Andrew Thompson, Co-Founder and CEO, Proteus Digital Health. Photo credit: Stuart Isett/Fortune Brainstorm Health, under Creative Commons license

Proteus Digital Health, a Redwood City, California-based health tech startup that was once valued as high as $1.5 billion by investors, has filed for Chapter 11 bankruptcy protection. The filing comes after reports of the company struggling to raise more cash to sustain operations, even after having raised nearly $500 million in private funding. Proteus is best-known for working on human-ingestible sensors that track and communicate when medicines are taken, alongside a wearable device that monitors the progress. The company appears to have run a series of trials with medical organizations but never gotten to the point of fully commercializing its product, even after nearly two decades of existence.

Throughout its existence, Proteus has managed to secure funding from investors including medical and pharmaceutical giants like Novartis, Kaiser Permanente, Medtronic, and Otsuka Pharmaceutical. Software giant Oracle is also an investor.

Proteus appears to have bailed out after years upon years of trying to deliver a product. The company’s bankruptcy filing indicates that it currently holds assets of between $100 million-$500 million and debt of between $50 million-$100 million.