Subcutaneous administration of TC007 reduces disease severity in an animal model of SMA

Abstract

Background: Spinal Muscular Atrophy (SMA) is the leading genetic cause of infantile death. It is caused by the loss of functional Survival Motor Neuron 1 (SMN1). There is a nearly identical copy gene, SMN2, but it is unable to rescue from disease due to an alternative splicing event that excises a necessary exon (exon 7) from the majority of SMN2-derived transcripts. While SMNDelta7 protein has severely reduced functionality, the exon 7 sequences may not be specifically required for all activities. Therefore, aminoglycoside antibiotics previously shown to suppress stop codon recognition and promote translation read-through have been examined to increase the length of the SMNDelta7 C-terminus.

Results: Here we demonstrate that subcutaneous-administration of a read-through inducing compound (TC007) to an intermediate SMA model (Smn-/-; SMN2+/+; SMNDelta7) had beneficial effects on muscle fiber size and gross motor function.

Conclusion: Delivery of the read-through inducing compound TC007 reduces the disease-associated phenotype in SMA mice, however, does not significantly extend survival.

Figure 1

TC007-treated mice have a slightly increased average lifespan. Kaplan-Meyer shown of TC007-treated (solid black, n = 16), Vehicle-treated (PBS; dotted black, n = 16), and Neo002-treated (dotted-grey, n = 8) SMA mice lifespans. Arrows on X-axis represent the average lifespan. No significant difference was seen between the groups.

Figure 2

No significant induction of SMN protein seen after subcutaneous TC007 administration. Representative western blots and quantification shown of (A) Brain, (B) Spinal cord and (C) Triceps of TC007- (black bar) or vehicle-treated (striped bar) SMA mice and uninjected wild-type (grey bar) mice. Actin used as a loading control. Error bars represent SEM and an "n" of 3 was used for each group.

Figure 3

TC007-treated mice have significantly increased gross motor function than vehicle treated as measured by time-to-right (TTR). (A) TC007-treated mice right faster than vehicle treated mice. Each circle (vehicle, n = 16) or square (TC007, n = 16) represents an individual mouse, with the bar (solid, TC007; dotted, vehicle) demonstrating the average. (B) More TC007-treated mice are able to right on average. Average percentage able to right plotted against day for each group. Black solid line represents TC007-treated group and grey dotted line represents vehicle-treated. Error bars represent SEM and significant days indicated by: *p < 0.05 or ** p < 0.02 as determined by two-way ANOVA.

Figure 4

Gastrocnemius muscle fibers from p10 mice were significantly larger in TC007-subcutaneously treated intermediate mice. (A) Representative pictures of fixed and H&E stained gastrocnemius fibers from Wild-type or SMA mice (TC007- or vehicle-treated, respectively). (B) Graph of mean fiber area of the three groups. Significance by Student's T Test between TC007- or vehicle-treated mice indicated on graph (*), error bars represent SEM, and an "n" of 3 was used for each group.

Figure 5

Ventral horn cells (VHCs) trend towards increased VHC numbers between TC007- versus vehicle-treated SMA mice. (A) Average VHC number in 14 sections of Wild-type, or vehicle- and TC007-treated p10 SMA mice. Each point represents an individual mouse, the horizontal line represents the average, and error bars represent SEM. (B) Representative pictures of fixed and cresyl violet-stained lumbar spinal cord sections from Wild-type or SMA mice (vehicle- or TC007-treated, respectively with an "n" of three for each group).