Autophagy: novel action of panitumumab in colon cancer

Panitumumab, a fully-human monoclonal antibody raised against epidermal growth factor receptor (EGFR), has been approved by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) for the treatment of patients with EGFR-expressing metastatic colorectal carcinoma (mCRC) after failure of standard chemotherapy. Additionally, the guideline of the EMEA includes the use of panitumumab in patients with wild-type KRAS. The goal of the current study was to evaluate the effect of panitumumab on colon cancer cells, proliferation, apoptosis, necrosis, cell cycle arrest and autophagy. The effect of panitumumab on the redox status of the cells was also studied.

The cell lines Caco-2, DLD-1 and HT-29 which differ in their expression of EGFR and HER-2 were used. Cell proliferation and apoptosis/necrosis were measured by methyl tetrazolium (MTT) assay and annexin V/propidium iodide assay, respectively. Cell cycle arrest was estimated by propidium iodide assay and autophagy was detected using Western blot analysis. Spectrophotometrical quantification of glutathione (GSH) levels and an analysis of KRAS sequence were applied.

Panitumumab reduced proliferation only in the DLD-1 cells despite the mutated KRAS in this cell line. However, panitumumab did not affect DLD-1 cell apoptosis, necrosis or cell cycle progression. Interestingly, immunoblotting analysis revealed that panitumumab increased protein levels of beclin-1, a marker of autophagy. In addition, an increase in the GSH level was noted following panitumumab treatment reflecting an imbalance in the redox status of the cells.

Panitumumab affects colon cancer cell proliferation independently of KRAS mutations and EGFR protein levels, possibly through the induction of autophagy.