CLDN18.2 (Claudin18.2)-targeting therapeutic antibodies have shown promising clinical efficacy in ~30% of gastric cancers expressing high levels of CLDN18.2 and less pronounced activity in low expressing malignancies. Here, we report that ZL-1211 is a monoclonal antibody targeting CLDN18.2 engineered to promote enhanced antibody-dependent cellular cytotoxicity (ADCC) with the goal of achieving more potent activity in a wider spectrum of high- and low-CLDN18.2 expressing tumors. ZL-1211 demonstrated more robust in vitro ADCC activity than clinical benchmark not only in CLDN18.2-high but also -low expressing gastric tumor cell lines. Greater anti-tumor efficacy was also observed in mouse xenograft models. Natural killer (NK) cell played critical roles in ZL-1211 efficacy and NK cell depletion abrogated ZL-1211-mediated ADCC activity in vitro. ZL-1211 efficacy in vivo was also dependent on the presence of an NK compartment. Strikingly, NK cells strongly induced an inflammatory response in response to ZL-1211 treatment, including increased IFNγ, TNFα, and IL-6 production, and were recruited into tumor microenvironment in patient-derived gastric tumors expressing CLDN18.2 upon ZL-1211 treatment to lyse the tumor cells. Taken together, our data suggest that ZL-1211 more effectively targets CLDN18.2-high gastric cancers as well as -low expressing malignancies that may not be eligible for treatment with the leading clinical benchmark by inducing enhanced ADCC response and activating NK cells with robust inflammation to enhance anti-tumor efficacy. Clinical activity of ZL-1211 is currently under evaluation in a Phase I clinical trial (NCT05065710).

<div><p>CLDN18.2 (Claudin18.2)-targeting therapeutic antibodies have shown promising clinical efficacy in approximately 30% of gastric cancers expressing high levels of CLDN18.2 and less pronounced activity in low expressing malignancies. Here, we report that ZL-1211 is a mAb targeting CLDN18.2 engineered to promote enhanced antibody-dependent cellular cytotoxicity (ADCC) with the goal of achieving more potent activity in a wider spectrum of high- and low-CLDN18.2 expressing tumors. ZL-1211 demonstrated more robust <i>in vitro</i> ADCC activity than clinical benchmark not only in CLDN18.2-high but also CLDN18.2-low expressing gastric tumor cell lines. Greater antitumor efficacy was also observed in mouse xenograft models. Natural killer (NK) cell played critical roles in ZL-1211 efficacy and NK-cell depletion abrogated ZL-1211–mediated ADCC activity <i>in vitro</i>. ZL-1211 efficacy <i>in vivo</i> was also dependent on the presence of an NK compartment. Strikingly, NK cells strongly induced an inflammatory response in response to ZL-1211 treatment, including increased IFNγ, TNFα, and IL6 production, and were recruited into tumor microenvironment in patient-derived gastric tumors expressing CLDN18.2 upon ZL-1211 treatment to lyse the tumor cells. Taken together, our data suggest that ZL-1211 more effectively targets CLDN18.2-high gastric cancers as well as -low expressing malignancies that may not be eligible for treatment with the leading clinical benchmark by inducing enhanced ADCC response and activating NK cells with robust inflammation to enhance antitumor efficacy. Clinical activity of ZL-1211 is currently under evaluation in a phase I clinical trial (NCT05065710).</p>Significance:<p>ZL-1211, anti-CLDN18.2 therapeutic antibody can target CLDN18.2-high as well as -low gastric cancers that may not be eligible for treatment with clinical benchmark. ZL-1211 treatment induces NK-cell activation with robust inflammation to further activate antitumor immunity in tumor microenvironment.</p></div>

<p>Supplementary Figure 5 shows IHC for gastric PDX models with anti-CLDN18.2, human IgG, or NKp46 antibody.</p>

<p>Supplementary Figure 2 shows CLDN18.2 expression in MIA-PaCa2 clones and ZL-1211-induced CDC for the MIA-PaCa2 clones.</p>

<p>Supplementary Figure 1 shows characterization of ZL-1211.</p>