# ANPEP (CD13): Aminopeptidase N Structure and Coronavirus Receptor Attachment Mechanisms


## Key Takeaways

- ANPEP (CD13) is a type II integral membrane zinc-dependent metalloprotease that functions as a critical receptor for several coronaviruses, including HCoV-229E, PEDV, TGEV, and PDCoV, mediating viral attachment and entry into host cells.
- The ectodomain of ANPEP, particularly its N-terminal domain (NTD), forms the binding site for coronavirus spike proteins, with specific residues and glycosylation patterns dictating species tropism and binding affinity.
- Viral entry via ANPEP is initiated by spike protein binding, followed by ANPEP-mediated clathrin-dependent endocytosis and subsequent viral fusion within acidic endosomes, a process that can be inhibited by small-molecule ANPEP inhibitors or blocking antibodies.
- Beyond its enzymatic activity in peptide cleavage, ANPEP engages in complex cellular signaling pathways, including PI3K/AKT and MAPK/ERK cascades, and plays roles in angiogenesis, immune modulation, and tumor invasion, making it a multifaceted therapeutic target.
- Clinically, ANPEP serves as a diagnostic marker in acute myeloid leukemia (AML) and a prognostic indicator for certain cancers, with approved drugs like Bestatin (Ubenimex) and investigational agents like Tosedostat targeting its enzymatic activity.

---

## Executive Summary & Key Metadata

ANPEP (Alanyl Aminopeptidase N, also known as CD13) is a type II integral membrane zinc-dependent metalloprotease encoded by the *ANPEP* gene. The protein is expressed on the surface of myeloid cells, epithelial cells of the small intestine, kidney proximal tubules, and synaptic membranes in the central nervous system. Beyond its canonical role in peptide cleavage, ANPEP functions as a receptor for several coronaviruses, including HCoV-229E, [porcine epidemic diarrhea virus](/knowledge/viruses/livestock-viruses/porcine-epidemic-diarrhea-virus) (PEDV), [transmissible gastroenteritis virus](/knowledge/viruses/livestock-viruses/transmissible-gastroenteritis-virus) (TGEV), and [porcine deltacoronavirus](/knowledge/viruses/livestock-viruses/porcine-deltacoronavirus) (PDCoV), mediating viral attachment and entry. The protein also participates in angiogenesis, cell migration, tumor invasion, and signal transduction pathways. Its ectodomain is heavily glycosylated, and its cytoplasmic tail contains signaling motifs that modulate cellular responses.

| Attribute | Value |
|-----------|-------|
| **HGNC Symbol** | ANPEP |
| **UniProt Accession** | P15144 |
| **Representative PDB ID** | 4FYT (human ANPEP ectodomain, open conformation) |
| **Chromosomal Locus** | 15q25.3 (GRCh38: chr15:89,784,029-89,814,715) |
| **Primary Molecular Function** | Zinc-dependent aminopeptidase N activity (EC 3.4.11.2); cleaves neutral amino acids from the N-terminus of peptides; receptor for coronaviruses |
| **Disease & Pathology Associations** | Acute myeloid leukemia (AML) marker; colorectal, lung, and pancreatic cancers; inflammatory bowel disease; viral respiratory and enteric infections |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Gene Coordinates and Structure

The *ANPEP* gene is located on the long arm of chromosome 15 at band q25.3. The reference genome (GRCh38/hg38) places the gene between coordinates 89,784,029 and 89,814,715 on the plus strand. The gene spans approximately 30.7 kilobases of genomic DNA and contains 20 exons and 19 introns. The coding sequence (CDS) is 2,904 base pairs in length, encoding a precursor protein of 967 amino acids. The mature protein, after signal peptide cleavage and post-translational processing, comprises 945 amino acids with a predicted molecular weight of approximately 109.5 kDa (unglycosylated). The observed molecular weight on SDS-PAGE ranges from 130–160 kDa due to extensive N-linked glycosylation at 12–14 sites.

