Mersana Enters Research and Exclusive License Agreement with Teva Pharmaceuticals for the Development and Commercialization of X

Mersana Enters Research and Exclusive License Agreement with Teva Pharmaceuticals for the Development and Commercialization of XMT-1107

-XMT-1107 is a novel anti-angiogenic agent that employs Mersana's
Fleximer(r) polymer platform-

CAMBRIDGE, Mass., April 13, 2010 - Mersana Therapeutics, a platform-based cancer therapeutics company, today announced that it has entered into a research and exclusive license agreement with Teva Pharmaceutical Industries Ltd. to develop and commercialize XMT-1107, a novel fumagillin analog, for the treatment of all indications, including cancer.  Mersana plans to initiate a Phase 1 clinical trial for XMT-1107 in the second quarter of 2010.  XMT-1107 will be the company's second oncology product to enter the clinic.  Mersana's XMT-1001, a conjugate of Fleximer and camptothecin (CPT), is currently completing a Phase 1 study.

Under the terms of the agreement, Teva will receive an exclusive license to XMT-1107 for all indications worldwide, excluding Japan, for which Mersana will retain rights.  Mersana will be eligible to receive up to
$334 million if all development, regulatory and commercial milestones are met across several indications.  In addition, Mersana will be eligible to receive royalties on net sales worldwide.  Teva will cover all development costs for XMT-1107, excluding those specific to Japan.

"We are very pleased to enter into this partnership with Teva as it not only provides the necessary resources for XMT-1107 to achieve broad therapeutic potential but also validates our Fleximer platform as a means to generate novel products," said Julie Olson, Ph.D., President and CEO of Mersana.  "We have now produced two clinical-stage oncology products and look forward to progressing our lead program, XMT-1001, beyond Phase 1 studies and to further expanding our Fleximer-based siRNA delivery program."

"Our agreement with Mersana is yet another example of Teva's commitment to early-stage partnering as a means to enhance our innovative pipeline," said Dr. Aharon Schwartz, Vice President of Teva Innovative Ventures.  "We have been impressed by Mersana's success with the Fleximer technology and the potential of XMT-1107.  With a focus on oncology, auto-immune and neurology, Teva, through its Innovative Ventures group, seeks partnerships with companies and academia to develop new specialty medicines."

About XMT-1107
XMT-1107 is a conjugate of Fleximer and a novel analog of fumagillin, an angiogenesis inhibitor with a mechanism of action distinct from agents that principally target vascular endothelial growth factor (VEGF).
Fumagillin analogs had been shown to have anti-tumor activity in Phase 1 and 2 trials, but development was discontinued due to pharmacokinetic
(PK) issues and reversible central nervous system (CNS) toxicity observed in patients.  XMT-1107 has been demonstrated, in preclinical pharmacology studies, to have a significantly improved PK profile as well as no evidence of CNS toxicity.  Additionally, in preclinical models, XMT-1107 has demonstrated efficacy as a single agent and in combination with other agents, including anti-angiogenics.

About Fleximer(r)
Fleximer is a novel, biodegradable and bio-inert polymer that can be chemically linked to small molecules, biologics and nucleic acids to enhance their pharmacokinetic and safety profiles.  Fleximer has been proven to transform existing and experimental agents into new, patentable drugs with superior properties.  The Fleximer platform has broad and versatile applications across therapeutic categories and enhances the delivery of small molecule, protein and nucleic acid-based therapeutics.

About Mersana Therapeutics.
Mersana Therapeutics employs its biodegradable polymer platform
(Fleximer(r)) to create new and better medicines.  We are advancing our own clinical-stage pipeline of novel compounds with the potential to address multiple oncology indications.  The company has also developed a proprietary Fleximer-based siRNA delivery system that is currently in preclinical studies.  Mersana Therapeutics has operations in Cambridge, MA and London, England.  For more information, visit www.mersana.com.