Seattle Genetics and Astellas Announce Results from Phase 1 Trial of Investigational Agent Enfortumab Vedotin in Combination with Immune Therapy Pembrolizumab as First-Line Treatment for Advanced Bladder Cancer

TOKYO & BOTHELL, Wash.

Seattle Genetics, Inc. (Nasdaq:SGEN) and Astellas Pharma Inc. (TSE: 4503, President and CEO: Kenji Yasukawa, Ph.D., “Astellas”) today announced initial results from the phase 1 clinical trial EV-103. Forty-five patients were evaluated for safety with the combination of the investigational agent enfortumab vedotin and the immune therapy pembrolizumab in previously untreated patients with locally advanced or metastatic urothelial cancer who were ineligible for treatment with cisplatin-based chemotherapy. The study met outcome measures for safety and exhibited encouraging clinical activity for this platinum-free combination in a first-line setting. The data will be presented during an oral session today at the European Society for Medical Oncology (ESMO) 2019 Congress in Barcelona, Spain (Abstract #901O).

Enfortumab vedotin is a first-in-class antibody drug conjugate (ADC) that targets Nectin-4, a protein present on almost all urothelial tumor cells and associated with cancer formation.¹

“Advanced urothelial cancer is an aggressive disease for which more options are needed, especially for patients who are ineligible for first-line treatment with cisplatin,” said Dr. Christopher J. Hoimes, Director, Genitourinary Oncology, Case Comprehensive Cancer Center at University Hospitals Seidman Cancer Center, Cleveland, Ohio. “This study tests the combination of the investigational agent enfortumab vedotin with the PD-1 inhibitor pembrolizumab, in a biomarker unselected population. Initial results provide support for further development of enfortumab vedotin combinations in this and other settings of urothelial cancer.”

Fifty-one percent of patients (23/45) had an adverse event greater than or equal to Grade 3. Among these events, an increase in lipase was the most frequent (13 percent; 6/45). Four patients (9 percent) discontinued treatment due to treatment-related adverse events, most commonly peripheral sensory neuropathy. There was one death deemed to be treatment-related by the investigator attributed to multiple organ dysfunction syndrome.

Treatment-related adverse events of clinical interest that were greater than or equal to Grade 3 were rash (11 percent; 5/45), hyperglycemia (7 percent; 3/45) and peripheral neuropathy (4 percent; 2/45); these rates were similar to those observed with enfortumab vedotin monotherapy.² Eleven percent (5/45) of patients had treatment-related immune-mediated adverse events of clinical interest greater than or equal to Grade 3 that required the use of systemic steroids (one event each of pneumonitis, dermatitis bullous, hyperglycemia, tubulointerstitial nephritis, myasthenia gravis). None of the adverse events of clinical interest were Grade 5 events.

The data demonstrated the combination of enfortumab vedotin plus pembrolizumab shrank tumors in the majority of patients, resulting in a confirmed objective response rate (ORR) of 71 percent (32/45; 95% Confidence Interval (CI): 55.7, 83.6). The complete response (CR) rate was 13 percent (6/45). Fifty-eight percent (26/45) of patients had a partial response and 22 percent (10/45) had stable disease. Ninety-one percent of responses were observed at the first assessment.

“These data are encouraging and support further exploration of a potential platinum-free combination of pembrolizumab and the investigational agent enfortumab vedotin,” said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics.

“We are motivated by these results, and we will continue to study enfortumab vedotin alone and in combination with other agents in different stages of urothelial cancer,” said Andrew Krivoshik, M.D., Ph.D., Senior Vice President and Oncology Therapeutic Area Head at Astellas.

Enfortumab vedotin is currently under review by the U.S. Food and Drug Administration (FDA) for the treatment of patients with locally advanced or metastatic urothelial cancer who have received a PD-1/L1 inhibitor and who have received a platinum-containing chemotherapy in a neoadjuvant/adjuvant, locally advanced or metastatic setting.

About the EV-103 Trial

EV-103 is an ongoing, multi-cohort, open-label, multicenter phase 1 trial of enfortumab vedotin alone or in combination, evaluating safety, tolerability and efficacy in muscle invasive, locally advanced and first- and second-line metastatic urothelial cancer.

The dose escalation-cohort and expansion cohort A include locally advanced or metastatic urothelial cancer patients who are ineligible for cisplatin-based chemotherapy. Patients were dosed in a 21-day cycle, receiving an intravenous (IV) infusion of enfortumab vedotin on Days 1 and 8 and pembrolizumab on Day 1. At the time of this initial analysis, 45 patients (5 from the dose-escalation cohort and 40 from the dose-expansion cohort A) with locally advanced and/or metastatic urothelial cancer had been treated with enfortumab vedotin (1.25 mg/kg) plus pembrolizumab in the first-line setting.

The primary outcome measure of the cohorts included in this analysis is safety. The analysis of these first cohorts included several of the study’s secondary objectives. Key secondary objectives related to efficacy include objective response rate (ORR), disease control rate (DCR), duration of response (DOR) and overall survival (OS). DOR and OS were not mature at the time of analysis and will be included in a future analysis.

Additional cohorts in the EV-103 study will evaluate enfortumab vedotin:

• with cisplatin or carboplatin in a first-line setting for metastatic disease;
• in combination with pembrolizumab and carboplatin or cisplatin in first-line metastatic disease;
• as a monotherapy or in combination with pembrolizumab in muscle invasive disease;
• with pembrolizumab in second-line metastatic disease; and
• with gemcitabine in first- or second-line metastatic disease.³

More information about enfortumab vedotin clinical trials can be found at clinicaltrials.gov.

