Iron Availability within the Leaf Vasculature Determines the Magnitude of Iron Deficiency Responses in Source and Sink Tissues in Arabidopsis.

Iron (Fe) uptake and translocation in plants are fine-tuned by complex mechanisms that are not yet fully understood. In Arabidopsis thaliana, local regulation of Fe homeostasis at the root level has been extensively studied and is better understood than the systemic shoot-to-root regulation. While the root system is solely a sink tissue that depends on photosynthates translocated from source tissues, the shoot system is a more complex tissue, where sink and source tissues occur synchronously. In this study, and to gain better insight into the Fe deficiency responses in leaves, we overexpressed Zinc/Iron-regulated transporter-like Protein (ZIP5), an Fe/Zn transporter, in phloem-loading cells (proSUC2::AtZIP5) and determined the timing of Fe deficiency responses in sink (young leaves and roots) and source tissues (leaves). Transgenic lines overexpressing ZIP5 in companion cells displayed increased sensitivity to Fe deficiency in root growth assays. Moreover, young leaves and roots (sink tissues) displayed either delayed or dampened transcriptional responses to Fe deficiency compared to wild-type (WT) plants. We also took advantage of the Arabidopsis mutant nas4x-1 to explore Fe transcriptional responses in the opposite scenario, where Fe is retained in the vasculature but in an unavailable and precipitated form. In contrast to proSUC2::AtZIP5 plants, nas4x-1 young leaves and roots displayed a robust and constitutive Fe deficiency response, while mature leaves showed a delayed and dampened Fe deficiency response compared to WT plants. Altogether, our data provide evidence suggesting that Fe sensing within leaves can also occur locally in a leaf-specific manner.

A New, Second Generation Trithiol Bifunctional Chelate for 72,77As: Trithiol(b)-(Ser)2-RM2.

Trithiol chelates are suitable for labeling radioarsenic (72As: 2.49 MeV ß+, 26 h; 77As: 0.683 MeV ß-, 38.8 h) to form potential theranostic radiopharmaceuticals for positron emission tomography (PET) imaging and therapy. A trithiol(b)-(Ser)2-RM2 bioconjugate and its arsenic complex were synthesized and characterized. The trithiol(b)-(Ser)2-RM2 bioconjugate was radiolabeled with no-carrier-added 77As in over 95% radiochemical yield and was stable for over 48 h, and in vitro IC50 cell binding studies of [77As]As-trithiol(b)-(Ser)2-RM2 in PC-3 cells demonstrated high affinity for the gastrin-releasing peptide (GRP) receptor (low nanomolar range). Limited biodistribution studies in normal mice were performed with HPLC purified 77As-trithiol(b)-(Ser)2-RM2 demonstrating both pancreatic uptake and hepatobiliary clearance.

A Third Generation Potentially Bifunctional Trithiol Chelate, Its nat,1XXSb(III) Complex, and Selective Chelation of Radioantimony (119Sb) from Its Sn Target.

The therapeutic potential of the Meitner-Auger- and conversion-electron emitting radionuclide 119Sb remains unexplored because of the difficulty of incorporating it into biologically targeted compounds. To address this challenge, we report the development of 119Sb production from electroplated tin cyclotron targets and its complexation by a novel trithiol chelate. The chelation reaction occurs in harsh solvent conditions even in the presence of large quantities of tin, which are necessary for production on small, low energy (16 MeV) cyclotrons. The 119Sb-trithiol complex has high stability and can be purified by HPLC. The third generation trithiol chelate and the analogous stable natSb-trithiol compound were synthesized and characterized, including by single-crystal X-ray diffraction analyses.

Synthesis and evaluation of Re/99mTc(I) complexes bearing a somatostatin receptor-targeting antagonist and labeled via a novel [N,S,O] clickable bifunctional chelating agent.

