177Lu-PSMA-617 Therapy in Mice, with or without the Antioxidant α1-Microglobulin (A1M), Including Kidney Damage Assessment Using 99mTc-MAG3 Imaging.

Anti-prostate specific membrane antigen (PSMA) radioligand therapy is promising but not curative in castration resistant prostate cancer. One way to broaden the therapeutic index could be to administer higher doses in combination with radioprotectors, since administered radioactivity is kept low today in order to avoid side-effects from a high absorbed dose to healthy tissue. Here, we investigated the human radical scavenger α1-microglobulin (A1M) together with 177-Lutetium (177Lu) labeled PSMA-617 in preclinical models with respect to therapeutic efficacy and kidney toxicity. Nude mice with subcutaneous LNCaP xenografts were injected with 50 or 100 MBq of [177Lu]Lu-PSMA-617, with or without injections of recombinant A1M (rA1M) (at T = 0 and T = 24 h). Kidney absorbed dose was calculated to 7.36 Gy at 4 days post a 100 MBq injection. Activity distribution was imaged with Single-Photon Emission Computed Tomography (SPECT) at 24 h. Tumor volumes were measured continuously, and kidneys and blood were collected at termination (3-4 days and 3-4 weeks after injections). In a parallel set of experiments, mice were given [177Lu]Lu-PSMA-617 and rA1M as above and dynamic technetium-99m mercaptoacetyltriglycine ([99mTc]Tc-MAG3) SPECT imaging was performed prior to injection, and 3- and 6-months post injection. Blood and urine were continuously sampled. At termination (6 months) the kidneys were resected. Biomarkers of kidney function, expression of stress genes and kidney histopathology were analyzed. [177Lu]Lu-PSMA-617 uptake, in tumors and kidneys, as well as treatment efficacy did not differ between rA1M and vehicle groups. In mice given rA1M, [99mTc]Tc-MAG3 imaging revealed a significantly higher slope of initial uptake at three months compared to mice co-injected with [177Lu]Lu-PSMA-617 and vehicle. Little or no change compared to control was seen in urine albumin, serum/plasma urea levels, RT-qPCR analysis of stress response genes and in the kidney histopathological evaluation. In conclusion, [99mTc]Tc-MAG3 imaging presented itself as a sensitive tool to detect changes in kidney function revealing that administration of rA1M has a potentially positive effect on kidney perfusion and tubular function when combined with [177Lu]Lu-PSMA-617 therapy. Furthermore, we could show that rA1M did not affect anti-PSMA radioligand therapy efficacy.

Formulation of lyophilized single vial kit of N-N-Ethylene-L-Dicysteine (EC) for labeling with 99mTc. II: Radiochemical and clinical evaluation as a renal tubular agent in comparison with 99mTc-MAG3.

A Technetium 99mTc labeled lyophilized single component kit of N-N-ethylene-I-dicysteine (EC) is developed to replace multiple step kit developed by others. The aim of study is to formulate a radionuclide that is easy to prepare, has rapid plasma clearance, produce high quality images and is an affective alternative to radioiodine labeled orthoiodohippurate, which has been remained the physiological 'gold standard' since long time. To achieve this goal, the systematically varied key parameters such as pH, the use of reducing agents, stabilizers and additives are optimized to obtain maximum radiochemical purity and optimum biodistribution in non human and human primates. Various pH levels of EC showed equally good results in animal experiments but only pH 10 was suitable for human use. Dynamic and renal Scintigraphic studies are carried out with 99mTc-EC at pH 8 in 12 volunteers and at pH 10 in 18 volunteers and compared with 99mTc-MAG3, Background ratios, renograms, relative renal function and semi quantitative parameters are available in all studies. The background ratios (mean ± SD) at 30th minute are 0229±0.024 and 0.236±0.018 for 99mTc-EC at pH 10 and 99mTc-MAG3 respectively. The mean ± standard error of mean (SEM) values of TMAX and time to half activity (T12) for 99mTc-EC (pH10) are 3.7±0.6 and 7.3±1.0 respectively while for 99mTc-MAG3, they are 4.0±0.8 and 7.9±1.4 with p values 0.001 and 0.049 respectively. The values of relative renal function (RRF) for 99mTc-EC and 99mTc-MAG3 are 50.8±3.11 and 51.2±3.4 respectively with p value of 0.822. The residual activity at 25th minute (A25 / A MAX) and renal uptake are 0. 209±12.67±2.80 for 99mTc-EC and 0.218±0.035 and 1053±2.98 for 99mTc-MAG3 (p=0.031 an 0.0003) respectively. The correlation coefficient (R2) for TMAX, T1/2, A25/AMAX and renal uptake are 0.96, 0.69, 0.93 and 0.85 respectively.

