CD123-targeted radiotheranostics of Acute Myeloid Leukemia with 89Zr/177Lu-labeled pivekimab Free

Introduction CD123, the interleukin-3 receptor alpha chain, is highly-expressed on AML blasts and stem cells but less on normal counterparts, making it an attractive target for targeted therapy. Pivekimab sunirine (IMGN632) is an antibody–drug conjugate (ADC) comprising a CD123-targeting antibody pivekimab (Pive) and indolinobenzodiazepine pseudodimers (IGNs), a DNA-interacting payload. We studied a dual-labeled CD123-targeted approach using ⁸⁹Zr-labeled Pive for immuno-positron emission tomography (immunoPET) imaging and ¹⁷⁷Lu-labeled Pive for radio-immune-therapy (RIT) in AML models. ImmunoPET enables noninvasive assessment of the target expression by integrating the high sensitivity of PET-imaging with antibody specificity. β-particle RIT induces both a cross-fire effect and a bystander effect, with low drug resistance, making it a great promise for hematologic malignancies. The safety of ¹⁷⁷Lu-labeled Pive will be completely evaluated in the future to avoid the off-target effects.

Methods [⁸⁹Zr]Zr-DFO-Pive and [¹⁷⁷Lu]Lu-DTPA-Pive were prepared by conjugating P-SCN-Bn-DFO and Bz-DTPA, incubating with ⁸⁹Zr and ¹⁷⁷Lu, and purifying through PD-10 column. Invitrostability of [⁸⁹Zr]Zr-DFO-Pive and [¹⁷⁷Lu]Lu-DTPA-Pive was determined by measuring the radio-chemical purity incubated for 0, 72, and 168 h using Radio-TLC. Small-animal PET/CT imaging of [⁸⁹Zr]Zr-DFO-Pive was done in MOLM-13 AML-bearing Balb/c nude mice (N ≥ 3). Mice were injected with [⁸⁹Zr]Zr-DFO-Pive (1.48 MBq in 0.1 mL saline) by tail vein. For the blocking PET/CT study, 0.5 mg Pive was injected into each mouse immediately after injection of the immunoradioligands. The exvivobiodistribution of the [⁸⁹Zr]Zr-DFO-Pive was done in MOLM-13 AML–bearing mice (N = 3). 1 dose of [¹⁷⁷Lu]Lu-DTPA-Pive was injected intravenously into MOLM-13 AML-bearing mice. Two cohorts at 11.1 MBq and 3.7 MBq of [¹⁷⁷Lu]Lu-DTPA-Pive and 4 control cohorts of [¹⁷⁷Lu]Lu-DTPA-hIgG (11.1 MBq), ¹⁷⁷LuCl₃ (11.1 MBq), Pive only, and saline control were analyzed. For a single mouse, the amount of Pive or IgG injected was about 50 µg.

Results The binding affinity of Pive to recombinant human CD123 was determined both before and after DFO/DTPA coupling by ELISA. DFO and DTPA conjugation did not reduce the binding ability of Pive to human CD123. The radiolabeling of [⁸⁹Zr]Zr-DFO-Pive and [¹⁷⁷Lu]Lu-DTPA-Pive yielded over 85% radiolabeling efficiency. The radiochemical purity of [⁸⁹Zr]Zr-DFO-Pive and [¹⁷⁷Lu]Lu-DTPA-Pive exceeded 99%, and the stability in PBS and FBS was satisfactory. Quantitative data from ROI (region of interest) analysis showed that the tumor uptake of [⁸⁹Zr]Zr-DFO-Pive increased from 14.8 ± 2.74 %ID/g at 4 h p.i. to 54 ± 7.52 %ID/g at 120 h p.i.. By contrast, low levels of radioactive uptake were observed in MOLM-13 AML blocked by Pive. The liver uptake of [⁸⁹Zr]Zr-DFO-Pive decreased from 15.07 ± 1.17 %ID/g at 4 h p.i. to 10.43 ± 0.49 %ID/g at 168 h p.i.. Following the PET/CT imaging, [¹⁷⁷Lu]Lu-DTPA-Pive exhibited higher tumor uptake at each time point. Tumor sizes and the survival rate were monitored after a single dose injection of [¹⁷⁷Lu]Lu-DTPA-Pive (high and low doses), [¹⁷⁷Lu]Lu-DTPA-hIgG, ¹⁷⁷LuCl₃, Pive only, and saline in MOLM-13 AML models. High doses of [¹⁷⁷Lu]Lu-DTPA-Pive showed the strongest AML suppression and significantly elongated the survival of MOLM-13 AML-bearing mice compared with other treatment groups (p = 0.0006 for high vs. saline, p = 0.0005 for high vs. Pive only, p = 0.0005 for high vs. ¹⁷⁷LuCl₃, p = 0.0005 for high vs. hIgG). Low doses of [¹⁷⁷Lu]Lu-DTPA-Pive also showed potent AML suppression in terms of the survival rate compared with other treatment groups (p = 0.0006 for low vs. saline, p = 0.0006 for low vs. Pive only, p = 0.0005 for low vs. ¹⁷⁷LuCl₃, p = 0.0005 for low vs. hIgG). There was an insignificant difference between high and low dose treatments (non-significant, p = 0.64).

Conclusions Wefound CD123 was a good target for imaging and therapy of AML in a mouse model. [⁸⁹Zr]Zr-DFO-Pive could capture all patients who may benefit from therapy targeting CD123 and monitor the therapeutic effects in real-time. [¹⁷⁷Lu]Lu-DTPA-Pive showed potent AML suppression and may be of significant help in AML patient management.