Receptor imaging by means of positron emission tomography (PET) and single photon emission computerized tomography (SPECT) may non-invasively address questions that are essential to the development and the clinical application of drugs targeting receptors expressed on human malignancies : is the receptor targeting drug getting to the tumor in the required concentration, is there a heterogeneity in tumor uptake, how fast is the drug cleared from the tumor and how is the receptor targeting drug metabolized. Such information may be used to assess the efficacy of strategies that aim to improve drug penetration through tumor tissue or to select compounds based on their ability to penetrate tumor tissue, thereby increasing the therapeutic index. In addition, imaging by means of PET and SPECT with receptor targeting radiopharmaceuticals may allow for the selection of patients that may benefit from receptor targeting therapies either ab initio, in the situation where the levels of receptor expression are proportional to the level of signaling via the receptor, or through sequential imaging in the situation where the level of receptor expression is not proportional to the level of signaling via the receptor and proof of downregulation of the number of receptors is required.
Keywords: PET, SPECT, receptor imaging, targeted therapie
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