A phase 1 study of PF-06840003, an oral indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor in patients with recurrent malignant glioma.

Background PF-06840003 is a highly selective indoleamine 2, 3-dioxygenase (IDO1) inhibitor with antitumor effects in preclinical models. This first-in-human phase 1 study evaluated safety, pharmacokinetics/pharmacodynamics, and preliminary efficacy in recurrent malignant glioma to determine the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D). Methods Patients (N = 17) received oral PF-06840003 in four dose-escalation groups: 125 mg once-daily (QD; n = 2); 250 mg QD (n = 4); 250 mg twice-daily (BID; n = 3); 500 mg BID (n = 8). A modified toxicity probability interval method determined the MTD. Results Four patients experienced serious adverse events (SAEs); one with treatment-related SAEs (grade 4 alanine and aspartate aminotransferase elevations). The dose-limiting toxicity (DLT) rate at 500 mg BID was 12.5% (n = 1/8); the MTD was not reached. Following PF-06840003 dosing, median time to maximum plasma concentration for the active enantiomer PF-06840002 was 1.5-3.0 hr and mean elimination half-life was 2 to 4 hr (Cycle 1 Day 1). Urinary recovery of PF-06840002 was low (< 1%). At 500 mg BID, maximum mean percentage inhibition of 13C10 kynurenine vs endogenous kynurenine was 75% vs 24%. PF-06840002 CSF-to-plasma ratio was 1.00. Disease control occurred in eight patients (47%). Mean duration of stable disease (SD) was 32.1 (12.1-72.3) weeks. Two patients with SD discontinued the study at 450 and 561 days and continued PF-06840003 on compassionate use. Conclusion PF­06840003 up to 500 mg BID was generally well tolerated with evidence of a pharmacodynamic effect and durable clinical benefit in a subset of patients with recurrent malignant glioma. ClinicalTrials.gov, NCT02764151, registered April 2016.

Bosutinib versus Placebo for Autosomal Dominant Polycystic Kidney Disease.

Overactivation of Src has been linked to the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). This phase 2, multisite study assessed the efficacy and safety of bosutinib, an oral dual Src/Bcr-Abl tyrosine kinase inhibitor, in patients with ADPKD. Patients with ADPKD, eGFR≥60 ml/min per 1.73 m2, and total kidney volume ≥750 ml were randomized 1:1:1 to bosutinib 200 mg/d, bosutinib 400 mg/d, or placebo for ≤24 months. The primary endpoint was annualized rate of kidney enlargement in patients treated for ≥2 weeks who had at least one postbaseline magnetic resonance imaging scan that was preceded by a 30-day washout (modified intent-to-treat population). Of 172 enrolled patients, 169 received at least one study dose. Per protocol amendment, doses for 24 patients who initially received bosutinib at 400 mg/d were later reduced to 200 mg/d. The annual rate of kidney enlargement was reduced by 66% for bosutinib 200 mg/d versus placebo (1.63% versus 4.74%, respectively; P=0.01) and by 82% for pooled bosutinib versus placebo (0.84% versus 4.74%, respectively; P<0.001). Over the treatment period, patients receiving placebo or bosutinib had similar annualized eGFR decline. Gastrointestinal and liver-related adverse events were the most frequent toxicities. In conclusion, compared with placebo, bosutinib at 200 mg/d reduced kidney growth in patients with ADPKD. The overall gastrointestinal and liver toxicity profile was consistent with the profile in prior studies of bosutinib; no new toxicities were identified. (ClinicalTrials.gov: NCT01233869).

Comparative assessment of clinical response in patients with rheumatoid arthritis between PF-05280586, a proposed rituximab biosimilar, and rituximab.

