RESUMO
Very late antigen 4 (VLA-4; also called integrin α4ß1) is overexpressed in melanoma tumor cells with an active role in tumor growth, angiogenesis, and metastasis, making VLA-4 a potential target for targeted alpha therapy (TAT). METHODS: An anti-VLA-4 antibody was conjugated to DOTA for [225Ac]Ac-labeling and DTPA for [111In]In-labeling. The resulting agents, [225Ac]Ac- or [111In]In-labeled anti-VLA-4 were evaluated in vitro, including binding affinity, internalization, and colony formation assays as well as in vivo biodistribution studies. In addition, the therapeutic efficacy of [225Ac]Ac-DOTA-anti-VLA-4 was evaluated in a disseminated disease mouse model of melanoma. RESULTS: [111In]In-DTPA-anti-VLA-4 demonstrated high affinity for VLA-4 (Kd = 5.2 ± 1.6 nM). [225Ac]Ac-DOTA-anti-VLA-4 was labeled with an apparent molar activity of 3.5 MBq/nmol and > 95% radiochemical purity. Colony formation assays demonstrated a decrease in the surviving fraction of B16F10 cells treated with [225Ac]Ac-DOTA-anti-VLA-4 compared to control. Biodistribution studies demonstrated accumulation in the VLA-4-positive tumor and VLA-4 rich organs. Therapeutic efficacy studies demonstrated a significant increase in survival in mice treated with [225Ac]Ac-DOTA-anti-VLA-4 as compared to controls. CONCLUSION: The work presented here demonstrated that [225Ac]Ac-DOTA-anti-VLA-4 was effective as a treatment in mice with disseminated disease, but potentially has dose limiting hematopoietic toxicity. Preliminary studies presented here also supported the potential to overcome this limitation by exploring a pre-loading or blocking dose strategy, to optimize the targeting vector to help minimize the absorbed dose to VLA-4 rich organs while maximizing the dose delivered to VLA-4-positive melanoma tumor cells.