A 419259 is a broad-spectrum pyrrolo-pyrimidine inhibitor, designed to enhance selectivity towards the Src family with IC₅₀ of 9 nM, <3 nM and <3 nM for Src, Lck and Lyn, respectively. IC50 & Target: IC50: 9 nM (Src), <3 nM (Lck), <3 nM (Lyn), 3 μM (Abl)^[1] In Vitro: A 419259 is a second-generation pyrrolo-pyrimidine designed to enhance selectivity towards the Src family relative to other cytoplasmic tyrosine kinases. A-419259 inhibits K-562 cells with an IC₅₀ between 0.1 and 0.3 μM, and Meg-01 proliferation with an IC₅₀ of approximately 0.1 μM. A-419259 also potently induces apoptosis in K-562 cells beginning at 0.1 μM and increasing in a dose-dependent manner. PP2 inhibits Src kinase autophosphorylation in both Ph⁺ cell lines (K-562 and Meg-01) with an IC₅₀ between 3 and 10 μM, while A-419259 blocks kinase activation between 0.1 and 0.3 μM. A-419259 strongly inhibits DAGM/Bcr-Abl cell proliferation in the absence of IL-3 with an IC₅₀ between 0.1 and 0.3 μM^[1]. A-419259 is a broad-spectrum pyrrolo-pyrimidine inhibitor, and blocks proliferation and induces apoptosis in CML cell lines. A-419259 inhibits overall SFK activity in K562 and other CML cell lines with an IC₅₀ value of 0.1-0.3 μM^[2].