Synonyms: LMT-X, Methylene Blue, Tau aggregation inhibitor (TAI)
Chemical Name: Methylthioninium chloride (MTC)
Therapy Type: Small Molecule
Target Type: Tau
Condition(s): Alzheimer's Disease, Frontotemporal Dementia
U.S. FDA Status: Alzheimer's Disease (Phase 3), Frontotemporal Dementia (Phase 3)
Company: TauRx Therapeutics Ltd
Approved for: Methylene Blue predates FDA. Used for treatment of malaria and methemoglobinemia.
TRx 0237 (LMTX™) is a second-generation tau protein aggregation inhibitor for the treatment of Alzheimer's disease (AD) and frontotemporal dementia. It is a replacement formulation for Rember®, the first company's first proprietary formulation of methylthioninium chloride (MTC). Both TRx 0237 and Rember are purified forms of Methylene Blue, an old drug that predates the FDA and is being widely used in Africa for the treatment for malaria, as well as for methemoglobinemia and other conditions. TRx 0237 and Rember share the same mode of action, but TRx 0237 has been designed as a stabilized, reduced form of MTC to improve the drug's absorption, bioavailability, and tolerability.
The rationale behind both TRx 0237 and Rember TM is that these compounds prevent tau aggregation or dissolve existing aggregates to interfere with downstream pathological consequences of aberrant tau in tauopathies including Alzheimer's and other neurodegenerative diseases. Tau pathology is widely considered to be downstream of Aβ pathology and is more closely linked to cognitive deficits in Alzheimer's disease. Mutations in the tau gene cause frontotemporal dementia, not Alzheimer's disease, but tau is considered a central drug target for all tauopathies, including Alzheimer's.
Prior to the first publicized Phase 2 trial on Rember TM in 2008, one peer-reviewed paper to support this rationale had been published, which reported that Methylene Blue interfered with the tau-tau binding necessary for aggregation (see Wischik et al., 1996). No peer-reviewed papers have been published on Rember TM or TRx 0237. However, since 2008, numerous independent academic investigations of the commercially available parent compound, Methylene Blue, have reported potentially beneficial effects on a growing list of cellular and system-level endpoints, including tau fibrillization in vitro (see Crowe et al., 2013), autophagy (e.g. Congdon et al., 2012), neuroprotection via mitochondrial antioxidant properties (e.g. Wen et al., 2011), as well as on Aβ clearance and proteasome function in transgenic AD mouse models (see Medina et al., 2011), and spatial learning and brain metabolism in rats (see Deiana et al., 2009; Riha et al., 2011). One mechanistic study found that Methylene Blue oxidizes cysteine sulfhydryl groups on tau in a way that keeps tau in the monomeric state (see Feb 2013 news story).
Some studies reported a generalized anti-aggregation effect for Methylene Blue against aggregation-prone proteins, such as prion protein and TDP-43 (e.g. Cavaliere et al., 2012; Arai et al., 2010). However, findings are mixed, with other papers reporting no inhibition of tau- and polyglutamine-mediated neurotoxicity in vivo (see van Bebber et al., 2010).
No information on Phase 1 trials of TRx0237 is available. A four-week Phase 2 safety study of 250 mg/day of TRx0237 in patients with mild to moderate Alzheimer's disease began in September 2012 but was terminated in April 2013, reportedly for administrative reasons.
Three Phase 3 studies are ongoing. One compares a single 200 mg/day dose to placebo in a planned 700 patients with a diagnosis of either all-cause dementia or Alzheimer's disease mild enough to score above an MMSE of 20. Begun in November 2012, this trial runs at more than 90 sites in North America and Europe. As primary outcomes, this trial uses standard cognitive (ADAS-Cog 11) and clinical (ADCS-CGIC) batteries, as well as temporal lobe brain metabolism as measured by FDG-PET and safety parameters.
The second Phase 3 trial compares 150 and 250 mg/day of TRx0237 to placebo in a planned 833 patients with mild to moderate Alzheimer's disease with an MMSE of 14 or higher. Started in 2013, this trial is ramping up to involve more than 80 sites in North America, Australia, Europe, and Asia. It uses clinical (ADCS-CGIC), cognitive (ADAS-Cog 11), and safety measures as primary outcomes.
The third Phase 3 trial is evaluating TRx0237 in the behavioral variant of frontotemporal dementia, the most common form of this disease. Begun in August 2013, this trial targets enrollment of 180 people with probable bvFTD who have frontotemporal atrophy confirmed by MRI and whose MMSE is above 20. The trial compares 200 mg/day to placebo for the drug's ability to show clinical benefit on activities of daily living as measured by the modified ADCS-CGIC Alzheimer's scale and the revised Addenbrooke's Cognitive Examination (ACE-R), a widely used pychometric tool in FTD clinical research. This trial is to be conducted at 45 sites in North America, Europe, Australia, and Singapore.
All three Phase 3 trials use “active placebo” tablets that include 4 mg of TRx0237 as a urinary and fecal colorant to help maintain blinding; hence the placebo group will receive a total of 8 mg/day of TRx0237. TRx0237's predecessor compound, RemberTM, colors urine and feces, and the blinding of its Phase 2 trial has been questioned. Hence a colorless TRx0237 was developed; however, it too, turns blue once metabolized in the body (for details and Q&A with TRx0237's founding scientist, Claude Wischik, see Oct 2012 news story).
Clinical Trial Timeline
- Phase 2
- Phase 3
- Study completed / Planned end date
- Planned end date unavailable
- Study aborted
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