Flavopiridol Hydrochloride (Alvocidib Hydrochloride) is a broad inhibitor of CDK, competing with ATP to inhibit CDKs including CDK1, CDK2, CDK4 with IC₅₀s of 30, 170, 100 nM, respectively. IC50 & Target: IC50: 30 nM (CDK1), 170 nM (CDK2), 100 nM (CDK4)^[3] In Vitro: Flavopiridol (2 μM) robustly induces a distinct pattern of ER stress in CLL cells that contributes to cell death through IRE1-mediated activation of ASK1 and possibly downstream caspases^[1]. Flavopiridol results in potent upregulation of a number of PRGs in treatments lasting 4-24 h. Flavopiridol has and immediate and long-term effect on the expression of several PRGs. In serum starved cells re-stimulated with serum, flavopiridol also inhibits the expression of these genes, but subsequently, JUNB, GADD45B and EGR1 are upregulated in the presence of flavopiridol^[2].