Beyond TfR1? IGF1R Unlocks Ultra-Rapid BBB Crossing and Superior Muscle siRNA Delivery

1. IGF1R: Validated Target in Thyroid Eye Disease (TED) and Oncology

Under pathological conditions, aberrant IGF1R activation is closely linked to disease progression. In the tumor microenvironment, IGF1R is frequently overexpressed and functions as an anti-apoptotic driver of malignant transformation, proliferation, and metastasis. In orbital fibroblasts from patients with thyroid-associated ophthalmopathy (TED), IGF1R forms a functional complex with the thyroid-stimulating hormone receptor (TSHR). Autoantibody stimulation of this complex triggers massive hyaluronic acid synthesis and release of inflammatory cytokines including IL-6 and IL-8, culminating in orbital inflammation, edema, and proptosis ^[4-6]. The FDA-approved antagonistic monoclonal antibody teprotumumab (Tepezza) blocks TSHR/IGF1R signaling crosstalk, significantly reducing proptosis and inflammatory symptoms and establishing IGF1R as a central therapeutic target in TED ^[6-7].

Figure 2. Pathological mechanism by which the TSHR–IGF1R complex drives orbital tissue remodeling in TED ^[7].

2. IGF1R vs TfR1: Ultra-Rapid Endocytosis BBB Shuttles for CNS Delivery

Macromolecular antibodies and oligonucleotides offer substantial promise for central nervous system (CNS) disorders, yet the BBB remains a formidable obstacle to brain exposure. Receptor-mediated transcytosis (RMT) platforms have attracted considerable attention, with transferrin receptor 1 (TfR1) currently the most advanced. Nevertheless, TfR1-based approaches face translational hurdles: widespread expression on peripheral reticulocytes raises systemic toxicity concerns, and receptor levels decline markedly with age, limiting utility in late-onset neurodegenerative diseases ^[8].

IGF1R, by contrast, is highly expressed on brain microvascular endothelial cells while showing relatively low expression in most peripheral tissues, creating an attractive safety margin for CNS delivery. ABL Bio’s Grabody-B platform exemplifies the multidimensional advantages of IGF1R-targeted BBB shuttles ^[9-12]:

• Ultra-rapid endocytosis: Unlike TfR1, which depends on the classical clathrin-mediated pathway (30–120 minutes), IGF1R engages both clathrin- and caveolin-dependent routes and relies heavily on fast endophilin-mediated endocytosis (FEME). High-resolution imaging reveals tight association with actin filaments, enabling formation of intracellular vesicles within 30 seconds.
• Remarkable delivery efficiency: Non-neutralizing IGF1R shuttle antibodies (e.g., those targeting the FnIII-2 domain) avoid interference with normal IGF1R signaling and have been shown to increase brain delivery of macromolecular payloads by nearly 10-fold in animal models.
• Lifespan stability: IGF1R expression remains stable across the lifespan, making the platform particularly suitable for late-onset neurodegenerative conditions such as Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Table 1. Comparison of IGF1R-BBB and TfR1-BBB delivery platforms ^[9-12].

3. IGF1R siRNA Conjugates Achieve Potent Muscle, Heart & Liver Knockdown

While BBB shuttling highlights IGF1R’s transport depth, its efficient uptake in muscle, heart, lung, and other peripheral tissues opens new avenues for nucleic acid therapeutics. Achieving efficient extrahepatic siRNA delivery to muscle and heart tissue has long been an industry challenge. Collaborative work between Ionis Pharmaceuticals and ABL Bio demonstrates the strong potential of the IGF1R shuttle platform in this setting. Researchers conjugated an siRNA targeting the Hprt gene to an IGF1R shuttle antibody (Clone F) to generate the Clone F-Hprt conjugate. Following intravenous (IV) or subcutaneous (SC) administration, the conjugate crossed the BBB and achieved robust gene knockdown in deep CNS structures (striatum, thalamus) as well as potent silencing in peripheral tissues including quadriceps muscle, heart, lung, and liver. Key findings include ^[13]:

• Exceptional muscle sensitivity: A single intravenous dose as low as 0.3 mg/kg produced ~50% Hprt mRNA knockdown in mouse quadriceps.
• Broad peripheral coverage: At 10 mg/kg, residual target-gene expression was reduced to 10.9% in liver, 22.0% in quadriceps muscle, and 38.3% in heart.
• Dramatically enhanced tissue uptake: Compared with naked siRNA, Clone F-Hprt increased siRNA accumulation ~170-fold in liver and by tens of fold in lung.

Figure 3. IGF1R antibody-based siRNA conjugates achieve efficient target knockdown in peripheral tissues ^[13].

Grabody-B-conjugated siRNA can effectively lower target gene expression in the central nervous system while also producing significant knockdown in skeletal muscle; in certain models the muscle knockdown effect even surpasses that observed in brain. This unexpected finding has reshaped thinking around treatments for metabolic and muscle disorders. Building on Grabody-B’s outstanding performance across BBB, muscle, and adipose tissues, Eli Lilly and ABL Bio entered a broad collaboration that included a $55 million upfront payment (plus equity investment). The partnership targets both neurological diseases and the high-interest areas of weight management and muscle preservation ^[14]. The IGF1R platform is thus positioned to evolve from a CNS-focused entry point into a versatile “master key” for systemic metabolic diseases such as obesity and sarcopenia.

