l-744832 and Pancreatic-Neoplasms

Activated ras is known to dysregulate TGF-beta signaling by altering the expression of TGF-beta type II receptor (RII). It is well documented that tumor cells harboring mutant ras are more resistant to radiation than cells with wild-type ras. In this study, we hypothesized that the use of farnesyltransferase inhibitor (FTI, L-744,832) may directly restore TGF-beta signaling through RII expression via ras dependent or independent pathway leading to induction of radiation sensitivity. Two pancreatic cancer cell lines, BxPC-3 and MIA PaCa-2 were used in this study. FTI inhibited farnesylation of Ras protein more significantly in MIA PaCa-2 than BxPC-3 cells. In contrast, MIA PaCa-2 cells were resistant to radiation when compared to BxPC-3 cells. BxPC-3 cells were more resistant to FTI than MIA PaCa-2 cells. In combination treatment, no significant radiosensitizing effect of FTI was observed in BxPC-3 cells at 5 or 10 microM. However, in MIA PaCa-2 cells, a significant radiosensitizing effect was observed at both 5 and 10 microM concentrations (P>0.004). The TGF-beta effector gene p21(waf1/cip1) was elevated in combination treatment in MIA PaCa-2 but not in BxPC-3 cells. In MIA PaCa-2 cells, FTI induced TGF-beta responsive promoter activity as assessed by 3TP-luciferase activity. A further induction of luciferase activity was observed in MIA PaCa-2 cells treated with radiation and FTI. Induction of TGF-beta signaling by FTI was mediated through restoration of the RII expression, as demonstrated by RT-PCR analysis. In addition, re-expression of RII by FTI was associated with a decrease in DNA methyltransferase 1 (DNMT1) levels. Thus, these findings suggest that the L-744,832 treatment restores the RII expression through inhibition of DNMT1 levels causing induction of TGF-beta signaling by radiation and this forms a novel molecular mechanism of radiosensitization by FTI.

Topics: Adenocarcinoma; Alkyl and Aryl Transferases; Apoptosis; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; DNA (Cytosine-5-)-Methyltransferase 1; DNA (Cytosine-5-)-Methyltransferases; DNA Methylation; Enzyme Induction; Enzyme Inhibitors; Farnesyltranstransferase; Gene Expression Regulation, Neoplastic; Genes, ras; Humans; Methionine; Neoplasm Proteins; Pancreatic Neoplasms; Protein Prenylation; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins p21(ras); Radiation Tolerance; Radiation-Sensitizing Agents; Receptor, Transforming Growth Factor-beta Type II; Receptors, Transforming Growth Factor beta; Recombinant Fusion Proteins; Regulatory Sequences, Nucleic Acid; Signal Transduction; Transforming Growth Factor beta