Inhibition of intracellular growth of Salmonella enterica serovar Typhimurium in tissue culture by antisense peptide-phosphorodiamidate morpholino oligomer. Antimicrob Agents Chemother. 2009;53:3700-3704. [PMID: 19581453 DOI: 10.1128/aac.00099-09]

Oligonucleotide probes for imaging and diagnosis of bacterial infections

The rise of infectious diseases as a public health concern has necessitated the development of rapid and precise diagnostic methods. Imaging techniques like nuclear and optical imaging provide the ability to diagnose infectious diseases within the body, eliminating delays caused by sampling and pre-enrichments of clinical samples and offering spatial information that can aid in a more informed diagnosis. Traditional molecular probes are typically created to image infected tissue without accurately identifying the pathogen. In contrast, oligonucleotides can be tailored to target specific RNA sequences, allowing for the identification of pathogens, and even generating antibiotic susceptibility profiles by focusing on drug resistance genes. Despite the benefits that nucleic acid mimics (NAMs) have provided in terms of stabilizing oligonucleotides, the inadequate delivery of these relatively large molecules into the cytoplasm of bacteria remains a challenge for widespread use of this technology. This review summarizes the key advancements in the field of oligonucleotide probes for in vivo imaging, highlighting the most promising delivery systems described in the literature for developing optical imaging through in vivo hybridization.

An alternative strategy to increasing influenza virus replication for vaccine production in chicken embryo fibroblast (DF-1) cells by inhibiting interferon alpha and beta using peptide-conjugated phosphorodiamidate morpholino oligomers

Introduction. Influenza is a global health issue causing substantial health and economic burdens on affected populations. Routine, annual vaccination for influenza virus is recommended for all persons older than 6 months of age. The propagation of the influenza virus for vaccine production is predominantly through embryonated chicken eggs.Hypothesis/Gap Statement. Many challenges face the propagation of the virus, including but not limited to low yields and lengthy production times. The development of a method to increase vaccine production in eggs or cell lines by suppressing cellular gene expression would be helpful to overcome some of the challenges facing influenza vaccine production.Aims. This study aimed to increase influenza virus titres by using a peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO), an antisense molecule, to suppress protein expression of the host genes interferon alpha (IFN-α) and interferon beta (IFN-β) in chicken embryo fibroblast (DF-1) cells.Methods. The toxicity of PPMOs was evaluated by cytotoxicity assays, and their specificity to inhibit IFN-α and IFN-β proteins was measured by ELISA. We evaluated the potential of anti-IFN-α and anti-IFN-β PPMOs to reduce the antiviral proteins in influenza virus-infected DF-1 cells and compared the virus titres to untreated controls, nonsense-PPMO and JAK/STAT inhibitors. The effects of complementation and reconstitution of IFN-α and IFN-β proteins in PPMO-treated-infected cells were evaluated, and the virus titres were compared between treatment groups.Results. Suppression of IFN-α by PPMO resulted in significantly reduced levels of IFN-α protein in treated wells, as measured by ELISA and was shown to not have any cytotoxicity to DF-1 cells at the effective concentrations tested. Treatment of the self-directing PPMOs increased the ability of the influenza virus to replicate in DF-1 cells. Over a 2-log10 increase in viral production was observed in anti-IFN-α and IFN-β PPMO-treated wells compared to those of untreated controls at the initial viral input of 0.1 multiplicity of infection. The data from complementation and reconstitution of IFN-α and IFN-β proteins in PPMO-treated-infected cells was about 82 and 97% compared to the combined PPMO-treated but uncomplemented group and untreated group, respectively. There was a 0.5-log10 increase in virus titre when treated with anti-IFN-α and IFN-β PPMO compared to virus titre when treated with JAK/STAT inhibitors.Conclusions. This study emphasizes the utility of PPMO in allowing cell cultures to produce increased levels of influenza for vaccine production or alternatively, as a screening tool to cheaply test targets prior to the development of permanent knockouts of host gene expression.

