Telomere in cancerous cells is conserved even after several rounds of cell division. By identifying the responsible protein in this process, i.e. telomerase, researchers have utilised it as a novel target for cancer treatment. So, how is the telomerase targetted? Are you ready to discover the truth?

1. Telomerase Inhibition as Novel
Cancer Therapeutic Method
Presented By :
Aayushree Kharel (0323131)
Bryan Chong Boon Hooi (0323527)
Cynthia Teo Yu Ai (0322550)
Hardeep Kaur (0323338)
Vincensa Nicko Widjaja (0322042)

2. Introduction
• Human telomere region consists of repetitive TTAGGG (Shay 2001a).
• Telomerase holoenzyme consists of 2 subunits : a reverse
transcriptase (hTERT), the catalytic subunit, and a RNA subunit (hTR)
(Tahtouh et al. 2015).
• Works by elongating the 3’ end of a telomere.
• Cancer is a condition in which a cell loses its cell division
regulation.
• Many factor contributes to cancer, however in this presentation,
its only limited to telomerase activity.
• Tracking to genomic level, it is believed that telomerase
expression has been increased to maximum rate. Thus, leading
to uncontrollable cell division (Shay 2001a).
Figure 1: Location of telomere region (Dreamstime 2011).
Figure 2: Telomerase function (Leslet
and Walker, 2014) shown on upper side
; A functional telomerase structure
(Carreno 2015) shown on lower side.

3. Discussion
• The RNA component of telomerase has been a popular and effective target for inhibiting
telomerase activity in cancer cells. In the case of TERT transcript knockdown, antisense
oligonucleotides against the human TR template can be employed to reduce or eliminate
telomerase activity.
• Result of this approach is that single-stranded templates, such as the TR component, are
specifically cleaved. The anticancer utility of this approach has been proven in vitro and in vivo.
• Hammerhead ribozymes and RNAi can be directed to the RNA component of telomerase.
• Effect is immediate growth inhibition of cancer cells both in vitro and in vivo independent of
telomere length of the target cancer cell.
• Advantage of this technique is that it greatly reduces the lag period that is often encountered in
approaches that are dependent upon the shortening of telomeres to inhibit cancer cell growth.
(Andrews & Tollefsbol 2008)
TR Inhibition as an Anticancer Approach

4. Discussion
• Approaches to telomerase inhibition have been
developed that do not directly inhibit the TERT or TR
components of telomerase but rather inhibit target
proteins that are associated with telomerase activity.
• Signaling pathways such as those carried out by mitogen-
activated protein (MAP) kinase can result in stimulation of
the TERT gene
• Inhibition of this pathway could be a novel approach to
reducing TERT expression and telomerase activity.
Targeting proteins associated with telomerase activity
(Andrews & Tollefsbol 2008)

5. Discussion
• Recent studies show that linoleic acid is able to lower the activity of
hTERT on the transcriptional level.
• Linoleic acid downregulates the production of as c-Myc and SP-1
which serve as transcription factors for the expression of hTERT.
• Only works on a limited range of cancer cells, which excludes
bladder and breast cancer cells (Choi 2014).
Blocking telomerase activity on the transcriptional level

6. Discussion
• Aside from the gene silencing methods, two chemical compounds have been tested
to have a direct effect on the activity of the ribonucleoprotein telomerase. The
compounds, β-rubromycin and oleic acid, act by competitively binding to the active
site of telomerase, thereby competing with the binding of primers and
deoxynucleotide substrates, two components crucial to the synthesis of telomeric
DNA in the chromosome (Mizushina et al. 2012).
• Outside of inhibition:
Another novel approach to cancer treatment would be using the human TERT as a
target in immunotherapy. TERT is found to be expressed by large number of
malignant cells, including melanoma cells, and it was found to also be a viable
target antigen for CD8+ CTL immune response. Upon antigen detection, CTLs will
perform standard protocol of cytokine secretion followed by lysis of target cell. This
would pave the way for potential vaccines against certain cancers in the future
(Vonderheide 2002).
Chemical regulator perspective

7. Figure 3: Cellular consequences of telomerase
and telosome targeting. Telomerase inhibitors may
induce either a delayed anti-proliferative effect
through a “slow” pathway mainly based on
telomere erosion (BIBR1532, hTR inhibitors) or a
quick anti-proliferative effect through a “fast”
pathway mainly based on telomere uncapping
(hTERT inhibitors). Inhibitors of telosome proteins
and G4 ligands mainly induce telomere uncapping.
(Folini et al. 2009)

