Abstract: The invention relates to compositions and methods for treating cancer comprising administering to a subject in need a pharmaceutically effective dose of a cancer stem cell inhibitor, methods of inhibiting the growth of cancer stem cells or tumor initiating cell comprising administering to a subject in need a pharmaceutically effective dose of a cancer stem cell inhibitor, and methods of enhancing the biological effects of chemotherapeutic drugs or irradiation on cancer cells comprising administering to a subject in need a pharmaceutically effective dose of a chemotherapeutic drug and a pharmaceutically effective dose of a cancer stem cell inhibitor.