SPI-5557

SPI-5557 is a preclinical **small interfering RNA** regenerative hearing-loss candidate being developed by Sound for **severe to profoundly impaired hearing loss**. It is described as a **locally injected siRNA** designed to inhibit **cyclin-dependent kinase inhibitor 1B**, also known as **p27** or **Kip1**, with the goal of driving cochlear supporting cells back into the cell cycle and promoting regeneration of supporting cells and sensory hair cells in the cochlea. The program represents a local RNA-based inner-ear regenerative approach intended to restore hearing in patients with severe to profound impairment; based on the provided pipeline information, it remains **preclinical** and **IND not yet filed**.