Rapamycin inhibits oncogenic intestinal ion channels and neoplasia in APCMin/+ mice

Abstract

The adenomatous polyposis coli (APC) gene is mutated in familial adenomatous polyposis. Mice with a heterozygous APC Min mutation develop multiple intestinal neoplasia (Min) leading to premature death. Early in colorectal carcinogenesis, APC Min/ þ mice show enhanced Akt-mammalian target of rapamycin (mTOR) signaling, which is paralleled by upregulation of oncogenic K þ channels. In this study, we tested the effect of mTOR inhibition with rapamycin on tumor formation in APC Min/ þ mice and evaluated ion channel regulation. We found that continuous long-term rapamycin treatment of APC Min/ þ mice dramatically inhibits intestinal neoplasia. Moreover, although untreated APC Min/ þ mice lose weight, experience intestinal bleeding and succumb to multiple neoplasia by 22.3±1.4 weeks of age, mice treated with rapamycin maintain stable weight and survive long term (39.6 ± 3.4 weeks), with more than 30% surviving >1 year. Impressively, abnormalities in colonic electrolyte transport typical for APC Min/ þ mice are abolished, along with the suppression of epithelial Na þ channel (ENaC) and oncogenic K þ ion channels BK, Elk1 and Erg1, both functionally and at mRNA levels. These results show that continuous prophylaxis by rapamycin markedly inhibits the development of APC mutation-related polyposis, and suggest a novel contributing mechanism of action through the blockade of intestinal oncogenic ion channels.

ENaCs and ASICs as therapeutic targets

“…It was suggested that increased ENaC-mediated salt absorption would lead to decreased hydration of the colonic contents, thus leading to constipation, which has been proposed as a precipitating factor in the development of colonic carcinoma (89,359). The increased ENaC expression and sodium absorption in this mouse were rescued by treatment with rapamycin, consistent with previous reports in lung epithelia and with the recently described role of mammalian target of rapamycin to increase ENaC currents via phosphorylation of SGK1 (227,257,290).…”

Adenomatous Polyposis Coli (APC) Regulates Multiple Signaling Pathways by Enhancing Glycogen Synthase Kinase-3 (GSK-3) Activity

“…As GSK-3 suppresses both Wnt and mTOR pathways (2,14), our demonstration that APC enhances GSK-3 activity provides a mechanistic link between APC loss of function and activation of these two downstream signaling pathways. In support of this mechanism, tumor formation in mice with similar APC mutations is blocked by mTOR inhibitors (54,55). Furthermore, bladder-specific ␤-catenin stabilization synergizes with PTEN deletion, which activates mTOR, to promote bladder cancer in mice (56).…”

Role of anoctamins in cancer and apoptosis

“…Notably, the mTOR-inhibitor rapamycin increased Ano1 expression in both proximal and distal colon (figure 4d). This inverse correlation between low Ano1 levels and upregulation of mTOR [51] suggests that Ano1 may be inhibitory on proliferation of mouse intestinal epithelial cells, similar to HT 29 cells. Interestingly, a fast growing subclone of T 84 colonic epithelial cells (T 84 fast) is lacking expression of Ano1, when compared with the slowly growing parental cells (T 84 slow) [28] ( figure 5a,b).…”