Non-small cell lung cancer (NSCLC) accounts for more than 80% of all lung cancers with two out of three patients having an inoperable disease at the time of diagnosis. Standard first-line treatments for these patients are combinations of two chemotherapy drugs, with one typically being cisplatin. Despite the use of new targeted therapies and attempts to develop triplet combinations, the overall 5-year survival rate for NSCLC remains below 20%. A genome-wide siRNA (small-interfering RNA) screen was performed in A549 cells to rapidly identify individual genes that, when silenced, would enhance cisplatin activity. One of the top targets that emerged from the screen was 3’-phosphoadenosine-5’-phosphosulfate (PAPS) synthase 1 (PAPSS1), a bi-functional enzyme that synthesizes PAPS, the universal sulfate donor. Here, we evaluated PAPSS1 as a cisplatin-potentiating gene target in NSCLC. The effect of PAPSS1 inhibition on cisplatin activity was assessed across eight different chemo-naïve NSCLC cell lines. Cells were transfected with lipid-complexed siRNA targeting PAPSS1 and treated with various concentrations of cisplatin 24 hours later. The dose response was determined based on viable cell count 72 hours post-treatment using the IN Cell Analyzer. Gene knockdown was confirmed via qPCR and Western blot analysis. Silencing of PAPSS1 resulted in significant reduction in the IC50 of cisplatin in five chemo-naïve NSCLC cell lines at siRNA concentrations that would not induce significant lipid toxicity over a 72-hour culture period. For example, PAPSS1 silencing was associated with a 5-fold decrease (p<0.001) in the cisplatin IC50 in A549 cells. No significant toxicity or enhancement in cisplatin activity was observed when PAPSS1 was knocked down in primary epithelial and endothelial cells of the airway. Preliminary studies performed with sodium chlorate, a known non-selective PAPSS1 inhibitor, yielded a 1.5-fold decrease in the IC50 of cisplatin in A549 cells. We have also demonstrated that the extent of cisplatin potentiation positively correlates with the level of PAPSS1 inhibition at the protein level. These results highlight the need for more potent PAPSS1 inhibitors to further investigate the feasibility of developing PAPSS1 as a cisplatin-potentiating therapeutic target. These results identify PAPSS1 as a novel cisplatin potentiating target in NSCLC and also confirm the validity of a drug combination discovery program designed to identify genes that when silenced/inhibited, enhance the action of standard of care cytotoxic agents used against chemo-naïve cancers.
Citation Format: Ada Leung, Brian Kwok, Daniel Ricaurte, Amith Ahluwalia, Mohammed A. Qadir, Marcel B. Bally. Silencing of PAPSS1 (3’-phosphoadenosine 5’-phosphosulfate synthase 1) potentiates cisplatin activity against non-small cell lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4362. doi:10.1158/1538-7445.AM2013-4362