Abstract 4773: AM E3-SG3249, a first-in-class α-CRLF2 antibody-drug conjugate for the treatment of CRLF2-rearranged Ph-like B-ALL

Abstract Background: Patients affected by Ph-like B-cell acute lymphoblastic leukemia (B-ALL) have a high mortality rate and elevated levels of disease relapse upon chemotherapy treatment. More than 60% of Ph-like B-ALL is characterized by genomic rearrangements resulting in high expression levels of the CRLF2/TLSPR receptor on the cell surface. While significant advances have been made in developing targeted agents for B-ALL treatment, the CRLF2-rearranged subpopulation is lacking selective and effective therapies. Here, we report the development and preclinical validation of AM E3-SG3249, a first-in-class α-CRLF2 Antibody-Drug Conjugate (ADC) for the treatment of CRLF2-rearranged Ph-like B-ALL. Materials and Methods: AM E3, a fully human α-CRLF2 monoclonal antibody with single-digit nanomolar affinity for the target (5.9 ± 1.0 nM), was identified leveraging our proprietary phage display platform. Due to its rapid internalization rate by CRLF2-expressing cells, AM E3 emerged as an ideal candidate for the development of an ADC targeting CRLF2. Upon conjugation with the cytotoxic payload tesirine (SG3249), a clinically-validated cross-linking agent, AM E3-SG3249 demonstrated a potent anti-tumor effect on both CRLF2-rearranged in vitro cell lines and in vivo orthotopic xenograft models. We also developed an ADC surrogate against murine CRLF2, which has low homology with the human counterpart (<35%), to further prove tolerability of the ADC therapy in preclinical mouse models. Results: AM E3-SG3249 was potently cytotoxic (EC50 = 40pM) against a panel of hCRLF2-rearranged B-ALL cell lines in vitro. Upon single injection in xenograft models, AM E3-SG3249 showed strong anti-tumor activity proportional to receptor density. Moreover, AM E3-SG3249 treatment extended survival of hCRLF2-rearranged B-ALL orthotopic xenografts over standard induction therapy combining vincristine, dexamethasone, and L-asparaginase (VXL). The ADC surrogate mB4 AM23-SG3249 was also efficacious and well-tolerated in xenograft models engineered to overexpress murine CRLF2. Conclusions: AM E3 is a novel monoclonal antibody with ideal features for the development of a first-in-class α-CRLF2 ADC therapy. AM E3 conjugated with the cytotoxic agent tesirine (SG3249) demonstrated remarkable anti-tumor efficacy and a reasonable therapeutic window for the treatment of CRLF2-rearranged Ph-like B-ALL. Citation Format: Claudia Dall'Armi, Valentina Di Biasio, Chantal Paolini, Daniela Natale, Francesco Scalabrì, Antonino Missineo, Nadine Alaimo, Maurizio Nuzzo, Anna Demartis, Pamela Di Pasquale, Roberto Benoni, Fulvia Caretti, Elisa Beghetto, Fabrizio Colaceci, Romina Sasso, Vincenzo Pucci, Carlo Toniatti, Alessandro Carugo. AM E3-SG3249, a first-in-class α-CRLF2 antibody-drug conjugate for the treatment of CRLF2-rearranged Ph-like B-ALL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4773.