MST-312: a telomerase inhibitor effectively blocking MYC oncogenic functions [array]
ABSTRACT: Reactivation of the telomerase reverse transcriptase subunit, TERT, is linked to tumourigenesis due to well-documented telomere-dependent and independent functions. The aim of this study was to investigate the effect of the telomerase inhibitor, MST-312, on TERT functions, focusing in particular, on its effects on MYC stabilty and MYC-regulated pathways, in order to assess its potential as a therapeutic agent. We demonstrate that MST-312 reduces MYC levels in cancer cells, leading to reduced MYC levels on chromatin, and subsequently affecting the MYC-regulated transcriptional program. As a result, MST-312 treatment increases the survival of lymphoma-bearing mice. Mechanistically, MST-312 affects the conformation of TERT, leading to TERT/Terc dissociation, and the subsequent loss of both its telomere-dependent and independent functions. Based on the presented data, we conclude that MST-312 treatment is a promising therapeutic strategy, in particular, in MYC-driven tumorus. Overall design: Total RNA was extracted from P493 cells treated with MST-312 and TET for 48 h, then released into fresh TET-free media with MST-312 for 0, 4, 8 and 24 hours.
Project description:Reactivation of the telomerase reverse transcriptase subunit, TERT, is linked to tumourigenesis due to well-documented telomere-dependent and independent functions. The aim of this study was to investigate the effect of the telomerase inhibitor, MST-312, on TERT functions, focusing in particular, on its effects on MYC stabilty and MYC-regulated pathways, in order to assess its potential as a therapeutic agent. We demonstrate that MST-312 reduces MYC levels in cancer cells, leading to reduced MYC levels on chromatin, and subsequently affecting the MYC-regulated transcriptional program. As a result, MST-312 treatment increases the survival of lymphoma-bearing mice. Mechanistically, MST-312 affects the conformation of TERT, leading to TERT/Terc dissociation, and the subsequent loss of both its telomere-dependent and independent functions. Based on the presented data, we conclude that MST-312 treatment is a promising therapeutic strategy, in particular, in MYC-driven tumorus. Overall design: ChIP was performed using anti-MYC (sc-764) in P493 cells and treated with MST-312.
Project description:Telomere maintenance by telomerase activity supports the infinite growth of cancer cells. MST-312, a synthetic telomerase inhibitor, gradually shortens telomeres at non-acute lethal doses and eventually induces senescence and apoptosis of telomerase-positive cancer cells. Here we report that MST-312 at higher doses works as a dual inhibitor of telomerase and DNA topoisomerase II and exhibits acute anti-proliferative effects on cancer cells and xenografted tumours in vivo. Our cell-based chemical fingerprinting approach revealed that cancer cells with shorter telomeres and lower expression of lamin A, a nuclear architectural protein, exhibited higher sensitivity to the acute deleterious effects of MST-312, accompanied by formation of telomere dysfunction-induced foci and DNA double-strand breaks. Telomere elongation and lamin A overexpression attenuated telomeric and non-telomeric DNA damage, respectively, and both conferred resistance to apoptosis induced by MST-312 and other DNA damaging anticancer agents. These observations suggest that sufficient pools of telomeres and a nuclear lamina component contribute to the cellular robustness against DNA damage induced by therapeutic treatment in human cancer cells.
Project description:Constitutively active MYC and reactivated telomerase often coexist in cancers. While reactivation of telomerase is thought to be essential for replicative immortality, MYC, in conjunction with cofactors, confers several growth advantages to cancer cells. It is known that the reactivation of TERT, the catalytic subunit of telomerase, is limiting for reconstituting telomerase activity in tumors. However, while reactivation of TERT has been functionally linked to the acquisition of several "hallmarks of cancer" in tumors, the molecular mechanisms by which this occurs and whether these mechanisms are distinct from the role of telomerase on telomeres is not clear. Here, we demonstrated that first-generation TERT-null mice, unlike Terc-null mice, show delayed onset of MYC-induced lymphomagenesis. We further determined that TERT is a regulator of MYC stability in cancer. TERT stabilized MYC levels on chromatin, contributing to either activation or repression of its target genes. TERT regulated MYC ubiquitination and proteasomal degradation, and this effect of TERT was independent of its reverse transcriptase activity and role in telomere elongation. Based on these data, we conclude that reactivation of TERT, a direct transcriptional MYC target in tumors, provides a feed-forward mechanism to potentiate MYC-dependent oncogenesis.
