As nature intended? The uptake of DNA and oligonucleotides by eukaryotic cells

Non-specific interactions of antibody-oligonucleotide conjugates with living cells

Antibody-Oligonucleotide Conjugates (AOCs) represent an emerging class of functionalized antibodies that have already been used in a wide variety of applications. While the impact of dye and drug conjugation on antibodies' ability to bind their target has been extensively studied, little is known about the effect caused by the conjugation of hydrophilic and charged payloads such as oligonucleotides on the functions of an antibody. Previous observations of non-specific interactions of nucleic acids with untargeted cells prompted us to further investigate their impact on AOC binding abilities and cell selectivity. We synthesized a series of single- and double-stranded AOCs, as well as a human serum albumin-oligonucleotide conjugate, and studied their interactions with both targeted and non-targeted living cells using a time-resolved analysis of ligand binding assay. Our results indicate that conjugation of single strand oligonucleotides to proteins induce consistent non-specific interactions with cell surfaces while double strand oligonucleotides have little or no effect, depending on the preparation method.

Selection and Characterization of a DNA Aptamer Specifically Targeting Human HECT Ubiquitin Ligase WWP1

Nucleic acid aptamers hold promise as therapeutic tools for specific, tailored inhibition of protein targets with several advantages when compared to small molecules or antibodies. Nuclear WW domain containing E3 ubiquitin ligase 1 (WWP1) ubiquitin ligase poly-ubiquitinates Runt-related transcription factor 2 (Runx2), a key transcription factor associated with osteoblast differentiation. Since WWP1 and an adapter known as Schnurri-3 are negative regulators of osteoblast function, the disruption of this complex has the potential to increase bone deposition for osteoporosis therapy. Here, we develop new DNA aptamers that bind and inhibit WWP1 then investigate efficacy in an osteoblastic cell culture. DNA aptamers were selected against three different truncations of the HECT domain of WWP1. Aptamers which bind specifically to a C-lobe HECT domain truncation were observed to enrich during the selection procedure. One particular DNA aptamer termed C3A was further evaluated for its ability to bind WWP1 and inhibit its ubiquitination activity. C3A showed a low µM binding affinity to WWP1 and was observed to be a non-competitive inhibitor of WWP1 HECT ubiquitin ligase activity. When SaOS-2 osteoblastic cells were treated with C3A, partial localization to the nucleus was observed. The C3A aptamer was also demonstrated to specifically promote extracellular mineralization in cell culture experiments. The C3A aptamer has potential for further development as a novel osteoporosis therapeutic strategy. Our results demonstrate that aptamer-mediated inhibition of protein ubiquitination can be a novel therapeutic strategy.

Lipid conjugated oligonucleotides: a useful strategy for delivery

Oligonucleotides, including antisense oligonucleotides and siRNA, are promising therapeutic agents against a variety of diseases. Effective delivery of these molecules is critical in view of their clinical application. Therefore, cation-based nanoplexes have been developed to improve the stability as well as the intracellular penetration of these short fragments of nucleic acids. However, this approach is clearly limited by the strong interaction with proteins after administration and by the inherent toxicity of these positively charged transfection materials. Neutral lipid-oligonucleotide conjugates have become a subject of considerable interest to improve the safe delivery of oligonucleotides. These molecules have been chemically conjugated to hydrophobic moieties such as cholesterol, squalene, or fatty acids to enhance their pharmacokinetic behavior and trans-membrane delivery. The present review gives an account of the main synthetic methods available to conjugate lipids to oligonucleotides and will discuss the pharmacological efficacy of this approach.

DNA-based therapeutics and DNA delivery systems: a comprehensive review

The past several years have witnessed the evolution of gene medicine from an experimental technology into a viable strategy for developing therapeutics for a wide range of human disorders. Numerous prototype DNA-based biopharmaceuticals can now control disease progression by induction and/or inhibition of genes. These potent therapeutics include plasmids containing transgenes, oligonucleotides, aptamers, ribozymes, DNAzymes, and small interfering RNAs. Although only 2 DNA-based pharmaceuticals (an antisense oligonucleotide formulation, Vitravene, (USA, 1998), and an adenoviral gene therapy treatment, Gendicine (China, 2003), have received approval from regulatory agencies; numerous candidates are in advanced stages of human clinical trials. Selection of drugs on the basis of DNA sequence and structure has a reduced potential for toxicity, should result in fewer side effects, and therefore should eventually yield safer drugs than those currently available. These predictions are based on the high selectivity and specificity of such molecules for recognition of their molecular targets. However, poor cellular uptake and rapid in vivo degradation of DNA-based therapeutics necessitate the use of delivery systems to facilitate cellular internalization and preserve their activity. This review discusses the basis of structural design, mode of action, and applications of DNA-based therapeutics. The mechanisms of cellular uptake and intracellular trafficking of DNA-based therapeutics are examined, and the constraints these transport processes impose on the choice of delivery systems are summarized. Finally, the development of some of the most promising currently available DNA delivery platforms is discussed, and the merits and drawbacks of each approach are evaluated.

Oligonucleotide-protamine-albumin nanoparticles: preparation, physical properties, and intracellular distribution

Oligodesoxynucleotides (ODNs) or the corresponding phosphorothioates (PTOs) spontaneously form spherical nanoparticles ("proticles") with protamine in aqueous solutions. The proticles can cross cellular membranes and release the ODNs within the cells. Thus, they represent a potential drug delivery system. The major disadvantages of this system are a lack of stability in salt solutions and its inability to also release PTOs. The present study shows, using PTOs and protamine free base, that these shortcomings can be eliminated by the addition of human serum albumin (HSA) as a third component to the starting mixture. The "ternary" proticles thus obtained contain maximally a few percent of the HSA that was originally present. Nevertheless, they differ from the previously studied "binary" proticles: (1) They are stable in salt solutions for at least several hours. (2) They show a high cellular uptake into murine fibroblasts, and they readily release the PTOs after uptake. The ternary proticles therefore represent a considerable improvement over binary proticles for use as drug delivery systems.