The somatostatin receptor subtype 2 (SSTR2) is often highly expressed on neuroendocrine tumors (NETs), making it a popular in vivo target for diagnostic and therapeutic approaches aimed toward management of NETs. In this work, an antagonist peptide (sst2-ANT) with high affinity for SSTR2 was modified at the N-terminus with a novel [N,S,O] bifunctional chelator (2) designed for tridentate chelation of rhenium(I) and technetium(I) tricarbonyl cores, [Re(CO)3]+ and [99mTc][Tc(CO)3]+. The chelator-peptide conjugation was performed via a Cu(I)-assisted click reaction of the alkyne-bearing chelator (2) with an azide-functionalized sst2-ANT peptide (3), to yield NSO-sst2-ANT (4). Two synthetic methods were used to prepare Re-4 at the macroscopic scale, which differed based on the relative timing of the click conjugation to the [Re(CO)3]+ complexation by 2. The resulting products demonstrated the expected molecular mass and nanomolar in vitro SSTR2 affinity (IC50 values under 30 nM, AR42J cells, [125I]iodo-Tyr11-somatostatin-14 radioligand standard). However, a difference in their HPLC retention times suggested a difference in metal coordination modes, which was attributed to a competing N-triazole donor ligand formed during click conjugation. Surprisingly, the radiotracer scale reaction of [99mTc][Tc(OH2)3(CO)3]+ (99mTc; t½â€¯= 6 h, 141 keV γ) with 4 formed a third product, distinct from the Re analogues, making this one of the unusual cases in which Re and Tc chemistries are not well matched. Nevertheless, the [99mTc]Tc-4 product demonstrated excellent in vitro stability to challenges by cysteine and histidine (≥98% intact through 24 h), along with 75% stability in mouse serum through 4 h. In vivo biodistribution and microSPECT/CT imaging studies performed in AR42J tumor-bearing mice revealed improved clearance of this radiotracer in comparison to a similar [99mTc][Tc(CO)3]-labeled sst2-ANT derivative previously studied. Yet despite having adequate tumor uptake at 1 h (4.9% ID/g), tumor uptake was not blocked by co-administration of a receptor-saturating dose of SS-14. Aimed toward realignment of the Re and Tc product structures, future efforts should include distancing the alkyne group from the intended donor atoms of the chelator, to reduce the coordination options available to the [M(CO)3]+ core (M = Re, 99mTc) by disfavoring involvement of the N-triazole.

NOTA and NODAGA [99mTc]Tc- and [186Re]Re-Tricarbonyl Complexes: Radiochemistry and First Example of a [99mTc]Tc-NODAGA Somatostatin Receptor-Targeting Bioconjugate.

With the long-term goal of developing theranostic agents for applications in nuclear medicine, in this work we evaluated the well-known NOTA and NODAGA chelators as bifunctional chelators (BFCs) for the [99mTc/186Re]Tc/Re-tricarbonyl core. In particular, we report model complexes of the general formula fac-[M(L)(CO)3]+ (M = Re, 99mTc, 186Re) where L denotes NOTA-Pyr (1) or NODAGA-Pyr (2), which are derived from conjugation of NOTA/NODAGA with pyrrolidine (Pyr). Further, as proof-of-principle, we synthesized the peptide bioconjugate NODAGA-sst2-ANT (3) and explored its complexation with the fac-[Re(CO)3]+ and fac-[99mTc][Tc(CO)3]+ cores; sst2-ANT denotes the somatostatin receptor (SSTR) antagonist 4-NO2-Phe-c(DCys-Tyr-DTrp-Lys-Thr-Cys)-DTyr-NH2. Rhenium complexes Re-1 through Re-3 were synthesized and characterized spectroscopically, and receptor binding affinity was demonstrated for Re-3 in SSTR-expressing cells (AR42J, IC50 = 91 nM). Radiolabeled complexes [99mTc]Tc/[186Re]Re-1/2 and [99mTc]Tc-3 were prepared in high radiochemical yield (>90%, determined by radio-HPLC) by reacting [99mTc]/[186Re][Tc/Re(OH2)3(CO)3]+ with 1-3 and correlated well with the respective Re-1 through Re-3 standards in comparative HPLC studies. All radiotracers remained intact through 24 h (99mTc-labeled complexes) or 48 h (186Re-labeled complexes) against 1 mM l-histidine and 1 mM l-cysteine (pH 7.4, 37 °C). Similarly, rat serum stability studies displayed no decomposition and low nonspecific binding of 9-24% through 4 h. Biodistribution of [99mTc]Tc-3 in healthy CF-1 mice demonstrated a favorable pharmacokinetic profile. Rapid clearance was observed within 1 h post-injection, predominantly via the renal system (82% of the injected dose was excreted in urine by 1 h), with low kidney retention (% ID/g: 11 at 1 h, 5 at 4 h, and 1 at 24 h) and low nonspecific uptake in other organs/tissues. Our findings establish NOTA and NODAGA as outstanding BFCs for the fac-[M(CO)3]+ core in the design and development of organometallic radiopharmaceuticals. Future in vivo studies of [99mTc]Tc- and [186Re]Re-tricarbonyl complexes of NODAGA/NOTA-biomolecule conjugates will further probe the potential of these chelates for nuclear medicine applications in diagnostic imaging and targeted radiotherapy, respectively.

