Tumor Cell Surface Research Articles

Abstract LB187: Investigating the roles of ROR1/2 in non-small cell lung carcinoma NSCLC and potential therapeutic applications

Abstract Lung cancer is the leading cause of cancer mortality worldwide, representing an unmet medical need. Receptor tyrosine kinase-like orphan receptors (RORs) are oncofetal antigens that act as receptors/co-receptors of WNT5A and other related noncanonical WNT proteins, in transducing β-catenin independent WNT signaling. Dysregulated ROR/WNT have been linked to cancer progression and therapy resistance. Recently, ROR receptors have drawn increasing attention as anti-cancer targets of antibody-drug conjugates (ADCs) due to their selective expression on the tumor cell surface. The ROR family contains ROR1 and ROR2, which share 58% sequence homology. However, their functional interactions between ROR/WNT5A and whether RORs have distinct or redundant roles in tumor phenotypes remain unclear. In this study, we sought to address these biological questions in NSCLC, and investigate the potential application of anti-ROR therapies. To this end, we used CRISPR/Cas9 to generate clones of ROR1 or ROR2 single knockouts (KOs) in the NSCLC LCLC-103H cell line and implemented an array of assays to characterize the effect of single ROR KOs. ROR KOs were confirmed by both western blot and flow cytometry. We found reduced ROR2 mean fluorescence intensity (MFI) on ROR1 KOs and increased ROR1 MFI on ROR2 KOs in flow cytometrical analysis. Phenotypically, ROR1 KOs did not affect tumor doubling time, but ROR2 KOs promoted cell proliferation in 2D cultures. Unlike 2D cultures, tumor 3D spheroid proliferation was significantly inhibited in both ROR1 and ROR2 KOs, implying that each ROR is indispensable in maintaining tumor growth featured by cell-cell/extracellular matrix interactions. Mechanistically, ROR1 KOs tended to decrease ROR2 and WNT5A/B protein expression, while ROR2 KOs caused compensatory upregulation of ROR1 and WNT5A/B. Both ROR1 and ROR2 KOs decreased SNAIL expression, which is a key driver of epithelial-to-mesenchymal plasticity (EMP). Furthermore, alterations in ROR1/2 signaling pathways were observed. We have identified pathways downstream of ROR1/2 including WNT, EMP, and survival, which may shed light on the biological roles of RORs in cancer and potential therapeutic intervention. Finally, the therapeutic application of ROR1/2 was evaluated by monomethyl auristatin F (MMAF) containing anti-ROR ADCs. ROR1 KOs demonstrated the on-target cytotoxicity of anti-ROR1 ADC, while ROR2 KOs showed increased sensitivity to anti-ROR1 ADC due to the increased ROR1 expression in ROR2 KOs. In vivo analysis is currently underway. Collectively, our results demonstrate that RORs have both distinct and compensatory functions in regulating tumor proliferation. We believe a greater understanding in ROR1/2 biology may lead to better targeted therapeutic applications. Citation Format: Wen-An Pan, Xin Guo, Christina Galang, Mira Ko, Jeff Kucharski, Nicole Miller, Haim Moskowitz, Jeff Watkins, Brian Lannutti, Katti Jessen, Hao Liu. Investigating the roles of ROR1/2 in non-small cell lung carcinoma NSCLC and potential therapeutic applications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB187.

Abstract LB340: Harnessing the gp70 endogenous retrovirus envelope protein as a universal tumor antigen for T cell therapy in mice

Abstract FDA approval for chimeric antigen receptor (CAR) T cell therapies targeting hematological cancers has unleashed the potential of utilizing live T cells as therapeutics. However, CAR-mediated targeting of solid tumors is currently limited by a paucity of suitable tumor antigens that are both specific and highly expressed on the tumor cell surface. In this report we explore the possibility of harnessing tumor-specific expression of endogenous retroviruses (ERVs) as a universal target for CAR T cell therapy. We found that gp70, the envelope protein from a murine ERV, is highly expressed on the surface of tumor cell lines derived from a diverse array of murine tumor types. We utilized the B16 melanoma model as a representative poorly inflamed tumor that does not respond to existing immunotherapies to examine efficacy of gp70 CAR T cells. T cells engineered to express a gp70 CAR suppress tumor growth in vivo and recognize B16 tumor cells with improved sensitivity compared to T cells expressing two previously described dominant tumor antigens (gp100 or P15e) due to low expression of MHC-I on B16 tumors. Co-incubation of B16 tumor cells with gp70 CAR T cells results in upregulation of MHC-I on the tumor cell surface suggesting that in addition to killing tumor cells directly, gp70 CAR T cells could facilitate recognition of the tumor by endogenous T cells through local release T cell derived IFNγ. We postulate that utilization of CAR T cells specific for cell surface ERV envelope proteins offers a promising strategy that could be harnessed to achieve local release of T cell derived payloads specifically within the tumor microenvironment. Citation Format: Sophie M. Lehar, Srirupa Roy, Lisa Liao, Haiyin Chen, Yongmei Chen, Mayra Cruz Tleugabulova, Eric Janezic, Azadeh Madjidi, Tamaki Jones, Vincent Javinal, James Ziai, Ira Mellman, Jill Schartner, Andrey Shaw. Harnessing the gp70 endogenous retrovirus envelope protein as a universal tumor antigen for T cell therapy in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB340.