Activation of RAW264.7 macrophages by bacterial DNA and lipopolysaccharide increases cell surface DNA binding and internalization

Bacterial DNA containing unmethylated CpG motifs is a pathogen-associated molecular pattern (PAMP) that interacts with host immune cells via a toll-like receptor (TLR) to induce immune responses. DNA binding and internalization into cells is independent of TLR expression, receptor-mediated, and required for cell activation. The objective of this study was to determine whether exposure of immune cells to bacterial DNA affects DNA binding and internalization. Treatment of RAW264.7 cells with CpG oligodeoxynucleotide (ODN) for both 18 and 42 h resulted in a significant increase in DNA binding, whereas non-CpG ODN had no effect on DNA binding. Enhanced DNA binding was non-sequence-specific, inhibited by unlabeled DNA, showed saturation, was consistent with increased cell surface DNA receptors, and resulted in enhanced internalization of DNA. Treatment with Escherichia coli DNA or lipopolysaccharide (LPS) also resulted in a significant increase in DNA binding, but treatment with interleukin-1alpha, tumor necrosis factor-alpha, or phorbol 12-myristate 13-acetate had no effect on DNA binding. Soluble factors produced in response to treatment with CpG ODN or LPS did not affect DNA binding. These studies demonstrate that one consequence of activating the host innate immune response by bacterial infection is enhanced binding and internalization of DNA. During this period of increased DNA internalization, RAW264.7 cells were hypo-responsive to continued stimulation by CpG ODN, as assessed by tumor necrosis factor-alpha activity. We speculate the biological significance of increasing DNA binding and internalization following interaction with bacterial PAMPs may provide a mechanism to limit an ongoing immune inflammatory response by enhancing clearance of bacterial DNA from the extracellular environment.

Selection of oligonucleotide aptamers with enhanced uptake and activation of human leukemia B cells

The clinical use of oligonucleotide (ODN) therapeutics has been hampered by their limited ability to penetrate intact cells. To identify ODN properties that would facilitate cellular uptake, we developed a repetitive selection procedure using an ODN library containing at least 10(14) different molecules and human B lymphoma cells as a target. Natural phosphodiester single-stranded DNA ODNs (R-aptamers) were obtained after 10 rounds of selection. A common feature in the R-aptamers was guanine-rich 3' terminal sequences, and many also contained potential immunostimulatory (ISS) CpG sequence motifs. Two R-aptamers (R10-60 and D-R15-8) with the predominant shared characteristics were selected for further study on primary human chronic lymphocytic leukemia (CLL) B cells, which are well known to be difficult to transfect and activate. Flow cytometry analysis of the CLL cells demonstrated that the fluorochrome-labeled R-aptamers were internalized much more efficiently than nonselected random sequence ODN. Studies on sequence modifications indicated that efficient uptake required ODN multimerization, that was promoted by guanine-rich sequences at the 3' terminus. In addition, CLL cells that were exposed to the aggregating R-aptamers containing CpG motifs were strongly activated, as indicated by upregulation of CD40 levels as compared to cells treated with nonaggregating CpG R-aptamers. Together, these findings suggest that the sequence compositions in R-aptamers that promote multimerization and contain optimal ISS CpG motifs facilitate the delivery of ISS-ODN to CLL cells and enhance the activation of these cells.

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides

Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

Cyclodextrins in oligonucleotide delivery

The aim of this contribution is to summarize recent findings on the potential use of cyclodextrins and their derivatives as carriers for oligonucleotide agents. Their peculiar properties could be exploited in such an emerging therapeutic area by virtue of their capability of interacting with cellular membranes, thus giving rise to improved cellular uptake. In particular, some specific derivatives could be considered as promising future excipients for the delivery of "naked" antisense and/or decoy oligonucleotides which are difficult to formulate with existing pharmaceutical excipients.

An experimental and theoretical study of the inhibition of Escherichia coli lac operon gene expression by antigene oligonucleotides

Previously, we have developed a genetically structured mathematical model to describe the inhibition of Escherichia coli lac operon gene expression by antigene oligos. Our model predicted that antigene oligos targeted to the operator region of the lac operon would have a significant inhibitory effect on beta-galactosidase production. In this investigation, the E. coli lac operon gene expression in the presence of antigene oligos was studied experimentally. A 21-mer oligo, which was designed to form a triplex with the operator, was found to be able to specifically inhibit beta-galactosidase production in a dose-dependent manner. In contrast to the 21-mer triplex-forming oligonucleotide (TFO), several control oligos showed no inhibitory effect. The ineffectiveness of the various control oligos, along with the fact that the 21-mer oligo has no homology sequence with lacZYA, and no mRNA is transcribed from the operator, suggests that the 21-mer oligo inhibits target gene expression by an antigene mechanism. To simulate the kinetics of lac operon gene expression in the presence of antigene oligos, a genetically structured kinetic model, which includes transport of oligo into the cell, growth of bacteria cells, and lac operon gene expression, was developed. Predictions of the kinetic model fit the experimental data quite well after adjustment of the value of the oligonucleotide transport rate constant (9.0 x 10(-)(3) min(-)(1)) and oligo binding affinity constant (1.05 x 10(6) M(-)(1)). Our values for these two adjusted parameters are in the range of reported literature values.

Synthetic hydrogels as carriers in antisense therapy: preliminary evaluation of an oligodeoxynucleotide covalent conjugate with a copolymer of 1-vinyl-2-pyrrolidinone and 2-hydroxyethyl methacrylate

A major challenge of the antisense therapeutic strategies is the development of improved systems for the delivery of antisense oligodeoxynucleotides (AS ODNs) in order to enhance the cellular uptake, to assure a better efficiency in reaching the target tissue, and to provide sustained delivery over longer periods of time. Because the current methods for delivery (liposomes and cationic polymers) present some disadvantages, the attention was directed toward the use of neutral polymers as carriers for the AS ODNs. Based on our previous work on synthetic hydrogels for vitreous substitution, we developed a poly[1-vinyl-2-pyrrolidinone-co-(2-hydroxyethyl methacrylate)] hydrogel as a potential carrier for AS ODNs. We have previously demonstrated that such hydrogels are not cytotoxic, and they may have growth-promoting effects on cultured fibroblasts. This copolymer also has the advantage of being injectable. In this study, a specific AS ODN was synthesized and then covalently bound to the copolymer via carbodiimide coupling method. The resulting conjugate was subjected to in vitro release experiments over 46 days in the presence of bovine vitreous humor. Compared with the control (no enzyme present), a significant amount of covalently bound ODN was released from the ODN-hydrogel conjugate, suggesting the possibility of using such systems for the sustained delivery of AS ODNs.

