Inhibition of gene expression in Entamoeba histolytica with antisense peptide nucleic acid oligomers

Nucleic acid nanoassembly-enhanced RNA therapeutics and diagnosis

RNAs are involved in the crucial processes of disease progression and have emerged as powerful therapeutic targets and diagnostic biomarkers. However, efficient delivery of therapeutic RNA to the targeted location and precise detection of RNA markers remains challenging. Recently, more and more attention has been paid to applying nucleic acid nanoassemblies in diagnosing and treating. Due to the flexibility and deformability of nucleic acids, the nanoassemblies could be fabricated with different shapes and structures. With hybridization, nucleic acid nanoassemblies, including DNA and RNA nanostructures, can be applied to enhance RNA therapeutics and diagnosis. This review briefly introduces the construction and properties of different nucleic acid nanoassemblies and their applications for RNA therapy and diagnosis and makes further prospects for their development.

Establishment of quantitative RNAi-based forward genetics in Entamoeba histolytica and identification of genes required for growth

While Entamoeba histolytica remains a globally important pathogen, it is dramatically understudied. The tractability of E. histolytica has historically been limited, which is largely due to challenging features of its genome. To enable forward genetics, we constructed and validated the first genome-wide E. histolytica RNAi knockdown mutant library. This library allows for Illumina deep sequencing analysis for quantitative identification of mutants that are enriched or depleted after selection. We developed a novel analysis pipeline to precisely define and quantify gene fragments. We used the library to perform the first RNAi screen in E. histolytica and identified slow growth (SG) mutants. Among genes targeted in SG mutants, many had annotated functions consistent with roles in cellular growth or metabolic pathways. Some targeted genes were annotated as hypothetical or lacked annotated domains, supporting the power of forward genetics in uncovering functional information that cannot be gleaned from databases. While the localization of neither of the proteins targeted in SG1 nor SG2 mutants could be predicted by sequence analysis, we showed experimentally that SG1 localized to the cytoplasm and cell surface, while SG2 localized to the cytoplasm. Overexpression of SG1 led to increased growth, while expression of a truncation mutant did not lead to increased growth, and thus aided in defining functional domains in this protein. Finally, in addition to establishing forward genetics, we uncovered new details of the unusual E. histolytica RNAi pathway. These studies dramatically improve the tractability of E. histolytica and open up the possibility of applying genetics to improve understanding of this important pathogen.

Target identification and intervention strategies against amebiasis

Entamoeba histolytica is the etiological agent of amebiasis, which is an endemic parasitic disease in developing countries and is the cause of approximately 70,000 deaths annually. E. histolytica trophozoites usually reside in the colon as a non-pathogenic commensal in most infected individuals (90% of infected individuals are asymptomatic). For unknown reasons, these trophozoites can become virulent and invasive, cause amebic dysentery, and migrate to the liver where they cause hepatocellular damage. Amebiasis is usually treated either by amebicides which are classified as (a) luminal and are active against the luminal forms of the parasite, (b) tissue and are effective against those parasites that have invaded tissues, and (c) mixed and are effective against the luminal forms of the parasite and those forms which invaded the host's tissues. Of the amebicides, the luminal amebicide, metronidazole (MTZ), is the most widely used drug to treat amebiasis. Although well tolerated, concerns about its adverse effects and the possible emergence of MTZ-resistant strains of E. histolytica have led to the development of new therapeutic strategies against amebiasis. These strategies include improving the potency of existing amebicides, discovering new uses for approved drugs (repurposing of existing drugs), drug rediscovery, vaccination, drug targeting of essential E. histolytica components, and the use of probiotics and bioactive natural products. This review examines each of these strategies in the light of the current knowledge on the gut microbiota of patients with amebiasis.

Antisense antimicrobial therapeutics

Antisense antimicrobial therapeutics are synthetic oligomers that silence expression of specific genes. This specificity confers an advantage over broad-spectrum antibiotics by avoiding unintended effects on commensal bacteria. The sequence-specificity and short length of antisense antimicrobials also pose little risk to human gene expression. Because antisense antimicrobials are a platform technology, they can be rapidly designed and synthesized to target almost any microbe. This reduces drug discovery time, and provides flexibility and a rational approach to drug development. Recent work has shown that antisense technology has the potential to address the antibiotic-resistance crisis, since resistance mechanisms for standard antibiotics apparently have no effect on antisense antimicrobials. Here, we describe current reports of antisense antimicrobials targeted against viruses, parasites, and bacteria.

