Synergistic Effect of SN-38 in Combination with Cetuximab on Angiogenesis and Cancer Cell Invasion

The combination of irinotecan, a topoisomerase I inhibitor with cetuximab, an antibody against epidermal growth factor receptor, produces synergistic and beneficial effects in patients with irinotecan-refractory colorectal cancer. Our hypothesis was that synergistic effects could be due to anti-angiogenesis and anti-invasion, but not to cytotoxicity.

Cytotoxicity was assessed by viability test and flow cytometry. Anti-angiogenesis, anti-invasion were studied by the endothelial cell capillary-like network formation and transmigration through an extracellular matrix. Protein kinase B (PKB, frequently cited as AKT), and extracellular signal-regulated kinases (ERK) activation was assayed by cell-based enzyme-linked immunosorbent assay (ELISA).

Combinations of SN-38 (the active of irinotecan) and cetuximab did not induce any synergistic cytotoxicity confirmed by viability test and cell-cycle analyses. Interestingly, their combination produced synergistic anti-angiogenesis and anti-invasion activities revealed by endothelial cell capillary-like network formation and cell invasion tests. Subsequently, their combination attenuated either expression or phosphorylation of AKT and ERK1/2 using cell-based ELISA.

SN-38/cetuximab combination has synergistic anti-angiogenesis and anti-invasion activities mediated by down-regulation of phosphatidylinositol-3-kinases/AKT and mitogen-activated protein kinase/ERK pathways.