Recent Patents on Anti-Telomerase Cancer Therapy

16 Pages·2011·0.32 MB·English

102 Recent Patents on Anti-Cancer Drug Discovery, 2012, 7, 102-117
Recent Patents on Anti-Telomerase Cancer Therapy
Apurva Agrawal, Shweta Dang and Reema Gabrani*
Department of Biotechnology, Jaypee Institute of Information Technology, A-10, Sector-62, NOIDA-201307, Uttar
Pradesh, India
Received: December 20, 2010; Accepted: March 29, 2011; Revised: April 26, 2011
Abstract: Telomerase, a specialised RNA-directed DNA polymerase extends and stabilises the telomeres at the ends of
the eukaryotic chromosomes. The progressive loss of telomeres results in limited number of cell divisions and has been
linked to the mechanism of human cellular ageing. Tumour cells marked by indefinite proliferation have stable telomere
length maintained by telomerase. The differential expression of the telomerase enzyme in normal and cancer cells have
led to the evolution of tumour specific anti-telomerase approaches which inhibit the telomerase enzyme activity so as to
destabilise and shorten the telomeres leading to senescence in cancer cells.
In the current review, we have selected nine tumour specific anti-telomerase approaches based on their mechanism of ac-
tion or the target components of the human telomerase enzyme: Antisense-oligonucleotides, hammerhead ribozymes,
dominant negative hTERT, reverse-transcriptase inhibitors, immunotherapy, G-quadruplex stabilisers, gene therapy, small
molecule inhibitors and RNA interference. Recent research developments for each of the anti-telomerase approaches with
the detailed analysis of specific granted patents from the perspective of different claims and downstream applications have
been provided. A comprehensive list of patents for the different anti-telomerase approaches which includes information
regarding the authors and institutional ownership along with the year of issue of the patent has also been provided.
Keywords: Antisense-oligonucleotides (AS-ODN), anti-telomerase, dominant negative hTERT (DN-hTERT), G-quadruplex
stabilisers, gene therapy, hammerhead ribozymes, immunotherapy, reverse transcriptase inhibitors, RNA interference, small
molecule inhibitors.
TELOMERASE: AN INTRODUCTION Besides this, telomeres also assist in positioning and anchor-
ing the chromosomes with the nuclear machinery to facilitate
The arcane demeanour of ~ 85% of the cancer cells lies
DNA replication during cell divisions [1].
in the immortality rendered by the RNA-directed DNA po-
lymerase known as Telomerase, which extends the telomeres Telomerase is a ribonucleoprotein composed of human
or the ends of the eukaryotic chromosomes in most of the Telomerase Reverse Transcriptase (hTERT) catalytic unit,
malignant cells [1, 2]. Telomerase associated protein 1 (TEP1) and human Telom-
erase RNA (hTR). The RNA subunit has an eleven nucleo-
Telomeres are progressively lost at every cell division
tide template sequence (5(cid:1)-CUAACCCUAAC-3(cid:1)) which acts
due to the inability of the DNA polymerases to replicate the
as a template for the addition of telomere repeats of
telomere ends [1]. Subsequently, the cells reach their Hay-
(TTAGGG)n in the 5(cid:1)- 3(cid:1) direction at the telomeric ends of
flick limit after a definite number of cell divisions [3] and
the chromosomes [1].
thus, short telomeres lead the cell towards senescence. Te-
lomerase stabilises the telomeres in human stem cells, cancer Telomerase is in repressed state in normal cells before
cells and reproductive cells but its expression remains in a birth and is expressed transiently or at undetectable levels
repressed state in the normal somatic cells [4]. The activation after birth [6]. Telomerase is expressed in a temporally regu-
of telomerase enables the cells to bypass this limit and hence, lated manner in a developing foetal lung during the late
induces immortalisation of the cells switching them into the stages of gestation with an increased expression just before
neoplastic cells [1]. Telomerase facilitates cell proliferation the birth. However, this expression of telomerase activity
not only by stabilising the telomeres but also by affecting the persists only for ephemeral time period in neonates, which is
expression levels of growth promoting genes [5]. progressively down regulated to undetectable levels by post-
natal day 9 [7]. It has been implicated that a member of
Telomeres in vertebrates are composed of tandem repeat
myc/max/mad network, Mad1 encodes a transcriptional re-
arrays of TTAGGG DNA sequence at the ends of linear
pressor which down regulates the hTERT activity during the
DNA. Telomeres help in averting the end replication prob-
differentiation in human somatic cells whereas myc onco-
lem, degradation by enzymes such as exonucleases and li-
gene can upregulate hTERT expression indicating its critical
gases and telomere shortening by oxidative stress [2].
role in tumorigenesis [8]. Furthermore, hTERT expression

has been found to be upregulated at early stages of gastric
*Address correspondence to this author at the Department of Biotechnology, carcinogenesis as well as in the development of Barret’s
Jaypee Institute of Information Technology, A-10, Sector-62, NOIDA- esophagus and esophageal adenocarcinoma [9, 10]. In a key
201307, Uttar Pradesh, India; Tel: [phone]; study, the in vivo carcinogenesis conditions were replicated
Fax: [phone]; E-mail: [email protected]
(cid:21)(cid:21)(cid:20)(cid:21)-(cid:22)9(cid:26)(cid:19)/12 $100.00+.00 © 2012 Bentham Science Publishers
Recent Patents on Anti-Telomerase Cancer Therapy Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 103
in vitro by Hahn et al., where the ectopic expression of te- ANTI-TELOMERASE CANCER THERAPY: TELOM-
lomerase catalytic subunit (hTERT) along with the expres- ERASE AS THE TARGET CANDIDATE
sion of two oncogenes (the simian virus 40 large-T oncopro-
Anti-telomerase cancer therapy focuses on inhibitors
tein and an oncogenic allele of H-ras) resulted in the creation
targeting different pathways to inhibit or suppress the telom-
of human immortalised or tumour cell lines from normal
erase activity in the cancerous cells and thereby, leading to
human epithelial and fibroblast cells. This study further pro-
destabilisation of the telomeres, telomere shortening and
vides evidence about the functional role of telomerase activ-
senescence.
