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.

One size does not fit all: navigating the multi-dimensional space to optimize T-cell engaging protein therapeutics.

T-cell engaging biologics is a class of novel and promising immune-oncology compounds that leverage the immune system to eradicate cancer. Here, we compared and contrasted a bispecific diabody-Fc format, which displays a relatively short antigen-binding arm distance, with our bispecific IgG platform. By generating diverse panels of antigen-expressing cells where B cell maturation antigen is either tethered to the cell membrane or located to the juxtamembrane region and masked by elongated structural spacer units, we presented a systematic approach to investigate the role of antigen epitope location and molecular formats in immunological synapse formation and cytotoxicity. We demonstrated that diabody-Fc is more potent for antigen epitopes located in the membrane distal region, while bispecific IgG is more efficient for membrane-proximal epitopes. Additionally, we explored other parameters, including receptor density, antigen-binding affinity, and kinetics. Our results show that molecular format and antigen epitope location, which jointly determine the intermembrane distance between target cells and T cells, allow decoupling of cytotoxicity and cytokine release, while antigen-binding affinities appear to be positively correlated with both readouts. Our work offers new insight that could potentially lead to a wider therapeutic window for T-cell engaging biologics in general.

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.

Disentangling individual and neighborhood differences in the intention to quit smoking in Asian American male smokers.

Numerous studies have assessed individual-level factors associated with intention to quit smoking. However, fewer studies have assessed how neighborhood and built environment also contribute towards individual-level behavior. We used baseline data of 340 Chinese and Vietnamese male daily smokers from August 2015 to November 2017 living in the San Francisco Bay Area, who enrolled in a lifestyle intervention trial. The outcome variable was intention to quit in 30 days. To understand the role of contextual factors participants' residential addresses were geocoded, and neighborhood median income, ethnic composition, and tobacco retail density were computed. Individual level analysis suggested that Vietnamese American men had greater intention to quit smoking (OR = 2.90 CI = 1.59, 5.26) in comparison to Chinese Americans. However, after adding neighborhood level factors to the model, no ethnic group difference was observed. Neighborhood household median income (OR = 0.74, CI = 0.64, 0.86) and tobacco retail counts (OR = 0.79, CI = 0.67, 0.94) were negatively associated with intention to quit. Years lived in the U.S. was the only individual level factor associated with intention to quit. By comparing two Asian American groups that live in heterogeneous neighborhoods, we identify key environmental and policy drivers that are associated with quit intention. Future studies aimed at influencing individual-level behavior should take into consideration the neighborhood context and built environment characteristics.

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.

An Optimized Full-Length FLT3/CD3 Bispecific Antibody Demonstrates Potent Anti-leukemia Activity and Reversible Hematological Toxicity.

FLT3 (FMS-like tyrosine kinase 3), expressed on the surface of acute myeloid leukemia (AML) blasts, is a promising AML target, given its role in the development and progression of leukemia, and its limited expression in tissues outside the hematopoietic system. Small molecule FLT3 kinase inhibitors have been developed, but despite having clinical efficacy, they are effective only on a subset of patients and associated with high risk of relapse. A durable therapy that can target a wider population of AML patients is needed. Here, we developed an anti-FLT3-CD3 immunoglobulin G (IgG)-based bispecific antibody (7370) with a high affinity for FLT3 and a long half-life, to target FLT3-expressing AML blasts, irrespective of FLT3 mutational status. We demonstrated that 7370 has picomolar potency against AML cell lines in vitro and in vivo. 7370 was also capable of activating T cells from AML patients, redirecting their cytotoxic activity against autologous blasts at low effector-to-target (E:T) ratio. Additionally, under our dosing regimen, 7370 was well tolerated and exhibited potent efficacy in cynomolgus monkeys by inducing complete but reversible depletion of peripheral FLT3+ dendritic cells (DCs) and bone marrow FLT3+ stem cells and progenitors. Overall, our results support further clinical development of 7370 to broadly target AML patients.

An Exceptionally Potent Inhibitor of Human CD73.

We recently reported the initiation of a Phase I clinical trial with AB680, a potent human CD73 inhibitor, being developed for the treatment of solid tumors (NCT03677973). We undertook a detailed kinetic analysis of the interaction between human CD73 and AB680 to determine the mode of inhibition. We found AB680 to be a reversible, slow-onset competitive inhibitor of human CD73 with a Ki of 5 pM. Clinical candidates of this potency are uncommon and deserve special consideration during lead optimization.