Copper-64-labeled anti-bcl-2 PNA-peptide conjugates selectively localize to bcl-2-positive tumors in mouse models of B-cell lymphoma

INTRODUCTION

The bcl-2 gene is overexpressed in non-Hodgkin's lymphoma (NHL). We have reported micro-SPECT/CT imaging of Mec-1 human lymphoma xenografts in SCID mice, using [(111)In]DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate. In order to reduce normal organ accumulation and improve imaging contrast, modified monomers with neutral hydrophilic (serine, TS) or negatively charged (aspartic acid, TD) residues were synthesized as substitutes for glycine at T(14) in the PNA sequence. The parent and modified PNA-peptide conjugates were labeled with (64)Cu and evaluated in biodistribution studies and high resolution PET/CT imaging of SCID mice bearing bcl-2-positive Mec-1 xenografts as well as bcl-2-negative Ramos xenografts.

METHODS

Mice were administered the (64)Cu-labeled conjugates for biodistribution and imaging studies. Biodistributions were obtained from 1 to 48 h post-injection. Mice were imaged from 1 to 48 h post-injection.

RESULTS

The parent glycine conjugate and two modified conjugates all showed selective tumor uptake in Mec-1 xenografts. The liver uptake of the serine conjugate was significantly reduced compared to the two other PNA conjugates. Its kidney uptake was highest of the three at 47.1% ID/g at 1h and dropped to 20.6% ID/g at 24h. [Copper-64]DOTA-anti-bcl-2-TS-PNA-Tyr(3)-octreotate showed tumor uptake of 1.38% ID/g at 1h and 1.06% ID/g at 24h. The tumor-to-blood ratio was increased by factor of 2 from 1h to 24h. This compound detected Mec-1 tumors by micro-PET/CT as early as 1h post-injection and at time points out to 48 h. However, the negative control Ramos tumor could not be detected.

CONCLUSIONS

These (64)Cu-labeled, amino acid-modified PNA conjugates showed selective tumor targeting in vivo, and tumor xenografts were detected by micro-PET/CT as early as 1h post-injection, suggesting that bcl-2 expression at the mRNA level can detected by PET in mouse models of NHL. Advances in knowledge and implications for patient care Down-regulating bcl-2, an anti-apoptotic proto-oncogene, is a mechanism to reverse chemotherapy resistance in humans with NHL. Thus, bcl-2 overexpression might be considered a new independent prognostic parameter in NHL, aiding in the identification of patients at risk for treatment failure. We have developed [(64)Cu]DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate conjugates for targeted antisense PET imaging. Our preclinical studies identified an effective combination of antisense and radionuclide imaging, with the goal of future clinical trials in patients. This imaging modality may improve clinical care by identifying patients who might respond better to conventional chemotherapy.

Targeted antisense radiotherapy and dose fractionation using a (177)Lu-labeled anti-bcl-2 peptide nucleic acid-peptide conjugate

INTRODUCTION

The overall goal of these studies was to test the hypothesis that simultaneous down-regulation of a tumor survival gene and delivery of internally emitted cytotoxic radiation will be more effective than either treatment modality alone. The objectives were to evaluate the therapeutic efficacy of a (177)Lu-labeled anti-bcl-2-PNA-Tyr(3)-octreotate antisense conjugate in a mouse model bearing human non-Hodgkin's lymphoma (NHL) tumor xenografts and to optimize targeted antisense radiotherapy by dose fractionation.

METHODS

In the initial therapy studies, tumor-bearing mice were given saline, nonradioactive DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate, (177)Lu-DOTA-Tyr(3)-octreotate, (177)Lu-DOTA-PNA-peptide alone, or (177)Lu-DOTA-PNA-peptide followed by a chase dose of nonradioactive PNA-peptide. The MTD of (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate was then determined. Subsequently single dose MTD and four weekly fractionated doses were directly compared, followed by histopathologic evaluation.

