Safety, pharmacokinetics, and preliminary assessment of efficacy of mecasermin (recombinant human IGF-1) for the treatment of Rett syndrome.

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder mainly affecting females and is associated with mutations in MECP2, the gene encoding methyl CpG-binding protein 2. Mouse models suggest that recombinant human insulin-like growth factor 1 (IGF-1) (rhIGF1) (mecasermin) may improve many clinical features. We evaluated the safety, tolerability, and pharmacokinetic profiles of IGF-1 in 12 girls with MECP2 mutations (9 with RTT). In addition, we performed a preliminary assessment of efficacy using automated cardiorespiratory measures, EEG, a set of RTT-oriented clinical assessments, and two standardized behavioral questionnaires. This phase 1 trial included a 4-wk multiple ascending dose (MAD) (40-120 µg/kg twice daily) period and a 20-wk open-label extension (OLE) at the maximum dose. Twelve subjects completed the MAD and 10 the entire study, without evidence of hypoglycemia or serious adverse events. Mecasermin reached the CNS compartment as evidenced by the increase in cerebrospinal fluid IGF-1 levels at the end of the MAD. The drug followed nonlinear kinetics, with greater distribution in the peripheral compartment. Cardiorespiratory measures showed that apnea improved during the OLE. Some neurobehavioral parameters, specifically measures of anxiety and mood also improved during the OLE. These improvements in mood and anxiety scores were supported by reversal of right frontal alpha band asymmetry on EEG, an index of anxiety and depression. Our data indicate that IGF-1 is safe and well tolerated in girls with RTT and, as demonstrated in preclinical studies, ameliorates certain breathing and behavioral abnormalities.

Mecasermin: new drug. Insufficient improvement in statural growth.

(1) Human insulin-like growth factor type 1 (IGF-1) is the main effector of growth hormone action. Primary IGF-1 deficiency is a rare disease, mainly resulting in very short stature; (2) Mecasermin is a recombinant IGF-1 marketed for this indication as a twice daily subcutaneous injection; (3) Clinical evaluation is mainly based on a non-comparative follow-up study of 76 children with an average age of 7 years, some of whom were treated for 8 years. The mean height at treatment initiation was 6.7 standard deviations below normal. Eight years later, it was 5.2 standard deviations below normal, i.e. their growth failure remained very severe; (4) The main short-term adverse effects of mecasermin are hypoglycaemia, headache and intracranial hypertension. Nearly one in 5 children developed tonsillar hypertrophy, resulting in otitis and hypoacusis; (5) Animal studies showed hypertrophy of other organs (kidneys, spleen and heart) as well as carcinogenic effects. The risk in humans is unknown; (6) The mecasermin packaging is not well-adapted (a multidose vial designed to be punctured several times), and is a potential source of contamination and errors. Prefilled pens or syringes would be easier to use; (7) In practice, the limited clinical benefits of mecasermin do not justify exposure to its potential risks.