Tetraspanin 8 (TSPAN 8) as a potential target for radio-immunotherapy of colorectal cancer

Tetraspanin 8 (TSPAN8) overexpression is correlated with poor prognosis in human colorectal cancer (CRC). A murine mAb Ts29.2 specific for human TSPAN8 provided significant efficiency for immunotherapy in CRC pre-clinical models. We therefore evaluate the feasability of targeting TSPAN8 in CRC with radiolabeled Ts29.2. Staining of tissue micro-arrays with Ts29.2 revealed that TSPAN8 espression was restricted to a few human healthy tissues. DOTA-Ts29.2 was radiolabeled with In-111 or Lu-177 with radiochemical purities > 95%, specific activity ranging from 300 to 600 MBq/mg, and radioimmunoreactive fractions > 80%. The biodistribution of [In-111] DOTA-Ts29.2 in nude mice bearing HT29 or SW480 CRC xenografts showed a high specificity of tumor localization with high tumor/blood ratios (HT29: 4.3; SW480-TSPAN8: 3.9 at 72h and 120h post injection respectively). Tumor-specific absorbed dose calculations for [Lu-177] DOTA-Ts29.2 was 1.89 Gy/MBq, establishing the feasibility of using radioimmunotherapy of CRC with this radiolabeled antibody. A significant inhibition of tumor growth in HT29 tumor-bearing mice treated with [Lu-177] DOTA-Ts29.2 was observed compared to control groups. Ex vivo experiments revealed specific DNA double strand breaks associated with cell apoptosis in [Lu-177] DOTA-Ts29.2 treated tumors compared to controls. Overall, we provide a proof-of-concept for the use of [In-111/Lu-177] DOTA-Ts29.2 that specifically target in vivo aggressive TSPAN8-positive cells in CRC.