# EGFR (Epidermal Growth Factor Receptor): Kinase Domain Mutations, Exon 19 Deletions, and TKI Resistance
## Key Takeaways
- Activating mutations in the EGFR kinase domain, particularly exon 19 deletions (Del19) and the L858R point mutation in exon 21, are oncogenic drivers in non-small cell lung cancer (NSCLC), conferring sensitivity to tyrosine kinase inhibitors (TKIs).
- Acquired resistance to first- and second-generation EGFR TKIs is most commonly mediated by the T790M "gatekeeper" mutation in exon 20, which sterically hinders drug binding, while resistance to third-generation TKIs like osimertinib is often due to the C797S mutation that abrogates covalent inhibitor binding.
- EGFR signaling is a central node in multiple oncogenic pathways, including MAPK and PI3K/AKT, and its aberrant activation drives tumorigenesis in various cancers, including glioblastoma and colorectal cancer, through mechanisms like gene amplification and specific splice variants such as EGFRvIII.
- EGFR plays a critical role in host-pathogen interactions, serving as an entry point or signaling modulator for viruses like influenza and HCMV, and bacteria like *H. pylori*, and can promote immune evasion by upregulating PD-L1 expression.
- Targeted therapies for EGFR-mutant cancers include monoclonal antibodies (mAbs) blocking the extracellular domain and small-molecule TKIs inhibiting the intracellular kinase domain, with drug selection dictated by specific mutation profiles and resistance mechanisms.
---
## Executive Summary & Key Metadata
The Epidermal Growth Factor Receptor (EGFR) is a type I transmembrane receptor tyrosine kinase (RTK) that orchestrates fundamental cellular programs, including proliferation, survival, differentiation, and migration. As the founding member of the ErbB receptor family, EGFR (also known as ErbB1/HER1) transduces signals from a diverse set of extracellular ligands, most notably EGF and transforming growth factor-alpha (TGF-α). Its central role in human physiology is underscored by the severe developmental and epithelial defects observed in knockout models. Conversely, aberrant EGFR signaling—through gene amplification, overexpression, or somatic activating mutations—is a hallmark of numerous solid tumors, particularly non-small cell lung cancer (NSCLC), colorectal cancer, and glioblastoma. The clinical management of EGFR-driven cancers has been revolutionized by two classes of targeted therapeutics: monoclonal antibodies (mAbs) that block the extracellular ligand-binding domain, and small-molecule tyrosine kinase inhibitors (TKIs) that compete with ATP for binding to the intracellular kinase domain. However, the efficacy of these agents is universally constrained by the emergence of acquired resistance, most notably the EGFR T790M "gatekeeper" mutation and, more recently, the C797S mutation that abrogates covalent inhibitor binding. This manual provides a comprehensive, biophysically grounded reference for the genomic architecture, structural biology, signaling networks, pathogenic mutation spectrum, and pharmacogenomic landscape of EGFR.
| **Attribute** | **Detail** |
| :--- | :--- |
| **HGNC Symbol** | EGFR |
| **UniProt Accession** | P00533 |
| **Representative PDB ID** | 1M11 (EGFR extracellular domain with EGF) |
| **Chromosomal Locus** | 7p11.2 (GRCh38: chr7:55,019,017-55,211,628) |
| **Primary Molecular Function** | Receptor tyrosine kinase; ligand-activated signal transduction (MAPK, PI3K/AKT, JAK/STAT pathways) |
| **Disease & Pathology Associations** | Non-small cell lung cancer (NSCLC), colorectal cancer, glioblastoma, head and neck squamous cell carcinoma; germline mutations in inflammatory skin disorders |
---
## 1. Genomic Locus, Chromosomal Organization & Isoforms
### 1.1 Gene Coordinates and Structural Architecture
The human *EGFR* gene is located on the short arm of chromosome 7 at cytogenetic band 7p11.2. In the GRCh38 reference genome assembly, the gene spans approximately 192.6 kilobases (kb) of genomic DNA, from base pair 55,019,017 to 55,211,628 on the forward strand. The gene is organized into 28 exons, with the coding sequence (CDS) spanning exons 1 through 28. The intronic regions are notably large; for instance, intron 1 is over 100 kb in length and harbors critical regulatory elements.
