Targeting of 4-1BB by monoclonal antibody PF-05082566 enhances T-cell function and promotes anti-tumor activity.

4-1BB (CD137, TNFRSF9) is a costimulatory receptor expressed on several subsets of activated immune cells. Numerous studies of mouse and human T cells indicate that 4-1BB promotes cellular proliferation, survival, and cytokine production. 4-1BB agonist mAbs have demonstrated efficacy in prophylactic and therapeutic settings in both monotherapy and combination therapy tumor models and have established durable anti-tumor protective T-cell memory responses. PF-05082566 is a fully human IgG2 that binds to the extracellular domain of human 4-1BB with high affinity and specificity. In preclinical studies, this agonist antibody demonstrated its ability to activate NF-κB and induce downstream cytokine production, promote leukocyte proliferation, and inhibit tumor growth in a human PBMC xenograft tumor model. The mechanism of action and robust anti-tumor efficacy of PF-05082566 support its clinical development for the treatment of a broad spectrum of human malignancies.

Thrombopoietin receptor activation: transmembrane helix dimerization, rotation, and allosteric modulation.

We report how rotational variations in transmembrane (TM) helix interactions participate in the activity states of the thrombopoietin receptor (TpoR), a type 1 cytokine receptor that controls the production of blood platelets. We also explore the mechanism of small-molecule agonists that do not mimic the natural ligand. We show, by a combination of cysteine cross-linking, alanine-scanning mutagenesis, and computational simulations, that the TpoR TM dimerizes strongly and can adopt 3 different stable, rotationally related conformations, which may correspond to specific states of the full-length receptor (active, inactive, and partially active). Thus, our data suggest that signaling and inactive states of the receptor are related by receptor subunit rotations, rather than a simple monomer-dimer transition. Moreover, results from experiments with and without agonists in vitro and in cells allow us to propose a novel allosteric mechanism of action for a class of small molecules, in which they activate TpoR by binding to the TM region and by exploiting the rotational states of the dimeric receptor. Overall, our results support the emerging view of the participation of mutual rotations of the TM domains in cytokine receptor activation.

Analysis of the role of the HIF hydroxylase family members in erythropoiesis.

HIF (hypoxia-inducible factor) hydroxylases have been implicated in EPO (erythropoietin) production and erythropoiesis. Here we examined the role of each of the three EGLN family members and the HIF asparaginyl hydroxylase FIH (factor inhibiting HIF) in EPO production. We examined the effect of inhibiting individual as well as combinations of HIF hydroxylases with RNAi. We found that inhibition of EGLN1 (egl nine homolog 1) as well as other members of the EGLN family (EGLN2 and EGLN3) led to accumulative EPO production in vitro. We then knocked down EGNL1 in vivo by injecting one-cell murine zygotes with lentivirus-containing RNAi. Progeny with demonstrated EGLN1 inhibition had elevated EPO production and erythropoiesis in vivo. Among all the in vitro and in vivo studies, no or minimal VEGF (vascular endothelial growth factor) mRNA or protein stimulation resulted from inhibition of EGLN1.

The identification of orally bioavailable thrombopoietin agonists.

Recently, we disclosed a series of potent pyrimidine benzamide-based thrombopoietin receptor agonists. Unfortunately, the structural features required for the desired activity conferred physicochemical properties that were not favorable for the development of an oral agent. The physical properties of the series were improved by replacing the aminopyrimidinyl group with a piperidine-4-carboxylic acid moiety. The resulting compounds possessed favorable in vivo pharmacokinetic properties, including good bioavailability.

Pyrimidine benzamide-based thrombopoietin receptor agonists.

A series of pyrimidine benzamide-based thrombopoietin receptor agonists is described. The lead molecule contains a 2-amino-5-unsubstituted thiazole, a group that has been associated with idiosyncratic toxicity. The potential for metabolic oxidation at C-5 of the thiazole, the likely source of toxic metabolites, was removed by substitution at C-5 or by replacing the thiazole with a thiadiazole. Potency in the series was improved by modifying the substituents on the pyrimidine and/or on the thiazole or thiadiazole pendant aryl ring. In vivo examination revealed that compounds from the series are not highly bioavailable. This is attributed to low solubility and poor permeability.

Piperazinyl CCR1 antagonists--optimization of human liver microsome stability.

The synthesis, biological activity, and pharmacokinetic profile of CCR1 antagonists are described.

Potent small molecule CCR1 antagonists.

The present manuscript details structure-activity relationship studies of lead structure 1, which led to the discovery of CCR1 antagonists >100-fold more potent than 1.

Novel CCR1 antagonists with improved metabolic stability.

The synthesis, biological activity, and pharmacokinetic profile of novel CCR1 antagonists are described.

CP-481,715, a potent and selective CCR1 antagonist with potential therapeutic implications for inflammatory diseases.

The chemokines CCL3 and CCL5, as well as their shared receptor CCR1, are believed to play a role in the pathogenesis of several inflammatory diseases including rheumatoid arthritis, multiple sclerosis, and transplant rejection. In this study we describe the pharmacological properties of a novel small molecular weight CCR1 antagonist, CP-481,715 (quinoxaline-2-carboxylic acid [4(R)-carbamoyl-1(S)-(3-fluorobenzyl)-2(S),7-dihydroxy-7-methyloctyl]amide). Radiolabeled binding studies indicate that CP-481,715 binds to human CCR1 with a Kd of 9.2 nm and displaces 125I-labeled CCL3 from CCR1-transfected cells with an IC50 of 74 nm. CP-481,715 lacks intrinsic agonist activity but fully blocks the ability of CCL3 and CCL5 to stimulate receptor signaling (guanosine 5'-O-(thiotriphosphate) incorporation; IC50 = 210 nm), calcium mobilization (IC50 = 71 nm), monocyte chemotaxis (IC50 = 55 nm), and matrix metalloproteinase 9 release (IC50 = 54 nm). CP-481,715 retains activity in human whole blood, inhibiting CCL3-induced CD11b up-regulation and actin polymerization (IC50 = 165 and 57 nm, respectively) on monocytes. Furthermore, it behaves as a competitive and reversible antagonist. CP-481,715 is >100-fold selective for CCR1 as compared with a panel of G-protein-coupled receptors including related chemokine receptors. Evidence for its potential use in human disease is suggested by its ability to inhibit 90% of the monocyte chemotactic activity present in 11/15 rheumatoid arthritis synovial fluid samples. These data illustrate that CP-481,715 is a potent and selective antagonist for CCR1 with therapeutic potential for rheumatoid arthritis and other inflammatory diseases.