Neurosteroids: Structure-Uptake Relationships and Computational Modeling of Organic Anion Transporting Polypeptides (OATP)1A2

Abstract

In this study, we investigated the delivery of synthetic neurosteroids into MCF-7 human breast adenocarcinoma cells via Organic Anionic Transporting Polypeptides (OATPs) (pH 7.4 and 5.5) to identify the structural components required for OATP-mediated cellular uptake and to get insight into brain drug delivery. Then, we identified structure-uptake relationships using in-house developed OATP1A2 homology model to predict binding sites and modes for the ligands. These binding modes were studied by molecular dynamics simulations to rationalize the experimental results. Our results show that carboxylic acid needs to be at least at 3 carbon-carbon bonds distance from amide bond at the C-3 position of the androstane skeleton and have an amino group to avoid efflux transport. Replacement of hydroxyl group at C-3 with any of the 3, 4, and 5-carbon chained terminal carboxylic groups improved the affinity. We attribute this to polar interactions between carboxylic acid and side-chains of Lys33 and Arg556. The additional amine group showed interactions with Glu172 and Glu200. Based on transporter capacities and efficacies, it could be speculated that the functionalization of acetyl group at the C-17 position of the steroidal skeleton might be explored further to enable OAT1A2-mediated delivery of neurosteroids into the cells and also across the blood-brain barrier.

Comparative Modelling of Organic Anion Transporting Polypeptides: Structural Insights and Comparison of Binding Modes

“…This arginine displays stable polar contacts in either the ligand’s carboxylate or carbonyl groups ( Figure 8 D,E), along the analysed trajectory, besides its interactions with Glu/Asp on TM2. Interestingly, TM11′s arginine is relevant to substrate transport on 1B1/1B3 [ 26 , 36 ], which supports the relevance of Arg (TM11) with the ligand.…”

“…Our work, on the other hand, aimed to use unbiased simulations to analyse relevant conformational changes in selected conserved motifs, to generate a dynamic ensemble of novel OATP models. It is relevant to notice that longer simulations of OATP1A2 have shown conformational changes, predicting open and closed states of the transporter [ 36 ].…”

Pharmacoproteomics of Brain Barrier Transporters and Substrate Design for the Brain Targeted Drug Delivery

“…Thus, due to the current limitations of structure-based molecular modeling, and improvements in the data accuracy and treatment consistency, ligand-based molecular modeling approaches, such as 3-dimensional quantitative structure-activity relationship (3D-QSAR) and pharmacophore modeling, have retained their favor in predicting the interactions with the transporters based on their molecular properties (125,126). We have recently found some critical structure-activity relationships (SAR) between novel neurosteroids and OATP1A2-mediated transport with the aid of the MDS (20). Structurally, a 3α5βandrostane core can be functionalized at both ends of C-3 and C-17 positions (Fig.…”

“…Since the transport carriers dynamically change their conformations to exert their function, the relationship between the substrate and the transport activity based on the crystal structure can be limited. On the other hand, Molecular Dynamics Simulations (MDS) can enable clarification of the dynamic structural changes of transporter proteins and elucidate the substrate recognition and translocation through the protein cavity (19)(20)(21).…”

Preparation, Characterization, and Evaluation of Liposomes Containing Oridonin from Rabdosia rubescens

“…The cytotoxicity of Ori solution, Ori liposomes, and blank liposomes on MCF-7 breast cancer cells was determined using MTT assay. MCF-7 cells in log phase of growth were seeded into a 96-well plate at a density of 8 × 10 3 cells/well and then incubated at 37 • C and 5% CO 2 for 24 h [26]. Different concentrations (10,20,30,40, 50 µmol/L) of Ori liposomes and Ori solution were added.…”