Mersana pushes fundraising past $120M, takes aim at the clinic

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Mersana Therapeutics has teed up its first clinical program for the lead antibody drug conjugate in its pipeline, gaining $33 million in a new round to fund the work while pushing ahead on pipeline expansion efforts. 

Mersana CEO Anna Protopapas says the round brings the Cambridge, MA-based biotech’s total take from venture groups and partnership cash to $120 million-plus, which has been fueling a swelling workforce as the company makes steady progress on its business plan.

Just a few months ago Takeda upped the ante in its two-year collaboration with Mersana, agreeing to hand over $80 million in near-term cash and an upfront while promising up to $750 million more in milestones to gain ex-U.S. rights to their lead drug. Takeda’s total pact with Mersana, including its earlier deals, rings up at more than $1 billion.

“We’re now in great financial condition,” says the CEO, an experienced hand in Cambridge biotech circles with a long stint at Millennium that included a turn at the helm. And while there’s no immediate plan to go public, she’s happy to point out that the new round expanded its group of investors to include public players, which would help make that leap when the time is right.

Wellington Management Company led the round, with contributions from Cormorant Asset Management, Arrowpoint Partners and Takeda Pharmaceutical Company as well as existing investors NEA and Rock Springs Capital.

The next big step for Mersana will be a Phase I study for XMT-1522, set to begin now later in the year. The ADC uses an antibody from Adimab with a unique linker construct to tie on a payload of multiple therapeutics aimed at HER2-positive breast cancer, looking to reach a broader base of patients than the current therapies can help. Investigators will put the drug through a two-stage study, starting with dose escalation over 9 to 12 months and following with dose expansion among multiple patient cohorts over the following 9 to 12 months.

The biotech has also identified its second drug in preclinical development. XMT-1536, an anti-sodium-dependent phosphate transport protein 2B (anti-NaPi2b) ADC, is now being moved ahead toward IND-enabling studies after the company discussed positive non-human primate data in April.

To get the work done, Mersana has grown its staff to 52, and plans another 15 hires by the end of the year. 

Mersana Chairman David Mott, the globe trotting partner at NEA and ex-CEO at MedImmune, has played a big role in developing the biotech, says Protopapas.

“He’s very committed to his companies,” she notes. “He’s someone who’s very direct, and I like that.”