Development and biological evaluation of radiolabeled anti-PSMA-specific nanobodies as tracers in oncology

Abstract

Prostate cancer is one of the leading causes of cancer deaths among men worldwide. To improve patient outcomes, early detection and the use of appropriate therapeutic approaches are crucial. As PSMA-targeted tracers provide superior accuracy to conventional imaging, there is a growing interest in developing new and potentially even better tracers. Nanobodies or single-domain antibody fragments derived from camelids, are a promising candidate. Their reduced size and rapid renal clearance may offer potential benefits for imaging, potentially resulting in a better detection of cancerous tissues with reduced background interference. <br/> For this purpose, this thesis characterized three nanobodies and their tracers, radiolabeled with Technetium-99m, using four assays. The assays included the Lindmo assay to measure the IRF, the determination of the IC50, the Scatchard assay for binding affinity, and internalization assays to determine the potential of these nanobodies for diagnostic and therapeutic applications. In this thesis, two different PSMA-positive cell lines were used, LNCap and I1-6, to assess binding characteristics and internalization efficiency of the anti-PSMA nanobody-based tracers. Within the research group of the Department of Nuclear Medicine at the University Hospital Bonn, initial results from further studies showed that the clinically established tracer [¹⁷⁷Lu]Lu-PSMA-I&T has a lower affinity for PSMA-positive cells compared to the tracers used in this study. <br/> This thesis indicates that nanobody-based tracers hold potential for both the diagnosis and treatment of prostate cancer. The anti-PSMA Nb07 tracer shows strong binding affinity and immunoreactivity along with efficient internalization, which could make it suitable for targeted therapy and potentially useful in molecular imaging. The Nb37 tracer, despite its slightly lower internalization efficiency, still presents characteristics that may make it a promising candidate for diagnostic and targeted therapy. The Nb13 tracer demonstrates, in comparison, weaker binding affinity and minimal internalization, indicating a more limited diagnostic potential. The work also discussed several limitations, such as the potential immunogenicity of nanobodies, given their non-human origin, which underlines the importance of strategies to humanize these molecules to mitigate immune responses. <br/> In conclusion, the findings presented in this thesis offer valuable insights into the evolving field of nanobody-based diagnostics and therapy, demonstrating their potential as next-generation tools in the fight against prostate cancer and possibly other cancers as well. Further <em>in vivo</em> research and clinical testing will be required to establish the effectiveness and safety of these nanobodies for human medical use.