Sequence specificity defines the effectiveness of PPMOs targeting Pseudomonas aeruginosa

Development of new therapeutics against antibiotic resistant pathogenic bacteria is recognized as a priority across the globe. We have reported using peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) as species-specific antibiotics. The oligo sequences, 11 bases are designed to be complementary to specific essential genes near the Shine-Dalgarno site and inhibit translation. Here, we analyzed target specificity and the impact of genetic mutations on lead PPMOs targeting the rpsJ or acpP gene of Pseudomonas aeruginosa. Mutants in P. aeruginosa PAO1 were generated with four, two, or one base-pair mutations within the 11-base target sequence of the rpsJ gene. All mutants exhibited increased MICs compared to wild-type PAO1 when treated with the RpsJ PPMO, and the increase in the MICs was proportional to the number of base-pair mutations. Among single base-pair mutants, mutations in the middle of the sequence were more impactful than mutations in 5' or 3' end of the sequence. The increased MICs shown by the rpsJ mutants could be reversed by PPMOs designed to target the mutated rpsJ sequence. BALB/c mice infected intratracheally with mutants demonstrated increased lung burden when treated with RpsJ PPMO compared to wild-type PAO1-infected mice treated with RpsJ PPMO. Treating mice with a PPMOs designed to specifically target the mutant sequence was more effective against these mutant strains. These experiments confirm target specificity of two lead P. aeruginosa PPMOs and illustrate one potential mechanism of resistance that could emerge from an antisense approach.

Antimicrobial peptides´ immune modulation role in intracellular bacterial infection

Intracellular bacteria cause a wide range of diseases, and their intracellular lifestyle makes infections difficult to resolve. Furthermore, standard therapy antibiotics are often unable to eliminate the infection because they have poor cellular uptake and do not reach the concentrations needed to kill bacteria. In this context, antimicrobial peptides (AMPs) are a promising therapeutic approach. AMPs are short cationic peptides. They are essential components of the innate immune response and important candidates for therapy due to their bactericidal properties and ability to modulate host immune responses. AMPs control infections through their diverse immunomodulatory effects stimulating and/or boosting immune responses. This review focuses on AMPs described to treat intracellular bacterial infections and the known immune mechanisms they influence.

Therapeutic effects, immunogenicity and cytotoxicity of a cell penetrating peptide-peptide nucleic acid conjugate against cagA of Helicobacter pylori in cell culture and animal model

BACKGROUND AND OBJECTIVES

Helicobacter pylori causes several gastrointestinal diseases, including asymptomatic gastritis, chronic peptic ulcer, duodenal ulcer, lymphoma of the mucosa-associated lymphoid tissue (MALT), and gastric adenocarcinoma. In recent years, failure to eradicate H. pylori infections has become an alarming problem for physicians. It is now clear that the current treatment strategies may become ineffective, necessitating the development of innovative antimicrobial compounds as alternative treatments.

MATERIALS AND METHODS

In this experimental study, a cell-penetrating peptide-conjugated peptide nucleic acid (CPP-PNA) was used to target the cagA expression. cagA expression was evaluated using RT-qPCR assay after treatment by the CPPPNA in cell culture and animal model. Additionally, immunogenicity and toxicity of the CPP-PNA were assessed in both cell culture and animal models.

RESULTS

Our analysis showed that cagA mRNA levels reduced in H. pylori-infected HT29 cells after treatment with CPPPNA in a dose-dependent manner. Also, cagA expression in bacterial RNA extracted from stomach tissue of mice treated with PNA was reduced compared to that of untreated mice. The expression of inflammatory cytokines also decreased in cells and tissue of H. pylori-infected mice after PNA treatment. The tested CPP-PNA showed no significant adverse effects on cell proliferation of cultured cells and no detectable toxicity and immunogenicity were observed in mice.

CONCLUSION

These results suggest the effectiveness of CPP-PNA in targeting CagA for various research and therapeutic purposes, offering a potential antisense therapy against H. pylori infections.

