Cytotoxicity of poly-guanidine in medulloblastoma cell lines.

Medulloblastoma (MB) is the most common pediatric brain tumor. The therapy frequently causes serious side effects, and new selective therapies are needed. MB expresses hyper sialylation, a possible target for selective therapy. The cytotoxic efficacy of a poly guanidine conjugate (GuaDex) incubated with medulloblastoma cell cultures (DAOY and MB-LU-181) was investigated. The cells were incubated with 0.05-8 µM GuaDex from 15 min to 72 h. A fluorometric cytotoxicity assay (FMCA) measured the cytotoxicity. Labeled GuaDex was used to study tumor cell interaction. FITC-label Sambucus nigra confirmed high expression of sialic acid (Sia). Immunofluorescence microscopy was used to visualize the cell F-actin and microtubules. The cell interactions were studied by confocal and fluorescence microscopy. Annexin-V assay was used to detect apoptosis. Cell cycle analysis was done by DNA content determination. A wound-healing migration assay determined the effects on the migratory ability of DAOY cells after GuaDex treatment. IC50 for GuaDex was 223.4 -281.1 nM. FMCA showed potent growth inhibition on DAOY and MB-LU-181 cells at 5 uM GuaDex after 4 h of incubation. GuaDex treatment induced G2/M phase cell cycle arrest. S. nigra FITC-label lectin confirmed high expression of Sia on DAOY medulloblastoma cells. The GuaDex treatment polymerized the cytoskeleton (actin filaments and microtubules) and bound to DNA, inducing condensation. The Annexin V assay results were negative. Cell migration was inhibited at 0.5 µM GuaDex concentration after 24 h of incubation. GuaDex showed potent cytotoxicity and invasion-inhibitory effects on medulloblastoma cells at low micromolar concentrations. GuaDex efficacy was significant and warrants further studies.

Therapeutic effects of guanidine hydrochloride on breast cancer through targeting KCNG1 gene.

BACKGROUND: Triple-negative breast cancer (TNBC) is one of the subtypes of breast cancer (BC) that is associated with poor survival rates and failure to respond to hormonal and targeted therapies. OBJECTIVE: The aim of this study was to identify a specific gene at the expression level for TNBC and targeting of this type of breast cancer based on it. Using TCGA database, genes that are particularly high expression in TNBC subtypes compared to other BC subtypes (in terms of receptor status) and normal samples were identified and their sensitivity and specificity were evaluated. Using PharmacoGX and Drug Bank data, drug sensitivity and drug-appropriate genes were identified, respectively. The effects of the identified drug on triple-negative cell lines (MDA-MB-468) were evaluated in comparison with the cell line of other subtypes (MCF7) by apoptosis and MTS tests. RESULTS: Data analyzes showed that the expression level of KCNG1 gene in the TNBC subgroup was significantly higher compared to other BC subtypes from the KCN gene family and ROC results showed that this gene had highest sensitivity and specificity in TNBC subtype. The results of drug resistance and sensitivity showed that an increase in the expression level of KCNG1 was associated with sensitivity to Cisplatin and Oxaliplatin. Moreover, Drug Bank results showed that Guanidine hydrochloride (GuHCl) was a suitable inhibitor for KCNG1. In vitro results showed that the expression level of KCNG1 was higher in MDA-MB-468 compared to MCF7. In addition, the rate of apoptosis in response to GuHCl treatment in MDA-MB-468 cell line as TNBC cell model was higher than MCF7 in the same concentration. CONCLUSION: This study revealed that GuHCl could be a suitable treatment for TNBC subtype by targeting of KCNG1.

Guanidinium-Decorated Nanostructure for Precision Sonodynamic-Catalytic Therapy of MRSA-Infected Osteomyelitis.

