Preparation,evaluation, and first clinical use of 177Lu‐labeled hydroxyapatite (HA) particles in the treatment of rheumatoid arthritis: utility of cold kits for convenient dose formulation at hospital radiopharmacy

While radiation synovectomy (RSV) constitutes a successful paradigm for the treatment of arthritis, a major cornerstone of its success resides in the selection of appropriate radiolabeled agent. Among the radionuclide used for RSV, the scope of using ¹⁷⁷Lu [T_1/2 = 6.65 d, E_β(max) = 497 keV, E_γ = 113 KeV (6.4%), 208 KeV (11%)] seemed to be attractive owing to its suitable decay characteristics, easy availability, and cost‐effective production route. The present article describes a formulation of ¹⁷⁷Lu‐labeled hydroxyapatite (HA) using ready‐to‐use kits of HA particles of 1–10 µm size range. The developed kits enable convenient one‐step preparation of ¹⁷⁷Lu‐HA (400 ± 30 MBq doses) in high radiochemical purity (>99%) and stability at hospital radiopharmacy. The preparation showed promising results in pre‐clinical studies carried out in Wistar rats bearing arthritis in knee joints. In preliminary clinical investigation, significant improvement in the disease conditions was reported in 10 patients with rheumatoid arthritis of knee joints treated with 333 ± 46 MBq doses of ¹⁷⁷Lu‐HA. The studies reveal that while ¹⁷⁷Lu labeled HA particles holds considerable promise as a cost‐effective agent for RSV, the adopted strategy of using HA kits could be a potential step toward wider clinical utilization of radiolanthanide‐labeled HA particles. Copyright © 2014 John Wiley & Sons, Ltd.     

A “mix‐and‐use” approach for formulation of human clinical doses of 177Lu‐DOTMP at hospital radiopharmacy for management of pain arising from skeletal metastases

Use of bone‐seeking radiopharmaceuticals is an established modality in the palliative care of pain due to skeletal metastases. ¹⁷⁷Lu‐DOTMP is a promising radiopharmaceutical for this application owing to the ideally suited decay properties of ¹⁷⁷Lu and excellent thermodynamic stability and kinetic rigidity of the macrocyclic complex. The aim of the present study is to develop a robust and easily adaptable protocol for formulation of clinical doses of ¹⁷⁷Lu‐DOTMP at hospital radiopharmacy. After extensive radiochemical studies, an optimized strategy for formulation of clinical doses of ¹⁷⁷Lu‐DOTMP was developed, which involves simple mixing of approximately 3.7 GBq of ¹⁷⁷Lu activity as ¹⁷⁷LuCl₃ solution to an aqueous solution containing 5 mg of DOTMP and 8 mg of NaHCO₃. The proposed protocol yielded ¹⁷⁷Lu‐DOTMP with >98% radiochemical purity, and the resultant formulation showed excellent in vitro stability and desired pharmacokinetic properties in animal model. Preliminary clinical investigations in 5 patients showed specific skeletal accumulation with preferential localization in the osteoblastic lesion sites and almost no uptake in soft tissue or any other major nontarget organ. The developed “mix‐and‐use” strategy would be useful for large number of nuclear medicine centers having access to ¹⁷⁷Lu activity and would thereby accelerate the clinical translation of ¹⁷⁷Lu‐DOTMP.     

Prospects of medium specific activity 177Lu in targeted therapy of prostate cancer using 177Lu‐labeled PSMA inhibitor

Targeted radionuclide therapy using ¹⁷⁷Lu‐labeled peptidomimetic inhibitor of prostate specific membrane antigen (PSMA) viz. PSMA‐617 is emerging as one the most effective strategies for management of metastatic prostate cancer, which is one of the leading causes of cancer related death. The aim of the present study is to develop a robust and easily adaptable protocol for formulation of therapeutic dose of ¹⁷⁷Lu‐PSMA‐617 at hospital radiopharmacy using moderate specific activity ¹⁷⁷Lu available at an affordable cost. Extensive radiochemical studies were performed to optimize the required [PSMA‐617] / [Lu] ratio and other parameters to formulate 7.4 GBq dose of ¹⁷⁷Lu‐PSMA‐617. Based on these, 7.4 GBq therapeutic dose of ¹⁷⁷Lu‐PSMA‐617 was formulated by incubating 160 µg of PSMA‐617 with indigenously produced ¹⁷⁷LuCl₃ (555 GBq/µg specific activity of ¹⁷⁷Lu) at 90 °C for 30 min. The radiochemical purity of the formulation was 98.3 ± 0.6% (n = 7) which was retained to the extent of >95% after 7 d in normal saline at room temperature and >96% after 2 d in human serum at 37 °C. Preliminary clinical studies showed specific targeting of the agent in the lesion sites and similar physiological distribution as in diagnostic ⁶⁸Ga‐PSMA‐11 PET scans performed earlier. The developed optimized protocol for formulating therapeutic dose of ¹⁷⁷Lu‐PSMA‐617 could be useful for large number of nuclear medicine therapy clinics across the world having access to moderate specific activity ¹⁷⁷Lu at an affordable cost.     