ity in carcinogenesis and hence, it can be used as a potential
marker for diagnosis of cancer [11]. The telomeres in malignant neoplastic cells are short in
length but are stabilised by telomerase. However, the te-
Telomerase plays a vital anti-apoptotic role by suppress-
lomeres in normal somatic tissues are long in length and are
ing the signalling cascades leading to apoptosis and hence,
not stabilised by telomerase, thus are shortened at a slower
circumvents senescence. The telomerase activity decreases in
pace. This predisposes the cancerous cells to be more sensi-
the cells undergoing apoptosis as well as during the course of
tive to the anti-telomerase inhibitions [2]. Hence, the anti-
cellular differentiation that makes the cells more susceptible
telomerase cancer therapy employing telomerase inhibitors is
to apoptosis [12]. The anti-apoptotic role of telomerase has
an effective aid against cancer cells without affecting the
been attributed to its reverse transcriptase (RT) activity and a
normal cells as they lack telomerase activity. Consequently,
protein termed as 14-3-3 which facilitates the nuclear local-
this therapy ensures high specificity to the cancer cells, less
ization of TERT, probably being critical for telomere main-
toxicity and less risk of side effects. Anti-telomerase therapy
tenance. Besides this, TERT suppresses apoptosis at an early
focuses on targeting the different components of the telom-
mitochondrial step before the release of cytochrome c and
erase which are hTERT and hTR. Different approaches to
apoptosis-inducing factor from mitochondria [13]. hTERT
inhibit the hTR and hTERT are schematically presented in a
suppresses apoptosis through a p21waf1-dependent pathway
flowchart as shown in Fig. (1).
by down regulating a key cyclin dependent kinase (CDK)
inhibitor p21waf1 which plays an important role in DNA dam- The uniqueness of telomerase to the cancer cells also
age induced cell cycle arrest [14]. makes it a potential diagnostic marker of cancer. Telomerase
Repeat Amplification Protocol (TRAP) is a standard sensi-
All these studies reflect that telomerase stands out to be
tive assay formulated for diagnosing cancer which can detect
the principal target for anti-cancer therapy such that telom-
even trace levels of telomerase activity [15].
erase activity inhibition will facilitate the shortening of te-
lomeres, and will subsequently lead to reduction in tumori- In the following sections, we have reviewed the different
genesis. potential anti-telomerase approaches that are currently under
G-Quadruplex RNA Interference
Stabilisation

ANTI-

TELOMERASE

CANCER

Small Molecule THERAPY Gene Therapy

Inhibitors

Catalytic Human
Telomerase
Hammerhead
Immunotherapy Telomerase RNA template
Ribozymes
Reverse
Transcriptase

Dominant- Reverse Antisense

Negative hTERT Transcriptase Oligonucleotides

Inhibitors

Fig. (1). Schematic Flowchart for Anti-Telomerase Approaches.
A schematic flowchart depicting different anti-telomerase approaches to inhibit human telomerase RNA template (hTR) and human telom-
erase reverse transcriptase (hTERT).
104 Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 Agrawal et al.
research investigations. The principal focus of the current GRN163L, a lipid modified N3(cid:2)(cid:1)P5(cid:2) thio-phosphora-
review lies on the comprehensive analysis of the specific midate oligonucleotide complementary to the template re-
granted patents associated with each anti-telomerase ap- gion of hTR has been observed to be one of the most effec-
proach encompassing a panoptic study of the different claims tive antisense oligonucleotides to selectively inhibit telom-
as well as downstream applications related to each patent. In erase activity. Presence of a palmitoyl group at the 5(cid:2) termi-
addition, a comprehensive list of recent patents for the dif- nal end of GRN163L improved its cellular uptake and
ferent anti-telomerase approaches including the authors and bioavailability as compared to the nonlipidated GRN163
institutional ownership has also been provided in Table 1. oligonucleotide. GRN163L effectively inhibits telomerase
activity in a dose dependent manner leading to progressive
APPROACHES AND PATENTS ASSOCIATED WITH loss of telomere lengths without any transfection enhancer
THE INHIBITION OF RNA (HTR) COMPONENT OF [25-27]. GRN163L (Imetelstat sodium) is currently in Phase
TELOMERASE II human clinical studies which consist of four different tri-
als. These trials would use GRN163L as a single agent or in
A. Antisense Oligodeoxynucleotides (AS-ODN) combination with Taxol and Avastin to assess its pharma-
codynamic effects on four different cancers viz. non-small
The use of AS-ODNs to transfect the cancerous cells has
cell lung cancer, metastatic breast cancer, thrombocythemia
been shown to effectually target the expression of genes in-
and multiple myeloma. These clinical trials are being spon-
volved in causing cancer [16]. AS-ODNs are short DNA sored by Geron Corporation [28].
constructs which bind to complimentary target RNA by Wat-
In US6468983, Silverman et al. claim to provide meth-
son-Crick hybridisation. The mode of mechanism includes
transcription inhibition, RNA processing modulation, trans- ods and composition for treating malignant neoplastic dis-
lation inhibition and the cleavage of hTR by RNase H, an ease by administering to a subject a concentration of an acti-
endonuclease. Inhibition of target RNA function can be vator-antisense complex effective to inhibit the telomerase
enzyme activity. The activator-antisense complexes com-
achieved by two mechanisms: firstly, passive mechanism
prise of an antisense oligonucleotide with a hydroxyl moiety
which involves the hybridisation of the AS-ODNs to the
and a linker at the first end to which an RNaseL activator is
target hTR competitively, while the second mechanism
termed as active mechanism involves the cleavage of the attached. The antisense oligonucleotide is complementary to
target hTR post-hybridisation by RNase H [16, 17]. It is to a region between about 12 and about 25 nucleotides of the
be noted that AS-ODNs are rather “template antagonists”, human telomerase RNA and specifically cleaves it to inhibit
the telomerase activity [29].
since they inhibit nucleic acid synthesis (elongation of the
telomere) not the protein synthesis as in real antisense inter- In addition, the antisense oligonucleotide provided con-
action. These oligonucleotides are highly specific and form a tains at least one 2(cid:2)O-methyl nucleotide as well as one or
stable duplex with the target hTR and are resistant to nucle- more phospho-moieties selected from a group consisting of
ase digestion. Thus, AS-ODNs binding leads to progressive phosphorothioate, methylphosphonate and methylphos-
telomere shortening and reduced cell growth [18, 19]. phonothioate [29].
AS-ODN activity has been improved by attaching 2, 5- The present patent assigned to the Cleveland Clinic
Oligoadenylate (2, 5-A) moiety as it employs RNase L, an Foundation (Cleveland, OH) and the United States of Amer-
endoribonuclease that assists in cleaving the target hTR ica as represented by the Department of Health and Human
along with RNase H [17, 20-22]. Some research studies in Services (Washington, DC) mentions that the 2-5A activator-
this regard have shown that 2, 5- A AS-ODNs have effec- antisense complexes can be used to treat brain cancers, pros-
tively induced apoptosis and inhibited telomerase activity in tate cancers, breast cancers, renal cancers and melanomas
cervical cancer cells and ovarian cancer cells [20, 21]. [29].
