Although nuclear decay characteristics are of paramount importance for selection of an intrinsically theranostic radiometal, its success in real clinical context also depends on the practicality of large-scale production with acceptable purity and the supply logistics. Several intrinsically theranostic radiometals such as 47Sc, 64Cu, 67Cu, 153Sm, 166Ho, 177Lu, 186Re, etc., with fascinating nuclear decay characteristics (as summarized in Table 1) have been studied for preparation of radiopharmaceuticals in preclinical and clinical settings. The use of the same radiometal would give an accurate idea regarding the pharmacokinetics of the radiopharmaceutical administered for dosimetric estimation.
A more preferable option in this regard is to use intrinsically theranostic radiometals which by virtue of their suitable γ or β + emission can be used for diagnostic imaging and due to suitable particulate emission can be used for targeted therapy. To meet the requirement of theranostics, the two radionuclides chosen are preferably of the same chemical element, even though chemically similar elements are also utilized occasionally. For the diagnostic part of the investigation, SPECT and PET imaging techniques are used. The fundamental requirement of theranostics is that the same or similar chemical compound should be labelled with a diagnostic and a therapeutic radionuclide. To circumvent this limitation, presently efforts are emerging towards combining the diagnosis (molecular imaging) and the internal radiotherapy (molecular targeted therapy) and this concept is known as “theranostics”. Dosimetry is the major challenge with internal radiotherapy due to uncertainty in measurement of radiation dose associated with particulate radiation from outside the patient body. Contrastingly, particulate emitting radiometals (α, β -, conversion and/or Auger electrons) are in high demand for internal radiotherapy.
Radiometals which are γ-emitters or positron emitters are generally used for diagnostic applications utilizing single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging modalities. This transition has been driven by the mutually essential advances in radiochemical processing, biomedical sciences, synthetic organic and inorganic chemistry, nuclear imaging technology and cancer biology. Over the last several decades, the production and application of radiometals have matured from largely ambiguous and experimental technologies to indispensable components of routine practices in nuclear medicine. Overall, the review amply demonstrates the practicality of the medium specific activity 177Lu towards formulation of various clinically useful radiopharmaceuticals, especially for the benefit of millions of cancer patients in developing countries with limited reactor facilities. This review also summarizes the results of clinical studies with potent 177Lu-based radiopharmaceuticals that have been prepared using medium specific activity 177Lu produced by direct neutron activation route in research reactors.
Research efforts that resulted in the growth of various 177Lu-based radiopharmaceuticals in preclinical and clinical settings are provided. Traditional bifunctional chelators (BFCs) that are used for 177Lu-labeling are discussed and the upcoming ones are highlighted. Its chemistry plays a vital role in the preparation of a wide variety of radiopharmaceuticals which demonstrate appreciable in vivo stability. Lutetium, is the last element in the lanthanide series. The specific nuances of 177Lu production by various routes are described and their pros and cons are discussed. The present review chronicles the advancement in the last decade in 177Lu-radiopharmacy with a focus on 177Lu produced via direct 176Lu (n, γ) 177Lu nuclear reaction in medium flux research reactors. Lutetium-177 is one of the most important theranostic radioisotope used for the management of various oncological and non-oncological disorders.
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