Cell-penetrating peptides as transporters for morpholino oligomers: effects of amino acid composition on intracellular delivery and cytotoxicity

Context Dependent Effects of Chimeric Peptide Morpholino Conjugates Contribute to Dystrophin Exon-skipping Efficiency

We have recently reported that cell-penetrating peptides (CPPs) and novel chimeric peptides containing CPP (referred as B peptide) and muscle-targeting peptide (referred as MSP) motifs significantly improve the systemic exon-skipping activity of morpholino phosphorodiamidate oligomers (PMOs) in dystrophin-deficient mdx mice. In the present study, the general mechanistic significance of the chimeric peptide configuration on the activity and tissue uptake of peptide conjugated PMOs in vivo was investigated. Four additional chimeric peptide-PMO conjugates including newly identified peptide 9 (B-9-PMO and 9-B-PMO) and control peptide 3 (B-3-PMO and 3-B-PMO) were tested in mdx mice. Immunohistochemical staining, RT-PCR and western blot results indicated that B-9-PMO induced significantly higher level of exon skipping and dystrophin restoration than its counterpart (9-B-PMO), further corroborating the notion that the activity of chimeric peptide-PMO conjugates is dependent on relative position of the tissue-targeting peptide motif within the chimeric peptide with respect to PMOs. Subsequent mechanistic studies showed that enhanced cellular uptake of B-MSP-PMO into muscle cells leads to increased exon-skipping activity in comparison with MSP-B-PMO. Surprisingly, further evidence showed that the uptake of chimeric peptide-PMO conjugates of both orientations (B-MSP-PMO and MSP-B-PMO) was ATP- and temperature-dependent and also partially mediated by heparan sulfate proteoglycans (HSPG), indicating that endocytosis is likely the main uptake pathway for both chimeric peptide-PMO conjugates. Collectively, our data demonstrate that peptide orientation in chimeric peptides is an important parameter that determines cellular uptake and activity when conjugated directly to oligonucleotides. These observations provide insight into the design of improved cell targeting compounds for future therapeutics studies.

Relationships between Cargo, Cell Penetrating Peptides and Cell Type for Uptake of Non-Covalent Complexes into Live Cells

Modulating signaling pathways for research and therapy requires either suppression or expression of selected genes or internalization of proteins such as enzymes, antibodies, nucleotide binding proteins or substrates including nucleoside phosphates and enzyme inhibitors. Peptides, proteins and nucleotides are transported by fusing or conjugating them to cell penetrating peptides or by formation of non-covalent complexes. The latter is often preferred because of easy handling, uptake efficiency and auto-release of cargo into the live cell. In our studies complexes are formed with labeled or readily detectable cargoes for qualitative and quantitative estimation of their internalization. Properties and behavior of adhesion and suspension vertebrate cells as well as the protozoa Leishmania tarentolae are investigated with respect to proteolytic activity, uptake efficiency, intracellular localization and cytotoxicity. Our results show that peptide stability to membrane-bound, secreted or intracellular proteases varies between different CPPs and that the suitability of individual CPPs for a particular cargo in complex formation by non-covalent interactions requires detailed studies. Cells vary in their sensitivity to increasing concentrations of CPPs. Thus, most cells can be efficiently transduced with peptides, proteins and nucleotides with intracellular concentrations in the low micromole range. For each cargo, cell type and CPP the optimal conditions must be determined separately.

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.

Advanced morpholino oligomers: a novel approach to antiviral therapy

Phosphorodiamidate morpholino oligomers (PMOs) are synthetic antisense oligonucleotide analogs that are designed to interfere with translational processes by forming base-pair duplexes with specific RNA sequences. Positively charged PMOs (PMOplus™) are effective for the postexposure protection of two fulminant viral diseases, Ebola and Marburg hemorrhagic fever in nonhuman primates, and this class of antisense agent may also have possibilities for treatment of other viral diseases. PMOs are highly stable, are effective by a variety of routes of administration, can be readily formulated in common isotonic delivery vehicles, and can be rapidly designed and synthesized. These are properties which may make PMOs good candidates for use during responses to emerging or reemerging viruses that may be insensitive to available therapies or for use during outbreaks, especially in regions that lack a modern medical infrastructure. While the efficacy of sequence-specific therapies can be limited by target-site sequence variations that occur between variants or by the emergence of resistant mutants during infections, various PMO design strategies can minimize these impacts. These strategies include the use of promiscuous bases such as inosine to compensate for predicted base-pair mismatches, the use of sequences that target conserved sites between viral strains, and the use of sequences that target host products that viruses utilize for infection.

