177Lu-DOTA-lanreotide: a novel tracer as a targeted agent for tumor therapy

Fabrication of gold nanocages and nanoshells using lanreotide acetate and a comparison study of their photothermal antitumor therapy

Functional gold nanoshells and nanocages were synthesized via self-assembly of lanreotide acetate.

Lanreotide-conjugated PEG-DSPE micelles: an efficient nanocarrier targeting to somatostatin receptor positive tumors

Lanreotide is an octapeptide analog of endogenous somatostatin, specifically binding with tumors over-express somatostatin receptor 2 (SSTR2). In this study, we conjugated lanreotide to 1, 2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (poly-(ethylene glycol))-2000] (PEG-DSPE), constructed active targeted micelles (lanreotide-PM), characterized their in vitro and in vivo targeting effect, and explored the receptor mediated transportion. The uptake of lanreotide-PM was found to be related to the expression level of SSTR2 in different cell lines and the competitive inhibition phenomenon indicated that the cellular uptake of lanreotide-PM was via a receptor meditated mechanism. In vivo, more lanreotide-PM accumulated in SSTR2 high expression tumor xenografts, endocytosed by the tumor cells, induced more apoptosis of tumor cells, and suppressed tumor growth efficiently. In conclusion, lanreotide-modified micelles containing antitumor drugs provide a promising strategy for the treatment of SSTR-expressing tumors.

Preparation and preliminary biological evaluation of a 177Lu labeled nitroimidazole derivative for possible use in targeted tumor therapy

The preparation and preliminary biological evaluation of a metronidazole-BFCA (bifunctional chelating agent) conjugate labeled with 177Lu is reported. Metronidazole, a well known hypoxia marker has been suitably derivatized and coupled with a polyazamacrocyclic BFCA, namely, para-aminobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (p-amino-benzyl-DOTA). 177Lu, which is presently being considered as one of the pivotal radionuclides for targeted therapy was produced in adequate specific activity (∼185 TBq/g) and high radionuclidic purity (99.99%) by irradiating enriched (60.6% 176Lu) Lu2O3 target at a moderate thermal neutron flux of 3×1013 n/cm2/s. The metronidazole-BFCA conjugate was radiolabeled with 177Lu in high radiochemical purity (97%). Preliminary biodistribution studies carried out in Swiss mice bearing fibrosarcoma tumors revealed good tumor uptake (1.30% ID/g at 30 min post-injection) with rapid renal clearance (94.48% ID at 30 min post-injection) and significant tumor to blood (28.00 at 3 h post-injection) and tumor to muscle (14.00 at 3 h post-injection) ratios.

Preparation and evaluation of [67Ga]-DTPA-β-1–24-corticotrophin in normal rats

β-1–24-corticotrophin was successively labeled with [67Ga]-gallium chloride after residulation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 ml of a β-1–24-corticotrophin pharmaceutical solution (1 mg/mL, pH=6.5) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25 °C with continuous mild stirring for 30 min. Radio-thin layer chromatography showed an overall radiochemical purity of >90% at optimized conditions after labeling. HPLC showed a radiochemical purity more than 95% (specific activity =300–500 MBq/mg, labeling efficiency 77%). The stability of the radioconjugate was tested in presence of human serum at 37 °C. Preliminary in vivo studies in normal rats were performed to determine the biodistribution of the radioimmunoconjugate up to 30 min. Lungs showed to have the major tracer uptake which is consistent with the natural distribution of ACTH receptors in human body. Pretreatment of animals with cold peptide following labeled compound administration reduced lung uptake at least 10 and 3 times after 15 and 30 min, respectively, as well as significant decrease in adrenal uptake after 15 min. These data support the specific receptor binding of the radiolabeled compound. This tracer can be used in detection of ACTH receptor in lung and adrenal malignancies.

Development of [201Tl](III)-DTPA-human polyclonal antibody complex for inflammation detection

Thallium-201 (T 1/2=3.04 d) in Tl+ form was converted to Tl3+ cation in presence of O3 in 6 M HCl controlled by RTLC/gel electrophoresis methods and used in the labeling of human polyclonal antibody (HIgG) after conjugation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 mL of a HIgG pharmaceutical solution (5 mg/ml, in phosphate buffer, pH=7) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25 °C with continuous mild stirring for 30 min. The final isotonic [201Tl](III)-DTPA-HIgG complex was checked by radio-TLC using several solvent systems to ensure the formation of only one species followed by filtration through a 0.22 μ filter (specific activity= 33.7 TBq/mM, radiochemical purity >95%). Preliminary bio-distribution studies in normal and inflammation-bearing rats were performed. The target/skin and target/blood ratios were 4 and 6 after 28 h respectively, showing the selectivity of the radiopharmaceutical for the inflammatory lesions.

