Novel (64)Cu- and (68)Ga-labeled RGD conjugates show improved PET imaging of α(ν)ß(3) integrin expression and facile radiosynthesis.

UNLABELLED: PET with (18)F-labeled arginine-glycine-aspartic acid (RGD) peptides can visualize and quantify α(ν)ß(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. METHODS: 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-tetraazabicyclo[6.6.2]hexadecane (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. RESULTS: 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. CONCLUSION: 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.

Activated platelets in carotid artery thrombosis in mice can be selectively targeted with a radiolabeled single-chain antibody.

BACKGROUND: Activated platelets can be found on the surface of inflamed, rupture-prone and ruptured plaques as well as in intravascular thrombosis. They are key players in thrombosis and atherosclerosis. In this study we describe the construction of a radiolabeled single-chain antibody targeting the LIBS-epitope of activated platelets to selectively depict platelet activation and wall-adherent non-occlusive thrombosis in a mouse model with nuclear imaging using in vitro and ex vivo autoradiography as well as small animal SPECT-CT for in vivo analysis. METHODOLOGY/PRINCIPAL FINDINGS: LIBS as well as an unspecific control single-chain antibody were labeled with (111)Indium ((111)In) via bifunctional DTPA ( = (111)In-LIBS/(111)In-control). Autoradiography after incubation with (111)In-LIBS on activated platelets in vitro (mean 3866 ± 28 DLU/mm(2), 4010 ± 630 DLU/mm(2) and 4520 ± 293 DLU/mm(2)) produced a significantly higher ligand uptake compared to (111)In-control (2101 ± 76 DLU/mm(2), 1181 ± 96 DLU/mm(2) and 1866 ± 246 DLU/mm(2)) indicating a specific binding to activated platelets; P<0.05. Applying these findings to an ex vivo mouse model of carotid artery thrombosis revealed a significant increase in ligand uptake after injection of (111)In-LIBS in the presence of small thrombi compared to the non-injured side, as confirmed by histology (49630 ± 10650 DLU/mm(2) vs. 17390 ± 7470 DLU/mm(2); P<0.05). These findings could also be reproduced in vivo. SPECT-CT analysis of the injured carotid artery with (111)In-LIBS resulted in a significant increase of the target-to-background ratio compared to (111)In-control (1.99 ± 0.36 vs. 1.1 ± 0.24; P < 0.01). CONCLUSIONS/SIGNIFICANCE: Nuclear imaging with (111)In-LIBS allows the detection of platelet activation in vitro and ex vivo with high sensitivity. Using SPECT-CT, wall-adherent activated platelets in carotid arteries could be depicted in vivo. These results encourage further studies elucidating the role of activated platelets in plaque pathology and atherosclerosis and might be of interest for further developments towards clinical application.

In vivo testing of 177Lu-labelled anti-PSMA antibody as a new radioimmunotherapeutic agent against prostate cancer.

AIM: The goal of the present study was to test the (177)Lu-labelled anti-PSMA monoclonal antibody 3/F11 ((177)Lu-DOTA-3/F11) as a new radioimmunotherapeutic agent in a prostate cancer SCID mouse xenograft model. MATERIALS AND METHODS: The mAb 3/F11 was (177)Lu labelled using 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as chelating agent. DOTA-3/F11 was tested for cell binding and serum immunoreactivity by flow cytometry. The biodistribution and the therapeutic efficacy of (177)Lu-DOTA-3/F11 in mice bearing PSMA-positive C4-2 prostate cancer xenografts were evaluated. RESULTS: 3/F11 and DOTA-3/F11 showed high and specific cell binding and similar serum half-lives of approximately seven days. Biodistribution studies revealed an increasing tumour uptake of (177)Lu DOTA-3/F11 over time with maximum tumour-to-muscle and tumour-to-blood ratios after 72 h. A single dose of 1 MBq (177)Lu-DOTA-3/F11 inhibited tumour growth and prolonged survival. CONCLUSION: This study indicated that (177)Lu-DOTA-3/F11 may be a suitable radioimmunotherapeutic agent for the treatment of prostate cancer.

Isolation and biological activity of new norhirsutanes from Creolophus cirrhatus.

Five new norhirsutanes, named creolophins A-E, and complicatic acid were isolated from the culture broth of the rare tooth fungus Creolophus cirrhatus by solvent extraction, silica gel column chromatography and HPLC. In addition, neocreolophin, a complex dimerization product, was formed as an artefact during purification. The structures were elucidated by spectroscopic methods and are published in a separate paper. Two of the metabolites showed moderate antibacterial, antifungal and cytotoxic activities.