Synthesis of [18F]Fluoroform with High Molar Activity

Fluoroform is an interesting motif for the isotopologue labelling of biologically active compounds with fluorine-18 for PET imaging. However, so far the building block [18F]fluoroform and consequently the [18F]trifluoromethylated products suffered from low molar activities ranging from 0.1 to 30 GBq/µmol due to isotopic dilution under the strongly basic standard radiofluorination conditions. In this article the synthesis of high molar activity [18F]fluoroform is described. By implementing a recently reported novel radiofluorination reagent, [18F]triflyl fluoride, the concentration of base-cryptand complex in the reaction could be reduced 100-fold compared to standard radiofluorination conditions and molar activities close to 100 GBq/µmol (at end of [18F]fluoroform synthesis) could be obtained, enabling the imaging of low density receptors. Furthermore, an automated procedure was developed on the commercially available NEPTIS® perform synthesizer to provide access of high molar activity [18F]fluoroform to other PET centres

High-quality 124I-labelled monoclonal antibodies for use as PET scouting agents prior to 131I-radioimmunotherapy

Purpose: Monoclonal antibodies (MAbs) labelled with 124I are an attractive option for quantitative imaging with positron emission tomography (PET) in a scouting procedure prior to 131I-radioimmunotherapy ( 131I-RIT). In this study, three important items in the labelling of MAbs with 124I were introduced to obtain optimal and reproducible product quality: restoration of radiation-induced inorganic deterioration of the starting 124I solution, radiation protection during and after 124I labelling, and synchronisation of the I/MAb molar ratio. Methods: A new method was applied, using an NaIO3/ NaI carrier mix, realising in one step >90% restoration of deteriorated 124I into the iodide form and chemical control over the I/MAb molar ratio. Chimeric MAb (cMAb) U36 and the murine MAbs 425 and E48 were labelled with 124I using the so-called lodogen-coated MAb method, as this method provides optimal quality conjugates under challenging radiation conditions. As a standardising condition, NaIO3/NaI carrier mix was added at a stoichiometric I/MAb molar ratio of 0.9. For comparison, MAbs were labelled with 131I and with a mixture of 124I, 123I, 126I and 130I. Results: Labelling with 124I in this setting resulted in overall yields of >70%, a radiochemical purity of >95%, and preservation of MAb integrity and immunoreactivity, including at the patient dose level (85 MBq). No significant quality differences were observed when compared with 131I products, while the iodine isotope mixture gave exactly the same labelling efficiency for each of the isotopes, excluding a different chemical reactivity of 124I-iodide. The scouting performance of 124I-cMAb U36 la-belled at the patient dose level was evaluated in biodistribution studies upon co-injection with 131I- labelled cMAb U36, and by PET imaging in nude mice bearing the head and neck cancer xenograft line HNX-OE. 124I-cMAb and 131I-cMAb U36 labelled with a synchronised I/MAb molar ratio gave fully concordant tissue uptake values. Selective tumour uptake was confirmed with immuno-PET, revealing visualisation of 15 out of 15 tumours. Conclusion: These results pave the way for renewed evaluation of the potential of 124I-immuno-PET for clinical applications

89Zr as a PET surrogate radioisotope for scouting biodistribution of the therapeutic radiometals 90Y and 177Lu in tumor-bearing nude mice after coupling to the internalizing antibody cetuximab

Immuno-PET as a scouting procedure before radioimmunotherapy (RIT) aims at confirming tumor targeting and accurately estimating radiation dose delivery to both tumor and normal tissues and might therefore be of value for selection of patient candidates for RIT. A prerequisite for this approach is that PET radioimmunoconjugates and RIT radioimmunoconjugates must show a similar biodistribution. In the present study, we evaluated the potential of the long-lived positron emitter 89Zr to predict biodistribution of the residualizing therapeutic radiometals 88Y (as a substitute for 90Y) and 177Lu when labeled to the monoclonal antibody (mAb) cetuximab via different types of chelates. Cetuximab was selected as a model mAb because it abundantly internalizes after binding to the epidermal growth factor receptor. Methods: Cetuximab was labeled with 89Zr using succinylated desferrioxamine B (N-sucDf). The chelates p-benzyl isothiocyanate-1,4,7,10-tetraazacyclododecane-1,4,7, 10-tetraacetic acid (p-SCN-Bz-DOTA) and p-isothiocyanatobenzyl diethylenetriaminepentaacetic acid (p-SCN-Bz-DTPA) were both used for radiolabeling with 88Y and 177Lu. For measurement of the in vitro stability of each of the 5 radioimmuno-conjugates, samples were incubated in freshly prepared human serum at 37°C up to 16 d. Biodistribution was assessed at 24, 48, 72, and 144 h after intraperitoneal coinjection of the PET and RIT conjugates in nude mice bearing the squamous cell carcinoma xenograft line A431. Results: Cetuximab premodification with N-sucDf, p-SCN-Bz-DOTA, or p-SCN-Bz-DTPA resulted in chelate-to-mAb molar ratios of about 1. After radiolabeling and purification, the radiochemical purity and immunoreactive fraction of the conjugates always exceeded 97% and 93%, respectively. All conjugates were stable in serum, showing a radioactivity release of less than 5% until day 7. From day 7 until day 16, an enhanced release was observed for the 89Zr-N-sucDf, 88Y-p-SCN-Bz-DTPA, and 177Lu-p-SCN-Bz-DTPA conjugates. The coinjected PET and RIT conjugates showed similar biodistributions, except for the thighbone and sternum. For example, the 89Zr-N-sucDf conjugate showed a 2.0-2.5 times higher radioactivity accretion in the thighbone than did the RIT conjugates at 72 h after injection. Conclusion: In view of the advantages of PET over SPECT, 89Zr-immuno-PET is a promising modality for in vivo scouting of 90Y- and 177Lu-labeled mAbs, although care should be taken when estimating bone marrow doses