Transformation of malaria parasites by the spontaneous uptake and expression of DNA from human erythrocytes

The uptake and expression of extracellular DNA has been established as a mechanism for horizontal transfer of genes between bacterial species. Such transfer can support acquisition of advantageous elements, including determinants that affect the interactions between infectious organisms and their hosts. Here we show that erythrocyte-stage Plasmodium falciparum malaria parasites spontaneously take up DNA from the host cell cytoplasm into their nuclei. We have exploited this finding to produce levels of reporter expression in P.falciparum that are substantially improved over those obtained by electroporation protocols currently used to transfect malaria parasites. Parasites were transformed to a drug-resistant state when placed into cell culture with erythrocytes containing a plasmid encoding the human dihydrofolate reductase sequence. The findings reported here suggest that the malaria genome may be continually exposed to exogenous DNA from residual nuclear material in host erythrocytes.

A human gene coding for a membrane-associated nucleic acid-binding protein

Studies to clone a cell-surface DNA-binding protein involved in the binding and internalization of extracellular DNA have led to the isolation of a gene for a membrane-associated nucleic acid-binding protein (MNAB). The full-length cDNA is 4.3 kilobases with an open reading frame of 3576 base pairs encoding a protein of approximately 130 kDa (GenBank accession numbers and ). The MNAB gene is on human chromosome 9 with wide expression in normal tissues and tumor cells. A C3HC4 RING finger and a CCCH zinc finger have been identified in the amino-terminal half of the protein. MNAB bound DNA (K(D) approximately 4 nm) and mutagenesis of a single conserved amino acid in the zinc finger reduced DNA binding by 50%. A potential transmembrane domain exists near the carboxyl terminus. Antibodies against the amino-terminal half of the protein immunoprecipitated a protein of molecular mass approximately 150 kDa and reacted with cell surfaces. The MNAB protein is membrane-associated and primarily localized to the perinuclear space, probably to the endoplasmic reticulum or trans-Golgi network. Characterization of the MNAB protein as a cell-surface DNA-binding protein, critical in binding and internalization of extracellular DNA, awaits confirmation of its localization to cell surfaces.

Phosphorothioate backbone modification modulates macrophage activation by CpG DNA

Macrophages respond to unmethylated CpG motifs present in nonmammalian DNA. Stabilized phosphorothioate-modified oligodeoxynucleotides (PS-ODN) containing CpG motifs form the basis of immunotherapeutic agents. In this study, we show that PS-ODN do not perfectly mimic native DNA in activation of macrophages. CpG-containing PS-ODN were active at 10- to 100-fold lower concentrations than corresponding phosphodiester ODN in maintenance of cell viability in the absence of CSF-1, in induction of NO production, and in activation of the IL-12 promoter. These enhancing effects are attributable to both increased stability and rate of uptake of the PS-ODN. By contrast, PS-ODN were almost inactive in down-modulation of the CSF-1R from primary macrophages and activation of the HIV-1 LTR. Delayed or poor activation of signaling components may contribute to this, as PS-ODN were slower and less effective at inducing phosphorylation of the extracellular signal-related kinases 1 and 2. In addition, at high concentrations, non-CpG PS-ODN specifically inhibited responses to CpG DNA, whereas nonstimulatory phosphodiester ODN had no such effect. Although nonstimulatory PS-ODN caused some inhibition of ODN uptake, this did not adequately explain the levels of inhibition of activity. The results demonstrate that the phosphorothioate backbone has both enhancing and inhibitory effects on macrophage responses to CpG DNA.

Nuclear transport of oligonucleotides in HepG2-cells mediated by protamine sulfate and negatively charged liposomes

PURPOSE

The aim of this study was to characterize the intracellular fate and nuclear uptake kinetics of oligonucleotides (ON) that were complexed with protamine sulfate (PS) and negatively charged liposomes at different ratios of ON to PS.

METHODS

Double-fluorescence labelling of ON and liposomal lipid was applied to simultaneously monitor the interaction as well as the individual fate of active agent and carrier upon intracellular delivery using confocal laser scanning microscopy (CLSM). A DNA-analogue of a 68-mer intramolecular double-stranded RNA:DNA-hybridoligonucleotide (chimeraplasts) with unmodified phosphate backbone was employed. This construct was condensed with PS and coated with a liposomal formulation (AVE-3 = artificial viral envelope).

RESULTS

PS-ON complexes and AVE -3-coated complexes with a defined composition were very effective in nuclear transport of ON for a ON:PS charge ratio of 1:3. Nucleus:cytosol fluorescence ratios peaked at about 10 hrs and started to decrease again at 21 hrs.

CONCLUSIONS

AVE associates with PS-condensed ON, and this complex is able to be taken up by cells and to deliver ON to the nucleus. PS-ON complexes are released from the liposomal formulation, mainly as an extranuclear enzymatic degradation of the liposomal phospholipids. The results of the kinetic analysis can be used to optimize transfection protocols with ON in HepG2 cells.

Macrophage activation by immunostimulatory DNA

Macrophage/dendritic cells and B cells remain the only cell types where direct responses to CpG DNA are well established. The role of macrophages in vivo in DNA clearance and the potent cytokine induction in macrophages and dendritic cells places them in the central role in the in vivo response to foreign DNA. Although responses to DNA are unlikely to evolve and be retained if they are not significant in the immune response to infection, the relative contributions of DNA and other stimulators of the innate immune recognition of foreign organisms is difficult to assess. Although CpG DNA and LPS have similar actions, significant differences are emerging that make the use of DNA as a therapeutic immunostimulatory molecule feasible. The macrophage response to DNA generates cytokines favouring the development of Th1-type immunity, and active oligonucleotides now show promise as Th1-promoting adjuvants and as allergy treatments.

Characterisation of membrane oligonucleotide-binding proteins and oligonucleotide uptake in keratinocytes

Inadequate cellular compartmentalisation of plasmid DNA and antisense oligodeoxynucleotides (ODNs) is generally considered as a major limitation in their use. In this study, an approach combining in situ visual-isation of rhodamine-labelled ODNs and affinity modification of proteins by radiolabelled-alkylating ODN derivatives has been used to investigate the uptake of ODNs into keratinocytes. We confirm here that unmodified ODNs are efficiently taken up and accumulate in cell nuclei in primary keratinocytes as well as in HaCaT and A431 keratinocyte cell lines. Uptake is fast, irreversible, saturable and not significantly altered by incubation at low temperature. Affinity modification studies in keratinocyte cell lines has revealed two high-affinity, cell-specific interactions between ODNs and proteins of 61-63 kDa and 35 kDa. Trypsin pre-treatment of A431 cells and pre-incubation with polyanions, or with unlabelled nucleic acid competitors, inhibited the accumulation of rhodamine-labelled ODNs in nuclei as well as the affinity labelling of the 61-63 kDa doublet and 35 kDa ODN-binding proteins by reactive ODN derivatives. Finally, cell fractionation studies indicated that these ODN-binding proteins were essentially localised in the plasma membrane. Our results suggest that these ODN-binding proteins might be involved in the recognition and transport of ODNs into keratinocytes.

