PO-484 Development of a two-step screening-and-confirmation approach to efficiently identify synergistic drug combinations with the PARP inhibitor niraparib

Abstract

IntroductionPoly (ADP-ribose) polymerases (PARPs) are important players in DNA damage repair. Inhibition of PARP activity is highly effective against cancers deficient in homologous recombination repair due to, a.o., BRCA1/2 mutations. Clinically, PARP inhibitors (PARPi) are used to treat, a.o., ovarium cancers. Although effective, repeated treatment with PARPi may lead to resistance. To identify new synergistic drug combinations, we developed a two-step approach of screening and confirmation using two of our platform technologies SynergyScreen and SynergyFinder. We first screen for synergy in presence of a fixed concentration of compound (e.g., PARPi), followed by confirmation using dose response curves. The PARPi niraparib was used as a proof-of-concept combinatorial drug at a fixed concentration, and combined with over 150 anti-cancer agents.Material and methodsProliferation of cell lines and patient derived primary ovarium cancer cells was measured using ATPLite 1 Step after 120 hours compound incubation. Growth was calculated relative to vehicle treated cells; relative IC50s were calculated from a four parameter logistics curve. The fixed concentration niraparib used in the SynergyScreen represented 80% viability. Anti-cancer agents were screened in absence and presence of niraparib, followed by analysis of IC50 shifts. Combinations with IC50shifts>2 fold indicated a synergistic hit and were re-examined using equipotent mixtures and calculation of Combination Index (CI) within our SynergyFinder platform.1 CI <1 indicates synergy. As a control, the combinatorial drug was tested against itself.Results and discussionsResults of the SynergyScreen showed various synergistic drug combinations from the high-throughput setup, i.e. niraparib in combination with the topoisomerase I inhibitor irinotecan (CI0.5=0.70) and the DNA alkylating agent temozolomide (CI0.5=0.42). These and other synergies were confirmed in patient samples. Independently from niraparib, the bromodomain inhibitor JQ1 and the histone acetyltransferase inhibitor anacardic acid showed synergy (CI0.5 0.42), which was not demonstrated before.ConclusionOur Synergy platforms can identify novel and reproducible synergistic drug combinations in an unbiased and efficient manner. Proof-of-concept was demonstrated and new synergistic drug combinations were found. Our method is therefore excellently suited for the in vitro discovery and validation of synergistic combinations.ReferenceUitdehaag, et al. PLoS ONE 2015;10(5): e0125021.