR antagonist AB928 is capable of inhibiting adenosine-induced pCREB in healthy human volunteer (HV) blood lymphocytes. AB928 has also been shown to relieve adenosine-mediated T-cell suppression in vitro and exhibit combinatorial effects with standard-of-care chemotherapeutics in mouse syngeneic tumor models. Herein, we show that AB928 is capable of inhibiting NECA-induced gene expression changes and CREB phosphorylation in non-small cell lung carcinoma (NSCLC) patient whole blood (WB). Additionally, observations from our in vitro human studies showing the combinatorial effect of AB928 and α-PD-1 were reproduced in B16F10 syngeneic tumors.

Methods: Human WB was stimulated with 5 μM of NECA and flow cytometry was used to quantify AB928-mediated inhibition of pCREB and CD3ζ phosphorylation. B16F10 tumors were treated with α-PD-1 +/- AB928 and gene expression was determined from excised mouse tumors using the nCounter PanCancer panel.

Results: To ensure AB928 can successfully inhibit the high levels of intratumoral adenosine, we found that 5 μM NECA provides maximal stimulation and is significantly more potent (>20 fold) than adenosine in the pCREB assay. Additional experiments demonstrated that AB928 has comparable potency in NECA-stimulated WB from both HV and NSCLC patients. In addition to blocking downstream signaling, NanoString analysis showed that AB928 could prevent NECA-stimulated gene expression changes in NSCLC WB. We also found that NECA stimulation, alone or in combination with PD-1 inhibition, significantly reduced proximal TCR signaling, leading to reduced levels of CD3ζ phosphorylation at TYR142 (pTYR142). These reduced pTYR142 levels, with and without α-PD-1, could be significantly rescued by AB928, suggesting that blocking adenosine immunosuppression may provide additional benefit to PD-1 inhibition in tumors. Consistent with these results, AB928 was capable of suppressing growth (volume in mm3) of B16-F10 tumors both as a single agent (vehicle: 462 +/- 58; AB928: 292 +/- 55; p<0.05) or in combination with α-PD-1 therapy (α-PD-1: 341 +/- 60; AB928+α-PD-1: 123 +/- 30; p<0.05). Further, NanoString analysis of the tumors showed an increased “T-cell Functions” score with both α-PD-1 and AB928 monotherapy, which was further enhanced in combination treatment.

Conclusions: Collectively, these results support a role for AB928 in relieving adenosine-mediated immunosuppression by blocking A2aR/A2bR-induced signaling events, gene expression changes, and suppressing tumor growth in vivo.

Citation Format: Daniel M. DiRenzo, Nell Narasappa, Dana Piovesan, Devika Ashok, Park Adam, Jenna L. Jeffrey, Manmohan R. Leleti, Joanne B.L. Tan, Lisa Seitz, Steve W. Young, Jay P. Powers, Matthew J. Walters. The dual A2aR/A2bR antagonist AB928 reverses adenosine-mediated immune suppression and inhibits tumor growth in vivo [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A10.

Abstract C050: A novel, potent, and selective hypoxia-inducible factor (HIF)-2α antagonist

The microenvironment of solid tumors is known to be hypoxic and requires induction of genes associated with metabolism, growth, proliferation, and angiogenesis for tumor cells to survive and metastasize. The master transcriptional regulator of hypoxia-induced genes is the Hypoxia-Inducible Factor (HIF), consisting of an oxygen-regulated alpha monomer, of which there are three isoforms (HIF-1α, HIF-2α, and HIF-3α), that can heterodimerize with a constitutively-expressed beta monomer (HIF-1β/ARNT) using Per-ARNT-SIM (PAS) protein-protein interaction domains. In normoxia, proline residues present in the oxygen-dependent degradation domain of the HIF-α subunits are hydroxylated, allowing for recognition by the von Hippel-Lindau (pVHL) E3-ubiquitin ligase complex and subsequent proteasomal degradation. Upon exposure to low oxygen conditions or in the case of VHL mutation or silencing, HIF-α subunits accumulate in the cell and mediate transcription of various pro-tumorigenic gene sets. In patients, overexpression of HIF is associated with poor prognosis, and both preclinical and clinical evidence is mounting that suggests inhibiting HIF-2α is a valid approach to destroy tumor cells, particularly in clear cell renal carcinoma, warranting development of next-generation inhibitors. Using a suite of in vitro and in vivo assays designed to evaluate HIF-2α-specific effects, herein we describe pharmacological properties associated with novel, potent, and selective small-molecule antagonists of HIF-2α. These compounds inhibited HIF-dependent reporter gene transcription as well as VEGF protein secretion in a human renal cell adenocarcinoma line. Compounds that were confirmed to bind the HIF-2α PAS-B domain by Microscale thermophoresis (MST) and Thermal shift assay (TSA) also significantly inhibited HIF-2α, but not HIF-1α, target gene expression in a hepatocellular carcinoma cell line (P<0.05). Further, NanoString analyses revealed pathway signatures upregulated in hypoxic conditions, including angiogenesis, metabolism, and metastasis, that were significantly decreased with antagonist treatment. Selective antagonists were evaluated in vivo to determine efficacy and PK-PD relationships. Additionally, syngeneic tumor models were used to characterize the effects of HIF-2α inhibition (alone or in combination with anti-PD-1 and anti-adenosine agents) on tumor growth, immune cell infiltration, and expression of genes associated with adenosine production/signaling. Collectively, these data support the rationale to target HIF-2α for the treatment of cancers, particularly indications with a HIF-2α-driven hypoxia signature, and describe the properties of novel and selective HIF-2α antagonists.

