Bevacizumab enhances the therapeutic efficacy of Irinotecan against human head and neck squamous cell carcinoma xenografts

Combining antiangiogenic agents with traditional cytotoxic chemotherapy offers the potential to target both vascular and cellular components of a growing tumor mass. Here, we examined the antitumor activity of the vascular endothelial growth factor antibody, Bevacizumab (Avastin®) in combination with the topoisomerase I inhibitor, Irinotecan (CPT-11) against human head and neck squamous cell carcinoma (HNSCC) xenografts. Bevacizumab was administered daily (at 5 or 20mg/kg) to nude mice bearing FaDu HNSCC xenografts for 28days with the first dose beginning seven days prior to Irinotecan (100mg/kg, weekly × 4). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and immunohistochemical (IHC) methods were employed to study the antiangiogenic effects of Bevacizumab in vivo. Kinetics of tumor response to treatment was studied by monitoring tumor volume over a 60-day period. DCE-MRI detected a significant reduction in vascular permeability following treatment with Bevacizumab (5mg/kg) while high dose Bevacizumab (20mg/kg) induced significant microvascular damage and tumor necrosis, confirmed by immunohistochemistry (IHC). Irinotecan alone resulted in complete tumor regression (cures) in ∼40% of animals while Bevacizumab alone did not result in any cures. Treatment with Bevacizumab (5mg/kg/day×28days) in combination with Irinotecan (100mg/kg, weekly × 4) was highly effective in inhibiting FaDu tumor growth and resulted in complete tumor regression in 80% of animals. These results demonstrate that long term administration of Bevacizumab effectively modulates chemotherapeutic efficacy against HNSCC xenografts. Further investigation into the therapeutic potential of this combination strategy against HNSCC is warranted.