Changes in iron availability in Arabidopsis are rapidly sensed in the leaf vasculature and impaired sensing leads to opposite transcriptional programs in leaves and roots.

The OLIGOPEPTIDE TRANSPORTER 3 (OPT3) has recently been identified as a component of the systemic network mediating iron (Fe) deficiency responses in Arabidopsis. Reduced expression of OPT3 induces an over accumulation of Fe in roots and leaves, due in part by an elevated expression of the IRON-REGULATED TRANSPORTER 1. Here we show however, that opt3 leaves display a transcriptional program consistent with an Fe overload, suggesting that Fe excess is properly sensed in opt3 leaves and that the OPT3-mediated shoot-to-root signaling is critical to prevent a systemic Fe overload. We also took advantage of the tissue-specific localization of OPT3, together with other Fe-responsive genes, to determine the timing and location of early transcriptional events during Fe limitation and resupply. Our results show that the leaf vasculature responds more rapidly than roots to both Fe deprivation and resupply, suggesting that the leaf vasculature is within the first tissues that sense and respond to changes in Fe availability. Our data highlight the importance of the leaf vasculature in Fe homeostasis by sensing changes in apoplastic levels of Fe coming through the xylem and relaying this information back to roots via the phloem to regulate Fe uptake at the root level.

Technetium and Rhenium Schiff Base Compounds for Nuclear Medicine: Syntheses of Rhenium Analogues to 99mTc-Furifosmin.

Rhenium, the third-row congener of technetium, is often used to develop the macroscopic chemistry of potential 99mTc diagnostic radiopharmaceuticals. The rhenium analogues to 99mTc-furifosmin are being developed for potential radiotherapy of multidrug-resistant tumors. Complexes of the form trans-[MIII(PR3)2(N2O2-Schiff base)]+ are of interest for the potential imaging and treatment of multidrug-resistant tumors. Reaction of the tetradentate Schiff ligand 4,4'-[(1 E,1' E)-[ethane-1,2-diylbis(azanylylidene)]bis(methanylylidene)]bis(2,2,5,5-tetramethyl-2,5-dihydrofuran-3-ol) (tmf2enH2) with the M(V) starting materials ( nBu4N)[TcOCl4] and ( nBu4N)[ReOCl4] gave the monomeric products trans-[TcOCl(tmf2en)] and trans-[ReOCl(tmf2en)], respectively. Reduction of in situ formed trans-[ReOCl(tmf2en)] by various tertiary phosphines yielded disubstitued Re(III) products of the general type trans-[ReIII(PR3)2(tmf2en)]+. The rhenium(III) compounds were found to be water-soluble and stable in aqueous solution. Reversible ReIII/ReIV and ReIII/ReII redox processes were observed at about 0.8-0.9 and -0.65 to -0.8 V, respectively, for each of the rhenium(III) species. Reaction of in situ formed trans-TcOCl(tmf2en) with triethylphosphine yielded the reduced, disubstituted trans-[Tc(PEt3)2(tmf2en)]PF6. A reversible TcIII/TcII redox couple was observed for the technetium(III) species, about 200 mV less negative than their rhenium(III) analogues, in addition to an irreversible TcIII/TcIV process. All compounds were characterized using conventional spectroscopic techniques, single-crystal X-ray crystallography, and cyclic voltammetry.