Citation Format: Kelsey E Sivick Gauthier, Kenneth V Lawson, Dana Piovesan, Matthew J Walters, Ada Chen, Xiaoning Zhao, Cesar Meleza, Nikki Kimura, Tim Park, Steve Young, Anh Tran, Samuel L Drew, Lixia Jin, Manmohan Leleti, Elaine Ginn, Jay P Powers. A novel, potent, and selective hypoxia-inducible factor (HIF)-2α antagonist [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C050. doi:10.1158/1535-7163.TARG-19-C050

Abstract 3168: Methods for assessment of the “adenosine fingerprint” in clinical trials of AB928

BACKGROUND: The tumor microenvironment (TME) contains high levels of immunosuppressive adenosine (ADO), which activates the A2aR and A2bR receptors on immune cells, leading to an ineffective anti-tumor response. Ecto-5’-nucleotidase (CD73) and tissue non-specific alkaline phosphatase (TNAP) are primarily responsible for the conversion of extracellular adenosine monophosphate (AMP) to ADO and exhibit both membrane-bound and secreted forms. We have previously shown that AB928, a dual A2aR/A2bR antagonist, rescues the immunosuppressive effects of ADO in experimental tumor models. Herein, we describe the development of assays to measure the expression and activity of adenosine-generating enzymes in human tumor samples and peripheral blood. These assays are being used to define an “adenosine fingerprint” that identifies tumor types and patients most sensitive to adenosine inhibition by AB928.

METHODS: CD73 and TNAP immuno-histochemistry (IHC) and mRNA analysis were performed on sections of formalin fixed paraffin embedded (FFPE) tumor tissue. Circulating levels of CD73 were quantified with an in-house developed ELISA, and AMP-ase enzymatic activity in serum was determined using an AMP-GloTM(Promega) assay. Gene expression data were extracted from The Cancer Genome Atlas (TCGA) and expressed as a ratio of log2 counts per million per sample.

RESULTS: TCGA data identified non-small cell lung (NSCLC), renal clear cell, triple-negative breast, ovarian, colorectal, and gastro-esophageal cancers as tumors that highly express the adenosine producing enzymes CD73 or TNAP. To confirm these gene expression patterns, IHC assays for both CD73 and TNAP were developed using normal and tumor human tissue. IHC for CD73 was strongest in NSCLC (54.3 +/- 11.2 µm2) and colorectal (22.5 +/- 8.1 µm2) adenocarcinomas, whereas prostate (1.0 +/- 0.3 µm2) cancer exhibited the weakest staining. In contrast, TNAP staining was strongest in ovarian cancer and NSCLC adenocarcinoma, whereas gastric and colorectal adenocarcinomas showed very little TNAP staining. Therefore, CD73 and TNAP IHC broadly recapitulate the gene expression patterns found in TCGA. A CD73-specific ELISA was developed using human cancer patient blood which established a range of circulating CD73 protein levels (2-8 ng/mL) and showed a strong correlation between plasma and serum levels (r2 = 0.94). To measure adenosine-generating enzyme activity in peripheral blood, the AMP-Glo biochemical assay was performed and showed strong concordance with the CD73 ELISA in cancer patient serum (r2 = 0.72).

CONCLUSIONS: These assays provide a detailed picture of the adenosine-generating capacity in the local TME as well as the peripheral activity and levels of CD73/TNAP to better identify patients that may benefit from adenosine inhibition.

Citation Format: Daniel DiRenzo, Devika Ashok, Amy E. Anderson, Akshata Udyavar, Joanne B. Tan, Irene M. Luu, Kristen Zhang, Jenna L. Jeffrey, Lisa Seitz, Manmohan R. Leleti, Stephen W. Young, Jay P. Powers, Matthew J. Walters. Methods for assessment of the “adenosine fingerprint” in clinical trials of AB928 [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 3168.

Abstract 3862: AB474, a potent orally bioavailable inhibitor of arginase, for the treatment of cancer

Introduction: It has been demonstrated that myeloid derived suppressor cells (MDSCs) have a direct role in tumor immune evasion, and increased MDSCs are associated with reduced overall survival in several types of cancer. Elevated levels of circulating MDSCs have been shown to correlate with a blunted response to checkpoint blockade. MDSCs secrete arginase, which depletes arginine, leading to decreased T cell activity and a suppressed anti-tumor response. Here we will present the characterization of AB474, a highly potent small molecule inhibitor of arginase.

