Clickable Radiocomplexes With Trivalent Radiometals for Cancer Theranostics: In vitro and in vivo Studies

Abstract

Pre-targeting approaches based on the inverse-electron-demand Diels-Alder (iEDDA) reaction between strained trans-cyclooctenes (TCO) and electron-deficient tetrazines (Tz) have emerged in recent years as valid alternatives to classic targeted strategies to improve the diagnostic and therapeutic properties of radioactive probes. To explore these pre-targeting strategies based on in vivo click chemistry, a small family of clickable chelators was synthesized and radiolabelled with medically relevant trivalent radiometals. The structure of the clickable chelators was diversified to modulate the pharmacokinetics of the resulting [111In]In-radiocomplexes, as assessed upon injection in healthy mice. The derivative DOTA-Tz was chosen to pursue the studies upon radiolabelling with 90Y, yielding a radiocomplex with high specific activity, high radiochemical yields and suitable in vitro stability. The [90Y]Y-DOTA-Tz complex was evaluated in a prostate cancer PC3 xenograft by ex-vivo biodistribution studies and Cerenkov luminescence imaging (CLI). The results highlighted a quick elimination through the renal system and no relevant accumulation in non-target organs or non-specific tumor uptake. Furthermore, a clickable bombesin antagonist was injected in PC3 tumor-bearing mice followed by the radiocomplex [90Y]Y-DOTA-Tz, and the mice imaged by CLI at different post-injection times (p.i.). Analysis of the images 15 min and 1 h p.i. pointed out an encouraging quick tumor uptake with a fast washout, providing a preliminary proof of concept of the usefulness of the designed clickable complexes for pre-targeting strategies. To the best of our knowledge, the use of peptide antagonists for this purpose was not explored before. Further investigations are needed to optimize the pre-targeting approach based on this type of biomolecules and evaluate its eventual advantages.

DOTA chelation through click chemistry enables favorable biodistribution of89Zr-radiolabeled antibodies: A comparison with DFO chelation

“…The effects of the Tz/TCO structure on biodistribution must be investigated in future research using metal radionuclides other than 89 Zr. Alternatively, this two-step radiolabeling method could be extended to label mAbs with alpha and beta emitters since a preparation method of M-DOTA-Tz (M = 90 Y, 177 Lu, 225 Ac) has already been established [28][29][30].…”

Bioorthogonal Chemistry Approach for the Theranostics of GRPR-Expressing Cancers

“…The chemical synthesis of the clickable DOTA-based ligands and their radiolabeling with 111 In have been previously reported. The chemical synthesis of the peptide AR and the preparation of the derivative AR-PEG 4 -TCO have also been previously described [30].…”

“…Inspired by the encouraging results reported for antibodies and their fragments, the main goal of the work here described was to show that the pretargeting approach might improve the in vivo performance of GRPRtargeting peptides, namely by reducing the associated nephrotoxicity and nontargeted effects in other critical organs such as the pancreas. Toward this goal, we used the small and hydrophilic tetrazine-containing radiocomplexes previously evaluated by our group [30]. These clickable DOTA-like radiocomplexes are in fact quickly excreted through the kidneys, reducing the overall radiation exposure since the radiopeptides are formed only at the tumor site.…”

Radiolabeled Bombesin Analogs

“…In another interesting approach depicted in Figure 6 , a pretargeting strategy has been proposed to circumvent pancreatic uptake. Pretargeting strategies have been applied with success to lower tumor-to-background radioactivity ratios of long-circulating high molecular weight molecules, for example, antibodies [ 111 , 112 ]. Preliminary studies in mice with derivatives of NeoBOMB1, carrying a clickable residue, have been applied in combination with the radiolabeled complementary small molecule [ 111 In]In-Tz, and thus far, have failed to improve tumor-to-pancreas ratios, most likely due to undesired folding of the targeting vector in the binding pocket of the GRPR [ 113 ].…”