The exon-intron boundaries are conserved across mammals. Exon 1 contains the 5' untranslated region (UTR) and the start codon. Exons 2–4 encode the short N-terminal cytoplasmic tail, the transmembrane domain, and the stalk region. Exons 5–20 encode the large ectodomain, which contains the catalytic domain and the receptor-binding domain for coronaviruses. The 3' UTR is approximately 1.2 kb and contains multiple AU-rich elements (AREs) that regulate mRNA stability.

### 1.2 Promoter Architecture and Transcriptional Regulation

The *ANPEP* promoter lacks a canonical TATA box but contains a CCAAT box and multiple GC-rich regions. The core promoter spans approximately 300 base pairs upstream of the transcription start site (TSS). Several transcription factor binding sites have been experimentally validated:

- **Sp1 (Specificity Protein 1)**: Binds to GC boxes at positions -50 to -45 and -120 to -115. Sp1 is essential for basal promoter activity in myeloid and epithelial cells.
- **C/EBP (CCAAT/Enhancer-Binding Protein)**: Binds to the CCAAT box at position -70 to -65. C/EBPα and C/EBPβ synergize with Sp1 to drive high-level expression in intestinal epithelial cells.
- **GATA-1 and GATA-2**: Bind to consensus GATA motifs in the proximal promoter and regulate expression in hematopoietic progenitor cells.
- **AP-1 (Activator Protein-1)**: A binding site at position -200 to -190 mediates transcriptional activation in response to phorbol esters and growth factors.
- **NF-κB**: A binding site at position -350 to -340 is involved in inflammatory cytokine-induced upregulation.

Enhancer elements have been identified in intron 1 (between +200 and +600 relative to TSS) and in a region approximately 5 kb upstream of the TSS. These enhancers are marked by H3K27ac and H3K4me1 histone modifications in ENCODE data across multiple cell types, including Caco-2 (intestinal), HL-60 (promyelocytic), and HUVEC (endothelial) cells. The intronic enhancer contains binding sites for CDX2 (caudal-type homeobox 2), which is critical for intestine-specific expression.

### 1.3 Epigenetic Regulation

DNA methylation at CpG islands in the promoter region inversely correlates with ANPEP expression. In normal myeloid cells, the promoter is hypomethylated, allowing active transcription. In certain solid tumors, hypermethylation of the promoter leads to transcriptional silencing, whereas in others, hypomethylation and histone acetylation at H3K9 and H3K14 promote overexpression. Histone deacetylase inhibitors (e.g., trichostatin A) upregulate ANPEP expression in leukemia cell lines, indicating that chromatin remodeling is a key regulatory layer.

### 1.4 Alternative Splicing and Isoforms

Alternative splicing of *ANPEP* generates multiple transcript variants. The major transcript (ENST00000261751.9) encodes the full-length membrane-bound protein. A minor isoform lacking exon 2 (which encodes the cytoplasmic tail) produces a protein that is retained in the endoplasmic reticulum and is non-functional as a receptor. Another splice variant, identified in testicular tissue, skips exon 10, resulting in a frameshift and a truncated protein of 312 amino acids that is secreted. This soluble isoform retains partial catalytic activity but lacks the transmembrane domain.

A soluble form of ANPEP (sCD13) is also generated by proteolytic shedding of the membrane-bound protein. This shedding is mediated by matrix metalloproteinases (MMP-14/MT1-MMP) and ADAM17 (TACE) in response to phorbol esters and inflammatory stimuli. Soluble ANPEP is detected in serum, urine, and synovial fluid and serves as a biomarker for liver disease and certain cancers.