RESULTS

Antisense radiotherapy using 4.44 MBq of the (177)Lu-DOTA-PNA-peptide followed by nonradioactive PNA-peptide was significantly more effective than other low dose treatment regimens. A dose of 18.5 MBq of (177)Lu-DOTA-PNA-peptide was determined to be the approximate maximum tolerated dose (MTD). The median times to progression to a 1cm(3) tumor volume were 32 and 49 days for single dose MTD and fractionated dose (4 × 4.63 MBq) groups, respectively. Histopathology revealed metastases in the single dose groups, but not in the dose fractionation group.

CONCLUSIONS

Targeted antisense radiotherapy using (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate and DOTA-PNA-peptide conjugate effectively inhibited tumor progression in a mouse model of NHL. Furthermore, a dose fractionation regimen had a significant advantage over a single high dose, in terms of tumor growth inhibition and prevention of metastasis.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Down-regulating bcl-2, an anti-apoptotic proto-oncogene, is a mechanism to reverse chemotherapy resistance or failure in humans with NHL. We have developed a (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate conjugate for targeted antisense radiotherapy, in which down-regulation of bcl-2 and delivery of cytotoxic radiation occur simultaneously. Our previous studies have shown highly specific inhibition of bcl-2 protein, additive in vitro cytotoxic effects on human lymphoma cells, and favorable biodistribution and dosimetric properties. Lutetium-177 targeted antisense radiotherapy demonstrates a significant advantage over conventional (177)Lu-peptide receptor radionuclide therapy in a mouse model of NHL. Our preclinical studies identified an effective combination of antisense and radionuclide therapy, with the goal of future clinical trials in patients.

Preparation and Evaluation of (99m)Tc-Epidermal Growth Factor Receptor (EGFR)-Peptide Nucleic Acid for Visualization of EGFR Messenger RNA Expression in Malignant Tumors

Epidermal growth factor receptor (EGFR) is overexpressed in many carcinomas and remains a prime target for diagnostic and therapeutic applications. There is a need to develop noninvasive methods to identify the subset of patients that is most likely to benefit from EGFR-targeted treatment. Noninvasive imaging of EGFR messenger RNA (mRNA) expression may be a useful approach. The aim of this study was to develop a method for preparation of single-photon-emitting probes, (99m)Tc-labeled EGFR mRNA antisense peptide nucleic acid (PNA) ((99m)Tc-EGFR-PNA), and nontargeting control ((99m)Tc-CTL-PNA) and to evaluate their feasibility for imaging EGFR mRNA overexpression in malignant tumors in vivo.

METHODS

On the 5' terminus of synthesized single-stranded 17-mer antisense EGFR mRNA antisense PNA and mismatched PNA, a 4-amino-acid (Gly-(D)-Ala-Gly-Gly) linker forming an N4 structure was used for coupling (99m)Tc. Probes were labeled with (99m)Tc by ligand exchange. The radiochemical purity of these (99m)Tc-labeled probes was determined by reversed-phase high-performance liquid chromatography. Cellular uptake, retention, binding specificity, and stability of the probes were studied either in vitro or in vivo. Biodistribution and radionuclide imaging were performed in BALB/c nude mice bearing SKOV3 (EGFR-positive) or MDA-MB-435S (EGFR-negative) carcinoma xenografts, respectively.

RESULTS

The average labeling efficiencies of (99m)Tc-EGFR-PNA and (99m)Tc-CTL-PNA were 98.80% ± 1.14% and 98.63% ± 1.36% (mean ± SD, n = 6), respectively, within 6 h at room temperature, and the radiochemical purity of the probes was higher than 95%. (99m)Tc-EGFR-PNA was highly stable in normal saline and fresh human serum at 37°C in vitro and in urine and plasma samples of nude mice after 2-3 h of injection. Cellular uptake and retention ratios of (99m)Tc-EGFR-PNA in SKOV3 cells were higher than those of (99m)Tc-CTL-PNA and the EGFR-negative control. Meanwhile, EGFR mRNA binding (99m)Tc-EGFR-PNA was blocked with an excess of unlabeled EGFR-PNA in SKOV3 cell lines. The biodistribution study demonstrated accumulation of (99m)Tc-EGFR-PNA primarily in the SKOV3 xenografts and in EGFR-expressing organs. Radionuclide imaging demonstrated clear localization of (99m)Tc-EGFR-PNA in the SKOV3 xenografts shortly after injection but not in (99m)Tc-CTL-PNA and the EGFR-negative control.

CONCLUSION

(99m)Tc-EGFR-PNA has the potential for imaging EGFR mRNA overexpression in tumors.

