Evidence of epithelial to mesenchymal transition associated with increased tumorigenic potential in an immortalized normal prostate epithelial cell line.

BACKGROUND: The majority of established human prostate cancer cell lines are derived from metastatic lesions and are already tumorigenic in vivo, therefore immortalized normal prostate cell lines may provide a more relevant model to unveil the mechanisms associated with cancer progression and metastasis. METHODS: PZ-HPV-7, an immortalized human prostate epithelial cell line was used to generate xenograft tumors in mice. A subline designated HPV-PZ-7T was subsequently derived from the subrenal capsule xenograft of a nude mouse. These cells were further characterized using karyotyping, immunofluorescence, qRT-PCR, Western blotting, and three-dimensional cultures in Matrigel. RESULTS: The PZ-HPV-7 cell line possesses a typical epithelial morphology, expresses basal cell markers, and is capable of forming web-like structures with evidence of budding on Matrigel. PZ-HPV-7 is non-tumorigenic in immunocompromised mice by either subcutaneous injection or subrenal grafting. In contrast, the PZ-HPV-7T cells, derived from a xenograft tumor induced by co-inoculation with matrigel using subrenal grafting, possess a mesenchymal phenotype as well as luminal cell markers and are highly tumorigenic and metastatic in nude mice. Functionally and biochemically, the PZ-HPV-7T subline appears to have undergone an epithelial-to-mesenchymal transition (EMT) from the parental PZ-HPV-7 line. CONCLUSION: We have developed a novel EMT model using an immortalized normal prostate epithelial cell line and generated a new prostate cancer cell line, PZ-HPV-7T, which may represent an excellent system to study mechanisms associated with prostate cancer progression and metastasis.

The telomerase antagonist, imetelstat, efficiently targets glioblastoma tumor-initiating cells leading to decreased proliferation and tumor growth.

PURPOSE: Telomerase activity is one of the hallmarks of cancer and is a highly relevant therapeutic target. The effects of a novel human telomerase antagonist, imetelstat, on primary human glioblastoma (GBM) tumor-initiating cells were investigated in vitro and in vivo. EXPERIMENTAL DESIGN: Tumor-initiating cells were isolated from primary GBM tumors and expanded as neurospheres in vitro. The GBM tumor-initiating cells were treated with imetelstat and examined for the effects on telomerase activity levels, telomere length, proliferation, clonogenicity, and differentiation. Subsequently, mouse orthotopic and subcutaneous xenografts were used to assess the in vivo efficacy of imetelstat. RESULTS: Imetelstat treatment produced a dose-dependent inhibition of telomerase (IC(50) 0.45 micromol/L). Long-term imetelstat treatment led to progressive telomere shortening, reduced rates of proliferation, and eventually cell death in GBM tumor-initiating cells. Imetelstat in combination with radiation and temozolomide had a dramatic effect on cell survival and activated the DNA damage response pathway. Imetelstat is able to cross the blood-brain barrier in orthotopic GBM xenograft tumors. Fluorescently labeled GBM tumor cells isolated from orthotopic tumors, following systemic administration of imetelstat (30 mg/kg every day for three days), showed approximately 70% inhibition of telomerase activity. Chronic systemic treatment produced a marked decrease in the rate of xenograft subcutaneous tumor growth. CONCLUSION: This preclinical study supports the feasibility of testing imetelstat in the treatment of GBM patients, alone or in combination with standard therapies.

The effects of telomerase inhibition on prostate tumor-initiating cells.

Prostate cancer is the most common malignancy in men, and patients with metastatic disease have poor outcome even with the most advanced therapeutic approaches. Most cancer therapies target the bulk tumor cells, but may leave intact a small population of tumor-initiating cells (TICs), which are believed to be responsible for the subsequent relapse and metastasis. Using specific surface markers (CD44, integrin alpha(2)beta(1) and CD133), Hoechst 33342 dye exclusion, and holoclone formation, we isolated TICs from a panel of prostate cancer cell lines (DU145, C4-2 and LNCaP). We have found that prostate TICs have significant telomerase activity which is inhibited by imetelstat sodium (GRN163L), a new telomerase antagonist that is currently in Phase I/II clinical trials for several hematological and solid tumor malignancies. Prostate TICs telomeres were of similar average length to the telomeres of the main population of cells and significant telomere shortening was detected in prostate TICs as a result of imetelstat treatment. These findings suggest that telomerase inhibition therapy may be able to efficiently target the prostate TICs in addition to the bulk tumor cells, providing new opportunities for combination therapies.

