Zr-labeled CEA-targeted IL-2 variant immunocytokine in patients with solid tumors: CEA-mediated tumor accumulation and role of IL-2 receptor-binding.

Cergutuzumab amunaleukin (CEA-IL2v) is an immunocytokine directed against carcinoembryonic antigen (CEA) containing an IL2v-moiety with abolished IL-2 receptor (IL-2R) α binding. We describe the biodistribution and tumor accumulation of Zr-labeled CEA-IL2v. Twenty-four patients with advanced solid CEA positive (CEA+) or negative (CEA-) tumors received CEA-IL2v 6 mg (4 CEA+; 3 CEA-), 20 mg (9 CEA+), or 30 mg (4 CEA+; 4 CEA-) biweekly. In cycle 1, 2 mg of the total dose comprised Zr-CEA-IL2v (50 MBq) and serial Zr-PET imaging was conducted. Four CEA+ patients with visually confirmed Zr-CEA-IL2v tumor accumulation at 20 mg had repeated Zr-PET imaging during cycle 4. Zr-CEA-IL2v immuno-PET demonstrated preferential drug accumulation in CEA+ tumors (%ID/mL CEA- 3.6 × 10 vs. CEA+ 6.7 ×∙10). There was a non-significant trend towards dose-dependent tumor uptake, with higher uptake at doses ≥20 mg. Biodistribution was dose- and CEA-independent with major accumulation in lymphoid tissue compatible with IL-2R binding. Reduced exposure and reduced tumor accumulation (%ID/mL 57% lower) on cycle 4 vs. cycle 1 was consistent with peripheral expansion of immune cells. The findings of this immune PET imaging study with Zr-CEA-IL2v support the therapeutic concept of CEA-IL2v, confirming selective and targeted tumor accumulation with this novel immunocytokine.