Inhibition of p53 expression by peptide-conjugated phosphorodiamidate morpholino oligomers sensitizes human cancer cells to chemotherapeutic drugs

The p53 tumor suppressor gene encodes a transcription factor that is commonly mutated in cancer. Tumors arise when premalignant cells are unable to undergo p53-dependent apoptosis, cell cycle arrest or DNA repair. The p53-signaling pathway affects not only tumor development, but also the response of tumors to chemotherapeutic drugs. In this study, we use cell penetrating peptide conjugates of phosphorodiamidate morpholino oligomers (PPMOs) to inhibit p53 expression. We examine the functional properties of endogenous p53 isoforms that are produced upon PPMO-mediated inhibition of p53 translation and splicing, and report that loss of N-terminal or C-terminal sequences interferes with the transcriptional activity of p53. Importantly, we report that PPMO-mediated inhibition of p53 expression sensitizes human cancer cells with wild-type p53 to chemotherapeutic drugs.

Internalization of nucleoside phosphates into live cells by complex formation with different CPPs and JBS-nucleoducin

Nucleoside phosphates can bind to many functional proteins like G-proteins or other GTP-binding proteins in signal transduction or translation processes. Till now internalization of nucleoside phosphates into live cells remains a challenge. We study the internalization of a fluorescent-labelled deoxyuridine triphosphate into HeLa cells and other adhesion and suspension cells. We use different cell-penetrating peptides and a cocktail suitable for formation of non-covalent complexes with the nucleotide. Internalization is observed by fluorescence microscopy, and the uptake efficiency is quantitatively estimated by fluorescence spectroscopy. The applied concentrations of CPPs and the cocktail were checked on cell viability (MTT test) and membrane integrity (bioluminescence test with peptidyl-luciferin), indicating that the CPPs and the complexes with the nucleotide are cytotoxic above certain concentrations. These concentrations depend on CPP and cell type and are the limiting factors for the cargo uptake.

Toxicity methods for CPPs

CPPs have for numerous years been utilized as delivery vectors of various pharmaceutically interesting cargoes, both in vitro and in vivo. As CPPs are gradually approaching the bedsides, investigating toxicity associated with these highly interesting peptides becomes increasingly important and thorough initial assessment of cytotoxicity in vitro is a first step towards advancing these delivery vehicles in to the clinics. The present chapter describes protocols for four cytotoxicity assays in order to provide a toolbox for toxicity assessment of CPPs. The foci lie on membrane integrity (deoxyglucose leakage and propidium iodide assays) and cell viability (the MTT assay), but the chapter also provides a protocol for assessing an important parameter for future clinical applications, namely the hemolytic properties of CPPs.

Inhibition of influenza virus infection in human airway cell cultures by an antisense peptide-conjugated morpholino oligomer targeting the hemagglutinin-activating protease TMPRSS2

Influenza A viruses constitute a major and ongoing global public health concern. Current antiviral strategies target viral gene products; however, the emergence of drug-resistant viruses highlights the need for novel antiviral approaches. Cleavage of the influenza virus hemagglutinin (HA) by host cell proteases is crucial for viral infectivity and therefore presents a potential drug target. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) are single-stranded-DNA-like antisense agents that readily enter cells and can act as antisense agents by sterically blocking cRNA. Here, we evaluated the effect of PPMO targeted to regions of the pre-mRNA or mRNA of the HA-cleaving protease TMPRSS2 on proteolytic activation and spread of influenza viruses in human Calu-3 airway epithelial cells. We found that treatment of cells with a PPMO (T-ex5) designed to interfere with TMPRSS2 pre-mRNA splicing resulted in TMPRSS2 mRNA lacking exon 5 and consequently the expression of a truncated and enzymatically inactive form of TMPRSS2. Altered splicing of TMPRSS2 mRNA by the T-ex5 PPMO prevented HA cleavage in different human seasonal and pandemic influenza A viruses and suppressed viral titers by 2 to 3 log(10) units, strongly suggesting that TMPRSS2 is responsible for HA cleavage in Calu-3 airway cells. The data indicate that PPMO provide a useful reagent for investigating HA-activating proteases and may represent a promising strategy for the development of novel therapeutics to address influenza infections.

