Abstract Cadherin 17 (CDH17), is an emerging target for antibody-based therapeutics in colorectal cancer (CRC), with multiple CDH17-directed chimeric antigen receptor-T/natural killer, bispecific antibodies and antibody drug conjugates (ADCs) in preclinical and early-stage clinical development. Success of these molecules depends on their ability to overcome high expression of P-glycoprotein (P-gp) pumps in CRCs and CDH17 in normal gut epithelium. Here, we investigate the therapeutic potential of CDH17-directed ADCs.High frequency expression of CDH17 in patient tumor microarrays and cell line derived xenografts (CDXs) was confirmed by IHC assay. CDH17-directed ADCs were generated through conjugation of a fully humanized CDH17 mAb to either an anti-mitotic (CDH17-MMAE) or topoisomerase 1 inhibitor (CDH17-exatecan) payload via a cleavable linker. Selective ADC binding and internalization were confirmed by flow cytometry and immunofluorescence.CDH17-MMAE treatment induced significant anti-tumor activity in 5/5 CDH17+ CRC CDXs models, with the strongest and most prolonged responses observed in xenografts that were P-gp low/negative. Head-to-head comparison of CDH17-MMAE and CDH17-exatecan payloads demonstrated improved efficacy for CDH17-exatecan over CDH17-MMAE in high P-gp expressing models. The functional role of P-gp in resistance to MMAE-based ADCs was confirmed using cell lines engineered to either overexpress P-gp through transfection or to lose P-gp expression through CRISPR knockdown. Forced overexpression of P-gp in SNUC1 CDH17+ cells conferred resistance to CDH17-MMAE, while sensitivity to CDH17-exatecan remained. Conversely, CRISPR knockdown of P-gp in CDH17+ LS513 cells reversed resistance to CDH17-MMAE. These findings were confirmed in xenograft studies.Due to lack of binding of the anti-human CDH17-ADCs with mouse or rat CDH17, a mouse model expressing human CDH17 extracellular ECD (B-hCDH17 mice) was used in pharmacokinetic (PK) studies. In wild-type mice, both ADCs exhibited PK profiles consistent with those typically observed for most ADCs. However, in humanized B-hCDH17 mice, both CDH17-MMAE and CDH17-exatecan ADCs were completely cleared from mouse serum less than 96 hours post-dosing, indicating that CDH17 expression in normal colon and ileum may act as a clearance sink for the ADCs.Data presented here support use of topoisomerase 1 inhibitor payloads in cancers where P-gp expression is high. Target-mediated clearance driven by normal gut CDH17 expression presents a pharmacokinetic challenge that may limit clinical utility and require dose optimization or alternative dosing strategies to achieve sufficient tumor exposure while managing potential on-target, off-tumor toxicity. Citation Format: Neil A. O'Brien, Jun Zhang, Martina SJ McDermott, Ke Wei Gong, Ming Lu, Benjamin Hoffstrom, Min Liang, Weiping Jia, Tong Luo, Athena M. Madrid, Raul Ayala, John A. Glaspy, Leonard Presta, Dennis J. Slamon.. Preclinical evaluation of target-mediated clearance and alternative payloads in CDH17-directed antibody drug conjugates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1323.

Supplemental Figure S1: Expression of CLDN6 by transcript in the GTEX dataset of normal tissue samples.

Supplemental Figure S2: Amino acid sequence alignment of CLDN6 (P56747) and CLDN9 (O95484) with the extracellular loops highlighted

Supplemental Figure S3. A, Efficacy of anti-CLDN6 mouse antibodies in CLDN6 positive OV90 ovarian cancer cell line xenografts. B, Efficacy in CLDN6 positive UMUC4 bladder cancer cell line xenografts. C, No efficacy in CLDN6 negative M202 melanoma cell line xenografts. All antibodies are dosed at 10 mg/kg QW IV in each study. Errors bars represent SEM of 8 replicate animals per group.

Supplemental Figure S5: Induction of apoptosis following 48 hr treatment of CLDN6 positive OVCA429 and CLDN6 negative M202 cells with a range of concentrations (50 μg/ml - 0.3658μg/ml) of CLDN6-23-ADC compared to control IgG ADC.

Supplemental Figure S6: In vivo efficacy of a range of doses of CLDN6-23-ADC in M202 xenograft models. ADC dosing is IV QW as indicated by the arrows

Supplemental Figure S8. A. Layout of tissues and B. Scanned whole-slide image of BN1021, normal human tissue microarray stained for CLDN6 expression showing no staining.

