Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
A Research on Arginine-Rich Peptides Conjugated
Oligonucleotide Targeting to Telomerase
Yuefeng Peng , Changpo Chen , Lihe Zhang
National Research Laboratory of Natural and Biomimetic Drugs, School of
Pharmaceutical Sciences and School of Chemistry & molecule engineering
Abstract:
Antisense oligonucleotide is a kind of important molecular biological
research tool and potent therapeutics. However, many classes of oligonucletides are
polyanions and can not pass through cell membrane. It was reported that arginine-rich
peptide such HIV Tat derived peptide has transmembrane function. Telomerase is a
new target of anticancer therapy. An on-resin fragment coupling method for the
peptide oligonucleotide conjugation is developed and is applied to the assembly of
arginine-rich peptide oligonucleotide conjugate. This method avoids the precipitation
occurred in the solution phase fragement coupling of basic peptide and
oligonucleotide. R9C，R6C and TAT conjugated ODNs targeting to telomerase are
synthesized with the on-resin method. The transmembrane activity of R9C conjugated
oligonucleotide was investigated using confocal fluorescence microscopy.
key words: peptide, oligonucleotide, peptide-conjugated antisense oligonucleotide,
telomerase
INTRODUCTION
With the achievement of HGP(human genome project) and the development of
functional genomics, antisense drugs and antisense technology find their way in the
new drug research and molecular biological science. For the therapeutic application,
the problem of the permeability to the cell membrane and its instability in cells limit
the biological activity of the antisense oligonucleotide. Scientists have tried to find
some ways to increase oligonucleotide’s ability of penetrating cell and nucleous
membrane. Recently it was demonstrated that the conjugate of transduction peptide
with oligonucleotide can both increase the stability and the antisense activity of the
oligonucleotide dramatically. The most attractive peptide sequence is the basic
fragment of HIV Tat protein which has a arginine-rich sequence.[1] It was reported
that Tat protein can penetrate both the outer membrane of cells and the membrane of
nucleus. A comparative research of Tat derived peptide and polyarginine demonstrates
that arginine residues play an important role in TAT protein penetrating cell
membrane. [2]
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Telomerase is a new target of cancer therapy. Relative studies demonstrate that
over 80 percent primary cancer cells have the higher telomerase activities comparing
to the normal cells. The higher activities of telomerase may relate to the maintenance
of the reproductive ability of the cancer cells. Hence the inhibitors of telomerase play
an important part in the research of the biological function of telomere and telomerase.
Telomerase inhibitor may be developed into a new kind of anticancer agents.
Telomerase consists of RNA template and enzyme protein, so the antisense
oligonucleotide targeting to its RNA template can effectively inhibit the activity of
telomerase in vitro. Some antisense sequences targeting to telomerase’s mRNA were
suggested by Sheng-qi Wang. TRAP-PCR analysis and the result of Weston-blot
showed that one of the sequences dramatically inhibits the activity of telomerase at
micromole concentration.
RESULT AND DISCUSSION
1. The peptide and oligonucletide sequences
The antisense sequence targeting to mRNA of the telomerse protein is
ACTCACTCAGGCCTCAGACT, and the antisense sequence targeting to the RNA
template is CTCAGTTAGGGTTAGACAA.
Considering the excellent transmembrane activity, we designed the argnine-rich
peptide sequence and investigated the synthetic conditions for the coupling reaction
between the argnine-rich peptide and ODN. The designed peptide sequences are as
follows:
ArgArgArgArgArgArgCys, （R6C）
ArgArgArgArgArgArgArgArgArgCys, （R9C）
D-ArgD-ArgD-ArgD-ArgD-ArgD-ArgD-ArgD-ArgCys, （D-R9C）
ArgLysLysArgArgGlnArgArgArgCys(Tat peptide), （TAT）
2. The synthetic strategy
As mentioned above, although scientists have undergone so many meaningful
exploration of the synthesis of the antisense oligonucleotide, there is not a general
method for the synthesis of peptide-oligonucleotide conjugate. There are several
methods for the synthesis of the argnine-rich peptide- oligonucleotide conjugates
[4,7-9]. Generally, -SH group is used in the peptide sequence and linked with the
ODN activated by maleimido or haloacetyl functions, or the –SH reacts with the
oligonucleotide containing –SH to form the conjugate linked by -S-S-. Robles used
Fmoc to protect the guanidine group of arginine and applied to synthesize the
arginine-rich peptide-oligonucletide conjugate by in-line synthesis. However, when
we used a double-Fmoc-protected arginine for the synthesis of the designed conjugate,
we only got a complicated product. Hence, we chose to use disulfide to link the ODN
and the peptide. This strategy can avoid the incompatibility of peptide chemistry and
oligonucleotide chemistry in the conjugate synthesis, on the other hand, the disulfide
linkage can be reduced after entering the cells and release the antisense
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
oligonucleotide to hybridize with complementary target.