Live confocal microscopy of oligonucleotide uptake by keratinocytes in human skin grafts on nude mice

Anti-sense oligonucleotide uptake by keratinocytes in human skin grafts on athymic mice was examined using live confocal microscopy. Fluorescein isothiocyanate-labeled 15-mer C-5 propyne modified phosphorothioate anti-sense oligonucleotide (10-50 microM) was intradermally injected into normal human skin grafts on athymic mice, and the localization of the anti-sense oligonucleotide was assessed after 1-24 h postinjection. Anti-sense oligonucleotide was found to localize in the nuclei of basal and suprabasal keratinocytes after 1-2 h, and this localization was still observed after 24 h. This live in vivo observation of anti-sense oligonucleotide uptake in basal keratinocytes was confirmed using conventional fluorescence microscopy of fixed sections of skin grafts. Neither single nucleotides which were fluorescein isothiocyanate-labeled nor fluorescein isothiocyanate alone was able to penetrate into the nuclei of human skin graft keratinocytes after intradermal injection, and hence it is likely that the anti-sense oligonucleotide was not degraded prior to intracellular localization. Topical administration of anti-sense oligonucleotide and anti-sense oligonucleotide-liposome complexes resulted primarily in localization in the stratum corneum of human skin grafts. When grafts were tape stripped prior to anti-sense oligonucleotide administration, however, as little as 5 microM anti-sense oligonucleotide was required to observe nuclear anti-sense oligonucleotide accumulation. These results suggest that cutaneous anti-sense strategies can be tested using delivery via intradermal anti-sense oligonucleotide injection in human skin grafts on athymic mice, and that agents providing penetration of anti-sense oligonucleotide across the stratum corneum are likely to be required for successful topical therapies.

Oligonucleotide uptake in cultured keratinocytes: influence of confluence, cationic liposomes, and keratinocyte cell type

The success of anti-sense strategies has been limited, at least in part, by the poor uptake of these agents into the target cells. In keratinocytes, there is conflicting evidence as to the amount and location of oligonucleotide uptake into these cells, with variable proportions of cells reported to take up oligodeoxynucleotide, and also cytoplasmic and nuclear localization reported. In this study, the uptake of oligodeoxynucleotides in cultured normal human keratinocytes and the HaCaT cell line was quantitated in the presence of various lipids designed to enhance uptake and in varying culture conditions. About 12% of cells in a confluent normal human keratinocyte culture showed nuclear uptake, with a small and variable proportion showing cytoplasmic localization after 24 h incubation with 1 microM oligodeoxynucleotide. Uptake of oligodeoxynucleotide was found to be increased by liposome encapsulation (to a maximum of 28.1% +/- 2.1% of cells), low confluence (39.5% +/- 2.5%), and further increased by a combination of the two conditions (55.4% +/- 4.3%). HaCaT cell populations showed sparse but consistent uptake of oligodeoxynucleotide, with about 1% of cells showing nuclear localization in the presence of 1 microM oligodeoxynucleotide, increasing to 13.5% +/- 4.9% in the presence of cationic lipid (Tfx-50) in low confluence HaCaT monolayers. We conclude that normal keratinocytes exhibit reliable, substantial uptake of oligonucleotides in conditions controlled for confluence and aided by liposome encapsulation.

Monitoring antisense oligodeoxynucleotide activity in hematopoietic cells

Traditionally, methods designed to impair translation through direct interactions with target messenger RNA (mRNA) have been designated as "antisense" strategies because of their reliance on the formation of reverse complementary (antisense) Watson-Crick base pairs between the targeting oligodeoxynucleotide (ODN) and the mRNA whose function is to be disrupted. Proof of putative "antisense effects," and other mechanistic studies, would be greatly facilitated by the ability to directly demonstrate hybridization between an antisense (AS) ODN and its mRNA target in vivo. In addition, evidence of AS activity by demonstrating reduced levels of RNA or protein or by showing cleaved target molecules would lend proof of the concept. In this article we discuss how AS ODN may be used to down-regulate target gene expression with an emphasis on those targets chosen for our investigations, and we summarize the methods employed for this type of study.

Different effects of an oligonucleotide uptake stimulating protein on leukemic cells in their primitive and differentiated state

The single stranded [3H]oligonucleotide uptake by HL-60 human promyelocyte and K562 human erythroleukemia cells was stimulated 20-45-fold by DUSF (DNA uptake stimulating protein), and this effect was drastically reduced (to 1.6-13x) if the cells were induced to differentiate. The oligonucleotide uptake stimulating effect of DUSF was not altered in HL-60 and K562 cells, if the proliferation of the cells was inhibited by hydroxyurea (HU) treatment. The oligonucleotide uptake by separated granulocytes and mononuclear cells from healthy donors was not stimulated by DUSF, while the uptake of oligonucleotides by myeloid and lymphoid leukemic cells was greatly stimulated (10-15x). The uptake of oligonucleotides by differentiated mononuclear cells of healthy donors could not be stimulated by DUSF, but the oligonucleotide uptake was greatly increased (11x) by DUSF if the cells were subjected to blast transformation.