An improved assay for 68Ga‐hydroxide in 68Ga‐DOTATATE formulations intended for neuroendocrine tumour imaging

The objective of this study was to identify a more rapid assay for ⁶⁸Ga(OH)₃ impurity in ⁶⁸Ga‐DOTATATE formulations. Three methods were used to prepare ⁶⁸Ga(OH)₃ reference material (pharmacopoeial, bench titration and automated radiosynthesis), and four quality control methods for its assessment (thin layer chromatography, membrane filtration, HPLC and solid phase extraction). The optimal method of preparing ⁶⁸Ga(OH)₃ was by titrating ⁶⁸Ga³⁺ with buffered sodium hydroxide solutions to pH 5.6 ± 0.2. The precipitate was quantitatively isolated by membrane filtration (0.02 µm)/hydrochloric acid (HCl; pH 5.6) solvent, and also it remained 100% at the origin on instant thin layer chromatography with silica gel paper/HCl (pH 5.6) solvent. For ⁶⁸Ga‐DOTATATE samples, the thin layer chromatography technique was used with a single paper strip developed separately on two occasions, once in HCl (pH 5.6) and next in methanol solvent. This so‐called double‐developed (DD) method separated ⁶⁸Ga(OH)₃ impurity located at the origin, from ⁶⁸Ga‐DOTATATE plus ⁶⁸Ga³⁺ at ~R_f 0.4, and it was superior to the other methods. It assayed for the impurity similarly to the pharmacopoeial method. The advantages of the DD method were that it required inexpensive test materials and it reproducibly determined % ⁶⁸Ga(OH)₃ in ⁶⁸Ga‐DOTATATE in 12 min, 13 min earlier than the pharmacopoeial method. This time efficiency resulted in a surplus of 12% ⁶⁸Ga‐DOTATATE counts in the product vial, and this provided a contingency of radioactivity or time for the injection/imaging processes in the Nuclear Medicine Department.     

177Lu‐5‐Fluorouracil a potential theranostic radiopharmaceutical: radiosynthesis,quality control,biodistribution, and scintigraphy

The aim of this study is to develop ¹⁷⁷Lu‐5‐Flourouracil as a potential cancer therapeutic radiopharmaceutical. 5‐Flourouracil (5‐FU) is widely accepted as an anticancer drug of broad spectrum fame. The labeling of 5‐FU was carried out at different set of experimental conditions using high specific activity of ¹⁷⁷LuCl₃. The optimum conditions for maximum radiochemical yield was set: 5‐FU (5 mg), ¹⁷⁷LuCl₃ (185 MBq), diethylenetriaminepentaacetic acid (10 µg), reaction volume (2 mL), pH (5.5), temperature (80°C), and reaction time (20 min). The radiochemical labeling was assessed with Whatman No. 2 paper, instant thin layer chromatographic, and radio‐HPLC, which revealed >94% labeling results with sufficient stability up to 6 h. Serum stability study also showed ¹⁷⁷Lu‐5‐FU promising stability. Biodistribution study in normal rats and rabbits showed liver, stomach, kidney, and heart as area of increased tracer accumulation just after injection, which decreased to 1.4%, 0.4%, 0.2%, and 0.39% ID/g, respectively, after 72 h. Glomerular filtration rate and cytotoxicity study results of ¹⁷⁷Lu‐5‐FU showed it had no adverse effect on renal function and nontoxic to blood cells. The promising characteristics of ¹⁷⁷Lu‐5‐FU, that is, clever elimination from kidney and nontoxic nature toward blood cells make it the radiopharmaceutical for further testing in patients for therapeutic purposes.     

