U.S. patent application number 11/236197 was filed with the patent office on 2006-07-06 for dna-based aptamers for human cathepsin g.
Invention is credited to Laura Iris Ferro, Barbara Gatto, Manlio Palumbo, Rodolfo Pescador, Roberto Porta.
Application Number | 20060148745 11/236197 |
Document ID | / |
Family ID | 33427291 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060148745 |
Kind Code |
A1 |
Palumbo; Manlio ; et
al. |
July 6, 2006 |
DNA-based aptamers for human cathepsin G
Abstract
The present research is directed to the identification of
non-peptidic inhibitors of cathepsin G characterised by high levels
of selectivity and which can be efficaciously used in the treatment
and prophylaxis of inflammatory occurrences and procoagulant
conditions. The cathepsin G-inhibiting aptamers according to the
invention consist of linear DNA or polynucleotide sequences having
a chain length of at least 60 nucleotides and being substantially
not subjected to undergo efficient base pairing.
Inventors: |
Palumbo; Manlio; (Padova,
IT) ; Gatto; Barbara; (Padova, IT) ; Pescador;
Rodolfo; (Milano, IT) ; Porta; Roberto;
(Cernobbio (CO), IT) ; Ferro; Laura Iris; (Milano,
IT) |
Correspondence
Address: |
INTELLECTUAL PROPERTY GROUP;FREDRIKSON & BYRON, P.A.
200 SOUTH SIXTH STREET
SUITE 4000
MINNEAPOLIS
MN
55402
US
|
Family ID: |
33427291 |
Appl. No.: |
11/236197 |
Filed: |
September 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP04/06599 |
Jun 18, 2004 |
|
|
|
11236197 |
Sep 27, 2005 |
|
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Current U.S.
Class: |
514/44R ;
536/23.2 |
Current CPC
Class: |
A61P 25/00 20180101;
C12N 2310/16 20130101; C12N 2310/343 20130101; C12N 15/115
20130101; A61P 29/00 20180101; A61P 35/00 20180101; A61P 43/00
20180101; A61K 38/00 20130101; A61P 7/02 20180101; A61P 17/00
20180101 |
Class at
Publication: |
514/044 ;
536/023.2 |
International
Class: |
A61K 48/00 20060101
A61K048/00; C07H 21/04 20060101 C07H021/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2003 |
EP |
03425428.4 |
Claims
1. Cathepsin G-inhibiting aptamers consisting of linear DNA or
polynucleotide sequences having a chain length of 70/120
nucleotides and undergoing inter and/or intra molecular base
pairing to an extent lower than 20%, said sequences being
characterized by: having a molar ratio AG/TC of 1.0/2.0; or being
(GT).sub.n or (AC).sub.n oligopolymers in which n is in the range
from 35 to 60; or being (T).sub.n or (G).sub.n or (A).sub.n or
(C).sub.n or (Inosine).sub.n omopolymers in which n is in the range
from 70 to 120.
2. Cathepsin G-inhibiting aptamers according to claim 1
characterized by having a chain length of 70/110 nucleotides.
3. Cathepsin G-inhibiting aptamers according to claim 1
characterized by having a chain length of 80/100 nucleotides.
4. Cathepsin G-inhibiting aptamers according to claim 1
characterized by the fact of being single stranded sequences.
5. Cathepsin G-inhibiting aptamers according to claim 1
characterized by having a molar ratio AG/TC of 1.2/1.8.
6. Cathepsin G-inhibiting aptamers according to claim 1
characterized by having a molar content in guanine of 25/50%.
7. Cathepsin G-inhibiting aptamers according to claim 1
characterized by having a molar content in guanine of 35/45%.
8. Cathepsin G-inhibiting aptamers according to claim 1
characterized by being (GT).sub.n or (AC).sub.n oligopolymers in
which n is in the range from 40 to 50.
9. Cathepsin G-inhibiting aptamers according to claim 1
characterized by being (T).sub.n or (G).sub.n or (A).sub.n or
(C).sub.n or (Inosine).sub.n omopolymers in which n is in the range
from 80 to 100.
10. Cathepsin G-inhibiting aptamers according to claim 1
characterized by undergoing inter and/or intra molecular base
pairing to an extent lower than 10%.
11. Cathepsin G-inhibiting aptamers according to claim 1
characterized by undergoing inter and/or intra molecular base
pairing to an extent lower than 5%.
