[en] 

Background

We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three, five-membered azaheterocyclic arms for the development of ⁶⁸Ga- and ⁶⁴Cu-based radiopharmaceuticals. Here, a ⁶⁸Ga-labelled conjugate comprising the bifunctional chelator NODIA-Me in combination with the α_vß₃-targeting peptide c(RGDfK) has been synthesized and characterized. The primary aim was to evaluate further the potential of our NODIA-Me chelating system for the development of ⁶⁸Ga-labelled radiotracers.

Results

The BFC NODIA-Me was conjugated to c(RGDfK) by standard peptide chemistry to obtain the final bioconjugate NODIA-Me-c(RGDfK) 3 in 72% yield. Labelling with [⁶⁸Ga]GaCl₃ was accomplished in a fully automated, cGMP compliant process to give [⁶⁸Ga]3 in high radiochemical yield (98%) and moderate specific activity (~ 8 MBq nmol− ¹). Incorporation of the Ga-NODIA-Me chelate to c(RGDfK) 2 had only minimal influence on the affinity to integrin α_vß₃ (IC₅₀ values [^natGa]3 = 205.1 ± 1.4 nM, c(RGDfK) 2 = 159.5 ± 1.3 nM) as determined in competitive cell binding experiments in U-87 MG cell line. In small-animal PET imaging and ex vivo biodistribution studies, the radiotracer [⁶⁸Ga]3 showed low uptake in non-target organs and specific tumor uptake in U-87 MG tumors.

Conclusion

The results suggest that the bifunctional chelator NODIA-Me is an interesting alternative to existing ligands for the development of ⁶⁸Ga-labelled radiopharmaceuticals.

[en] The present study aims at evaluating the preclinical and the clinical performance of [${}^{68}$Ga]Ga-DATA${}^{5m}$.SA.FAPi, which has the advantage to be labeled with gallium-68 at room temperature. [${}^{68}$Ga]Ga-DATA${}^{5m}$.SA.FAPi was assessed in vitro on FAP-expressing stromal cells, followed by biodistribution and in vivo imaging on prostate and glioblastoma xenografts. Moreover, the clinical assessment of [${}^{68}$Ga]Ga-DATA${}^{5m}$.SA.FAPi was conducted on six patients with prostate cancer, aiming on investigating, biodistribution, biokinetics, and determining tumor uptake. [${}^{68}$Ga]Ga-DATA${}^{5m}$.SA.FAPi is quantitatively prepared in an instant kit-type version at room temperature. It demonstrated high stability in human serum, affinity for FAP in the low nanomolar range, and high internalization rate when associated with CAFs. Biodistribution and PET studies in prostate and glioblastoma xenografts revealed high and specific tumor uptake. Elimination of the radiotracer mainly occurred through the urinary tract. The clinical data are in accordance with the preclinical data concerning the organ receiving the highest absorbed dose (urinary bladder wall, heart wall, spleen, and kidneys). Different to the small-animal data, uptake of [${}^{68}$Ga]Ga-DATA${}^{5m}$.SA.FAPi in tumor lesions is rapid and stable and tumor-to-organ and tumor-to-blood uptake ratios are high. The radiochemical, preclinical, and clinical data obtained in this study strongly support further development of [${}^{68}$Ga]Ga-DATA${}^{5m}$.SA.FAPi as a diagnostic tool for FAP imaging.

[en] Introduction: The efflux transporters P-glycoprotein (P-gp, ABCB1) and breast cancer resistance protein (BCRP, ABCG2) are expressed at the blood–brain barrier (BBB), and can limit the access of a wide range of drugs to the brain. In this study we developed a PET-CT imaging method for non-invasive, quantitative analysis of the effect of ABCB1 and ABCG2 on brain penetration of the anti-cancer drug gefitinib, and demonstrated the applicability of this method for identification and quantification of potential modulators of ABCB1 and ABCB2 using the dual inhibitor elacridar. Methods: In vitro cellular accumulation studies with ["1"4C]-gefitinib were conducted in LLC-PK1, MDCKII, and the corresponding ABCB1/Abcb1a and ABCG2/Abcg2 overexpressing cell lines. Subsequently, in vivo brain penetration of ["1"8F]-gefitinib was quantified by PET-CT imaging studies in wild-type, Abcg2"−"/"−, Abcb1a/1b"−"/"−, and Abcb1a/1b;Abcg2"−"/"− mice. Results: In vitro studies showed that ["1"4C]-gefitinib is a substrate of the human ABCB1 and ABCG2 transporters. After i.v. administration of ["1"8F]-gefitinib (1 mg/kg), PET-CT imaging showed 2.3-fold increased brain levels of ["1"8F]-gefitinib in Abcb1a/1b;Abcg2"−"/"− mice, compared to wild-type. Levels in single knockout animals were not different from wild-type, showing that Abcb1a/1b and Abcg2 together limit access of ["1"8F]-gefitinib to the brain. Furthermore, enhanced brain accumulation of ["1"8F]-gefitinib after administration of the ABCB1 and ABCG2 inhibitor elacridar (10 mg/kg) could be quantified with PET-CT imaging. Conclusions: PET-CT imaging with ["1"8F]-gefitinib is a powerful tool to non-invasively assess potential ABCB1- and ABCG2-mediated drug–drug interactions (DDIs) in vivo. Advances in knowledge and implications for patient care: This minimally-invasive, ["1"8F]-based PET-CT imaging method shows the interplay of ABCB1 and ABCG2 at the BBB in vivo. The method may be applied in the future to assess ABCB1 and ABCG2 activity at the BBB in humans, and for personalized treatment with drugs that are substrates of ABCB1 and/or ABCG2.

[en] In recent years, [¹⁸F]gefitinib PET has successfully been employed for a number of applications ranging from oncology to in vivo studies of drug transporter proteins. We here report a reliable, automated procedure for routine synthesis of this radiotracer on an Eckert and Ziegler modular system. The 3-step radiosynthesis followed by preparative HPLC-purification provided [¹⁸F]gefitinib in 17.2±3.3% (n=22) overall decay-corrected radiochemical yield with radiochemical purity >99% in a total synthesis time of about 2.5 h. - Highlights: ► Automated production of [¹⁸F]gefitinib on a commercially available modular system. ► 3-Step synthesis provides [¹⁸F]gefitinib in 17.2±3.3 % radiochemical yield. ► Radiochemical purity at the end of synthesis was >99% (n=22).

[en] We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three five-membered azaheterocyclic arms for complexation of the PET nuclides gallium-68 and copper-64. The main objective of this study was to evaluate the stability and pharmacokinetics of ⁶⁸Ga- and ⁶⁴Cu-complexes of the bifunctional chelator NODIA-Me 1 covalently bound to a PSMA targeting vector in vivo.

[en] Pretargeted radioimmunoimaging and -therapy approaches building on the bioorthogonal inverse-electron-demand Diels–Alder (IEDDA) reaction between strained trans-cyclooctenes (TCO) and electron-deficient tetrazines (Tz) have yielded impressive results in recent years and have proven a vital alternative to biological pretargeting systems. After improvement of the TCO–antibody conjugates, we here report on our evaluation of a new series of radiolabeled Tz-probes.