Novel reagents for human prolactin research: large-scale preparation and characterization of prolactin receptor extracellular domain, non-pegylated and pegylated prolactin and prolactin receptor antagonist

Preparation of Superactive Prolactin Receptor Antagonists

Most breast cancer deaths are caused by malignant estrogen receptor-positive breast tumors that later recur as metastatic disease. Prolactin (PRL) has been documented as a factor promoting breast cancer development and metastasis. We therefore developed superactive prolactin receptor (PRLR) antagonists aimed at blocking PRL action. We purified 12 novel mutants to homogeneity as monomers, and the most potent antagonist was over 95-fold more active than the previously reported weak antagonist, the mutant Del 1-9 human PRL G129R. This enhanced antagonistic activity resulted mostly from prolonged interaction with the extracellular domain (ECD) of PRLR. All mutants were properly refolded, as indicated by interaction with human PRLR-ECD and by circular dichroism analysis. We then prepared monopegylated variants of the most active mutants to extend their biological half-life in vivo.

Periplasmic synthesis and purification of the human prolactin antagonist Δ1-11-G129R-hPRL

The human prolactin antagonist Δ_1-11-G129R-hPRL is a 21.9 kDa recombinant protein with 188 amino acids that downregulates the proliferation of a variety of cells expressing prolactin receptors. Periplasmic expression of recombinant proteins in E. coli has been considered an option for obtaining a soluble and correctly folded protein, as an alternative to cytoplasmic production. The aim of this work was, therefore, to synthesize for the first time, the Δ_1-11-G129R-hPRL antagonist, testing different activation temperatures and purifying it by classical chromatographic techniques. E. coli BL21(DE3) strain was transformed with a plasmid based on the pET25b( +) vector, DsbA signal sequence and the antagonist cDNA sequence. Different doses of IPTG were added, activating under different temperatures, and extracting the periplasmic fluid via osmotic shock. The best conditions were achieved by activating at 35 °C for 5 h using 0.4 mM IPTG, which gave a specific expression of 0.157 ± 0.015 μg/mL/A₆₀₀ at a final optical density of 3.43 ± 0.13 A₆₀₀. Purification was carried out by nickel-affinity chromatography followed by size-exclusion chromatography, quantification being performed via high-performance size-exclusion chromatography (HPSEC). The prolactin antagonist was characterized by SDS-PAGE, Western blotting, reversed-phase high-performance liquid chromatography (RP-HPLC) and MALDI-TOF–MS. The final product presented > 95% purity and its antagonistic effects were evaluated in vitro in view of potential clinical applications, including inhibition of the proliferation of cancer cells overexpressing the prolactin receptor and specific antidiabetic properties, taking also advantage of the fact that this antagonist was obtained in a soluble and correctly folded form and without an initial methionine.

Preparation, Characterization and Pharmacokinetic Study of N-Terminal PEGylated D-Form Antimicrobial Peptide OM19r-8

Recently, new cationic antibacterial peptide OM19R has been designed with low minimum inhibitory concentration (MIC) values against some gram-negative bacteria, such as Escherichia coli, Salmonella, and Shigella. However, this hybrid peptide, like most antibacterial peptides, has low enzyme stability and short half-life, which, in turn, increases the drug's cost. In this study, an antibacterial peptide (OM19r-8) was obtained containing some D-Arg amino acids. The new preparations were carried out through the replacement of l-Arginine by d-Arginine and the addition of PEG chains. Firstly, eight OM19r series of antibacterial peptides were obtained by designing D-Arg. Then, a polyethylene glycol-modified product mPEG₅-butyrALD-OM19r-8 (mPEG₅-OM19r-8) was isolated and purified by reverse-phase high-performance liquid chromatography (RT-HPLC). The enzyme stability test showed that the resistance of antibacterial peptide OM19r-8 to protease degradation increased by 4-32-fold. Moreover, the Time-kill studies showed that the germicidal kinetics curves of mPEG₅-OM19r-8 and OM19r-8 to Escherichia coli had a similar trend, thus suggesting that PEG modification has an acceptable effect on the activity of the original peptide. Furthermore, the elimination of half-life (28.09 ± 2.81min) of mPEG₅-OM19r-8, and the area under the drug concentration-time curve (2686.48 ± 651.36min∗ug/ml) was significantly prolonged. The current study demonstrates an example that optimizes the AMP by utilizing L-to-D amino acid replacement and including PEG chains. These results provide useful data for the clinical application of the mPEG₅-OM19r-8.