RNA interference in Entamoeba histolytica: implications for parasite biology and gene silencing

Entamoeba histolytica is a major health threat to people in developing countries, where it causes invasive diarrhea and liver abscesses. The study of this important human pathogen has been hindered by a lack of tools for genetic manipulation. Recently, a number of genetic approaches based on variations of the RNAi method have been successfully developed and cloning of endogenous small-interfering RNAs from E. histolytica revealed an abundant population of small RNAs with an unusual 5´-polyphosphate structure. However, little is known about the implications of these findings to amebic biology or the mechanisms of gene silencing in this organism. In this article we review the literature relevant to RNAi in E. histolytica, discuss its implications for advances in gene silencing in this organism and outline potential future directions towards understanding the repertoire of RNAi and its impact on the biology of this deep-branching eukaryotic parasite.

Molecular imaging of bcl-2 expression in small lymphocytic lymphoma using 111In-labeled PNA-peptide conjugates

The bcl-2 gene is overexpressed in non-Hodgkin's lymphoma (NHL), such as small lymphocytic lymphoma (SLL), and many other cancers. Noninvasive imaging of bcl-2 expression has the potential to identify patients at risk for relapse or treatment failure. The purpose of this study was to synthesize and evaluate radiolabeled peptide nucleic acid (PNA)-peptide conjugates targeting bcl-2 gene expression. An (111)In-labeled PNA complementary to the translational start site of bcl-2 messenger RNA was attached to Tyr(3)-octreotate for somatostatin receptor-mediated intracellular delivery.

METHODS

DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate (1) and 3 control conjugates (DOTA-nonsense-PNA-Tyr(3)-octreotate (2), DOTA-anti-bcl-2-PNA-Ala[3,4,5,6]-substituted congener (3), and DOTA-Tyr(3)-octreotate (4) [DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid]) were synthesized by standard solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. In vitro studies were performed in Mec-1 SLL cells, which express both bcl-2 messenger RNA and somatostatin receptors. Biodistributions and microSPECT/CT studies were performed in Mec-1-bearing SCID (severe combined immunodeficiency) mice, a new animal model of human SLL.

RESULTS

(111)In-Labeled conjugate 1 was taken up by Mec-1 cells through a somatostatin receptor-mediated mechanism. Biodistribution studies showed specific tumor uptake of conjugate 1, the somatostatin analog 4, and the PNA nonsense conjugate 2, but not of the mutant peptide conjugate 3. Mec-1 tumors could be detected by microSPECT/CT using (111)In-labeled DOTA-Tyr(3)-octreotate (4) and the targeted anti-bcl-2 conjugate (1), but not using the 2 negative control conjugates 2 and 3.

CONCLUSION

A new (111)In-labeled antisense PNA-peptide conjugate demonstrated proof of principle for molecular imaging of bcl-2 expression in a new mouse model of human SLL. This imaging agent may be useful for identifying NHL patients at risk for relapse and conventional treatment failure.

Loss of dsRNA-based gene silencing in Entamoeba histolytica: implications for approaches to genetic analysis

The ability to regulate gene expression in the protozoan parasite Entamoeba histolytica is critical in determining gene function. We previously published that expression of dsRNA specific to E. histolytica serine threonine isoleucine rich protein (EhSTIRP) resulted in reduction of gene expression [MacFarlane, R.C., Singh, U., 2007. Identification of an Entamoeba histolytica serine, threonine, isoleucine, rich protein with roles in adhesion and cytotoxicity. Eukaryotic Cell 6, 2139-2146]. However, after approximately one year of continuous drug selection, the expression of EhSTIRP reverted to wild-type levels. We confirmed that the parasites (i) contained the appropriate dsRNA plasmid, (ii) were not contaminated with other plasmids, (iii) the drug selectable marker was functional, and (iv) sequenced the dsRNA portion of the construct. This work suggests that in E. histolytica long term cultivation of parasites expressing dsRNA can lead to the loss of dsRNA based silencing through the selection of "RNAi" negative parasites. Thus, users of the dsRNA silencing approach should proceed with caution and regularly confirm gene down regulation. The development and use of constructs for inducible expression of dsRNA may help alleviate this potential problem.

