Hemangioma Cell Models for Research

Hemangiomas are the most common benign tumors of infancy, affecting approximately 4-5% of infants, with a higher prevalence in premature infants (up to 23%) and females (3:1 ratio). Most lesions are cutaneous and self-limiting, but a subset can cause complications such as ulceration, bleeding, or visual/airway obstruction. The exact global incidence is not systematically tracked by WHO, but the condition is recognized as a significant pediatric health concern. NCI does not report survival statistics for benign hemangiomas, as they are not malignant; however, malignant transformation is extremely rare. The economic burden is mainly from diagnostic procedures and treatment of complicated cases, with propranolol as the first-line therapy.

Hemangiomas provide a unique model for studying angiogenesis, endothelial cell biology, and vascular development. The disease is characterized by distinct phases: proliferating, involuting, and involuted, offering a dynamic system to study cell proliferation and regression. Research questions include the role of stem cells, hypoxia signaling, and genetic mutations in endothelial cells. Public datasets such as GEO contain transcriptomic profiles of hemangioma tissues, but there is a lack of well-characterized cell lines, making gene-edited models essential for mechanistic studies.

Hemangioma pathogenesis involves dysregulated angiogenesis, driven by several key pathways:

1. VEGF/VEGFR2 signaling: Overexpression of vascular endothelial growth factor (VEGF) and its receptor VEGFR2 (KDR) promotes endothelial cell proliferation and migration.

2. HIF-1α hypoxia pathway: Hypoxia-inducible factor 1 alpha (HIF1A) is stabilized under low oxygen conditions, upregulating VEGF and other angiogenic factors.

3. PI3K/AKT/mTOR pathway: Activation of this pathway supports cell survival and proliferation, often downstream of VEGFR2.

4. Notch signaling: Modulates endothelial cell fate and vessel maturation.

These pathways are potential targets for therapeutic intervention.

Unlike malignant tumors, hemangiomas have few recurrent somatic mutations. However, studies have identified mutations in genes related to angiogenesis and endothelial function. The following table summarizes key alterations reported in the literature and databases (COSMIC, ClinVar):

Note: Frequencies are approximate and based on small cohort studies; TCGA does not include benign tumors.

The interplay of signaling networks in hemangioma includes:

• • VEGF/VEGFR2 axis: Key nodes include VEGFA, VEGFR2, and downstream PLCγ, PI3K, and MAPK.
• • Hypoxia response: HIF1A and HIF2A (EPAS1) regulate VEGF, GLUT1, and other genes.
• • PI3K/AKT/mTOR: PTEN, AKT1, MTOR, and downstream effectors like S6K1.
• • MAPK/ERK: RAS, RAF, MEK, ERK, promoting proliferation.
• • Notch pathway: NOTCH1, DLL4, and HEY1/2, involved in arterial-venous specification.

These networks are interconnected, and gene-edited models can help dissect their individual contributions.

Established hemangioma cell lines are scarce. Primary endothelial cells isolated from hemangioma tissues are used, but they have limited passage. Commercially available cell lines such as EOMA (murine hemangioendothelioma) are used as a surrogate. Organoid models derived from patient tissues or iPSCs are emerging as more physiologically relevant. The table below lists common cell models:

Organoids offer advantages: 3D architecture, cell-cell interactions, and long-term culture.

Animal models for hemangioma include:

• • PDX models: Patient-derived xenografts in immunodeficient mice, but limited due to benign nature and slow growth.
• • GEMMs: Genetically engineered mouse models with endothelial-specific activation of oncogenes (e.g., VEGFR2) or knockout of tumor suppressors.
• • Induced models: Chemical or viral induction of hemangioma-like lesions.
• • Chick embryo chorioallantoic membrane (CAM) assay: Used for angiogenesis studies.

These models are useful for studying pathogenesis and testing therapies.

CRISPR-based gene editing enables the creation of isogenic cell lines with precise mutations or knockouts in genes relevant to hemangioma, such as VEGFR2, HIF1A, PIK3CA, and TEK. These models are essential for functional studies and drug testing. For example, a VEGFR2 knockout in endothelial cells can be used to study the role of VEGF signaling in proliferation. Similarly, introducing a PIK3CA E545K mutation into a wild-type endothelial cell line can model the activated PI3K pathway. Commercially available, sequence-verified gene-edited cell lines accelerate research by providing consistent and reproducible models, but it is important to validate the genetic modification and phenotype.

Gene-edited cells allow systematic study of gene function. For example:

• • Knockout of VEGFR2 in endothelial cells reduces proliferation and migration, confirming its role.
• • Knock-in of PIK3CA E545K in endothelial cells activates AKT signaling, promoting survival.
• • CRISPR screens can identify genes that modulate hemangioma cell growth, such as those involved in hypoxia response.

These models help validate candidate genes from genomic studies.

Isogenic pairs (wild-type vs. mutant) are powerful for drug screening. For instance, a VEGFR2-mutant cell line can be used to test selective inhibitors, while a PIK3CA-mutant line can assess PI3K inhibitors. Resistance mechanisms can be modeled by exposing cells to increasing drug concentrations and identifying secondary mutations. Gene-edited cells also enable high-throughput screening for compounds that specifically target mutant proteins.

CRISPR-based synthetic lethality screens can identify vulnerabilities in hemangioma cells. For example, knocking out genes that are essential only in the presence of a specific mutation (e.g., PIK3CA) can reveal new therapeutic targets. Additionally, gene-edited cells can be used to discover biomarkers for disease progression or response to therapy, such as cell surface markers or secreted proteins.

The following databases provide valuable data for hemangioma research: