With de sired water stability and properties such com

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radiopharmaceuticals with de- sired water stability, and properties. Such com- plexes may be injected at concentrations of 10 -6_10 -8 M. For example, iso- cyanide complexes such as [Tc(CNR)6] + = t-Bu, CH 2 C0 2 But, etc.) have been found to be taken up selectively into heart tissue and thus have the poten- tial to be used as heart-imaging agents. Figure 9.2 displays bone as imaged a 99mTc bone agent. The dark correspond to surface areas of metabolic which can be used to diagnose or disease. One Table 9.2 Radionuclides most commonly employed in diagnostic nuclear medicine. a Radionuclide Half-Life Energy (ke V) 57CO 271 d 836 67Ga 78 h 1,001 99mTc 6h 140 lilln 67 h 172,247 113mln 104 m 392 123 1 13 1,230 169Yb 32 d 207 197Hg 64h 159 201TI 72h 135, 167 a Data are from Table of the Isotopes in D. R. Lide, ed., CRC Handbook of Chemistry and Physics, CRC Press, 71 st ed., 1990-91, pp. 11-33 ff.
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IV. SURVEY OF METALS USED FOR DIAGNOSIS AND CHEMOTHERAPY 515 Figure 9.2 Human skeleton (bone) imaged with 99mTc. Both anterior (left) and posterior (right) views are shown. goal of research in this field is to images of myocardial in- farcts or clogged arteries for physicians who can watch the patient's heart on a video surgery. Although chemical details responsible for the selective tissue of Tc isocyanide, and other complexes are largely synthetic modifications are and have many new compounds for evaluation. Among the few known to be absorbed selectively tumor cells is the ,24,25 the structure of which is por- trayed in Figure 9.3. binds most radioactive metal ions, but the 57Co(III) complex has the best tumor-to-blood ratio. Unfortunately, the long 57CO 9.2) has limited its clinical Attempts to prepare 99mTc complexes of BLM with selective uptake properties ap- proaching that of the cobalt have not yet been successful, although the
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516 CrONH2H~ 0 R N CONH 2 tripeptide ~ CH N ~ N:?' N 3 0 ~ I H S ~ 0 HO N NH CH 3 N CH 3 HO CH 3 S deglyco ~ \ ') tetrapeptide HO HO 0 0 ~ R = terminal amine \--O~OH A 2 : R "N~S/CH3 HO ~OH H "CH 3 H~ 8 2: R = "N~~yNH2 O~R / C)'" 'NH 2 H NH+ decarbamoyl 2 N ~ H,N')<H, r~N N(8 H \ i. N ;,YCO - Peptide ----lL ) ~ N __ '/ S _~~e ---N N ' H2NOC N ~ ~: H O-Sugar , 0 O 2 CH 3 Figure 9.3 Structure of bleomycin and its proposed iron complex (reproduced by permission from Reference 25). target molecule would be a most valuable radiodiagnostic agent. One imagina- tive solution 26 to this problem was achieved by covalent attachment of an EDTA moiety to the terminal thiazole ring of BLM (Figure 9.3). The resulting Co(III) BLM-EDTA molecule was radiolabeled with lIlIn3+ and found to be useful for diagnosis of cancer in humans. Also used for tumor imaging are 99mTc and 67Ga citrate complexes, the latter being the agent of choice for many applications. Again, there is little known at the molecular level about the mechanism of tu- mor-cell specificity. An alternative approach to radionuclide-based tumor-imaging agents for di- agnosis of disease is to modify, with metal chelating agents, antibodies raised against a biological substance, such as a tumor-cell antigen, hormone, or other target. Antibodies are proteins that are synthesized by specialized cells of the immune system in response to an external stimulant, or antigen. The high spec-
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