Trofinetide was found in 2002 by Brimble's team at the University of Auckland in New Zealand, while researching a candidate molecule for traumatic brain injury, and pursued by two biopharmaceutical companies in a host of neurological disorders. Methylating the proton of proline makes trofinetide more metabolically resistant to protease and hence long-lived. In the animals, trofinetide increased branching and synaptic plasticity signaling of dendrites.
The FDA cleared trofinetide (oral solution) in March 2023 for the treatment of Rett syndrome 2 years of age and over. Rett syndrome is a rare and highly complex neurodevelopmental disorder that's usually caused by a mutation in the MECP2 gene, which was identified to interfere with synaptic transmission. In Rett syndrome we have normal development 6-18 months in advance, followed by gross motor and language deficits. The official US count of confirmed cases of Rett syndrome stands at about 4,500.
Fig.1 The development timeline of Trofinetide. (Hudu, Shuaibu A., et al.,2023)
Preclinical Study of Trofinetide
Trofinetide has shown neuroprotective and anti-inflammatory activity in preclinical research – in neurodevelopmental disorders and neurodegenerative diseases, for example. We don't yet know the exact mechanism of action, but it is assumed that Trofinetide alters the activity and shape of neurons and synapses – principally through a boost in dendritic branching and increased synaptic plasticity signaling. And it backs this up with findings of its animal experiments.
Security
Trofinetide was not toxic at high doses (up to 1000 mg/kg BID, administered orally) in the rat study studies. In the cardiovascular system, QTcV was slightly longer at doses higher than 400 mg/kg, but did not change heart rate or arterial blood pressure. In the test of genotoxicity, there was no risk for genetic mutations on either Ames or any other test.
Pharmacokinetics (ADME)
Plasma Tmax will be reached around 2 hours after Trofinietide is taken by mouth. The drug is found in the vast majority of the rats' tissues and, so far, no important metabolites have been discovered. Trofinietide gets largely excreted in the urine and feces, and there is no major effect of metabolism on its excretion. We've conducted extended-term dose studies of Trofinietide in rats (26 weeks) and dogs (39 weeks).
Toxicity and Reproductive Toxicity
Trofinietide peaks in plasma about 2 hours after oral administration and was distributed across the majority of rats' tissues without apparent metabolites. The drug is largely cleared through urine and feces, and its elimination by metabolism is not very different. Trofinietide did well in long-term dosing studies with rats (26 weeks) and dogs (39 weeks). In rats and rabbits, the exposure was as high at 1000 mg/kg BID with no adverse effects on fetuses or embryos. No studies on Trofinietide have been performed on carcinogenicity, but the FDA still needs post-marketing validation.
Clinical Trial of Trofinetide
Trofinetide has seen a few clinical trials since it was first identified, but these have mainly been with Rett syndrome. Here is a summary of the large clinical trials.
Phase I Trial
The researchers performed the phase I trial where they studied the safety and pharmacokinetics of Trofinetide in healthy volunteers. They found no relationship between diet and daily medications on the pharmacokinetics of Trofinetide. The medication is primarily eliminated through the urine, its half-life is approximately 1.4 hours and you have to take it twice or three times a day.
Phase II Trial
One phase II trial (NCT02715115) assessed safety and effectiveness of trofinetide in Rett patients. They found that the medication was well-tolerated in patients at between 35 and 200 mg/kg, and that there was a small clinical benefit for relief of symptoms.
Phase III Trial
The Phase III trial had 187 Rett syndrome patients in its Lavender trial who were assessed for the effectiveness of trofinetide. While the complete data are not publicly available yet, the FDA approval shows that the trial lends robust support to Trofinetide. A second phase III trial, NCT04279314 (Lilac trial), was focused on long-term safety of trofinetide. A total of 154 patients were given the treatment for 40 weeks and the data shows that it is safe and tolerable on a long-term basis.
Trials in Children
In the NCT04988867 (Daffodil trial), they also studied 2–5 year olds with Rett syndrome, setting the stage for taking the drug in the very young.
Key Findings
Trofinetide is effective both short- and long-term for symptomatic relief in patients with Rett syndrome. Safeness is reasonable, diarrhea and weight gain are the only serious side-effects, and the majority of reactions are mild or moderate. Weight-adjusting, twice daily dosage.
Pharmacological Data of Trofinetide
Trofinetide's drug activity allows for the medical treatment of Rett syndrome to be supported by science. Here are some highlights.
Pharmacokinetic Parameters
Trofinetide has a good bioavailability of 84% and is present in the plasma concentration to the fullest within 2-3 hours. It has a distribution volume of about 80 liters and protein binding rate is low (6%) with very good distribution in the body. During the meantime, liver metabolism affected it in a small way, and there were no major metabolites. Excess 80% of the prototype drug went in the urine, 15% in the feces, which means it was largely excreted in the urine.
Metabolism
CYP450 and uridine diphosphate glucuronosyltransferase (UGT) have little to do with trofinetide metabolism. Hepatic metabolism is not significant. No large metabolites have been observed. Trofinetide is a poor CYP3A4 inhibitor. Trofinetide is an OATP1B1 and OATP1B3 inhibitor in vitro.
Summary
Trofinetide represents a major scientific development in neuroscience, especially as a useful drug for the management of the severe, and often rare, condition of Rett syndrome. From animal to human research, Trofinetide has been shown to be safely, tolerably and in some cases even to be efficacious, primarily for enhancement of synaptic function and the shape of neurons. But its primary side-effects, including diarrhea and weight gain, are concerning. Second, the long-term safety data and application effects in special populations remain unexplored. Eventually, Trofinetide's commercialization and mass availability could offer novel approaches to treating more brain disorders and potentially transform the lives of more patients with Rett syndrome.
Reference
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Hudu, Shuaibu A., et al., Trofinetide for Rett syndrome: highlights on the development and related inventions of the first USFDA-approved treatment for rare pediatric unmet medical need. Journal of Clinical Medicine 12.15 (2023): 5114.
