Inorganic Nanoparticles in Pharmaceutical Development
The pharmaceutical nanoparticle landscape extends well beyond lipid and polymer systems. Metal and metal oxide nanoparticles, particularly gold nanoparticles and iron oxide nanoparticles, have physical properties that make them uniquely useful in diagnostic imaging, thermal therapy, and the emerging field of theranostics, where a single agent combines diagnostic and therapeutic functions.
Interest in these materials has grown steadily alongside advances in nanomedicine formulation science, and several iron oxide nanoparticle products are already approved for clinical use as MRI contrast agents. The broader field of metal nanoparticle applications in pharmaceuticals is advancing through clinical development, with programmes in cancer imaging, hyperthermia therapy, and targeted drug delivery among those in active investigation.
Iron Oxide Nanoparticles: MRI Contrast and Beyond
How Iron Oxide Nanoparticles Enhance MRI Contrast
Superparamagnetic iron oxide nanoparticles (SPIONs) enhance the contrast of magnetic resonance imaging by shortening the T2 and T2* relaxation times of water protons in tissues where the particles accumulate. This produces a signal reduction (darkening) in T2-weighted images, allowing tissues with SPION accumulation to be distinguished from surrounding tissue. The degree of contrast enhancement depends on the size, surface coating, and magnetic properties of the particles.
Approved SPION-based MRI contrast agents including ferumoxytol are used clinically for imaging of the lymphatic system, the liver, and the vasculature. The EMA’s reflection paper on non-clinical studies for generic nanoparticle medicinal products provides guidance relevant to the development of SPION-based imaging agents and new nanoparticle therapeutics.
Emerging Applications: Hyperthermia and Drug Delivery
Beyond MRI contrast, iron oxide nanoparticles can generate heat when exposed to an alternating magnetic field, a phenomenon known as magnetic hyperthermia. Localised heat generation in tumour tissue can directly kill cancer cells or sensitise them to concurrent chemotherapy or radiotherapy. Magnetic hyperthermia using iron oxide nanoparticles has been investigated in clinical trials for glioblastoma and prostate cancer.
Surface-functionalised iron oxide nanoparticles can also act as drug carriers, with the magnetic core providing imaging capability and the surface providing a platform for drug loading and targeting ligand attachment. This combination of imaging and therapeutic function in a single particle is the theranostic concept at its most direct.
Gold Nanoparticles: Optical Properties and Biomedical Applications
Surface Plasmon Resonance
Gold nanoparticles exhibit a phenomenon known as surface plasmon resonance: the conduction electrons on the gold surface oscillate in resonance with incident light at specific wavelengths, producing intense absorption and scattering at those wavelengths. The resonance wavelength depends on the size and shape of the particle and can be tuned from the visible to the near-infrared range by controlling particle geometry during synthesis.
This optical tunability makes gold nanoparticles attractive for photothermal therapy, where near-infrared light penetrates tissue and is absorbed by gold nanoparticles localised in the tumour, generating heat that destroys tumour cells. Near-infrared light causes minimal damage to surrounding tissue, making this a highly targeted thermal ablation approach.
Surface Functionalisation for Drug Delivery
The surface of gold nanoparticles can be functionalised with a wide range of chemical groups, including thiol-linked molecules, antibodies, oligonucleotides, and polymer coatings. This versatility makes gold nanoparticles a flexible platform for targeted drug delivery, where the gold core provides photothermal or imaging capability and the surface carries therapeutic cargo and targeting ligands.
Characterisation Requirements for Inorganic Nanoparticles
| Property | Measurement Technique | Regulatory Relevance |
| Core size and size distribution | Transmission electron microscopy (TEM); X-ray diffraction | Core size affects magnetic and optical properties; must be defined and controlled |
| Hydrodynamic diameter and PDI | Dynamic light scattering (DLS) | Reflects particle size in biological media including protein corona formation |
| Surface chemistry and coating | X-ray photoelectron spectroscopy (XPS); FTIR; NMR | Surface coating determines colloidal stability, protein adsorption, and biological fate |
| Zeta potential | Electrophoretic light scattering | Colloidal stability indicator; relevant to aggregation and non-specific interactions |
| Metal content and purity | ICP-MS or ICP-OES | Precise metal quantification for dose control; impurity profiling required for regulatory filing |
| Endotoxin and sterility | LAL assay; sterility testing | Critical for injectable products; inorganic nanoparticles can interfere with standard LAL assays |
Characterisation requirements for metal nanoparticle pharmaceuticals are evolving. Regulatory expectations should be confirmed with the relevant agency for each specific application and development stage.
Ardena’s Metal and Metal Oxide Nanoparticle Platform
Ardena’s nanomedicine team at Oss has experience with metal and metal oxide nanoparticle systems, including formulation development, physicochemical characterisation, and GMP manufacturing support for inorganic nanoparticle products. The analytical capabilities at Oss include DLS, zeta potential measurement, and the infrastructure for handling metal-containing pharmaceutical materials under GMP conditions.
