Targeting of drugs and diagnostics in biological systems

To bring drugs, diagnostics and similar ligands directly to the site of their action is presently an urgent task of molecular pharmacology. Biophysical problems associated with this task consist in a rather less specific distribution of substances administered in a compartmented biological system, and frequently also in insufficient affinities of the ligands to their targets (receptors, enzymes, epitopes of diverse antigens, membranes, binding proteins etc.). These affinities vary within broad limits - from high (antibodies) to very low (enzymes). Thus, the presentation is focused i) on biophysical factors that determine final concentration of ligands in the vicinity of their targets, ii) on structure and affinity of these targets, and iii) on some pragmatic aspects of the targeting concept.