Diaphragm rescue alone prevents heart dysfunction in dystrophic mice

Duchenne muscular dystrophy (DMD) is an X-linked recessive disease caused, in most cases, by the complete absence of the 427 kDa cytoskeletal protein, dystrophin. There is no effective treatment, and affected individuals die from respiratory failure and cardiomyopathy by age 30. Here, we investigated whether cardiomyopathy could be prevented in animal models of DMD by increasing diaphragm utrophin or dystrophin expression and thereby restoring diaphragm function. In a transgenic mdx mouse, where utrophin was over expressed in the skeletal muscle and the diaphragm, but not in the heart, we found cardiac function, specifically right and left ventricular ejection fraction as measured using in vivo magnetic resonance imaging, was restored to wild-type levels. In mdx mice treated with a peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) that resulted in high levels of dystrophin restoration in the skeletal muscle and the diaphragm only, cardiac function was also restored to wild-type levels. In dystrophin/utrophin-deficient double-knockout (dKO) mice, a more severely affected animal model of DMD, treatment with a PPMO again produced high levels of dystrophin only in the skeletal muscle and the diaphragm, and once more restored cardiac function to wild-type levels. In the dKO mouse, there was no difference in heart function between treatment of the diaphragm plus the heart and treatment of the diaphragm alone. Restoration of diaphragm and other respiratory muscle function, irrespective of the method used, was sufficient to prevent cardiomyopathy in dystrophic mice. This novel mechanism of treating respiratory muscles to prevent cardiomyopathy in dystrophic mice warrants further investigation for its implications on the need to directly treat the heart in DMD.

Therapeutic potential of splice-switching oligonucleotides

Alternative splicing enables a single pre-messenger RNA transcript to yield multiple protein isoforms, making it a major contributor to the diversity of the proteome. While this process is essential for normal development, aberrations in alternative splicing are the cause of a multitude of human diseases. Methods for manipulating alternative splicing would thus be of therapeutic value. Chemically modified antisense oligonucleotides that alter alternative splicing by directing splice site selection have been developed to achieve this end. These splice-switching oligonucleotides (SSOs) have been applied to correct aberrant splicing, induce expression of a therapeutic splice variant, or induce expression of a novel therapeutic splice variant in a number of disease-relevant genes. Recently, in vivo efficacy of SSOs has been reported using animal disease models, as well as in results from the first clinical trial.

Inhibition of Japanese encephalitis virus replication in cultured cells and mice by a peptide-conjugated morpholino oligomer

Background

Japanese encephalitis virus (JEV) has a significant impact on public health throughout Asia, and there is a pressing need for development of new therapeutics against it.

Methods

Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) are antisense agents that enter cells readily and interfere with gene expression. Four PPMOs, targeting various locations in the JEV genome, were evaluated for antiviral activity against JEV in cultured cells and the mouse model of JEV infection.

Results

A PPMO (P10882) targeting the JEV 3′ cyclization sequence (3′CSI) had significant antiviral activity in Vero (epithelial), Neuro2A (neuronal) and J774E (macrophage) cells at concentrations that were not cytotoxic. P10882 added before infection suppressed JEV replication to an undetectable level in Vero cells and produced a 93% and 66% reduction in titre in J774E and Neuro2A cells, respectively, when measured at 24 h post-infection. In uninfected cells, fluorescein-labelled PPMOs entered J774E cells most efficiently, followed by Vero and Neuro2A cells. The antiviral effect of P10882 was also demonstrated in vivo, where 60%–80% of 1-week-old mice treated intracerebrally with a 20 mg/kg dose of P10882 every 12 h for 5 days were protected from a lethal dose of JEV and showed an undetectable level of virus in brain tissue at 2 days post-infection.

Conclusions

P10882, which targets sequence that is highly conserved across members of the JEV serocomplex, was previously shown to be effective in a mouse model of West Nile disease, and represents a candidate antiviral agent against members of the JEV serocomplex.

A fusion peptide directs enhanced systemic dystrophin exon skipping and functional restoration in dystrophin-deficient mdx mice

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene that abolish the synthesis of dystrophin protein. Antisense oligonucleotides (AOs) targeted to trigger excision of an exon bearing a mutant premature stop codon in the DMD transcript have been shown to skip the mutated exon and partially restore functional dystrophin protein in dystrophin-deficient mdx mice. To fully exploit the therapeutic potential of this method requires highly efficient systemic AO delivery to multiple muscle groups, to modify the disease process and restore muscle function. While systemic delivery of naked AOs in DMD animal models requires high doses and is of relatively poor efficiency, we and others have recently shown that short arginine-rich peptide-AO conjugates can dramatically improve in vivo DMD splice correction. Here we report for the first time that a chimeric fusion peptide (B-MSP-PMO) consisting of a muscle-targeting heptapeptide (MSP) fused to an arginine-rich cell-penetrating peptide (B-peptide) and conjugated to a morpholino oligomer (PMO) AO directs highly efficient systemic dystrophin splice correction in mdx mice. With very low systemic doses, we demonstrate that B-MSP-PMO restores high-level, uniform dystrophin protein expression in multiple peripheral muscle groups, yielding functional correction and improvement of the mdx dystrophic phenotype. Our data demonstrate proof-of-concept for this chimeric peptide approach in DMD splice correction therapy and is likely to have broad application.