Pertechnetate-Induced Addition of Sulfide in Small Olefinic Acids: Formation of [TcO(dimercaptosuccinate)2]5- and [TcO(mercaptosuccinate)2]3- Analogues.

Technetium-99 (99Tc) is important to the nuclear fuel cycle as a long-lived radionuclide produced in ∼6% fission yield from 235U or 239Pu. In its most common chemical form, namely, pertechnetate (99TcO4-), it is environmentally mobile. In situ hydrogen sulfide reduction of pertechnetate has been proposed as a potential method to immobilize environmental 99TcO4- that has entered the environment. Reactions of 99TcO4- with sulfide in solution result in the precipitation of Tc2S7 except when olefinic acids, specifically fumaric or maleic acid, are present; a water-soluble 99Tc species forms. NMR (1H, 13C, and 2D methods) and X-ray absorption spectroscopy [XAS; near-edge (XANES) and extended fine structure (EXAFS)] studies indicate that sulfide adds across the olefinic bond to generate mercaptosuccinic acid (H3MSA) and/or dimercaptosuccinic acid (H4DMSA), which then chelate(s) the 99Tc to form [99TcO(MSA)2]3-, [99TcO(DMSA)2]5-, or potentially [99TcO(MSA)(DMSA)]4-. 2D NMR methods allowed identification of the products by comparison to 99Tc and nonradioactive rhenium standards. The rhenium standards allowed further identification by electrospray ionization mass spectrometry. 99TcO4- is essential to the reaction because no sulfide addition occurs in its absence, as determined by NMR. Computational studies were performed to investigate the structures and stabilities of the potential products. Because olefinic acid is a component of the naturally occurring humic and fulvic acids found in soils and groundwater, the viability of in situ hydrogen sulfide reduction of environmental 99TcO4- as an immobilization method is evaluated.

Dithiol Aryl Arsenic Compounds as Potential Diagnostic and Therapeutic Radiopharmaceuticals.

Arsenic-72 ((72)As) and (77)As have nuclear properties useful for positron emission tomography (PET) and radiotherapy, respectively. The thiophilic nature of arsenic led to the evaluation of dithioarylarsines for potential use in radiopharmaceuticals. Several dithioarylarsines were synthesized from their arylarsonic acids and dithiols and were fully characterized by NMR, ESI-MS, and X-ray crystallography. This chemistry was translated to the no-carrier-added (nca) (77)As level. Because arsenic was available at the nca nanomolar level only as [(77)As]arsenate, this required addition of an aryl group directly to the As to form the [(77)As]arylarsonic acid. The [(77)As]arsenate was reduced from (77)As (V) to (77)As (III), and a modified Bart reaction was used to incorporate the aryl ring onto the (77)As, which was followed by dithiol addition. Various modifications and optimizations resulted in 95% radiochemical yield of nca [(77)As]p-ethoxyphenyl-1,2-ethanedithiolatoarsine.

Synthesis, Characterization, and In Vitro Evaluation of New (99m)Tc/Re(V)-Cyclized Octreotide Analogues: An Experimental and Computational Approach.

