Olaparib has synergistic effects with DNA damaging agents in pancreatic ductal adenocarcinoma.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) remains among the most lethal malignancies. Poly (ADP-ribose) polymerase (PARP) enzymes have a crucial function in the DNA repair and their inhibition has been recently shown to be effective in PDAC management.

OBJECTIVES: Our study seeks to assess the anticancer efficacy of PARP inhibitor, olaparib, in combination with DNA-damaging agents including doxorubicin, mitoxantrone, oxaliplatin, and gemcitabine against PDAC cell lines.

METHOD: The MTT assay was employed to evaluate the growth inhibitory effects of olaparib and chemotherapeutic drugs against two PDAC cells, namely AsPC-1 and Suit-2 cell lines, either alone or in combination. The determination of synergistic drug interactions was accomplished by computing combination index (CI) values by employing CalcuSyn software. Combinations exhibiting synergistic effects were further validated in spheroid three-dimensional cultures, and colony formation assays. Apoptosis induction was examined using Hoechst 33258 staining. Additionally, the 2',7'-dichlorofluorescein-diacetate (DCFH-DA) assay was conducted to evaluate the amounts of reactive oxygen species (ROS) in PDAC cells. DNA damage was assessed by evaluating γH2AX foci accumulation using immunocytochemistry.

RESULTS: Combination of olaparib with doxorubicin or mitoxantrone demonstrated synergistic effects. The CI values were 0.58 and 0.75 for doxorubicin, and 0.79 and 0.66 for mitoxantrone in AsPC-1 and Suit-2 cells, respectively. In contrast, combinations of olaparib with other agents produced antagonistic effects. The synergistic combinations of olaparib with doxorubicin and mitoxantrone resulted in significant inhibition of spheroid growth, clonogenic ability, and apoptosis induction in AsPC-1 cells. Additionally, we also observed that synergy between olaparib and doxorubicin or mitoxantrone may be attributed to increased ROS production and DNA damage.

CONCLUSION: The synergistic effects observed in PDAC cancer cells when combining the PARP inhibitor, olaparib, with the DNA damaging agents, doxorubicin and mitoxantrone, provide a preclinical rationale for considering this combination as a potential therapeutic approach in PDAC patients.