Long-term treatment with eteplirsen in nonambulatory patients with Duchenne muscular dystrophy

This analysis aims to describe the outcomes of two nonambulatory patients with Duchenne muscular dystrophy (DMD) who participated in two clinical studies. The two consecutive trials of eteplirsen (studies 201 and 202) were conducted in patients with DMD (N = 12) and confirmed genetic mutations amenable to exon 51 skipping.In study 201, 12 patients were randomized to receive once-weekly, double-blind intravenous infusions of eteplirsen 30 or 50 mg/kg or placebo for 24 weeks; patients then received open-label eteplirsen during weeks 25 through 28. All 12 patients continued onto open-label extension study 202 and received long-term treatment with eteplirsen. We compared cardiac, pulmonary, and upper limb function and dystrophin production in the nonambulatory twin patients versus the 10 ambulatory patients through 240 combined treatment weeks.Ten study patients remained ambulatory through both studies, while the identical twin patients both experienced early, rapid loss of ambulation. The twin patients had greater disease severity at baseline (6-minute walk test [6MWT], 330 and 256 m) versus the other patients (n = 10; 6MWT range, 341-418 m). They maintained cardiac and upper limb function through combined week 240, with outcomes similar to those of the patients who remained ambulatory. Dystrophin production was confirmed following eteplirsen treatment.Despite the loss of ambulation, other markers of disease progression remained relatively stable in the eteplirsen-treated twin patients and were similar to those of the ambulatory patients.

Eteplirsen treatment for Duchenne muscular dystrophy: Exon skipping and dystrophin production

OBJECTIVE

To describe the quantification of novel dystrophin production in patients with Duchenne muscular dystrophy (DMD) after long-term treatment with eteplirsen.

METHODS

Clinical study 202 was an observational, open-label extension of the randomized, controlled study 201 assessing the safety and efficacy of eteplirsen in patients with DMD with a confirmed mutation in the DMD gene amenable to correction by skipping of exon 51. Patients received once-weekly IV doses of eteplirsen 30 or 50 mg/kg. Upper extremity muscle biopsy samples were collected at combined study week 180, blinded, and assessed for dystrophin-related content by Western blot, Bioquant software measurement of dystrophin-associated immunofluorescence intensity, and percent dystrophin-positive fibers (PDPF). Results were contrasted with matched untreated biopsies from patients with DMD. Reverse transcription PCR followed by Sanger sequencing of newly formed slice junctions was used to confirm the mechanism of action of eteplirsen.

RESULTS

Reverse transcription PCR analysis and sequencing of the newly formed splice junction confirmed that 100% of treated patients displayed the expected skipped exon 51 sequence. In treated patients vs untreated controls, Western blot analysis of dystrophin content demonstrated an 11.6-fold increase (p = 0.007), and PDPF analysis demonstrated a 7.4-fold increase (p < 0.001). The PDPF findings were confirmed in a re-examination of the sample (15.5-fold increase, p < 0.001). Dystrophin immunofluorescence intensity was 2.4-fold greater in treated patients than in untreated controls (p < 0.001).

CONCLUSION

Taken together, the 4 assays, each based on unique evaluation mechanisms, provided evidence of eteplirsen muscle cell penetration, exon skipping, and induction of novel dystrophin expression.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence of the muscle cell penetration, exon skipping, and induction of novel dystrophin expression by eteplirsen, as confirmed by 4 assays.

Thermolabile MTHFR genotype and retinal vascular occlusive disease

BACKGROUND

Raised levels of total plasma homocysteine (tHcy) are associated with an increased risk of retinal vascular occlusive disease. A thermolabile form of a pivotal enzyme in homocysteine metabolism, methylenetetrahydrofolate reductase (MTHFR), has been associated with vascular occlusive disease and raised tHcy levels. The relation between thermolabile MTHFR genotype, tHcy, and retinal vascular occlusive disease has not been determined.

METHODS

A retrospective case-control study involving hospital based controls and cases with retinal vascular occlusions in whom tHcy levels had been determined was undertaken. Genotyping for the MTHFR 677 C-T mutation that specifies the thermolabile form of the enzyme was performed by established methods in all subjects. The relation between homozygosity for thermolabile MTHFR genotype (TT), raised tHcy levels, and risk of retinal vascular occlusive disease was examined.

RESULTS

87 cases of retinal vascular occlusive disease (mean age 68.7 years) comprising 26 cases of retinal artery occlusion and 61 of retinal vein occlusion were compared with 87 controls (mean age 70.2 years). The TT genotype did not confer a significantly increased risk of retinal vascular occlusive disease. The mean tHcy level was significantly higher in the cases than in the controls (p<0.0001). Overall, and in both the cases and controls, the frequency of the TT genotype was higher in those with normal tHcy levels than in those with increased levels of tHcy. However, the TT genotype did not significantly alter the risk of increased tHcy levels in these patients.

CONCLUSIONS

The TT genotype is not associated with an increased risk of retinal vascular occlusive disease or increased tHcy levels in this group of elderly patients. In older patients, nutritional rather than genetic factors may be more important in increasing tHcy levels, a known risk factor for retinal vascular occlusive disease.

