Anti-inflammatory 25(OH)D3, a natural steroid hormone, may complement all-trans retinoic acid therapy for differentiation syndrome in acute promyelocytic leukemia.

Differentiation syndrome (DS) is a serious complication with an unclear pathogenesis that arises following all-trans retinoic acid (ATRA) or arsenic trioxide induction therapy in acute promyelocytic leukemia (APL). DS symptoms include pyrexia, respiratory compromise, increased body mass, fluid accumulation, pulmonary infiltrates, hypotension, tachycardia, edema, and sepsis. It can also affect the kidneys and the central nervous system. The standard treatment to counteract DS involves the temporary cessation of ATRA or arsenic trioxide treatment and the administration of high-dose steroids to mitigate the inflammatory response. If left untreated, DS can be fatal. Further research has revealed that the inability to promptly recognize intracranial hemorrhage (ICH) in patients with APL may result in lethal consequences, with the cytokine storm identified as the principal factor in this scenario as well. ATRA therapy is known to induce transglutaminase 2 (TG2), which functions as a catalyst for DS development. In this study, we used NB4 cell lines and cells from a human patient with APL to investigate the ex vivo effects of ATRA and 25(OH)D3 cotreatment on NF-κB-regulated luciferase reporter gene activity. ATRA alone substantially enhanced cellular NF-κB luciferase reporter gene activity, whereas 25(OH)D3 dose-dependently reduced this activity. During ATRA-initiated cell maturation, 25(OH)D3, known as calcidiol, suppressed the mRNA expression of NF-κB (p65/p50) and Rel family members, as well as the expression of genes associated with increased NF-κB activity. 25(OH)D3 also inhibited the ATRA-induced production of cytokines (e.g., IL-8), including IL-1β, TNF-α, and MCP-1, associated with the "cytokine storm." Combined treatment with ATRA plus 25(OH)D3 reduced cellular phospho-p65 and transglutaminase 2 (TG2) levels and increased the level of inhibitor of Rel (IκB), thereby attenuating the cytokine storm. These findings provide a molecular interpretation for clinical DS and IHC observations and may support future exploration of ATRA plus 25(OH)D3 cotreatment as a therapy for APL.