The promoter region of *EGFR* is unusual in that it lacks a canonical TATA box. Instead, it is a GC-rich promoter containing multiple Sp1 (Specificity Protein 1) transcription factor binding sites. These Sp1 sites are essential for basal transcriptional activity. The promoter also contains binding sites for other transcription factors, including p53, which can transactivate *EGFR* expression in response to cellular stress, and AP-1 (Activator Protein-1) complexes, which mediate responses to growth factor signaling and phorbol esters. A well-characterized enhancer element is located within intron 1, which contains a polymorphic CA simple sequence repeat (CA-SSR). The length of this CA repeat inversely correlates with transcriptional activity; shorter repeats are associated with higher EGFR expression levels and have been linked to increased cancer risk in some populations.
### 1.2 Regulation of Gene Expression
The expression of *EGFR* is tightly controlled at multiple levels. The 5' untranslated region (UTR) is relatively short, but the 3' UTR is extensive and contains multiple AU-rich elements (AREs) that mediate mRNA instability. These AREs are recognized by RNA-binding proteins such as HuR (ELAVL1), which stabilizes the mRNA, and by factors like TTP (Tristetraprolin), which promote its degradation. MicroRNAs, including miR-7, miR-128, and miR-146a, also target the 3' UTR to suppress EGFR translation.
The EGFR protein itself is subject to complex post-translational regulation. Ligand binding induces receptor dimerization and autophosphorylation, which is followed by rapid internalization via clathrin-mediated endocytosis. The receptor is then either recycled back to the cell surface or targeted for lysosomal degradation. The E3 ubiquitin ligase Cbl (Casitas B-lineage Lymphoma) binds to phosphorylated EGFR and ubiquitinates it, tagging it for degradation. This endocytic sorting represents a major negative feedback loop that attenuates signal duration and intensity.
### 1.3 Alternative Splicing and Isoforms
Alternative splicing of the *EGFR* primary transcript generates several isoforms with distinct functional properties. The canonical, full-length isoform (isoform 1) is a 1,210-amino acid protein. A well-studied splice variant is **EGFRvIII** (also known as de2-7 EGFR or ΔEGFR), which results from an in-frame deletion of exons 2–7. This deletion removes a large portion of the extracellular ligand-binding domain, generating a constitutively active receptor that is unable to bind ligands. EGFRvIII is frequently expressed in glioblastoma and is associated with enhanced tumorigenicity and resistance to conventional therapies. It is not expressed in normal tissues, making it an attractive target for immunotherapy.
Other splice variants include a soluble isoform that lacks the transmembrane and intracellular domains, potentially acting as a dominant-negative decoy receptor, and a variant that retains intron 1, leading to a truncated protein. The regulation and functional significance of these minor isoforms remain areas of active investigation.
---
## 2. 3D Protein Domain Architecture & Structural Biology
### 2.1 Primary Structure and Domain Organization
The EGFR protein is a single-pass type I transmembrane glycoprotein of 1,210 amino acids (isoform 1). Its domain architecture is modular, comprising an extracellular region, a single hydrophobic transmembrane helix, and an intracellular region. The domain boundaries are defined by the UniProt annotation and structural studies:
- **Signal Peptide (aa 1–24):** Cleaved during translocation to the endoplasmic reticulum.
- **Extracellular Domain (ECD) (aa 25–645):** Comprises four subdomains (I–IV).
- **Transmembrane Domain (TMD) (aa 646–668):** A single α-helix that anchors the receptor to the plasma membrane.
- **Juxtamembrane Domain (JMD) (aa 669–712):** A flexible linker that plays a role in receptor dimerization and downregulation.
- **Kinase Domain (KD) (aa 713–979):** The catalytic tyrosine kinase domain.
