Epidermal growth factor receptor inhibitors for radiotherapy: biological rationale and preclinical results

Area of Science:

• Oncology
• Radiation Oncology
• Pharmacology

Background:

• Blocking the epidermal growth factor receptor (EGFR) is a validated strategy for enhancing radiotherapy outcomes.
• EGFR inhibitors are investigated for their potential to improve tumor control when combined with radiation therapy.

Purpose of the Study:

• To evaluate the efficacy of two distinct EGFR inhibitors, BIBX1382BS and cetuximab, in combination with fractionated radiotherapy for local tumor control.
• To explore the radiobiological mechanisms underlying the effects of cetuximab when combined with radiation.

Main Methods:

• Experiments involved FaDu human squamous cell carcinomas xenografted into nude mice.
• BIBX1382BS was administered concurrently, post-irradiation, or between surgery and adjuvant irradiation.
• Cetuximab was administered concurrently with fractionated radiotherapy, and its effects on tumor cell number, radiosensitivity, repopulation, and reoxygenation were assessed.

Main Results:

• BIBX1382BS, an intracellular EGFR tyrosine kinase inhibitor, did not improve local tumor control despite positive effects on tumor growth.
• Cetuximab, a monoclonal antibody targeting the extracellular EGFR domain, significantly improved local tumor control when given concurrently with radiation.
• Mechanistic studies suggested cetuximab enhanced tumor control through decreased clonogenic cells, increased radiosensitivity, reduced repopulation, and improved reoxygenation.

Conclusions:

• Different classes of EGFR inhibitors exhibit distinct potentials for improving local tumor control in combination with fractionated radiotherapy.
• Targeting the extracellular domain of EGFR with antibodies like cetuximab may be more effective in enhancing radiotherapy outcomes than inhibiting the intracellular tyrosine kinase domain.