Figure 2. Apoptotic priming can affect response to chemotherapy.

(A) A cell that is primed for apoptosis is more likely to undergo cell death in response to chemotherapy than an unprimed cell. (B) A cell that is primed for apoptosis nonetheless does not undergo cell death in response to a targeted agent if it does not exhibit a dependence on the target of the therapy. A cell that is unprimed, but exhibits a strong dependence on the target of the therapy may unleash sufficient pro-apoptotic signaling to trigger apoptosis. (C) Two cells that exhibit similar dependence on the target of the therapy may have different treatment outcomes based on levels of apoptotic priming present in cells prior to therapy. (D) A cell that is unprimed yet exhibits dependence on the target of the therapy may become primed in response to the therapy if apoptosis is not triggered directly by the single agent. An additional bolus of pro-apoptotic signaling, here provided by treatment with a cytotoxic chemotherapy which would not kill an unprimed cell, is sufficient to trigger apoptosis.