In various aspects the invention provides methods of predicting sensitivity of a cancer cell to a therapeutic agent by contacting a test cell population BH3 domain peptide; measuring the amount of BH3 domain peptide induced mitochondrial outer membrane permeabilization in the test cell population; and comparing the amount of BH3 domain peptide induced mitochondrial outer membrane permeabilization in the test cell population to a control cell population that has not been contacted with the therapeutic agent. An increase in mitochondrial membrane permeabilization in the test cell population compared to the control cell population indicates the cell is sensitive to the therapeutic agent.
