Background: Overexpression of insulin-like growth factor binding protein-3 (IGFBP-3) induces apoptosis in non-small-cell lung cancer (NSCLC) cells in vitro and in vivo. However, Ras-mediated signaling pathways could develop resistance to apoptotic activities of IGFBP-3 in NSCLC cells. We thus evaluated the therapeutic potential of the combination of IGFBP-3 and SCH66336, a farnesyltransferase inhibitor that blocks Ras activation, in NSCLC cell lines.
Methods: The effects of the combination of adenoviral IGFBP-3 (Ad-IGFBP3) and SCH66336 on proliferation and apoptosis of NSCLC cell lines (H1299, H596, A549, H460, H358, H322, and H226B) were assessed in vitro and in vivo by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, a flow cytometry-based terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling assay, western blot analyses, and an NSCLC xenograft tumor model. The specific effects of Ad-IGFBP 3 and SCH66336 on mitogen-activated protein kinase and Akt were assessed by using adenoviral vectors that express constitutively active MEK1 or constitutively active Akt. Synergy was assessed by median effect analysis.
Results: The combination of Ad-IGFBP3 and SCH66336 had synergistic antiproliferative effects in five cell lines (H1299, H596, A549, H460, and H322). Antiproliferative effects were accompanied by increased apoptosis in H460 cells in vitro. Overexpression of a constitutively active Akt but not a constitutively active MEK-1 rescued H460 cells from apoptosis induced by single or combined treatment of Ad-IGFBP3 and SCH66336. In H1299 tumor xenografts, Ad-IGFBP3 and SCH66336 was associated with decreased tumor volume, increased apoptosis, and decreased Akt levels.
Conclusions: The combination of Ad-IGFBP3 and SCH66336 decreased Akt expression and increased apoptosis in NSCLC cells in vitro and in vivo. Simultaneous treatment with IGFBP-3 and SCH66336 may have the potential to be an effective therapeutic strategy in NSCLC.