Radioactivity In Liver Tissue Research Articles

64 Cu-NOTA-8-Aoc-BBN(7-14)NH 2 ] targeting vector for positron-emission tomography imaging of gastrin-releasing peptide receptor-expressing tissues

Radiolabeled peptides hold promise as diagnostic/therapeutic targeting vectors for specific human cancers. We report the design and development of a targeting vector, [(64)Cu-NOTA-8-Aoc-BBN(7-14)NH(2)] (NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid, 8-Aoc = 8-aminooctanoic acid, and BBN = bombesin), having very high selectivity and affinity for the gastrin-releasing peptide receptor (GRPr). GRPrs are expressed on a variety of human cancers, including breast, lung, pancreatic, and prostate, making this a viable approach toward site-directed localization or therapy of these human diseases. In this study, [NOTA-X-BBN(7-14)NH(2)] conjugates were synthesized, where X = a specific pharmacokinetic modifier. The IC(50) of [NOTA-8-Aoc-BBN(7-14)NH(2)] was determined by a competitive displacement cell-binding assay in PC-3 human prostate cancer cells using (125)I-[Tyr(4)]-BBN as the displacement ligand. An IC(50) of 3.1 +/- 0.5 nM was obtained, demonstrating high binding affinity of [NOTA-8-Aoc-BBN] for the GRPr. [(64)Cu-NOTA-X-BBN] conjugates were prepared by the reaction of (64)CuCl(2) with peptides in buffered aqueous solution. In vivo studies of [(64)Cu-NOTA-8-Aoc-BBN(7-14)NH(2)] in tumor-bearing PC-3 mouse models indicated very high affinity of conjugate for the GRPr. Uptake of conjugate in tumor was 3.58 +/- 0.70% injected dose (ID) per g at 1 h postintravenous injection (p.i.). Minimal accumulation of radioactivity in liver tissue (1.58 +/- 0.40% ID per g, 1 h p.i.) is indicative of rapid renal-urinary excretion and suggests very high in vivo kinetic stability of [(64)Cu-NOTA-8-Aoc-BBN(7-14)NH(2)] with little or no in vivo dissociation of (64)Cu(2+) from the NOTA chelator. Kidney accumulation at 1 h p.i. was 3.79 +/- 1.09% ID per g. Molecular imaging studies in GRPr-expressing tumor models produced high-contrast, high-quality micro-positron-emission tomography images.

Influence of dietary protein concentration on the oxidation of phenylalanine by the young pig.

1. Piglets were weaned at 3 d of age and reared to 2.5 kg on a liquid diet in which the protein was supplied by dried skim milk and a mixture of free amino acids. The oxidation of L-[1-14C]phenylalanine was measured as an indication of the partition of amino acids between retention and catabolism in pigs (2.5 kg) offered meals containing varied concentrations of crude protein (nitrogen x 6.25). 2. The dietary protein concentration was varied either by increasing the inclusion of a mixture of free amino acids in a series of diets containing 100 g protein/kg from skim milk, or by increasing the level of inclusion of the skim milk in a series of diets containing the equivalent of 100 g protein/kg from the free amino acid mixture. 3. The oxidation of phenylalanine was minimized by dietary protein concentrations of 240 and 258 g/kg for the diets containing increasing concentrations of free amino acids or skim milk respectively. 4. These results show that a mixture of free amino acids is used more effectively than intact protein for promoting retention of essential amino acids. 5. The recovery of radioactivity in expired carbon dioxide was inversely related to the recovery of radioactivity in liver tissue when the concentration of dietary crude protein was increased from deficient to adequate, demonstrating that the fractional oxidation of the indicator amino acid was inversely related to protein synthesis.

Depletion patterns of radioactivity and tissue residues in beef cattle after the withdrawal of oral C-diethylstilbestrol.

Seven beef heifers and eight beef steers were orally administered monoethyl-1 14C-diethylstilbestrol (14C-DES) and then one heifer and one steer were slaughtered on each of the following days after the withdrawal of DES: .75, 1.5, 3, 5, 7, 9 and 14. One steer was slaughtered 30 days after withdrawal. Total recovery of the administered radioactivity averaged 95.5%. Approximately 99.5% of the recovered radioactivity was excreted within 5 days after withdrawal of DES; however, a low level of radioactivity above background was measured in excreta up to 12 days after withdrawal. Semilog plots of the radioactivity in liver tissue, urine and feces versus withdrawal time were quadratic. A similar quadratic trend was noted for bile, but the quadratic function was not significant. Radioactivity above background was measurable up to 5 days after withdrawal in kidney tissue, 7 days in liver tissue, 9 days in bile and 11 to 12 days in urine and feces. DES residues in liver tissue were not measurable by gas chromatography (GLC) techniques after withdrawal periods of 3 days and longer. The percentage of total radioactivity in liver tissue presumptively identified by radioisotope dilution techniques as being associated with DES or its glucuronide conjugate decreased with increasing withdrawal time: from approximately 77% at .75 days to 4% at 7 days. The proportion of total radioactivity in liver tissue extracted by the routine GLC method decreased from 39% at .75 days to 2% at 7 days. The remainder of the radioactivity was not identified. Approximately 75% of the presumptively identified radioactivity was associated with conjugated DES and 25% was associated with free DES. Combining the quadratic depletion curve for radioactivity in liver tissue with the change in percentage of presumptively identified radioactivity resulted in a linear semilog plot for depletion from liver with a half-life of 17 hours. The biological half-life of the more slowly depleted unidentified fraction of radioactivity in liver tissue was 5.5 days.

Effect of secondary injections of antigen upon the retention in liver of a primary injection.

The retention of antigen in rabbit liver tissue, resulting from a primary intravenous injection, is influenced by immunization brought about by subsequent intravenous injections of the same antigen. In rabbits given a single primary intravenous injection of radioactive antigen, the retention of radioactivity in liver tissue, after a period of 21 days, was greater than when the primary injection was followed by secondary injections of the same, but non-radioactive antigen. The results were similar for both S(35)-azohemocyanin and S(35)-azo-bovine-serum-albumin, except the hemocyanin was retained to a greater extent than the albumin. There was very little if any correlation between the number of secondary injections and retention of the initial injection. Quantitative antibody nitrogen data, obtained for the serum of each rabbit showed, in general, an inverse relationship between circulating antibody and radioactivity retained, i.e. the higher the circulating antibody titer, the lower the retention of radioactivity in liver tissue. Passively administered homologous antibody did not produce a change in the retention of the primary injection of antigen nor did secondary injections of a heterologous native protein injected according to the same immunization schedule as the homologous azoprotein. From these results it may be concluded that an intracellular antibody-forming activity influences the loss (or retention) of antigen deposited in liver tissue and that the mechanism is immunologically specific.