Improved synthesis and biological evaluation of Tc-99m radiolabeled AMO for miRNA imaging in tumor xenografts.

MicroRNAs (miRNAs) have been considered as important biomarkers for malignant tumors. In this study, we introduced an improved (99m)Tc labeling method for noninvasive visualization of overexpressed miRNAs in tumor-bearing mice. Anti-miRNA-21 oligonucleotide (AMO) with partial 2'-O-methyl and phosphorothioate modification was designed and chemically synthesized. After conjugated with NHS-MAG3, AMO was labeled with (99m)Tc. Optimization was made to shorten reaction time and to improve labeling efficiency. Labeling efficiency was 97%, and specific activity was 2.78 MBq/ng. During 12 h, (99m)Tc-AMO showed no significant degradation by gel electrophoresis. Its radiochemical purity was stable, between 95.8% and 99.1%. Further, (99m)Tc-AMO decreased the level of miR-21 and increased the expression of PTEN protein at cellular level, shown by qRT-PCR and Western blot. Fluorescent protein labeled AMO displayed specific distribution and good stability in tumor cells. After the administration in tumor-bearing mice, (99m)Tc-AMO showed more radioactive uptake in the miR-21 over-expressed tumors than scramble control. Biodistribution results further proved the significant difference of tumor uptake between (99m)Tc-AMO and (99m)Tc-control. Therefore, this study presents an improved method with shorten time to prepare a (99m)Tc radiolabeled AMO. In addition, it supports the role of (99m)Tc-AMO for noninvasive visualization of miR-21 in malignant tumors.

(99m)Tc-MAG3-aptamer for imaging human tumors associated with high level of matrix metalloprotease-9.

The human matrix metalloprotease 9 (hMMP-9) is involved in many physiological processes such as tissue remodeling. Its overexpression in tumors promotes the release of cancer cells thus contributing to tumor metastasis. It is a relevant marker of malignant tumors. We selected an RNA aptamer containing 2'-fluoro, pyrimidine ribonucleosides, that exhibits a strong affinity for hMMP-9 (K(d) = 20 nM) and that discriminates other human MMPs: no binding was detected to either hMMP-2 or -7. Investigating the binding properties of different MMP-9 aptamer variants by surface plasmon resonance allowed the determination of recognition elements. As a result, a truncated aptamer, 36 nucleotides long, was made fully resistant to nuclease following the substitution of every purine ribonucleoside residue by 2'-O-methyl analogues and was conjugated to S-acetylmercaptoacetyltriglycine for imaging purposes. The resulting modified aptamer retained the binding properties of the originally selected sequence. Following (99m)Tc labeling, this aptamer was used for ex vivo imaging slices of human brain tumors. We were able to specifically detect the presence of hMMP-9 in such tissues.

[A comparison on radiochemical behavior and biological property of antisense oligonucleotide labeled with technetium-99m by two methods: NHS-MAG3 versus SHNHP].