Radiolabeled proteolytic degradation-resistant somatostatin analogues have been of long-standing interest as cancer imaging and radiotherapy agents for targeting somatostatin receptor-positive tumors. Our interest in developing (186)Re- and (188)Re-based therapeutic radiopharmaceuticals led to investigation of a new Re(V)-cyclized octreotide analogue, Re(V)-cyclized, thiolated-DPhe(1)-Cys(2)-Tyr(3)-DTrp(4)-Lys(5)-Thr(6)-Cys(7)-Thr(OH)(8) (Re-SDPhe-TATE) using both experimental and quantum chemical methods. The metal is directly coordinated to SDPhe-TATE through cyclization of the peptide around the [ReO](3+) core. Upon complexation, four isomers were observed; the isolated/semi-isolated isomers exhibited different somatostatin receptor (sstr) binding affinities, 0.13 to 1.5 µM, in rat pancreatic tumor cells. Two-dimensional NMR experiments and electronic structure calculations were employed to elucidate the structural differences among the different isomers. According to NMR studies, the metal is coordinated to three thiolates and the backbone amide of Cys(2) in isomers 1 and 4, whereas the metal is coordinated to three thiolates and the backbone amide of Tyr(3) in isomer 2. Quantum chemical methods clarified the stereochemistry of Re-SDPhe-TATE and the possible peptide arrangements around the [ReO](3+) core. The re-cyclization reaction was translated to the (99m)Tc radiotracer level with four isomers observed on complexation with comparable HPLC retention times as the Re-SDPhe-TATE isomers. About 85% total (99m)Tc labeling yield was achieved by ligand exchange from (99m)Tc-glucoheptonate at 60 °C for an hour. About 100% and 51% of (99m)Tc(V)-cyclized SDPhe-TATE remained intact in phosphate buffered saline and 1 mM cysteine solution under physiological conditions at 6 h, respectively.

Chemical Kinetics Laboratory Discussion Worksheet.

A laboratory discussion worksheet and its answer key provide instructors and students a discussion model to further the students' understanding of chemical kinetics. This discussion worksheet includes a section for students to augment their previous knowledge about chemical kinetics measurements, an initial check on students' understanding of basic concepts, a group participation model where students work on solving complex-conceptual problems, and a conclusion to help students connect this discussion to their laboratory or lecture class. Additionally, the worksheet has a detailed solution to a more advanced problem to help students understand how the concepts they have put together relate to problems they will encounter during later formal assessments.

Inorganic chemistry in nuclear imaging and radiotherapy: current and future directions.

Radiometals play an important role in diagnostic and therapeutic radiopharmaceuticals. This field of radiochemistry is multidisciplinary, involving radiometal production, separation of the radiometal from its target, chelate design for complexing the radiometal in a biologically stable environment, specific targeting of the radiometal to its in vivo site, and nuclear imaging and/or radiotherapy applications of the resultant radiopharmaceutical. The critical importance of inorganic chemistry in the design and application of radiometal-containing imaging and therapy agents is described from a historical perspective to future directions.

Development and biodistribution studies of 77As-labeled trithiol RM2 bioconjugates for prostate cancer: Comparison of [77As]As-trithiol-Ser-Ser-RM2 vs. [77As]As-trithiol-Glu-Ser-RM2.

INTRODUCTION: Recent progress with the production of 72As (2.49 Mev ß+max (64%), 3.33 Mev ß+max (16%), 834 keV γ (81%), t1/2: 26 h) and 77As (0.683 Mev ß-max (97%), 239 keV γ (1.59%), t1/2: 38.8 h) has facilitated their evaluation as a potential "theranostic pair" for PET imaging and radiotherapy. Our 3rd generation trithiol chelate with two carboxylic acid groups was further developed as a bifunctional chelate for radioarsenic. METHODS: The As complex with the trithiol chelate was synthesized and characterized. No carrier added (nca) [77As][H2AsO4-] was used for radiolabeling studies. The trithiol chelate was conjugated to the RM2 peptide (DPhe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2) via solid phase peptide synthesis with two different linkers, Ser-Ser and Glu-Ser. The trithiol chelate and its RM2 bioconjugates were radiolabeled with nca 77As, and the RM2 bioconjugates were compared in initial biodistribution studies. RESULTS: The As diacid trithiol complex was characterized by 1H NMR, 13C NMR and HR-ESI-MS. The trithiol-RM2 precursor and As trithiol bioconjugates were characterized by HR-ESI-MS and/or LC-ESI-MS. Radiolabeling of the RM2 bioconjugates with 77As resulted in over 85% radiochemical yield for [77As]As-trithiol-Ser-Ser-RM2 ([77As]8) and 90% for [77As]As-trithiol-Glu-Ser-RM2 ([77As]9). Both radiotracers demonstrated excellent in vitro stability (≥ 90% remaining intact through 24 h in PBS buffer) and were more hydrophilic than previous analogues based on log D7.4 values. Biodistribution results of the two radiotracers in healthy CF-1 male mice demonstrated blockable pancreatic uptake at 1 h (82% for ([77As]8 and 78% for [77As]9) indicating specific gastrin-releasing peptide receptor (GRPR) uptake. The primary route of excretion was through the gastrointestinal system for both radiotracers. CONCLUSIONS: A new trithiol chelate with improved hydrophilicity was successfully conjugated to the RM2 peptide via two linkers, and high radiolabeling yield with nca 77As was achieved. In vivo biodistribution studies with both radiotracers demonstrated blockable pancreatic uptake suggestive of specific receptor uptake.