Another type of oligonucleotides, Peptide nucleic acids The above mentioned patent also claims the methods for
(PNAs) oligonucleotides, are analogs of DNA and RNA, in administering an effective amount of the 2-5A activator-
which pentose-phosphate backbone is replaced by an oli- antisense complex. It mentions that the activator antisense
gomer of N-(2-aminoethyl) glycine. It augments their resis- complexes can be administered in combination with one or
tance to the exo- and endonucleases along with an increase more chemotherapeutic agents such as cisplatin, doxorubi-
in specificity in their hybridisation with target hTR [17]. cin, mitomycin, daunorubicin, bleomycin, actinomycin D,
Besides this, the use of 2(cid:2)-O alkyl RNA such as 2(cid:2)-O-methyl and neocarzinostatin, etc. Further, various delivery systems
RNA, 2(cid:2)-O- methoxyethyl RNA [23] and chimeric 2(cid:2)- can be used such as encapsulation in liposomes, microparti-
methoxy-ethoxy RNAs, have been reported to improve the cles, microcapsules, receptor-mediated endocytosis, con-
affinity and specificity to hTR, along with improved resis- struction of a therapeutic nucleic acid as part of a retroviral
tance to nucleases. They involve modification in the sugar or other vector, etc. with their possible introduction through
moieties of the RNA bases flanking the antisense DNA plus intradermal, intramuscular, intraperitoneal, intravenous, sub-
one of the oxygen atoms in the phosphate group is replaced cutaneous, intranasal, epidural, and oral routes. The com-
with sulphur to form phosphorothioate linkages in lieu of the pounds can also be administered by infusion or bolus injec-
phosphodiester bonds [17, 24]. They act by passive mecha- tion, by absorption through epithelial or mucocutaneous lin-
nism as ODNs after modification competitively bind to tar- ings (e.g., oral mucosa, rectal and intestinal mucosa, etc.).
get hTR but RNase H cannot be activated by them. Administration can be systemic or local. Moreover, it can
Recent Patents on Anti-Telomerase Cancer Therapy Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 105
Table 1. Patents List for Anti-Telomerase Approaches.
S. No. Patent No. Patent Title Anti-Telomerase Inventors/ Patent Assignee Year of
Approach Issue
1 US7157436 Therapeutically useful syn- Antisense Oligo Nucleo- Phillips, N. C., Filion, M. C. Bioniche Life Sci- 2007
thetic oligonucleotides tides ences, Inc. (Pointe-Claire, CA)
2 US6468983 RNase L activators and an- Antisense Oligo Nucleo- Silverman, R. H., Kondo, S., Cowell, J. K., Li, G., 2002
tisense oligonucleotides tides Torrence, P. F. The Cleveland Clinic Founda-
effective to treat telomerase- tion (Cleveland, OH);
expressing malignancies The United States of America as represented by
the Department of Health and Human Services
(Washington, DC)
3 US6194206 Use of oligonucleotide te- Antisense Oligo Nucleo- West, M. D., Shay, J., Wright, W. University of 2001
lomerase inhibitors to reduce tides Texas System Board of Regents (Austin, TX)
telomere length
4 US7732402 Mammalian telomerase Hammerhead Ribozymes Villeponteau, B., Feng, J., Funk, W., Andrews, 2010
W. Geron Corporation (Menlo Park, CA)
5 US7517971 Muteins of human telomerase Dominant Negative Cech, T. R., Lingner, J., Nakamura, T., Chapman, 2009
reverse transcriptase lacking hTERT K. B., Morin, G. B., Harley, C. B., Andrews, W.
telomerase catalytic activity H. Geron Corporation (Menlo Park, CA);
The Regents of the University of Colo-
rado (Boulder, CO)
6 US6593306 Methods for modulation and Reverse Transcriptase Chen, S., Maine, I., Kerwin, S. M., Fletcher, T. 2003
inhibition of telomerase Inhibitors M., Salazar, M., Mamiya, B., Wajima, M., Win-
dle, B. E. Board of Regents, University of Texas
System (Austin); CTRC Research Founda-
tion (San Antonio, TX)
7 US6372742 Substituted indole com- Reverse Transcriptase Chin, A. C., Tolman, R. L., Nguyen, M. Q., Hol- 2002
pounds and methods of their Inhibitors comb, R. Geron Corporation (Menlo Park, CA)
use
8 US6054442 Methods and compositions Reverse Transcriptase Chen, S., Maine, I., Kerwin, S. M., Fletcher, T. 2000
for modulation and inhibition Inhibitors M., Salazar, M., Mamiya, B., Windle, B. E., Wa-
of telomerase in vitro jima, M. Board of Regents, University of Texas
System (Austin); CTRC Research Founda-
tion (San Antonio, TX)
9 US6004939 Methods for modulation and Reverse Transcriptase Chen, S., Maine, I., Kerwin, S. M., Fletcher, T. 1999
inhibition of telomerase Inhibitors M., Salazar, M., Mamiya, B., Wajima, M., Win-
dle, B. E. CTRC Research Foundation Board of
Regents (San Antonio, TX);
The University of Texas System (Austin, TX)
10 US7662361 Methods and compositions Reverse Transcriptase Au, J. L.-S., Wientjes, M. G. 2010
for modulating drug activity Inhibitors
through telomere damage
11 US7622549 Human telomerase reverse Immunotherapy Cech, T. R., Lingner, J., Nakamura, T., Chapman, 2009
transcriptase polypeptides K. B., Morin, G. B., Harley, C. B., Andrews, W.
H., Geron Corporation (Menlo Park, CA); The
Regents of the University of Colorado (Boulder,
CO)
12 US7560437 Nucleic acid compositions Immunotherapy Cech, T. R., Lingner, J., Nakamura, T., Chapman, 2009
for eliciting an immune re- K. B., Morin, G. B., Harley, C. B., Andrews, W.
sponse against telomerase H. Geron Corporation (Menlo Park, CA); The
reverse transcriptase Regents of the University of Colorado (Boulder,
CO)
(cid:1)
106 Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 Agrawal et al.
(Table 1) Contd….
