Antisense oligodeoxynucleotides as clinical therapeutic agents

Review : p53 in the pathogenesis, diagnosis, and treatment of cancer

Objective. The cellular functions of p53, the conse quences of the loss of p53 function, and the potential impact of p53 in oncology are reviewed within the framework of an overview of the molecular basis of cancer and cell cycle control.

Data Sources. A MEDLINE search of articles from 1976 to the present was conducted using the terms p53 protein and p53 gene. The search was restricted to the English language. Oncology and molecular biology textbooks were used as additional references.

Data Extraction. We reviewed the literature to discuss the cellular function of p53, the mechanisms of p53 inactivation, the cellular consequences of the loss of p53 function, the role of p53 loss in tumori genesis, and the potential applications of this knowl edge.

Data Synthesis. p53 mutations are found in ~ 50% of human cancers. Knowledge of p53 functions and defects provides the basis for potential applica tions in the areas of cancer epidemiology, cancer diagnosis, and determination of prognosis. An under standing of the functions and defects of p53 also presents a host of opportunities for the design of novel cancer therapies. Therapeutic approaches be ing studied include the restoration of p53 by gene therapy, the alteration of mutant p53 expression by antisense therapy, and the use of p53 mutations as a target for directing therapy to cancer cells; some of these approaches are already under phase I investiga tion. As knowledge of p53 unfolds, additional thera peutic approaches will certainly be developed. The story of p53 illustrates that the manipulation of mo lecular interactions is a new frontier in therapeutics and offers an additional role for oncology pharmacy specialists.

Gene modulation for treating liver fibrosis

Despite tremendous progress in our understanding of fibrogenesis, injury stimuli process, inflammation, and hepatic stellate cell (HSC) activation, there is still no standard treatment for liver fibrosis. Delivery of small molecular weight drugs, proteins, and nucleic acids to specific liver cell types remains a challenge due to the overexpression of extracellular matrix (ECM) and consequent closure of sinusoidal gaps. In addition, activation of HSCs and subsequent release of inflammatory cytokines and infiltration of immune cells are other major obstacles to the treatment of liver fibrosis. To overcome these barriers, different therapeutic approaches are being investigated. Among them, the modulation of certain aberrant protein production is quite promising for treating liver fibrosis. In this review, we describe the mechanism of antisense, antigene, and RNA interference (RNAi) therapies and discuss how the backbone modification of oligonucleotides affects their in vivo stability, biodistribution, and bioactivity. Strategies for delivering these nucleic acids to specific cell types are discussed. This review critically addresses various insights developed with each individual strategy and for multipronged approaches, which will be helpful in achieving more effective outcomes.

Antisense therapy: recent advances and relevance to prostate cancer

Currently employed treatment options for patients with advanced and metastatic cancer such as surgery, radiation, hormone therapy, and chemotherapy are limited. In particular, the well known limitations of chemotherapy are at least in part due to a lack of specificity. The activation of dominant oncogenes and inactivation of tumor suppressor genes may represent novel targets for cancer therapy. Antisense therapy has been widely used to specifically and selectively inhibit the expression of selected genes at the messenger RNA level. Combinations of antisense oligonucleotides with chemotherapeutic agents may offer important advantages in cancer treatment. Several antisense drugs, especially oblimersen (G3139), have shown interesting results in experiments in animals, and have entered clinical trials. However, control oligonucleotides must be carefully chosen to separate antisense effects from the many potential nonspecific effects of oligonucleotides. This review summarizes the advantages and limitations of antisense therapy and its use in the treatment of androgen-independent prostate cancer.

