Abstract 1778: Preclinical characterization of the safety and antitumor activity of IMAB027-vcMMAE, an anticlaudin 6 antibody-drug conjugate

Background Claudin 6 (CLDN6) is a tight junction membrane protein whose expression in normal tissue is confined to embryonic cells, but aberrantly expressed in various human cancer types, including some with a high medical need (eg, ovarian and uterine cancers). This tumor-specific expression in adult organs makes CLDN6 an attractive drug target; as such, IMAB027, an anti-CLDN6 monoclonal antibody (mAb), was developed. This report describes the preclinical characteristics of IMAB027. Methods IMAB027 was generated by hybridoma technology; the discovery process was set up so that mAbs that were good binders as well as inducers of the immune effector mechanisms of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) activity would be detected. ADCC and CDC were assessed in vitro. Apoptosis of CLDN6+ cells was assessed by caspase 3/7, annexin V, and TUNEL assays. Xenografted mouse tumors with human CLDN6+ cells were generated to investigate the in vivo antitumor effects of IMAB027 both as a single agent and in combination with chemotherapeutic agents such as paclitaxel. Results: IMAB027 binds specifically to CLDN6 without cross-reactivity with other closely related family members, such as Claudins 3, 4, and 9. IMAB027 induced target-selective ADCC and CDC in a number of CLDN6+ ovarian and testicular cancer cell lines; median EC50 values for ADCC and CDC were of the order of ng/mL in representative cell lines. Direct induction of apoptosis did not appear to be a contributor to the antitumor effect of IMAB027. In cancer cell lines that heterogeneously expressed CLDN6, but not in those with high or homogeneous CLDN6 levels, pretreatment with chemotherapeutic agents upregulated CLDN6 expression. Increased CLDN6 expression sensitized the cells to IMAB027-induced ADCC, resulting in increased cell lysis. In vivo, treatment with IMAB027 was associated with reduced tumor growth and increased overall survival in different mouse tumor models. These potent antitumor effects were observed in both early and advanced ovarian cancer xenografts. IMAB027, in combination with paclitaxel administered to mice with CLDN6+ xenografts, also prolonged survival compared with paclitaxel alone. Conclusions In these preclinical studies, binding of IMAB027 was CLDN6 specific. IMAB027 as a single agent induced cell death in CLDN6+ cancer cells via ADCC and CDC, thereby exerting in vitro and in vivo antitumor activity. Further, in tumors that have heterogeneous CLDN6 expression, chemotherapy sensitizes cells to IMAB027-induced ADCC, and the combination of IMAB027 and chemotherapeutic agents may enhance the antitumor effect of chemotherapy. Citation Format: Özlem Türeci, Maria Kreuzberg, Korden Walter, Stefan Wöll, Ramona Schmitt, Rita Mitnacht-Kraus, Ikumi Nakajo, Tomohiro Yamada, Ugur Sahin. The anti-claudin 6 antibody, IMAB027, induces antibody-dependent cellular and complement-dependent cytotoxicity in claudin 6-expressing cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 882.

