Abstract 579: A novel nanobody-based radionuclide drug conjugate (RDC) platform through introducing a human serum albumin (HSA) binder by the intelligent ligase-dependent conjugation (iLDC) technology: an innovative and versatile approach for next-ge

Abstract Background: RDC has become an attractive strategy in cancer treatment, but still faces significant drawbacks due to poor tumor penetration and undesirable pharmacokinetics of the most used targeting carriers, such as peptides, small molecules and nanobodies. To address these limitations, we developed a robust and versatile nanobody-based RDC platform, that site-specifically conjugates an small molecular HSA binder into the nanobody-based RDC to improve its druggability by increasing its circulation half-life. The validation of the RDC platform is exemplified by 64Cu/177Lu-NBC-02, a theranostic anti-PSMA nanobody-based RDC. Method: Using iLDC technology, a diverse and high-quality RDC library was generated by site-specifically conjugating various stable branch linkers containing different HSA binders and a DOTA into multiple anti-PSMA nanobodies with varying affinities, followed by labeling with 64Cu and 177Lu. Following the screening of those RDCs through PET imaging study and in vivo anti-tumor efficacy study, the theranostic anti-PSMA RDC, 64Cu/177Lu-NBC-02, was developed. Subsequently, an IIT study was conducted to confirm the distribution of 177Lu-NBC-02in mCRPC patients. Results: PET imaging studies performed in the LNCaP CDX model showed enhanced circulation half-life of 64Cu-NBC-02, which resulted in a higher accumulation and retention over time in the tumor with a much higher tumor-to-background ratio. Remarkably, 177Lu-NBC-02 demonstrated superior antitumor efficacy to 177Lu-PSMA-617 (Pluvicto®) with complete tumor regression in all treated mice. In addition, 177Lu-NBC-02 can reduce tumor volume significantly when the tumors became refractory to Pluvicto®. This demonstrated 177Lu-NBC-02’s potential to overcome resistance to Pluvicto®. An IIT study in several mCRPC patients injected with a single dose showed that 177Lu- NBC-02 was well tolerated. SPECT images revealed longer blood circulation of 177Lu- NBC-02 with much higher uptake in tumor lesions and lower uptake in salivary glands compared with published data of Pluvicto®. Conclusion: The novel RDC platform combining iLDC technology with a unique HSA-binding linker-chelator design can generate 177Lu-NBC-02 with an extended circulation half-life, higher tumor uptake and lower salivary gland uptake in both CDX model and mCRPC patients compared to Pluvicto®. The IND enabling of this potential BIC anti-PSMA RDC is underway for the exploration of therapeutic effects on the treatment of mCRPC. Furthermore, the applied strategy provides a promising next-generation platform for future RDC discovery which requires nanobody as a targeting carrier, hence significantly expanding promise beyond the current format. Citation Format: Chong Liu, Sipeng Li, Zengyan Mu, Yajun Sun, Haibo He, Lili Shi, Paul Song, Gang Qin. A novel nanobody-based radionuclide drug conjugate (RDC) platform through introducing a human serum albumin (HSA) binder by the intelligent ligase-dependent conjugation (iLDC) technology: an innovative and versatile approach for next-generation RDCs with enhanced pharmacokinetics and druggability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 579.