cis-Diamminedichloroplatinum/cisplatin (CDDP) is a major drug used in cancer chemotherapy; however, the toxic side-effects and development of drug resistance represent major challenges to the clinical use of CDDP. The aim of the present study was to identify effective drug combination regimens through high-throughput drug screening that can enhance the efficacy of CDDP, and to investigate the underlying mechanisms. A cell-based high-throughput screening methodology was implemented, using a library of 1,280 Food and Drug Administration (FDA)-approved drugs, to identify clinical compounds that act synergistically with CDDP. Our study identified two compounds, namely potassium antimony tartrate and topotecan, that significantly enhanced the sensitivity of colorectal and non-small cell lung cancer cells to CDDP. The synergistic action of both compounds with CDDP was confirmed by further quantitative analyses. Topotecan is a topoisomerase-1 inhibitor that has previously been shown to enhance the clinical response and overall patient survival when combined with CDDP by a yet unclear mechanism. We demonstrated that the combination of topotecan with CDDP significantly inhibited colony formation ability and increased the apoptosis of several cancer cell lines. Mechanistic analyses revealed that topotecan enhanced CDDP-induced DNA damage and inhibited the repair of DNA strand breaks, without affecting the cellular platinum content. Overall, the findings of this study demonstrated that the use of the FDA-approved drug panel in high-throughput screening is an effective method for identifying effective therapeutic regimens that are clinically relevant, and may have high feasibility for translation into clinical practice.