Methods: Arginase inhibition was measured using a coupled enzyme assay in the presence and absence of both mouse and human serum. IC50 was determined in buffer, human plasma, and serum by LC-MS/MS quantification of ornithine, while plasma protein binding was determined by equilibrium dialysis. Tumor transcript analysis was performed on homogenized whole murine tumors using Taqman probes. Arginase inhibition by AB474 was tested on human CD4 and CD8 T cells, with proliferation and effector functions being determined in the presence of recombinant and endogenous human ARG1. Assays were performed using standard CD2/CD3/CD28 activation conditions: proliferation was measured by flow cytometry, and IFNγ secretion by ELISA.

Results: AB474 inhibits arginase with low-nanomolar potency. It effectively inhibits both recombinant and endogenous arginase, while displaying low plasma protein binding across species. Pharmacokinetic characterization of AB474 demonstrated oral bioavailability in both mice and rats, displaying qualities compatible with human dosing. Measuring transcript of Arg1 in murine tumor models revealed expression in both tumor and immune compartments. Flow cytometry analysis shows ARG1+ MDSCs exist in both the tumor and periphery, with higher expression levels seen in Ly6c+ mMDSC populations. Consistent with the elevation of arginase in tumor-bearing mice, levels of arginine are decreased when compared to naïve littermates. Addition of arginase to activated CD4 or CD8 T-cells results in a significant suppression of proliferation, CD3 expression, and IFNγ secretion. Addition of AB474 results in a significant restoration of normal T cell effector functions (P < 0.001).

Conclusions: AB474 is a potent orally bioavailable inhibitor of arginase. Inhibition of arginase will block one of the primary immune-suppressive functions of MDSCs resulting in restored T cell activation and anti-tumor responses.

Citation Format: Sterling C. Eckard, Yu Chen, Dana Piovesan, Nell Narasappa, Timothy W. Park, Jarek Kalisiak, Eric T. Newcomb, Manmohan R. Leleti, Divyank Soni, Elaine Ginn, Jie Chen, Dan DiRenzo, Kristen Zhang, Lixia Jin, Stephen W. Young, Matthew J. Walters, Ulrike Schindler, Jay P. Powers. AB474, a potent orally bioavailable inhibitor of arginase, for the treatment of cancer [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 3862.

Abstract 3769: Pharmacokinetic-pharmacodynamic relationship for AB928, a dual antagonist of the A2aR and A2bR adenosine receptors

INTRODUCTION: CD73 converts extracellular adenosine monophosphate (AMP), derived from adenosine triphosphate, into adenosine (ADO). ADO suppresses immune responses, including those of T cells, natural killer (NK) cells and dendritic cells, via A2aR and A2bR receptors. Activation of these receptors results in increased intracellular levels of cyclic AMP (cAMP) and phosphorylation of the cAMP response element-binding protein (CREB). Monitoring the degree of pCREB induced by activation of the Aa2R and A2bR receptors in peripheral blood allows for a specific measurement of target engagement by AB928. In mice, the pCREB assay, coupled with changes in immune cell infiltrate and tumor growth rates, allows for a fuller understanding of the drug's PK/PD relationship.

METHODS: Mouse and human whole blood was stimulated with the adenosine agonist NECA (5'-N-Ethylcarboxamidoadenosine) following in vitro spike in or in vivo dosing with AB928. Multi-color phospho-flow cytometry was used to assess levels of pCREB on immune cells. AB928 levels in plasma samples were determined using LC-MS-MS after protein precipitation.

RESULTS: A2aR mRNA was the most prevalent adenosine receptor in CD4+ and CD8+ T cells. NK cells also express primarily A2aR, although A2bR was also detected. Dendritic cells and CD14+ monocytes expressed both A2aR and A2bR. NECA stimulation of mouse whole blood resulted in a significant increase in the levels of pCREB within CD8+ T cells with an EC50 of 100 nM, while in human whole blood the EC50 was higher at 700 nM. AB928 (100 nM) exhibited comparable shifts in the NECA dose response between human and murine whole blood, 15 and 16-fold, respectively. Due to the high level of adenosine in the tumor microenvironment, doses of AB928 associated with plasma levels that significantly inhibited 5 μM NECA in the whole-blood pCREB assay were selected for mouse efficacy studies. At these doses, significant reductions in tumor growth were noted. In human whole blood, approximately 90 nM AB928 was required to inhibit 50% of the 5 μM NECA-induced pCREB signal. Inhibition was observed on both CD4+ and CD8+ T cells. NECA-induced pCREB elevations were observed in CD14+ cells less frequently than T cells; however, when the signal was observed, AB928 inhibited it. The human pCREB assay is being utilized to monitor the PD responses in an ongoing clinical trial. Preliminary PK/PD results from this study will be presented.

