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

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

Business Wire

CAMBRIDGE, Mass. -- 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

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. For more information, please visit


MacDougall Biomedical Communications
Jennifer Conrad or Kari Watson, 781-235-3060 or
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