Preparation and crystal structure of polymeric lithium[dioxoTc(V)-tetraazaundecane]-bis(trifluoromethanesulfonate) complex

[99mTc]Demotensin 5 and 6 in the NTS1-R-targeted imaging of tumours: synthesis and preclinical results

PURPOSE

The aim of this study was to evaluate the applicability of [(99m)Tc]Demotensin 5 and 6 [Formula: see text] in the targeted diagnostic imaging of neurotensin subtype 1 receptor (NTS1-R)-expressing tumours.

METHODS

Labelling of Demotensin 5 and 6 with (99m)Tc was conducted by brief incubation with (99m)TcO(4) (-), SnCl(2) and citrate anions in alkaline medium at ambient temperature. Affinities of conjugates for the NTS1-R were determined by competition binding experiments in WiDr cell membranes using [(125)I-Tyr(3)]NT as the radioligand. Saturation binding assays were conducted for [(99m)Tc/(99g)Tc]Demotensin 6 in WiDr cell membranes. Internalisation of [(99m)Tc]Demotensin 5 and 6 was studied at 37 degrees C in WiDr cells. Biodistribution of [(99m)Tc]Demotensin 5 and 6 was performed in female Swiss nu/nu mice bearing human WiDr xenografts.

RESULTS

Unlabelled conjugates showed a high affinity for the human NTS1-R (Demotensin 5 IC(50)=0.03+/-0.01 nM; Demotensin 6 IC(50)=0.08+/-0.02 nM), while high affinity was also exhibited by (radio)metallated [(99m)Tc/(99g)Tc]Demotensin 6 (K (d)=0.13+/-0.01 nM). [(99m)Tc]Demotensin 5 and 6 internalised rapidly and specifically in WiDr cells. After injection in WiDr tumour-bearing mice, radiopeptides, and especially the doubly stabilised [(99m)Tc]Demotensin 6, showed NTS1-R-mediated uptake in the intestines and in the implanted tumour (4.30+/-0.45%ID/g at 1 h post injection) and rapid renal excretion from non-target tissues into the urine.

CONCLUSION

[(99m)Tc]Demotensin 6 shows a favourable preclinical profile and further testing in patients is warranted to monitor its eventual applicability as a radiotracer in the diagnostic imaging of NTS1-R-positive tumours.

Toward stable N4-modified neurotensins for NTS1-receptor-targeted tumor imaging with 99mTc

A series of Gly-neurotensin(8-13) analogues modified at the N-terminus by acyclic tetraamines (Demotensin 1-4) were obtained by solid-phase peptide synthesis techniques. Strategic replacement of amino acids and/or reduction of sensitive peptide bonds were performed to enhance conjugate resistance against proteolytic enzymes. During 99mTc-labeling, single species radiopeptides, [99mTc]Demotensin 1-4, were easily obtained in high yields and typical specific activities of 1 Ci/micromol. Peptide conjugates displayed a high affinity binding to the human neurotensin subtype 1 receptor (NTS1-R) expressed in colon adenocarcinoma HT-29 or WiDr cells and/or in human tumor sections. [99mTc]Demotensin 1-4 internalized very rapidly in HT-29 or WiDr cells by a NTS1-R-mediated process. [99mTc]Demotensin 3 and 4, which remained stable during 1 h incubation in murine plasma, were selectively studied in nude mice bearing human HT-29 and WiDr xenografts. After injection, [99mTc]Demotensin 3 and 4 effectively and specifically localized in the experimental tumors and were rapidly excreted via the kidneys into the urine, exhibiting overall biodistribution patterns favorable for NTS1-R-targeted tumor imaging in man.

[99mTc]Demotate 2 in the detection of sst2-positive tumours: a preclinical comparison with [111In]DOTA-tate

PURPOSE

The aim of this study was to evaluate [(99m)Tc]Demotate 2 ([(99m)Tc-N(4) (0-1),Asp(0),Tyr(3)]octreotate) as a candidate for in vivo imaging of sst(2)-positive tumours and to compare it with [(111)In]DOTA-tate ([(111)In-DOTA(0),Tyr(3)]octreotate).

METHODS

Labelling of Demotate 2 with (99m)Tc was performed at room temperature using SnCl(2) as reductant in the presence of citrate at alkaline pH. Radiochemical analysis involved ITLC and HPLC methods. Peptide conjugate affinities for sst(2) were determined by receptor autoradiography on rat brain cortex sections using [DOTA(0),(125)I-Tyr(3)]octreotate as the radioligand. The affinity profile of Demotate 2 for human sst(1)-sst(5) was studied by receptor autoradiography in cell preparations using the universal somatostatin radioligand [(125)I][Leu(8),(D: )Trp(22),Tyr(25)]somatostatin-28. The internalisation rates of [(99m)Tc]Demotate 2 and [(111)In]DOTA-tate were compared in sst(2)-positive and -negative control cell lines. Biodistribution of radiopeptides was studied in male Lewis rats bearing CA20948 tumours.

