Abstract 1386: A novel approach to develop anti-VEGFR2/KDR therapeutics: characterizing and targeting the G-quadruplex

The anti-angiogenic approach is traditionally considered for solid malignancies, but increasing evidence has also highlighted its involvement in the progression of hematological oncologies. Angiogenesis, including expression of key proteins, is aberrant in blood cancers such as leukemias, lymphomas, and myelomas, in addition to many solid malignancies, including pancreatic cancer. The most critical mediator of oncogenic angiogenesis is vascular endothelial growth factor (VEGF), which is recognized by two high-affinity receptor tyrosine kinases, VEGFR1 and VEGFR2 (KDR gene). VEGFR2 is necessary for the survival, growth, and differentiation of endothelial cells as its downstream effects include activation of the MAPK and the PI3K pathways, and its upregulation is observed under conditions of pathological angiogenesis. While VEGF/VEGFR2 signaling is known to act in a paracrine manner on endothelial cells, autocrine signaling has been observed in both malignant cells and hematopoietic stem cells. For endothelial and hematological malignancies, both autocrine and paracrine pathways can be targeted with anti-VEGFR2 therapies, potentially doubling the clinical efficacy. Intriguingly, the promoter region of KDR contains a GC-rich region of DNA within its the core promoter located −120 to −31 basepairs (bp) upstream of the transcriptional start site (TSS), putatively able to form several G-quadruplexes. These are unique DNA secondary structures that often serve as transcriptional silencer elements. In the present study, G-quadruplex formation has been isolated −80 to −38 bp upstream of the TSS, which contains five strings of guanines that form a mixed parallel/anti-parallel G-quadruplex, as determined by circular dichroism. The cleavage pattern of DMS footprinting and the major stop product of the polymerase stop assay confirmed that the dominant isoform is a parallel G-quadruplex occurring within the four 3’ runs of guanines. Mutant studies were performed to further determine guanines integral to G-quadruplex formation. An electrophoretic mobility shift assay was used to confirm the formation of a biologically relevant intramolecular structure. High-throughput screening identified a novel KDR-interactive agent, NSC643735, which thermally stabilized the G-quadruplex. This compound is currently being tested in vitro, and has high potential to transcriptionally downregulate KDR mRNA and, subsequently, VEGFR2 protein. These data characterizing the formation of a unique secondary structure in an important oncogene are promising to develop novel and specific anti-KDR therapy for the treatment of hematological and solid malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1386.