The role of multidrug resistance associated protein 1 (MRP1) in the multidrug resistance (MDR) of colorectal cancer (CRC) remains unclear. The present study aimed to investigate the effect of MRP1 in MDR CRC and its therapeutic potential for the treatment of patients with this disease. The human MDR CRC cell lines HCT‑8 and Colo205 were established through stable exposure to 5‑florouracil (5‑FU) over a 5‑month period. MRP1 was knocked‑down in MDR CRC cells through the transfection of short hairpin RNA targeting MRP1 (shMRP1). Western blotting was performed to assess the efficiency of this silencing. MTT and apoptosis assays were conducted to detect cell viability and apoptosis, respectively. Compared with their parental cells, HCT‑8/5‑FU and Colo205/5‑FU cells were 23.1 and 15.8 times more resistant to 5‑FU, and 17.2 and 20.9 times more resistant oxaliplatin, respectively. The knockdown of MRP1 resulted in the attenuation of the MDR phenotype through the induction of apoptosis. The shMRP1‑transfected Colo205/5‑FU cells were injected subcutaneously into the right scapular region of BALB/c nude mice and tumor size was measured for 15 days post‑injection. This in vivo experiment demonstrated that MRP1 knockdown inhibited tumor growth. On the 9, 12 and 15th day post‑injection, tumor volume in the shMRP1‑transfected Colo205/5‑FU cell‑injected group was significantly lower compared with that in the Colo205/5‑FU cell‑injected group (day 9, 2.1±0.8 vs. 6.9±1.9 mm3, P=0.009; day 12, 3.1±1.4 vs. 14.3±4.0 mm3, P=0.008; day 15, 4.8±2.7 vs. 21.3±3.4 mm3; all P<0.001). These results demonstrate that MRP1 serves a role in the MDR phenotype of CRC through inhibiting apoptosis and may serve as a potential therapeutic target for inhibition, which would increase the efficacy of other chemotherapeutic agents in the treatment of CRC.

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