Development of Theranostic for Acute Myeloid Leukemia (AML) targeting activated conformation of integrin 2

Introduction: There is an unmet clinical need for improved imaging methods for the detection and treatment of Acute Myeloid Leukemia (AML). Recently, using an in house developed structural proteomics approach, we reported active conformation of integrin-b₂, as a protein-conformation-specific immunotherapeutic target of AML. We were successfully able to engineer a conformationally selective antibody (ID-7065) that binds only to the active conformation of integrin-b₂. Upon reconstruction to CAR-T format, ID-7065 showed potent cytotoxicity against AML cell lines in vitro as well as in patient-derived xenografts. CD33 has been one of the most explored targets for the theranostic development in AML although limitation arises from its expression on normal myeloid cells^4. Integrin-b₂ is much more tumor-specific which may be beneficial for both imaging specificity as well as reduced toxicity of the radioimmunotherapy. Herein, we are reporting the development and pre-clinical evaluation of the first immunoPET probe [⁸⁹Zr]DFO*-7065 for the imaging of AML in a disseminated model. Additionally, we prepared [²²⁵Ac]Macropa-7065 and performed radioligand therapy in the disseminated AML model.

Methods: In vitro integrin-b₂ saturation- and cell-binding assays were performed with three different AML cell lines (NOMO-1, HL-60, THP-1) and one integrin-b₂ knock-out cell line (NOMO-1 ITGB2-KO) as a negative control. ImmunoPET imaging using [⁸⁹Zr]DFO*-7065 was performed in immunodeficient mice (NSG) bearing metastatic xenografts. For radioligand therapy, [²²⁵Ac]Macropa-7065 was prepared and a treatment study was performed in mice bearing NOMO-1 Luc metastatic xenografts. In vitro, cell killing assay was performed to analyze the treatment efficacy of [²²⁵Ac]Macropa-7065. Tumor burden was analyzed using bioluminescence imaging. The body weight and overall survival of the animals were also recorded to assess the antitumor effect and underscore the toxicity of the radiotherapy.

Results: [⁸⁹Zr]DFO*-7065 demonstrates a high affinity for all AML cell lines (K_d values between 1-15 nM) harboring/expressing active conformation of integrin-b₂ Figure 1A. Cell binding showed that [⁸⁹Zr]DFO*-7065 demonstrated high binding with integrin-b₂ expressing cell lines as compared to negative control Figure 1B. [⁸⁹Zr]DFO*-7065 specifically detects AML lesions with high specificity leading to target-mediated uptake, as compared to other three negative controls NOMO-1 ITGB2 KO model, a 25-fold excess of ID-7065 as well as imaging with non-specific binding antibody probe [⁸⁹Zr]DFO*-IgG Figure 1C. In vitro cell killing assay indicates the specific killing of active integrin-b₂ expressing NOMO-1 cells with [²²⁵Ac]Macropa-7065 with IC₅₀ value of 22.5 pM as compared to NOMO-I ITGB2 KO cells with IC₅₀ value of 2.05 nM Figure 1D. A pilot treatment study using 0.25 µCi of [²²⁵Ac]Macropa-7065 in the NOMO-1 disseminated model demonstrated a reduction in tumor volume and survival benefit in the treated groups as compared to the control group Figure 1E.

Conclusions: Our study showed that the activated conformation of integrin-b₂ targeted probe [⁸⁹Zr]DFO*-7065 can successfully image AML xenografts in murine models, and [²²⁵Ac]Macropa-7065 can effectively inhibit the growth of AML. These results demonstrate that the activated form of integrin-b₂ is a promising theranostic target for AML, with the potential for clinical translation.

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