Investigational Antibody-drug Conjugate Research Articles

Abstract CT077: An open-label phase 1 study to investigate SGN-CEACAM5C in adults with advanced solid tumors (SGNCEA5C-001, Trial in Progress)

Abstract Background Patients (pts) with recurrent or metastatic solid tumors, including non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), colorectal cancer (CRC), gastric adenocarcinoma (GC), and pancreatic ductal adenocarcinoma (PDAC), have limited treatment options with short PFS and OS despite recent advances (Bordry 2021; Chakrabarti 2022; Merle 2022). Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) is highly expressed across multiple solid tumors, such as CRC, GC, PDAC, and NSCLC. Restricted normal tissue expression and efficient lysosomal trafficking of CEACAM5 highlight its potential as an anticancer target. SGN-CEACAM5C is a novel investigational antibody-drug conjugate (ADC) directed to CEACAM5 composed of the humanized immunoglobulin G (IgG1) anti-CEACAM5 monoclonal antibody tusamitamab chemically conjugated to 8 molecules of the topoisomerase 1 inhibitor 7-aminomethyl-10,11-methylenedioxycamptothecin (AMDCPT). SGN-CEACAM5C selectively binds to CEACAM5 present on the cell surface and is internalized via the endo-lysosomal pathway, with subsequent release of the payload through enzymatic cleavage. Release of the cytotoxic payload induces DNA damage, cell cycle arrest in S phase, and apoptosis in tumor cells. In vitro bystander activity was observed against tumor cells without CEACAM5 surface expression. SGN-CEACAM5C is highly active in multiple patient-derived xenograft models, including CRC, GC, and NSCLC, across various levels of CEACAM5 expression (Baudat 2023; Baudat 2024). These preclinical findings justify evaluation of SGN-CEACAM5C in a clinical trial setting. Methods SGNCEA5C-001 (NCT06131840) is a phase 1, open-label, multicenter study designed to characterize the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary antitumor activity of SGN-CEACAM5C in adults with select advanced solid tumors. This study consists of dose escalation (Part A), dose and schedule optimization (Part B), and dose expansion (Part C). Eligible pts are adults ≥18 years of age with confirmed metastatic or unresectable solid tumor malignancy, measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1, an ECOG PS of 0-1, and 1 of the following tumor types: CRC, GC/gastroesophageal junction adenocarcinoma (GEJ), PDAC, NSCLC (squamous/non-squamous), or SCLC. Primary endpoints include incidence of AEs, laboratory abnormalities, dose modifications due to AEs, dose-limiting toxicities, and cumulative safety. Secondary endpoints include estimates of PK parameters, incidence of antidrug antibodies, objective response rate and best response per RECIST v1.1 by investigator, duration of response, PFS, and OS. Safety and antitumor activity endpoints will be summarized using descriptive statistics. Recruitment is ongoing for Part A in North America. Citation Format: Funda Meric-Bernstam, Cesar A. Perez, Nehal Lakhani, Meredith Pelster, Justin Call, Suzanne McGoldrick, Tianhua Wang, Brigitte Demers, Amita Patnaik. An open-label phase 1 study to investigate SGN-CEACAM5C in adults with advanced solid tumors (SGNCEA5C-001, Trial in Progress) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT077.

Abstract B145: Clinical features of progression and outcomes with subsequent therapies in patients treated with RET-inhibitors

Abstract Background: RET fusions can be found in 1-2% of patients (pts) with advanced non-small cell lung cancer (aNSCLC). While targeted treatment with RET inhibitors (RETi) has significantly improved prognosis, resistance eventually develops. Current knowledge regarding the pattern of disease progression and the optimal therapeutic sequence for patients treated with RETi is limited. Methods: We conducted a retrospective multicentric collection of clinical and biological data on pts with RET-rearranged (RET+) aNSCLC treated with first-generation RETi. Patients with a progression-free survival (PFS) period of less than 8 months on RETi were classified as poor responders. We investigated the clinical patterns of disease progression (PD) and outcomes with subsequent therapies, evaluated by the overall response rate (ORR by investigator assessment) and PFS. PFS2 was calculated from RETi start to PD after subsequent line. Results: 173 pts from 32 centres were identified. Median age was 65, 61% were female, 41% were smokers, 81% had an ECOG performance status <2, 95% had adenocarcinoma, 18% had brain metastasis, 76% had RETi in first or second line. The administered RETi were selpercatinib in 55%, pralsertinib in 42%, other first generation RETi in 3% of pts. After a median follow up of 30.4 months (mo) (95%CI 26-32.1), 84 pts (48.6%) had PD after RETi, with a median PFS (mPFS) of 15.6 mo (95%CI 12.2-23.3) and an ORR of 72.2%. Radiological PD patterns included multisite PD in 46 (71%), oligoPD in 15 (23%), mixed response in 4 (6%). 7/15(47%) received local treatment while continuing RETi. Subsequent treatment line after RETi was administered in 37 pts (21%). Considering chemotherapy-based treatments, ORR and mPFS were 46% and 5.52 mo (4.07-11.3) overall, 57% and 4.53 mo (95%CI 1.4-NA) in 9 pts with chemo-immunotherapy, 27% and 5.88 mo (95%CI 2.1-NA) in 11 pts with platinum-doublet, 83% and 10.4 mo (8.28-NR) in 6 pts with bevacizumab plus chemotherapy (p=0.77 vs chemotherapy alone). Targeted therapy was administered in 8 patients: 6 received RETi after RETi (first generation) with 33% ORR and 3.83 mo (1.77-NR) mPFS, one patient had crizotinib plus RETi to target MET amplification found at resistance, with a PFS of 5.95 mo, one had alectinib alone, targeting SQSTM1-ALK fusion found at resistance, with PD after 1.58 mo. Cabozantinib was chosen for one pt, with a PFS of 5.52 mo and obtaining PR; one pt was treated with single-agent immunotherapy, with rapid PD after 1 month; one pt had an investigational antibody-drug conjugate, experiencing SD and a 4 mo PFS. PFS to subsequent treatment was not different between long and poor responders to RETi (13 and 15 pts,5.88 vs 4.53 m, respectively, p=0.75); PFS2 was longer in good responders to RETi (25 vs 16 mo,p=0.012). Conclusions: Disease progression to RETi most frequently involved multiple sites. Chemotherapy plus bevacizumab seemed to perform better than chemotherapy alone or chemo-immunotherapy. The benefit of tailored treatment basing on the molecular profile at PD needs to be further explored. Citation Format: Arianna Marinello, Wael Salem Zrafi, Giacomo Massa, Fabrizio Tabbò, Fabrizio Citarella, Filippo Gustavo Dall'Olio, Lindsay Colin, Emilio Bria, Giulio Metro, Josè Nicolas Minatta, Antonio Calles, Isabelle Monnet, Marco Tagliamento, Hortense Gaultier De Saint Basile, Nicolas Girard, Arianna Pagliaro, Diego Luigi Cortinovis, Judith Raimbourg, Carol Zanchetta, Giannis Mountzios, Frank Aboubakar Nana, Safae Terrisse, Alessandro Russo, Patricia Iranzo, Clarisse Audigier-Valette, Philippe Rochigneux, Vincent Fallet, Michael Duruisseaux, Sophie Cousin, Florian Guisier, Laura Mezquita, Jordi Remon, Anas Gazzah, David Planchard, Benjamin Besse, Mihaela Aldea. Clinical features of progression and outcomes with subsequent therapies in patients treated with RET-inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B145.

