Purpose: super(131)I- and super(90)Y-labelled anti-CD20 antibodies have been shown to be effective in the treatment of low-grade, B-cell non-Hodgkin's lymphoma (NHL). However, the most appropriate ...radionuclide in terms of high efficiency and low toxicity has not yet been established. In this study we evaluated an immunoconjugate formed by the anti-CD20 antibody rituximab and the chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). DOTA-rituximab was prepared as a kit formulation and can be labelled in a short time (<20min) with either super(177)Lu or super(90)Y. Materials and methods: Immunoconjugates with different numbers of DOTA molecules per rituximab were prepared using p-SCN-Bz-DOTA. In vitro immunoreactivity and stability were tested and preliminary dosimetric results were acquired in two patients. Results: The immunological binding properties of DOTA-rituximab to the CD20 antigen were found to be retained after conjugation with up to four chelators. The labelled product was stable against a 10 super(5) times excess of diethylenetriaminepentaacetic acid (DTPA, 37 degree C, 7days). Two patients with relapsed NHL were treated with 740MBq/m super(2) body surface super(177)Lu-DOTA-rituximab. Scintigraphic images showed specific uptake at tumour sites and acceptable dosimetric results. The mean whole-body dose was found to be 314mGy. The administration of super(177)Lu-DOTA-rituximab was tolerated well. Conclusion: Our results show that DOTA-rituximab (4:1) can be labelled with super(177)Lu with sufficient stability while the immunoconjugate retains its immunoreactivity. super(177)Lu-DOTA-rituximab is an interesting, well-tolerated radiolabelled antibody with clinical activity in a low dose range, and provides an approach to the efficient treatment with few side effects for patients with relapsed NHL.
Purpose
131
I- and
90
Y-labelled anti-CD20 antibodies have been shown to be effective in the treatment of low-grade, B-cell non-Hodgkin’s lymphoma (NHL). However, the most appropriate radionuclide in ...terms of high efficiency and low toxicity has not yet been established. In this study we evaluated an immunoconjugate formed by the anti-CD20 antibody rituximab and the chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). DOTA-rituximab was prepared as a kit formulation and can be labelled in a short time (<20 min) with either
177
Lu or
90
Y.
Materials and methods
Immunoconjugates with different numbers of DOTA molecules per rituximab were prepared using p-SCN-Bz-DOTA. In vitro immunoreactivity and stability were tested and preliminary dosimetric results were acquired in two patients.
Results
The immunological binding properties of DOTA-rituximab to the CD20 antigen were found to be retained after conjugation with up to four chelators. The labelled product was stable against a 10
5
times excess of diethylenetriaminepentaacetic acid (DTPA, 37°C, 7 days). Two patients with relapsed NHL were treated with 740 MBq/m
2
body surface
177
Lu-DOTA-rituximab. Scintigraphic images showed specific uptake at tumour sites and acceptable dosimetric results. The mean whole-body dose was found to be 314 mGy. The administration of
177
Lu-DOTA-rituximab was tolerated well.
Conclusion
Our results show that DOTA-rituximab (4:1) can be labelled with
177
Lu with sufficient stability while the immunoconjugate retains its immunoreactivity.
177
Lu-DOTA-rituximab is an interesting, well-tolerated radiolabelled antibody with clinical activity in a low dose range, and provides an approach to the efficient treatment with few side effects for patients with relapsed NHL.
PET with (18)F-labeled arginine-glycine-aspartic acid (RGD) peptides can visualize and quantify α(ν)β(3) integrin expression in patients, but radiolabeling is complex and image contrast is limited in ...some tumor types. The development of (68)Ga-RGD peptides would be of great utility given the convenience of (68)Ga production and radiolabeling, and (64)Cu-RGD peptides allow for delayed imaging with potentially improved tumor-to-background ratios.
We used the chelators DOTA,1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), and 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo6.6.2hexadecane (CB-TE2A) to radiolabel the cyclic pentapeptide c(RGDfK) with (68)Ga or (64)Cu. NODAGA-c(RGDfK) was labeled at room temperature with both radionuclides within 10 min. Incubation at 95°C for up to 30 min was used for the other conjugates. The affinity profile of the metallopeptides was evaluated by a cell-based receptor-binding assay. Small-animal PET studies and biodistribution studies were performed in nude mice bearing subcutaneous U87MG glioblastoma xenografts.
