Effective Targeting Survivin, Caspase-3 and MicroRNA-16-1 Expression by Methyl-3-pentyl-6-methoxyprodigiosene Triggers Apoptosis in Colorectal Cancer Stem-Like Cells

Over-expression of the proto-oncogene survivin in colorectal cancer stem cells (CCSCs) is thought to be one the primary causes for therapy failure. It has also been reported that tumor suppressor miR-16-1 is down-regulated in colorectal cancer (CRC) cells. Therefore, the search for new anti-proliferative agents which target survivin or miR-16-1 in CCSCs is warranted. Several studies have shown that prodigiosin isolated from cell wall of Serratia marcescens induces apoptosis in different kinds of cancer cells. Here, we investigated the effects of prodigiosin on HCT-116 cells that serve as a model for CRC initiating cells with stem-like cells properties. HCT-116 cells were treated with 100, 200 and 400 nM prodigiosin after which cell number, viability, growth-rate, survivin and miRNA-16-1 expression, caspase-3 activation and apoptotic rate were evaluated. Prodigiosin decreased significantly growth-rate in a dose-and time-dependent manner. After a 48 h treatment with 100, 200 and 400 nM prodigiosin, growth-rates were measured to be 84.4 ± 9.2 %, 58 ± 6.5 % and 46.3 ± 5.2 %, respectively, compared to untreated cells. We also found that treatment for 48 h with indicated concentrations of prodigiosin resulted in 41 %, 54.5 % and 63 % decrease in survivin mRNA levels and induced 32 %, 48 % and 61 % decrease in survivin protein levels as well as resulted in 128.3 ± 10 %, 178.7 ± 6.1 % and 205 ± 7.6 % increase in caspase-3 activation respectively compared to untreated cells. Prodigiosin caused a significant increase in miRNA-16-1 expression at a concentration of 100 nM and treatment with different concentrations of prodigiosin resulted in 2.2- to 3-fold increase in miRNA-16-1/survivin ratios compared to untreated cells. An increase in number of apoptotic cells ranging from 28.2 % to 86.8 % was also observed with increasing prodigiosin concentrations. Our results provide the first evidence that survivin and miRNA-16-1 as potential biomarkers could be targeted in CRC initiating cells with stem-like cells properties by prodigiosin and this compound with high pro-apoptotic capacity represents the possibility of its therapeutic application directed against CCSCs.