Microtubule-disrupting Agent Monomethyl Auristatin E Research Articles

Abstract PO1-04-07: Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy and in combination with tucatinib in preclinical breast cancer models

Abstract Disitamab vedotin (DV, RC48-ADC) is an antibody-drug conjugate (ADC) that targets cancers expressing HER2. DV consists of an anti-HER2 monoclonal antibody, disitamab, conjugated with the microtubule-disrupting agent monomethyl auristatin E (MMAE) via a cleavable vedotin linker. DV has multimodal antitumor mechanisms of action that include direct cytotoxicity of HER2-expressing cancer cells and bystander effect-based cytotoxicity of neighboring cells, both of which are mediated by the intracellular release of MMAE. Released MMAE can also induce immunogenic cell death, which promotes immune cell recruitment to the tumor. In addition, DV stimulates Fc-gamma receptor mediated antibody-dependent cellular cytotoxicity, which can lead to target cell death. DV also inhibits HER2-activated downstream signaling pathways, further blocking cell growth, survival, and proliferation. Previously, we showed the cytotoxic activity of DV against a panel of breast cancer cell lines with varying levels of HER2 expression, including the HER2-low range. Here, we sought to further characterize the preclinical antitumor activity of DV in patient-derived 3D models and patient-derived xenographs (PDX). In cultured breast cancer cells, DV was more potent and internalized to a greater magnitude than the HER2-directed ADCs trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd). In patient-derived 3D models, DV had superior activity compared to T-DXd. We further explored whether dual HER2 targeting with DV in combination with the HER2-selective oral TKI tucatinib improved the antitumor outcomes. In PDX models with varying HER2 IHC levels and models refractory to T-DXd, DV as a monotherapy and in combination with tucatinib showed significant tumor growth inhibition. This result is consistent with previous in vitro results that showed increased cytotoxicity of the combination of DV and tucatinib in cell lines with a wide range of HER2 expression, which may be mechanistically attributed to elevated HER2 cell surface levels upon treatment with tucatinib. Overall, these findings provide scientific rationale to explore DV in HER2-positive and HER2-low breast cancer patients as a monotherapy or in combination with tucatinib. Citation Format: Kelsi Willis, Renee Hein, Katie Snead, Robert Thurman, Anita Kulukian. Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy and in combination with tucatinib in preclinical breast cancer models [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-04-07.

Abstract PO3-18-04: MBRC-101: a novel antibody-drug conjugate (ADC) targeting the membrane-associated tyrosine kinase receptor EphA5 in breast cancer

Abstract Objectives: ADCs have emerged as a major advance in contemporary medical oncology. The receptor tyrosine kinase (RTK) EphA5 possesses the classical receptor kinase topology with an extracellular-binding domain, a single-pass transmembrane domain, and a cytoplasmic kinase domain. We have previously shown that EphA5 is highly expressed in non-small cell lung cancer and contributes to DNA-damage repair and radiation therapy resistance. Others have reported EphA5 expression in gastric, ovarian, and pancreatic cancers. Here, we investigated the expression of EphA5 in breast cancer (BC) and assessed EphA5 as a potential cancer-specific target using a novel ADC designated MBRC-101. Methods: MBRC-101 is composed of a humanized anti-EphA5 IgG1 kappa monoclonal antibody conjugated to the small molecule microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease cleavable valine-citrulline (vc) ThioBridge linker (ThioBridge™-Glu-[Val-Cit-PAB-MMAE] PEG [24u]). MBRC-101 averages a drug-to-antibody ratio (DAR)=4. The specificity profile of the anti-EphA5 monoclonal antibody was characterized using a Membrane Proteome Array (MPA). Receptor-mediated antibody internalization was determined by real-time live-cell analysis; cell killing assays used both live-cell analysis of cell confluence and the CellTiter-Glo® luminescent cell viability assay. Expression of EphA5 in archival human breast tumor tissue sections was evaluated by immunohistochemistry (IHC) using a commercial polyclonal antibody against human EphA5. In vivo efficacy studies used patient-derived xenograft (PDX) models of BC. Results: IHC demonstrated robust and selective EphA5 expression in 87% (20 of 23) of triple negative breast cancer (TNBC) and 88% (23 of 26) of hormone receptor-positive (HR+) patient tumors tested. EphA5 expression was not detected in adjacent, non-malignant breast tissue. Antibody-specificity profile testing showed that the anti-EphA5 antibody bound exclusively to EphA5 and did not cross-react with other members of the Eph receptor/ephrin ligand family. Binding of the anti-EphA5 antibody to EphA5 on the cell surface triggered rapid internalization and processing of the EphA5/antibody complex through the endosomal-lysosomal system. Consistently, MBRC-101 was cytotoxic to EphA5-expressing cells and its activity was concentration-dependent and commensurate to the levels of EphA5 on the cell surface. In PDX murine models of TNBC, once weekly administrations of intravenous (IV) MBRC-101 showed dose-dependent, robust, and reproducible anti-tumor activity in vivo. Partial tumor responses were observed at doses of 2.5 mg/Kg IV and complete and nearly complete tumor responses starting at 5 mg/Kg IV. Doses up to 10 mg/Kg IV were well-tolerated in tumor-bearing mice with no observable weight loss. Pre-clinical safety confirmed MBRC-101 is also well tolerated in rats and in cynomolgus monkeys. Conclusions: These results support EphA5 as a new and promising membrane-associated molecular target for the design and development of ADC-based therapies against hormone-positive breast cancer and TNBC and support the conduct of a Phase 1/1b study of MBRC-101 in patients with breast cancer. Citation Format: Fernanda Staquicini, Fenny Tang, Vanessa de Oliveira, Daniela Staquicini, Yongjian Wu, Kirstin Barnhart, J Kellogg Parsons, Wadih Arap, Isan Chen, Renata Pasqualini. MBRC-101: a novel antibody-drug conjugate (ADC) targeting the membrane-associated tyrosine kinase receptor EphA5 in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-04.