Radiolabeling,quality control,biodistribution, and imaging studies of 177Lu‐ibandronate

The purposes of this study were as follows: (1) to radiolabel ibandronic acid (IBA, a third‐generation bisphosphonate) with ¹⁷⁷Lu, investigating optimal labeling conditions, and (2) to analyze biodistribution and imaging properties of intravenous ¹⁷⁷Lu‐ibandronate (¹⁷⁷Lu‐IBA) administered in animals. ¹⁷⁷Lu‐labeled methylene diphosphonate (¹⁷⁷Lu‐MDP) served as a comparator agent. Differing proportions of IBA solution and ¹⁷⁷LuCl₃ solution were combined to determine an optimal ratio for radiolabeling purposes, varying pH, temperature, and time to establish ideal reactivity conditions. Radiochemical purity of the labeled compounds was then assessed by paper chromatography. In vitro and in vivo stabilities were also measured at specific time intervals. In Kunming mice, biodistributions of ¹⁷⁷Lu‐IBA and ¹⁷⁷Lu‐MDP and respective agent activities in various organs were monitored by gamma counter, and we performed single photon computed tomography/computed tomography (SPECT/CT) imaging of ¹⁷⁷Lu‐IBA in normal New Zealand White rabbits. Radiolabeling yields for ¹⁷⁷Lu‐IBA proved to be >97% within 30 minutes at 90°C, and its radiochemical purity ensured stability in vitro and in vivo. Furthermore, we found that ¹⁷⁷Lu‐IBA is readily soluble in water, showing higher skeletal uptake than ¹⁷⁷Lu‐MDP but lower uptake by liver and spleen. The image quality of ¹⁷⁷Lu‐IBA was so clear that even after 6 days, analysis was still feasible.     

Preparation of clinical‐scale 177Lu‐Rituximab: Optimization of protocols for conjugation,radiolabeling, and freeze‐dried kit formulation

Rituximab is a monoclonal chimeric antibody, which has been approved by the US Food and Drug Administration for immunotherapy of non–Hodgkin lymphoma. Bexxar and Zevalin are the two other approved radiolabeled antibodies for radioimmunotherapy of non–Hodgkin lymphoma; however, they are of murine origin that reduces their treatment efficacy. So as to circumvent this, efforts have been made to radiolabel Rituximab with various therapeutic radioisotopes. In the present study, an effort has been made to optimize the conjugation (bifunctional chelating agent and antibody) and radiolabeling procedures for the preparation of clinical‐scale ¹⁷⁷Lu‐labeled Rituximab. An attempt was also made to prepare the freeze‐dried Rituximab kit for the easy and convenient clinical translation of the agent. Clinical‐scale ¹⁷⁷Lu‐Rituximab (40 mCi, 1.48 GBq) was prepared with >95% radiochemical purity using the kit. Biological evaluation of ¹⁷⁷Lu‐Rituximab was performed by in vitro cell binding studies in Raji cell lines, which showed satisfactory binding at 4°C and 37°C. Pharmacokinetic behavior of the agent, evaluated by biodistribution studies in normal Swiss mice, revealed high blood and liver uptake at the initial time points, although it exhibited slow and gradual clearance with time. The study indicates that clinical‐scale ¹⁷⁷Lu‐Rituximab could be conveniently formulated using the methodology described in the present article.     

Detailed evaluation of different 68Ge/68Ga generators: an attempt toward achieving efficient 68Ga radiopharmacy

The present study is aimed at carrying out a comparative performance evaluation of different types of ⁶⁸Ge/⁶⁸Ga generators to identify the best choice for use in ⁶⁸Ga‐radiopharmacy. Over the 1 year period of evaluation, the elution yields from the CeO₂‐based and SiO₂‐based ⁶⁸Ge/⁶⁸Ga generators remained almost consistent, in contrast to the sharp decrease observed in the elution yields from TiO₂ and SnO₂‐based generators. The level of ⁶⁸Ge impurity in ⁶⁸Ga eluates from the CeO₂ and SiO₂‐based ⁶⁸Ge/⁶⁸Ga generator was always <10^?3%, while this level increased from 10^?3% to 10^?1% in case of TiO₂ and SnO₂‐based generators. The level of chemical impurities in ⁶⁸Ga eluates from CeO₂ and SiO₂‐based ⁶⁸Ge/⁶⁸Ga generators was negligibly low (<0.1 ppm) in contrast to the significantly higher level (1–20 ppm) of such impurities in eluates from other two generators. As demonstrated by radiolabeling studies carried out using DOTA‐coupled dimeric cyclic RGD peptide derivative (DOTA‐RGD₂), CeO₂‐PAN and SiO₂‐based generators are directly amenable for radiopharmaceutical preparation, whereas the other generators can be only used after post‐elution purification of ⁶⁸Ga eluates. Clinically relevant dose of ⁶⁸Ga‐DOTA‐RGD₂ was prepared in a hospital radiopharmacy for non‐invasive visualization of tumors in breast cancer patients using positron emission tomography.     

