Rapid kit-based (68)Ga-labelling and PET imaging with THP-Tyr(3)-octreotate:a preliminary comparison with DOTA-Tyr(3)-octreotate

BACKGROUND: Ge/(68)Ga generators provide an inexpensive source of a PET isotope to hospitals without cyclotron facilities. The development of new (68)Ga-based molecular imaging agents and subsequent clinical translation would be greatly facilitated by simplification of radiochemical syntheses. We report the properties of a tris(hydroxypyridinone) conjugate of the SSTR2-targeted peptide, Tyr(3)-octreotate (TATE), and compare the (68)Ga-labelling and biodistribution of [(68)Ga(THP-TATE)] with the clinical radiopharmaceutical [(68)Ga(DOTATATE)]. METHODS: A tris(hydroxypyridinone) with a pendant isothiocyanate group was conjugated to the primary amine terminus of H(2)N-PEG(2)-Lys(iv-Dde)(5)-TATE, and the resulting conjugate was deprotected to provide THP-TATE. THP-TATE was radiolabelled with (68)Ga(3+) from a (68)Ge/(68)Ga generator. In vitro uptake was assessed in SSTR2-positive 427-7 cells and SSTR2-negative 427 (parental) cells. Biodistribution of [(68)Ga(THP-TATE)] was compared with that of [(68)Ga(DOTATATE)] in Balb/c nude mice bearing SSTR2-positive AR42J tumours. PET scans were obtained 1 h post-injection, after which animals were euthanised and tissues/organs harvested and counted. RESULTS: [(68)Ga(THP-TATE)] was radiolabelled and formulated rapidly in <2 min, in ≥95 % radiochemical yield at pH 5–6.5 and specific activities of 60–80 MBq nmol(−1) at ambient temperature. [(68)Ga(THP-TATE)] was rapidly internalised into SSTR2-positive cells, but not SSTR2-negative cells, and receptor binding and internalisation were specific. Animals administered [(68)Ga(THP-TATE)] demonstrated comparable SSTR2-positive tumour activity (11.5 ± 0.6 %ID g(−1)) compared to animals administered [(68)Ga(DOTATATE)] (14.4 ± 0.8 %ID g(−1)). Co-administration of unconjugated Tyr(3)-octreotate effectively blocked tumour accumulation of [(68)Ga(THP-TATE)] (2.7 ± 0.6 %ID g(−1)). Blood clearance of [(68)Ga(THP-TATE)] was rapid and excretion was predominantly renal, although compared to [(68)Ga(DOTATATE)], [(68)Ga(THP-TATE)] exhibited comparatively longer kidney retention. CONCLUSIONS: Radiochemical synthesis of [(68)Ga(THP-TATE)] is significantly faster, proceeds under milder conditions, and requires less manipulation than that of [(68)Ga(DOTATATE)]. A (68)Ga-labelled tris(hydroxypyridinone) conjugate of Tyr(3)-octreotate demonstrates specificity and targeting affinity for SSTR2 receptors, with comparable in vivo targeting affinity to the clinical PET tracer, [(68)Ga(DOTATATE)]. Thus, peptide conjugates based on tris(hydroxypyridinones) are conducive to translation to kit-based preparation of PET tracers, enabling the expansion and adoption of (68)Ga PET in hospitals and imaging centres without the need for costly automated synthesis modules

Elucidation of the Origin of nOes or rOes That Show the Hydration in the Minor and Major Grooves of DNA duplex with ATTAAT tract by a Combination of NOESY and ROESY Experiments

Abstract. A combination of NOESY and ROESY experiments (using ammonia as a catalyst across the pH range of 5 to 8.6) has given us a clear understanding regarding the origin of nOes that are attributed to the stereochemical location and the residence time of water in the major and the minor grooves of d 5&apos; ( 1 C 2 C 3 A 4 T 5 T 6 A 7 A 8 T 9 G 10 G) 2 3&apos; duplex Our conclusions are the following: (i) In the major groove, the presence of ammonia in the buffer does not influence on the process of exchange between bound and bulk water. (ii) It has been found that the observation of the bound water in the minor groove is a result of straight dipole-dipole effect at the physiological pH. (iii) The residence time of water near H2 of adenine (H2A) in the minor groove has been estimated to be in the range of 0.3 -0.5ns, which is closer to the residence time of the bound water found on the surface of protein. (iv) The hydration pattern in the minor groove in the physiological pH, under our NMR measurement condition, is similar to the ones found in the X-ray structure. (v) It has been shown that at pH &gt; 8.0 the nOe/rOe intensities of the water-H2A crosspeaks dramatically increase due to dipole-dipole and/or relayed magnetization transfer from H2A to water through ammonia catalyst. The nuclear Overhauser effect based NMR experiments have proved to be sensitive and efficient tool to identify sequentially assigned protein and DNA/RNA protons that have nOe/rOe interactions with nearby water protons [1