S. No. Patent No. Patent Title Anti-Telomerase Ap- Inventors/ Patent Assignee Year of Issue
proach
13 US7413864 Treating cancer using a te- Immunotherapy Cech, T. R., Lingner, J., Nakamura, T., 2008
lomerase vaccine Chapman, K. B., Morin, G. B., Harley, C. B.,
Andrews, W. H. Geron Corporation (Menlo
Park, CA); The Regents of the University of
Colorado (Boulder, CO)
14 US7056513 Telomerase Immunotherapy Cech, T. R., Lingner, J., Nakamura, T., 2006
Chapman, K. B., Morin, G. B., Harley, C. B.,
Andrews, W. H. Geron Corporation (Menlo
Park, CA); The Regents of the University of
Colorado (Boulder, CO)
15 US7824849 Cellular telomerase vaccine Immunotherapy Gaeta, F. C. A. Geron Corporation (Menlo 2010
and its use for treating can- Park, CA)
cer
16 US7851591 Cancer immunotherapy and Immunotherapy Nadler, L. M., Hahn, W. C., Schultze, J. L., 2010
diagnosis using universal Vonderheide, R. H. Dana Farber Cancer
tumor associated antigens, Institute, Inc. (Boston, MA)
including hTERT
17 US7794723 Antigenic peptides derived Immunotherapy Gaudernack, G., Eriksen, J. A., Moller, M., 2010
from telomerase Gjertsen, M. K., S.ae butted.terdal, I., S.ae
butted.boe-Larsen, S. GemVax AS (Oslo, NO)
18 US7750121 Antibody to telomerase re- Immunotherapy Cech, T. R., Lingner, J., Nakamura, T., 2010
verse transcriptive Chapman, K. B., Morin, G. B., Harley, C. B.,
Andrews, W. H. Geron Corporation (Menlo
Park, CA); The Regents of the University of
Colorado (Boulder, CO)
19 US7045523 Combination comprising N- G-Quadruplex stabilisa- Tauchi, T. Novartis AG (Basel, CH) 2006
{5-[4-(4-methyl-piperazino- tion
methyl)-benzoylamido]-2-
methylphenyl}-4-(3-p-
yridyl)-2-pyrimidine-amine
and telomerase inhibitor
20 US7205311 Therapeutic acridone and G-Quadruplex stabilisa- Neidle, S., Harrison, R. J., Kelland, L. R., 2007
acridine compounds tion Gowan, S. M., Read, M. A., Reszka, A. Can-
cer Research Technology Limited (London)
21 US7429660 ATM inhibitors Synergistic action with Smith, G. C. M., Martin, N. M. B., Cockcroft, 2008
anti-telomerase drugs X. F., Matthews, I. T. W., Menear, K. A.,
Rigoreau, L. J. M., Hummersone, M. G.,
Griffin, R. J. Kudos Pharmaceuticals Lim-
ited (Cambridge, GB)
22 US7642254 ATM inhibitors Synergistic action with Hummersone, M. G., Menear, K. A., Rigo- 2010
anti-telomerase drugs reau, L. J. M., Smith, G. C. M., Martin, N. M.
B., Griffin, R. J. Kudos Pharmaceuticals
Limited (Cambridge, GB)
23 US7049313 ATM inhibitors Synergistic action with Smith, G. C. M., Martin, N. M. B., Jackson, 2006
anti-telomerase drugs S. P., O'Connor, M. J., Lau, A. Y. K., Cock-
croft, X. F., Matthews, I. T. W., Menear, K.
A., Rigoreau, L. J. M., Hummersone, M. G.,
Griffin, R. J. Kudos Pharmaceuticals
Ltd. (GB)
(cid:1)
Recent Patents on Anti-Telomerase Cancer Therapy Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 107
(Table 1) Contd….
S. No. Patent No. Patent Title Anti-Telomerase Ap- Inventors/ Patent Assignee Year of Issue
proach
24 US7795416 Telomerase expression re- Telomerase repressor Andrews, W. H., Foster, C. A., Fraser, S., 2010
pressor proteins and methods proteins Mohammadpour, H., Briggs, L. Sierra Scien-
of using the same ces Inc. (Reno, NV)
25 US7897752 RNA interference mediated RNA interference McSwiggen, J., Beigelman, L. Sirna Thera- 2011
inhibition of telomerase gene peutics, Inc. (San Francisco, CA)
expression using short inter-
fering nucleic acid (siNA)
26 US7893248 RNA interference mediated RNA interference McSwiggen, J., Beigelman, L. Sirna Thera- 2011
inhibition of Myc and/or peutics, Inc. (San Francisco, CA)
Myb gene expression using
short interfering nucleic acid
(siNA)
27 US7659389 RNA interference mediated RNA interference McSwiggen, J., Beigelman, L. Sirna Thera- 2010
inhibition of MYC and/or peutics, Inc. (San Francisco, CA)
MYB gene expression using
short interfering nucleic acid
(siNA)
A comprehensive list of recent patents related to different anti-telomerase approaches along with their patent number, authors, assignee and the year of issue.

also be introduced by direct injection at the site of a malig- phosphodiester bond is also highly conserved and helps in
nant tumour or neoplastic or pre-neoplastic tissue [29]. cleavage. A ribozyme specific for a target RNA can be ob-
tained by designing the stem I and III sequences complemen-
In another US6194206, West et al. provide methods to
tary to target RNAs. Hence, in this way the binding of ri-
determine telomere length and telomerase activity as well as
bozymes to the target RNAs results in their cleavage [31].
claims that telomerase enzyme activity is inhibited with a
After cleavage, the substrate is also accessible by ribonucle-
therapeutically effective amount of a composition consisting
ases resulting in its inactivation.
of a carrier and a polynucleotide which is an oligonucleotide
comprising of at least about two to about fifty telomeric re- Folini et al. used a hammerhead ribozyme designed with
peats such that the oligonucleotide comprises of a nucleotide flanking sequences complimentary to the human telomerase
sequence complementary to an RNA component of telom- RNA (hTR) which successfully inhibited the telomerase ac-
erase [30]. tivity in two human melanoma cell lines possessing telom-
erase activity in a concentration and time-dependent manner.
The current patent assigned to University of Texas Sys-
However, no telomere shortening was observed in ribozyme
tem Board of Regents (Austin, TX) also claims a method to
infected clones which were still able to proliferate even after
diagnose a condition associated with an elevated level of
20 passages [33]. In a similar study led by Yeo et al., ham-
telomerase activity within a cell in a patient by determining
merhead ribozymes designed against 7 NUX sequences lo-
the presence or amount of telomerase within the cells of that
cated in the open loops of hTR secondary structure, success-
patient [30].
fully cleaved the target hTR in human breast cancer MCF-7
An impediment in the feasibility of AS-ODN lies in the cells. As a consequence, the transfected cells displayed
accessibility of AS- ODNs to target the hTR as the presence shortening in telomeres with lower proliferating rates than
of secondary structures may pose hurdles in the hybridisation the parental cells and hence, reduced telomerase activity
of AS- ODNs to the hTR [16]. Despite this, there are other [32]. Consistent results were observed by Kanazawa et al.
problems associated with them such as a transfection agent while working on human hepatocellular carcinoma cell lines
being a pre-requisite for transfecting these AS-ODNs into which further prove the efficient telomerase inhibiting activ-
the target cells plus inside the cell, they are also susceptible ity of the ribozymes [34].
to the digestion by different exo- and endonucleases [17].