- **C-terminal Tail (CT) (aa 980–1210):** Contains multiple tyrosine autophosphorylation sites and regulatory motifs.
### 2.2 Extracellular Domain (ECD) Architecture
The ECD is composed of four subdomains: two large homologous ligand-binding domains (I and III, also known as L1 and L2) and two cysteine-rich domains (II and IV, also known as CR1 and CR2). Domains I and III are β-helix solenoids that form the ligand-binding pocket. Domains II and IV are characterized by multiple disulfide-bonded modules. In the unliganded (inactive) state, the ECD adopts a "tethered" or "closed" conformation, where a dimerization arm in domain II is buried by intramolecular interactions with domain IV. Ligand binding to domains I and III induces a dramatic conformational change, swinging domain II outward and exposing the dimerization arm. This "extended" or "open" conformation is competent for receptor dimerization, where the exposed arm of one receptor inserts into a pocket on domain II of another receptor. This ligand-induced dimerization is the initiating event in EGFR activation.
### 2.3 Intracellular Kinase Domain
The intracellular kinase domain is a bilobal structure typical of protein kinases. The N-terminal lobe (N-lobe) is composed primarily of β-sheets and contains the conserved glycine-rich P-loop (GxGxxG motif) that anchors ATP. The C-terminal lobe (C-lobe) is predominantly α-helical and contains the catalytic loop (HRDLAARN) and the activation loop (A-loop). The A-loop is a critical regulatory element; in the inactive state, it adopts a conformation that blocks the substrate-binding site. Phosphorylation of specific tyrosine residues within the A-loop (e.g., Tyr845) stabilizes the active conformation.
The kinase domain is allosterically regulated by the juxtamembrane domain. The JMD forms a latch that stabilizes the inactive conformation of the kinase. Upon ligand-induced dimerization, the JMD of one monomer interacts with the C-lobe of the other monomer, releasing the latch and promoting an asymmetric dimer of the kinase domains. In this asymmetric dimer, one kinase domain (the "activator") allosterically activates the other (the "receiver") by inducing conformational changes that stabilize the active state. The receiver kinase then phosphorylates tyrosine residues in its own C-terminal tail.
### 2.4 C-terminal Tail and Autophosphorylation Sites
The C-terminal tail is intrinsically disordered but contains five major autophosphorylation sites: Tyr992, Tyr1068, Tyr1086, Tyr1148, and Tyr1173. These phosphotyrosine residues serve as docking sites for downstream signaling proteins containing Src Homology 2 (SH2) or Phosphotyrosine-binding (PTB) domains. For example, Tyr1068 is a docking site for the adaptor protein GRB2, while Tyr1148 and Tyr1173 are binding sites for the Shc adaptor protein. The tail also contains a conserved YXXΦ motif that mediates interaction with the clathrin adaptor AP-2, facilitating receptor endocytosis.
> **🔬 Interactive 3D Protein Visualizer**
>
> Explore the three-dimensional structure of the EGFR extracellular domain in complex with EGF. Load the structure into the interactive visualizer to inspect the ligand-binding pocket, the dimerization arm, and the domain architecture.
>
> [**Interactive 3D Protein Visualizer: Load EGFR (PDB: 1M11)**](/tools/protein-structure-viewer?source=direct&pdbId=1M11)
---
## 3. Cellular Signaling Pathways & Molecular Function
### 3.1 Ligand Binding and Receptor Activation
EGFR is activated by a family of at least seven ligands, including EGF, TGF-α, amphiregulin (AREG), betacellulin (BTC), epiregulin (EREG), heparin-binding EGF-like growth factor (HB-EGF), and epigen (EPGN). These ligands are synthesized as type I transmembrane precursors and are cleaved by metalloproteases, such as ADAM17 (TACE), to release soluble, active growth factors. Ligand binding induces a 1:1 stoichiometric complex, and the conformational change described in Section 2.2 promotes the formation of receptor dimers. EGFR can form homodimers or heterodimers with other ErbB family members (ErbB2/HER2, ErbB3/HER3, ErbB4/HER4). Heterodimerization with HER2 is particularly potent, as HER2 is a ligand-less co-receptor that is constitutively in an open conformation, ready to dimerize.