Background Claudin 6 (CLDN6) is a tight junction membrane protein whose expression in normal tissue is confined to embryonic cells, but is aberrantly expressed in various human cancers, such as ovarian cancer (OC) and testicular cancer (TC). A monoclonal antibody against CLDN6, IMAB027, has shown promising antitumor activity in preclinical human CLDN6-positive (CLDN6+) cancer models. In this series of nonclinical studies, we investigated CLDN6 expression in normal and cancer tissues, as well as the localization and possible function of CLDN6 in cancer cells. Methods Expression of CLDN6 was assessed in a wide range of human tissues (eg, lung, colon, skin, ovary) and cultured cells by quantitative RT-PCR, immunohistochemistry (IHC), flow cytometry, and western blotting. To investigate the effect of dedifferentiation on CLDN6 expression, human-induced pluripotent cells were generated by transfecting foreskin fibroblasts with a reprogramming cocktail, and then CLDN6 expression was evaluated. To characterize CLDN6 as a potential novel marker to identify cancer stem cells (CSCs) in OC, coexpression of CLDN6 with known CSC surface markers were analyzed by flow cytometry, and CLDN6+ and CLDN6-negative cells were tested in colony formation and sphere formation assay. Human OC cell lines were transplanted intraperitoneally into nude mice and assessed for metastasis to investigate tumorigenecity of CLDN6+ cells. Results Except for low mRNA levels measured in placenta, testis, umbilical cord, cerebellum, and lung samples, no CLDN6 (mRNA or protein) was detected in the vast majority of normal tissues. Additionally, there was also a lack of CLDN6 protein expression in tissue zones where stem cells for tissue homeostasis would normally be found as determined by IHC with an anti-CLDN6 antibody. CLDN6 was expressed on the cell surface of several solid tumors, including ovarian, testicular, uterine, and lung cancer tissues; OC and TC samples had high level expression. CLDN6 expression was strongly activated in human-induced pluripotent stem cells generated from fibroblasts. CLDN6 showed selective coexpression with known CSC markers such as CD44, CD24, and CD90 in OC and TC cell lines. In addition, some CLDN6+ OC cells exhibited CSC-like behavior in vitro: CLDN6+ populations were clonogenic and formed well-defined spheres in low attachment conditions; these spheres had the ability to self-renew into secondary spheres. Analysis of OC metastases in mouse xenografts showed when xenografts were generated by OC cells that had <10% of CLDN6+ cells, the metastases were enriched in CLDN6+ cells, suggesting CLDN6+ cells had selective growth advantage. Conclusions CLDN6 is a cancer cell-specific surface molecule aberrantly expressed in several cancers, and its expression may be an identifier for cells with CSC-like traits. These characteristics make CLDN6 an attractive target candidate for tumor-specific therapeutic antibodies. Citation Format: Özlem Türeci, Meike Wagner, Claudia Paret, Maria M. Kreuzberg, Stefan Wöll, Korden Walter, Sabine C. Häcker, Ikumi Nakajo, Tomohiro Yamada, Ugur Sahin. Claudin 6 is a carcinoembryonic antigen with cancer stem cell marker features [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1907.

<div>AbstractPurpose:<p>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.</p>Experimental Design:<p>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.</p>Results:<p>CLDN6–23-ADC selectively binds to CLDN6, versus other CLDN family members, inhibits the proliferation of CLDN6+ cancer cells <i>in vitro</i>, 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.</p>Conclusions:<p>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.</p></div>

<div>AbstractPurpose:<p>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.</p>Experimental Design:<p>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.</p>Results:<p>CLDN6–23-ADC selectively binds to CLDN6, versus other CLDN family members, inhibits the proliferation of CLDN6+ cancer cells <i>in vitro</i>, 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.</p>Conclusions:<p>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.</p></div>

<div>Abstract<p>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 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 anti-tumor efficacy of CLDN6-23-ADC was assessed for anti-tumor 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 lead to markedly enhanced survival of CLDN6+ PDX tumors following treatment with CLDN6-23-ADC. IHC assessment of ovarian 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 antibody-drug conjugate, 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.</p></div>

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.

Background: Claudin 6 (CLDN6), a member of the claudin family of tight junction proteins, is expressed at high levels in multiple human malignancies including ovarian and endometrial cancers. Conversely it has little or no expression in normal tissues. This expression profile makes CLDN6 an ideal target for development of potential therapeutic antibody-drug conjugates (ADCs). This study describes the generation and preclinical characterization of an anti-CLDN6 ADC consisting of a humanized anti-CLDN6 monoclonal antibody coupled to MMAE via a cleavable linker. Materials and Methods: A fully humanized anti-CLDN6 antibody was initially characterized for binding affinity, selectivity/specificity, internalization characteristics and in vivo efficacy. It was then conjugated to MMAE resulting in the potential therapeutic anti-CLDN6 ADC. The anti-tumor efficacy of the ADC was next assessed for anti-tumor efficacy in CLDN6 positive (CLDN6+) and negative (CLDN6-) xenografts and patient-derived xenograft (PDX) models of specific cancers including ovarian and endometrial cancer. Results: Selective binding of the ADC to CLDN6, without cross reactivity to other CLDN family members CLDN3, CLDN4 and CLDN9, was confirmed in human cancer cell lines and cells engineered to overexpress each protein. The ADC was also shown to rapidly internalize in CLDN6+ cells. Robust tumor regressions following treatment with the ADC were observed in CLDN6+ xenografts that were sustained beyond the treatment window. Conversely, there was limited to no activity of the ADC in CLDN6- xenografts models. In addition, the prevalence of CLDN6 expression in human ovarian and endometrial cancers was assessed by IHC in tissue microarrays and found to be 28% (ovarian epithelial carcinomas) and 11% (endometrial carcinomas), respectively. Discussion: Overall, these data suggest that our anti-CLDN6 ADC may be a promising treatment for patients with CLDN6+ tumors and it is currently in Phase I clinical testing. Citation Format: Martina S. McDermott, Ke Wei Gong, Neil A. O'Brien, Dylan Conklin, Benjamin Hoffstrom, Ming Lu, Jun Zhang, Tong Luo, Weiping Jia, Jenny J. Hong, Kevin Chau, Simon Davenport, Michael F. Press, Abram Handly-Santana, Joan S. Brugge, Ronny Drapkin, John A. Glaspy, Leonard Presta, Dennis J. Slamon. Development and characterization of a novel anti-CLDN6 antibody drug conjugate for the treatment of CLDN6 positive cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 342.

