Inhibition of Vesivirus infections in mammalian tissue culture with antisense morpholino oligomers

Comparative analysis of protein synthesis rate in COVID-19 with other human coronaviruses

The genetic code contains information that impacts the efficiency and rate of translation. Translation elongation plays a crucial role in determining the composition of the proteome, errors within a protein contributes towards disease processes. It is important to analyze the novel coronavirus (2019-nCoV) at the codon level to find similarities and variations in hosts to compare with other human coronavirus (CoVs). This requires a comparative and comprehensive study of various human and zoonotic nature CoVs relating to codon usage bias, relative synonymous codon usage (RSCU), proportions of slow codons, and slow di-codons, the effective number of codons (ENC), mutation bias, codon adaptation index (CAI), and codon frequencies. In this work, seven different CoVs were analyzed to determine the protein synthesis rate and the adaptation of these viruses to the host cell. The result reveals that the proportions of slow codons and slow di-codons in human host of 2019-nCoV and SARS-CoV found to be similar and very less compared to the other five coronavirus types, which suggest that the 2019-nCoV and SARS-CoV have faster protein synthesis rate. Zoonotic CoVs have high RSCU and codon adaptation index than human CoVs which implies the high translation rate in zoonotic viruses. All CoVs have more AT% than GC% in genetic codon compositions. The average ENC values of seven CoVs ranged between 38.36 and 49.55, which implies the CoVs are highly conserved and are easily adapted to host cells. The mutation rate of 2019-nCoV is comparatively less than MERS-CoV and NL63 that shows an evidence for genetic diversity. Host-specific codon composition analysis portrays the relation between viral host sequences and the capability of novel virus replication in host cells. Moreover, the analysis provides useful measures for evaluating a virus-host adaptation, transmission potential of novel viruses, and thus contributes to the strategies of anti-viral drug design.

The Threat from Viruses

Infectious disease represent the most significant threat to human health. Significant geologic cataclysmic events have caused the extinction of countless species, but these “Wrath of God” events predate the emergence of Homo sapiens. Pandemic infections have accompanied the rise of human civilization frequently re-occurring leaving a lasting imprint on human history punctuated by profound loss of life. Emerging infections become endemic and are here to stay marking their presence with an annual death toll. Each decade brings a new onslaught of emerging infectious agents. We are surprised again and again but are never prepared. The long-term consequences often remain unrecognized and are always inconvenient including cancer, cardiovascular disease and immune associated diseases that threaten our health. Reliance on clusters of clinical symptoms in the face of diverse and non-descriptive viral infection symptoms is a foolhardy form of crisis management. Viral success is based on rapid replication resulting in large numbers. Single-stranded RNA viruses with their high replication error rate represent a paradigm for resilience.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Prologue

All living things are associated with a boundary defined ecological niche. Steady state conditions are rarely constant but evolutionary adaptation is too slow to adapt to daily threats so a surrogate variation mechanism is necessary. The genome defines the most basic instructions for life so that a molecular biology perspective provides the foundation for understanding resilience. Variations in the expression of RNA offers rapid variation and this book proposes this is the basis of resilience. This book attempts to illuminate mechanisms of resilience beginning with elaborating threats leading to disruption in steady state conditions. Recognition of threats and defense systems are described followed by adaptive changes in gene expression that refine responses. Finally, environmental conditions are discussed that serve to dampen the adaptive response oscillator to disruptive threats at the level of RNA expression.

This prologue is intended to acquaint the reader with my background and the genesis of optimism for an idea that the benefit of transcriptome plasticity is resilience. I grew up in several National Parks, remote regions of the United States that are set aside to preserve natural environments. I attended 12 schools by the time I graduated from high school, a fact that forced me to develop personal resilience. My career path as a scientist followed a path from ecologist to pharmacologist to molecular biologist. I was a professor that transitioned to biotechnology ensuring research subjects involving very diverse in subject matter so I appreciate the value of plasticity.

