Figure 2. Efficacy of cetuximab and erlotinib correlates to STAT3 transcriptional activity in colon cancer cell lines in vitro. Wild-type K-Ras expressing colon cancer cells were treated in triplicate with (A) cetuximab (± 10 µg/ml) and (B) erlotinib (± 2.5 µM) to assess their effect on cell viability (□) and STAT3 transcriptional activity (■). Cell viability was determined using a commercially available Cell Titer-Glo kit and samples read on a bioluminometer. Data are expressed as % viability compared with untreated control cells ± SD. STAT3 transcriptional activity was determined using a bioluminometer after infection with the Ad-APRE-luc adenovirus and treatment with cetuximab and erlotinib. Data are expressed as percentage STAT3 activity relative to untreated cells ± SD.