Biological evaluation of 153Sm and 166Ho complexes with tetraazamacrocycles containing methylcarboxylate and/or methylphosphonate pendant arms

153Sm and 166Ho complexes with two series of tetraazamacrocyclic ligands containing methylcarboxylate and/or methylphosphonate pendant arms were synthesized and their charge, lipophilicity, protein binding and in vitro and in vivo behaviour evaluated. The first series has the same backbone, a 14-membered tetraazamacrocycle containing a pyridine unit with different pendant arms, namely methylcarboxylates (ac3py14) or methylphosphonates (MeP2py14 and P3py14). The second series comprises 12- to 14-membered tetraazamacrocycles having methylcarboxylates and/or methylphosphonates as pendant arms (trans-DO2A2P, TRITA, TRITP, TETA and TETP). The 153Sm/166Ho complexes with the 14-membered tetraazamacrocycles containing the pyridine unit are neutral, hydrophilic, have a significant plasmatic protein binding, are unstable in vivo and present a slow rate of radioactivity excretion and high hepatic retention. 153Sm/166Ho complexes with the 12- to 14-membered tetraazamacrocycles are quantitatively prepared, except those with TETP. These complexes are hydrophilic, have an overall negative charge and present a medium to low plasmatic protein binding.

The 153Sm/166Ho- trans-DO2A2P, 153Sm/166Ho-TRITA and 166Ho-TRITP complexes are stable in vitro and in vivo, presenting a rapid clearance from main organs and a high rate of whole body radioactivity excretion. Biological profile of 153Sm/166Ho-TRITA complexes makes them promising candidates for therapy when conjugated to a biomolecule, while 166Ho-TRITP is potentially useful for bone targeting due to its considerable uptake by bone.

Labeling internalizing anti-epidermal growth factor receptor variant III monoclonal antibody with (177)Lu: in vitro comparison of acyclic and macrocyclic ligands

INTRODUCTION

The monoclonal antibody (mAb) L8A4, reactive with the epidermal growth factor receptor variant III (EGFRvIII), internalizes rapidly in glioma cells after receptor binding. Combining this tumor-specific mAb with the low-energy beta-emitter (177)Lu would be an attractive approach for brain tumor radioimmunotherapy, provided that trapping of the radionuclide in tumor cells after mAb intracellular processing could be maximized.

MATERIALS AND METHODS

L8A4 mAb was labeled with (177)Lu using the acyclic ligands [(R)-2-amino-3-(4-isothiocyanatophenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-pentaacetic acid (CHX-A''-DTPA), 2-(4-isothiocyanatobenzyl)-diethylenetriaminepenta-acetic acid (pSCN-Bz-DTPA) and 2-(4-isothiocyanatobenzyl)-6-methyldiethylenetriaminepentaacetic acid (1B4M-DTPA), and the macrocyclic ligands S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-tetraacetic acid (C-DOTA) and alpha-(5-isothiocyanato-2-methoxyphenyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (MeO-DOTA). Paired-label internalization and cellular processing assays were performed on EGFRvIII-expressing U87.DeltaEGFR glioma cells over 24 h to directly compare (177)Lu-labeled L8A4 to L8A4 labeled with (125)I using either iodogen or N-succinimidyl 4-guanidinomethyl-3-[(125)I]iodobenzoate ([(125)I]SGMIB). In order to facilitate comparison of labeling methods, the primary parameter evaluated was the ratio of (177)Lu to (125)I activity retained in U87.DeltaEGFR cells.

RESULTS

All chelates demonstrated higher retention of internalized activity compared with mAb labeled using iodogen, with (177)Lu/(125)I ratios of >20 observed for the three DTPA chelates at 24 h. When compared to L8A4 labeled using SGMIB, except for MeO-DOTA, internalized activity for (125)I was higher than (177)Lu from 1-8 h with the opposite behavior observed thereafter. At 24 h, (177)Lu/(125)I ratios were between 1.5 and 3, with higher values observed for the three DTPA chelates.

CONCLUSIONS

The nature of the chelate used to label this internalizing mAb with (177)Lu influenced intracellular retention in vitro, although at early time points, only MeO-DOTA provided more favorable results than radioiodination of the mAb via SGMIB.

On the preparation of a therapeutic dose of 177Lu-labeled DOTA–TATE using indigenously produced 177Lu in medium flux reactor

177Lu could be produced with a specific activity of approximately 23,000 mCi/mg (850GBq/mg) by neutron activation using enriched 176Lu (64.3%) target when irradiation was carried out at a thermal neutron flux of 1 x 10(14) n/cm(2)/s for 21 d. 177Lu-DOTA-TATE could be prepared in high radiochemical yield (approximately 99%) and adequate stability using the 177Lu produced indigenously. The average level of radionuclidic impurity burden in 177Lu due to 177mLu was found to be 250 nCi of 177mLu/1 mCi of 177Lu (9.25 kBq/37 MBq) at the end of bombardment, which corresponds to 0.025% of the total activity produced. The maximum specific activity achievable via careful optimization of the irradiation parameters was found to be adequate for the preparation of a therapeutic dose of the radiopharmaceutical. The in-house preparation of this agent using 25 microg (17.41 nmole) of DOTA-TATE and indigenously produced 177Lu (0.8 microg, 4.52 nmole), corresponding to peptide/Lu ratio of 3.85 yielded 98.7% complexation. Allowing possibility of decay due to transportation to users, it has been possible to demonstrate that at our end, a single patient dose of 150-200 mCi (5.55-7.40 GBq) can be prepared by using 250-333 microg of DOTA-TATE conjugate. This amount compares well with 177Lu-DOTA-TATE prepared for a typical peptide receptor radionuclide therapy (PRRT) procedure which makes use of 100 microg of the DOTA-TATE conjugate, which incorporates 50 mCi (1.85 GBq) of 177Lu activity, thereby implying that in order to achieve a single patient dose of 150-200 mCi (5.55-7.40 GBq), 300-400 microg of the conjugate needs to be used.

