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The low percentage of human mesenchymal stem cells (hMSCs) in bone marrow necessitates their in vitro expansion prior to clinical use in regenerative medicine. We evaluated the effect of long-term culture of hMSCs on telomere length and transformation capacity by TERT transfection. hMSCs were isolated from the bone marrow aspirates of 24 donors and cultured with fibroblast growth factor-2 (FGF-2). Six cell lines with >500 population doubling levels were considered immortalized. TERT was transfected into two of the six lines for a comparison of telomere length, telomerase activity, differential capacity, colony formation capacity in soft agar and tumorigenicity in immunodeficient (NOD-SCID) mice. hMSC lines exhibited elongated telomeres without the activation of telomerase and retained multi-lineage differentiation potential upon chondrogenic or adipogenic differentiation, while non-immortalized hMSCs showed a marked reduction in telomere length in the differentiation process. Immortalized hMSCs showed anchorage-independence and formed tumors in NOD-SCID mice. Histologically, these tumors consisted of differentiated cells such as fat tissue and cartilage. Two TERT-transfected hMSC lines showed high rates of tumor formation in NOD-SCID mice. These tumors were histologically similar to teratocarcinoma without differentiated cells. These cells may provide a model for the origin of cancer stem cells from adult stem cells, and indicate the possibility that telomerase activation has a major role in the malignant transformation of human stem cells. These data suggest that adult hMSCs have a potential for neoplastic transformation and have implications for the use of hMSCs in tissue engineering and regenerative medicine.

Existence of cancer stem cells (CSCs) is still hypothetical and their practical marker is not available yet in lung cancer. To verify the possible existence of CSCs and to find their markers in lung cancer, we compared the p16/Rb and telomerase status in 83 lung cancer tissues and 15 lung cancer cell lines, since inactivation of p16/Rb pathway is considered to be a prerequisite for normal somatic cells to become immortal cancer cells. We found that 7 of 14 adenocarcinoma, but not squamous cell carcinoma, tissues with high telomerase activity and 3 adenocarcinoma cell lines likely had intact p16/Rb. Such cell lines showed higher colony formation capacity in soft agar compared with inactivated ones with similar growth rate. Moreover, cisplatin-resistant cell line PC9/CDDP with intact p16/Rb, but not PC14/CDDP with its inactivation, increased the colony formation capacity compared with the parent cells. Since CSCs are considered to be resistant to conventional anticancer drugs, they could have been concentrated as long as CSCs existed. We propose that half of immortal lung adenocarcinomas are derived from innately telomerase-positive stem cells, which might be the origin of CSCs, and that high telomerase activity with intact p16/Rb could be a marker of stem cell origin.

Prior laboratory prediction of individual drug response is of key importance in esophageal squamous cell carcinoma (ESCC), because of the extremely narrow therapeutic index of chemotherapy. However, very few critical markers have been validated to date for ESCC. We previously demonstrated that simultaneous performance of two different types of comprehensive gene expression analysis might provide a way to identify potent marker genes for drug sensitivity from the expression-sensitivity correlation analysis alone, but the screening method appeared not to be always effective. Therefore, we attempted to identify novel potent marker genes using a new statistical analysis of oligonucleotide microarray expression data, based on a two-dimensional mixed normal model, and selected 3 and 7 novel candidates for 5-fluorouracil (5-FU) and cis-platinum (CDDP), respectively. Interferon induced transmembrane protein 1 (IFITM1) gene alone, being suggested as a key gene of Wnt pathway, was commonly selected in both screening methods. The transfection analyses and siRNA-mediated knock-down experiments revealed that expression of IFITM1 closely related to cellular sensitivity to CDDP. Considering the fact that drug sensitivity is determined by multiple genes, we established the best linear model using quantified expression data of a set of all the selected marker genes including IFITM1, which converted the quantified expression data of ESCC cell lines into an IC50 value of each drug. In the same way, using the representative genes selected in vitro, we developed highly predictive formulae for disease-free survival (DFS) of the CDDP/5-FU combination after curative operation in esophageal cancer patients (R=0.917). A two-dimensional mixed normal model can be a powerful tool to identify novel drug-response determinants, and the IFITM1 gene selected by the statistical method a novel critical biomarker of CDDP response in ESCC.