Folate-liposome-mediated antisense oligodeoxynucleotide targeting to cancer cells: evaluation in vitro and in vivo

The objective of this study was to investigate the use of folate-targeted liposomes for the delivery of encapsulated oligonucleotides to folate receptor (FR)-positive tumor cells in vitro and in vivo. This project involved the synthesis and biological evaluation of many folate-PEG-lipid conjugates, where the chemical form of the folate moiety (pteroate) and the length of the PEG linker chain were varied widely. Folate-targeted oligonucleotide-containing liposomes were prepared using conventional methods, and the extent of cell uptake was evaluated using, among others, the FR positive KB cell line. Oligonucleotide-loaded folate-targeted liposomes were found to rapidly associate with the KB cells, and saturation was typically reached within the first hour of incubation at 37 degrees C. Nearly 100,000 liposomes per cell were bound or internalized at saturation. Importantly, cell association was blocked by a large excess folic acid, thus reflecting the FR-specific nature of the cell interaction. Full targeting potential was achieved with PEG linkers as low as 1000 in molecular weight, and pteroates bearing glycine or gamma-aminobutyryl residues juxtaposed to the pteroic acid moiety were also effective for targeting, provided that a terminal cysteine moiety was present at the distal end of the PEG chain for added hydrophilicity. When tested in vivo, folate-targeted liposomes were found to deliver approximately 1.8-fold more oligonucleotide to the livers of nude mice (relative to the nontargeted PEG-containing formulations); however, no improvement in KB tumor uptake was observed. We conclude from these results that folate liposomes can effectively deliver oligonucleotides into folate receptor-bearing cells in vitro, but additional barriers exist in vivo that prevent or decrease effective tumor uptake and retention.

Inhibition of Plasmodium falciparum proliferation in vitro by antisense oligodeoxynucleotides against malarial topoisomerase II

The development of new effective antimalarial agents is urgently needed due to the ineffectiveness of current drug regimes on the most virulent human malaria parasite Plasmodium falciparum. Antisense (AS) oligodeoxynucleotides (ODNs) have shown promise as chemotherapeutic agents. Phosphorothioate AS ODNs against different regions of P. falciparum topoisomerase II gene were investigated. Chloroquine- and pyrimethamine-resistant P. falciparum K1 strain was exposed to phosphorothioate AS ODNs for 48 h and growth was determined by flow cytometric assay or by microscopic assay. Exogenous delivery of phosphorothioate AS ODNs between 0.01 and 0.5 microM significantly inhibited parasite growth compared with sense sequence controls suggesting sequence specific inhibition. This inhibition was shown to occur during maturation stages, with optimal inhibition being detected after 36 h. These results should prove useful in future designs of novel antimalarial agents.

The quest for an efficacious antiviral for respiratory syncytial virus

Respiratory syncytial virus (RSV) continues as an emerging infectious disease not only among infants and children, but also for the immune-suppressed, hospitalized and the elderly. To date, ribavirin (Virazole) remains the only therapeutic agent approved for the treatment of RSV. The prophylactic administration of palivizumab is problematic and costly. The quest for an efficacious RSV antiviral has produced a greater understanding of the viral fusion process, a new hypothesis for the mechanism of action of ribavirin, and a promising antisense strategy combining the 2'-5' oligoadenylate antisense (2-5A-antisense) approach and RSV genomics.

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.

Targeted delivery of antisense oligonucleotides in cancer

Formulations of antisense oligonucleotides (asODNs) against c-myb or c-myc protooncogenes have been prepared by a new technique that sequesters cationic lipid in the interior of a lipid particle. This technique results in high loading efficiency for the asODNs, small particle size and good stability. When targeted against melanoma cells or neuroblastoma cells via anti-GD(2) coupled at the particle surface, increased cell binding to the cells could be demonstrated. Targeted formulations showed greater inhibition of cell proliferation compared to non-targeted formulations or free drug. Inhibition of cell proliferation was demonstrated to be due to down-regulation of c-myb or c-myc protein expression. The formulations have long-circulation times in vivo, and evaluation for in vivo antitumor activity is currently underway.