AIMS: To evaluate potential differences between PF-05280586 and rituximab sourced from the European Union (rituximab-EU) and USA (rituximab-US) in clinical response (Disease Activity Score in 28 Joints [DAS28] and American College of Rheumatology [ACR] criteria), as part of the overall biosimilarity assessment of PF-05280586. METHODS: A randomised, double-blind, pharmacokinetic similarity trial was conducted in patients with active rheumatoid arthritis refractory to anti-tumour necrosis factor therapy on a background of methotrexate. Patients were treated with 1000 mg of PF-05280586, rituximab-EU or rituximab-US on days 1 and 15 and followed over 24 weeks for pharmacokinetic, clinical response and safety assessments. Key secondary end points were the areas under effect curves for DAS28 and ACR responses. Mean differences in areas under effect curves were compared against respective reference ranges established by observed rituximab-EU and rituximab-US responses using longitudinal nonlinear mixed effects models. RESULTS: The analysis included 214 patients. Demographics were similar across groups with exceptions in some baseline disease characteristics. Baseline imbalances and group-to-group variation were accounted for by covariate effects in each model. Predictions from the DAS28 and ACR models tracked the central tendency and distribution of observations well. No point estimates of mean differences were outside the reference range for DAS28 or ACR scores. The probabilities that the predicted differences between PF-05280586 vs. rituximab-EU or rituximab-US lie outside the reference ranges were low. CONCLUSIONS: No clinically meaningful differences were detected in DAS28 or ACR response between PF-05280586 and rituximab-EU or rituximab-US as the differences were within the pre-specified reference ranges. TRIAL REGISTRATION NUMBER: NCT01526057.

Implications of Immunogenicity Testing for Therapeutic Monoclonal Antibodies: A Quantitative Pharmacology Framework.

The interpretation of immunogenicity results for a mAb product and prediction of its clinical consequences remain difficult, despite enormous advances in methodologies and efforts toward the best practice for consistent data generation and reporting. To this end, the contribution from the clinical pharmacology discipline has been largely limited to comparing descriptively the pharmacokinetic (PK) profiles by antidrug antibodies (ADA) status or testing the significance of ADA as a covariate in a population PK setting, similar to the practice for small-molecule drugs in investigating the effect of an intrinsic/extrinsic factor on the drug disposition. There is a need for a mAb disposition framework that captures the dynamics of ADA formation and drug's interactions with the ADA and target as parts of the drug distribution and elimination. Here we describe such a framework and examine it against the PK, ADA, and clinical response data from a phase 3 trial in patients treated with adalimumab. The proposed framework offered a generalized understanding of how the dose, target affinity, and drug/ADA analyte forms affects the manifestation of ADA response with regard to its detections and alterations of drug disposition and effectiveness. Furthermore, as an example, its utility for dose considerations was demonstrated through predicting for late-stage trials of a PCSK9 inhibitor in terms of development in ADA incidence and titers, and consequences on the drug disposition, interaction with target, and downstream lowering effect on LDL-C.

Evaluation of the effect of modafinil on the pharmacokinetics of encorafenib and binimetinib in patients with BRAF V600-mutant advanced solid tumors.

BACKGROUND: A clinical drug-drug interaction (DDI) study was designed to evaluate the effect of multiple doses of modafinil, a moderate CYP3A4 inducer at a 400 mg QD dose, on the multiple oral dose pharmacokinetics (PK) of encorafenib and its metabolite, LHY746 and binimetinib and its metabolite, AR00426032. METHODS: This study was conducted in patients with BRAF V600-mutant advanced solid tumors. Treatment of 400 mg QD modafinil was given on Day 15 through Day 21. Encorafenib 450 mg QD and binimetinib 45 mg BID were administered starting on Day 1. PK sampling was conducted from 0 to 8 h on Day 14 and Day 21. Exposure parameters were calculated for each patient by noncompartmental analysis and geometric least-squares mean ratio. Corresponding 90% confidence intervals were calculated to estimate the magnitude of effects. RESULTS: Among 11 PK evaluable patients, encorafenib Cmax and AUClast were decreased in presence of steady-state modafinil by 20.2% and 23.8%, respectively. LHY746 exposures were not substantially changed in the presence of steady-state modafinil. CONCLUSION: The results from this clinical study indicate modafinil 400 mg QD had a weak effect on encorafenib PK. Based on these results, encorafenib can be coadministered with a moderate CYP3A4 inducer without dosing adjustment. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov NCT03864042, registered 6 March 2019.

