Abstract 1766: SGN-ALPV a novel, investigational vedotin ADC demonstrates highly effective targeting of oncofetal phosphatases ALPP and ALPPL2 in preclinical models

Abstract Antibody-drug conjugates (ADC) leverage the specificity of antibodies to direct the delivery of potent cytotoxic agents to cancer cells. To fully leverage this specificity, targets with significant differential tumor versus normal tissue expression are ideal for ADC development. Placental alkaline phosphatases, ALPP and ALPPL2, are proteins present during fetal development but are found in several tumor types, making them an attractive ADC target. These cell membrane-attached phosphatases form homo- and heterodimers and play key roles in nucleotide recycling. SGN-ALPV is a novel investigational vedotin ADC comprised of a humanized IgG1 monoclonal antibody conjugated to the microtubule disrupting agent monomethyl auristatin E (MMAE) via a protease-cleavable peptide linker that has been clinically validated in multiple ADC programs. Here we characterize the target antigens, ALPP and ALPPL2, and evaluate SGN-ALPV antitumor activity in preclinical models. Immunohistochemistry and genomic data mining showed that ALPP and ALPPL2 have a highly restricted normal tissue expression yet high expression in several solid tumor types including ovarian, endometrial, germ cell, non-small cell lung and gastric carcinomas. Importantly, normal tissue expression is restricted to placenta and reproductive tissue, with low levels in lung tissue. SGN-ALPV utilizes a humanized antibody, h12F3, that is highly specific for both human and cynomolgus monkey ALPP and ALPPL2 proteins, but not other related phosphatases. In vitro, upon binding to SGN APLV, the antigens, ALPP and ALPPL2, are internalized to lysosomal vesicles releasing the MMAE payload, whose cytotoxic features drive mitotic arrest, apoptosis, and the induction of immunogenic cell death. Additionally, SGN-ALPV mediates antibody dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) in vitro but lacks complement-dependent cytotoxicity. In preclinical studies, SGN-ALPV exhibits robust antitumor activity in cell line- and patient-derived xenograft models of ovarian, lung, pancreatic, and gastric carcinoma including models with both homogenous and heterogeneous expression of ALPP and ALPPL2, consistent with robust bystander activity of vedotin ADCs. Although, the contribution of ADCC and ADCP in vivo is currently unknown, it is expected that the antitumor activity of SGN-ALPV is mediated by MMAE cytotoxicity. SGN-ALPV was well tolerated in non-human primates (NHP) and exhibited linear pharmacokinetic characteristics, with a toxicity profile consistent with other vedotin-based ADCs. In summary, differential expression of ALPP and ALPPL2 in the tumor versus normal tissue, antibody specificity, antitumor activity, and tolerability of SGN-ALPV provide a strong rationale for the initiation of a planned first-in-human Phase 1 clinical study. Citation Format: Sarah Anderson, Nanna Hansen, Robert Lawrence, Aroon T. Chande, David Ortiz, Christopher Carosino, Esther Trueblood, Nicole Stevens, Kerry Klussman, Angela Epp, Bill Arthur, Shyra Gardai, Hector Rincon. SGN-ALPV a novel, investigational vedotin ADC demonstrates highly effective targeting of oncofetal phosphatases ALPP and ALPPL2 in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1766.