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Trojan A, Lone YC, Briceno I, Trojan J. Anti-Gene IGF-I Vaccines in Cancer Gene Therapy: A Review of a Case of Glioblastoma. Curr Med Chem 2024; 31:1983-2002. [PMID: 38031775 DOI: 10.2174/0109298673237968231106095141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 06/27/2023] [Accepted: 10/10/2023] [Indexed: 12/01/2023]
Abstract
OBJECTIVE Vaccines for the deadliest brain tumor - glioblastoma (GBM) - are generally based on targeting growth factors or their receptors, often using antibodies. The vaccines described in the review were prepared to suppress the principal cancer growth factor - IGF-I, using anti-gene approaches either of antisense (AS) or of triple helix (TH) type. Our objective was to increase the median survival of patients treated with AS and TH cell vaccines. METHODOLOGY The cells were transfected in vitro by both constructed IGF-I AS and IGF-I TH expression episomal vectors; part of these cells was co-cultured with plant phytochemicals, modulating IGF-I expression. Both AS and TH approaches completely suppressed IGF-I expression and induced MHC-1 / B7 immunogenicity related to the IGF-I receptor signal. RESULTS This immunogenicity proved to be stronger in IGF-I TH than in IGF-I AS-prepared cell vaccines, especially in TH / phytochemical cells. The AS and TH vaccines generated an important TCD8+ and TCD8+CD11b- immune response in treated GBM patients and increased the median survival of patients up to 17-18 months, particularly using TH vaccines; in some cases, 2- and 3-year survival was reported. These clinical results were compared with those obtained in therapies targeting other growth factors. CONCLUSION The anti-gene IGF-I vaccines continue to be applied in current GBM personalized medicine. Technical improvements in the preparation of AS and TH vaccines to increase MHC-1 and B7 immunogenicity have, in parallel, allowed to increase in the median survival of patients.
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Affiliation(s)
- Annabelle Trojan
- INSERM UMR 1197, Cancer Center & University of Paris / Saclay, PO Box: 94802 Villejuif, France
- Faculty of Medicine, University of Cartagena, PO Box: 130014 Cartagena de Indias, Colombia
| | - Yu-Chun Lone
- INSERM UMR 1197, Cancer Center & University of Paris / Saclay, PO Box: 94802 Villejuif, France
- CEDEA / ICGT - Center of Oncological Diseases Diagnosis, PO Box: 110231 Bogota, Colombia
| | - Ignacio Briceno
- Faculty of Medicine, University of La Sabana, PO Box: 250008 Chia, Colombia
| | - Jerzy Trojan
- INSERM UMR 1197, Cancer Center & University of Paris / Saclay, PO Box: 94802 Villejuif, France
- CEDEA / ICGT - Center of Oncological Diseases Diagnosis, PO Box: 110231 Bogota, Colombia
- National Academy of Medicine - ANM, PO Box: 75272 Paris, France
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Szabat M, Kierzek E, Kierzek R. Modified RNA triplexes: Thermodynamics, structure and biological potential. Sci Rep 2018; 8:13023. [PMID: 30158667 PMCID: PMC6115336 DOI: 10.1038/s41598-018-31387-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 08/17/2018] [Indexed: 12/23/2022] Open
Abstract
The occurrence of triplexes in vivo has been well documented and is determined by the presence of long homopurine-homopyrimidine tracts. The formation of these structures is the result of conformational changes that occur in the duplex, which allow the binding of a third strand within the major groove of the helix. Formation of these noncanonical forms by introducing synthetic triplex-forming oligonucleotides (TFOs) into the cell may have applications in molecular biology, diagnostics and therapy. This study focused on the formation of RNA triplexes as well as their thermal stability and biological potential in the HeLa cell line. Thermodynamics studies revealed that the incorporation of multiple locked nucleic acid (LNA) and 2-thiouridine (2-thioU) residues increased the stability of RNA triplexes. These data suggest that the number and position of the modified nucleotides within TFOs significantly stabilize the formed structures. Moreover, specificity of the interactions between the modified TFOs and the RNA hairpin was characterized using electrophoretic mobility-shift assay (EMSA), and triplex dissociation constants have been also determined. Finally, through quantitative analysis of GFP expression, the triplex structures were shown to regulate GFP gene silencing. Together, our data provide a first glimpse into the thermodynamic, structural and biological properties of LNA- and 2-thioU modified RNA triplexes.
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Affiliation(s)
- Marta Szabat
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland
| | - Elzbieta Kierzek
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland
| | - Ryszard Kierzek
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland.
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Unlocked nucleic acids: implications of increased conformational flexibility for RNA/DNA triplex formation. Biochem J 2015; 464:203-11. [PMID: 25226286 DOI: 10.1042/bj20141023] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Unlocked nucleic acids (UNAs) have been introduced at specific positions in short model DNA hairpins and RNA/DNA triplexes for the first time. UNA residues destabilize the hairpins and decrease triplex thermodynamic stability or suppress triplex formation for most of the evaluated structures. Nevertheless, the incorporation of UNA residues at certain positions of dsDNA was found to be energetically favourable or at least did not affect triplex stability. Notably, the most thermodynamically stable UNA-modified triplexes exhibited improved stability at both acidic and physiological pH. The specificity of the interactions between the triplex-forming oligonucleotide and dsDNA was characterized using EMSA for the most thermodynamically stable structures, and triplex dissociation constants were determined. One of the modified triplexes exhibited an improved Kd in comparison with the unmodified triplex. CD and thermal difference spectra indicated that UNA residues do not alter the overall structure of the most thermodynamically stable triplexes. In addition, incubation of the modified oligonucleotides with human serum indicated that the UNAs demonstrate the potential to improve the biological stability of nucleic acids.