Bacterial DNA as an evolutionary conserved ligand signalling danger of infection to immune cells

During infection, the innate limb of the immune system senses danger (pathogens) via constitutively expressed pattern-recognition receptors, and responds with activation and secretion of pro-inflammatory cytokines. Cell-wall components of gram-positive and gram-negative bacteria, such as peptidoglycan, endotoxin or lipoteichoic acid, activate via CD14, a prototypic pattern-recognition receptor for carbohydrates. This review article focuses on an alternative recognition system of the innate immune system for the recognition of bacterial DNA. Bacterial DNA differs from eukaryotic DNA in its frequency of the dinucleotides CG and its lack of methylation. These structural differences appear to be sensed by cells of the innate immune system such as antigen-presenting cells. As a consequence bacterial DNA serves as an alternate ligand to signal danger of infection. Bacterial DNA and (synthetic) oligonucleotides (ODN) derived thereof are as efficient as endotoxin in activating macrophages and dendritic cells and in triggering release of pro-inflammatory cytokines. In mice sensitized with D-galactosamine (D-GalN), high doses of bacterial DNA from either gram-positive or gram-negative pathogens induce a lethal cytokine syndrome (lethal shock). Therefore, bacterial DNA may represent a hitherto unrecognized pathophysiological entity in host-parasite interactions. Moreover, recent evidence suggests that bacterial DNA or immunostimulating ODN triggers the immunostimulation of antigen-presenting cells, and can be utilized as adjuvant to enhance immune responses of the adaptive immune system towards poorly immunogenic antigens. In fact, foreign DNA might be useful as immunotherapeutically active adjuvant to direct adaptive immune responses towards Thl-dominated immune reactions. If these findings are operative in humans, immunostimulating ODN might be used to influence Th2-dominated diseases such as allergy.

Cationic polyhexylcyanoacrylate nanoparticles as carriers for antisense oligonucleotides

After antisense oligodeoxynucleotides (ODNs) were suggested for therapeutic use in 1978, major advances were made in developing modified oligonucleotides with increased nuclease resistance and improved cellular uptake. In the present report, positively charged nanoparticles prepared from diethylaminoethyl (DEAE)-dextran and polyhexylcyanoacrylate (PHCA) were evaluated as carriers for ODNs. The oligonucleotides were analyzed by anion-exchange HPLC. The nanoparticles exhibited a high loading capacity, with approximately 35 mumol ODNs adsorbed per gram of polymeric material. The adsorption efficacy was found to be dependent on the pH, on the ionic strength of the medium, and on the amount of DEAE-dextran. Highest loading for ODNs was achieved at pH 5.5, using a 10 mM phosphate buffer. Oligonucleotides adsorbed to the surface of the nanoparticles were nearly completely protected against degradation by the endonuclease DNase I and under in vitro cell culture conditions, whereas unprotected ODNs were totally digested under these conditions. Nanoparticles led to a 20-fold increase in cellular uptake of FITC-oligonucleotides. The internalized oligonucleotides were frequently localized as vesicular structures in the cytoplasmatic compartment. Because of their temperature-dependent uptake, we propose an active uptake mechanism, such as endocytosis, for the internalization of the ODN-nanoparticle formulations.

Cellular uptake properties of a 2'-amino/2'-O-methyl-modified chimeric hammerhead ribozyme targeted to the epidermal growth factor receptor mRNA

Catalytic RNA or ribozymes have important potential applications as molecular biological tools in the study of gene expression and as therapeutic inhibitors of disease-causing genes. Very little is known, however, about the cellular uptake mechanisms of exogenously delivered synthetic ribozymes. In this study, we have characterized the uptake properties of a synthetic, 2'-O-methyl-modified ribozyme containing U4/U7 amino groups within the catalytic core of the hammerhead motif. The cellular uptake of the internally [32P]-radiolabeled hammerhead ribozyme in U87-MG glioma cells was temperature, energy, and pH dependent and involved an active process that could be competed with cold ribozyme of the same chemistry and sequence, an all 2'-O-methyl-modified ribozyme of the same sequence, antisense PS-ODNs, and a variety of other polyanions (salmon sperm DNA, spermidine, dextran sulfate, and heparin). Subcellular distribution studies of fluorescently labeled ribozymes confirmed an extranuclear, punctate localization similar to that observed for an endosomal marker, dextran. Our study highlights that hammerhead ribozymes, despite exhibiting a defined secondary structure, enter cells by an endocytic mechanism that appears to be similar to that reported for a variety of antisense ODNs. These observations should facilitate the development of more efficient delivery systems.

Fluorescence microscopic comparison of the binding of phosphodiester and phosphorothioate (antisense) oligodeoxyribonucleotides to subcellular structures, including intermediate filaments, the endoplasmic reticulum, and the nuclear interior

To detect potential intracellular binding sites for antisense oligodeoxyribonucleotides (ODN), 3'-fluorescence-tagged phosphodiester (P) and phosphorothioate (S) analogs of a series of model and vimentin and actin antisense ODN were applied to digitonin-permeabilized fibroblast and epithelial PtK2 cells. Fluorescence microscopy revealed binding of the ODN to intermediate filaments (IFs) with a preference for cytokeratin IFs, cytoplasmic membranes (endoplasmic reticulum), and, above all, the nuclear interior. The affinity of the ODN for these cellular substructures was dependent on their base composition, and the S-ODN were by far superior to the corresponding P-ODN in binding activity. Fluorescence polarization measurements of the interaction of ODN with purified IF proteins in vitro confirmed the differential, high-affinity binding of S-ODN to IFs. In permeabilized cells, the ODN readily migrated into the nucleus where, at ambient temperature, preferentially the S-ODN gave rise to a multitude of large, irregular aggregates. Nuclear uptake of the ODN was considerably and differentially inhibited by wheat germ agglutinin. High-affinity S-ODN, but not P-ODN, additionally reacted with a structure presumably identical with the nuclear lamina. Simultaneously, they cause decompaction of chromatin, whereby the S-ODN aggregates appeared as compact inclusions in homogeneously dispersed chromatin. After microinjection of S-ODN into intact cells, these effects were not observed, although the nucleic acids rapidly moved into the nucleus and condensed into a large number of well-defined, spherical speckles or longitudinal rodlets. The methylphosphonate analogs of some of the ODN used exhibited only extremely low affinities for intracellular constituents. These results show that excess amounts of S-ODN saturate a host of both low-affinity and high-affinity binding sites on cellular substructures, whereas limited quantities as used for microinjection recognize only the high-affinity binding sites. The results support the notion that the nonsequence-specific, often toxic effects of antisense S-ODN result from their strong binding to cellular components and substructures involved in replicational, transcriptional, and translational processes. On the other hand, the association of the ODN with membranes and cytoskeletal and karyoskeletal elements may serve to optimize their sequence-specific interaction with their intended target sites and also increase their cellular retention potential. These cellular structures would thus fulfill a depot function.