### 3.2 Downstream Signaling Cascades
Upon dimerization and autophosphorylation, the activated EGFR recruits a complex network of downstream effectors. The primary signaling pathways are:
1. **RAS/RAF/MEK/ERK (MAPK) Pathway:** The adaptor protein GRB2 binds directly to phospho-Tyr1068 or indirectly via Shc. GRB2 recruits the guanine nucleotide exchange factor SOS to the membrane, which activates RAS by promoting the exchange of GDP for GTP. Active RAS recruits RAF kinase, initiating a phosphorylation cascade (RAF → MEK → ERK). ERK translocates to the nucleus and phosphorylates transcription factors such as ELK1, MYC, and FOS, driving cell cycle progression and proliferation.
2. **PI3K/AKT/mTOR Pathway:** EGFR activates PI3K either directly (via the p85 regulatory subunit binding to phospho-Tyr) or indirectly through the adaptor protein GAB1. PI3K generates PIP3 at the plasma membrane, which recruits AKT via its PH domain. AKT is then phosphorylated and activated by PDK1 and mTORC2. Active AKT promotes cell survival by phosphorylating pro-apoptotic proteins like BAD and FOXO transcription factors, and it stimulates protein synthesis via mTORC1.
3. **JAK/STAT Pathway:** EGFR can directly phosphorylate and activate STAT transcription factors (particularly STAT1, STAT3, and STAT5), either directly or through JAK kinases. Activated STATs dimerize and translocate to the nucleus, where they regulate genes involved in cell survival, proliferation, and immune evasion.
4. **PLCγ/PKC Pathway:** Phospholipase C-γ (PLCγ) binds to phospho-Tyr992 and is phosphorylated by EGFR. Active PLCγ hydrolyzes PIP2 to generate diacylglycerol (DAG) and inositol trisphosphate (IP3). DAG activates Protein Kinase C (PKC), while IP3 triggers calcium release from the endoplasmic reticulum. This pathway modulates cell motility and secretion.
### 3.3 Regulatory Feedback Loops
EGFR signaling is subject to potent negative feedback regulation to prevent uncontrolled proliferation. Key mechanisms include:
- **Receptor Downregulation:** As described in Section 1.2, ligand-induced endocytosis and lysosomal degradation of the receptor is a primary mechanism of signal termination.
- **Dephosphorylation:** Protein tyrosine phosphatases (PTPs), such as PTPN1 (PTP1B) and PTPN6 (SHP-1), directly dephosphorylate EGFR and its substrates, attenuating signaling.
- **Induction of Negative Regulators:** ERK activation leads to the transcription of dual-specificity phosphatases (DUSPs) that inactivate ERK itself. Additionally, ERK phosphorylates SOS, promoting its dissociation from GRB2 and terminating RAS activation.
- **Sprouty Proteins:** The SPRY family of proteins is transcriptionally induced by EGFR signaling and acts as intracellular inhibitors of the RAS/MAPK pathway.
### 3.4 Protein-Protein Interaction Networks
The EGFR interactome is vast and dynamic. BioGRID lists over 500 physical interactions for human EGFR. Key interaction hubs include the adaptor proteins (GRB2, SHC1, GAB1), E3 ubiquitin ligases (CBL, NEDD4), phosphatases (PTPN1, PTPN6), and kinases (SRC, JAK2). The interaction with SRC is particularly important, as SRC can phosphorylate EGFR at non-canonical sites (e.g., Tyr845) and modulate its activity. STRING analysis reveals that EGFR is a central node in a network enriched for growth factor signaling, cell adhesion, and cytoskeletal remodeling.
---
## 4. Pathogenic Hotspot Mutations & Clinical Differentials
### 4.1 Somatic Mutations in Non-Small Cell Lung Cancer (NSCLC)
Activating somatic mutations in the EGFR kinase domain are found in approximately 15-20% of NSCLC patients in Western populations and up to 50% in East Asian populations. These mutations cluster in specific "hotspots" and confer sensitivity to first- and second-generation TKIs (gefitinib, erlotinib, afatinib, dacomitinib).