In US7732402 assigned to Geron Corporation (Menlo
Park, CA), Villeponteau et al. claim a method to inhibit te-
B. Hammerhead Ribozymes
lomerase activity in vitro by contacting the cancer cells with
Hammerhead ribozymes are small catalytic RNA mole- a polynucleotide encoding a ribozyme in an amount suffi-
cules which possess specific endonuclease activity and cient to inhibit the telomerase activity. The invention eluci-
hence, catalyse self- cleavage reaction [31]. These ribozymes dates the use of an adenovirus based expression vector en-
are composed of three potential base-paired helical stems coding a hammerhead or Group I intron ribozyme linked to a
and two single-stranded regions which form a highly con- constitutively active promoter to inhibit telomerase activity
served core of residues which mediate in the cleavage [17, in cancer cells. Thus, the ribozyme expressed, specifically
31, 32]. GCC sequence in stem III just before the susceptible
108 Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 Agrawal et al.
cleaves the RNA component of human telomerase (hTR), These studies further corroborate the fact that telomerase
rendering the enzyme inactive [35]. is involved in maintaining telomere lengths and hence, te-
lomerase inhibition as reflected in these studies can poten-
Furthermore, the patent also provides diagnostic methods
tially eliminate tumorigenesis.
for determining the level, amount, or presence of the RNA
component of human telomerase (hTR), telomerase, or te- In US7517971, Cech et al. claim about a recombinant
lomerase activity in a cell, cell population, or tissue sample polynucleotide which encodes an activity-modified hTERT
[35]. polypeptide with at least 95% sequence identity to hTERT,
comprises of alanine in place of aspartic acid at position 712
A major advantage associated with the application of
of hTERT protein and is catalytically inactive, wherein cata-
hammerhead ribozymes to attenuate telomerase activity is its
lytically inactive means the polypeptide has less than 1% of
catalytic activity and the specific targeting of the telomerase
the catalytic activity of the hTERT polypeptide. The present
RNA. The other advantage associated with this technique is
invention provides recombinant and synthetic nucleic acids
that it reduces the lag period as it is independent of the te-
which express a non-functional mutated hTERT possessing
lomere shortening to inhibit the proliferation of cancerous
partial activity but not full activity of telomerase [38].
cells. Moreover, low concentration of ribozymes is required
for such an effect as a single hammerhead ribozyme can help The patent has been assigned to Geron Corpora-
in cleaving several target RNAs [17, 33]. Although, research tion (Menlo Park, CA) and the Regents of the University of
studies indicate towards the telomerase inhibition potential Colorado (Boulder, CO). The present invention claims kits
of ribozymes, but inconsistent results have been observed in useful for the screening, monitoring, diagnosis and prognosis
terms of any change in proliferation rates of the cancerous of patients with a telomerase-related condition by determin-
cells. ing the amount of hTERT gene product in a cancer cell ob-
tained from the patient and comparing the amount of hTERT
Such inconsistent results may have led to the unavailabil-
in the cancer cell with a prognostic value of hTERT consis-
ity of significant number of patents regarding hammerhead
tent with a prognosis for the cancer. Moreover, the present
ribozymes.
invention also provides reagents and assays for detecting
hTERT-specific immunoglobulins as well as for the detec-
APPROACHES AND PATENTS ASSOCIATED WITH
tion of hTERT polypeptides. In another aspect of the inven-
THE INHIBITION OF TELOMERASE REVERSE
tion, human antibodies against an hTERT polypeptide are
TRANSCRIPTASE (HTERT) COMPONENT OF TE-
provided [38].
LOMERASE
The invention renders a vaccine comprising an hTERT
A. Dominant Negative hTERT polypeptide and an adjuvant. It also mentions about methods
of diagnosing and prognosing cancer in a patient. Further-
Dominant negative (DN)-hTERT constructs are catalyti-
more, the present invention provides methods and composi-
cally inactive hTERT mutants which can potentially inhibit tions such as antisense oligonucleotides, ribozymes, pep-
telomerase activity from maintaining telomeres by binding tides, gene therapy vectors encoding antisense oligonucleo-
and sequestering hTR [17]. Such mutated telomerase binds tides or activity altering proteins, and anti-hTERT antibodies
telomeric structures, but does not bind telomerase-associated
for reducing telomerase activity in tumour cells and for treat-
RNA (hTR). Thus, if expressed at high enough levels, such a
ing cancer [38].
telomerase mutant can be used to deplete a necessary telom-
erase component (hTR) and thereby functions as an inhibitor
B. Reverse Transcriptase Inhibitors
of wild-type telomerase activity.
Reverse transcriptase inhibitors (RTI) are a class of
The ability of mutant hTERT to inhibit telomere length
molecules which hinder the proper functioning of reverse
and arrest cell growth has been shown in various human can-
transcriptase enzyme. They usually act by competing with
cer cell lines. Hahn et al. designed a dominant negative
the endogenous nucleic acids to integrate into the DNA and
hTERT in which the aspartic acid and valine at positions 710
hence subsequently, they interfere with the chain elongation
and 711 in the third RT motif of hTERT were substituted
function of reverse transcriptase [17, 39]. RTIs have been
with alanine and isoleucine, respectively which led to re-
extensively studied and used in the treatment of HIV.
duced telomere length and senescence in malignant cells
[36]. Nakajima et al. too observed similar inhibition in te- We know that telomerase is composed of hTERT, a re-
lomerase activity and apoptopic cell death while examining verse transcriptase enzyme which uses RNA component of
the effects of telomerase inhibition by DN-hTERT on a te- telomerase to extend the telomere ends onto the 3(cid:1)-end G-
lomerase-positive human acute lymphoblastic leukaemia cell rich strand. Hence, various reverse transcriptase inhibitors
line, HAL-01 [37]. DN-hTERT clones have also shown to such as azidothymidine (AZT), dideoxyguanosine (ddG),
eliminate tumorigenesis in nude mice models [36]. dideoxyinosine (ddI), arabinofuranyl-guanosine (Ara-G) and
AZT-5(cid:1) triphosphate (AZT-TP) have been reported to sig-
The specifcity of the DN-hTERT was proven by studying
nificantly inhibit telomerase activity by integrating into the
its effect on immortal human cell line GM847, which main-
telomeric repeats, thereby converting the processive telom-
tains telomere length by a telomerase independent alternative
erase into non-processive and non-functional form [40-43].