Project description:Chromatin immunoprecipitation sequencing (ChIP-seq) was performed to analyze the effect of telomerase inhibition on TNFα-induced genome-wide p65 binding in HeLa cells. By obtaining over 40 million uniquely mappable reads per sample from ChIP-seq, maps for TNFα-induced p65 binding in absence and presence of an hTERT inhibitor, MST-312, were generated. As expected, TNFα treatment significantly increased genome-wide p65 occupancy. Interestingly, when cells were treated with MST-312 prior to TNFα stimulation, the number of p65 binding sites was reduced. In addition, some binding sites, including important p65 targets like IL6 and TNF, showed a reduced p65 occupancy with a minimum fold change of 1.5, after MST-312 exposure. Taken together, our ChIP-seq data indicate that telomerase is required for optimal p65 binding at a small proportion of p65 target sites upon inflammatory stimuli. Examination of p65 binding in HeLa cells in absence and presence of TNFα and MST-312.
Project description:The expression of telomerase in approximately 85% of cancers and its absence in the majority of normal cells makes it an attractive target for cancer therapy. However the lag period between initiation of telomerase inhibition and growth arrest makes direct inhibition alone an insufficient method of treatment. However, telomerase inhibition has been shown to enhance cancer cell radiosensitivity. To investigate the strategy of simultaneously inhibiting telomerase while delivering targeted radionuclide therapy to cancer cells, 123I-radiolabeled inhibitors of telomerase were synthesized and their effects on cancer cell survival studied. An 123I-labeled analogue of the telomerase inhibitor MST-312 inhibited telomerase with an IC50 of 1.58 ?M (MST-312 IC50: 0.23 ?M). Clonogenic assays showed a dose dependant effect of 123I-MST-312 on cell survival in a telomerase positive cell line, MDA-MB-435.
Project description:Testicular germ cell tumors (TGCTs) are classified into two main subtypes, seminoma (SE) and non-seminoma (NSE), but their molecular distinctions remain largely unexplored. Here, we used expression data for mRNAs and microRNAs (miRNAs) from The Cancer Genome Atlas (TCGA) to perform a systematic investigation to explain the different telomere length (TL) features between NSE (n = 48) and SE (n = 55). We found that TL elongation was dominant in NSE, whereas TL shortening prevailed in SE. We further showed that both mRNA and miRNA expression profiles could clearly distinguish these two subtypes. Notably, four telomere-related genes (TelGenes) showed significantly higher expression and positively correlated with telomere elongation in NSE than SE: three telomerase activity-related genes (TERT, WRAP53 and MYC) and an independent telomerase activity gene (ZSCAN4). We also found that the expression of genes encoding Yamanaka factors was positively correlated with telomere lengthening in NSE. Among them, SOX2 and MYC were highly expressed in NSE versus SE, while POU5F1 and KLF4 had the opposite patterns. These results suggested that enhanced expression of both TelGenes (TERT, WRAP53, MYC and ZSCAN4) and Yamanaka factors might induce telomere elongation in NSE. Conversely, the relative lack of telomerase activation and low expression of independent telomerase activity pathway during cell division may be contributed to telomere shortening in SE. Taken together, our results revealed the potential molecular profiles and regulatory roles involving the TL difference between NSE and SE, and provided a better molecular understanding of this complex disease.