RESULTS

Peptide conjugates showed selectivity and a high affinity binding for sst(2) (Demotate 2 IC(50)=3.2 nM and DOTA-tate IC(50)=5.4 nM). [(99m)Tc]Demotate 2, like [(111)In]DOTA-tate, internalised rapidly in all sst(2)-positive cells tested, but not in sst(2)-negative control cells. After injection in CA20948 tumour-bearing rats both radiopeptides showed high and specific uptake in the sst(2)-positive organs and in the implanted tumour and rapid excretion from non-target tissues via the kidneys.

CONCLUSION

[(99m)Tc]Demotate 2, similarly to the known sst(2)-targeting agent [(111)In]DOTA-tate, showed promising biological qualities for application in the scintigraphy of sst(2)-positive tumours.

Tetraamine-modified octreotide and octreotate: labeling with99mTc and preclinical comparison in AR4-2J cells and AR4-2J tumor-bearing mice

Two somatostatin analogues, [(99m)Tc]Demotide and [(99m)Tc]Demotate 4, were compared with [(99m)Tc]Demotate 1, a previously reported somatostatin receptor subtype 2 (sst(2)) targeting tracer. Conjugates were prepared by coupling an open-chain tetraamine chelator to D-Phe(1) of [Tyr(3)]-octreotide or [Tyr(3)]-octreotate, respectively, via a p-benzylaminodiglycolic acid spacer adopting solid-phase peptide synthesis techniques. Peptide conjugates were collected in a highly pure form after chromatographic purification. Eventually, [(99m)Tc]Demotide and [(99m)Tc]Demotate 4 were obtained in approximately 1 Ci/micromol specific activity and >96% purity after labeling under alkaline conditions. Demotide and Demotate 4 exhibited similar high binding affinities for the sst(2) expressed in AR4-2J cells with IC(50) values 0.16 and 0.10 nM, respectively. The (radio)metallated analogues [(99m)Tc]Demotide and [(99m)Tc]Demotate 4 showed equally high affinities to the sst(2) during saturation binding assays in AR4-2J cell membranes (K(d)s 0.08 and 0.07 nM, respectively). During incubation at 37 degrees C with AR4-2J cells, the radiopeptides internalized effectively via a receptor-mediated process, with [(99m)Tc]Demotate 4 exhibiting a faster internalization rate than [(99m)Tc]Demotide. After injection in athymic mice bearing sst(2)-expressing AR4-2J tumors, the radiotracers showed high and specific uptake in the tumor (>25%ID/g at 1 h) and in the sst(2)-positive organs. However, both [(99m)Tc]Demotide and [(99m)Tc]Demotate 4 showed unfavorably higher background activity, especially in the abdomen, in comparison to [(99m)Tc]Demotate 1 and are, therefore, less suited than [(99m)Tc]Demotate 1 for sst(2)-targeted tumor imaging in man.

Potent Bombesin-like Peptides for GRP-Receptor Targeting of Tumors with 99mTc: A Preclinical Study

Four open chain tetraamine-functionalized bombesin (BB) analogues were synthesized [parent tetradecapeptide-based Demobesin 3 and 4 and BB(7-14)-based Demobesin 5 and 6]. Labeling with (99m)Tc afforded high-purity and high specific activity radiotracers. Peptides showed high affinity for the human GRP-R (GRP-R = gastrin releasing peptide receptor) expressed in PC-3 cells. In human tumors preferentially expressing single bombesin receptor subtypes, they showed high affinity for the GRP-R, less affinity for the NMB-R (NMB-R = neuromedin B receptor) and no affinity for the orphan BB(3)-R (bombesin subtype 3 receptor). [(99m)Tc]Demobesin 3-6 efficiently internalized in a time- and dose-dependent manner in PC-3 cells and showed a high and specific uptake in human PC-3 xenografts and the pancreas of nude mice. [(99m)Tc]Demobesin 3 and 4 were rapidly excreted via the kidneys while the truncated analogues were predominantly processed by the hepatobiliary system. Patient studies are scheduled for validating the suitability of [(99m)Tc]Demobesin 3 and 4 in the GRP-R-targeted imaging of tumors.