Abstract LB125: Tri-specific T cell engager targeting of selective surface cancer-selective ligands recruits both T cells and APC targeting of cancer neoantigens of tumor-initiating stem-like cells

Abstract Chemotherapy does not sufficiently eliminate tumor-initiating cells (TICs) of hepatocellular carcinoma (HCC). To remove TICs and achieve personalized cancer therapy, dendritic cells (DC) were vaccinated against tumor germline mutations, but metastatic cancers recurred in many cases. Emerging data suggest that nanoparticle-based siRNA delivered targeting of stemness transcription factor NANOG (pluripotency transcription factor) potentiates anti-tumor immunity. We hypothesized that pre-treatment of selective TIC inhibitors targeting stemness genes sensitized the efficacy of immunotherapy targeting of liver TICs. Novel TIC-targeting immunoglobulin, variable chain fragments were identified by phage-display library screening. The top single chain camelid antibody (scFv) candidates were identified and individually cloned into mammalian expression vectors to test binding to TICs. A Tri-specific T cell engager (TriTE) was constructed to connect TIC-targeting scFv with anti-dendritic cell (DC) scFv (anti-CD14) and CD3. Such scFv vectors were tested for target cell lysis. Candidate ligands of anti-TIC ScFvs present on the tumor cell surface were identified through a series of bioinformatic analysis., The latter provided the preconditions for one of our aims to identify the target, tumor surface ligand(s) of anti-TIC ScFv to better understand the mechanism of TriTE action upon a tumor cell. IP-Mass spectrometry analyses demonstrated that two target surface antigens, TBCE and CEP170, along with their respective mRNAs were highly expressed in CD133+ TIC Huh7 cells when compared to CD133- non-TIC Huh7 cells. This accounted for specific TriTE binding to TIC cells, but not to CD133(-) Huh7 cells or primary hepatocytes. These data demonstrated that these unique tumor antigens, primarily arising during neoplastic transformation, elicited T and/or monocyte immunity capable of protecting the host from cancer progression. These conjunctive with PD1 antibody therapeutic modality leads to the personalized immune/chemotherapy of HCC patients. Human monocyte-derived DCs, TIC and T cells were incubated with TriTE to measure IFNγ production during CTL killing effects against TICs. TriTE treatment significantly reduced tumor growth of PDX tissues in NSG-SG3 mice with humanized immunity. Other novel surface antigens on TIC were identified by mass spectroscopy analyses. These data demonstrated that the presence of unique tumor antigens, primarily arising during neoplastic transformation, which elicited T and/or myeloid cell immunity capable of protecting the host from cancer progression. Self-adapting antigen-targeting machinery with Trite therapy is adaptable and fine-tuning next-generation immunotherapy. Citation Format: Wei Ma, Nuan Wang, Hye Yeon Choi, Lin Ziying, Nicolette Fajardo, Royce Ilaga, Risa Machida, Zhou Lin, Ambika Ramrakhiani, Yvonne Y. Chen, Linda Sher, Stanley M. Tahara, Keigo Machida. Tri-specific T cell engager targeting of selective surface cancer-selective ligands recruits both T cells and APC targeting of cancer neoantigens of tumor-initiating stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB125.

Abstract LB282: Therapeutic efficacy and dosimetry for a 177-lutetium radiolabeled minibody targeting DLL3 in a preclinical model of small cell lung cancer

Abstract Small cell lung cancer (SCLC) is the most aggressive subtype of lung carcinoma with a 5-year survival rate below 7%. While the addition of anti-PD-1 antibody treatment has improved SCLC patient outcomes, nearly all patients relapse, indicating an unmet need for more efficacious therapeutics. Delta-like ligand 3 (DLL3) is an inhibitory Notch ligand that is over-expressed on the surface of SCLC tumor cells. Due to this, DLL3 has become a target of interest for SCLC treatment and several agents are in preclinical and clinical evaluation using different strategies such as antibody-drug conjugates, bispecific T cell engagers, and DLL3-targeting CAR-T. Minibodies are antibody fragments that provide optimal pharmacokinetics for the delivery of radioactive payloads. Their molecular weight of 80 kDa allows for rapid tumor uptake and faster circulation clearance than full-length antibodies. These scaffolds also present deeper tumor penetration relative to full-length antibodies, and higher target specificity and retention at the tumor site, with respect to small molecules. We hypothesized that a minibody targeting DLL3 (IAB57) would be a valid approach for radiopharmaceutical therapy (RPT) of SCLC and tested its efficacy in a preclinical model of SCLC. We conjugated the IAB57 minibody with DOTAGA and radiolabeled the protein with the β-emitter 177-Lu. Nu/J female mice were inoculated subcutaneously with the non-encapsulated lung carcinoma cell line SHP77, and the tumor size was measured 3 times per week until it reached 100-150 mm3. 24-hour biodistribution results revealed a tumor uptake of 18.8% injected dose per gram (%ID/gr). Mice were treated with 13.3 MBq and 13.6 MBq doses of 177-Lu-DOTAGA-IAB57 7 days apart to determine if there was a therapeutic effect and improved animal survival. A subgroup of mice was not treated and was considered controls. A time course biodistribution was performed to assess organs dosimetry. The dosimetry results were extrapolated to human organ exposure showing kidneys and liver uptakes of 2.2 and 4.6 Gy which is 10 times and 7 times below published exposure thresholds (23 Gy and 32 Gy respectively). Exposure at bone marrow (b.m., 0.1 Gy), spleen (1.5 Gy) and lungs (0.4 Gy) were 20 times, 27 times and 68 times below published toxicity thresholds (b.m.: 2 Gy; spleen: 40 Gy; lungs: 27 Gy). The RPT data showed a significant decrease in tumor size beginning on day 11 in the treated group compared to the control group. The decreased tumor size also coincided with a doubling in the survival rate. Overall, these results indicate that the IAB57 minibody targeting DLL3 is a promising and effective agent for RPT treatment of SCLC via β-emitting radionuclides. Citation Format: Kelley C. Atkinson, Leticia M. De Souza Cordeiro, Fang Jia, Argin Aivazian, Gareth E. Smith, Ian Wilson, Alessandro Mascioni. Therapeutic efficacy and dosimetry for a 177-lutetium radiolabeled minibody targeting DLL3 in a preclinical model of small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB282.