NHFmoc
NHCO
i
ii
NH 2
iii
(AA)n
NHCO AA
Peptide
i. 20%piperidine/DMF ii. HOBt/HBTU/DIEA/AA iii. TFA/scavenger
Fig.1
Fmoc strategy of synthesizing peptide in solid phase
3. oligonucleotide synthesis
The method for the synthesis of oligonucleotide was standard phosphoramidite
chemistry and the block containing –S-S- functional group was coupled during the
last step of the synthesis. After the –S-S- of ODN (I) was reduced with DTT, the
mixture was purified by HPLC, and the oligonucleotide containing free –SH reacted
with dithiodipyridine to form oligonucleotide (II) with the terminal sulfhlydral group.
In order to investigate the penetrating activity of the designed conjugate, we also
synthesized the 3’-FITC-5’-S-S-ODN (III). The 3’-amino compound (II) could react
with fluorescence isothiocyanate(FITC) to produce 3’-FITC-5’-S-S-ODN (III). The
resultant product was conjugated with the peptide to produce the fluorescence-labeled
conjugate (IV). (Fig.2, Fig.3)
B NCH2CH2CO
DMTO
O
P
O
O
n
O
H O
C
FmocHN
O
O
C
O
FmocHN
I\OCH2CH2CN
DMTO(CH2)6SS(CH2)6O P
N(iPr)2
OCH2CH2CN B NCH CH CO
2
2
DMTO(CH2)6SS(CH2)6O P
O
O
P
O
O
n
O
O
FmocHN
B
OH
DMTO(CH2)6SS(CH2)6O
P
C
HO
O
O
P
n
O
O
NH2
O
OH
i) DTT
(I)
ii)
SS
N
N
B
OH
SS(CH2)6O
P
O
O
P
O
O
N
OH
NH2
O
(I(II)I)
n
OH
Fig.2 the synthesis of 3’-amido-5’-sulfhydryl-ODN
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
4.peptide synthesis
PAL resin was used as the solid carrier and Fmoc method was adopted during the
synthesis of peptide. The condensation reaction was carried out using the rapid in situ
neutralization method. All the protected amino acids used in the experiment were
Fmoc-Arg(pbf)COOH, Fmoc-Gln(Trt)COOH, Fmoc-D-Arg-(Pbf)COOH, FmocLys(Boc)COOH, Fmoc-Cys(Trt)COOH. A Cys was introduced at the end of the C-end
of peptide, the –SH of Cys could be linked with the –SH of the ODN, and the peptide
N
B
OH
SS(CH2)6O
P
HO
O
O
P
n
O
O
NH2
O
OH
OH
S
C
N
(II)
O
HOOC
OH
O
N
B
OH
SS(CH2)6O
P
HO
O
O
P
O
n
O
O
NHCSNH
O
HOOC
OH
( III )
O
Peptide
SH
OH
B
OH
HO
Peptide
SS(CH2)6O
P
O
O
O
P
NHCSNH
O
O
n
O
HOOC
OH
(IV)
O
was cleaved from the resin, meanwhile the peptide was deprotected (Fig.1).
