Mecasermin: Mechanism, Dosing & Research Data

Mecasermin (Increlex) is recombinant human insulin-like growth factor-1 (rhIGF-1), FDA-approved for growth failure in children with severe primary IGF-1 deficiency or growth hormone gene deletion with neutralizing GH antibodies. As the native IGF-1 molecule, it activates the IGF-1 receptor directly and serves as the reference standard for all IGF-1 analogs and research.

Mechanism of Action

Binds IGF-1R alpha subunits, triggering beta subunit tyrosine kinase autophosphorylation and IRS-1/PI3K/Akt/mTOR signaling cascade
Direct growth-promoting effects on cartilage (chondrocyte proliferation), bone, muscle, and organ growth without requiring pituitary GH
In GH-deficient or GH-unresponsive states: mecasermin bypasses the GH-IGF-1 axis requirement by delivering IGF-1 directly
Metabolic: IGF-1R activation suppresses hepatic glucose output and enhances peripheral glucose uptake (insulin-like hypoglycemic effect)
Promotes nitrogen retention, protein synthesis, and lipolysis via IGF-1R/mTOR in muscle and adipose

Research Findings

Phase III: mecasermin in Laron syndrome (GHR defect) increased height velocity from 2-3 cm/year to 8-10 cm/year; maintained over 10+ years of treatment
FDA approval (2005): Increlex approved for growth failure in severe primary IGF-1 deficiency (Laron syndrome and GH insensitivity)
Long-term Laron syndrome patients: mecasermin prevents the metabolic syndrome, insulin resistance, and body composition abnormalities seen in untreated adults
Research use: mecasermin IV in healthy subjects shows anabolic effects on muscle protein synthesis comparable to GH with less glucose dysregulation
ALS (amyotrophic lateral sclerosis): mecasermin Phase II/III trials showed modest slowing of respiratory decline; FDA orphan drug designation

Research Protocols

FDA-approved (Increlex): 0.04-0.12 mg/kg SC twice daily in children with severe primary IGF-1 deficiency; must be given with food to reduce hypoglycemia
Research adults: 0.02-0.04 mg/kg SC twice daily (lower than pediatric due to lower GH-driven IGF-1 deficit)
ALS research: 0.08-0.12 mg/kg SC twice daily; monitor FVC (forced vital capacity) and ALS functional rating scale
Monitor: IGF-1 levels (target 1-2 SD above normal for age/sex); fasting glucose; screen for hypoglycemia symptoms

Interactions

Insulin: additive hypoglycemic effect; reduce insulin dose when starting mecasermin; careful blood glucose monitoring required
GH: do not combine; GH stimulates endogenous IGF-1; exogenous mecasermin already provides the IGF-1 that GH would produce
IGFBP-3 (mecasermin rinfabate form): co-formulation with IGFBP-3 extends half-life and reduces hypoglycemia severity

Safety Profile

FDA-approved with comprehensive safety data. Hypoglycemia (dose-dependent; mitigated by giving with food), lymphoid tissue hyperplasia (tonsillar/adenoid enlargement), intracranial hypertension (rare), lipohypertrophy at injection sites. Long-term safety in Laron syndrome patients shows normal life expectancy without increased cancer incidence.