Aptamers: a novel class of radiopharmaceutical with diagnostic and therapeutic potential

Excerpt

Receptor imaging using positron emission tomography or single-photon emission tomography technology has gained considerable importance during the past 20 years. These procedures are subsumed under the term "molecular imaging" in order to illustrate that they allow the detection of diseases at the molecular level. Their advantage over magnetic resonance imaging, computer tomography and ultrasound is that only "traces" of a ligand are required for receptor imaging, whereas milligrams or grams of contrast media have to be applied otherwise. Each cell—whether normal, benign or malignant—expresses epitopes or "targets" that can be recognised by ligands. When viewed as molecular surfaces, there are in principle only minor differences between neuroreceptors and tumour epitopes as far as the mechanisms of ligand binding are concerned. Biotechnology offers a plethora of unique technologies for designing, selecting or isolating ligands for molecular recognition; in addition, antibodies that recognise tumour antigens can be produced by hybridoma technology. However, the production of anti-tumour antibodies requires the use of in vivo animal models, which entails the inherent problem of the formation of human anti-mouse antibodies (HAMAs). Although this problem can be circumvented by using either humanised antibodies or single chain fragments (scFv), there are only a few examples showing that they can be applied in nuclear medicine in robust fashion. …