An in vivo half-life extended prolactin receptor antagonist can prevent STAT5 phosphorylation

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• The prolactin/prolactin receptor axis fuels the growth of various cancers, including glioblastoma, breast, and ovarian carcinomas.
• Existing prolactin receptor antagonists have limited clinical use due to their short in vivo half-life.

Purpose of the Study:

• To develop a fusion protein combining a prolactin receptor antagonist (PrlRA) with an albumin-binding domain to enhance its half-life for potential cancer drug applications.

Main Methods:

• The fusion protein was expressed in Escherichia coli, refolded, and purified.
• Binding affinities for the prolactin receptor and mouse serum albumin were determined using dissociation constants (KD).
• Inhibition of prolactin-mediated STAT5 phosphorylation was assessed in vitro, and in vivo pharmacokinetics were evaluated in rats.

Main Results:

• The fusion protein demonstrated high affinity for both the prolactin receptor (KD = 2.3±0.2 nM) and mouse serum albumin (KD = 0.38±0.01 nM).
• It effectively inhibited STAT5 phosphorylation at concentrations of 100 nM and above, comparable to PrlRA alone.
• Complexation with human serum albumin (HSA) slightly reduced receptor affinity but retained STAT5 inhibition efficacy.
• In rats, the fusion protein exhibited a 100-fold higher blood concentration after 24 hours compared to PrlRA.

Conclusions:

• The engineered fusion protein successfully extends the half-life of the prolactin receptor antagonist.
• This enhanced protein maintains potent inhibition of prolactin signaling, indicating significant potential as a future cancer therapeutic agent.