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

October 15, 2013

Mersana Therapeutics, Inc. announced today that it successfully achieved the first preclinical milestone in its collaboration with Endo Pharmaceuticals (Nasdaq: ENDP). In recognition of the significant progress made to date, Mersana has received an undisclosed milestone payment from Endo. In 2012, Mersana and Endo entered into a multi-target, oncology focused partnership to develop next-generation Fleximer® antibody-drug conjugates (ADCs).

“We are very encouraged with the rapid progress in this collaborative research effort, and based on the preclinical results to date, we are excited about the future prospects of this novel Fleximer-ADC,” said Timothy Lowinger, Ph.D., Chief Scientific Officer of Mersana. “We look forward to rapidly advancing this program through preclinical development and into the clinic.”

“We are very pleased with the results in our ADC collaboration with Mersana, and based on the preclinical proof-of-concept data, we hope to progress this novel ADC through preclinical development as rapidly as possible,” stated Sandeep Gupta, Ph.D., Senior Vice President of Discovery and Early Development at Endo. ”We believe this Fleximer-ADC has potential to be the best-in-class agent for treating various cancers. This effort further validates Endo’s virtual drug discovery model, which was initiated in 2009 to discover novel treatments addressing unmet medical needs and provide options to patients and providers.”

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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