Mersana Therapeutics, Inc. Initiates Phase I Trial of Anti-Cancer Agent, XMT-1001, in Solid Tumors

Mersana Therapeutics, Inc. Initiates Phase I Trial of Anti-Cancer Agent, XMT-1001, in Solid Tumors

May 30, 2007

-- First Compound Based on Company's Proprietary
Fleximer(R) Polymer Platform Enters Clinical Trials


    CAMBRIDGE, Mass., May 30 /Xinhua-PRNewswire/ -- Mersana
Therapeutics, a cancer therapeutics company, announced today
that it has initiated a Phase I open-label, dose-escalation
trial of its lead product candidate, XMT-1001, in patients
with solid tumors. XMT-1001 is a polymer-based prodrug of
camptothecin (CPT), a well-characterized topoisomerase I
inhibitor with potent anti-tumor activity.

    The primary objectives of the study are to determine
the safety, tolerability and pharmacokinetic profile of
XMT-1001. Patients also will be assessed for evidence of
anti-tumor activity. The study is being conducted at three
clinical sites: University of Maryland, Greenbaum Cancer
Center under the supervision of Dr. Edward Sausville; TGen
Clinical Research Services at Scottsdale Heathcare's
Virginia G. Piper Center under the supervision of Stephen
P. Anthony, D.O. and Daniel Von Hoff, M.D.; and U.S.
Oncology in Albany, NY under the supervision of Lawrence
Garbo, M.D.

    "Taking our first compound into the clinic in less
than eighteen months from financing for IND-enabling studies
is a major milestone for Mersana," said Julie Olson,
Ph.D., President and CEO of Mersana.  "In addition to
XMT-1001, we have several other active programs in our
pipeline that take advantage of the unique features of our
Fleximer(R) platform and we look forward to advancing these
compounds into the clinic," she concluded.

    Preclinical data from studies with XMT-1001 presented
at the recent American Association of Cancer Research
annual meeting showed that the agent was a potent and
efficacious agent against tumor xenografts of human colon
cancer and human ovarian cancer.  Fleximer helps deliver up
to 75 times more active CPT (camptothecin) to cancer tumors
than with free CPT administration.  
 
    "Derivatives of the anticancer agent camptothecin,
such as Camptosar(R), have been successful but their true
clinical potential has been limited by safety issues,"
commented Robert J. Fram, M.D., Chief Medical Officer at
Mersana. "It is our hope that our Fleximer-based CPT
conjugate, XMT-1001, will significantly improve the safety
and therapeutic window of CPT and position the compound to
be effective in a broad range of solid tumors."

    About XMT-1001

    XMT-1001 is Mersana's most advanced Fleximer-based
product candidate.  It utilizes a novel, dual release
mechanism to liberate a camptothecin prodrug, which is then
converted within cells into camptothecin, a DNA
topoisomerase I inhibitor.  In pre-clinical studies,
XMT-1001 was better tolerated and more efficacious than
either camptothecin or irinotecan in models of human
cancer, showing extended plasma half-life and high
concentrations in tumor tissue.

    About Fleximer Technology

    Fleximer technology improves the therapeutic index of
cytotoxic compounds useful as anti-cancer agents by
uniquely combining biodegradability with "biological
stealth" properties, making Fleximer materials and
their conjugates long-circulating and non-immunotoxic. 
Fleximer molecules are characterized by solubility in
water, stability in common manufacturing procedures and in
normal physiological conditions, and non-enzymatic
biodegradability upon uptake by cells.  

    About Mersana Therapeutics, Inc.

    Mersana, a privately held, venture-backed company, is
developing novel oncology agents based on clinically
validated compounds through the use of Fleximer(R), a
proprietary bio-degradable and bio-inert material that
enhances the pharmacokinetics, safety, and solubility of
drugs.  Mersana has an exclusive license from the
Massachusetts General Hospital for its core technologies.  
Mersana's pipeline includes compounds with activity against
multiple tumor types and human proof-of-concept that are
improved by its proprietary technologies.  Mersana's
investors include Fidelity Biosciences, ProQuest
Investments, Rho Ventures, Harris & Harris Group and
PureTech Ventures.
 
    Camptosar(R) is a registered trademark of Pfizer.


    For more information, please contact:

     Pete Leone
     Chief Operating Officer
     Mersana Therapeutics, Inc.
     Tel:   [phone]

    Media:
     Kathryn Morris, KMorrisPR
     Tel:   [phone]
     Email: [e-mail]