A Neutralizing Prolactin Receptor Antibody Whose In Vivo Application Mimics the Phenotype of Female Prolactin Receptor-Deficient Mice

Abstract

The prolactin receptor (PRLR) has been implicated in a variety of physiological processes (lactation, reproduction) and diseases (breast cancer, autoimmune diseases). Prolactin synthesis in the pituitary and extrapituitary sites is regulated by different promoters. Dopamine receptor agonists such as bromocriptine can only interfere with pituitary prolactin synthesis and thus do not induce a complete blockade of PRLR signaling. Here we describe the identification of a human monoclonal antibody 005-C04 that blocks PRLR-mediated signaling at nanomolar concentrations in vitro. In contrast to a negative control antibody, the neutralizing PRLR antibody 005-C04 inhibits signal transducer and activator of transcription 5 phosphorylation in T47D cells and proliferation of BaF3 cells stably expressing murine or human PRLRs in a dose-dependent manner. In vivo application of this new function-blocking PRLR antibody reflects the phenotype of PRLR-deficient mice. After antibody administration female mice become infertile in a reversible manner. In lactating dams, the antibody induces mammary gland involution and negatively interferes with lactation capacity as evidenced by reduced milk protein expression in mammary glands and impaired litter weight gain. Antibody-mediated blockade of the PRLR in vivo stimulates hair regrowth in female mice. Compared with peptide-derived PRLR antagonists, the PRLR antibody 005-C04 exhibits several advantages such as higher potency, noncompetitive inhibition of PRLR signaling, and a longer half-life, which allows its use as a tool compound also in long-term in vivo studies. Therefore, we suggest that this antibody will help to further our understanding of the role of auto- and paracrine PRLR signaling in health and disease.

Preclinical Activity of the Novel Anti-Prolactin Receptor (PRLR) Antibody–Drug Conjugate REGN2878-DM1 in PRLR-Positive Breast Cancers

“…However, the clinical utility of these antagonists has been limited to date because of issues such as their short serum half-life and the immunogenicity and toxicity associated with the use of Pseudomonas exotoxin A. Recently, antibodies to PRLR such as LFA-102 and 005-C04 have demonstrated the ability to inhibit PRL-mediated signaling in vitro and in vivo (14,15,23). In a phase I study of LFA-102, doses of up to 60 mg/kg were tolerated, although they did not result in significant antitumor efficacy (24).…”

Monoclonal Antibody Against Prolactin Receptor: A Randomized Placebo-Controlled Study Evaluating Safety, Tolerability, and Pharmacokinetics of Repeated Subcutaneous Administrations in Postmenopausal Women

“…BAY 1158061 was derived from a precursor antibody that has been extensively preclinically characterized in vitro and in vivo. 20 The IgG2 format of BAY 1158061 was chosen to reduce effector function, that is, to exclude cytolytic activity as a result of its binding to target cells, thus preserving cell populations expressing PRLRs and avoiding irreversible treatment effects caused by cytolysis. 21 Safety, tolerability, and pharmacokinetics (PK) of increasing doses of BAY 1158061 after single subcutaneous (sc) dosing and the intended route of administration in patients were previously investigated in a single-dose escalation study in postmenopausal women.…”

“…Complete inhibition of PRL signaling was expected to lead to increased systemic PRL levels likely resulting from a compensatory feedback mechanism as observed in preclinical investigations (data on file). 20,22 A further aim of the study was to identify a suitable dose that would deliver sufficient drug exposure levels for therapeutic effects in future clinical studies by achieving plasma concentrations exceeding the human half maximal inhibitory concentration (IC 50 ) value (concentration required for >50% inhibition in an in vitro PRL signaling blocking assay) of BAY 1158061, that is, 0.17 mg/L, throughout a 28-day interval. 20 For the repeated-dose investigation, a parallel-group design was chosen.…”

“…20,22 A further aim of the study was to identify a suitable dose that would deliver sufficient drug exposure levels for therapeutic effects in future clinical studies by achieving plasma concentrations exceeding the human half maximal inhibitory concentration (IC 50 ) value (concentration required for >50% inhibition in an in vitro PRL signaling blocking assay) of BAY 1158061, that is, 0.17 mg/L, throughout a 28-day interval. 20 For the repeated-dose investigation, a parallel-group design was chosen. Three different dose regimens were simultaneously investigated by using blinded administrations once or twice a month.…”

“…BAY 1158061 was derived from a precursor antibody that has been extensively preclinically characterized in vitro and in vivo. 20 The IgG2 format of BAY 1158061 was chosen to reduce effector function, that is, to exclude cytolytic activity as a result of its binding to target cells, thus preserving cell populations expressing PRLRs and avoiding irreversible treatment effects caused by cytolysis. 21…”