Using Morpholinos to Control Gene Expression

Morpholino oligonucleotides are stable, uncharged, water-soluble molecules used to block complementary sequences of RNA, preventing processing, read-through, or protein binding at those sites. Morpholinos are typically used to block translation of mRNA and to block splicing of pre-mRNA, though they can block other interactions between biological macromolecules and RNA. Morpholinos are effective, specific, and lack non-antisense effects. They work in any cell that transcribes and translates RNA, but must be delivered into the nuclear/cytosolic compartment to be effective. Morpholinos form stable base pairs with complementary nucleic acid sequences but apparently do not bind to proteins to a significant extent. They are not recognized by any proteins and do not undergo protein-mediated catalysis-nor do they mediate RNA cleavage by RNase H or the RISC complex. This work focuses on techniques and background for using Morpholinos. © 2017 by John Wiley & Sons, Inc.

Delayed Time-to-Treatment of an Antisense Morpholino Oligomer Is Effective against Lethal Marburg Virus Infection in Cynomolgus Macaques

Marburg virus (MARV) is an Ebola-like virus in the family Filovirdae that causes sporadic outbreaks of severe hemorrhagic fever with a case fatality rate as high as 90%. AVI-7288, a positively charged antisense phosphorodiamidate morpholino oligomer (PMOplus) targeting the viral nucleoprotein gene, was evaluated as a potential therapeutic intervention for MARV infection following delayed treatment of 1, 24, 48, and 96 h post-infection (PI) in a nonhuman primate lethal challenge model. A total of 30 cynomolgus macaques were divided into 5 groups of 6 and infected with 1,830 plaque forming units of MARV subcutaneously. AVI-7288 was administered by bolus infusion daily for 14 days at 15 mg/kg body weight. Survival was the primary endpoint of the study. While none (0 of 6) of the saline group survived, 83–100% of infected monkeys survived when treatment was initiated 1, 24, 48, or 96 h post-infection (PI). The antisense treatment also reduced serum viremia and inflammatory cytokines in all treatment groups compared to vehicle controls. The antibody immune response to virus was preserved and tissue viral antigen was cleared in AVI-7288 treated animals. These data show that AVI-7288 protects NHPs against an otherwise lethal MARV infection when treatment is initiated up to 96 h PI.

Marburg virus (MARV) is a filovirus closely related to Ebola virus and similarly causes hemorrhagic fever in humans. MARV is endemic throughout parts of tropical Africa. Severe outbreaks of Marburg virus disease (MVD) have occurred involving hundreds of human cases. No effective MARV antiviral therapies are available. In this study, we used a positive charged phosphorodiamidate morpholino oligomer (PMOplus) targeting the mRNA of the MARV nucleoprotein gene as a medical countermeasure to treat disease in a lethal nonhuman primate model of MVD. The intravenous treatment regimen was well tolerated with no treatment related adverse effects. We showed that when using this antisense treatment, serum virus levels decreased and 83–100% of the animals survived, even when the treatment was delayed as much as 96 hours after infection. None of the untreated animals survived the viral challenge in this model. Our results suggest that antisense therapies, such as PMOs, hold great promise for the treatment of severe viral diseases such as MVD.

Inhibition of Tulane virus replication in vitro with RNA interference

RNA interference (RNAi), a conserved mechanism triggered by small interfering RNA (siRNA), has been used for suppressing gene expression through RNA degradation. The replication of caliciviruses (CVs) with RNAi was studied using the Tulane virus (TV) as a model. Five siRNAs targeting the non-structural, the major (VP1) and minor (VP2) structural genes of the TV were developed and the viruses were quantified using quantitative real time PCR (qPCR) and tissue culture infective dose (TCID(50) ) assay. Treatment of the cells with siRNA 4 hr before viral inoculation significantly reduced viral titer by up to 2.6 logs and dramatically decreased viral RNA copy numbers and viral titers 48 hr post infection in four of the five siRNAs studied. The results were confirmed by Western blot, in which the major structural protein VP1 was markedly reduced in both the cells and the culture medium. Two small protein bands of the shell (S) and protruding (P) domains of the viral capsid protein were also detected in the cell lysates, although their role in viral replication remains unknown. Since the TV shares many biological properties with human noroviruses (NoVs), the successful demonstration of RNAi in TV replication would provide valuable information in control of acute gastroenteritis caused by human NoVs.

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.

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.