Peptide-morpholino conjugate: a promising therapeutic for Duchenne muscular dystrophy

Steric-blocking oligos can correct reading frame errors or skip premature termination codons. For Duchenne muscular dystrophy (DMD), systemic administration of oligos produces limited delivery into muscle cells. Conjugation to a cell-penetrating peptide greatly enhances muscle uptake of morpholino oligos. A peptide-morpholino conjugate (PPMO) restored dystrophin in mdx mice to > 80% and 50% of normal levels in skeletal and cardiac muscles, respectively, after a single intravenous 30-mg/kg injection. Six injections over 3 months restored dystrophin to nearly normal levels in all muscles. One PPMO injection daily at 12 mg/kg each for 4 days caused exon skipping clearly detectable in the muscles of the mdx mice 9 weeks later, showing prolonged activity. PPMO significantly improved muscle pathology, strength and function, and the survival rate of mice whose hearts were challenged by chemical-induced heart failure. No toxicity or immunogenicity was detected. Our studies demonstrated that muscle functions can be restored with a low dose of PPMO, making it a promising therapeutic for DMD.

Long-term improvement in mdx cardiomyopathy after therapy with peptide-conjugated morpholino oligomers

AIMS

The cardiomyopathy found in Duchenne muscular dystrophy (DMD) is responsible for death due to heart failure in approximately 30% of patients and additionally contributes to many DMD morbidities. Strategies to bypass DMD-causing mutations to allow an increase in body-wide dystrophin have proved promising, but increasing cardiac dystrophin continues to be challenging. The purpose of this study was to determine if therapeutic restoration of cardiac dystrophin improved the significant cardiac hypertrophy and diastolic dysfunction identified in X-linked muscular dystrophy (mdx) dystrophin-null mouse due to a truncation mutation over time after treatment.

METHODS AND RESULTS

Mice lacking dystrophin due to a truncation mutation (mdx) were given an arginine-rich, cell-penetrating, peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) that delivered a splice-switching oligonucleotide-mediated exon skipping therapy to restore dystrophin in mdx mice before the development of detectable cardiomyopathy. PPMO successfully restored cardiac dystrophin expression, preserved cardiac sarcolemma integrity, and prevented the development of cardiac pathology that develops in mdx-null mice over time. By echocardiography and Doppler analysis of the mitral valve, we identified that PPMO treatment of mdx mice prevented the cardiac hypertrophy and diastolic dysfunction identified in sham-treated, age-matched mdx mice, characteristic of DMD patients early in the disease process, in as little as 5-6 weeks after the initiation of treatment. Surprisingly, despite the short-term replacement of cardiac dystrophin (<1% present after 12 weeks by immunodetection), PPMO therapy also provided a durable cardiac improvement in cardiac hypertrophy and diastolic dysfunction for up to 7 months after the initiation of treatment.

CONCLUSION

These results demonstrate for the first time that PPMO-mediated exon skipping therapy early in the course of DMD may effectively prevent or slow down associated cardiac hypertrophy and diastolic dysfunction with significant long-term impact.

A peptide-based dendrimer that enhances the splice-redirecting activity of PNA conjugates in cells

The full therapeutic potential of oligonucleotide (ON)-based agents has been hampered by cellular delivery challenges. Cell-penetrating peptides (CPP) represent promising delivery vectors for nucleic acids, and their potential has recently been evaluated using a functional splicing redirection assay, which capitalizes on the nuclear delivery of splice-correcting steric-block ON analogues such as peptide nucleic acids (PNA). Despite encouraging in vitro and in vivo data with arginine-rich CPP-steric block conjugates, mechanistic studies have shown that entrapment within the endosome/lysosome compartment after endocytosis remains a limiting factor. Previous work from our group has shown that CPP oligomerization greatly improves cellular delivery and increases transfection of plasmid DNA. We now report the chemical synthesis and the evaluation of multivalent CPP-PNA constructs incorporating monomeric (p53(mono)) and dendrimer-like tetrameric (p53(tet)) forms of the p53 tetramerization domain containing peptide, a 10 arginine CPP domain (R10), and a splice redirecting PNA (PNA705). These CPP-PNA conjugates were termed R10p53(tet)-PNA705 and R10p53(mono)-PNA705, referring to their oligomerization state. The present study demonstrates that the splicing redirection efficiency of PNA705 is much greater in the context of the tetrameric R10p53(tet)-PNA705 construct than for the monomeric and occurs at nanomolar concentrations, demonstrating that multivalency is an important factor in delivering PNA into cells.