Association between historically high frequencies of neural tube defects and the human T homologue of mouse T (Brachyury)

The human T developmental gene has been implicated in the etiology of neural tube defects (NTDs) on the basis both of mouse studies of its homologue, T (Brachyury), and of allelic association in a Caucasian population. We have investigated the frequency of the T allelic variant TIVS7-2 in 218 Irish NTD case-parent triads. This population showed the same trend as previously reported, with an excess of the TIVS7-2 allele among cases. Log-linear modeling of case and maternal genotypic effects within families indicated that TIVS7-2 was elevated in cases (relative risk, RR = 1.36) but not in mothers (RR = 0.91). The TIVS7-2 allele is markedly associated with cases born before 1980 (RR = 2.09; CI = 1.23-3.55; corrected p = 0.030), but not with more recent cases (RR = 0.92). Cases carrying a TIVS7-2 allele did not show any increased tendency to be homozygous for the thermolabile variant of the folate-dependent enzyme 5,10-methylene tetrahydrofolate reductase, which is an established genetic risk factor for NTDs. Since the incidence of NTDs has declined markedly in Ireland over the last few decades, we suggest that the T-associated risk is potentiated by nutritional or environmental risk factor(s), the impact of which have been diminishing over time.

Prospective evaluation of the risk conferred by factor V Leiden and thermolabile methylenetetrahydrofolate reductase polymorphisms in pregnancy

Factor V (FV) Leiden and thermolabile methylenetetrahydrofolate reductase (MTHFR) are 2 common polymorphisms that have been implicated in vascular thrombosis. We determined whether these mutations predicted an adverse outcome in pregnancy. Second, we looked for an interaction between these 2 mutations in patients with recurrent fetal loss or thrombosis in pregnancy. Primigravid subjects at their booking visit to the National Maternity Hospital (Holles Street, Dublin, Ireland) were screened for the polymorphisms. Thermolabile MTHFR and FV Leiden genotypes were detected by either restriction fragment length polymorphism or heteroduplex capillary chromatography. The carrier frequency of FV Leiden in the screened primigravid population was 2.7% (allele frequency 1.36%), all being heterozygous for the mutation. This value was lower than expected from previous studies in European populations. Forty-nine percent of the screened population (289 of 584) were heterozygous for thermolabile MTHFR, and 10.6% were homozygous (62 of 584). The frequency of the 2 polymorphisms was no higher in those who subsequently developed preeclampsia (n=12) or intrauterine growth retardation (n=9), and none of the screened population developed thrombosis. However, the frequency of FV Leiden was higher in patients who subsequently miscarried after the first trimester of pregnancy (allele frequency of 5.5%, P=0.0356). Among those positive for FV Leiden, 3 of 27 miscarried, compared with 24 of 572 of FV Leiden-negative patients (11% versus 4.2%). No interaction was found between the 2 mutations in the control or patient populations. In patients with a prior history of venous thrombosis, the carrier rate of FV Leiden was increased (4 of 33, allele frequency of 7.6%, P=0. 0115). In contrast, the carrier frequency for thermolabile MTHFR was no higher, and there was no interaction between the 2 mutations. Neither mutation occurred at a significantly higher frequency in patients with a prior history of recurrent fetal loss. In conclusion, FV Leiden is a risk factor for thrombosis in pregnancy and possibly for second-trimester miscarriage independent of thermolabile MTHFR. However, prospective analysis suggests that the risk conferred by FV Leiden is low in a primigravid population. The thermolabile MTHFR genotype was not implicated in any adverse outcome.

Use of magnetic resonance imaging to analyze the performance of hollow-fiber bioreactors

Preliminary experiments were described that demonstrate that MRI is an effective tool for the noninvasive study of hollow-fiber bioreactors. Flow-compensated velocity-encoding pulse sequences were successively applied to analyze the velocity patterns in a module operated without cells, with an artificially induced flow field perturbation. Diffusion damping pulse sequences were also used to spatially resolve regions of cell growth in a bioreactor. These experiments provide the necessary basis from which future flow and spectroscopic studies can be conducted.

Effect of sodium butyrate on estrogen receptor and epidermal growth factor receptor gene expression in human breast cancer cell lines

Estrogen receptor (ER) binding has been shown to decrease in breast cancer cell lines exposed to sodium butyrate; however, the underlying mechanisms are unknown. In MCF-7 breast cancer cells, butyrate caused a rapid time- and concentration-dependent decrease in ER mRNA levels, apparent by 3 h at 3 mM butyrate. ER gene transcription rate was decreased and cycloheximide co-treatment did not relieve this inhibitory effect, suggesting that the butyrate effect was not dependent on ongoing protein synthesis. In both MCF-7 and T-47D cells the decrease in ER mRNA was mirrored by an increase in the level of epidermal growth factor receptor (EGF-R) mRNA. A marked inverse relationship exists between ER and EGF-R in human breast cancer biopsies and cell lines, and the reciprocal modulation of these genes by butyrate suggests that the expression of ER and EGF-R may be co-regulated. This relationship was further investigated in lines expressing only one or the other receptor. In the ER-positive EGF-R-negative line, MDA-MB-134-VI, butyrate exposure decreased ER mRNA levels, implying that the regulation of ER mRNA by butyrate is independent of EGF-R expression. However, butyrate decreased EGF-R mRNA in two ER-negative lines, MDA-MB-231 and HBL-100. As this effect differed from that in ER-positive lines, the regulation of EGF-R may depend on the expression of ER. The possibility that ER and EGF-R gene expression are closely linked has implications in the understanding of progression of human breast cancers to a hormone-independent phenotype and for the use of ER and EGF-R levels as independent prognostic indicators.