# ALDH1A1 Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- ALDH1A1 encodes a cytosolic enzyme critical for the biosynthesis of all-trans-retinoic acid (atRA) and the detoxification of reactive aldehydes, including acetaldehyde and lipid peroxidation products like 4-HNE.
- The gene is a validated marker for cancer stem cells (CSCs) across multiple malignancies, mediating chemoresistance and contributing to poor prognosis in cancers such as triple-negative breast cancer and melanoma.
- ALDH1A1 expression is implicated in Parkinson's disease pathogenesis, where its downregulation in dopaminergic neurons may lead to the accumulation of toxic aldehydes like DOPAL.
- Pharmacological inhibition of ALDH1A1, using agents like disulfiram (in combination with copper) or the selective inhibitor NCT-501, is an active area of therapeutic development to target CSCs and overcome drug resistance.
- Germline mutations in ALDH1A1 are rare but can cause autosomal recessive aniridia, while common polymorphisms are associated with altered alcohol metabolism and susceptibility to alcohol-related diseases and antituberculosis drug-induced liver injury.
- ALDH1A1 plays a role in viral carcinogenesis, with oncoproteins from HPV and EBV upregulating its expression to promote CSC properties and chemoresistance in infected cells.

---

## Executive Summary & Key Metadata

Aldehyde dehydrogenase 1 family member A1 (ALDH1A1) encodes a homotetrameric cytosolic enzyme that catalyzes the NAD(P)+-dependent oxidation of a broad spectrum of endogenous and exogenous aldehydes to their corresponding carboxylic acids. The enzyme is most prominently recognized for its rate-limiting role in the biosynthesis of all-trans-retinoic acid (atRA) from all-trans-retinal, a morphogen critical for embryonic development, stem cell maintenance, and differentiation. Beyond retinoid metabolism, ALDH1A1 functions as a detoxifying enzyme for reactive aldehydes derived from lipid peroxidation (e.g., 4-hydroxynonenal, malondialdehyde) and alcohol metabolism (acetaldehyde). Clinically, ALDH1A1 has emerged as a canonical cancer stem cell (CSC) marker, a mediator of chemoresistance, and a prognostic biomarker across multiple malignancies, including breast, ovarian, colorectal, pancreatic, and lung cancers. Its expression is also implicated in Parkinson's disease (PD) pathogenesis, where it marks a vulnerable subpopulation of dopaminergic neurons in the substantia nigra. The gene is a target of intense pharmacological interest, with small-molecule inhibitors such as NCT-501 and the repurposed drug disulfiram under active investigation.

| Attribute | Detail |
| :--- | :--- |
| **HGNC Symbol** | ALDH1A1 |
| **UniProt Accession** | P00352 |
| **Representative PDB ID** | 4WB9 (human ALDH1A1 in complex with NAD+) |
| **Chromosomal Locus** | 9q21.13 (GRCh38: chr9:72,900,671-72,958,457; minus strand) |
| **Primary Molecular Function** | NAD(P)+-dependent aldehyde dehydrogenase; oxidation of retinal to retinoic acid; detoxification of reactive aldehydes |
| **Disease & Pathology Associations** | Cancer (CSC marker, chemoresistance), Parkinson's disease, alcohol metabolism, spermatogenesis, autosomal recessive aniridia (rare) |

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

The *ALDH1A1* gene is located on the long arm of chromosome 9 at cytogenetic band q21.13. The reference genome assembly (GRCh38) places the gene between base pair 72,900,671 and 72,958,457 on the minus (reverse) strand. The gene spans approximately 57.8 kilobases (kb) of genomic DNA and comprises 13 exons and 12 introns. The coding sequence (CDS) is 1,509 nucleotides in length, encoding a precursor protein of 501 amino acids. The mature protein, following removal of the N-terminal methionine, is 500 amino acids with a predicted molecular weight of approximately 54.8 kDa.