3082 Background: CLDN6, a member of the claudin family of tight junction proteins, is expressed at high levels in multiple human malignancies and has little to no expression in normal tissues. This expression profile makes CLDN6 an ideal target for development of new therapeutics. TORL-1-23 is first-in-class ADC targeting the tumor-specific antigen CLDN6. Methods: TORL123-001 (NCT05103683) is an ongoing, 2-part, first in human study to characterize the safety, tolerability, dose-limiting toxicities (DLTs), maximum tolerated dose (MTD), and recommended phase 2 dose (RP2D) of TORL-1-23 monotherapy in participants with advanced solid tumors. Serum pharmacokinetics (PK), immunogenicity and clinical efficacy are also assessed. TORL-1-23 is administered as a 30-minute IV infusion once every 3 weeks in 21-day cycles. During Part 1 (Dose Escalation), cohorts of 1 to 6 participants are evaluated at each dose level according to an accelerated titration design. In Part 2 (Dose Expansion), several cohorts of patients with CLDN6-expressing cancers will be evaluated to confirm the RP2D in ovarian cancer, NSCLC, and other CLDN6-expressing cancers using a CLDN6 IHC companion diagnostic. Results: As of 01FEB2023, 22 patients with ovarian (n=18), testicular (n=3), and endometrial (n=1) cancers were enrolled and treated across 8 dose levels ranging from 0.2 to 2.4 mg/kg IV every 3 weeks. 95% of pts had received ≥ 3 prior lines of treatment in the metastatic setting. The most common treatment-related adverse events were Gr1/2 fatigue (n=5), Gr1 peripheral neuropathy (n=4), and Gr1 nausea (n=3). No DLTs have been reported and no dose reductions have been required. Preliminary PK data demonstrate sustained exposure of TORL-1-23 ADC over the 21 day dosing interval and low levels of serum MMAE indicating low off-target MMAE exposure outside of tumor. Partial responses (PR) were observed in 4/17 efficacy evaluable participants with CLDN6+ disease (3 ovarian, 1 testicular). Dose escalation is ongoing and updated results will be presented. Conclusions: TORL-1-23 has a favorable safety/tolerability profile and PK characteristics with preliminary antitumor activity in pts with heavily-pretreated CLDN6-expressing ovarian and testicular cancers. Doses above the historic MTD for MMAE containing ADCs may be explored given the safety/tolerability and PK data observed up to 2.4 mg/kg. Dose finding is ongoing to identify the MTD and optimal doses for subsequent development. Clinical trial information: NCT05103683 .

<div>Abstract<p>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 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 anti-tumor efficacy of CLDN6-23-ADC was assessed for anti-tumor 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 lead to markedly enhanced survival of CLDN6+ PDX tumors following treatment with CLDN6-23-ADC. IHC assessment of ovarian 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 antibody-drug conjugate, 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.</p></div>

