Dexpramipexole Is Ineffective in Two Models of ALS Related Neurodegeneration

<div><p>Treatment options for people living with amyotrophic lateral sclerosis (ALS) are limited and ineffective. Recently, dexpramipexole (RPPX) was advanced into human ALS clinical trials. In the current studies, we investigated RPPX in two parallel screening systems: 1) appropriately powered, sibling-matched, gender-balanced survival efficacy screening in high-copy B6-SJL-SOD1^G93A/Gur1 mice, and 2) high-content neuronal survival screening in primary rat cortical neurons transfected with wild-type human TDP43 or mutant human TDP43. In both cases, we exposed the test systems to RPPX levels approximating those achieved in human Phase II clinical investigations. In SOD1^G93A mice, no effect was observed on neuromotor disease progression or survival. In primary cortical neurons transfected with either mutant or wild-type human TDP43, a marginally significant improvement in a single indicator of neuronal survival was observed, and only at the 10 µM RPPX treatment. These systems reflect both mutant SOD1- and TDP43-mediated forms of neurodegeneration. The systems also reflect both complex non-cell autonomous and neuronal cell autonomous disease mechanisms. The results of these experiments, taken in context with results produced by other molecules tested in both screening systems, do not argue positively for further study of RPPX in ALS.</p></div

Kaplan-Meier survival plot for age at death in SOD1^G93A mice.

<p>Left panel shows data from all animals (All); middle and right panels show data from females (F) and males (M), respectively. Vehicle control (CTRL) animals received 0.22 micron filtered animal facility drinking water. Dexpramipexole-treated (DRUG) animals received daily 200 mg/kg/day dexpramipexole (1.19 g/L) in filtered drinking water. Results of statistical analysis for these data are given in the lower portion of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091608#pone-0091608-t004" target="_blank">Table 4</a>.</p

Steady-state dexpramipexole concentrations in SOD1^G93A mice receiving drug ad libitum in drinking water.

<p>Three males and three females in each group received 0.179, 0.9, or 1.79 mg/mL dexpramipexole dihydrochloride in the drinking water. Mean ± standard error of the mean concentration in plasma and spinal cord at steady-state after 14 days of treatment is shown at each dose level. A concentration of 1.19 mg/mL in the drinking water was chosen for the survival study in SOD1G93A mice to emulate steady-state concentrations attained by the 300 mg/d group reported in the human clinical trial (1).</p

Effect of Treatment on Neurological Severity Score.¹

<p>Daily neurological severity scores were taken from study start until death. These ordinal scores ranging from 0 to 4 were modeled in relation to the animal's median age at each score level using ordinal logistic regression. The model fits cumulative response probabilities to the logistic function of a linear model using maximum likelihood. Likelihood-ratio and Wald Chi-square test probabilities are provided for the treatment effect. Plots comparing fitted neurological score over time by treatment are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091608#pone-0091608-g003" target="_blank">Fig. 3</a>.</p><p>Effect of Treatment on Neurological Severity Score.¹</p

Cortical Neuron Survival Data, TDP43-EGFP with RPPX Treatment.

<p>Cortical Neuron Survival Data, TDP43-EGFP with RPPX Treatment.</p

Cortical Neuron Survival Data, TDP43^A315T-EGFP with RPPX Treatment.

<p>Cortical Neuron Survival Data, TDP43^A315T-EGFP with RPPX Treatment.</p

Time-to-Event Analysis for Onset of Neurological Symptoms and for Survival Duration.^1–3

<p>Testing Terms: In Kaplan-Meier analysis the Log-Rank test places more weight on later event times; the Wilcoxon test places more weight on early event times and is the optimum rank test if the error distribution is logistic. Prob > ChiSq lists the probability of obtaining, by chance alone, a Chi-square value greater than the one computed if the time-to-event functions are the same for all groups. In Cox proportional hazards analysis the Effect Likelihood Test is the likelihood-ratio Chi-square test on the null hypothesis that the parameter estimate for the Treatment covariate is zero (no effect of treatment). Testing term descriptions are taken from the JMP 10.0.0 Help file. A neurological score of two in both hind limbs is taken to be the definitive onset of neurological symptoms. Animals that did not reach a neurological severity score of 2 prior to termination of the experiment at 180 days of age were right-censored in the onset analysis. Animals that did not die by 180 days of age were right-censored in the survival analysis.</p><p>Time-to-Event Analysis for Onset of Neurological Symptoms and for Survival Duration.^1–3</p

Change from Initial Body Weight over Time.¹^,²

1<p>Daily body weight for each individual animal from study start until death was evaluated and treatment group mean values and statistical probabilities from Student's 2-tailed independent t-test are presented. The difference between DRUG and CTRL groups (D-C) is also given.</p>2<p>Peak change from initial body weight was detected after spline smoothing (stiffness 100) of each animal's body weight change over time during the period from study start to death.</p><p>Change from Initial Body Weight over Time.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091608#nt101" target="_blank">1</a>}^,^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091608#nt102" target="_blank">2</a>}</p

Dexpramipexole Stability in Drinking Water over One Week by HPLC.

<p>Dexpramipexole Stability in Drinking Water over One Week by HPLC.</p

Cortical Neuron Survival Data, TDP43^M337V-EGFP with RPPX Treatment.

<p>Cortical Neuron Survival Data, TDP43^M337V-EGFP with RPPX Treatment.</p