Telomeres and the telomerase enzyme play important roles in cellular aging and cancer development. In cancer cells, telomerase is abnormally overexpressed, allowing cells to overcome the Hayflick limit and become immortal. The telomerase enzyme maintains telomere length through its reverse transcriptase activity, using an RNA component as a template. Several approaches are being explored to develop telomerase inhibitors as anti-cancer drugs, including targeting the enzyme's components or using them together with conventional chemotherapy to increase treatment effectiveness against various cancer types. By inhibiting telomerase, cells would be unable to maintain telomere length and would eventually senesce or die.

1. ROLE OF TELOMERE, TELOMERASE
IN CANCER
-a future drug target
By
Jeet Mazumder
M.Pharm(Pharmacology) 1st Year
Bengal School of Technology

2. What is Telomere ?
Telomeres are specialized structures at the ends of all
eukaryotic chromosomes and have special biological
functions. They protect chromosomes from nucleolytic
degradation, endto-end fusions, and to be recognized as
damaged DNA. Telomeres also contribute to the functional
organizations of the chromosomes within the nucleus,
participate in the regulation of gene expression, and most
importantly, they serve as a molecular clock that controls
the replicative capacity of the cells

3. By What Actually Telomeres Are Made Up Of
Humans like other vertebrates, have telomeres composed of repetitive 5’-TTAGGG-
3’ sequences Human telomeres end in a 3’ overhang composed of TTAGGG track
which is 50-500 nucleotides long
SHELTERIN - and its importance
Shelterin complex represses DNA damage signaling responses at the chromosome
ends. It also participates in the formation of t-loops and regulation of telomere
length. This complex consists of six subunits including TRF1, TRF2, TIN2, Rap1,
POT1, and TPP1. The expression of shelterin is ubiquitous and it is present at
telomeres throughout cell cycle. Shelterin binds to double stranded telomeric DNA via
its DNA binding proteins TRF1 (TTAGGG-repeat-binding factor 1) and TRF2

4. Why Telomere Is Called Cellular Clock
Telomeres cap and protect the ends of chromosomes from degradation and
illegitimate recombination. The termini of a linear template cannot,
however, be completely replicated by conventional DNA-dependent DNA
polymerases, and thus in the absence of a mechanisms to counter this effect,
telomeres of eukaryotic cells shorten every round of DNA replication. In
humans and possibly other higher eukaryotes, telomere shortening may
have been adopted to limit the life span of somatic cells. Human somatic
cells have a finite proliferative capacity and enter a viable growth arrested
state called senescence. Life span appears to be governed by cell division,
not time. The regular loss of telomeric DNA could therefore serve as a
mitotic clock in the senescence programme, counting cell divisions. In most
eukaryotic organisms, however, THERE ARE CERTAIN CASES
WHERE CELL BECOME IMMORTAL

5. What is Hayflick Limit?
The Hayflick Limit is a concept that helps to explain the mechanisms
behind cellular aging The concept states that a normal human cell can only
replicate and divide forty to sixty times before it cannot divide anymore, and will
break down by programmed cell death or apoptosis. The concept of the Hayflick
Limit revised Alexis Carrel's earlier theory, which stated that cells can replicate
themselves infinitely. Leonard Hayflick developed the concept while at the Wistar
Institute in Philadelphia.
• BUT MAJORITY OF CANCEROUS CELLS HAS VERY VERY HIGH
HAYFLICK LIMIT SO THEY MAY BE CALLED IMMORTAL BEST
EXAMPLE OF ONE SUCH IMMORTAL CELL LINE IS
HeLa CELL LINES
THIS IMMORTALITY ARE ASSOCIATED WITH TELOMERE

6. What is Telomerase
Telomeric Sequence is Maintained by a special Enzyme Called TELOMERASE.
Telomerase, also called terminal transferase,[1] is a ribonucleoprotein that adds
a species-dependent telomere repeat sequence to the 3' end of telomeres. A
telomere is a region of repetitive sequences at each end
of eukaryotic chromosomes in most eukaryotes. Telomeres protect the end of
the chromosome from DNA damage or from fusion with neighboring
chromosomes.
Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule
which is used as a template when it elongates telomeres. Telomerase is active
in normal stem cells and most cancer cells, but is normally absent from, or at
very low levels in, most somatic cells.

7. Mechanism of Telomerase
By using TERC, TERT can add a six-nucleotide repeating sequence,
5'-TTAGGG (in vertebrates, the sequence differs in other organisms)
to the 3' strand of chromosomes. These TTAGGG repeats are called
telomeres. The template region of TERC is 3'-CAAUCCCAAUC-5'.
Telomerase can bind the first few nucleotides of the template to the
last telomere sequence on the chromosome, add a new telomere repeat
(5'-GGTTAG-3') sequence, let go, realign the new 3'-end of telomere
to the template, and repeat the process. Telomerase reverses telomere
shortening

8. Constitute Of Telomerase
Telomerase is a ribonucleoprotein complex composed of
1 Telomerase reverse transcriptase (TERT) or hTERT
Regulation Of Telomere
Enhancement of stem cells
2 Telomerase RNA (TR or TERC)
3 Dyskerin (DKC1)