Preparation of 177Lu‐labeled Nimotuzumab for radioimmunotherapy of EGFR‐positive cancers: Comparison of DOTA and CHX‐A″‐DTPA as bifunctional chelators

This study was aimed at evaluating the role of bifunctional chelators DOTA‐NCS and CHX‐A″‐DTPA‐NCS used for conjugating ¹⁷⁷Lu with Nimotuzumab on the radiochemical yields, purity, in vitro stability, and specificity of the radioimmunoconjugates to EGFR. Two immunoconjugates were prepared wherein Nimotuzumab was conjugated with the acyclic ligand p‐NCS‐Bn‐CHX‐A″‐DTPA and macrocyclic ligand p‐NCS‐Bn‐DOTA. These were radiolabeled with ¹⁷⁷Lu, purified on PD‐10 column, and characterized by SE‐HPLC. In vitro stability was determined up to 4 days post preparation. Specificity of the radioimmunoconjugates was ascertained by in vitro studies in A431 cells while the biodistribution patterns were studied in normal Swiss mice up to 96 hours post injection. Four to five molecules of CHX‐A″‐DTPA/DOTA were attached to one molecule of Nimotuzumab. Radiochemical purity of both ¹⁷⁷Lu‐CHX‐A″‐DTPA‐Nimotuzumab and ¹⁷⁷Lu‐DOTA‐Nimotuzumab was determined to be greater than 98%. Both the radioimmunoconjugates exhibited good in vitro stability at 37°C up to 4 days post preparation in saline, and their clearance was largely by the hepatobiliary route. The DOTA‐ and CHX‐A″‐DTPA‐based radioimmunoconjugates could be prepared with good radiochemical purity, in vitro stability, and specificity to EGFR. Further studies in EGFR‐positive cancers would pave way for them for use in the clinics.     

177Lu‐labeled monomeric,dimeric and multimeric RGD peptides for the therapy of tumors expressing α(ν)β(3) integrins

The conjugation of peptides to gold nanoparticles (AuNPs) produces biocompatible and stable multimeric systems with target‐specific molecular recognition. Peptides based on the cyclic Arg‐Gly‐Asp (RGD) sequence have been reported as high‐affinity agents for the α(ν)β(3) integrin. The aim of this research was to prepare a multimeric system of ¹⁷⁷Lu‐labeled gold nanoparticles conjugated to c(RGDfK)C (cyclo(Arg‐Gly‐Asp‐Phe‐Lys)Cys) and to compare the radiation‐absorbed dose with that of ¹⁷⁷Lu‐labeled monomeric and dimeric RGD peptides to α(ν)β(3) integrin‐positive U87MG tumors in mice. DOTA‐GGC (1,4,7,10‐tetraazacyclododecane‐N‐N′,N″,N?‐tetraacetic acid‐Gly‐Gly‐Cys) and c(RGDfK)C peptides were synthesized and conjugated to AuNPs by a spontaneous reaction of the thiol groups. Transmission electron microscopy, ultraviolet–visible, X‐ray photoelectron spectroscopy, Raman and far‐infrared spectroscopy techniques demonstrated that AuNPs were functionalized with the peptides. For the ¹⁷⁷Lu‐AuNP‐c(RGDfK)C to be obtained, the ¹⁷⁷Lu‐DOTA‐GGC radiopeptide was first prepared and added to a solution of AuNPs followed by c(RGDfK)C (25 µl, 5 µ m ) at 18 °C for 15 min. ¹⁷⁷Lu‐DOTA‐GGC, ¹⁷⁷Lu‐DOTA‐cRGDfK and ¹⁷⁷Lu‐DOTA‐E‐c(RGDfK)₂ were prepared by adding ¹⁷⁷LuCl₃ (370 MBq) to 5 µl (1 mg/ml) of the DOTA derivative diluted with 50 µl of 1 m acetate buffer pH 5. The mixture was incubated at 90 °C in a block heater for 30 min. Radiochemical purity was determined by ultrafiltration and HPLC analyses. Biokinetic studies were accomplished in athymic mice with U87MG‐induced tumors. The radiochemical purity for all ¹⁷⁷Lu‐RGD derivatives was 96 ± 2%. ¹⁷⁷Lu‐absorbed doses per injected activity delivered to U87MG tumors were 0.357 ± 0.052 Gy/MBq (multimer), 0.252 ± 0.027 Gy/MBq (dimer) and 0.102 ± 0.018 Gy/MBq (monomer). ¹⁷⁷Lu‐labeled dimeric and multimeric RGD peptides demonstrated properties suitable for targeted radionuclide therapy of tumors expressing α(ν)β(3) integrins. Copyright © 2012 John Wiley & Sons, Ltd.     

