Ropinirole, retigabine, and bosutinib
In several drug discovery and repurposing screens using human, ALS patient-derived induced pluripotent stem cells (ALS-iPSC) have been used in search of new candidate ALS treatments. For example, the following potential anti-ALS drugs were identified using ALS-iPSCs: ropinirole (a dopamine receptor agonist), retigabine ( a Kv7 or KCNQ voltage-gated potassium channel activator)\cite{Wainger_2014}, and bosutinib (a Src/c-Abl inhibitor )\cite{Imamura2017} \cite{Okano_2020}. Of these three drugs, bosutinib, indicated for chronic myelocytic leukemia, reduced phosphorylated TDP-43 (pTDP-43 ) in human ALS-derived iPSC motor neurons \cite{Imamura2017}. Bosutinib was also able to increase survival and autophagy of these cells, while decreasing the misfolded mutant SOD1 protein and overall improved the ALS-associated altered expression of mitochondrial genes \cite{Okano2020}\cite{Imamura2017}. In human-derived neural progenitor cells (NPCs) and iPSCs, TDP-43 mRNA was reduced to 15% of the endogenous levels using lentiviral-encoded short hairpin RNAs and decreased long intron–containing pre-mRNA, including the E3 ubiquitin ligase parkin \cite{Lagier-Tourenne2012}\cite{Polymenidou2011} \cite{Wenqiang2014}. Other genes besides parkin that were downregulated included SET and MYND domain-containing protein 3 (SMYD3), neurexin 3 (NRXN3), neuroligin 1 (NLGN1), Na+/K+ transporting ATPase interacting 2 or T-cell lymphoma breakpoint associated target 1 (NKAIN2 or TCBA1), ataxin 1 (ATXN1), potassium voltage-gated channel (KCND2), and the noncoding RNA imprinted in Prader-Willi (IPW). What is important about these findings is that aberrant cytoplasmic clustering of TDP-43 is associated with a loss of proteins which are encoded by long pre-mRNA and is a contributing factor to ALS pathology \cite{Lagier-Tourenne2012}.
In addition, currently underway in Japan is a phase I/IIa double blind, randomized, placebo-controlled, clinical trial, The ROPALS trial (UMIN000034954 and JMA-IIA00397), with an enrollment of 20 ALS patients and 5 controls \cite{Morimoto2019} . The primary aim is to assess the drug safety and tolerability of ropinirole hydrochloride in patients with ALS treated with 2 to 16 mg of extended-release tablet (Requip CR) along with the standard ALS treatment of riluzole at 24 weeks. The secondary endpoints of ALSFRS-R, change in the Combined Assessment of Function and Survival (CAFS) and molecular effects on patient-derived iPSCs will also be analyzed and the study is expected to conclude in November of 2020.
Rasagiline monoamine oxidase B (MAO-B) inhibitor:
Rasagiline is a drug used in Parkinson's disease that is known to have a good safety profile, and it has antioxidant, mitochondrial, and anti-apoptotic properties that may be important for its therapeutic activity \cite{Statland2019}. A clinical trial was conducted to ascertain rasagiline's efficacy in patients with ALS in a double placebo, randomized, trial of 80 ALS patients assigned in a 3:1 ratio to treatment with 2 mg/day rasagiline or placebo ( rasagiline n=60, placebo n=20 ), stratified by riluzole use and bulbar onset ( speech or swallowing problems ) at 10 testing centers in the United States, with the drug provided by TEVA Pharmaceuticals. The trial was registered at clincaltrials.gov under identifier NCT01786603. The primary outcome that was measured was the decline in ALSFRS, and secondary measures were the vital capacity and decline in vital capacity since these predictors of survival, ALS quality of life (ALSQOL; 0=very bad to 10 =excellent ). An exploratory biomarker tested was TDP-43, measured indirectly (instead of in CNS) as a peripheral biomarker in platelet cytoplasm. It was found that TDP-43, collected at baseline and 12 months, did not differ between treated and placebo, although there was a decrease in both. Since rasagiline was reported to increase mitochondrial membrane potential, decrease oxidative stress, and increase anti-apoptotic : pro-apoptotic protein ratios, the authors measured these mitochondrial and oxidative stress pathology biomarkers important neuropathology. At baseline 6 and 12 months they measured the following peripheral biomarkers: mitochondrial membrane potential (JC-1 and MitoTracker Red oxidative stress ( 15-F(2t)-isoprostane and Oxygen Radical Antioxidant Capacity assay ,ORAC ), and apoptosis ( Bcl2/Bax mRNA Ratio and Annexin V ) and reported inconsistent trends between rasagiline and placebo groups.