Progress and prospects of gene inactivation in Entamoeba histolytica

Over the last few years, numerous methods have been exploited in the attempt to study Entamoeba histolytica gene functions. Yet several features of E. histolytica, like their variable DNA content and complex ploidity have made it difficult to perform classical genetic studies such as homologous recombination. As a result, the methods currently in use target genes at the protein or RNA level. This review summarizes the experimental approaches that have been used to date and it provides an overview of the limitations and contributions of these methods in our understanding of E. histolytica's gene functions and biology.

Entamoeba histolytica: intracellular distribution of the sec61alpha subunit of the secretory pathway and down-regulation by antisense peptide nucleic acids

The Sec61alpha protein is defined as a highly conserved essential integral component of the endoplasmic reticulum in eukaryotic cells. We report a detailed immunolocalization of the Entamoeba histolytica homologue of the Sec61alpha subunit (EhSec61alpha), which shows an irregular pattern throughout the cell and is also found on the cell surface, its effective down-regulation by means of antisense peptide nucleic acids and its effects on cell proliferation, subcellular distribution of two virulence factors, and the ability of the trophozoites to cause liver abscess in hamsters. Although Sec61alpha levels are specifically decreased in antisense PNA-treated trophozoites, which proliferate more slowly than the controls, mobilization of the cysteine protease 5 and amoebapore to the cell surface is not significantly impeded and the capacity to induce liver abscess in hamsters is largely unaffected. The implications of these findings are discussed in the context of the peculiar cell biology of E. histolytica.

PNA Technology

Peptide nucleic acids (PNA) are deoxyribonucleic acid (DNA) mimics with a pseudopeptide backbone. PNA is an extremely good structural mimic of DNA (or of ribonucleic acid [RNA]), and PNA oligomers are able to form very stable duplex structures with Watson-Crick complementary DNA and RNA (or PNA) oligomers, and they can also bind to targets in duplex DNA by helix invasion. Therefore, these molecules are of interest in many areas of chemistry, biology, and medicine, including drug discovery, genetic diagnostics, molecular recognition, and the origin of life. Recent progress in studies of PNA properties and applications is reviewed.

Inhibition of gene expression with double strand RNA interference in Entamoeba histolytica

In order to inhibit gene expression in Entamoeba histolytica, we have developed a method based on expressing double strand RNA interference constructs in stable transformants. The 5' end of Eh Dia was cloned head to head with an intervening non-specific stuffer fragment in the E. histolytica expression vector pJST4. This construct was transformed in E. histolytica HM1:IMSS trophozoites and stable transformants were selected with 20microg/ml G418. Our results show that expression of Eh Dia was completely inhibited in these transformants. These stable transformants could be maintained indefinitely without expression of Eh Dia. This method therefore provides an effective tool to study the phenotypic changes, which occur due to inhibition of gene expression in the absence of mutants and other microbiological manipulations in this protozoan parasite.

Recent advances in the development of peptide nucleic acid as a gene-targeted drug

Peptide nucleic acid (PNA) is a non-ionic mimic of DNA that binds to complementary DNA and RNA sequences with high affinity and selectivity. Targeting of single-stranded RNA leads to antisense effects, whereas PNAs directed toward double-stranded DNA exhibit antigene properties. Recent advances in cell uptake and in antisense and antigene effects in biological systems are summarised in this review. In addition to traditional targets, namely genomic DNA and messenger RNA, applications for PNA as a bacteriocidal antibiotic, for regulating splice site selection and as a telomerase inhibitor are described.

Combination of a new generation of PNAs with a peptide-based carrier enables efficient targeting of cell cycle progression

The design of potent systems for the delivery of charged and noncharged molecules that target genes of interest remains a challenge. We describe a novel technology that combines a new generation of peptide nucleic acids (PNAs), or HypNA-pPNAs, with a new noncovalent peptide-based delivery system, Pep-2, which promotes efficient delivery of PNAs into several cell lines. We have validated the potential of this technology by showing that Pep2-mediated delivery of an antisense HypNA-pPNA chimera directed specifically against cyclin B1 induces rapid and robust downregulation of its protein levels and efficiently blocks cell cycle progression of several cell lines, as well as proliferation of cells derived from a breast cancer. Pep-2-based delivery system was shown to be 100-fold more efficient in delivering HypNA-pPNAs than classical cationic lipid-based methods. Whereas Pep-2 is essential for improving the bioavailability of PNAs and HypNA-pPNAs, the latter contribute significantly to the efficiency and specificity of the biological response. We have found that Pep-2/HypNA-pPNA strategy promotes potent antisense effects, which are approximately 25-fold greater than with classical antisense oligonucleotide directed specifically against the same cyclin B1 target. Taken together, these data demonstrate that peptide-mediated delivery of HypNA-pPNAs constitutes a very promising technology for therapeutic applications.