Osteomyelitis caused by methicillin-resistant Staphylococcus aureus (MRSA) biofilm infection is difficult to eradicate and can even be life-threatening. Given that the infection is persistent and deep-seated in the bone tissue, controlled and efficient treatment of osteomyelitis remains challenging. Herein, an activatable nanostructure (Au/TNT@PG) is presented for synergistic sonodynamic-catalytic therapy of MRSA-infected osteomyelitis. The Au/TNT@PG backbone is obtained by conjugating a guanidinium-rich polymer (PG), a component that penetrates the biofilm matrix, onto ultrasound (US)-absorbing gold-doped titanate nanotubes (Au/TNTs). Under deep-penetrating US irradiation, the nanocomposite generates 1 O2 for sonodynamic therapy and catalyzes the decomposition of endogenous H2 O2 into toxic •OH in the acidic infection microenvironment for catalytic therapy, leading to bacterial cell death. Its robust antibacterial effectiveness is attributable to its bacteria-capturing ability, the biofilm penetrability of positively charged guanidinium, and the subsequent synergistic effect of sonodynamic-catalytic action of Au/TNT. Such a remotely controlled approach potentiates the polarization of macrophages to M2-type while suppressing the M1-type, leading to topical inflammation resolution and enhanced osteoblast proliferation and differentiation to inhibit bone loss. Therefore, this study provides a generic nanotherapeutic approach for efficient sonodynamic-catalytic therapy with respect to osteomyelitis.

Puerarin attenuates diabetic kidney injury through interaction with Guanidine nucleotide-binding protein Gi subunit alpha-1 (Gnai1) subunit.

Radix puerariae, a traditional Chinese herbal medication, has been used to treat patients with diabetic kidney disease (DKD). Our previous studies demonstrated that puerarin, the active compound of radix puerariae, improves podocyte injury in type 1 DKD mice. However, the direct molecular target of puerarin and its underlying mechanisms in DKD remain unknown. In this study, we confirmed that puerarin also improved DKD in type 2 diabetic db/db mice. Through RNA-sequencing odf isolated glomeruli, we found that differentially expressed genes (DEGs) that were altered in the glomeruli of these diabetic mice but reversed by puerarin treatment were involved mostly in oxidative stress, inflammatory and fibrosis. Further analysis of these reversed DEGs revealed protein kinase A (PKA) was among the top pathways. By utilizing the drug affinity responsive target stability method combined with mass spectrometry analysis, we identified guanine nucleotide-binding protein Gi alpha-1 (Gnai1) as the direct binding partner of puerarin. Gnai1 is an inhibitor of cAMP production which is known to have protection against podocyte injury. In vitro, we showed that puerarin not only interacted with Gnai1 but also increased cAMP production in human podocytes and mouse diabetic kidney in vivo. Puerarin also enhanced CREB phosphorylation, a downstream transcription factor of cAMP/PKA. Overexpression of CREB reduced high glucose-induced podocyte apoptosis. Inhibition of PKA by Rp-cAMP also diminished the effects of puerarin on high glucose-induced podocyte apoptosis. We conclude that the renal protective effects of puerarin are likely through inhibiting Gnai1 to activate cAMP/PKA/CREB pathway in podocytes.

Poly-guanidine shows high cytotoxicity in glioma cell cultures and glioma stem cells.

Glioblastoma multiforme (GBM) is a malignant CNS tumor with a poor prognosis. GBM shows aberrant glycosylation with hypersialylation. This property is a potential target for therapy. This study investigates the growth inhibitory efficacy of poly-guanidine (GuaDex), with an affinity for sialic acid (Sia). Glioma cell cultures and patient-derived glioma cell lines (PDGCLs) expressing Prominin-1 (CD133) were used. Human fibroblasts and astrocyte-derived cells were used as controls. Temozolomide (standard GBM drug, TMZ) and DMSO were used as a comparison. GuaDex at 1-10 µM concentrations, were incubated for 3.5-72 h and with PDGCLs cells for 6-24 h. The cytotoxicity was estimated with a fluorometric cytotoxicity assay (FMCA). Fluorescence-labelled GuaDex was used to study the cell interactions. Sia expression was confirmed with a fluorescence labelled Sia binding lectin. Expression of glial fibrillary acidic protein was determined. GuaDex induction of growth inhibition was fast, showing after less than 5 min incubation while the control cells were not affected even after 50 min incubation. The growth inhibitory effect on PDGCLs spheroids was persistent still showing after 4 weeks post-treatment. The growth inhibition of GuaDex was induced at low µM concentrations while TMZ induced only a slight inhibition at mM concentrations. GuaDex efficacy appears significant and warrants further studies.

Residual meta-iodobenzyl guanidine (MIBG) positivity following therapy for metastatic neuroblastoma: Patient characteristics, imaging, and outcome.