A sensitive and rapid LC-MS/MS assay for quantitation of free payload Aur0101 from antibody drug conjugate (ADC) PYX-201 in human plasma

PYX-201 is an investigational antibody drug conjugate (ADC) with an engineered, fully human IgG1 antibody, a cleavable chemical linker, and a toxin (Aur0101) with an average drug-antibody ratio (DAR) of ∼ 4. A sensitive and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and fully validated to determine the presence in human plasma, of free payload Aur0101 from PYX-201 to assess drug safety and efficacy. Aur0101 and its deuterated internal standard (IS), Aur0101_d8, were extracted from 25 µL of human plasma using a solid liquid extraction (SLE) method. Chromatographic analysis was carried out on a Waters Acquity UPLC BEH C18 (2.1 mm × 50 mm, 1.7 µm, 130 A) column. Quantitation of free Aur0101 was conducted on a Sciex triple quadrupole mass spectrometer API 6500 + using multiple reaction monitoring (MRM) mode via positive electrospray ionization. The calibration curve was linear over the concentration range of 25.0 to 12,500 pg/mL with correlation coefficient, r2 ≥ 0.9988. The intra-assay %RE was between −4.3% to 14.3% with % CV was ≤ 6.2%. The inter–assay %RE was between −0.2% to 9.5% with % CV was ≤ 6.1%. The average analyte recovery was 89.7% and the average IS recovery was 88.7%. Aur0101 was found to be stable in human plasma and human whole blood under various tested conditions with and without the presence of PYX-201. To our knowledge, this is the first published fully validated assay for free, unconjugated Aur0101 in any matrix, from any species. This assay has been successfully applied to clinical sample analysis to support clinical studies.

Abstract OT1-03-06: Phase 1b/2 study of ladiratuzumab vedotin (LV) in combination with pembrolizumab for first-line treatment of triple-negative breast cancer (SGNLVA-002, trial in progress)

Abstract Background Patients with metastatic triple-negative breast cancer (mTNBC) have a poor prognosis. Treatment combinations of anti-programmed death protein 1 (anti–PD-1) agents with chemotherapy have shown promise in mTNBC. Ladiratuzumab vedotin (LV) is an investigational antibody-drug conjugate directed to LIV-1, a protein highly expressed on breast cancer cells, via a humanized IgG1 monoclonal antibody conjugated to approximately 4 molecules of monomethyl auristatin E (MMAE) by a protease-cleavable linker. LIV-1–mediated delivery of MMAE disrupts microtubules and induces cell cycle arrest and apoptosis. LV has also been shown to drive immunogenic cell death (ICD) to elicit an immune response. LV + pembrolizumab may result in synergistic activity through LV-induced ICD, creating a microenvironment favorable for enhanced anti–PD-1 activity. Interim results from an ongoing, multi-part, open-label study investigating the safety and efficacy of LV in patients with metastatic breast cancer (SGNLVA-001, NCT01969643), showed weekly LV monotherapy at doses up to 1.5 mg/kg were clinically active and generally well tolerated (Tsai 2021). Based on pharmacokinetic and pharmacodynamic modeling and simulation analysis, an intermittent LV + pembrolizumab dosing regimen is being evaluated to further enhance efficacy and improve the tolerability profile. Due to an unmet medical need for patients with unresectable locally advanced (LA)/mTNBC who are programmed death ligand 1 (PD-L1) low or negative, Part D will focus on this patient population. Trial Design SGNLVA-002 (NCT03310957) is an ongoing global single-arm, open-label phase 1b/2 study of LV + pembrolizumab as 1L therapy for patients with unresectable LA/mTNBC. Part D is currently enrolling ~40 patients. Eligible patients must have advanced disease with no prior cytotoxic/anti–PD-1 treatment, PD-L1 combined positive score < 10, measurable disease per RECIST v1.1, and an ECOG performance status ≤1. Patients with Grade ≥2 pre-existing neuropathy or active central nervous system metastases are not permitted. Patients will receive LV at 1.5 mg/kg on Days 1 and 8 every 21 days plus pembrolizumab 200 mg on Day 1 q3w. The primary objectives are to evaluate the safety/tolerability and objective response rate of LV + pembrolizumab. Secondary objectives include duration of response, disease control rate, progression-free survival, and overall survival. Safety and efficacy endpoints will be summarized with descriptive statistics. Global enrollment is ongoing in the US, EU, and Asia. Citation Format: Patrick Dillon, Reva Basho, Hyo S. Han, Hans-Christian Kolberg, Katherine Tkaczuk, George Zahrah, Maria Gion, Herman Voss, Jane Meisel, Timothy Pluard, Jenny Fox, Mafalda Oliveira, Ursa Brown-Glaberman, Erica Stringer-Reasor, Luis Manso, Sherko Küemmel, Lin Chi Chen, Sheng Wu, Brandon Croft, Valentina Boni. Phase 1b/2 study of ladiratuzumab vedotin (LV) in combination with pembrolizumab for first-line treatment of triple-negative breast cancer (SGNLVA-002, trial in progress) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT1-03-06.