Esophageal cancer is a highly lethal disease and the optimal therapy remains unclear. Since adjuvant chemotherapy gives a better chance of survival, we attempted to develop a chemosensitivity prediction model to improve individual responses to therapy. Comprehensive gene expression analyses (cDNA and oligonucleotide microarrays) and MTT assay of 8 drugs in 20 KYSE squamous cell carcinoma cell lines were performed to distinguish candidate marker genes whose expression levels reproducibly correlated with cellular drug sensitivities. After confirmation with real-time RT-PCR, we performed multiple regression analyses to develop drug-sensitivity prediction formulae using the quantified expression data of selected marker genes. Using the same sets of genes, we also constructed prediction models for individual clinical responses to 5-FU-based chemotherapy using 18 cases. We selected 5 better marker genes, known as drug sensitivity determinants, identified 9 novel predictive genes for 4 of 8 anticancer drugs [5-FU, CDDP, DOX, and CPT-11 (SN-38)], and developed highly predictive formulae of in vitro sensitivities to the 4 drugs and clinical responses to 5-FU-based adjuvant chemotherapies in terms of overall and disease-free survivals. Our selected genes are likely to be effective drug-sensitivity markers and formulae using the 9 novel genes would provide advantages in prediction.

It is widely accepted that activation of telomerase and maintenance of telomeres play central roles in cellular immortalization for most cancer cells. However, they seem to be insufficient for normal human cells. To elucidate critically responsible genes for telomerase mediated cellular immortalization in non-cancerous cells, we explored the genes that are differentially expressed throughout the immortalization process of normal human cells using cDNA microarrays with novel normalization procedures. We found that the number of genes, differentially expressed during cellular immortalization after ectopic expression of telomerase, dramatically increased in a later phase, especially in fibroblasts. We identified 18 and 20 genes/ESTs dysregulated throughout the cellular immortalization processes in fibroblasts and endothelial cells, respectively, but none of them overlapped. Only BGN and COL5A2 were commonly downregulated, except for at early phase in fibroblasts, and a few genes showed controversial expression changes, with regard to previous reports in cancer cells. These findings indicate that normal somatic cells would require cell-type specific events in addition to telomerase activation, and a rare population that eventually experience such events would acquire immortality. The key molecules that distinguish the immortalization mechanisms in cancerous and non-cancerous cells may become crucial targets for anticancer therapy and regenerative therapy.

It is widely accepted that telomerase, which compensates for telomere shortening, is finally activated in almost all kinds of human malignant neoplasms, and ectopic expression of telomerase may endow some kinds of human somatic cells with indefinite proliferation capacity, i.e., immortality. To clarify the intrinsic responses required in acquiring immortality, we investigated the chronological changes in the expression levels of the cell cycle and apoptosis-related genes by real-time RT-PCR in human normal fibroblasts and endothelial cells after hTERT transfection. We found that fibroblast MJ90 required intrinsic responses including reversible upregulation of cell-cycle promoting genes and down-regulation of apoptosis-inducing genes in early phase after transfection, whereas the endothelial cell HUE142-2 did not. In addition, the microarray analysis of the fibroblast strains revealed that the dysregulated genes during cellular immortalization were different from those reported in fibroblasts probably having acquired telomere maintenance mechanism concomitant with hTERT induction. These findings indicate that cell-type specific differential gene expression after telomerase activation may be important to acquire telomere-maintenance capacity and immortality in some non-cancerous human cells. Investigation of these molecules may elucidate the differences in the capacity of acquiring immortality in cancer and normal somatic cells in future.