Pharmaceutical Physical Chemistry
The goal with our research is to clarify the relationships between the molecular structure of drug molecules, their physicochemical properties and the possibilities to control how they are stored in and released from different types of particulate drug carriers and formulations. The purpose is to create new knowledge making it possible to develop new or improved systems for the administration of drugs, including macromolecular drugs such as peptides and proteins, and small and amphiphilic drug molecules including cancer drugs. In our investigations we use a combination of experimental and theoretical methods. The experimental techniques include static and dynamic light scattering, small-angle x-ray scattering, small-angle neutron scattering, micropipette-assisted microscopy, confocal microscopy, atomic force microscopy, ellipsometry, and static and time-resolved fluorescence methods.
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Image of flow pipette microscopy of single microgels with LRI Olympus BX-51 light microscope
Subcutaneous drug delivery
The rapidly growing biopharmaceutical market has been driven by the discovery of new molecules and innovative therapies with great medical potential. However, large classes of the newly available molecules are not suitable for oral and intravenous administration. Subcutaneous (SC) injection is an important alternative administration route but the way biopharmaceuticals behave immediately after administration is still largely unknown. SC therapies used today are characterized by incomplete and variable bioavailability often related to the use of widely different types of formulations, different sites and methods of injection, and the physiological responses to the tissue damage and stress that might be the consequence of an injected formulation.
Our research in this field is part of the parenteral drug delivery platform of the Swedish Drug Delivery Forum (SDDF). We develop novel in vitro methods that can predict the behaviour of drug formulations after SC administration. As part of the work we study how the constituents of the extracellular matrix in human SC adipose tissue interact with formulations of biotherapeutics such as polypeptides, human growth hormone, and monoclonal antibodies, with focus on polyelectrolyte-based formulations.
→ Novel in-vitro models. In this project we develop and evaluate novel in vitro methods to model the behavior of pharmaceutical products administered subcutaneously. The purpose is to improve the mechanistic understanding to facilitate the innovation and development of formulations with high bioavailability of the active pharmaceutical ingredient (API) and small variability between patients. A special focus is on pharmaceutical products based on biologics. By constructing a physiologically relevant model of the extracellular matrix, we will mimic in vitro the fate of different types of drug formulations after administration in humans, including the rate of release and absorption of the API by uptake into the blood and lymph capillaries. The goal is to determine the key factors governing the transport of the pharmaceutical product in the SC environment and the absorption kinetics of the API and to establish in vitro methods useful in the development of drug formulations intended for subcutaneous administration (Fig.1).
Fig.1: Subcutaneous administration
→ Physicochemical aspects. In this project we investigate how active pharmaceutical ingredients (APIs) and excipients in subcutaneously administered drug formulations interact with the components in the extracellular matrix in the subcutaneous adipose tissue (hypodermis). The purpose is to provide a basis for the development of novel in vitro methods to model the behavior of pharmaceutical products administered subcutaneously. The aim is to improve the mechanistic understanding to facilitate the innovation and development of formulations with high bioavailability of the APIs and small variability between patients. A special focus is on pharmaceutical products based on biologics. To increase our knowledge about the factors controlling the drug release rate and absorption by blood and lymphatic vessels we investigate how biological and self-associating drugs organize and interact with the biopolymers in the subcutaneous environment.
Amphiphilic properties of drug molecules
Many pharmacologically active compounds are made up of amphiphilic molecules and possess many similar properties to ordinary surface active agents. Amphiphilic drugs may be found within several classes of drugs including tranquilizers, analgesics, antibiotics, antidepressants, antihistamines, local anaesthetics, anti-inflammatory drugs and anticancer drugs. The amphiphilic nature of these molecules is expected to play a crucial role for their pharmacological activity as well as important properties related to toxicity and haemolysis. In drug formulations the amphiphilic properties of the active substance is decisively important for the molecular mechanisms of solubilisation and drug delivery.
In this research program, we study various aspects of the self-assembly process of amphiphilic drugs in presence of relevant drug delivery components such as phospholipid bilayers, surfactants, proteins and other biomacromolecules. The structural behaviour is mainly investigated using various scattering techniques such as static and dynamic light scattering, small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS), but also complementary techniques such as cryo-TEM electron microscopy (Fig.2).
Fig.2: Cryo-TEM image of mixed sodium dodecyl sulfate/adiphenine hydrochloride vesicles.
