Mersana Therapeutics Earns Second Milestone Payment in Fleximer ADC Collaboration with Endo Pharmaceuticals

January 9, 2014

Mersana Therapeutics, Inc. announced today that it has achieved its second preclinical milestone in its collaboration with Endo Pharmaceuticals (Nasdaq: ENDP). In 2012, Mersana and Endo entered into a multi-target, oncology focused partnership to develop next-generation Fleximer® antibody-drug conjugates (ADCs).

“We are pleased that this novel Fleximer-ADC has passed yet another important milestone as it advances toward clinical development,” said Timothy Lowinger, Ph.D., Chief Scientific Officer of Mersana. “The rapid progress made on this molecule since the last milestone provides further validation that our proprietary conjugation technology and Fleximer polymer make an optimal platform for the development of next-generation ADCs.”

“We are very pleased to see that this novel ADC has successfully completed pilot toxicology assessments,” said Sandeep Gupta, Ph.D., Senior Vice President of Discovery and Early Development at Endo. “Taken together with the excellent efficacy observed in numerous pre-clinical cancer models, we are excited about the potential this molecule has for the treatment of a variety of cancer types.”

The collaboration between Mersana and Endo leverages Mersana’s proprietary conjugation technology, comprised of the Fleximer® polymer and a broad array of customizable linker chemistries for attaching diverse, potent payloads to antibodies. Under the terms of the agreement, Mersana is responsible for conducting research and creating Fleximer-ADC development candidates with antibodies provided by Endo. The rights to these ADCs have been licensed to Endo in exchange for research funding, milestone payments and royalties on worldwide net sales of any resulting ADC products.

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 novel linkers that allow for the attachment of a broad range of anti-tumor payloads to Fleximer. Once loaded with drug, Fleximer is then attached, through a different highly stable linker, 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 potent payloads once inside the targeted cancer cell. Mersana’s Fleximer-ADC technology provides several key advantages over currently available approaches, including: ability to deliver alternative payloads beyond anti-tubulins; opportunity to significantly increase drug loading per antibody; and potential use with antibody fragments and alternative targeting moieties in addition to monoclonal antibodies.

About Mersana Therapeutics, Inc.

Mersana 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-ADCs 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.

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