TPS424 Background: Testicular cancer (TC) is the most common solid malignancy in men aged 15-35 yrs; germ cell tumors (GCTs) account for 95% of TC. Claudin 6 (CLDN6) is a tight junction membrane protein whose expression in normal tissue is confined to embryonic cells but is frequently aberrantly expressed in GCTs. ASP1650 (also known as IMAB027) is a monoclonal antibody targeted against CLDN6 that can induce antibody-dependent cell-mediated and complement-dependent cytotoxicity in CLDN6-expressing cells and has demonstrated potent antitumor effects in preclinical models of TC. Methods: This phase 2 study with a safety run-in (NCT03760081) will enroll ≤46 male patients (pts) with advanced GCTs who have had prior cisplatin-based combination chemotherapy and ≥1 salvage regimen. In the safety run-in, an initial ASP1650 dose level will be evaluated in 3 pts. If tolerated, a new cohort of 3 pts will begin at the next dose level per the Bayesian Optimal Interval Design. A Dose Evaluation Committee will assess tolerability and determine maximum tolerated dose. Once the recommended phase 2 dose (RP2D) has been established, ≤34 pts will be enrolled in phase 2 and will receive ASP1650 in 2-week cycles for up to 12 cycles or until study discontinuation criteria is met. Phase 2 of the study will utilize a Simon’s 2-stage design to allow for early termination. In stage I, 13 pts, including pts from the RP2D cohort of the safety run-in, will be evaluated for response. If there is ≤1 response among these 13 pts, the study will be stopped, otherwise an additional 21 pts will be enrolled in stage II. Primary endpoints of the study include establishment of the RP2D and confirmation of overall response rate, as assessed by modified RECIST v1.1 response criteria (RECIST v1.1 + serum tumor markers [βhCG and AFP]). Secondary endpoints include the determination of safety/tolerability and pharmacokinetic profiles as well as other efficacy measures (eg, clinical benefit rate; progression-free survival; change in serum tumor biomarkers). Enrollment is currently ongoing; as of Sept 12, 2019, 6 pts have enrolled and 2 are still on active treatment. Clinical trial information: NCT03760081.

Background: Claudin 6 (CLDN6) is a clinically validated target for many solid tumors notably ovarian, endometrial, and testicular cancer. Its expression is restricted to tumor cells and fetal tissues with little or no detectable in normal tissues. As such, CLDN6 represents an attractive therapeutic target for the development of an antibody drug conjugate (ADC). Here, we describe the development and preclinical characterization of a novel ADC called PLB-002, which consists of a highly selective CLDN6 targeting antibody, PLB-002-ab7, conjugated to a FDA-approved microtubule inhibitor, eribulin, via a Primelink Biotherapeutics proprietary enzyme-cleavable linker with an optimized average drug-to-antibody ratio (DAR) of 4.0. PLB-002-ab7 is a novel humanized anti-CLDN6 single-domain antibody (Mw. 78.8 kDa) with highly binding affinity and selectivity to CLDN6 with barely binding to related CLDN family members (CLDN9, CLDN3, and CLDN4) in protein and cell based binding assays. Methods: The in vitro binding affinity of the PLB-002 was determined by flow cytometry on OVCAR3, PA-1, OVCA429, OV90, and NEC-8 cells. Cell internalization effect was evaluated by an in-direct flow cytometry assay on OVCAR3, PA-1, and OV90 cells. In vitro cytotoxicity was measured using Cell-Titer Glo assay on OVCAR3, OV90, and NEC-8 cells. In vivo anti-tumor efficacy was investigated using several cancer cell derived xenograft (CDX) models of OVCAR3, OV90, and NEC-8 cells, as well as patient derived xenograft (PDX) models of ovarian cancer with CLDN6 high, moderate, low and negative expression. A dose-range finding (DRF) safety study of PLB-002 was performed in cynomolgus monkeys. Pharmacokinetics (PK) and pharmacodynamics (PD) data of PLB-002 in CDX mice were determined by LC-MS/MS method. Results: PLB-002 exhibited strong binding, rapid internalization effect, and potent antitumor activity in vitro on OV90 (CLDN6 low expression) and OVCAR3 (CLDN6 high expression) cells with nano-molar range of IC50. When evaluated in OVCAR3 and OV90 CDXs of ovarian cancer, NEC-8 CDX of testicular germ cell tumor, and OV PDXs, PLB-002 showed strong tumor regression in a dose-dependent manner, which is consistent with the PK analyses showing high exposure, slow clearance and long half-life for both total antibody and conjugated drug. In a non-human primate study using cynomolgus monkey, PLB-002 showed favorable safety profile with no clinical symptoms of toxicities up to the highest tested dose. Conclusions: These results show that PLB-002 has remarkable antitumor activity and support the clinical development as a therapeutic ADC for the treatment of ovarian cancer and other CLDN6 expressing solid cancer. Citation Format: Haitao Pan, Qing Zhang, Ganyuan Xiao, Guangchao Zhang, Jiaxin Li, Ling Xin, Kia J. Puan, Ling Xu, Yingdong Lu, Mao Yin. PLB-002 is a novel Claudin 6 antibody-drug conjugate for ovarian cancer and testicular germ cell cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2945.