12. A method for the treatment and prophylaxis of inflammatory
occurrences, procoagulant conditions, genetic diseases,
degenerative diseases, DNA damages, neoplasia and/or skin diseases
wherein cathepsin G-inhibiting aptamers according to claim 1 are
administered to a patient in need of such a treatment.
13. A pharmaceutical composition containing at least one cathepsin
G-inhibiting aptamer according to claim 1 together with customary
eccipients and/or adjuvants.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
International Application No. PCT/EP2004/006599, filed Jun. 18,
2004, which in turn claims priority to European Application No.
03425428.4, filed Jun. 30, 2003, the teachings of both of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Cathepsin G is a serine protease commonly found in the
azurophilic granules of neutrophils and monocytes. Together with
elastase and proteinase 3 it belongs to the chymotrypsin family and
cleaves extracellular matrix proteins such as elastin, collagen,
fibronectin and laminin causing extensive lung tissue damage in the
animal. Cathepsin G also plays a role in blood clotting; in fact,
it is involved in an alternative pathway of leukocytes initiation
of coagulation, and by activating coagulation factor X and factor V
it can cleave and potentially modulate the thrombin receptor and it
can activate platelets in vitro. It is also able to convert
angiotensin I into angiotensin II with only minor cleavage
occurring elsewhere in the molecule.
[0003] It was shown that cathepsin G kills bacteria and fungi but
this property is not related to its activity, in fact peptides
derived from its cleavage showed direct antimicrobial properties.
It can also degrade necrotic tissues and is therefore related to
several inflammatory diseases like lung emphysema, bronchitis,
cystic fibrosis and psoriasis.
[0004] The enzymatic activity of cathepsin G is regulated by two
types of protein proteinase inhibitors: the so called "canonical"
inhibitors and the serpins. The former are relatively small
proteins (29-190 amino acids) and are tight-binding reversible
inhibitors; among them are Mucus proteinase inhibitor (MPI), eglin
c and aprotinin. Serpins are larger proteins (400-450 residues)
that form an irreversible complex with their cognate protein due to
the formation of a non-hydrolysable acyl bond between the catalytic
site of cathepsin G and their reactive site loop. Among serpins
1-antichymotrypsin is the most important: inhibitors of this family
are not selective because they are able to bind to and inhibit
other chymotripsins. Moreover, their stability and distribution in
vivo is affected by their peptidic nature.
[0005] Several synthetic inhibitors were found starting from
peptidomimetic scaffolds containing 1,2,5-thiadiazolidin-3-one 1,1
dioxide or 1,3-diazetidine-2,4-diones and some of them
(particularly those with aromatic side chains) showed a remarkably
specific activity for cathepsin G. However, they form
non-reversible acyl complexes with the enzyme. Recently, it was
shown that both the full length and cleaved chromosomal DNA is able
to bind and inhibit Cathepsin G in vitro and in vivo. A 30 bpDNA
fragment tightly binds cathepsin G at physiological conditions and
showed a decreasing order of affinity for human neutrophil elastase
when compared to proteinase 3 in accordance with their decreasing
cationic character.
[0006] In particular, EP-775745 discloses oligonucleotide cathepsin
G-inhibiting aptamers having a chain length of about 40 nucleotides
(and in any case lower than 55 nucleotides) and containing G-pairs
repeating units which are useful in the treatment and prophylaxis
of inflammatory occurrences and procoagulant conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 represents a comparison of the Kd of the tested
oligonucleotides.
[0008] FIG. 2 represents a summarization of the Log
concentration-effect curves of GT and AC aptamers.
[0009] FIG. 3 represents a summarization of the Log
concentration-effect curves of PolyT aptamers.
DESCRIPTION THE INVENTION
[0010] The present research is mainly directed to the
identification of non-peptidic inhibitors of cathepsin G
characterised by high levels of selectivity and which can be thus
more efficaciously used in the treatment and prophylaxis of the
above conditions and also in that of genetic diseases, degenerative
diseases, DNA damages, neoplasia and/or skin diseases. Like
antibodies, DNA molecules are able to assume a variety of
tridimensional structures depending on their sequence. Some of
these might be relevant for binding to the target. In the present
study we applied a method called SELEX (Systematic evolution of
ligands by exponential enrichment) to select and identify ssDNA or
RNA molecules, called aptamers, exhibiting high affinity for
cathepsin G.
[0011] Aptamer technology combines the capacity of generating huge
structural diversity in random pools of oligonucleotides with the
power of the polymerase chain reaction (PCR) to amplify selected
sequences. This technology involves the screening of large,
random-sequence pool of oligonucleotides and is based on the fact
that they assume a large number of tertiary structures, some of
which may possess desirable binding or catalytic activity against
target molecules.
