Cetuximab directly inhibits P-glycoprotein function in vitro independently of EGFR binding.

Purpose: Cancer chemotherapy typically combines anticancer drugs from different mechanisms of action. However, cancer cells could become resistant to chemotherapy via P-gp or other ATP binding cassette proteins. The objective of this study was to evaluate whether cetuximab, monoclonal antibody directed toward epidermal growth factor receptor, could increase intracellular concentration of conventional chemotherapy by interacting with P-gp.

Methods: Two human ovarian carcinoma (IGROV1) and two human embryonary kidney (HEK) cell lines, overexpressing or weakly expressing P-gp, were used. Their EGFR expressions were compared. Cetuximab effect on P-gp functionality was evaluated by measuring doxorubicin (P-gp fluorescent substrate) intracellular accumulation. Cetuximab ability to increase doxorubicin cytotoxicity was evaluated by MTT test. A quaternary structure model of the P-gp-Cetuximab complex was established.

Results: Exposure of cetuximab in therapeutic concentrations range with doxorubicin led to significant doxorubicin accumulation and reversion of doxorubicin resistance in P-gp expressing cells lines. Molecular modeling of P-gp-cetuximab interactions showed that cetuximab is able to bind P-gp extracellular part.

Conclusions: Cetuximab increases a P-gp substrate intracellular accumulation in both P-gp expressing cell lines, independently of their EGFR expression. One hypothesis is that cetuximab binding on P-gp could hamper the conformational changes that occur during drugs efflux. Our results offer new possibilities of research on monoclonal antibodies influence in MDR phenomena.