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Jakobsen U, Vogel S. Assembly of liposomes controlled by triple helix formation. Bioconjug Chem 2013; 24:1485-95. [PMID: 23885785 DOI: 10.1021/bc300690m] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Attachment of DNA to the surface of different solid nanoparticles (e.g., gold and silica nanoparticles) is well established, and a number of DNA-modified solid nanoparticle systems have been applied to thermal denaturation analysis of oligonucleotides. We report herein the noncovalent immobilization of oligonucleotides on the surface of soft nanoparticles (i.e., liposomes) and the subsequent controlled assembly by DNA triple helix formation. The noncovalent approach avoids tedious surface chemistry and necessary purification procedures and can simplify and extend the available methodology for the otherwise difficult thermal denaturation analysis of complex triple helical DNA assemblies. The approach is based on lipid modified triplex forming oligonucleotides (TFOs) which control the assembly of liposomes in solution in the presence of single- or double-stranded DNA targets. The thermal denaturation analysis is monitored by ultraviolet spectroscopy at submicromolar concentrations and compared to regular thermal denaturation assays in the absence of liposomes. We report on triplex forming oligonucleotides (TFOs) based on DNA and locked nucleic acid (LNA)/DNA hybrid building blocks and different target sequences (G or C-rich) to explore the applicability of the method for different triple helical assembly modes. We demonstrate advantages and limitations of the approach and show the reversible and reproducible formation of liposome aggregates during thermal denaturation cycles. Nanoparticle tracking analysis (NTA) and dynamic light scattering (DLS) show independently from ultraviolet spectroscopy experiments the formation of liposome aggregates.
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Affiliation(s)
- Ulla Jakobsen
- Nucleic Acid Center, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark , Campusvej 55, 5230 Odense M, Denmark
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5
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Rossetti L, D'Isa G, Mauriello C, Varra M, De Santis P, Mayol L, Savino M. A model for triple helix formation on human telomerase reverse transcriptase (hTERT) promoter and stabilization by specific interactions with the water soluble perylene derivative, DAPER. Biophys Chem 2007; 129:70-81. [PMID: 17560709 DOI: 10.1016/j.bpc.2007.05.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 05/14/2007] [Accepted: 05/14/2007] [Indexed: 01/07/2023]
Abstract
The promoter of human telomerase reverse transcriptase (hTERT) gene, in the region from -1000 to +1, contains two homopurine-homopyrimidine sequences (-835/-814 and -108/-90), that can be considered as potential targets to triple helix forming oligonucleotides (TFOs) for applying antigene strategy. We have chosen the sequence (-108/-90) on the basis of its unfavorable chromatin organization, evaluated by theoretical nucleosome positioning and nuclease hypersensitive sites mapping. On this sequence, anti-parallel triplex with satisfactory thermodynamic stability is formed by two TFOs, having different lengths. Triplex stability is significantly increased by specific interactions with the perylene derivative N,N'-bis[3,3'-(dimethylamino) propylamine]-3,4,9,10-perylenetetracarboxylic diimide (DAPER). Since DAPER is a symmetric molecule, the induced Circular Dichroism (CD) spectra in the range 400-600 nm allows us to obtain information on drug binding to triplex and duplex DNA. The drug-induced ellipticity is significantly higher in the case of triplex with respect to duplex and, surprisingly, it increases at decreasing of DNA. A model is proposed where self-stacked DAPER binds to triplex or to duplex narrow grooves.
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Affiliation(s)
- Luigi Rossetti
- Dipartimento di Genetica e Biologia Molecolare, Università di Roma La Sapienza, Piazzale Aldo Moro, 5, c.a.p. 00185, Roma, Italy
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6
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Insulin-like growth factor type I biology and targeting in malignant gliomas. Neuroscience 2007; 145:795-811. [DOI: 10.1016/j.neuroscience.2007.01.021] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Revised: 01/04/2007] [Accepted: 01/05/2007] [Indexed: 11/20/2022]
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Rathinavelan T, Yathindra N. Base triplet nonisomorphism strongly influences DNA triplex conformation: Effect of nonisomorphic G∗︁ GC and A∗︁ AT triplets and bending of DNA triplexes. Biopolymers 2006; 82:443-61. [PMID: 16493655 DOI: 10.1002/bip.20484] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Structural understanding of DNA triplexes is grossly inadequate despite their efficacy as therapeutic agents. Lack of structural similarity (isomorphism) of base triplets that figure in different DNA triplexes brings in an added complexity. Recently, we have shown that the residual twist (Deltat degrees ) and the radial difference (Deltar A) adequately define base triplet nonisomorphism in structural terms and allow assessment of their role in conferring stability as well as sequence-dependent structural variations in DNA triplexes. To further corroborate these, molecular dynamics (MD) simulations are carried out on DNA triplexes comprising nonisomorphic G* GC and A* AT base triplets under different sequential contexts. Base triplet nonisomorphism between G* GC and A* AT triplets is dominated by Deltat degrees (9.8 degrees ), in view of small Deltar (0.2 A), and is in contrast to G* GC and T* AT triplets where both Deltat degrees (10.6 degrees ) and Deltar (1.1A) are prominent. Results show that Deltat degrees alone enforces mechanistic influence on the triplex-forming purine strand so as to favor a zigzag conformation with alternating conformational features that include high (40 degrees ) and low (20 degrees ) helical twists, and high anti(G) and anti(A) glycosyl conformation. Higher thermal stability of this triplex compared to that formed with G* GC and T* AT triplets can be traced to enhanced base-stacking and counterion interactions. Surprisingly, it is found for the first time that the presence of a nonisomorphic G* GC or A* AT base triplet interrupting an otherwise mini A* AT or G* GC isomorphic triplex can induce a bend/curvature in a DNA triplex. These observations should prove useful in the design of triplex-forming oligonucleotides and in the understanding the binding affinities of this triplex with proteins.
