Background: In metastatic colorectal cancer (mCRC) only 3 cytotoxic drugs (oxaliplatin, irinotecan and fluorouracil (5-FU)) are approved and the first and second line response rates are about 50% and 10-15%, respectively. Thus, new treatment options are needed. Novel anti-cancer drug candidates are primarily tested in an environment of drug resistance and the majority of novel drug candidates fail during clinical development. Therefore, “repurposing” of drugs has emerged as a promising strategy to apply established drugs in novel indications. The aim of this project was to screen established anti-cancer drugs to identify candidates for testing in mCRC patients relapsing on standard therapy. Methods: We applied 3 parental (drug sensitive) CRC cell lines (HCT116, HT29 and LoVo) and for each cell line also an oxaliplatin and irinotecan (SN38) resistant cell line. We obtained 129 FDA approved anti-cancer drugs from the Developmental Therapeutics Program (DTP) at the National Cancer Institute (NCI) (https://dtp.cancer.gov/). The parental HT29 cell line and the drug resistant sublines HT29-SN38 and HT29-OXPT were exposed to 3 concentrations of each of the anti-cancer drugs. The effect on cell viability was analyzed by MTT assays. Nine of the drugs were analyzed for effect in the LoVo and HCT116 and the SN38- and oxaliplatin-resistant derived cell lines. Results: None of the drugs caused evident differential response between the resistant and sensitive cells or between the SN38 and oxaliplatin resistant cells. The screening confirmed the resistance as the cells displayed resistance to drugs in the same class as the one they were made resistant to. Of the drugs, 45 decreased cell viability in the HT29 parental and oxaliplatin- or SN-38 resistant cell lines. Nine drugs were tested in all nine CRC cell lines and eight decrease cell viability in the nine cell lines. These included drugs in different classes such as epigenetic drugs, antibiotics, mitotic inhibitors and targeted therapies. Conclusions: This study revealed several possible new “repurposing” drugs for CRC therapy, by showing that 45 FDA-approved anti-cancer drugs decrease cell viability in CRC cell lines with acquired drug resistance.