β-carotene plus 5-FU: a promising strategy to fight uL3-mediated drug resistance in colorectal cancer cells

The human ribosomal protein uL3 has been identified as a key sensor in the cell response to 5-FU in colorectal (CRC) cancer cells lacking p53. Specifically, uL3 downregulation is associated with 5-FU drug resistance, alteration in cell motility, epithelial-mesenchymal transition and autophagy. Emerging evidence indicates that natural products, like β-carotene, have the ability to enhance cancer cell response to cytotoxic drugs and may provide a safer choice to defeat drug resistance in cancer. Here, we report the transcriptomic RNA-seq analysis of CRC cell lines silenced for uL3 revealing that the Hedgeog signaling pathway was iperactivated and was associated with the high expression of specific ABC transporters (ABCB1, ABCC9, and ABCC11). Interestingly, RT-qPCR analysis confirmed the upregulation of these ABC transporters in condition of uL3 silencing and revealed that the higher expression levels of ABCB1 and ABCC9 could be in part due to an increase in mRNA stability. Notably, using transcriptomic analysis on a large cohort of CRC patients, we discovered that uL3 transcriptional state was inversely correlated with the expression of these specific ABC genes. Then, in our model of CRC cells lacking p53, we looked at the effect of a novel combination therapy based on 5-FU plus β-carotene. Our findings demonstrate that the combined treatment induces cell cycle arrest and apoptosis, associated with a reduction in the expression levels of analyzed ABC genes. Furthermore, preliminary in vivo data from the chorioallantoic membrane (CAM) assay suggest that the proposed combination of 5-FU plus β-carotene could significantly reduce the tumor size of CAM xenografts. In conclusion, our data reveal the effectiveness of β-carotene in combination with 5-FU in overcoming 5-FU resistance of p53 deleted CRC cells expressing low levels of uL3.