James Kanter

Platelet and osteoclast β3 integrins are critical for bone metastasis

Mice with a targeted deletion of β3 integrin were used to examine the process by which tumor cells metastasize and destroy bone. Injection of B16 melanoma cells into the left cardiac ventricle resulted in osteolytic bone metastasis in 74% of β3+/+ mice by 14 days. In contrast, only 4% of β3–/– mice developed bone lesions. Direct intratibial inoculation of tumor resulted in marrow replacement by tumor in β3–/– mice, but no associated trabecular bone resorption as seen inβ3+/+ mice. Bone marrow transplantation studies showed that susceptibility to bone metastasis was conferred by a bone marrow-derived cell. To dissect the roles of osteoclast and platelet β3 integrins in this model of bone metastasis, osteoclast-defective src–/– mice were used. Src-null mice were protected from tumor-associated bone destruction but were not protected from tumor cell metastasis to bone. In contrast, a highly specific platelet aggregation inhibitor of activated αIIbβ3 prevented B16 metastases. These data demonstrate a critical role for platelet αIIbβ3 in tumor entry into bone and suggest a mechanism by which antiplatelet therapy may be beneficial in preventing the metastasis of solid tumors.

Discovery of betrixaban (PRT054021), N-(5-chloropyridin-2-yl)-2-(4-(N,N-dimethylcarbamimidoyl)benzamido)-5-methoxybenzamide, a highly potent, selective, and orally efficacious factor Xa inhibitor.

Systematic SAR studies of in vitro factor Xa inhibitory activity around compound 1 were performed by modifying each of the three phenyl rings. A class of highly potent, selective, efficacious and orally bioavailable direct factor Xa inhibitors was discovered. These compounds were screened in hERG binding assays to examine the effects of substitution groups on the hERG channel affinity. From the leading compounds, betrixaban (compound 11, PRT054021) has been selected as the clinical candidate for development.

Design, synthesis, and SAR of substituted acrylamides as factor Xa inhibitors.

Substituted acrylamides were used as templates that bridge P1 and P4 binding elements, resulting in a series of potent (sub-nanomolar) and selective factor Xa inhibitors. In this template, cis-geometry of P1 and P4 ligands is highly preferred. SAR on the substituting groups, as well as on modification of P1 and P4 moieties is described. Compounds in this series show good in vivo efficacy in animal models.

Design and synthesis of glycolic and mandelic acid derivatives as factor Xa inhibitors

A series of glycolic and mandelic acid derivatives was synthesized and investigated for their factor Xa inhibitory activity. These analogues are highly potent and selective inhibitors against fXa. In a rabbit deep vein thrombosis model, compound 26 showed significant antithrombotic effects (81% inhibition of thrombus formation) at 1.1 microM plasma concentration following intravenous administration.