SAR of Carbon‐Linked, 2‐Substituted Purines: Synthesis and Characterization of AP23451 as a novel Bone‐Targeted Inhibitor of Src Tyrosine Kinase With In Vivo Anti‐Resorptive Activity

Abstract

Targeted disruption of the pp60(src) (Src) gene has implicated this tyrosine kinase in osteoclast-mediated bone resorption and as a therapeutic target for the treatment of osteoporosis and other bone-related diseases. Here, we describe structure activity relationships of a novel series of carbon-linked, 2-substituted purines that led to the identification of AP23451 as a potent inhibitor of Src tyrosine kinase with antiresorptive activity in vivo. AP23451 features the use of an arylphosphinylmethylphosphinic acid moiety which confers bone-targeting properties to the molecule, thereby increasing local concentrations of the inhibitor to actively resorbing osteoclasts at the bone interface. AP23451 exhibited an IC50 = 68 nm against Src kinase; an X-ray crystal structure of the molecule complexed with Src detailed the molecular interactions responsible for its Src inhibition. In vivo, AP23451 demonstrated a dose-dependent decrease in PTH-induced hypercalcemia. Moreover, AP23517, a structurally and biochemically similar molecule with comparable activity (IC50 = 73 nm) except devoid of the bone-targeting element, demonstrated significantly reduced in vivo efficacy, suggesting that Src activity was necessary but not sufficient for in vivo activity in this series of compounds.

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“…5A). Since this may not show a VEGF-Cdependent mechanism because no resorption occurred in Src Ϫ/Ϫ osteoclasts even in the absence of VEGF-C, we used an Src inhibitor that we demonstrated previously to reduce bone resorption (42) and PTH-induced hypercalcemia (43). We found that it also prevented VEGF-C-induced osteoclastic bone resorption (Fig.…”

Development and experimental test of support vector machines virtual screening method for searching Src inhibitors from large compound libraries

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