#### 4.1.1 Exon 19 Deletions (Del19)
In-frame deletions in exon 19 (spanning amino acids 746–750, most commonly delE746-A750) are the most frequent activating mutations, accounting for ~45-50% of all EGFR mutations. These deletions remove a conserved LREA motif within the N-lobe of the kinase domain. The deletion stabilizes the active conformation of the kinase by altering the positioning of the C-helix, leading to constitutive activation. Del19 mutations are strongly associated with a high objective response rate (ORR) to TKIs and improved progression-free survival (PFS) compared to patients with wild-type EGFR.
#### 4.1.2 Exon 21 Point Mutation (L858R)
The L858R missense mutation in exon 21 is the second most common activating mutation, accounting for ~40-45% of cases. This mutation is located in the activation loop (A-loop) of the kinase domain. The substitution of a leucine with a bulky arginine disrupts the hydrophobic interactions that stabilize the inactive conformation of the A-loop, shifting the equilibrium toward the active state. Like Del19, L858R confers sensitivity to TKIs.
#### 4.1.3 Other Sensitizing Mutations
Less common sensitizing mutations include G719X (exon 18), L861Q (exon 21), and S768I (exon 20). These are generally less common but still confer sensitivity to TKIs, albeit with slightly lower response rates.
### 4.2 Primary and Acquired Resistance Mutations
#### 4.2.1 T790M "Gatekeeper" Mutation
The T790M mutation (exon 20) is the most common mechanism of acquired resistance to first- and second-generation TKIs, occurring in ~50-60% of patients who progress on these agents. The threonine at position 790 is the "gatekeeper" residue, which controls access to a hydrophobic pocket at the back of the ATP-binding site. The substitution to a bulky methionine sterically hinders the binding of reversible TKIs like gefitinib and erlotinib. Importantly, T790M does not significantly alter the kinase's affinity for ATP, but it restores the kinase activity in the presence of the inhibitor. This mutation can also arise de novo (primary resistance) in a small percentage of untreated patients.
#### 4.2.2 C797S Mutation
The C797S mutation (exon 20) is the primary mechanism of resistance to third-generation TKIs (osimertinib, rociletinib). These drugs form an irreversible covalent bond with the cysteine residue at position 797 in the ATP-binding site. The C797S mutation abolishes this covalent bond, rendering the drugs ineffective. The clinical management of C797S-mediated resistance is challenging, particularly when it occurs in *cis* with the T790M mutation.
#### 4.2.3 Other Resistance Mechanisms
- **MET Amplification:** Amplification of the *MET* gene bypasses EGFR signaling by activating the PI3K/AKT pathway through the ERBB3 receptor.
- **HER2 Amplification:** Similar to MET, amplification of *ERBB2* (HER2) can drive signaling independent of EGFR.
- **PIK3CA Mutations:** Activating mutations in the p110α subunit of PI3K can activate the downstream pathway.
- **Histological Transformation:** Resistance can also occur through transformation of NSCLC to small cell lung cancer (SCLC) or through epithelial-to-mesenchymal transition (EMT).
### 4.3 Mutations in Other Cancers
- **Glioblastoma:** EGFR amplification and the EGFRvIII deletion mutant are hallmarks of primary glioblastoma. EGFRvIII is a constitutively active, ligand-independent receptor that drives aggressive tumor growth.
- **Colorectal Cancer:** EGFR is overexpressed in many colorectal cancers, and anti-EGFR mAbs (cetuximab, panitumumab) are used clinically. However, mutations in downstream effectors (e.g., *KRAS*, *NRAS*, *BRAF*) confer primary resistance to these agents.
- **Head and Neck Cancer:** EGFR overexpression is common and is targeted by cetuximab.