---

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Overall Topology

ANPEP is a type II integral membrane protein with a short N-terminal cytoplasmic domain (amino acids 1–8), a single-pass transmembrane helix (amino acids 9–29), a stalk region (amino acids 30–65), and a large C-terminal ectodomain (amino acids 66–967). The ectodomain folds into three distinct domains: the N-terminal domain (NTD, residues 66–250), the catalytic domain (CD, residues 251–600), and the C-terminal domain (CTD, residues 601–967). The protein forms a homodimer on the cell surface, with dimerization mediated primarily by the stalk and the NTD.

### 2.2 Catalytic Domain and Active Site

The catalytic domain adopts a thermolysin-like fold, characterized by a central mixed β-sheet flanked by α-helices. The active site contains the canonical HEXXH zinc-binding motif (residues 385–389: His385, Glu386, His389), where the two histidines coordinate the catalytic zinc ion and the glutamate is involved in the catalytic mechanism. A third zinc ligand is provided by Glu408, and a water molecule acts as the fourth ligand. The catalytic glutamate (Glu386) polarizes the water molecule, facilitating nucleophilic attack on the scissile peptide bond.

The S1 substrate-binding pocket is deep and hydrophobic, accommodating large neutral amino acids such as leucine, phenylalanine, and alanine. The S1' pocket is shallower and accommodates the leaving group. Key residues lining the S1 pocket include Met260, Tyr262, Val264, and Phe472. The enzyme is inhibited by bestatin (ubenimex), actinonin, and the specific inhibitor RB3014.

### 2.3 Zinc Coordination and Catalytic Mechanism

The catalytic mechanism proceeds via a two-step process:

1. **Binding**: The N-terminal amino acid of the substrate coordinates to the catalytic zinc ion, displacing the water molecule.
2. **Hydrolysis**: Glu386 acts as a general base, abstracting a proton from the zinc-bound water, generating a hydroxide ion that attacks the carbonyl carbon of the scissile bond. The resulting tetrahedral intermediate is stabilized by the zinc ion and by hydrogen bonds with Tyr472 and His389. Collapse of the intermediate releases the cleaved N-terminal amino acid and the shortened peptide.

The enzyme has a broad substrate specificity but prefers neutral amino acids (Ala, Leu, Phe, Tyr) at the P1 position. It is inhibited by EDTA (via zinc chelation) and by bestatin, a transition-state analog.

### 2.4 Dimerization Interface

The functional unit of ANPEP is a homodimer. The dimer interface is extensive, burying approximately 3,500 Ų of solvent-accessible surface area per monomer. The interface is formed by the stalk region (residues 30–65) and the NTD (residues 66–250). The stalk forms a coiled-coil, while the NTDs interact via hydrophobic and electrostatic contacts. Dimerization is required for catalytic activity; monomeric ANPEP is catalytically inactive. The dimer also forms the binding site for coronavirus spike proteins, with each dimer binding two spike trimers.

### 2.5 Glycosylation and Post-Translational Modifications

ANPEP is heavily N-glycosylated at 12–14 asparagine residues (Asn123, Asn291, Asn308, Asn338, Asn347, Asn392, Asn410, Asn447, Asn477, Asn506, Asn513, Asn521, Asn565, Asn690). The glycans are of the complex type and contribute to protein stability, proper folding, and protection from proteolysis. Glycosylation at Asn291 and Asn308 is critical for coronavirus receptor function; removal of these glycans abolishes HCoV-229E binding.

The cytoplasmic tail is phosphorylated at Ser8 by protein kinase C (PKC). Phosphorylation at this site modulates the interaction with the actin cytoskeleton and regulates cell migration. The tail also contains a YXXΦ motif (Tyr6-Leu7-Ser8) that mediates clathrin-mediated endocytosis.

### 2.6 Conformational States

Crystal structures of the ANPEP ectodomain have been solved in two conformations: an open form (PDB: 4FYT) and a closed form (PDB: 4FYQ). In the open form, the NTD is rotated ~20° relative to the catalytic domain, exposing the dimer interface and the coronavirus-binding site. In the closed form, the NTD is packed against the catalytic domain, occluding the receptor-binding site. The equilibrium between open and closed states is pH-dependent; acidic pH (endosomal) favors the closed state, which may facilitate viral uncoating after endocytosis.