Inhibition of norovirus replication by morpholino oligomers targeting the 5'-end of the genome

Noroviruses are an important cause of non-bacterial epidemic gastroenteritis, but no specific antiviral therapies are available. We investigated the inhibitory effect of phosphorodiamidiate morpholino oligomers (PMOs) targeted against norovirus sequences. A panel of peptide-conjugated PMOs (PPMOs) specific for the murine norovirus (MNV) genome was developed, and two PPMO compounds directed against the first AUG of the ORF1 coding sequence near the 5'-end of the genome proved effective in inhibiting MNV replication in cells. A consensus PPMO (designated Noro 1.1), designed to target the corresponding region of several diverse human norovirus genotypes, decreased the efficiency of protein translation in a cell-free luciferase reporter assay and inhibited Norwalk virus protein expression in replicon-bearing cells. Our data suggest that PPMOs directed against the relatively conserved 5'-end of the norovirus genome may show broad antiviral activity against this genetically diverse group of viruses.

Using morpholinos to control gene expression

Morpholino oligonucleotides are stable, uncharged, water-soluble molecules used to block complementary sequences of RNA, preventing processing, read-through, or protein binding at those sites. Morpholinos are typically used to block translation of mRNA and to block splicing of pre-mRNA, though they can block other interactions between biological macromolecules and RNA. Morpholinos are effective, specific, and lack non-antisense effects. They work in any cell that transcribes and translates RNA, but must be delivered into the nuclear/cytosolic compartment to be effective. Morpholinos form stable base pairs with complementary nucleic acid sequences but apparently do not bind to proteins to a significant extent. They are not recognized by any proteins and do not undergo protein-mediated catalysis; nor do they mediate RNA cleavage by RNase H or the RISC complex. This work focuses on techniques and background for using Morpholinos.

Using Morpholinos to control gene expression

Morpholino oligonucleotides are stable, uncharged, water-soluble molecules that bind to complementary sequences of RNA, thereby inhibiting mRNA processing, read-through, and protein binding at those sites. Morpholinos are typically used to inhibit translation of mRNA, splicing of pre-mRNA, and maturation of miRNA, although they can also inhibit other interactions between biological macromolecules and RNA. Morpholinos are effective, specific, and lack non-antisense effects. They work in any cell that transcribes and translates RNA. However, unmodified Morpholinos do not pass well through plasma membranes and must therefore be delivered into the nuclear or cytosolic compartment to be effective. Morpholinos form stable base pairs with complementary nucleic acid sequences but apparently do not bind to proteins to a significant extent. They are not recognized by proteins and do not undergo protein-mediated catalysis; nor do they mediate RNA cleavage by RNase H or the RISC complex. This work focuses on techniques and background for using Morpholinos.

Peptide-conjugated morpholino oligomers inhibit porcine reproductive and respiratory syndrome virus replication

Porcine reproductive and respiratory syndrome (PRRS) has been devastating the global swine industry for more than a decade, and current strategies to control PRRS are inadequate. In this study we characterized the inhibition of PRRS virus (PRRSV) replication by antisense phosphorodiamidate morpholino oligomers (PMO). Of 12 peptide-conjugated PMO (PPMO), four were found to be highly effective at inhibiting PRRSV replication in cell culture in a dose-dependant and sequence-specific manner. PPMO 5UP2 and 5HP are complementary to sequence in the 5′ end of the PRRSV genome, and 6P1 and 7P1 to sequence in the translation initiation regions of ORF6 and ORF7, respectively. Treatment of cells with 5UP2 or 5HP caused a 4.5 log₁₀ reduction in PRRSV yield, compared to a control PPMO. Combination of 6P1 and 7P1 led to higher level reduction than 6P1 or 7P1 alone. 5UP2, 5HP, and a combination of 6P1 and 7P1 inhibited PRRSV replication in porcine alveolar macrophages and protected the cells from PRRSV-induced cytopathic effect. Northern blot and real-time RT-PCR results demonstrated that the effective PPMO led to a reduction of PRRSV RNA level. 5UP2 and 5HP inhibited virus replication of 10 other strains of PRRSV. Results from this study suggest potential applications of PPMO for PRRS control.