### 4.4 Germline Mutations
Germline loss-of-function mutations in EGFR are rare but have been associated with autosomal recessive inflammatory skin disorders, characterized by severe dermatitis, diarrhea, and failure to thrive, reflecting the essential role of EGFR in epithelial maintenance.
---
## 5. Host-Pathogen & Viral Interactions
EGFR is a critical host factor exploited by a variety of pathogens for entry, replication, and immune evasion.
### 5.1 Viral Interactions
- **Hepatitis C Virus (HCV):** The HCV core protein and NS5A protein have been shown to upregulate EGFR expression and activate its downstream signaling pathways. This activation promotes hepatocyte survival and proliferation, which is beneficial for viral replication and contributes to the development of hepatocellular carcinoma.
- **Influenza A Virus:** EGFR signaling is activated upon influenza virus infection. The virus exploits the EGFR-mediated endocytic pathway for entry. Furthermore, EGFR activation suppresses the host's innate immune response, particularly the type I interferon response, by downregulating IRF7 expression.
- **Human Cytomegalovirus (HCMV):** HCMV uses EGFR as a co-receptor for entry into fibroblasts and monocytes. Viral glycoprotein B (gB) binds to EGFR, triggering the PI3K/AKT pathway, which is required for efficient viral entry.
- **Epstein-Barr Virus (EBV):** The EBV latent membrane protein 1 (LMP1) can transactivate EGFR expression, promoting cell proliferation and contributing to the oncogenic potential of EBV in nasopharyngeal carcinoma.
- **Human Papillomavirus (HPV):** The HPV E5 oncoprotein interacts with EGFR and prevents its degradation, leading to enhanced EGFR signaling. This is thought to contribute to the proliferative phenotype of HPV-infected epithelial cells.
### 5.2 Bacterial Interactions
- ***Helicobacter pylori*:** The CagA oncoprotein of *H. pylori* is delivered into gastric epithelial cells and can activate EGFR signaling. This activation is implicated in the pathogenesis of gastric cancer.
- ***[Pseudomonas aeruginosa](/knowledge/bacteria/gram-negative/pseudomonas-aeruginosa-multidrug-resistance-biofilms)*:** This opportunistic pathogen can bind to EGFR on airway epithelial cells, triggering internalization and promoting bacterial invasion.
### 5.3 Immune Evasion
EGFR signaling can promote immune evasion in the tumor microenvironment. EGFR activation upregulates the expression of PD-L1 (CD274), the ligand for the PD-1 immune checkpoint, on tumor cells. This allows tumor cells to suppress the activity of cytotoxic T lymphocytes. This provides a mechanistic link between EGFR-driven oncogenesis and resistance to anti-tumor immunity.
---
## 6. [Pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles), Drug Targets & Small-Molecule Inhibitors
EGFR is one of the most successful drug targets in oncology. Therapeutics are broadly divided into two categories: monoclonal antibodies (mAbs) and small-molecule tyrosine kinase inhibitors (TKIs).
### 6.1 Monoclonal Antibodies (mAbs)
These agents target the extracellular domain of EGFR, preventing ligand binding and receptor dimerization.
- **Cetuximab (Erbitux):** A chimeric IgG1 mAb approved for the treatment of RAS wild-type metastatic colorectal cancer and head and neck squamous cell carcinoma.
- **Panitumumab (Vectibix):** A fully human IgG2 mAb approved for RAS wild-type metastatic colorectal cancer.
- **Necitumumab (Portrazza):** A human IgG1 mAb approved for metastatic squamous NSCLC in combination with chemotherapy.
- **Zalutumumab, Nimotuzumab, Matuzumab:** Investigational or regionally approved mAbs with similar mechanisms of action.
### 6.2 Small-Molecule Tyrosine Kinase Inhibitors (TKIs)
These agents compete with ATP for binding to the intracellular kinase domain.
#### 6.2.1 First-Generation (Reversible, ATP-Competitive)
- **Gefitinib (Iressa):** Approved for EGFR-mutant NSCLC.
- **Erlotinib (Tarceva):** Approved for EGFR-mutant NSCLC and pancreatic cancer.