9. hTERT and telomerase Regulation
hTERT is encoded by hTERT gene located at 5p15.33 This gene spans
approximately 40 kb of the genome and contains 16 exons. Molecular
Location: base pairs 1,253,167 to 1,295,047 on chromosome 5
ACTIVATION
The regulation of telomerase activity in human cells plays a significant role in the
development of cancer. Telomerase is tightly Repressed in the vast majority of
Normal Human Somatic Cells but becomes activated during cellular immortalization
and in CANCER. While the mechanisms for telomerase activation in cancers have
not been fully defined, they include Telomerase catalytic subunit gene (hTERT)
amplification and trans-activation of the hTERT promoter by the myc
oncogene product. Ectopic expression of hTERT is sufficient to restore telomerase
activity in cells that lack the enzyme and can immortalize many cell types.
Understanding telomerase biology will eventually lead to several clinically relevant
telomerase-based therapies. These applications include inhibiting or targeting
telomerase as a novel antineoplastic strategy and using cells immortalized by
telomerase for therapeutic applications.

10. the TRAP assay is a popular method to determine telomerase activity in
mammalian cells and tissue samples The TRAP assay includes three steps:
extension, amplification, and detection of telomerase products. In the extension
step, telomeric repeats are added to the telomerase substrate (which is actually a
non telomeric oligonucleotide, TS) by telomerase. In the amplification step, the
extension products are amplified by the polymerase chain reaction (PCR) using
specific primers (TS upstream primer and ACX downstream primer) and in the
detection step, the presence or absence of telomerase is analyzed by
electrophoresis. TSNT is, an internal standard control, amplified by TS primer. NT is
its own reverse primer, which is not a substrate for telomerase.
TRAP ASSAY
TELOMERASE REPETED AMPLIFICATION PROTOCOL

11. CANCER-a brief introduction
• Cancer is actually a group of many related diseases that
all have to do with cells. Cancer happens when cells that
are not normal grow and spread very fast. Normal body
cells grow and divide and know to stop growing. Over
time, they also die. Unlike these normal cells, cancer cells
just continue to grow and divide out of control and don't
die when they're supposed to.
• Cancer cells usually group or clump together to form
tumors A growing tumor becomes a lump of cancer cells
that can destroy the normal cells around the tumor and
damage the body's healthy tissues. Sometimes cancer
cells break away from the original tumor and travel to
other areas of the body, where they keep growing and
can go on to form new tumors. This is how cancer
spreads. The spread of a tumor to a new place in the
body is called Metastasis

12. HALL MARKS OF CANCER
• Cancer has 6 major hallmarks
IMMORTALITY CONTINOUS CELL DIVISION AND LIMIT
LESS CELL DIVISION
PRODUCE GO SIGNAL GROWTH FACTOR FROM ONCOGENES
OVER RIDE STOP SIGNALS OVERIDE STOP SIGNAL
RESISTANCE TO CELL DEATH APPOTOSIS
ANGIOGENESIS INDUCTION OF NEW BLOOD VESSELS
GROWTH
METASTASIS SPREAD TO OTHER CELLS

13. HOW CANCER AND TELOMERASE RELATED
Telomerase expression in humans is limited to rare stem
cells of renewal tissues (gastrointestinal track, blood and
skin). Telomerase is almost always aberrantly overexpressed
in cancer. This overexpression is detected in 85% of all
cancers, irrespective of the tumour type. Telomerase is being
developed as a marker to allow the detection of cancer cells
in otherwise telomerase‐negative normal tissues.

14. CANCER CELLS ARE IMMORTAL

15. TELOMERASE INHIBITORS-a new horizon
Telomerase inhibitors are possible in near future they are group of
drugs that inhibit the enzyme telomeres and cause cell death
APPORACHES
TARGETING TELOMERASE ENZYME COMPONENTS
Antisense and Related Oligonucleotide
RNA Interference
Selective Expression of Cytotoxic or Pro-Apoptotic Genes
Mutant-Template Telomerase RNA
Selective Expression of Cytotoxic or Pro-Apoptotic Genes

16. Some Cancer That Can Be Treated By This
• Gastric Cancer
• Breast Cancer
• Pancreatic Cancer
• Ovarian Cancer
• Melanoma
• Lymphoma

17. TELOMERASE INHIBITORS WITH CONVENTIONAL
THERAPY
• As reviewed here, telomerase inhibitors have been shown
to be effective by themselves as potentially valuable
therapeutic agents. However, their greatest use may come
not as stand-alone pharmaceuticals but as part of a
coordinated treatment strategy in conjunction with
standard treatments including various chemotherapeutics
and radiation therapy. Several of the studies cited in this
review demonstrated success with their telomerase
inhibitors both alone and with synergistic effects when
combined with other chemotherapeutics. The method of
action of the various chemotherapeutic agents include
topoisomerase inhibitors
'-O-methoxyethyl RNA Cisplatin/carboplatin Synergistic effect
Antisense-hTR Paclitaxel
Significant increase in
sensitivity
Antisense-hTR Cisplatin Increase in sensitivity
DN-hTERT
Cisplatin/taxanes/etoposi
de
Increase in induction of
apoptosis
DN-hTERT Daunorubicin Increase in apoptosis
Ribozyme-hTERT Doxorubicin Increase in sensitivity
RNAi-hTERT
Topoisomerase
inhibitors/bleomycin/radi
ation
Increase in sensitivity
hTR-NAT [131
I]MIBG Induced uptake
AZT Paclitaxel
Increased activity and
effect

