Iodine-131-labeled diphosphonates for the palliative treatment of bone metastases--III. Considerations of interaction, binding and absorbed dose

Targeted Radionuclide Therapy of Painful Bone Metastases: Past Developments, Current Status, Recent Advances and Future Directions

Bone pain arising from secondary skeletal malignancy constitutes one of the most common types of chronic pain among patients with cancer which can lead to rapid deterioration of the quality of life. Radionuclide therapy using bone-seeking radiopharmaceuticals based on the concept of localization of the agent at bone metastases sites to deliver focal cytotoxic levels of radiation emerged as an effective treatment modality for the palliation of symptomatic bone metastases. Bone-seeking radiopharmaceuticals not only provide palliative benefit but also improve clinical outcomes in terms of overall and progression-free survival. There is a steadily expanding list of therapeutic radionuclides which are used or can potentially be used in either ionic form or in combination with carrier molecules for the management of bone metastases. This article offers a narrative review of the armamentarium of bone-targeting radiopharmaceuticals based on currently approved investigational and potentially useful radionuclides and examines their efficacy for the treatment of painful skeletal metastases. In addition, the article also highlights the processes, opportunities, and challenges involved in the development of bone-seeking radiopharmaceuticals. Radium-223 is the first agent in this class to show an overall survival advantage in Castration-Resistant Prostate Cancer (CRPC) patients with bone metastases. This review summarizes recent advances, current clinical practice using radiopharmaceuticals for bone pain palliation, and the expected future prospects in this field.

Pharmaceutical and clinical development of phosphonate-based radiopharmaceuticals for the targeted treatment of bone metastases

Therapeutic phosphonate-based radiopharmaceuticals radiolabeled with beta, alpha and conversion electron emitting radioisotopes have been investigated for the targeted treatment of painful bone metastases for >35years. We performed a systematic literature search and focused on the pharmaceutical development, preclinical research and early human studies of these radiopharmaceuticals. The characteristics of an ideal bone-targeting therapeutic radiopharmaceutical are presented and compliance with these criteria by the compounds discussed is verified. The importance of both composition and preparation conditions for the stability and biodistribution of several agents is discussed. Very few studies have described the characterization of these products, although knowledge on the molecular structure is important with respect to in vivo behavior. This review discusses a total of 91 phosphonate-based therapeutic radiopharmaceuticals, of which only six agents have progressed to clinical use. Extensive clinical studies have only been described for (186)Re-HEDP, (188)Re-HEDP and (153)Sm-EDTMP. Of these, (153)Sm-EDTMP represents the only compound with worldwide marketing authorization. (177)Lu-EDTMP has recently received approval for clinical use in India. This review illustrates that a thorough understanding of the radiochemistry of these agents is required to design simple and robust preparation and quality control methods, which are needed to fully exploit the potential benefits of these theranostic radiopharmaceuticals. Extensive biodistribution and dosimetry studies are indispensable to provide the portfolios that are required for assessment before human administration is possible. Use of the existing knowledge collected in this review should guide future research efforts and may lead to the approval of new promising agents.

Therapeutic efficiency of rhenium-188-HEDP in human prostate cancer skeletal metastases

Rhenium-188-HEDP ((188)Re-HEDP) is a new and attractive radiopharmaceutical for the treatment of metastatic bone pain. As a product of (188)W/(188)Re generator, it is convenient for clinical therapeutic use with a short physical half-life of 16.9 h and a maximal beta-energy of 2.1 MeV. We investigated the effect of (188)Re-HEDP on pain relief, analgesic intake and impairment of bone marrow function in 27 patients with bone metastases induced from prostate cancer. All patients were interviewed using a standardised set of questions before, and after therapy for 12 weeks. The patients were treated with 2700-3459 MBq of (188)Re-HEDP. Blood samples were taken weekly for 12 weeks, and a blood count was performed. Patients described an improvement on the Karnofsky performance scale from 74+/-7 to 85+/-9% 12 weeks after therapy (P=0.001). The pain score showed a maximum decrease from 44+/-18 to 27+/-20% in the third to the eight week after therapy (P=0.009). Seventy-six percent of the patients described a pain relief without increase of analgesic intake. Twenty percent of the patients could discontinue their analgesics and were pain free. Mean platelet count decreased from (286+/-75)*10(3) microl(-1) to (215+/-92)*10(3) microl(-1), and mean leucocyte count from (7.7+/-1.5)*10(3) microl(-1) to (6.0+/-1.9)*10(3) microl(-1) in the second to the fourth week after therapy. The maximal differences between the values of platelets and leucocytes before and after therapy were not statistically significant (P=0.021 and 0.094). In conclusion, (188)Re-HEDP is an effective radiopharmaceutical used in the palliative treatment of metastatic bone pain in prostate cancer and shows minimal bone marrow toxicity.

131I labeled diphosphonates for the palliative treatment of bone metastases--IV. Syntheses of benzylidenediphosphonates and their organ distribution in rats

Palliative treatment of bone pain induced by disseminated bone metastases can be performed with osteotropic, beta(-)-emitting radionuclides. Newly developed 131I labeled benzylidenediphosphonic acid (BDP) derivatives show osteotropic characteristics which suggest that they might possibly be useful radiopharmaceuticals for that purpose. Six BDP derivatives were synthesized with H, OH or NH2 in the 4- and alpha-position. Syntheses were performed by the formal addition of 2 mol of phosphorous acid in the presence of PBr3 to 1 mol of the respective benzonitrile. Transformation of the 4-methoxy and 4-nitro substituents, which were stable during the diphosphonate formation, to 4-HO and 4-NH2 was achieved by hydrolytic ether cleavage in boiling HBr and catalytic hydrogenation with Pd/C, respectively. Transformation of the alpha-amino to alpha-hydroxy group was achieved by the action of NaNO2 in HCl. 4-Hydroxybenzylidenediphosphonic acid (9) was formed unexpectedly during the reaction of 4-hydroxybenzoic acid with H3PO3/PBr3. The addition of 2 mol of phosphorous acid to the benzoic acid was accompanied by an additional reduction at the alpha-carbon. The new BDP derivatives were analyzed by HPLC, NMR and elemental analysis. After labeling with 131I the BDP derivatives were tested in female Sprague-Dawley rats to obtain organ uptake and kinetic data. The various substituents showed an influence on the bone affinity and the uptake in other organs. Among the BDP derivatives tested alpha-amino-(3-[131I]iodo-4-hydroxybenzylidene)diphosphonate (4a) showed the best biological characteristics.