Abstract 1901: Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy in preclinical urothelial cancer models

Abstract Disitamab vedotin (DV, RC48-ADC) is an antibody-drug conjugate (ADC) that selectively delivers cytotoxic drug to HER2-expressing cancer cells. DV is composed of disitamab, a HER2-directed monoclonal antibody, and a vedotin linker-payload system, which enables conjugation of the microtubule-disrupting agent monomethyl auristatin E (MMAE) to the antibody via a protease-cleavable linker. The proposed mechanism of action (MOA) of DV occurs through direct cytotoxicity of HER2-expressing tumor cells following internalization of DV and intracellular release of MMAE. DV may also induce antitumor activity through bystander-mediated cytotoxicity of neighboring cells and via the inhibition of HER2 signaling pathways. Moreover, cellular response to MMAE includes the induction of immunogenic cell death and recruitment of immune cells to the tumor site. DV is currently being evaluated globally in subjects with HER2-expressing locally advanced or metastatic urothelial carcinoma (la/mUC) and has gained conditional approval in China following an overall response rate of 50.5% (pooled analysis from studies NCT03507166 and NCT03809013). RNA sequencing data from a large cohort of urothelial cancer patient tumors revealed expression of HER2 in many urothelial tumors; however, the relationship between HER2 expression and efficacy of DV is not well understood. Here, we sought to evaluate the antitumor activity of DV monotherapy in preclinical urothelial cancer models with varying levels of HER2 expression. Multiple patient-derived xenografts (PDX) and patient-derived 3D in vitro urothelial cancer models showed potent antitumor response to DV monotherapy in tumors with varying HER2 expression levels including HER2-low tumors. Overall, these findings support ongoing clinical trials in subjects with HER2-expressing la/mUC and provide scientific rationale to further explore DV monotherapy in HER2-positive and HER2-low urothelial cancer clinical settings. Citation Format: Renee Hein, Kelsi Willis, Gina LoMastro, Suhas Vasaikar, Vinita Gupta, Katie Snead, Sharsti Sandall, Anita Kulukian. Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy in preclinical urothelial cancer models [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 1901.

A phase II open-label study of enfortumab vedotin in patients with previously treated locally advanced, recurrent, or metastatic pancreatic adenocarcinoma (EPIC).

TPS719 Background: Nectin-4 is a type I transmembrane protein member of the nectin family involved in the formation and maintenance of adherens junctions. In contrast to its limited expression in normal tissues, aberrant overexpression of nectin-4 has been identified in various solid tumors, including in pancreatic adenocarcinoma. About 71% of human PDAC specimens stain positive and 13% stain strongly positive for nectin-4. Mechanistically, nectin-4 has been associated with various pro-oncogenic cellular processes, including the promotion of tumor cell proliferation and metastasis via WNT- βcatenin pathway activation. It interacts with ERBB2/HER2 and activates Rac1 (small G protein) to ultimately upregulate PI3K-AKT pathway signaling, leading to cell survival and proliferation. Enfortumab vedotin (EV) is an antibody-drug conjugate that delivers the microtubule-disrupting agent monomethyl auristatin E (MMAE) to cells expressing Nectin-4. EV is FDA approved as a single agent for the treatment of adult patients with locally advanced or metastatic urothelial cancer who have previously received a programmed death receptor-1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitor and platinum-containing chemotherapy based on the EV-301 Trial which demonstrated overall survival benefit. Taken together, the above data and the efficacy of EV seen in bladder cancer warrants the evaluation of EV in advanced pancreatic adenocarcinoma. Methods: Design: Open-label, phase II single-arm trial of EV (n=28) in previously treated locally advanced, recurrent, or metastatic pancreatic adenocarcinoma. Treatment schedule: EV 1.25 mg/kg administered IV on D1, D8, D15 every 28 days until disease progression or unacceptable toxicity. Imaging assessment will be done every 8 weeks. A biopsy prior to therapy and a biopsy on treatment (between days 15-21 of cycle 1) is required. Eligibility: Patients with previously treated, locally advanced, recurrent, or metastatic pancreatic adenocarcinoma. Inclusion criteria also include ECOG PS 0-1 and at least 1 line of prior therapy. Objectives: The primary objective is to determine anti-tumor activity by overall response rate using RECIST 1.1. Secondary objectives include safety, duration of response, disease control rate, progression-free survival and overall survival. Exploratory objectives include Nectin-4 expression (H-score) in tumor tissue and the relationship between the mutational profile of the tumor and response. Statistical Plan: A Simon’s two-stage Minimax design will be used. In the first stage, 18 pts will be accrued. If there is less than 1 response in these 18 pts, the study will be stopped for futility. Otherwise, 10 additional pts will be accrued for a total of 28 pts. The null hypothesis will be rejected if 3 or more responses are observed in 28 pts. Enrollment is currently ongoing. Clinical trial information: NCT05915351 .

A Novel Fc-Optimized Antibody Drug Conjugate Targeting CD7 As a Therapeutic Strategy in T-Cell Acute Lymphoblastic Leukemia

Despite progress in improving treatment regimens for patients with T-cell acute lymphoblastic leukemia (T-ALL), the therapeutic options are still limited, and especially antibody-based immunotherapy is not established. The CD7 antigen represents a promising target structure in T-ALL since it is strongly expressed in different T-ALL subtypes including early T-cell precursor (ETP)-ALL. Therefore, different approaches are currently pursued for targeting CD7, including CAR-T cell therapy. Due to its high internalization capacity CD7 also represents an ideal target structure for antibody drug conjugates (ADC). Here, a novel antibody engineering approach for CD7-targeting was evaluated in vitro and in xenograft mouse models of T-ALL. A CD7 antibody was optimized for its ability to trigger antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) by introducing two amino acid substitutions (S239D/I332E; DE-variant) in the Fc-domain. In addition, the Fc-engineered antibody was conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via an enzymatic-cleavable linker (mc-vc-PABC). The Fc-optimized ADC, CD7-DE-vcMMAE, as well as the unconjugated antibody, CD7-DE, showed improved binding to activating Fcγ receptors (FcγRIIa, FcγRIIIa) compared to a CD7 antibody lacking the DE-modification. This resulted in potent ADCC- and ADCP-activity against different T-ALL cell lines mediated by NK-cells or macrophages as effector cells (EC 50 ADCC, 1-7 pM). In contrast to the CD7-DE antibody, CD7-DE-vcMMAE showed strong cytotoxic effects independently of immune effector cell engagement by releasing its cytotoxic compound into T-ALL cells in an antigen-restricted manner, thereby inducing G2/M cell cycle arrest and apoptosis. CD7-DE-vcMMAE was active at subnanomolar concentrations demonstrating dose-dependent cytotoxic effects in six T-ALL cell lines (IC 50 0.2 - 1 nM). The extent of maximum growth inhibition ranged between 54-98 % and correlated with CD7 antigen density. Yet, although CD7-DE-vcMMAE did not kill CD7-negative cells directly, the linker design facilitated bystander killing activity. Thus, in co-culture experiments using CEM cells and CEM-CD7-knockout cells mimicking CD7-antigen escape, the ADC demonstrated significant killing of neighbouring CD7-negative cells, thereby extending its mode of action. The antitumor activity of the CD7-ADC was further investigated in xenograft mouse models of T-ALL. In a first model, CEM cells were injected subcutaneously into NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice and CD7-DE-vcMMAE treatment was evaluated in comparison to the unconjugated antibody CD7-DE. Treatment with CD7-DE-vcMMAE led to a significantly reduced tumor growth in comparison to CD7-DE or untreated animals (p<0.05; see panel A). A preclinical phase II-like patient-derived xenograft (PDX) study employing eight randomly selected T-ALL-PDX samples from pediatric and adult patients was conducted. PDX-cells were injected intravenously into NSG mice and treatment was started when the leukemia load reached 1 % human blasts in the peripheral blood, reflecting an overt leukemia situation. Animals receiving therapy with CD7-DE-vcMMAE showed significant prolongation of median survival in comparison to animals treated with a similarly designed control ADC targeting an irrelevant antigen (control-DE-vcMMAE) or which were left untreated (median survival time; CD7-DE-vc-MMAE: 82 days; untreated/control-DE-vcMMAE: 60 days; p<0.05; see panel B). Importantly, no leukemic blasts were found in the peripheral blood, spleen or bone marrow in animals treated with CD7-DE-vcMMAE and surviving the experimental period of 150 days. Together, the novel ADC CD7-DE-vcMMAE showed a unique set of Fc effector functions, potent direct growth inhibitory effects, bystander killing activity and efficacy in xenograft models of T-ALL. These results exhibit CD7-DE-vcMMAE as a promising therapeutic strategy and form the basis for new approaches in the treatment of T-ALL.

