Mecasermin

Mecasermin (brand name Increlex) is a recombinant form of human insulin-like growth factor 1 (rhIGF-1) produced by recombinant DNA technology in E. coli that has been modified to express the human IGF-1 gene. The amino acid sequence is identical to that of endogenous human IGF-1. Each multiple-dose vial contains 40 mg mecasermin in 4 mL solution (10 mg/mL). Mecasermin is approved by the FDA for treatment of growth failure in pediatric patients 2 years of age and older with severe primary IGF-1 deficiency (SPIGFD) or with growth hormone (GH) gene deletion who have developed neutralizing antibodies to GH.

The molecule received FDA approval on August 30, 2005, the first FDA-approved IGF-1 replacement therapy. The original sponsor was Tercica (later acquired by Ipsen). Ipsen marketed Increlex from 2008 through 2024 when the asset was sold to Eton Pharmaceuticals. The Eton acquisition closed on December 20, 2024, with Increlex now available through AnovoRx, a specialty pharmacy dedicated to serving patients with rare and chronic conditions. The molecule is approved in 40 territories including the United States and the European Union.

Mecasermin is distinct from the synthetic IGF-1 analog IGF-1 LR3, which is used in adult research-chemical settings without regulatory approval and which has structural modifications (N-terminal extension, arginine substitution) that produce a 20 to 30 hour half-life and reduced IGFBP binding. Mecasermin is the native human IGF-1 sequence with the standard short half-life and IGFBP binding profile.

The Approved Indication: Severe Primary IGF-1 Deficiency

The approved indication is narrow and tightly defined.

Severe primary IGF-1 deficiency (SPIGFD). Defined by:

• Height standard deviation score ≤ -3.0
• Basal IGF-1 standard deviation score ≤ -3.0
• Normal or increased GH levels (to exclude GH deficiency as the cause)
• Exclusion of secondary forms of IGF-1 deficiency (GH deficiency, malnutrition, hypothyroidism, chronic anti-inflammatory corticosteroid use)

GH gene deletion with neutralizing antibodies. A small subgroup of patients with growth hormone gene deletion who have developed neutralizing antibodies to administered GH. These patients cannot benefit from recombinant GH replacement and require direct IGF-1 replacement.

Patient population. SPIGFD includes patients with mutations in the growth hormone receptor (GHR), post-GHR signaling pathway, and IGF-1 gene defects. In Canada, approximately 4.88 cases of SPIGFD are diagnosed each year, or 1 case in every 77,000 births.

Dosing. Recommended starting dose is 0.04 mg/kg to 0.08 mg/kg twice daily by subcutaneous injection. If well-tolerated for at least one week, the dose may be increased by 0.04 mg/kg per dose to a maximum dose of 0.12 mg/kg given twice daily.

Treatment duration. Long-term therapy continued until completion of bone growth (epiphyseal closure). Bone age less than 14 years for girls and less than 16 years for boys is required for ongoing treatment.

The narrow indication is one of the key features of Increlex regulatory positioning. The drug is not approved for idiopathic short stature, GH deficiency, adult growth hormone deficiency, age-related decline, sarcopenia, or any of the other contexts where IGF-1 increase might be theoretically beneficial. The FDA label is explicit: Increlex is not a substitute for GH for approved GH indications and is not indicated for secondary forms of IGFD.

The Clinical Evidence Base

The clinical evidence for Increlex is concentrated in long-term efficacy and safety studies in SPIGFD patients.

Original registration studies. The combined clinical-trial dataset that supported the 2005 FDA approval included approximately 71 patients treated for up to 12 years. The primary efficacy outcome was height velocity, the rate of height increase per year. Treated patients showed significant improvement in height velocity compared with pre-treatment values.

Chernausek et al. (2007), JCEM. Long-term treatment with recombinant insulin-like growth factor I in children with severe IGF-I deficiency due to growth hormone insensitivity. Documented sustained height velocity improvements and acceptable safety profile over multiple years of treatment.

Guevara-Aguirre et al. (1997). Two-year treatment of GH receptor deficiency (GHRD) with rhIGF-1 in 22 children. Compared two dosage levels and to GH-treated GH deficiency. Established efficacy in the largest specifically GHRD population studied.

Long-term efficacy. Cumulative treatment data over 10+ years documents that Increlex produces meaningful height gains in SPIGFD patients, though absolute final adult heights remain typically below normal population means due to the severity of the underlying condition.

Off-label research interest. Increlex has been investigated in Rett syndrome (O'Leary et al. crossover trial) and other neurodevelopmental conditions with mixed results. Off-label use in adult growth hormone deficiency, anti-aging contexts, and athletic performance is explicitly not supported by the FDA label or by the published clinical evidence.

Mecasermin acts on the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase expressed on many tissue types including liver, kidney, muscle, cartilage, and bone.

