Profile of Trofinetide in the Treatment of Rett Syndrome: Design, Development and Potential Place in Therapy

Trofinetide is a first-in-class pharmacological treatment proposed for patients with Rett Syndrome. It is a long half-life derivative of glycine-proline-glutamate, the tripeptide normally excided from Insulin-like Growth Factor 1 upon degradation. Due to containing glutamate and glycine in its structure, trofinetide is thought to act through NMDA receptor modulation, thus providing a normalization of neuronal activity and survival. Trofinetide was tested in a series of short and long-term trials, showing good efficacy at improving scores on the Clinical Global Impression-Improvement scale and Rett Syndrome Behavior Questionnaire, with specific effect only on some subscales, ie General Mood subscale and Repetitive Face Movement subscale. No effects were documented on other subscales or on epilepsy, heart and bone -related symptoms. The main adverse effects of trofinetide, severe enough to determine discontinuation, include diarrhea, vomiting, and consequent weight loss. These may be scarcely avoidable, given the need to assume a very large amount of trofinetide per day. Other inherent limitations of use possibly regard the limited duration of drug supplies, as one bottle may last three days only, depending on weight, and the relatively high cost per bottle. Trofinetide has no direct competitors: single symptoms of the Rett Syndrome, for instance, seizures or aggressive behaviors, are currently treated with drugs that have been developed for patients without the Rett Syndrome. This leads to suboptimal efficacy and increased risk of adverse effects. The place in therapy of trofinetide is yet to be determined, based on the results of clinical trials, on its practical usability, and on the windows of opportunity for intervention. Moreover, trofinetide may be curative if given early enough during brain development, or merely symptomatic if given to young adults, and no data exist on this aspect. The place in therapy of trofinetide will require reassessment after competing treatments enter the market.