Abstract 3253: CD30 is a marker of activated effector regulatory T cells in solid tumors providing clinical rationale for the combination of brentuximab vedotin and PD-1 inhibitors

Abstract Regulatory T cells (Tregs) play an important role in maintaining immune homeostasis by preventing excessive inflammation in normal tissues. In cancer, Tregs hamper antitumor immunosurveillance and may be a resistance mechanism to anti-PD-1 therapies. In preclinical cancer models, Treg depletion enhances antitumor cytotoxic immune responses, but systemic and persistent Treg removal can elicit immunopathology. Therapeutic strategies that selectively deplete highly suppressive activated intratumoral Tregs may avoid immune-related toxicities and amplify the activity of antitumor CD8 T cells during PD-1 blockade. CD30 is a member of the TNF receptor superfamily and is expressed by a subset of activated lymphocytes and various lymphomas. Here, transcriptomics and flow cytometry data from tumor and peripherally derived Tregs demonstrated CD30 is enriched on intratumoral Tregs. Among peripheral Tregs, CD30 expression was associated with an activated effector phenotype (FoxP3hiCD45RA-, fraction II). Further, treatment of dissociated NSCLC tumor spheroids with anti-PD-1 resulted in upregulated CD30 expression by Tregs but not intratumoral CD4 or CD8 T cells, which is consistent with Treg reactivation and supports CD30 as an activated Treg target. In vitro, CD30 expression on Tregs was dependent on signaling through the TCR and was significantly amplified by IL-2 and IL-15, suggesting CD30 may identify a subpopulation of activated antigen-specific Tregs. Brentuximab vedotin (BV) is an antibody-drug conjugate approved for clinical use in multiple types of lymphomas including cHL and PTCL. BV consists of a CD30-directed monoclonal antibody conjugated to the highly potent microtubule-disrupting agent monomethyl auristatin E (MMAE). The activity of BV in lymphomas is thought to primarily result from tumor-directed intracellular MMAE release leading to apoptosis, though multiple immunomodulatory effects of BV have also been suggested. We have demonstrated through in vitro and in vivo preclinical model systems of human T cell activation that BV can selectively deplete CD30-expressing Tregs, amplifying cytotoxic CD8 T cell expansion. These and Treg CD30 expression data motivated the clinical exploration of BV plus pembrolizumab in metastatic PD-1 refractory melanoma and NSCLC (NCT04609566). Consistent with preclinical data, preliminary biomarker analysis from these studies showed a small but significant decrease in Tregs (CD4+CD25+CD127low/-) in peripheral blood after treatment with BV plus pembrolizumab. Further, limited on-treatment biopsies showed a trend toward increased intratumoral CD8:Treg (FoxP3) ratio in some patients receiving combination therapy. These data support the ongoing evaluation of BV in combination with PD-1 inhibitors in solid tumors and a potential additional mechanism of action for BV. Citation Format: Ryan A. Heiser, Bryan M. Grogan, Reice D. James, Michelle L. Ulrich, Jason D. Berndt, Brian P. O'Connor, Shyra J. Gardai, Hailing Lu, Scott M. Knowles. CD30 is a marker of activated effector regulatory T cells in solid tumors providing clinical rationale for the combination of brentuximab vedotin and PD-1 inhibitors [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 3253.

Brentuximab in Children, Adolescent and Young Adults with Relapsed/Refractory Anaplastic Large Cell Lymphoma