mechanism. The retroviral vectors encoding DN-hTERT and
Wild Type-hTERT did not show any affect on telomere AZT has been found to induce an irreversible telomere
length and cell survival which proved that DN-hTERT was shortening as well as inhibit cell growth in metastatic murine
catalytically inactive in nature [36]. melanoma cell line, a human breast cancer cell line and some
Recent Patents on Anti-Telomerase Cancer Therapy Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 109
but not all T- and B- cell cultures [44-47]. Moreover, chronic The patent assigned to Geron Corporation (Menlo Park,
exposure of metastatic mouse mammary tumour cells to CA) mentions that the compositions of the invention include
AZT was observed to cause senescence and reduce tumori- a therapeutically effective amount of the compounds in a
genecity in mice [48]. AZT functions as a thymidine analog pharmaceutically acceptable carrier which can be adminis-
and hence, gets incorporated into the nucleic acid chain in tered for prophylactic and/or therapeutic treatments. In
lieu of thymidine. However, it lacks 3´-OH functional group, therapeutic applications, therapeutically effective amounts of
as a result, no additional nucleotides can be added and re- the compositions can be administered in vivo to a patient
verse transcription is blocked. already suffering from a disease or ex vivo to achieve thera-
peutic effects, for example, in case of patients suffering from
Pai et al. while working on deoxynucleoside analogues
leukemia. In prophylactic applications (e.g. chemopreven-
reported that ddGTP was found to be the most potent inhibi-
tion), prophylactically effective amounts of the compositions
tor among all dideoxynucleosides taken under study [49].
of the compounds of the invention are administered to a pa-
ddGTP is known to inhibit DNA synthesis upon its incorpo-
tient susceptible to or otherwise at risk of a particular disease
ration into the DNA sequence as it lacks 3(cid:2)-OH functional
wherein the precise amounts again depend on the patient's
group. However, ddGTP may cause telomere shortening by
state of health and weight [53].
binding to and competing for nucleoside triphosphate bind-
ing site of telomerase as observed in vitro in human cells Further in US6593306, US6054442 and US6004939,
[44]. While investigating the anti-telomerase potential of Chen et al. demonstrate about the applications of nucleotide
various deoxyguanosine nucleotide analogs, Tendian et al. analogs, such as 7-deaza-2(cid:2)-deoxyquanosine-5(cid:2)-triphosphate
observed that 2(cid:2), 3(cid:2)-dideoxyguanosine 5(cid:2)-triphosphate, 6- (7-deaza-dGTP) as potential substrates for processive telom-
thio-2(cid:2)-deoxyguanosine 5(cid:2)-triphosphate (T-dGTP), carbovir erase which are subsequently incorporated into telomeric
5(cid:2)-triphosphate (CBV-TP), and D-carbocyclic-2(cid:2)-deoxy- sequence [54, 55].
guanosine 5(cid:2)-triphosphate (D-CdG-TP) were able to inhibit
The patents assigned to Board of Regents, University of
telomerase activity by 50% with half-maximal inhibitory
Texas System (Austin) and CTRC Research Foundation (San
concentrations (IC ) of 3±2(cid:1)M, 8±2(cid:1)M, 6±1.5(cid:1)M and
50 Antonio, TX) claim methods for prematurely shortening a
11±2(cid:1)M, respectively [50]. In addition, compounds such as
telomere in vitro, for inhibiting G-quartet formation in a te-
7-deaza-2(cid:2)-deoxyguanosine-5(cid:2)-triphosphate (7-deaza-dGTP)
lomere in vitro and converting processive telomerase in vitro
and 7-deaza-2(cid:2)-deoxyadenosine-5’-triphosphate (7-deaza-
to non-processive telomerase by administering an amount of
dATP) potentially inhibited telomerase activity by compet-
7-deaza purine nucleoside or 7-deaza purine nucleotide in an
ing with natural substrates dGTP and dATP, respectively and
amount sufficient to inhibit telomere extension, to suffi-
hence getting incorporated into telomeric DNA by telom-
ciently incorporate into telomeric DNA in the presence of the
erase. However, they act as poor substrates for telomerase
telomerase or to cleave the telomerase RNA component. The
and lead to the dissociation and decreased processivity of
incorporation of this nucleotide 7-deaza-dGTP and its ana-
telomerase [51]. Besides this, two more compounds 6-
logs, once incorporated into the telomere, was observed to
methoxy-7-deaza-2(cid:2)-deoxyguanosine 5(cid:2)-triphosphate
alter the telomeric secondary structure so that telomerase can
(OMDG-TP) and 6-thio-7-deaza-2(cid:2)-deoxyguanosine 5(cid:2)-
no longer recognize it properly for processive telomere syn-
triphosphate (TDG-TP) were also found to be potent telom-
thesis [54, 55].
erase inhibitory agents where TDG-TP significantly inhib-
ited telomerase with an half-maximal inhibitory concentra- The present inventions further mention that the nucleo-
tions (IC ) of 60nM while the less potent telomerase inhibi- side analogs were also found to be capable of a variety of
50
tor OMDG-TP was observed to give rise to short telomerase activities including mediating allosteric-like inhibition of
products, but less efficiently than TDG-TP [52]. telomerase, premature termination and shortening of te-
lomeric DNA, destabilization of telomeric structure and
All these studies shed light on the significance of reverse
function and eventually cell death [54, 55].
transcriptase inhibitors to be used as anti-telomerase agents
but further work has to be done in this direction to find more
C. Immunotherapy
novel potential reverse transcriptase inhibitors which can be
used as anti-cancer agents. Cancer immunotherapy is one of the potential anti-
telomerase inhibition approaches that targets telomerase
In US6372742, Chin et al. describe about the synthesis
positive malignant cells. Human telomerase reverse tran-
and characterization of thiazolidinedione indole and 5-(3-
scriptase (hTERT) as previously mentioned, which is acti-
isatinylidenyl)-2, 4-thiazolidinedione compounds and their
vated in almost 85% of the cancerous cells but is negligibly
subsequent use to inhibit the telomerase in a cancer cell. The
present in normal tissues, can be targeted as a tumour associ-
patent further mentions that substituted indole and isatin
ated antigen (TAA). It is a source of peptides which in asso-
compounds of the present invention are telomerase specific
ciation with Class I MHC molecules can be used to elicit
[53].
cytotoxic T-lymphocytes to target and kill cancerous cells
The patent claims that the compounds and compositions [56].
of the present invention may also be used for treating other
Cancer vaccines are categorised into peptide/protein vac-
telomerase mediated diseases such as hyper proliferative or
cine, tumour cell vaccine, DNA vaccine, recombinant virus
autoimmune disorders such as psoriasis, rheumatoid arthritis,
vaccine as well as dendritic cell (DC) vaccine [57, 58]. Vari-
immune system disorders requiring immune system suppres-
ous studies have outlined the fact that hTERT derived pep-
sion, immune system reactions to poison ivy or poison oak,
tides are naturally processed by tumours by the proteosomal
etc. [53].