[0012] Although inhibition is not demanded by the selection, in
many cases these ligands directly inhibit the biological functions
of the targeted proteins. In these cases, the inhibitory functions
of the ligands are presumably due to overlapping of their binding
sites with the functional region of proteins.
[0013] The outcome of our research has lead us to define a new
class of cathepsin G-inhibiting aptamers possessing particularly
high levels of selectivity.
[0014] The new cathepsin G-inhibiting aptamers of the present
invention are single or double stranded linear DNA or
polynucleotide sequences characterized by having a chain length of
at least 60 nucleotides, preferably 70, and by being substantially
not subjected to inter and/or intra molecular base pairing.
[0015] According to the best embodiment of the invention the DNA
sequences may have a chain length of 70/120 nucleotides, preferably
of 70/110 nucleotides, even more preferably of 80/100 nucleotides.
Although the sequences according to the present invention may be
single or double stranded, single stranded sequences are preferred.
The sequences according to the present invention are also
preferably characterized by having a molar content in guanine of
about 25/50%, preferably 35/45% and/or by having a molar ratio
AG/TC of about 1.0/2.0, preferably 1.2/1.8 (for the purposes of the
present invention AG means the total number of A and G nucleotides
of the sequence whereas TC means the total number of T and C
nucleotides of the sequence).
[0016] Preferred Embodiments of the Invention are: [0017]
(GT).sub.n or (AC).sub.n oligopolymers in which n is in the range
from 35 to 60, preferably from 40 to 50; [0018] (T).sub.n or
(G).sub.n or (A).sub.n or (C).sub.n or (Inosine).sub.n omopolymers
in which n is in the range from 70 to 120, preferably from 80 to
100.
[0019] Within the terms of the present invention the expression
"substantially not subjected to inter and/or intra molecular base
pairing" means that the DNA or polynucleotide sequences do not
undergo inter and/or intra molecular base pairing to an extent
higher than 20%, preferably than 10%, even more preferably than 5%,
under both stringent and non stringent conditions. Such a result is
the direct consequence of their structure, since the fact of:
[0020] having a molar ratio AG/TC of 1.0/2.0; or [0021] being
(GT).sub.n or (AC).sub.n oligopolymers in which n is higher than
30; or [0022] being (T).sub.n or (G).sub.n or (A).sub.n or
(C).sub.n or (Inosine).sub.n omopolymers in which n is higher than
60; defacto prevents any sort of hybridization.
[0023] As it will be apparent from the following discussion, the
aptamers according to the present invention do selectively and
efficaciously inhibit cathepsin G and, consequently, they can be
used in the manufacture of a medicament for the treatment and
prophylaxis of inflammatory occurrences, procoagulant conditions,
genetic diseases, degenerative diseases, DNA damages, neoplasia
and/or skin diseases, which represents therefore an object of the
invention. A further object of the invention is also represented by
the pharmaceutical composition containing the cathepsin
G-inhibiting aptamers of the invention together with customary
eccipients and/or adjuvants. Other objects of the invention may be
represented by the cathepsin G-inhibiting aptamers selected from
those reported in the sequence listing (i.e. from SEQ ID NO: 1 to
SEQ ID NO: 18).
Experimental Section
Materials
[0024] Cathepsin G was purchased from Europa Bioproducts or from
Calbiochem. All oligonucleotides were obtained from Eurogentec Bel
SA (Belgium) and purified by PAGE before use. Some
oligonucleotides, already purified by PAGE were obtained from Gibco
BRL Custom Primers. Taq polymerase was from Pharmacia Amersham
Biotech while dNTPs were purchased as sodium salt from Boehringer
Mannheim. T4-polynucleotide kinase, ligase and the restriction
enzymes were from Gibco Life Technologies. Qiagen kits were used
for plasmid miniprep purification, and sequencing was performed
using T7 Sequenase (Pharmacia Amersham Biotech) and
[gamma-.sup.33P]dATP (Nen Life Sciences).
ssDNA Library
[0025] The synthesised random pool is 96 base length, the central
part of the molecule has a randomised region that is flanked by two
constant regions for amplification, cloning and sequencing; its
sequence is 5'-CGTACGGAATTCGCTAGC(N).sub.60GGATCCGAGCTCCACGTG-3'.