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Affiliation(s)
- T Rathinavelan
- Department of Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai-600 025, India
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Cogoi S, Quadrifoglio F, Xodo LE. G-rich oligonucleotide inhibits the binding of a nuclear protein to the Ki-ras promoter and strongly reduces cell growth in human carcinoma pancreatic cells. Biochemistry 2004; 43:2512-23. [PMID: 14992588 DOI: 10.1021/bi035754f] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Oligonucleotides are able to recognize both nucleic acids and proteins with a high degree of specificity and are therefore investigated as a new and innovative class of therapeutic anticancer drugs. In the present study, we have constructed from Panc-1 cells a stable transfectant (AG transfectant) generating constitutively a short transcript (T-22AG), which is potentially capable of forming a triplex with a critical polypurine/polypyrimidine (pur/pyr) motif located in the Ki-ras promoter. Because of the presence of a G-rich element in its sequence, transcript T-22AG was also capable, under physiological conditions, of adopting a tetraplex conformation. We found that the levels of Ki-ras mRNA and p21(RAS) protein in the AG transfectant were, respectively, 52 +/- 8 and 40 +/- 4% of those observed in the control cell lines: untransfected Panc-1 cells and stably transfected Panc-1 cells producing a control transcript (T-22SCR). The downregulation of Ki-ras resulted in a strong reduction of colony formation (42 +/- 7% of the control) and cell proliferation (34 +/- 5% of the control) capacity. As in vitro experiments showed that the G-rich element of T-22AG (22AG) formed with the Ki-ras pur/pyr motif a triplex of low thermodynamic stability, it is unlikely that the strong bioactivity exhibited by transcript T-22AG is mediated by a triplex-based mechanism, although we cannot totally exclude that in vivo polyamine levels may increase the triplex stability. We found that 22AG adopted a tetraplex conformation and competitively inhibited the binding of a nuclear factor to the Ki-ras pur/pyr sequence. This effect was specific and virtually entirely abrogated when 22AG was denatured by heating. Our data showed that transcript T-22AG acted as a molecular aptamer, binding specifically to a nuclear factor essential for Ki-ras expression. The biological implications of this study are discussed.
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Affiliation(s)
- Susanna Cogoi
- Department of Biomedical Science and Technology, School of Medicine, University of Udine, Piazzale Kolbe, 4, 33100 Udine, Italy
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Carbone GM, McGuffie E, Napoli S, Flanagan CE, Dembech C, Negri U, Arcamone F, Capobianco ML, Catapano CV. DNA binding and antigene activity of a daunomycin-conjugated triplex-forming oligonucleotide targeting the P2 promoter of the human c-myc gene. Nucleic Acids Res 2004; 32:2396-410. [PMID: 15121897 PMCID: PMC419437 DOI: 10.1093/nar/gkh527] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Triplex-forming oligonucleotides (TFO) that bind DNA in a sequence-specific manner might be used as selective repressors of gene expression and gene-targeted therapeutics. However, many factors, including instability of triple helical complexes in cells, limit the efficacy of this approach. In the present study, we tested whether covalent linkage of a TFO to daunomycin, which is a potent DNA-intercalating agent and anticancer drug, could increase stability of the triple helix and activity of the oligonucleotide in cells. The 11mer daunomycin-conjugated GT (dauno-GT11) TFO targeted a sequence upstream of the P2 promoter, a site known to be critical for transcription of the c-myc gene. Band-shift assays showed that the dauno-GT11 formed triplex DNA with enhanced stability compared to the unmodified TFO. Band shift and footprinting experiments demonstrated that binding of dauno-GT11 was highly sequence-specific with exclusive binding to the 11 bp target site in the c-myc promoter. The daunomycin-conjugated TFO inhibited transcription in vitro and reduced c-myc promoter activity in prostate and breast cancer cells. The daunomycin-conjugated TFO was taken up by cells with a distinctive intracellular distribution compared to free daunomycin. However, cationic lipid-mediated delivery was required for enhanced cellular uptake, nuclear localization and biological activity of the TFO in cells. Dauno-GT11 reduced transcription of the endogenous c-myc gene in cells, but did not affect expression of non-target genes, such as ets-1 and ets-2, which contained very similar target sequences in their promoters. Daunomycin-conjugated control oligonucleotides unable to form triplex DNA with the target sequence did not have any effect in these assays, indicating that daunomycin was not directly responsible for the activity of daunomycin-conjugated TFO. Thus, attachment of daunomycin resulted in increased triplex stability and biological activity of the 11mer GT-rich TFO without compromising its specificity. These results encourage further testing of this approach to develop novel antigene therapeutics.