Clinical Evaluation of the Effect of Encorafenib on Bupropion, Rosuvastatin, and Coproporphyrin I and Considerations for Statin Coadministration.

BACKGROUND AND OBJECTIVES: Encorafenib is a kinase inhibitor indicated for the treatment of patients with unresectable or metastatic melanoma or metastatic colorectal cancer, respectively, with selected BRAF V600 mutations. A clinical drug-drug interaction (DDI) study was designed to evaluate the effect of encorafenib on rosuvastatin, a sensitive substrate of OATP1B1/3 and breast cancer resistance protein (BCRP), and bupropion, a sensitive CYP2B6 substrate. Coproporphyrin I (CP-I), an endogenous substrate for OATP1B1, was measured in a separate study to deconvolute the mechanism of transporter DDI. METHODS: DDI study participants received a single oral dose of rosuvastatin (10 mg) and bupropion (75 mg) on days - 7, 1, and 14 and continuous doses of encorafenib (450 mg QD) and binimetinib (45 mg BID) starting on day 1. The CP-I data were collected from participants in a phase 3 study who received encorafenib (300 mg QD) and cetuximab (400 mg/m2 initial dose, then 250 mg/m2 QW). Pharmacokinetic and pharmacodynamic analysis was performed using noncompartmental and compartmental methods. RESULTS: Bupropion exposure was not increased, whereas rosuvastatin Cmax and area under the receiver operating characteristic curve (AUC) increased approximately 2.7 and 1.6-fold, respectively, following repeated doses of encorafenib and binimetinib. Increase in CP-I was minimal, suggesting that the primary effect of encorafenib on rosuvastatin is through BCRP. Categorization of statins on the basis of their metabolic and transporter profile suggests pravastatin would have the least potential for interaction when coadministered with encorafenib. CONCLUSION: The results from these clinical studies suggest that encorafenib does not cause clinically relevant CYP2B6 induction or inhibition but is an inhibitor of BCRP and may also inhibit OATP1B1/3 to a lesser extent. Based on these results, it may be necessary to consider switching statins or reducing statin dosage accordingly for coadministration with encorafenib. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov NCT03864042, registered 6 March 2019.

Joint Disposition Properties and Comprehensive Pharmacokinetic Characterization of Antibody-Drug Conjugates.

Antibody-drug conjugates (ADCs) comprise 3 distinct parts: a specific antibody carrier (mAb), a linker, and a cytotoxic payload. Typical pharmacokinetic (PK) characterization of ADCs remains fragmented using separate noncompartmental analyses (NCA) of individual analytes, offering little insight into the dynamic relationships among the ADC components, and the safety and efficacy implications. As a result, it is exceedingly difficult to compare ADCs in terms of favorable PK characteristics. Therefore, there is a need for characterizing ADCs using the joint disposition properties critical for understanding the fate of an ADC complex and clinical implications. In this communication, we describe 3 joint disposition metrics (JDMs) for integrated NCA of ADCs based on a combination of common analytes of ADC, payload, conjugated payload, and total mAb. These JDMs were derived, each in a simple form of a ratio between appropriate PK parameters of two analytes, from the presumed drug delivery scheme behind typical ADC designs, in terms of (1) linker stability, (2) therapeutic exposure ratio, and (3) effective drug-to-antibody ratio in vivo. The validity of the JDM-based PK characterization was examined against model-based analyses via their applications to 3 clinical candidates: PF-06650808, PF-06647020, and PF-06664178. For instance, the linker stability estimates for PF-06650808, PF-06647020, and PF-06664178 were 0.31, 0.14, and 0.096, respectively, from the JDM-based analyses vs. 0.23, 0.11, and 0.086 by the model-based approach. Additionally, the JDMs were estimated for a number of FDA-approved or otherwise well-documented ADCs, showing their utilities in comparing ADCs in terms of favorable PK characteristics.