The underlined sequences refer to restriction sites for EcoRI and
BamHI enzymes respectively. The pool was amplified by PCR using
primer II-up, which sequence is 5'-CGTACGGAATTCGCTAGC-3', and
primer III-Down 5'Biot-CACGTCGAGCTCGGATCC-3' which is biotinylated
at the 5' end in order to be bound to a streptavidin column to get
ssDNA.
Selection Protocol
[0026] The starting random pool was radioactive labelled with
.sup.32P, denaturated at high temperature and incubated with
cathepsin G in Incubation buffer (buffer IB: 30 mM Tris HCl pH7.5,
150 mM NaCl, 5 mM KCl and 5 mM MgCl.sub.2) which is close to the
physiological conditions.
[0027] The incubation was conducted for 90 minutes in ice, then the
sample was loaded in an affinity chromatography mini-column filled
with Sepharose SP (Amersham Pharmacia Biotech), swollen and
equilibrated in buffer IB. The ssDNA/protein solution was incubated
with the resin for 30 minutes at 4.degree. C. The unbound
oligonucleotide molecules were washed away with buffer IB, while
the remaining, more selective ones were eluted from the column a
high ionic force elution buffer (buffer EB: 0.8 M NaCl e 50 mM Tris
pH 7.8).
[0028] The washing volumes were modified during the selection in
order to increase the stringency as well as the DNA concentration
which was twice the protein at the first cycle, but it was
progressively reduced.
[0029] The fractions were counted and the yield of the Selex cycle
was expressed as a percentage of the total radioactivity. The flow
through and the first two fractions of the EB wash were collected
and amplified.
Polymerase Chain Reaction
[0030] Polymerase chain reaction was done using Taq polymerase at a
concentration of 0.3-0.5 u/50 .mu.l in the buffer indicated by the
producer. The number of cycles was adjusted after every different
selection.
[0031] Before the insertion in the plasmid vector for cloning, the
DNA was subjected to a polishing reaction in order to get blunt
ends: an aliquot of the normal PCR reaction was incubated with 2.5
u/.mu.l of Pfu Turbo polymerase (Stratagene) in the suggested
buffer at 72.degree. C. for 30 minutes.
Generation of ssDNA
[0032] In order to get ssDNA from the amplified dsDNA we used
alkaline denaturation protocol. The DNA was amplified using a
biotinilated Down-II primer and bound to a chromatography column
filled with streptavidin Sepharose (Pierce). After 30 minutes
incubation the unbound dsDNA was washed away with buffer NaCl 50
mM, Tris/HCl 100 mM, EDTA 10 mM (SBB-strepavidin Binding Buffer)
while the remaining one was denaturated and washed with NaOH 0.15
N. Then it was precipitated and collected for the selection
cycles.
Cloning and Sequencing
[0033] Both the amplified dsDNA and the vector pUC19
(Amersham-Pharmacia Biotech) were treated with 2.5 units of EcoRI
while only the plasmid was treated with SmaI that gives blunt
ends.
[0034] After precipitation 3 pmols of dsDNA and 0.6 pmols of pUC19
were reacted with T4 ligase in the suggested buffer.
[0035] The plasmid was then inoculated in E. coli competent cells
(SURE strain Stratagene) by the electroporation method using E.
coli pulser (Biorad) and plated in solid LB media in the presence
of Ampicillin, X-Gal and IPTG (for the blue/white screening). 50
white different colonies were picked, grown and harvested
separately in liquid LB broth. Plasmids were purified by alkaline
lysis and their quality was every time tested by agarose gel
electrophoresis.
[0036] The sequence of the aptamers was determined with the
Sanger's method, labeling with [gamma-.sup.33P]dATP and employing
two different primers EleA457: 5'-ACG-CCA-AGC-TTG-CAT-3' (sense)
and Ele S: 5'-GGG-TTT-TCC-CAG-TCA-CGA-3' (antisense).
Kd and Ki Determination
[0037] The affinity of the oligonucleotides was determined by
affinity chromatography as performed in the selection. Different
aliquots of each oligonucleotide were previously incubated with 15
.mu.g of Cathepsin G in ice. The solution was then loaded in the
min-chromatography column used for the selection and washed with 15
volumes of buffer IB. After one hour incubation, it was washed with
six volumes of buffer EB. Fractions of the same volumes were
collected and counted.
