A long-acting GH receptor antagonist through fusion to GH binding protein

Abstract

Acromegaly is a human disease of growth hormone (GH) excess with considerable morbidity and increased mortality. Somatostatin analogues are first line medical treatment but the disease remains uncontrolled in up to 40% of patients. GH receptor (GHR) antagonist therapy is more effective but requires frequent high-dose injections. We have developed an alternative technology for generating a long acting potent GHR antagonist through translational fusion of a mutated GH linked to GH binding protein and tested three candidate molecules. All molecules had the amino acid change (G120R), creating a competitive GHR antagonist and we tested the hypothesis that an amino acid change in the GH binding domain (W104A) would increase biological activity. All were antagonists in bioassays. In rats all antagonists had terminal half-lives >20 hours. After subcutaneous administration in rabbits one variant displayed a terminal half-life of 40.5 hours. A single subcutaneous injection of the same variant in rabbits resulted in a 14% fall in IGF-I over 7 days. In conclusion: we provide proof of concept that a fusion of GHR antagonist to its binding protein generates a long acting GHR antagonist and we confirmed that introducing the W104A amino acid change in the GH binding domain enhances antagonist activity.

Targeting growth hormone function: strategies and therapeutic applications

“…More recently Wilkinson et al demonstrated that fusion of GHBP to a GHR antagonist protein similar to B2036 significantly reduced IGF1 by 14% after a single subcutaneous injection in rabbits and may be useful for treating acromegaly. 128 Introduction of a W104A mutation in the fused GHBP prevented intra- and inter-molecular binding. Three chimeric GHR antagonists were generated with extended in vivo clearance times; the terminal half-life of the fusion proteins was greater than 20 h in rats.…”

“…Three chimeric GHR antagonists were generated with extended in vivo clearance times; the terminal half-life of the fusion proteins was greater than 20 h in rats. 128…”

Pegvisomant: uso clínico en pacientes con acromegalia

“…La GH posee una estructura tridimensional que comprende cuatro hélices alfa, empaquetadas estrechamente con cadenas adyacentes no helicoidales en un haz antiparalelo que contiene dos puentes de disulfuro (18,20). Las hélices antiparalelas se conectan en un patrón de "arriba-arriba-abajo-abajo" con el núcleo del haz de cuatro hélices que contribuye a estabilizar la estructura y a mantener la configuración empaquetada (21), posee dos dominios de unión al receptor separados: el sitio 1 y el sitio 2 (22), donde el sitio 1 es de alta afinidad mientras que el 2 es más débil (23).…”

“…Fuente: elaboración propia. (20,23) y se compone de aproximadamente 620 aminoácidos (19), este se encuentra en diferentes tejidos como hígado, tejido adiposo, músculo, próstata, riñón, placenta, corazón, cerebro y glándula mamaria (21,27).…”

“…El receptor se elimina mediante su degradación proteolítica y un proceso continuo de internalización dependiente de ubiquitina y degradación endolisosómica (29). La escisión proteolítica del dominio extracelular genera GHBP (19,23) y aunque su función no es clara, se considera que funciona como un reservorio de GH, modula su actividad al competir con el GHR (19), reduce la tasa de eliminación (17) y sirve como marcador de la renovación de GHR (20).…”