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.

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.

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 (A2a and A2b). 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,ß-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.

Discovery of AB680: A Potent and Selective Inhibitor of CD73.

Extracellular adenosine (ADO), present in high concentrations in the tumor microenvironment (TME), suppresses immune function via inhibition of T cell and NK cell activation. Intratumoral generation of ADO depends on the sequential catabolism of ATP by two ecto-nucleotidases, CD39 (ATP → AMP) and CD73 (AMP → ADO). Inhibition of CD73 eliminates a major pathway of ADO production in the TME and can reverse ADO-mediated immune suppression. Extensive interrogation of structure-activity relationships (SARs), structure-based drug design, and optimization of pharmacokinetic properties culminated in the discovery of AB680, a highly potent (Ki = 5 pM), reversible, and selective inhibitor of CD73. AB680 is further characterized by very low clearance and long half-lives across preclinical species, resulting in a PK profile suitable for long-acting parenteral administration. AB680 is currently being evaluated in phase 1 clinical trials. Initial data show AB680 is well tolerated and exhibits a pharmacokinetic profile suitable for biweekly (Q2W) iv-administration in human.

Discovery of Potent and Selective Non-Nucleotide Small Molecule Inhibitors of CD73.

CD73 is an extracellular mediator of purinergic signaling. When upregulated in the tumor microenvironment, CD73 has been implicated in the inhibition of immune function through overproduction of adenosine. Traditional efforts to inhibit CD73 have involved antibody therapy or the development of small molecules, the most potent of which mimic the acidic and ionizable structure of the enzyme's natural substrate, adenosine 5'-monophosphate (AMP). Here, we report the systematic discovery of a novel class of non-nucleotide CD73 inhibitors that are more potent than all other nonphosphonate inhibitor classes reported to date. These efforts have culminated in the discovery of 4-({5-[4-fluoro-1-(2H-indazol-6-yl)-1H-1,2,3-benzotriazol-6-yl]-1H-pyrazol-1-yl}methyl)benzonitrile (73, IC50 = 12 nM) and 4-({5-[4-chloro-1-(2H-indazol-6-yl)-1H-1,2,3-benzotriazol-6-yl]-1H-pyrazol-1-yl}methyl)benzonitrile (74, IC50 = 19 nM). Cocrystallization of 74 with human CD73 demonstrates a competitive binding mode. These compounds show promise for the improvement of drug-like character via the attenuation of the acidity and low membrane permeability inherent to known nucleoside inhibitors of CD73.

Safety, tolerability, and pharmacology of AB928, a novel dual adenosine receptor antagonist, in a randomized, phase 1 study in healthy volunteers.

Adenosine suppresses antitumor immune responses via A2a and A2b receptors expressed on intratumoral immune cells. This effect is mediated by increased cyclic adenosine 5'-monophosphate (AMP) levels and phosphorylation of cyclic AMP response element binding protein (CREB). We conducted a phase 1, placebo-controlled, single-ascending-dose (SAD) and multiple-ascending-dose (MAD) study to assess the safety, tolerability, pharmacokinetics (PK), including food effect (FE), and pharmacodynamics (PD) of oral AB928, a novel dual A2aR/A2bR antagonist, in healthy volunteers. AB928 doses between 10 and 200 mg once daily and 100 mg twice daily were evaluated. The study enrolled 85 subjects (randomized 3:1, AB928:placebo), 40 each in the SAD and MAD cohorts, and 5 in the FE cohort. AB928 was well tolerated up to the highest dose tested and did not affect any physiologic parameters potentially sensitive to adenosine inhibition. No safety concern was identified. The PK profile of AB928 was linear and dose-proportional, and a clear PK/PD correlation was demonstrated. Significant inhibition of adenosine receptor-mediated phosphorylated CREB was observed at peak plasma concentrations in all dose cohorts and at trough plasma concentrations in the higher-dose cohorts. AB928 plasma levels ≥1 µM were associated with ≥90% adenosine receptor inhibition. In the postprandial state, the rate of AB928 absorption decreased but the extent of absorption was unchanged. Together, these data support further clinical development of oral AB928 in cancer patients.

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.

CCR9 Antagonists in the Treatment of Ulcerative Colitis.

While it has long been established that the chemokine receptor CCR9 and its ligand CCL25 are essential for the movement of leukocytes into the small intestine and the development of small-intestinal inflammation, the role of this chemokine-receptor pair in colonic inflammation is not clear. Toward this end, we compared colonic CCL25 protein levels in healthy individuals to those in patients with ulcerative colitis. In addition, we determined the effect of CCR9 pharmacological inhibition in the mdr1a(-/-) mouse model of ulcerative colitis. Colon samples from patients with ulcerative colitis had significantly higher levels of CCL25 protein compared to healthy controls, a finding mirrored in the mdr1a(-/-) mice. In the mdr1a(-/-) mice, CCR9 antagonists significantly decreased the extent of wasting and colonic remodeling and reduced the levels of inflammatory cytokines in the colon. These findings indicate that the CCR9:CCL25 pair plays a causative role in ulcerative colitis and suggest that CCR9 antagonists will provide a therapeutic benefit in patients with colonic inflammation.

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

In this letter, we reported the design and synthesis of three potent, selective, and orally bioavailable 11ß-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.

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.

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.

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.

CCR9 inhibition does not interfere with the development of immune tolerance to oral antigens.

Recent literature indicates that mice deficient in the chemokine receptor CCR9 (CCR9(-/-) mice) are unable to generate oral tolerance. The present report describes how such inability can be overcome by increasing the dose of oral antigen. Pharmacological inhibition of CCR9 did not affect the generation of oral tolerance, regardless of antigen dose. These results highlight the inadequacy of genetic deletion of CCR9 when predicting the effects of pharmacological CCR9 inhibition on intestinal biology.

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.

Discovery and optimization of benzenesulfonanilide derivatives as a novel class of 11ß-HSD1 inhibitors.

A novel series of benzenesulfonanilide derivatives of 11ß-HSD1 inhibitors were identified via modification of the sulfonamide core of the arylsulfonylpiperazine lead structures. The synthesis, in vitro biological evaluation, and structure-activity relationship of these compounds are presented. Optimization of this series rapidly resulted in the discovery of compounds (S)-10 and (S)-23 (11ß-HSD1 SPA IC(50)=1.8 and 1.4 nM, respectively).

Discovery of amide replacements that improve activity and metabolic stability of a bis-amide smoothened antagonist hit.

A bis-amide antagonist of Smoothened, a seven-transmembrane receptor in the Hedgehog signaling pathway, was discovered via high throughput screening. In vitro and in vivo experiments demonstrated that the bis-amide was susceptible to N-acyl transferase mediated amide scission. Several bioisosteric replacements of the labile amide that maintained in vitro potency were identified and shown to be metabolically stable in vitro and in vivo.

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

The synthesis and SAR of a series of 4,4-disubstituted cyclohexylbenzamide inhibitors of 11ß-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.