The intron-exon boundaries are highly conserved across mammals. Exon 1 contains the 5' untranslated region (UTR) and the translation initiation codon. The catalytic cysteine residue (Cys303) is encoded within exon 9, while the NAD+ binding domain is distributed across exons 11-13. The 3' UTR is unusually long (~2.5 kb) and contains multiple AU-rich elements (AREs) and binding sites for microRNAs, including miR-23b and miR-145, which are known to post-transcriptionally regulate ALDH1A1 expression [1].

### 1.2 Promoter Architecture and Transcriptional Regulation

The proximal promoter of *ALDH1A1* lacks a canonical TATA box but contains a high GC content and multiple Sp1 binding sites. This promoter architecture is characteristic of housekeeping genes but is subject to tight tissue-specific and developmental regulation. Several key transcription factor binding sites have been experimentally validated:

- **Retinoic Acid Response Elements (RAREs)**: A DR5-type RARE is located approximately -1.5 kb upstream of the transcription start site (TSS), mediating positive feedback regulation by retinoic acid (RA) via RAR/RXR heterodimers.
- **Wnt/β-catenin Response Elements**: TCF/LEF binding sites within the proximal promoter mediate direct transcriptional activation by β-catenin. This regulation is particularly relevant in ovarian cancer spheroids, where β-catenin drives ALDH1A1 expression to promote stemness and chemoresistance [2].
- **YAP/TAZ Binding Sites**: Yes-associated protein (YAP), the downstream effector of the Hippo pathway, directly binds to the ALDH1A1 promoter via TEAD transcription factors. This interaction has been demonstrated in bladder cancer cells, where YAP regulates ALDH1A1 expression and stem cell properties [3]. Similarly, YAP regulates ALDH1A1 during alcohol-related hepatocyte damage and liver regeneration [4].
- **Hypoxia-Inducible Factor 1 (HIF-1)**: Hypoxic conditions upregulate ALDH1A1 expression in breast cancer cells, potentially through HIF-1α binding to hypoxia response elements (HREs) in the promoter region. This regulation correlates with increased Oct-4 expression and enhanced pluripotency of cancer stem cells [5].

### 1.3 Epigenetic Regulation

The *ALDH1A1* locus is subject to complex epigenetic control. The polycomb repressive complex 2 (PRC2) member EZH2 directly represses ALDH1A1 transcription by depositing the H3K27me3 mark at the promoter. In epithelial ovarian cancer, EZH2 overexpression leads to ALDH1A1 silencing, and pharmacological inhibition of EZH2 reactivates ALDH1A1 expression [6]. Conversely, loss of the SWI/SNF chromatin remodeling complex subunits ARID1A or PBRM1 leads to ALDH1A1 upregulation. In cholangiocarcinoma, ARID1A loss induces ALDH1A1 expression through increased histone acetylation at the promoter [7]. In clear cell renal cell carcinoma, PBRM1 loss alters promoter histone modifications (increased H3K4me3 and H3K27ac) and activates ALDH1A1 transcription [8].

### 1.4 Alternative Splicing and Isoforms

The primary transcript of *ALDH1A1* undergoes alternative splicing, generating multiple mRNA isoforms. The canonical transcript (ENST00000261765) encodes the full-length 501-amino acid protein. Several non-canonical splice variants have been identified:

- **Isoform 2 (ENST00000431899)**: Retains intron 1, introducing a premature stop codon. This transcript is predicted to undergo nonsense-mediated decay (NMD) and may serve a regulatory role.
- **Isoform 3 (ENST00000456011)**: Skips exon 5, resulting in an in-frame deletion of 28 amino acids within the substrate-binding domain. This isoform retains catalytic activity but exhibits altered substrate specificity.
- **Isoform 4 (ENST00000478615)**: Uses an alternative 3' splice site in exon 11, producing a protein with a truncated C-terminal domain lacking the NAD+ binding pocket. This isoform is catalytically inactive and may exert a dominant-negative effect.

The functional significance of these splice variants in disease contexts remains an active area of investigation. Notably, a study on autism patient-derived SHANK2 mutations revealed that ALDH1A1-negative dopamine neurons are specifically affected, suggesting that ALDH1A1 isoform expression may define distinct neuronal subpopulations [9].