Radiolabeling,quality control,and biological characterization of 177Lu‐labeled kanamycin

Kanamycin is an antibiotic, isolated from Streptomyces kanamyceticus, which is used to treat serious bacterial infections. The fact that the present radioligand ^99mTc‐kanamycin used for diagnosis is short‐lived, raised a need to label and study kanamycin with one of the most important beta (β) radiation emitting isotope ¹⁷⁷Lu. Labeling yield of ¹⁷⁷Lu‐kanamycin was confirmed by different chromatography techniques such as paper chromatography, TLC, HPLC. Several experiments were performed to optimize labeling with changing reaction conditions such as pH, temperature, amount of ligand, and reaction time. In vitro stability analysis was performed incubation with human serum. Electrophoresis analysis was also conducted to determine the charge on ¹⁷⁷Lu‐kanamycin. The biodistribution and scintigraphy were performed in normal mice and rabbit, respectively, at different time intervals of postinjection. ¹⁷⁷Lu‐kanamycin was prepared with very high yield (~100%), with excellent stability in vivo and in vitro (>99% 6 hr postprep.), at pH 7. Maximum labeling was achieved at less reaction time (15 min), with maximum conjugation of the ligand (12.5 mg) with ¹⁷⁷Lu. Electrophoresis analysis showed net neutral charge. The radioligand showed rapid clearance from body in biodistribution and scintigraphy studies. The preparation ¹⁷⁷Lu‐kanamycin could be used as a radio‐pharmaceutical for infection imaging purpose, especially when transporting the radioligand to long‐range distances.     

177Lu‐DOTMP induces G2/M cell cycle arrest and apoptosis in MG63 cell line

Bone pain is the major manifestation of skeletal metastases. Although various treatment modalities are available for bone pain palliation, use of radiolabeled phosphonates is documented to be more effective. Among radionuclides available for this purpose, lutetium‐177 is gaining popularity due to its moderate beta energy, theranostic capability, favorable half‐life and convenient production logistics. ¹⁷⁷Lu‐DOTMP has shown considerable promise as a metastatic bone pain palliating agent in preliminary evaluations and recent clinical studies. Therefore, an attempt was made to elucidate the possible mechanism of in vitro cell death induced by ¹⁷⁷Lu‐DOTMP in MG63 cells. ¹⁷⁷Lu‐DOTMP binding studies were carried out in mineralized bone of MG63 cells and around 50% binding was observed. Skeletons of Wistar rats showed 1.78 ± 0.5% IA/g at a 3 h time period which was almost constant up to 7 days. MG63 cells were incubated with 3.7 and 37 MBq of ¹⁷⁷Lu‐DOTMP for 48 h prior to perform assays. An increase in the magnitude of cell toxicity and apoptotic DNA fragmentation was observed. Enhancement of G2/M phase cell cycle arrest and apoptosis were documented which were dose‐dependent. Thus, ¹⁷⁷Lu‐DOTMP induced apoptotic cell death in MG63 cells, which might be one of the primary causes of pain relief in osseous metastases.     