A multi-mode Rhein-based nano-platform synergizing ferrotherapy/chemotherapy-induced immunotherapy for enhanced tumor therapy

Ferroptosis has emerged as a promising strategy for treating triple-negative breast cancer (TNBC) due to bypassing apoptosis and triggering immunogenic cell death (ICD) of tumor cells. However, the antitumor efficacy has been limited by the insufficient intracellular ferrous iron concentration required for ferroptosis and inadequate antitumor immune response. To address these limitations, we designed a multi-mode nano-platform (MP-FA@R-F NPs), which exhibited a synergistic effect of ferroptosis, apoptosis and induced immune response for enhanced antitumor therapy. MP-FA@R-F NPs target folate receptors, which are over-expressed on the tumor cell's surface to promote intracellular uptake. The cargoes, including Rhein and Fe3O4, would be released in intracellular acid, accelerating by NIR laser irradiation. The released Rhein induced apoptosis of tumor cells mediated by the caspase 3 signal pathway, while the released Fe3O4 triggered ferroptosis through the Fenton reaction and endowed the nanoplatform with magnetic resonance imaging (MRI) capabilities. In addition, ferroptosis-dying tumor cells could release damage-associated molecular patterns (DAMPs) to promote T cell activation and infiltration for immune response and induce immunogenic cell death (ICD) for tumor immunotherapy. Together, MP-FA@R-F NPs represent a potential synergistic ferro-/chemo-/immuno-therapy strategy with MRI guidance for enhanced antitumor therapy. Statement of significanceThe massive strategies of cancer therapy based on ferroptosis have been emerging in recent years, which provided new insights into designing materials for cancer therapy. However, the antitumor efficacy of ferroptosis is still unsatisfactory, mainly due to insufficient intracellular pro-ferroptotic stimuli. In the current study, we designed a multi-mode nano-platform (MP-FA@R-F NPs), which represented a potential synergistic ferro-/chemo-/immuno-therapy strategy with MRI guidance for enhanced antitumor therapy.

Assessment of Inhibition of the Growth of Breast and Colon Tumors when Blocking VEGFR-1 with Monoclonal Antibodies

Vascular endothelial growth factor receptor-1 (VEGFR-1) plays a critical role in tumor-associated angiogenesis. VEGFR-1 is found on the surface of tumor cells and cells in the tumor microenvironment. Blocking this receptor leads to the suppression of proliferation and increased apoptosis of tumor cells, reduction of tumor vascularization, inhibition of the production of immunosuppressive cytokines by tumor-associated macrophages, and the suppression of tumor invasion and metastasis. The creation of monoclonal antibody drugs that block VEGFR-1 is an urgent task in the development of potential antitumor therapeutic drugs. Target molecules created on the basis of antibodies that bind to VEGFR-1 are a promising basis for the creation of theranostic radiopharmaceuticals for the diagnosis and treatment of malignant neoplasms. To study the therapeutic potential of VEGFR-1 inhibition in breast and colon cancers using antibodies, monoclonal antibodies against recombinant human VEGFR-1 protein are developed. The resulting monoclonal antibodies bind to the VEGFR-1 receptor on the cell surface and effectively inhibit the proliferation of breast and colon cancer cells in vitro, reduce the growth rate of the tumor node in vivo, and prolong the survival of tumor-inoculated mice.

Folate-modified liposomes mediate the co-delivery of cisplatin with miR-219a-5p for the targeted treatment of cisplatin-resistant lung cancer

Cisplatin (DDP) resistance, often leading to first-line chemotherapy failure in non-small cell lung cancer (NSCLC), poses a significant challenge. MiR-219a-5p has been reported to enhance the sensitivity of human NSCLC to DDP. However, free miR-219a-5p is prone to degradation by nucleases in the bloodstream, rendering it unstable. In light of this, our study developed an efficient nanodrug delivery system that achieved targeted delivery of DDP and miR-219a-5p by modifying liposomes with folate (FA). Based on the results of material characterization, we successfully constructed a well-dispersed and uniformly sized (approximately 135.8 nm) Lipo@DDP@miR-219a-5p@FA nanodrug. Agarose gel electrophoresis experiments demonstrated that Lipo@DDP@miR-219a-5p@FA exhibited good stability in serum, effectively protecting miR-219a-5p from degradation. Immunofluorescence and flow cytometry experiments revealed that, due to FA modification, Lipo@DDP@miR-219a-5p@FA could specifically bind to FA receptors on the surface of tumor cells (A549), thus enhancing drug internalization efficiency. Safety evaluations conducted in vitro demonstrated that Lipo@DDP@miR-219a-5p@FA exhibited no significant toxicity to non-cancer cells (BEAS-2B) and displayed excellent blood compatibility. Cellular functional experiments, apoptosis assays, and western blot demonstrated that Lipo@DDP@miR-219a-5p@FA effectively reversed DDP resistance in A549 cells, inhibited cell proliferation and migration, and further promoted apoptosis. In summary, the Lipo@DDP@miR-219a-5p@FA nanodrug, through specific targeting of cancer cells and reducing their resistance to DDP, significantly enhanced the anti-NSCLC effects of DDP in vitro, providing a promising therapeutic option for the clinical treatment of NSCLC.

Cx1Mab-1: A Novel Anti-mouse CXCR1 Monoclonal Antibody for Flow Cytometry.

The C-X-C motif chemokine receptor-1 (CXCR1) is a rhodopsin-like G-protein-coupled receptor, expressed on the cell surface of immune cells and tumors. CXCR1 interacts with some C-X-C chemokines, such as CXCL6, CXCL7, and CXCL8/interleukin-8, which are produced by various cells. Since CXCR1 is involved in several diseases including tumors and diabetes mellitus, drugs targeting CXCR1 have been developed. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CXCR1 has been desired for the diagnosis and treatment. This study established a novel anti-mouse CXCR1 (mCXCR1) mAb, Cx1Mab-1 (rat IgG1, kappa), using the Cell-Based Immunization and Screening method. Cx1Mab-1 reacted with mCXCR1-overexpressed Chinese hamster ovary-K1 (CHO/mCXCR1) and mCXCR1-overexpressed LN229 glioblastoma (LN229/mCXCR1) in flow cytometry. Cx1Mab-1 demonstrated a high binding affinity for CHO/mCXCR1 and LN229/mCXCR1 with a dissociation constant of 2.6 × 10-9 M and 2.1 × 10-8 M, respectively. Furthermore, Cx1Mab-1 could detect mCXCR1 by Western blot analysis. These results indicated that Cx1Mab-1 is useful for detecting mCXCR1, and provides a possibility for targeting mCXCR1-expressing cells in vivo experiments.

