ARTICLE ABSTRACTPurpose: We aimed to investigate the therapeutic efficacy of single agent and the combination of quinacrine and suberoylanilide hydroxamic acid (SAHA) in wt- and mut-p53 upper gastrointestinal cancer (UGC) cell models.Experimental Design: ATP-Glo, clonogenic cell survival, Annexin V, comet, DNA double-strand breaks (DSBs), qPCR, and Western blot analysis assays were utilized.Results: Using clonogenic cell survival, ATP-Glo cell viability, Annexin V, and sub-G0 population analysis, we demonstrated that a combination of quinacrine and SAHA significantly decreased colony formation and increased cancer cell death (range, 4–20 fold) in six UGC cell models, as compared with single-agent treatments, irrespective of the p53 status (P < 0.01). The combination of quinacrine and SAHA induced high levels of DSB DNA damage (>20-fold, P < 0.01). Western blot analysis showed activation of caspases-3, 9, and γ-H2AX in all cell models. Of note, although quinacrine treatment induced expression of wt-p53 protein, the combination of quinacrine and SAHA substantially decreased the levels of both wt-P53 and mut-P53. Furthermore, cell models that were resistant to cisplatin (CDDP) or gefitinib treatments were sensitive to this combination. Tumor xenograft data confirmed that a combination of quinacrine and SAHA is more effective than a single-agent treatment in abrogating tumor growth in vivo (P < 0.01).Conclusions: Our novel findings show that the combination of quinacrine and SAHA promotes DNA damage and is effective in inducing cancer cell death, irrespective of p53 status and resistance to CDDP or gefitinib in UGC models. Clin Cancer Res; 24(8); 1905–16. ©2018 AACR.