Preclinical evaluation of new GnRH‐I receptor radionuclide therapy with 177Lu‐peptide tracer

The purpose of this study was to develop preclinical evaluation of a novel radiolabeled gonadotropin‐releasing hormone (GnRH) receptor targeting peptide for prostate cancer therapy. The new antiproliferative agent of GnRH‐I analogue was developed on the basis of the D‐Trp⁶‐GnRH‐I scaffold, and in vivo pharmacokinetics and receptor binding affinity were enhanced by the substitution of Gly‐NHNH₂ for Gly‐NH₂ at position 10 in D‐Trp⁶‐GnRH‐I. To evaluate ¹⁷⁷Lu‐DOTA‐triptorelin‐hydrazide as radionuclide therapy of tumor, the quality control tests and preclinical stage assessment were carried out. Solid‐phase method was used to synthesize new peptide. Characterization and purity of peptide were done by mass spectroscopy and high‐performance liquid chromatography (HPLC). In order to be utilized in targeted therapy, the new GnRH‐I agonist was coupled with pSCN‐Bn‐DOTA. The precipitate crude of DOTA‐triptorelin‐hydrazide was then purified via preparative HPLC. At optimal conditions of time, temperature, ligand amount, and lutetium content, DOTA‐triptorelin‐hydrazide was labeled with ¹⁷⁷Lu (specific activity not less than 925 GBq/mg). Investigation of the in vivo biodistribution and in vitro studies for ¹⁷⁷Lu‐DOTA‐TRPHYD was performed in three different ways, and the binding of radiopeptide to GnRH receptors was expressed on the human cell lines using ¹²⁵I‐labeled D‐TRP⁶GnRH‐I as a tracer, respectively. Synthesized novel GnRH‐I was obtained with purity greater than 98%. Paper chromatography was found to be the most suitable with R_f of the complex and observed radiochemical purity of RTLC and HPLC greater than 97%. For in vivo studies, ¹⁷⁷Lu‐DOTA‐triptorelin‐hydrazide showed promising results with fast clearance from the blood and resulted in good T/NT ratios at 1, 4, and 24 hours postinjection and satisfactory biodistribution with no significant activity seen in normal tissue. The values of internalization efficiency and receptor affinity of new radiopeptide binding were IC₅₀ = 0.47 ± 0.06 vs 0.13 ± 0.01 nM for triptorelin and cellular uptake: 3.4 ± 0.7% at 1 hour and 6.8 ± 1.17% at 4 hours of the internal reference. The results showed a good stability and radiochemical purity of the obtained radioconjugate. For in vivo and in vitro studies, new radiopeptide showed a high uptake of ¹⁷⁷Lu conjugate in tumor and rapid clearance from the blood stream almost entirely via the renal/urinary pathway and binding to the GnRH receptors with high specificity and affinity, respectively.     

Development of a single vial kit formulation of [99mTc]‐labeled doxorubicin for tumor imaging and treatment response assessment‐preclinical evaluation and preliminary human results

The present study describes the successful radiolabeling of [99mTcO^?₄] with doxorubicin, and the resultant product was formulated in to a ready‐to‐label lyophilized single vial kit preparation for convenient use in a routine clinical setting. The radiolabeled preparation of [99mTc]‐doxorubicin exhibited a high radiolabeling efficiency of more than 95.0%, serum stability for up to 24 h, and shelf‐life of lyophilized cold kits was more than 6 months. Animal imaging data in tumor‐bearing mice demonstrated that [99mTc]‐doxorubicin accumulated in the tumor site with high target (tumor) to non‐target (contra‐lateral thigh) ratio (3.2 ± 0.5). The ratio decreased to 1.2 ± 0.6 indicating a good response on follow up imaging performed after 2 weeks of doxorubicin treatment. [99mTc]‐doxorubicin scintigraphic data in human volunteers supported the hepato‐renal excretion of the radiotracer as reflected by the increased accumulation of the radiotracer as a function of time in intestine, kidneys, and urinary bladder. Further, imaging in patients (very limited number) indicated that the technique may be useful in the detection of active sarcoma and post treatment (surgery/chemotherapy) remission or absence of the disease. The technique, however, needs validation through further preclinical evaluation and imaging in a larger number of patients.     