About Urothelial Cancer

Urothelial cancer is the most common type of bladder cancer (90 percent of cases).⁴ In 2018, more than 82,000 people were diagnosed with bladder cancer in the United States. Globally, approximately 549,000 people were diagnosed with bladder cancer last year, and there were approximately 200,000 deaths worldwide.⁵

The recommended first-line treatment for patients with advanced urothelial cancer is a cisplatin-based chemotherapy. For patients who are ineligible for cisplatin, such as people with kidney impairment, a carboplatin-based regimen is recommended. However, fewer than half of patients respond to carboplatin-based regimens and outcomes are typically poorer compared to cisplatin-based regimens.⁶

About Enfortumab Vedotin

Enfortumab vedotin is an investigational antibody-drug conjugate (ADC) composed of an anti-Nectin-4 monoclonal antibody attached to a microtubule-disrupting agent, MMAE, using Seattle Genetics’ proprietary linker technology. Enfortumab vedotin targets Nectin-4, a cell adhesion molecule that is expressed on many solid tumors, and that has been identified as an ADC target by Astellas.

The safety and efficacy of enfortumab vedotin are under investigation and have not been established. There is no guarantee that the agent will receive regulatory approval or become commercially available for the uses being investigated.

About Seattle Genetics

Seattle Genetics, Inc. is an emerging multi-product, global biotechnology company that develops and commercializes transformative therapies targeting cancer to make a meaningful difference in people’s lives. The company is headquartered in Bothell, Washington, and has a European office in Switzerland. For more information on our robust pipeline, visit www.seattlegenetics.com and follow @SeattleGenetics on Twitter.

About Astellas

Astellas Pharma Inc., based in Tokyo, Japan, is a company dedicated to improving the health of people around the world through the provision of innovative and reliable pharmaceutical products. For more information, please visit our website at https://www.astellas.com/en.

About the Astellas and Seattle Genetics Collaboration

Seattle Genetics and Astellas are co-developing enfortumab vedotin under a collaboration that was entered into in 2007 and expanded in 2009. Under the collaboration, the companies are sharing costs and profits on a 50:50 basis worldwide.

Seattle Genetics Forward-Looking Statements

Certain statements made in this press release are forward looking, such as those, among others, relating to the EV-103 clinical trial; clinical development plans relating to enfortumab vedotin; and the therapeutic potential of enfortumab vedotin including its possible safety, efficacy, and therapeutic uses, including in the first-line setting, and the potential FDA approval of enfortumab vedotin for the treatment of patients with locally advanced or metastatic urothelial cancer who have received a PD-1/L1 inhibitor and who have received a platinum-containing chemotherapy in the neoadjuvant/adjuvant, locally advanced or metastatic setting. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include the possibility that ongoing and subsequent clinical trials of enfortumab vedotin may fail to establish sufficient efficacy; that adverse events or safety signals may occur; that adverse regulatory actions or other setbacks could occur as enfortumab vedotin advances in clinical trials even after promising results in earlier clinical trials; and that the Biologics License Application submission and any future potential supplemental Biologics License Application submissions for enfortumab vedotin may not be approved by the FDA in a timely manner or at all or with the requested label(s). More information about the risks and uncertainties faced by Seattle Genetics is contained under the caption “Risk Factors” included in the company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2019 filed with the Securities and Exchange Commission. Seattle Genetics disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

Astellas Cautionary Notes

In this press release, statements made with respect to current plans, estimates, strategies and beliefs and other statements that are not historical facts are forward-looking statements about the future performance of Astellas. These statements are based on management’s current assumptions and beliefs in light of the information currently available to it and involve known and unknown risks and uncertainties. A number of factors could cause actual results to differ materially from those discussed in the forward-looking statements. Such factors include, but are not limited to: (i) changes in general economic conditions and in laws and regulations, relating to pharmaceutical markets, (ii) currency exchange rate fluctuations, (iii) delays in new product launches, (iv) the inability of Astellas to market existing and new products effectively, (v) the inability of Astellas to continue to effectively research and develop products accepted by customers in highly competitive markets, and (vi) infringements of Astellas’ intellectual property rights by third parties.

Information about pharmaceutical products (including products currently in development), which is included in this press release is not intended to constitute an advertisement or medical advice.

¹ Vlachostergios P, Jakubowski C, Niaz J, et al. (2018). Antibody-Drug Conjugates in Bladder Cancer. Bladder Cancer (Version 4.2018). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6087439/pdf/blc-4-blc180169.pdf

² Rosenberg J. Pivotal Trial of Enfortumab Vedotin in Urothelial Carcinoma After Platinum and Anti-Programmed Death 1/Programmed Death Ligand 1 Therapy. J Clin Oncol. 2019; DOI: 10.1200/JCO.19.01140

³ ClinicalTrials.gov. A Study of Enfortumab Vedotin Alone or With Other Therapies for Treatment of Urothelial Cancer (EV-103). https://clinicaltrials.gov/ct2/show/NCT03288545

⁴ American Society of Clinical Oncology. Bladder Cancer: Introduction (05-2019). https://www.cancer.net/cancer-types/bladder-cancer/introduction

⁵ International Agency for Research on Cancer. Cancer Tomorrow: Bladder. http://gco.iarc.fr/tomorrow

⁶ National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Bladder Cancer. Version 4; July 10, 2019. https://www.nccn.org/professionals/physician_gls/pdf/bladder.pdf

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