This study was undertaken to explore and compare the radiochemical behavior and biological property of antisense oligonucleotide (ASON) labeled with Technetium-99m using two methods: N-hydroxysuccinimidyl S-acetylmercaptoacetyltriglycline (NHS-MAG3) versus hydrazino nicotinamide derivative (SHNH). After SHNH and NHS-MAG3 were synthesized, ASON was labeled with Technetium-99m using SHNH and NHS-MAG3 as a bifunctional chelator, separately. The stability in vivo and in vitro, the combination with plasma albumen of rabbit, the biodistribution in BALB/ C mice and the HT29 cellular uptake were compared between labeled compound 99mTc-SHNH-ASON, using SHNH as a bifunctional complex reagent, and 99mTc-MAG3-ASON, using NHS-MAG3 as a bifunctional chelator. The results revealed that the labeling rate and the stability of 99mTc-MAG3-ASON were evidently higher than that of 99mTc-SHNH-ASON (P < 0.05), the combination rate of 99mTc-MAG3-ASON with plasma albumen was markedly lower than that of 99mTc-SHNH-ASON (P < 0.05); the biodistribution of 99mTc-MAG3-ASON was markedly lower than that of 99mTc-SHNH-ASON in blood, heart, stomach and intestines (P < 0.05), slightly lower than that of 99mTc-SHNH-ASON in liver and spleen (P > 0.05), and markedly higher than that of 99mTc-SHNH-ASON in kidney (P < 0.05); the HT29 cellular uptake rates of 99mTc-MAG3-ASON was markedly higher than that of 99mTc-SHNH-ASON (P < 0.05). Therefore, the radiochemical behavior and biological property of 99mTc-MAG3-ASON labeled using NHS-MAG3 is better than that of 99mTc-SHNH-ASON labeled using SHNH.

[The radiolabeling property of oligonucleotide with 99mTc using NHS-MAG3 as a chelator].

OBJECTIVE: To explore the radiolabeling property of oligonucleotide with 99mTc using NHS-MAG3 as a bifunctional chelator. METHODS: Three 15-base single-stranded amine-derivitized oligonucleotides, which were antisense(ASON), sense(SON) and mismatched oligonucleotides(MON) of c-myc oncogene mRNA, were coupled with NHS-MAG3 and labeled with 99mTc. The labeled oligonucleotide was purified by Sephadex G25 column chromatogram, then the stability was evaluated. The labeling efficiency of ON-MAG3 was assessed 15 days, 1 month and 2 months after storage at -20 degrees C. The binding rate of 99mTc-ON with plasma protein was measured by the trichloroacetic acid precipitation method. RESULTS: The average labeling efficiency of 99mTc-ASON, 99mTc-SON and 99mTc-ON was 68.41%, 66.24% and 69.38% respectively, and the radiochemical purity was 96.98%, 95.34% and 94.62%. 99mTc-ON was stable when placed at room temperature or incubated in human serum at 37 degrees C. The labeling efficiency of ON-MAG3 did not significantly change 2 months after storage at -20 degrees C. The plasma protein binding rate of 99mTc-ON was lower than 13%. CONCLUSION: 99mTc-ON labeled with NHS-MAG3 method showed superior radiochemical characteristics. The labeling efficiency and radiochemical purity were desirable. The label was stable in serum and the binding with plasma protein was low. 99mTc-ON could be a sort of potential radiopharmaceutical for in vivo applications.

Identity confirmation of 99mTc-MAG3, 99mTc-sestamibi and 99mTc-ECD using radio-LC-MS.

Due to the low concentrations in which 99mTc-radiopharmaceuticals are obtained (4-40 ng/ml), confirmation of the identity of these tracer agents in the European Pharmacopoeia is generally performed only indirectly by assessment of their retention times on RP-HPLC. We have investigated whether it is possible to obtain more direct proof of the identity of technetium-99m labelled radiopharmaceuticals using radio-LC-MS. As representative examples, negatively charged 99mTc-MAG3, positively charged 99mTc-Sestamibi and neutral 99mTc-ECD were used. The three technetium-99m radiopharmaceuticals were prepared in several conditions to obtain variable relative amounts of radiochemical impurities and variable concentrations of the complexes (pico- to nanomolar). The preparations were analyzed on a reversed phase C18 HPLC column using a radio-LC-MS system equipped with a time of flight mass spectrometer with electrospray ionization in positive (99mTc-Sestamibi, 99mTc-ECD) or negative (99mTc-MAG3, 99mTc-ECD) mode. For each of the studied complexes, the main peak in the radiometric channel coincided with the expected molecular ion mass of the corresponding technetium complex in the mass spectrometer channel. The relative error on the measured accurate mass was in the range of 10 ppm. The identity of several radiochemical impurities of the three technetium complexes was also confirmed or established. It is concluded that radio-LC-MS can be a sensitive aid in quality control of 'no carrier added' radiopharmaceuticals.

