Clinical significance of aberrant mammalian target of rapamycin expression in stage IIIB colon cancer

Phosphorylated mTOR Expression Profiles in Human Normal and Carcinoma Tissues

Mammalian target of rapamycin (mTOR) is a key controller of cell growth and proliferation in normal tissues and solid tumors. In the present study, an immunohistochemical analysis of the expression pattern of phosphorylated mTOR (p-mTOR) was performed in human normal fetal and adult tissues and various carcinoma tissues. p-mTOR expression showed tissue and cell type specificity in normal and cancer tissues. In normal fetal and adult tissues, p-mTOR staining was observed in the intestinal crypt, intrahepatic bile ductule, pancreatic duct, distal nephron of the kidney, umbrella cell of urothelium, mesothelial cell, and choroid plexus. In cancer tissues, p-mTOR expression was higher in adenocarcinoma than in other types of cancers, in metastatic cancer than in primary cancer, and in the forefront of the infiltrating cancer cells. These results suggest that p-mTOR is implicated not only in cell proliferation but also in tubular morphogenesis in normal and cancer tissues. In addition, mTOR activation appears to be associated with cancer cell invasion and migration in solid tumors.

mTOR activity and its prognostic significance in human colorectal carcinoma depending on C1 and C2 complex-related protein expression

AIMS

Tumour heterogeneity and altered activation of signalling pathways play important roles in therapy resistance. The PI3K/Akt/mTOR signalling network is a well-known regulator of several functions that contribute to tumour growth. mTOR exists in two functionally different multiprotein complexes. We aimed to determine mTOR activity-related proteins in clinically followed, conventionally treated colon carcinomas and to analyse the correlation between clinical data and mTORC1 and mTORC2 activity.

METHODS

Immunohistochemistry was performed with different antibodies on tissue microarray blocks from 103 patients with human colorectal adenocarcinoma. mTORC1- and mTORC2-related activity were scored on different stainings including analysis of the expression of Raptor and Rictor-specific elements of mTORC1 and C2 complexes. The staining scores and clinical/survival data were compared and analysed.

RESULTS

Detailed characterisation showed stage and grade independent high mTOR activity in 74% of cases. High mTOR activity was present in mTORC1 and/or mTORC2 complexes; >60% of cases had mTORC2-related high mTOR activity. Based on our analysis, high mTOR activity and Rictor overexpression could be markers of a bad prognosis. Combined phosphoprotein and Rictor/Raptor expression evaluation revealed even stronger statistical correlation with prognosis.

CONCLUSIONS

The presented staining panel could be appropriate and highly recommended for the accurate specification of mTORC1 and C2 activity of tumour tissues. This could help in the selection of mTOR inhibitors and can provide information about prognosis, which may guide decisions about the intensity of therapy.