Development of CAL101-a humanized monoclonal antibody targeting S100A4 to inhibit proinflammatory and profibrotic...

S100A4, a member of the S100 family of calcium-binding proteins, acts as a damage-associated molecular pattern with a central role in modulating inflammatory and fibrotic responses. Upon extracellular release, S100A4 engages receptors such as toll-like receptor 4, triggering signaling cascades that amplify proinflammatory cytokine production and promote fibrotic tissue remodeling, positioning it as a promising therapeutic target. This study describes the development and characterization of CAL101, a humanized IgG4 monoclonal antibody, which binds with high affinity to the S100A4 target-binding interface. CAL101 exhibits strong cross-species reactivity, effectively binding S100A4 from human, cynomolgus monkey, mouse, and rat. Functional assays demonstrate that CAL101 inhibits toll-like receptor 4 and transforming growth factor β pathway activation in reporter cell lines and decreases cytokine release in human monocytes and whole blood cell cultures. These findings support continued development of CAL101 as a therapeutic candidate for fibrotic and chronic inflammatory diseases. A recently completed phase I trial (ClinicalTrials.gov ID NCT05965089) established the safety, pharmacokinetic, and immunogenicity profile of CAL101. A phase II trial in patients with idiopathic pulmonary fibrosis has been initiated (ClinicalTrials.gov ID NCT06736990). SIGNIFICANT STATEMENT: This article presents the development and characterization of CAL101, a first-in-class humanized IgG4 antibody that neutralizes S100A4 by blocking its receptor interactions. CAL101 suppresses inflammatory and fibrotic signaling and is currently in phase II trial for idiopathic pulmonary fibrosis.