Preparation and In Vitro and In Vivo Evaluation of Technetium-99m-Labeled Folate and Methotrexate Conjugates as Tumor Imaging Agents

The cell-membrane folic acid (FA) receptors are known to be responsible for cellular accumulation of FA and FA analogs, such as methotrexate (MTX), and are overexpressed on several tumor cells. Folate, as well as antifolates (i.e., MTX), possess high affinity for the folate-receptor positive cells and tissues and were deemed useful for diagnostic imaging. We have prepared and evaluated technetium-99m (99mTc)- labeled FA and MTX analogs using MAG3 and MAG2 chelating agents in an attempt to develop folate-receptor targeting radiopharmaceuticals. Folate and MTX-conjugates after labeling with 99mTc by ligand exchange method displayed high in vitro stability in human plasma. In vitro cell binding and internalization on MCF-7 and MDA-MB-231 cells indicated the affinity and specificity of the radioconjugates toward human breast cancer cells. In mice, all radioconjugates showed rapid clearance from the blood and excretion mainly through the renal/urinary pathway, with some elimination by way of the biliary route. There was no significant accumulation of radioactivity observed in other organs, with the exception of the intestines. Uptake in the breast tumor was moderate in nude mice. These findings could be of potential diagnostic interest in designing and developing FA/MTX-based radiopharmaceuticals for tumor imaging.

Labelling monoclonal antibodies with macrocyclic radiometal complexes. A challenge for coordination chemists

The technique consisting of labelling antibodies with radionuclides is a promising approach for the diagnosis and therapy of human cancers. In this paper the chemical aspects of radiolabelling with macrocyclic metal complexes are dealt with. The choice of the radioisotope, its coordination chemistry, the design of the bifunctional macrocyclic ligand, and its attachment to the monoclonal antibody are discussed. Finally several newer ideas for a better application are presented.

Synthesis and evaluation of bifunctional chelating agents derived from bis(2-aminophenylthio)alkane for radioimaging with 99mTc

Novel bifunctional chelating agents bearing an aromatic rigid backbone have been synthesized and characterized on the basis of spectroscopic techniques. These macrocyclic multidentate chelating agents were conjugated with monoclonal antibody which forms stable complexes with 99mTc with high radiochemical purity.

An estradiol-conjugate for radiolabelling with 177Lu: an attempt to prepare a radiotherapeutic agent

177Lu is presently being considered as one of the most promising radionuclide for targeted therapy owing to its suitable decay characteristics. 177Lu in high radionuclidic purity (99.99%) and moderate specific activity (100-110 TBq/g) was produced using enriched (60.6% 176Lu) Lu2O3 target. The macrocycle 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) is known to form stable complexes with lanthanides. Herein, we describe a novel attempt to introduce 177Lu in the estradiol moiety through a steroidal-BFCA (Bifunctional Chelating Agent) conjugate. The preparation of a steroid conjugate via coupling of 6alpha-amino-17beta-estradiol with a C-functionalized DOTA derivative viz. p-NCS-benzyl-DOTA as a BFCA and thereafter the radiolabelling of the conjugate with 177Lu is reported. Biological activity of the resultant estradiol-DOTA conjugate after radiolabelling was studied by carrying out preliminary in vitro cell uptake studies with MCF-7, human breast carcinoma cell line expressing estrogen receptors as well as binding studies with anti-estradiol antibodies.

Convenient Synthesis of Multifunctional EDTA-Based Chiral Metal Chelates Substituted with anS-Mesylcysteine

We describe the synthetic route to ethylenediaminetetraacetic acid (EDTA) derivatives that can be attached to surface-exposed thiol functional groups of cysteine residues in proteins, via a methylthiosulfonate moiety that is connected in a stereochemically unique way to the C-1 carbon atom of EDTA. Such compounds can be used to align proteins in solution without the need to add liquid crystalline media, and are, therefore, of great interest for the NMR spectroscopic analysis of biomolecules. The binding constant for the paramagnetic tag to lanthanide ions was determined by measuring luminescence. For the Tb(+3)-ligand complex, a K(b) value of 6.5 x 10(17) M(-1) was obtained. This value is in excellent agreement with literature values for the related EDTA compound. In addition, it could be shown that there is no significant reduction in the luminescence intensity upon addition of a 10(4) excess of Ca2+ ions, indicating that this paramagnetic tag is compatible with buffers containing high concentrations of divalent alkaline earth ions.