PARP1 and cancer: If NAD+ levels are reduced, for example, by limiting the carbon sources (glucose or pyruvate) or by inhibiting NAD+ synthesis/recycling, then cancer cells become more sensitive to other stresses, such as cytotoxic agents and PARP inhibitors (Bajrami et al, 2012; Chan et al, 2014; Piacente et al, 2017), or to the blockage of OXPHOS (our results, see later).