Abstract
BackgroundThe efficacy of oxaliplatin in cancer chemotherapy is limited by the development of drug resistance. MMP7 has been related to the loss of tumor cell response to cytotoxic agents although the exact mechanism is not fully understood. Moreover, MMP7 is an independent prognosis factor for survival in patients with colorectal cancer. The aim of the present study was to analyze the role of MMP7 and its cross-talk with the Fas/FasL system during the acquisition of oxaliplatin resistance in colon cancer cells.Principal FindingsFor this purpose we have developed three different oxaliplatin-resistant cell lines (RHT29, RHCT116 p53+/+, RHCT116 p53−/−) from the parental HT29, HCT116 p53+/+ and HCT116 p53−/− colon cancer cells. MMP7 basal expression was higher in the resistant compared to the parental cell lines. MMP7 was also upregulated by oxaliplatin in both HT29 (p53 mutant) and RHCT116 p53−/− but not in the RHCT116 p53+/+. Inhibition of MMP by 1,10-phenantroline monohydrate or siRNA of MMP7 restores cell sensitivity to oxaliplatin-induced apoptosis in both HT29 and RHCT116 p53−/− but not in the RHCT116 p53+/+. Some of these effects are caused by alterations in Fas receptor. Fas is upregulated by oxaliplatin in colon cancer cells, however the RHT29 cells treated with oxaliplatin showed a 3.8-fold lower Fas expression at the cell surface than the HT29 cells. Decrease of Fas at the plasma membrane seems to be caused by MMP7 since its inhibition restores Fas levels. Moreover, functional analysis of Fas demonstrates that this receptor was less potent in inducing apoptosis in RHT29 cells and that its activation induces MAPK signaling in resistant cells.ConclusionsTaking together, these results suggest that MMP7 is related to the acquisition of oxaliplatin-resistance and that its inhibition restores drug sensitivity by increasing Fas receptor. Furthermore, Fas undergoes a change in its functionality in oxaliplatin-resistant cells inducing survival pathways instead of apoptotic signals.
Highlights
Oxaliplatin has shown excellent efficacy in the treatment of colorectal cancer in combination with 5-fluorouracil
Some authors have observed that addition of MMP7 to cell cultures protects cells from drug cytotoxicity [4] and from cytotoxic T-cell killing [8], but whether MMP7 exerts these effects physiologically or if its expression is related to the acquisition of drug resistance remains unresolved
To analyze the role of MMP7 in these processes, we first generated cell lines resistant to oxaliplatin treatment by exposure of the parental cells to the drug over 5 months. These oxaliplatin-resistant cells show an IC50 several fold higher (RHT29 80 mM, RHCT116 p53+/+,8 mM and,15 mM RHCT116 p532/2) than the parental (HT29,5– 7 mM, HCT116 p53+/+,1.75 mM and,2 mM HCT116 p532/2), as determined by MTS assay (Figure 1A), and they are more resistant to oxaliplatin induced apoptosis (Figure 1B), as analyzed by annexin/IP staining (5-fold double staining for HT29 compared to 2-fold double staining for RHT29)
Summary
Oxaliplatin has shown excellent efficacy in the treatment of colorectal cancer in combination with 5-fluorouracil. Despite the fact that the mechanisms influencing treatment responses are well known, it appears that the major process leading to chemotherapy resistance [4] is the ability of cancer cells to evade cell death signals. This loss of response to apoptosis-induction during development of drug resistance resembles the normal tumor progression process, in which malignant cells undergo molecular changes providing them with mechanisms against cell death induction [5,6]. The aim of the present study was to analyze the role of MMP7 and its cross-talk with the Fas/FasL system during the acquisition of oxaliplatin resistance in colon cancer cells
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