Abstract

Deregulation of epidermal growth factor receptor (EGFR) pathways contributes to the progression of a wide range of cancers, and the EGFR is an attractive therapeutic target. The humanized EGFR-specific monoclonal antibody EMD72000 has shown potent inhibitory activity in preclinical experiments and is under investigation in clinical studies. Using the human L3.6pl pancreatic cancer cell line, we investigated whether the efficacy of EMD72000 can be enhanced in combination with gemcitabine. Nude mice were orthotopically injected with L3.6pl cells followed by biweekly treatment of 40 mg/kg EMD72000 and 100 mg/kg gemcitabine (either alone or in combination). Under two treatment schedules we evaluated a) the influence of different time points of initiation of single agent and combined treatment after tumor cell injection into nude mice and b) the influence of different treatment durations. In the first experiment, treatment was initiated at four different time-points after tumor cell injection (days 8 - 28). Exposure to EMD72000 or gemcitabine alone resulted in detectable tumor shrinkage and reduced lymph node and liver metastases, however, these effects were enhanced in the EMD72000 plus gemcitabine groups. Furthermore, combination treatment as well as EMD72000 monotherapy led to a significant reduction of microvessel density and tumor cell proliferation in primary pancreatic tumors following immunohistochemical analysis for CD31 and Ki67, respectively. Overall, the effects were strongest when treatment was initiated at early time points after tumor cell injection. In a second experimental set-up, treatment was initiated at day 8 after tumor cell injection in all cases and stopped at four different time-points (days 15 - 33). Interestingly, there was no significant difference in the average tumor weight of the groups treated for short versus longer time periods. The treatment was most effective when given shortly after tumor cell injection, whereas the duration of the treatment appeared less important in this model. In conclusion, in this model the anti-angiogenic and anti-tumor activity of EMD72000 in combination with gemcitabine was substantially more effective than either treatment alone.