BACKGROUND: Meta-iodobenzylguanidine(MIBG) scans are used to detect neuroblastoma metastatic lesions at diagnosis and during posttreatment surveillance. MIBG positivity following induction chemotherapy correlates with poor outcome; however, there are reports of patients with progression-free survival despite MIBG positivity at the end of therapy. The factors distinguishing these survivors from patients who progress or relapse are unclear. FDG-positron-emission tomography (PET) scans can also detect metastatic lesions at diagnosis; however, their role in posttherapy surveillance is less well studied. METHODS: We performed a retrospective analysis of International Neuroblastoma Staging System (INSS) stage 4 patients to identify those with residual MIBG-avid metastatic lesions on end-of-therapy scans without prior progression. Data collected included age, disease sites, histopathology, biomarkers, treatment, imaging studies, and response. RESULTS: Eleven of 265 patients met inclusion criteria. At diagnosis three of 11 patients were classified as intermediate and eight of 11 high risk; nine of 11 had documented marrow involvement. Histologic classification was favorable for four of 10 and MYCN amplification was detected in zero of 11 cases. The median time with persistent MIBG positivity following treatment was 1.5 years. Seven patients had at least one PET scan with low or background activity. Biopsies of three of three MIBG-avid residual lesions showed differentiation. All patients remain alive with no disease progression at a median of 4.0 years since end of therapy. CONCLUSION: Persistently MIBG-avid metastatic lesions in subsets of patients following completion of therapy may not represent active disease that will progress. Further studies are needed to determine whether MYCN status or other biomarkers, and/or PET scans, may help identify patients with residual inactive MIBG lesions who require no further therapy.

Potential Anti-Alzheimer Agents from Guanidinyl Tryptophan Derivatives with Activities of Membrane Adhesion and Conformational Transition Inhibitions.

Guanidinyl tryptophan derivatives TGN1, TGN2, TGN3, and TGN4 were synthesized, and these compounds were shown to possess in vitro inhibitory activity for amyloid aggregation in a previous study. Nevertheless, the influence of the TGN series of compounds on the binding and permeation behaviors of an Aß monomer to the cell membranes was not elucidated. In this study, we investigated the effect of compounds in the TGN series on the behavior of an Aß monomer regarding its toxicity toward the bilayer lipid membrane using molecular dynamics (MD) simulation. MD simulations suggest that TGN4 is a potential agent that can interfere with the movement of the Aß monomer into the membrane. The MM-GBSA result demonstrated that TGN4 exhibits the highest affinity to the Aß1-42 monomer but has the lowest affinity to the bilayer. Moreover, TGN4 also contributes to a decrease in the binding affinity between the Aß1-42 monomer and the POPC membrane. Regarding the results of the binding mode and conformational analyses, a high number of amino-acid residues were shown to provide the binding interactions between TGN4 and the Aß1-42 monomer. TGN4 also reduces the conformational transition of the Aß1-42 monomer by means of interacting with the monomer. The present study presents molecular-level insights into how the TGN series of compounds affect the membrane adsorption and the conformational transition of the Aß1-42 monomer, which could be valuable for the further development of new anti-Alzheimer agents.

Discovery of Nanomolar Melanocortin-3 Receptor (MC3R)-Selective Small Molecule Pyrrolidine Bis-Cyclic Guanidine Agonist Compounds Via a High-Throughput "Unbiased" Screening Campaign.

The central melanocortin-3 and melanocortin-4 receptors (MC3R, MC4R) are key regulators of body weight and energy homeostasis. Herein, the discovery and characterization of first-in-class small molecule melanocortin agonists with selectivity for the melanocortin-3 receptor over the melanocortin-4 receptor are reported. Identified via "unbiased" mixture-based high-throughput screening approaches, pharmacological evaluation of these pyrrolidine bis-cyclic guanidines resulted in nanomolar agonist activity at the melanocortin-3 receptor. The pharmacological profiles at the remaining melanocortin receptor subtypes tested indicated similar agonist potencies at both the melanocortin-1 and melanocortin-5 receptors and antagonist or micromolar agonist activities at the melanocortin-4 receptor. This group of small molecules represents a new area of chemical space for the melanocortin receptors with mixed receptor pharmacology profiles that may serve as novel lead compounds to modulate states of dysregulated energy balance.

In vitro characterization, ADME analysis, and histological and toxicological evaluation of BM1, a macrocyclic amidinourea active against azole-resistant Candida strains.

