The role of mTOR inhibitors in targeting a putative cancer stem cell-like population in esophageal cancer.

Abstract

43 Background: Despite modern advances in the treatment of esophageal cancer (EC), using neoadjuvant chemoradiotherapy (CRT) and esophagectomy, most patients face poor outcome. Growing evidence indicates that cancer stem cells (CSCs) might contribute to the poor prospects. CSCs are usually resistant to CRT and ultimately can generate a new tumor. The mammalian target of rapamycin (mTOR) pathway is associated with cancer stemness. However, its role in EC CSC-like populations needs to be elucidated. Here, we investigate the role of mTOR pathway on the stemness of a putative CSC-like population. Methods: Previously, we identified a putative CSC-like population (CD44+/CD24-) in EC cell lines and in tumor biopsy from EC patients. qPCR was used to measure the expression of mTOR in CD44+/CD24- CSC-like population of OE21 squamous cell carcinoma and OE33 adenocarcinoma cell lines compared to controls, that consisted of solid tumors generated from the same cell lines obtained from xenografts. mTOR inhibitors rapamycin and torin-1 were used to see their effect on CD44+/CD24- expression and sphere formation. Results: mTOR expression was 2-fold up-regulated in the OE33 CD44+/CD24- CSC-like population compared to control. Furthermore, in OE21 this up-regulation was 1.9-fold. Surprisingly, inhibiting the mTOR pathway with rapamycin enhanced OE33 CD44+/CD24- expression compared to its control (p = 0.01). In pilot experiments this effect was dose dependent and cells treated with rapamycin formed more spheres than control. Rapamycin did not alter the expression of CD44+/CD24- in OE21. Inhibiting the mTOR pathway with Torin-1 enhanced OE21 CD44+/CD24- expression by 1.2-fold compared to control (N = 2). In another pilot experiment Torin-1 treated cells were able to form more spheres compared to control. Torin-1 did not have an effect on the expression of CD44+/CD24- in OE33. Conclusions: These findings indicate that inhibiting the mTOR pathway may enhance CSC-like properties in EC. Additional research needs to be done to further support this hypothesis and elucidate the mechanism in this process. Furthermore, the effect of mTOR pathway inducers in EC needs to be explored.