Surface Plasmon Resonance (SPR) Experiments
[0038] Cathepsin G, from human neutrophils, dissolved in HBS EP
buffer, pH 7.40 (Biacore) was immobilized on the surface of a CM 5
research grade sensor chip flow cell, according to the procedure
suggested by Biacore and using the Biacore amine coupling kit. A
blank flow cell was prepared using all the above reagents but
Cathepsin G. The amount of Cathepsin G immobilized on the surface
of the flow cell was 5178.91.+-.129.63 RU. Aptamers [Poly GT (chain
length: 20, 30, 40, 60, 80 and 100) and Poly AC (chain length: 20,
40 and 80,] were dissolved in 30 mM Tris-HCl buffer, pH 7.50, 150
mM NaCl, 5 mM KCl, and 5 mM MgCl 2 and injected over the Cathepsin
G surface or the blank surface. Three sets of experiments were run.
The first at a concentration of 500 nM, for all the aptamers, the
second at a concentration of 6595 .mu.g/L, for all the aptamers,
and the third one at concentrations ranging from 15.6 to 8000 nM,
according to the aptamer being tested. All the above experiments
were run at 25.degree. C., using as running buffer the Biacore HBS
EP Buffer, pH 7.40 The Cathepsin G surface was regenerated by two
injections of 2 M NaCl. The blank sensorgram was subtracted from
each sample sensorgram and the the binding response evaluated. The
binding responses, generated in the third set of experiments, were
plotted as a function of the Log concentration (nM) to get
concentration-effect curves to find out the relative potencies of
aptamers in binding Cathepsin G from human neutophils.
Results
Selection and Identification of Aptamers
[0039] We selected aptamers for cathepsin G starting from a DNA
pool with a randomised region of 60 nucleotides flanked by two
regions with conserved sequence for the PCR reaction and
restriction sites for the following cloning step (see above).
[0040] We chose affinity chromatography as selection method,
binding the protein to the resin. This appeared to be the easiest
protocol because cathepsin G, which is positively charged at
physiologic conditions (theoretical isoelectric point 11), can be
tightly bound to an ion exchange resin, while an unspecific binding
of the DNA molecules to the resin is highly reduced. In fact only
the DNA molecules that recognise the protein remain on the column
while the unbound material is washed away. We tried to render the
binding process between the labelled ssDNA and the protein more
selective by including potassium and magnesuim chloride 5 mM in the
binding buffer thus increasing ionic strength in the buffer and
stabilising oligonucleotide folding.
[0041] The selected molecules were then efficiently removed from
the column, together with the bound protein, using a high ionic
strength buffer (buffer EB), and then counted by radioactivity. The
first two fractions and the flow through were then collected,
amplified by PCR and reduced to single stranded molecules in order
to be used for the next cycle (see methods section for
details).
[0042] We performed nine cycles of selection: after four cycles a
significant increase of yield was observed, but the SELEX was
terminated when no further increase in pool affinity was observed
over three rounds, reaching a final yield of 42% (table 1). The
stringency of the selection was increased changing the number and
the volumes of the washes. After cycles 5 and 7 precolumn cycles
were performed in order to avoid an unspecific binding of the
aptamers to the resin: the pool coming from the previous cycle were
loaded in the column without the protein: the first fractions
eluted from the column were then amplified and used for the next
cycle. TABLE-US-00001 TABLE 1 scheme of the SELEX cycles. Cycle
Column Cycle number Protein .mu.g Volume (.mu.g) Wash Fraction
Yield % 1 100 2000 8 .times. 1000 .mu.l 0.4 2 50 500 8 .times. 500
.mu.l 0.7 3 50 400 8 .times. 600 .mu.l 1.6 4 50 400 8 .times. 500
.mu.l 38 5 40 1000 9 .times. 1000 .mu.l 22 precolumn 1000 10
.times. 250 .mu.l 6 33 1000 20 .times. 250 .mu.l 22 7 30 500 23
.times. 500 .mu.l 21 precolumn 300 10 .times. 200 .mu.l 8 30 500 22
.times. 500 .mu.l 31 9 30 500 25 .times. 500 .mu.l 42
Sequence Analysis
[0043] The selected molecules were cloned into E. coli cells as
described in the experimental selection and sequenced. We found 19
different sequences out of 50 clones. We used two sequence
alignment programs, Clustal W and FastA-align, searching for a
repeated consensus motif, but the molecule diversity was too high
to yield a good alignment even within subsets of the sequenced
molecules. Further analysis showed that GT motifs are clearly
repeated in 14 sequences. Moreover, a closer look at these
molecules showed that they are not prone to undergo either inter
and intra molecular base pairing to an appreciable extent, nor do
they form more complex tridimensional structures like G quartets.