Phase 2 clinical study evaluating the efficacy and safety of disitamab vedotin with or without pembrolizumab in patients with HER2-expressing urothelial carcinoma (RC48G001).

TPS594 Background: Urothelial carcinoma (UC) is the 10th most diagnosed cancer worldwide, and nearly 50% of patients cannot tolerate the current first-line (1L) standard of care. There is a need to improve outcomes in 1L and later lines of therapy. HER2 is overexpressed in UC and may be associated with poor outcomes. Despite this, no HER2-directed therapies are currently approved for UC. Disitamab vedotin (DV; RC48-ADC) is an investigational antibody-drug conjugate comprising a novel HER2-directed monoclonal antibody, disitamab, conjugated to monomethyl auristatin E (MMAE) via a protease-cleavable mc-vc linker. DV elicits antitumor activity through multimodal mechanisms of action including MMAE-mediated direct cytotoxicity, bystander effect, and immunogenic cell death. Methods: RC48G001 (NCT04879329) is a phase 2, multi-cohort, open-label, multicenter trial to evaluate DV in patients with HER2-expressing locally advanced/metastatic UC (LA/mUC). Patients are enrolled in 3 cohorts based on prior treatment and tumor HER2 expression by immunohistochemistry (IHC) and gene amplification (via in situ hybridization [ISH]), assessed centrally. Cohorts A and B are enrolling patients who have received prior systemic therapy (1 or 2 lines, including platinum-containing chemotherapy) and whose tumors are HER2-positive (IHC 3+, or 2+ and ISH-positive) or HER2-low (IHC 2+ and ISH-negative, or IHC 1+), respectively. Cohort C is enrolling 1L treatment-naive patients in the LA/mUC setting, whose tumors have HER2-positive or HER2-low expression. Cohorts A and B will evaluate DV as monotherapy (intravenous [IV] administration, once every 2 weeks [Q2W]). Cohort C will evaluate DV (IV, Q2W) +/– pembrolizumab (IV, Day 1 of each 6-week cycle). Patients in all cohorts must have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 and an Eastern Cooperative Oncology Group Performance Status of 0–1 in Cohorts A and B, and 0–2 in Cohort C. The primary endpoint is confirmed objective response rate (cORR) per blinded independent central review (BICR). Secondary endpoints include cORR by investigator assessment, overall survival, duration of response, progression-free survival, disease control rate per RECIST v1.1 by BICR and investigator, safety, and pharmacokinetic parameters. Enrollment for all cohorts is ongoing in North America and Europe, and planned in Latin America, Asia-Pacific, and Israel. Clinical trial information: NCT04879329 .

1779TiP Phase II clinical study evaluating the efficacy and safety of disitamab vedotin in patients (pts) with HER2-expressing urothelial carcinoma (RC48G001)

More than 212,000 deaths annually are related to bladder cancer worldwide (Sung 2021), with 5-year survival rates of <5% in metastatic urothelial carcinoma (UC) (Witjes 2021). Nearly half of all pts cannot tolerate standard cisplatin-based first line (1L) chemotherapy and opportunity still exists to improve outcomes in both 1L and later lines of therapy. Human epidermal growth factor receptor 2 (HER2) is overexpressed in multiple malignant tumors and overexpression of HER2 may be associated with poor outcomes in UC (Zhao 2015). No HER2-directed therapies are currently approved for locally advanced unresectable or metastatic UC (LA/mUC). Disitamab vedotin (DV; RC48-ADC) is an investigational antibody–drug conjugate (ADC) comprised of a HER2-directed monoclonal antibody conjugated to monomethyl auristatin E (MMAE) via a protease-cleavable linker. DV elicits antitumor activity through MMAE-directed cytotoxicity and bystander effect (Li 2020). DV is conditionally approved in LA/mUC and gastric cancer in China and was granted Breakthrough Therapy designation by the FDA for second-line treatment of HER2-expressing LA/mUC after platinum-containing chemotherapy. RC48G001 (NCT04879329) is a phase 2, multicohort, open-label, multicenter trial to evaluate DV in pts with HER2-expressing LA/mUC. Pts are enrolled in 2 cohorts defined by HER2 expression (by immunohistochemistry [IHC]) and gene amplification (by in situ hybridization [ISH]) by central laboratory: Cohort A (IHC 3+, or 2+ and ISH+) and Cohort B (IHC 2+ and ISH-, or IHC 1+). Eligible pts must have measurable disease per RECIST v1.1, ECOG Performance Status of 0 or 1, and must have received 1 or 2 lines of prior systemic therapy, including 1 line of platinum-containing chemotherapy. The primary endpoint is confirmed objective response rate (ORR) assessed by blinded independent central review. Secondary endpoints include ORR assessed by investigator, duration of response, progression-free survival, disease control rate, overall survival, safety, and pharmacokinetic parameters. Enrollment for cohorts A and B is ongoing in North America and EU, and planned in LATAM, APAC, and Israel. NCT04879329. Under guidance of the authors, assistance in medical writing was provided by Hanna Thomsen, PhD, of Seagen Inc. and was funded by Seagen Inc. in accordance with Good Publication Practice (GPP3) guidelines. Seagen Inc.