Anabolic and growth-promoting effects. Mecasermin mediates the anabolic and growth-promoting effects normally produced by growth hormone (GH) signaling. Under normal physiology, GH binds its receptor in the liver and other tissues to stimulate IGF-1 synthesis and secretion. IGF-1 then acts on peripheral tissues to drive growth and metabolic effects. In SPIGFD patients, the GH-IGF-1 axis is broken at the level of GH receptor signaling or IGF-1 production. Direct IGF-1 replacement bypasses the broken step.

Required for normal growth and brain development. IGF-1 is required for normal statural growth in children and for proper brain development. Severe IGF-1 deficiency produces short stature, developmental delays, and other consequences of inadequate IGF-1 signaling.

Metabolic effects. IGF-1 is directed in part toward stimulating uptake of glucose, fatty acids, and amino acids so that metabolism supports growing tissues. Mecasermin also produces measurable increases in insulin sensitivity by mimicking some actions of insulin at the insulin receptor.

Disulfide bridge structure. The native IGF-1 structure includes three intramolecular disulfide bridges that produce the characteristic three-dimensional fold required for IGF-1R binding. Mecasermin replicates this structure faithfully.

Pharmacokinetic profile. Plasma half-life is approximately 5.8 hours in pediatric patients. The half-life is longer than native free IGF-1 due to binding to IGF binding proteins (IGFBP-3 primarily) in plasma. Twice-daily subcutaneous administration is required to maintain therapeutic levels.

The approved indication is narrow and tightly defined.

Severe primary IGF-1 deficiency (SPIGFD). Defined by:

• Height standard deviation score ≤ -3.0
• Basal IGF-1 standard deviation score ≤ -3.0
• Normal or increased GH levels (to exclude GH deficiency as the cause)
• Exclusion of secondary forms of IGF-1 deficiency (GH deficiency, malnutrition, hypothyroidism, chronic anti-inflammatory corticosteroid use)

GH gene deletion with neutralizing antibodies. A small subgroup of patients with growth hormone gene deletion who have developed neutralizing antibodies to administered GH. These patients cannot benefit from recombinant GH replacement and require direct IGF-1 replacement.

Patient population. SPIGFD includes patients with mutations in the growth hormone receptor (GHR), post-GHR signaling pathway, and IGF-1 gene defects. In Canada, approximately 4.88 cases of SPIGFD are diagnosed each year, or 1 case in every 77,000 births.

Dosing. Recommended starting dose is 0.04 mg/kg to 0.08 mg/kg twice daily by subcutaneous injection. If well-tolerated for at least one week, the dose may be increased by 0.04 mg/kg per dose to a maximum dose of 0.12 mg/kg given twice daily.

Treatment duration. Long-term therapy continued until completion of bone growth (epiphyseal closure). Bone age less than 14 years for girls and less than 16 years for boys is required for ongoing treatment.

The narrow indication is one of the key features of Increlex regulatory positioning. The drug is not approved for idiopathic short stature, GH deficiency, adult growth hormone deficiency, age-related decline, sarcopenia, or any of the other contexts where IGF-1 increase might be theoretically beneficial. The FDA label is explicit: Increlex is not a substitute for GH for approved GH indications and is not indicated for secondary forms of IGFD.

Regulatory status

United States (FDA). Approved August 30, 2005. Current status: Active marketing authorization. NDA 021839. Increlex prescribing information was last revised in March 2024 (Ipsen) and is now distributed by Eton Pharmaceuticals through AnovoRx specialty pharmacy.

European Union (EMA). Approved 2007 by EMA centralized procedure. Same indication as the FDA approval (SPIGFD in pediatric patients aged 2 years and older).

Other markets. Approved in 40 territories globally.

FDA Orphan Drug Designation. SPIGFD is an orphan disease (low prevalence), and Increlex has orphan drug designation in the United States and similar designations in other jurisdictions. Orphan designation supports the commercial viability of the small patient population.

WADA status. Mecasermin is on the WADA Prohibited List under section S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics) as an IGF-1 / growth factor analog. Use in competitive sport is a doping violation. Approved pediatric use through legitimate prescribing channels is generally protected under Therapeutic Use Exemption rules.

The approved indication is narrow and tightly defined.

Severe primary IGF-1 deficiency (SPIGFD). Defined by:

• Height standard deviation score ≤ -3.0
• Basal IGF-1 standard deviation score ≤ -3.0
• Normal or increased GH levels (to exclude GH deficiency as the cause)
• Exclusion of secondary forms of IGF-1 deficiency (GH deficiency, malnutrition, hypothyroidism, chronic anti-inflammatory corticosteroid use)

GH gene deletion with neutralizing antibodies. A small subgroup of patients with growth hormone gene deletion who have developed neutralizing antibodies to administered GH. These patients cannot benefit from recombinant GH replacement and require direct IGF-1 replacement.