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Affiliation(s)
- Giuseppina M Carbone
- Laboratory of Experimental Oncology, Oncology Institute of Southern Switzerland, Bellinzona, Via Vela 6, 6500 Bellinzona, Switzerland
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10
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Ly A, Duc HT, Kalamarides M, Trojan LA, Pan Y, Shevelev A, François JC, Noël T, Kane A, Henin D, Anthony DD, Trojan J. Human glioma cells transformed by IGF-I triple helix technology show immune and apoptotic characteristics determining cell selection for gene therapy of glioblastoma. Mol Pathol 2001; 54:230-9. [PMID: 11477137 PMCID: PMC1187073 DOI: 10.1136/mp.54.4.230] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AIMS Insulin-like growth factor type I (IGF-I) antisense cellular gene therapy of tumours is based on the following data: rat glioma or hepatoma cells transfected with the vector encoding IGF-I antisense cDNA lose their tumorigenicity and induce a tumour specific immune response involving CD8(+) T cells. Recently, using the IGF-I triple helix approach in studies of tumorigenicity, major histocompatibility complex class I (MHC-I) antigens were demonstrated in rat glioma transfected cells. This study used comparative IGF-I antisense and triple helix technologies in human primary glioma cells to determine the triple helix strategy that would be most appropriate for the treatment of glioblastoma. METHODS The cells were transfected using the IGF-I triple helix expression vector, pMT-AG, derived from the pMT-EP vector. pMT-AG contains a cassette comprising a 23 bp DNA fragment transcribing a third RNA strand, which forms a triple helix structure within a target region of the human IGF-I gene. Using pMT-EP, vectors encoding MHC-I or B7 antisense cDNA were also constructed. RESULTS IGF-I triple helix transfected glioma cells are characterised by immune and apoptotic phenomena that appear to be related. The expression of MHC-I and B7 in transfected cells (analysed by flow cytometry) was accompanied by programmed cell death (detected by dUTP fluorescein terminal transferase labelling of nicked DNA and electron microscopic techniques). Cotransfection of these cells with MHC-I and B7 antisense vectors suppressed the expression of MHC-I and B7, and was associated with a pronounced decrease in apoptosis. CONCLUSION When designing an IGF-I triple helix strategy for the treatment of human glioblastoma, the transfected tumour cells should have the following characteristics: the absence of IGF-I, the presence of both MHC-I and B7 molecules, and signs of apoptosis.
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Affiliation(s)
- A Ly
- Laboratory of Developmental Neurology, INSERM and University Paris VII, Hôpital Robert Debré, 75019 Paris, France
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Xodo LE, Rathinavelan T, Quadrifoglio F, Manzini G, Yathindra N. Targeting neighbouring poly(purine.pyrimidine) sequences located in the human bcr promoter by triplex-forming oligonucleotides. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:656-64. [PMID: 11168404 DOI: 10.1046/j.1432-1327.2001.01919.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Most poly(purine.pyrimidine) [poly(R.Y)] sequences in eukaryotic genomes are interrupted by one or more base pair inversions. When the inversions are centrally located, the poly(R.Y) sequences can be regarded as the sum of two abutting sites, each potentially capable of forming a triple helix. Employing band-shift, footprinting and modeling methods we examined the formation of triple helices at a critical 27 bp poly(R.Y) sequence interrupted by two adjacent CG inversions, and located in the promoter of the human bcr gene at transcription initiation. We designed several 13-mer and 14-mer triplex-forming oligonucleotides (TFOs) capable of binding the bcr abutting sites, thereby generating different base juxtapositions at the triple helical junction, to examine whether triplex formation occurs in a cooperative manner. It is found that in 50 mM Tris/HCl, pH 7.4, 10 mM MgCl2, 2 mM spermine, 37 degrees C, the 13-and the 14-mer TFOs bind to one half of the bcr site with Delta G between -30 and -35 kJ x mol-1. However, when different 13-mer/14-mer combinations of TFOs were directed against the abutting poly(R x Y) sites, triplex formation has been found to be enhanced only for the triple helical junction formed by the 5'-A-T-3' base juxtaposition, in keeping with a partial stacking suggested from modeling analysis. On the other hand, a longer 24-mer TFO, binding noncooperatively to the same abutting sites, forms a much more stable triplex (Delta G = -51 kJ x mol-1), notwithstanding the two T x CG triads in the middle. Modeling investigations reveal that there is no continuity or propagation of base stacking involving adjacent bases of the third strand at the site of base inversion as well as on the 5' side. The data indicate that the entropy penalty of forming a triplex with two oligonucleotides is much higher than the energy gained from base stacking interactions at the triplex junction formed between the two TFOs.
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Affiliation(s)
- L E Xodo
- Dipartimento di Scienze e Tecnologie Biomediche, Facoltà di Medicina, Università di Udine, Italia.
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Lin FL, Majumdar A, Klotz LC, Reszka AP, Neidle S, Seidman MM. Stability of DNA triplexes on shuttle vector plasmids in the replication pool in mammalian cells. J Biol Chem 2000; 275:39117-24. [PMID: 10993885 DOI: 10.1074/jbc.m005404200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Triple helix-forming oligonucleotides may be useful as gene-targeting reagents in vivo, for applications such as gene knockout. One important property of these complexes is their often remarkable stability, as demonstrated in solution and in cells following transfection. Although encouraging, these measurements do not necessarily report triplex stability in cellular compartments that support DNA functions such as replication and mutagenesis. We have devised a shuttle vector plasmid assay that reports the stability of triplexes on DNA that undergoes replication and mutagenesis. The assay is based on plasmids with novel variant supF tRNA genes containing embedded sequences for triplex formation and psoralen cross-linking. Triple helix-forming oligonucleotides were linked to psoralen and used to form triplexes on the plasmids. At various times after introduction into cells, the psoralen was activated by exposure to long wave ultraviolet light (UVA). After time for replication and mutagenesis, progeny plasmids were recovered and the frequency of plasmids with mutations in the supF gene determined. Site-specific mutagenesis by psoralen cross-links was dependent on precise placement of the psoralen by the triple helix-forming oligonucleotide at the time of UVA treatment. The results indicated that both pyrimidine and purine motif triplexes were much less stable on replicated DNA than on DNA in vitro or in total transfected DNA. Incubation of cells with amidoanthraquinone-based triplex stabilizing compounds enhanced the stability of the pyrimidine triplex.