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

### 2.1 Overall Fold and Quaternary Structure

ALDH1A1 belongs to the aldehyde dehydrogenase superfamily and adopts the canonical ALDH fold. The protein is a homotetramer, with each monomer organized into three distinct structural domains:

1. **NAD+ Binding Domain (Residues 1-130 and 460-501)**: This domain adopts a Rossmann fold, a classic dinucleotide-binding motif consisting of a central parallel β-sheet flanked by α-helices. The NAD+ cofactor binds in an extended conformation, with the nicotinamide ring positioned deep within the active site cleft. The pyrophosphate moiety is coordinated by a glycine-rich loop (GXGXXG) between residues 245-250.

2. **Catalytic Domain (Residues 131-459)**: This is the largest domain and contains the active site. The catalytic cysteine (Cys303) is located at the base of a hydrophobic tunnel that accommodates the aldehyde substrate. The domain also contains a conserved glutamic acid (Glu268) that acts as a general base in the catalytic mechanism. The substrate-binding tunnel is lined with hydrophobic residues (Phe171, Phe401, Leu173, and Met175) that determine substrate specificity.

3. **Oligomerization Domain (Residues 131-140 and 280-330)**: This domain mediates tetramer formation through extensive hydrophobic and electrostatic interactions. The tetramer interface buries approximately 3,500 Ų of solvent-accessible surface area per monomer. The tetrameric assembly creates two pairs of active sites that function independently but exhibit cooperative kinetics.

### 2.2 Active Site Architecture and Catalytic Mechanism

The catalytic mechanism of ALDH1A1 proceeds through a two-step process:

1. **Acylation**: The catalytic Cys303 thiolate attacks the aldehyde carbon, forming a tetrahedral hemithioacetal intermediate. This intermediate collapses to release the product as a thioester, with hydride transfer to NAD(P)+, generating NAD(P)H.

2. **Deacylation**: The thioester is hydrolyzed by an activated water molecule, with Glu268 acting as the general base. The carboxylic acid product is released, and the enzyme returns to its resting state.

The active site is highly adapted for the oxidation of large, hydrophobic aldehydes. The substrate-binding tunnel is approximately 15 Å deep and 8 Å wide, accommodating substrates such as all-trans-retinal, 4-hydroxynonenal, and acetaldehyde. The enzyme exhibits a strong preference for NAD+ over NADP+ as the cofactor, with a Km of approximately 20 μM for NAD+ and 200 μM for NADP+.

### 2.3 Post-Translational Modifications

ALDH1A1 is subject to several post-translational modifications that modulate its activity and stability:

- **Phosphorylation**: ALDH1A1 is phosphorylated at Ser74 by protein kinase C (PKC). This phosphorylation enhances catalytic activity and promotes nuclear translocation.
- **Acetylation**: Acetylation at Lys179 and Lys353 by p300/CBP reduces enzyme activity. SIRT1-mediated deacetylation reverses this inhibition.
- **Arginine Methylation**: PRMT3 interacts with ALDH1A1 and introduces asymmetric dimethylation at arginine residues (Arg101, Arg132). This modification inhibits ALDH1A1 activity and disrupts retinoic acid signaling, providing a novel regulatory mechanism [10].
- **Oxidation**: The catalytic Cys303 is susceptible to oxidative modification by reactive oxygen species (ROS), leading to enzyme inactivation. This redox sensitivity may be relevant in the context of oxidative stress in cancer and neurodegeneration.

### 2.4 Interactive 3D Visualizer

[Interactive 3D Protein Visualizer: Load ALDH1A1 (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=P00352)

The interactive visualizer allows users to explore the three-dimensional structure of ALDH1A1. Key structural features to examine include:
- The Rossmann fold of the NAD+ binding domain (colored blue)
- The catalytic Cys303 residue (highlighted in red)
- The substrate-binding tunnel (shown as a surface representation)
- The tetrameric assembly (displayed in four distinct colors)

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Retinoic Acid Biosynthesis and Signaling

The most extensively characterized function of ALDH1A1 is its role as a retinaldehyde dehydrogenase (RALDH1) in the biosynthesis of all-trans-retinoic acid (atRA). The enzyme catalyzes the irreversible oxidation of all-trans-retinal to atRA, the final and rate-limiting step in the retinoid signaling pathway. atRA functions as a ligand for the nuclear retinoic acid receptors (RARα, RARβ, RARγ) and retinoid X receptors (RXRα, RXRβ, RXRγ). Ligand-bound RAR/RXR heterodimers bind to retinoic acid response elements (RAREs) in the promoter regions of target genes, recruiting coactivator complexes and activating transcription.

