RK-33 is an inhibitor of DEAD box 3 (DDX3), an ATP-dependent RNA helicase. RK-33 inhibits the growth of lung cancer cells that overexpress DDX3 (IC50s = 4.4-8.4 μM) but is less effective in cells with low DDX3 expression (IC50 > 25 μM). It also promotes radiation sensitization in cells overexpressing DDX3. RK-33 in combination with radiation induces tumor regression in multiple animal models of lung cancer. MW: 428.45. Purity ≥98% by HPLC