Potent Antitumor Efficacy of a Novel ALPPL2/ALPP-Targeting Antibody-Drug Conjugate in Preclinical Models

Abstract: Background The antitumor efficacy of antibody-drug conjugates (ADCs) is primarily determined by the tissue-specific distribution of target antigens. Placental alkaline phosphatase-like protein 2 (ALPPL2) and placental alkaline phosphatase (ALPP) are highly homologous and aberrantly overexpressed in multiple human malignancies, while minimally expressed in most normal adult tissues, rendering them ideal targets for tumor-targeted therapeutics. However, ALPPL2/ALPP-targeted therapeutics remain in their infancy, with no clinically approved agents, presenting a significant translational opportunity. Methods Antibodies were prepared via hybridoma technology. Their binding specificity, affinity, cross-species reactivity and internalization were characterized using flow cytometry and biolayer interferometry (BLI). Competitive epitope binning was applied to delineate the epitope diversity. Lead candidates were conjugated with monomethyl auristatin E (MMAE) to construct ALPPL2 ADCs, and their antitumor potency was systematically evaluated in vitro and in vivo across various tumor models. Results A panel of chimeric antibodies featuring high affinity, high specificity, and rapid internalization was generated and grouped into discrete epitope bins. The lead candidate AL71 shares substantial but non-identical epitope overlap with the benchmark SGN-ALPV and displays improved cross-reactivity against cynomolgus monkey ALPP. Critically, AL71-ADC surpasses SGN-ALPV, demonstrating enhanced in vitro cytotoxicity across multiple tumor cell models and potent in vivo antitumor activity in xenograft models. Conclusions AL71-ADC generated herein exhibits superior preclinical antitumor efficacy and cross-species reactivity relative to benchmark SGN-ALPV. Given the tumor-restricted expression of ALPPL2/ALPP alongside unmet clinical demands, AL71-ADC represents a promising therapeutic candidate for the treatment of ALPPL2/ALPP-positive malignancies.