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 1281: SGN-B7H4V shows immunomodulatory activity through induction of immunogenic cell death

Abstract SGN-B7H4V is a novel investigational antibody-drug conjugate composed of a B7-H4-directed human monoclonal antibody conjugated to the validated vedotin drug linker, which incorporates the microtubule disrupting agent monomethyl auristatin E (MMAE) via a protease-cleavable peptide linkage. This vedotin drug linker system has been clinically validated by multiple ADC programs, including brentuximab vedotin, enfortumab vedotin, tisotumab vedotin, and polatuzumab vedotin. B7-H4 is an immune checkpoint ligand with elevated expression on a variety of solid tumor types, including breast, ovarian, and endometrial tumors. SGN-B7H4V is designed to bind and internalize the B7-H4/ADC complex from the surface of malignant cells and release the cytotoxic payload MMAE. The antitumor activity of SGN-B7H4V may be multimodal as SGN-B7H4V can induce tumor cell death through several mechanisms, including MMAE-mediated direct cytotoxicity and bystander killing as well as antibody-mediated functions including antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP). Previously, vedotin ADCs have been described to elicit antitumor immune responses in part through induction of immunogenic cell death (ICD) mediated by the MMAE payload. These immunomodulatory effects potentially position vedotin ADCs to uniquely synergize with checkpoint inhibitors, supported by recent clinical activity observed when vedotin ADCs are paired with anti-PD1 agents. Here, we characterize SGN-B7H4V-mediated ICD and subsequent immunomodulatory activity. We also evaluate the contribution of SGN-B7H4V-induced immune activation to antitumor activity in combination with an anti-PD1 agent in an immunocompetent mouse model. In vitro, tumor cells treated with SGN-B7H4V showed several hallmarks of immunogenic cell death, including calreticulin exposure and release of ATP. In vivo, treatment of B7-H4-expressing tumors with SGN-B7H4V led to immune changes in the tumor microenvironment, including recruitment of macrophages and T cells. Finally, SGN-B7H4V drove robust, curative activity in an immunocompetent tumor model as a monotherapy and paired well with an anti-PD1 agent. Altogether, these data support the evaluation of SGN-B7H4V as a monotherapy in a first-in-human phase 1 clinical study and potential future clinical combinations with immunotherapies. Citation Format: Elizabeth E. Gray, Michelle Ulrich, Angela Epp, Patrick Younan, Kelly Hensley, Sean Allred, Julie Hahn, Kristen Gahnberg, Piper M. Treuting, John J. Gosink, Robert Thurman, Alyson J. Smith, Jason Schrum, Natalya Nazarenko, Shyra J. Gardai. SGN-B7H4V shows immunomodulatory activity through induction of immunogenic cell death [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 1281.

Phase 1b/2 study of ladiratuzumab vedotin (LV) in combination with pembrolizumab for first-line treatment of triple-negative breast cancer (SGNLVA-002, trial in progress).

TPS1127 Background: Patients with metastatic triple-negative breast cancer (mTNBC) have a poor prognosis. Treatment combinations of anti-programmed death ligand 1 (anti–PD-L1) agents with chemotherapy have shown promise in mTNBC. LV is an investigational antibody–drug conjugate directed to LIV-1, a protein highly expressed on breast cancer cells, via a humanized IgG1 monoclonal antibody conjugated to monomethyl auristatin E (MMAE) by a protease-cleavable linker. LIV-1–mediated delivery of MMAE disrupts microtubules and induces cell cycle arrest and apoptosis. LV has also been shown to drive immunogenic cell death (ICD) to elicit an immune response. LV + pembrolizumab may result in synergistic activity through LV-induced ICD, creating a microenvironment favorable for enhanced anti–PD-L1 activity. Preliminary results show LV delivered once every 3 weeks (Q3W) + pembrolizumab was tolerable with encouraging antitumor activity in patients with mTNBC (Han 2019). Additionally, interim results of weekly LV monotherapy at doses up to 1.5 mg/kg were clinically active and generally well tolerated (Tsai 2021). Based on pharmacokinetic and pharmacodynamic modeling and simulation analysis, an intermittent LV + pembrolizumab dosing regimen is being evaluated to further enhance efficacy and improve the tolerability profile. Due to an unmet medical need for patients with mTNBC who are PD-L1 low or negative, Part D will focus on this patient population. Methods: SGNLVA-002 (NCT03310957) is an ongoing global single-arm, open-label phase 1b/2 study of LV + pembrolizumab as 1L therapy for patients with unresectable locally advanced/mTNBC. Part D is currently enrolling ̃40 patients. Eligible patients must have advanced disease with no prior cytotoxic/anti–PD-L1 treatment, PD-L1 combined positive score &lt; 10, measurable disease per RECIST v1.1 and an ECOG score ≤1. Patients with Grade ≥2 pre-existing neuropathy or active central nervous system metastases are not permitted. Patients will receive LV at 1.5 mg/kg on Days 1 and 8 plus pembrolizumab 200 mg on Day 1 Q3W. The primary objectives are to evaluate the safety/tolerability and objective response rate of LV + pembrolizumab. Secondary objectives include duration of response, disease control rate, progression-free survival, and overall survival. Safety and efficacy endpoints will be summarized with descriptive statistics. Global enrollment is ongoing in the US, EU, and Asia. Clinical trial information: NCT03310957.