There is a large unmet need for targeted therapies to treat ovarian cancer and other solid tumors. A promising strategy is the use of T cell engaging bispecific antibodies that recruit T cells to kill cancer cells by simultaneously binding to tumor-associated antigens (TAA) on cancer cells and CD3 on T cells. Effective and safe use of these therapeutics depends on selective targeting of cancer cells over normal tissue, feasible when a TAA is more highly expressed on cancer cells versus normal tissues. Selectivity can also be improved by using a mixed valency “2 + 1” bispecific format, coupled with target affinity tuning, to achieve avid binding to the TAA. Claudin-6 (CLDN6) is a tetraspan membrane protein, a member of the claudin family of tight junction proteins, and has been identified as a promising TAA for ovarian cancer due to its high expression on ovarian and other cancer tissues and low expression on normal tissue. However, a complicating factor is that many proteins in the claudin family have high sequence identity. Most similar to CLDN6 is CLDN9, and the two proteins differ at only 3/76 residues in their extracellular loops, creating a challenge for the development of highly selective CLDN6 antibodies. We analyzed CLDN6 and CLDN9 expression using a combination of normal tissue gene expression data (GTEx), cancer cell genomics data (TCGA), and immunohistochemistry (IHC) on a panel of cancer and normal tissues. Data confirmed the tumor-specific expression pattern of CLDN6 but indicated high CLDN9 expression in normal tissues, suggesting that strong antibody selectivity for CLDN6 versus CLDN9 is critical. We created CLDN6-selective T cell engaging bispecific antibodies by starting with a highly selective monoclonal antibody humanized from a mouse hybridoma. Selectivity was further improved by engineering the CDR regions. Variant antibodies were screened for binding to transiently transfected HEK293E cells that highly expressed either CLDN6, CLDN9, or other homologous claudin family members. Selective variants were converted into the XmAb® 2 + 1 bispecific antibody format and tested in T cell-dependent cellular cytotoxicity (TDCC) assays using cancer cell lines expressing CLDN6, or HEK293E cells transfected with claudin homologs. A set of lead CLDN6 x CD3 bispecifics displaying a range of potencies on CLDN6+ cancer cell lines and high selectivity for CLDN6 over CLDN9 and other homologous claudins was identified. Tolerability and pharmacokinetics of these molecules are currently being assessed in non-human primates, and activity will be evaluated in humanized mouse models of ovarian cancer. Citation Format: Matthew S. Faber, Sung-Hyung Lee, Yoon Kyung Kim, Jing Qi, Kendra N. Avery, Duc-Hanh T. Nguyen, Rumana Rashid, Araz Eivazi, Seung Y. Chu, Juan E. Diaz, Connie Ardila, Ruschelle Love, Alex Nisthal, Norman J. Barlow, Christine Bonzon, Umesh S. Muchhal, Matthew J. Bernett, John R. Desjarlais. Bispecific claudin-6 x CD3 antibodies in a 2 + 1 format demonstrate selectivity and activity on human ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1860.