CONCLUSIONS: Systemic extent of receptor (A2aR and A2bR) occupancy by the novel dual antagonist AB928 can be assessed in humans and mice based on the extent of receptor-mediated CREB phosphorylation in blood lymphocytes. AB928 retains much of its inherent potency when competing against high concentrations of adenosine under physiologically relevant conditions (i.e., whole blood).

Citation Format: Lisa Seitz, Devika Ashok, Manmohan R. Leleti, Jay P. Powers, Brandon Rosen, Dillon Miles, Lixia Jin, Adam Park, Tim Park, Steve Young, Ferdie Soriano, Aimee Rieger, Ulrike Schindler, Joyson Karakunnel, Matt J. Walters. Pharmacokinetic-pharmacodynamic relationship for AB928, a dual antagonist of the A2aR and A2bR adenosine receptors [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 3769.

Abstract 710: CD73 inhibitors (CD73i) reverse the AMP/adenosine-mediated impairment of immune effector cell activation by immune checkpoint inhibitors (ICI)

INTRODUCTION: CD73 catalyzes the extracellular generation of adenosine (ADO) from adenosine monophosphate (AMP). ADO suppresses immune responses, including those of T cells, NK cells and dendritic cells through activation of A2aR and A2bR receptors. Exhausted T cells and NK cells express high levels of several immune checkpoint proteins, including PD-1 and TIGIT. We present here preclinical data on the ability of CD73i to reverse effector cell suppression from exposure to ADO even in the presence of ICI.

METHODS: CD73i effects in a monotherapeutic setting were assessed by CD3/CD28/CD2 T cell stimulation and cytolytic assays. Combinatorial settings were assessed using mixed lymphocyte reactions (MLRs). In vivo effects of CD73i + ICI were determined using syngeneic tumor models.

RESULTS: CD73 is expressed across a wide range of tumor types, including those with limited response to anti-PD-1 therapy. CD73i completely rescued AMP-mediated inhibition of T cell proliferation and effector function as well as NK cell cytolytic function. AMP abrogated the enhanced allogeneic CD4+ T cell activation and IFN-γ production mediated by blocking PD-1/PD-L1 and TIGIT, an effect that was reversed by CD73i. Mechanistically, addition of AMP in MLRs repressed expression of activation markers and immune checkpoint proteins. Thus, activation of the adenosinergic pathway may limit the efficacy of ICI. TCGA data from anti-PD-1-treated melanoma patients identified CD73 expression as a negative prognostic factor. Finally, co-administration of a CD73i with an anti-PD-1 mAb resulted in significant reduction of tumor volume associated with increases in immune cell infiltration.

CONCLUSIONS: CD73 inhibition, alone or in combination with anti-PD-1 and anti-TIGIT antibodies, translates into potent enhancement of immune cell activation in a variety of studies. These data provide a rationale for CD73i + ICI combinations.

Citation Format: Annette Becker, Nell Narasappa, Fangfang Yin, Kristen Zhang, Daniel DiRenzo, Timothy Park, Jaroslaw Kalisiak, Ken Lawson, Jenna Jeffrey, Jay P. Powers, Ulrike Schindler, Matthew J. Walters, Joanne B. Tan. CD73 inhibitors (CD73i) reverse the AMP/adenosine-mediated impairment of immune effector cell activation by immune checkpoint inhibitors (ICI) [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 710.

Abstract B46: Small-molecule inhibitors of ecto-nucleotidase CD73 promote activation of human CD8+ T cells and have profound effects on tumor growth and immune parameters in experimental tumor models

Introduction: The intra-tumoral generation of adenosine (ADO), a potent inhibitor of T-cell activation, depends on the coordinated and sequential cleavage of extracellular adenosine triphosphate (ATP) by the ecto-nucleotidases CD39 (which produces adenosine monophosphate, AMP) and CD73 (which hydrolyzes AMP to form ADO). For this reason, a number of anti-CD73 antibodies are being advanced into clinical trials; however, to date there have been few reports of potent, selective, small-molecule CD73 inhibitors, such as those described here.

Methods: Ecto-nucleotidase activity was calculated using the Malachite green assay after 50-min incubation with 25µM AMP, in the presence of varying concentrations of test compound(s). The following systems were used. Endogenous expression: hCD73/SKOV-3 cells; hCD73/CD8 T cells. Stable over-expression: hCD73/CHO. Transient expression: mCD73/CHO; NTPDase2/CHO; NTPDase3/CHO; NTPDase8/CHO. Human CD8 T cells enriched from buffy coats or leukopaks were pre-treated with varying concentrations of CD73 inhibitors prior to addition of 50 μM AMP + 10 μM EHNA and activated with T cell Activation/Expansion kit (Miltenyi). In some experiments, exogenous recombinant human IL12p70 (1-10 ng/mL) was added to the culture. Activation (CD25) and effector functions (Granzyme B and IFNγ) were measured by flow cytometry. CT26 cells were implanted into the shaved right flank of 7-8 week old Balb/c mice and measured three times a week starting at 7 days. Mice were enrolled into 4 cohorts and dosed according to the following conditions when tumour volume reached ~100 mm3.