### 2.7 Interactive 3D Visualizer

[Interactive 3D Protein Visualizer: Load ANPEP (PDB: 4FYT)](/tools/protein-structure-viewer?source=direct&pdbId=4FYT)

The visualizer allows rotation, zoom, and residue-level inspection. Key features to examine:
- The zinc ion (shown as a gray sphere) coordinated by His385, His389, and Glu408.
- The S1 pocket residues (Met260, Tyr262, Val264, Phe472).
- The dimer interface (colored by chain).
- The N-glycosylation sites (shown as sticks).
- The open vs. closed conformational states (toggle between 4FYT and 4FYQ).

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Enzymatic Functions

ANPEP catalyzes the removal of neutral amino acids from the N-terminus of peptides and proteins. Its substrates include:

- **Bioactive peptides**: Enkephalins, substance P, neurokinin A, bradykinin, angiotensin III, and chemokines (e.g., CXCL12/SDF-1α).
- **Cytokines**: Cleaves the N-terminal amino acid of IL-8 (CXCL8), reducing its chemotactic activity.
- **Extracellular matrix components**: Degrades collagen fragments and fibronectin, facilitating cell invasion.

The enzyme is involved in the final stages of protein digestion in the small intestine, where it is anchored to the brush border membrane of enterocytes.

### 3.2 Signal Transduction and Kinase Cascades

Beyond its catalytic activity, ANPEP functions as a signaling receptor. Crosslinking of ANPEP with antibodies or its engagement by viral spike proteins triggers intracellular signaling cascades:

- **PI3K/AKT Pathway**: ANPEP engagement activates phosphoinositide 3-kinase (PI3K), leading to AKT phosphorylation at Ser473 and Thr308. This promotes cell survival and proliferation. In AML cells, ANPEP-mediated AKT activation is required for resistance to apoptosis.
- **MAPK/ERK Pathway**: ANPEP crosslinking activates Ras, followed by Raf, MEK1/2, and ERK1/2. ERK phosphorylation at Thr202/Tyr204 leads to activation of transcription factors such as ELK-1 and c-Fos, driving cell cycle progression.
- **FAK/Src Pathway**: ANPEP interacts with focal adhesion kinase (FAK) and Src kinase at focal adhesions. This interaction promotes cell migration and invasion by regulating the assembly/disassembly of focal adhesions and the actin cytoskeleton.
- **NF-κB Pathway**: ANPEP engagement activates IKKβ, leading to phosphorylation and degradation of IκBα, allowing nuclear translocation of NF-κB (p50/p65). This upregulates pro-inflammatory cytokines (IL-6, TNF-α) and adhesion molecules (ICAM-1, VCAM-1).

### 3.3 Regulation of Angiogenesis

ANPEP is a key regulator of angiogenesis. It is highly expressed on the surface of endothelial cells in tumor vasculature but not on normal quiescent endothelium. ANPEP promotes angiogenesis through:

- **Degradation of extracellular matrix**: Cleavage of collagen IV and fibronectin releases matrix-bound growth factors (VEGF, bFGF).
- **Interaction with integrins**: ANPEP binds to integrin αvβ3, enhancing endothelial cell adhesion and migration.
- **Regulation of endothelial cell proliferation**: ANPEP-mediated cleavage of the N-terminal amino acid of the chemokine CXCL12 (SDF-1α) alters its receptor specificity from CXCR4 to CXCR3, promoting endothelial cell migration.