Design and development of the theranostic pair 177Lu‐OPS201/68Ga‐OPS202 for targeting somatostatin receptor expressing tumors

Radiolabeled somatostatin receptor (sstr) antagonists have shown superiority in different preclinical and clinical settings compared with the well‐established and clinically used agonists for targeting sstr‐expressing tumors, with regard to pharmacokinetics, tumor uptake, and retention. The theranostic pair ¹⁷⁷Lu‐OPS201/⁶⁸Ga‐OPS202, based on the sstr2 antagonist JR11 (Cpa‐c[d ‐Cys‐Aph(Hor)‐d ‐Aph(Cbm)‐Lys‐Thr‐Cys]‐d ‐Tyr‐NH₂), is the most advanced pair of the antagonist family in terms of preclinical development and is currently under clinical evaluation. OPS201 and OPS202 share the same amino acid sequence (JR11) but feature different conjugated chelators needed for radiolabeling, DOTA for OPS201 and NODAGA for OPS202. In this review, the design and development of the peptidic analog, JR11, and the selection of chelators and radiometals that led to ¹⁷⁷Lu‐OPS201/⁶⁸Ga‐OPS202 are discussed. Furthermore, the preclinical evaluation of both radiolabeled analogs from bench to bedside and the clinical trials involving the theranostic pair are presented.     

Preparation,characterization and biodistribution of a new technetium‐99 m nitrido complex with 2‐methoxyisobutylisonitrile and comparison with 99mTc–MIBI

The preparation of complex ^99mTcN–MIBI was carried out using two alternative procedures that led to the formation of the complex with high radiochemical purity (>90%). The partition coefficient, electrophoresis and cationic resin exchange experiments showed that the ^99mTcN–MIBI is a lipophilic and neutral complex, the structure of this complex is six‐coordinate distorted octahedral, its composition may be [^99mTcNCl₂(MIBI)₃], and the optimized geometry of this complex was calculated by using Gaussian 98 for Window (G98W) program. The biodistribution of ^99mTcN–MIBI shows high myocardial uptake and good target/non‐target ratios in mice at early post‐injection time, for 5 min post‐injection the heart‐to‐blood, heart‐to‐lungs and heart‐to‐liver ratios are 3.18, 1.72 and 1.42, respectively. In respect of the relatively good rations after 5 min and the rapid clearance from non‐target, the complex ^99mTcN–MIBI may be suitable for instant myocardial imaging. In addition, the lyophilized kit enables the convenient preparation of this complex for clinical use. Based on these promising properties, ^99mTcN–MIBI should be a new potential myocardial perfusion‐imaging agent. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and characterization of new 99mTc‐radiopharmaceuticals with dithiobenzoate derivatives for the study of septic inflammatory processes

Improved methods for the preparation of ^99mTc‐radiopharmaceuticals containing dithiobenzoate ligands, in sterile and pyrogen free conditions, are described. These procedures are based on the reaction of these ligands either with [^99mTc] pertechnetate in the presence of a strong reducing agent (HCl/tertiary phosphine, SnCl₂·2H₂O), or with pre‐reduced complexes obtained from different kit formulations. All the preparations led to the high‐yield formation of the neutral and lipophilic ^99mTc‐complex [^99mTc][Tc(S₃CPh)₂(S₂CPh)], which is analogous to the corresponding compounds obtained with rhenium and the long‐lived β‐emitting isotope technetium‐99 g recently described. HPLC analysis and thin layer chromatography were used to confirm the characterisation of the resulting ^99mTc‐radiopharmaceutical which was found to be potentially suitable for blood‐cell labelling as applied to the diagnosis of inflammatory processes. Copyright © 2003 John Wiley & Sons, Ltd.     

An improved kit formulation for one‐pot synthesis of [99mTc]Tc‐HYNIC‐E[c(RGDfK)]2 for routine clinical use in cancer imaging