556TiP A phase I study of SGN-STNV, a novel antibody–drug conjugate targeting sialyl-thomsen-nouveau antigen (STn), in adults with advanced solid tumors (SGNSTNV-001)

STn is a tumor-associated carbohydrate antigen with high prevalence across various solid tumor types, including ovarian and non-small cell lung cancer (NSCLC). While its expression is restricted in normal tissues, it presents with several tumor-associated proteins, such as MUC1 and MUC16. STn is thought to influence cancer progression by affecting cell adhesion, migration and propagation of invasiveness, and has been linked to advanced disease, chemotherapy resistance, and decreased survival. SGN-STNV is an investigational antibody–drug conjugate which directs monomethyl auristatin E (MMAE) to STn-expressing cells.

555TiP A first-in-human trial of the integrin beta-6-targeted antibody–drug conjugate, SGN-B6A, in patients with advanced solid tumors

The integrins comprise a multifaceted family of membrane-associated proteins that regulate cellular adhesion, motility and cytokinesis. Higher levels of integrin beta-6 predict poorer outcomes in patients with solid tumors such as colorectal, non-small cell lung, gastric and cervical cancers. The vedotin SGN-B6A is an investigational antibody–drug conjugate designed to deliver the cytotoxic agent monomethyl auristatin E (MMAE) to integrin beta-6-expressing cells. Once internalized, intracellular MMAE disrupts microtubules causing cell cycle arrest and apoptosis.

930TiP innovaTV 207: New dosing cohort in the open label phase II study of tisotumab vedotin in solid tumors

Tisotumab vedotin (TV) is an investigational antibody-drug conjugate directed to Tissue Factor (TF). In the phase I/II innovaTV 201 and phase II innovaTV 204 studies, TV demonstrated encouraging antitumor activity with a manageable safety profile in patients (pts) with multiple TF-expressing tumor types. The innovaTV 207 trial is a global, open label, multicenter phase II trial assessing the safety, tolerability, and activity of TV in solid tumors known to express TF. This abstract presents the addition of Part C, testing TV in squamous non-small cell lung cancer (NSCLC) and squamous cell carcinoma of the head and neck (SCCHN).

Abstract 914: Activity of SGN-B6A in patient-derived xenograft models of non-small cell lung cancer

Abstract The integrins are a large family of cell surface receptors with diverse roles in cellular adhesion, motility, and cytokinesis. Functional integrins exist as heterodimers consisting of single alpha and beta chains. Within this family, integrin beta-6, which dimerizes exclusively with isoform alpha-v, is expressed constitutively at low levels in numerous epithelial tissues and induced by tissue injury due to its role in tissue remodeling and wound repair. Numerous solid tumors, including non-small cell lung cancer (NSCLC), have been reported to overexpress integrin beta-6. Its role in tissue remodeling is believed to be the function that malignant cells exploit through its overexpression, allowing them to become more invasive into surrounding healthy tissue. Integrin beta-6 has also been reported to be among the integrins that can promote the epithelial to mesenchymal transition as well as provide resistance to anoikis, thus increasing the metastatic potential of malignant cells expressing it. SGN-B6A is an investigational antibody-drug conjugate (ADC) targeting integrin beta-6 to deliver the clinically validated payload monomethyl auristatin E (MMAE). We have previously presented data illustrating the antitumor activity of SGN-B6A in cell line-derived xenograft models originating from multiple carcinoma indications. Here we present results from a study of SGN-B6A activity dosed weekly at 3 mg/kg in patient-derived xenograft models of NSCLC, representing both squamous and adenocarcinoma histology. These results suggest that SGN-B6A is a promising ADC for the treatment of NSCLC and support further clinical investigation in the ongoing Phase I study (NCT04389632). Citation Format: Robert P. Lyon, John J. Gosink, Christopher J. Hale, Jackie L. Stilwell, Sean Allred, Kelly M. Hensley, Vineet Kumar, Gabby Patilea-Vrana, Natalya Nazarenko. Activity of SGN-B6A in patient-derived xenograft models of non-small cell lung cancer [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 914.

