NW024-1, a novel ALPP/ALPPL2-targeting antibody drug conjugate with a topoisomerase 1 inhibitor payload, demonstrates potent antitumor efficacy

Background: Placental alkaline phosphatases, ALPP and ALPPL2, are highly homologous (97%) membrane-bound proteins involved in fetal development. They are highly expressed in a variety of tumor cells including ovarian (70%), endometrial (41%), lung (NSCLC, 25%) and gastric (25%), but have limited expression levels in normal tissues, making them ideal targets for the development of antibody-drug conjugates (ADCs). Here, an ALPP/ALPPL2-targeting ADC NW024-1 was developed, consisting of a humanized IgG1 anti-ALPP/ALPPL2 antibody conjugated via a hydrophilic linker to a topoisomerase 1 inhibitor payload (TOP1i), designed to selectively deliver the cytotoxic agent to ALPP/ALPPL2-expressing cells. NW024-1 was tested in vitro and in vivo to evaluate its therapeutic potential. Methods: A library of ALPP/ALPPL2-binding clones was screened for cell binding, internalization and affinity. The humanized antibody was conjugated to the TOP1i payload with DAR8 using a cleavable linker. The in vivo efficacy of NW024-1 was evaluated in a mouse xenograft model of gastric cancer (NCI-N87), administered with a single dose of 3 mg/kg and 10 mg/kg to evaluate anti-tumor activity. Results: The antibody showed strong binding to human ALPP/ALPPL2 (EC50 = 1.32 nM) low expressing cells, but no binding to human ALPI /ALPL high expressing cells. In vitro, it displayed robust internalization into ALPP/ALPPL2 positive cells and low nanomolar affinity to ALPP (KD = 1.32 nM) and ALPPL2 (KD = 0.85 nM). NW024-1 showed ALPP/ALPPL2-dependent cell killing. In vivo, NW024-1 achieved near-complete tumor regression (TGI > 95%) at 3 and 10 mg/kg for single dose, and was well tolerated in mice as indicated by body weight. Conclusions: NW024-1 is a novel ADC exhibiting a favorable profile and potent antitumor efficacy. These findings highlight its promising therapeutic potential for ALPP-expressing tumors and support its further advancement into clinical investigation.