Moonwalk raises $70 million to push fat-targeting RNAi obesity drug toward human trials

Moonwalk Biosciences, a San Francisco-area biotech company, said on Sept. 8, 2026 that it raised $70 million in a Series B financing round to move an experimental obesity drug toward human testing ^[1][2]. The drug, MW101, is designed to act on fat tissue rather than appetite, and the company plans to begin first-in-human studies by the end of 2027 ^[1][2].

The round was co-led by Alpha Wave Global and YK Bioventures, according to BioPharma Dive ^[2]. BioSpace reported the co-leads as Alpha Wave Ventures and YK Bioventures ^[1]. Eli Lilly, Gaorong Ventures, ARCH Venture Partners, Khosla Ventures and Future Ventures also took part ^[1][2].

MW101 is a small interfering RNA, or siRNA, treatment. These medicines are designed to stop a gene from making a specific protein. Moonwalk's version targets adipose tissue, the body fat stored under the skin, which the company says is thought to contain underlying causes of obesity ^[1]. The technology was licensed from Suzhou Siran Biotechnology Co. earlier this year, CEO Alex Aravanis told BioPharma Dive ^[2].

In preclinical studies in mice, MW101 produced weight loss and fat reduction while maintaining muscle mass, and did so without reducing food intake, according to BioSpace ^[1]. Aravanis described the mechanism this way: "Our mechanisms are around modulating, so increasing the metabolism and lipolysis, which break down fat, and the energy regulation within the fat cells" ^[2].

That differs from the GLP-1 drugs that currently dominate the obesity market, including semaglutide (sold as Ozempic, Wegovy and Rybelsus) and tirzepatide (sold as Mounjaro and Zepbound) ^[1]. Those drugs work in part by suppressing appetite. Moonwalk says its candidates are not appetite suppressants, an approach it argues could avoid gastrointestinal side effects and help preserve muscle ^[1][2].

"This financing brings us closer to developing a new generation of adipose-targeted medicines designed to improve outcomes for people living with obesity and related cardiometabolic diseases," Aravanis said in a company release ^[1]. Rick Gerson, CEO of investor Alpha Wave, said the preclinical approach could "redefine how obesity is treated by delivering therapies with the potential for durable efficacy, lean muscle preservation and infrequent dosing" ^[1].

Moonwalk has several other candidates in preclinical development that aim to lower fat ^[1]. Its discovery engine is an AI platform that combines genetics, epigenomics and other data to find siRNA therapies ^[1]. This is not the company's first raise: it launched in 2024 with $57 million and plans to mine the epigenome, using gene editing technology licensed from the Broad Institute ^[1][2]. Aravanis told BioPharma Dive the shift to RNAi was "more of an evolution of the story," because the company decided RNAi "would be a faster way for us to bring it to the clinic" ^[2].

Other biotechs are working on nucleic acid therapies for obesity. ADARx Pharmaceuticals filed plans for an initial public offering the week before, and Wave Life Sciences has an siRNA drug, WVE-007, in mid-stage testing in people with obesity ^[2]. That drug targets the liver rather than fat cells; earlier data showed "substantial reductions of fat" and waist circumference but fell short of investor expectations, according to BioPharma Dive ^[2].

Why it matters for patients

MW101 is early. No human testing has been reported, so there is no evidence about whether it works, what side effects it causes or how it compares with approved medicines. The results described so far come from mice, and drugs that work in mice often behave differently in people ^[1].

The muscle question is one reason this approach draws attention. Loss of lean muscle during rapid weight loss has been a concern raised around GLP-1 drugs, and Moonwalk's mouse data suggests its drug preserved muscle while reducing fat ^[1]. Whether that holds true in people has not been shown.

Lilly's participation is notable because Lilly sells the competing tirzepatide medicines Mounjaro and Zepbound, but an investment is not evidence that a drug works or that it will reach the market. Nothing about currently approved GLP-1 medicines changes based on this financing.

It also has not been disclosed how MW101 would be given, how often, what it would cost, or whether it would be a shot or another form.

What happens next

Moonwalk says the $70 million will support work needed before human testing, with first-in-human studies planned for late 2027 ^[1][2]. No dates for later-stage trials have been announced, and no timeline for seeking FDA approval has been disclosed.