The synthesis and conformation of 2'- and 3'-hypermodified tricyclic nucleosides and their use in the synthesis of novel 2'- or 3'-isomeric 4(7)- substituted isoxazolidine-nucleosides

Intramolecular 1,3-dipolar cycloaddition reactions of a number of C- alkenyl nitrones of nucleoside derivatives 7, 9, 19 and 28 afforded 2'- and 3'-hypermodified tricyclic nucleoside derivatives 10 (56%), 11 (43%), 20 (91%) and 29 (15%), respectively. The solution structures of these tricyclic nucleoside derivatives have been investigated using the 3J(HH) (1H at 500 MHz) and the NMR-derived torsion angle constrained energy minimizations with the aid of MacroModel's AMBER force field. Subsequent Tamao oxidation of the hypermodified nucleoside derivatives 20 and 29 gave spiro-4(7)-substituted isoxazolidine-nucleoside derivatives 21 and 30, respectively.link_to_subscribed_fulltex

PET tracer development—a tale of mice and men

PET scanning is an emerging technology for the clinical evaluation of many disease processes in man. The vast majority of clinical positron emission tomography (PET) studies are performed using a single tracer, fluorodeoxyglucose. Despite the excellent diagnostic performance of this tracer, it has recognised limitations. New tracers offer the potential to both address these limitations, and to establish new applications for PET. Small animal PET is a logical technique for validating new tracers relevant to human diseases. However, interspecies differences in the handling of chemicals may significantly influence the handling of novel tracers. This requires caution in extrapolating findings in animals to expectations of performance in man. Already there are several examples where biodistribution studies in mice would not have predicted the clinical utility of existing PET tracers. Nevertheless, application of a systematic approach to tracer development is likely to speed transition of new tracers from animals into man

Preclinical characterization of 18F-D-FPHCys, a new amino acid-based PET tracer

The imaging potential of a new F-18-labelled methionine derivative, S-(3-[F-18]fluoropropyl)-d-homocysteine (F-18-D-FPHCys), and its selectivity for amino acid transporter subtypes were investigated in vitro and by imaging of human tumour xenografts. Expression of members of the system L (LAT isoforms 1-4 and 4F2hc) and ASCT (ASCT isoforms 1 and 2) amino acid transporter subclasses were assessed by quantitative real-time PCR in four human tumour models, including A431 squamous cell carcinoma, PC3 prostate cancer, and Colo 205 and HT-29 colorectal cancer lines. The first investigations for the characterization of F-18-D-FPHCys were in vitro uptake studies by comparing it with [1-C-14]-l-methionine (C-14-MET) and in vivo by PET imaging. In addition, the specific involvement of LAT1 transporters in F-18-D-FPHCys accumulation was tested by silencing LAT1 mRNA transcription with siRNAs. To determine the proliferative activity in tumour xenografts ex vivo, Ki-67 staining was used as a biomarker. A431 cells showed the highest F-18-D-FPHCys uptake in vitro and in vivo followed by Colo 205, PC3 and HT-29. A similar pattern of retention was observed with C-14-MET. F-18-D-FPHCys retention was strongly correlated with LAT1 expression both in vitro (R (2) = 0.85) and in vivo (R (2) = 0.99). Downregulation of LAT1 by siRNA inhibited F-18-D-FPHCys uptake, demonstrating a clear dependence on this transporter for tumour uptake. Furthermore, F-18-D-FPHCys accumulation mirrored cellular proliferation. The favourable properties of F-18-D-FPHCys make this tracer a promising imaging probe for detection of tumours as well as for the noninvasive evaluation and monitoring of tumour growth.© 2012, Springer