Concomitant Targeting of EGF Receptor, TGF-beta and Src Points to a Novel Therapeutic Approach in Pancreatic Cancer

To test the hypothesis that concomitant targeting of the epidermal growth factor receptor (EGFR) and transforming growth factor-beta (TGF-beta) may offer a novel therapeutic approach in pancreatic cancer, EGFR silencing by RNA interference (shEGFR) was combined with TGF-beta sequestration by soluble TGF-beta receptor II (sT beta RII). Effects on colony formation in 3-dimensional culture, tumor formation in nude mice, and downstream signaling were monitored. In both ASPC-1 and T3M4 cells, either shEGFR or sT beta RII significantly inhibited colony formation. However, in ASPC-1 cells, combining shEGFR with sT beta RII reduced colony formation more efficiently than either approach alone, whereas in T3M4 cells, shEGFR-mediated inhibition of colony formation was reversed by sT beta RII. Similarly, in vivo growth of ASPC-1-derived tumors was attenuated by either shEGFR or sT beta RII, and was markedly suppressed by both vectors. By contrast, T3M4-derived tumors either failed to form or were very small when EGFR alone was silenced, and these effects were reversed by sT beta RII due to increased cancer cell proliferation. The combination of shEGFR and sT beta RII decreased phospho-HER2, phospho-HER3, phoshpo-ERK and phospho-src (Tyr416) levels in ASPC-1 cells but increased their levels in T3M4 cells. Moreover, inhibition of both EGFR and HER2 by lapatinib or of src by SSKI-606, PP2, or dasatinib, blocked the sT beta RII-mediated antagonism of colony formation in T3M4 cells. Together, these observations suggest that concomitantly targeting EGFR, TGF-beta, and src may constitute a novel therapeutic approach in PDAC that prevents deleterious cross-talk between EGFR family members and TGF-beta-dependent pathways.