Preclinical Development and Comparison of [ ^99m Tc]Tc/[ ¹⁷⁷ Lu]Lu-Labeled Anti-Trop2 Fc-Fused Nanobodies as Pancreatic Cancer Theranostics

Antibody-based radiotheranostics hold significant promise for tumor diagnosis and treatment; however, the clinical translation of radiotherapeutic agents is significantly hindered by suboptimal pharmacokinetics, particularly undesirable retention in healthy tissues. In this study, we developed novel high-affinity anti-Trop2 nanobodies using phage display technology and then generated two VHH-Fc constructs, B9 and C10, which are recombinant single-chain antibodies fused with IgG1-Fc. These were radiolabeled with [^99mTc]Tc and [¹⁷⁷Lu]Lu. A systematic comparison was then conducted against the clinically relevant monoclonal antibody hRS7 (sacituzumab). The [^99mTc]Tc-labeled-B9 exhibited high Trop2-binding affinity, rapid tumor accumulation, and substantially decreased hepatic and renal uptake in BxPC-3 xenograft models compared with [^99mTc]Tc-hRS7. Comprehensive SPECT/CT imaging and quantitative biodistribution studies further corroborated its prolonged intratumoral retention. When radiolabeled with [¹⁷⁷Lu]Lu, [¹⁷⁷Lu]Lu-B9 maintained robust tumor uptake while demonstrating faster clearance from nontarget tissues than the monoclonal antibody (hRS7). Quantitative analysis over 168 h postinjection revealed a 56.17% reduction in hepatic uptake and a 23.68% decrease in renal uptake compared to [¹⁷⁷Lu]Lu-hRS7. In a preclinical mouse model, two-cycle administration of [¹⁷⁷Lu]Lu-B9 induced significant tumor growth inhibition, prolonged survival, and minimal systemic toxicity. These findings highlight VHH-Fc-based radiotheranostics as a promising strategy to achieve favorable tumor retention while reducing off-target organ exposure.