Djojosubroto, M. W. et al. Telomerase antagonists GRN163 and GRN163L inhibit tumor growth and increase chemosensitivity of human hepatoma. Hepatology 42, 1127-1136

Department of Gastroenterology, Hepatology, and Endocrinology, Medical School Hannover, Hannover, Germany.
Hepatology (Impact Factor: 11.06). 11/2005; 42(5):1127-36. DOI: 10.1002/hep.20822
Source: PubMed


Most cancer cells have an immortal growth capacity as a consequence of telomerase reactivation. Inhibition of this enzyme leads to increased telomere dysfunction, which limits the proliferative capacity of tumor cells; thus, telomerase inhibition represents a potentially safe and universal target for cancer treatment. We evaluated the potential of two thio-phosphoramidate oligonucleotide inhibitors of telomerase, GRN163 and GRN163L, as drug candidates for the treatment of human hepatoma. GRN163 and GRN163L were tested in preclinical studies using systemic administration to treat flank xenografts of different human hepatoma cell lines (Hep3B and Huh7) in nude mice. The studies showed that both GRN163 and GRN163L inhibited telomerase activity and tumor cell growth in a dose-dependent manner in vitro and in vivo. The potency and efficacy of the lipid-conjugated antagonist, GRN163L, was superior to the nonlipidated parent compound, GRN163. Impaired tumor growth in vivo was associated with critical telomere shortening, induction of telomere dysfunction, reduced rate of cell proliferation, and increased apoptosis in the treatment groups. In vitro, GRN163L administration led to higher prevalence of chromosomal telomere-free ends and DNA damage foci in both hepatoma cell lines. In addition, in vitro chemosensitivity assay showed that pretreatment with GRN163L increased doxorubicin sensitivity of Hep3B. In conclusion, our data support the development of GRN163L, a novel lipidated conjugate of the telomerase inhibitor GRN163, for systemic treatment of human hepatoma. In addition to limiting the proliferative capacity of hepatoma, GRN163L might also increase the sensitivity of this tumor type to conventional chemotherapy.

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    • "Meanwhile, the second type is based on the reverse-transcriptional property of telomerase , which requires short RNA pieces as template. Oligonucleotides are therefore good candidates for telomerase inhibition, e.g. one oligonucleotide, GRN163L, has been used as a telomerase antagonist in clinical trail [15] [16]. These types of inhibitors indirectly interact with telomerase. "
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    ABSTRACT: Enhanced telomerase activity is a hallmark in the majority of cancer cells. Thus, understanding the interactions between telomerase and its inhibitors is fundamentally important for the development of novel anticancer drugs without severe side effects. In this study, the covalent binding of helenalin to CYS445 of telomerase (PDB ID: 3DU6) was simulated using combined quantum chemical and molecular mechanical (QM/MM) methods. The results showed that the reaction was a reversible Michael-type addition and a hydrogen bond was formed between helenalin and the side chain of LYS416 of telomerase during the reaction procedure. The LYS416 residue is vital to telomere DNA recognition by interacting with DNA base through hydrogen bonds. The alkylation of CYS445 of telomerase by helenalin may interfere with the telomere DNA recognition at the telomerase active site, thus resulting in inhibition of the enzyme activity.
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    • "At nanomolar concentrations, GRN163L inhibits telomerase in a large spectrum of cancer cell lines [20]. In follow-up studies, long term GRN163L exposure could limit the lifespan of cultivated cancer cells derived from glioblastoma [29], multiple myeloma [30] and Barrett’s esophageal adenocarcinoma [31] as well as breast [32], [33], lung [34] and liver [35] cancers. In mouse models, the inhibitor could inhibit the growth of xenografts produced in mice by the implantation of these human cancer cells [29], [30], [31], [33], [34], [35]. "
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    ABSTRACT: Telomerase is required for the unlimited lifespan of cancer cells. The vast majority of pancreatic adenocarcinomas overexpress telomerase activity and blocking telomerase could limit their lifespan. GRN163L (Imetelstat) is a lipid-conjugated N3'→P5' thio-phosphoramidate oligonucleotide that blocks the template region of telomerase. The aim of this study was to define the effects of long-term GRN163L exposure on the maintenance of telomeres and lifespan of pancreatic cancer cells. Telomere size, telomerase activity, and telomerase inhibition response to GRN163L were measured in a panel of 10 pancreatic cancer cell lines. The cell lines exhibited large differences in levels of telomerase activity (46-fold variation), but most lines had very short telomeres (2-3 kb in size). GRN163L inhibited telomerase in all 10 pancreatic cancer cell lines, with IC50 ranging from 50 nM to 200 nM. Continuous GRN163L exposure of CAPAN1 (IC50 = 75 nM) and CD18 cells (IC50 = 204 nM) resulted in an initial rapid shortening of the telomeres followed by the maintenance of extremely short but stable telomeres. Continuous exposure to the drug eventually led to crisis and to a complete loss of viability after 47 (CAPAN1) and 69 (CD18) doublings. Crisis In these cells was accompanied by activation of a DNA damage response (γ-H2AX) and evidence of both senescence (SA-β-galactosidase activity) and apoptosis (sub-G1 DNA content, PARP cleavage). Removal of the drug after long-term GRN163L exposure led to a reactivation of telomerase and re-elongation of telomeres in the third week of cultivation without GRN163L. These findings show that the lifespan of pancreatic cancer cells can be limited by continuous telomerase inhibition. These results should facilitate the design of future clinical trials of GRN163L in patients with pancreatic cancer.
    PLoS ONE 01/2014; 9(1):e85155. DOI:10.1371/journal.pone.0085155 · 3.23 Impact Factor
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    • "The combination of imetelstat with existing chemotherapeutic agents has been demonstrated to enhance chemosensitivity in various human cancer cells (Djojosubroto et al., 2005; Godblatt et al., 2009a, 2009b). More specifically, imetelstat increased doxorubicin sensitivity of Hep3B human hepatoma cells (Djojosubroto et al., 2005), sensitized human breast cancer cells to paclitaxel and trastuzumab (Godblatt et al., 2009a, 2009b), and also enhanced hyperthermia-mediated radiosensitization in human 293 cell lines (Gomez-Millan et al., 2007). Recently, imetelstat in combination with radiation and temozolomide had a statistically significant effect on cell survival and activated the DNA damage response pathway in GBM tumor-initiating cells (Marian et al., 2010). "

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