#### 6.2.2 Second-Generation (Irreversible, Pan-ErbB)
- **Afatinib (Gilotrif):** An irreversible inhibitor that covalently binds to Cys797 and also inhibits HER2 and HER4. Approved for EGFR-mutant NSCLC.
- **Dacomitinib (Vizimpro):** An irreversible pan-ErbB inhibitor approved for EGFR-mutant NSCLC.
#### 6.2.3 Third-Generation (Irreversible, Mutant-Selective)
- **Osimertinib (Tagrisso):** An irreversible inhibitor that is highly selective for sensitizing mutations (Del19, L858R) and the T790M resistance mutation, while sparing wild-type EGFR. It is the standard first-line therapy for EGFR-mutant NSCLC.
- **Rociletinib (CO-1686), Olmutinib (HM61713):** Other third-generation inhibitors, though their clinical development has been less successful than osimertinib.
#### 6.2.4 Fourth-Generation (Investigational)
- **EAI045, JBJ-04-125-02, BLU-945, BBT-176:** These agents are designed to overcome the C797S resistance mutation. They often target the allosteric site of the kinase domain rather than the ATP-binding site.
### 6.3 Pharmacogenomic Considerations
The efficacy of EGFR TKIs is strictly dependent on the presence of activating mutations in the tumor. Therefore, molecular testing of the tumor (or circulating tumor DNA) for EGFR mutations is mandatory before initiating TKI therapy. The presence of the T790M mutation dictates the use of third-generation inhibitors. Conversely, the presence of *KRAS* or *NRAS* mutations in colorectal cancer predicts a lack of response to anti-EGFR mAbs.
### 6.4 Antibody-Drug Conjugates (ADCs)
- **Depatuxizumab mafodotin (Depatux-M):** An ADC targeting EGFRvIII, conjugated to the microtubule inhibitor monomethyl auristatin F (MMAF). It has been investigated in glioblastoma.
- **MRG003:** An ADC targeting EGFR, currently in clinical trials for solid tumors.
---
## 7. Bioinformatic Resources & Database Accessions
The following table provides the primary database accessions for the EGFR gene and protein.
| **Database** | **Identifier** | **Description** |
| :--- | :--- | :--- |
| **NCBI Gene** | 1956 | Gene-specific information, genomic context, and links to related data. |
| **Ensembl** | ENSG00000146648 | Genome annotation, transcripts, and comparative genomics. |
| **UniProt** | P00533 | Protein sequence, function, post-translational modifications, and domain structures. |
| **RCSB PDB** | 1M11 | Experimentally determined 3D structures (extracellular domain). Other structures: 1NQL, 2GS6, 2GS7, 3W2S, 4HJO, 6JXK. |
| **ClinVar** | (Various) | Curated records of human genetic variants and their clinical significance. |
| **COSMIC** | EGFR | Catalogue of Somatic Mutations in Cancer; curated data on somatic mutations. |
| **STRING** | 9606.ENSP00000275493 | Protein-protein interaction networks. |
| **BioGRID** | 108338 | Curated protein and genetic interactions. |
| **Gene Ontology (GO)** | GO:0004713 (protein tyrosine kinase activity), GO:0007165 (signal transduction), GO:0016021 (integral component of membrane) | Standardized terms for molecular function, biological process, and cellular component. |
| **PharmGKB** | PA27487 | Pharmacogenomic knowledge base with dosing guidelines and drug pathways. |
| **Reactome** | R-HSA-177929 (Signaling by EGFR) | Curated pathway database. |
| **KEGG** | hsa:1956 | Pathway maps (e.g., ErbB signaling pathway, hsa04012). |
---
## 8. Mermaid Diagram: EGFR Signaling and Resistance
The following Mermaid flowchart illustrates the core signaling pathways and the points of therapeutic intervention and resistance.