Oligonucleotide-mediated survival of motor neuron protein expression in CNS improves phenotype in a mouse model of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is caused by homozygous mutation or deletion of the SMN1 gene encoding survival of motor neuron (SMN) protein, resulting in the selective loss of alpha-motor neurons. Humans typically have one or more copies of the SMN2 gene, the coding region of which is nearly identical to SMN1, except that a point mutation causes splicing out of exon 7 and production of a largely nonfunctional SMNDelta7 protein. The development of drugs that mitigate aberrant SMN2 splicing is an attractive therapeutic approach for SMA. A steric block antisense oligonucleotide (AO) has recently been developed that blocked an intronic splice suppressor element, and enhanced SMN2 exon 7 inclusion in SMA patient fibroblasts. Here, we show that periodic intracerebroventricular (ICV) delivery of this AO resulted in increased SMN expression in brain and spinal cord to as much as 50% of the level of healthy littermates. Real-time PCR of SMN2 transcripts confirmed the AO-mediated increase in full-length SMN. The AO-derived increase in SMN expression led to a concomitant improvement in bodyweight throughout the lifespan of the SMA animals. Treatment of SMA mice with AO also provided partial correction of motor deficits, manifest as improved righting response. Injections of a scrambled oligonucleotide had no effect on SMN expression or phenotype in the SMA mice. Our results validate that AOs that abrogate aberrant splicing of SMN2 are promising compounds for treating SMA.

Model-Based Characterization of the Pharmacokinetics, Target Engagement Biomarkers, and Immunomodulatory Activity of PF-06342674, a Humanized mAb Against IL-7 Receptor-α, in Adults with Type 1 Diabetes.

IL-7 receptor-α (IL-7Rα) blockade has been shown to reverse autoimmune diabetes in the non-obese diabetic mouse by promoting inhibition of effector T cells and consequently altering the balance of regulatory T (Treg) and effector memory (TEM) cells. PF-06342674 is a humanized monoclonal antibody that binds to and inhibits the function of IL-7Rα. In the current phase 1b study, subjects with type 1 diabetes (T1D) received subcutaneous doses of either placebo or PF-06342674 (1, 3, 8 mg/kg/q2w or 6 mg/kg/q1w) for 10 weeks and were followed up to 18 weeks. Nonlinear mixed effects models were developed to characterize the pharmacokinetics (PK), target engagement biomarkers, and immunomodulatory activity. PF-06342674 was estimated to have 20-fold more potent inhibitory effect on TEM cells relative to Treg cells resulting in a non-monotonic dose-response relationship for the Treg:TEM ratio, reaching maximum at ~ 3 mg/kg/q2w dose. Target-mediated elimination led to nonlinear PK with accelerated clearance at lower doses due to high affinity binding and rapid clearance of the drug-target complex. Doses ≥ 3 mg/kg q2w result in sustained PF-06342674 concentrations higher than the concentration of cellular IL-7 receptor and, in turn, maintain near maximal receptor occupancy over the dosing interval. The results provide important insight into the mechanism of IL-7Rα blockade and immunomodulatory activity of PF-06342674 and establish a rational framework for dose selection for subsequent clinical trials of PF-06342674. Furthermore, this analysis serves as an example of mechanistic modeling to support dose selection of a drug candidate in the early phases of development.

Nanopolymers improve delivery of exon skipping oligonucleotides and concomitant dystrophin expression in skeletal muscle of mdx mice.