Background: Anaplastic Large Cell Lymphoma (ALCL) is an aggressive malignancy characterized by strong expression of CD30. Multi-agent chemotherapy cures 65-90% of newly diagnosed patients, the rate of relapse approaching 30%. Targeted agents eventually followed by allogeneic stem cell transplantation (SCT) may represent a valuable salvage therapy in patients with relapsed/refractory ALCL. Brentuximab vedotin is a CD30-directed monoclonal antibody-drug conjugate (ADC) that comprises a monoclonal human/murine antibody linked to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease-cleavable linker. Design and methods: We retrospectively analyzed monocentric data of 20 patients with ALCL treated with Brentuximab from 2.10.2014 to 22.05.2022. Treatment was characterized by the intravenous infusion of 1.8 mg/kg Brentuximab in monotherapy or as part of a polychemotherapy regimen, in children with either relapsed disease or not fully responding to first-line treatment. More in detail, chemotherapy regimens administered in combination with the immunotherapy were: bendamustine, AM and BM blocks (ALCL99 Trial), or AA, BB and CC blocks (LNH97 Trial). Objective response rate (ORR) was assessed through computed tomography (CT)/FDG-PET scans. Results: Eight patients received Brentuximab for incomplete response to first-line treatment (2 of them had haemophagocytic lymphohistiocytosis at diagnosis, and underwent genetic testing that revealed the heterozygous variant c.1336C>T (p.Arg446Trp) in IKBKB gene and the hemizygous variant c.622T>C (p.Ala91Val) in IL2RG gene, respectively). In these patients, Brentuximab was mostly used in combination with the ALCL99 regimen. Three of these 8 patients experienced a subsequent relapse and were re-exposed to the drug after disease recurrence. Fifteen patients received Brentuximab at relapse. Median time between diagnosis and relapse was 10.3 months (range 3.4-34 months). The median number of Brentuximab infusions was 7 (range 2-25). The combination of Brentuximab 1.8 mg/kg/dose on Day 1 and Bendamustine 120 mg/m2/dose on Day 2 and 3, was the principal reinduction regimen in the relapsed cohort, having been infused in 9 patients with a median of 4 cycles (range 2 to 5). This drug combination was very well tolerated and showed a 100% complete response (CR) assessed by CT and FDG-PET scans, allowing to perform allogeneic SCT in all of them. Allogeneic SCT was performed in 15 patients (one of them was the child with haemophagocytic lymphohistiocytosis at diagnosis given Brentuximab during the first-line treatment because of incomplete response), while the remaining child, who had relapsed 34 months after the diagnosis, was treated with Brentuximab monotherapy and remains in CR. Nine patients received HLA-haploidentical SCT, while the remaining 6 were transplanted using either a matched sibling donor (3 patient) or an unrelated volunteer (3 patients) respectively. Sixteen out of the 20 patients (80%) are alive and disease free with a median follow-up of 28.6 months (range 3-78.7). Three patients died due to transplant related causes and 1 patient due to disease progression. Conclusions: Despite the limitations of a limited number of patients analyzed and the retrospective nature of the study, our data suggest that Brentuximab administered either in monotherapy or in combination with chemotherapy is a valuable salvage option and may represent a suitable bridge to allogeneic SCT.

Population pharmacokinetic analysis for tisotumab vedotin in patients with locally advanced and/or metastatic solid tumors.

Tisotumab vedotin is an investigational antibody–drug conjugate (ADC) for treatment of solid tumors expressing tissue factor with accelerated approval from the US Food and Drug Administration for treatment of recurrent or metastatic cervical cancer with disease progression during or after chemotherapy. This study describes development of a population pharmacokinetic (PK) model to assess the PK profile of tisotumab vedotin and microtubule‐disrupting agent monomethyl auristatin E (MMAE) using data from 399 patients with solid tumors across four phase I/II trials. The ADC–MMAE model describes ADC and MMAE concentrations following intravenous administration of tisotumab vedotin. This four‐compartment model comprises a two‐compartment ADC model with parallel linear and Michaelis–Menten elimination, a delay compartment, and a one‐compartment MMAE model. Nonspecific linear clearance of ADC was 1.42 L/day, central volume of distribution (V c) was 3.10 L, and median terminal half‐life of ADC was 4.04 days. Apparent clearance of MMAE was 42.8 L/day, and apparent volume of distribution was 2.09 L. Terminal slope of the MMAE concentration–time curve was defined by the delay compartment rate with a half‐life of 2.56 days. Patients with higher body weight and lower albumin concentration had faster ADC clearance. Male patients and those with higher body weight and lower albumin concentration had higher V c. Body weight was the most influential covariate influencing distribution and elimination of ADC and MMAE, thus supporting weight‐based dosing of tisotumab vedotin. Presence of antidrug antibodies (detected in 3.3% of patients) did not affect key PK parameters or exposures for ADC and MMAE.

Abstract 955: Preclinical characterization of a novel SSEA-4-targeting antibody drug conjugate, OBI-998

Abstract Stage-specific embryonic antigen-4 (SSEA-4) ceramide, a globo-series hexasaccharide glycosphingolipid, has been reported to be a tumor-associated antigen. Here, we present a novel antibody-drug conjugate (ADC) targeting SSEA-4 to evaluate its potential as a therapeutic agent for cancer treatment. OBI-998 is an ADC comprising the humanized anti-SSEA-4 antibody (OBI-898) that is conjugated to the highly potent microtubule-disrupting agent monomethyl auristatin E (MMAE) through maleimide and PEGylated cleavable linkers. We demonstrated the specificity of the naked antibody to SSEA-4 by screening against a panel of 21 related carbohydrate antigens using ELISA. OBI-998 displayed potent cytotoxic activity against cells (SKOV3) with a high level of SSEA-4 expression at sub-nanomolar potency but no effect on the viability of cells (SKBR3) with negligible SSEA-4 expression. The bystander killing effect of OBI-998 was shown by the transferring of conditioned medium from SKOV3 cells treated with 1 or 5 nM of OBI-998 to SKBR3 cells. Furthermore, significant bystander effects were observed by co-culturing high (NCI-N87) and low (PANC-1/GFP) SSEA-4-expressing cell lines at different ratios in the presence of 5 or 10 nM of OBI-998. OBI-998 was found to be rapidly internalized into cancer cells within 5 minutes upon binding to its target on the cell surface by confocal microscopy. OBI-998 showed significant anti-tumor efficacy in multiple cancer cell–derived xenograft models at doses of 1, 3, and 10 mg/kg in a dose-dependent manner. More importantly, OBI-998 at a dose of 10 mg/kg showed complete tumor regression in an EGFR-triple mutation non–small cell lung cancer xenograft model, which is resistant to the current last-line tyrosine kinase inhibitor, osimertinib. Pharmacokinetic analysis of OBI-998 revealed that total antibody and the conjugated antibody exhibited similar pharmacokinetic profiles, suggesting OBI-998 is highly stable in vivo. The biodistribution study in HCC1428 tumor-bearing mice indicated that MMAE accumulated in the tumor site at a higher level compared with other blood-rich organs. In addition, the MMAE levels in tumors reached peak level at 24 hours post-treatment, which was much higher than the maximum levels in other organs, and the level was sustained for 168 hours with tumor-to-muscle ratio of 329. OBI-998 is a novel ADC targeting SSEA-4 that possesses desired properties such as high target specificity, rapid internalization, potent cytotoxicity, and significant bystander effects. Furthermore, OBI-998 showed a high level of deposition and a persistent presence of MMAE in tumors and significant anti-tumor efficacy in a variety of animal models. Taken together, these results support the further development of OBI-998 as a therapeutic agent for SSEA-4-targeting cancer therapy. Citation Format: I-Ju Chen, Chun-Chung Wang, Chi-Sheng Shia, Chung-Chen Su, Chi-Huan Lu, Hui-Wen Chang, Ping-Tzu Chiu, Yueh-Chin Wu, Ming-Tain Lai, Wei-Chien Tang, Hsin-Yi Tung, Ren-Yu Hsu. Preclinical characterization of a novel SSEA-4-targeting antibody drug conjugate, OBI-998 [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 955.

