Wild-type Gastrointestinal Tumors Research Articles

A naphthalene diimide G-quadruplex ligand inhibits cell growth and down-regulates BCL-2 expression in an imatinib-resistant gastrointestinal cancer cell line

Gastro-intestinal tumours (GISTs) are driven by aberrant expression of the c-KIT oncoprotein. They can be effectively treated by the kinase inhibitor imatinib, which locks the c-KIT kinase domain into an inactive conformation. However resistance to imatinib, driven by active-site mutations, is a recurrent clinical challenge, which has been only partly met by the subsequent development of second and third-generation c-KIT inhibitors.It is reported here that a tetra-substituted naphthalene diimide derivative, which is a micromolar inhibitor of cell growth in a wild-type patient-derived GIST cell line, has a sub-micromolar activity in two distinct patient-derived imatinib-resistant cell lines. The compound has been previously shown to down-regulate expression of the c-KIT protein in a wild-type GIST cell line. It does not affect c-KIT protein expression in a resistant cell line to the same extent, whereas it profoundly down-regulates the expression of the anti-apoptopic protein BCL-2. It is proposed that the mechanism of action involves targeting quadruplex nucleic acid structures, and in particular those in the BCL-2 gene and its RNA transcript. The BCL-2 protein is up-regulated in the GIST-resistant cell line, and is strongly down-regulated after treatment. The compound strongly stabilises a range of G-quadruplexes including a DNA one from the BCL-2 promoter and an RNA quadruplex from its 5′-UTR region. A reporter assay construct incorporating the 5′-UTR quadruplex sequence demonstrates down-regulation of BCL-2 expression.

PDGFRα Gene Mutation and Protein Expression in Gastrointestinal Stromal Tumors

Objective: Mutation of the PDGFRα is a potential candidate in the pathogenesis of KIT wild-type gastrointestinal tumors (GISTs). In this study, we evaluated the prevalence of PDGFRα mutations and corresponding protein expression in GISTs, to determine their usefulness in obtaining a prognosis. Methods: Genomic DNA was extracted from paraffin-embedded tumor tissues from 194 GISTs. Exons 12, 14 and 18 of the PDGFRα were amplified and sequenced. Immunohistochemical staining was performed in 179 patients. Results: Mutations in the PDGFRα were detected in 6 (3.1%) patients, and were observed solely in KIT wild-type GISTs. Among the 6 patients with PDGFRα gene mutations, 5 patients with localized GISTs showed no relapse after resection during the 19- to 80-month follow-up period. Intensity of PDGFRα expression was classified as 0 in 26 (14.5%), 1+ in 69 (38.5%), 2+ in 71 (39.7%) and 3+ in 13 (7.3%) patients. Levels of PDGFRα expression showed no correlation with relapse-free survival. Conclusion:PDGFRα mutations in GISTs were found to be rare in this Korean population. Although localized GISTs with PDGFRα mutations showed relatively good prognosis after resection, the difference was not statistically significant.