Bioorthogonal In Situ Polymerization of Dendritic Agents for Hijacking Lysosomes and Enhancing Antigen Presentation in Cancer Cells.

A low-generation lysine dendrimer, SPr-G2, responds to intracellular glutathione to initiate bioorthogonal in situ polymerization, resulting in the formation of large assemblies in mouse breast cancer cells. The intracellular large assemblies of SPr-G2 can interact with lysosomes to induce lysosome expansion and enhance lysosomal membrane permeabilization, leading to major histocompatibility complex class I upregulation on tumor cell surfaces and ultimately tumor cell death. Moreover, the use of the SPr-G2 dendrimer to conjugate the chemotherapeutic drug, camptothecin (CPT), can boost the therapeutic potency of CPT. Excellent antitumor effects in vitro and in vivo are obtained from the combinational treatment of the SPr-G2 dendrimer and CPT. This combinational effect also enhances antitumor immunity through promoting activation of cytotoxic T cells in tumor tissues and maturation of dendritic cells. This study can shed new light on the development of peptide dendritic agents for cancer therapy.

Abstract 5157: Development and evaluation of a high-throughput method for rapid detection of surface antigen expression in fixed cells

Abstract Cell surface proteins are increasingly considered in the development of novel anticancer agents, as demonstrated by recent clinical successes in the field of immuno-oncology and antibody-drug conjugates (ADCs). These conjugates specifically target antigens present on the surface of tumor cells, enabling the delivery of cytotoxic agents to specific tumor sites. During the preclinical development of such compounds, for example, when they are tested on a wide panel of cell lines, it is essential to have a rapid and reliable method for monitoring target expression and distribution. Complementing our 160 Cell line panel ProLiFiler™, we report here the development of a novel method named oncoFLOW-Profiler™ which includes steps of cell fixation, micronic storage, staining, and measurement by flow cytometry. This method is applied in a 96-well format, enabling screening of all cell lines in parallel and analysis of the expression of different targets in just one day. In this proof-of-concept study, we investigated the level of ERBB2 expression across the ProLiFiler panel of 160-cell lines in order to validate this methodology. We first compared the impact of fixation methods and sample storage on knowingly positive and negative control cell lines over a period of several months. ERBB2 measurements from the oncoFLOW-Profiler™ will be analyzed and validated by comparison with various OMICs datasets from the Cancer DataMiner platform (4HF Biotec), including RNA expression, mutational status, and protein expression levels. To determine the expression cutoff of ERBB2 amplified models, results will be analyzed according to gene copy number variation. Finally, the flow cytometry data generated will be investigated for use as a predictor of response to clinically approved ADCs targeting ERBB2: Kadcyla and Enhertu. Here we present a method that we have demonstrated is feasible for investigating cell surface receptor/antigens during preclinical phase of drug development. Our method has enabled us to successfully assess ERBB2 in biological samples and to identify models sensitive to ADCs targeting ERBB2. We will also discuss the results of ongoing experiments analyzing the applicability of this screen to intracellular targets and carbohydrate-based surface antigens, which cannot be analyzed either by transcriptomics or proteomics. Citation Format: Kaja Holtorf, Anne-Lise Peille, Daniel Feger, Vincent Vuaroqueaux, Jan Erik Ehlert, Nadine Obier. Development and evaluation of a high-throughput method for rapid detection of surface antigen expression in fixed cells [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 5157.

Abstract 2736: Ligand-independent targeting of tumor cells for antibody-dependent cell-mediated cytotoxicity

Abstract Introduction: Biological targeting is a key concept in cancer treatment utilized by most therapeutics. Targeted agents that selectively treat diseased tissues while reducing off-target effects to normal tissues are widely used for cancer therapies. However, key hurdles include: (i) a limited number of tumor-specific biomarkers expressed in sufficiently high levels for targeted therapy, (ii) lack of specific biomarkers amenable to targeting, and (iii) current technologies rely on largely protein-based targeting ligands limiting the applications of these therapies due to final conjugates with low payloads. We developed a novel method for tumor-specific delivery by combining metabolic glycoengineering and nanomedicine to engineer targetable chemical groups on cancer cells and enable directed treatments. We hypothesize that increased Fc fragments on the surface of tumor cells can enable antibody-dependent cell mediated cytotoxicity (ADCC) response to tumor cells, providing innate immunotherapy. Materials/Methods: We formulated nanoparticles (NPs) using polyethylene glycol-ply lactic acid-co-glycolic acid (PEG-PLGA). Using the Dolomite microfluidic device, we formed NPs by nanoprecipitation of PEG-PLGA with tetraacetylated N-azidoacetyl-D-mannosamine (Ac4ManNAz), a sialic acid analogue containing a click chemistry group. We targeted this reactive group by functionalizing the Fc fragment with dibenzylcyclooctyne (DBCO). We characterized the NPs using dynamic light scattering (DLS), charge measurements and transmission electron microscopy (TEM). We evaluated toxicity using a cell viability assay and assessed preliminary efficacy with a tumor growth delay study. Results: NP characterization revealed a size of 30-40 nm via DLS, congruent with TEM imaging. Charge measurements ranged from -4 to +4 mV. Toxicity studies revealed no differences in cell viability amongst different treatment groups. Preliminary efficacy studies demonstrated improved tumor growth delay in the cohort of mice treated with a combination of NPs and Fc-DBCO conjugate, as well as a survival benefit. Median OS was 31.5 days for the control groups vs 57.5 days for the combination treated group (p = 0.0067). Conclusion: There is growing interest in harnessing the power of the innate immune response to shape anti-tumor immunity. This is because clinical data demonstrates tumor cells can evade the adaptive immune system through mutations as well as downregulate MHC receptors. One of the most effective innate immune responses is ADCC. To this end, we developed a novel method for tumor-specific delivery of Fc fragments to enhance ADCC. While this data reveals improved tumor growth delay and a survival benefit, the sample size is limited, and a larger study is needed to evaluate the potential benefits of this strategy. Furthermore, correlative studies are needed to identify the mechanism for treatment response. Citation Format: Maureen L. Aliru, Nikhila R. Sultanpuram, Kin Man Au, Tian Zhang, Andrew Z. Wang. Ligand-independent targeting of tumor cells for antibody-dependent cell-mediated cytotoxicity [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 2736.

