One-year Treatment of Morpholino Antisense Oligomer Improves Skeletal and Cardiac Muscle Functions in Dystrophic mdx Mice

http://www.ncbi.nlm.nih.gov/pubmed/21179007

 

"Previous studies observed significant accumulation in dystrophin protein by short-term weekly or daily injections.

 

Therefore, we expected that the levels of dystrophin after 1-year biweekly 

injections would be significantly higher than that after single injection when the same dose of PMO is used. Unexpectedly, the results 

showed that the long-term accumulative effect of PMO was limited. 

The mechanism(s) is not understood, but the following factors may 

be involved. Firstly, a biweekly regimen will certainly have less accumulative effect than a weekly regimen. Perhaps more importantly, 

the dependence of unmodified PMO on the increased membrane 

permeability for effective delivery may constitute another possible 

explanation. Since the efficiency of PMO relies heavily on permeability of muscle fibers and dystrophic muscles undergo cycles of degeneration and regeneration, the initial a few doses of PMO 

would achieve higher efficiency through the fraction of muscle 

fibers with higher permeability. However, such fiber population 

decreases gradually and most muscle fibers become less permeable 

to PMO eventually, leading to a diminishing delivery efficiency, 

thus accumulative effect. This hypothesis is consistent with the fact 

that normal muscles are resistant to PMO delivery.

 

While the limited accumulative effect may indicate the improvement in muscle 

membrane permeability after the treatment, it also suggests that 

long-term efficiency in exon skipping with PMO and 2OMePS may 

be difficult to exceed that achieved by a single dose of AO."

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Ofelia,

The text on the link does not match the message you posted. Is the conclusion on long term benefits in the paper?

 

That aside the I do feel that long terms benefits will be significanlty better than the short term studies. We have seen only one case where about 50% of the fibre was dystrophin positive. When the drug is available for a longer term the % of dystrophin +ve fibers should also reach to a higher average mean than that seen a short term study. Any thoughts.

That's the last paragraph of the paper...just shows that the headlines make everything sound a lot better. :) They do present the results in heart but also talk about the very limited accumulation of dystrophin after one year of treatment. I'll attach the full paper here.



Tulika said:

Ofelia,

The text on the link does not match the message you posted. Is the conclusion on long term benefits in the paper?

 

That aside the I do feel that long terms benefits will be significanlty better than the short term studies. We have seen only one case where about 50% of the fibre was dystrophin positive. When the drug is available for a longer term the % of dystrophin +ve fibers should also reach to a higher average mean than that seen a short term study. Any thoughts.

Attachments:

This paper also says that efficiency is very high at high dosage (1500mg/kg), while safety is also ensured.

 

What I am reading form this paper is that smaller dosage but longer duration of PMO may not translate into better results but certainly higher dosage and longer duration PMO of do give the desired benefits.

  

 

 

 

 

 


Increasing the dose of PMO to 1.5 g/kg saw further improvement

of dystrophin induction in all muscles. Nearly 100% fibers in

all skeletal muscles expressed dystrophin by immunohistochemistry

with the levels of the protein reaching 25–50% (

This level of dystrophin expression was associated with significant

improvement in muscle function with the grip force reaching the

strength near to the normal C57BL/6 mice (

reduced dramatically compared to those untreated control mice

(

size, and degenerating fibers and inflammatory infiltrates were

absent in all muscles (

fibers expressed dystrophin although most of them had weak

signal for the protein. During the 6-month treatment with these

two high dosages, the mice showed no sign of abnormal behavior

and change in body weight. No pathological change of the liver,

kidney, and lung was observed by hematoxylin and eosin staining

Figure 4a,c).Figure 5c). CK levelsFigure 5b). All skeletal muscle fibers became highly uniform inFigure 5a). More than 40% of cardiac muscle

They cannot use more than 100 mg/kg in humans. That's the highest level proved safe by the tox package submitted to FDA. In fact they are testing 50 and 100 mg/kg in the next trial. Not sure what 1500 mg/kg in mice equates in humans but I am sure that it is higher than 100 mg/kg. 

 

What I get from this paper is that improved delivery morpholinos are the way to go (something like PPMOs) since just increasing the dose to decent levels does not help penetrating the cell membrane after a few injections when that becomes "better" (has fewer holes). Hoping that's not going to be the case in humans of course...but this was the question we always asked, will longer term trt help increase the dystrophin levels after the membrane is better, b/c we do know what levels we get after 12 weekly injections and we all hoped that they will increase in time (at least in the GSK case when the dose stays low; we do not know yet for AVI's 30 or 100 mg/kg).



Tulika said:

This paper also says that efficiency is very high at high dosage (1500mg/kg), while safety is also ensured.

 

What I am reading form this paper is that smaller dosage but longer duration of PMO may not translate into better results but certainly higher dosage and longer duration PMO of do give the desired benefits.

 

 

 

 

 

 


Increasing the dose of PMO to 1.5 g/kg saw further improvement

of dystrophin induction in all muscles. Nearly 100% fibers in

all skeletal muscles expressed dystrophin by immunohistochemistry

with the levels of the protein reaching 25–50% (

This level of dystrophin expression was associated with significant

improvement in muscle function with the grip force reaching the

strength near to the normal C57BL/6 mice (

reduced dramatically compared to those untreated control mice

(

size, and degenerating fibers and inflammatory infiltrates were

absent in all muscles (

fibers expressed dystrophin although most of them had weak

signal for the protein. During the 6-month treatment with these

two high dosages, the mice showed no sign of abnormal behavior

and change in body weight. No pathological change of the liver,

kidney, and lung was observed by hematoxylin and eosin staining

Figure 4a,c).Figure 5c). CK levelsFigure 5b). All skeletal muscle fibers became highly uniform inFigure 5a). More than 40% of cardiac muscle
Since the tears in the muscle membrane are a big part of the disease process, I'm not sure that this result is negative.

Yes, indeed. The only question remaining is if the dystrophin produced is enough to generate improvement. We were always told, more dystrophin higher chance of improvement. We did see in the AVI trial that after 12 weeks of treatment there was NO improvement in function. So the scientists (Steve Wilton etc.) hoped that dystrophin will accumulate in time, they said the duration might have been too short or the dose level too low (since they continue to say that there was no immune response hence that's not the problem...). GSK cannot increase the dose level due to possible toxicity. If that is the case, and this paper says that after one year of treatment dystrophin doesn't accumulate, maybe we should not look at improvement but lack of degeneration instead?  

 

Has anyone seen any data presented by GSK after their 26-week trial? It would be interesting to see what happened after 26 weeks, have they seen more dystrophin than after the initial 12 weeks? Their trial was 12 weeks and then 14 additional weeks extension.

Paul Cliff said:

Since the tears in the muscle membrane are a big part of the disease process, I'm not sure that this result is negative.

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