New N(3)S donor ligand small peptide analogues of the N-mercaptoacetyl-glycylglycylglycine ligand in the clinically used Tc-99m renal imaging agent: evidence for unusual amide oxygen coordination by two new ligands.

Three new X-ray structurally characterized Re(V)O complexes, ReO(MEG(3)H(2)) (10), ReClO(MAEG(2)H(3)) (11), and [ReO(MECG(2)H(2))](2) (12), were prepared from protected forms of three new ligands, mercaptoethyl-glycylglycylglycine (MEG(3)H(5)), mercaptoacetamide-ethyl-glycylglycine (MAEG(2)H(5)), and mercaptoethyl-carbamoylmethyl-glycylglycine (MECG(2)H(5)). (Subscript on H indicates the number of dissociable protons.) Mercaptoacetyltriglycine (MAG(3)H(5)) is the ligand precursor for the clinically used Tc-99m renal imaging agent. The new potentially N(3)S donor ligands have a glycylglycine carboxyl end as in MAG(3)H(5), but a secondary amine (sp(3) N) replaces one amide (sp(2) N) of MAG(3)H(5). ReO(MEG(3)H(2)) (10) is a typical five-coordinate pseudo-square-pyramidal complex with the oxo ligand at the apex and the trianionic form of MEG(3)H(5) coordinated in the basal plane via N(3)S. In the other complexes, the quadridentate ligand has N(2)OS ligation, with the carbonyl oxygen of the glycyl amide group coordinated trans to the oxo ligand. This unusual ligation mode, which is facilitated by the preferred endo configuration of the ligated glycyl sp(3) N, leaves a vacant basal coordination site. In 11, the chloro ligand completes the equatorial plane, whereas, in 12, a glycine carboxylate oxygen of the ligand on the partner Re completes the equatorial plane. Both complexes thus possess an unexpected pseudo-octahedral geometry. For 10, 11, and 12, the (1)H NMR spectra, monitored from high to low pH, exhibited changes only when the pH was lowered below 6. This finding indicates that at physiological pH these complexes possess the desirable characteristic of existing as one monomeric species having only one ionization state, with the coordinated sp(3) N deprotonated. Below pH 6 and above pH approximately 4, changes in the (1)H NMR shifts indicate that this sp(3) N has become protonated. Thus, the N(3)S ligands in all three complexes exhibit normal coordination above pH approximately 4. However, X-ray data for 11 and 12 and some NMR evidence for 11 indicate that the ligands of the two complexes rearrange at low pH (<3). The striking differences between the solution- and solid-state structures reinforce the caveat that solution structural studies conducted at physiological pH are necessary in order to gain insight into the nature of radiopharmaceuticals.

Synthesis and evaluation of 99mTc/99Tc-MAG3-biotin conjugates for antibody pretargeting strategies.