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Affiliation(s)
- F L Lin
- Laboratory of Molecular Genetics, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, USA
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13
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Cogoi S, Suraci C, Del Terra E, Diviacco S, van der Marel G, van Boom J, Quadrifoglio F, Xodo L. Downregulation of c-Ki-ras promoter activity by triplex-forming oligonucleotides endogenously generated in human 293 cells. ANTISENSE & NUCLEIC ACID DRUG DEVELOPMENT 2000; 10:283-95. [PMID: 10984122 DOI: 10.1089/108729000421466] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Exogenous triplex-forming oligodeoxynucleotides (TFO) have the capacity to modulate in vivo the expression of individual genes. As the administration of TFO to cells is not without problems, we analyzed the possibility of generating them directly in the cell, using specific expression vectors. We constructed three vectors, mU6-GA, mU6-CA, and mU6-CT, that direct the synthesis in human 293 cells of 76-mer CU, GU, and AG motif TFO (rTFO) potentially capable of binding to a critical poly (R x Y) sequence contained in the promoter of the Ki-ras proto-oncogene. The ability of the CU, GU, and AG motif rTFO to interact with the double helix of the c-Ki-ras target was investigated in vitro by footprinting and band-shift experiments, using both synthetic and endogenously synthesized oligoribonucleotides. The human 293 cells were transfected with DNA mixtures containing a plasmid, which bears the reporter chloramphenicol acetyltransferase (CAT) gene downstream from the c-Ki-ras promoter (pKRS-413), as well as an rTFO-generating vector (mU6-GA, mU6-CA, or mU6-CT). As control, the cells were transfected with DNA mixtures containing vector mU6-C1 or mU6-C2. These generated transcripts unable to form triple helices with the poly (R x Y) sequence of the c-Ki-ras promoter. Intracellular synthesis of the 76-mer CU, GU, and AG rTFO by mU6-GA, mU6-CA, and mU6-CT was checked by Northern blot hybridization. Through beta-gal and CAT ELISA immunoassays, we found that the 293 cells transfected with either mU6-GA, mU6-CA, or mU6-CT showed a significant inhibition of CAT expression compared with cells transfected with control plasmids mU6-C1 or mU6-C2. The results of five separate transient transfection experiments showed that endogenous GU and AG rTFO, generated by mU6-CA and mU6-CT, produce, respectively, 40% (+/- 4% SE) and 47% (+/- 8% SE) CAT inhibition, whereas CU rTFO, generated by mU6-GA, produces 38% (+/- 7% SE) CAT inhibition. In conclusion, this study suggests that it is possible to downregulate the expression of an individual gene through the use of recombinant vectors encoding the information for the intracellular synthesis of short triplex-forming RNA strands.
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Affiliation(s)
- S Cogoi
- Department of Biomedical Sciences and Technologies, School of Medicine, Udine, Italy
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Upegui-Gonzalez LC, François JC, Ly A, Trojan J. The approach of triple helix formation in control of gene expression and the treatment of tumors expressing IGF-I. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2000; 465:319-32. [PMID: 10810636 DOI: 10.1007/0-306-46817-4_27] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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Arimondo PB, Moreau P, Boutorine A, Bailly C, Prudhomme M, Sun JS, Garestier T, Hélène C. Recognition and cleavage of DNA by rebeccamycin- or benzopyridoquinoxaline conjugated of triple helix-forming oligonucleotides. Bioorg Med Chem 2000; 8:777-84. [PMID: 10819166 DOI: 10.1016/s0968-0896(00)00012-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Indolocarbazole and benzopyridoquinoxaline derivatives have been shown to have anti-tumor activity and to stimulate DNA topoisomerase I-mediated cleavage. Two indolocarbazole compounds (R-6 and R-95) and one benzopyridoquinoxaline derivative (BPQ(1256)) were covalently attached to the 3'-end of a 16mer triple helix-forming oligonucleotide (TFO). These conjugates bind to DNA with a higher affinity than the unsubstituted oligonucleotides. Furthermore, they induce topoisomerase I-mediated and triplex-directed DNA cleavage in a sequence-specific manner.
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Affiliation(s)
- P B Arimondo
- Laboratoire de Biophysique, UMR 8646 CNRS-Muséum National d'Histoire Naturelle, INSERM U201, Paris, France
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Ritchie S, Boyd FM, Wong J, Bonham K. Transcription of the human c-Src promoter is dependent on Sp1, a novel pyrimidine binding factor SPy, and can be inhibited by triplex-forming oligonucleotides. J Biol Chem 2000; 275:847-54. [PMID: 10625617 DOI: 10.1074/jbc.275.2.847] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The tyrosine kinase pp60(c-src) has been implicated in the regulation of numerous normal physiological processes as well the development of several human cancers. However, the mechanisms regulating its expression have not been addressed. In the present study, we report the presence of two Sp1/Sp3 binding sites and three polypurine:polypyrimidine (Pu:Py) tracts in the c-Src promoter that are essential for controlling expression. We demonstrate that Sp1, but not Sp3, is capable of activating the c-Src promoter and that Sp3 is also capable of inhibiting Sp1-mediated transactivation. The presence of multiple Pu:Py tracts conferred S1 sensitivity on plasmids in vitro, suggesting they are capable of adopting non B-DNA conformations. These tracts specifically bind a nuclear factor we named SPy (Src pyrimidine binding factor), which demonstrates both novel double- and single-stranded binding specificities. Mutations eliminating SPy binding compromised Src transcriptional activity, especially in concert with additional mutations affecting Sp1 binding, suggesting the two factors may cooperate in regulating c-Src expression. Finally, we demonstrate that triplex-forming oligonucleotides designed to target both Sp1 and SPy binding sites can down-regulate c-Src expression in vitro, suggesting a potential therapeutic approach to controlling c-Src expression in diseases where aberrant expression or activity has been documented.