Group 1: 1% HPMC (sc/QD) + 2A3 (10 mg/kg; IP/Q3D)

Group 2: A000830 (30 mg/kg; sc/QD) + 2A3 (10 mg/kg; IP/Q3D)

Group 3: 1% HPMC (sc/QD) + RMP1-14 (10 mg/kg; IP/Q3D)

Group 4: A000830 (30 mg/kg; sc/QD) + RMP1-14 (10 mg/kg; IP/Q3D)

For interim analysis, single cell suspension was generated from tissues, blocked (clone 2.4G2), and stained with antibodies. For intracellular FOXP3 staining, samples were fixed and stained using FOXP3/Transcription Factor Staining Buffer Set. Non-specific blocking was performed with 20% normal rat serum prior to addition of anti-mouse FOXP3 antibody.

Results: We have designed a series of potent and specific small-molecule inhibitors of human and mouse CD73, represented by A000830 and A001190 with the following IC50 values in overexpression systems:

A000830: Mouse IC50 (1 nM); Human IC50 (3 nM)

A001190: Mouse IC50 (n.d.); Human IC50 (0.03 nM)

A000830 and A001190 also blocked AMP hydrolysis by freshly isolated human CD8 T cells at potencies comparable to the over-expression systems. In in vitro models of AMP/ADO-driven inhibition of human CD8+ T-cell activation, A000830 and A001190 showed robust rescue of CD25 expression and granzyme B production. Complete rescue of IFNγ; production was achieved by adding exogenous IL12. In vivo, A000830 was well-tolerated in mice, resulting in sustained plasma concentrations above IC90. Therapeutic dosing of A000830 to these mice in combination with an α-PD1 antibody resulted in robust CT26 tumor growth inhibition, greater than either treatment alone.

Conclusions: Cumulatively, these data provide the initial characterization of a novel class of potent and selective small-molecule CD73 inhibitors that effectively block the generation of ADO from extracellular ATP, reverse the ADO-driven inhibition of human T-cell activation, and display promising anti-tumor activity when dosed in combination with PD-1 blockade.

Citation Format: Joanne BL Tan, Ada Chen, Manmohan Leleti, Annette Becker, Erick Lindsey, Jaroslaw Kalisiak, Jay P. Powers, Steve Young, Ulrike Schindler, Juan C. Jaen. Small-molecule inhibitors of ecto-nucleotidase CD73 promote activation of human CD8+ T cells and have profound effects on tumor growth and immune parameters in experimental tumor models. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B46.

Discovery of potent, selective, and orally bioavailable inhibitors of interleukin-1 receptor-associate kinase-4

In this Letter, we report the continued optimization of the N-acyl-2-aminobenzimidazole series, focusing in particular on the N-alkyl substituent and 5-position of the benzimidazole based on the binding mode and the early SAR. These efforts led to the discovery of 16, a highly potent, selective, and orally bioavailable inhibitor of IRAK-4.

Abstract 4290: Potent and selective next generation inhibitors of indoleamine-2,3-dioxygenase (IDO1) for the treatment of cancer

The IDO1 pathway has been proposed to mediate immunosuppressive effects in the tumor microenvironment through its role in the catabolism of tryptophan, resulting in effects on the differentiation and proliferation of T cells. IDO1 inhibition has shown promising clinical benefit as well as exacerbated toxicity in the treatment of melanoma, when combined with the anti-CTLA-4 antibody ipilimumab.

We have discovered a novel class of highly selective small molecule inhibitors of IDO1 which surpass the potency of the compounds currently in clinical development. These compounds potently inhibit IDO1 activity in IFN-γ stimulated HeLa cells with single digit nM potency. Importantly, they also retain their potency in the presence of human serum, with IC50 values ranging between 5 and 15 nM in this more physiologically relevant media. Consistent with the role of IDO1+ dendritic cells in the suppression of T cell proliferation, this series of molecules is capable of restoring the proliferative capacity of human T cells (which is inhibited by allogeneic IDO1+ dendritic cells) with EC50 values of 2-3 nM. The molecules exhibit preclinical PK characteristics that are suitable for assessing the contribution of IDO1 to tumor growth in murine models, both alone and in combination with other therapeutic agents. The compounds have high metabolic stability against cultured human hepatocytes and exhibit preclinical PK and ADME characteristics consistent with once-daily dosing in humans. The full preclinical profile of one of these molecules, selected for clinical evaluation, will be the focus of this presentation.

In conclusion, we have discovered a novel class of small molecule inhibitors of IDO1, which provides a preclinical basis for the clinical evaluation of a next generation IDO1 inhibitor in combination with other therapeutic agents.

