BACKGROUND AND OBJECTIVE: In recent studies, undifferentiated CD₄₄ cells have been introduced as the major cause of chemotherapeutic drug resistance in esophageal cancer. In this study, we aimed to evaluate the effects of all-trans retinoic acid on reducing chemotherapeutic drug resistance and improving the associated toxic effects.

METHODS: In this clinical study, CD₄₄⁺ and CD₄₄^- cells were separated from KYSE-30 cell line, using magnetic-activated cell sorting (MACS) method. The cytotoxic effects of retinoic acid treatment, combined with cisplatin and 5-fluorouracil, were separately evaluated in two cell groups, i.e., CD₄₄⁺ and CD₄₄^-. Cytotoxicity was determined by identifying cellular metabolic activity, acridine orange/ethidium bromide staining, and flow cytometry.

FINDINGS: In this study, CD₄₄ marker was expressed in 6.25% of the cell population in KYSE-30 cell line. The results of flow cytometry revealed that treatment with a combination of retinoic acid and chemotherapeutic drugs could improve cell cycle arrest in CD₄₄⁺ cells (p<0.05), unlike CD₄₄^- cells. Determination of cellular metabolic activity, increased cell apoptosis along with decreased half maximal inhibitory concentration (IC₅₀), and acridine orange/ethidium bromide staining were indicative of the increased percentage of primary and secondary apoptotic CD₄₄⁺ cells. However, in CD₄₄^- cells, these effects were only observed by using a combination of retinoic acid and cisplatin (p<0.05).

CONCLUSION: The present results showed that all-trans retinoic acid could increase the toxicity of cisplatin and 5-fluorouracil in CD₄₄⁺ cells.