BACKGROUND: Candida species are one of the most common causes of nosocomial bloodstream infections among the opportunistic fungi. Extensive use of antifungal agents, most of which were launched on the market more than 20 years ago, led to the selection of drug-resistant or even multidrug-resistant fungi. We recently described a novel class of antifungal macrocyclic compounds with an amidinourea moiety that is highly active against azole-resistant Candida strains. OBJECTIVE: A compound from this family, BM1, was investigated in terms of in vitro activity against various Candida species, including C. auris isolates, interaction with the ABC transporter, CDR6, and in vivo distribution and safety. METHODS: In vitro assays (CYP inhibition, microsomal stability, permeability, spot assays) were used to collect chemical and biological data; animal models (rat) paired with LC-MS analysis were utilised to evaluate in vivo toxicology, pharmacokinetics, and distribution. RESULTS: The current research shows BM1 has a low in vivo toxicity profile, affinity for the renal system in rats, and good absorption, distribution, metabolism, and excretion (ADME). BM1 also has potent activity against azole-resistant fungal strains, including C. auris isolates and CDR6-overexpressing strains. CONCLUSIONS: The results confirmed low minimum inhibitory concentrations (MICs) against several Candida species, including preliminary data vs. C. auris. BM1 has good ADME and biochemical characteristics, is suitable and safe for daily administration and is particularly indicated for renal infections. These data indicate BM1 and its derivatives form a novel, promising antifungal class.

Amifampridine for the treatment of Lambert-Eaton myasthenic syndrome.

Introduction: The present status of amifampridine (AFP) for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) is reviewed. Areas covered: All relevant literature identified through a PubMed search under treatment of LEMS, aminopyridine, and amifampridine are reviewed. An expert opinion on AFP was formulated. Expert opinion: AFPs, 3,4-DAP and 3,4-DAPP, are the most studied drugs in neuromuscular diseases. Randomized and non-randomized studies showed the most effective drug as symptomatic medication for LEMS. AFPs are safe and tolerable. Thus, AFPs should be the drug of choice for the symptomatic treatment in LEMS. As long as the daily dose is less than 80 mg a day, there is no concern for the serious side-reaction, seizure. Because of short-acting drug effects, it should be given three or four times a day. Peri-oral and finger paresthesia, the most common side-reaction, is accepted as a sign of drug-intake by many patients. Gastro-intestinal side reactions, the next common side-reaction of AFPs, are tolerable. AFPs are also the drug of choice and life-saving for LEMS crisis. For the long-term usage, it is proven to be safe and AFPs can be supplemented with liberal amount of pyridostigmine to sustain a symptomatic improvement without any undue side-reaction.

Evaluation of antiviral therapies in respiratory and neurological disease models of Enterovirus D68 infection in mice.

Enterovirus D68 (EV-D68) is unique among enteroviruses because of the ability to cause severe respiratory disease as well as neurological disease. We developed separate models of respiratory and neurological disease following EV-D68 infection in AG129 mice that respond to antiviral treatment with guanidine. In four-week-old mice infected intranasally, EV-D68 replicates to high titers in lung tissue increasing the proinflammatory cytokines MCP-1 and IL-6. The respiratory infection also produces an acute viremia. In 10-day-old mice infected intraperitoneally, EV-D68 causes a neurological disease with weight-loss, paralysis, and mortality. In our respiratory model, treatment with guanidine provides a two-log reduction in lung virus titers, reduces MCP-1 and IL-6, and prevents histological lesions in the lungs. Importantly, viremia is prevented by early treatment with guanidine. In our neurological model, guanidine treatment protects mice from weight-loss, paralysis, and mortality. These results demonstrate the utility of these models for evaluation of antiviral therapies for EV-D68 infection.

Novel bis-cyclic guanidines as potent membrane-active antibacterial agents with therapeutic potential.

We designed a class of small dimeric cyclic guanidine derivatives which display potent antibacterial activity against both multidrug-resistant Gram-negative and Gram-positive bacteria. They could compromise bacterial membranes without developing resistance, inhibit biofilms formed by E. coli, and exhibit excellent in vivo activity in the MRSA-infected thigh burden mouse model.

Dominant drug targets suppress the emergence of antiviral resistance.

