急性髓系白血病（AML）和多发性骨髓瘤（MM）患者的骨髓可用于评估新型抗体药物偶联物（ADC）的靶点表达及靶向疗效

The clinical efficacy of an ADC is heavily influenced by its ability to selectively target its designated epitope, however ADCs exhibit high off-target toxicity to tissues without epitope expression, thus limiting clinical efficacy. We evaluated an in-vitro platform to characterize potential hematological toxicity (neutropenia) associated with ADCs in patients with AML and MM. ADCs may still cause hematotoxicity, for example Trastuzumab vedotin, which targets human epidermal growth factor receptor 2 (HER2) which is not present on hematopoietic cells. Gemtuzumab ozogamicin (Mylotarg), Belantamab Mofodotin (Blenrep) and Trastuzumab vedotin were evaluated for toxicity to hematopoietic progenitor cells using the colony forming cell assay (CFC) in diseased (on-target efficacy) and normal bone marrow (NBM) (off-target toxicity). Mylotarg, an ADC targeting CD33, was evaluated for on-target efficacy on AML bone marrow and for off-target toxicity on NBM. Blenrep, an ADC targeting B-cell maturation antigen (BCMA) in MM, was evaluated on MM and NBM. Trastuzumab vedotin was evaluated on AML, MM and NBM. Cells were pretreated with ADCs for 72 hours, and then transferred to methylcellulose containing appropriate cytokines (AML, NBM) or conditioned medium (MM) and placed in a humidified incubator for 14 days. CFU-GM, AML-blast CFC or MM-blast CFC were assessed microscopically and colony numbers enumerated. Additionally, flow cytometric analyses of CD33 and BCMA expression were performed on the relevant diseased and NBM. Mylotarg significantly inhibited AML- blast CFC with an average IC 50 value of 0.008 µg/mL (on-target efficacy). The IC 50 values for AML-blast inhibition were not associated with CD33 expression. Mylotarg additionally significantly inhibited NBM progenitors with an average IC 50 value of 0.01 µg/mL (off-target toxicity) and once again, was not associated with the CD33 expression. There was no significant difference between the IC 50 values on AML versus NBM clonal growth. Trastuzumab vedotin also demonstrated toxicity to NBM progenitors with a mean IC 50 value of 3.8 µg/mL demonstrating off-target toxicity. Blenrep exhibited different effects to the disease progenitors as compared to the healthy donor progenitors. Blenrap in MM patient bone marrow had IC 50 values which ranged from 4.4 to 46 µg/mL with an average IC 50 value of 21 µg/mL, compared to evaluation in NBM which resulted in IC 50 values > 30 µg/mL (highest tested concentration) and rarely had any impact on colony growth. These data suggest that the CFC assays with primary normal and diseased bone marrow cells may provide insight as to relative potency of an ADC on a disease-specific target as well as potential off-target toxicity to normal hematopoietic progenitors.