Abstract 1344: Improvement of the anti-tumor activity of NK cells and the efficacy of anti-CD20 monoclonal antibodies in the therapy of B cell-derived malignancies

Abstract Resistance of tumor cells to immunotherapy with monoclonal antibodies (mAbs) often relies on the reduced level of the antigen targeted by the particular mAb. We have therefore screened for the compounds able to upregulate selected antigens on the surface of lymphoma/leukemia cells, to minimize the possibility of resistance acquired by the tumor cells. We have found that members of a specific class of antibiotics, known as cation carriers, namely salinomycin (SAL), monensin (MON), narasin, and nigericin exhibit great CD20 antigen-upregulating abilities. A variety of Burkitt’s lymphoma and diffuse large B-cell lymphoma (DLBCL) cell lines as well as patients-derived primary malignant cells, such as DLBCL and chronic lymphocytic leukemia (CLL) cells exhibited upregulation of surface CD20 upon the treatment with SAL and MON at concentrations as low as 250nM and 50 nM, respectively. As a consequence, these compounds appeared to be beneficial for the therapy of lymphoma/leukemia with anti-CD20 mAbs, both in vitro and in animal models.Moreover, the proteomics analysis revealed that besides CD20, cation carriers upregulated a number of different proteins on the surface of tumor cells, including proteins implicated in the interaction with immune cells. These included ICAM1, HLA-A/B/C, CD155, CD80, CD86 and ULBP2/5/6. Particularly important appears to be the upregulation of antigens interacting with the activating receptors on NK cells, helping them to overcome the inhibitory signals and stimulate the lysis of tumor cells. Thus, the results of proteomics analysis explained why SAL- or MON-pretreated tumor cells were efficiently eliminated by NK cells, even in the absence of therapeutic mAb. In light of our discoveries, it seems reasonable to consider the cation carriers as promising drug candidates for the improvement of NK cell anti-tumor activity and potential treatment of B-cell non-Hodgkin lymphoma patients, in combination with anti-CD20 mAbs.Funding: National Science Centre (NCN, Poland), grants 2019/35/B/NZ5/01445 and 2020/39/B/NZ6/03513. Citation Format: Abdessamad Zerrouqi, Aleksandra Zdanowicz, Anna Torun, Andrzej Ciechanowicz, Bhaskar Pradhan, Grzegorz Rymkiewicz, Dimitar Efremov, Beata Pyrzynska. Improvement of the anti-tumor activity of NK cells and the efficacy of anti-CD20 monoclonal antibodies in the therapy of B cell-derived malignancies [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 1344.

Abstract 4017: CAR T cell-mediated cytotoxicity and cytokine release in response to varying levels of antigen expression on target cells

Abstract The development of immunotherapies relies on the use of in vitro potency assays, which are crucial for understanding the complex interactions between immune cells (effectors) and cancer cells (targets). Chimeric antigen receptor (CAR) T-cell therapy is an immunotherapeutic approach that exhibits promise; however, varying levels of antigen expression on the surface of tumor cells can influence the efficacy of CAR T cell-mediated killing. To fully understand the impact of target antigen density on CAR T cell activity, we utilized a matrix approach to assess both target cell death, using an impedance-based in vitro potency assay to quantify CAR T cell-mediated cytotoxicity, as well as cytokine release with homogeneous LumitTM immunoassays. SKOV3 (high HER2 expression), A549 (low HER2 expression), or MDA-MB-231 (no HER2 expression) target cells were seeded into a 96-well microplate with embedded electrodes in the substrate that detect the attachment and proliferation of target cells. HER2 CAR T cells were added after 24 hours at effector-to-target (E:T) ratios of 1:5 or 1:1 and target cell cytolysis was recorded continuously by the Maestro Z for 72 hours. Cytolysis of the target cells was calculated by comparing the treated wells to no treatment control wells and full lysis wells (1% TritonX). At 72 hours post CAR T cell addition, complete killing was observed in SKOV3 cells at the 1:1 ratio, while A549 cells exhibited only 80% cytolysis. MDA-MB-231 cells showed 20% cytolysis, likely due to nonspecific killing by non-engineered T cells, as approximately only 78% of the CAR T cell population was CAR positive. Because the cytolysis assay was label-free, cytokine analysis was able to be multiplexed with the same plates. To assess release of pro-inflammatory cytokines, TNF-α and IFN-γ, we collected supernatant post-antigen exposure at 24, 48, and 72 h. At the 1:1 E:T ratio, CAR T cells co-cultured with target cells expressing low (A549) or high (SKOV3) levels of HER2 had the highest TNF-α production at 24 hours, with CAR T cells co-cultured with SKOV3 cells releasing 30.6% more TNF-α when compared to A549 cells. The highest levels of IFN-γ were detected in both A549 and SKOV3 groups at the 1:1 E:T ratio, with the highest levels observed from CAR T cells co-cultured with SKOV3 cells at 72 hours, releasing approximately 1459.6 +/- 357.3 pg/mL of IFN-γ, compared to 1093.8 +/- 387.5 pg/mL IFN-γ released by CAR T cells co-cultured with A549 cells. As expected, CAR T cells co-cultured with MDA-MB-231 cells did not release any detectable TNF-α or IFN-γ at either E:T ratios during the duration of the experiment. Future work will continue to explore multiplexed potency assays for the evaluation of CAR T cell therapies. Citation Format: Sierra Barnes, Denise Sullivan, Dan Lazar, Kim Haupt, Danielle Califano, Stacie Chvatal, Daniel Millard. CAR T cell-mediated cytotoxicity and cytokine release in response to varying levels of antigen expression on target cells [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 4017.

