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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

Volumes of Magnevist and siRNA distributions by monkey. Data plotted are the volume of siRNA at a concentration ≥ 0.65 mg of siRNA per gram of tissue and the volume of Magnevist distribution. Lines connect values from the same monkey (gray dotted lines, monkeys receiving siRNA in putamen for 1 day; solid black lines, monkeys receiving siRNA in putamen for 3 days).
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fig2: Volumes of Magnevist and siRNA distributions by monkey. Data plotted are the volume of siRNA at a concentration ≥ 0.65 mg of siRNA per gram of tissue and the volume of Magnevist distribution. Lines connect values from the same monkey (gray dotted lines, monkeys receiving siRNA in putamen for 1 day; solid black lines, monkeys receiving siRNA in putamen for 3 days).

Mentions: To determine whether an infusion of Magnevist would have utility in assessing the extent of siRNA distribution achieved in an individual's brain, the volume of distribution of Magnevist was determined from the T1-weighted MRI images taken at the completion of the 3 days infusion period and compared to the distribution of siRNA assessed later by autoradiography (Figure 1b,c). The volume of Magnevist distribution was obtained by thresholding the gray scale MRI image using a voxel value that was 10% of the maximum T1 intensity obtained from the Magnevist signal at the catheter tip in the putamen. Since the absolute concentration of Magnevist did not vary at this point, it provided a reference to standardize the threshold from scan to scan. The volume of siRNA delivery was quantified by identifying the regions of autoradiography sections with a signal corresponding to 0.65 mg or more of siRNA per gram of tissue, which is the concentration of siRNA previously found to correspond to approximately 45% suppression of HTT mRNA.7 We refer to this as the “volume of ≥45% suppression.” Only the animals terminated immediately after 2 days of infusion (group 2, 1 day of siRNA delivery to the brain) or 4 days of infusion (group 3, 3 days of siRNA delivery to the brain) had sufficient radioactive material in the brain tissue to visualize intraparenchymal distribution of siRNA by autoradiography. All other groups (with longer survival intervals postinfusion) had negligible signal. The volume of ≥45% suppression (mean ± SE) obtained in the monkeys at time points 1 and 3 was 584.8 ± 45.6 and 674.5 ± 58.4 mm3, respectively, a difference that is not statistically significant (t = 1.21, df = 4, P = 0.29). The volume of Magnevist distribution in these groups was 1,262.8 ± 307.9 and 1,747.8 ± 641.8 mm3, respectively (t = 0.68, df = 4, P = 0.533). For every animal, the volume of Magnevist distribution exceeded the volume of ≥45% suppression, but the difference between the volume of Magnevist distribution and the volume of ≥45% suppression was highly variable from animal to animal (Figure 2) and was not significant (875.7 ± 350.6, t = 2.5, df = 5, P = 0.055). The correlation between the volumes was r = −0.32 (P = 0.54). Thus, a quantitative relationship between the volume of Magnevist distribution and the subsequent siRNA volume of ≥45% suppression could not be defined using the observations from this small number of animals.


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)

Volumes of Magnevist and siRNA distributions by monkey. Data plotted are the volume of siRNA at a concentration ≥ 0.65 mg of siRNA per gram of tissue and the volume of Magnevist distribution. Lines connect values from the same monkey (gray dotted lines, monkeys receiving siRNA in putamen for 1 day; solid black lines, monkeys receiving siRNA in putamen for 3 days).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: Volumes of Magnevist and siRNA distributions by monkey. Data plotted are the volume of siRNA at a concentration ≥ 0.65 mg of siRNA per gram of tissue and the volume of Magnevist distribution. Lines connect values from the same monkey (gray dotted lines, monkeys receiving siRNA in putamen for 1 day; solid black lines, monkeys receiving siRNA in putamen for 3 days).
Mentions: To determine whether an infusion of Magnevist would have utility in assessing the extent of siRNA distribution achieved in an individual's brain, the volume of distribution of Magnevist was determined from the T1-weighted MRI images taken at the completion of the 3 days infusion period and compared to the distribution of siRNA assessed later by autoradiography (Figure 1b,c). The volume of Magnevist distribution was obtained by thresholding the gray scale MRI image using a voxel value that was 10% of the maximum T1 intensity obtained from the Magnevist signal at the catheter tip in the putamen. Since the absolute concentration of Magnevist did not vary at this point, it provided a reference to standardize the threshold from scan to scan. The volume of siRNA delivery was quantified by identifying the regions of autoradiography sections with a signal corresponding to 0.65 mg or more of siRNA per gram of tissue, which is the concentration of siRNA previously found to correspond to approximately 45% suppression of HTT mRNA.7 We refer to this as the “volume of ≥45% suppression.” Only the animals terminated immediately after 2 days of infusion (group 2, 1 day of siRNA delivery to the brain) or 4 days of infusion (group 3, 3 days of siRNA delivery to the brain) had sufficient radioactive material in the brain tissue to visualize intraparenchymal distribution of siRNA by autoradiography. All other groups (with longer survival intervals postinfusion) had negligible signal. The volume of ≥45% suppression (mean ± SE) obtained in the monkeys at time points 1 and 3 was 584.8 ± 45.6 and 674.5 ± 58.4 mm3, respectively, a difference that is not statistically significant (t = 1.21, df = 4, P = 0.29). The volume of Magnevist distribution in these groups was 1,262.8 ± 307.9 and 1,747.8 ± 641.8 mm3, respectively (t = 0.68, df = 4, P = 0.533). For every animal, the volume of Magnevist distribution exceeded the volume of ≥45% suppression, but the difference between the volume of Magnevist distribution and the volume of ≥45% suppression was highly variable from animal to animal (Figure 2) and was not significant (875.7 ± 350.6, t = 2.5, df = 5, P = 0.055). The correlation between the volumes was r = −0.32 (P = 0.54). Thus, a quantitative relationship between the volume of Magnevist distribution and the subsequent siRNA volume of ≥45% suppression could not be defined using the observations from this small number of animals.

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