Long-Term Morpholino Oligomers in Hexose Elicits Long-Lasting Therapeutic Improvements in mdx Mice

Abstract

Approval of antisense oligonucleotide eteplirsen highlights the promise of exon-skipping therapeutics for Duchenne muscular dystrophy patients. However, the limited efficacy of eteplirsen underscores the importance to improve systemic delivery and efficacy. Recently, we demonstrated that a glucose and fructose (GF) delivery formulation effectively potentiates phosphorodiamidate morpholino oligomer (PMO). Considering the clinical potential of GF, it is important to determine the long-term compatibility and efficacy with PMO in mdx mice prior to clinical translation. Here, we report that yearlong administration of a clinically applicable PMO dose (50 mg/kg/week for 3 weeks followed by 50 mg/kg/month for 11 months) with GF elicited sustainably high levels of dystrophin expression in mdx mice, with up to 45% of the normal level of dystrophin restored in most peripheral muscles without any detectable toxicity. Importantly, PMO-GF resulted in phenotypical rescue and mitochondrial biogenesis with functional improvement. Carbohydrate metabolites measurements revealed improved metabolic and energetic conditions after PMO-GF treatment in mdx mice without metabolic anomaly. Collectively, our study shows PMO-GF's ability to elicit long-lasting therapeutic effects with tolerable toxicity and represents a new treatment modality for Duchenne muscular dystrophy, and provides guidelines for antisense oligonucleotides with GF in clinical use.

Keywords: Duchenne muscular dystrophy; GF; exon skipping; mitochondria; morpholino oligomers.

Figure 1

Dystrophin Restoration in mdx Mice with Yearlong Systemic Administration of PMO-GF Dystrophin restoration in mdx mice treated with PMO-GF at the dosage of 50 mg/kg/week for 3 weeks followed by 50 mg/kg/month for 11 months intravenously. (A) Diagram to illustrate the dosing regimen and time for tissue collection. (B) Immunohistochemistry for dystrophin expression in body-wide muscles from mdx mice treated with PMO-GF (scale bar, 200 μm). (C) Representative western blot image to show dystrophin restoration in mdx mice treated with PMO-GF. 12.5, 25, and 50 μg of total protein from C57BL6 and 50 μg from untreated and treated mdx muscle samples were loaded, respectively. α-Actinin was used as the loading control. (D) Quantitative analysis of western blot results with ImageJ. Four biological replicates were examined and quantified based on densitometry as described in the Materials and Methods. The data present as mean + SEM unless otherwise specified (n = 4). (E) Quantification of PMO in muscle tissues with ELISA. No significant difference was detected between 6-month and yearlong treatment of PMO-GF (n = 4). A, abdominal muscle; D, diaphragm; Q, quadriceps; G, gastrocnemius; i.v., intravenous injection; T, triceps; TA, tibialis anterior.

Figure 2

Functional Improvement in mdx Mice Treated with PMO-GF for 1 Year Functional improvement in mdx mice treated with PMO-GF at the dosage of 50 mg/kg/week for 3 weeks followed by 50 mg/kg/month for 11 months intravenously. (A) Re-localization of dystrophin-associated protein complex (DAPC) components in treated mdx mice to assess dystrophin function and recovery of normal myoarchitecture. (B) Measurement of serum creatine kinase (CK) levels. Data show a significant fall in mdx mice treated with PMO-GF compared with untreated age-matched mdx controls (two-tailed t test, n = 5, *p < 0.05). (C) Evaluation of CNFs in tibialis anterior and quadriceps from mdx mice treated with PMO-GF. A significant decrease was detected between PMO-GF-treated mdx mice and age-matched mdx controls (two-tailed t test, n = 5, **p < 0.01). (D) Collagen deposition analysis in diaphragm and quadriceps from mdx mice treated with PMO-GF (scale bar, 200 μm). (E) Muscle function was assessed to determine the physical improvement. A significant improvement was detected between PMO-GF-treated mdx mice and untreated age-matched mdx controls at different time points (two-tailed t test, n = 5, *p < 0.05). (F) Measurement of serum levels of liver enzymes in mdx mice treated with PMO-GF compared with untreated mdx controls. Data show improved pathological parameters in mdx mice treated with PMO-GF compared with untreated age-matched mdx controls (two-tailed t test, n = 5, *p < 0.05). (G) Analysis of biochemical indicators for kidney function and glucose in mdx mice treated with PMO-GF. Data show no difference in the level of serum creatinine (Cr), BUN, urea, and glucose in mdx mice treated with PMO-GF compared with untreated mdx and normal controls (n = 5).

