Abstract 2610: Discovery of AM E3: A novel α-TLSPR monoclonal antibody for the ADC 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 level 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 in complete absence of selective and effective therapies. Here, we report the identification of α-TLSPR monoclonal antibodies with therapeutic potential and the preclinical validation of AM E3 as an Antibody-Drug Conjugate (ADC) for the treatment of CRLF2-rearranged Ph-like B-ALL. Material and Methods: Leveraging a high-complex phage display platform we have first identified several fully human α-TLSPR monoclonal antibodies with single-digit nanomolar affinity for the target. Among them, AM E3 emerged as suitable for ADC development due to its rapid internalization by CRLF2-expressing cells. As a proof of concept, upon conjugation with the cytotoxic payload tesirine (SG3249) AM E3 was validated for anti-tumor response in both CRLF2-rearranged in vitro cell lines and in vivo xenograft models. Further, since human/mouse CRLF2 homology is low (˂35%), we have also developed an ADC surrogate against murine TLSPR to establish a therapeutic window for the ADC therapy in CRLF2-rearranged preclinical models. Results: ADC AM E3 demonstrated strong cytotoxicity (EC50=40pM) on cell lines derived from hCRLF2-rearranged B-ALL patients. In xenograft models a single injection of ADC AM E3 (0. 7mg/Kg) showed antitumoral activity proportional to hCRLF2/TSLPR receptor density at the cell surface. Moreover, ADC AM E3 treatment reduces tumor growth and disease burden of hCRLF2-rearranged B-ALL orthotopic xenografts and extends survival over standard induction therapy. ADC surrogate mB4 AM23, which retains similar properties as the human ADC AM E3, reduces tumor growth and is well tolerated in xenograft models engineered to express mCRLF2/TSLPR. Conclusions: AM E3 is a novel α-TLSPR mAb with ideal features for the development of a first-in-class ADC therapy. α-TLSPR ADC demonstrated in vitro and in vivo efficacy as a monotherapy for the treatment of CRLF2/TLSPR rearranged Ph-like B-ALLs and proven to be well-tolerated in surrogate animal studies. 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, Alessandro Carugo, Licia Tomei, Carlo Toniatti. Discovery of AM E3: A novel α-TLSPR monoclonal antibody for the ADC treatment of CRLF2-rearranged Ph-like B-ALL abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2610.