Merck quietly ditches its sac-tmt copy

Just three weeks after ApexOnco revealed that Merck & Co’s MK-6837 was a TROP2-directed ADC – just like the company's high-profile, Kelun-originated project sacituzumab tirumotecan – the molecule has been discontinued.

MK-6837 had been in clinical trials since mid-2024, but it was only in April that its mechanism and modality came to light, in a listing on an obscure Israeli registry. On its first-quarter call on Thursday Merck was asked by an analyst about MK-6837, and Dean Li, president of Merck Research Laboratories, stated: “We have discontinued that.”

Li gave no reason for the discontinuation, but it seemed strange that Merck’s 2022 deal with Kelun didn’t preclude the US company from developing an in-house asset that would theoretically compete against sac-tmt. That said, the details of this tie-up are confidential, so this matter can only be speculated on.

But one possibility is that Kelun took issue with Merck’s development of such a project. At the time of publication Kelun hadn’t responded to a request from ApexOnco to comment on whether it had had any input into Merck’s decision to drop MK-6837.

Unique payload

ApexOnco earlier asked Merck to provide any further information on MK-6837’s design characteristics, how it differed from sac-tmt, and what the reasoning was behind developing both ADCs, but the group wouldn’t comment.

In response to Deutsche Bank’s James Shin on Thursday, however, Li revealed that MK-6837 was “another ADC, which had a unique payload”. He added: “We've always said that we're very interested in the ADC field in changing the target, but also changing the payload and thinking about combinatory [approaches] or cycling different payloads.”

He cited the “profound impact of sac-tmt” as one reason why the decision was taken to abandon MK-6837.

As of 1 May the clinicaltrials.gov listing for MK-6837’s phase 1 solid tumour study remains marked “active”, having recruited 168 patients, higher than the initial enrolment target of 100. This suggests that the decision to discontinue MK-6837 was recent.