Background

TRx0237 (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 TRx0237 and Rember are derivatives 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. TRx0237 and Rember share the same mode of action, but TRx0237 has been designed as a stabilized, reduced form of MTC to improve the drug's absorption, bioavailability, and tolerability. 

The rationale behind this approach 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 (Wischik et al., 1996). In 2015, the same lab published on LMTX®, claiming a Ki of 0.12 micromolar for inhibition of intracellular tau aggregation, and a similar potency for disrupting tau aggregates isolated from AD brain (Harrington et al., 2015).

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 (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 (Medina et al., 2011), and spatial learning and brain metabolism in rats (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 (Feb 2013 news). Subsequently, TRx0237’s developers reported that the inhibition of tau aggregation is cysteine-independent (Al-Hilaly et al., 2018).

In preclinical work, LMTX was reported to improve learning and reduced brain tau load in two strains of tau transgenic mice (Melis et al., 2015). The compound increased cholinergic signaling, mitochondrial function, and expression of synaptic proteins and neuroprotection in mice (Kondak et al., 2023; Schwab et al., 2024; Zadrozny et al., 2024). These effects, but not tau aggregation, were blocked by chronic pretreatment with an acetylcholinesterase inhibitor or memantine (Riedel et al., 2020; Kondak et al., 2022; Santos et al., 2022). Proteomic analysis of tau mice suggested LMTX acts via tau-dependent and -independent actions (Schwab et al., 2021). These studies all originate from one lab. An independent group reported that neither Methylene Blue not LMTM protected cells in a high throughput screen for tau-mediated toxicity (Lim et al. 2023).

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., 2013; Arai et al., 2010). Other papers report no inhibition of tau- and polyglutamine-mediated neurotoxicity in vivo (see van Bebber et al., 2010). In mice overexpressing human α-synuclein, LMTM treatment reduced α-synuclein inclusions in the brain, and normalized movement and anxiety-related behaviors (Schwab et al., 2017). It did not alter glutamate release or related behaviors in these mice (Schwab et al., 2022).

According to a case report, an asymptomatic carrier of the P301S MAPT mutation remained cognitively stable and cerebral atrophy progressed more slowly than expected after 5 years on LMTM treatment during the expected time of onset of frontotemporal dementia symptoms (Bentham et al., 2021).

Findings

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.

In November 2012, TauRx started a Phase 3 study comparing 200 mg/day of LMTM to placebo in a planned 800 patients with a diagnosis of either all-cause dementia or Alzheimer's disease mild enough to score above an MMSE of 20. The trial ran at more than 90 sites in North America and Europe. As primary outcomes, it used 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. Results were presented—and disputed—at the 2016 CTAD meeting. Participants on LMTM declined on cognition (ADAS-Cog) and functional scales (ADCS ADL) as rapidly as did patients on placebo, which contained a low dose of active compound for coloring purposes (Dec 2016 conference news; Wilcock et al., 2018). 

Another Phase 3 trial compared 150 and 250 mg/day of TRx0237 with placebo in 891 patients with mild to moderate Alzheimer's disease with an MMSE of 14 or higher. Started in 2013, this trial involved more than 80 sites in North America, Australia, Europe, and Asia. It used clinical (ADCS-CGIC), cognitive (ADAS-Cog 11), and safety measures as primary outcomes. Negative results from this trial were presented at the 2016 AAIC conference in Toronto and later published after peer review (Jul 2016 conference news; Gauthier et al., 2016).

A third Phase 3 trial evaluated TRx0237 in the behavioral variant of frontotemporal dementia, the most common form of this disease. Begun in August 2013, this trial targeted enrollment of 180 people with probable bvFTD who have frontotemporal atrophy confirmed by MRI and whose MMSE is above 20. The trial compared 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 psychometric tool in FTD clinical research. This trial was to be conducted at 45 sites in North America, Europe, Australia, and Singapore. At the 2016 ICFTD conference in Munich, this trial was reported to have missed its co-primary endpoints (Sep 2016 conference news; company press release). Results were published after peer review (Shiells et al., 2020).

These three Phase 3 trials used “active placebo” tablets that include 4 mg of TRx0237 as a urinary and fecal colorant to help maintain blinding; hence the "placebo" group received a total of 8 mg/day of TRx0237. TRx0237's predecessor compound, Rember TM, colors urine and feces, and the blinding of its Phase 2 trial has been questioned (see Oct 2012 news for details and Q&A with TRx0237's founding scientist, Claude Wischik). However, post-hoc pharmacokinetic analyses of the Phase 3 trials led the investigators to claim that even 8 mg daily TRx0237 was sufficient to induce changes in brain structure and function (e.g., see Schelter et al., 2019).

In January 2018, TauRx started a Phase 2/3 monotherapy trial aiming to enroll 180 people with all-cause dementia and Alzheimer's disease, at 55 sites in North America, Belgium, Poland, and the U.K. The trial compares a six-month course of 4 mg of LMTM—renamed to HMTM—twice daily. This is the daily dose of HMTM previously admixed to "active placebo'' in the prior Phase 3 trials. LMTM is compared to 4 mg Methylene Blue twice weekly. Acetylcholinesterase inhibitors or memantine are not allowed. Primary outcomes include 18F-FDG-PET imaging and safety; secondary outcomes include structural MRI, as well as measures of cognition and activities of daily living.

In September 2018, TauRx changed the trial protocol to add a third treatment arm of 8 mg HMTM twice daily. The trial increased enrollment to 375, and extended dosing to nine months. Eligibility criteria were changed to accept only people with mild cognitive impairment due to AD, a Global Clinical Dementia Rating of 0.5, and a positive amyloid PET scan. Primary outcomes were also changed, to include a composite measure of cognition and function comprising selected items from the ADAS-Cog and ADCS-ADL scales. The trial was enlarged to 147 sites in North America and Europe.

Recruitment ended in October 2019. In late 2019, the first of three listed primary outcomes was changed from 18F FDG PET to ADAS-Cog 11; the composite measure was changed to the ADSC-ADL23. The inclusion criteria were relaxed to once again include people with more advanced disease, from an earlier MMSE range of 20-27 to 16-27, from a CDR of 0.5 to now include CDR 0.5 to 2, and from excluding all epilepsy to including people with a single episode. Enrollment changed from 375 to 450, study duration changed from nine to 12 months, with a one-year open-label extension. This final protocol was published (Wischik et al., 2022).

According to a trade news report, the company announced top-line results in an October 2022 press release; however, this information is no longer available on the company web site.

According to a company presentation at the December 2022 CTAD conference, the trial failed on both primary endpoints (Medscape). In July 2023, the company showed some biomarker results at the AAIC in Amsterdam. Plasma neurofilament light was shown to have increased in the Methylene Blue control group, but not in the treated group. NfL levels reportedly correlated with trends in plasma p-tau181. At the March 2024 AD/PD conference, the company presented post hoc subgroup analyses of the MCI group, claiming that progression from a CDR of 0.5 to 1 was halved by treatment, that the ADAS-Cog11 declined less in MCI participants who had taken 16 mg per day for two years compared to those who took placebo the first year, and that, when compared to historical controls, the MCI group had declined less on the ADAS-Cog11 and preserved more brain volume over 24 months (Mar 2024 conference news).

TauRx will apply for marketing authorization for HMTM in the U.K. and is in discussions with the European Medicines Agency and Chinese regulators.

For all clinical trials with TRx0237, see clinicaltrials.gov.

Clinical Trial Timeline