Tisotumab vedotin versus investigator’s choice chemotherapy in second- or third-line recurrent or metastatic cervical cancer (innovaTV 301/ENGOT-cx12/GOG 3057, trial in progress).

TPS5596 Background: Doublet chemotherapy (paclitaxel plus either platinum or topotecan) with bevacizumab (if eligible) is recommended for first-line treatment of recurrent (not amenable to curative therapy) or metastatic cervical cancer (r/mCC; Tewari 2014). In the second-line setting, there are limited data for currently available treatment options. Tisotumab vedotin (TV) is an investigational antibody-drug conjugate (ADC) composed of a tissue factor (TF)-directed human monoclonal antibody covalently linked to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease-cleavable linker. TV is directed to cells expressing TF and releases MMAE upon internalization, resulting in cell cycle arrest and apoptotic cell death. TV has anti-tumor activity on multiple tumor types and kills tumor cells by direct cytotoxicity, bystander cytotoxicity, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and in a manner consistent with immunogenic cell death. In a recent phase 2 pivotal trial (innovaTV 204), TV demonstrated a clinically meaningful objective response rate (ORR) of 24% and median duration of response (DOR) of 8.3 months, as well as a manageable and tolerable safety profile with most adverse events being mild to moderate, in r/mCC patients with disease progression on or after chemotherapy. These findings support further investigation of TV in patients with r/mCC who progress on available first-line treatment options. Methods: The innovaTV 301 trial (NCT04697628) is a global, randomized, open-label, phase 3 clinical trial evaluating the efficacy and safety of TV in patients with previously treated r/mCC. Eligible patients must be ≥18 years, have r/mCC, and have experienced disease progression after receiving 1-2 prior lines of therapy (either standard of care systemic chemotherapy doublet or platinum-based therapy [if eligible; paclitaxel+cisplatin+bevacizumab, paclitaxel+carboplatin+bevacizumab, or paclitaxel+topotecan/nogitecan+bevacizumab]). Approximately 482 patients will be randomized 1:1 to receive 21-day cycles of either TV (2.0 mg/kg IV once every 3 weeks) or investigator’s choice of chemotherapy: topotecan (1 or 1.25 mg/m2 IV; Day 1 [D1] to D5 of each cycle), vinorelbine (30 mg/m2 IV; D1 and D8 of each cycle), gemcitabine (1000 mg/m2 IV; D1 and D8 of each cycle), irinotecan (100 or 125 mg/m2 IV; weekly for 28days, then every 42 days), or pemetrexed (500 mg/m2 IV, D1 of each cycle). The primary endpoint of this trial is overall survival. Key secondary endpoints are progression-free survival, ORR, time to response, DOR, safety, and quality of life outcomes. The study is currently enrolling and will have sites open in the US, EU, Japan, Latin America, Taiwan, Singapore, and South Korea. Clinical trial information: NCT04697628.

Study EV-103: Update on durability results and long term outcome of enfortumab vedotin + pembrolizumab in first line locally advanced or metastatic urothelial carcinoma (la/mUC).

4528 Background: Significant unmet need remains for people with cisplatin-ineligible (cis-ineligible) locally advanced or metastatic urothelial carcinoma (la/mUC). In the first-line (1L) setting, carboplatin-based regimens have demonstrated poor tolerability, modest objective response rate (ORR) and limited durability. PD-1/PD-L1 inhibitors demonstrate durable responses; however, only a minority of pts achieve a response (ORR 24-29%). Enfortumab vedotin (EV) is an antibody-drug conjugate (ADC) delivering the microtubule-disrupting agent monomethyl auristatin E (MMAE) to targeted tumor cells expressing Nectin-4. EV has shown an overall survival benefit versus chemotherapy in previously treated la/mUC. Preclinical studies show that ADCs utilizing MMAE can induce immunogenic cell death and may enhance antitumor immunity. Clinical data suggests the combination of EV + pembrolizumab (P) may have the potential to induce greater antitumor activity compared to either agent alone. Preliminary data on EV + P was previously presented, and the FDA granted breakthrough therapy designation to EV + P for the treatment of pts with 1L cis-ineligible la/mUC in Feb 2020. Here we report updated data with 24.9 months median follow-up. Methods: This multi-cohort EV-103 study (NCT03288545) evaluates the safety/activity of EV + P (Dose Escalation/Cohort A). This report highlights 1L cis-ineligible pts treated with 3-week cycles of EV 1.25 mg/kg (Days 1, 8) and P (Day 1). Endpoints include safety/tolerability, investigator response per RECIST v1.1, DOR, PFS, and OS. Results: As of 13 Oct 2020, the median follow-up for the 45 1L la/mUC pts (median age 69 yrs [51-90]) was 24.9 months. The median number cycles of EV + P was 9 (range 1-34). The most common treatment-related adverse events were peripheral sensory neuropathy (56%, 4% ≥G3), fatigue (51%, 11% ≥G3), and alopecia (49%). There was one death reported as possibly related to study treatment (multiple organ dysfunction syndrome) per investigator assessment. Confirmed ORR is 73.3% (95% CI: 58.1, 85.4) including 17.8% CR and an ORR of 57.1% (8/14) in pts with liver metastasis. The median DOR was 25.6 months (95% CI: 8.3, -). Fifty-three percent of the responders had DOR at 24 months. Additionally, the DCR is 93.3%, the median PFS is 12.3 months (95% CI: 8.0, -), and the median OS is not reached. The OS rate at 24 months is 56.3% (95% CI: 39.8, 69.9). Conclusions: EV + P, a platinum-free option, continues to demonstrate promising activity with a durable response profile in 1L cis-ineligible pts with la/mUC. The safety profile is manageable and stable over time with no new safety signals. Cohort K of EV-103 in cis-ineligible pts with la/mUC is actively randomizing pts to EV monotherapy or EV + P to evaluate the contribution of each agent. Clinical trial information: NCT03288545.

Development and biological assessment of MMAE-trastuzumab antibody-drug conjugates (ADCs).