Antigenic epitopes fused to cationic peptide bound to oligonucleotides facilitate Toll-like receptor 9-dependent, but CD4+ T cell help-independent, priming of CD8+ T cells

A priority in current vaccine research is the development of adjuvants that support the efficient priming of long-lasting, CD4(+) T cell help-independent CD8(+) T cell immunity. Oligodeoxynucleotides (ODN) with immune-stimulating sequences (ISS) containing CpG motifs facilitate the priming of MHC class I-restricted CD8(+) T cell responses to proteins or peptides. We show that the adjuvant effect of ISS(+) ODN on CD8(+) T cell priming to large, recombinant Ag is enhanced by binding them to short, cationic (arginine-rich) peptides that themselves have no adjuvant activity in CD8(+) T cell priming. Fusing antigenic epitopes to cationic (8- to 10-mer) peptides bound to immune-stimulating ISS(+) ODN or nonstimulating NSS(+) ODN (without CpG-containing sequences) generated immunogens that efficiently primed long-lasting, specific CD8(+) T cell immunity of high magnitude. Different MHC class I-binding epitopes fused to short cationic peptides of different origins showed this adjuvant activity. Quantitative ODN binding to cationic peptides strikingly reduced the toxicity of the latter, suggesting that it improves the safety profile of the adjuvant. CD8(+) T cell priming supported by this adjuvant was Toll-like receptor 9 dependent, but required no CD4(+) T cell help. ODN (with or without CpG-containing sequences) are thus potent Th1-promoting adjuvants when bound to cationic peptides covalently linked to antigenic epitopes, a mode of Ag delivery prevailing in many viral nucleocapsids.

Cellular delivery of peptide nucleic acid (PNA)

Peptide nucleic acid (PNA) is a DNA mimic having a pseudopeptide backbone that makes it extremely stable in biological fluids. PNA binds complementary RNA and DNA with high affinity and specificity. These qualities make PNA a leading agent among "third generation" antisense and antigene agents. Unfortunately, fast progress in the exploration of PNA as an experimental and therapeutical regulator of gene expression has been hampered by the poor cellular uptake of PNA. However, a number of transfection protocols for PNA have now been established. These include microinjection, electroporation, co-transfection with DNA, conjugation to lipophilic moieties, conjugation to peptides, etc. Here we give a short introduction to the basic findings on PNA as an antisense and antigene agent in cell-free in vitro systems. This is followed by a comprehensive evaluation of the most interesting literature concerning cellular delivery and the intracellular effect of PNA. Also the current progress as regards using PNA as co-factor in DNA delivery is reviewed.

Peptide nucleic acid antisense prolongs skin allograft survival by means of blockade of CXCR3 expression directing T cells into graft

CXCR3, predominantly expressed on memory/activated T cells, is a receptor for both IFN-gamma-inducible protein 10/CXC chemokine ligand (CXCL)10 and monokine induced by IFN-gamma/CXCL9. It was reported that CXC chemokines IFN-gamma-inducible protein 10/CXCL10 and monokine induced by IFN-gamma/CXCL9 play a critical role in the allograft rejection. We report that CXCR3 is a dominant factor directing T cells into mouse skin allograft, and that peptide nucleic acid (PNA) CXCR3 antisense significantly prolongs skin allograft survival by means of blockade of CXCR3 expression directing T cells into allografts in mice. We found that CXCR3 is highly up-regulated in spleen T cells and allografts from BALB/c recipients by day 7 of receiving transplantation, whereas CCR5 expression is moderately increased. We designed PNA CCR5 and PNA CXCR3 antisenses, and i.v. treated mice that received skin allograft transplantations. The PNA CXCR3 at a dosage of 10 mg/kg/day significantly prolonged mouse skin allograft survival (17.1 +/- 2.4 days) compared with physiological saline treatment (7.5 +/- 0.7 days), whereas PNA CCR5 (10 mg/kg/day) marginally prolonged skin allograft survival (10.7 +/- 1.1 days). The mechanism of prolongation of skin allograft survival is that PNA CXCR3 directly blocks the CXCR3 expression in T cells, which is responsible for directing T cells into skin allograft to induce acute rejection, without interfering with other functions of the T cells. These results were obtained at mRNA and protein levels by flow cytometry and real-time quantitative RT-PCR technique, and confirmed by chemotaxis, Northern and Western blot assays, and histological evaluation of skin grafts. The present study indicates the therapeutic potential of PNA CXCR3 to prevent acute transplantation rejection.

