Deglycosylation of a bifunctional lutropin-follitropin agonist reduced itsfollitropin activity more than its lutropin activity

Objective: To design a drug that blocks the gonadal actions of lutropins an d follitropins. Design: Controlled in vitro study. Setting: Academic laboratory. Patient(s): None. Intervention(s): We removed three glycosylation signals from an hCG-hFSH ch imera known to have high affinity for LH and FSH receptors, expecting this would create a bifunctional antagonist (dgCFC). To offset the inhibition of subunit combination caused by deglycosylation of alpha-subunit loop 2, we prepared dgCFC as a single-chain fusion protein containing the alpha-subuni t downstream of the chimeric beta-subunit. Main Outcome Measure(s): Receptor binding, cyclic adenosine monophosphate a ccumulation. Result(s): dgCFC bound LH or FSH receptors similar to hCG or hFSH. It was a partial agonist and had one tenth the efficacy of hFSH and two thirds the efficacy of hCG. Conclusion(s): The surprising high residual lutropin activity of dgCFC indi cated that its FSH residues offset the effects of deglycosylation, suggesti ng this approach to preparing a bifunctional antagonist is unlikely to lead to a useful drug. The increased lutropin efficacy of dgCFC relative to deg lycosylated hCG supports the idea that oligosaccharides modulate glycoprote in hormone efficacy through an influence on hormone conformation. (C) 1999 by American Society for Reproductive Medicine.