→ Amphiphilic properties of drug molecules and their self-assembly in presence of phospholipids
Molecular components such as phospholipids, surfactants, proteins and drug molecules consist of both hydrophilic and lipophilic parts and are involved in various drug delivery systems. As a result, these components are able to self-assemble and interact strongly with one another in ways that usually determine molecular release mechanisms in drug delivery systems. The aim of the project is to study the interactions and self-assembly in mixtures of different amphiphilic drug molecules and phospholipids. The study includes structural characterization of the drug-phospholipid aggregates (micelles, liposomes, bilayer structures) as well as investigating the location and impact of drug molecules on phospholipid bilayers, by mainly using various small-angle scattering techniques.
Gels for drug delivery
Charged polymer networks have the possibility to absorb water to form hydrogels, soft materials with interesting mechanical properties. In drug delivery they are useful as carriers of various types of drugs, including small molecules for cancer therapy and large molecules of biological origin for treatment of infections and genetic diseases. Microgels are microscopic hydrogel particles that can be injected into the body or applied to the skin. Hydrogels are useful in drug delivery, in part because they have the capacity to encapsulate and store large amounts of drugs in an environment that protects the drugs from degradation, and in part because the polymer network offers ways to control the rate of release of the drug.
Our research in this field is mainly focused on fundamental aspects of the interaction between hydrogels and different categories of drugs and excipients (helper molecules) where the interplay between electrostatic and hydrophobic interactions and the elastic properties of the polymer networks is important. To this end we study the microstructure and stability of complexes formed between polyelectrolyte networks, drug molecules and excipients. A combination of experimental and theoretical methods are used to explain how the charge of proteins and peptides and the self-assembling properties of amphiphilic molecules determine their partitioning between the hydrogel and the surroundings, how they are distributed inside a hydrogel and between different hydrogels. To study the dynamics we measure the rate of binding and release and the related hydrogel volume response and make determinations of microstructures and compositions during intermediate stages. The aim is to reach a mechanistic understanding of the interactions to be able to predict the kinetics of drug release from hydrogels, and to develop new principles for controlled and triggered release from hydrogel based formulations (Fig 3).
Fig 3: The rheological study on hyaluronic acid gel (hydrogel)
→ Amphiphilic drugs in microgels. Amphiphilic drug molecules is an important group of active substances which are commonly used in cancer therapy, as antidepressants and antihypertensive agents. They have properties in common with regular micelle-forming surfactants but the relationships between their molecular structure and self-assembling properties are not well understood. To realize the potential of polyelectrolyte microgels as drug delivery system for amphiphilic drugs we study the basic principles governing the drug loading and release properties. The aim is to relate the microstructure and thermodynamic stability of drug self-assemblies in microgels to the molecular properties of drugs and microgel networks and to the mechanisms and kinetics of release under physiological conditions. We use two in-house developed micromanipulator techniques to monitor the size and internal morphology of single microgels during binding and release of drugs in the microscope. With the ‘flow-pipette’ we study microgels in contact with bulk solutions under conditions of controlled liquid flow (Fig.4); with the ‘micro-drop’ we study microgels in contact with a small solution volume under unstirred conditions (Fig. 5). In addition, we use a µDiss profiler to determine equilibrium binding isotherms and to monitor the kinetics of binding and release, and scattering techniques to determine the microstructure of complexes. The determined equilibrium and dynamic properties are compared with theoretical models developed within the group. The goal is to construct release models that contribute to the development of novel release systems for amphiphilic drugs. In a project run in collaboration with the Biopharmaceutical research group (Prof. H. Lennernäs) at the department we investigate in vitro a system of therapeutic microgels (DC bead®) for parenteral delivery of the amphiphilic drug doxorubicin used clinically for palliative treatment of liver cancer.
Fig.4: Schematic representation of the experimental setup. A single gel bead is immersed in the bulk solution and held in place in the center of the flow pipette.
Fig 5: Schematic illustrations of single-microgel inverse microscopy experiments in which the microgel is selected from the aqueous solution and then transferred into a drug´s solution by using the micropipette.
→ Segregation and mixing in polyelectrolyte hydrogels. In this project we investigate the phase behavior of mixtures of two different macroions confined to the same polyelectrolyte hydrogel. The macroions are of opposite charge to the polyelectrolyte network and include proteins, peptides and surfactant micelles. The main purpose is to investigate if electrostatic interactions can be responsible for segregative phase separation. Our hypothesis is that the interaction with the polyelectrolyte gives rise to net repulsion between two macroions of different charge density. As a first approach we investigate cytochrome c (+7) and mixed micelles of non-ionic and cationic surfactants in negatively charged networks. Segregative core-shell phase separation is observed when the mole fraction of the cationic surfactant in the micelles is large enough. Understanding the driving force behind segregation and core-shell phase separation in gels can help developing new strategies for encapsulating protein drugs and ways to accomplish triggered release, as well as explaining mechanisms behind protein sorting in secretory cells.