Inhibition of multiple subtypes of influenza A virus in cell cultures with morpholino oligomers

Peptide-conjugated phosphorodiamidate morpholino oligomers (P-PMO) are single-stranded nucleic acid-like antisense agents that can reduce gene expression by sterically blocking complementary RNA sequence. P-PMO are water soluble and nuclease resistant, and they readily achieve uptake into cells in culture under standard conditions. Eight P-PMO, each 20 to 22 bases in length, were evaluated for their ability to inhibit influenza A virus (FLUAV) A/PR/8/34 (H1N1) replication in cell culture. The P-PMO were designed to base pair with FLUAV RNA sequences that are highly conserved across viral subtypes and considered critical to the FLUAV biological-cycle, such as gene segment termini and mRNA translation start site regions. Several P-PMO were highly efficacious, each reducing viral titer in a dose-responsive and sequence-specific manner in A/PR/8/34-infected cells. Two P-PMO, one designed to target the AUG translation start site region of PB1 mRNA and the other the 3'-terminal region of nucleoprotein viral genome RNA, also proved to be potent against several other FLUAV strains, including A/WSN/33 (H1N1), A/Memphis/8/88 (H3N2), A/Eq/Miami/63 (H3N8), A/Eq/Prague/56 (H7N7), and the highly pathogenic A/Thailand/1(KAN-1)/04 (H5N1). The P-PMO exhibited minimal cytotoxicity in cell viability assays. High efficacy by two of the P-PMO against multiple FLUAV subtypes suggests that these oligomers represent a broad-spectrum therapeutic approach against a high percentage of known FLUAV strains.

Modulation of gene expression by antisense and antigene oligodeoxynucleotides and small interfering RNA

Antisense oligodeoxynucleotides, triplex-forming oligodeoxynucleotides and double-stranded small interfering RNAs have great potential for the treatment of many severe and debilitating diseases. Concerted efforts from both industry and academia have made significant progress in turning these nucleic acid drugs into therapeutics, and there is already one FDA-approved antisense drug in the clinic. Despite the success of one product and several other ongoing clinical trials, challenges still exist in their stability, cellular uptake, disposition, site-specific delivery and therapeutic efficacy. The principles, strategies and delivery consideration of these nucleic acids are reviewed. Furthermore, the ways to overcome the biological barriers are also discussed so that therapeutic concentrations at their target sites can be maintained for a desired period.

Suppression of porcine reproductive and respiratory syndrome virus replication by morpholino antisense oligomers

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of a contagious disease characterized by reproductive failure in sows and respiratory disease in piglets. This infectious disease results in significant losses in the swine industry and specific anti-PRRSV drugs are needed. In this study, we evaluated a novel class of antisense compounds, peptide-conjugated phosphorodiamidate morpholino oligomers (P-PMOs), for their ability to suppress PRRSV replication in cell culture. P-PMOs are analogs of single-stranded DNA and contain a modified backbone that confers highly specific binding to RNA and resistance to nucleases. Of six P-PMOs tested, one ('5UP1'), with sequence complementary to the 5'-terminal 21 nucleotides of the PRRSV genome, was found to be highly effective at reducing PRRSV replication in a specific and dose-dependent manner in CRL11171 cells in culture. 5UP1 treatment generated up to a 4.5log reduction in infectious PRRSV yield, while a control P-PMO had no effect on viral titer. Immunofluorescence assay with an anti-PRRSV monoclonal antibody confirmed the titer observations. The sequence-specificity of 5UP1 effect was confirmed in part by a cell-free luciferase reporter assay system, which showed that 5UP1-mediated inhibition of translation decreased if the target-RNA contained mispairings in relation to the 5UP1 P-PMO. Real-time RT-PCR showed that the production of PRRSV negative-sense RNA was reduced if 5UP1 was added to cells at up to 6h post-virus inoculation. Cell viability assays detected no cytotoxicity of 5UP1 within the concentration-range of this study. These results indicate that P-PMO 5UP1 has potential as an anti-PRRSV agent.