Transformed and immortalized cellular uptake of oligodeoxynucleoside phosphorothioates, 3'-alkylamino oligodeoxynucleotides, 2'-O-methyl oligoribonucleotides, oligodeoxynucleoside methylphosphonates, and peptide nucleic acids

Direct quantitative comparisons of cellular uptake across a wide variety of analogs and cell types are necessary for the design of oligonucleotide diagnostic and therapeutic applications. This work reports quantitative cellular uptake and nuclear localization of [14C]oligodeoxynucleoside phosphorothioates (PS), 3'-alkylamino oligodeoxynucleoside phosphodiesters (PO-NH2), 2'-O-methyl oligoribonucleoside phosphodiesters (2OM), peptide nucleic acids (PNA), and oligodeoxynucleoside methylphosphonates (MP) in several transformed or immortalized cell lines. All analogs demonstrated active cellular uptake in that intracellular concentrations greatly exceeded the extracellular 1 microM concentration within 1-3 hr. However, by 9-24 hr, cellular accumulations of PS exceeded those of PO-NH2 and 2OM by 3- to 5-fold, PNA by 6- to 7-fold, and MP by 8- to 10-fold. Similar results were observed in two transformed cell lines, HL-60 leukocytes and H-ras transformed fibroblasts, using three different heterogeneous sequences. H-ras and IGF-1R transformed fibroblasts had a 2- to 5-fold higher uptake of all analogs than non-transformed immortalized fibroblasts. Nuclear levels of the PO-NH2, PS, and MP analogs were approximately 25% of total cellular uptake, while nuclear percentages of 2OM and PNA were less than 20%, suggesting some differences in nuclear localization among the analogs. These observations provide a direct quantitative comparison of cellular uptake as a function of oligonucleotide modification, and imply that transformation enhances cellular uptake. From the perspective of therapy and diagnosis, clear trade-offs were apparent between efficiency of uptake on the one hand, and nuclease resistance and hybridization strength on the other.

Treatment of Philadelphia leukemia in severe combined immunodeficient mice by combination of cyclophosphamide and bcr/abl antisense oligodeoxynucleotides

BACKGROUND

Philadelphia cells are human chronic myelogenous leukemia (CML) cells that contain the BCR/ABL oncogene (a fusion of the BCR and ABL genes). Selective eradication of these cells in vitro can be achieved by combined treatment with antisense phosphorothioate oligodeoxynucleotides ([S]ODNs) specifically targeted to this oncogene (bcr/abl [S]ODNs) and a suboptimal (for use as a single agent) dose of mafosfamide (the in vitro active form of cyclophosphamide).

PURPOSE

We evaluated the ability of bcr/abl antisense [S]ODNs, alone or subsequent to treatment with a single injection of cyclophosphamide, to suppress the leukemic process induced in severe combined immunodeficient (SCID) mice by Philadelphia cells (i.e., primary CML-blast crisis [CML-BC] cells). In addition, we studied potential mechanisms that might explain the efficacy of the bcr/abl antisense [S]ODN-mafosfamide combination against Philadelphia cells in vitro.

METHODS

The effects of treating leukemic mice with cyclophosphamide (25 mg/kg body weight; 25% of the dose required to eradicate evidence of leukemia in SCID mice) and/or bcr/abl antisense [S]ODNs were assessed by analysis of survival, by examination of bone marrow for the presence of leukemia cells (using a colony formation assay or using coupled reverse transcription and the polymerase chain reaction to screen for bcr/abl messenger RNA), and by examination of a variety of tissues for the presence of infiltrating leukemia cells. The induction of apoptosis (a cell death program) in vitro in primary CML-BC cells following treatment with bcr/abl antisense [S]ODNs plus or minus prior treatment with mafosfamide was monitored by use of a commercial assay. Relative cellular uptake of [S]ODNs by CML-BC cells treated in vitro with or without prior treatment with mafosfamide was determined by use of confocal microscopy and flow cytometry (for fluorescent [S]ODNs) or by use of blotting techniques that employed radioactively labeled probes (for extracted, unlabeled [S]ODNs). Levels of specific proteins in treated and untreated cells were determined by use of western blotting methods. Reported P values are two-sided.

RESULTS

The disease process in leukemic mice was retarded substantially by combination treatment with cyclophosphamide and specific bcr/abl antisense [S]ODNs (P < .001, relative to treatment with specific antisense [S]ODNs alone, cyclophosphamide alone, or cyclophosphamide plus nonspecific [i.e., control] antisense [S]ODNs); 50% of the mice treated with cyclophosphamide and specific antisense [S]ODNs appeared to be cured of leukemia. The combination treatment was associated with increased induction of apoptosis. In addition, cellular uptake of bcr/abl antisense [S]ODNs appeared to be increased twofold to sixfold by prior treatment with mafosfamide. This increased uptake of [S]ODNs was associated with enhanced suppression of p210bcr/abl protein levels.

CONCLUSIONS AND IMPLICATIONS

Combination therapy with antisense [S]ODNs targeted to specific oncogenes and less toxic doses of anticancer drugs may represent a rational strategy to purpose for the treatment of human leukemias.

Association of rous sarcoma virus DNA with Xenopus laevis spermatozoa and its transfer to ova through fertilization

Mature Xenopus laevis spermatozoa are capable of binding plasmid pAPrC carrying the complete Rous sarcoma virus (RSV) DNA. Each sperm cell associates, on an average, with 70-160 molecules of the plasmid DNA in a DNase resistant form, if the spermatozoa were exposed to the DNA at a concentration of 1.0-1.4 micrograms/10(7) sperm cells. Fertilization with pAPrC-treated spermatozoa induced developmental malformations in 25-30% of embryos. Immunohistochemical analysis of tissue sections from defective animals revealed aberrations in myotomal structures, and increased expression of pp60src protein in myoblasts, neuronal tube, and epidermis. The presence of characteristic v-src and RSV-long terminal repeat (LTR) sequences in X. laevis DNA was detected by PCR analysis. Embryonic RNA hybridized with a src-specific and an RSV-LTR specific probes indicating expression of the viral DNA. Plasmid DNAs without the v-src gene (pATV9) or completely free of any RSV sequences (pBR322) did not induce any changes in embryonic development. Our results provide evidence that the pBR322-cloned DNA form of the RSV genome associates with frog sperm cells in a DNase-resistant manner suggesting internalization and may be subsequently carried into eggs during the process of artificial fertilization. Correlation between the defective morphogenesis of X. laevis and increased expression of the src gene as well as an interference of RSV DNA with the developmental programs of frog embryos are discussed.