Peptides and Antibiotic Therapy: Advances in Design and Delivery

Antibiotic resistance (AMR) is an increasing public health crisis worldwide. This threatens our ability to adequately care for patients with infections due to multi-drug-resistant (MDR) pathogens. As such, there is an urgent need to develop new classes of antimicrobials that are not based on currently utilized antibiotic scaffolds. One promising avenue of antimicrobial research that deserves renewed examination involves the use of peptides. Although antimicrobial peptides (AMPs) have been studied for a number of years, innovations in peptide design and their applications are increasingly making this approach a viable alternative to traditional small-molecule antibiotics. This review will provide updates on two ways in which peptides are being explored as antibiotics. The first topic will focus on novel types of peptides and conjugation methods that are being exploited to act as antibiotics themselves. These direct-acting modified peptides could serve as potentially useful drugs while mitigating many of the known liabilities of AMPs. The second topic relates to the use of peptides as delivery vehicles for other active compounds with antimicrobial activity. Cell-penetrating peptides (CPPs) are peptides designed to carry compounds across cell membranes and are a promising method for delivering a variety of antimicrobial compounds. When conjugated to other compounds, CPPs have been shown to be effective at increasing the uptake of both small- and large-molecular-weight compounds. This includes conjugation to antisense molecules and traditional antibiotics, resulting in increased effectiveness of these antimicrobials. One particular approach utilizes CPPs conjugated to phosphorodiamidate morpholino oligomers (PMOs). PMOs are designed to target particular pathogens in a gene-specific way. They target mRNA and block protein translation. Peptide-conjugated PMOs (PPMOs) allow for efficient delivery into the Gram-negative cytoplasm, and recent updates to their in vitro and in vivo activity are reviewed. This includes recent data to suggest that PPMOs maintain activity in the setting of multi-drug-resistant (MDR) strains, an important finding as it relates to the further development of this therapeutic approach. Other topics include the ability to have activity in the biofilm setting, a finding that likely relates to the peptide portion of the conjugate. Finally, what is known and anticipated related to the development of resistance to these peptides will be discussed.

Polyamide Microsized Particulate Polyplex Carriers for the 2'-OMethylRNA EFG1 Antisense Oligonucleotide

Anti-EFG1 2'-OMethylRNA is an antisense oligonucleotide (ASO) that has the ability to recognize and block the EFG1 gene and to control Candida albicans filamentation. However, it is important to protect the anti-EFG1 2'-OMethylRNA ASO from the environmental human body conditions and to ensure that they will be delivered to their site of action, and polyplex microparticles (MPs) represent a class of vehicles to ASO cargo with these functionalities. Thus, the goal of this work was to develop polyplexes based on porous poly(γ-butyrolactam) (PA4) or poly(ε-caprolactam) (PA6) MPs for the anti-EFG1 2'-OMethylRNA ASO cargo and delivery. Two types of polyplexes were prepared with payloads of anti-EFG1 2'-OMethylRNA molecules, either entrapped or immobilized on prefabricated polyamide MPs. Our data confirm that PA4 and PA6 polyplex MPs can be feasible carriers for anti-EFG1 2'-OMethylRNA ASO molecules, using either the entrapment or immobilization strategies, whereby the released ASO maintains its activity against C. albicans cells.

Antisense antibacterial compounds

Extensive antibiotic use combined with poor historical drug stewardship practices have created a medical crisis in which once treatable bacterial infections are now increasingly unmanageable. To combat this, new antibiotics will need to be developed and safeguarded. An emerging class of antibiotics based upon nuclease-stable antisense technologies has proven valuable in preclinical testing against a variety of bacterial pathogens. This review describes the current state of development of antisense-based antibiotics, the mechanisms thus far employed by these compounds, and possible future avenues of research.

Influence of Different Cell-Penetrating Peptides on the Antimicrobial Efficiency of PNAs in Streptococcus pyogenes

Streptococcus pyogenes is an exclusively human pathogen causing a wide range of clinical manifestations from mild superficial infections to severe, life-threatening, invasive diseases. S. pyogenes is consistently susceptible toward penicillin, but therapeutic failure of penicillin treatment has been reported frequently. At the same time, streptococcal resistance to alternative antibiotics, e.g., macrolides, is common. To reduce the application of antibiotics for treatment of S. pyogenes infections, it is mandatory to develop novel therapeutic strategies. Antisense peptide nucleic acids (PNAs) are synthetic DNA derivatives widely applied for hybridization-based microbial diagnostics. They have a high potential as therapeutic agents, because PNA antisense targeting of essential genes was shown to reduce growth of several pathogenic bacterial species. Spontaneous cellular uptake of PNAs is restricted in eukaryotes and in bacteria. To overcome this problem, PNAs can be coupled to cell-penetrating peptides (CPPs) that support PNA translocation over the cell membrane. In bacteria, the efficiency of CPP-mediated PNA uptake is species specific. Previously, HIV-1 transactivator of transcription (HIV-1 TAT) peptide-coupled anti-gyrA PNA was shown to inhibit growth of S. pyogenes. Here, we investigate the effect of 18 CPP-coupled anti-gyrA PNAs on S. pyogenes growth and virulence. HIV-1 TAT, oligolysine (K8), and (RXR)₄XB peptide-coupled anti-gyrA PNAs efficiently abolished bacterial growth in vitro. Consistently, treatment with these three CPP-PNAs increased survival of larvae in a Galleria mellonella infection model.

