Mersana Therapeutics, Inc.,a developer of antibody drug conjugates (ADCs), has expanded its ongoing collaboration with Takeda Pharmaceutical Company Limited to create novel Fleximer ADC drug candidates to include additional oncology-relevant targets. Mersana is eligible to receive additional upfront and milestone payments potentially totaling over $300 million under the expanded collaboration subject to future success of the programs. The partners' collaboration was announced in April 2014, and since then, Mersana and Takeda have been conducting pre-clinical, proof-of-concept studies for several Fleximer-ADCs against an undisclosed oncology target under a research license to Mersana's Fleximer-ADC technology. Takeda has already exercised an option to license commercial rights for the first drug candidate developed under this collaboration, which was announced in October 2014.

Takeda signed an agreement with Mersana through its wholly owned subsidiary, Millennium Pharmaceuticals, Inc. Under that agreement, Takeda provided an upfront payment to Mersana for the right to use Fleximer technology to develop novel ADC candidates for indications in oncology. Mersana is currently conducting research and creating ADCs that are conjugates of Takeda's antibodies and Mersana's payload platforms, which combine a cytotoxic payload with the Fleximer polymer and custom linkers. In addition to providing antibodies, Takeda is responsible for product development, manufacturing, and commercialization of any Fleximer-ADC products. Mersana remains eligible to receive milestone payments and royalties on worldwide net sales of any resulting ADC products. When Takeda exercised its option for commercial rights to the first ADC product, Mersana received a license fee.

Mersana's Fleximer ADC technology is based on the company's proprietary biodegradable polymer system, known as Fleximer, and a wide variety of linkers that allow for the attachment of an extensive range of anti-tumor payloads to Fleximer. As an example, once loaded with drug(s), Fleximer is then attached through a stable linker that is different from the drug linker(s) to the antibody or antibody alternative to create a Fleximer-ADC. Mersana's linker systems are designed to be stable in the bloodstream and to release the drug payloads once inside the targeted cell. Mersana's Fleximer-ADC technology provides several key benefits: the ability to deliver diverse payloads; the opportunity to increase drug loading per antibody; improved physicochemical properties; and facile manufacturing. Mersana's proprietary polymer payload platforms include Dolaflexin, an auristatin-polymer conjugate; Vindeflexin, a vindesine-polymer conjugate; and Cytoflexin, a tubulysin-polymer conjugate.

Source: Mersana Therapeutics