Mersana Therapeutics Enters Collaboration with Takeda to Develop Next-Generation Antibody-Drug Conjugates

Mersana Therapeutics Inc. announced today that it has entered into a collaboration agreement with Millennium Pharmaceuticals Inc. a wholly-owned subsidiary of Takeda Pharmaceutical Company Limited (TSE:4502) to develop next-generation Fleximer® antibody-drug conjugates (ADCs). Mersana's proprietary conjugation technology is comprised of the company's biodegradable Fleximer polymer and a broad array of customizable linker chemistries matched to Mersana's diverse cytotoxic payloads.

Under the agreement Takeda will provide an upfront payment to Mersana for the right to utilize Fleximer technology to develop novel ADC candidates. Mersana is responsible for conducting research and creating ADCs that are conjugates of Takeda's antibodies and Mersana's diverse payload platforms which combine a cytotoxic payload with the Fleximer polymer and custom linkers. In addition to providing antibodies Takeda is responsible for product development manufacturing and commercialization of any Fleximer-ADC products. In addition to an upfront payment Mersana is eligible to receive milestones and royalties on worldwide net sales of any resulting ADC products.

"Collaboration is key to Takeda's business model and is at the root of our success in leading innovation in medicine. Mersana's unique approach to ADCs allows a wide variety of antibody and payload combinations to be investigated" said Christopher Claiborne Ph.D. Head of the Oncology Drug Discovery Unit at Takeda. "We believe that working with Mersana and investigating Fleximer-ADCs in oncology one of Takeda's core therapeutic areas will strengthen our leadership and experience in developing and bringing innovative ADC therapeutics to patients worldwide."

"Mersana has a pattern of successful collaborations with industry leaders in which we have quickly advanced several Fleximer-ADC candidates through research and preclinical development" said Eva M. Jack Mersana's Chief Business Officer. "Mersana's proprietary Fleximer technology offers a new and highly differentiated approach to creating ADC therapeutics and we look forward to working with Takeda to develop novel Fleximer-ADC candidates."

About Fleximer® Antibody-Drug Conjugate Technology

Mersana's next-generation Fleximer® antibody-drug conjugate (ADC) technology is based on the Company's proprietary biodegradable polymer system known as Fleximer® and a wide variety of linkers that allow for the attachment of an extensive range of anti-tumor payloads to Fleximer. As an example once loaded with the drug(s) Fleximer is then attached through a stable linker that is different from the drug linker(s) to an antibody or antibody alternative to create a Fleximer-ADC. Mersana's novel linker systems are designed to be stable in the blood stream and release the cytotoxic payloads once inside the targeted cancer cell. Mersana's Fleximer-ADC technology provides several key advantages over currently available approaches including: ability to deliver diverse payloads; opportunity to significantly increase drug loading per antibody; potential use with antibody fragments and alternative targeting moieties in addition to monoclonal antibodies and to optimize the size of the drug conjugate to efficiently perfuse solid tumors while retaining a long half-life associated with antibody-based ADCs.

About Mersana Therapeutics

Mersana Therapeutics engineers novel drug conjugates that maximize the potential of new and established therapeutic classes. Mersana is developing with select pharmaceutical partners a portfolio of next-generation Fleximer® antibody-drug conjugates (ADC) with superior properties not found with current ADC technologies. The company is also advancing its own pipeline of Fleximer-ADCs with best-in-class potential to address unmet needs and improve patient outcomes in multiple oncology indications. www.mersana.com