Hippocampal administration of kappa-opioid receptor antisense exacerbates isolation-induced hypertension

Isolation of young male Sprague Dawley rats for 7 days provoked hypertension which was exacerbated by hippocampal administration of an antisense oligodeoxynucleotide targeted to the kappa-opioid receptor (1 microg/0.5 microL bilaterally, twice daily, during the isolation or grouping period). Systolic blood pressure rose from a mean of 134 to 162 mmHg in isolated rats treated with antisense and only 139 to 151 mmHg in grouped rats treated with antisense. In grouped rats treated with either vehicle or missense, isolation caused a mean increase in systolic blood pressure of only 16 and 14 mmHg respectively. Neither the missense oligodeoxynucleotide nor the vehicle had any significant effects upon systolic pressure in grouped rats, which had not been isolated. Pharmacological studies indicated that rats previously treated with the antisense had no significant depressor response to U62, 066E (a non-peptide kappa agonist known to reduce blood pressure acutely when administered into the hippocampus), however rats previously treated with vehicle or missense exhibited a significant hypotensive response to the drug. This implies that the antisense had reduced the density or activity of the kappa receptors within the hippocampal formation. These data are in accordance with our previous studies, i.e. in several rat models of hypertension, the increase in blood pressure may be modulated via hippocampal kappa opioid receptors.

Responses of human B cells to DNA and phosphorothioate oligodeoxynucleotides

Emerging information has documented that certain DNA and sODNs can be both immunogenic and immunostimulatory. sODNs, but not DNA, induce T-cell-independent polyclonal activation of human B cells by engaging cell-surface receptors. Manifestations of sODN-induced human B-cell activation include expression of activation markers, proliferation, Ig production and anti-DNA antibody production. IL-2 and intact T cells enhanced B-cell responses to sODNs but were not required. Monocytes also provided a modest enhancement of human B-cell responses induced by sODNs. The chemical nature of sODNs capable of stimulating human B cells and the specific cell-surface receptors involved have not been completely delineated. Further studies will be necessary to elucidate the potential role of stimulatory sODNs in disease pathogenesis and to develop a means to employ ODNs as therapeutic agents in humans.

Chiral and steric effects in the efficient binding of alpha-anomeric deoxyoligonucleoside N-alkylphosphoramidates to ssDNA and RNA

We report hybridization properties of new phosphate-modified alpha-oligonucleoside analogs with non-ionic or cationic internucleotide linkages such as methoxy-ethylphosphoramidate (PNHME), phosphoromorpholi-date (PMOR) and dimethylaminopropylphosphor-amidate (PNHDMAP). First we evaluated the chirality effect of the phosphorus atom on the affinity of alpha- or beta-dodecanucleoside phosphodiesters containing one chirally enriched N -alkylphosphoramidate linkage located in the middle of the sequence d(TCTT-AA*CCCACA). As for P-substituted beta-oligonucleo-tides, a difference in binding behavior between the two diastereoisomers (difference in Delta T (m)) exists in the hybridization properties of alpha-analogs when DNA was the target but this effect was not detrimental to duplex stability. This effect was considerably reduced when RNA was the target. Secondly we studied the effect of steric hindrance around phosphorus on the affinity of fully modified beta- and alpha-oligonucleoside N -alkylphosphoramidates for their DNA and RNA targets. This effect was very weak with alpha-analogs whereas it was more pronounced with beta-oligos. PNHME-modified alpha-oligonucleosides formed more stable duplexes with DNA (Delta T (m)+9.6 degrees C) and RNA (Delta T (m)+1.4 degrees C) targets than the 'parent' phosphodiester. Finally, base pairing specificity of these alpha-oligonucleo-side N -alkylphosphoramidates for their targets was found to be as high as for natural oligonucleoside phosphodiesters.