Comparison of pretargeted and conventional CC49 radioimmunotherapy using 149Pm, 166Ho, and 177Lu.

The therapeutic efficacies of radiolabeled biotin, pretargeted by monoclonal antibody (mAb)-streptavidin fusion protein CC49 scFvSA, were compared to those of radiolabeled mAb CC49, using the three radiolanthanides in an animal model of human colon cancer. The purpose of the present study was to compare antibody pretargeting to conventional radioimmunotherapy using (149)Pm, (166)Ho, or (177)Lu. Nude mice bearing LS174T colon tumors were injected sequentially with CC49 scFvSA, the blood clearing agent biotin-GalNAc(16), and (149)Pm-, (166)Ho-, or (177)Lu-DOTA-biotin. Tumor-bearing mice were alternatively administered (149)Pm-, (166)Ho-, or (177)Lu-MeO-DOTA-CC49. Therapy with pretargeted (149)Pm-,(166)Ho-, and (177)Lu-DOTA-biotin increased the median time of progression to a 1 g tumor to 50, 41, and 50 days post-treatment, respectively. Therapy with (149)Pm-,(166)Ho-, and (177)Lu-MeO-DOTA-CC49 increased the median time to progression to 53, 24, and 67 days post-treatment, respectively. In contrast, saline controls showed a median time to progression of 13 days postinjection. Treatment with pretargeted (149)Pm-, (166)Ho-, and (177)Lu-biotin or (149)Pm-, (166)Ho-, and (177)Lu-CC49 increased tumor doubling time to 18-36 days, compared to 3 days for saline controls. Among treated mice, 23% survived >84 days post-therapy, and 11% survived 6 months, but controls survived <29 days. Long-term survivors showed tumor growth inhibition or partial regression, extensive necrosis in residual masses, and no evidence of nontarget tissue toxicity at necropsy. Both pretargeted and conventional RIT demonstrated considerable efficacy in an extremely aggressive animal model of cancer. Our results identified (177)Lu as an optimal radiolanthanide for future evaluation of these agents in toxicity and multiple-dose therapy studies.

Design and synthesis of a bombesin peptide-conjugated tripodal phosphino dithioether ligand topology for the stabilization of the fac-[M(CO)3]+ core (M=(99 m)Tc or Re).

A new tumor-seeking tridentate topology consisting of a phosphino dithioether ((HOCH(2))(2)PCH(2)CH(2)S(CH(2))(n)CH(2)SR; PS(2)) ligand framework for the production of kinetically inert and in vivo stable facial [(99m)Tc(CO)(3)(PS(2))](+) or [Re(CO)(3)(PS(2))](+) is described. The X-ray crystal structure of fac-Re(CO)(3)(PS(2))PF(6) is reported. The bioconjugation strategies for incorporating bombesin (BBN) peptides on to the PS(2) tripodal framework and, thereby, de novo designing of GRP receptor-seeking Tc(PS(2)-BBN)(CO)(3) are developed.

