Mersana Therapeutics Announces Poster Presentations Demonstrating Differentiating Aspects of ADC Platform Technology at the American Association for Cancer Research Annual Meeting 2018

CAMBRIDGE, Mass., April 09, 2018 -- Mersana Therapeutics, Inc. (NASDAQ:MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody drug conjugates (ADCs) based on its Dolaflexin® and other proprietary platforms, today announced that company scientists are presenting data on Mersana’s lead ADC platform and its unique Dolalock technology at the 2018 American Association for Cancer Research (AACR) Annual Meeting being held April 14-18 at the McCormick Place in Chicago, IL. In addition, the Company co-authored a poster that will be presented by its partner, Takeda, demonstrating that XMT-1522 (TAK-522) showed significant inhibition of tumor growth in combination with an anti-PD1 antibody in preclinical breast cancer models. Details of the poster sessions are as follows:

Poster Title: Unique pharmacologic properties of Dolaflexin-based ADCs – a controlled bystander effect
Session: Antibody-Drug Conjugates: Agents and Technologies
Session Date and Time: April 15, 2018, 1:00 – 5:00 P.M. (CST)
Location: McCormick Place South, Exhibit Hall A, Poster Section 35
Poster Board Number: 754/21

Poster Title: Synergy of an anti-HER2 ADC TAK-522 (XMT-1522) in combination with anti-PD1 monoclonal antibody (mAb) in a syngeneic breast cancer model expressing human HER2
Session: Late-Breaking Research: Immunology 2
Session Date and Time: Tuesday Apr 17, 2018 1:00 PM - 5:00 PM (CST)
Location: McCormick Place South, Exhibit Hall A, Poster Section 44
Poster Board Number: LB 294/16

About XMT-1522

XMT-1522 is a Dolaflexin ADC targeting HER2-expressing tumors. XMT-1522 comprises a novel, proprietary HER2 antibody which is conjugated with Mersana’s Dolaflexin platform – a Fleximer polymer linked with a proprietary auristatin payload. XMT-1522 provides a drug load of approximately 12 molecules per antibody, specifically designed to improve potency while simultaneously increasing tolerability. XMT-1522 has the potential to extend HER2-targeted therapy beyond the current “HER2-positive” populations into patients with lower levels of HER2 expression. The Phase 1 protocol will evaluate XMT-1522 in patients with advanced HER2-positive breast and gastric cancer, as well as advanced breast cancer with low HER2 expression and non-small cell lung cancer. Mersana received FDA clearance of its Investigational New Drug application for XMT-1522 in October 2017. More information can be found on the ongoing Phase 1 clinical study at clinicaltrials.gov.

About Dolaflexin

The Dolaflexin platform is designed to increase the efficacy, safety and tolerability of ADCs by overcoming key limitations of existing technologies based on direct conjugation of a payload molecule to an antibody. Dolaflexin consists of Fleximer, a biodegradable, highly biocompatible, water soluble polymer, to which are attached multiple molecules of our proprietary auristatin drug payload, using a linker specifically optimized for use with our polymer. The high-water solubility of the Fleximer polymer compensates for the low solubility of the payload, surrounding the payload and protecting it from aggregation and maintaining stability in circulation. Multiple molecules of this Dolaflexin polymer-drug conjugate can then be attached to an antibody of choice, which significantly increases the payload capacity of the resulting ADC. This approach differs from most other ADC technologies where the payload is directly conjugated to the antibody via a linker. Using its Dolaflexin platform, Mersana has been able to generate ADCs with Drug-to-Antibody Ratio (DAR) between 12 to 15 while maintaining acceptable pharmacokinetics and drug-like properties in animal models. This represents a three to four-fold increase in DAR relative to traditional ADC approaches.

About Mersana Therapeutics

Mersana Therapeutics is a clinical-stage biopharmaceutical company using its differentiated and proprietary ADC platforms to develop highly targeted drugs with increased tolerability and expanded opportunities to deliver meaningful clinical benefit to patients.  Mersana’s product candidate XMT-1522 is in Phase 1 clinical trials in patients with advanced tumors expressing HER2, including breast cancer, non-small-cell-lung-cancer (NSCLC) and gastric cancer patients. The Company’s second product candidate, XMT-1536, is in Phase 1 clinical trials in patients with tumors expressing NaPi2b, including ovarian cancer, NSCLC and other cancers. In addition, multiple partners are using Mersana’s platform to advance their ADC pipelines.

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