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Onset Time and Durability of Huntingtin Suppression in Rhesus Putamen After Direct Infusion of Antihuntingtin siRNA.

Grondin R, Ge P, Chen Q, Sutherland JE, Zhang Z, Gash DM, Stiles DK, Stewart GR, Sah DW, Kaemmerer WF - Mol Ther Nucleic Acids (2015)

Bottom Line: After a 1-week washout period, monkeys received radiolabeled siRNA targeting huntingtin.After 1 or 3 days of siRNA delivery, monkeys were either terminated, or their pumps were shut off and they were terminated 10 or 24 days later.These findings indicate the rapid onset and durability of siRNA-mediated target gene suppression observed in other organs also occurs in the brain, and support the use of episodic delivery of siRNA into the brain for treatment of Huntington's disease and possibly other neurodegenerative diseases.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, Lexington, Kentucky, USA.

ABSTRACT
One possible treatment for Huntington's disease involves direct infusion of a small, interfering RNA (siRNA) designed to reduce huntingtin expression into brain tissue from a chronically implanted programmable pump. Here, we studied the suppression of huntingtin mRNA achievable with short infusion times, and investigated how long suppression may persist after infusion ceases. Rhesus monkeys received 3 days of infusion of Magnevist into the putamen to confirm catheter patency and fluid distribution. After a 1-week washout period, monkeys received radiolabeled siRNA targeting huntingtin. After 1 or 3 days of siRNA delivery, monkeys were either terminated, or their pumps were shut off and they were terminated 10 or 24 days later. Results indicate that the onset of huntingtin mRNA suppression in the rhesus putamen occurs rapidly, achieving a plateau throughout the putamen within 4 days. Conversely, loss of huntingtin suppression progresses slowly, persisting an estimated 27-39 days in the putamen and surrounding white matter. These findings indicate the rapid onset and durability of siRNA-mediated target gene suppression observed in other organs also occurs in the brain, and support the use of episodic delivery of siRNA into the brain for treatment of Huntington's disease and possibly other neurodegenerative diseases.

No MeSH data available.


Related in: MedlinePlus

Illustration of alternative curve fits for time course of suppression onset. Linear, sigmoidal, and concave down curve fit to onset of suppression of huntingtin measured in RNA from punch location B02 from the putamen of monkeys after 1, 3, and 6 days of siRNA delivery (group 2, group 3, and group 6, respectively). Dotted line: best linear fit, Supp = 12.84 + (8.53 * day); gray dashed curve: best sigmoidal fit, Supp = 57.69 * exp(–exp(1.45 – 1.83 * day)); solid black curve = best concave down fit, Supp = 59.88 * (1 – exp(–0.73*day)). The curve fits for each punch location in the putamen are provided in the supplemental materials. †Group 6 is the group from a prior study used for this meta-analysis of suppression onset.
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fig4: Illustration of alternative curve fits for time course of suppression onset. Linear, sigmoidal, and concave down curve fit to onset of suppression of huntingtin measured in RNA from punch location B02 from the putamen of monkeys after 1, 3, and 6 days of siRNA delivery (group 2, group 3, and group 6, respectively). Dotted line: best linear fit, Supp = 12.84 + (8.53 * day); gray dashed curve: best sigmoidal fit, Supp = 57.69 * exp(–exp(1.45 – 1.83 * day)); solid black curve = best concave down fit, Supp = 59.88 * (1 – exp(–0.73*day)). The curve fits for each punch location in the putamen are provided in the supplemental materials. †Group 6 is the group from a prior study used for this meta-analysis of suppression onset.

Mentions: A main objective of the current study was to characterize whether the onset of suppression is linear or curvilinear, the shape of any curvilinear relationship, and the likely timing of the asymptote of suppression levels, and thus the time point beyond which continuous exposure of the brain tissue to the siRNA could be suspended for awhile without sacrificing the potential for even greater suppression. For this purpose, the analysis plan was to identify the best-fitting linear regression line and the best fitting-fitting parameter values for two curvilinear functions, each computed on a punch-location-by-punch-location basis, in a meta-analysis using Groups 2, 3, and 6, mathematically fixing the percent suppression at time zero to zero. Figure 4 illustrates the shape of the equations. Using the difference in percent suppression above the PBS group average at the corresponding punch location in the brain as the measure, this analysis yielded no consistent result, and no consensual estimate regarding the time of siRNA exposure sufficient to reach an asymptote. Rather, in 11 of 40 punch locations, the best-fitting relationship between time and suppression was concave down, in 4 punch locations (not anatomically contiguous) the best-fitting relationship was sigmoidal, in 11 locations it was linear, and in 14 locations it followed an exponential growth curve, implying no limit to the amount of suppression attainable (or at least that in a variety of non-contiguous punch locations scattered through the putamen the asymptote was not yet attained after 6 days of exposure).