Inhibition of intracellular growth of Salmonella enterica serovar Typhimurium in tissue culture by antisense peptide-phosphorodiamidate morpholino oligomer

Two types of phosphorodiamidate morpholino oligomers (PMOs) were tested for inhibition of growth of Salmonella enterica serovar Typhimurium. Both PMOs have the same 11-base sequence that is antisense to the region near the start codon of acpP, which is essential for lipid biosynthesis and viability. To the 3' end of each is attached the membrane-penetrating peptide (RXR)4XB (R, X, and B indicate arginine, 6-aminohexanoic acid, and beta-alanine, respectively). One peptide-PMO (AcpP PPMO) has no charge on the PMO moiety. The second PPMO has three cations (piperazine) attached to the phosphorodiamidate linkages (3+Pip-AcpP PPMO). A scrambled-sequence PPMO (Scr PPMO) was synthesized for each type of PMO. The MICs of AcpP PPMO, 3+Pip-AcpP PPMO, and either one of the Scr PPMOs were 1.25 microM (7 microg/ml), 0.156 microM (0.94 microg/ml), and >160 microM (>900 microg/ml), respectively. 3+Pip-AcpP PPMO at 1.25 or 2.5 microM significantly reduced the growth rates of pure cultures, whereas AcpP PPMO or either Scr PPMO had no effect. However, the viable cell count was significantly reduced at either concentration of 3+Pip-AcpP PPMO or AcpP PPMO, but not with either Scr PPMO. In other experiments, macrophages were infected intracellularly with S. enterica and treated with 3 microM 3+Pip-AcpP PPMO. Intracellular bacteria were reduced >99% with 3+Pip-AcpP PPMO, whereas intracellular bacteria increased 3 orders of magnitude in untreated or Scr PPMO-treated cultures. We conclude that either AcpP PPMO or 3+Pip-AcpP PPMO inhibited growth of S. enterica in pure culture and that 3+Pip-AcpP PPMO reduced intracellular viability of S. enterica in macrophages.

Gene knockdowns in adult animals: PPMOs and vivo-morpholinos

Antisense molecules do not readily cross cell membranes. This has limited the use of antisense to systems where techniques have been worked out to introduce the molecules into cells, such as embryos and cell cultures. Uncharged antisense bearing a group of guanidinium moieties on either a linear peptide or dendrimer scaffold can enter cells by endocytosis and subsequently escape from endosomes into the cytosol/nuclear compartment of cells. These technologies allow systemic administration of antisense, making gene knockdowns and splice modification feasible in adult animals; this review presents examples of such animal studies. Techniques developed with PPMOs, which are an arginine-rich cell-penetrating peptide linked to a Morpholino oligo, can also be performed using commercially available Vivo-Morpholinos, which are eight guanidinium groups on a dendrimeric scaffold linked to a Morpholino oligo. Antisense-based techniques such as blocking translation, modifying pre-mRNA splicing, inhibiting miRNA maturation and inhibiting viral replication can be conveniently applied in adult animals by injecting PPMOs or Vivo-Morpholinos.

Vivo-Morpholinos: a non-peptide transporter delivers Morpholinos into a wide array of mouse tissues

We have developed a new transporter structure that provides effective delivery of Morpholino antisense oligomers into a wide variety of tissues in living mice. This transporter comprises a dendritic structure assembled around a triazine core which serves to position eight guanidinium head groups in a conformation effective to penetrate cell membranes. This transporter structure is conjugated to a Morpholino oligomer to form a delivery-enabled product referred to as a Vivo-Morpholino. Vivo-Morpholinos are shown to effectively enter and function within cultured cells in the presence of 100% serum using a rigorous positive test system based on correction of a defined splicing error in a pre-messenger RNA. In addition, Vivo-Morpholinos are demonstrated to enter into a wide variety of tissues in a similar positive test system in transgenic mice, as evidenced by correction of the targeted splicing error in all tissues assessed, including near-complete splice correction in the small intestine, colon, stomach, liver kidney, and a number of muscles. Finally, Vivo-Morpholinos, which target the exon-skipping of exon 23 harboring a premature termination codon in the mdx mouse model, effectively restore the reading frame of dystrophin and restore expression of a functional dystrophin protein.

Chemical modifications of antisense morpholino oligomers enhance their efficacy against Ebola virus infection

Phosphorodiamidate morpholino oligomers (PMOs) are uncharged nucleic acid-like molecules designed to inactivate the expression of specific genes via the antisense-based steric hindrance of mRNA translation. PMOs have been successful at knocking out viral gene expression and replication in the case of acute viral infections in animal models and have been well tolerated in human clinical trials. We propose that antisense PMOs represent a promising class of therapeutic agents that may be useful for combating filoviral infections. We have previously shown that mice treated with a PMO whose sequence is complementary to a region spanning the start codon of VP24 mRNA were protected against lethal Ebola virus challenge. In the present study, we report on the abilities of two additional VP24-specific PMOs to reduce the cell-free translation of a VP24 reporter, to inhibit the in vitro replication of Ebola virus, and to protect mice against lethal challenge when the PMOs are delivered prior to infection. Additionally, structure-activity relationship evaluations were conducted to assess the enhancement of antiviral efficacy associated with PMO chemical modifications that included conjugation with peptides of various lengths and compositions, positioning of conjugated peptides to either the 5' or the 3' terminus, and the conferring of charge modifications by the addition of piperazine moieties. Conjugation with arginine-rich peptides greatly enhanced the antiviral efficacy of VP24-specific PMOs in infected cells and mice during lethal Ebola virus challenge.

