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Seattle Genetics Highlights Phase 1 Data for Novel Antibody-Drug Conjugate SGN-LIV1A in Patients with Metastatic Breast Cancer at San Antonio Breast Cancer Symposium

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SAN ANTONIO--(BUSINESS WIRE)--

Seattle Genetics, Inc. (NASDAQ: SGEN), a global biotechnology company, today presented data from an ongoing phase 1 clinical trial evaluating SGN-LIV1A for patients with metastatic breast cancer (MBC), with particular focus on triple-negative MBC (TN MBC), at the 39th San Antonio Breast Cancer Symposium (SABCS) taking place in San Antonio, Texas, December 6-10, 2016. SGN-LIV1A is an investigational antibody-drug conjugate (ADC) which consists of a LIV-1-targeted monoclonal antibody linked to the cell-killing agent monomethyl auristatin E (MMAE) by a protease-cleavable linker. LIV-1 is a protein expressed by most metastatic breast cancers. SGN-LIV1A is one of four clinical-stage empowered antibody therapies under development by Seattle Genetics for solid tumors.

"Breast cancer is the most common cancer among women, with an estimated 1.67 million new cases per year worldwide. About 15 to 20 percent of breast cancers are triple negative, which means they lack expression of three breast cancer-associated proteins that serve as key therapeutic targets. Triple-negative breast cancers are more aggressive and generally have poor prognoses," said Jonathan Drachman, M.D., Chief Medical Officer and Executive Vice President, Research and Development at Seattle Genetics. "The data presented at SABCS on SGN-LIV1A demonstrate promising early antitumor activity with a 37 percent partial response rate in patients with triple negative metastatic breast cancer, for which there are no available targeted treatments. We are enrolling additional patients with triple negative metastatic breast cancer in our phase 1 study to optimize the dose and inform the next steps for development of SGN-LIV1A in this population with high unmet need."

Interim data from the ongoing phase 1 study of SGN-LIV1A in patients with MBC were previously presented at the 2015 SABCS. The following updated results from this trial describe safety data for all patients and antitumor activity data for patients with TN MBC.

Interim Analysis of a Phase 1 Study of the Antibody-Drug Conjugate SGN-LIV1A in Patients with Metastatic Breast Cancer (Poster# P6-12-04, Poster Session 6 - Treatment: New Drugs and Treatment Strategies at 7:30 – 9:00 a.m. CT on Saturday, December 10, 2016)

Data were reported from 53 patients with LIV-1-expressing MBC who were treated with SGN-LIV1A monotherapy administered every three weeks. Of these patients, 35 had TN MBC. The median age of all patients was 56 years. Patients had received a median of four prior systemic therapies for metastatic disease. Key findings presented by Dr. Andres Forero-Torres, University of Alabama at Birmingham included:

  • Thirty of 47 efficacy-evaluable patients had TN MBC. Among these patients, 11 (37 percent) achieved a partial response (PR). The disease control rate (DCR) was 67 percent and the clinical benefit rate (CBR) was 47 percent. DCR is defined as patients achieving a complete response (CR), PR or stable disease (SD). CBR is defined as patients achieving CR or PR of any duration plus patients achieving SD lasting at least 24 weeks.
  • At the time of this interim data analysis, the estimated median progression-free survival for TN MBC patients was 12 weeks with seven patients remaining on treatment.
  • The maximum tolerated dose was not reached among doses ranging from 0.5 to 2.8 milligrams per kilogram (mg/kg). Dose escalation is complete and a disease-specific expansion cohort of TN MBC patients is currently enrolling.
  • For all patients in the study, the most common adverse events of any grade occurring in 20 percent or more of patients included fatigue (57 percent), nausea (53 percent), alopecia (42 percent), decreased appetite (34 percent) and constipation (32 percent).
  • The incidence of grade 3/4 neutropenia at the 2.5 mg/kg dose was 50 percent. Two patients (seven percent) experienced febrile neutropenia, and there was one treatment-related death due to sepsis. Based on these safety data, a separate expansion cohort at 2.0 mg/kg is currently being evaluated.
  • Peripheral neuropathy events occurred in 38 percent of patients and were generally low grade and manageable.
  • Enrollment continues for patients with TN MBC in the SGN-LIV1A monotherapy part of the study. In addition, enrollment is ongoing for patients with HER2+ breast cancer to evaluate SGN-LIV1A in combination with trastuzumab.

