Fig 1.

Erlotinib and gemcitabine synergistically increased their rate of apoptosis in EGFR-overexpressing A-431 epidermoid cancer cells with intrinsic (parental) or acquired (pools 1 and 2) erlotinib resistance. Cells were treated with 2 µM erlotinib, 7 nM gemcitabine, or both simultaneously. After 72 h of drug treatment, the cells were fixed, resuspended in propidium iodide, and analyzed for DNA content using a FACScan cytometer. The extent of changes in sub-diploid content (sub-G1 cell-cycle phase) relative to untreated cells was assessed to determine the levels of apoptosis.