Anti-SV2C single domain nanobodies for molecular imaging in androgen receptor positive prostate cancer

Prostate cancer (PCa) is one of the most prevalent malignant tumors in men worldwide. Because of its highly heterogeneous, the accurate diagnosis of PCa is critical to the selection of appropriate treatment strategy. In present work, high affinity nanobody 1-H9, a variable domain of heavy-chain antibody (VHH) against SV2C was developed by phage display library screening. Showing by 1-H9, SV2C was selectively expressed in androgen receptor (AR) positive prostate tumor cell LNCaP, but not AR negative tumor cell PC3. In LNCaP cells, SV2C and AR were first observed to co-localize on the mitochondrial membrane. Subsequent pull-down assays confirmed that AR, when used as bait, directly interacted with SV2C (the prey), suggesting a physical association between the two proteins. Furthermore, on clinical PCa biopsy specimens, SV2C and AR staining were highly correlated in immunohistochemistry assay. Confirmed in pre-clinical animal models, both fluorescence imaging and ⁶⁸Ga PET/CT imaging showed SV2C was significant enriched in LNCaP tumor. Our results suggest that in contrast to SV2A being used for neuronal endocrine PCa diagnosis, SV2C is a novel biomarker for accurate diagnosis of AR positive PCa. The nanobody 1-H9 developed against SV2C-LD4 domain is promising to be used as an effective molecular imaging probe for AR positive PCa.