Mersana Therapeutics has granted Takeda Pharmaceutical rights to its lead product candidate, the clinic-bound cancer therapy XMT-1522, outside the U.S. and Canada under an expanded partnership that could generate up to $830 million for Mersana.

The deal marks the third collaboration between the companies—the first was launched in April 2014—and expands the total value of all three partnerships to more than $1 billion.

Takeda and Mersana also agreed to expand an earlier collaboration by giving Takeda additional access to Mersana’s Fleximer® antibody-drug conjugate (ADC) platform. In return, Mersana gained an option at the end of Phase I to codevelop and co-commercialize one of the ADC programs in the U.S. The company also agreed to identify and co-develop new payloads for use in new ADC therapies using Takeda’s proprietary small molecule libraries.

Mersana said it anticipates filing an IND for XMT-1522 with the FDA in mid-2016. XMT-1522 is a preclinical Fleximer-based ADC therapy designed to target HER2-expressing tumors, including breast, gastric, and non-small cell lung cancers. According to the company, XMT-1522 has generated preclinical data showing significant anti-cancer activity, including in HER2 low-expressing tumor models refractory to currently available therapies.

Takeda and Mersana agreed to co-develop XMT-1522, with Mersana to lead a planned Phase I trial. Mersana will retain full commercial rights in the U.S. and Canada.

“We believe XMT-1522 has the potential to make a dramatic difference for HER2 low-expressing patients who currently have limited treatment options, and are confident that our Fleximer-based technology can address significant patient needs not currently met by other ADC platform technologies,” Mersana President and CEO Anna Protopapas said in a statement.

Protopapas joined Mersana last year after previously serving as president of Takeda’s wholly owned subsidiary Millennium Pharmaceuticals. Through Millennium, Takeda agreed to pay Mersana $40 million up front and an additional $20 million upon clearance of the IND for XMT-1522 by the FDA. Mersana is also eligible to receive more than $750 million in payments tied to achieving milestones for the XMT-1522 and ADC programs, as well as royalties. Takeda also agreed to invest up to $20 million in equity in future rounds of Mersana financing.

“We see great potential for Mersana’s Fleximer technology, combined with our oncology expertise and resources, to extend the benefits of targeted therapy with ADCs to underserved cancer patient populations,” stated Andrew Plump M.D., Ph.D., Takeda’s chief medical and scientific officer.

Oncology is part of Takeda’s “general medicine” core therapeutic area, one of six areas on which the company focuses R&D efforts. The others are cardiovascular and metabolic, central nervous system, gastrointestinal, respiratory and immunology, and vaccines.