Variations in amino acid composition of antisense peptide-phosphorodiamidate morpholino oligomer affect potency against Escherichia coli in vitro and in vivo

The potency of antisense peptide-phosphorodiamidate morpholino oligomers (PPMOs) was improved by varying the peptide composition. An antisense phosphorodiamidate morpholino oligomer (PMO) complementary to the mRNA of the essential gene acpP (which encodes the acyl carrier protein required for lipid biosynthesis) in Escherichia coli was conjugated to the 5' ends of various cationic membrane-penetrating peptides. Each peptide had one of three repeating sequence motifs: C-N-N (motif 1), C-N (motif 2), or C-N-C (motif 3), where C is a cationic residue and N is a nonpolar residue. Variations in the cationic residues included arginine, lysine, and ornithine (O). Variations in the nonpolar residues included phenylalanine, valine, beta-alanine (B), and 6-aminohexanoic acid (X). The MICs of the PPMOs varied from 0.625 to >80 microM (about 3 to 480 microg/ml). Three of the most potent were the (RX)(6)B-, (RXR)(4)XB-, and (RFR)(4)XB-AcpP PMOs, which were further tested in mice infected with E. coli. The (RXR)(4)XB-AcpP PMO was the most potent of the three conjugates tested in mice. The administration of 30 microg (1.5 mg/kg of body weight) (RXR)(4)XB-AcpP PMO at 15 min postinfection reduced CFU/ml in blood by 10(2) to 10(3) within 2 to 12 h compared to the numbers in water-treated controls. All mice treated with 30 microg/dose of (RXR)(4)XB-AcpP PMO survived infection, whereas all water-treated mice died 12 h postinfection. The reduction in CFU/ml in blood was proportional to the dose of PPMO from 30 to 300 microg/ml. In summary, the C-N-C motif was more effective than the other two motifs, arginine was more effective than lysine or ornithine, phenylalanine was more effective than 6-aminohexanoic acid in vitro but not necessarily in vivo, and (RXR)(4)XB-AcpP PMO reduced bacterial infection and promoted survival at clinically relevant doses.

Effective rescue of dystrophin improves cardiac function in dystrophin-deficient mice by a modified morpholino oligomer

Antisense oligonucleotide-mediated exon skipping is able to correct out-of-frame mutations in Duchenne muscular dystrophy and restore truncated yet functional dystrophins. However, its application is limited by low potency and inefficiency in systemic delivery, especially failure to restore dystrophin in heart. Here, we conjugate a phosphorodiamidate morpholino oligomer with a designed cell-penetrating peptide (PPMO) targeting a mutated dystrophin exon. Systemic delivery of the novel PPMO restores dystrophin to almost normal levels in the cardiac and skeletal muscles in dystrophic mdx mouse. This leads to increase in muscle strength and prevents cardiac pump failure induced by dobutamine stress in vivo. Muscle pathology and function continue to improve during the 12-week course of biweekly treatment, with significant reduction in levels of serum creatine kinase. The high degree of potency of the oligomer in targeting all muscles and the lack of detectable toxicity and immune response support the feasibility of testing the novel oligomer in treating Duchenne muscular dystrophy patients.

Delivery of steric block morpholino oligomers by (R-X-R)4 peptides: structure-activity studies

Redirecting the splicing machinery through the hybridization of high affinity, RNase H- incompetent oligonucleotide analogs such as phosphoramidate morpholino oligonucleotides (PMO) might lead to important clinical applications. Chemical conjugation of PMO to arginine-rich cell penetrating peptides (CPP) such as (R-Ahx-R)₄ (with Ahx standing for 6-aminohexanoic acid) leads to sequence-specific splicing correction in the absence of endosomolytic agents in cell culture at variance with most conventional CPPs. Importantly, (R-Ahx-R)₄–PMO conjugates are effective in mouse models of various viral infections and Duchenne muscular dystrophy. Unfortunately, active doses in some applications might be close to cytotoxic ones thus presenting challenge for systemic administration of the conjugates in those clinical settings. Structure–activity relationship studies have thus been undertaken to unravel CPP structural features important for the efficient nuclear delivery of the conjugated PMO and limiting steps in their internalization pathway. Affinity for heparin (taken as a model heparan sulfate), hydrophobicity, cellular uptake, intracellular distribution and splicing correction have been monitored. Spacing between the charges, hydrophobicity of the linker between the Arg-groups and Arg-stereochemistry influence splicing correction efficiency. A significant correlation between splicing correction efficiency, affinity for heparin and ability to destabilize model synthetic vesicles has been observed but no correlation with cellular uptake has been found. Efforts will have to focus on endosomal escape since it appears to remain the limiting factor for the delivery of these splice-redirecting ON analogs.

