Abstract :
[en] Among the various therapeutic strategies, radioligand therapy is a promising approach for cancer treatment as it can precisely target tumor cells with minimal damage to healthy tissues. Targeted alpha therapy (TAT) involves using α-emitter radionuclides to exert cytotoxic effects using a vector specifically directed at cancer cells. The high energy and short range of α-radiation offer precise targeting and killing while minimizing damage to healthy tissues1. Single-domain antibody fragments (sdAbs), derived from Camelidae heavy-chain antibodies, are advantageous vectors for TAT due to their small size (~15 kDa), strong target binding, overall stability and suitable pharmacokinetics2. In this context, the sdAb#2F8 has shown promise for radioligand therapy in multiple myeloma (MM) by targeting the overexpressed glycoprotein CD383. Here we focus on developing TAT for treating MM by labeling sdAb#2F8 with 100 kBq/nmols actinium-225 (225Ac), using a conventional DOTA chelator. The random coupling of p-SCN-Bn-DOTA on sdAb lysines was performed in sodium carbonate buffer at 4 mg/mL for 3 hours at room temperature, obtaining an average of 1.3 DOTA molecules per sdAb. Biolayer interferometry confirmed CD38 binding of sdAb#2F8-DOTA. 225Ac labelling was performed in buffer TRIS 250 mM, NaCl 750 mM, pH 9 at 55°C for 30 min. Radiochemical purity (RCP) was assessed by radio-instant thin layer chromatography and radio-size-exclusion chromatography. The RCP was >99% after 30 min and remained stable (> 90%) in human serum for 24 hours, indicating proper stability over time. In vitro studies with [225Ac]Ac-DOTA-2F8 were carried out using CD38+ RPMI cells taking along the 177Lu-labelled analogue for comparison. [225Ac]Ac-DOTA-2F8 was able to bind CD38+ RPMI cells. Further studies are planned to obtain the binding affinity. These studies indicate the feasibility of labelling sdAb#2F8 with 225Ac for realizing TAT. Future work will focus on optimizing the in vitro studies and conducting in vivo studies to evaluate [225Ac]Ac-DOTA-2F8 as a radiopharmaceutical for treating MM.
1 Hatcher-Lamarre, J. L., Sanders, V. A., Rahman, M., Cutler, C. S., & Francesconi, L. C. (2021). Alpha emitting nuclides for targeted therapy. Nuclear medicine and biology, 92, 228–240. https://doi.org/10.1016/j.nucmedbio.2020.08.004
2 D'Huyvetter, M., Xavier, C., Caveliers, V., Lahoutte, T., Muyldermans, S., & Devoogdt, N. (2014). Radiolabeled nanobodies as theranostic tools in targeted radionuclide therapy of cancer. Expert opinion on drug delivery, 11(12), 1939–1954. https://doi.org/10.1517/17425247.2014.941803
3 Duray, E., Lejeune, M., Baron, F., Beguin, Y., Devoogdt, N., Krasniqi, A., Lauwers, Y., Zhao, Y. J., D'Huyvetter, M., Dumoulin, M., & Caers, J. (2021). A non-internalised CD38-binding radiolabelled single-domain antibody fragment to monitor and treat multiple myeloma. Journal of hematology & oncology, 14(1), 183. https://doi.org/10.1186/s13045-021-01171-6
