A G-quadruplex binding compound down-regulates KIT, BCL2 and PDGFRβ expression in human gastric carcinoma cell line

INTRODUCTION Proto-oncogene KIT, a tyrosine kinase receptor, is involved in the initiation and progress of human tumors, e.g. gastrointestinal stromal tumors, melanoma, mastocytosis and acute leukemia. The stabilization of DNA secondary structures called G-quadruplexes, located in promoter regions of KIT and other proto-oncogenes, could result in a block of gene transcription. MATERIALS AND METHODS An “in house” library of compounds were screened for the recognition of two KIT G-quadruplex regions. Three positive hits were tested in a human gastric carcinoma cell line (HGC27). The 50% inhibitory concentration (IC50) was measured by using the Alamar Blue cytotoxicity test. The effects of these ligands upon mRNA of KIT and other proto-oncogenes, PDGFRβ and BCL2 were evaluated after 6, 12 and 24 hours of incubation and by using two concentrations for each ligand. RESULTS Compound 1 was the most effective ligand in stabilizing the two KIT G-quadruplex regions. The IC50 value was obtained for compounds 1 and 2, while it was not determinable for the third ligand (>10 µM). Overall, compound 1 was the most effective in inhibiting proto-oncogene transcription; it lowered KIT and PDGFRβ mRNA expression in a dose-dependent manner, while a time- and concentration-dependents down-regulation was observed for BCL2. CONCLUSIONS Compound 1 might represent a promising candidate for targeting KIT-dependent neoplasia, and such an assumption needs to be confirmed with further molecular studies. Comparative studies about the efficacy of these ligands in another human cell line are currently underway. REFERENCES Bejugam M., Sewitz, S., Shirude P. S., Rodriguez R., Shahid R. & Balasubramanian S. (2007). Trisusbstituted isoalloxazines as a new class of G-quadruplex binding ligands: small molecule regulation of c-kit oncogene expression. Journal of the American Chemical Society, 129(43), 12926-12927. Gunaratnam M., Swank S., Haider S. M., Galeasa K., Reszka A. P., Beltran M., Cuenca F., Fletcher J. A. & Neidle S. (2009). Targeting human gastrointestinal stromal tumor cells with a quadruplex-binding small molecule. Journal of Medicinal Chemistry, 52(12), 3774-3783.