Seattle Genetics Announces Initiation of Phase 1 Clinical Trials for Two Novel Antibody-Based Drug Candidates

– Effector Function Enhanced Anti-TIGIT Antibody –

– Antibody-Drug Conjugate Targeting Integrin Beta-6 –

– Both Drug Candidates to be Evaluated in Multiple Tumor Types –

BOTHELL, Wash.–(BUSINESS WIRE)–Seattle Genetics, Inc. (Nasdaq:SGEN) today announced dosing of the first patient in a phase 1 clinical trial evaluating investigational agent SEA-TGT, also known as SGN-TGT, an anti-TIGIT antibody for patients with solid tumors and lymphomas. TIGIT (T-cell immune receptor with Ig and ITIM domains) is an inhibitory immune receptor that is emerging as a clinically relevant immuno-oncology target. SEA-TGT is a nonfucosylated human IgG1 antibody that uses the Company’s proprietary Sugar Engineered Antibody (SEA) technology. The Company also announced the dosing of the first patient in a phase 1 clinical trial evaluating investigational agent SGN-B6A, an antibody-drug conjugate (ADC) targeting integrin beta-6, which is overexpressed in numerous solid tumors and has been demonstrated to be a negative prognostic indicator across a diverse range of cancers.

Preclinical data indicate that SEA-TGT has enhanced effector function enabled by the Company’s SEA technology. These data indicate that SEA-TGT may have best-in-class potential through enhanced depletion of TIGIT-positive regulatory T-cells (Tregs), distinct immune changes including amplified naïve and memory T-cell responses, and induction of innate immune cell activation. Curative anti-tumor activity in preclinical models was observed as a single agent and in combination with a PD-1 checkpoint inhibitor. These data support potential for improved monotherapy and combinatorial clinical activity as compared to a non-enhanced TIGIT antibody.

SGN-B6A is an ADC targeting integrin beta-6 to deliver the clinically validated payload monomethyl auristatin E (MMAE). In preclinical research, this ADC has demonstrated in vivo activity in models spanning a range of antigen expression levels and tumor types.

“We believe that anti-TIGIT antibodies may have an important therapeutic role in the evolving immuno-oncology landscape,” said Roger Dansey, M.D., Chief Medical Officer at Seattle Genetics. “SEA-TGT utilizes our novel SEA technology, which in preclinical research has demonstrated enhanced effector function that potentially differentiates it from other TIGIT antibodies in the clinic. The initiation of clinical trials for both SEA-TGT and the ADC, SGN-B6A, underscore our commitment to advancing novel drug candidates from our pipeline into clinical testing.”

SEA-TGT Phase 1 Trial

The phase 1 trial of SEA-TGT will evaluate the safety and anti-tumor activity of SEA-TGT as a single agent as well as in combination with the anti-PD-1 antibody, pembrolizumab. The phase 1 trial will evaluate SEA-TGT in advanced solid tumors and lymphomas, including non-small cell lung cancer, gastric carcinoma, Hodgkin and selected non-Hodgkin lymphomas. The study is currently open in multiple sites in the United States and is expected to enroll approximately 111 participants. More information about the study of SEA-TGT is available at clinicaltrials.gov.

SGN-B6A Phase 1 Trial

SGN-B6A is an ADC targeting integrin beta-6 to deliver the clinically validated payload MMAE. The phase 1 trial will evaluate SGN-B6A in solid tumors, including non-small cell lung cancer, head and neck squamous cell cancer, breast, esophageal, ovarian, bladder, cervical and gastric cancers. The study is currently open in multiple sites in the United States and is expected to enroll approximately 235 participants. More information about the study of SGN-B6A is available at clinicaltrials.gov.

About Seattle Genetics

Seattle Genetics, Inc. is a global biotechnology company that discovers, develops and commercializes transformative cancer medicines to make a meaningful difference in people’s lives. ADCETRIS^® (brentuximab vedotin) and PADCEV™ (enfortumab vedotin-ejfv) use the Company’s industry-leading antibody-drug conjugate (ADC) technology. ADCETRIS is approved in certain CD30-expressing lymphomas, and PADCEV is approved in certain metastatic urothelial cancers. TUKYSA™ (tucatinib), a small molecule tyrosine kinase inhibitor, is approved in certain HER2-positive metastatic breast cancers. The company is headquartered in the Seattle, Washington area, with locations in California, Switzerland and the European Union. For more information on our robust pipeline, visit www.seattlegenetics.com and follow @SeattleGenetics on Twitter.

Forward Looking Statements

Certain of the statements made in this press release are forward looking, such as those, among others, relating to therapeutic potential of SEA-TGT and SGN-B6A, their possible safety, efficacy, and therapeutic uses and anticipated development activities including the enrollment of patients in the Company’s phase 1 studies, future clinical trials and intended regulatory actions. 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 difficulty and uncertainty of pharmaceutical product development, the risk of adverse events or safety signals, the inability to show sufficient activity in clinical trials and the possibility of adverse regulatory actions as product candidates are evaluated in clinical trials even after promising results in preclinical research. 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 March 31, 2020 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.

Contacts

Media:

Monique Greer

(425) 527-4641

[email protected]

Investors:

Peggy Pinkston

(425) 527-4160

[email protected]