Citation Format: Jay P. Powers, Matthew J. Walters, Rajkumar Noubade, Stephen W. Young, Lisa Marshall, Jan Melom, Adam Park, Nick Shah, Pia Bjork, Jordan S. Fridman, Hilary P. Beck, David Chian, Jenny V. McKinnell, Maksim Osipov, Maureen K. Reilly, Hunter P. Shunatona, James R. Walker, Mikhail Zibinsky, Juan C. Jaen. Potent and selective next generation inhibitors of indoleamine-2,3-dioxygenase (IDO1) for the treatment of cancer. [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 4290. doi:10.1158/1538-7445.AM2015-4290

Synthesis, in Vitro Covalent Binding Evaluation, and Metabolism of (14)C-Labeled Inhibitors of 11β-HSD1

In this letter, we reported the design and synthesis of three potent, selective, and orally bioavailable 11β-HSD1 inhibitors labeled with (14)C: AMG 456 (1), AM-6949 (2), and AM-7715 (3). We evaluated the covalent protein binding of the labeled inhibitors in human liver microsomes in vitro and assessed their potential bioactivation risk in humans. We then studied the in vitro mechanism of 2 in human hepatocytes and the formation of reactive intermediates. Our study results suggest that 1 and 3 have low potential for metabolic bioactivation in humans, while 2 has relatively high risk.

Inhibition of CXCR7 extends survival following irradiation of brain tumours in mice and rats

Background:

In experimental models of glioblastoma multiforme (GBM), irradiation (IR) induces local expression of the chemokine CXCL12/SDF-1, which promotes tumour recurrence. The role of CXCR7, the high-affinity receptor for CXCL12, in the tumour's response to IR has not been addressed.

Methods:

We tested CXCR7 inhibitors for their effects on tumour growth and/or animal survival post IR in three rodent GBM models. We used immunohistochemistry to determine where CXCR7 protein is expressed in the tumours and in human GBM samples. We used neurosphere formation assays with human GBM xenografts to determine whether CXCR7 is required for cancer stem cell (CSC) activity in vitro.

Results:

CXCR7 was detected on tumour cells and/or tumour-associated vasculature in the rodent models and in human GBM. In human GBM, CXCR7 expression increased with glioma grade and was spatially associated with CXCL12 and CXCL11/I-TAC. In the rodent GBM models, pharmacological inhibition of CXCR7 post IR caused tumour regression, blocked tumour recurrence, and/or substantially prolonged survival. CXCR7 expression levels on human GBM xenograft cells correlated with neurosphere-forming activity, and a CXCR7 inhibitor blocked sphere formation by sorted CSCs.

Conclusions:

These results indicate that CXCR7 inhibitors could block GBM tumour recurrence after IR, perhaps by interfering with CSCs.

Experimental evidence for the use of CCR2 antagonists in the treatment of type 2 diabetes

OBJECTIVE

CCR2 inhibition has produced promising experimental and clinical anti-hyperglycemic effects. These results support the thesis that insulin resistance and Type 2 diabetes (T2D) are associated with chronic unresolved inflammation. The aim of this study was to provide a broad analysis of the various physiological changes occurring in mouse models of T2D in connection with pharmacological CCR2 inhibition.

MATERIALS/METHODS

A mouse-active chemical analogue of the clinical candidate CCX140-B was tested in diet-induced obese (DIO) mice and db/db mice. Measurements included: adipose tissue inflammatory macrophage counts; peripheral blood glucose levels at steady-state and after glucose and insulin challenges; peripheral blood insulin and adiponectin levels; 24-h urine output and urinary glucose levels; pancreatic islet number and size; hepatic triglyceride and glycogen content; and hepatic glucose-6-phosphatase levels.

RESULTS

In DIO mice, the CCR2 antagonist completely blocked the recruitment of inflammatory macrophages to visceral adipose tissue. The mice exhibited reduced hyperglycemia and insulinemia, improved insulin sensitivity, increased circulating adiponectin levels, decreased pancreatic islet size and increased islet number. It also reduced urine output, glucose excretion, hepatic glycogen and triglyceride content and glucose 6-phosphatase levels. Similar effects were observed in the db/db diabetic mice.

CONCLUSIONS

These data indicate that pharmacological inhibition of CCR2 in models of T2D can reduce inflammation in adipose tissue, alter hepatic metabolism and ameliorate multiple diabetic parameters. These mechanisms may contribute to the promising anti-diabetic effects seen in humans with at least one CCR2 antagonist.

C5a receptor (CD88) blockade protects against MPO-ANCA GN

Necrotizing and crescentic GN (NCGN) with a paucity of glomerular immunoglobulin deposits is associated with ANCA. The most common ANCA target antigens are myeloperoxidase (MPO) and proteinase 3. In a manner that requires activation of the alternative complement pathway, passive transfer of antibodies to mouse MPO (anti-MPO) induces a mouse model of ANCA NCGN that closely mimics human disease. Here, we confirm the importance of C5aR/CD88 in the mediation of anti-MPO-induced NCGN and report that C6 is not required. We further demonstrate that deficiency of C5a-like receptor (C5L2) has the reverse effect of C5aR/CD88 deficiency and results in more severe disease, indicating that C5aR/CD88 engagement enhances inflammation and C5L2 engagement suppresses inflammation. Oral administration of CCX168, a small molecule antagonist of human C5aR/CD88, ameliorated anti-MPO-induced NCGN in mice expressing human C5aR/CD88. These observations suggest that blockade of C5aR/CD88 might have therapeutic benefit in patients with ANCA-associated vasculitis and GN.

