Our fluorescence imaging platforms feature a multi-channel system for near-infrared (NIR) based three-dimensional whole body, fluorescence imaging in mice and rats.
Fluorescence imaging (FLI) relies on light emission from a fluorophore or fluorescent protein after excitation by a light source at the appropriate wavelength. FLI can be applied to cell lines or transgenics expressing fluorescent proteins or by the use of exogenous probes labeled with fluorophores. A variety of targeted, activatable, and vascular probes has been developed to enable in vivo imaging of specific biological processes, molecular events, and tissue vascularity.
Fluorescence Molecular Tomography (FMT)
FMT enables quantitative imaging of the fluorescent probe concentration to the picomolar level without tissue dept limitation in mice or rats. With NIR probes, FMT provides greater versatility to accessing fluorescent imaging biomarkers. FMT aids in the assessment of disease progression and enables drug response at the molecular, cellular, and target levels. It can also be used as a discovery screening tool for rapid and cost-effective assessment of biologics biodistribution.
NIR Probes: Biodistribution
These NIR probes provide a high-efficiency, low-cost method for discovery stage screening and later stage decision making for therapeutic biologics.
Standard labeling techniques using a variety of commercially available, NIR fluorophore kits enable three-dimensional, FMT-based imaging of biodistribution including:
- Clearance times and pathways
NIR Probes: Blood Pooling
A variety of blood-pooling NIR probes of varying sizes can be used for imaging vessel permeability, blood flow, and vessel density.
- Blood volume quantification
- Angiogenesis measurement
- Tumor burden tracking
NIR Probes: Targeted
NIR probes can be targeted to a variety of cell surface markers and receptors to enable imaging of target expression and treatment-based target modulation. At MI Bioresearch, we have successfully utilized a number of NIR probes during in vivo studies.
Examples of commercially available probes include those targeted to:
- αvβ3: The αvβ3 integrin is involved in vessel formation. αvβ3-targeted probes, such as IntegriSense, (PerkinElmer, co-developed by Merck) allow the imaging of new vessel formation and tumor burden.
- Hypoxia: The HypoxiSense probe (PerkinElmer) allows three-dimensional, FMT-based imaging of tissue hypoxia through targeting to the carbonic anhydrase 9 (CA IX) protein. This protein increases in hypoxic regions within many tumors, especially in cervical, colorectal, and non-small cell lung tumors.
- Annexin/Apoptosis: The Annexin Vivo contrast agent (PerkinElmer) selectively binds phosphatidylserine exposed in the outer leaflet of the cell membrane during the early stages of apoptosis. This enables FMT-based imaging of apoptosis.
- Her2: Her2 is commonly over-expressed in human breast cancer and is the target of many breast cancer therapeutics. A Her2-targeted probe can be used for imaging of Her2 expression and therapeutic knockdown.
- Transferrin: Transferrins (Tf) are single-chain glycoproteins containing a molecular mass of 79-kDa that bind to transferrin receptors (TfRs) at extracellular pH (Kd = 1–100 nM) and trigger receptor-mediated endocytosis. TfR is a cell-membrane internalizing receptor that is responsible for almost all the iron sequestration in mammalian cells. Because of rapid cell division and stringent demand for iron (for heme synthesis), many cancer cell types overexpress TfRs. It has been used as a targeting agent for cancer cells. In addition, TfR accumulates in locals of inflammation due to the leakage of plasma proteins and to the expression of TfR receptors by inflammatory cells. During inflammation, monocytes leave the blood and differentiate into macrophages at the extravascular tissues, macrophages express surface Tf receptors.
- Folate: The FolateRSense™ (PerkinElmer) targeted fluorescence imaging agent is highly specific and sensitive in its detection of folate receptor alpha (FRA) and can be used to closely monitor and quantitate tumor growth and metabolism. Over-expression of FRA protein is associated with tumor growth, and uptake of folic acid is a necessary part of tumor metabolism.
NIR Probes: Activated
NIR-activated probes provide the opportunity to image the modulation of target-specific molecules. These probes are in a quiescent or quenched fluorescence state prior to activation and fluorescent activity. Commercially available, activatable NIR probes exist for a variety of target molecules including:
- Cathepsins: Cathepsins are upregulated in a variety of disease states including inflammation and cancer. These probes can quantify the early and specific aspects of rheumatoid arthritis and other inflammatory diseases. They can also be used for tumor-burden tracking since tumors broadly produce high levels of cathepsins. Pan-cathepsin probes are available (e.g., ProSense) as well as probes specific to Cathepsin B (e.g., CatB FAST) and Cathepsin K (e.g., CatK FAST). Notably, Cathepsin K is commonly upregulated in the osteoblastic components of bone degradation and can be used to assess therapeutics targeted against this process in bone disease.
- Matrix metalloproteinases (MMPs): MMPs are active in inflammation diseases and cancer. MMP-activatable fluorescent probes can be used both for quantifying the early and mechanistic aspects of rheumatoid arthritis and other inflammatory diseases. They can also be used for tumor burden tracking since tumors commonly produce high levels of MMPs.
- Neutrophil elastase: Neutrophil elastase is a protease involved in a variety of indications including acute lung injury and acute respiratory distress syndrome, as well as many other inflammatory processes such as emphysema, cystic fibrosis, COPD, wound healing, rheumatoid arthritis, and ischemia-reperfusion.
- PSA: Prostate specific antigen (PSA) is one of the most studied biomarkers for prostate cancer. However, serum PSA levels are mildly elevated in both malignant and non-malignant prostate conditions. Enzymatically active PSA, present at detectable levels only in prostate tumor tissue, provides a better target to measure the malignancy of prostate cancer.