Synthesis if new [Y-90]-DOTA based Meleimides for the prelabeling of thiol-bearing L-oligonucleotides and peptides


Synthesis if new [Y-90]-DOTA based Meleimides for the prelabeling of thiol-bearing L-oligonucleotides and peptides

Pietzsch, H.-J.; Schlesinger, J.; Fischer, C.; Közle, I.; Vonhoff, S.; Klussmann, S.; Bergmann, R.; Steinbach, J.

Objectives: A common chelator for radioisotopes of Y and the lanthanides is DOTA. However, the elevated temperatures necessary to achieve sufficient radiochemical yields may be a drawback, especially for the radiolabeling of thermally sensitive molecules such as DOTA-modified antibodies. A promising alternative to the “direct” radiolabeling of DOTA conjugates (“postlabeling”) is the use of so-called “prelabeling” agents. Here, we present the synthesis of two novel [90Y]-DOTA-based maleimide reagents, [90Y]2 and [90Y]3, suitable for the mild radiolabeling of thiol-bearing peptides or thiol-modified L-RNAs. Application and reactivity of both maleimide reagents were evaluated by the labeling of glutathione (GSH) and a thiol-modified 12mer L-RNA as model substances.
Methods: L‑RNA [sequence: 5’‑(1-hydroxy-7,8-dithia-tetradecyl) UGACUGACUGAC‑3’, MW 4124] was synthesized at NOXXON Pharma AG (Germany). (S)‑p‑NH2‑Bn‑DOTA was purchased from Macrocyclics (USA). 90Y was purchased as [90Y]YCl3 from QSA Global GmbH (Germany). Measurements of 90Y were done in the 90Y channel of a dose calibrator ISOMED 2000 (Nuklear-Medizintechnik Dresden, Germany) by measuring the bremsstrahlung. The compounds were characterized by HPLC, gel electrophoresis and mass spectrometry.
Results: A straightforward method to synthesize [90Y]‑MAD [90Y]2 and [90Y]‑MABD [90Y]3 is to initially complex [90Y]Y3+ with (S)‑p‑NH2‑Bn‑DOTA and to subsequently transform the purified complex [90Y((S)‑p‑NH2‑Bn‑DOTA)]- into the corresponding maleimides by using activating agents. The scheme illustrates the subsequent preparation of [90Y]‑MAD‑GSH and [90Y]‑MABD‑GSH and the 90Y-labeling of an L‑RNA via the pre- and postlabeling approach. In comparison to the N‑aryl maleimide [90Y]‑MAD, N‑alkyl maleimide [90Y]-MABD showed an increased hydrolytic stability at pH ≥ 7. A slightly higher reactivity was found for [90Y]‑MAD by prelabeling of 0.1 and 1 μg glutathione, respectively in phosphate buffer (pH 7.2) at room temperature. In terms of high radiochemical yields, the direct radiolabeling of DOTA-L-RNA with [90Y]YCl3 proved to be more suitable than the prelabeling of the thiol-modified 12mer L-RNA derivative with [90Y]‑MABD.
Conclusions: We could demonstrate the applicability of maleimide reagents [90Y]‑MAD and [90Y]-MABD for the prelabeling approach. Both reagents showed a high potential for that purpose. Concerning high radiochemical yields, the direct labeling of DOTA‑l‑RNA with [90Y]YCl3 proved to be more efficient than the prelabeling of the thiol-modified 12mer l‑RNA with [90Y]‑MABD at low activity levels. With regard to 90Y‑labeling of thermally sensitive molecules prelabeling could have more advantages than the direct radiolabeling, due to the milder labeling conditions.

  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S491
    ISSN: 0362-4803

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Publ.-Id: 13105