File containing supplemental data

Supplemental Figure S4: Binding of CLDN6-23-ADC (5 μg/ml) in artificial cell lines overexpressing CLDN3, CLDN4, CLDN6 or CLDN9 by flow cytometry.

Supplemental Figure S7. CLDN6 expression in ovarian and endometrial cancer tissue samples.

Abstract Delta like non-canonical Notch ligand 1 (DLK1) is a transmembrane protein that belongs to the NOTCH non-canonical ligand family. It has been implicated in adipogenesis, the regulation of stem cell pools, tissue differentiation during development, cancer differentiation, and cancer stem-like cell maintenance. DLK1 is highly expressed in adrenocortical, uterine, and testicular cancers as well as in a large portion of pancreatic, sarcoma, liver and squamous lung cancer patient samples. In contrast there is limited normal tissue expression beyond the normal adrenal gland, pituitary, and ovarian tissue samples. This expression profile makes DLK1 an attractive target for development of a therapeutic antibody-drug conjugate (ADC). This study describes the generation and preclinical characterization of TORL-4-500, an ADC consisting of a humanized anti-DLK1 monoclonal antibody coupled to monomethyl auristatin E (MMAE) via a cleavable linker. TORL-4-500 showed strong binding to DLK1 by flow cytometry in DLK1 native and artificial overexpressing cell lines. In contrast no binding was observed in DLK1 non-expressing cell lines. TORL-4-500 exhibits nanomolar binding affinity for both human and cynomolgus monkey DLK1 and is rapidly internalized in DLK1 expressing cells. TORL-4-500 exhibited selective efficacy in cell line xenograft models of DLK1 positive human cancers. Treatment with TORL-4-500 induced significant regressions in four DLK1 expressing human cancer cell line xenograft studies encompassing liver, small cell lung cancer (SCLC) and sarcoma cancer. Furthermore, anti-tumor responses were sustained in each of the DLK1 expressing models for several weeks post-final dose. In the case of the two SCLC cell lines, complete regressions of xenograft tumors were measured out past 100 days in the TORL-4-500 treated animals. No significant impact on xenograft tumor growth was observed in either a DLK1 non-expressing colon cell line xenograft or in a DLK1 non-expressing melanoma xenograft study. Each of the doses tested in this study was well tolerated in mice with no dose-limiting toxicity observed. The nonclinical pharmacokinetics and toxicokinetics of TORL-4-500 were characterized in mice and monkeys and results support dosing in humans. In summary, TORL-4-500 is a novel therapeutic for DLK1 positive cancers and on the basis of these promising preclinical efficacy results, a first in human trial to evaluate safety, tolerability, pharmacokinetics, and antitumor activity of TORL-4-500 has been launched in patients with advanced cancer and is currently ongoing (NCT06005740). Citation Format: Martina S. McDermott, Neil A. O'Brien, Ming Lu, Jun Zhang, KeWei Gong, Benjamin Hoffstrom, Tong Luo, Min Liang, Weiping Jia, Kevin Chau, Leonard Presta, John Glaspy, Dennis J. Slamon. Therapeutic potential of TORL-4-500, an antibody-drug conjugate directed against delta like non-canonical notch ligand 1 (DLK1) [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 1896.

Background The paucity of tumor-specific targets for chimeric antigen receptor (CAR) T-cell therapy of solid tumors necessitates careful preclinical evaluation of the therapeutic window for candidate antigens. Human epidermal growth factor receptor 2 (HER2) is an attractive candidate for CAR T-cell therapy in humans but has the potential for eliciting on-target off-tumor toxicity. We developed an immunocompetent tumor model of CAR T-cell therapy targeting murine HER2 (mHER2) and examined the effect of CAR affinity, T-cell dose, and lymphodepletion on safety and efficacy.Methods Antibodies specific for mHER2 were generated, screened for affinity and specificity, tested for immunohistochemical staining of HER2 on normal tissues, and used for HER2-targeted CAR design. CAR candidates were evaluated for T-cell surface expression and the ability to induce T-cell proliferation, cytokine production, and cytotoxicity when transduced T cells were co-cultured with mHER2+ tumor cells in vitro. Safety and efficacy of various HER2 CARs was evaluated in two tumor models and normal non-tumor-bearing mice.Results Mice express HER2 in the same epithelial tissues as humans, rendering these tissues vulnerable to recognition by systemically administered HER2 CAR T cells. CAR T cells designed with single-chain variable fragment (scFvs) that have high-affinity for HER2 infiltrated and caused toxicity to normal HER2-positive tissues but exhibited poor infiltration into tumors and antitumor activity. In contrast, CAR T cells designed with an scFv with low-affinity for HER2 infiltrated HER2-positive tumors and controlled tumor growth without toxicity. Toxicity mediated by high-affinity CAR T cells was independent of tumor burden and correlated with proliferation of CAR T cells post infusion.Conclusions Our findings illustrate the disadvantage of high-affinity CARs for targets such as HER2 that are expressed on normal tissues. The use of low-affinity HER2 CARs can safely regress tumors identifying a potential path for therapy of solid tumors that exhibit high levels of HER2.