Abstract 50: Targeting Sialyl-Thomsen nouveau (STn) antigen with the SGN-STNV antibody-drug conjugate is effective in preclinical studies

Abstract Targeting glyco-epitopes with antibody-drug conjugates (ADCs) provides a unique advantage as multiple cell surface proteins expressing the same carbohydrate can be harnessed to deliver drug. Sialyl-Thomsen nouveau (STn) is a tumor associated carbohydrate antigen that has historically been difficult to target with specificity. Using glycan array screening, h2G12 was identified as a highly specific human IgG1 antibody, that exclusively binds the STn glyco-epitope independent of protein backbone. Here we introduce SGN-STNV, an investigational antibody-drug conjugate (ADC) targeting monomethyl auristatin E (MMAE) to STn expressing tumor cells with the clinically validated vedotin linker technology. STn has restricted normal tissue expression and is expressed on various solid tumors including ovarian, non-small cell lung, gastric, and endometrial carcinomas. Our work shows correlation of enzyme ST6GALNAC1 expression with STn expression on tumors. Given the frequent O-glycosylation of mucins, we also confirmed high STn expression in mucinous subtypes of ovarian, pancreatic, colorectal, and lung adenocarcinomas. Previous reports have confirmed STn is found on mucins MUC1, MUC5A, and MUC16 (CA-125), as well as cell surface receptors CD44 and integrin β1. These proteins are known to play functional roles in tumor progression and, importantly for ADC delivery, they internalize well to deliver cytotoxic payload. We sought to identify other proteins that may contribute to cytotoxic activity of SGN-STNV and determined that additional surface receptors are tagged with STn. These receptors are internalized and likely contribute to SGN-STNV activity. After binding to STn, SGN-STNV is internalized into cells and releases the microtubule inhibitor MMAE to drive mitotic arrest, apoptosis, and to induce immunogenic cell death. SGN-STNV further mediates anti-tumor response through Fc-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). In preclinical xenograft studies, SGN-STNV monotherapy treatment leveraged h2G12 specificity and ability to target STn on multiple tumor associated proteins to drive durable tumor regressions. SGN-STNV was well tolerated in non-human primates (NHP), with no concerning target-mediated toxicities and a maximum tolerated dose similar to other vedotin-platform ADCs. In summary, the antibody specificity, unique mechanism of targeting a carbohydrate, anti-tumor activity, and tolerability provide a strong rationale for initiation of a phase I study to investigate the therapeutic potential of SGN-STNV. Citation Format: Alyssa Schwartz, Hector Rincon, Nanna Hansen, Robert Lawrence, Sarah Anderson, Nicole Blesie, Kerry Klussman, Angela Epp, Shyra Gardai, William Arthur. Targeting Sialyl-Thomsen nouveau (STn) antigen with the SGN-STNV antibody-drug conjugate is effective in preclinical studies [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 50.

P-45 An open-label, phase 2 study of patritumab deruxtecan in patients with previously treated advanced/metastatic colorectal cancer

Patritumab deruxtecan (HER3-DXd) is a novel, investigational antibody-drug conjugate comprising an anti-HER3 monoclonal antibody, a tetrapeptide-based linker, and a topoisomerase I inhibitor payload. Ongoing clinical trials of HER3-DXd in patients with metastatic breast cancer or non-small cell lung cancer have shown promising clinical activity and acceptable safety. HER3 (human epidermal growth receptor 3), a member of the tyrosine kinase receptor family, is overexpressed in most colorectal cancer tumors (≈50%-90%) and associated with an adverse prognosis.

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.

Abstract OT-03-03: SGNLVA-001: A phase 1 open-label dose escalation and expansion study of SGN-LIV1A administered weekly in breast cancer

Abstract Background: LIV-1 is a highly prevalent transmembrane protein in breast cancer cells. Ladiratuzumab vedotin (LV), SGN-LIV1A, is an investigational antibody-drug conjugate (ADC) that targets LIV-1 via a humanized IgG1 monoclonal antibody conjugated to monomethyl auristatin E (MMAE) by a protease-cleavable linker. LV is internalized when it binds LIV-1 on cell surfaces and MMAE is released, which binds tubulin and induces apoptosis. LV has been shown to be active and tolerable in metastatic breast cancer (mBC) at a recommended dose of 2.5 mg/kg every 21 days (Modi 2017). More frequent, fractionated dosing has improved the activity and/or safety of other ADCs. Thus, this study is actively accruing subjects with metastatic triple negative breast cancer (mTNBC; estrogen receptor (ER)/progesterone receptor (PR)/human epidermal growth factor receptor 2 (HER2) receptor-negative) and endocrine-resistant ER+ or PR+ (hormone receptor [HR+])/HER2-negative mBC to test weekly dosing of LV (Days 1, 8, and 15 of every 3-week cycle). Methods: This study is enrolling up to 82 subjects (42 HR+/HER2-negative and 40 mTNBC) into dose escalation and dose expansion cohorts (NCT01969643). Eligible subjects are females ≥18 years old with pathologically and radiologically confirmed metastatic HR+/HER2-negative or mTNBC with at least 1 measurable lesion per RECIST v1.1. Subjects with HR+/HER2-negative disease must have received no more than 1 prior line of cytotoxic chemotherapy in the locally advanced (LA)/mBC setting, either as single agent or combination therapy. Subjects with mTNBC must have received 1 prior line of cytotoxic chemotherapy in the LA/mBC setting. Progression within 6 months of completion of neoadjuvant or adjuvant therapy is considered an LA/mBC regimen. Subjects must have adequate organ function, ECOG status of ≤1, and no ≥ Grade 2 peripheral neuropathy. Subjects with brain lesions must have received definitive treatment of the lesions. Prior therapy with MMAE-containing agents is not allowed. Dose escalation follows the modified toxicity probability interval method (Ji 2010). Dose expansion cohorts will provide data about activity and tolerability. Tumor assessments will be conducted every 2 cycles per RECIST v1.1 and all subjects will be followed for safety. Pharmacokinetics and markers of pharmacodynamics will be assessed. Primary safety endpoint is the incidence of adverse events and dose-limiting toxicities. Key efficacy endpoints include confirmed overall response rate, duration of response, and progression-free survival. Citation Format: Heather C Beckwith, Diana C Medgyesy, Jame Abraham, Rita Nanda, Katherine HR Tkaczuk, Ian E Krop, Lajos Pusztai, Shanu Modi, Monica M Mita, Jennifer M Specht, Sara A Hurvitz, Hyo S Han, Kevin Kalinsky, Sharon Wilks, Joyce O’Shaughnessy, Lowell L Hart, Hope S Rugo, Zahi I Mitri, Phillip M Garfin, Howard A Burris III. SGNLVA-001: A phase 1 open-label dose escalation and expansion study of SGN-LIV1A administered weekly in breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-03-03.

