Moonwalk raises $70 million, with Lilly investing, for an adipose-targeted RNAi obesity drug

Moonwalk Biosciences, a California biotech, has closed a $70 million Series B funding round to push its lead obesity drug candidate, MW101, toward human testing ^[1][2]. The round was co-led by Alpha Wave Ventures and YK Bioventures, with participation from Eli Lilly, Gaorong Ventures, ARCH Venture Partners, Khosla Ventures and Future Ventures ^[1][2]. The company said the financing was oversubscribed [2 headline context, 1].

MW101 uses small interfering RNA, or siRNA, technology licensed in part from Suzhou Siran Biotechnology Co., a Chinese drugmaker ^[2]. Unlike GLP-1 drugs such as Ozempic, Wegovy, Mounjaro and Zepbound, which work mainly by suppressing appetite, Moonwalk's approach is designed to act directly on adipose tissue, the fat stored under the skin that the company says harbors underlying drivers of obesity ^[1][2]. CEO Alex Aravanis said the mechanism works by "modulating, so increasing the metabolism and lipolysis, which break down fat, and the energy regulation within the fat cells" ^[2].

In preclinical studies in mice, MW101 produced weight loss and fat reduction while preserving muscle mass, and it did this without reducing how much the animals ate ^[1]. Moonwalk has not yet disclosed detailed data from these studies ^[2]. The company plans to use the new funding for IND-enabling work, the studies and paperwork needed before starting first-in-human trials, which it expects to begin in late 2027 ^[1][2].

Moonwalk launched in 2024 with $57 million in seed funding backed by MIT neuroscientist Feng Zhang, initially aiming to mine the epigenome, the set of chemical marks that control how genes are switched on and off, for new drug targets ^[1][2]. Aravanis described the shift toward siRNA and adipose-targeted obesity drugs as "an evolution of the story" rather than a departure from the company's original plan ^[2].

Why it matters for patients

MW101 is years away from being available to patients. It has only been tested in mice so far, and human trials are not expected to start until late 2027 at the earliest ^[1][2]. That means there is no evidence yet on how it works, or how safe it is, in people.

Still, the approach is notable because it targets a different biological pathway than current GLP-1 medicines. Semaglutide (Ozempic, Wegovy, Rybelsus) and tirzepatide (Mounjaro, Zepbound) work by mimicking gut hormones that reduce appetite, and gastrointestinal side effects like nausea are common with these drugs. Loss of muscle mass alongside fat loss has also been a concern with GLP-1 treatment. Moonwalk's Aravanis said the siRNA approach could avoid gastrointestinal side effects and help preserve muscle because it does not work by suppressing appetite ^[2]. Whether that preclinical promise holds up in people is not yet known.

For patients weighing today's options, this development does not change what is currently approved or available. It is a sign that drug companies, including Lilly, are investing in a range of approaches beyond GLP-1s, but it does not offer a new treatment choice now or in the near term.

What happens next

Moonwalk plans to complete IND-enabling studies, the safety and manufacturing work regulators require before human testing can begin, using the new $70 million ^[1][2]. The company expects to start first-in-human trials for MW101 in late 2027 ^[1][2]. Moonwalk also has other siRNA candidates for obesity and related cardiometabolic diseases still in earlier, preclinical stages ^[1][2]. The company is one of several exploring RNA-based obesity treatments; competitors named in reporting include ADARx Pharmaceuticals, which recently filed for an initial public offering, and Wave Life Sciences, which has a liver-targeted siRNA obesity drug in mid-stage human testing ^[2].