Fig.3 the synthesis of 3’-FITC-5’- sulfhydryl –ODN
The synthesis of arginine-rich peptide:
The peptide assembly was performed in a home-made manual synthesizer. (Fig.4
shows the home-made manual synthesizer). This special reactor was made from 5ml
PVC injector. 2.5 mole equivalent of amino acid was added into DMF containing 2.5
Mole equivalent of HBTU/HOBt, the amino acid was activated for 2 minutes after
DIEA was added, then the activated amino acid was added into the reactor, the
solution was collected to stay at room temperature for an hour. A little resin was
sampled to detect if the reaction was completed by ninhydrin test. If the ninhydrin test
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
was negative, the resin was washed with DMF, and Ac2O:DIEA:DMF(1:1:2) were
used to cap the unreacted residual amino group. DMF containing 20% piperidine was
used to deprotect the Fmoc, and the next amino acid was linked. After the last amino
acid was linked, DMF containing 20% piperidine was used to deprotect the Fmoc,
then DMF, DCM were used to wash the resin, and the resin was dried in vacuo for the
next step.
To find a method which is suitable for the cleavage and the deprotection of the
arginine-rich peptide, we explored two prescriptions for the procedure according to
some reference [11].
Prescription1: TFA:H2O: phenol:TIS:EDT:anisole (88:4:2:2:2:2) (reagent A)
Prescription2:
TFA:H2O: phenol: thioanisole :EDT (82.5:5:5:5:2.5)
(reagent B)
The link tube
Liquid can go into the hole,
but it can’t be out without
another injector’s drawing
Fig4.1
This special column
is the new cap.
Fig4.2
The special reactor
The amount of the reagent A or B was 150 μl/10mg resin, and the time of the
reaction was 10 hours. 1 ml water was used to quash the reaction, the aqueous phase
was washed 3 times by cold t-BuOMe, and the organic phase was separated carefully.
The aqueous phase was concentrated and purified by HPLC on a Delat PAK C18
column, (100Å, 7.8×300mm). Samples were monitored at UV 225 nm. The purified
peptides were lyophilized and kept in -20℃. When the cleavage was carried out by
reagent A, there was a peak of an impurity, and its molecule weight was that of MW
(peptide) + EDT(shown by MAIDI-TOF MS ). So we chose reagent B. Fig. 5 shows
the results.
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
1
2
11
3
4
Fig.5 semi-preparative HPLC chart of the arginine-rich peptide (the amount of the injection is
1.5 ml, Delta PAK) 1,2,3,4 are respectively the semi- preparative HPLC charts of R6C, R9C,
D-R9C, TAT; See the condition of HPLC at the experiment section.
The four sequences of the peptide (R6C, R9C, D-R9C, TAT) were designed,
synthesized and purified by the HPLC using the methods mentioned above. The result
of the MALDI-TOF MS showed that the molecule weights of the designed peptides
were in accordance to their theoretical molecule weights. The amino acid analysis of
TAT derived peptide showed that Arg:Lys:Gln:Cys=6.1:2.0:1.2:0.7 (the theoretical
result is 6:2:1:1).
5.on-resin fragment coupling of arginine-rich peptide and oligonucleotide
In order to link the peptide with ODN by the disulfide bond, we must modify the
oligonucleotide by introducing –SH group. The syntheses of oligonucleotide
containing –SH group and fluorescence-labeled peptide-oligonucleotide are shown in
Fig.2&3. The solid support used in the syntheses was CPG and the di-functional
oligonucleotide was synthesized by the standard phosphoramidite method.
C6SSC6ODMT was introduced by the standard method at the last step. The efficiency
of each single step was above 95%.
Astriab-Fisher and his partners [12] used 3’-end labeled and 5’-end –SH
activated ODN to react with the 3 time TAT derived peptide in 0.3M KBr, 0.002M
K2HPO4 (pH7.5), 5M CO(NH2) 2, and separated the product with ion-exchange
column, they got the fluorescence-labeled peptide-oligonucleotide conjugate
NH2RKKRRQRRRPPQC(COOH)-SS-5`- TCCCGACCTCGCGCTCC-3`-TAMAR.
Vives studied the synthesis of the basic-peptide oligonucleotide conjugate by
fragment condensation. In order to solve the problem of precipitation during the
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
synthesis, the author dissolved the fluorescence-labeled conjugate into H2O
containing KCl and CH3CN, and the final concentration of KCl was 0.4M, the
concentration of CH3CN was 40%(v/v). [13] After the reaction, the product was
separated and purified by DEAE ion-exchange HPLC column, and the desired
molecule was obtained. Wei and his partners [14] synthesized the conjugate of 9 mer
ODN and poly arginine R7, and the conjugate of R7 and two pieces of 9 mer ODN
(linked by -S-S-); the reaction was performed in 0.1M NaHCO3 solution, and the yield
was 50%. Recently, it was reported that the synthesis of the conjugate of R7 and 18
mer ODN linked by hydrazone, the reaction was performed in the citric acid buffer
solution (pH5.3), the time of the reaction was 20 hours, and the purification yield was
47%.
