As an example application, we utilised this methodology to elucidate the first direct and quantitative comparison between the intracellular response in ADP-ribosylation to two clinical PARP inhibitors, Olaparib and Rucaparib, which are able to induce synthetic lethality in homologous recombination (HR)-deficient cancers due to germline and/or somatic mutations in BRACA1 or BRACA2 genes2. Here, PARP1 is linked to cancer.