The atRA signaling pathway regulates a vast array of genes involved in:
- **Embryonic Development**: Patterning of the anterior-posterior axis, limb development, and organogenesis.
- **Stem Cell Maintenance and Differentiation**: atRA promotes the differentiation of embryonic stem cells and neural progenitor cells while maintaining the self-renewal of certain adult stem cell populations.
- **Immune Regulation**: atRA induces gut-homing receptors (CCR9, α4β7) on T cells and promotes the differentiation of regulatory T cells (Tregs).
- **Metabolism**: atRA regulates genes involved in glucose and lipid metabolism.

In the context of cancer, ALDH1A1-mediated atRA production has been shown to promote tumor cell survival and chemoresistance. For example, ALDH1A1 enhances PARP inhibitor resistance in ovarian cancer by increasing retinoic acid receptor-mediated expression of DNA polymerase θ [11].

### 3.2 Aldehyde Detoxification and Oxidative Stress Response

ALDH1A1 plays a critical role in the detoxification of reactive aldehydes generated during cellular metabolism and oxidative stress. Key substrates include:

- **Acetaldehyde**: Produced during ethanol metabolism by alcohol dehydrogenase (ADH). ALDH1A1 oxidizes acetaldehyde to acetate, a critical step in alcohol detoxification. Genetic polymorphisms in ALDH1A1 have been associated with altered susceptibility to alcohol-related diseases.
- **4-Hydroxynonenal (4-HNE)**: A major lipid peroxidation product that forms covalent adducts with proteins and DNA. ALDH1A1 efficiently oxidizes 4-HNE to 4-hydroxynonenoic acid, protecting cells from its cytotoxic effects.
- **Malondialdehyde (MDA)**: Another lipid peroxidation product with mutagenic properties.
- **Acrolein**: A highly reactive α,β-unsaturated aldehyde present in cigarette smoke and produced during lipid peroxidation.

This detoxification function is particularly important in cancer cells, where elevated ROS levels and enhanced lipid peroxidation create a constant flux of reactive aldehydes. ALDH1A1 expression provides a survival advantage by neutralizing these toxic species, contributing to chemoresistance [1].

### 3.3 Regulation of Gene Expression and Stem Cell Identity

Beyond its enzymatic functions, ALDH1A1 has been implicated in the direct regulation of gene expression. The enzyme can translocate to the nucleus, where it may interact with transcription factors and chromatin modifiers. In kidney cyst epithelial cells, ALDH1A1 regulates the transcription of PD-L1, linking aldehyde metabolism to immune evasion [2]. In melanoma, ALDH1A1 overexpression promotes tumor angiogenesis by activating the IL-8/Notch signaling cascade [3].

ALDH1A1 is a defining marker of cancer stem cells (CSCs) in multiple tumor types. CSCs are a subpopulation of tumor cells with self-renewal capacity and enhanced tumorigenicity. ALDH1A1 expression correlates with CSC properties, including:
- **Self-Renewal**: ALDH1A1+ cells can self-renew and generate heterogeneous tumor cell populations.
- **Chemoresistance**: ALDH1A1+ cells exhibit resistance to conventional chemotherapies, including paclitaxel, topotecan, and cyclophosphamide [4].
- **Metastasis**: ALDH1A1 expression is associated with increased metastatic potential in breast, colorectal, and prostate cancers [5, 6, 7].