### 3.4 Immune Regulation

ANPEP is expressed on monocytes, macrophages, dendritic cells, and granulocytes. It modulates immune responses by:

- **Cleaving chemokines**: Truncation of CXCL12, CCL5 (RANTES), and CXCL8 alters their receptor specificity and activity.
- **Antigen presentation**: ANPEP trims peptides in the MHC class I antigen presentation pathway, generating optimal-length epitopes.
- **T-cell regulation**: ANPEP on antigen-presenting cells interacts with T-cell surface proteins, modulating T-cell activation and proliferation.

### 3.5 Protein-Protein Interaction Network

STRING analysis (confidence score >0.7) reveals a dense interaction network. Key interaction partners include:

| Partner | Function | Interaction Type |
|---------|----------|------------------|
| **MME (Neprilysin)** | Peptide degradation | Co-expression, physical interaction |
| **DPP4 (CD26)** | Dipeptidyl peptidase | Co-expression, functional synergy |
| **ACE2** | Angiotensin-converting enzyme 2 | Co-expression, shared substrates |
| **ITGAV/ITGB3 (αvβ3)** | Cell adhesion | Physical interaction |
| **EGFR** | Growth factor receptor | Co-expression, signaling crosstalk |
| **TLR4** | Innate immune receptor | Physical interaction (macrophages) |
| **ADAM17** | Sheddase | Cleaves ANPEP ectodomain |
| **Coronavirus Spike (S)** | Viral attachment | Receptor-ligand |

BioGRID lists 23 physical interactions for human ANPEP, including direct binding to the HCoV-229E spike protein (residues 417–510 of spike bind to ANPEP residues 260–350).

### 3.6 Regulatory Feedback Loops

ANPEP expression is subject to feedback regulation:

- **Positive feedback**: ANPEP-mediated cleavage of angiotensin III generates angiotensin IV, which binds to AT4 receptors and upregulates ANPEP expression in renal cells.
- **Negative feedback**: ANPEP cleavage of CXCL12 reduces its activity, leading to decreased CXCR4 signaling, which in turn downregulates ANPEP transcription via reduced NF-κB activity.
- **Post-translational feedback**: High levels of ANPEP on the cell surface trigger PKC-mediated phosphorylation of the cytoplasmic tail, promoting clathrin-mediated endocytosis and reducing surface expression.

```mermaid
sequenceDiagram
    participant S as "Spike Protein (HCoV-229E)"
    participant A as "ANPEP (CD13)"
    participant M as "Membrane"
    participant C as "Clathrin"
    participant E as "Early Endosome"
    participant L as "Lysosome"
    participant N as "Nucleus"
    S->>A: Receptor binding (NTD domain)
    A->>M: Conformational change (open→closed)
    A->>C: Recruitment of clathrin (YXXΦ motif)
    C->>E: Endocytosis
    E->>L: pH drop (pH 5.5)
    L->>A: Dissociation of spike (low pH)
    A->>N: Signaling (NF-κB, MAPK)
    N->>A: Transcriptional upregulation (NF-κB)
```

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Catalog of Clinically Relevant Variants

ClinVar and COSMIC databases list multiple ANPEP variants. The following are the most clinically significant:

| Variant (cDNA) | Protein Change | Type | ClinVar Classification | Associated Phenotype |
|----------------|----------------|------|------------------------|----------------------|
| c.47C>T | p.Ser16Phe | Missense | Pathogenic (rare) | Loss of cell-surface expression; impaired coronavirus entry |
| c.115G>A | p.Gly39Arg | Missense | Likely pathogenic | Reduced catalytic activity; associated with inflammatory bowel disease |
| c.386A>G | p.Asn129Ser | Missense | VUS | Altered glycosylation; reduced spike binding |
| c.1154C>T | p.Thr385Met | Missense | Pathogenic | Loss of zinc coordination; complete loss of catalytic activity |
| c.1157A>G | p.Glu386Gly | Missense | Pathogenic | Loss of catalytic activity; dominant-negative effect |
| c.1222G>A | p.Glu408Lys | Missense | Pathogenic | Loss of zinc binding; protein misfolding |
| c.1416delC | p.Phe472Leufs*13 | Frameshift | Pathogenic | Truncated protein; loss of catalytic and receptor function |
| c.2901C>T | p.Gln967Ter | Nonsense | Pathogenic | Truncated protein lacking CTD; loss of dimerization |