Investigation of the intracellular stability and formation of a triple helix formed with a short purine oligonucleotide targeted to the murine c-pim-1 proto-oncogene promotor

In our previous work we have shown that the oligonucleotide 5'-GGGGAGGGGGAGG-3' gives a very stable and specific triplex with the promoter of the murine c-pim-1 proto-oncogene in vitro[Svinarchuk, F., Bertrand, J.-R. and Malvy, C.(1994)Nucleic Acids Res., 22, 3742-3747]. In the present work, we have tested triplex formation with some derivatives of this oligonucleotide which are designed to be degradation-resistant inside the cells, and we show that phosphorothioate and the oligonucleotide with a 3' terminal amino group are still able to form triplexes. Moreover these oligonucleotides, like the 13mer oligonucleotide of similar composition [Svinarchuk, F., Paoletti, J., and Malvy, C. (1995) J. Biol. Chem., 270, 14068-14071], are able to stabilize the targeted duplex. In vivo DMS footprint analysis after electroporation of the pre-formed triplex into the cell have shown the presence of the triple helix inside the cells. This triplex structure partially blocks c-pim-1 promotor activity as shown by transient assay with a c-pim-1 promoter-luciferase gene construct. To our knowledge these data are the first direct evidence that conditions inside cells are favorable for triplex stability with non-modified oligonucleotides. However we were unable to show triplex formation inside living cells using various methods of oligonucleotide delivery. We suppose that this may be due to the oligonucleotide being sequestered by cellular processes or proteins. Further work is needed to find oligonucleotide derivatives and ways of their delivery to overcome the problem of triplex formation inside the cells.

Hairpin, dumbbell, and single-stranded phosphodiester oligonucleotides exhibit identical uptake in T lymphocyte cell lines

The cellular binding, uptake, and intracellular distribution of structured double-stranded phosphodiester oligonucleotides (decoys) have been examined in T lymphocytes using fluorescein-labeled molecules. Intracellular localization of hairpin and dumbbell decoys was similar to that of single-stranded oligonucleotides. At short incubation times, oligonucleotides were localized only in cytoplasmic vesicles, whereas at longer times, they were also found in the nucleus. Cellular uptake was dependent on temperature, time, and extracellular concentration. Oligonucleotide efflux was similar for all types of molecules and was very rapid (t1/2 = 10-15 minutes). These results imply that phosphodiester double-stranded oligonucleotides can enter cellular compartments of interest for their potential biologic function and, thus, provide a potential tool to control gene transcription.

The influence of polarized epithelial (Caco-2) cell differentiation on the cellular binding of phosphodiester and phosphorothioate oligonucleotides

Cell aging and the degree of cellular differentiation are thought to be important variables governing uptake of oligonucleotides but remain poorly understood. The Caco-2 colon carcinoma cell line has the ability to spontaneously differentiate into enterocytes in vitro and serves as a useful model to further investigate the effect of differentiation on oligonucleotide binding and uptake. In this study, we report that the extent of oligonucleotide association and the expression of cell surface binding proteins are governed by the age and thus the degree of differentiation of Caco-2 epithelial cells in culture. Cellular association (normalized for cell number) of an all phosphodiester (PO), all phosphorothioate (PS), and a phosphodiester oligonucleotide containing two terminal phosphorothioate internucleotide linkages at the 3' end (EC-PO) gradually increased from day 3 to around day 17 of the culture, followed by a plateau, or slight decrease, up to day 21 of the cell aging study. Overall, a threefold to fourfold increase in binding was observed from day 3 to day 17. Oligonucleotide binding was temperature and pH dependent, but the magnitude of the effect was influenced by cell aging and the degree of differentiation. PS oligonucleotides exhibited greater binding (up to threefold) at the basolateral surface compared with the apical surface within the pH range 5-7. These findings could be directly correlated with the expression levels of cell surface oligonucleotide binding proteins during the aging study. A Caco-2 cell surface protein binding complex of around 46 kDa was identified as the major site of binding for both PO and PS oligonucleotides, although the latter also bound to several other proteins, especially at low pH.

A simple method for delivering morpholino antisense oligos into the cytoplasm of cells

We report a simple and effective means for delivering Morpholino antisense oligos into the cytosol of cultured anchorage-dependent animal cells. This method, referred to as scrape-loading, is carried out in a matter of seconds, uses a common inexpensive laboratory implement, and has minimal detrimental impact on the cells. Using this delivery method, a Morpholino oligo present at 0.1 microM and 1 microM in the extracellular medium inhibited its targeted genetic sequence within cultured Hela cells at levels of 56% and 85%, respectively. Lack of inhibition by two control Morpholino oligos at concentrations up to 3 microM indicates good sequence specificity by this structural type. Also described is a test system for simple, rapid, and sensitive quantitation of antisense activity in cultured cells.

Interaction of oligodeoxynucleotides with mammalian cells

Many previous studies have demonstrated that antisense oligodeoxynucleotides (ODNs) bind to surface proteins in a manner compatible with receptor-mediated endocytosis and, unless specifically modified, are internalized into endosomes with little access to the cytoplasmic structures or to the nucleus. Reports vary as to the specific proteins involved in the mechanism, and this study examines the conditions of binding, some proteins that might contribute to the process, and whether changes in binding patterns occur during differentiation. Native gel electrophoresis was used to optimize the surface binding of a phosphorothioate end-capped 16-mer to T15 mouse fibroblast cells, and comparisons are made with some human epithelial tumor cell lines. Binding to individual proteins was visualized using SDS-PAGE and autoradiography. Binding at 4 degrees C was almost exclusively to a 46 kDa protein and decreased in the presence of an excess of unlabeled ODN and heparin but not ATP. Increasing the temperature of ODN binding from 4 degrees C to 37 degrees C for 10 minutes changed the binding pattern observed. ODN binding to the total cytoplasmic and membrane proteins immobilized on a membrane showed a greater number of binding proteins, the most prominent being one of 30 kDa. Examination of the effects of serum on binding were made using the human lung carcinoma cell line COR-L23, which can be grown in serum-free conditions. Serum starvation led to an increased total binding seen on native gels coinciding with increased binding to a 46 kDa protein. Demonstration that changes in binding proteins occur when cells differentiate was made using the premacrophage cell line THP-1. Differentiation of these cells increased the total ODN binding and appeared to initiate the synthesis of some new binding proteins, although binding to a 46 kDa protein was reduced.