Abstract PD1-10: Evaluation of SGN-LIV1a followed by AC in high-risk HER2 negative stage II/III breast cancer: Results from the I-SPY 2 TRIAL

Abstract Background: I-SPY 2 is a multicenter, phase 2 trial using response-adaptive randomization within molecular subtypes defined by receptor status and MammaPrint (MP) risk to evaluate novel agents as neoadjuvant therapy for women with high-risk stage II/III breast cancer. The primary endpoint is pathologic complete response (pCR, ypT0/Tis ypN0). SGN-LIV1A is an investigational antibody drug conjugate consisting of an antibody to LIV1A, a zinc transporter highly prevalent in breast cancer, and a highly potent microtubule inhibitor, monomethyl auristatin E. Retrospective IHC analysis of LIV1A expression levels amongst tumor samples from 100 previous ISPY-2 patients showed 88% of breast tumor samples with moderate to high expression of LIV1A (Yau, C. et al SABCS 2018).Methods: Women with tumors ≥ 2.5cm were eligible for screening. Only HER2 negative (HER2-) patients were eligible for this treatment, hormone-receptor positive (HR+) patients had to have MP high molecular profile. Treatment included SGN-LIV1A 2.5 mg/kg (max dose 250 mg) every 3 weeks x 4, followed by doxorubicin/cyclophosphamide (AC) every 2-3 weeks x 4. The control arm was weekly paclitaxel x 12 followed by AC every 2-3 weeks x 4. All patients undergo serial MR imaging where response at 3 &amp; 12 weeks combined with accumulating pCR data are used to estimate, and continuously update, predicted pCR rate for the trial arm. Analysis set was modified intention to treat with patients who switched to non-protocol therapy counted as non-pCR and not as their pCR status at time of surgery. The goal is to identify/graduate regimens with ≥85% Bayesian predictive probability of success (i.e. demonstrating superiority to control) in a future 300-patient phase 3 neoadjuvant trial with a pCR endpoint within signatures defined by HR &amp; HER2 status &amp; MP result. This investigational arm was eligible for graduation in 3 of 10 pre-defined signatures: HER2-, HR+HER2- and HR-HER2-. Regimens may also leave the trial for futility (&amp;lt; 10% probability of success), maximum sample size accrual (10% &amp;lt; probability of success &amp;lt;85%), maximum time in trial (2 years) or for safety as recommended by the independent DSMB. Results: Sixty patients were randomized and evaluable to SGN-LIV1A. The study arm was stopped due to reaching the predetermined time limit for patient accrual of 2 yrs. Final estimated pCR rates are below. The estimated pCR rates were similar between the SGN-LIV1A and control arms for any tumor subtype. Preliminary safety events for SGN-LIV1A include increased rates of transaminitis and hyperglycemia and reduced rates of peripheral neuropathy compared to control. One patient was removed from the analysis as she was determined to have angiosarcoma of the breast. Notably, this patient had a dramatic early response and subsequent pCR to SGN-LIV1A treatment. Conclusion: The value of I-SPY 2 is to give insight about the performance of an investigational agent’s likelihood of achieving pCR. SGN-LIV1A delivered every 3 weeks was comparable to paclitaxel for the primary endpoint of pCR in I-SPY2 and may have a similar side effect profile, however, with less peripheral neuropathy. Clinical trials evaluating weekly dosing of SGN-LIV1A are ongoing. A trial of SGN-LIV1A in the treatment of angiosarcoma is under consideration at this time. Final Estimated pCR Rates and Predictive ProbabilitiesEstimated pCR rate(95% prob interval)SignatureSGN-LIV1AControlProbability SGNLIV1A Superior to ControlPredictive Probability of Success in Phase 3HER2-0.16 (0.08-0.24) N= 600.20 (0.16-0.25) N= 3270.180.02HR-/HER2-0.25 (0.12-0.37) N=360.28 (0.21-0.35) N=1460.310.06HR+/HER2-0.09 (0-0.18) N=240.14 (0.09-0.19) N=1810.150.03 Citation Format: Heather Beckwith, Richard Schwab, Christina Yau, Erica Stringer-Reasor, Shi Wei, A. Jo Chien, Kathy S Albain, Kevin Kalinsky, Anne Wallace, Anthony Elias, Douglas Yee, Amy S Clark, Judy C Boughey, Heather Han, Rita Nanda, Claudine Isaacs, Zahi Mitri, Julie E Lang, Alexandra Thomas, Tara Sanft, Angela DeMichele, Jane Perlmutter, Hope S Rugo, Nola M Hylton, W. Fraser Symmans, Michelle E Melisko, Laura J van't Veer, I-SPY 2 Consortium, Amy Wilson, Smita M Asare, Ashish Sanil, Donald A Berry, Laura J Esserman. Evaluation of SGN-LIV1a followed by AC in high-risk HER2 negative stage II/III breast cancer: Results from the I-SPY 2 TRIAL [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD1-10.