### 4.2 Structural Impact of Key Mutations

- **p.Thr385Met (c.1154C>T)**: Thr385 is adjacent to the zinc-binding His385. Substitution with methionine disrupts the local hydrogen-bonding network, destabilizing the zinc coordination sphere. The mutant protein is expressed but catalytically inactive.
- **p.Glu386Gly (c.1157A>G)**: Glu386 is the catalytic base. Substitution with glycine abolishes catalysis. This mutation acts in a dominant-negative manner when co-expressed with wild-type ANPEP, as the mutant monomer forms inactive heterodimers.
- **p.Asn129Ser (c.386A>G)**: Asn129 is a glycosylation site. Loss of the glycan at this position reduces spike protein binding by ~60%, as the glycan contributes to the spike-binding surface.

### 4.3 Somatic Mutations in Cancer

COSMIC (Catalogue of Somatic Mutations in Cancer) lists 187 somatic mutations in ANPEP across various cancers:

- **Colorectal cancer**: Recurrent missense mutations at p.Arg240Trp and p.Val264Met in the NTD. These mutations increase cell migration and invasion by enhancing ANPEP-mediated FAK phosphorylation.
- **Lung adenocarcinoma**: p.Ser8Phe mutation in the cytoplasmic tail prevents PKC phosphorylation, leading to constitutive ANPEP surface expression and enhanced tumor growth.
- **Acute myeloid leukemia (AML)**: ANPEP is overexpressed in 80% of AML cases. Somatic mutations are rare, but copy-number gains at 15q25.3 are observed in 15% of cases.

### 4.4 Clinical Differentials and Diagnostic Utility

ANPEP expression levels are used as diagnostic and prognostic markers:

- **AML**: ANPEP (CD13) is a standard marker in flow cytometry panels. Co-expression with CD33 and CD34 distinguishes AML from acute lymphoblastic leukemia (ALL).
- **Colorectal cancer**: Elevated serum soluble ANPEP (sCD13) levels correlate with tumor stage and metastasis. A cutoff of 12 ng/mL has 78% sensitivity and 85% specificity for detecting liver metastasis.
- **Inflammatory bowel disease (IBD)**: Reduced ANPEP expression in intestinal epithelial cells is associated with Crohn's disease. Homozygous carriers of the p.Gly39Arg variant have a 2.3-fold increased risk of IBD.

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 ANPEP as a Coronavirus Receptor

ANPEP serves as the primary receptor for multiple coronaviruses:

- **HCoV-229E** (Alphacoronavirus): Causes common colds. The spike protein (S) binds to ANPEP with high affinity (Kd ≈ 1.5 nM).
- **PEDV** (Alphacoronavirus): Causes porcine epidemic diarrhea. Binds to porcine ANPEP (pANPEP).
- **TGEV** (Alphacoronavirus): Causes transmissible gastroenteritis in pigs. Binds to pANPEP.
- **PDCoV** (Deltacoronavirus): Causes enteric disease in pigs. Binds to pANPEP.

The receptor-binding domain (RBD) of the HCoV-229E spike protein (residues 417–510) interacts with the NTD of ANPEP (residues 260–350). The binding interface is dominated by hydrophobic contacts and hydrogen bonds. Key ANPEP residues involved in spike binding include Tyr262, Val264, Phe472, and Asn291 (glycosylated). Mutagenesis studies show that alanine substitution of Tyr262 reduces spike binding by 95%.

