Abstract 5907: Pre-clinical evaluation of a novel antibody drug conjugate (ADC) LM-317 targeting NaPi2b

Introduction: NaPi2b is a multi-transmembrane type II sodium-dependent phosphate transporters that regulates phosphate homeostasis in normal physiological condition [1]. It is highly expressed in ovarian cancer (OC), non-small-cell lung cancer (NSCLC), and papillary thyroid cancer, with limited expression in normal tissue, making it a promising target for antibody-drug conjugates (ADCs) [2,3]. LM-317 is a novel NaPi2b targeted humanized monoclonal antibody LM-117 conjugated to the next-generation topoisomerase I inhibitor LDX2 via a cleavable linker, with antibody-drug ratio of 8. Here, we present the preclinical in vivo and in vitro results of LM-317.

Results: LM-317 is highly specific cross-reactive with rhesus monkeys, cynomolgus monkeys, mouse, and rat NaPi2b. Concentration-dependent cell binding and internalization effects of LM-317 were observed in human NaPi2b-expressing cells, and OC and NSCLC cells expressing NaPi2b, with EC-50 of 0.92 - 9.7 nM and 1.51 - 4.76 nM, respectively. The cytotoxicity effect of LM-317 in NaPi2b -positive tumor cells was superior to LM-117-DXD, with IC-50 of 0.002 - 0.52nM. The in vivo studies showed that 1 mg/kg of LM-317 almost completely eradicated tumors in the OVCAR-3 xenograft mice model of OC, and similar antitumor activity was observed in the NCI-H175-xenograft mice model of NSCLC at the dose of 3 mg/kg. Single dose of 6 mg/kg of LM-317 showed sustained tumor eradication in the NSCLC xenograft -mouse model. LM-317 also exhibited potent tumor regression in the PDX model of OC and NSCLC. The tumor growth inhibition (TGI) value was 80%-100% in OC and NSCLC PDX models with different expression degree of NaPi2b after treatment with LM-317. The antitumor activity of LM-317 in cell line- and PDX models of OC and NSLCL was comparable to those of LM-117-DXD.

Conclusion: The novel ADC LM-317 targeting NaPi2b showed robust antitumor activity in vitro, and in the OC and NSCLC cell line derived models and PDX models. LM-317 could potentially provide therapeutic benefit to treat NaPi2b-positive tumors including OC and NSCLC in the future.

Reference: 1.S. Banerjee et al. Cancer Treatment Reviews 112 (2023) 1024892.Finstad CL, Lloyd KO, Federici MG, et al. Clin. Cancer Res. 1997;3(8):1433-14423.Zhang et al. Tumor Biology July 2017: 1-7.

Citation Format: Wentao Huang, Zhifang Liu, Yifan Li, Heng Pan, Xia Qin, Da Fei, Runsheng Li. Pre-clinical evaluation of a novel antibody drug conjugate (ADC) LM-317 targeting NaPi2b [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(6_Suppl):Abstract nr 5907.