The present invention relates to novel therapies for cancer and, in particular, to therapies that are particularly suited to tumor cells resistant to other types of therapies, such as radiation therapy, chemotherapy, or a combinations thereof. The invention provides methods for identifying and implementing strategies to inhibit a transcription factor involved in promoting resistance and inhibition of apoptosis. The invention provides a compound that alters ATF2 activity, specifically amino-terminal fragments of ATF2 that retain the JNK binding domain. The invention provides methods for inhibiting tumor cell growth and for sensitizing tumor cells to apoptosis with such peptides.