110 Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 Agrawal et al.
digestion [59]. The probable mechanism of immunotherapy Active immunotherapy based on cancer vaccines target-
is that such tumour peptides or antigens are processed by ing tumour antigens to generate an endogenous anti-tumour
antigen presenting cells such as dendritic cells and then re- immune responses stands as a promising strategy to elimi-
stricted to the Major Histocompatibility Complex (MHC) nate the cancerous cells with the advantages of being highly
class I molecules. The processed antigen is recognised by the specific and less toxic [57, 58, 61]. The implementation of
cytotoxic T lymphocytes leading to a T-cell immune re- immunotherapy to target cancer cells also provisions to re-
sponse of cytokine secretion and targeted tumour cell lysis move the lag phase before the cell death [17, 4].
[60].
In US7622549 assigned to Geron Corporation (Menlo
Various hTERT derived peptides have been identified Park, CA) and the Regents of the University of Colo-
restricted to common alleles which elicit T cell immune re- rado (Boulder, CO), Cech et al. describe about the composi-
sponses. It has been observed that HLA-A2 is expressed by tions and methods related to human telomerase reverse tran-
nearly 50% Caucasian, Asian and Hispanics and 33% Afri- scriptase (hTERT) which can be used for diagnosis, progno-
can-Americans. Hence by priming T lymphocytes that can sis and treatment of diseases like cancers. The patent claims
specifically recognize hTERT derived peptide-HLA-A2 about compositions comprising of isolated polypeptides
complex would help in specifically eliminating hTERT tu- wherein the compositions elicit an adaptive immune re-
mour cells [60]. The first immunogenic peptide obtained sponse against human telomerase reverse transcriptase [65].
from hTERT (I540- ILAKFLHWL) was restricted to the
The present invention claims the immunogenic peptides
MHC class I allele HLA-A*0201(HLA-A2) and was effec-
or polypeptides having an hTERT sequence which can be
tive in killing a variety of hTERT positive tumour cell lines.
used to elicit an anti-hTERT and Class I MHC restricted
In a phase I clinical trial hTERT specific lymphocytes were
cytotoxic lymphocyte immune response in a patient as a vac-
found to be induced in four out of seven patients afflicted
cine. It also mentions about the anti-hTERT antibodies, e.g.,
with advanced breast or prostate carcinoma after vaccination
murine, human, or humanized monoclonal antibodies that
with the same HLA-A2-restricted hTERT I540 peptide pre-
may also be administered to a patient (passive immunization)
sented with keyhole limpet hemocyanin by ex vivo generated
to affect an immune response against telomerase-expressing
autologous dendritic cells [61].
cells [65].
In one of the research studies, Arai et al. demonstrated
The patent further mentions about methods for monitor-
that two hTERT derived peptides denoted as p324
ing the ability of a compound or anticancer treatment in
(VYAETKHFL sequence) and p461 (VYGFVRACL se-
modulating the levels of a telomerase reverse transcriptase
quence) were found to elicit hTERT peptide specific cyto-
activity or hTERT expression. It also provides kits and a
toxic T-lymphocytes restricted by HLA-A24 (HLA-
wide variety of sensitive, inexpensive, convenient, and
A*2402), which is the most common allele in Japanese
widely applicable diagnostic and prognostic assays for the
(more than 60%) and European (nearly 20%) populations
detection of an hTERT gene or gene product. The assays of
[62]. In a similar study by Minev et al., it was shown that
the invention also allow discrimination between different
two hTERT derived HLA-A2.1 restricted peptides denoted
classes and grades of human tumours or other cell-
as p540 (ILAKFLHWL sequence) and p865 (RLVDDFLLV
proliferative diseases by providing quantitative assays for the
sequence) were found to evoke hTERT specific CTLs in a
hTERT gene and their products and thereby facilitate the
majority of normal individuals and patients with prostate
selection of appropriate treatment regimens and accurate
cancer immunized in vitro against them [56].
diagnoses [65].
Further, Vonderheide et al. too reported that hTERT de-
As, certain embryonic and fetal cells, as well as certain
rived peptide K973 (KLFGVLRLK sequence) generated
adult stem cells, express telomerase, the present invention
CD8+ CTLs from HLA-A3+ cancer patients and healthy in-
also provides methods for determining other conditions, such
dividuals which subsequently lysed hTERT+ tumours in an
as pregnancy, by the detection or isolation of telomerase
MHC-restricted fashion. HLA-A3 allele is expressed in
positive fetal cells from maternal blood. Inter alia, the pre-
15%-20% patients [63]. These studies show that hTERT can
sent invention also furnishes methods and compositions for
be used as a potential universal cancer vaccine against vari-
reducing telomerase activity in tumour cells and for treating
ous malignancies. These results implicate towards the feasi-
cancer which include antisense oligonucleotides, ribozymes,
bility of employing hTERT derived peptides to vaccinate
peptides, gene therapy vectors encoding antisense oligonu-
patients against telomerase.
cleotides or activity altering proteins, and anti-hTERT anti-
Interestingly, in a study performed by Nair et al., it was bodies [65].
shown that TERT-RNA transfected human Dendritic Cells
Similarly, in US7056513 with the same assignee, Cech
generated TERT-specific CTLs in vitro, that lysed human
et al. provide methods for inducing anti-hTERT specific
tumour cells, including Epstein Barr virus (EBV)-
antibody so as to elicit an immune response to telomerase
transformed B cells as well as autologous tumour targets
reverse transcriptase protein by using an immunogenic com-
from patients with renal and prostate cancer. They also
position comprising of a pharmaceutically acceptable carrier
showed that immunization with tumour RNA was generally
and an isolated polypeptide which does not possess the nor-
more effective than immunization with TERT RNA, suggest-
mal telomerase catalytic activity [66]. Further in
ing that an optimal immunization protocol must be formu-
US7560437, Cech et al. provide an isolated, substantially
lated to include hTERT as well as additional tumour antigens
pure, or recombinant protein preparation of a telomerase
[64].
reverse transcriptase protein such that the composition elicits
Recent Patents on Anti-Telomerase Cancer Therapy Recent Patents on Anti-Cancer Drug Discovery, 2012, Vol. 7, No. 1 111
an adaptive immune response against hTERT when adminis- G-QUADRUPLEX STABILISATION
tered to a subject [67].