It seemed that the selection led to unstructured, linear and
flexible molecules that can tightly bind to the positive protein
because of a charge-charge interaction. To confirm this hypothesis,
we compared the affinity of one of the selected aptamers, the 60mer
CG51, with other oligonucleotides having non-pairing sequences such
as oligo GT or AC TABLE-US-00002 CG1
GGGTGGCCCCCTAGTCGCGCACTGGAAGCGGTAGTGTCGTGAGAT TCGTATCTGGGGTAT CG3
CAACGAGTCAGGGCGTGATTGGTGAAGATGTGTGGTTTGGCCAGA AAGGGCGATGGTGGA CG11
AGAGCTGAGACGGACATGCTGCCCATGGAGACTGTTCGAGAGGGT GAGCGGGAGTGGG CG16
ACCCCTAGGTCAGCACGTAGTGTAGGGCGATGTGTTCATGGCGGG AATGTGAGTTGTGGG CG20
GGGCGGCTCGCGTTGTGGAACATTCGTGGTGCCAATGCGTACCAG GGATTGCCTCCTGT CG25
GGGCGATTGGCGAATGCAAGGGTAAGGTTGGGCGATTGATGTGCA CGTAGCGCAGAGCAT CG28
GGAACGTGGTAGGTGTGTCTGCTGTGTGTGGCTCGGGCAGGTTGT CAGGGTGTTT CG32
GGGCATAGGGCGTCGTAGCCTGAAGGTGTGATTCGTGCGTTAGAT GGGGGGCAGTCTGC CG39
CGGTGGAGAGGTCGCAATGACACGGTTGACGATAGGCCCCTTGCT AACATCGGTTGGTG CG43
CAACGTGTGATATGTGGGTATACGCTTGGGTGTTACGCTGAGCAC AGAGGGTATTCGTGT CG48
AGSGGGCAGCAGCACACCACACATGTACGTGGGGGATTGCATTGT GTACTTAGACGGTAT CG49
GGCCTGGGTGATGTACTATGTATGCGTCGTGGTGGCTGGTAAAGG GGGTCTGCTATGGGT CG51
CAACGTGTGATATGTGGGTATACGCTTGGGTGTTACGCTGAGCAC AGAGGGTATTCGTGT CG2
CCACGGACGCTGTGAGCGGCCAACGGATGGGAATCACGATCTGGC CCGAACCACATACCG CG31
TCACACTAGGGCACTTGCTAAGTAGCTATGTAACTCGATCATACT TATTAGGCTTG CG23
AATCGATGGACACTTCAACGCAACTTGACATGGCGGTACGTGGAC TCTTGTGGCGACAGTT CG34
AACCCGTGTGATAAGGATATGGTGACTTCGTGGCACAGCGTCGAC GGACTGCCCATTCCA CG45
GGCGGGCGGTATGGGCTGCAGGATATGCAGGGGCGCAGAGGACAG TCTGGCCATGTACTA CG40
GGCAGGGACGTTCCCAGGAATGCGGCACAGGCAGACAGCTCCCGA CGAGTACCAGGGTG
structures. The sequences of the oligonucleotides coming from the
last selection cycle are reported here-below; each one is marked
with a different number (CG51 and CG43 are the same).
[0044] The above sequences have the following correspondence in the
sequence listing: CG1=SEQ ID NO: 1, CG3=SEQ ID NO: 2, CG11=SEQ ID
NO: 3, CG16=SEQ ID NO: 4, CG20=SEQ ID NO: 5, CG25=SEQ ID NO: 6,
CG28=SEQ ID NO: 7, CG32=SEQ ID NO: 8, CG39=SEQ ID NO: 9, CG43 (and
CG51)=SEQ ID NO: 10, CG48=SEQ ID NO: 11, CG49=SEQ ID NO: 12,
CG2=SEQ ID NO: 13, CG31=SEQ ID NO: 14, CG23=SEQ ID NO: 15, CG34=SEQ
ID NO: 16, CG45=SEQ ID NO: 17, CG40=SEQ ID NO: 18.
