Abstract: The invention provides genetic suppressor elements that are derived from the apoptosis-related gene BCL2. The invention provides genetic suppressor elements that are capable of inhibiting BCL2 gene expression and BCL2-mediated suppression of apoptosis in mammalian cells. The GSEs provided by the invention are also useful for sensitizing cancer cells to the cytotoxic effects of chemotherapeutic drugs. The invention provides methods for identifying and obtaining such elements, and therapeutic methods of using such elements for treatment of cancer cells and animals bearing malignant tumors.