An open-label, phase II study of patritumab deruxtecan (HER3-DXd, U3-1402) in patients (pts) with previously treated advanced/metastatic colorectal cancer (CRC).

TPS157 Background: Patritumab deruxtecan (HER3-DXd; U3-1402) is a novel, investigational antibody drug conjugate comprising an anti-HER3 monoclonal antibody, a tetrapeptide-based linker, and a topoisomerase I inhibitor payload. Ongoing clinical trials of HER3-DXd in pts with metastatic breast cancer or non-small cell lung cancer have shown promising clinical activity and acceptable safety. HER3 (human epidermal growth receptor 3), a member of the tyrosine kinase receptor family, is overexpressed in most CRC tumors and associated with an adverse prognosis. Significant tumor regression with HER3-DXd has been observed in CRC murine xenograft models, regardless of KRAS mutation status. Here we introduce the design of a phase 2 study (U31402-A-U202) that is evaluating HER3-DXd in previously treated pts with advanced/metastatic CRC. Methods: U31402-A-U202 (NCT04479436) is an open-label, multicenter phase 2 study that will enroll 80 pts in the USA, Europe and Asia. Pts are enrolled who are aged ≥ 18 years with advanced/metastatic colorectal adenocarcinoma that is resistant/refractory/intolerant to ≥ 2 prior lines of therapy including a fluoropyrimidine, irinotecan, a platinum agent, an anti-EGFR agent (if clinically indicated), an anti-VEGF agent (unless contraindicated [CI]), and an immune checkpoint inhibitor (unless CI) for microsatellite instability-high CRC. Pts with current/previous interstitial lung disease or clinically severe pulmonary compromise are excluded. Archival tumor biopsy and pre-treatment tumor biopsy are collected from all pts at screening, with HER3 protein expression measured by immunohistochemistry (IHC). In part 1, results of the HER3 IHC assay from the pre-treatment tumor biopsy are used to assign pts into 1 of 2 cohorts (C). C1: HER3 high (IHC 3+, 2+), n = 24; C2: HER3 low/negative (IHC 1+, 0), n = 12. Pts receive 5.6 mg/kg HER3-DXd IV every 3 weeks. An interim futility analysis will be conducted separately for C1 and C2 and will determine enrollment in part 2, with 2 potential scenarios: enrollment continues irrespective of HER3 IHC status, or enrollment continues in HER3 high pts only. The primary objective is the evaluation of the antitumor activity of HER3-DXd as measured by objective response rate (ORR) (assessed by BICR according to RECIST v1.1). ORR will be summarized with the 2-sided 95% confidence interval. Secondary objectives include the evaluation of efficacy as measured by ORR (assessed by investigator according to RECIST v1.1), duration of response, time to tumor response, disease control rate, progression-free survival (assessed by investigator and BICR according to RECIST v1.1), overall survival, safety and tolerability, HER3 protein expression in tumor tissue and relationship with efficacy, and pharmacokinetic properties. Clinical trial information: NCT04479436.

357TiP SGNLVA-002: Single arm, open-label, phase Ib/II study of ladiratuzumab vedotin (LV) in combination with pembrolizumab for first-line treatment of triple-negative breast cancer

Patients (pts) with metastatic triple-negative breast cancer (mTNBC) have a poor prognosis. Treatment combinations of anti-programmed death (ligand) 1 [anti-PD(L)1] agents with chemotherapy have shown promise in mTNBC. LIV-1 is a transmembrane protein highly expressed on breast cancer cells. SGN-LIV1A, or ladiratuzumab vedotin (LV), is an investigational antibody-drug conjugate that combines a humanized anti-LIV-1 IgG1 monoclonal antibody with the microtubule-disrupting agent, monomethyl auristatin E (MMAE) via a protease-cleavable linker. LIV-1 mediated delivery of MMAE disrupts microtubules and induces cell cycle arrest and apoptosis. Additionally, LV has been shown to drive immunogenic cell death (ICD) to elicit an immune response. Combining LV and pembrolizumab may result in synergistic activity through LV induced ICD that creates a microenvironment favorable for enhanced anti-PD(L)1 activity. Preliminary results of LV delivered once every 3 weeks with pembrolizumab was shown to be tolerable with encouraging antitumor activity in pts with mTNBC (SABCS 2019). In order to enhance efficacy and improve the tolerability profile, LV delivered weekly with pembrolizumab is being evaluated. SGNLVA-002 is a global single-arm, open-label phase Ib/II study of LV with pembrolizumab as first-line therapy for pts with unresectable locally-advanced or mTNBC. The study is currently enrolling approximately 24 pts to evaluate the safety and efficacy of LV at either 1.00 or 1.25 mg/kg/week on Days 1, 8, and 15 plus pembrolizumab 200 mg on Day 1 of each 21 day cycle. Pts must not have had prior cytotoxic or anti-PD(L)1 treatment for advanced disease, have measurable disease per RECIST v1.1, and an ECOG score of 0 or 1. The primary objectives are to evaluate the safety/tolerability and objective response rate of weekly LV plus pembrolizumab, and to identify the recommended phase II dose and schedule of weekly LV in combination with pembrolizumab. The secondary objectives include evaluation of duration of response, disease control rate, progression-free survival, and overall survival. Study enrollment is ongoing in the US, Asia, and EU. Medical writing assistance was funded by Seattle Genetics, Inc., and provided by William Losin of MMS Holdings, Inc. Seattle Genetics/Merck.