Affinity of Selected Molecules and Related Sequences to Cathepsin
G
[0045] We evaluated the oligonucleotide binding to cathepsin G by
affinity chromatography in analogy with the selection method. The
affinity of the aptamer CG51 was firstly compared with AC and GT
oligonucleotides of the same length that, as mentioned, are clearly
unable to fold into any structure characterised by Watson-Crick
base pairs or G quartets formation. The complementary sequence of
CG51, called cmpCG51, was included as a control. Moreover, in order
to demonstrate whether the oligonucleotide length was an important
factor in the binding to the protein, the affinity of AC and GT
oligonucleotides longer and shorter than 60 nucloetides was
measured.
[0046] As expected from the high yield of the SELEX, the selected
CG51 showed a high affinity for cathepsin G (Kd 0.9 nM). Besides,
its Kd was comparable with AC and GT oligonucleotides of the same
length (Kd 0.8 nM and 1 nM respectively) and with cmpCG51 (Kd 0.6
nM) (FIG. 1). These data indicate that our hypothesis about tight
binding by unstructured and flexible molecules was correct.
[0047] Molecules longer than the 60mer like (AC).sub.60 and
(GT).sub.40, which are respectively a 120mer and a 80mer, showed an
affinity of 1.2 nM. On the other hand, the shorter (GT).sub.20 and
(GT).sub.10 that are shorter molecules, have a Kd of 1.5 nM and 2
nM respectively, suggesting that the length of the selected
oligonucleotides is important to grant efficient binding. Aptamer
THR, that was selected against thrombin, was also included as a
control in order to prove whether the oligonucleotide structure was
important for cathepsin binding. This aptamer is known to form
stable G quartets. The low Kd (4 nM) found in this case shows that
this type of structure is not likely to represent an effective
recognition motif. Interestingly, double stranded CG51 showed an
affinity lower than the single stranded, even if the latter bears a
larger number of charged groups. Indeed, the double stranded
oligonucleotide is bulkier and stiffer, hence unable to optimally
bind the protein.
Surface Plasmon Resonance (SPR) Experiments
[0048] The data generated in the first set of experiments (each
aptamer at 500 nM) gave the first evidence that, in the instance of
GT aptamers, increasing the chain length over 60 brings forth an
increase in binding but this increase is less steep than that in
the range 30-60. The binding is poor in the range 20-30. In the
instance of AC aptamers, their binding was less pronounced than
that of GT aptamers. SPR resonse is related to the change in
surface mass concentration of analyte (in the present instance
aptamer) and therefore it depends on the molecular weight of the
analyte in relation to the number of binding sites on the surface
(made of Cathepsin G, in the present instance). To get rid of the
doubt that the apparent aptamer binding was not dependent on the
aptamer mass but just on the aptamer structural feature, a second
set of experiments was carried out at the same mass concentration
(each aptamer at 6595 .mu.g/L). The results were the same as those
obtained in the first set of experiments (data not shown for the
sake of brevity). In FIG. 2, the Log concentration-effect curves of
GT and AC aptamers are summarized. In this figure, just each
aptamer responses, referring to the concentration range over which
a linear regression was obtained, are reported. GT 100 is the most
potent aptamer and it has been arbitrarily assigned a potency of
one (the relative standard). GT 80 has a relative potency of about
0.32, GT 60 of about 0.144, AC 80 of about 0.017, GT 40 of about
0.016, AC 40 of about 0.0047 and GT 30 of about 0.0020. GT 20 and
AC 20 were not evaluable because of their poor binding. Rougly the
aptamers can be divided into three families (FIG. 2); first family:
GT 100, GT 80 and GT 60; second family: AC 80, GT 40, AC 40 and GT
30; third family: AC 20 and GT 20.
[0049] In FIG. 3, the Log concentration-effect curves of PolyT
aptamers are summarized. As it can be appreciated, PolyT1000 and
PolyT80, i.e. the aptamers having sequence (T).sub.100 and
(T).sub.80, respectively, are much more potent than PolyT60.
Discussion
[0050] After four cycles of selection only, a huge increase of the
percentage of molecules bound to the protein was seen and, at the
ninth cycle, corresponding to a yield of 42%, it was not possible
to further enrich the pool. However sequence analysis of the
selected aptamers did not show evidence for a common consensus
motif repeated among them. At a closer glance it was found that a
large number of these molecules were GT/C deficient, therefore
unlikely to undergo pairing and to fold into G quartets. Probably
single stranded DNA molecules, negative and flexible, bind to this
positively charged protein best. Even in the presence of
significant amounts of sodium and magnesium chloride in the SELEX
buffer, the binding between the target and the protein could be
still mainly governed by charged interactions.
