Mersana Therapeutics, Inc. Strikes $270 Million Antibody-drug Conjugate Deal With Endo Pharmaceuticals

CAMBRIDGE, MASS. MARCH 7, 2012 – Mersana Therapeutics, Inc. announced today that it has entered into a collaboration agreement with Endo Pharmaceuticals (Nasdaq: ENDP) to develop next-generation antibody-drug conjugates (ADCs). Mersana’s proprietary conjugation technology is comprised of the Company’s Fleximer® polymer and a broad array of customizable linker chemistries for attaching diverse, potent payloads and targeted antibodies. Under this agreement, Endo will pay an upfront fee to Mersana for the right to utilize the Fleximer technology to develop novel ADC candidates against a single cancer target.

“Our proprietary conjugation technologies, centered on Fleximer, are particularly well-suited to expand the therapeutic potential of ADCs by enabling greater cytotoxic payload, diverse mechanisms of action, better tumor penetration, and improved stability achieved with optimized linkers,” said Nick Bacopoulos, CEO of Mersana. “We look forward to working with Endo to incorporate their antibodies against a very promising oncology target into next-generation Fleximer-ADC candidates. We expect this to be just the first of several important Fleximer-ADC collaborations for Mersana.” Under the collaboration, Mersana is responsible for conducting research and creating ADCs that are conjugates of the Company’s diverse, highly potent cytotoxic payloads, its Fleximer polymer and custom linkers, and Endo’s novel antibodies. In addition to providing novel antibodies, Endo is responsible for product development, manufacturing and commercialization of any Fleximer-ADC products. Mersana and Endo may mutually agree to pursue two additional targets over the next two years. In the event that all three targets are pursued, Mersana is eligible to receive more than $270 million in progress-dependent milestones as well as royalties on worldwide net sales of any resulting ADC products. “The collaboration with Mersana further enhances Endo’s Discovery and Early Development portfolio and is validation of our collaborative R&D approach for drug discovery and development. Using Mersana’s Fleximer-ADC technology, we aim to develop more efficacious and safer treatment options to improve patient outcomes,” said Ivan Gergel, Executive Vice President of R&D and Chief Scientific Officer, Endo Pharmaceuticals.

About Fleximer Antibody-Drug Conjugate Technology

Mersana’s next-generation 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 fragment to create an 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 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. To view a video demonstrating how Mersana’s Fleximer-ADC technology works, please click here.

About Mersana Therapeutics, Inc.

Mersana engineers novel drug conjugates that maximize the potential of new and established therapeutic classes. Utilizing its proprietary conjugation technology, which is comprised of the Fleximer® polymer and a broad array of customizable linker chemistries, Mersana is developing a portfolio of next-generation antibody-drug conjugates (ADC) with superior properties not found with current ADC technologies. The company is also advancing its own pipeline of next-generation drugs with best-in-class potential to address unmet needs and improve patient outcomes in multiple oncology indications. Mersana’s clinical pipeline consists of two cancer therapeutics: XMT-1001, a potentially best-in-class novel "tecan" conjugate that is currently being investigated in a Phase 1b extension trial in patients with lung cancers; and XMT-1107, a first-in-class anti-angiogenic conjugate with a unique mechanism of action that is currently in a Phase 1 trial in patients with refractory, advanced solid tumors. XMT-1107 was licensed to Teva Pharmaceutical Industries Ltd. (TEVA) on a worldwide basis, except for Japan, where Mersana elected to retain rights.

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