When we synthesized the conjugate, we tried all of the methods mentioned above;
however, we didn’t get the desired conjugate because of the problem of the
precipitation formed by oligonucleotide and poly arginine during the reaction. The
increase of the concentration of CH3CN and the salt did not prevent the occurrence of
the precipitation. The precipitation couldn’t dissolve in H2O, DMF, and the mixture of
H2O and CH3CN. Considering the strong electrostatic interaction between one peptide
molecule with two or even more oligonucleotides, Fmoc-Tat-C-SH or Fmoc-R9-C-SH
reacted with the 5’-end activated antisense oligonucleotide. We got the desired
molecule in 0.4M KCl, 40% CH3CN solution. The peptide-oligonucleotide conjugate
was purified by the HPLC, ESI-TOF MS showed the detected molecule weight was
identical with the theoretical value.
Table.1 the molecule weight of the conjugate of ODN and
Fmoc protected peptide
Compounds
Theoretical
Molecule
Detected
weight
weight
Fmoc-Tat-C-SH
1662.78
1665.20
Fmoc-R9-C-SH
1747.20
1746.85
Fmoc-Tat-C-SS-ODN
7917.78
7896.93
Fmoc-R9-C-SS-ODN
8002.20
7989.79
Molecule
The sequence of the ODN is CTCAGTTAGGGTTAGACAA.
i
SS
N
oligonucleotide
ii
S
CTC AGT TAG GGT TAG ACA A
S
PEPTIDE
i) PEPTIDE-SH,buffer,pH7.0
ii) 1M NaCl
Fig.6 The synthesis of the conjugate
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
Fig.7 the results of the fragment condensation reaction (anion-exchange HPLC,
SOURCETM)
Left: D-R9C reacted with the ODN on the solid support for 2 hours, the later peak was
the original ODN’s, the earlier one was the conjugate’s. Right: D-R9C reacted with the
ODN on the solid support for 8 hours, and the peak of the original ODN was small
The interaction between arginine and oligonucleotide in solution can be avoided
if the solid phase stepwise synthesis is adopted. Although some scientists have tried to
synthesize this kind of conjugate by the traditional solid phase synthesis, only a low
yield was obtained and the product was complicated because of the incompatibility of
the protecting group. We tried to absorb the oligonucleotide to the weak anion
exchange resin, so part of negative charges on the ODN could be offset. The
anion-exchange resin absorbing oligonucleotide was used for the synthesis of the
conjugate of oligonucleotide and rich-arginine peptide. (Fig 6)
An aliquot of purified oligonucleotide with pyridine sulfenyl-activated thiol
function (10 OD) was dissolved in water ,then the solution was absorbed on 0.5ml of
anion-exchange resin (SOURCE,AMERSHAM PHARMACIA) contained in a
column (diameter 4mm). Before addition of the peptide, the availability of the
cysteine residue sulfhydryl group was determined by its absorbance at 412nm after
reaction with 2-4,dithio(bis)nitrobenzioc acid, and the column was flushed by
nitrogen. About threefold equivlent peptide dissolved in 20mM phosphate buffer
(pH7.0) was added to the column. Eight hours later, the column was washed with
water. The molecules absorbed on the resin was eluted out by 1M NaCl. The
collected solution is desalted through oligonucleotide purification cartridge(OPC) and
purified by HPLC using a DEAE column(column 8×100mm,resin: SOURCE)
with a linear gradient from 0-80% in 30min of 1M NaCl in water and recorded at
260nm. After desalting through OPC, the conjugate was dried in Speed-Vac(yield
50%). The conjugate is further identified by ESI-TOF MS [Table 2, three peptides are
used in the conjugation, these are: (D-Arg)9-Cys, (Arg)9-Cys, (Arg)6-Cys].