WNT signaling is frequently dysregulated in cancers. However, pan-WNT inhibitors regularly induce adverse effects in patients, mostly notably in bone, creating a need for more specific WNT-pathway targeting strategies. Frizzled-7 (FZD7), a cell-surface receptor for WNT proteins, is a strong target candidate due to its high expression pattern in many tumor types (including but not limited to breast, ovarian, liver, gastric, and skin cancers) and low to modest expression in few normal adult tissues. We validated FZD7 protein expression in primary patient melanomas and breast and ovarian tumor samples, and developed an antibody-drug conjugate (ADC) that targets human FZD7, hereafter referred to as “FZD7 ADC.” Our ADC consists of a chimeric human-mouse IgG1 antibody conjugated to four molecules of antimitotic drug, monomethyl auristatin E (MMAE), by cleavable valine-citrulline linkers. By flow cytometry, we confirmed that the antibody component binds FZD7 and does not cross-react with the other nine human FZD receptors, FZD(1-6,8-10). We have identified MA-148 and PA-1 as human ovary-derived cancer cell lines responsive to our ADC. We also generated a negative control line, MA-148 FZD7-KO, by CRISPR/Cas9 knockout. In a cell viability assay, we demonstrated FZD7 ADC efficacy in inducing direct, FZD7-dependent cytotoxicity. A single dose of ADC killed MA-148 and PA-1 cells in vitro, with an IC50 of ~0.76 ug/mL (~5 nM) in both lines. MA-148 FZD7-KO cells exhibited an IC50 of ~9 ug/mL (~60 nM). Here, we established a therapeutic window in which our ADC specifically kills FZD7-positive cells. We are currently evaluating FZD7 ADC tumor-killing efficacy in vivo. Because our ADC only binds human FZD7, and not mouse Fzd7, we are utilizing a xenograft model in female nude mice. In a preliminary three-armed study, we established subcutaneous human MA-148-Luciferase (Luc) tumors in mice and treated with a PBS control, 1 mg/kg FZD7 ADC (~0.15 nmole), or 3 mg/kg FZD7 ADC (~0.5 nmole), n = 3-5 per group. We performed an identical study with mice bearing MA-148 FZD7-KO-Luc tumors in parallel. Treatments were delivered twice per week by tail vein injection. Tumor size was measured weekly by an IVIS Spectrum after intraperitoneal luciferin injection. After eight doses over 27 days, MA-148-Luc tumors treated with 3 mg/kg FZD7 ADC completely or partially regressed compared to the control tumors (p = 0.0101 by one-way ANOVA and Tukey's multiple comparisons test). The 1 mg/kg dose did not produce a therapeutic effect in the MA-148-Luc. Importantly, the negative-control MA-148 FZD7-KO-Luc tumors treated with 3- or 1 mg/kg of ADC were not statistically different from the control tumors. Here, we have established a therapeutic FZD7 ADC dose for tumor regression and demonstrated its specificity to FZD7-positive tumors in vivo. Our data show that the FZD7 ADC is an effective strategy to combat cancers expressing FZD7. Citation Format: Myan Do, Christina C. Wu, Stephen Adams, Dennis Carson, Sunil Advani, Karl Willert. Targeting FZD7-positive cancers using a novel antibody-drug conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1848.

Background: Globo H (GH) is highly expressed in a variety of epithelial tumors with a limited expression in normal tissues rendering it a novel therapeutic target. OBI-999 is an antibody drug conjugate (ADC) consisting of a GH-specific monoclonal antibody conjugated with monomethyl auristatin E (MMAE) through a cathepsin B cleavable linker. MMAE is known to induce immunogenic cell death (ICD) which involves in the activation of cytotoxic T lymphocyte-driven adaptive immunity with long-term immunological memory. Aim: The aim of this study was to evaluate the synergistic effects of OBI-999 + pembrolizumab on tumor growth suppression in several xenograft tumor models. Methods: OBI-999-induced ICD was examined in vitro by the detection of damaging-associated molecular patterns (DAMPs) such as calreticulin (CRT), HMGB1, and ATP in incubated Globo H expressing cells. The synergistic effects with the combination of OBI-999 and pembrolizumab as well as the ICD-related immunity were assessed in vivo using advanced severe immunodeficient mice that were reconstituted with human peripheral blood mononuclear cells (PBMCs). Results: Incubation of OBI-999 with high GH expression cancer cell lines (HCC-1428, NCI-N87 and NCI-H526) and mid GH expression cancer cell line (SW-480) induced the release of DAMPs including CRT, HMGB1, and ATP, in a dose- and time-dependent manner, indicating that OBI-999 is capable of inducing ICD in vitro. In the high GH expression human breast cancer cell line HCC-1428 xenograft model, OBI-999+pembrolizumab exhibited significantly stronger inhibition of tumor growth compared to either OBI-999 or pembrolizumab alone. Similar synergistic effects were observed in other xenograft tumor models including gastric (NCI-N87), small cell lung (NCI-H526), and colorectal (SW-480) cancers. Analysis of tumor-infiltrating lymphocytes (TILs) in HCC-1428 humanized mice showed that OBI-999 + pembrolizumab induced populations of activated cytotoxic CD8 T-cells and mature dendritic cells. Pembrolizumab decreased PD-1 expression on CD8 and CD4 cells, and OBI-999 decreased PD-L1 expression on tumor cells, which reversed the exhausted status of immune cells and alleviated immunosuppression in the tumor microenvironment. Conclusion: We demonstrated significant synergistic effects of OBI-999 and pembrolizumab in several animal models. These synergistic effects may be attributed to the ability of OBI-999 to induce ICD, as demonstrated by the release of DAMPs in vitro and tumor-specific immunity in vivo, suggesting that OBI-999 can create a tumor microenvironment that enhances the function of pembrolizumab. The results suggest that combination therapy with OBI-999 and immune checkpoint inhibitors is warranted in human clinical studies. OBI-999 is currently in Phase 1/2 clinical trials for the treatment of advanced solid tumors with high GH expression (NCT04084366). Citation Format: Chun-Chung Wang, Chi-Huan Lu, Jhih-Jie Yang, Wan-Fen Li, Ming-Tain Lai. OBI-999, an anti-Globo H antibody drug conjugate, exhibits synergistic anti-tumor effect in combination with pembrolizumab [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5946.

