Thiol-Reactive Bifunctional Chelators for the Creation of Site-Selectively Modified Radioimmunoconjugates with Improved Stability

Abstract

Maleimide-bearing bifunctional chelators have been used extensively for the site-selective bioconjugation and radiolabeling of peptides and proteins. However, bioconjugates obtained using these constructs inevitably suffer from limited stability in vivo, a trait that translates into suboptimal activity concentrations in target tissues and higher uptake levels in healthy, nontarget tissues. To circumvent this issue, phenyloxadiazolyl methylsulfones have previously been reported as alternatives to maleimides for thiol-based ligations, but these constructs have scarcely been used in the field of radiochemistry. In this report, we describe the synthesis of two thiol-reactive bifunctional chelators for Zr andLu based on a new, easy-to-make phenyloxadiazolyl methylsulfone reagent, PODS. Radioimmunoconjugates created using these novel bifunctional chelators displayed in vitro stability that was higher than that of their maleimide-derived cousins. More importantly, positron emission tomography imaging in murine models of cancer revealed that a Zr-labeled radioimmunoconjugate created using a PODS-bearing bifunctional chelator produced a rate of uptake in nontarget tissues that is significantly lower than that of its analogous maleimide-based counterpart.

Thiol-Reactive PODS-Bearing Bifunctional Chelators for the Development of EGFR-Targeting [18F]AlF-Affibody Conjugates

“…The favorable tumor-to-muscle ratios for the two PODS-bearing radioconjugates resulted in high-contrast PET images already 1 h post-injection (Table 2). In contrast to Adumeau et al, there was no difference in both the biodistribution profile and the tumor-to-tissue ratios between the [ 18 F]AlF PODS-bearing conjugates and the malemide-based product ( Table 2, Table S3) [15].…”

“…The Z EGFR:03115 -Cys affibody molecule was provided by Affibody AB (Solna, Sweden http://www.affibody.com) as a solution in 0.2 M sodium acetate. Phenyloxadiazolyl methylsulfone (PODS) was synthesized as described in the literature [15]. The maleimide-bearing affibody analogue NOTA-Z EGFR:03115 was prepared and radiolabeled as previously reported [22].…”

“…Among the promising molecules, oxadiazolyl methyl sulfone-based compounds showed not only rapid and selective reaction with thiols in proteins but also the capacity of forming conjugates (via an oxadiazole-protein thiolate bond) which were more stable than those derived from maleimides [11,12]. The preparation of thiol-reactive bifunctional chelators and prosthetic groups containing the oxadiazolyl methylsulfone moiety (e.g., phenyloxadiazolyl methylsulfone or PODS) and their attachment to proteins and peptides have been examined [13][14][15]. Once radiolabeled, the conjugates were found to be more stable in vitro than the maleimide-derived counterparts.…”

“…Once radiolabeled, the conjugates were found to be more stable in vitro than the maleimide-derived counterparts. Moreover, when used in vivo, the oxadiazolyl methylsulfone linker-derived agents demonstrated reduced uptake in non-targeted tissues than the maleimide equivalents [13][14][15]. Based on these promising reports, we have prepared two novel phenyloxadiazolyl methylsulfone-containing (PODS) bifunctional chelators (NOTA-PODS and NODAGA-PODS) for the conjugation and aluminum fluoride ([ 18 F]AlF) radiolabeling of a cysteine-containing biomolecule.…”

“…Table S3)[15]. 2020,25, x FOR PEER REVIEW 6 of 12 derivative [ 18 F]AlF-NOTA-ZEGFR:03115 was performed.…”