Evaluation of VLA-4 (Integrin α4β1) as a Shared Target for Radiopharmaceutical Therapy across Solid Tumors

Radiopharmaceutical therapy (RPT) is a promising approach to treating solid tumors, but therapeutic advances are impeded by the lack of broadly expressed targets and shared molecular vulnerability across different tumor types. Here, we evaluate VLA-4 (integrin α4β1) as a potential target for RPT in solid tumors and use radiolabeled copper-64 ([64Cu]Cu-) and copper-67 ([67Cu]Cu-CB-TE1A1P-PEG4-LLP2A) LLP2A, a peptidomimetic ligand of VLA-4, for preclinical imaging and RPT testing. Expression of ITGA4, the gene encoding the alpha 4 subunit (CD49d) of VLA-4, was evaluated in a variety of cancer tissues from publicly available datasets. VLA-4 protein expression was determined by flow cytometry in 22 different human and murine cancer cell lines. We used orthotopic syngeneic (i.e., B16-F10, B78, 4T1, GL261, TH-MYCN, and E2A-PBX1) and human (i.e., SK-MEL-37, 143B, and IMR-5) cancer models for in vivo PET/CT imaging and biodistribution studies. Selected models were used for dosimetry calculations with [64Cu]Cu-LLP2A. To assess in vivo tolerability and efficacy, we performed studies of [67Cu]Cu-LLP2A in tumor-free and B16-F10-bearing C57BL/6J mice (activity range, 0-74 MBq [0-2 mCi]), respectively. We found ITGA4 is overexpressed in hematological malignancies and a variety of solid tumors compared with healthy tissue. VLA-4 was expressed at medium to high levels in 17/22 (77%), at low levels in 4/22 (18%), and negative in 1/22 (5%) tested cell lines. PET/CT imaging with [64Cu]Cu-LLP2A showed tracer uptake in tumors and on-target off-tumor uptake in lymphoid tissues. [67Cu]Cu-LLP2A administered at an activity range of 37 to 74 MBq (1-2 mCi) was tolerated and did not cause long-term hematological or tissue toxicity, except for thymic atrophy. We observed tumor dose response to the activity administered to mice with B16-F10 melanoma. In summary, VLA-4 is broadly expressed across a variety of different cancer tissues and preclinical cancer cell lines, making it a promising target for [67Cu]Cu-LLP2A RPT. With proven on-target on-tumor effect, acceptable toxicity profile, and favorable dosimetry in preclinical models, further investigation of [67Cu]Cu-LLP2A as an RPT agent is warranted.