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Affiliation(s)
- S Ritchie
- Saskatoon Cancer Center Research Unit, Saskatchewan Cancer Agency. Division of Oncology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 4H4, Canada
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17
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Morassutti C, Scaggiante B, Dapas B, Xodo L, Tell G, Quadrifoglio F. Effect of phosphorothioate modifications on the ability of GTn oligodeoxynucleotides to specifically recognize single-stranded DNA-binding proteins and to affect human cancer cellular growth. Biochimie 1999; 81:1115-22. [PMID: 10607406 DOI: 10.1016/s0300-9084(99)00350-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We have previously identified phosphodiester oligonucleotides exclusively made of G and T bases, named GTn, that significantly inhibit human cancer cell growth and recognize specific nuclear single-stranded DNA binding proteins. We wished to examine the ability of the modified GTn oligonucleotides with different degrees of phosphorothioate modifications to bind specifically to the same nuclear proteins recognized by the GTn phosphodiester analogues and their cytotoxic effect on the human T-lymphoblastic CCRF-CEM cell line. We showed that the full phosphorothioate GTn oligonucleotide was neither able to specifically recognize those nuclear proteins, nor cytotoxic. In contrast, the 3'-phosphorothioate-protected GTn oligonucleotides can maintain the specific protein-binding activity. The end-modified phosphorothioate oligonucleotides were also able to elicit the dose-dependent cell growth inhibition effect, but a loss in the cytotoxic ability was observed increasing the extent of sulphur modification of the sequences. Our results indicate that phosphorothioate oligonucleotides directed at specific single-stranded DNA-binding proteins should contain a number of phosphorothioate end-linkages which should be related to the length of the sequence, in order to maintain the same biological activities exerted by their phosphodiester analogues.
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Affiliation(s)
- C Morassutti
- Department of Biomedical Sciences & Technologies, School of Medicine, University of Udine, Italy
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18
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Mills M, Arimondo PB, Lacroix L, Garestier T, Hélène C, Klump H, Mergny JL. Energetics of strand-displacement reactions in triple helices: a spectroscopic study. J Mol Biol 1999; 291:1035-54. [PMID: 10518941 DOI: 10.1006/jmbi.1999.3014] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
DNA triple helices offer exciting new perspectives toward oligonucleotide-directed inhibition of gene expression. Purine and GT triplexes appear to be the most promising motifs for stable binding under physiological conditions compared to the pyrimidine motif, which forms at relatively low pH. There are, however, very little data available for comparison of the relative stabilities of the different classes of triplexes under identical conditions. We, therefore, designed a model system which allowed us to set up a competition between the oligonucleotides of the purine and pyrimidine motifs targeting the same Watson-Crick duplex. Several conclusions may be drawn: (i) a weak hypochromism at 260 nm is associated with purine triplex formation; (ii) delta H degree of GA, GT and TC triplex formation (at pH 7.0) was calculated as -0.1, -2.5 and -6.1 kcal/mol per base triplet, respectively. This unexpectedly low delta H degree for the purine triple helix formation implies that its delta G degree is nearly temperature-independent and it explains why these triplexes may still be observed at high temperatures. In contrast, the pyrimidine triplex is strongly favoured at lower temperatures; (iii) as a consequence, in a system where two third-strands compete for triplex formation, displacement of the GA or GT strand by a pyrimidine strand may be observed at neutral pH upon lowering the temperature. This original purine-to-pyrimidine triplex conversion shows a significant hypochromism at 260 nm and a hyperchromism at 295 nm which is similar to the duplex-to-triplex conversion in the pyrimidine motif. Further evidence for this triplex-to-triplex conversion is provided by mung bean-nuclease foot-printing assay.
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Affiliation(s)
- M Mills
- Department of Biochemistry, University of Cape Town, Republic of South Africa
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19
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Morassutti C, Scaggiante B, Xodo LE, Dapas B, Paroni G, Tolazzi G, Quadrifoglio F. Reduction of mdr1 gene amplification in human multidrug-resistant LoVo DX cell line is promoted by triple helix-forming oligonucleotides. ANTISENSE & NUCLEIC ACID DRUG DEVELOPMENT 1999; 9:261-70. [PMID: 10435751 DOI: 10.1089/oli.1.1999.9.261] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We have demonstrated previously that the GT triplex-forming oligodeoxyribonucleotide (TFO) d(TGTGTTTTTGTTTTGTTGGTTTTGTTT), named TFO ID, targeted to a polypyrimidine-polypurine coding sequence located within human multidrug-resistance mdrl gene, specifically and significantly reduced mdrl mRNA levels in the drug-resistant T-leukemic CEM-VLB100 cell line. In this article, we demonstrate that TFO 1D is effective at inhibiting not only transcription but also replication of mdrl genes, leading to a loss of amplified gene copies in the drug-resistant colon adenocarcinoma LoVo DX cell line. In contrast, TFO ID does not alter replication of the constitutive mdrl gene copy in the corresponding parental sensitive LoVo 109 cell line. A specific reduction in mdrl gene amplification levels was also obtained with the pyrimidine TFO d(CTTTTTCTTTTCTTCCTTTTCTTT), named TFO 24TC, directed against the same polypyrimidine-polypurine sequence of the mdrl gene. We suggest that triple helix-forming oligonucleotides might affect the replication of unstable chromosomal elements as amplicons in actively replicating cells by causing a local impairment of DNA polymerase activity. This study lends support to the notion that TFO may be used to reduce gene amplification aiming to control neoplastic progression in cancer cells bearing amplified oncogenes.