Table.2 the reservation time and the molecule weight of the conjugate condensed
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through the ON-RESIN
Substance
ODN
D-R9C-ODN
R9C-ODN
R6C-ODN
The reservation time of HPLC
33.5 min
28.27min
28.37min
29.51min
Theoretically
7782.06
7782.06
7313.50
Actually
7780.50
7780.00
7311.00
Molecule
weight
6.transmembrane activity of peptide conjugated oligonucleotide
We investigated the transmembrane activity of arginine-rich peptide conjugated
oligonucleotide targeting to telomerase mRNA in HepG2 cells. The fluorescence
could be found in HepG2 cells under confocal microscope after incubation of the
labeled antisense oligonucleotide conjugate (IV) with HepG2 cells for 5hr. (Fig 8)
Further investigation is to be continued.
EXPERIMENT AND METHODS
(I)
General method
1. The treatment of the solvent, raw material and the reagent
All the solvent, raw material and reagent are analytical or chemical purity. CH3CN
and MeOH, used as the mobile phase of the HPLC, were of HPLC grade purity, the
water used was the re-distilled water, and the reagent was treated by the normal
method.
2. Instrument and Method
GF254 silica gel, 200 and 300 mesh, was used for chromatographic column , and the
silica gel H was produced by Qingdao oceanic chemical factory; TLC was detected by
UV-detector at the wavelength of 254nm, MS was performed with FAB, MALDI－
TOF, ESI-TOF MS(VG － ZAB － HS, Bruker APEXTMII, Bruker Reflex3, and
Micromass ESI-MS-MS Q-TOF2). NMR was performed with Varian VXR-500, JEOL
AL300, Bruker Advance300. HPLC was performed with Gilson HPLC, and the
chromatographic columns are Delta PAKC18(7.8×300), Nucleosil C18(4.6×250).
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Fig. 8.1 Fluorescence micrographs of HpeG2 cells treated with R9Coligonucleotide-FITC conjugate
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
Fig. 8.2
Control (without conjugate)
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Series of Selected Papers from Chun-Tsung Scholars,Peking University (2002)
3. The method of the HPLC purification and analysis
Purification of the peptide:
Chromatographic column: Delta PAK C18, 7.8×300mm, 100Å.
The HPLC gradient: 0-80%B/0-30min, pump A was 0.08% TFA/H2O, pump B was
0.08% TFA/ CH3CN,
Flow: 3ml/min
Purification of the peptide-oligonucleotide conjugate: Delta-PAK C18column,
Waters,100Å,15 μ m,7.8 × 300mm, gradient elution, 0 － 40 ％ B/0-25min,
40-100%B/25-40min, the mobile phase in pump A was 0.1M TEAA, pH7.0, in pump
B was CH3CN, and the flow rate was 3ml/min.
Analysis of the peptide-oligonucleotide conjugate: Nucleosil C18 column,
Phenomenex,100Å,10μm,4.6×250mm, the gradient was 0－40％B/0-25min,
40-100%B/25-40min, the mobile phase in pump A was 20mM TEAA, in pump B wa
50% CH3CN, and the flow was 1ml/min.
Purification of the oligonucleotide: DEAE anion-exchange column 6×100 mm，the
solid phase was the SOURCE made by Pharmacia Company, the gradient was 0－
80%B/0-40 min, mobile phase A was 20mM phosphate buffer solution, pH 7.0,
mobile phase B was 20mM phosphate buffer solution (pH 7.0) containing 2M NaCl.
(II)
synthesis of arginine-rich peptide conjugated oligonucleotide
The fragment condensation method of the conjugate of the peptide and the
antisense oligonucleotide:
1. The synthesis of the peptide
PAL resin (0.11mmol/g) and Fmoc-L-amino acids were purchased from
Advanced Chemtech. Rapid in situ neutralization protocols based on
Fmoc/HBTU/HOBt/DIPEA chemistry were used in the peptide synthesis. The Fmoc
amino acid derivatives were: Fmoc-L-Arg(Pbf), Fmoc-D-Arg(Pbf), Fmoc-Cys(Trt).
The peptide synthesis was carried out in a home-made manual synthesizer.