MCR-1 Inhibition with Peptide-Conjugated Phosphorodiamidate Morpholino Oligomers Restores Sensitivity to Polymyxin in Escherichia coli

In late 2015, the first example of a transferrable polymyxin resistance mechanism in Gram-negative pathogens, MCR-1, was reported. Since that report, MCR-1 has been described to occur in many Gram-negative pathogens, and the mechanism of MCR-1-mediated resistance was rapidly determined: an ethanolamine is attached to lipid A phosphate groups, rendering the membrane more electropositive and repelling positively charged polymyxins. Acquisition of MCR-1 is clinically significant because polymyxins are frequently last-line antibiotics used to treat extensively resistant organisms, so acquisition of this mechanism might lead to pan-resistant strains. Therefore, the ability to inhibit MCR-1 and restore polymyxin sensitivity would be an important scientific advancement. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) are antisense molecules that were designed to target mRNA, preventing translation. Peptide conjugation enhances cellular entry, but they are positively charged, so we tested our lead antibacterial PPMOs by targeting an essential Escherichia coli gene, acpP, and demonstrated that they were still effective in mcr-1-positive E. coli strains. We then designed and synthesized two PPMOs targeted to mcr-1 mRNA. Five clinical mcr-1-positive E. coli strains were resensitized to polymyxins by MCR-1 inhibition, reducing MICs 2- to 16-fold. Finally, therapeutic dosing of BALB/c mice with MCR-1 PPMO combined with colistin in a sepsis model reduced morbidity and bacterial burden in the spleen at 24 h and offered a survival advantage out to 5 days. This is the first example of a way to modulate colistin resistance with an antisense approach and may be a viable strategy to combat this globally emerging antibiotic resistance threat.

Polymyxin use has been increasing as a last line of defense against Gram-negative pathogens with high-level resistance mechanisms, such as carbapenemases. The recently described MCR-1 is a plasmid-mediated mechanism of resistance to polymyxins. MCR-1 is currently found in Gram-negative organisms already possessing high-level resistance mechanisms, leaving clinicians few or no antibacterial options for infections caused by these strains. This study utilizes antisense molecules that target mRNA, preventing protein translation. Herein we describe antisense molecules that can be directly antibacterial because they target genes essential to bacterial growth or blockade of MCR-1, restoring polymyxin sensitivity. We also demonstrate that MCR-1 antisense molecules restore the efficacies of polymyxins in mouse models of E. coli septicemia. Considering all things together, we demonstrate that antisense molecules may be effective therapeutics either alone when they target an essential gene or combined with antibiotics when they target specific resistance mechanisms, such as those seen with MCR-1.

Targeting the hard to reach: challenges and novel strategies in the treatment of intracellular bacterial infections

Infectious diseases continue to threaten human and animal health and welfare globally, impacting millions of lives and causing substantial economic loss. The use of antibacterials has been only partially successful in reducing disease impact. Bacterial cells are inherently resilient, and the therapy challenge is increased by the development of antibacterial resistance, the formation of biofilms and the ability of certain clinically important pathogens to invade and localize within host cells. Invasion into host cells provides protection from both antibacterials and the host immune system. Poor delivery of antibacterials into host cells causes inadequate bacterial clearance, resulting in chronic and unresolved infections. In this review, we discuss the challenges associated with existing antibacterial therapies with a focus on intracellular pathogens. We consider the requirements for successful treatment of intracellular infections and novel platforms currently under development. Finally, we discuss novel strategies to improve drug penetration into host cells. As an example, we discuss our recent demonstration that the cell penetrating cationic polymer polyhexamethylene biguanide has antibacterial activity against intracellular Staphylococcus aureus.

LINKED ARTICLES

This article is part of a themed section on Drug Metabolism and Antibiotic Resistance in Micro-organisms. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.14/issuetoc.

