Seagen, Merck put $1.6B ADC collab on the back burner citing 'emerging treatment landscape'

Seagen is putting a phase 2 Merck & Co.-partnered antibody-drug conjugate on the shelf for now, nearly three years after signing on to a $1.6 billion partnership for the asset.

The company—which is in the process of being acquired by Pfizer—briefly noted in a second-quarter earnings filing Thursday that ladiratuzumab vedotin, or LV, is being deprioritized. Merck confirmed in an email Thursday afternoon that the company is in the process of discontinuing the program. 

"LV has been shown to be clinically active with a tolerable safety profile, however, the emerging treatment landscape with newer therapeutics introduces a higher efficacy threshold," Seagen said in a statement to Fierce Biotech. 

Merck in September 2020 ponied up $600 million for the ADC, alongside a $1 billion investment in Seagen, at the time known as Seattle Genetics. The companies planned to co-develop LV in combination with Keytruda for breast cancer and other solid tumors. The therapy was in phase 2 testing at the time but little has been detailed about the clinical program since. LV could have been a rival to Gilead Sciences’ Trodelvy.

"Several attempts have been made to optimize the profile of LV through combination therapy and varying the dosing regimens, which were insufficient to elevate the efficacy profile of LV to justify moving to a pivotal trial whether as a monotherapy or in combination with Keytruda," the Seagen statement said. 

LV uses Seagen’s ADC technology—the gem of the Pfizer megadeal—to target LIV-1, which is expressed in most metastatic breast cancers as well as in melanoma, prostate, ovarian, uterine and cervical cancers.

Merck was rumored to be in the running to buy Seagen last year, but the deal—reportedly valued around $40 billion—stalled when the parties could not agree on the right price. Pfizer came out the victor with a $43 billion offer.

The Seagen statement noted that the collaboration agreement signed in 2020 is still active. 

Merck did not return a request for comment on the future of the LV program as of publication.