Abstract 4755: Extracellular GRP78 inhibition reverses drug and immune resistance in cancer cells

Abstract CBT300 was created from Creative BioTherapeutics’ discovery that drug resistant recurrent cancer cells up-regulate a survival pathway that results in the expression of extracellular Glucose-Regulated Protein 78 (ecGRP78) in the tumor microenvironment (TME). This TME ecGRP78 binds to cancer and immune cell surfaces, which induces a cascade of events to increase drug resistance, immune suppression, and cancer stem cell (CSC) formation. CBT300 targets surface bound ecGRP78 that has been found on breast, lung, ovarian, prostate, melanoma, multiple myeloma, colon, pediatric and adult brain tumors. We can now show that inhibition of ecGRP78 can a) induce apoptosis of drug resistant tumor cells, b) eliminate drug and immune resistance showing synergistic effects with chemotherapy and immunotherapy, c) decrease the amount of chemotherapy about 90% in combination with CBT300. Recent publications show that ecGRP78 is found on many types of tumor cell surfaces but not on normal cell surfaces. In fact, cell surface bound ecGRP78 is important for many aspects of cancer development, including cell survival, proliferation, chemoresistance, angiogenesis, metastasis formation, immune suppression, and stem cell formation. Recently, it has been shown that increased ecGRP78 expression in metastatic breast cancer, glioblastoma and multiple myeloma patients was significantly associated with later stage, increased distant metastasis, increased aggressiveness, shorter disease-free survival, and decreased overall survival. In studies to help understand how ecGRP78 causes tumor progression and drug and immune resistance, we discovered a novel ecGRP78 binding transmembrane protein on TNBC, and brain cancer cells called Receptor Tyrosine Kinase Orphan Receptor-1 (ROR1). Using the GRP78 binding domain from ROR1 and a human Fc domain, we created a biologic fusion protein that is a potent and specific ecGRP78 inhibitor called CBT300. We now show that CBT300’s elimination of csGRP78 destabilizes and removes oncofetal proteins ROR1, and Cripto, and checkpoint protein PD-L1 from tumor cell surfaces resulting in reversal of chemoresistance, reduction in immune suppression, inhibition of stem cell phenotype and increased tumor cell apoptosis. Our results with CBT300 demonstrate proof of concept data in vitro and in vivo for our novel ecGRP78 inhibitor on several drug resistant cancers demonstrating the potential to provide a major advance in the treatment of drug resistant cancers either alone or in combination with lower doses of chemotherapy. Exploiting a novel mechanism of action with a non-toxic, efficacious and cost effective biologic therapy that has shown increased survival in recurrent cancers will bring new hope for these patients. Citation Format: Donald J. Davidson, Jorryn Zelek, Elizabeth Stolarik, Mariah Thigpen, Anita Davidson, DPT. Extracellular GRP78 inhibition reverses drug and immune resistance in cancer cells [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 4755.

Abstract 6656: Revolutionizing solid tumor treatment: Viral protein-targeted CAR-T with oncolytic virus

Abstract Major challenges for CAR-T cell therapy in solid tumors include various limitations due to the issue of appropriate antigen selection, tumor heterogeneity, and the immune-suppressive tumor microenvironment (TME). To overcome these hurdles, we’ve developed a novel therapy, CLM-202 which is a combination therapy of oncolytic Newcastle disease virus (NDV) and NDV F protein-targeted CAR-T cell therapy (NDV F CAR-T). After NDV infects tumor cells, NDV envelope protein F is expressed on the tumor cell surface. NDV F CAR-T recognizes NDV F protein and kills the tumor cells. This approach can be applied to patients with various indications, regardless of the presence of the target protein. Using NDV to deliver antigens minimizes the risk of tumor recurrence due to tumor heterogeneity. Furthermore, it mitigates off-target toxicity by targeting oncolytic virus-derived proteins, not human proteins. Oncolytic NDV also triggers a potent immune response within the tumor microenvironment, thereby altering the immunosuppressive conditions of the tumor and improving CAR-T efficacy. Therefore, CLM-202 can be a multipurpose solution for solid tumors. We have developed a second-generation CAR-T cell therapy, NDV F CAR-T, which can be used in combination with an oncolytic virus known as NDV. NDV F CAR-T is designed to specifically target the F protein expressed when cells are infected by NDV. It incorporates a single-chain variable fragment (scFv) derived from an antibody that can bind specifically to the F protein of NDV-infected cells. To assess the activity of NDV F CAR-T in tumor cells against a variety of solid tumors as indications, we conducted several experiments. We initially confirmed the expression of the F protein in NDV-infected tumor cells. We also conducted cytotoxicity tests to confirm NDV F CAR-T's ability to induce death in NDV-infected tumor cell lines. Furthermore, to assess the efficacy of NDV F CAR-T in an in vivo model, we established an orthotopic mouse model. In this model, we administered NDV via intratumoral injection, followed by the single-dose administration of NDV F CAR-T to perform the efficacy test. We have confirmed that NDV infects all solid tumor cell lines representing different indications and induces the expression of the F protein in infected tumor cells. Furthermore, we have observed that NDV infection in these diverse tumor cells results in robust tumor cell-killing activity by NDV F CAR-T and the subsequent activation of CAR-T. Moreover, in an orthotopic mouse model, we have demonstrated that the administration of NDV followed by NDV F CAR-T induces potent tumor growth inhibition. In summary, our research proposes a novel therapeutic strategy, CLM-202 that utilizes NDV F CAR-T and NDV to overcome the limitations of CAR-T cell therapy in solid tumors, including tumor heterogeneity and immune-suppressive tumor microenvironments. This approach aims to effectively treat a wide range of indications. Citation Format: Soyoung Choi, Kiwan Kim, Sangeun Lee, Jeongeun Choi, Song-Jae Lee, Yong Gu Lee, Jeonghun Kim, Hoyoung Lee, Kisoon Kim, Man-Seong Park, Seong-Won Song. Revolutionizing solid tumor treatment: Viral protein-targeted CAR-T with oncolytic virus [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 6656.