A Genome-Scale Modeling Approach to Quantify Biofilm Component Growth of Salmonella Typhimurium

Salmonella typhimurium (S. typhimurium) is an extremely dangerous foodborne bacterium that infects both animal and human subjects, causing fatal diseases around the world. Salmonella's robust virulence, antibiotic-resistant nature, and capacity to survive under harsh conditions are largely due to its ability to form resilient biofilms. Multiple genome-scale metabolic models have been developed to study the complex and diverse nature of this organism's metabolism; however, none of these models fully integrated the reactions and mechanisms required to study the influence of biofilm formation. This work developed a systems-level approach to study the adjustment of intracellular metabolism of S. typhimurium during biofilm formation. The most advanced metabolic reconstruction currently available, STM_v1.0, was 1st extended to include the formation of the extracellular biofilm matrix. Flux balance analysis was then employed to study the influence of biofilm formation on cellular growth rate and the production rates of biofilm components. With biofilm formation present, biomass growth was examined under nutrient rich and nutrient deficient conditions, resulting in overall growth rates of 0.8675 and 0.6238 h^-1 respectively. Investigation of intracellular flux variation during biofilm formation resulted in the elucidation of 32 crucial reactions, and associated genes, whose fluxes most significantly adapt during the physiological response. Experimental data were found in the literature to validate the importance of these genes for the biofilm formation of S. typhimurium. This preliminary investigation on the adjustment of intracellular metabolism of S. typhimurium during biofilm formation will serve as a platform to generate hypotheses for further experimental study on the biofilm formation of this virulent bacterium.

Antimicrobial activity of antisense peptide-peptide nucleic acid conjugates against non-typeable Haemophilus influenzae in planktonic and biofilm forms

BACKGROUND

Antisense peptide nucleic acids (PNAs) are synthetic polymers that mimic DNA/RNA and inhibit bacterial gene expression in a sequence-specific manner.

METHODS

To assess activity against non-typeable Haemophilus influenzae (NTHi), we designed six PNA-peptides that target acpP, encoding an acyl carrier protein. MICs and minimum biofilm eradication concentrations (MBECs) were determined. Resistant strains were selected by serial passages on media with a sub-MIC concentration of acpP-PNA.

RESULTS

The MICs of six acpP-PNA-peptides were 2.9-11 mg/L (0.63-2.5 μmol/L) for 20 clinical isolates, indicating susceptibility of planktonic NTHi. By contrast, MBECs were up to 179 mg/L (40 μmol/L). Compared with one original PNA-peptide (acpP-PNA1-3'N), an optimized PNA-peptide (acpP-PNA14-5'L) differs in PNA sequence and has a 5' membrane-penetrating peptide with a linker between the PNA and peptide. The optimized PNA-peptide had an MBEC ranging from 11 to 23 mg/L (2.5-5 μmol/L), indicating susceptibility. A resistant strain that was selected by the original acpP-PNA1-3'N had an SNP that introduced a stop codon in NTHI0044, which is predicted to encode an ATP-binding protein of a conserved ABC transporter. Deletion of NTHI0044 caused resistance to the original acpP-PNA1-3'N, but showed no effect on susceptibility to the optimized acpP-PNA14-5'L. The WT strain remained susceptible to the optimized PNA-peptide after 30 serial passages on media containing the optimized PNA-peptide.

CONCLUSIONS

A PNA-peptide that targets acpP, has a 5' membrane-penetrating peptide and has a linker shows excellent activity against planktonic and biofilm NTHi and is associated with a low risk for induction of resistance.

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.

Oligonucleotides containing a piperazino-modified 2'-amino-LNA monomer exhibit very high duplex stability and remarkable nuclease resistance

Incorporation of a piperazino-modified 2'-amino-LNA monomer (PipLNA-T) into oligonucleotides conferred very high affinity and base-pairing selectivity towards complementary DNA and RNA strands. Furthermore, one PipLNA-T modification provided a robust nuclease resistance that safeguarded three neighbouring natural nucleosides from 3'-exonucleolytic degradation. These favourable properties render PipLNA-T a promising oligonucleotide modification for various biological applications.