Kappa-opioid receptor antisense oligonucleotide injected into rat hippocampus causes hypertension

Bi-hippocampal microinjection treatment (1 microg per side, twice a day for 5 days) with an antisense phosphorothioate oligodeoxynucleotide antisense oligodeoxynucleotide to the rat kappa-opioid receptor, caused hypertension in normotensive Wistar Kyoto (WKY) rats and increased the blood pressure of spontaneously hypertensive rats (SHR). Systolic blood pressure in WKY rats increased from 121+/-4 to 153+/-6 mm Hg, and in SHR systolic blood pressure increased from 153+/-4 to 183+/-5 mm Hg. Similar results were observed with mean blood pressure, however, there were no changes in heart rate. No significant responses were seen with either vehicle or missense injections. Radioligand binding studies indicated that there was a significant decrease in apparent kappa-opioid receptor density due to antisense oligodeoxynucleotide treatment. The results are in accord with our earlier suggestions that the kappa-opioid system in the hippocampus may have a role in the neural control of blood pressure.

Inhibition of DNA synthesis by downregulation of cyclin A but not Skp 2 overexpression in human hepatocellular carcinoma cells

Cyclin A is an S and G2/M phase regulatory protein and associates with Skp 2 in many transformed cells. Our previous results showed that 12 (39%) and 17 (55%) out of 31 hepatocellular carcinoma (HCC) patients exhibited higher protein expression levels of cyclin A and Skp 2, respectively, in their tumorous compared to non-tumorous tissues. In the present study, we used Western blot analysis to show that 3 out of 6 HCC cell lines, HA59T, HA22T and HCC36, exhibited overexpression of cyclin A, among which the HCC36 cell line also expressed a higher Skp 2 protein level. Moreover, we used the antisense oligonucleotide phosphorothioates to down regulate the overexpression of cyclin A and Skp 2 proteins to determine whether or not these two proteins are involved in the mitogenesis of HCC36 cells. After treatment with antisense oligonucleotide phosphorothioates, the gene product of cyclin A or Skp 2 was suppressed dose-dependently as revealed by Western blot analyses. By [3H]thymidine incorporation assay, we found that downregulation of cyclin A but not Skp 2 overexpression could inhibit the DNA synthesis ability of HCC36 cells, suggesting that abnormal Skp 2 expression is not directly correlated with the HCC proliferation.

Anomeric inversion (from beta to alpha) in methylphosphonate oligonucleosides enhances their affinity for DNA and RNA

Here we report that the poor binding of methylphosphonate oligodeoxynucleosides (MP-ODNs) to their nucleic acid targets can be improved by additional inversion of the anomeric configuration (from beta to alpha) in the sugar moieties to give a new class of analogs, MP alpha-oligonucleosides. MP alpha-dT12and MP 5' alpha-d(TCTTAACCCACA) 3' were synthesized and their ability to form hybrids with complementary single stranded (ss)DNA and ssRNA, as well as with double stranded (ds)DNA, was evaluated. The thermal stability of hybrids formed with MP alpha-analogs was compared with the affinity of phosphodiester (PO) and phosphorothioate (PS) beta- and alpha-oligomers for their targets. Non-ionic MP alpha-oligonucleosides bound to their complementary DNA and RNA strands more tightly than their homologues with natural beta-anomeric configuration did. With DNA target, MP alpha-oligomers formed duplexes more stable than the corresponding natural PO beta-oligomer did. MP alpha-heteropolymer hybridized to RNA target better than PS beta-oligonucleotide did but the hybrid was less stable (DeltaTm-0.5 degrees C per mod.) than the hybrid formed with the natural PO beta-oligomer. Only MP alpha-dT12 bound to dsDNA target at low salt concentration (0.1 M NaCl).

Localization of a FITC-labeled phosphorothioate oligodeoxynucleotide in the skin after topical delivery by iontophoresis and electroporation

PURPOSE

The aim of this study was to verify the hypothesis that the application of high voltage to the skin enhances both stratum corneum and keratinocyte permeability. Therefore, the transport of FITC labelled phosphorothioate oligonucleotides (FITC-PS) administered by passive diffusion, iontophoresis or electroporation was localized.