Abstract Cadherin 17 (CDH17) is a cell-to-cell adhesion protein that is a member of the cadherin superfamily. In normal tissues, expression of this single pass transmembrane protein is restricted to the lateral surfaces of intestinal and pancreatic ductal epithelial cells. However, in cancer, CDH17 is frequently overexpressed in tumors of the colon, stomach, and pancreas. The selective expression of this cell surface protein in these hard-to-treat cancer makes it an attractive target for the development of antibody-based therapeutics. Here, we describe the preclinical development of TORL-3-600, a novel CDH17-targeting antibody drug conjugate (ADC). CDH17 specific monoclonal antibodies were generated using traditional hybridoma technology and splenocytes isolated from mice immunized with cocktails of NIH3T3 cells overexpressing full length hCHD17 plus purified mammalian expressed hCDH17 extracellular domain protein (aa 23-787). Selective mAb binding was confirmed by flow cytometry and mAb internalization rate was assessed by immunofluorescence (IF). TORL-3-600 was generated from a fully humanized CDH17 mAb by MMAE conjugation with a cleavable linker. Cell membrane staining of CDH17 in patient tumor microarrays (TMAs), cell line (CDX) and patient derived xenografts (PDX) was evaluated by IHC assay. Selective binding of the TORL-3-600 to CDH17 was confirmed in human cancer cell lines and cells engineered to overexpress CDH17. Binding of TORL-3-600 to cell surface CDH17 induced Internalization and translocation to the lysosome of the protein-ADC complex for release of the MMAE payload. Treatment with TORL-3-600 induced significant regressions and tumor growth inhibition (TGI) in four CDH17-positive (CDH17+) human colorectal cancer (CRC) CDXs (103.6 - 140.4% TGI) and three CDH17+ CRC PDXs (63.3 - 102.2% TGI). Responses in these models were sustained for up to nine-weeks following cessation of treatment. Sustained inhibition of xenograft tumor progression was also observed in a cell line model of CDH17+ pancreatic cancer (85.8% TGI). In contrast, greatly reduced responses (37.3 - 58.2% TGI) to TORL-3-600 were observed in the CDH17- human colon cancer CDX and PDX models. Each of the doses tested in this study were well tolerated in mice with no dose-limiting toxicities observed. Analyses of large human patient TMAs by CDH17 IHC assay demonstrated detectable expression of CDH17 in 90.1% (173/193) of CRC, 51.8% (86/166) of gastric and 20.4% (69/331) of pancreatic cancers. These numbers suggest that an ADC directed against CDH17 could provide benefit to a significant number of patients diagnosed with these cancers. These data support the clinical development of TORL-3-600 for the treatment of CDH17+ cancers. TORL-3-600 has completed IND enabling toxicity studies with acceptable PK and toxicity profiles and is now in phase 1 clinical testing (NCT05948826). Citation Format: Neil A. O'Brien, Martina SJ McDermott, Jun Zhang, Ming Lu, Ke Wei Gong, Benjamin Hoffstrom, Wei Ping Jia, Tong Luo, Athena M. Madrid, Min Liang, John A. Glaspy, Dennis J. Slamon. TORL-3-600, a novel antibody drug conjugate directed against cadherin 17 (CDH17), has preclinical efficacy in colorectal, gastric, and pancreatic cancer [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 1900.