Discordance of genetic alterations between primary head and neck tumors and corresponding metastases associated with mutational status of the TP53 gene

Ample molecular data are available on the progression from normal mucosa to invasive head and neck squamous cell carcinoma (HNSCC), but information on further genetic progression to metastatic disease is scarce. To obtain insight into the metastatic process, we compared 23 primary HNSCCs with 25 corresponding lymph node metastases (LNMs) and 10 corresponding distant metastases (DMs) with respect to TP53 mutations and patterns of loss of heterozygosity (LOH) based on 26 microsatellite markers on six chromosome arms (3p, 9p, 17p, 13q, 8p, and 18q). In 18 of the 23 patients, a TP53 mutation was detected in the primary tumor, and in all cases the same TP53 mutation was present in the corresponding LNM or DM. In nine of 20 patients with LNMs and three of seven patients with DMs, the LOH pattern of metastasis differed from that of the corresponding primary tumor by at least one marker. Microsatellite markers located on chromosome arms 13q, 8p, and 18q were most frequently discordant, providing evidence that alterations at these chromosomes occur late in HNSCC carcinogenesis. Moreover, evidence was found that DMs had developed directly from the primary tumor and not from LNMs. Remarkably, we observed that the mutational status of the TP53 gene is associated significantly with the degree of genetic differences between primary HNSCCs and corresponding metastases. All patients with TP53 wild-type primary tumors showed significantly more discordant LOH patterns in the corresponding LNMs and DMs than patients with TP53-mutated tumors. The percentages were 100% versus 27% (LNMs) and 100% versus 0% (DMs), respectively (P = 0.008 and P = 0.029; two-sided Fisher exact test). This finding suggests that TP53-mutated tumors need fewer additional genetic alterations to develop metastases compared with TP53 wild-type primary tumors

Long-lived positron emitters zirconium-89 and iodine-124 for scouting of therapeutic radioimmunoconjugates with PET

Antibody-PET imaging might be of value for the selection of radioimmunotherapy (RIT) candidates to confirm tumor targeting and to estimate radiation doses to tumor and normal tissues. One of the requirements to be set for such a scouting procedure is that the biodistributions of the diagnostic and therapeutic radioimmunoconjugates should be similar. In the present study we evaluated the potential of the positron emitters zirconium-89 ( 89Zr) and iodine-124 (124I) for this approach, as these radionuclides have a relatively long half-life that matches with the kinetics of MAbs in vivo (t1/2 3.27 and 4.18 days, respectively). After radiolabeling of the head and neck squamous cell carcinoma (HNSCC)-selective chimeric antibody (cMAb) U36, the biodistribution of two diagnostic (cMAb U36-N-sucDf-89Zr and cMAb U36-124I) and three therapeutic radioimmunoconjugates (cMAb U36-p-SCN-Bz-DOTA-88Y-with 88Y being substitute for 90Y, cMAb U36-131I, and cMAb U36-MAG3-186Re) was assessed in mice with HNSCC-xenografts, at 24, 48, and 72 hours after injection. Two patterns of biodistribution were observed, one pattern matching for 89Zr- and 88Y-labeled cMAb U36 and one pattern matching for 124I-, 131I-, and 186Re-cMAb U36. The most remarkable differences between both patterns were observed for uptake in tumor and liver. Tumor uptake levels were 23.2 ± 0.5 and 24.1 ± 0.7%ID/g for the 89Zr- and 88Y-cMAb U36 and 16.0 ± 0.8, 15.7 ± 0.79 and 17.1 ± 1.6%ID/g for 124I-, 131I-, and 186Re-cMAb U36-conjugates, respectively, at 72 hours after injection. For liver these values were 6.9 ± 0.8 (89Zr), 6.2 ± 0.8 (88Y), 1.7 ± 0.1 (124I), 1.6 ± 0.1 (131I), and 2.3 ± 0.1 (186Re), respectively. These preliminary data justify the further development of antibody-PET with 89Zr-labeled MAbs for scouting of therapeutic doses of 90Y-labeled MAbs. In such approach 124I-labeled MAbs are most suitable for scouting of 131I- and 186Re-labeled MAbs