Inhibition of replication and transcription activator and latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus by morpholino oligomers

Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with Kaposi's sarcoma and primary effusion lymphoma (PEL). The KSHV replication and transcription activator (RTA) and latency-associated nuclear antigen (LANA) play key roles in activating KSHV lytic replication and maintaining KSHV latency, respectively. Phosphorodiamidate morpholino oligomers (PMO) are similar to short single-stranded DNA oligomers, but possess a modified backbone that confers highly specific binding and resistance to nucleases. In this study, RTA and LANA mRNA in PEL cells were targeted by antisense peptide-conjugated PMO (P-PMO) in an effort to suppress KSHV replication. Highly efficient P-PMO uptake by PEL cells was observed. Treatment of PEL cells with a RTA P-PMO (RP1) reduced RTA expression in a dose-dependent and sequence-specific manner, and also caused a significant decrease in several KSHV early and late gene products, including vIL-6, vIRF-1, and ORF-K8.1A. KSHV viral DNA levels were reduced both in cells and culture supernatants of RP1 P-PMO-treated cells, indicating that KSHV lytic replication was suppressed. Treatment of BCBL-1 cells with P-PMO against LANA resulted in a reduction of LANA expression. Cell viability assays detected no cytotoxicity from P-PMO alone, within the concentration range used for the experiments in this study. These results suggest that RP1 P-PMO can specifically block KSHV replication, and further study is warranted.

VP35 knockdown inhibits Ebola virus amplification and protects against lethal infection in mice

Phosphorodiamidate morpholino oligomers (PMO) are a class of uncharged single-stranded DNA analogs modified such that each subunit includes a phosphorodiamidate linkage and morpholine ring. PMO antisense agents have been reported to effectively interfere with the replication of several positive-strand RNA viruses in cell culture. The filoviruses, Marburg virus and Ebola virus (EBOV), are negative-strand RNA viruses that cause up to 90% lethality in human outbreaks. There is currently no commercially available vaccine or efficacious therapeutic for any filovirus. In this study, PMO conjugated to arginine-rich cell-penetrating peptide (P-PMO) and nonconjugated PMO were assayed for the ability to inhibit EBOV infection in cell culture and in a mouse model of lethal EBOV infection. A 22-mer P-PMO designed to base pair with the translation start site region of EBOV VP35 positive-sense RNA generated sequence-specific and time- and dose-dependent inhibition of EBOV amplification in cell culture. The same oligomer provided complete protection to mice when administered before or after an otherwise lethal infection of EBOV. A corresponding nonconjugated PMO, as well as nonconjugated truncated versions of 16 and 19 base residues, provided length-dependent protection to mice when administered prophylactically. Together, these data suggest that antisense PMO and P-PMO have the potential to control EBOV infection and are promising therapeutic candidates.

Gene-specific countermeasures against Ebola virus based on antisense phosphorodiamidate morpholino oligomers

The filoviruses Marburg virus and Ebola virus (EBOV) quickly outpace host immune responses and cause hemorrhagic fever, resulting in case fatality rates as high as 90% in humans and nearly 100% in nonhuman primates. The development of an effective therapeutic for EBOV is a daunting public health challenge and is hampered by a paucity of knowledge regarding filovirus pathogenesis. This report describes a successful strategy for interfering with EBOV infection using antisense phosphorodiamidate morpholino oligomers (PMOs). A combination of EBOV-specific PMOs targeting sequences of viral mRNAs for the viral proteins (VPs) VP24, VP35, and RNA polymerase L protected rodents in both pre- and post-exposure therapeutic regimens. In a prophylactic proof-of-principal trial, the PMOs also protected 75% of rhesus macaques from lethal EBOV infection. The work described here may contribute to development of designer, “druggable” countermeasures for filoviruses and other microbial pathogens.

Ebola virus (EBOV) causes a highly lethal hemorrhagic fever that results in up to 50%–90% mortality in humans. There are currently no available vaccines or therapeutics to treat EBOV infection. To date, multiple pre- and post-exposure therapeutic strategies, primarily focused on bolstering the host immune response or inhibiting viral replication, have been undertaken with limited success. Here, Bavari and colleagues report the development of a successful therapeutic regimen for EBOV infection based on antisense phosphorodiamidate morpholino oligomers (PMOs). PMOs are a subclass of chemically modified antisense oligonucleotides that interfere with the translation of viral mRNA, thus inhibiting viral amplification. Using a cell-free translation system, a cell-based assay, and survival studies in rodents, we identified several efficacious EBOV-specific PMOs. Further, prophylactic administration of a combination of three EBOV-specific PMOs specifically targeting VP24, VP35, and the viral polymerase L protected rhesus macaques from lethal EBOV infection. This is the first successful antiviral intervention against filoviruses in nonhuman primates. These findings may serve as the basis for a new strategy to quickly develop virus-specific therapies in defense against known, emerging, and genetically engineered bioterrorism threats.