Fmoc-amino acid were used in 2.5 mol equiv and activated with 2.5 mol equiv of
HOBt, 2.5 mol equiv of HBTU and 3 mol equiv of DIPEA in DMF for 3 min,
followed by a 1 hr coupling. Fmoc deprotection was performed in 20% piperidine in
DMF. Cleavage and side chain deprotection involved treating the peptide with a
mixture containing 82.5%TFA, 5% thioanisole, 5% phenol, 5% water and 2.5%
ethylene disulfhydrate overnight at room temperature under shaking. After the solid
support was filtered, cold methyl t-butyl ether was added to the filtrate. The
precipitated peptide was purified by HPLC, which was carried out using a Waters
column (7.8×300mm). Samples were monitored at 225nm .The gradient was 0-80%
B in 30 min. Mobile phase A was 0.1% TFA in water and mobile phase B was 0.1%
TFA in acetonitrile. The purified peptides were lyophilized and kept in -20℃.
The synthesis of the oligonucleotide:
The synthesis of the 5’-SH oligonucleotide: The phosporothioate
oligonucleotide 5`-ACT CAC TCA GGC CTC AGA CT-3`-DMT tagerting to the
RNA template of the telomerase was synthesized with the Expedite 8909 DNA
synthesizer by the standard phosporamidite chemistry. After the last DMT was
cleaved and deprotected, phosporamidite of DMT-protected bis-(6-hydroxyhexyl
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disufide) was linked. The oxidizing agent in the reaction was 0.02M I2. When the
synthesis is over, the solid supporter was filtered and the filtrate was dry in Vac Speed.
The dried residue was applied to HPLC. The collected portion of purified
oligonucleotide was concentrated and dried in vacuo. The dry powder of
oligonucleotide was kept at the temperature of -20℃ for the next step.
The synthesis of the 3`-amino-5`-sulfhydryl-oligonucleotide: The amino CPG
was used as the solid support and the antisense oligonucleotide (5`-ACT CAC TCA
GGC CTC AGA CT-3`) targeting to the RNA of the telomerase was synthesized with
the Expedite 8909 DNA synthesizer by the standard phosporamidite chemistry. After
the last DMT was cleaved, the phosporamidite of DMT-protected bis-(6-hydroxyhexyl)
disufide was coupled using Becaurage thiolating reagent. When the synthesis was
over, the solid supporter was filtered and the filtrate was concentrated in Vac Speed.
The dried residue was applied to HPLC. The collected portion of purified
oligonucleotide was concentrated and dried in vacuo. The dry powder of
oligonucleotide was kept at the temperature of -20℃ for the next step.
The activation of the terminal –SH: Either 5’-sulfhydryl oligonucleotide or
3’-amino-5’- sulfhydryl oligonucleotide (20OD) was used and dissolved in 0.5ml
0.2M pH8.4 phosphate buffer, then the suitable amount of DTT is added and the final
concentration was 0.2M, and reacted 30 min at the room temperature under the
protection of Ar. The reaction mixture was purified by the HPLC, the intended
fraction was collected in a test tube containing 2ml CH3CN/ phosphate (20%,v/v)
buffer solution (pH5.5) of 2mg dithiodipyridine, and reacted for 24 hours at the room
temperature under the protection of Ar. Then the mixture was concentrated, filtrated to
remove the precipitation and purified by the HPLC, and the resultant sulfhydrylactivated oligonucleotide was obtained.
The synthesis of 3’-FITC-5’- sulfhydryl-oligonucleotide: 8OD 3’-FITC-5’sulfhydryl-oligonucleotide was dissolved in the 50μl 2M CH3COONa/0.2M Na2CO3
pH9.3 buffer solution, and 25 mole equivalent of FITC (isomer I) was added. The
reaction was carried out for 5 hours at the temperature of 37 ℃, then 25 mole
equivalent FITC (isomer I) was added into the reactor and reacted for 24 hours at the
temperature of 37 ℃. 0.25 ml of cold anhydrous EtOH（-20℃）was added into the
reactor to precipitate the oligonucleotide. The FITC which did not react was washed
away through Sephadex G25 gel column(2×25cm), and the mobile phase was 5%
n-BuOH in H2O. Then the resultant product was purified by the reverse phase HPLC,
and preserved in refrigerator for the next step.