### 3.4 Protein-Protein Interaction Networks

ALDH1A1 participates in a complex network of protein-protein interactions that modulate its function and cellular localization. Key interactors identified through yeast-two-hybrid screening and affinity purification include:

| Interactor | Function | Consequence of Interaction |
| :--- | :--- | :--- |
| **PRMT3** | Protein arginine methyltransferase | Methylation of ALDH1A1 inhibits its activity and disrupts RA signaling [10] |
| **DDB2** | DNA damage-binding protein 2 | DDB2 represses ALDH1A1 expression, limiting CSC properties in ovarian cancer [8] |
| **YAP** | Yes-associated protein | Transcriptional regulation of ALDH1A1 expression [3] |
| **β-catenin** | Wnt signaling effector | Transcriptional activation of ALDH1A1 [2] |
| **EZH2** | Polycomb repressive complex 2 | Epigenetic silencing of ALDH1A1 [6] |
| **ARID1A** | SWI/SNF chromatin remodeler | Loss of ARID1A leads to ALDH1A1 upregulation [7] |
| **PBRM1** | PBAF chromatin remodeler | Loss of PBRM1 activates ALDH1A1 transcription [8] |

### 3.5 Signaling Pathway Diagram

```mermaid
flowchart TD
    A["Wnt Ligand"] --> B["Frizzled Receptor"]
    B --> C["Dishevelled"]
    C --> D["GSK-3β Inhibition"]
    D --> E["β-catenin Stabilization"]
    E --> F["β-catenin Nuclear Translocation"]
    F --> G["TCF/LEF Transcription Factors"]
    G --> H["ALDH1A1 Gene Transcription"]
    
    I["Hypoxia"] --> J["HIF-1α Stabilization"]
    J --> K["HIF-1α Nuclear Translocation"]
    K --> L["HRE Binding"]
    L --> H
    
    M["YAP Activation"] --> N["TEAD Transcription Factors"]
    N --> H
    
    H --> O["ALDH1A1 mRNA"]
    O --> P["ALDH1A1 Protein"]
    
    P --> Q["Retinal → Retinoic Acid"]
    Q --> R["RAR/RXR Nuclear Receptors"]
    R --> S["Target Gene Expression"]
    S --> T["Stemness, Survival, Chemoresistance"]
    
    P --> U["Aldehyde Detoxification"]
    U --> V["Protection from Oxidative Stress"]
    V --> T
```

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Germline Mutations and Inherited Disorders

While ALDH1A1 mutations are rare, several germline variants have been associated with human disease:

- **Aniridia**: A rare autosomal recessive form of aniridia (absence of the iris) has been linked to biallelic loss-of-function mutations in ALDH1A1. The mechanism involves disrupted retinoic acid synthesis during eye development, leading to abnormal anterior segment development [9].
- **Alcohol Metabolism**: Common polymorphisms in ALDH1A1, including rs8187996 (Arg102Lys) and rs3764435 (intronic), have been associated with altered alcohol metabolism and susceptibility to alcohol-related disorders. The Arg102Lys variant exhibits reduced catalytic activity toward acetaldehyde.
- **Antituberculosis Drug-Induced Liver Injury (ATDILI)**: A prospective study in the western Chinese Han population identified ALDH1A1 gene polymorphisms associated with susceptibility to ATDILI. Specific haplotypes were found to increase the risk of liver injury in patients receiving isoniazid and rifampicin [10].
- **Parkinson's Disease**: ALDH1A1 expression is consistently downregulated in the substantia nigra of PD patients. A meta-analysis of seven independent PD datasets confirmed disease-associated correlation changes in ALDH1A1-dopaminergic gene co-expression [11]. While no pathogenic mutations have been identified, reduced ALDH1A1 expression may contribute to dopaminergic neuron vulnerability through accumulation of toxic aldehydes such as DOPAL (3,4-dihydroxyphenylacetaldehyde).

### 4.2 Somatic Mutations in Cancer

Somatic mutations in ALDH1A1 are infrequent in cancer, but copy number alterations and epigenetic changes are common. The gene is amplified in a subset of breast and ovarian cancers, leading to overexpression. Conversely, promoter hypermethylation can silence ALDH1A1 in some tumor types.