Claudin 6 (CLDN6) is an oncofetal protein involved in tight junction formation and is responsible for regulating cell polarity, adhesion and permeability. CLDN6 has recently emerged as an ideal target for novel oncology therapeutics, given the expression in various solid tumors, with limited normal tissue expression. High-levels of CLDN6 cell-surface protein expression are commonly detected in testicular cancer and epithelial ovarian cancer (EOC), with lower frequency expression in additional solid tumors such as gastric-, cervical-, endometrial-, and lung cancer. Using normal human tissue microarrays (TMA) and a highly selective commercially available CLDN6 antibody, minimal staining of CLDN6 was confirmed across a large panel of normal tissues by IHC, where sparse and limited apical staining of CLND6 was detected in pancreas, stomach, salivary gland, kidney and uterine tissues. High CLDN6 expression in ovarian tumors was demonstrated with the same selective antibody, confirming CLDN6 as a unique solid tumor target with limited normal tissue expression. ARC101 is a bispecific antibody that targets CLDN6 on tumor cells and CD3 on T cells, leading to T-cell-mediated tumor cell lysis. Generation of CLDN6-specific therapeutic antibodies has been challenging given the high degree of homology that exists between CLDN6 and CLN9, and to a lesser extent CLDN4. ARC101 was selected as a therapeutic candidate, due to the high degree of specificity obtained with this molecule. ARC101 bound to and induced cytotoxicity of a CLDN6 overexpressing SKOV3 ovarian cell line. No significant binding or cytotoxicity was observed for CLDN9 or CLDN4 overexpressing SKOV3 cell lines, underscoring the high specificity of ARC101 for CLDN6 over other highly homologous claudins. ARC101 bound to CLDN6-positive human ovarian cancer cell lines OVCAR3, PA1, and OV90, while binding to OVCAR3 cells was completely abolished when CLDN6 expression was deleted via knock out. ARC101 induced potent T cell activation and cytotoxicity at low effector to target (E:T) cell ratios across the panel of CLDN6-positive cells (2D and 3D models), with no activity observed on the CLDN6-negative OVCAR3 knock out cell line. In vivo, ARC101 demonstrated potent and dose-dependent anti-tumor activity in an ovarian tumor xenograft model. Overall, ARC101 is a highly specific CLDN6-directed T-cell engager with significant therapeutic potential for CLDN6-positive solid tumors. A Phase 1 first-in-human (FIH) clinical trial of ARC101 (NCT06672185) is planned to commence in 2025. Citation Format: Sanjaya Singh, Danlin Yang, Joseph Erhardt, Theresa McDevitt, Scott R. Brodeur, Bridget Larkin, Cassandra Lowenstein, Desmond Lewis, Tabitha Soto, Brinda Shah. Pharmacologic characterization of a highly specific and potent CLDN6xCD3 T cell engager (TCE), ARC101, for the treatment of CLDN6+ cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7325.