Abstract 542: Development of novel syngeneic tumor models with intrinsic or extrinsic resistance mechanisms to PD-1 blockade

Abstract Programmed cell death-1 (PD-1) blockade has demonstrated remarkable clinical efficacy across various tumor types. However, the current PD-1 blockade monotherapy benefits only a small proportion of patients, and primary or acquired resistance can ultimately lead to cancer progression in clinical settings. Understanding the underlying mechanisms of resistance is both necessary and urgent to enhance clinical outcomes. Increasing evidence suggests that resistance to PD-1 therapy can arise from both tumor-cell-intrinsic and tumor-cell-extrinsic factors. Loss-of-function mutations in the antigen presentation pathway and downstream elements represent intrinsic mechanisms, while tumor-infiltrating immunosuppressive cells such as regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) contribute to immune tolerance as extrinsic factors. Currently, the rational design of combination therapies based on these resistance mechanisms remains to be achieved. In this study, we developed two types of anti-PD-1 antibody-resistant models based on the intrinsic anti-PD-1 treatment-sensitive MC38 models. These models include genetically engineered resistant models with B2M or STK11 knockout (KO) and induced resistant models through in vivo progressive drug selection. STK11 KO mutations resulted in reduced expression of PD-L1 on tumor cells and a lower infiltration of CD8+ cytotoxic T lymphocytes in the tumor microenvironment, while B2M KO led to a lack of antigen presentation on the tumor cell surface, blocking the binding of the anti-PD-1 antibody. In terms of the induced anti-PD-1 resistant models, a higher proportion of immunosuppressive cells, including Tregs, MDSCs, and TAMs, were observed in the tumor microenvironment compared to the parental counterparts, contributing to immune escape from PD-1 blockade. These models simulate extrinsic and intrinsic mechanism-based anti-PD-1 resistance, allowing for the identification of combination therapies to overcome resistance to anti-PD-1. Our study enhances our understanding of the biological basis of anti-PD-1 resistance and supports the discovery of mechanistically-designed combination therapies to overcome resistance to anti-PD-1 therapy, potentially broadening its clinical applicability. Citation Format: Xiaomin Wang, Ziwei Zhang, Longzhou Liu, Xue Zhang, Dong Wang, Nengwei Xu, Xiangnan Qiang, Qingyang Gu, Jian Xiang, Zhixiang Zhang. Development of novel syngeneic tumor models with intrinsic or extrinsic resistance mechanisms to PD-1 blockade [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 542.

Abstract 2082: Identification of nonsense-mediated decay inhibitors that alter the tumor immune landscape

Abstract Despite exciting developments in cancer immunotherapy, its broad application is limited by the paucity of targetable antigens on the tumor cell surface. As an intrinsic cellular pathway, nonsense-mediated decay (NMD) conceals neoantigens through the destruction of the RNA products from genes harboring truncating mutations. We developed and conducted a high throughput screen, based on the ratiometric analysis of transcripts, to identify critical mediators of NMD. This screen revealed disruption of kinase SMG1’s phosphorylation of UPF1 as a potent disruptor of NMD. This led us to design a novel SMG1 inhibitor, KVS0001, that elevates the expression of transcripts and proteins resulting from truncating mutations in vivo and in vitro. Most importantly, KVS0001 concomitantly increased the presentation of immune-targetable HLA class I-associated peptides from NMD-downregulated proteins on the surface of cancer cells. KVS0001 provides new opportunities for studying NMD and the diseases in which NMD plays a role, including cancer and inherited diseases. Citation Format: Ashley L. Cook, ojit Sur, Laura Dobbyn, Evangeline Watson, Joshua D. Cohen, Blair Ptak, Bum Seok Lee, Suman Paul, Emily Hsiue, Maria Popoli, Bert Vogelstein, Nickolas Papadopoulos, Chetan Bettegowda, Kathy Gabrielson, Shibin Zhou, Kenneth Kinzler, Nicolas Wyhs. Identification of nonsense-mediated decay inhibitors that alter the tumor immune landscape [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 2082.

Abstract 186: Tumor exosome-macrophage interactions: The role of tumor-associated glycans and scavenger receptor class A

Abstract Introduction: Increased macrophage infiltration and polarization towards a breast tumor-supportive phenotype have been linked to therapy resistance, immune suppression, and poor patient prognosis. Despite their importance, the specific interactions that drive tumor-associated macrophage (TAM) polarization remain poorly understood. The class A scavenger receptor (SR-A) is a pattern-recognition receptor expressed by macrophages, and the accumulation of SR-A-expressing TAMs has been correlated with poor patient outcomes. Our preliminary data show that SR-A binds to tumor-associated glycans (TAGs) on the surface of breast cancer cells. However, how macrophages bind tumor cell ligands in the tumor microenvironment (TME) is not clear. Tumor-derived exosomes (TDEs) are secreted extracellular vesicles that resemble the tumor cell membrane, carrying cargo that may mediate an immune response within the TME. In this study, we investigated whether TDE glycans represent tumor cell-surface TAGs and whether TDEs interact with macrophages through SR-A. Methods: TDEs were isolated from the murine breast cancer cell line (E0771) by ultracentrifugation of the cell culture medium and then sized and counted using nanoparticle tracking analysis and electron microscopy. The glycans present on the tumor cell surface and TDEs were characterized using plant lectins in flow cytometry and sandwich ELISAs. The isolated TDEs were then fluorescently labeled, and their binding to the murine macrophage cell line Raw 264.7 was assayed by flow cytometry and fluorescence microscopy. Results: SR-A binds strongly to breast cancer cell lines, and a significant portion of the binding depends on the presence of cell surface N-linked glycans. Lectins reactive with sialylated and fucosylated terminal structures showed differential binding to tumor cells and TDEs. We observed that the glycan profiles of E0771 cells and exosomes isolated from E0771 cultures were similar. Our results indicate that TDEs interact with Raw 264.7 cells, and the interaction is mediated by SR-A. Conclusions: TDEs released in the TME can potentially interact with TAMs through SR-A. The glycan profile of TDEs is representative of host cells and may contribute to SR-A-mediated interaction with TAMs. Citation Format: Fariba Jousheghany, Emily S. Blitz, Samir V. Jenkins, Steven R. Post, Vinay Raj, Rajshekar A. Kore, Azemat Jamshidi-Parsian, Robert J. Griffin, Thomas J. Kelly, Behjatolah Monzavi-Karbassi. Tumor exosome-macrophage interactions: The role of tumor-associated glycans and scavenger receptor class A [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 186.