Prostate tumor-initiating cells: a new target for telomerase inhibition therapy?

Conventional therapies for prostate cancer, especially in its androgen-independent form, may result in the survival of small populations of resistant cells with tumor-initiating potential. These "cancer stem cells" are believed to be responsible for cancer relapse, and therapeutic strategies targeting these cells are of great importance. Telomerase is a ribonucleoprotein enzyme responsible for telomere elongation and is activated in the majority of malignancies, including prostate cancer, but is absent in most normal cells. Putative tumor-initiating cells have significant levels of telomerase, indicating that they are an excellent target for telomerase inhibition therapy. In this review, we present some evidence for the hypothesis that conventional therapies (standard chemotherapy and/or radiation therapy) in combination with telomerase inhibitors may result in effective and more durable responses.

The Terminal acidic SANT 1 (Tacs1) gene of maize is expressed in tissues containing meristems and encodes an acidic SANT domain similar to some chromatin-remodeling complex proteins.

While screening for plant homologs of telomeric-complex proteins, we isolated a cDNA for the Terminal acidic SANT 1 (Tacs1) gene of maize, encoding a 45-kDa protein with a C-terminal Myb/SANT-like domain. Gene expression and protein modeling data indicate that the TACS1 protein may function in chromatin remodeling within shoot primordia or other meristem-containing tissues.

Dehydrin variability among rhododendron species: a 25-kDa dehydrin is conserved and associated with cold acclimation across diverse species.

• Here we examine the accumulation pattern of dehydrins in non- vs cold-acclimated leaves of 21 species comprising two divergent groups of Rhododendron, Subgenus Hymenanthes and Subgenus Rhododendron. Individuals from five other Ericaceous genera were also evaluated in the same way. Quantitative comparisons of cold-inducibility of a 25-kDa dehydrin and cold acclimation ability in six Rhododendron species were also performed. • Leaf freezing tolerance assay and dehydrin detection and quantification were performed as previously described. • Eleven dehydrins, ranging from 25- to 73-kDa, were observed among the 21 species, and most were more abundant in winter-collected leaves than in summer-collected leaves. One dehydrin, a 25-kDa protein, was uniquely conserved across most (95%) of the species surveyed, and was absent only in R. brookeanum, a tropical species that may not be capable of cold acclimation. The 25-kDa dehydrin was also identified in Kalmia, a genus closely related to Rhododendron but not in four other less related Ericaceous genera. Comparison of dehydrin profiles in non- and cold-acclimated leaf tissue from six species (three very hardy, and three less hardy, species) indicated a close association (R2  = 0.95) between relative changes in leaf freezing tolerance and 25-kDa dehydrin accumulation. • The taxonomic and physiological comparisons suggest a central, but as yet unknown, function for the 25-kDa dehydrin in protecting rhododendron leaves from freezing injury.

The maize Single myb histone 1 gene, Smh1, belongs to a novel gene family and encodes a protein that binds telomere DNA repeats in vitro.

We screened maize (Zea mays) cDNAs for sequences similar to the single myb-like DNA-binding domain of known telomeric complex proteins. We identified, cloned, and sequenced five full-length cDNAs representing a novel gene family, and we describe the analysis of one of them, the gene Single myb histone 1 (Smh1). The Smh1 gene encodes a small, basic protein with a unique triple motif structure of (a) an N-terminal SANT/myb-like domain of the homeodomain-like superfamily of 3-helical-bundle-fold proteins, (b) a central region with homology to the conserved H1 globular domain found in the linker histones H1/H5, and (c) a coiled-coil domain near the C terminus. The Smh-type genes are plant specific and include a gene family in Arabidopsis and the PcMYB1 gene of parsley (Petroselinum crispum) but are distinct from those (AtTRP1, AtTBP1, and OsRTBP1) recently shown to encode in vitro telomere-repeat DNA-binding activity. The Smh1 gene is expressed in leaf tissue and maps to chromosome 8 (bin 8.05), with a duplicate locus on chromosome 3 (bin 3.09). A recombinant full-length SMH1, rSMH1, was found by band-shift assays to bind double-stranded oligonucleotide probes with at least two internal tandem copies of the maize telomere repeat, TTTAGGG. Point mutations in the telomere repeat residues reduced or abolished the binding, whereas rSMH1 bound nonspecifically to single-stranded DNA probes. The two DNA-binding motifs in SMH proteins may provide a link between sequence recognition and chromatin dynamics and may function at telomeres or other sites in the nucleus.