The JAK/STAT (signal transducer and activator of transcription) signal cascade is another important pathway in oncogenesis in general[52], and in the pathogenesis of CC in particular, since it has already been shown that upregulation of anti-apoptotic Mcl-1 (myeloid cell leukemia-1) by interleukin-6 depends Compound C on Stat-3 activation[53,54]. Moreover, RACK1 (receptor for activated C kinase 1) may be the adaptor for IGF-1R-mediated Stat-3 activation[55]. Moser et al[39] recently reported a decrease of Stat-3 phosphorylation after blockade of IGF-1R in pancreatic cell line HPAF-II. In our own in vitro experiments, this effect was only seen in cell line EGI-1, but not in cell line MzChA-1. Further results of our experiments showed that effects of NVP-AEW541 seem to be based mainly on an inhibition of cell growth, at least at low concentrations, while only high doses seem to trigger apoptosis.

Although we could not detect any apoptosis by caspase-3 assay, levels of anti-apoptotic protein Bcl-xL decreased after treatment of MzChA-1 cells. In flow cytometry, the rate of apoptotic cells (sub-G1 peak) increased markedly at drug concentrations above 1 ��mol/L. Another possible anti-cancer mechanism of NVP-AEW541, which was not examined in our experiments, might be the inhibition of angiogenesis, since it has been demonstrated that IGF-1 can induce expression of VEGF[9] and that NVP-AEW541 significantly reduces vascularization and VEGF expression in an in vivo mouse model for pancreatic cancer[39]. In addition, it has recently been shown that IGF-1R blockade reduces the invasiveness of gastrointestinal cancers via blocking production of matrilysin[37].

Regarding the obviously different response rates of extrahepatic CC cell line EGI-1 and GBC cell line Mz-ChA-1, it is not easy to find a simple explanation. While a longer replication time and resistance to Stat-3 dephosphorylation would predict the lower response of Mz-ChA-1 cells to NVP-AEW541, it is unclear why resistance to dephosphorylation of p-p42/44 via k-ras mutation and resistance to Bcl-xL downregulation didnot induce a lower response of EGI-1 cells to NVP-AEW541. Perhaps these factors have a different impact of contribution to resistance. Batimastat A possible side effect of NVP-AEW541 could be induction of diabetes due to the high homology of the kinase region of IGF-1R and the insulin receptor. While in vitro kinase assays showed a 27-fold selectivity of NVP-AEW541 towards IGF-1R[11], a recent in vivo study found neither an increase of blood glucose level nor other side effects in treated animals[20]. Since resistance against anti-cancer drugs evolves rapidly, a combination of different approaches seems necessary.