Rational design and binding mode duality of MDM2-p53 inhibitors

Structural analysis of both the MDM2-p53 protein-protein interaction and several small molecules bound to MDM2 led to the design and synthesis of tetrasubstituted morpholinone 10, an MDM2 inhibitor with a biochemical IC50 of 1.0 μM. The cocrystal structure of 10 with MDM2 inspired two independent optimization strategies and resulted in the discovery of morpholinones 16 and 27 possessing distinct binding modes. Both analogues were potent MDM2 inhibitors in biochemical and cellular assays, and morpholinone 27 (IC50 = 0.10 μM) also displayed suitable PK profile for in vivo animal experiments. A pharmacodynamic (PD) experiment in mice implanted with human SJSA-1 tumors showed p21(WAF1) mRNA induction (2.7-fold over vehicle) upon oral dosing of 27 at 300 mg/kg.

CCR1 blockade reduces tumor burden and osteolysis in vivo in a mouse model of myeloma bone disease

The chemokine CCL3/MIP-1α is a risk factor in the outcome of multiple myeloma (MM), particularly in the development of osteolytic bone disease. This chemokine, highly overexpressed by MM cells, can signal mainly through 2 receptors, CCR1 and CCR5, only 1 of which (CCR1) is responsive to CCL3 in human and mouse osteoclast precursors. CCR1 activation leads to the formation of osteolytic lesions and facilitates tumor growth. Here we show that formation of mature osteoclasts is blocked by the highly potent and selective CCR1 antagonist CCX721, an analog of the clinical compound CCX354. We also show that doses of CCX721 selected to completely inhibit CCR1 produce a profound decrease in tumor burden and osteolytic damage in the murine 5TGM1 model of MM bone disease. Similar effects were observed when the antagonist was used prophylactically or therapeutically, with comparable efficacy to that of zoledronic acid. 5TGM1 cells were shown to express minimal levels of CCR1 while secreting high levels of CCL3, suggesting that the therapeutic effects of CCX721 result from CCR1 inhibition on non-MM cells, most likely osteoclasts and osteoclast precursors. These results provide a strong rationale for further development of CCR1 antagonists for the treatment of MM and associated osteolytic bone disease.

The effect of the CXCR7 inhibitor CCX662 on survival in the ENU rat model of glioblastoma

e13580

Background: Glioblastoma (GBM) is the most common form of malignant brain cancer. Despite aggressive therapy, consisting of radiotherapy, surgical resection, and chemotherapeutic treatment, mean survival from time of diagnosis remains little more than one year. The chemokine receptor CXCR7 is highly expressed on both human glioma cells and tumor-associated vasculature, and may play a key role in tumor growth and survival. Methods: The in vitro activity of the CXCR7 antagonist CCX662 was determined using radioligand binding assays and trans-endothelial migration assays. The therapeutic effects of CCX662 were investigated in the ENU-induced rat model of GBM in combination with radiotherapy. Results: CCX662 is a highly potent and selective small molecule inhibitor of CXCR7. CCX662 inhibits the binding of 125I-CXCL12 to CXCR7 with an IC50 of 9 nM in buffer, and displays minimal serum shift with an IC50 of 18 nM in 100% human serum. CCX662 inhibits the CXCR4-directed trans-endothelial migration of CXCR4+/CXCR7+ NC37 cells towards CXCL12 (SDF1) with an IC50 of 106 nM. CCX662 also potently inhibits binding of 125I-CXCL12 to rat CXCR7 in the presence of 100% rat serum with an IC50 of 14 nM. In vivo inhibition of CXCR7 with CCX662, in concert with radiotherapy, results in a significant extension of survival time in the ENU-induced rat model of GBM. The median survival time for rats (reflective of GBM tumor progression) treated with the combination of irradiation and CCX662 was 234 days compared with 160 days for untreated rats (p<0.01) or compared with 174 days for rats given irradiation plus vehicle (p<0.01). As expected for a non-cytotoxic drug, dose-range finding 14-day toxicology studies in rats and dogs have demonstrated large (> 10 and 25-fold, respectively) safety margin relative to highly effective levels of the drug. Conclusions: CCX662 is a highly selective and potent small molecule inhibitor of CXCR7 with profound, therapeutic benefit in an aggressive rodent model of GBM. These data indicate that inhibition of CXCR7, using CCX662, may be a promising strategy for the treatment of glioblastoma.