Abstract Background: Alkaline phosphatase placental-like 2 (ALPPL2) is a member of the alkaline phosphatase family. ALPPL2 is currently being investigated as a novel therapeutic target due to its cancer-specific expression. However, our knowledge of ALPPL2 biological function in cancer is limited. Here we describe an interaction between ALPPL2 and MAPK signaling pathway in pancreatic cancer. Materials and Methods: ALPPL2 mRNA expression in a panel of 27 pancreatic cell lines was determined by RNAseq. Protein expression and phosphorylation were measured by Western blot. ALPPL2 or ALPP were overexpressed in pancreas cell lines through a Lentiviral packaging system. MEK inhibitor (trametinib) activity was assessed in the same panel of cell lines using a 6-day cell proliferation assay on a Synentec Cellavista imaging system. MEK inhibitor resistant cell lines were developed by culturing cells in increasing concentrations of MEK162. Results: We hypothesized that pancreatic cancer cells with high ALPPL2 expression may be less sensitive to MEK inhibition. Our study from a panel of 27 pancreatic cancer cell lines showed that there was no correlation between ALPPL2 expression and response to trametinib. Western blot showed that the level of phospho-ERK was reduced in PANC1 and HPAC cells at 6 hours after trametinib treatment. Signaling rebounded at 24 and 48 hours, though it remained below baseline. Surprisingly, ALPPL2 expression increased at 24 and 48 hours after trametinib treatment, however, the mRNA of ALPPL2 and ALPP was down-regulated in three pancreatic cancer cell lines conditioned to be MEK inhibitor resistant. To understand the role of ALPPL2 in the MAPK signaling pathway in response to MEK inhibition, ALPPL2 and ALPP were overexpressed in 2 pancreatic cancer cell lines: YAPC and PSN-1 whose ALPPL2 and ALPP were undetected by Western blot prior to transfection. Overexpression of ALPPL2 or ALPP in YAPC cells resulted in more ERK phosphorylation with no change in total ERK, it also resulted in increased total and phospho-S6, and decreased phospho-STAT3 with no change in total STAT3. The amount of total and phospho-ERK were not changed in PSN-1 with overexpression of ALPPL2 or ALPP, however, it did result in increased total and phospho-S6, decreased phospho-STAT3. Interestingly, the expression of ALPPL2 and ALPP in YAPC cells with ALPPL2 or ALPP overexpression was increased at 48 hours after trametinib treatment. Discussion: To our knowledge, this is the first study to report that ALPPL2 interacts with the MAPK signaling pathway in pancreatic cancer cells. The activated MAPK signaling pathway appears to control ALPPL2 expression. The MAPK signaling pathway may regulate ALPPL2 expression through transcription and protein metabolism. We have also shown that ALPPL2 expression can activate MAPK signaling pathway. Our findings that ALPPL2 expression can be increased after trametinib treatment provide further rationale for targeting ALPPL2 in cancer. Citation Format: Ke Wei Gong, Bilal Hamid, Kenny W. Castro, Martina S. McDermott, Forrest Epstein, Kevin Chau, Chuhong Hu, Jun Zhang, Ming Lu, Benjamin G. Hoffstrom, Neil A. O'Brien, Dennis J. Slamon. ALPPL2 is involved in MAPK signal pathway of pancreatic cancer [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 4375.

Maximum % cytotoxicity and phagocytosis and EC50 values for CLDN18.2-307-mAb in HUPT4 cels

Abstract Purpose: This study examines cell surface ROR1 expression in human tumors and normal tissues. ROR1 is considered a promising target for cancer therapy due to putative tumor-specific expression, and multiple groups are developing antibodies and/or chimeric antigen receptor–modified T cells to target ROR1. On-target, off-tumor toxicity is a challenge for most nonmutated tumor antigens; however, prior studies suggest that ROR1 is absent on most normal tissues. Experimental Design: Our studies show that published antibodies lack sensitivity to detect endogenous levels of cell surface ROR1 by immunohistochemistry (IHC) in formalin-fixed, paraffin-embedded tissues. We developed a ROR1-specific monoclonal antibody (mAb) targeting the carboxy-terminus of ROR1 and evaluated its specificity and sensitivity in IHC. Results: The 6D4 mAb is a sensitive and specific reagent to detect cell surface ROR1 by IHC. The data show that ROR1 is homogenously expressed on a subset of ovarian cancer, triple-negative breast cancer, and lung adenocarcinomas. Contrary to previous findings, we found ROR1 is expressed on several normal tissues, including parathyroid; pancreatic islets; and regions of the esophagus, stomach, and duodenum. The 6D4 mAb recognizes rhesus ROR1, and ROR1 expression was similar in human and macaque tissues, suggesting that the macaque is a suitable model to evaluate safety of ROR1-targeted therapies. Conclusions: ROR1 is a promising immunotherapeutic target in many epithelial tumors; however, high cell surface ROR1 expression in multiple normal tissues raises concerns for on-target off-tumor toxicities. Clinical translation of ROR1-targeted therapies warrants careful monitoring of toxicities to normal organs and may require strategies to ensure patient safety. Clin Cancer Res; 23(12); 3061–71. ©2016 AACR.