METHODS

Fluorescent microscopy and laser scanning confocal microscopy were used to visualize the FITC-PS transport at the tissue and cell level respectively in hairless rat skin after electroporation (5 x (200 V approximately 500 ms) or iontophoresis (same amount of charges transferred).

RESULTS

FITC-PS did not penetrate the viable skin by passive diffusion. Molecular transport in the skin upon electroporation or iontophoresis was localized and implied mainly hair follicles for iontophoresis. In the stratum corneum, the pathways for FITC-PS transport were more transcellular during electroporation and paracellular during iontophoresis. FITC-PS were detected in the nucleus of the keratinocytes a few minutes after pulsing. In contrast, iontophoresis did not lead to an uptake of the oligomer.

CONCLUSIONS

The internalization of FITC-PS in the keratinocytes after electroporation confirms the hypothesis and suggests that electroporation, which allows both efficient topical delivery and rapid cellular uptake of the oligonucleotides, might be useful for antisense therapy of epidermal diseases.

Overview of recent topics in clinical pharmacology of anticancer agents

The rationale for studying the clinical pharmacology of antineoplastic agents is that the information obtained will result in enhanced drug development and enhanced or improved clinical use. A great deal of effort has been expended in studying the pharmacokinetics and pharmacodynamics of investigational and noninvestigational antineoplastic agents. More recently, a deeper appreciation has developed regarding the importance of the metabolism of antineoplastic agents and the potential role of metabolites in their activity or toxicity, as well as the potential for drug-drug interactions. Investigators studying the clinical pharmacology of antineoplastic agents face an increasingly challenging task as new agents continue to be developed. Some of these challenges arise from the enhanced potency of new agents, resulting in increased difficulty in measuring such agents in biological matrices. Furthermore, as agents have been developed to affect specific biological targets, the necessity of assessing pharmacodynamics at the biochemical or molecular level has become increasingly important. In addition, development of agents with cytostatic, as opposed to cytotoxic, properties poses a further challenge to assessment of pharmacologic effect. In addressing these challenges, a great deal of effort has been expended to develop increasingly sensitive analytical chemical techniques, in evaluating alternative biological matrices, such as saliva, in which to monitor drug concentrations in a less invasive fashion, and in developing limited sampling strategies to assess both the pharmacokinetics and pharmacodynamics of antineoplastic agents. Similarly, a great deal of effort has been expended in providing suitable means for assessing the numerous novel targets for which antineoplastic agents are being developed. These include the assessment of cell cycle kinetics and specific oncoproteins, definition of cell damage such as cleavable complexes, and formation of drug-macromolecular adducts in suitable target cells. Additional effort is being expended to explore nontraditional means of drug delivery. In this regard, the increasing importance of orally administered agents reflects a fundamental change in the approach to antineoplastic drug delivery. Finally, the increased computational power made available by faster personal computers has facilitated a number of innovative modeling techniques involving population modeling, modeling of combination chemotherapy, and assessment of drug-drug interactions.

Biological effects and cellular uptake of c-myc antisense oligonucleotides and their cationic liposome complexes

The biological effects and cellular uptake of human c-myc antisense oligonucleotides and their liposome complexes were investigated in vitro using human promonocytic leukemia U937 cells. Antisense phosphorothioate oligonucleotides (S-Oligo) significantly inhibited the growth of U937 cells in a dose-dependent manner. However, no significant effect on cell proliferation was observed with unmodified phosphodiester (P-Oligo) and partially phosphorothioated (PS3-Oligo) oligonucleotides with an antisense sequence and S-Oligo with sense and G-quartet control sequences. In cellular uptake experiments, radiolabeled S-Oligo was taken up by U937 cells more than P-Oligo and PS3-Oligo. Similar results were obtained in mouse peritoneal macrophages used for comparison. Confocal microscopic studies demonstrated a significant distribution of FITC-labeled oligonucleotides on the cell surface and in the cytoplasm in a punctate pattern, but not in the nucleus. When complexed with cationic liposomes, cellular uptake of FITC-labeled P-Oligo or S-Oligo was significantly increased and the fluorescence was located mainly in the nucleus, indicating that the uptake and intracellular pharmacokinetics of both oligonucleotides can be modified by complexation. An inhibitory effect of the complexes was observed at a dose which is ineffective in the case of the oligonucleotides alone. However, this effect was also associated with cytotoxicity of the cationic liposomes, suggesting that optimization of this formulation will be necessary to achieve a more efficient delivery of the oligonucleotides to U937 cells.