Four 99mTc-MAG3-biotin conjugates were synthesized to determine their potential use in antibody pretargeting strategies for radioimmunoscintigraphy (RIS). To use these 99mTc-MAG3-biotin conjugates as model compounds for 186Re-MAG3-biotin conjugates for radioimmunotherapy (RIT), nanomolar amounts of 99Tc were added as carrier to 99mTc. The biotin derivatives used for the preparation of the conjugates-biocytin, biotin hydrazide, biotinyl-piperazine, and biotinyl-diaminosuccinic acid-differed at the site that is regarded to be susceptible to hydrolysis by biotinidase present in human plasma. All four conjugates were produced with high radiochemical purity, were stable in PBS, and demonstrated full binding capacity to streptavidin. The 99mTc/99Tc-MAG3-labeled biotinyl-piperazine and biotinyl-diaminosuccinic acid conjugates were stable in mouse as well as human plasma, whereas the corresponding biocytin and biotin hydrazide conjugates were rapidly degraded. The biodistribution in nude mice at 30 min after injection was similar for all conjugates, and a rapid blood clearance and high intestinal excretion were both observed. It is concluded that the metabolic routing of a conjugate containing biotin and MAG3 is dominated by these two moieties. For this reason, MAG3-biotin conjugates do not seem suited for pretargeted RIT, for which quantitative and fast renal excretion is a prerequisite to minimize radiation toxicity. However, in a pretargeted RIS approach the 99mTc-MAG3-biotin conjugates might have potential.

188Re- and 99mTc-MAG3 as prosthetic groups for labeling amines and peptides: approaches with pre- and postconjugate labeling.

Either radiolabeled Tc-99m- or Re-188-labeled MAG3-4-nitrophenylester or unlabeled Bz-MAG3-4-nitrophenylester was reacted with amines and peptides to follow a pre- or a postconjugate radiolabeling route, respectively. The model compounds were N'-t-butyloxycarbonyl-1,6-diaminohexane (DH-Boc) and a Lys-protected derivative of the somatostatin analog RC-160 (cyclic D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2). In the case of labeling DH-Boc, both the preconjugate labeling and the postconjugate labeling were found by using analytical HPLC to provide identical radiolabeled compounds regardless whether Re-188 or Tc-99m was used. The results are supported by infrared and mass-spectral data obtained from compounds synthesized using stable rhenium. The 188Re- or 99mTc-MAG3-RC-160 somatostatin analog were synthesized following the preconjugate labeling route and subsequent removal of the protecting group. Biodistributions of 188Re-and 99mTc-MAG3-RC-160 were evaluated in normal and tumor-bearing mice, and were similar to those of radioiodinated 131-RC-160. All radiolabeled analogs of RC-160 were rapidly cleared from the blood and were excreted through the hepatobiliary system with very little normal organ uptake. The tumor uptake (PC-3, human prostate adenocarcinoma) of systemically administered Re-188-MAG3-RC160 was very low, and it reached only 0.28% injected dose/g (%IDg) at 24 h postinjection, similar to what was obtained with I-131-RC-160. Intratumor injections resulted in significant tumor retentions (9.3% ID/g at 24 h).

3'-99mTc-labeling and biodistribution of a CAPL antisense oligodeoxynucleotide.

CAPL is a cancer-related gene shown to be overexpressed during tumor metastasis formation. A CAPL antisense oligodeoxynucleotide (ODN), GX-1, and a random control ODN (CTRL1) were 3'-conjugated to MAG3, labeled with technetium-99m, purified, and the biodistribution of the radiolabeled conjugates in normal mice was studied. A 99mTc-MAG3-GX-1 complex of >97% radiochemical purity was obtained and the product was stable for >6 h as determined by reversed phase high performance liquid chromatography (HPLC). Biodistribution studies of the 99mTc-MAG3-ODNs in groups of four normal mice, sacrificed 5 min and 60 min after injection, demonstrated that the radiolabeled ODNs were distributed in an unspecific manner. The excretion route was mainly urinary. At 60 min, 55.2% of the injected dose of 99mTc-MAG3-GX-1 and 72.4% of 99mTc-MAG3-CTRL1 was found in the urine. This finding is clearly different from previously reported data on tritiated 20-mer phosphodiester ODNs, as well as the unconjugated 99mTc-MAG3 chelate, suggesting that 99mTc-MAG3 coupled to the 3'-end of ODNs has an influence on the biodistribution of the oligo, and possibly has a protective function to enzymatic degradation in vivo.