The role of the prolactin receptor pathway in the pathogenesis of glioblastoma: what do we know so far?

Introduction: Prolactin (PRL) and its receptor (PRLR) have been associated with the development of hormone-dependent tumors and have been detected in glioblastoma (GBM) biopsies. GBM is the most common and aggressive primary brain tumor in adults and the prognosis for patients is dismal; hence researchers are exploring the PRLR pathway as a therapeutic target in this disease. Areas covered: This paper explores the effects of PRLR activation on the biology of GBM, the correlation between PRL and PRLR expression and GBM progression and survival in male and female patients. Finally, we discuss how a better understanding of the PRLR pathway may allow the development of novel treatments for GBM. Expert opinion: We propose PRL and PRLR as potential prognosis biomarkers and therapeutic targets in GBM. Local administration of PRLR inhibitors using gene therapy may offer a beneficial strategy for targeting GBM cells disseminated in the non-neoplastic brain; however, efficacy and safety require careful and extensive evaluation. The data depicted herein underline the need to (i) improve our understanding of sexual dimorphism in GBM, and (ii) develop accurate preclinical models that take into consideration different hormonal contexts, specific genetic alterations, and tumor grades.

From Synthesis to Characterization of Site-Selective PEGylated Proteins

Covalent attachment of therapeutic proteins to polyethylene glycol (PEG) is widely used for the improvement of its pharmacokinetic and pharmacological properties, as well as the reduction in reactogenicity and related side effects. This technique named PEGylation has been successfully employed in several approved drugs to treat various diseases, even cancer. Some methods have been developed to obtain PEGylated proteins, both in multiple protein sites or in a selected amino acid residue. This review focuses mainly on traditional and novel examples of chemical and enzymatic methods for site-selective PEGylation, emphasizing in N-terminal PEGylation, that make it possible to obtain products with a high degree of homogeneity and preserve bioactivity. In addition, the main assay methods that can be applied for the characterization of PEGylated molecules in complex biological samples are also summarized in this paper.

Pegylated Human Leptin D23L Mutant-Preparation and Biological Activity In Vitro and In Vivo in Male ob/ob Mice

Recombinant monomeric human leptin (hLEP) and its D23L mutant were prepared in Escherichia coli and pegylated at their N-terminus using 20-kDa methoxy pegylated (PEG)-propionylaldehyde. As determined by both SDS-PAGE and size-exclusion chromatography, the pegylated proteins consisted of >90% monopegylated and <10% double-pegylated species. Circular dichroism spectra showed that their secondary structure, characteristic of all four α-helix bundle cytokines, was not affected by either the D23L mutation or pegylation. Because of the D23L mutation, affinity for hLEP receptor increased 25- and 40-fold for the pegylated and nonpegylated mutant, respectively. However, whereas the proliferation-promoting activity in vitro of nonmutated and mutated nonpegylated hLEP was identical, that of the respective pegylated mutant was approximately sixfold higher compared with the pegylated nonmutated hLEP. This difference was also seen in vivo. Both pegylated hLEPs at all doses significantly decreased body weight and food consumption, as compared with the vehicle-treated control. Once-daily administration of pegylated hLEP D23L at doses of 0.1, 0.3, and 1 mg/kg for 14 consecutive days in ob/ob mice resulted in significantly decreased body weight and food consumption as compared with respective pegylated hLEP-treated animals, with the biggest difference observed at 0.1 mg/kg. Repeated administration of either pegylated hLEP D23L or pegylated hLEP significantly decreased blood glucose levels compared with the control before glucose challenge and after oral glucose tolerance test, but with no difference between the two treatments. The pegylated hLEP D23L mutant seems to be a more potent reagent suitable for in vivo studies than the pegylated nonmutated hLEP.