Structural basis for the potent and selective binding of LDN-212854 to the BMP receptor kinase ALK2.

Eleanor Williams,Alex N Bullock

doi:10.1016/j.bone.2017.09.004

Abstract

Individuals with the rare developmental disorder fibrodysplasia ossificans progressiva (FOP) experience disabling heterotopic ossification caused by a gain of function mutation in the intracellular region of the BMP type I receptor kinase ALK2, encoded by the gene ACVR1. Small molecule BMP type I receptor inhibitors that block this ossification in FOP mouse models have been derived from the pyrazolo[1,5-a]pyrimidine scaffold of dorsomorphin. While the first derivative LDN-193189 exhibited pan inhibition of BMP receptors, the more recent compound LDN-212854 has shown increased selectivity for ALK2. Here we solved the crystal structure of ALK2 in complex with LDN-212854 to define how its binding interactions compare to previously reported BMP and TGFβ receptor inhibitors. LDN-212854 bound to the kinase hinge region as a typical type I ATP-competitive inhibitor with a single hydrogen bond to ALK2 His286. Specificity arising from the 5-quinoline moiety was associated with a distinct pattern of water-mediated hydrogen bonds involving Lys235 and Glu248 in the inactive conformation favoured by ALK2. The structure of this complex provides a template for the design of future ALK2 inhibitors under development for the treatment of FOP and other related conditions of heterotopic ossification.

Highlights

Individuals with the rare developmental disorder fibrodysplasia ossificans progressiva (FOP) experience disabling heterotopic ossification caused by a gain of function mutation in the intracellular region of the BMP type I receptor kinase ALK2, encoded by the gene ACVR1
Type I receptors ALK1/ACVRL1, ALK2/ACVR1, ALK3/BMPR1A and ALK6/BMPR1B all participate in BMP signalling and phosphorylate SMAD1/5/8
Fibrodysplasia ossificans progressiva (FOP) is a rare monogenic condition in which a gain of function germline mutation in ACVR1 leads to increased signalling through ALK2 in response to BMP ligands as well as neofunction in response to Activin A and the consequent formation of heterotopic bone in muscle and connective tissue [11,12]

Summary

Introduction

Individuals with the rare developmental disorder fibrodysplasia ossificans progressiva (FOP) experience disabling heterotopic ossification caused by a gain of function mutation in the intracellular region of the BMP type I receptor kinase ALK2, encoded by the gene ACVR1. Specificity arising from the 5-quinoline moiety was associated with a distinct pattern of water-mediated hydrogen bonds involving Lys235 and Glu248 in the inactive conformation favoured by ALK2 The structure of this complex provides a template for the design of future ALK2 inhibitors under development for the treatment of FOP and other related conditions of heterotopic ossification. A second series of pyridinebased small molecule BMP type I receptor inhibitors was identified from a biochemical screen against the purified ALK2 kinase domain (Fig. 1b). The compound LDN-212854 is of particular interest for the development of inhibitors against heterotopic ossification It has demonstrated notable efficacy in two different mouse models, including one using an inducible constitutively-active ACVR1Q207D transgene [33] and another harboring an Acvr1R206H knock-in allele that more faithfully recapitulates human FOP [39]. We determined the crystal structure of ALK2 in complex with LDN-212854 revealing subtle differences in its binding compared to LDN-193189

Methods

Results

Conclusion