I-Serum albumin-manganese-magnetism-engineered iron oxide nanoparticles

The superparamagnetic iron oxide (SPIO) structure is composed of ferric iron (Fe) and ferrous iron (Fe). The iron oxide particles are coated with a protective layer of dextran or other polysaccharide. These particles have large combined magnetic moments or spins that are randomly rotated in the absence of an applied magnetic field. SPIO is used mainly as a T2 contrast agent in magnetic resonance imaging (MRI), though it can shorten both T1 and T2/T2* relaxation processes. SPIO particle uptake into the reticuloendothelial system is by endocytosis or phagocytosis. SPIO particles are taken up by phagocytic cells such as monocytes, macrophages, and oligodendroglial cells. (1). SPIO agents are classified by their sizes with coating material (~20 nm to 3,500 nm in diameter) as large SPIO (LSPIO) nanoparticles, standard SPIO (SSPIO) nanoparticles, ultra small SPIO (USPIO) nanoparticles, and cross-linked iron oxide (CLIO) nanoparticles. A new class of iron oxide nanoparticles has been created with high and tunable nanomagnetism: magnetism-engineered iron oxide (MEIO) nanoparticles (2). These MEIO nanoparticles were doped with manganese (MnMEIO) to provide further MRI signal enhancement. The sentinel lymph node (SLN) is considered to be the first lymph node to receive lymphatic flow from tumor sites and thus will contain metastatic tumor cells (3). SLN mapping has been used in the diagnosis of metastasis of solid tumors (4). Radical lymph node dissection is performed in patients with malignant cells in the SLNs. SLN mapping is currently performed with a combination of radioactive tracer and blue dye. The current procedure is also time-consuming and requires a steep learning curve. Near-infrared quantum dots have been studied in SLN mapping in small animals (5, 6); however, there are only limited studies of long-term quantum dot toxicity in animals (7). Choi et al. (8) have designed a multimodal magnetic nanoparticle-based positron emission tomography (PET)/MRI probe for non-invasive mapping of SLNs in small animals. MnMEIO was coated with serum albumin (SA) and radiolabeled with I to form I-SA-MnMEIO nanoparticles.