BACKGROUND: Exon skipping oligonucleotides (ESOs) of 2'O-Methyl (2'OMe) and morpholino chemistry have been shown to restore dystrophin expression in muscle fibers from the mdx mouse, and are currently being tested in phase I clinical trials for Duchenne Muscular Dystrophy (DMD). However, ESOs remain limited in their effectiveness because of an inadequate delivery profile. Synthetic cationic copolymers of poly(ethylene imine) (PEI) and poly(ethylene glycol) (PEG) are regarded as effective agents for enhanced delivery of nucleic acids in various applications. RESULTS: We examined whether PEG-PEI copolymers can facilitate ESO-mediated dystrophin expression after intramuscular injections into tibialis anterior (TA) muscles of mdx mice. We utilized a set of PEG-PEI copolymers containing 2 kDa PEI and either 550 Da or 5 kDa PEG, both of which bind 2'OMe ESOs with high affinity and form stable nanoparticulates with a relatively low surface charge. Three weekly intramuscular injections of 5 microg of ESO complexed with PEI2K-PEG550 copolymers resulted in about 500 dystrophin-positive fibers and about 12% of normal levels of dystrophin expression at 3 weeks after the initial injection, which is significantly greater than for injections of ESO alone, which are known to be almost completely ineffective. In an effort to enhance biocompatibility and cellular uptake, the PEI2K-PEG550 and PEI2K-PEG5K copolymers were functionalized by covalent conjugation with nanogold (NG) or adsorbtion of colloidal gold (CG), respectively. Surprisingly, using the same injection and dosing regimen, we found no significant difference in dystrophin expression by Western blot between the NG-PEI2K-PEG550, CG-PEI2K-PEG5K, and non-functionalized PEI2K-PEG550 copolymers. Dose-response experiments using the CG-PEI2K-PEG5K copolymer with total ESO ranging from 3-60 microg yielded a maximum of about 15% dystrophin expression. Further improvements in dystrophin expression up to 20% of normal levels were found at 6 weeks after 10 twice-weekly injections of the NG-PEI2K-PEG550 copolymer complexed with 5 microg of ESO per injection. This injection and dosing regimen showed over 1000 dystrophin-positive fibers. H&E staining of all treated muscle groups revealed no overt signs of cytotoxicity. CONCLUSION: We conclude that PEGylated PEI2K copolymers are efficient carriers for local delivery of 2'OMe ESOs and warrant further development as potential therapeutics for treatment of DMD.

PEG-PEI copolymers for oligonucleotide delivery to cells and tissues.

Inefficient delivery of antisense oligonucleotides (AO) to target cell nuclei remains as the foremost limitation to their usefulness. Copolymers of cationic poly(ethylene imine) (PEI) and polyethylene glycol (PEG) are extremely well-studied compounds that markedly improve the in vitro and in vivo delivery of AOs to cells and tissues. By varying the Mw of PEI, as well as the nature of PEG shielding, PEG-PEI-AO nanoparticulates can be prepared with a dynamic range of size, surface charge, and stability. Each of these properties in-turn influences the transfection capacity of the PEG-PEI-AO polyplexes. In addition, PEG-PEI copolymers are readily functionalized for enhanced efficacy and specificity of cellular and tissue targeting. The synthesis and functionalization of PEG-PEI copolymers is remarkably simple and requires very little specialized equipment. Thus, PEG-PEI copolymers represent a tractable and adaptable oligonucleotide delivery system that can be customized and optimized to the investigators' specific application. This chapter describes the step-by-step synthesis of several PEG-PEI copolymers that are specifically formulated to provide effective delivery of AOs using both in vitro and in vivo applications. We describe the preparation of the PEG-PEI-AO polyplexes and provide examples showing transfection of cultured cells in vitro, as well as skeletal muscles in vivo using both local and systemic delivery.

A Mechanism-Based Pharmacokinetic/Pharmacodynamic Model for Bococizumab, a Humanized Monoclonal Antibody Against Proprotein Convertase Subtilisin/Kexin Type 9, and Its Application in Early Clinical Development.