[0051] To confirm the hypothesis of a peculiar "consensus"
rationale, the affinity of one of the selected aptamers, CG51, was
compared with several AC and GT oligonucleotides. We validated the
fact that CG51 has a remarkably high affinity for cathepsin G with
a Kd in the nanomolar range, showing that the selection had
effectively lead to a pool of efficient binders. The dissociation
constants of (AC).sub.30, (GT).sub.30 and cmpCG51 that have the
same length (and overall structural characteristics) of CG51 were
comparable, while shorter molecules showed lower affinity. Double
stranded CG51 showed a lower affinity for cathepsin G: this is very
interesting considering that it was proven that chromosomal DNA
with an average length of 30 bp is able to bind to this
protein.
[0052] We demonstrated that a linear and flexible single stranded
DNA chain, with a length of at least 60, preferably more than
70-80, is more effective in binding cathepsin G than the
chromosomal counterpart and also more effective than shorter DNA
chains.
Sequence CWU 1
1
22 1 60 DNA unknown chemically synthesized 1 gggtggcccc ctagtcgcgc
actggaagcg gtagtgtcgt gagattcgta tctggggtat 60 2 60 DNA unknown
chemically synthesized 2 caacgagtca gggcgtgatt ggtgaagatg
tgtggtttgg ccagaaaggg cgatggtgga 60 3 58 DNA unknown chemically
synthesized 3 agagctgaga cggacatgct gcccatggag actgttcgag
agggtgagcg ggagtggg 58 4 60 DNA unknown chemically synthesized 4
acccctaggt cagcacgtag tgtagggcga tgtgttcatg gcgggaatgt gagttgtggg
60 5 59 DNA unknown chemically synthesized 5 gggcggctcg cgttgtggaa
cattcgtggt gccaatgcgt accagggatt gcctcctgt 59 6 60 DNA unknown
chemically synthesized 6 gggcgattgg cgaatgcaag ggtaaggttg
ggcgattgat gtgcacgtag cgcagagcat 60 7 55 DNA unknown chemically
synthesized 7 ggaacgtggt aggtgtgtct gctgtgtgtg gctcgggcag
gttgtcaggg tgttt 55 8 59 DNA unknown chemically synthesized 8
gggcataggg cgtcgtagcc tgaaggtgtg attcgtgcgt tagatggggg gcagtctgc 59
9 59 DNA unknown chemically synthesized 9 cggtggagag gtcgcaatga
cacggttgac gataggcccc ttgctaacat cggttggtg 59 10 60 DNA unknown
chemically synthesized 10 caacgtgtga tatgtgggta tacgcttggg
tgttacgctg agcacagagg gtattcgtgt 60 11 60 DNA unknown chemically
synthesized 11 agsgggcagc agcacaccac acatgtacgt gggggattgc
attgtgtact tagacggtat 60 12 60 DNA unknown chemically synthesized
12 ggcctgggtg atgtactatg tatgcgtcgt ggtggctggt aaagggggtc
tgctatgggt 60 13 60 DNA unknown chemically synthesized 13
ccacggacgc tgtgagcggc caacggatgg gaatcacgat ctggcccgaa ccacataccg
60 14 56 DNA unknown chemically synthesized 14 tcacactagg
gcacttgcta agtagctatg taactcgatc atacttatta ggcttg 56 15 61 DNA
unknown chemically synthesized 15 aatcgatgga cacttcaacg caacttgaca
tggcggtacg tggactcttg tggcgacagt 60 t 61 16 60 DNA unknown
chemically synthesized 16 aacccgtgtg ataaggatat ggtgacttcg
tggcacagcg tcgacggact gcccattcca 60 17 60 DNA unknown chemically
synthesized 17 ggcgggcggt atgggctgca ggatatgcag gggcgcagag
gacagtctgg ccatgtacta 60 18 59 DNA unknown chemically synthesized
18 ggcagggacg ttcccaggaa tgcggcacag gcagacagct cccgacgagt accagggtg
59 19 96 DNA unknown chemically synthesized 19 cgtacggaat
tcgctagcnn nnnnnnnnnn nnnnnnnnnn nnnnnnnnnn nnnnnnnnnn 60
nnnnnnnnnn nnnnnnnngg atccgagctc cacgtg 96 20 18 DNA unknown
chemically synthesized 20 cacgtcgagc tcggatcc 18 21 15 DNA unknown
chemically synthesized 21 acgccaagct tgcat 15 22 18 DNA unknown
chemically synthesized 22 gggttttccc agtcacga 18
* * * * *