The conjugates were labeled with a radiochemical purity greater than 97% and specific activities of 15-20 GBq/μmol. The affinity profile was similar for all metallopeptides and comparable to the reference standard c(RGDfV). In the biodistribution studies, all compounds demonstrated a relatively similar tumor and normal organ uptake at 1 h after injection that was comparable to published data on (18)F-labeled RGD peptides. At 18 h after injection, however, (64)Cu-NODAGA-c(RGDfK) and (64)Cu-CB-TE2A-c(RGDfK) showed up to a 20-fold increase in tumor-to-organ ratios. PET studies demonstrated high-contrast images of the U87MG tumors at 18 h, confirming the biodistribution data.
The ease of radiolabeling makes (68)Ga-NODAGA-c(RGDfK) an attractive alternative to (18)F-labeled RGD peptides. The high tumor-to-background ratios of (64)Cu-NODAGA-c(RGDfK) and (64)Cu-CB-TE2A-c(RGDfK) at 18 h warrant testing of (64)Cu-labeled RGD peptides in patients.
Bombesin (BN), a 14 amino acid peptide, is an analogue of human gastrin-releasing-peptide (GRP) that binds to GRP receptors (GRP-R) with high affinity and specificity. In addition to this ...physiological role, GRP, through its interaction with GRP-R, promotes tumour growth in a number of human cancer cell lines. The GRP receptors are over-expressed on a variety of human cancer cells. Aim of the present work is the study of two novels BN-like peptides, by investigating the radiochemical and radiopharmacological behaviour of their complexes with metals. The derivatives under study are: Gly–Gly–Cys–Aca–BN 2–14 where Aca: 6-amino-hexanoic acid. Pyroglutamic acid in the bombesin molecule has been replaced by the chemical group Gly–Gly–Cys–Aca, which bears an amino-acid combination capable of complexing a variety of radiometals. The other derivative under study is: Gly–Gly–Cys–Aca–BN 7–14. This moiety of the peptide has been chosen because it has been proven to be a potent GRP agonist. The peptide derivatives were synthesized by SPPS, according to the Fmoc strategy and were identified by reverse phase high performance liquid chromatography (RP-HPLC). Radiolabelling with
99mTc was performed via the precursor
99mTc-gluconate. The stability of the radiolabelled species was examined with time. In vivo studies of the two
99mTc-labelled derivatives were performed, comparatively, in normal mice, attention being focused on GRP receptor-bearing organs, and in experimentally induced prostate cancer models. Experimental tumours were imaged in a small field-of-view animal gamma camera.
Chelated somatostatin agonists have been shown to be sensitive to N-terminal radiometal modifications, with Ga-DOTA agonists having significantly higher binding affinity than their Lu-, In-, and ...Y-DOTA correlates. Recently, somatostatin antagonists have been successfully developed as alternative tracers to agonists. The aim of this study was to evaluate whether chelated somatostatin antagonists are also sensitive to radiometal modifications and how. We have synthesized 3 different somatostatin antagonists, DOTA-p-NO(2)-Phe-cD-Cys-Tyr-D-Aph(Cbm)-Lys-Thr-Cys-D-Tyr-NH(2), DOTA-Cpa-cD-Cys-Aph(Hor)-D-Aph(Cbm)-Lys-Thr-Cys-D-Tyr-NH(2) (DOTA-JR11), and DOTA-p-Cl-Phe-cD-Cys-Tyr-D-Aph(Cbm)-Lys-Thr-Cys-D-Tyr-NH(2), and added various radiometals including In(III), Y(III), Lu(III), Cu(II), and Ga(III). We also replaced DOTA with 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) and added Ga(III). The binding affinity of somatostatin receptors 1 through 5 was evaluated in all cases. In all 3 resulting antagonists, the Ga-DOTA analogs were the lowest-affinity radioligands, with a somatostatin receptor 2 binding affinity up to 60 times lower than the respective Y-DOTA, Lu-DOTA, or In-DOTA compounds. Interestingly, however, substitution of DOTA by the NODAGA chelator was able to increase massively its binding affinity in contrast to the Ga-DOTA analog. The 3 NODAGA analogs are antagonists in functional tests. In vivo biodistribution studies comparing (68)Ga-DOTATATE agonist with (68)Ga-DOTA-JR11 and (68)Ga-NODAGA-JR11 showed not only that the JR11 antagonist radioligands were superior to the agonist ligands but also that (68)Ga-NODAGA-JR11 was the tracer of choice and preferable to (68)Ga-DOTA-JR11 in transplantable HEK293-hsst(2) tumors in mice. One may therefore generalize that somatostatin receptor 2 antagonists are sensitive to radiometal modifications and may preferably be coupled with a (68)Ga-NODAGA chelator-radiometal complex.