Figure 3

Analysis of Membrane Integrity and Tissue Distribution in mdx Mice Treated with PMO-GF (A) IgG staining to assess the membrane integrity in quadriceps from mdx mice treated with PMO-GF (treated) and untreated age-matched (aged) and adult (adult) mdx controls (scale bar, 200 μm). (B) Quantitative analysis of IgG fluorescence intensity in quadriceps from mdx mice treated with PMO-GF and untreated age-matched and adult mdx controls (n = 3, *p < 0.05). (C) Tissue distribution of lissamine-labeled PMO in body-wide tissues from mdx mice with IVIS spectrum series. Body-wide tissues were harvested 48 hr after a single intravenous injection of lissamine-labeled PMO-GF at the dose of 25 mg/kg/day for 1 day. Lissamine (Lissa)-PMO+GF in adult control (Ctrl), Lissa-PMO+GF in aged Ctrl, and Lissa-PMO+GF in 1-year treated represents adult, aged mdx controls, or 1-year-treated mdx mice injected with a single dose of lissamine-labeled PMO in GF. (D) Quantitative evaluation of fluorescence intensity in body-wide tissues from mdx mice treated with lissamine-labeled PMO in GF. Significant differences were detected in untreated mdx controls (NC) compared with other groups (n = 3; *p < 0.05), and significant differences were detected in A and TA from age-matched mdx controls (aged) compared with adult and PMO-GF treated mdx mice (n = 3; *p < 0.05). Significant differences were detected in Q, G, and TA from adult mdx mice compared with PMO-GF-treated mdx mice (n = 3; *p < 0.05). (E) RT-PCR to determine the level of exon skipping in muscles treated with lissamine-labeled PMO in GF at 25mg/kg for a single injection. Δexon 23 or Δexon 22&23 for exon 23 or exons 22 and 23 skipped bands, respectively. (F) Quantitative analysis of exon 23 skipping efficiency. Significant increases in levels of exon skipping were found in A, Q, TA, and triceps from mdx mice treated with PMO-GF for 1 year compared with age-matched and adult mdx controls (n = 3; *p < 0.05). Significance was determined with two-tailed t test. A, abdominal muscle; G, gastrocnemius; H, heart; K, kidney; L, liver; NC, untreated controls; Q, quadriceps; T, triceps; TA, tibialis anterior; treated, mdx mice treated with PMO-GF for 1 year.

Figure 4

Dystrophin Restoration Increases Sub-sarcolemmal Mitochondria Pool Density in mdx Mice Treated with PMO-GF for 1 Year (A) Transmission electron microscopy micrographs of the SSM pool in tibialis anterior skeletal muscles from wild-type C57BL6, age-matched untreated mdx controls, and PMO-GF-treated mdx mice (scale bars, 1 μm). Arrowheads point to SSMs. (B) Quantitative analysis of SSM densities. Number of mitochondria per micron length of sarcolemma was determined from transmission electron micrographs. In both wild-type C57BL6 and PMO-GF-treated mdx mice skeletal muscle, SSMs were heavily concentrated along the subsarcolemmal space and averaged around three SSMs per micron of sarcolemma. SSM density in PMO-GF-treated mdx mice was significantly increased compared with aged-matched untreated mdx controls (two-tailed t test, n = 5, *p < 0.05). (C) Measurement of basal and maximal oxygen consumption rate (OCR) in skeletal muscles from mdx mice treated with PMO-GF for 1 year. Data show a significant reduction at the maximal OCR in mdx mice treated with PMO-GF compared with untreated mdx controls (two-tailed t test, n = 5, **p < 0.01).

Figure 5

Investigation of Energetic and Carbohydrate Metabolic Conditions in PMO-GF-Treated mdx Mice (A) Measurement of ATP levels in mdx mice treated with PMO-GF for 1 year. Significant differences were achieved in energy stores in TA and Q from mdx mice treated with PMO-GF compared with untreated age-matched mdx controls (n = 5; *p < 0.05). (B) Analysis of levels of AMP, ADP, NADH, and NAD⁺ in skeletal muscles from mdx mice treated with PMO-GF. (C) Assessment of key components in the TCA cycle with LC-MS/MS. A significant rise was detected in fumarate in mdx mice treated with PMO-GF compared with untreated age-matched mdx controls (n = 5; *p < 0.05). (D) Measurement of intermediates in glycolytic pathways in skeletal muscles from mdx mice treated with PMO-GF. A significant increase was detected in pyruvate in mdx mice treated with PMO-GF compared with untreated age-matched mdx controls (n = 5; *p < 0.05). Significance was determined with two-tailed t test.