The emergence of drug resistance can defeat the successful treatment of pathogens that display high mutation rates, as exemplified by RNA viruses. Here we detail a new paradigm in which a single compound directed against a 'dominant drug target' suppresses the emergence of naturally occurring drug-resistant variants in mice and cultured cells. All new drug-resistant viruses arise during intracellular replication and initially express their phenotypes in the presence of drug-susceptible genomes. For the targets of most anti-viral compounds, the presence of these drug-susceptible viral genomes does not prevent the selection of drug resistance. Here we show that, for an inhibitor of the function of oligomeric capsid proteins of poliovirus, the expression of drug-susceptible genomes causes chimeric oligomers to form, thus rendering the drug-susceptible genomes dominant. The use of dominant drug targets should suppress drug resistance whenever multiple genomes arise in the same cell and express products in a common milieu.

Characterization of imidazoline receptors in blood vessels for the development of antihypertensive agents.

It has been indicated that activation of peripheral imidazoline I2-receptor (I-2R) may reduce the blood pressure in spontaneously hypertensive rats (SHRs). Also, guanidinium derivatives show the ability to activate imidazoline receptors. Thus, it is of special interest to characterize the I-2R using guanidinium derivatives in blood vessels for development of antihypertensive agent(s). Six guanidinium derivatives including agmatine, amiloride, aminoguanidine, allantoin, canavanine, and metformin were applied in this study. Western blot analysis was used for detecting the expression of imidazoline receptor in tissues of Wistar rats. The isometric tension of aortic rings isolated from male rats was also estimated. The expression of imidazoline receptor on rat aorta was identified. However, guanidinium derivatives for detection of aortic relaxation were not observed except agmatine and amiloride which induced a marked relaxation in isolated aortic rings precontracted with phenylephrine or KCl. Both relaxations induced by agmatine and amiloride were attenuated by glibenclamide at concentration enough to block ATP-sensitive potassium (KATP) channels. Meanwhile, only agmatine-induced relaxation was abolished by BU224, a selective antagonist of imidazoline I2-receptors. Taken together, we suggest that agmatine can induce vascular relaxation through activation of peripheral imidazoline I2-receptor to open KATP channels. Thus, agmatine-like compound has the potential to develop as a new therapeutic agent for hypertension in the future.

Development of the first oral bioprecursors of bis-alkylguanidine antimalarial drugs.

Plasmodium falciparum is responsible of the most severe form of malaria, and new targets and novel chemotherapeutic scaffolds are needed to fight emerging multidrug-resistant strains of this parasite. Bis-alkylguanidines have been designed to mimic choline, resulting in the inhibition of plasmodial de novo phosphatidylcholine biosynthesis. Despite potent in vitro antiplasmodial and in vivo antimalarial activities, a major drawback of these compounds for further clinical development is their low oral bioavailability. To solve this issue, various modulations were performed on bis-alkylguanidines. The introduction of N-disubstituents on the guanidino motif improved both in vitro and in vivo activities. On the other hand, in vivo pharmacological evaluation in a mouse model showed that the N-hydroxylated derivatives constitute the first oral bioprecursors in bis-alkylguanidine series. This study paves the way for bis-alkylguanidine-based oral antimalarial agents targeting plasmodial phospholipid metabolism.

Novel approaches to screening guanidine derivatives.

INTRODUCTION: Compounds containing guanidine moiety, originating both from natural and synthetic sources, have found potential applications in both synthetic and medicinal chemistry. Indeed, guanidine functionality can be found in many natural and pharmaceutical products as well as in cosmetic ingredients produced by synthetic methods. AREAS COVERED: This review covers the latest developments in the research undertaken for the therapeutic application of newly synthesized guanidine derivatives including: small peptides and peptidomimetics. This article encompasses the selected literature published in the last three decades with a focus on the novel approaches for screening of lead drug candidates with their pharmacological action. EXPERT OPINION: Guanidines, as they are both organically based and also hydrophilic in nature, have undergone a mammoth amount of screening and testing to discover promising lead structures with a CN3 core, appropriate for potential future drug development. The compounds have the potential to be neurodegenerative therapeutic options, as well as: anti-inflammatory, anti-protozoal, anti-HIV, chemotherapeutic, anti-diabetic agents and so on. It is true that guanidine-based compounds of natural sources also, like synthetic and virtually designed drugs, have been of significant interest and have the potential to be useful therapeutic options in the future. As for now, however, there is not sufficient data to support their use in a number of the suggested areas, and further studies are required.

Synthesis of novel phosphorylated guanidine derivatives from cyanamide and their anti-inflammatory activity.

