ImmunoPET, [⁶⁴Cu]Cu-DOTA-anti-CD33 PET-CT, imaging of an AML xenograft model

Purpose: Acute myeloid leukemia (AML) is a highly aggressive form of leukemia, which results in poor survival outcomes. Currently, diagnosis and prognosis are based on invasive single-point bone marrow biopsies (iliac crest). There is currently no AML-specific noninvasive imaging method to detect disease, including in extramedullary organs, representing an unmet clinical need. About 85% to 90% of human myeloid leukemia cells express CD33 cell surface receptors, highlighting CD33 as an ideal candidate for AML immunoPET. Experimental Design: We evaluated whether [⁶⁴Cu]Cu-DOTA-anti-CD33 murine mAb can be used for immunoPET imaging of AML in a preclinical model. MicroCT was adjusted to detect spatial/anatomical details of PET activity. For translational purposes, a humanized anti-CD33 antibody was produced; we confirmed its ability to detect disease and its distribution. We reconfirmed/validated CD33 antibody-specific targeting with an antibody–drug conjugate (ADC) and radioimmunotherapy (RIT). Results: [⁶⁴Cu]Cu-DOTA-anti-CD33–based PET-CT imaging detected CD33⁺ AML in mice with high sensitivity (95.65%) and specificity (100%). The CD33⁺ PET activity was significantly higher in specific skeletal niches [femur (P < 0.00001), tibia (P = 0.0001), humerus (P = 0.0014), and lumber spine (P < 0.00001)] in AML-bearing mice (over nonleukemic control mice). Interestingly, the hybrid PET-CT imaging showed high disease activity in the epiphysis/metaphysis of the femur, indicating regional spatial heterogeneity. Anti-CD33 therapy using newly developed humanized anti-CD33 mAb as an ADC (P = 0.02) and [²²⁵Ac]Ac-anti-CD33-RIT (P < 0.00001) significantly reduced disease burden over that of respective controls. Conclusions: We have successfully developed a novel anti-CD33 immunoPET-CT–based noninvasive modality for AML and its spatial distribution, indicating a preferential skeletal niche.