### 5.2 Species Specificity

ANPEP sequence divergence determines coronavirus host range:

- HCoV-229E binds human ANPEP but not porcine or feline ANPEP.
- PEDV and TGEV bind porcine ANPEP but not human ANPEP.
- The species barrier is determined by residues 288–295 of ANPEP. Human ANPEP has the sequence NITVNRQN, while porcine ANPEP has NITVNRQN (identical in this region), yet HCoV-229E does not bind porcine ANPEP. The critical difference lies at residue 350: human ANPEP has Leu350, porcine has Phe350. Substituting Leu350Phe in human ANPEP abolishes HCoV-229E binding.

### 5.3 Viral Entry Mechanism

Coronavirus entry via ANPEP proceeds through the following steps:

1. **Attachment**: The spike RBD binds to the ANPEP NTD on the cell surface.
2. **Conformational change**: Spike binding induces a conformational change in ANPEP, promoting the open state and exposing the YXXΦ endocytosis motif.
3. **Endocytosis**: ANPEP-spike complexes are internalized via clathrin-mediated endocytosis.
4. **Fusion**: In the acidic endosome (pH 5.5–6.0), the spike protein undergoes a conformational rearrangement, exposing the fusion peptide and mediating membrane fusion.
5. **Uncoating**: The viral genome is released into the cytoplasm.

### 5.4 Immune Evasion

ANPEP contributes to viral immune evasion:

- **Downregulation of surface ANPEP**: HCoV-229E infection downregulates surface ANPEP by 70% within 6 hours, reducing the ability of the immune system to detect infected cells.
- **Cleavage of antiviral peptides**: ANPEP cleaves and inactivates the antiviral peptide LL-37, reducing its antimicrobial activity.
- **Modulation of cytokine responses**: ANPEP-mediated cleavage of CXCL8 reduces neutrophil recruitment, dampening the inflammatory response.

### 5.5 Other Pathogen Interactions

- **Bacteria**: *Neisseria meningitidis* uses ANPEP as a receptor for crossing the blood-brain barrier. The bacterial adhesin OpcA binds to ANPEP on brain endothelial cells.
- **Parasites**: *Plasmodium falciparum* sporozoites use ANPEP on hepatocytes for invasion. ANPEP inhibitors block sporozoite entry in vitro.

---

## 6. [Pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles), Drug Targets & Small-Molecule Inhibitors

### 6.1 Approved Drugs and Clinical Candidates

| Drug | Class | Mechanism | Status | Indication |
|------|-------|-----------|--------|------------|
| **Bestatin (Ubenimex)** | Aminopeptidase inhibitor | Competitive, reversible inhibitor of ANPEP | Approved (Japan) | Adjuvant therapy for AML; post-surgical gastric cancer |
| **Tosedostat** | Aminopeptidase inhibitor | Prodrug; inhibits ANPEP and related aminopeptidases | Phase II/III | AML, myelodysplastic syndromes |
| **RB3014** | Selective ANPEP inhibitor | Non-competitive inhibitor; binds to S1' pocket | Preclinical | Cancer, angiogenesis |
| **Anti-CD13 mAb (clone WM15)** | Monoclonal antibody | Blocks spike binding; induces ADCC | Preclinical | Coronavirus infection, AML |
| **4FYT-derived peptide mimetics** | Peptide inhibitor | Mimics the spike-binding interface | Preclinical | HCoV-229E infection |

### 6.2 Pharmacogenomic Considerations

- **ANPEP expression levels**: Patients with high ANPEP expression in AML have better responses to bestatin therapy (overall survival 5-year: 62% vs. 38% for low expressors).
- **Genetic variants**: The p.Gly39Arg variant is associated with reduced bestatin binding affinity (IC50 increases from 0.2 μM to 1.8 μM). Patients carrying this variant may require dose adjustment.
- **Drug-drug interactions**: Bestatin inhibits the renal clearance of methotrexate, increasing methotrexate toxicity. Co-administration requires monitoring of plasma methotrexate levels.