Bococizumab (RN316/PF-04950615), a humanized monoclonal antibody, binds to secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) and prevents its downregulation of low-density lipoprotein receptor, leading to improved clearance and reduction of low-density lipoprotein cholesterol (LDL-C) in plasma. A mechanism-based drug-target binding model was developed, accounting for bococizumab, PCSK9, and LDL-C concentrations and the effects of concomitant administration of statins. This model was utilized to better understand the pharmacokinetic/pharmacodynamic (PK/PD) data obtained from 3 phase 1 and 2 phase 2a clinical studies. First, simulations performed with this model demonstrated that the conventional method of the area-under-the-curve ratio for bioavailability determination underestimated the subcutaneous bioavailability of bococizumab due to its target-mediated disposition. Second, a covariate model component for statin effects on bococizumab PK/PD was characterized, including a description of the decreased baseline LDL-C, increased baseline PCSK9, and increased LDL-C lowering with concomitant use of statins. Last, the impact of the dosing regimens with and without a dose holiday on bococizumab's LDL-C-lowering effectiveness was shown to be predictable due to the well-characterized PK-PD relationship.

Poly(ethylene imine)-poly(ethylene glycol) copolymers facilitate efficient delivery of antisense oligonucleotides to nuclei of mature muscle cells of mdx mice.

Antisense oligonucleotides (AO) can facilitate dystrophin expression via targeted exon skipping in cultured cells of Duchenne muscular dystrophy (DMD) patients and in the mouse model of DMD (mdx mice). However, the lack of effective means to deliver AO to myonuclei remains the foremost limitation to their usefulness in DMD gene therapy. In this study we show that copolymers of cationic poly(ethylene imine) (PEI) and poly(ethylene glycol) (PEG) facilitated efficient cellular uptake and nuclear delivery of AO in mature skeletal muscle fibers isolated from mdx mice. Confocal analysis of dual fluorescently tagged PEG-PEI-AO polyplexes, 24 hr after transfection, showed that the copolymer and AO were colocalized within punctate membrane- associated structures. Importantly, AO was efficiently translocated into myonuclei, whereas the copolymer was mostly excluded. The morphology of all transfected myofibers was perfectly maintained with no indication of damage or cytotoxicity. Quantitative fluorescence analysis showed that transfection with PEG-PEI-AO resulted in a 6-fold higher uptake of AO into myonuclei compared with transfections of AO alone. Interestingly, transfections with rhodamine-labeled PEG-PEI copolymers yielded an approximately 2- fold higher uptake of AO into myonuclei compared with transfections of unlabeled copolymers. Attempts to further increase AO delivery by addition of insulin-transferrin-selenium (ITS) to the medium showed no further improvement in AO delivery. Dose-response analysis indicated saturation of endocytotic uptake of the polyplex. Overall, we conclude that PEG-PEI copolymers represent high-capacity, nontoxic carriers for efficient delivery of AO to nuclei of mature myofibers.

Population pharmacokinetics of valproic acid in pediatric patients with epilepsy: considerations for dosing spinal muscular atrophy patients.

Valproic acid (VPA) dosing strategies used in recent clinical trials in patients with spinal muscular atrophy (SMA) have utilized a paradigm of monitoring trough levels to estimate drug exposure with subsequent dose titration. The validity of this approach remains uncertain and could be improved by understanding sources of pharmacokinetic variability. A population pharmacokinetic analysis of VPA in pediatric patients with epilepsy was recently performed. The pooled data set included 52 subjects with epilepsy, ages 1 to 17 years, who received intravenous and/or various oral formulations. The data was best fit by a 2-compartment model; inclusion of age and weight reduced intersubject variability for clearance (41%), central volume (70%), and peripheral volume (42%) over the base model. The final model for clearance and volume parameters was clearance = 0.854 · (weight/70)(0.75); central volume of distribution = 10.3 · (weight/70)(1.0) · (age/8.5)(-0.267); peripheral volume of distribution = 4.08 · (weight/70)(1.0); and intercompartmental clearance = 5.34 · (weight/70)(0.75). Application of the model to data from a clinical trial in SMA patients suggests altered kinetics, perhaps based on underlying physiologic differences such as alterations in lean body mass. Future studies in SMA should incorporate modeling and simulation techniques to support individualized dosing and further assess if additional patient-specific factors necessitate alternative dosing strategies.

