pf-4708671 and Colorectal-Neoplasms

Agents targeting insulin-like growth factor 1 receptor (IGF-1R) are being actively examined in clinical trials. Although there has been some initial success of single-agent targeting IGF-1R, attempts in later studies failed because of resistance. This study aimed to understand the effects of programmed cell death 4 (Pdcd4) on the chemosensitivity of the IGF-1R inhibitor OSI-906 in colorectal cancer cells and the mechanism underlying this impact. Using OSI-906-resistant and -sensitive colorectal cancer cells, we found that the Pdcd4 level directly correlates with cell chemosensitivity to OSI-906. In addition, tumors derived from Pdcd4 knockdown cells resist the growth inhibitory effect of OSI-906 in a colorectal cancer xenograft mouse model. Moreover, Pdcd4 enhances the antiproliferative effect of OSI-906 in resistant cells through suppression of p70S6K1 activation. Knockdown of p70S6K1, but not p70S6K2, significantly increases the chemosensitivity of OSI-906 in cultured colorectal cancer cells. Furthermore, the combination of OSI-906 and PF-4708671, a p70S6K1 inhibitor, efficiently suppresses the growth of OSI-906-resistant colon tumor cells in vitro and in vivo. Taken together, activation of p70S6K1 that is inhibited by Pdcd4 is essential for resistance to the IGF-1R inhibitor in colon tumor cells, and the combinational treatment of OSI-906 and PF-4708671 results in enhanced antiproliferation effects in colorectal cancer cells in vitro and in vivo, providing a novel venue to overcome the resistance to the IGF-1R inhibitor in treating colorectal cancer.

Topics: Animals; Apoptosis Regulatory Proteins; Caco-2 Cells; Carcinoma; Cell Line, Tumor; Cell Proliferation; Colorectal Neoplasms; Drug Resistance, Neoplasm; Female; HCT116 Cells; HT29 Cells; Humans; Imidazoles; Mice; Mice, Nude; Piperazines; Protein Kinase Inhibitors; Pyrazines; Receptor, IGF Type 1; Ribosomal Protein S6 Kinases, 70-kDa; RNA-Binding Proteins; Xenograft Model Antitumor Assays

Selumetinib (AZD6244, ARRY-142886) is a MEK1/2 inhibitor that has gained interest as an anti-tumour agent. We have determined the degree of sensitivity/resistance to Selumetinib in a panel of colorectal cancer cell lines using cell proliferation and soft agar assays. Sensitive cell lines underwent G1 arrest, whereas Selumetinib had no effect on the cell cycle of resistant cells. Some of the resistant cell lines showed high levels of ERK1/2 phosphorylation in the absence of serum. Selumetinib inhibited phosphorylation of ERK1/2 and RSK and had no effect on AKT phosphorylation in both sensitive and resistant cells. Furthermore, mutations in KRAS, BRAF, or PIK3CA were not clearly associated with Selumetinib resistance. Surprisingly, Selumetinib was able to inhibit phosphorylation of p70 S6 kinase (p70S6K) and its downstream target ribosomal protein S6 (RPS6) in sensitive cell lines. However, p70S6K and RPS6 phosphorylation remained unaffected or even increased in resistant cells. Moreover, in some of the resistant cell lines p70S6K and RPS6 were phosphorylated in the absence of serum. Interestingly, colorectal primary cultures derived from tumours excised to patients exhibited the same behaviour than established cell lines. Pharmacological inhibition of p70S6K using the PI3K/mTOR inhibitor NVP-BEZ235, the specific mTOR inhibitor Rapamycin and the specific p70S6K inhibitor PF-4708671 potentiated Selumetinib effects in resistant cells. In addition, biological inhibition of p70S6K using siRNA rendered responsiveness to Selumetinib in resistant cell lines. Furthermore, combination of p70S6K silencing and PF-47086714 was even more effective. We can conclude that p70S6K and its downstream target RPS6 are potential biomarkers of resistance to Selumetinib in colorectal cancer.

Topics: Antineoplastic Combined Chemotherapy Protocols; Benzimidazoles; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Class I Phosphatidylinositol 3-Kinases; Colorectal Neoplasms; Drug Resistance, Neoplasm; Enzyme Activation; Humans; Imidazoles; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Molecular Targeted Therapy; Mutation; Phosphatidylinositol 3-Kinases; Phosphorylation; Piperazines; Protein Kinase Inhibitors; Proto-Oncogene Proteins; Proto-Oncogene Proteins B-raf; Proto-Oncogene Proteins p21(ras); Quinolines; ras Proteins; Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 70-kDa