Isolation and characterization of a new Vesivirus from rabbits

This report describes the isolation, cDNA cloning, complete genome nucleotide sequence, and partial characterization of a new cultivable calicivirus isolated from juvenile feeder European rabbits (Oryctolagus cuniculus) showing symptoms of diarrhea. Absence of neutralization by type-specific neutralizing antibodies for 40 caliciviruses and phylogenetic sequence comparisons of the open reading frame 1-encoded polyprotein with those of other caliciviruses demonstrate that this new calicivirus is a putative novel member of the Vesivirus genus which is closely related to the marine calicivirus subgroup. According to its putative classification, this new virus has been named rabbit vesivirus.

Inhibition of infectious haematopoietic necrosis virus in cell cultures with peptide-conjugated morpholino oligomers

Delivery of phosphorodiamidate morpholino oligomers (PMO) into fish cells in vitro and tissues in vivo was examined. Uptake was evaluated by fluorescence microscopy and flow cytometry after treating cultured cells or live rainbow trout with 3' fluorescein-tagged PMO. Arginine-rich peptide conjugated to the 5' end of the PMO markedly enhanced cellular uptake in culture by 8- to 20-fold compared with non-peptide-conjugated PMO as determined by flow cytometry. Enhanced uptake of PMO conjugated to peptide was also observed in tissues of fish treated by immersion. The efficacy of PMO as inhibitors of infectious haematopoietic necrosis virus (IHNV) replication was determined in vitro. Peptide-conjugated PMOs targeting sequences within the IHNV genomic RNA (negative polarity) or antigenomic RNA (positive polarity) significantly inhibited replication in a dose-dependent and sequence-specific manner. A PMO complementary to sequence near the 5' end of IHNV genomic RNA was the most effective, diminishing titre by 97%, as measured by plaque assay and Western blot. These data demonstrate that replication of a negative-stranded non-segmented RNA virus can be inhibited by antisense compounds that target positive polarity viral RNA, or by a compound that targets negative polarity viral RNA.

Inhibition of dengue virus serotypes 1 to 4 in vero cell cultures with morpholino oligomers

Five dengue (DEN) virus-specific R5F2R4 peptide-conjugated phosphorodiamidate morpholino oligomers (P4-PMOs) were evaluated for their ability to inhibit replication of DEN virus serotype 2 (DEN-2 virus) in mammalian cell culture. Initial growth curves of DEN-2 virus 16681 were obtained in Vero cells incubated with 20 microM P4-PMO compounds. At 6 days after infection, a P4-PMO targeting the 3'-terminal nucleotides of the DEN-2 virus genome and a random-sequence P4-PMO showed relatively little suppression of DEN-2 virus titer (0.1 and 0.9 log10, respectively). P4-PMOs targeting the AUG translation start site region of the single open reading frame and the 5' cyclization sequence region had moderate activity, generating 1.6- and 1.8-log10 reductions. Two P4-PMO compounds, 5'SL and 3'CS (targeting the 5'-terminal nucleotides and the 3' cyclization sequence region, respectively), were highly efficacious, each reducing the viral titer by greater than 5.7 log10 compared to controls at 6 days after infection with DEN-2 virus. Further experiments showed that 5'SL and 3'CS inhibited DEN-2 virus replication in a dose-dependent and sequence-specific manner. Treatment with 10 microM 3'CS reduced the titers of all four DEN virus serotypes, i.e., DEN-1 (strain 16007), DEN-2 (16681), DEN-3 (16562), and DEN-4 (1036) viruses by over 4 log10, in most cases to below detectable limits. The extent of 3'CS efficacy was affected by the timing of compound application in relation to viral infection of the cells. The 5'SL and 3'CS P4-PMOs did not suppress the replication of West Nile virus NY99 in Vero cells. These data indicate that further evaluation of the 5'SL and 3'CS compounds as potential DEN virus therapeutics is warranted.