18. SOME TELOMERASE INHIBITORS
• Yes, Recently some of the Telomerase inhibitors are
in development with promising out comes some of
them are

19. BIBR 1532
• BIBR 1532 is a mixed-type non-competitive inhibitor of telomeras that has little effect
on several mammalian DNA and RNA polymerases, bacterial DNA helicase, or HIV-1
reverse transcriptase.It specifically targets the telomerase reverse transcriptase catalytic
subunit, TERT. Through its effects on telomerase, BIBR 1532 induces senescence or
apoptosis in cancer cells. Apoptosis in triple negative breast cancer cells induced by
BIBR 1532 is potentiated by glucose restriction. The synthetic, non-nucleosidic
compound, BIBR1532, is a potent and selective telomerase inhibitor capable of inducing
senescence in human cancer cells
• NO SIGNIFICANT SIDE EFFECT
• PHASE 2 CLINICAL TRIAL
• DRUG OF CHOICE FOR BREAST, PANCREATIC CANCER
• BIBR1532 + PACITAXEL = SYNERGESTIC EFFECT

20. IMETELESAT (GRN163L)
Originally known as GRN163L, imetelstat sodium (imetelstat) is a 13-
mer N3’---P5’ thio-phosphoramidate (NPS) oligonucleotide that has a
covalently bound 5’ palmitoyl (C16) lipid group. The proprietary nucleic
acid backbone provides resistance to the effect of cellular nucleases, thus
conferring improved stability in plasma and tissues, as well as significantly
improved binding affinity to its target. The lipid group enhances cell
permeability to increase potency and improve pharmacokinetic and
pharmacodynamic properties. The compound has a long residence time in
bone marrow, spleen and liver. Imetelstat binds with high affinity to the
template region of the RNA component of telomerase, resulting in
direct, competitive inhibition of telomerase enzymatic activity, rather
than elicit its effect through an antisense inhibition of protein
translation. Imetelstat is administered by intravenous infusion.
PANCREATIC CANCER
PHASE 2 CLINICA TRIAL
HIGHLY SELECTIVITY

21. GV1OO1 VACCINE
• GV1001, a peptide vaccine representing a 16-aa hTERT sequence. GV1001
binds multiple HLA class II molecules and harbors putative HLA class I
epitopes. The peptide may therefore elicit combined CD4/CD8 T-cell
responses, considered important to initiate tumor eradication and long-
term memory. Phase I/II trials in advanced pancreatic and pulmonary
cancer patients have demonstrated GV1001-specific T-cell responses in >
50% of subjects, without clinically important toxicity. The results indicate a
correlation between development of GV1001-specific responses and
prolonged survival.
LUNGS CANCER
PHASE II CLINICAL TRIALS

22. GRN VAC 1
• GRMNVAC1 as an anti-cancer vaccine, aims to help
the immune system recognize cells expressing
telomerase as a target to be destroyed.
PHASE II CLINICAL TRIALS

23. ADVANTAGES
HIGHLY SELECTIVITY AS TELOMERASE ENZYME IS
GENERALLY PRODUCED IN CANCEROUS CELLS VERY
LOW CONCENTRATION IN SOMATIC CELLS
LESS TOXIC
A SINGLE DRUG CANDIDATE CAN BE USED IN
MULTIPLE CANCER AS TELOMERASE IS PRESENT IN
90% CANCERS

24. CHALLENGES
• AGENING (VERY MINIMAL)
• POOR ABSORTION AT THE SITE OF ACTION

25. CONCLUSION
• This, may be the most promising approach, and it is
likely that many new advances will develop that
merge different types of anti-telomerase methods or
combine telomerase inhibition with other proven
modes of anticancer therapy. The continued
development of novel tools will likely be at the
forefront of cancer therapy, many different anti-
telomerase approaches that may revolutionize cancer
therapeutics in the future

26. REFFERENCES
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• 2. Weinrich SL, Pruzan R, Ma L, Ouellette M, Tesmer VM, Holt
SE, Bodnar AG, Lichtsteiner S, Kim NW, Trager JB, Taylor RD,
Carlos R, Andrews WH, Wright WE, Shay JW, Harley CB, Morin
GB. Reconstitution of human telomerase with the template
RNA component hTR and the catalytic protein subunit
hTRT. Nat. Genet. 1997;17:498–502. [PubMed]
• 3. Beattie TL, Zhou W, Robinson MO, Harrington L.
Reconstitution of human telomerase activity in vitro. Curr.
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