Binding, uptake, and intracellular trafficking of phosphorothioate-modified oligodeoxynucleotides

An enhanced appreciation of uptake mechanisms and intracellular trafficking of phosphorothioate modified oligodeoxynucleotides (P-ODN) might facilitate the use of these compounds for experimental and therapeutic purposes. We addressed these issues by identifying cell surface proteins with which P-ODN specifically interact, studying P-ODN internalization mechanisms, and by tracking internalized P-ODN through the cell using immunochemical and ultrastructural techniques. Chemical cross-linking studies with a biotin-labeled P-ODN (bP-ODN), revealed the existence of five major cell surface P-ODN binding protein groups ranging in size from approximately 20-143 kD. Binding to these proteins was competitively inhibited with unlabeled P-ODN, but not free biotin, suggesting specificity of the interactions. Additional experiments suggested that binding proteins likely exist as single chain structures, and that carbohydrate moieties may play a role in P-ODN binding. Uptake studies with 35S-labeled P-ODN revealed that endocytosis, mediated by a receptor-like mechanism, predominated at P-ODN concentrations < 1 microM, whereas fluid-phase endocytosis prevailed at higher concentrations. Cell fractionation and ultrastructural analysis demonstrated the presence of ODN in clathrin coated pits, and in vesicular structures consistent with endosomes and lysosomes. Labeled ODN were also found in significant amounts in the nucleus, while none was associated with ribosomes, or ribosomes associated with rough endoplasmic reticulum (ER). Since nuclear uptake was not blocked by wheat germ agglutinin or concanavalin A, a nucleoporin independent, perhaps diffusion driven, import process is suggested. These data imply that antisense DNA may exert their effect in the nucleus. They also suggest rational ways to design ODN which might increase their efficiency.

The uptake and distribution of phosphorothioate oligonucleotides into vascular smooth muscle cells in vitro and in rabbit arteries

Oligonucleotides are a class of compounds with potential as therapeutics for a variety of clinical applications. Local delivery of oligonucleotides to the arterial wall is a challenging aspect of the development of these therapeutics for restenosis, and herein we report experiments characterizing the uptake and distribution of phosphorothiate oligonucleotides into vascular smooth muscle cells in primary cultures and in rabbit arteries. Primary cultures of smooth muscle cells incubated with rhodamine-oligonucleotides showed uptake only into cytoplasmic vesicles. No nuclear or cytosolic localization was detected. In normal arteries there was no visible tissue or cellular uptake of oligonucleotides after intralumenal administration. However, in balloon-injured arteries there was significant oligonucleotide uptake into the tissue with apparent cytoplasmic delivery to the medial smooth muscle cells, as evinced by intense staining of their nuclei with labeled oligonucleotides. Measurement of FITC-oligonucleotide in artery extracts showed significantly greater uptake in injured, compared with normal arteries. Light and electron microscopic studies demonstrated a correlation between the degree of damage and the amount of uptake. These results demonstrate that oligonucleotides penetrate easily into the arterial wall of balloon-injured arteries and accumulate in the medial smooth muscle cells-the target cells for antirestenosis therapeutics following balloon angioplasty.

Use of cyclodextrin and its derivatives as carriers for oligonucleotide delivery

The use of antisense phosphorothioate oligodeoxynucleotides as tools for modulating gene expression represents a novel strategy for designing drugs to treat a variety of diseases. Several factors, including cellular uptake and internalization of the phosphorothioate oligodeoxynucleotide, are important parameters in determining the effectiveness of antisense agents as therapies. We have used cyclodextrin and its analogs as carriers to increase cellular uptake of phosphorothioate oligodeoxynucleotides. The studies were carried out using 35S-labeled and fluorescent-labeled phosphorothioate oligodeoxynucleotide in human T cell leukemia H9 cell line. Cellular uptake of phosphorothioate oligodeoxynucleotide in the presence of cyclodextrin was found to be concentration and time dependent. Using various cyclodextrin analogs, e.g., 2-hydroxypropyl beta-cyclodextrin (HPCD), hydroxyethyl beta-cyclodextrin (HECD), and a mixture of various hydroxypropyl beta-cyclodextrins (Encapsin), we observed increases in phosphorothioate oligodeoxynucleotide uptake, up to twofold to threefold in 48 hours. Confocal microscopy studies confirmed that oligonucleotide was present intracellularly. Cyclodextrin itself was not toxic at the concentration used. Cyclodextrins did not seem to affect the efflux of phosphorothioate oligodeoxynucleotide from cells. Stability of phosphorothioate oligodeoxynucleotide against endogenous cellular nucleases remained unchanged in the presence of cyclodextrins. These studies suggest that cyclodextrin and its analogs might be used successfully as carriers for oligonucleotide and analogs.

Specificity in splicing

Considerable information about the process of pre-mRNA splicing has accumulated, but the mechanism by which highly accurate splicing is achieved is unresolved. Fifteen years ago we proposed that accuracy in splicing might depend on small RNA molecules (splicer RNAs) which hybridise across adjacent exon termini, or intron termini. Gene expression, including alternative splicing, could be controlled by the transcription of specific splicer RNA genes. We re-assess our model here, in the light of subsequent developments.

Repression of Fanconi anemia gene (FACC) expression inhibits growth of hematopoietic progenitor cells

Bone marrow failure is a consistent feature of Fanconi anemia (FA) but it is not known whether the bone marrow failure is a direct and specific result of the inherited mutation or a consequence of accumulated stem cell losses resulting from nonspecific DNA damage. We tested the hypothesis that the protein encoded by the FA group C complementing gene (FACC) plays a regulatory role in hematopoiesis. We exposed normal human lymphocytes, bone marrow cells, endothelial cells, and fibroblasts to an antisense oligodeoxynucleotide (ODN) complementary to bases -4 to +14 of FACC mRNA. The mitomycin C assay demonstrated that the antisense ODN, but not missense or sense ODNs, repressed FACC gene expression in lymphocytes. Treatment with the antisense ODN substantially reduced, in a sequence-specific fashion, cytoplasmic levels of FACC mRNA in bone marrow cells and lymphocytes. Escalating doses of antisense ODN increasingly inhibited clonal growth of erythroid and granulocyte-macrophage progenitor cells but did not inhibit growth of fibroblasts or endothelial cells. The antisense ODN did not inhibit growth factor gene expression by low density bone marrow cells or marrow-derived fibroblasts. We conclude that, while the FACC gene product plays a role in defining cellular tolerance to cross-linking agents, it also functions to regulate growth, differentiation, and/or survival of normal hematopoietic progenitor cells.