Trastuzumab, a humanized monoclonal antibody targeting Human Epidermal growth factor Receptor 2 (HER2), is a therapeutic option used for the treatment of patients with HER2-overexpressing breast cancers. The primary purpose of the present study wasto establish a trastuzumab-based antibody drug conjugate (ADC) to enhance the biopharmaceutical profile of trastuzumab. In this study, trastuzumab was linked to the microtubule-disrupting agent monomethyl auristatin E (MMAE) through a peptide linker. Following conjugation, MMAE-trastuzumab ADCs were characterized using SDS-PAGE, UV/VIS, and cell-based ELISA. The inhibitory effects of the ADCs were measured on MDA-MB-453 (HER2-positive cells) and HEK-293 (HER2-negative cells) using in vitro cell cytotoxicity and colony formation assays. Our findings showed that approximately 3.4 MMAE payloads were conjugated to trastuzumab. MMAE-trastuzumab ADCs produced six bands, including H2L2, H2L, HL, H2, H, and L in non-reducing SDS-PAGE. The conjugates exhibited the same binding ability to MDA-MB-453 as unconjugated trastuzumab. The MTT assay showed a significant improvement in the trastuzumab activity following MMAE conjugation, representing ahigher antitumor activity as compared with unconjugated trastuzumab. Furthermore, ADCs were capable of potentially inhibiting colony formation in HER2-positive cells, as compared with trastuzumab. MMAE-trastuzumab ADCs represent a promising therapeutic strategy to treat HER2-positive breast cancer.

Phase Ib/II trial of tisotumab vedotin (TV) ± bevacizumab (BEV), pembrolizumab (PEM), or carboplatin (CBP) in recurrent or metastatic cervical cancer (innovaTV 205/ENGOT-cx8/GOG-3024).

TPS6095 Background: Patients (pts) with recurrent/metastatic cervical cancer (r/mCC) receive paclitaxel/platinum or paclitaxel/topotecan ± BEV as first-line standard-of-care therapy. Tissue factor (TF) expression has been associated with poor prognosis in solid tumors, and TF is highly expressed in r/mCC. TV is an investigational antibody-drug conjugate composed of a fully human, TF-directed monoclonal antibody covalently attached to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease-cleavable linker. Upon internalization, MMAE is released resulting in cell cycle arrest and apoptotic cell death. In pts with previously treated r/mCC, TV monotherapy (IV 2.0 mg/kg Q3W) demonstrated a manageable safety profile and encouraging antitumor activity (investigator-assessed confirmed ORR, 24%; median DOR, 4.2 mo) [Hong DS et al. Clin Cancer Res. 2019. doi: 10.1158/1078-0432.CCR-19-2962]. The preliminary safety and efficacy data for TV monotherapy suggest a positive benefit/risk profile and warrant further investigation of TV in combination with therapies commonly administered to pts with r/mCC. The global, open-label, phase Ib/II trial innovaTV 205/ENGOT-cx8/GOG-3024 (NCT03786081) evaluates the safety and antitumor activity of TV monotherapy and TV in combination with BEV, PEM, or CBP in pts with untreated or previously treated r/mCC. This abstract presents the new TV monotherapy weekly dosing schedule. Results from this study will inform the further clinical development of TV in the treatment of r/mCC. Methods: Approximately 170 adult pts with recurrent or stage IVB squamous, adenosquamous, or adenocarcinoma of the cervix; measurable disease; and ECOG PS 0-1 will be enrolled. The phase I part of the study will consist of 3 dose-escalation arms for identification of the recommended phase II dose (RP2D) of TV administered Q3W with BEV, PEM, or CBP. In this part, previously treated pts will receive escalating doses of TV (IV Q3W) in combination with escalating doses of BEV (IV Q3W), a fixed dose of PEM (IV Q3W), or a fixed dose of CBP (IV Q3W). The phase II part will include 4 expansion arms. In this phase, pts who have not received prior systemic therapy for r/mCC will receive 1) TV RP2D + PEM or 2) TV RP2D + CBP; pts who received 1-2 prior treatments for r/mCC will receive 3) TV RP2D + PEM or 4) TV monotherapy with weekly dosing (IV 3Q4W). The primary endpoint of phase II is ORR by RECIST v1.1. Secondary endpoints include DOR, time to response, PFS, OS, and safety. Clinical trial information: NCT03786081.

Brentuximab Vedotin in Front-Line Therapy of Hodgkin Lymphoma (HL) and CD30-Expressing Peripheral T-Cell Lymphoma (PTCL) in Adults Age 60 and Above

Background Despite the advances in therapy of classical Hodgkin lymphoma (cHL) and CD30-expressing peripheral T-cell lymphoma (PTCL) over the years, the outcomes seen in younger patients with the disease have not been attained in patients ≥60 years of age. Studies cite 5-year progression-free survival (PFS) and freedom from treatment failure rates of 30%-45% in older patients with HL, as compared to rates of 75%-80% expected in younger patients (Evens 2008; Proctor 2009). In a recent retrospective study of patients >60 years of age diagnosed with PTCL between 2008-2014, a multivariate analysis demonstrated that a Charlson Comorbidity Index (CCI) ≥2 and high IPI score (3-5) were independent risk factors for worse overall survival (OS) and PFS (Zhao 2016). Similarly, multivariate analysis of registry data from Sweden shows that a CCI ≥2, when adjusted for age, is independently associated with worse OS and PFS outcomes (Ellin 2018). There is no standard treatment regimen for elderly patients with cHL and PTCL, and co-morbidities including depressed cardiac and renal function limit the ability to use combination chemotherapy, and represent a high unmet need. Brentuximab vedotin (BV, ADCETRIS®) is a CD30-directed antibody-drug conjugate (ADC) consisting of the chimeric IgG1 antibody cAC10, specific for human CD30; the microtubule-disrupting agent monomethyl auristatin E (MMAE); and a protease-cleavable linker that covalently attaches MMAE to cAC10. Following the binding of BV to CD30-expressing cells, the ADC-CD30 complex is internalized, and MMAE released via proteolytic cleavage. Binding of MMAE to tubulin disrupts the microtubule network within the cell, subsequently inducing cell cycle arrest and apoptosis. Single-agent BV has demonstrated robust activity in patients with HL refractory to several lines of chemotherapy and the ECHELON-1 study (Connors 2017) established its efficacy in combination with chemotherapy for the front line treatment of HL. In a phase 2 study of single-agent BV in 27 patients aged ≥ 60 years with HL, there was an objective response rate of 92%, with 73% achieving complete remission (Forero-Torres, 2015). For CD30-expressing PTCL, single-agent BV is an active and well-tolerated treatment for patients with relapsed or refractory disease (Horwitz 2014) and the ECHELON-2 study showed that the addition of BV to combination chemotherapy in the frontline treatment improves both PFS and OS (Horwitz 2018). In the elderly patient populations who are not candidates for multi-agent chemotherapy, frontline treatment with single-agent BV may have the potential to be an active and well-tolerated treatment. Study Design Two additional cohorts have been added to the SGN35-015 phase 2 open-label study (NCT01716806) to evaluate the efficacy and tolerability of BV as monotherapy in treatment-naive patients with cHL, which excludes nodular lymphocyte-predominant HL (Part E) or treatment-naive patients with CD30-expressing PTCL (Part F). The primary objective of these cohorts is to assess objective response rates of single-agent BV as frontline therapy in patients ≥60 years of age and ineligible for conventional chemotherapy for HL (Part E) or CD30-expressing PTCL (Part F). Eligible patients in Parts E and F must be ≥75 years or ≥60 years of age and have one of the following: confirmed ejection fraction <45% or estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2 and <50 mL/min/1.73 m2, as determined by the Modification of Diet in Renal Disease study equation. Approximately 30 evaluable patients will be enrolled in Parts E and F of the study and administered BV 1.8 mg/kg as a single intravenous infusion on Day 1 of each 21-day cycle. Patients achieving a complete remission, partial remission, or stable disease will receive up to 16 cycles of treatment. Treatment response will be assessed by spiral CT scans of the chest, abdomen, and pelvis and PET scans at Cycles 2, 6, and 11. Response assessment will be determined by blinded independent central review. Disclosures Yasenchak: BMS: Consultancy; Seattle Genetics: Consultancy. Bordoni:Phillips & Gilmore: Honoraria; Genentech: Speakers Bureau; Merck: Speakers Bureau; Seattle Genetics, Inc.: Research Funding; Practice Point Communication: Honoraria; Deciphera: Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Honoraria; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Yazbeck:Celgene: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Gilead Sciences: Research Funding. Patel-Donnelly:Seattle Genetics, Inc.: Research Funding. Larson:Seattle Genetics, Inc.: Research Funding. Newhook:Seattle Genetics, Inc.: Employment. Ho:Seattle Genetics, Inc.: Employment, Equity Ownership. Mei:Seattle Genetics, Inc.: Research Funding.

