Astellas Pharma will use Ambrx’ technology in an up-to-$300 million collaboration designed to develop and commercialize antibody drug conjugates (ADCs) against cancer, the companies said today.

Astellas agreed to pay Ambrx $15 million up front, plus up to $285 million in payments tied to potential near- and long-term R&D, regulatory, and sales-based milestones for an undisclosed number of targets for ADCs in oncology. An unspecified portion of the milestone payments, plus royalties on any net sales, will hinge on the partnership successfully commercializing products.

In return for the money, Ambrx will use its site-specific conjugation technology, plus its linkers and drug payloads, to produce ADCs for Astellas. The deal gives Astellas worldwide rights to develop and commercialize the ADCs for oncology.

Astellas will carry out the collaboration through its Agensys affiliate, which is looking to expand its capabilities in R&D on therapeutic antibodies for use as cancer drugs.

“Ambrx offers a novel approach to allow creation of site-specific and highly stable conjugations that have the potential to further optimize drug delivery to tumor cells,” David Stover, Ph.D., svp and Agensys site head, said in a statement.

Ambrx is among biotechs that have focused on developing ADCs, hoping to follow in the successful footsteps of drug developers like Roche’s Genentech unit and ImmunoGen, which won FDA approval of their breast cancer conjugate Kadcyla. More recently on March 22, LinXis granted APO-T an exclusive worldwide license for the development and commercialization of fully human ADCs using APO-T’s MAGE-HLA targeted antibodies and LinXis’ Lx®, the firm’s linker technology. In exchange, LinXis will receive undisclosed milestone payments and royalties.

The deal with Astellas almost matches what Ambrx stands to receive from Merck & Co. in a collaboration announced last year. Merck agreed to pay Ambrx $15 million up front, and up to $288 in milestone payments, in return for use of Ambrx’ technology to develop a new family of protein conjugates of undisclosed indication that selectively deliver small molecules to their site of action.

Astellas and Merck have joined Bristol-Myers Squibb, Eli Lilly, and several undisclosed companies that have launched collaborations with Ambrx to use its technology in developing new drugs. With BMS, for example, Ambrx is developing Phase I drug candidate ARX618 for diabetes, and the preclinical candidate Relaxin for heart failure.

Ambrx’ lead product, ARX201, is a long-acting growth hormone that has successfully completed Phase IIb clinical trials.

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