Although Sanofi recently deprioritized the Grabody-B-based Parkinson’s candidate ABL301 (SAR446159), this decision does not reflect a mechanistic failure. Reports indicate the move was made to ensure rigorous efficacy assessment; Sanofi is developing a dedicated α-synuclein detection assay and plans to optimize dosing via a Phase Ib study prior to Phase II. The adjustment leaves IGF1R’s potential advantages in age-related neurological diseases intact ^[15].

Table 2 . Key BD Transactions Validating the Grabody-B Platform ^[14-15].

4. Cyagen hIGF1R Humanized Mouse Models for BBB Shuttles and Preclinical Validation

Despite rapid progress in IGF1R-targeted therapeutics, sequence and conformational differences between human and mouse proteins often prevent accurate assessment of highly specific humanized antibodies or brain-shuttle molecules in wild-type mice. To accelerate translation of IGF1R-targeted therapies and macromolecular delivery platforms, Cyagen has developed multiple IGF1R humanized mouse models.

Key validation data are summarized below:

● hIGF1R mice (C57BL/6 background, product code: C001623)

Figure 4. Human and mouse IGF1R gene and protein expression across tissues in hIGF1R mice.

Note: Due to antibody cross-reactivity, mouse IGF1R protein (mIGF1R) is detectable in both humanized and control tissues.

● hIGF1R (BALB/c) mice (BALB/c background, product code: C001624)

Figure 5. Human and mouse IGF1R gene and protein expression across tissues in hIGF1R (BALB/c) mice.

Note: Due to antibody cross-reactivity, mouse IGF1R protein (mIGF1R) is detectable in both humanized and control tissues.

Translating IGF1R-targeted therapies from concept to clinical success requires robust, highly predictive in vivo tools. Cyagen empowers your preclinical pipeline with our fully validated hIGF1R humanized mouse models, which achieve stable expression of human IGF1R at both the gene and protein levels. This ensures precise human receptor binding for accurate antibody and siRNA conjugate screening.

Whether you are conducting pharmacodynamic evaluations of TED antagonistic antibodies or rigorously assessing IGF1R-based shuttle modules for brain and muscle delivery, these models provide high-clinical-translation-value data. They serve as ideal in vivo platforms for exploring targeted therapies across neurodegenerative diseases, autoimmune eye disorders, and muscle metabolic conditions.

Evaluating multiple transcytosis platforms? Leverage our unique dual-humanized hIGF1R/huTFRC models (Cat. No. C001985) to conduct rigorous side-by-side comparative efficacy and biodistribution studies. De-risk your CNS and muscle delivery programs with data you can trust, and stop letting species cross-reactivity delay your milestones.

References

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[2] Bailes J, et al. Insulin-Like Growth Factor-1 (IGF-1) and Its Monitoring in Medical Diagnostic and in Sports. Biomolecules. 2021.

[3] Werner H. The IGF1 Signaling Pathway: From Basic Concepts to Therapeutic Opportunities. Int J Mol Sci. 2023.

[4] Kim DW, et al. Transcriptomic profiling of thyroid eye disease orbital fat demonstrates differences in adipogenicity and IGF-1R pathway. JCI Insight. 2024.

[5] Cui X, et al. A review of TSHR- and IGF-1R-related pathogenesis and treatment of Graves' orbitopathy. Front Immunol. 2023.

[6] Wiersinga WM, et al. Thyroid eye disease (Graves' orbitopathy): clinical presentation, epidemiology, pathogenesis, and management. Lancet Diabetes Endocrinol. 2025.

[7] Girnita L, et al. It Takes Two to Tango: IGF-I and TSH Receptors in Thyroid Eye Disease. J Clin Endocrinol Metab. 2022.

[8] Sheff J, et al. Defining the epitope of a blood-brain barrier crossing single domain antibody specific for the type 1 insulin-like growth factor receptor. Sci Rep. 2021.

[9] Shin JW, et al. Grabody B, an IGF1 receptor-based shuttle, mediates efficient delivery of biologics across the blood-brain barrier. Cell Rep Methods. 2022.

[10] Costain WJ, et al. In vivo brain delivery of BBB-enabled iduronate 2-sulfatase in rats. Fluids Barriers CNS. 2025.

[11] Shugart J. TfR, no longer lone star? New shuttles use other keys to unlock brain. AlzForum. 2025.

[12] An S, et al. A brain-shuttled antibody targeting alpha synuclein aggregates for the treatment of synucleinopathies. NPJ Parkinsons Dis. 2025.

[13] Tian M, et al. Systemic and local delivery of siRNA to the CNS and periphery via anti-IGF1R antibody conjugation. bioRxiv. 2026.

[14] Kim J-h. ABL Bio seals $2.6 bil. Lilly brain-drug deal and $15m stake to back new cancer drugs. Korea Biomedical Review. 2025.

[15] Park H-j. ABL Bio's Parkinson's drug licensed to Sanofi deprioritized: What it means. Seoul Economic Daily. 2026.