8. Current Development
• Anti-telomerase therapeutics aims to selectively
induce apoptosis and cell death in cancer cells while
minimizing the effects on normal cells (Buseman et
al. 2012).
• Vaccines, antisense oligonucleotides, and small-
molecule inhibitors targeting hTERT has been
developed (Jafri et al. 2016).
• Oligonucleotide imetelstat is the only anti-telomerase
compound that has been extensively evaluated in
clinical trials (Jafri et al. 2016).
• A novel telomerase inhibitor, BIBR1532, has been
reported but this compound has not yet progressed
to clinical trial (Jafri et al. 2016).
Figure 4: Structure (a) and action of imetelstat (b).
Jafri et al. 2016

9. Challenges
 Treatment needs to be coordinated in conjunction with other treatments like
chemotherapeutics and radiation therapy (Cunningham et al. 2006).
 Intestinal crypt, hematopoietic stem cells and cells lining the endometrium express
telomerase (Cunningham et al. 2006). Hence, these cells should be less affected than
tumor cells and telomere shortening should not occur in absence of cell division (Shay
et al. 2001).
 Telomerase inhibition should not affect the rate of cell growth until progressive
telomere shortening (Shay et al. 2001b).
 The response for telomerase inhibition varies. These varying results are due to the
extra-telomeric functions of telomerase which includes cell protection, anti-apoptotic
function and support of the tumorigenic phenotype (Chung et al. 2005).

10. Challenges
 Some cells might undergo telomerase independent mechanism- alternative
lengthening of telomeres (ALT) pathway (Henson et al. 2002). Inhibiting the telomerase
activity may promote the development of ALT pathway.
 TERT are intracellular components, and are dependent on MHCs (major
histocompatibility complexes) particularly MHC1 to be presented on the cell surface for
CTL detection. Some cancer cells are shown to possess the ability to downregulate
MHC1 in efforts to avoid detection (Wang et al. 2007).

11. Conclusion
Telomerase inhibition is one potential treatment for cancer
This might be done either :
• TERT inhibition by complement oligonucleotides
• Inhibition of telomerase-associated proteins (MAP kinase)
• Further until transcriptional level (linoleic acid)
Currently developed : Imetelstat
Challenges to overcome :
• Involvement of other treatments (financial problem).
• Increase the specificity of telomerase inhibitors until transformed cell level.
• Ability to produce one result – the telomerase inhibition itself. (not to
produce other effects)

12. References
 Andrews, LG & Tollefsbol, TO 2008, ‘Methods of Telomerase Inhibition’, Methods of Molecular Biology, vol. 405, pp. 1-8, viewed 14 September 2016,
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2423206/
 Buseman, C, Wright, W & Shay, J, 2012, 'Is telomerase a viable target in cancer?', Science Direct, viewed 16 September 2016, http://ac.els-
cdn.com/S0027510711001825/1-s2.0-S0027510711001825-main.pdf?_tid=ab9dd4ae-7e22-11e6-bbcc-
00000aacb35d&acdnat=1474259985_5e0186bcdc0aac61ca2307697c66ec72
 Carreno, T 2015, ‘Telomerase might have an important role in the mechanism of action of various psychiatric medications’, viewed 13 September
2016, https://sussexdrugdiscovery.wordpress.com/2015/12/
 Choi, Y 2014, ‘Linoleic Acid-Induced Growth Inhibition of Human Gastric Epithelial Adenocarcinoma AGS Cells is Associated with Down-Regulation of
Prostaglandin E2 Synthesis and Telomerase Activity’, Journal of Cancer Prevention, vol. 19, no. 1, pp.31-38, viewed 17 September 2016,
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4189473/
 Chung, HK, Cheong, C, Song, J & Lee HW 2005, ‘Extratelomeric functions of telomerase’, Current Molecular Medicine, vol. 5, pp. 233-241,viewed 17
September 2016, http://www.ncbi.nlm.nih.gov/pubmed/15974878
 Cunningham, AP, Love, WK, Zhang, RW, Andrews, LG & Tollefsbol, TO 2006, ‘Telomerase Inhibition in Cancer Therapeutics: Molecular- Based
Approaches’, Current Medicinal Chemistry, vol. 13, no. 24, pp. 2875-2888, viewed 17 September 2016,
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2423208/#
 Dreamstime 2011, 'Telomere, cell division and human chromosomes', viewed 14 September, https://www.dreamstime.com/royalty-free-stock-image-
telomere-cell-division-human-chromosomes-telomeres-ends-serve-to-protect-coding-dna-genome-telomeres-shorten-image36972246
 Folini, M, Gandellini, P & Zaffaroni, N 2009, ‘Targeting the telosome: Therapeutic implications’, Molecular Basis of Disease, vol. 1792, no. 4, pp. 309-
316, viewed 17 September 2016, http://www.sciencedirect.com/science/article/pii/S0925443909000301
 Gilboa, E, Nair, S, Heiser, A, Boczkowski, D, Majumdar, A, Naoe, M, Lebkowski, J & Vieweg, J 2000, ‘Induction of cytotoxic T cell responses and
tumor immunity against unrelated tumors using telomerase reverse transcriptase RNA transfected dendritic cells’, Nature Medicine, vol. 6, no. 9,
pp.1011-1017, viewed 15 September 2016, http://www.ncbi.nlm.nih.gov/pubmed/10973321
 Henson, JD, Neumann AA, Yeager TR & Reddel RR 2002, ‘Alternative lengthening of telomeres in mammalian cells’, Oncogene, vol. 21, no.4, pp.
598-610, viewed 17 September 2016, http://www.nature.com/onc/journal/v21/n4/full/1205058a.html
 Jafri, M, Ansari, S, Alqahtani, M & Shay, J 2016, ‘Roles of telomeres and telomerase in cancer, and advances in telomerase- targeted therapies’,
viewed 16 September 2016, http://genomemedicine.biomedcentral.com/articles/10.1186/s13073-016-0324-x
 Lesley, A & Walker, C 2014, ‘Using Telomerase for Targeted Gene Therapy in Cancer Patients’, viewed 16 September 2016,
http://Islaslab.wikispaces.com

13. References
 Mizushina, Y, Takeuchi, T, Sugawara, F & Yoshida, H 2012, ‘Anti-Cancer Targeting Telomerase Inhibitors: & beta;-Rubromycin and Oleic Acid’,
MRMC, vol. 12, no. 11, pp.1135-1143, viewed 13 September 2016, http://www.ncbi.nlm.nih.gov/pubmed/22876944
 Shay, J 2001a, ‘Telomerase and cancer’, Human Molecular Genetics, vol. 10, no. 7, pp.677-685, viewed 16 September 2016,
http://hmg.oxfordjournals.org/content/10/7/677.full.pdf
 Shay, JW, Zou, Y, Hiyama, E & Wright, WE 2001b, ‘Telomerase and cancer’, Oxford Journals, vol. 10, no.7, pp. 677-685, viewed 18 September 2016,
http://hmg.oxfordjournals.org/content/10/7/677.full
 Tahtouh, R, Azzi, A, Alaaeddine, N, Chamat, S, Bouharoun-Tayoun, H, Wardi, L, Raad, I, Sarkis, R, Antoun, N & Hilal, G 2015, ‘Telomerase Inhibition
Decreases Alpha-Fetoprotein Expression and Secretion by Hepatocellular Carcinoma Cell Lines: In Vitro and In Vivo Study’, PLOS ONE, vol. 10, no.
3, viewed 16 September 2016, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4379025/pdf/pone.0119512.pdf
 Vonderheide, R 2002, ‘Telomerase as a universal tumor-associated antigen for cancer immunotherapy’, Oncogene, vol. 21 no.4 , pp.674-679, viewed
16 September 2016, http://www.nature.com/onc/journal/v21/n4/pdf/1205074a.pdf
 Wang, Z, Zhang, L, Qiao, A, Watson, K, Zhang, J and Fan, G 2007, ‘Activation of CXCR4 Triggers Ubiquitination and Down-regulation of Major
Histocompatibility Complex Class I (MHC-I) on Epithelioid Carcinoma HeLa Cells’, Journal of Biological Chemistry, vol. 283, no.7, pp.3951-3959,
viewed 17 September 2016, http://www.jbc.org/content/283/7/3951.full.pdf