Use of siRNA molecular beacons to detect and attenuate mycobacterial infection in macrophages

Tuberculosis is one of the leading infectious diseases plaguing mankind and is mediated by the facultative pathogen, Mycobacterium tuberculosis (MTB). Once the pathogen enters the body, it subverts the host immune defenses and thrives for extended periods of time within the host macrophages in the lung granulomas, a condition called latent tuberculosis (LTB). Persons with LTB are prone to reactivation of the disease when the body’s immunity is compromised. Currently there are no reliable and effective diagnosis and treatment options for LTB, which necessitates new research in this area. The mycobacterial proteins and genes mediating the adaptive responses inside the macrophage is largely yet to be determined. Recently, it has been shown that the mce operon genes are critical for host cell invasion by the mycobacterium and for establishing a persistent infection in both in vitro and in mouse models of tuberculosis. The YrbE and Mce proteins which are encoded by the MTB mce operons display high degrees of homology to the permeases and the surface binding protein of the ABC transports, respectively. Similarities in structure and cell surface location impute a role in cell invasion at cholesterol rich regions and immunomodulation. The mce4 operon is also thought to encode a cholesterol transport system that enables the mycobacterium to derive both energy and carbon from the host membrane lipids and possibly generating virulence mediating metabolites, thus enabling the bacteria in its long term survival within the granuloma. Various deletion mutation studies involving individual or whole mce operon genes have shown to be conferring varying degrees of attenuation of infectivity or at times hypervirulence to the host MTB, with the deletion of mce4A operon gene conferring the greatest degree of attenuation of virulence. Antisense technology using synthetic siRNAs has been used in knocking down genes in bacteria and over the years this has evolved into a powerful tool for elucidating the roles of various genes mediating infectivity and survival in mycobacteria. Molecular beacons are a newer class of antisense RNA tagged with a fluorophore/quencher pair and their use for in vivo detection and knockdown of mRNA is rapidly gaining popularity.

Acyl carrier protein is a bacterial cytoplasmic target of cationic antimicrobial peptide LL-37

In addition to membrane disruption, the cathelicidin antimicrobial peptide (AMP) LL-37 translocates through the bacterial inner membrane to target intracellular molecules. The present study aims to identify an alternate mechanism and a cytoplasmic target of LL-37 in Francisella. LL-37 binding proteins from Francisella novicida U112 bacterial lysates were precipitated by using biotinylated LL-37 (B-LL-37) and NeutrAvidin-agarose beads. Bound proteins were identified by LC-MS/MS, validated and characterized by bead pull-down assays and differential scanning fluorimetry (DSF). The cationic AMP (CAMP) LL-37 was able to interact with Francisella cytoplasmic acyl carrier protein (AcpP; FTN1340/FTT1376). Further study confirmed that LL-37 peptide could bind to AcpP and that the sheep cathelicidin SMAP-29 (Sheep Myeloid Antimicrobial Peptide 29) further increased LL-37 binding to AcpP, suggesting a synergistic effect of SMAP-29 on the binding. LL-37 could also bind to both AcpP of Escherichia coli and Bacillus anthracis, implying a mechanism of broad action of LL-37-AcpP binding. Overexpression of the acpP gene in F. novicida led to an increase in LL-37 susceptibility. LL-37 binding to AcpP changed the fatty acid composition profiles. Taken together, we identified a novel cytoplasmic target of LL-37 in Francisella, suggesting a mechanism of action of this peptide beyond membrane permeabilization. Our findings highlight a novel mechanism of antimicrobial activity of this peptide and document a previously unexplored target of α-helical CAMPs.

Penicillin facilitates the entry of antisense constructs into Streptococcus mutans

Antisense oligonucleotides (AS-ODN) target genes in a sequence-specific manner inhibit gene function and have potential use as antimicrobial agents. Cell barriers, such as peptidoglycan, cell surface proteins and lipopolysaccharide membranes, prevent delivery of AS-ODN into the bacterial cell, limiting their use as an effective treatment option. The β-lactam antibiotic penicillin was examined for its ability to deliver phosphorothioate oligodeoxyribonucleotides (PS-ODNs) and γ(32) P-ODN into Streptococcus mutans OMZ175. Treatment of lag-phase S. mutans OMZ175 cells with penicillin and FBA (PS-ODN targeting the fructose-biphosphate aldolase gene), resulted in prolonged suppression of growth (> 24 h) and fba expression (656.9 ± 194.4-fold decrease at 5 h). Suppression of both cell growth and fba expression corresponded with a greater amount of γ(32) P-ODN becoming cell associated, with a maximum γ(32) P-ODN concentration per cell achieved 5 h after penicillin treatment (6.50 ± 1.39 × 10(8) molecules per CFU). This study confirms that for S. mutans OMZ175, the peptidoglycan layer acts as a major barrier preventing AS-ODN penetration and suggests that the use of agents such as penicillin that interfere with peptidoglycan integrity can significantly increase the uptake of PS-ODN by these cells.