Cell-penetrating peptide-conjugated antisense oligonucleotides restore systemic muscle and cardiac dystrophin expression and function

Antisense oligonucleotides (AOs) have the potential to induce functional dystrophin protein expression via exon skipping by restoring in-frame transcripts in the majority of patients suffering from Duchenne muscular dystrophy (DMD). AOs of morpholino phosphoroamidate (PMO) and 2'-O-methyl phosphorothioate RNA (2'Ome RNA) chemistry have been shown to restore dystrophin expression in skeletal muscle but not in heart, following high-dose systemic delivery in murine models of muscular dystrophy (mdx). Exploiting the cell transduction properties of two basic arginine-rich cell penetrating peptides, we demonstrate widespread systemic correction of dystrophin expression in body-wide muscles and cardiac tissue in adult dystrophic mdx mice, with a single low-dose injection of peptide-conjugated PMO AO. This approach was sufficient to restore uniform, high-level dystrophin protein expression in peripheral muscle and cardiac tissue, with robust sarcolemmal relocalization of the dystrophin-associated protein complex and functional improvement in muscle. Peptide-conjugated AOs therefore have significant potential for systemic correction of the DMD phenotype.

Subnanomolar antisense activity of phosphonate-peptide nucleic acid (PNA) conjugates delivered by cationic lipids to HeLa cells

In the search of facile and efficient methods for cellular delivery of peptide nucleic acids (PNA), we have synthesized PNAs conjugated to oligophosphonates via phosphonate glutamine and bis-phosphonate lysine amino acid derivatives thereby introducing up to twelve phosphonate moieties into a PNA oligomer. This modification of the PNA does not interfere with the nucleic acid target binding affinity based on thermal stability of the PNA/RNA duplexes. When delivered to cultured HeLa pLuc705 cells by Lipofectamine, the PNAs showed dose-dependent nuclear antisense activity in the nanomolar range as inferred from induced luciferase activity as a consequence of pre-mRNA splicing correction by the antisense-PNA. Antisense activity depended on the number of phosphonate moieties and the most potent hexa-bis-phosphonate-PNA showed at least 20-fold higher activity than that of an optimized PNA/DNA hetero-duplex. These results indicate that conjugation of phosphonate moieties to the PNA can dramatically improve cellular delivery mediated by cationic lipids without affecting on the binding affinity and sequence discrimination ability, exhibiting EC(50) values down to one nanomolar. Thus the intracellular efficacy of PNA oligomers rival that of siRNA and the results therefore emphasize that provided sufficient in vivo bioavailability of PNA can be achieved these molecules may be developed into potent gene therapeutic drugs.

Design and synthesis of dendritic molecular transporter that achieves efficient in vivo delivery of morpholino antisense oligo

Safe and efficient in vivo delivery of Morpholino antisense oligos was probably the last and most difficult challenge for the broad application of antisense in animal research and therapeutics. Several arginine-rich peptides effective for in vivo delivery of Morpholino antisense oligos require rather complex and expensive procedures for synthesis and conjugation. This work describes the design and synthesis of a dendritic transporter in a most concise manner where the selection of the core scaffold, functional group multiplication, orthogonal protecting group manipulation, solid phase conjugation, and off-resin perguanidinylation of the transporter structure are all orchestrated for efficient assembly. We utilized triazine as a core to provide a site for on-column conjugation to the Morpholino oligo and to anchor functional side arms which, after extension, multiplication, and deprotection, are subsequently converted from primary amines to the eight guanidinium headgroups that serve for transport across cell membranes. Intravenous administration of the delivery-enabled Morpholino into a splice-reporter strain of transgenic living mice results in de novo expression of splice-corrected green fluorescent protein in a broad range of tissues and organs in those treated mice. This rigorously demonstrates that this new dendritic transporter achieves effective delivery of a Morpholino oligo into the cytosol/nuclear compartment of cells systemically in vivo. The practical conjugation process may overcome any availability limitation for routine use by the scientific community, and the efficient delivery ability of this transporter may advance the application of Morpholino antisense technology in animals.