More information about the SGN-LIV1A phase 1 clinical trial, including enrolling centers, is available by visiting www.clinicaltrials.gov.

About SGN-LIV1A

SGN-LIV1A is a novel investigational ADC targeted to LIV-1 protein utilizing Seattle Genetics' proprietary ADC technology. LIV-1 is expressed by most metastatic breast cancers. It has also been detected in a number of other cancers, including melanoma, prostate, ovarian, and cervical cancer. SGN-LIV1A consists of a LIV-1-targeted monoclonal antibody linked to a potent microtubule-disrupting agent, monomethyl auristatin E (MMAE) by a protease-cleavable linker, using the same technology as ADCETRIS (brentuximab vedotin). It is designed to bind to LIV-1 on cancer cells and release the cell-killing agent into target cells upon internalization. SGN-LIV1A may also cause antitumor activity through other mechanisms, including activation of an immune response.

About Breast Cancer

Breast cancer is a cancer which forms in breast tissue. Metastatic breast cancer occurs when the cancer has spread to other parts of the body. While most new diagnoses of breast cancer are made at an early stage, approximately one-third of these patients will eventually develop recurrent or metastatic disease. Breast cancers are commonly categorized by the expression (or lack thereof) of three key proteins, which serve are targets for therapeutics. These include the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Triple-negative breast cancer (TNBC) lacks all three proteins and HR+/HER2- breast cancer expresses one or both hormone receptors (HR) but not HER2. According to the World Health Organization, breast cancer is the second most common cancer in the world and the most frequent cancer among women with an estimated 1.67 million new cancer cases diagnosed in 2012. Furthermore, breast cancer ranks as the fifth cause of death from cancer overall. New treatment approaches are needed to improve outcomes for breast cancer patients, particularly for those with TNBC where there are currently no available targeted therapies.

About Seattle Genetics

Seattle Genetics is an innovative biotechnology company that develops and commercializes novel antibody-based therapies for the treatment of cancer. The company's industry-leading antibody-drug conjugate (ADC) technology harnesses the targeting ability of antibodies to deliver cell-killing agents directly to cancer cells. ADCETRIS® (brentuximab vedotin), the company's lead product, in collaboration with Takeda Pharmaceutical Company Limited, is the first in a new class of ADCs commercially available globally in 65 countries for relapsed classical Hodgkin lymphoma (HL) and relapsed systemic anaplastic large cell lymphoma (sALCL). Seattle Genetics is also advancing vadastuximab talirine (SGN-CD33A; 33A), an ADC in a phase 3 trial for acute myeloid leukemia. Headquartered in Bothell, Washington, Seattle Genetics has a robust pipeline of innovative therapies for blood-related cancers and solid tumors designed to address significant unmet medical needs and improve treatment outcomes for patients. The company has collaborations for its proprietary ADC technology with a number of companies including AbbVie, Astellas, Bayer, Celldex, Genentech, GlaxoSmithKline and Pfizer. More information can be found at www.seattlegenetics.com

Forward Looking Statements

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of SGN-LIV1A and its possible benefits and uses, and planned development activities including clinical trials to optimize dose. 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 inability to show sufficient activity in this recently initiated clinical trial and the risk of adverse events as SGN-LIV1A advances in clinical trials and regulatory actions. 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 September 30, 2016 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.

Seattle Genetics, Inc.
Investors:
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com
or
Media:
Kavita V. Shah, Ph.D., 425-527-4188
kshah@seagen.com

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