Discovery and early development of AVI-7537 and AVI-7288 for the treatment of Ebola virus and Marburg virus infections

There are no currently approved treatments for filovirus infections. In this study we report the discovery process which led to the development of antisense Phosphorodiamidate Morpholino Oligomers (PMOs) AVI-6002 (composed of AVI-7357 and AVI-7539) and AVI-6003 (composed of AVI-7287 and AVI-7288) targeting Ebola virus and Marburg virus respectively. The discovery process involved identification of optimal transcript binding sites for PMO based RNA-therapeutics followed by screening for effective viral gene target in mouse and guinea pig models utilizing adapted viral isolates. An evolution of chemical modifications were tested, beginning with simple Phosphorodiamidate Morpholino Oligomers (PMO) transitioning to cell penetrating peptide conjugated PMOs (PPMO) and ending with PMOplus containing a limited number of positively charged linkages in the PMO structure. The initial lead compounds were combinations of two agents targeting separate genes. In the final analysis, a single agent for treatment of each virus was selected, AVI-7537 targeting the VP24 gene of Ebola virus and AVI-7288 targeting NP of Marburg virus, and are now progressing into late stage clinical development as the optimal therapeutic candidates.

Targeting essential genes in Salmonella enterica serovar typhimurium with antisense peptide nucleic acid

We investigated the capability of antisense peptide nucleic acids (PNAs) conjugated to the (KFF)(3)K cell-penetrating peptide to target possible essential genes (ligA, rpoA, rpoD, engA, tsf, and kdtA) in Salmonella enterica serovar Typhimurium and inhibit bacterial growth in vitro and in cell culture. All targeted PNA-based gene inhibition has shown great potency in gene expression inhibition in a sequence-specific and dose-dependent manner at micromolar concentrations. Among tested PNAs, the anti-rpoA and -rpoD PNAs showed the greatest potency.

Bacterial antisense RNAs: how many are there, and what are they doing?

Antisense RNAs encoded on the DNA strand opposite another gene have the potential to form extensive base-pairing interactions with the corresponding sense RNA. Unlike other smaller regulatory RNAs in bacteria, antisense RNAs range in size from tens to thousands of nucleotides. The numbers of antisense RNAs reported for different bacteria vary extensively, but hundreds have been suggested in some species. If all of these reported antisense RNAs are expressed at levels sufficient to regulate the genes encoded opposite them, antisense RNAs could significantly impact gene expression in bacteria. Here, we review the evidence for these RNA regulators and describe what is known about the functions and mechanisms of action for some of these RNAs. Important considerations for future research as well as potential applications are also discussed.

Antisense phosphorodiamidate morpholino oligomers targeted to an essential gene inhibit Burkholderia cepacia complex

BACKGROUND

Members of the Burkholderia cepacia complex (Bcc) cause considerable morbidity and mortality in patients with chronic granulomatous disease and cystic fibrosis. Many Bcc strains are antibiotic resistant, which requires the exploration of novel antimicrobial approaches, including antisense technologies such as phosphorodiamidate morpholino oligomers (PMOs).

METHODS

Peptide-conjugated PMOs (PPMOs) were developed to target acpP, which encodes an acyl carrier protein (AcpP) that is thought to be essential for growth. Their antimicrobial activities were tested against different strains of Bcc in vitro and in infection models.

RESULTS

PPMOs targeting acpP were bactericidal against clinical isolates of Bcc (>4 log reduction), whereas a PPMO with a scrambled base sequence (scrambled PPMO) had no effect on growth. Human neutrophils were infected with Burkholderia multivorans and treated with AcpP PPMO. AcpP PPMO augmented killing, compared with neutrophils alone and compared with neutrophils alone plus scrambled PPMO. Mice with chronic granulomatous disease that were infected with B. multivorans were treated with AcpP PPMO, scrambled PPMO, or water at 0, 3, and 6 h after infection. Compared with water-treated control mice, the AcpP PPMO-treated mice showed an approximately 80% reduction in the risk of dying by day 30 of the experiment and relatively little pathology.

CONCLUSION

AcpP PPMO is active against Bcc infections in vitro and in vivo.