SOUTH SAN FRANCISCO, Calif. | June 23, 2026
Calico Life Sciences has announced that the U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy Designation (BTD) to fosigotifator, its investigational eIF2B activator, for the treatment of Vanishing White Matter (VWM) disease, an ultra-rare and progressive neurological disorder with no approved therapies. The designation recognizes the potential of fosigotifator to offer a substantial improvement over existing treatment options based on preliminary clinical evidence. The milestone follows the therapy’s earlier inclusion in the FDA’s Support for Clinical Trials Advancing Rare Disease Therapeutics (START) Program and supports the continued advancement of Calico’s ongoing Phase 1b/2 clinical trial evaluating the drug in adult, pediatric, and infant patients with VWM disease.
Breakthrough Designation Supports Development of First eIF2B Activator
Fosigotifator is the first eIF2B activator to enter clinical development for Vanishing White Matter disease, targeting one of the key biological mechanisms responsible for disease progression. The investigational therapy is designed to restore the activity of the eIF2B protein complex, helping regulate the Integrated Stress Response (ISR), a cellular pathway involved in protein synthesis and stress regulation. In patients with VWM disease, mutations affecting the eIF2B enzyme result in chronic ISR activation, leading to degeneration of the brain’s white matter and progressive neurological impairment. The ongoing Phase 1b/2 clinical trial (NCT05757141) is evaluating the safety, tolerability, pharmacokinetics, and exploratory efficacy of fosigotifator across multiple age groups, marking the first time this therapeutic approach has been tested in individuals living with VWM.
Preclinical Research Demonstrated Promising Disease-Modifying Potential
According to Calico Life Sciences, preclinical studies demonstrated that fosigotifator successfully increased the activity of eIF2B complexes carrying disease-causing genetic variants. In animal models of Vanishing White Matter disease, treatment reduced Integrated Stress Response activation in the brain and spinal cord while improving motor coordination, movement function, and overall survival. Researchers believe restoring normal eIF2B function may help prevent or slow the progressive loss of brain white matter that characterizes the disease. VWM typically presents during childhood but can develop at any age, causing symptoms including impaired movement, cognitive decline, seizures, and episodes of rapid neurological deterioration triggered by stress, infections, or mild head injuries. The condition currently has no approved treatment or cure, highlighting the urgent need for innovative therapeutic approaches.
Advertisement
Milestone Strengthens Calico’s Rare Disease Development Program
The FDA Breakthrough Therapy Designation provides opportunities for enhanced regulatory guidance and accelerated development pathways for therapies targeting serious conditions with significant unmet medical needs. Calico Life Sciences, founded by Alphabet Inc. and Arthur D. Levinson, believes the designation validates its research into eIF2B biology and the Integrated Stress Response as promising therapeutic targets for rare neurological diseases. The company remains focused on advancing fosigotifator through clinical development while continuing its broader mission of applying cutting-edge biological research to address diseases linked to aging and cellular stress. If future clinical studies confirm its safety and effectiveness, fosigotifator could become the first approved disease-modifying treatment for patients living with Vanishing White Matter disease, offering new hope to affected individuals and their families.
Source: Calico Life Sciences press release