The synthesis of 5’-peptide-antisense oligonucleotide: (See the synthesis of
the 3’-FITC-5’-peptide-antisense oligonucleotide)
The synthesis of the 3’-FITC-5’-peptide-antisense oligonucleotide: 10OD
3’-FITC-5’- sulfhydryl-oligonucleotide was absorbed to 0.5ml of anion-exchange
resin (SOURCE, AMERSHAM PHARMACIA), and the gel was washed by the
deionized water. 10 mole of terminal- sulfhydryl –activated peptide dissolved in the
1ml 0.1M phosphate buffer solution (pH5.5) was added into the gel, and the mixture
reacted for 8 hours under the protection of Ar. The gel was washed by deionized water,
and the oligonucleotide was eluted by 1M NaCl, then it was desalted through OPC
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column, concentrated, and purified by the HPLC.
(III) investigation on the transmembrane activity of conjugate(IV in Fig.3)
HepG2 cells were seeded in 96-well culture plate at concentration of 5000
cells/well (40-50%) confluence. After overnight culture in DMEM containing 10%
fetal bovine serum, 100 units/ml penicillin G sodium and 100 g/ml streptomycin
sulfate, the complete medium was removed and the cells was washed by DMEM
without antibiotics. Fluorescence-labelled conjugate was dissolved in DMEM, the
final concentrations was 1M, then added to the well. After 5hr incubation at 37℃
in a humiddified 5% CO2 incubator, the plain medium was removed. The cells were
washed with PBS(phosphate buffered saline)and the cells were applied to confocal
fluorescence microscope with blank as control.
Acknowledgement:
This work was supported by Chun-Tsung fund which is sponsored by a Nobel prize laureate
Tsung Dao Li and Mrs. Li, by National Natural Science Foundation of China and by National
Key Project for Basic Research (G1998051103) awarded by The Ministry of Science and
Technology, People’s Republic of China.
Reference:
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[3] Vives E., Lebleu B. Selective coupling of a highly basic peptide to an oligonucleotide,
Tetrahedron Lett., 1997, 38, 1183-1186.
[4] Wei Z,Tung CH,Zhu T,Stein S,Synthesis of oligoarginine-oligonucleotide conjugates and
oligoarginine-bridged oligonucleotide pairs,Bioconjugate Chem,1994,5,468-474
[5] Wang Sheng Qi，Lin Li，Chen Zhong Fu，Lin Ru Xian，Chen Su Hong，Guan Wei，Wang
Xiao Hong. The evaluation of the invitro anticancer activity of the oligonucleotide targeting at the
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作者简介：鹏越峰，男，满族，1980年出生于黑龙江省哈尔滨市，1999年考入北
京大学化学与分子工程学院，并参加北大理科试验班的学习，学习成绩优秀，曾
获IET奖学金和理科试验班雏鹰奖学金。2001年5月受到“ 政基金”资助，从师
张礼和院士进行科研。
感悟和寄语：在从事“ 政”科研工作那难忘的 1800 多个小时里，我认为最大
的收获并不是我最后所取得的成果，而是我从中领悟到的科学研究的真谛，即在
一次次的失败中成长。我很喜欢一句话——我们追求成功，并为之而努力奋斗；
但当我们最后取得我们所期望的成功时，我们才发现其实最大的幸福并不是最终
的成功，而是我们为之奋斗过程中的点点滴滴。张老师对科研尽善尽美，兢兢业
业的精神令我无比钦佩，他向我展示了科学家的人格魅力。在从事“ 政”科研
的道路上，我不仅受到张老师的指引，而且还更多地感受到的是科学家的思想和
科学家的品德。“ 政”使我能够有机会与著名的科学家一同探索科学，导师那
治学严谨的科研作风更是令我受益终生。
指导教师简介：张礼和，男，汉族，1937 年 9 月出生于江苏省扬州市，1958 年
毕业于北京医学院药学系，有机药物化学家、教授、博士研究生导师，1995 年
当选为中国科学院院士。现任北京大学医学部药学学院院长，天然药物及仿生药
物国家重点实验室主任，长期从事核酸化学及抗肿瘤抗病毒药物研究，并取得丰
硕研究成果。
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