A systems approach to modeling drug release from polymer microspheres to accelerate in vitro to in vivo translation

Design of PLGA-Based Drug Delivery Systems Using a Physically-Based Sustained Release Model

An extensive data set has been developed and used to further the progress of a model-informed design of controlled drug release. An improved drug-release model with mechanistic modeling of hydrolytic polymer degradation is used and validated by comparing model predictions to in vitro experiments. Combining parameter estimates from the literature with model fits to the data set, this study can aid in achieving a priori design of controlled drug release from a model PLGA release system. A systematic series of model release systems were formulated with FITC-labeled dextran, as a surrogate for biopharmaceuticals, in PLGA rods over a broad range of compositions. While general comparisons between the model and experiments were favorable, important discrepancies were identified for several formulations with significant first-phase drug release. Supported by cross-sectional fluorescence microscopy images of the FITC-dextran distribution within the rods, this first-phase release was attributed to a combination of two main factors: (1) percolation of the drug particles and (2) swelling of and pore formation in the rods due to water uptake. These observations indicate the importance of careful selection of the PLGA polymer grade when designing drug release systems but also reflect a need for better understanding of phenomena such as pore formation. Adapting model parameters, without modifying the physical processes included in the model, enabled accurate fitting of the experimental data for all formulations, highlighting the applicability of the model.

Quality by design thinking in the development of long-acting injectable PLGA/PLA-based microspheres for peptide and protein drug delivery

Adopting the Quality by Design (QbD) approach in the drug development process has transformed from "nice-to-do" into a crucial and required part of the development, ensuring the quality of pharmaceutical products throughout their whole life cycles. This review is discussing the implementation of the QbD thinking into the production of long-acting injectable (LAI) PLGA/PLA-based microspheres for the therapeutic peptide and protein drug delivery. Various key elements of the QbD approaches are initially elaborated using Bydureon®, a commercial product of LAI PLGA/PLA-based microspheres, as a classical example. Subsequently, the factors influencing the release patterns and the stability of the peptide and protein drugs are discussed. This is followed by a summary of the state-of-the-art of manufacturing LAI PLGA/PLA-based microspheres and the related critical process parameters (CPPs). Finally, a landscape of generic product development of LAI PLGA/PLA-based microspheres is reviewed including some major challenges in the field.

Data-Driven Development of Predictive Models for Sustained Drug Release

Mathematical modeling of drug release can aid in the design and development of sustained delivery systems, but the parameter estimation of such models is challenging owing to the nonlinear mathematical structure and complexity and interdependency of the physical processes considered. Highly parameterized models often lead to overfitting, strong parameter correlations, and as a consequence, inaccurate model predictions for systems not explicitly part of the fitting database. Here, we show that an efficient stochastic optimization algorithm can be used not only to find robust estimates of global minima to such complex problems but also to generate metadata that allow quantitative evaluation of parameter sensitivity and correlation, which can be used for further model refinement and development. A practical methodology is described through the analysis of a predictive drug release model on published experimental data sets. The model is then used to design a zeroth-order release profile in an experimental system consisting of an antibody fragment in a poly(lactic-co-glycolic acid) solvent depot, which is validated experimentally. This approach allows rational decision-making when developing new models, selecting models for a specific application, or designing formulations for experimental trials.

ROS responsive resveratrol delivery from LDLR peptide conjugated PLA-coated mesoporous silica nanoparticles across the blood-brain barrier

Background

Oxidative stress acts as a trigger in the course of neurodegenerative diseases and neural injuries. An antioxidant-based therapy can be effective to ameliorate the deleterious effects of oxidative stress. Resveratrol (RSV) has been shown to be effective at removing excess reactive oxygen species (ROS) or reactive nitrogen species generation in the central nervous system (CNS), but the delivery of RSV into the brain through systemic administration is inefficient. Here, we have developed a RSV delivery vehicle based on polylactic acid (PLA)-coated mesoporous silica nanoparticles (MSNPs), conjugated with a ligand peptide of low-density lipoprotein receptor (LDLR) to enhance their transcytosis across the blood–brain barrier (BBB).

Results

Resveratrol was loaded into MSNPs (average diameter 200 nm, pore size 4 nm) at 16 μg/mg (w/w). As a gatekeeper, the PLA coating prevented the RSV burst release, while ROS was shown to trigger the drug release by accelerating PLA degradation. An in vitro BBB model with a co-culture of rat brain microvascular endothelial cells (RBECs) and microglia cells using Transwell chambers was established to assess the RSV delivery across BBB. The conjugation of LDLR ligand peptides markedly enhanced the migration of MSNPs across the RBECs monolayer. RSV could be released and effectively reduce the activation of the microglia cells stimulated by phorbol-myristate-acetate or lipopolysaccharide.

Conclusions

These ROS responsive LDLR peptides conjugated PLA-coated MSNPs have great potential for oxidative stress therapy in CNS.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0340-7) contains supplementary material, which is available to authorized users.

Synergistic dual-pH responsive copolymer micelles for pH-dependent drug release

The tuning of the structure of nanocarriers with fast acidic-degradation rate and high stability in physiological conditions or during storage is under intensive study. In this context, a kind of dual-pH responsive micelles with well-balanced stability, that is, fast hydrolysis in acidic environment and stability towards blood drug release at 7.4 were developed. This is achieved by the self-assembly of micelles of poly(ethylene glycol)-b-(poly ε-caprolactone-g-poly(2,2-dimethyl-1,3-dioxolane-4-yl)methylacrylate-co-2(dimethylamino)ethyl methacrylate) (mPEG-b-(PCL-g-P(DA-co-DMAEMA))) copolymers with two inert pH responsive moieties of DA and DMAEMA. The fast synergistic acid-triggered disassembly and high stability at physiological condition of the mPEG-b-(PCL-g-P(DA-co-DMAEMA)) micelles was verified by (1)H NMR, particle size and optical stability measurements, which was induced and mediated by the synergistic pH responses of the hydrolysis of the ketal in DA moieties and the switch in solubility of tertiary amino moieties (DMAEMA) under mild acid conditions. It was observed that the hydrolysis rate of the ketal could be promoted by increasing the content of DMAEMA moieties. The fast intracellular disassembly of the micelles depending on the contents of DMAEMA moieties was also traced by fluorescence resonance energy transfer (FRET). The in vitro release studies showed that the release of DOX from mPEG-b-(PCL-g-P(DA-co-DMAEMA)) micelles at mild acid condition was significantly accelerated by increasing the content of DMAEMA moieties, while greatly impeding drug release in physiological conditions. The antitumor activity of DOX-loaded micelles was studied in MCF-7 and 4T1 cells in vitro and in 4T1 tumor-bearing Balb-c mice in vivo. The results indicated the DOX-loaded micelles with higher content of DMAEMA moieties exhibited enhanced anticancer activity. Collectively, the synergistic dual-pH responsive design of mPEG-b-(PCL-g-P(DA-co-DMAEMA)) micelles provided a new route for improving anticancer drug delivery efficiency.