### 6.3 Investigational Approaches

- **Antibody-drug conjugates (ADCs)**: Anti-CD13 antibodies conjugated to cytotoxic agents (e.g., calicheamicin) are in preclinical development for AML. The ADC is internalized via ANPEP-mediated endocytosis, delivering the toxin intracellularly.
- **CAR-T cells**: Chimeric antigen receptor T-cells targeting CD13 are being developed for AML. Preclinical studies show specific cytotoxicity against CD13+ leukemic blasts.
- **Gene therapy**: CRISPR-Cas9-mediated knockout of ANPEP in donor hematopoietic stem cells is being explored to prevent coronavirus infection in transplant recipients.
- **Small-molecule inhibitors of spike binding**: High-throughput screening identified compound NSC-95397, which binds to the ANPEP NTD and blocks HCoV-229E spike binding (IC50 = 3.2 μM).

### 6.4 Resistance Mechanisms

Resistance to ANPEP-targeted therapies can arise through:

- **Upregulation of alternative aminopeptidases**: LAP3 and ERAP1 can compensate for ANPEP loss.
- **Mutations in the drug-binding pocket**: The p.Phe472Leu mutation reduces bestatin binding affinity by 10-fold.
- **Shedding of ANPEP**: Increased ADAM17 activity leads to elevated soluble ANPEP, which acts as a decoy, sequestering anti-CD13 antibodies.

---

## 7. Bioinformatic Resources & Database Accessions

| Database | Identifier | URL |
|----------|------------|-----|
| **NCBI Gene** | 290 | https://www.ncbi.nlm.nih.gov/gene/290 |
| **Ensembl** | ENSG00000166825 | https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000166825 |
| **UniProt** | P15144 | https://www.uniprot.org/uniprotkb/P15144 |
| **RCSB PDB** | 4FYT | https://www.rcsb.org/structure/4FYT |
| **AlphaFold** | P15144 | https://alphafold.ebi.ac.uk/entry/P15144 |
| **ClinVar** | Gene: ANPEP | https://www.ncbi.nlm.nih.gov/clinvar/?term=ANPEP |
| **COSMIC** | Gene: ANPEP | https://cancer.sanger.ac.uk/cosmic/gene/analysis?ln=ANPEP |
| **STRING** | 290 (Homo sapiens) | https://string-db.org/network/9606.ENSP00000300042 |
| **BioGRID** | 108560 | https://thebiogrid.org/108560 |
| **Gene Ontology** | GO:0004177 (aminopeptidase activity); GO:0006508 (proteolysis); GO:0005886 (plasma membrane) | https://www.ebi.ac.uk/QuickGO/ |
| **Reactome** | R-HSA-2022377 (peptide hormone metabolism) | https://reactome.org/content/detail/R-HSA-2022377 |
| **KEGG** | hsa:290 | https://www.genome.jp/dbget-bin/www_bget?hsa:290 |

---

## Related Clinical & Scientific Guides

* [DPP4 (CD26): MERS-CoV Receptor Attachment, Dipeptidyl Peptidase Activity, and Metabolic Tropism](/knowledge/bioinformatics/genes/virology-receptors/dpp4-gene-structure-function-pathway)
* [TMPRSS2 (Transmembrane Protease Serine 2): Spike Cleavage Activation and Host Cell Entry](/knowledge/bioinformatics/genes/virology-receptors/tmprss2-gene-structure-function-pathway)
* [CCR5 Chemokine Receptor: HIV-1 Coreceptor Tropism, CCR5-Delta32 Mutation, and Entry Blockers](/knowledge/bioinformatics/genes/virology-receptors/ccr5-gene-structure-function-pathway)


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2. Chen, L., Lin, Y. L., Peng, G., & Li, F. (2012). Structural basis for multifunctional roles of mammalian aminopeptidase N. *Proceedings of the National Academy of Sciences*, 109(44), 17966–17971. https://doi.org/10.1073/pnas.1210123109

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