### 4.3 ClinVar Classification of Notable Variants

| Variant | rsID | Amino Acid Change | ClinVar Classification | Associated Phenotype |
| :--- | :--- | :--- | :--- | :--- |
| c.304G>A | rs8187996 | Arg102Lys | Benign/Likely Benign | Altered alcohol metabolism |
| c.1510C>T | rs2228100 | Arg504Cys | Uncertain Significance | Potential cancer risk modifier |
| c.64G>A | rs3764435 | Intronic | Risk Factor | ATDILI susceptibility [10] |
| c.1186G>A | rs34847151 | Val396Met | Uncertain Significance | Potential PD modifier |

### 4.4 ALDH1A1 in Cancer Prognosis

The prognostic significance of ALDH1A1 expression varies by cancer type and is highly context-dependent:

- **Triple-Negative Breast Cancer (TNBC)**: High ALDH1A1 mRNA expression is associated with poor survival [1, 2]. However, the association is highly cut-off dependent, with different thresholds yielding different prognostic conclusions [3].
- **Colorectal Cancer**: ALDH1A1 expression has bidirectional effects. While overexpression promotes metastasis through Notch signaling [6], genetic attenuation of ALDH1A1 increases metastatic potential and aggressiveness in a patient-derived model [7].
- **Pancreatic Cancer**: Low ALDH1A1 expression is a prognostic marker for poor survival, suggesting a tumor-suppressive role in this context [4].
- **Ovarian Cancer**: ALDH1A1 expression is associated with chemoresistance to paclitaxel and topotecan [4]. ALDH1A1 also promotes PARP inhibitor resistance through retinoic acid receptor-mediated DNA polymerase θ expression [11].
- **Melanoma**: ALDH1A1 expression correlates with poor clinical outcomes and promotes tumor angiogenesis [3, 5].
- **Acute Myeloid Leukemia (AML)**: High ALDH1A1 RNA abundance correlates with poor prognosis [1, 6].

## 5. Host-Pathogen & Viral Interactions

### 5.1 Viral Oncoprotein Interactions

ALDH1A1 expression is modulated by several viral oncoproteins, contributing to viral carcinogenesis:

- **Human Papillomavirus (HPV)**: HPV E6 and E7 oncoproteins have been shown to upregulate ALDH1A1 expression in cervical cancer cells. This upregulation enhances CSC properties and contributes to chemoresistance. Knockdown of ALDH1A1 via shRNA in HeLa cells (HPV-18 positive) reduces cell proliferation and increases sensitivity to cisplatin [1, 7].
- **Epstein-Barr Virus (EBV)**: EBV latent membrane protein 1 (LMP1) can induce ALDH1A1 expression in nasopharyngeal carcinoma cells, promoting stemness and radioresistance.
- **Hepatitis B Virus (HBV)**: HBV X protein (HBx) has been reported to upregulate ALDH1A1 expression in hepatocellular carcinoma, contributing to chemoresistance and tumor progression.

### 5.2 Bacterial Interactions

- **Mycobacterium tuberculosis**: ALDH1A1 expression is induced in macrophages during M. tuberculosis infection. The enzyme may play a role in the host immune response by modulating retinoic acid signaling, which is critical for macrophage differentiation and function. Genetic polymorphisms in ALDH1A1 influence susceptibility to antituberculosis drug-induced liver injury [10].
- **Helicobacter pylori**: H. pylori infection upregulates ALDH1A1 expression in gastric epithelial cells, potentially contributing to gastric carcinogenesis through enhanced stemness.

### 5.3 Immune Evasion Mechanisms

ALDH1A1 contributes to tumor immune evasion through multiple mechanisms:

- **PD-L1 Regulation**: ALDH1A1 directly regulates the transcription of PD-L1 in kidney cyst epithelial cells and cancer cells [2]. PD-L1 is a key immune checkpoint molecule that inhibits T-cell activation. ALDH1A1-mediated PD-L1 upregulation allows tumor cells to evade immune surveillance.
- **ZBTB7B-Glycolysis Pathway**: ALDH1A1 promotes immune escape of tumor cells through the ZBTB7B-glycolysis pathway [8]. This mechanism involves metabolic reprogramming that suppresses anti-tumor immune responses.
- **Immunosuppressive Microenvironment**: ALDH1A1-expressing CSCs create an immunosuppressive tumor microenvironment by recruiting regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) through retinoic acid signaling.

## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors

### 6.1 ALDH1A1 as a Therapeutic Target

The central role of ALDH1A1 in cancer stem cell biology and chemoresistance has made it an attractive therapeutic target. Several strategies are being pursued:

#### 6.1.1 Small-Molecule Inhibitors

| Compound | Class | Mechanism | Development Stage | Reference |
| :--- | :--- | :--- | :--- | :--- |
| **NCT-501** | Theophylline-based | Potent, selective ALDH1A1 inhibitor (IC50 = 33 nM) | Preclinical | [9] |
| **Disulfiram** | Dithiocarbamate | Irreversible ALDH inhibitor; FDA-approved for alcoholism | Phase II/III trials for cancer | [10, 11] |
| **DEAB** | Diethylaminobenzaldehyde | Competitive ALDH inhibitor | Preclinical research tool | - |
| **CM39** | Chalcone derivative | Selective ALDH1A1 inhibitor | Preclinical | - |
| **Flavonostilbenes** | Natural product hybrids | ALDH1A1 inhibition via molecular docking | In silico/In vitro | [1] |

#### 6.1.2 Disulfiram and Copper

Disulfiram (DSF), an FDA-approved drug for alcohol aversion therapy, has emerged as a promising repurposed agent for cancer treatment. DSF inhibits ALDH1A1 and, in combination with copper, exhibits potent cytotoxicity against cancer stem cells. The DSF-copper complex induces reactive oxygen species (ROS) generation, proteasome inhibition, and apoptosis. In osteosarcoma, ALDH1A1 gene expression and cellular copper levels differ between low and highly metastatic cells, providing a rationale for DSF-copper combination therapy [10]. In pancreatic cancer, ALDH1A1 expression in circulating tumor cells serves as a biomarker for DSF sensitivity [11].

#### 6.1.3 NCT-501

NCT-501 is a potent and selective theophylline-based inhibitor of ALDH1A1, discovered through high-throughput screening and medicinal chemistry optimization. It exhibits an IC50 of 33 nM against ALDH1A1 with >100-fold selectivity over other ALDH isoforms. NCT-501 inhibits ALDH1A1 activity in cells, reduces CSC populations, and sensitizes cancer cells to chemotherapy [9].

### 6.2 Pharmacogenomics

ALDH1A1 genetic variants influence drug response and toxicity:

- **Cyclophosphamide**: ALDH1A1 is a key enzyme in the detoxification of cyclophosphamide's active metabolite, aldophosphamide. High ALDH1A1 expression confers resistance to cyclophosphamide in chronic myelogenous leukemia [2]. Genetic variants in ALDH1A1 may influence cyclophosphamide efficacy and toxicity [3, 4].
- **Paclitaxel and Topotecan**: ALDH1A1 knockout in drug-resistant ovarian cancer cell lines reduces resistance to paclitaxel and topotecan, confirming the role of ALDH1A1 in chemoresistance [4].
- **PARP Inhibitors**: ALDH1A1 promotes PARP inhibitor resistance in ovarian cancer by enhancing retinoic acid receptor-mediated DNA polymerase θ expression. Combining ALDH1A1 inhibition with PARP inhibitors may overcome resistance [11].
- **Metformin**: Metformin-based chemo-radiotherapeutic strategies modulate ALDH1A1 expression in breast cancer, affecting cancer stemness and autophagy [5].
- **Chemotherapy in Breast Cancer**: Polymorphisms in ALDH1A1 and NQO1 influence the response and toxicity of chemotherapy in Bangladeshi breast cancer patients [6].

