Small Molecule Proprotein Convertase Inhibitors for Inhibition of Embryo Implantation

Huiting Ho,Harmeet Singh,Guan-Sheng Jiao,Alan T Johnson,Michael W Parker,Tracy L Nero,Guiying Nie,Sarah Paule,Sophea Heng,Haibin Wang

doi:10.1371/journal.pone.0081380

Abstract

Uterine proprotein convertase (PC) 6 plays a critical role in embryo implantation and is pivotal for pregnancy establishment. Inhibition of PC6 may provide a novel approach for the development of non-hormonal and female-controlled contraceptives. We investigated a class of five synthetic non-peptidic small molecule compounds that were previously reported as potent inhibitors of furin, another PC member. We examined (i) the potency of these compounds in inhibiting PC6 activity in vitro; (ii) their binding modes in the PC6 active site in silico; (iii) their efficacy in inhibiting PC6-dependent cellular processes essential for embryo implantation using human cell-based models. All five compounds showed potent inhibition of PC6 activity in vitro, and in silico docking demonstrated that these inhibitors could adopt a similar binding mode in the PC6 active site. However, when these compounds were tested for their inhibition of decidualization of primary human endometrial stromal cells, a PC6-dependent cellular process critical for embryo implantation, only one (compound 1o) showed potent inhibition. The lack of activity in the cell-based assay may reflect the inability of the compounds to penetrate the cell membrane. Because compound's lipophilicity is linked to cell penetration, a measurement of lipophilicity (logP) was calculated for each compound. Compound 1o is unique as it appears the most lipophilic among the five compounds. Compound 1o also inhibited another crucial PC6-dependent process, the attachment of human trophoblast spheroids to endometrial epithelial cells (a model for human embryo attachment). We thus identified compound 1o as a potent small molecule PC6 inhibitor with pharmaceutical potential to inhibit embryo implantation. Our findings also highlight that human cell-based functional models are vital to complement the biochemical and in silico analyses in the selection of promising drug candidates. Further investigations for compound 1o are warranted in animal models to test its utility as an implantation-inhibiting contraceptive drug.

Highlights

The proprotein convertases (PCs) are a family of nine serine proteases implicated in the processing of a multitude of precursor proteins [1,2]
The four guanidino substituents on the 2,5dideoxystreptamine ring can adopt a variety of conformations within the human PC6 (hPC6) active site; the 2,5-dideoxystreptamine ring is physically restricted to the triangular region connecting subpockets S1, S2 and S19 (Figure 3)
PC6 plays a crucial role in embryo implantation and HIV infection; it is highly desirable to develop inhibitors of PC6 for potential non-hormonal female contraceptives that could protect women from HIV

Summary

Introduction

The proprotein convertases (PCs) are a family of nine serine proteases implicated in the processing of a multitude of precursor proteins [1,2]. The uterus must acquire epithelial receptivity and undergo a process known as decidualization to differentiate stromal fibroblasts into phenotypically and functionally distinct decidual cells [5]. Decidualization of primary human endometrial stromal cells (HESCs) was inhibited when PC6 activity was blocked [8,10]. It has been demonstrated in mice that when uterine PC6 production was blocked, decidualization was inhibited and implantation was prevented [11]. PCs including PC6 play an important role in HIV infection [12,13,14]. Inhibition of PC6 is an attractive approach to develop novel, non-hormonal and female-controlled contraceptives that could protect women from HIV infection

Methods

Results

Conclusion