SP600125, an anthrapyrazolone compound, was identified as a potent inhibitor of Jun N-terminal kinase (JNK) with a Ki of 0.19 μM. It exhibits >20-fold selectivity against a range of kinases and enzymes. In cellular assays, SP600125 dose dependently inhibited the phosphorylation of c-Jun, the expression of inflammatory genes (COX-2, IL-2, IFN-γ, TNF-α), and prevented the activation and differentiation of primary human CD4+ cells. In animal studies, SP600125 blocked LPS-induced TNF-α expression and inhibited anti-CD3-induced apoptosis of CD4+ CD8+ thymocytes. These findings support the potential of targeting JNK as a therapeutic strategy in inflammatory diseases, apoptotic cell death, and cancer.SP600125, an anthrapyrazolone compound, was identified as a potent inhibitor of Jun N-terminal kinase (JNK) with a Ki of 0.19 μM. It exhibits >20-fold selectivity against a range of kinases and enzymes. In cellular assays, SP600125 dose dependently inhibited the phosphorylation of c-Jun, the expression of inflammatory genes (COX-2, IL-2, IFN-γ, TNF-α), and prevented the activation and differentiation of primary human CD4+ cells. In animal studies, SP600125 blocked LPS-induced TNF-α expression and inhibited anti-CD3-induced apoptosis of CD4+ CD8+ thymocytes. These findings support the potential of targeting JNK as a therapeutic strategy in inflammatory diseases, apoptotic cell death, and cancer.