Trastuzumab-monomethyl auristatin E conjugate exhibits potent cytotoxic activity in vitro against HER2-positive human breast cancer.

Targeted therapy using specific monoclonal antibodies (mAbs) conjugated to chemotherapeutic agents or toxins has become one of the top priorities in cancer therapy. Antibody-drug conjugates (ADCs) are emerging as a promising strategy for cancer-targeted therapy. In this study, trastuzumab, a humanized monoclonal anti-HER2 antibody, was reduced by dithiothreitol and conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE) through a valine-citrulline peptide linker (trastuzumab-MC-Val-Cit-PABC-MMAE [trastuzumab-vcMMAE]). After conjugation, ADCs were characterized by using UV-vis, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and flow cytometry. The antitumor activity of the ADC was evaluated in breast cancer cells in vitro. In addition, ADCs were further characterized using purification by the protein A chromatography, followed by assessment using apoptosis and MTT (3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assays. Hydrophobic interaction chromatography was used to determine drug-to-antibody ratio species of ADCs produced. Our finding showed that approximately 5.12 drug molecules were conjugated to each mAb. H2L2, H2L, HL, H2, H, and L forms of ADCs were detected in nonreducing SDS-PAGE. The binding of trastuzumab-vcMMAE to HER2-positive cells was comparable with that of the parental mAb. The MTT assay showed that our ADCs induced significant cell death in HER2-positive cells, but not in HER2-negative cells. The ADCs produced was a mixture of species, unconjugated trastuzumab (14.147%), as well as trastuzumab conjugated with two (44.868%), four (16.886%), six (13.238%), and eight (10.861%) molecules of MMAE. These results indicated that MMAE-conjugated trastuzumab significantly increases the cytotoxic activity of trastuzumab, demonstrating high affinity, specificity, and antitumor activity in vitro. Trastuzumab-vcMMAE is an effective and selective agent for the treatment of HER2-positive breast tumors.

Population PK and Exposure-Response Relationships for the Antibody-Drug Conjugate Brentuximab Vedotin in CTCL Patients in the Phase III ALCANZA Study.

The antibody–drug conjugate (ADC) brentuximab vedotin consists of the CD30‐directed antibody attached to the microtubule‐disrupting agent monomethyl auristatin E (MMAE). In pharmacokinetic models, including data from six studies (380 patients with classical Hodgkin's, systemic anaplastic large‐cell, and cutaneous T‐cell (CTCL) lymphomas), lower clearance of ADC and modestly higher ADC exposure in CTCL patients did not translate into higher MMAE exposure. In CTCL patients from the phase III ALCANZA study (n = 66), improved progression‐free survival with brentuximab vedotin vs. controls was not related to ADC exposure. ADC exposure was a predictor of grade ≥3 treatment‐emergent adverse events (TEAEs). Results support the consistent benefit observed with brentuximab vedotin 1.8 mg/kg every 3 weeks across the range of exposures in ALCANZA and support dose reductions in patients experiencing TEAEs at the starting dose.

EV-103 study: A phase 1b dose-escalation and dose-expansion study of enfortumab vedotin in combination with immune checkpoint inhibitor (CPI) therapy for treatment of patients with locally advanced or metastatic urothelial cancer.

TPS532 Background: Immune checkpoint inhibitors (CPIs) are approved for patients (pts) with locally advanced or metastatic urothelial cancer (la/mUC) who progress on prior platinum or are ineligible for first line cisplatin. However, only a minority of pts respond to CPI monotherapy and a combination approach may be beneficial. Enfortumab vedotin (EV), an antibody-drug conjugate (ADC), delivers the microtubule-disrupting agent monomethyl auristatin E (MMAE) to tumors expressing Nectin-4, which is overexpressed in mUC. Preliminary results from an ongoing phase 1 study of EV monotherapy in pts with mUC (Petrylak ASCO 2017) showed that EV was well tolerated in pts with mUC. EV showed a 41% (29 out of 71 pts) objective response rate (ORR) across all doses (24 wks median response duration). In pts with liver metastasis the ORR was 47% (9 out 19 pts) across all doses. Preclinical data show that an MMAE ADC, but not the unconjugated antibody, increases tumor immunogenicity by inducing immunogenic cell death, antigen presentation and tumor immune infiltration (Gardai 2015). Based on encouraging phase 1 study results and potential enhanced immune response, combining EV with a CPI may result in improved response rates with longer durability. Methods: This phase 1b study (NCT03288545) evaluates the safety/activity of EV + CPI in pts with la/mUC who have not previously received a CPI. The study has 2 parts: dose escalation (EV + pembrolizumab) and dose expansion (EV + CPI [pembrolizumab or atezolizumab]). Pts must have la/m transitional cell carcinoma of the urothelium, be eligible for treatment with a CPI, and be either ineligible for first-line cisplatin-based chemotherapy or have disease progression during or following treatment with ≥1 platinum-containing regimen. The primary objective is to assess the safety/tolerability of EV + CPI. Secondary objectives include determining a recommended dose of EV + CPI in pts with la/mUC, antitumor activity as measured by ORR, disease control rate, duration of response, PFS, and OS. Response is assessed per RECIST v1.1 and iRECIST. Study enrollment began in Oct 2017. Clinical trial information: NCT03288545.

