Labeling of PeptidePNAPeptide Chimeras

3.3.1. Tc-99m Labeling of Peptide-PNA-Peptide Chimeras

Purified peptide-PNA chimeras were labeled with Tc-99m as described above. Unchelated free Tc-99m, Rf 1.0, was 1.5%, determined by instant TLC on silica gel (ITLC-SG; Gelman) developed with methylethyl ketone. Colloid formation, Rf 0.0, was 1.0%, determined using instant TLC also on silica gel (ITLC-SG; Gelman) developed with pyridine/HOAc/H2O (3:5:1.5). These preparations were stable at 22 °C for more than 4 h, as determined by HPLC (Fig. 14), and were stable to challenges with 100 molar excesses of DTPA, HAS, or cysteine. Similar results were obtained for the MYC mismatch PNA (WT3629). Specific activities of the preparations were 7-10 Ci/^mol E(92).

3.3.2. Cu-64 Labeling of Peptide-PNA-Peptide Chimeras

Recently, in Thakur Laboratory (106), we have labeled vasoactive intestinal peptide (VIP) analog TP3982 with Cu-64 (Fig. 15). Free Cu-64, 3.4%, eluted at 4.3 min, and the Cu-64-TP3982, 96.6%, at 8.0 min. VIP, a 28-amino-acid endogenous hormone, is a muscle relaxant that has a high affinity for VPAC1

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