Antisense Oligodeoxynucleotide Technology: Potential Use for the Treatment of Malignant Brain Tumors

BACKGROUND: Antisense oligodeoxynucleotides (ODNs) have been proposed as a new therapy for patients with cancer, including malignant brain tumors. Antisense ODNs are taken up by tumor cells and selectively block gene expression. Use of ODNs for brain tumors is attractive due to their theoretical specificity, relative ease of production and, to date, paucity of reported adverse effects. This article presents current information regarding antisense ODNs and their possible future use for the treatment of brain tumors. METHODS: The available published experimental and clinical information regarding antisense ODN treatment of glioblastoma cells and administration into the central nervous system (CNS) was reviewed. Other clinically relevant information pertaining to the molecular biology of antisense ODNs was also collected and summarized. RESULTS: Targets for antisense ODN therapy in malignant glioma cells have included c-myc, c-myb, c-sis, c-erb B, CD44, p34cdc2, bFGF, PDGF, TGF-beta, IGF-1, PKC-alpha tumor necrosis factor, urokinase, and S100beta protein. Few in vivo studies of ODN treatment of brain tumors have yet been reported. Systemically administered ODNs enter the brain only in extremely small quantities; therefore, microinfusion into the brain has been recommended. CONCLUSIONS: Antisense ODNs have been used successfully to block glioblastoma gene expression in vitro and expression of multiple genes within the CNS of experimental animals. Upcoming clinical trials will address the safety of antisense ODN use against malignant brain tumors.

Antisense inhibition of phosphodiesterase expression

Cyclic nucleotide phosphodiesterases (PDEs) are represented by a superfamily of structurally and functionally related enzymes of which more than 30 different forms have so far been identified and grouped into seven broad gene families, some of which contain multiple genes and many splice variants, within a given gene family. Since all of the forms of PDE have the potential to regulate levels of the second messenger, cAMP or cGMP, and some of the forms appear to be tissue specific in their expression and differentially regulated, it would be useful to be able to selectively inhibit a given form of PDE, to study the physiological consequences of this inhibition, with the intent of possible therapeutic application. While gene family-specific pharmacological inhibitors exist for six of the seven gene families, none of these inhibitors is yet capable of distinguishing PDE members within a given gene family in its inhibition. One approach to selectively inhibit a specific form of PDE, without affecting others, is through use of antisense oligonucleotides to block the expression of a given PDE form. This article describes ways to optimally develop and test antisense oligonucleotides to inhibit expression of PDE.

Antisense properties of end-modified oligonucleotides targeted to Ha-ras oncogene

Phosphodiester oligodeoxyribonucleotides linked to an intercalating agent or a dodecanol tail or both complementary to the 12th codon region of Ha-ras mRNA were compared with the unmodified oligonucleotides of the same size and sequence with respect to their ability to induce RNaseH cleavage and antisense activity in cell culture. The hydrophobic tail not only protected the oligonucleotide from nucleases but also enhanced RNase H cleavage of the target. Oligonucleotides carrying both an acridine and a dodecanol substituent inhibited the proliferation of HBL100ras1 cells (human mammary cells stably transformed with the T24 Ha-ras gene carrying a G-->T point mutation in codon 12) at a 20-fold to 30-fold lower concentration than unmodified ones. Therefore, these modified oligonucleotides may prove useful for antisense applications.