AGS67E, an Anti-CD37 Monomethyl Auristatin E Antibody-Drug Conjugate as a Potential Therapeutic for B/T-Cell Malignancies and AML: A New Role for CD37 in AML.

CD37 is a tetraspanin expressed on malignant B cells. Recently, CD37 has gained interest as a therapeutic target. We developed AGS67E, an antibody-drug conjugate that targets CD37 for the potential treatment of B/T-cell malignancies. It is a fully human monoclonal IgG2 antibody (AGS67C) conjugated, via a protease-cleavable linker, to the microtubule-disrupting agent monomethyl auristatin E (MMAE). AGS67E induces potent cytotoxicity, apoptosis, and cell-cycle alterations in many non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL) cell lines and patient-derived samples in vitro. It also shows potent antitumor activity in NHL and CLL xenografts, including Rituxan-refractory models. During profiling studies to confirm the reported expression of CD37 in normal tissues and B-cell malignancies, we made the novel discovery that the CD37 protein was expressed in T-cell lymphomas and in AML. AGS67E bound to >80% of NHL and T-cell lymphomas, 100% of CLL and 100% of AML patient-derived samples, including CD34(+)CD38(-) leukemic stem cells. It also induced cytotoxicity, apoptosis, and cell-cycle alterations in AML cell lines and antitumor efficacy in orthotopic AML xenografts. Taken together, this study shows not only that AGS67E may serve as a potential therapeutic for B/T-cell malignancies, but it also demonstrates, for the first time, that CD37 is well expressed and a potential drug target in AML.

Abstract OT2-3-01: SGN-LIV1A: A phase 1 trial evaluating a novel antibody-drug conjugate in patients with LIV-1-positive breast cancer

Abstract Background First identified as an estrogen-inducible gene in a breast cancer cell line, LIV-1 is a multispan transmembrane protein of the solute-carrier family 39 with putative zinc transporter and metalloproteinase activity. As a downstream target of STAT3, it promotes the epithelial-to-mesenchymal transition that is important in the malignant progression to metastasis. LIV-1 is expressed in a number of cancers with the highest prevalence and level of expression in breast, prostate, and melanoma. Additionally, LIV-1 has been linked with malignant progression to metastasis and associated with lymph node involvement in breast cancer. Normal tissue expression is predominantly limited to hormonally regulated tissues, including breast and prostate. In metastatic breast cancer tissue samples, the current validated immunohistochemistry assay for LIV-1 has detected moderate to high expression in 82% of samples tested, with 88% positivity in hormone receptor-positive tumors and 73% in triple-negative tumors. SGN-LIV1A is an antibody-drug conjugate (ADC) composed of a humanized anti-LIV-1 monoclonal antibody conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease-cleavable linker. In vitro, SGN-LIV1A shows target-specific internalization and cytotoxic activity against LIV-1-positive neoplastic cell lines. Significant dose-dependent tumor regression was demonstrated in mouse xenograft models. Methods The primary objective of this first-in-human phase 1, open label, multicenter study is to evaluate the safety and tolerability, and to identify the maximum tolerated dose of SGN-LIV1A using a 3+3 dose-escalation study design. Pharmacokinetics, immunogenicity, and antitumor activity will also be evaluated (ClinicalTrials.gov #NCT01969643). Enrollment to this US-based trial began in late 2013. Eligible patients are adult females who have hormone receptor-positive/HER2-negative or triple-negative metastatic breast cancer. Tumor tissue must be positive for expression of LIV-1 per central assessment. Patients must have received at least 2 prior cytotoxic regimens in the metastatic setting and have measurable disease per RECIST v1.1. Pre-existing neuropathy ≥ Grade 2 is not permitted. SGN-LIV1A is administered intravenously every 3 weeks at protocol-defined doses starting at 0.5 mg/kg. Patients who achieve an objective response or stable disease per RECIST v1.1 are eligible to continue treatment until disease progression. At the completion of dose escalation, expansion cohorts may be opened to enroll patients with specific breast cancer subtypes to further define safety and antitumor activity. Tumor biopsies are being obtained at baseline and after one cycle of treatment to evaluate the role of LIV-1 expression, target saturation, and other tumor-specific measurements in the antitumor activity of SGN-LIV1A. Citation Format: Andres Forero, Howard Burris III, Patricia LoRusso, Jennifer Specht, Kathy Miller, Monica Mita, Minetta C Liu, Shanu Modi, Lajos Pusztai, Django Sussman, Ana Kostic. SGN-LIV1A: A phase 1 trial evaluating a novel antibody-drug conjugate in patients with LIV-1-positive breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr OT2-3-01.

Anti-CD22 and anti-CD79B antibody drug conjugates are active in different molecular diffuse large B-cell lymphoma subtypes.

Antibody drug conjugates (ADCs), in which cytotoxic drugs are linked to antibodies targeting antigens on tumor cells, represent promising novel agents for the treatment of malignant lymphomas. Pinatuzumab vedotin is an anti-CD22 ADC and polatuzumab vedotin an anti-CD79B ADC that are both linked to the microtubule-disrupting agent monomethyl auristatin E (MMAE). In the present study, we analyzed the activity of these agents in different molecular subtypes of diffuse large B-cell lymphoma (DLBCL) both in vitro and in early clinical trials. Both anti-CD22-MMAE and anti-CD79B-MMAE were highly active and induced cell death in the vast majority of activated B-cell-like (ABC) and germinal center B-cell-like (GCB) DLBCL cell lines. Similarly, both agents induced cytotoxicity in models with and without mutations in the signaling molecule CD79B. In line with these observations, relapsed and refractory DLBCL patients of both subtypes responded to these agents. Importantly, a strong correlation between CD22 and CD79B expression in vitro and in vivo was not detectable, indicating that patients should not be excluded from anti-CD22-MMAE or anti-CD79B-MMAE treatment because of low target expression. In summary, these studies suggest that pinatuzumab vedotin and polatuzumab vedotin are active agents for the treatment of patients with different subtypes of DLBCL.