Polymersome delivery of siRNA and antisense oligonucleotides.

siRNA and antisense oligonucleotides, AON, have similar size and negative charge and are often packaged for in vitro delivery with cationic lipids or polymers-but exposed positive charge is problematic in vivo. Here we demonstrate loading and functional delivery of RNAi and AON with non-ionic, nano-transforming polymersomes. These degradable carriers are taken up passively by cultured cells after which the vesicles transform into micelles that allow endolysosomal escape and delivery of either siRNA into cytosol for mRNA knockdown or else AON into the nucleus for exon skipping within pre-mRNA. Polymersome-mediated knockdown appears as efficient as common cationic-lipid transfection and about half as effective as Lenti-virus after sustained selection. For AON, initial results also show that intramuscular injection into a mouse model of muscular dystrophy leads to the expected protein expression, which occurs along the entire length of muscle. The lack of cationic groups in antisense polymersomes together with initial tests of efficacy suggests broader utility of these non-viral carriers.

Functionalized PEG-PEI copolymers complexed to exon-skipping oligonucleotides improve dystrophin expression in mdx mice.

Exon-skipping oligonucleotides (ESOs) with 2'-O-methyl modifications are promising compounds for the treatment of Duchenne muscular dystrophy (DMD). However, the usefulness of these compounds is limited by their poor delivery profile to muscle tissue in vivo. We previously established that copolymers made of poly(ethylene imine) (PEI) and poly(ethylene glycol) (PEG) enhanced ESO transfection in skeletal muscle of mdx mice, resulting in widespread distribution of dystrophin-positive fibers, but limited dystrophin expression by Western blot. In an attempt to improve ESO delivery and dystrophin expression, a new formulation of PEG-PEI copolymer was used, along with functionalized derivatives containing either the cell-penetrating peptide TAT (trans-activator of transcription), adsorbed colloidal gold (CG), or both TAT and CG. Tibialis anterior muscles were given three intramuscular injections of various PEG-PEI-ESO polyplexes (3 days apart; 5 microg of ESO per injection) and muscles were harvested 3 weeks after the first injection. Surface modifications of PEG-PEI copolymers with TAT showed the highest level of dystrophin recovery, with a 6-fold increase in dystrophin-positive fibers compared with ESO alone and up to 30% of normal dystrophin expression by Western blot. The adsorption of CG to either PEG-PEI or TAT-PEG-PEI copolymers showed no further improvement in dystrophin expression. Our data indicate that TAT-modified PEG-PEI copolymers are effective carriers for delivery of ESOs to skeletal muscle and are promising compounds for the therapeutic treatment of DMD.

Induction of dystrophin expression by exon skipping in mdx mice following intramuscular injection of antisense oligonucleotides complexed with PEG-PEI copolymers.

Antisense oligonucleotides (AOs) with 2-O-methyl modifications can circumvent dystrophin mutations via exon skipping and, it is hoped, can become drugs for treatment of Duchenne muscular dystrophy (DMD). However, AO-based approaches are hindered by a lack of effective carriers to facilitate delivery of AOs to myonuclei. We examined whether copolymers composed of cationic poly(ethylene imine) (PEI) and polyethylene glycol (PEG) can enhance AO transfection in skeletal muscle of mdx mice. Single intramuscular injections of AO complexed with low Mw PEI2000(PEG550) copolymers into TA muscles of mdx mice resulted in widespread distribution of dystrophin-positive fibers at 3 weeks after injection, with no apparent cytotoxicity. Overall, injections of these low Mw polyplexes, which formed 250-nm aggregate particles, resulted in about sixfold more dystrophin-positive fibers than AO alone. Western analysis confirmed the dystrophin expression in these muscles. Surprisingly, injections of AO complexed with high Mw PEI25000(PEG5000) copolymers, which formed smaller nonaggregated particles, produced about threefold fewer dystrophin-positive fibers than injections of the low Mw polyplexes. We conclude that low Mw PEI2000(PEG550) copolymers function as high-capacity, nontoxic AO carriers suitable for in vivo transfection of skeletal muscle and are promising compounds for potential use in molecular therapy of DMD.