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Cancer Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois

Requests for reprints: Daniel H. Albert, Cancer Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R47J, Building AP9/2, 100 Abbott Park Road, Abbott Park, IL 60064-3500. Phone: 847-937-3844; Fax: 847-935-3622. E-mail: daniel.h.albert{at}abbott.com

ABT-869 is a structurally novel, receptor tyrosine kinase (RTK) inhibitor that is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor families (e.g., KDR IC₅₀ = 4 nmol/L) but has much less activity (IC₅₀s > 1 µmol/L) against unrelated RTKs, soluble tyrosine kinases, or serine/threonine kinases. The inhibition profile of ABT-869 is evident in cellular assays of RTK phosphorylation (IC₅₀ = 2, 4, and 7 nmol/L for PDGFR-ß, KDR, and CSF-1R, respectively) and VEGF-stimulated proliferation (IC₅₀ = 0.2 nmol/L for human endothelial cells). ABT-869 is not a general antiproliferative agent because, in most cancer cells, >1,000-fold higher concentrations of ABT-869 are required for inhibition of proliferation. However, ABT-869 exhibits potent antiproliferative and apoptotic effects on cancer cells whose proliferation is dependent on mutant kinases, such as FLT3. In vivo ABT-869 is effective orally in the mechanism-based murine models of VEGF-induced uterine edema (ED₅₀ = 0.5 mg/kg) and corneal angiogenesis (>50% inhibition, 15 mg/kg). In tumor growth studies, ABT-869 exhibits efficacy in human fibrosarcoma and breast, colon, and small cell lung carcinoma xenograft models (ED₅₀ = 1.5–5 mg/kg, twice daily) and is also effective (>50% inhibition) in orthotopic breast and glioma models. Reduction in tumor size and tumor regression was observed in epidermoid carcinoma and leukemia xenograft models, respectively. In combination, ABT-869 produced at least additive effects when given with cytotoxic therapies. Based on pharmacokinetic analysis from tumor growth studies, efficacy correlated more strongly with time over a threshold value (cellular KDR IC₅₀ corrected for plasma protein binding = 0.08 µg/mL, 7 hours) than with plasma area under the curve or C_max. These results support clinical assessment of ABT-869 as a therapeutic agent for cancer. [Mol Cancer Ther 2006;5(4):995–1006]

¹ J. Li et al. ABT-869 a multi-targeted receptor tyrosine kinase inhibitor: inhibition of FLT3 phosphorylation and signaling in acute myeloid leukemia. Cancer Res, submitted for publication.

Received 10/ 7/05; revised 1/30/06; accepted 2/21/06.