Radiolabeled octreotide

VAIDYANATHAN, G, et al., Specific and high-level targeting of radiolabelled octreotide analogues to human medulloblastoma xenografts, Clin. Cancer Res. 9 (2003) 1868-1876. 

Slooter GD, Breeman WAP, Marquet RL, Krenning EP, Van Eijck CHJ. Anti-prolifera-tive effect of radiolabelled octreotide in a metastasis model in rat liver. Int J Cancer 1999 81 767-771. 

DTPA has also been used in the peptide-based " in-DTPA-octreotide. Octreotide is a shortened peptide analog of somatostatin designed to be more stable in vivo. Radiolabeling of octreotide for diagnostic imaging applications with radioisotopes for PET or SPECT has been investigated,... 

De Jong M et al (1998) Internalization of radiolabelled [DTPA(0)]octreotide and [DOTA(O), Tyr(3)]octreotide Peptides for somatostatin receptor-targeted scintigraphy and radionuclide therapy. Nucl Med Com 19 283-288... 

In analysis of the hver metabolism in rats treated with anti-colorectal carcinoma mAh 1A3 radiolabeled with Cu through three different macrocyclic bifunctional chelates, it was apparent that the radiocopper was transchelated and bound to proteins such as superoxide dismutase (SOD see Copper Proteins with Type Sites). Transchelation of the copper radiolabel appears to be a major factor for liver accumulation ofthe Cu-labeledBFC-lA3 conjugates After extensive evaluation, experimental results are consistent with in vivo transchelation of Cu from TETA-octreotide to superoxide dismutase (SOD) in rat liver. ... 

Guhlke S, Wester H-J, Bruns C, et al. (1994). (2-[ F]fluoropropionyl-(D)phe )-octreotide, a potential radiopharmaceutical for quantitative somatostatin receptor imaging with PET synthesis, radiolabeling, in vitro validation and biodistribution in mice. Nucl. Med. Biol. 21 819-825. 

Bakker W H, Albert R, Bruns C, et al. (1991). [ Tn-DTPA-D-Phe ]-octreotide, a potential radiopharmaceutical for imaging of somatostatin receptor-positive tumors Synthesis, radiolabeling and in-vitro validation. Life. Sci. 49 1583-1591. 

I-Laheled Octreotide. Initial studies of a radiolabeled tyrosine-bearing derivative, I-tyr-3-octreotide, successfully imaged both primary endocrine tumors and their metas-tases, in some cases even revealed ones previously undetected by CT scanning. In addition to endocrine tumors, this octreotide derivative also imaged tumors of the pancreatic endocrine system and the pituitary gland. ... 

Comparisons to the known structure of indium DTPA and to other divalent metal DTPA bis-amide complexes indicate that the indium cation binds to the three amine nitrogen atoms, the four carboxylate oxygen atoms, and the one carboxairdde oxygen atom of the DTPA monoamide ligand. Addition of an acidic In chloride solution to a ly-ophilized DTPA-octreotide pellet at room temperature readily fomis In DTPA-octreotide, known clinically as OctreoScan. In a rat model of pancreatic carcinoma In DTPA-octreotide showed clear visualization of the tumors and rapid, primarily renal, clearance of the radiophamiaceutical/ Moreover, pretreatment with 1 mg of octreotide prevents uptake of " in DTPA-octreotide in the tumors and adrenal glands, an observation that verifies that this radiolabeled peptide binds to receptor sites. 

Radioiodination of lyt -octreotide using Chloramine-T (modified from Bakker et al 1990). Twenty-five microliters oflCT M Tyr -octreotide is mixed in a reaction vial with 10 MBq 10 pi of a freshly prepared solution oflCT M Chloramine-T in 0.25 M phosphate buffer pH 7.4 is added. After 30 s, 10 pi of a saturated solution of methionine in 0.25 M phosphate buffer pH 7.4 is added and the reaction mixture is vortexed. Purification is accomplished by reversed-phase HPLC. As Chloramine-T reveals a very similar retention time as the labeled Tyr -octreotide, the eluent system H20/acetonitrile containing TFA is not suited for this purpose. Using a gradient of0% B —> 100% B in 30 min (A = Tris-phosphate buffer pH 2.6 and B = methanol), flow rate = 0.7 ml mirT, the radiolabeled peptide can be purified. The 1-labeled peptide can be stored for up to 1 month at —20°C. 

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