Onset Time and Durability of Huntingtin Suppression in Rhesus Putamen After Direct Infusion of Antihuntingtin siRNA.

Grondin R, Ge P, Chen Q, Sutherland JE, Zhang Z, Gash DM, Stiles DK, Stewart GR, Sah DW, Kaemmerer WF - Mol Ther Nucleic Acids (2015)

Illustration of alternative curve fits for time course of suppression onset. Linear, sigmoidal, and concave down curve fit to onset of suppression of huntingtin measured in RNA from punch location B02 from the putamen of monkeys after 1, 3, and 6 days of siRNA delivery (group 2, group 3, and group 6, respectively). Dotted line: best linear fit, Supp = 12.84 + (8.53 * day); gray dashed curve: best sigmoidal fit, Supp = 57.69 * exp(–exp(1.45 – 1.83 * day)); solid black curve = best concave down fit, Supp = 59.88 * (1 – exp(–0.73*day)). The curve fits for each punch location in the putamen are provided in the supplemental materials. †Group 6 is the group from a prior study used for this meta-analysis of suppression onset.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561652&req=5

fig4: Illustration of alternative curve fits for time course of suppression onset. Linear, sigmoidal, and concave down curve fit to onset of suppression of huntingtin measured in RNA from punch location B02 from the putamen of monkeys after 1, 3, and 6 days of siRNA delivery (group 2, group 3, and group 6, respectively). Dotted line: best linear fit, Supp = 12.84 + (8.53 * day); gray dashed curve: best sigmoidal fit, Supp = 57.69 * exp(–exp(1.45 – 1.83 * day)); solid black curve = best concave down fit, Supp = 59.88 * (1 – exp(–0.73*day)). The curve fits for each punch location in the putamen are provided in the supplemental materials. †Group 6 is the group from a prior study used for this meta-analysis of suppression onset.
Mentions: A main objective of the current study was to characterize whether the onset of suppression is linear or curvilinear, the shape of any curvilinear relationship, and the likely timing of the asymptote of suppression levels, and thus the time point beyond which continuous exposure of the brain tissue to the siRNA could be suspended for awhile without sacrificing the potential for even greater suppression. For this purpose, the analysis plan was to identify the best-fitting linear regression line and the best fitting-fitting parameter values for two curvilinear functions, each computed on a punch-location-by-punch-location basis, in a meta-analysis using Groups 2, 3, and 6, mathematically fixing the percent suppression at time zero to zero. Figure 4 illustrates the shape of the equations. Using the difference in percent suppression above the PBS group average at the corresponding punch location in the brain as the measure, this analysis yielded no consistent result, and no consensual estimate regarding the time of siRNA exposure sufficient to reach an asymptote. Rather, in 11 of 40 punch locations, the best-fitting relationship between time and suppression was concave down, in 4 punch locations (not anatomically contiguous) the best-fitting relationship was sigmoidal, in 11 locations it was linear, and in 14 locations it followed an exponential growth curve, implying no limit to the amount of suppression attainable (or at least that in a variety of non-contiguous punch locations scattered through the putamen the asymptote was not yet attained after 6 days of exposure).

Bottom Line: After a 1-week washout period, monkeys received radiolabeled siRNA targeting huntingtin.After 1 or 3 days of siRNA delivery, monkeys were either terminated, or their pumps were shut off and they were terminated 10 or 24 days later.These findings indicate the rapid onset and durability of siRNA-mediated target gene suppression observed in other organs also occurs in the brain, and support the use of episodic delivery of siRNA into the brain for treatment of Huntington's disease and possibly other neurodegenerative diseases.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, Lexington, Kentucky, USA.

ABSTRACT
One possible treatment for Huntington's disease involves direct infusion of a small, interfering RNA (siRNA) designed to reduce huntingtin expression into brain tissue from a chronically implanted programmable pump. Here, we studied the suppression of huntingtin mRNA achievable with short infusion times, and investigated how long suppression may persist after infusion ceases. Rhesus monkeys received 3 days of infusion of Magnevist into the putamen to confirm catheter patency and fluid distribution. After a 1-week washout period, monkeys received radiolabeled siRNA targeting huntingtin. After 1 or 3 days of siRNA delivery, monkeys were either terminated, or their pumps were shut off and they were terminated 10 or 24 days later. Results indicate that the onset of huntingtin mRNA suppression in the rhesus putamen occurs rapidly, achieving a plateau throughout the putamen within 4 days. Conversely, loss of huntingtin suppression progresses slowly, persisting an estimated 27-39 days in the putamen and surrounding white matter. These findings indicate the rapid onset and durability of siRNA-mediated target gene suppression observed in other organs also occurs in the brain, and support the use of episodic delivery of siRNA into the brain for treatment of Huntington's disease and possibly other neurodegenerative diseases.

No MeSH data available.


Related in: MedlinePlus