A series of novel guanidine derivatives were synthesized in three steps and their anti-inflammatory activities in vitro and in vivo evaluated. 2-Aminopyridin-3-ol (1) was reacted with thiophosphoryl chloride (2) to give a monochloride (3). It was further reacted with cyanamide to afford the corresponding cyanamine (4), which was subsequently reacted with different heterocyclic amines to form the title compounds (5a-l). The substituent in the guanidine function affected the potency of anti-inflammatory activity. The compounds having benzothiazole, fluorophenyl, and piperazinyl moieties enhanced the anti-inflammatory activity.

In vitro evaluation of guanidine analogs as sigma receptor ligands for potential anti-stroke therapeutics.

Currently, the only Food and Drug Administration-approved treatment of acute stroke is recombinant tissue plasminogen activator, which must be administered within 6 hours after stroke onset. The pan-selective σ-receptor agonist N,N'-di-o-tolyl-guanidine (o-DTG) has been shown to reduce infarct volume in rats after middle cerebral artery occlusion, even when administered 24 hours after stroke. DTG derivatives were synthesized to develop novel compounds with greater potency than o-DTG. Fluorometric Ca(2+) imaging was used in cultured cortical neurons to screen compounds for their capacity to reduce ischemia- and acidosis-evoked cytosolic Ca(2+) overload, which has been linked to stroke-induced neurodegeneration. In both assays, migration of the methyl moiety produced no significant differences, but removal of the group increased potency of the compound for inhibiting acidosis-induced [Ca(2+)](i) elevations. Chloro and bromo substitution of the methyl moiety in the meta and para positions increased potency by ≤160%, but fluoro substitutions had no effect. The most potent DTG derivative tested was N,N'-di-p-bromo-phenyl-guanidine (p-BrDPhG), which had an IC(50) of 2.2 µM in the ischemia assay, compared with 74.7 µM for o-DTG. Microglial migration assays also showed that p-BrDPhG is more potent than o-DTG in this marker for microglial activation, which is also linked to neuronal injury after stroke. Radioligand binding studies showed that p-BrDPhG is a pan-selective σ ligand. Experiments using the σ-1 receptor-selective antagonist 1-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine dihydrochloride (BD-1063) demonstrated that p-BrDPhG blocks Ca(2+) overload via σ-1 receptor activation. The study identified four compounds that may be more effective than o-DTG for the treatment of ischemic stroke at delayed time points.

Treatment in Lambert-Eaton myasthenic syndrome.

Besides antitumor therapy for patients with the paraneoplastic form of Lambert-Eaton myasthenic syndrome (LEMS), the mainstay of symptomatic treatment in LEMS is 3,4-diaminopyridine (3,4-DAP). Data from four randomized, placebo-controlled trials have revealed that muscle strength scores increased significantly with 3,4-DAP. A limited meta-analysis performed on two trials using the Quantitative Myasthenia Gravis score indicated that the clinical benefits seen were modest. Meta-analysis of the mean change in compound muscle action potential amplitude following 3,4-DAP treatment revealed a significant improvement compared to placebo. However, most patients with noncancer LEMS require long-term immunosuppression, usually with prednisolone and azathioprine. A single crossover study has previously shown significant short-term benefit in limb strength following intravenous immunoglobulin, and there are isolated case reports of medium term benefit from rituximab. Overall, a combination of symptomatic treatment with 3,4-DAP and immunosuppression, with or without antitumor therapy, is often successful for most LEMS patients, with other more aggressive regimens rarely needed.

An octaguanidine-morpholino oligo conjugate improves muscle function of mdx mice.

INTRODUCTION: Skeletal muscles of mdx mice lack functional levels of dystrophin due to a mutation in Dmd exon 23. Morpholino antisense oligomers can induce expression of a truncated dystrophin by redirecting splicing to skip processing of exon 23. METHODS: We tested whether systemic administration of Vivo-Morpholino, an octaguanidine delivery moiety-Morpholino conjugate that targets exon 23 (VMO23), restored function to muscles of mdx mice. RESULTS: Extensor digitorum longus (EDL) muscles of mdx mice were weaker, less powerful, and showed greater functional deficits after eccentric contractions than normal. VMO23 treatment normalized EDL force and power of mdx mice and eliminated their exaggerated sensitivity to eccentric contractions. Diaphragm muscle strips from mdx mice also produced lower-than-normal force and power, and these variables were restored to normal, or near-normal, levels by VMO23 treatment. CONCLUSION: These results provide a functional basis for continuing development of VMO23 as a treatment for Duchenne muscular dystrophy.