Abstract 2650: IGFBP2 assists EGFRvIII-positive glioblastoma to evade immune elimination

Abstract In recent years, immunotherapy has achieved significant success in the treatment of a variety of cancer types, including melanoma, non-small cell lung cancer, and colorectal cancer. However, in stark contrast, patients with glioblastoma (GBM) show remarkably poor responses to immunotherapy, failing to derive any therapeutic benefit. Thus, an understanding of the immunosuppressive microenvironment of GBM, which is considered an immunotherapy-cold tumor, is of paramount importance. One common and distinctive genetic mutation found in gliomas is that of EGFRvIII, which is linked with enhanced cell proliferation, invasion, migration, and angiogenesis in GBM. Intriguingly, we found that this mutation induced a significantly more severe immunosuppressive microenvironment compared with wild-type EGFR. To unravel the mechanisms underlying EGFRvIII mutation-induced immunosuppression in GBM, we posited that the mutant variant secretes an array of immunosuppression-related proteins into the glioma microenvironment. To investigate this, we conducted proteomic analysis of conditioned media from EGFRvIII mutant cell lines and discovered significant changes in the expression of insulin-like growth factor-binding protein-2 (IGFBP2), a well-documented oncogenic protein. Although IGFBP2 is known to be upregulated in various tumor types and is associated with malignant behaviors such as proliferation and invasion in gliomas, its role in glioma immunology remains largely unexplored. In line with our earlier bioinformatic analyses, our study revealed significant enrichment of IGFBP2 in pathways related to immunosuppression in GBM. Thus, in the present investigation, we analyzed the mechanisms by which IGFBP2 induces an immunosuppressive microenvironment. Using co-culture models, we found that IGFBP2-overexpressing glioma cells as well as glioma cells treated with exogenous IGFBP2 recruited immune cells through binding to integrin αvβ5. Furthermore, we demonstrated that IGFBP2 promoted the secretion of the classical macrophage polarization factor IL-10 by phosphorylation of STAT3. These findings indicate the significant influence of IGFBP2 in steering glioma-associated macrophages toward a pro-tumor M2-like phenotype. We also observed that IGFBP2 upregulated the expression of PD-L1 on tumor cell surfaces. These results were verified in animal experiments. Intriguingly, our preliminary data indicated that exogenous IGFBP2 translocated to the cell nucleus within hours, and immunoprecipitation assays confirmed its interaction with STAT3 in vitro. These findings collectively underscore the pivotal role of IGFBP2 in the creation of the immunosuppressive microenvironment induced by EGFRvIII mutation. Consequently, targeting IGFBP2 holds great promise for advancing immunotherapeutic approaches in EGFRvIII-mutant glioblastomas, offering an exciting avenue for potential treatments of GBM. Citation Format: Jikang Fan, Xisen Wang, Tao Li, Xuejun Yang, Wei Zhang. IGFBP2 assists EGFRvIII-positive glioblastoma to evade immune elimination [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 2650.

Abstract 2615: Preclinical development of a next generation antibody drug conjugate (ADC) targeting cMET for treatment of solid tumors

Abstract cMET (mesenchymal-epithelial transition factor), which belongs to the MET family, is a type of receptor tyrosine kinase that is expressed on the surfaces of various epithelial cells. The elevation of cMET can promote the development and progression of multiple cancers. cMET- ADCs have shown promising clinical activity with highest cMET levels, indicating tumor cMET levels may be limited for efficacy. YL211, a novel cMET-ADC was developed by leveraging on MediLink’s tumor microenvironment activable linker-payload platform (TMALIN platform), which could release the payload both in the tumor cell and in the tumor microenvironment. YL211 is comprised of an anti-cMET humanized monoclonal antibody conjugated to a novel topoisomerase 1 inhibitor via a protease-cleavable linker. The novel linker-payload and site-specific conjugation of YL211 results in a homogeneous product with a DAR (Drug-to-Antibody Ratio) of 8. Furthermore, the advancement in linker-payload design has facilitated the development of more hydrophilic ADCs, which exhibit minimal impact on the antibody's characteristics while being less prone to aggregation and showcasing lower systematic clearance. Along with release of the payload in the tumor microenvironment extracellularly, upon binding to cMET on tumor cell surfaces, the antigen-ADC complexes are internalized to lysosomal vesicles and subsequently release the toxic payload. The cytotoxic features drive cell cycle arrest, apoptosis, elevation of PARP/caspase 7 expression, as well as cell death and bystander effect. These findings translated in vivo where YL211 showed superior efficacy in causing tumor regressions and good tolerability in both cell lines and patient-derived xenograft (CDX and PDX) mouse models with both low to high cMET expression levels (H358, CR5088, ect.). The in vivo pharmacokinetics in monkeys showed that YL211 is highly stable with less than 0.1% (molar ratio) payload released in circulation. GLP safety evaluations demonstrated good safety profiles and no off-target toxicity in monkeys. These non-clinical data suggest the stability of the linker in circulation as well as efficient release of the payload in tumors with improved therapeutic window. Taken together, preclinical data suggest that YL211 could be a promising treatment strategy for cMET positive cancer patients. Citation Format: Liang Xiao, Wei Lian, Shuai Song, Qigang Liu, Qing Zong, Sasha Stann, Jiaqiang Cai, Tongtong Xue. Preclinical development of a next generation antibody drug conjugate (ADC) targeting cMET for treatment of solid tumors [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 2615.