EGFR tyrosine kinase inhibitors decrease VEGF expression by both hypoxia-inducible factor (HIF)-1-independent and...

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Epidermal growth factor receptor (EGFR) inhibitors are known to reduce tumor angiogenesis by decreasing vascular endothelial growth factor (VEGF) expression.
• Understanding the precise molecular mechanisms underlying this effect is crucial for optimizing cancer therapy.

Purpose of the Study:

• To investigate the molecular pathways through which EGFR inhibitors, specifically gefitinib and erlotinib, decrease VEGF expression.
• To elucidate the roles of Sp1 transcription factor and hypoxia-inducible factor-1alpha (HIF-1alpha) in mediating these effects.

Main Methods:

• Utilized SQ20B and HSC3 squamous carcinoma cell lines.
• Employed adenoviral expression of Akt to study its influence on VEGF regulation.
• Performed reporter assays to assess VEGF promoter activity.
• Conducted gel shift assays to evaluate DNA-protein binding.
• Analyzed HIF-1alpha expression at both mRNA and protein levels.

Main Results:

• Gefitinib decreased VEGF expression, an effect opposed by Akt expression.
• VEGF promoter down-regulation by gefitinib did not require the HIF-1 binding site but involved the region containing Sp1 binding sites.
• Gefitinib reduced Sp1 binding to the VEGF promoter and decreased Sp1 phosphorylation.
• Gefitinib decreased HIF-1alpha protein expression via reduced translation, not altered mRNA levels.
• Similar effects were observed with erlotinib and in different cell lines, indicating conserved mechanisms.

Conclusions:

• EGFR inhibitors decrease VEGF expression through at least two distinct molecular mechanisms.
• These mechanisms involve the inhibition of Sp1 binding to the proximal VEGF promoter and the down-regulation of HIF-1alpha expression.
• The findings provide a deeper understanding of EGFR inhibitor action and potential therapeutic strategies in cancer treatment.