Eli Lilly and Company announced a definitive agreement to acquire SiteOne Therapeutics, a clinical-stage biotechnology company, for up to $1.0 billion in cash to strengthen its pain management pipeline with non-opioid therapies. The transaction, announced on May 27, 2025, includes STC-004, a Phase 2-ready Nav1.8 inhibitor being developed as a next-generation treatment for chronic pain.
Strategic Focus on Non-Opioid Pain Management
The acquisition addresses a critical unmet medical need in pain management. "The global burden of chronic pain continues to increase, and an effective non-opioid treatment remains elusive," said Mark Mintun, Lilly group vice president Neuroscience Research and Development. "Lilly is eager to continue the development of STC-004 with the outstanding SiteOne team as part of our efforts to advance novel, addiction-free pain therapies."
SiteOne has dedicated more than a decade to developing safer, more effective alternatives to opioid-based pain treatments. The company's approach focuses on highly selective small molecule inhibitors targeting Nav1.7, Nav1.8, and other ion channels to treat pain, cough, and other conditions involving hyperexcitability of the peripheral nervous system.
STC-004: A Novel Sodium Channel Inhibitor
The centerpiece of the acquisition is STC-004, a Nav1.8 inhibitor that has reached Phase 2 readiness. This compound represents SiteOne's lead program in developing non-opioid pain therapeutics without the significant addiction potential and side effects associated with current opioid treatments. The drug candidate targets sodium channels specifically involved in pain signaling, offering a mechanistically distinct approach to pain management.
SiteOne's platform extends beyond STC-004, with additional novel drug candidates exhibiting precise selectivity for individual ion channel subtypes to treat other sensory hyperexcitability disorders, including chronic cough and chronic ocular surface pain.
Financial Terms and Strategic Rationale
Under the agreement terms, SiteOne shareholders could receive up to $1.0 billion in cash, structured as an upfront payment plus subsequent milestone payments tied to regulatory and commercial achievements. The transaction is subject to customary closing conditions and will be reflected in Lilly's financial results upon completion.
"Lilly shares our deep commitment to scientific rigor, innovation, and patient-centered drug development," said John Mulcahy, Ph.D., chief executive officer and cofounder of SiteOne Therapeutics. "We believe their global capabilities and neuroscience leadership will accelerate our efforts to realize the full potential of STC-004 and our broader platform."
Addressing Critical Medical Need
The acquisition aligns with Lilly's broader strategy to address significant health challenges through innovative drug development. Mintun emphasized that "innovation in pain management is critical to address the unmet needs of millions of patients around the world," highlighting the substantial patient population that could benefit from effective non-opioid pain treatments.
SiteOne's approach to developing pain therapeutics without addiction potential addresses a major public health concern, as the opioid crisis has underscored the urgent need for safer pain management alternatives. The company's focus on peripheral nervous system hyperexcitability disorders represents a targeted approach to treating pain at its source while minimizing systemic side effects.
The transaction involves multiple advisory firms, with J.P. Morgan Securities LLC serving as Lilly's exclusive financial advisor and Jones Day as legal counsel. For SiteOne, Centerview Partners LLC acts as exclusive financial advisor, with Skadden, Arps, Slate, Meagher & Flom LLP and Cooley LLP providing legal counsel.