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Affiliation(s)
- C Morassutti
- Department of Biomedical Sciences and Technologies, School of Medicine, University of Udine, Italy
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20
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Floris R, Scaggiante B, Manzini G, Quadrifoglio F, Xodo LE. Effect of cations on purine.purine.pyrimidine triple helix formation in mixed-valence salt solutions. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 260:801-9. [PMID: 10103010 DOI: 10.1046/j.1432-1327.1999.00219.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The effect of various monovalent, divalent and oligovalent cations on the reaction of triplex formation by GT and AG motif triplex-forming oligonucleotides, designed to bind to biologically relevant polypurine-polypyrimidine sequences occurring in the promoters of the murine Ki-ras and human bcr genes, has been investigated by means of electrophoresis mobility shift assays (EMSA) and DNase I footprinting experiments. We found that in the presence of 10 mm MgCl2 the triple helices were progressively destabilized by adding increasing amounts of NaCl, from 20 to 140 mm, to the solution. We also observed that, while the total monovalent-ion concentration was constant at 100 mm, the exchange of sodium with potassium, but not lithium, results in a further destabilization of the triple helices, due to self-association equilibria involving the G-rich triplex-forming oligonucleotides. Potassium was found to destabilize triplex DNA even when the triple helices are preformed in the absence of K+. However, footprinting experiments also showed that the inhibitory effect of K+ on triplex DNA is partially compensated for by millimolar amounts of divalent transition metal ions such as Mn2+ and Ni2+, which upon coordinating to N7 of guanine are expected to enhance hydrogen-bond formation between the target and the third strand, and to reduce the assembly in quadruple structures of G-rich triplex-forming oligonucleotides. Triplex enhancement in the presence of potassium was also observed, but to a lesser extent, when spermine was added to the reaction mixture. Here, the ion effect on triplex DNA is rationalized in terms of competition among the different valence cations to bind to triplex DNA, and differential cation stabilization of unusual quadruplex structures formed by the triplex-forming oligonucleotides.
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Affiliation(s)
- R Floris
- Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, Universitá di Trieste, Italy
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Xodo LE, Manzini G, Quadrifoglio F. Formation of stable DNA triple helices within the human bcr promoter at a critical oligopurine target interrupted in the middle by two adjacent pyrimidines. ANTISENSE & NUCLEIC ACID DRUG DEVELOPMENT 1998; 8:477-88. [PMID: 9918112 DOI: 10.1089/oli.1.1998.8.477] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Antigene strategies based on the use of triplex-forming oligonucleotides (TFO) as artificial repressors are constrained by the need for genomic targets with a polypurine-polypyrimidine [poly (R.Y)] DNA motif. In this study, we demonstrate that both A/G and G/T motif oligonucleotides recognize and bind strongly to a critical polypurine sequence interrupted in the middle by two adjacent cytosines and located in the promoter of the human bcr gene at the transcription initiation. The interaction between the designed TFO and this irregular poly (R.Y) target has been studied using a number of techniques, including electrophoretic mobility shift assay (EMSA), circular dichroism (CD), DNase I, and dimethyl sulfate (DMS) footprinting. Although CD shows that the 24-mer TFO self-aggregate in solution, they bind to the bcr target at 37 degrees C, forming stable triplexes that do not dissociate during electrophoretic runs performed up to 50 degrees C in 50 mM Tris-acetate, pH 7.4, 10 mM MgCl2, 50 mM NaCl (buffer A). We used EMSA to determine the equilibrium dissociation constants (Kd) for the reaction T <==> D + TFO at 37 degrees C, either in buffer A or in 50 mM Tris-acetate, pH 7.4, 10 mM MgCl2, 5 mM NaCl (buffer B). The triplexes were found to be more stable in buffer B, a behavior that can be rationalized in terms of monovalent and divalent cation competition for binding to DNA. Footprinting experiments showed that the TFO interact with the irregular poly (R.Y) target in a highly sequence-specific way and that the A/G motif oligonucleotide, juxtaposing T to the double CG inversions of the target, formed the most stable triplex (e.g., 1 microM TFO promoted strong footprints at 37 degrees C). These triplexes, except the one containing two A.C.G mismatched triads, are not destabilized under near physiologic conditions, that is, in 50 mM Tris-acetate, pH 7.4, 80 mM KCl, 20 mM NaCl, 2 mM spermidine. Moreover, we found that guanine N7 in T.C.G and guanine N7 in A.C.G are both accessible to DMS and that the first is less reactive than the second. In conclusion, the results of this study indicate that a critical sequence in the human ber promoter may be used as a potential binding site for TFO designed to repress artificially the transcription of the fused bcr/abl gene expressed in leukemia cells.