Patient population. SPIGFD includes patients with mutations in the growth hormone receptor (GHR), post-GHR signaling pathway, and IGF-1 gene defects. In Canada, approximately 4.88 cases of SPIGFD are diagnosed each year, or 1 case in every 77,000 births.

Dosing. Recommended starting dose is 0.04 mg/kg to 0.08 mg/kg twice daily by subcutaneous injection. If well-tolerated for at least one week, the dose may be increased by 0.04 mg/kg per dose to a maximum dose of 0.12 mg/kg given twice daily.

Treatment duration. Long-term therapy continued until completion of bone growth (epiphyseal closure). Bone age less than 14 years for girls and less than 16 years for boys is required for ongoing treatment.

The narrow indication is one of the key features of Increlex regulatory positioning. The drug is not approved for idiopathic short stature, GH deficiency, adult growth hormone deficiency, age-related decline, sarcopenia, or any of the other contexts where IGF-1 increase might be theoretically beneficial. The FDA label is explicit: Increlex is not a substitute for GH for approved GH indications and is not indicated for secondary forms of IGFD.

The Increlex safety profile is well characterized through nearly two decades of clinical use.

Hypoglycemia. The most clinically significant adverse event. IGF-1 has insulin-like activity and can produce hypoglycemia, particularly with concurrent insulin or with food restriction. The standard prescribing guidance requires food intake within 20 minutes before or after injection to prevent hypoglycemic episodes. Patients and caregivers are trained in hypoglycemia recognition and management.

Lipohypertrophy. Injection-site lipohypertrophy can develop with repeated injection at the same site. Rotation of injection sites is required.

Intracranial hypertension. Increased intracranial pressure has been reported in some patients, typically presenting with headaches, vision changes, or papilledema. Funduscopic examination is recommended at treatment initiation and periodically thereafter.

Tonsillar hypertrophy. Some patients develop tonsillar overgrowth which can produce obstructive sleep apnea symptoms. Periodic clinical evaluation is recommended.

Slipped capital femoral epiphysis (SCFE). Risk of SCFE in growing children, presenting with hip or knee pain or altered gait. Standard pediatric endocrinology evaluation applies.

Risk of serious adverse reactions in infants. Increlex contains benzyl alcohol as a preservative. Serious and fatal adverse reactions including "gasping syndrome" can occur in neonates and infants treated with benzyl alcohol-preserved solutions. Increlex is not indicated for use in patients under 2 years of age.

Acromegaly-like effects with overdose. Long-term overdose with Increlex may result in signs and symptoms of acromegaly. The standard dosing schedule prevents this if followed correctly.

Hypersensitivity reactions. Allergic reactions including anaphylaxis have been reported.

The safety profile is acceptable for the approved indication (where the alternative is severe short stature with limited intervention options). The safety considerations become more relevant when discussing off-label use in adults or in contexts where the benefit-risk ratio is different.

The IGF-1 receptor pharmacology has several clinical and research points of reference.

Mecasermin vs IGF-1 LR3. Mecasermin is the native human IGF-1 sequence, FDA-approved for narrow pediatric indication, with the standard short half-life and IGFBP binding. IGF-1 LR3 is a synthetic analog with N-terminal extension and arginine substitution producing 20 to 30 hour half-life and reduced IGFBP binding. IGF-1 LR3 has no approval and is on FDA Category 2 list. The two are not interchangeable for clinical or research purposes.

Mecasermin vs Recombinant GH (somatropin). Somatropin is the standard treatment for pediatric and adult growth hormone deficiency. The mechanism is GH replacement, which then stimulates IGF-1 production in patients with intact GH-IGF-1 axis. Mecasermin is direct IGF-1 replacement for patients whose GH-IGF-1 axis is broken at the IGF-1 production level (i.e., GH resistance rather than GH deficiency). The two are complementary rather than competing therapies.

Mecasermin vs Mecasermin rinfabate (rhIGF-1/rhIGFBP-3 complex). Iplex was a co-formulation of rhIGF-1 with rhIGFBP-3 that was approved by FDA in 2005 but withdrawn from the US market in 2007 due to commercial reasons. The combination was designed to extend IGF-1 half-life through native IGFBP-3 binding. Iplex is no longer available in the United States.

Mecasermin vs MGF (Mechano Growth Factor). MGF is a splice variant of IGF-1 produced in muscle in response to mechanical loading. Synthetic MGF is sold through research-chemical vendors. The published clinical evidence is much smaller than for mecasermin and shares similar safety concerns related to IGF-1 receptor activation.

For legitimate clinical use, Increlex is the FDA-approved option for the narrow SPIGFD indication. For any other use case (adult IGF-1 replacement, anti-aging, athletic performance), Increlex is not approved and the off-label use is not supported by the published clinical evidence.