ABT-869, a multitargeted receptor tyrosine kinase inhibitor, reduces tumor microvascularity and improves vascular wall integrity in preclinical tumor models.

N-[4-(3-amino-1H-indazol-4-yl)phenyl]-N1-(2-fluoro-5-methyl phenyl)-urea (ABT-869) is a novel multitargeted receptor tyrosine kinase inhibitor that demonstrates single-agent activity in preclinical studies and has undergone phase I and II clinical trials. We characterized the mechanism of action of ABT-869 by examining vascular changes after treatment (25 mg/kg per day) in HT1080 fibrosarcoma and SW620 colon carcinoma cells, using immunohistochemistry, dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI), and hypoxic protein detection. We observed the inhibition of vascular endothelial growth factor receptor 2 and platelet-derived growth factor receptor ß phosphorylation in both tumors and changes in tumor vasculature. Reductions in microvessel density and diameter were observed. Vascular-wall integrity was assessed by colocalization of pericytes and basement membrane. Although both microvessel density and total number of pericytes decreased with treatment, the percentage of pericyte coverage on remaining vessels significantly increased. These data suggest the selective ablation of microvessels lacking pericyte coverage. Functional vascular measures DCE-MRI and hypoxia formation were also tested. After 2 days of treatment on the HT1080 model, vascular permeability, K(trans), was reduced by >60% and hypoxic tumor fraction was significantly decreased, which was also seen in the SW620 tumors after 4 days of treatment. Taken together, decreases in vascular permeability and changes in vascular integrity observed in these studies define the mode of action of ABT-869 and may aid in optimizing the timing of therapeutic window for combination therapies.

Identification and characterization of novel antagonists of the CCR3 receptor.

Eotaxin, an inducer of eosinophil migration and activation, exerts its activity by binding to CCR3, the C-C chemokine receptor 3. An inhibitor of the eotaxin-CCR3 binding interaction may have potential as an anti-inflammatory drug for treatment of asthma, parasitic infections, and allergic disorders. A radioligand binding assay was developed using HEK cells transfected with CCR3, with (125)I eotaxin as the ligand. Whole cells grown on polylysine-coated plates were used as the receptor source for the screen. Screening of more than 200,000 compounds with this assay yielded a number of screening hits, and of these, 2 active novel antagonists were identified. These compounds showed inhibitory effects on eosinophil chemotaxis in both in vitro and in vivo assays.