Physical and chemical properties of radionuclide therapy.

As more radionuclide therapies move from laboratory feasibility studies into clinical reality, it becomes increasingly important for the labeling chemistry to produce consistently a stable radiopharmaceutical that remains intact under the challenge of human catabolism. Similarly, once proof of principle is established to bring a radionuclide conjugate into clinical therapy trials, dosimetric estimates should be made to select the appropriate radionuclide properties, which are based on animal-specific or patient-specific pharmacokinetics and match a set of specific clinical endpoints. These properties may include the radionuclide physical half-life, radiolabeled conjugate biological uptake and clearance, product-specific activity, range and type of emissions, and resultant effects on tumor and normal tissue cellular survival. The immunologist and labeling chemist have now produced a variety of strategies that have potential to increase the therapeutic ratio (tumor-to-normal tissue dose ratio). The advent of normal tissue clearing agents, fragmented or chimerized carriers to improve targeting, and the method of bispecific or two-step and three-step targeting agents has increased the need for realistic modeling of the carrier in vivo to guide prospectively the competitive development of these radiopharmaceuticals. In this article, examples have been taken from the literature to elucidate the benchmark of success that careful experimental design has fostered to bring these agents into clinical practice by creative and logical methodologies.