Search Results (3)

Immune checkpoint inhibitors targeting the programmed cell death-1 (PD-1) and its ligand PD-L1 have proven to be efficient cancer therapies in a subset of patients. From all the patients with various cancer types, only 20% have a positive response. Being able to distinguish patients that do express PD-1/PD-L1 from patients that do not allows patients to benefit from a more personalized and efficient treatment of tumor lesion(s). Expression of PD-1 and PD-L1 is typically assessed via immunohistochemical detection in a tumor biopsy. However, this method does not take in account the expression heterogeneity within the lesion, nor the possible metastasis. To visualize whole-body PD-L1 expression by PET imaging, we developed a nanobody-based radio-immunotracer targeting PD-L1 site-specifically labeled with gallium-68. The cysteine-tagged nanobody was site-specifically conjugated with a maleimide (mal)-NOTA chelator and radiolabeling was tested at different nanobody concentrations and temperatures. Affinity and specificity of the tracer, referred to as [⁶⁸Ga]Ga-NOTA-mal-hPD-L1 Nb, were assayed by surface plasmon resonance and on PD-L1^POS or PD-L1^NEG 624-MEL cells. Xenografted athymic nude mice bearing 624-MEL PD-L1^POS or PD-L1^NEG tumors were injected with the tracer and ex vivo biodistribution was performed 1 h 20 min post-injection. Ideal ⁶⁸Ga-labeling conditions were found at 50 °C for 15 min. [⁶⁸Ga]Ga-NOTA-mal-hPD-L1 Nb was obtained in 80 ± 5% DC-RCY with a RCP > 99%, and was stable in injection buffer and human serum up to 3 h (>99% RCP). The in vitro characterization showed that the NOTA-functionalized Nb retained its affinity and specificity. Ex vivo biodistribution revealed a tracer uptake of 1.86 ± 0.67% IA/g in the positive tumors compared with 0.42 ± 0.04% IA/g in the negative tumors. Low background uptake was measured in the other organs and tissues, except for the kidneys and bladder, due to the expected excretion route of Nbs. The data obtained show that the site-specific ⁶⁸Ga-labeled NOTA-mal-hPD-L1 Nb is a promising PET radio-immunotracer due to its ease of production, stability and specificity for PD-L1. Full article

Site-selective bioconjugation of cysteine-containing peptides and proteins is currently achieved via a maleimide–thiol reaction (Michael addition). When maleimide-functionalized chelators are used and the resulting bioconjugates are subsequently radiolabeled, instability has been observed both during radiosynthesis and post-injection in vivo, reducing radiochemical yield and negatively impacting performance. Recently, a phenyloxadiazolyl methylsulfone derivative (PODS) was proposed as an alternative to maleimide for the site-selective conjugation and radiolabeling of proteins, demonstrating improved in vitro stability and in vivo performance. Therefore, we have synthesized two novel PODS-bearing bifunctional chelators (NOTA-PODS and NODAGA-PODS) and attached them to the EGFR-targeting affibody molecule Z_EGFR:03115. After radiolabeling with the aluminum fluoride complex ([¹⁸F]AlF), both conjugates showed good stability in murine serum. When injected in high EGFR-expressing tumor-bearing mice, [¹⁸F]AlF-NOTA-PODS-Z_EGFR:03115 and [¹⁸F]AlF-NODAGA-PODS-Z_EGFR:03115 showed similar pharmacokinetics and a specific tumor uptake of 14.1 ± 5.3% and 16.7 ± 4.5% ID/g at 1 h post-injection, respectively. The current results are encouraging for using PODS as an alternative to maleimide-based thiol-selective bioconjugation reactions. Full article

Two basic and simple synthetic routes for mono- and bis-maleimide bearing 1,4,7-triazacyclononane-N,N’,N’’-triacetic acid (NOTA) chelators as new bifunctional chelators are described. The syntheses are characterized by their simplicity and short reaction times, as well as practical purification methods and acceptable to very good chemical yields. The usefulness of these two synthetic pathways is demonstrated by the preparation of a set of mono- and bis-maleimide functionalized NOTA derivatives. In conclusion, these two methods can easily be expanded to the syntheses of further tailored maleimide-NOTA chelators for diverse applications. Full article