G- Quadruplexes are tetra-stranded DNA structures held
Besides these, US7824849 assigned to Geron Corpora- together by Hoogsteen hydrogen bonded arrays of guanine
tion (Menlo Park, CA) claims to provide a method of treat- bases. These secondary structures are formed by the 150-200
ment of cancer by activating T lymphocytes when exposed to nucleotide bases long Guanine rich 3(cid:1)-overhangs of te-
antigen presenting cells such as dendritic cells expressing lomeres in vitro [70]. These structures have been found to
telomerase reverse transcriptase (TERT) polypeptide [68]. inhibit telomerase activity in various studies by impediment-
ing the telomerase to extend 3(cid:1) overhangs as 3(cid:1)-end cannot be
The patent illustrates that the dendritic cells can be made
further recognised by the hTR RNA template of the telom-
to express hTERT peptide by isolating and pulsing the den-
erase. Hence, quadruplex binding ligands which could effec-
dritic cells with TERT peptides which is followed by admin-
tually act as Telomerase Targeting Agents (TTA) and could
istering these antigenically pulsed dendritic cells to the sub-
potentially stabilise these structures would act as feasible
ject. Moreover, TERT expressing dendritic cells can also be
anti-telomeric agents by leading to telomere shortening, se-
obtained by isolating and genetically modifying hema-
nescence and cell death [17, 71-74].
topoietic stem cells to express a TERT polypeptide. Subse-
quently, these precursor cells are differentiated into dendritic Various compounds like porphyrins, 2, 6-diamido-
cells followed by their administration to the patient. Alterna- anthraquinones, acridine derivatives [75], perylenes, ethid-
tively, the pulsed or genetically modified dendritic cells can ium derivatives, quinolones, piperazines, pentacyclicacridi-
be cultured ex vivo with HLA-matched T lymphocytes to nium salts, and fluoroquinophenoxazines have been shown
activate those T cells that are TERT specific. Thus, the den- to stabilise the G-quadruplexes and hence inhibit telomerase
dritic cells displaying TERT peptide with MHC molecule on [17, 71, 76].
the cell surface are capable of inducing MHC restricted cyto-
Telomestatin has been observed to be the first natural
toxic T-lymphocyte response against TERT specific target
product to be an effective TTA which facilitates the forma-
cancer cells [68].
tion or stabilisation of G-quadruplex structures [76]. Te-
The patent also describes the suitable administration of lomestatin is isolated from Streptomyces anulatus 3533-SV4.
the cells to the patients in a dose sufficient to induce an im- Telomestatin causes dissociation of TRF2 from the G-rich
mune response through intravenous, intra-articular, intra- overhangs without having any adverse effects on the normal
muscular, intradermal, intraperitoneal, and subcutaneous fibroblasts and epithelial cells. These results indicate that
routes along with a pharmaceutically acceptable carrier such telomestatin inhibits telomerase activity by hindering te-
as saline [68]. lomere elongations as well as by disrupting the capping func-
tions at the telomere ends [77]. Telomere dysfunction by
Interestingly, GRNVAC1, a cellular telomerase based
telomestatin activates ATM-dependent DNA damage re-
vaccine has shown promising results in Phase-II human
sponse by inducing the activation of ATM and Chk2 with a
clinical trials. GRNVAC1 is an autologous product which
subsequent increase in the expression of p21CIP1 and p27KIP1
consists of mature dendritic cells pulsed with RNA for the
[78].
protein component of human telomerase (hTERT) and a por-
tion of a lysosomal targeting signal (LAMP). Subsequently, In US7045523, Tauchi claims a method which can be
GRNVAC1 is injected into the patient's skin from where the used to treat BCR-ABL positive leukaemia. It comprises of
dendritic cells travel to the lymph nodes and induce cyto- administering the combination of N-{5-[4-(4-methyl-
toxic T-cells to kill cancer cells expressing telomerase on piperazino-methyl)-benzoylamido]-2-methylphenyl}-4-(3-
their surface. These Phase-II clinical trials used a prime- pyridyl)-2-pyrimidine-amine, or a pharmaceutically accept-
boost vaccination protocol in patients with acute myeloge- able salt thereof, and telomestatin in synergistically effective
nous leukemia (AML) in complete clinical remission. These amounts [79].
clinical trials were sponsored by Geron Corporation [69].
In the present invention, the telomerase inhibitor, te-
As we know that besides the expression of hTERT in lomestatin was characterized for its ability to inhibit BCR-
human tumour cells, it is also expressed in normal tissues ABL transformation as, when telomestatin was used to treat
such as hematopoietic stem cells, germ cells, activated lym- BCR-ABL positive OM9; 22 cells, it led to strong inhibition
phocytes and basal keratinocytes. Hence, there can be possi- of telomerase activity and reduction of telomere length [79].
ble adverse effects of anti-hTERT cancer immunotherapy on
The current patent has been assigned to Novartis
normal hTERT positive cells and tissues such as autoim-
AG (Basel, CH). Moreover, the present invention also pro-
mune reactions and destruction of normal cells [56, 57].
vides a commercial package comprising a combination of the
However, based on research studies carried out so far, no
invention, together with instructions for simultaneous, sepa-
such adverse effects have been reported, but still further
rate or sequential use in the delay of progression or treatment
work and clinical trials have to be carried out in this avenue
of a proliferative disease. The invention also claims that the
to aspirate out the real potential of cancer immunotherapy.
administration of the combination, especially comprising
Besides this, an increasing understanding of the tumour-host
telomestatin as combination partner results in beneficial ef-
interactions will help us to design hTERT targeted cancer
fects such as less side-effects, an improved quality of life and
vaccines with high specificity and efficacy, with minimal
a decreased mortality and morbidity as compared to a mono-
risk of adverse effects, ease of production and administration
therapy. It also facilitates for the usage of lower doses of the
coupled with the advantage of developing simple ex vivo
active ingredients of the combination which can also be ap-
assays to measure the elicited immune responses [57].
plied less frequently. The patent further delineates its appli-