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Apr 1 – 5, 2019
Fairmont Château Laurier Hotel
UTC timezone

The therapeutic potential of anti-HER2 2Rs15d nanobody labeled with 225Ac – an in vitro and in vivo evaluation

Not scheduled
15m
Fairmont Château Laurier Hotel

Fairmont Château Laurier Hotel

Speaker

Dr Marek Pruszynski (Institute of Nuclear Chemistry and Technology)

Description

**Objectives:** Nanobodies (Nbs) are the smallest antibody-derived fragments with beneficial pharmacokinetic properties for molecular imaging and radionuclide therapy. Human Epidermal Growth Factor Receptor type 2 (HER2) is overexpressed in numerous carcinomas and portends a poor prognosis. Therefore, HER2-targeting nanobodies are very attractive vectors for TRT, especially when labeled with α-particle emitters. The aim of this study was to evaluate the therapeutic potential of the anti-HER2 Nb 2Rs15d labeled with 225Ac. **Methods:** Anti-HER2 Nb 2Rs15d was coupled with the bifunctional chelate p-SCN-Bn-DOTA and further was labeled with 225Ac. Its binding affinity and specificity for HER2, together with immunoreactive fraction (IF), were evaluated on SKOV-3 (HER2+) and MDA-MB-231 (HER2-) cells. Its in vitro cytotoxicity was assessed using MTS and clonogenic assays. In vivo, 225Ac-DOTA-Nb 2Rs15d and a non-targeting control 225Ac-DOTA-Nb R3b23 were evaluated in female athymic nude mice subcutaneously xenografted with SKOV-3 and MDA-MB-231 tumors, both alone and with molar excess of unlabeled 2Rs15d. After determination of maximum tolerated dose (MTD), the therapeutic efficacy of 225Ac-DOTA-Nb 2Rs15d was investigated in mice bearing intraperitoneal SKOV-3.IP1/luciferase+ xenografted metastases against several controls, a trastuzumab regimen and a combination of both 225Ac-DOTA-Nb 2Rs15d and trastuzumab. **Results:** The yield of DOTA-Nb 2Rs15d labeling was high (>90%), with radiochemical purity ≥95%. 225Ac-DOTA-Nb 2Rs15d bound specifically to HER2+ cells with ~75% IF, a KD of 3.50±0.17nM and lack of competition with trastuzumab or pertuzumab in vitro. Cytotoxicity studies demonstrated that 225Ac-DOTA-Nb 2Rs15d significantly reduced SKOV-3 cell viability in a dose-dependent and HER2-mediated manner, compared to 225Ac-DOTA or 225Ac-DOTA-Nb R3b23 as controls. Tumor uptake in SKOV-3 xenografted mice was high and specific (~8%), whereas in MDA-MB-231 was <0.5% already 1h pi. Its accumulation in kidneys was reduced almost 3-fold by coinjection 225Ac-DOTA-Nb 2Rs15d with 150 mg/kg Gelofusine. Therapy studies indicated that 225Ac-DOTA-Nb 2Rs15d increased Median Survival significantly, which measured 83 days compared to about 49 days for animals treated with controls PBS and 225Ac-DOTA-Nb R3b23, and to 72 days in case of trastuzumab regimen. The most extensive therapeutic effect (MD~97 days) was observed for the combination of both 225Ac-DOTA-Nb 2Rs15d and trastuzumab. **Conclusions:** 225Ac-DOTA-Nb 2Rs15d efficiently targets HER2+ cells both in vitro and in vivo. Strong signs of therapeutic potential were observed in vitro, which were confirmed also at in vivo setting in mice bearing SKOV-3 xenografts. This study underlines the strong potential of 225Ac-DOTA-Nb 2Rs15d as a new radioconjugate for TAT and supports its further development towards the clinic. **Acknowledgments:** This work was supported by the National Science Center Poland under grant 2013/09/D/ST4/03791. Matthias D’Huyvetter is a postdoctoral researcher and Tony Lahoutte a senior clinical investigator of the Research Foundation – Flanders (FWO), Belgium.
Email Address m.pruszynski@ichtj.waw.pl
Presentation Type Contributed Oral

Primary author

Dr Marek Pruszynski (Institute of Nuclear Chemistry and Technology)

Co-authors

Prof. Alfred Morgenstern (Joint Research Centre – Department for Nuclear Safety and Security, Karlsruhe, GERMANY) Mrs Edyta Cedrowska (Institute of Nuclear Chemistry and Technology, Warsaw, POLAND) Prof. Frank Bruchertseifer (Joint Research Centre – Department for Nuclear Safety and Security, Karlsruhe, GERMANY) Ms Magdalena Rodak (Institute of Nuclear Chemistry and Technology, Warsaw, POLAND) Dr Matthias D'Huyvetter (In Vivo Cellular and Molecular Imaging Lab, Vrije Universiteit Brussel, Brussels, BELGIUM) Prof. Tony Lahoutte (In Vivo Cellular and Molecular Imaging Lab, Vrije Universiteit Brussel, Brussels, BELGIUM) Ms Yana Dekempeneer (In Vivo Cellular and Molecular Imaging Lab, Vrije Universiteit Brussel, Brussels, BELGIUM)

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