Mechanisms and strategies for effective delivery of antisense and siRNA oligonucleotides

The potential use of antisense and siRNA oligonucleotides as therapeutic agents has elicited a great deal of interest. However, a major issue for oligonucleotide-based therapeutics involves effective intracellular delivery of the active molecules. In this Survey and Summary, we review recent reports on delivery strategies, including conjugates of oligonucleotides with various ligands, as well as use of nanocarrier approaches. These are discussed in the context of intracellular trafficking pathways and issues regarding in vivo biodistribution of molecules and nanoparticles. Molecular-sized chemical conjugates and supramolecular nanocarriers each display advantages and disadvantages in terms of effective and nontoxic delivery. Thus, choice of an optimal delivery modality will likely depend on the therapeutic context.

Sustained dystrophin expression induced by peptide-conjugated morpholino oligomers in the muscles of mdx mice

Cell-penetrating peptides (CPPs), containing arginine (R), 6-aminohexanoic acid (X), and/or beta-alanine (B) conjugated to phosphorodiamidate morpholino oligomers (PMOs), enhance their delivery in cell culture. In this study, the potency, functional biodistribution, and toxicity of these conjugates were evaluated in vivo, in EGFP-654 transgenic mice that ubiquitously express the aberrantly spliced EGFP-654 pre-mRNA reporter. Correct splicing and enhanced green fluorescence protein (EGFP) upregulation serve as a positive readout for peptide-PMO (PPMO) entry into cells and access to EGFP-654 pre-mRNA in the nucleus. Intraperitoneal injections of a series of PPMOs, A-N (12 mg/kg), administered once a day for four successive days resulted in splicing correction in numerous tissues. PPMO-B was highly potent in the heart, diaphragm, and quadriceps, which are key muscles in the treatment of Duchenne muscular dystrophy. We therefore investigated PPMO M23D-B, designed to force skipping of stop-codon containing dystrophin exon 23, in an mdx mouse model of the disease. Systemic delivery of M23D-B yielded persistent exon 23 skipping, yielding high and sustained dystrophin protein expression in body-wide muscles, including cardiac muscle, without detectable toxicity. The rescued dystrophin reduced serum creatinine kinase to near-wild-type levels, indicating improvement in muscle integrity. This is the first report of oligonucleotide-mediated exon skipping and dystrophin protein induction in the heart of treated animals.

Cell penetrating peptide conjugates of steric block oligonucleotides

Charge neutral steric block oligonucleotide analogues, such as peptide nucleic acids (PNA) or phosphorodiamidate morpholino oligomers (PMO), have promising biological and pharmacological properties for antisense applications, such as for example in mRNA splicing redirection. However, cellular uptake of free oligomers is poor and the utility of conjugates of PNA or PMO to cell penetrating peptides (CPP), such as Tat or Penetratin, is limited by endosomal sequestration. Two new families of arginine-rich CPPs named (R-Ahx-R)(4) AhxB and R(6)Pen allow efficient nuclear delivery of splice correcting PNA and PMO at micromolar concentrations in the absence of endosomolytic agents. The in vivo efficacy of (R-Ahx-R)(4) AhxB PMO conjugates has been demonstrated in mouse models of Duchenne muscular dystrophy and in various viral infections.

c-MYC antisense phosphosphorodiamidate morpholino oligomer inhibits lung metastasis in a murine tumor model

BACKGROUND

c-MYC amplification and overexpression has been correlated with progression and chemotherapy resistance in lung cancer. AVI-4126, a neutral antisense phosphorodiamidate morpholino oligomer (PMO) has been identified to specifically inhibit c-MYC expression in multiple disease models and identified in Phase I clinical studies to be safe and bioavailable in solid tumors. The present study evaluates AVI-4126 on the development of lung metastasis in the LLC1 syngeneic murine tumor model. Further, this is the first study to show in vivo mis-splicing of c-MYC post-AVI-4126 treatment.

METHODS AND RESULTS

Subcutaneous administration of AVI-4126 at local tumor site (50 microg/day) for 3 cycles of 5 days a week starting day 1 post-tumor cell implantation showed significantly decreased tumor burden, number of tumorlets formed in the lung in comparison to saline or control PMO treatment groups, although no significant reduction of the subcutaneous tumor was observed. AVI-4126 treated lung had markedly reduced mitotic activity but higher rate of apoptosis compared to the controls. HPLC-based analysis of tumor and lung lysates confirmed the presence of intact PMO. In addition to decrease in c-MYC expression, a moderate reduction in the levels of MMP-9 mRNA, a pro-angiogenic extracellular matrix protein postulated to be involved in extravasation of cells from the localized tumor or implantation into the distant metastatic site was observed in the LLC1 tumor tissue of AVI-4126 treated animals.

CONCLUSIONS

The study results are significant in the development of novel anti-tumoral therapeutic strategies directed to c-MYC-overexpressing tumors and establish AVI-4126 as a strong clinical candidate for metastatic disease.