ImmunoPET, [⁶⁴Cu]Cu-DOTA-Anti-CD33 PET-CT, Imaging of an AML Xenograft Model.

Abstract

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. 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). [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 (<i>P</i> < 0.00001), tibia (<i>P</i> = 0.0001), humerus (<i>P</i> = 0.0014), and lumber spine (<i>P</i> < 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 (<i>P</i> = 0.02) and [²²⁵Ac]Ac-anti-CD33-RIT (<i>P</i> < 0.00001) significantly reduced disease burden over that of respective controls. We have successfully developed a novel anti-CD33 immunoPET-CT-based noninvasive modality for AML and its spatial distribution, indicating a preferential skeletal niche.