Radiolabeled Arg‐Gly‐Asp (RGD) peptide derivatives have immense potential for non‐invasive monitoring of malignancies overexpressing integrin α_vβ₃ receptors. Easy availability of suitable radiotracers would augment the utility of this class of molecular imaging agents. Towards this, the present article describes the development of an improved lyophilized kit for the routine clinical formulation of [^99mTc]Tc complex of HYNIC‐conjugated dimeric cyclic RGD peptide derivative E‐[c(RGDfK)]₂ (E = glutamic acid, f = phenyl alanine, K = lysine) without using Sn²⁺ and systematic evaluation of its efficacy. Five batches of the kits were prepared, and [^99mTc]Tc‐HYNIC‐E[c(RGDfK)]₂ radiotracer was synthesized with high radiochemical purity (98.6 ± 0.5%) and specific activity (124.8 GBq/μmol) using the kits. Biodistribution studies in C57BL/6 mice bearing melanoma tumor exhibited significant accumulation of the radiotracer in tumor (5.32 ± 0.56 %ID/g at 60 min p.i.), and this uptake was also found to be receptor‐specific by blocking studies. Preliminary human clinical investigations carried out in 10 breast cancer patients revealed high radiotracer uptake in the tumor along with good tumor‐to‐background contrast. The developed kit formulation showed an exceptionally high shelf‐life of at least 18 months. These results demonstrated promising attributes of the developed kit formulation and warrant more extensive clinical investigations.     

90Y/177Lu‐labelled Cetuximab immunoconjugates: radiochemistry optimization to clinical dose formulation

Radiolabelled monoclonal antibodies (mAbs) are increasingly being utilized in cancer theranostics, which is a significant move toward tailored treatment for individual patients. Cetuximab is a recombinant, human–mouse chimeric IgG₁ mAb that binds to the epidermal growth factor receptor with high affinity. We have optimized a protocol for formulation of clinically relevant doses (~2.22 GBq) of ⁹⁰Y‐labelled Cetuximab and ¹⁷⁷Lu‐labelled Cetuximab by conjugation of the mAb with a suitable bifunctional chelator, N‐[(R)‐2‐amino‐3‐(paraisothiocyanato‐phenyl)propyl]‐trans‐(S,S)‐cyclohexane‐1,2‐diamine‐N,N,N′,N″,N″‐pentaacetic acid (CHX‐A″‐DTPA). The radioimmunoconjugates demonstrated reasonably high specific activity (1.26 ± 0.27 GBq/mg for ⁹⁰Y‐CHX‐A″‐DTPA‐Cetuximab and 1.14 ± 0.15 GBq/mg for ¹⁷⁷Lu‐CHX‐A″‐DTPA‐Cetuximab), high radiochemical purity (>95%) and appreciable in vitro stability under physiological conditions. Preliminary biodistribution studies with both ⁹⁰Y‐CHX‐A″‐DTPA‐Cetuximab and ¹⁷⁷Lu‐CHX‐A″‐DTPA‐Cetuximab in Swiss mice bearing fibrosarcoma tumours demonstrated significant tumour uptake at 24‐h post‐injection (p.i.) (~16%ID/g) with good tumour‐to‐background contrast. The results of the biodistribution studies were further corroborated by ex vivo Cerenkov luminescence imaging after administration of ⁹⁰Y‐CHX‐A″‐DTPA‐Cetuximab in tumour‐bearing mice. The tumour uptake at 24 h p.i. was significantly reduced with excess unlabelled Cetuximab, suggesting that the uptake was receptor mediated. The results of this study hold promise, and this strategy should be further explored for clinical translation.     

Cyclic‐RGD penta‐peptides cRGDyK derivatized with cyclopentadienyl complexes of technetium and rhenium as radiopharmaceutical probes

The present study reports the syntheses of half‐sandwich complexes of the type [M(η⁵‐C₅H₄CONH‐R)(CO)₃] (M═Re,^99mTc;R═cyclic RGD peptide (cRGDyK) for potential imaging of α_vβ₃ integrin expression. The ^99mTc complex was prepared directly from the reaction of [^99mTc(OH₂)₃(CO)₃]⁺ with cRGDyK, doubly conjugated to Thiele's acid [(C₅H₅COOH)₂] in water. This approach extends the viability of metal‐mediated retro Diels‐Alder reactions for the preparation of small molecules such as linear tripeptides to a more complex cyclic peptide carrying a [(η⁵‐C₅H₄)^99mTc(CO)₃] tag. The Diels‐Alder product [(C₅H₅CONH‐cRGDyK)₂] was prepared from Thiele's acid via double peptide coupling. The Re‐complex [Re(η⁵‐C₅H₄CONH‐cRGDyK)(CO)₃] was obtained by attaching [Re(η⁵‐C₅H₄COOH)(CO)₃] directly to the N‐terminus of cRGDyK. The identity of the ^99mTc‐complex is confirmed by chromatographic comparison with the corresponding rhenium complex, fully characterized by spectroscopic techniques.