Third Rock-backed autoimmune biotech turns off the lights

A Third Rock Ventures biotech created to make new medicines for autoimmune and inflammatory diseases has shuttered, Endpoints News has learned.

Rheos Medicines changed its registered office address and registered agent last month to that of a Foxborough, MA accounting firm that specializes in bankruptcies, per January documents. A Third Rock spokesperson confirmed to Endpoints that Rheos wound down “late last year.”

“They made the decision to partner assets and technology and some of these efforts are still ongoing,” the spokesperson said in an emailed statement.

The closing of Rheos Medicines adds to a dreary winter for the drug development industry, in which dozens of startups have laid off workers, pruned pipelines, sold assets or ultimately folded, including other Third Rock companies Ambys Medicines and Goldfinch Bio. Some new biotechs have also come to the fore in that time, but at a subtler pace and with money that likely came through before the financial markets soured.

Launched in 2018 with $60 million in backing from Third Rock, Schroders Capital, Mirae Asset and others, Rheos set out to create precision treatments for immune-mediated diseases, including autoimmune disorders, inflammatory diseases and cancer.

Rheos had lined up Roche as a partner in 2019, inking a multi-target pact that started with $42.5 million, another $90 million on the line for research and preclinical milestones and $660 million waiting in the wings had the assets made it through development, regulatory and sales milestones. That partnership was no longer active “as of the second quarter of 2022,” a spokesperson for the Swiss Big Pharma told Endpoints via email.

In the pipeline were a suite of assets, with MALT1 inhibitor RHX-317 up first. Internet archives show Rheos considered testing the drug in patients with chronic graft-versus-host disease, rheumatoid arthritis, psoriasis and other indications.

Barbara Fox

The FDA greenlit a Phase I to investigate the drug last year, with a healthy volunteer study expected to begin in the second half of 2022, Rheos said last summer. At the time, CEO Barbara Fox said Rheos would be the first to test a MALT1 inhibitor in autoimmune and inflammatory diseases, whereas other drug developers focus on oncology.

The planned study does not show up on the federal clinical trials database, per searches for the drug name and Rheos and Rheos Medicines.

Preclinical assets included RHX-889, RHX-552, RHX-714 and RHX-829 for autoimmunity and inflammation.

Fox joined in 2019 after selling Tilos Therapeutics to Merck that year. Fox’s LinkedIn profile lists a switch to a consulting role at Rheos as of December 2022. She’s also a board member at stealth mode antibodies biotech Diagonal Therapeutics, backed by Atlas and Lightspeed.

Prior to Fox’s arrival, Rheos’ early days were led by Third Rock partner Abbie Celniker and Sanjay Keswani, who went on to become CMO at Annexon Biosciences and then startup MiroBio last year, shortly before the UK biotech sold to Gilead.

Co-founders included Johns Hopkins’ Erika Pearce and Edward Pearce, Yale’s Richard Flavell, Duke’s E. William St. Clair, Cambridge University’s Ken Smith and Laurence Turka, who was founding CSO and until recently held the same post at Rubius Therapeutics, a one-time Flagship Pioneering upstart that is searching for strategic alternatives.

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