Antisense morpholino-oligomers directed against the 5' end of the genome inhibit coronavirus proliferation and growth

Conjugation of a peptide related to the human immunodeficiency virus type 1 Tat represents a novel method for delivery of antisense morpholino-oligomers. Conjugated and unconjugated oligomers were tested to determine sequence-specific antiviral efficacy against a member of the Coronaviridae, Mouse hepatitis virus (MHV). Specific antisense activity designed to block translation of the viral replicase polyprotein was first confirmed by reduction of luciferase expression from a target sequence-containing reporter construct in both cell-free and transfected cell culture assays. Peptide-conjugated morpholino-oligomers exhibited low toxicity in DBT astrocytoma cells used for culturing MHV. Oligomer administered at micromolar concentrations was delivered to >80% of cells and inhibited virus titers 10- to 100-fold in a sequence-specific and dose-responsive manner. In addition, targeted viral protein synthesis, plaque diameter, and cytopathic effect were significantly reduced. Inhibition of virus infectivity by peptide-conjugated morpholino was comparable to the antiviral activity of the aminoglycoside hygromycin B used at a concentration fivefold higher than the oligomer. These results suggest that this composition of antisense compound has therapeutic potential for control of coronavirus infection.

HIV Tat peptide enhances cellular delivery of antisense morpholino oligomers

Phosphorodiamidate morpholino oligomers (PMO) are uncharged antisense molecules that bind complementary sequences of RNA, inhibiting gene expression by preventing translation or by interfering with pre-mRNA splicing. The techniques used to deliver PMO into cultured cells have been mostly mechanical methods. These delivery methods, although useful, have limitations. We investigated the ability of the HIV Tat peptide (pTat) and other cationic peptides to deliver PMO into cultured cells. Fluorescence was seen in 100% of HeLa cells treated with pTat-PMO-fluorescein conjugate. pTat-PMO conjugate targeted to c-myc mRNA downregulated c-myc reporter gene expression with an IC50 of 25 microM and achieved nearly 100% inhibition. pTat-PMO conjugate targeted to a mutant splice site of beta-globin pre-mRNA dose-dependently corrected splicing and upregulated expression of the functional reporter gene. Neither unconjugated PMO nor unconjugated pTat caused antisense activities. However, compared with mechanically mediated delivery, pTat-mediated PMO delivery required higher concentrations of PMO (>10 microM) to cause antisense activity and caused some toxicity. Most pTat-PMO conjugate was associated with cell membranes, and internalized conjugate was localized in vesicles, cytosol, and nucleus. The other three cationic peptides are much less effective than pTat. pTat significantly enhances delivery of PMO in 100% of cells assayed. pTat-mediated delivery is a much simpler procedure to perform than other delivery methods.

Inhibition of human chorionic gonadotropin beta-subunit modulates the mitogenic effect of c-myc in human prostate cancer cells

BACKGROUND

Amplification of the proto-oncogene c-myc has been identified as one of the most common genetic alterations in prostate cancer, thus making it an attractive therapeutic target. However, certain prostate cancer cells are unresponsive to c-Myc inhibition. The purpose of this study was to test the hypothesis that effective growth inhibition in the refractory cancer cells can be achieved by blocking c-myc along with a growth factor using a novel phosphorodiamidate morpholino antisense oligomer-based approach. Human chorionic gonadotropin, a growth factor implicated in neoplasm, causes activation of c-myc through a G-protein-coupled pathway of signal transduction.

METHODS

In this study, the effect of inhibition of beta-hCG and c-myc singly or in combination was evaluated in DU145 (RB -/-, p53-/-, androgen-independent) and LNCaP (Rb+/+, p53 +/+, androgen-sensitive) human prostate cancer cell lines and in a DU145 subcutaneous xenograft murine model.

RESULTS

Antisense phosphorodiamidate morpholino oligomers directed against beta-hCG and c-myc caused a specific decrease of the target protein levels. Unlike LNCaP cells, DU145 cell growth was refractory to c-Myc inhibition. Unresponsiveness to c-myc inhibition in DU145 cells was overcome by targeting both beta-hCG and c-myc genes, resulting in potentiation of the antiproliferative effect seen with inhibition of beta-hCG alone.

CONCLUSIONS

The inhibition of beta-hCG sensitizes prostate cancer cells to the antiproliferative effects of c-Myc inhibition, including tumors that are refractory to c-Myc decrease alone.