Abstract Purpose: Claudin-6 (CLDN6) is expressed at elevated levels in multiple human cancers including ovarian and endometrial malignancies, with little or no detectable expression in normal adult tissue. This expression profile makes CLDN6 an ideal target for development of a potential therapeutic antibody–drug conjugate (ADC). This study describes the generation and preclinical characterization of CLDN6–23-ADC, an ADC consisting of a humanized anti-CLDN6 monoclonal antibody coupled to monomethyl auristatin E (MMAE) via a cleavable linker. Experimental Design: A fully humanized anti-CLDN6 antibody was conjugated to MMAE resulting in the potential therapeutic ADC, CLDN6–23-ADC. The antitumor efficacy of CLDN6–23-ADC was assessed for antitumor efficacy in CLDN6-positive (CLDN6+) and -negative (CLDN6−) xenografts and patient-derived xenograft (PDX) models of human cancers. Results: CLDN6–23-ADC selectively binds to CLDN6, versus other CLDN family members, inhibits the proliferation of CLDN6+ cancer cells in vitro, and is rapidly internalized in CLDN6+ cells. Robust tumor regressions were observed in multiple CLDN6+ xenograft models and tumor inhibition led to markedly enhanced survival of CLDN6+ PDX tumors following treatment with CLDN6–23-ADC. IHC assessment of cancer tissue microarrays demonstrate elevated levels of CLDN6 in 29% of ovarian epithelial carcinomas. Approximately 45% of high-grade serous ovarian carcinomas and 11% of endometrial carcinomas are positive for the target. Conclusions: We report the development of a novel ADC, CLDN6–23-ADC, that selectively targets CLDN6, a potential onco-fetal-antigen which is highly expressed in ovarian and endometrial cancers. CLDN6–23-ADC exhibits robust tumor regressions in mouse models of human ovarian and endometrial cancers and is currently undergoing phase I study.

Abstract Gastric and pancreatic cancers are malignancies of high unmet clinical need. Expression of CLDN18.2 in these cancers, coupled with it's absence from most normal tissues, provides a potential therapeutic window against this target. We present preclinical development and characterization of a novel therapeutic mAb and antibody–drug conjugate (ADC) targeting CLDN18.2. A humanized CLDN18.2 specific mAb, CLDN18.2-307-mAb, was generated through immunization in mice followed by full humanization of the mouse mAb sequences. Antibody clones were screened by flow cytometry for selective binding to membrane bound CLDN18.2. A CLDN18.2-directed ADC (CLDN18.2–307-ADC) was also generated by conjugating MMAE to CLDN18.2 mAb using a cleavable linker. Tissue expression of CLDN18.2 was determined by IHC assay using a CLDN18.2-specific mAb. CLDN18.2-307-mAb binds with high affinity to CLDN18.2-positive (CLDN18.2+) cells and induces antibody-dependent cell-mediated cytotoxicity (ADCC). Treatment with this CLDN18.2-mAb blocked the growth of CLDN18.2+ gastric and pancreas cancer cell line xenograft (CDX) models. Upon binding to the extracellular domain of this target, the CLDN18.2-ADC/CLDN18.2 protein was internalized and subsequently localized to the lysosomal compartment inducing complete and sustained tumor regressions in CLDN18.2+ CDXs and patient-derived pancreatic cancer xenografts (PDX). A screen of human cancer tissues, by IHC, found 58% of gastric, 60% of gastroesophageal junction, and 20% of pancreatic adenocarcinomas to be positive for membrane expression of CLDN18.2. These data support clinical development of the CLDN18.2-307-mAb and CLDN18.2-307-ADC for treatment of CLDN18.2+ cancers. Both are now being investigated in phase I clinical studies.

Expression of CLDN18.2 is normal tissues.

CLDN18.2 expression in human pancreas PDX models.