Direct labeling of a somatostatin receptor antagonist via peptide cyclization with Re, 99mTc and 186Re metal centers: Radiochemistry and in vitro evaluation.

INTRODUCTION: With the long-term goal of developing a diagnostic (99mTc) and therapeutic (186Re) agent pair for targeting somatostatin receptor (SSTR)-positive neuroendocrine tumors (NETs), we developed novel metal-cyclized peptides through direct labeling of the potent SSTR2 antagonist Ac-4-NO2-Phe-c(DCys-Tyr-DTrp-Lys-Thr-Cys)-DTyr-NH2 (1) with Re (in Re-1), 99mTc (in [99mTc]Tc-1) and 186Re (in [186Re]Re-1). METHODS: Re-1 was characterized by LC-ESI-MS and HR-ESI-MS and was tested for receptor affinity in SSTR-expressing cells (AR42J). Radiolabeling of the peptide was achieved via ligand exchange from 99mTc-labeled glucoheptonate or [186Re]ReOCl3(PPh3)2, yielding [99mTc]Tc-1 or [186Re]Re-1, respectively. In vitro stability of [99mTc]Tc-1/[186Re]Re-1 in PBS (10 mM) at pH 7.4 and 37 °C was determined by HPLC analysis. Moreover, [99mTc]Tc-1 stability was tested in cysteine (1 mM) and rat serum under the same conditions. RESULTS: Re-1 consisted of two isomers, confirmed by LC-ESI-MS, with good SSTR2 affinity (IC50 = 43 ± 6 nM). Optimization of the 99mTc labeling through varying reaction parameters such as pH, reaction time, and Sn2+ and ligand concentrations resulted in high radiochemical yield (RCY ≥92%). Similarly, [186Re]Re-1 was prepared in reasonable RCY (≥50%). Both 99mTc/186Re-tracers consisted of two product isomers as identified by HPLC co-injection with Re-1. While [99mTc]Tc-1 was sufficiently stable in vitro (≥71% intact through 4 h in PBS, cysteine and rat serum), [186Re]Re-1 exhibited more moderate in vitro stability (58% intact after 1 h in PBS). CONCLUSIONS: Novel 99mTc/186Re-cyclized SSTR2 antagonist peptides were synthesized and characterized using the Re-cyclized analogue as a reference. Due to the nanomolar SSTR2 affinity of Re-1 and good in vitro stability of [99mTc]Tc-1, the latter shows early promise for development as a radiodiagnostic agent for SSTR-expressing NETs. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: The 99mTc-cyclized complex showed promising in vitro properties, and future in vivo studies will determine the potential for translating such a design into the human clinic.

Development and Preclinical Evaluation of 99mTc- and 186Re-Labeled NOTA and NODAGA Bioconjugates Demonstrating Matched Pair Targeting of GRPR-Expressing Tumors.

