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International audience; Recently we have shown that the mitogen-activated protein kinase (MAPK) MAPK14/p38α is involved in resistance of colon cancer cells to camptothecin-related drugs. Here we further investigated the cellular mechanisms involved in such drug resistance and showed that, in HCT116 human colorectal adenocarcinoma cells in which TP53 was genetically ablated (HCT116-TP53KO), overexpression of constitutively active MAPK14/p38α decreases cell sensitivity to SN-38 (the active metabolite of irinotecan), inhibits cell proliferation and induces survival-autophagy. Since autophagy is known to facilitate cancer cell resistance to chemotherapy and radiation treatment, we then investigated the relationship between MAPK14/p38α, autophagy and resistance to irinotecan. We demonstrated that induction of autophagy by SN38 is dependent on MAPK14/p38α activation. Finally, we showed that inhibition of MAPK14/p38α or autophagy both sensitizes HCT116-TP53KO cells to drug therapy. Our data proved that the two effects are interrelated, since the role of autophagy in drug resistance required the MAPK14/p38α. Our results highlight the existence of a new mechanism of resistance to camptothecin-related drugs: upon SN38 induction, MAPK14/p38α is activated and triggers survival-promoting autophagy to protect tumor cells against the cytotoxic effects of the drug. Colon cancer cells could thus be sensitized to drug therapy by inhibiting either MAPK14/p38 or autophagy.

Despite recent advances in the treatment of colon cancer, tumor resistance is a frequent cause of chemotherapy failure. To better elucidate the molecular mechanisms involved in resistance to irinotecan (and its active metabolite SN38), we established SN38-resistant clones derived from HCT-116 and SW48 cell lines. These clones show various levels (6- to 60-fold) of resistance to SN-38 and display enhanced levels of activated MAPK p38 as compared with the corresponding parental cells. Because four different isoforms of p38 have been described, we then studied the effect of p38 overexpression or downregulation of each isoform on cell sensivity to SN38 and found that both α and β isoforms are involved in the development of resistance to SN38. In this line, we show that cell treatment with SB202190, which inhibits p38α and p38β, enhanced the cytotoxic activity of SN38. Moreover, p38 inhibition sensitized tumor cells derived from both SN38-sensitive and -resistant HCT116 cells to irinotecan treatment in xenograft models. Finally, we detected less phosphorylated p38 in primary colon cancer of patients sensitive to irinotecan-based treatment, compared with nonresponder patients. This indicates that enhanced level of phosphorylated p38 could predict the absence of clinical response to irinotecan. Altogether, our results show that the p38 MAPK pathway is involved in irinotecan sensitivity and suggest that phosphorylated p38 expression level could be used as a marker of clinical resistance to irinotecan. They further suggest that targeting the p38 pathway may be a potential strategy to overcome resistance to irinotecan-based chemotherapies in colorectal cancer. Cancer Res; 71(3); 1041–9. ©2010 AACR.

Additional file 1: Figure S1. Similar bacterial components in the faecal and caecal microbiomes. Figure S2. Faecal butyrate levels and time taken for tumours to reach 50 mm3. Figure S3. Differences in composition of the gut microbiome when tumours reached 350 mm3. Figure S4. Individual mouse tumour growth curves. Figure S5. Cell survival analysis of RT112 bladder tumour cells treated with SCFAs and bacterial supernatants. Figure S6. Correlation of time to culling with B. acidifaciens or Parabacteroides genus abundance different groups. Figure S7. Effect of cage location of mice on relative abundance of B. acidifaciens and Parabacteroides genus. Table S1. Rodent diets used in the study with varying levels of cellulose or inulin per 4000 kcal. Table S2. Details mouse diets, cages, B. acidifaciens relative abundance and time of culling.

Additional file 1: Figure S1. Similar bacterial components in the faecal and caecal microbiomes. Figure S2. Faecal butyrate levels and time taken for tumours to reach 50 mm3. Figure S3. Differences in composition of the gut microbiome when tumours reached 350 mm3. Figure S4. Individual mouse tumour growth curves. Figure S5. Cell survival analysis of RT112 bladder tumour cells treated with SCFAs and bacterial supernatants. Figure S6. Correlation of time to culling with B. acidifaciens or Parabacteroides genus abundance different groups. Figure S7. Effect of cage location of mice on relative abundance of B. acidifaciens and Parabacteroides genus. Table S1. Rodent diets used in the study with varying levels of cellulose or inulin per 4000 kcal. Table S2. Details mouse diets, cages, B. acidifaciens relative abundance and time of culling.