```mermaid
flowchart TD
A["Ligand (EGF/TGF-α)"] --> B("EGFR Extracellular Domain")
B --> C{"Conformational Change"}
C --> D["Receptor Dimerization"]
D --> E["Kinase Domain Activation"]
E --> F["Autophosphorylation of C-tail"]
F --> G["Recruitment of Adaptors GRB2/SHC"]
G --> H["RAS Activation"]
H --> I["RAF/MEK/ERK Cascade"]
I --> J["Cell Proliferation & Survival"]
F --> K["Recruitment of PI3K"]
K --> L["PIP3 Generation"]
L --> M["AKT Activation"]
M --> N["Cell Survival & Metabolism"]
E --> O{"Inhibitor Action"}
O --> P["1st/2nd Gen TKIs
Gefitinib, Erlotinib, Afatinib"]
O --> Q["3rd Gen TKIs
Osimertinib"]
O --> R["Monoclonal Antibodies
Cetuximab, Panitumumab"]
P --> S["ATP-binding site blockade"]
Q --> T["Covalent binding to Cys797"]
S --> U{"Resistance Mechanism"}
U --> V["T790M Gatekeeper Mutation"]
U --> W["C797S Mutation"]
U --> X["MET/HER2 Amplification"]
T --> W
V --> Y["Loss of 1st/2nd Gen TKI efficacy"]
W --> Z["Loss of 3rd Gen TKI efficacy"]
```
---
## Related Clinical & Scientific Guides
* [PIK3CA (PI3K Alpha): Helical and Kinase Domain Hotspot Mutations and Isoform-Specific Inhibition](/knowledge/bioinformatics/genes/cancer-genomics/pik3ca-gene-structure-function-pathway)
* [ENTPD5 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/entpd5-gene-structure-function-pathway)
* [PDGFB Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/pdgfb-gene-structure-function-pathway)
## References
The following references provide the foundational and contemporary literature on EGFR biology, structure, and clinical targeting. Citations in the text are indicated by bracketed numbers.
1. **Ullrich, A., Coussens, L., Hayflick, J. S., et al. (1984).** Human epidermal growth factor receptor cDNA sequence and aberrant expression of the amplified gene in A431 epidermoid carcinoma cells. *Nature*, 309(5967), 418–425. [https://doi.org/10.1038/309418a0](https://doi.org/10.1038/309418a0)
2. **Ogiso, H., Ishitani, R., Nureki, O., et al. (2002).** Crystal structure of the complex of human epidermal growth factor and receptor extracellular domains. *Cell*, 110(6), 775–787. [https://doi.org/10.1016/S0092-8674(02)00963-7](https://doi.org/10.1016/S0092-8674(02)00963-7) *(PDB: 1IVO, related to 1M11)*
3. **Zhang, X., Gureasko, J., Shen, K., Cole, P. A., & Kuriyan, J. (2006).** An allosteric mechanism for activation of the kinase domain of epidermal growth factor receptor. *Cell*, 125(6), 1137–1149. [https://doi.org/10.1016/j.cell.2006.05.013](https://doi.org/10.1016/j.cell.2006.05.013)
4. **Lynch, T. J., Bell, D. W., Sordella, R., et al. (2004).** Activating mutations in the epidermal growth factor receptor underlying responsiveness of non-small-cell lung cancer to gefitinib. *New England Journal of Medicine*, 350(21), 2129–2139. [https://doi.org/10.1056/NEJMoa040938](https://doi.org/10.1056/NEJMoa040938)
5. **Paez, J. G., Jänne, P. A., Lee, J. C., et al. (2004).** EGFR mutations in lung cancer: correlation with clinical response to gefitinib therapy. *Science*, 304(5676), 1497–1500. [https://doi.org/10.1126/science.1099314](https://doi.org/10.1126/science.1099314)
6. **Kobayashi, S., Boggon, T. J., Dayaram, T., et al. (2005).** EGFR mutation and resistance of non-small-cell lung cancer to gefitinib. *New England Journal of Medicine*, 352(8), 786–792. [https://doi.org/10.1056/NEJMoa044238](https://doi.org/10.1056/NEJMoa044238)
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