PURPOSE: The goal of this work was to develop hydrophilic gastrin-releasing peptide receptor (GRPR)-targeting complexes of the general formula fac-[M(CO)3(L)]+ [M = natRe, 99mTc, 186Re; L: NOTA for 1, NODAGA for 2] conjugated to a powerful GRPR peptide antagonist (DPhe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2) via a 6-aminohexanoic acid linker. PROCEDURES: Metallated-peptides were prepared employing the [M(OH2)3(CO)3]+ [M = Re, 99mTc, 186Re] precursors. Re-1/2 complexes were characterized with HR-MS. IC50 studies were performed for peptides 1/2 and their respective Re-1/2 complexes in a binding assay utilizing GRPR-expressing human PC-3 prostate cancer cells and [125I]I-Tyr4-BBN as the competing ligand. The 99mTc/186Re-complexes were identified by HPLC co-injection with their Re-analogues. All tracers were challenged in vitro at 37 °C against cysteine/histidine (phosphate-buffered saline 10 mM, pH 7.4) and rat serum. Biodistribution and micro-SPECT/CT imaging of [99mTc]Tc-1/2 and [186Re]Re-2 were performed in PC-3 tumor-bearing ICR SCID mice. RESULTS: High in vitro receptor affinity (IC50 2-3 nM) was demonstrated for all compounds. The 99mTc/186Re-tracers were found to be hydrophilic (log D7.4 ≤ - 1.35) and highly stable. Biodistribution in PC-3 xenografted mice revealed good tumor uptake (%ID/g at 1 h: 4.3 ± 0.7 for [99mTc]Tc-1, 8.3 ± 0.9 for [99mTc]Tc-2 and 4.2 ± 0.8 for [186Re]Re-2) with moderate retention over 24 h. Rapid renal clearance was observed for [99mTc]Tc-2 and [186Re]Re-2 (> 84 % at 4 h), indicating favorable pharmacokinetics. Micro-SPECT/CT images for the 99mTc-tracers clearly visualized PC-3 tumors in agreement with the biodistribution data and with superior imaging properties found for [99mTc]Tc-2. CONCLUSIONS: [99mTc]Tc-2 shows promise for further development as a GRPR-imaging agent. [186Re]Re-2 demonstrated very similar in vivo behavior to [99mTc]Tc-2, and further studies are therefore justified to explore the theranostic potential of our approach for targeting of GRPR-positive cancers.

Recovery, recycling and re-irradiation of enriched 104Ru metal targets for cost effective production of 105Rh.

Rhodium-105 (0.567 MeV ß-, 319 keV γ, 35.4 h half-life) was produced by neutron irradiation of enriched 104Ru (>99%) over multiple decades. A method is reported to recover the previously irradiated 104Ru (trapped in HCl as RuO42-) as the metal. The 104Ru was recovered in >93% yield and >98% enrichment. Neutron re-irradiation of the recycled 104Ru produced 105Rh, which was successfully radiolabeled with tetrathioethers in high yield. This recovery and recycling method for enriched 104Ru makes 105Rh production and utilization economical.

Radioactive gold nanoparticles in cancer therapy: therapeutic efficacy studies of GA-198AuNP nanoconstruct in prostate tumor-bearing mice.

Biocompatibility studies and cancer therapeutic applications of nanoparticulate beta-emitting gold-198 (198Au; beta(max) = 0.96 MeV; half-life of 2.7 days) are described. Gum arabic glycoprotein (GA)-functionalized gold nanoparticles (AuNPs) possess optimum sizes (12-18 nm core diameter and 85 nm hydrodynamic diameter) to target individual tumor cells and penetrate through tumor vasculature and pores. We report the results of detailed in vivo therapeutic investigations demonstrating the high tumor affinity of GA-198AuNPs in severely compromised immunodeficient (SCID) mice bearing human prostate tumor xenografts. Intratumoral administration of a single dose of beta-emitting GA-198AuNPs (70 Gy) resulted in clinically significant tumor regression and effective control in the growth of prostate tumors over 30 days. Three weeks after administration of GA-198AuNPs, tumor volumes for the treated animals were 82% smaller as compared with tumor volume of control group. The treatment group showed only transitory weight loss in sharp contrast to the tumor-bearing control group, which underwent substantial weight loss. Pharmacokinetic studies have provided unequivocal evidence for the optimum retention of therapeutic payload of GA-198AuNPs within the tumor site throughout the treatment regimen with minimal or no leakage of radioactivity to various nontarget organs. The measurements of white and red blood cells, platelets, and lymphocytes within the treatment group resembled those of the normal SCID mice, thus providing further evidence on the therapeutic efficacy and concomitant in vivo tolerance and nontoxic features of GA-198AuNPs. FROM THE CLINICAL EDITOR: In this study, the biocompatibility and cancer therapeutic applications of glycoprotein (GA) functionalized gold nanoparticles containing b-emitting Au-198 are described in SCID mice bearing human prostate tumor xenografts. The findings of significant therapeutic efficacy, good in vivo tolerance and non-toxic features make these particles ideal candidates for future human applications.