Characterization and mapping of the double-stranded regions involved in activation of PKR within a cellular RNA from 3T3-F442A cells

PKR is a doubled-stranded RNA-dependent protein kinase which is implicated in the regulation of several cellular processes, including cell proliferation. PKR undergoes phosphorylation and activation in mouse embryonic 3T3-F442A cells in response to endogenous RNA(s). Activation of PKR is related to growth and differentiation of these cells. A cellular regulatory RNA (R-RNA) which activates PKR has been isolated from these cells and its cDNA partially sequenced. Here we have characterized the R-RNA transcript with respect to nuclease sensitivity and the extent of double-stranded structure involved in activation of PKR. The location of the activating sequence was mapped to a contiguous 226/252 nt region of the R-RNA transcript by hybridization to its cDNA fragments. Hybridization with a panel of short oligodeoxynucleotides complementary to the R-RNA, coupled with protein kinase analysis, was used to probe the 252 nt region for critical sequences. Three short non-contiguous sequences which appear most important for activation of PKR were identified within the 252 nt region. Thus, these studies have identified specific sequences most important for activation of PKR. Furthermore, since the above antisense oligodeoxynucleotides inhibit enzyme activation, our results exemplify an unusual mode of action of antisense sequences on the activation of PKR by disruption of RNA secondary structure.

Development of targeted delivery systems for nucleic acid drugs

Our increased understanding of disease pathogenesis is the basis for developing novel nucleic acid drugs. The main challenge encountered in this development is how to maintain therapeutically meaningful concentrations of the drugs in the vicinity of their targets for the desired periods. The intrinsic difficulty arises from the fact that nucleic acid drugs are not readily transported across membranes. Hence, their delivery and transport characteristics at the whole body, organ and cellular levels need to be thoroughly examined. Liposomes and receptor-mediated polycation systems are promising carriers for their delivery in vivo. There are many barriers to be overcome for successful antisense and gene therapies. Along with other factors, disposition, stability against nucleases, binding to cell surface receptor and internalization, and intracellular trafficking affect the in vivo delivery and efficacy of nucleic acid drugs. This review article discusses the delivery and transport of these compounds.

Antisense technology and prospects for therapy of viral infections and cancer

Eighteen years ago, antisense oligonucleotide therapeutics that can selectively knock out disease-causing genes could easily have been viewed as science fiction. Yet today, through much persistence and focused investment, the technology has nearly evolved to the point of realization. A number of first-generation antisense compounds have entered human clinical trials. Some of these compounds appear to work by an antisense mechanism to inhibit the expression of disease-causing genes, while others probably work by unanticipated, yet clinically beneficial, mechanisms. In this review, the current status of antisense oligonucleotide development will be described as it relates to two areas of concentrated effort: antiviral and anticancer applications.

Impact of the cyclin-dependent kinase inhibitor p27Kip1 on resistance of tumor cells to anticancer agents

A low proliferating fraction in solid tumors limits the effectiveness of cell cycle-dependent chemotherapeutic agents. To understand the molecular basis of such "kinetic" resistance we cultured tumor cells as multicellular spheroids and examined levels of p27Kip1, a cyclin-dependent kinase inhibitor known to be upregulated by intercellular contact in normal cells. When transferred from monolayer to three-dimensional culture, a consistent upregulation (up to 15-fold) of p27 protein was observed in a panel of mouse and human carcinoma cell lines. Antisense-oligonucleotide-mediated downregulation of p27 in EMT-6 mammary tumor cell spheroids reduced intercellular adhesion, increased cell proliferation, sensitized tumor cells to 4-hydroperoxycyclophosphamide, and restored drug- or radiation-induced cell-cycle perturbations repressed in spheroid culture. Our results implicate p27 as a regulator of drug resistance in solid tumors and suggest that tumor-targeted p27 antagonists may be useful chemosensitizers in conjunction with conventional anticancer therapy.