Vascular Endothelial Growth Factor (VEGF) is one of the molecules which regulate angiogenesis, a phenomenon observed in many diseases, including cancer. VG76e, an anti-VEGF monoclonal antibody, was ...labeled with
Lu
p-SCN-Bz-DOTA and CHX-A″-DTPA chelating systems, in order to investigate its possible therapeutic use. Labeling was performed by a 30 min incubation of
LuCl
and each immunoconjugate, at 37 °C. Radiochemical analysis showed the formation of a single radioactive species, at a yield higher than 98%, for both immunoconjugates. Kits have been formulated for both VG76e-DOTA and VG76e-DTPA. Stability studies, in the presence of a competitor excess, showed that both radiolabeled species remained sufficiently stable (95%) for at least 48 h. Biodistribution results in normal mice were similar for both radioimmunoconjugates, with no significant bone uptake. Gamma camera images of tumor-bearing mice showed satisfactory visualization of the tumor 24 h p.i., while a higher uptake was observed at 48 h p.i. Our findings indicate that both the bifunctional chelating agents p-SCN-Bz-DOTA and CHX-A″-DTPA can be used for the labeling of VG76e with
Lu, with high labeling yield and stability. Their
behaviour in normal and tumor-bearing mice looks promising and they can be successfully used for tumor imaging studies.
Vascular Endothelial Growth Factor (VEGF) is one of the molecules which regulate angiogenesis, a phenomenon observed in many diseases, including cancer. VG76e, an anti-VEGF monoclonal antibody, was ...labeled with
177
Lu
via
p-SCN-Bz-DOTA and CHX-A″-DTPA chelating systems, in order to investigate its possible therapeutic use. Labeling was performed by a 30 min incubation of
177
LuCl
3
and each immunoconjugate, at 37 °C. Radiochemical analysis showed the formation of a single radioactive species, at a yield higher than 98%, for both immunoconjugates. Kits have been formulated for both VG76e-DOTA and VG76e-DTPA. Stability studies, in the presence of a competitor excess, showed that both radiolabeled species remained sufficiently stable (95%) for at least 48 h. Biodistribution results in normal mice were similar for both radioimmunoconjugates, with no significant bone uptake. Gamma camera images of tumor-bearing mice showed satisfactory visualization of the tumor 24 h p.i., while a higher uptake was observed at 48 h p.i. Our findings indicate that both the bifunctional chelating agents p-SCN-Bz-DOTA and CHX-A″-DTPA can be used for the labeling of VG76e with
177
Lu, with high labeling yield and stability. Their
in vivo
behaviour in normal and tumor-bearing mice looks promising and they can be successfully used for tumor imaging studies.
The anti-CEA monoclonal antibody, which selectively localizes in colon cancer, was labeled with Samarium-153 (153Sm). 153Sm is mainly a beta-emitter which can be used for therapeutic purposes, while ...its gamma-ray facilitates imaging studies. Labeling was achieved using the bicyclic anhydride of DTPA as chelator for Sm-153 tagging onto the antibody. 153Smanti-CEA was biologically evaluated in nude mice bearing tumors of different weight (0.5-2.5 g), at diverse time intervals (4-72 hours), by anatomic and imaging methods. Biodistribution studies showed slow blood clearance and high retention in the liver, kidneys and lungs. In nude mice bearing tumors of about the same weight, uptake increased with time, from 4 to 72 hours post injection (p.i.). Highest uptake was observed in 0.5-0.8 g tumors compared to those of 1.5-2.5 g. The results agreed with imaging studies performed on a gamma camera at 4 to 72 hours p.i. Tumor uptake depended on time and tumor weight. The tumor can be visualized 24 hours p.i. but, due to the high background, it can be clearly distinguished at 72 hours p.i.
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