The advanced-stage
colon cancer spreads from primary
tumor site to distant organs where the colon-unassociated stromal population provides a favorable niche for the growth of
tumor cells. The heterocellular interactions between
colon cancer cells and colon-unassociated fibroblasts at distant metastatic sites are important, yet these cell-cell interactions for therapeutic strategies for metastatic
colon cancer remain underestimated. Recent studies have shown the therapeutic potential of
DNA-demethylating epi-drugs
5-azacytidine (AZA) and
5-aza-2'-deoxycytidine (DAC) for the treatment of solid
tumors. While the effects of these epi-drugs alone or in combination with other anticancer
therapies are well described, the influence of stromal cells and their secretome on
cancer cell response to these agents remain elusive. In this study, we determined the effect of normal and senescent colon-unassociated fibroblasts and their
conditioned medium on
colorectal cancer (CRC) cell response to AZA and DAC using a cell-based DNA demethylation reporter system. Our data show that fibroblasts accelerate cell proliferation and differentially regulate the expression of DNA methylation-regulating
enzymes, enhancing DAC-induced demethylation in CRC cells. In contrast, the
conditioned medium from senescent fibroblasts that upregulated NF-κB activity altered
deoxycytidine kinase levels in drug-untreated CRC cells and abrogated DAC effect on degradation of
DNA methyltransferase 1. Similar to 2D cultures, senescent fibroblasts increased DNA demethylation of CRC cells in coculture spheroids, in addition to increasing the stemness of CRC cells. This study presents the first evidence of the effect of normal and senescent stromal cells and their
conditioned medium on DNA demethylation by DAC. The data show an increased activity of DAC in high stromal cell cocultures and suggest the potential of the
tumor-stroma ratio in predicting the outcome of
DNA-demethylating epigenetic
cancer therapy.