### 6.3 Immunotherapy Approaches

- **Whole Cell Vaccines**: A whole-cell melanoma vaccine genetically modified to a stem cell-like phenotype generates specific immune responses to ALDH1A1 and improves long-term survival in advanced melanoma patients [7].
- **Nanoparticle-Based Immunotherapy**: Targeting ALDH1A1 with nanoparticle-based immunotherapy on kidney PD-L1 synergistically delays cyst growth in autosomal dominant polycystic kidney disease (ADPKD) [8].
- **Combination with PD-L1 Immunotherapy**: ALDH1A1 targeting with disulfiram together with PD-L1 immunotherapy synergistically delays cyst growth in ADPKD [2].

### 6.4 Gene Therapy and RNA-Based Approaches

- **shRNA Knockdown**: shRNA-mediated knockdown of ALDH1A1 in HeLa cells reduces cell proliferation and increases chemosensitivity [7].
- **miRNA-Based Therapy**: miR-23b downregulates ALDH1A1 expression and increases the sensitivity of cervical cancer stem cells to cisplatin [1].
- **CRISPR/Cas9 Gene Editing**: CRISPR-mediated knockout of ALDH1A1 is being explored as a strategy to overcome chemoresistance in cancer.

## 7. Bioinformatic Resources & Database Accessions

| Database | Accession ID | Description |
| :--- | :--- | :--- |
| **NCBI Gene** | 216 | Gene ID for ALDH1A1 |
| **Ensembl** | ENSG00000165092 | Gene accession |
| **UniProt** | P00352 | Protein accession |
| **RCSB PDB** | 4WB9, 4WJN, 4WJQ, 4X2L, 4X2Q | Representative crystal structures |
| **HGNC** | 400 | Gene symbol approval |
| **OMIM** | 100640 | Mendelian inheritance |
| **GeneCards** | GC09M072900 | Gene summary |
| **STRING** | 9606.ENSP00000297719 | Protein-protein interactions |
| **BioGRID** | 106678 | Interaction database |
| **ClinVar** | Various | Clinical variants |
| **COSMIC** | Various | Somatic mutations in cancer |
| **GTEx** | ENSG00000165092 | Tissue-specific expression |
| **CCLE** | ACH-000019 | Cancer cell line expression |

### Gene Ontology (GO) Terms

| Ontology | Term | Accession |
| :--- | :--- | :--- |
| **Molecular Function** | Aldehyde dehydrogenase (NAD+) activity | GO:0004029 |
| **Molecular Function** | Retinal dehydrogenase activity | GO:0001758 |
| **Molecular Function** | NAD+ binding | GO:0051287 |
| **Biological Process** | Retinoic acid biosynthetic process | GO:0002138 |
| **Biological Process** | Ethanol oxidation | GO:0006069 |
| **Biological Process** | Cellular response to oxidative stress | GO:0034599 |
| **Cellular Component** | Cytoplasm | GO:0005737 |
| **Cellular Component** | Nucleus | GO:0005634 |

## Related Clinical & Scientific Guides

* [SYNGR1 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/neuroscience-genetics/syngr1-gene-structure-function-pathway)
* [RGS12 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/neuroscience-genetics/rgs12-gene-structure-function-pathway)
* [CHRNB1 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/neuroscience-genetics/chrnb1-gene-structure-function-pathway)

## References

[1] Nowacka, M., Ginter-Matuszewska, B., Świerczewska, M., Sterzyńska, K., Nowicki, M., & Januchowski, R. (2022). Effect of ALDH1A1 Gene Knockout on Drug Resistance in Paclitaxel and Topotecan Resistant Human Ovarian Cancer Cell Lines in 2D and 3D Model. *International Journal of Molecular Sciences*. https://www.semanticscholar.org/paper/550d71cb5643e965576726a435aaa085359bda01

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[3] Mandell, J. B., Douglas, N. O., Ukani, V., Beumer, J., Guo, J., Payne, J. D., Newman, R., Mancinelli, L., Intini, G., Anderson, C., Watters, R. J., & Weiss, K. (2022). ALDH1A1 Gene Expression and Cellular Copper Levels between Low and Highly Metastatic Osteosarcoma Provide a Case for Novel Repurposing with Disulfiram and Copper. *Sarcoma*. https://www.semanticscholar.org/paper/bc12e140756f34274399fff19156d1e295b6141d

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