To Prime, or Not to Prime: That Is the Question.

Mitochondrial priming is regulated by the B-cell lymphoma 2 (BCL-2) family of proteins and determines a cell's "readiness" for apoptosis. A highly primed cell will undergo apoptosis more easily than an unprimed cell in response to apoptotic stimuli via the intrinsic apoptotic pathway. Priming can be measured via BH3 profiling, which uses BH3 peptides derived from the BH3 domain of pro-apoptotic BH3-only BCL-2 family members to provoke a response from viable mitochondria. BH3 profiling can be performed on tumor cells and can identify mechanisms a cell uses to evade apoptosis and anti-apoptotic dependency to the anti-apoptotic BCL-2 family members. Priming correlates with chemosensitivity of patients in multiple cancers. Therapeutics that enhances priming of patient tumor cells ex vivo could be used to aid therapeutic decisions for patients in the future.