Antiproliferative effect in chronic myeloid leukaemia cells by antisense peptide nucleic acids

Peptide nucleic acid (PNA) is a synthetic DNA analogue that is resistant to nucleases and proteases and binds with exceptional affinity to RNA. Because of these properties PNA has the potential to become a powerful therapeutic agent to be used in vivo. Until now, however, the use of PNA in vivo has not been much investigated. Here, we have attempted to reduce the expression of the bcr/abl oncogene in chronic myeloid leukaemia KYO-1 cells using a 13mer PNA sequence (asPNA) designed to hybridise to the b2a2 junction of bcr/abl mRNA. To enhance cellular uptake asPNA was covalently linked to the basic peptide VKRKKKP (NLS-asPNA). Moreover, to investigate the cellular uptake by confocal microscopy, both PNAs were linked by their N-terminus to fluorescein (FL). Studies of uptake, carried out at 4 and 37 degrees C on living KYO-1 cells stained with hexidium iodide, showed that both NLS-asPNA-FL and asPNA-FL were taken up by the cells, through a receptor-independent mechanism. The intracellular amount of NLS-asPNA-FL was about two to three times higher than that of asPNA-FL. Using a semi-quantitative RT- PCR technique we found that 10 micro M asPNA and NLS-asPNA reduced the level of b2a2 mRNA in KYO-1 cells to 20 +/- 5% and 60 +/- 10% of the control, respectively. Western blot analysis showed that asPNA promoted a significant inhibition of p210(BCR/ABL) protein: residual protein measured in cells exposed for 48 h to asPNA was approximately 35% of the control. Additionally, asPNA impaired cell growth to 50 +/- 5% of the control and inhibited completion of the cell cycle. In summary, these results demonstrate that a PNA 13mer is taken up by KYO-1 cells and is capable of producing a significant and specific down-regulation of the bcr/abl oncogene involved in leukaemogenesis.

Antisense peptide nucleic acids conjugated to somatostatin analogs and targeted at the n-myc oncogene display enhanced cytotoxity to human neuroblastoma IMR32 cells expressing somatostatin receptors

Peptide nucleic acid (PNA) sequences are synthetic versions of naturally occurring oligonucleotides which display improved binding properties to DNA and RNA, but are still poorly internalized across cell membranes. In an effort to employ the rapid binding/internalization properties of somatostatin agonist analogs and the over-expression of somatostatin receptors on many types of tumor cells, PNAs complementary to target sites throughout 5'-UTR, translation start site and coding region of the n-myc oncogene were conjugated to a somatostatin analog (SSA) with retention of high somatostatin biological potency. IMR32 cells, which over-express somatostatin receptor type 2 (SSTR2) and contain the n-myc oncogene, were treated with these PNA-SSA conjugates. The results show that PNA conjugates targeted to the 5'-UTR terminus and to regions at or close to the translation start site could effectively inhibit n-myc gene expression and cell growth, whereas the non-conjugate PNAs were without effect at similar doses. The most potent inhibition of cell growth was achieved with PNAs binding to the translation start site, but those complementary to the middle coding region or middle upstream site between 5'-UTR and translation start site displayed no inhibition of gene expression. These observations were extended to four other cell lines: GH3 cells which express SSTRs with the n-myc gene, SKNSH cells containing a silent n-myc gene without SSTR2, HT-29 cells carrying the c-myc but no n-myc gene, and CHO-K1 cells lacking SSTR2 with n-myc gene. The results show that there was almost no effect on these four cell lines. Our study indicates that PNAs conjugated to SSA exhibited improved inhibition of gene expression possibly due to facilitated cellular uptake of the PNAs. These conjugates were mRNA sequence- and SSTR2-specific suggesting that many other genes associated with tumor growth could be targeted using this approach and that SSA could be a novel and effective transportation vector for the PNA antisense strategy.