1 research outputs found
Evaluation of an Anti-HER2 Nanobody Labeled with <sup>225</sup>Ac for Targeted α‑Particle Therapy of Cancer
Human
epidermal growth factor receptor type 2 (HER2) is overexpressed
in numerous carcinomas. Nanobodies (Nbs) are the smallest antibody-derived
fragments with beneficial characteristics for molecular imaging and
radionuclide therapy. Therefore, HER2-targeting nanobodies could offer
a valuable platform for radioimmunotherapy, especially when labeled
with α-particle emitters, which provide highly lethal and localized
radiation to targeted cells with minimal exposure to surrounding healthy
tissues. In this study, the anti-HER2 2Rs15d-nanobody was conjugated
with 2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic
acid (<i>p</i>-SCN-Bn-DOTA) and radiolabeled with an α-emitter <sup>225</sup>Ac with a high yield (>90%) and a radiochemical purity
above
95%. The <sup>225</sup>Ac-DOTA-Nb binding affinity was 4.12 ±
0.47 nM with an immunoreactive fraction above 80%. Binding to low
HER2-expressing MDA-MB-231 cells was negligible, whereas HER2-overexpressing
SKOV-3 cells could be blocked with an excess of unlabeled nanobody,
confirming the specificity of binding. Noncompeting binding to HER2
was observed in the presence of an excess of trastuzumab. The cell-associated
fraction of <sup>225</sup>Ac-DOTA-Nb was 34.72 ± 16.66% over
24 h. <i>In vitro</i>, the radioconjugate was toxic in an
HER2-mediated and dose-dependent manner, resulting in IC<sub>50</sub> values of 10.2 and 322.1 kBq/mL for <sup>225</sup>Ac-DOTA-Nb and
the <sup>225</sup>Ac-DOTA control, respectively, on SKOV-3 cells,
and 282.2 kBq/mL for <sup>225</sup>Ac-DOTA-Nb on MDA-MB-231 cells. <i>Ex vivo</i> biodistribution studies, performed in mice bearing
subcutaneous HER2-overexpressing and low HER2-expressing tumors, showed
a fast uptake in SKOV-3 tumors compared to MDA-MB-231 (4.01 ±
1.58% ID/g vs 0.49 ± 0.20% ID/g after 2 h), resulting also in
high tumor-to-normal tissue ratios. In addition, coinjection of <sup>225</sup>Ac-DOTA-Nb with Gelofusine reduced kidney retention by 70%.
This study shows that <sup>225</sup>Ac-DOTA-Nb is a promising new
radioconjugate for targeted α-particle therapy and supports
its further development