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Affiliation(s)
- L E Xodo
- Department of Biomedical Sciences and Technologies, School of Medicine, University of Udine, Italy
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Aich P, Ritchie S, Bonham K, Lee JS. Thermodynamic and kinetic studies of the formation of triple helices between purine-rich deoxyribo-oligonucleotides and the promoter region of the human c-src proto-oncogene. Nucleic Acids Res 1998; 26:4173-7. [PMID: 9722637 PMCID: PMC147831 DOI: 10.1093/nar/26.18.4173] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The thermodynamic and kinetic parameters of triplex formation between four purine-rich oligonucleotides and a 22 bp pyrimidine. purine tract in the promoter region of the c-src gene were determined by fluorescence polarization studies. Three of these four oligonucleotides were 11 nt in length, corresponding to the left, central or right portion of the tract, while the fourth was a 22mer covering the whole tract. Binding constants ( Ka) were measured as a function of Mg2+ concentration (0-10 mM) and temperature (0-41 degrees C). In 10 mM Mg2+, K a for the left, central and right 11mers were 0.26, 0.75 and 1.4 x 10(8)/M, respectively, while for the 22mer the value was 1.8 x 10(8)/M at 22 degrees C. Under the same conditions, Ka was estimated by an electrophoretic band shift technique. The agreement between the two methods was acceptable for the 22mer but not for the 11mers. Kinetic measurements demonstrated that the rate of dissociation of the 22mer from the triplex was significantly slower than that of the 11mers, providing an explanation for the observed discrepancy. The entropy and enthalpy of triplex formation were calculated from van't Hoff plots. In all cases the entropy was favourable, especially for the 22mer and for the 11mer with the lowest guanine content. The enthalpy was unfavourable for the 22mer and most favourable for the 11mer with the highest guanine content. These results provide a thermodynamic explanation for length and sequence effects on the formation of purine.pyrimidine.purine triplexes.
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Affiliation(s)
- P Aich
- Department of Biochemistry, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada and Saskatoon Cancer Research Unit, 20 Campus Drive, Saskatoon, SK S7N 5E5, Canada
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23
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Xodo LE, Pirulli D, Quadrifoglio F. A kinetic study of triple-helix formation at a critical R x Y sequence of the murine c-Ki-ras promoter by (A,G)- and (G,T) oligonucleotides. EUROPEAN JOURNAL OF BIOCHEMISTRY 1997; 248:424-32. [PMID: 9346298 DOI: 10.1111/j.1432-1033.1997.00424.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The kinetics of triplex formation between the oligonucleotides d(AGGGAGG-GAGGAAGGGAGGG) (20AG), d(TGGGTGGGTGGTTGGGTGGG) (20GT) and a 29-bp polypurine-polypyrimidine sequence located in the c-Ki-ras promoter (D) was studied by electrophoretic experiments in 50 mM Tris/acetate, pH 7.4, 50 mM NaCl, 5 mM MgCl2. Rates of triplex formation were determined at three different temperatures (20 degrees C, 37 degrees C and 45 degrees C), under pseudo-first order conditions obtained by using the triplex-forming oligonucleotide (TFO) 500-fold in excess over the target duplex (5 nM). Measurements at TFO/target ratios of 20 and 100 were also carried out. At 37 degrees C the pseudo first-order constants, k(obs), were 18.9 x 10(-5) s(-1) for 20AG and 13.0 x 10(-5) s(-1) for 20GT, yielding association half-lives of 1 h and 1.5 h, respectively. Second-order association constants were found to be in the order of 10(2) M(-1) s(-1): these are slightly lower if compared with those measured for triplex formation by polypyrimidine (C,T) oligonucleotides (10(3) M(-1) s(-1)) [Maher, L. J., Dervan, P. B. & Wolf, B. J. (1990) Biochemistry 29, 8820-8826; Xodo, L. E. (1995) Eur. J. Biochem. 228, 918-926; Bates, P. J., Dosanjh, H. S., Jenkins, T. C., Laughton, C. A. & Neidle, S. (1995) Nucleic Acids Res. 23, 3627-3632] but dramatically lower when compared with duplex recombination from complementary strands (10(6) M(-1) s(-1)) [Craig, M. E., Crothers, D. M. & Doty, P. (1971) J. Mol. Biol. 62, 383-401; Pörschke, D. & Eigen, M. (1971) J. Mol. Biol. 62, 361-381]. Dissociation rate constants, k(-1), were indirectly obtained from equilibrium constants (Kd) and found to be, at 37 degrees C, 6.7 x 10(-7) s(-1) and 5.4 x 10(-6) s(-1) for 20AG and 20GT, respectively. From the rate constants obtained at 20 degrees C, 37 degrees C and 45 degrees C we estimated activation energies of triplex formation between D plus 20AG and D plus 20GT of respectively 134 +/- 29 and 88 +/- 21 kJ/mol. Moreover, the activation energies for the reaction of triplex dissociation were 385 +/- 50 kJ/mol for 20AG and 330 +/- 42 kJ/mol for 20GT. Decreasing the TFO/target ratio from 500 to 100 or 20, we observed a concomitant decrease of the association rate, in keeping with the finding that triplex formation occurs through a bimolecular process. We found that the effect of salt on triplex formation is rather complex, as, the addition of 2 mM spermidine boosted the binding rate of 20GT, but slightly reduced that of 20AG; the increase of NaCl from 50 mM to 100 mM or 150 mM decreased the rate of triplex formation. Finally, the biological implications of the kinetic behaviour exhibited by the two triplex-forming oligonucleotides specific for the c-Ki-ras promoter are discussed.
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Affiliation(s)
- L E Xodo
- Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, Università di Trieste, Italia.
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24
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Affiliation(s)
- M C Lin
- Department of Pharmaceutical Sciences, University of Toronto, Ontario, Canada
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