Abstract 1095: A combination of suberoylanilide hydroxamic acid and quinacrine is an effective therapeutic approach in preclinical settings of upper gastrointestinal cancers

Abstract

Abstract Background: Quinacrine (QC), an antimalarial drug, has been shown to possess anticancer effects. Suberoylanilide hydroxamic acid (SAHA) inhibits class I and class II HDACs and is approved for cancer therapy. Developing novel approaches to overcome cancer drug resistance could significantly enhance current therapeutic approaches and improve patient care. Methods: ATP-GLO, clonogenic survival, Annexin-V apoptosis assay, comet assay and DNA double-strand breaks (DSB) kits were used. The mRNA and protein levels were evaluated by quantitative real-time PCR and Western blot analyses. Results: A combination of QC/SAHA significantly increased cell death in all cancer cell lines and had no effect on immortalized non-cancer cell lines (HFE145, NIH-3T3 and EPC2) (P<0.01). Clonogenic survival assay indicated that QC/SAHA co-treatment led to significantly lower number of cancer cell colonies, as compared to single agents and controls (P<0.01). Of note, the QC/SAHA combination led to an increase in the the sub-G0 population in AGS (9-fold), MKN-28 (14-fold), FLO1 (5.6-fold), and SNU1 (4-fold) cells (P<0.01). These results were confirmed using the Annexin V apoptosis induced significantly higher levels of apoptosis (10 - 20 fold) as compared to single agent and control (P<0.01). Treatment with QC/SAHA combination induced high levels of DSB (>20 fold, P<0.01). Comet assay data showed increased DNA damage compared with vehicle-treated cells (8-fold, P<0.01). Western blot analysis demonstrated a notable increase in activation of PARP, caspases 3, 9 and γ-H2AX following QC/SAHA co-treatment in all cancer cell lines. Interestingly, the combination of QC/SAHA substantially decreased the protein levels of both wtP53 and mutP53 in these cells. Tumor xenograft data confirmed that a combination of QC/SAHA is more effective than a single agent in abrogating tumor growth (P<0.05). Conclusion: Our novel findings show that QC and SAHA have a synergistic effect on cancer cell death. The results provide compelling evidence that increased DNA damage mediates the cytotoxic effect of combined QC/SAHA. Such effect is likely related to mutP53 and wtP53 protein degradation induced by QC/SAHA combination. Our findings provide a rationale for a clinical evaluation of combined QC/SAHA therapy in gastro-esophageal cancers. Ongoing studies are currently being undertaken to understand mechanisms that regulate the degradation of wtp53 and mutp53 proteins. Citation Format: Shoumin Zhu, Wael El-Rifai. A combination of suberoylanilide hydroxamic acid and quinacrine is an effective therapeutic approach in preclinical settings of upper gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1095. doi:10.1158/1538-7445.AM2017-1095