Synthesis and optimization of novel 4,4-disubstituted cyclohexylbenzamide derivatives as potent 11β-HSD1 inhibitors

The synthesis and SAR of a series of 4,4-disubstituted cyclohexylbenzamide inhibitors of 11β-HSD1 are described. Optimization rapidly led to potent, highly selective, and orally bioavailable inhibitors demonstrating efficacy in both rat and non-human primate ex vivo pharmacodynamic models.

The synthesis and SAR of novel diarylsulfone 11β-HSD1 inhibitors

In this communication, human 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitory activities of a novel series of diarylsulfones are described. Optimization of this series resulted in several highly potent 11β-HSD1 inhibitors with excellent pharmacokinetic (PK) properties. Compound (S)-25 showed excellent efficacy in a non-human primate ex vivo pharmacodynamic model.

Design of 1-piperazinyl-4-arylphthalazines as potent Smoothened antagonists

The Hedgehog (Hh) signaling pathway regulates cell proliferation and differentiation in developing tissues, and abnormal activation of the Hh pathway has been linked to several tumor subsets. As a transducer of Hh signaling, the GPCR-like protein Smoothened (Smo) is a promising target for disruption of unregulated Hh signaling. A series of 1-amino-4-arylphthalazines was developed as potent and orally bioavailable inhibitors of Smo. A representative compound from this class demonstrated significant tumor volume reduction in a mouse medulloblastoma model.

Discovery and optimization of piperidyl benzamide derivatives as a novel class of 11beta-HSD1 inhibitors

Discovery and optimization of a piperidyl benzamide series of 11beta-HSD1 inhibitors is described. This series was derived from a cyclohexyl benzamide lead structures to address PXR selectivity, high non-specific protein binding, poor solubility, limited in vivo exposure, and in vitro cytotoxicity issues observed with the cyclohexyl benzamide structures. These efforts led to the discovery of piperidyl benzamide 15 which features improved properties over the cyclohexyl benzamide derivatives.

Discovery and initial SAR of arylsulfonylpiperazine inhibitors of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1)

High-throughput screening of a small-molecule compound library resulted in the identification of a series of arylsulfonylpiperazines that are potent and selective inhibitors of human 11beta-Hydroxysteroid Dehydrogenase Type 1 (11beta-HSD1). Optimization of the initial lead resulted in the discovery of compound (R)-45 (11beta-HSD1 IC(50)=3nM).

An Efficient and Scalable One-Pot Double Michael Addition-Dieckmann Condensation for the Synthesis of 4,4-Disubstituted Cyclohexane β-Keto Esters

A simple, scalable, and efficient one-pot methodology for the synthesis of 4,4-disubstituted cyclohexane beta-keto esters from benzylic nitriles or esters and methyl acrylate promoted by potassium tert-butoxide is described. The process relies on a tandem double Michael addition-Dieckmann condensation reaction, which results in the formation of three discrete carbon-carbon bonds in a single pot, including a quaternary center. The method allows for the convenient and rapid synthesis of a variety of 4-aryl-4-cyano-2-carbomethoxycyclohexanone and 4-aryl-2,4-biscarbomethoxycyclohexanone building blocks for use in natural products synthesis and medicinal chemistry.

SAR studies on a novel series of human cytomegalovirus primase inhibitors

A novel series of imidazolylpyrimidines were found to possess inhibitory activity against the human CMV UL70 primase. Extensive SAR studies on an HTS lead led to potent, orally bioavailable compounds with anti-CMV IC(50) values of 150 nM in both viral yield and viral DNA replication assays and with a much reduced cytotoxicity compared to marketed treatments ganciclovir and cidofovir.

Discovery of a novel series of inhibitors of human cytomegalovirus primase

Infection by human cytomegalovirus (hCMV) remains a potent threat to susceptible people throughout the world. We have discovered a series of imidazolyl-pyrimidine compounds, which were found to be irreversible inhibitors of the hCMV UL70 primase based on results from radiolabeling and SAR studies. Two promising analogs are described that rival ganciclovir and cidofovir in antiviral potency and possess improved cytotoxicity profiles.

SAR and mode of action of novel non-nucleoside inhibitors of hepatitis C NS5b RNA polymerase

Novel non-nucleoside inhibitors of the HCV RNA polymerase (NS5b) with sub-micromolar biochemical potency have been identified which are selective for the inhibition of HCV NS5b over other polymerases. The structures of the complexes formed between several of these inhibitors and HCV NS5b were determined by X-ray crystallography, and the inhibitors were found to bind in an allosteric binding site separate from the active site. Structure-activity relationships and structural studies have identified the mechanism of action for compounds in this series, several of which possess drug-like properties, as unique, reversible, covalent inhibitors of HCV NS5b.

Discovery and initial SAR of inhibitors of interleukin-1 receptor-associated kinase-4

High-throughput screening of a small-molecule compound library resulted in the identification of a novel series of N-acyl 2-aminobenzimidazoles that are potent inhibitors of interleukin-1 receptor-associated kinase-4.