TRACER’s PET proficiency provides a solution to the increasing pressure to develop new inventive drugs at a low cost and fast pace. With PET imaging early in-human data on the dynamics of a drug can be obtained. This allows for enhanced decision-making before moving the compound to the next development phase where costs are larger and valuable time is lost.
What is PET?
Positron emission tomography (PET) is a medial imaging technique. As with other nuclear imaging modalities, PET uses small doses of radioactive substances to visualize biological processes in the body. These radioactive substances can be referred to as tracers. In a body, tracers will accumulate in areas with a higher degree of chemical activity. Often a higher level of chemical activity coincides with the area of disease.
A PET scan produces 3D images of the whole body and indicates the areas where the tracers have accumulated with radiant colors. In other words, a PET scan shows the distribution of the radiopharmaceutical throughout the body.
An industry example.
One of the most well-known examples of PET uses a tracer made out of glucose labeled with the positron emitter fluorine-18 ([18F]FDG). This tracer is used for the detection of tumors and it’s metastases. In the case of [18F]FDG, the substance is administered to the patient via an intravenous (IV) injection. In other words, IV directly injects the tracer into the vein. The radioactive glucose analog accumulates in cells that have a high glucose consumption, such as the tumor. The [18F]FDG that is not consumed by the tissues in the body is cleared by renal excretion in the urine. After this biological process the PET scanner can detect the gamma ray pairs emitted from the [18F]FDG accumulated in the tissues. Thus, the creation of a 3D image of where the tracers have accumulated is made possible.
The advantages of PET in drug development.
Besides saving on cost and reducing the time to market, using PET in drug development has many other great advantages. The main advantage of PET is the very high sensitivity. This means very low concentrations of a radiopharmaceutical can be detected. As a result, low doses can be administered resulting in no or very low biological effect of the radiopharmaceutical and low damage caused by the radiation. By this biological processes in the body can be studied without saturating the molecular process.
Another advantage of PET is the ability to generate 3-dimensional images of the distribution of the radiopharmaceutical throughout the body. The technique also offers the possibility for acquisition of a whole body image. Since the gamma rays have high penetration characteristics in tissue, this imaging method is suited for the detecting of lesion seated deep in the body. This is in contrast to fluorescence imaging and ultrasound, which have a limited penetration depth.
Moreover, PET is intrinsically quantitative. This allows for accurate quantification of concentrations of the radiopharmaceuticals in the body. Quantification of the radiopharmaceutical concentration grant the use of PET for monitoring of treatment response by measurement before and after treatment and the consecutive measurement of the radiopharmaceutical concentration.
The good temporal resolution of PET allows for “dynamic imaging”. With dynamic imaging the distribution of the radiopharmaceutical can be followed over time. A dynamic PET scan starts at the moment of the radiopharmaceutical and generally last an hour. Afterwards, images of various time frames are reconstructed to visualize the distribution over time. This provides additional information of the metabolic processes in tissues of interest.