Abstract
Vascular endothelial growth factor (VEGF) is an angiogenic mitogen involved in promoting tumor angiogenesis inside the body. VEGF is a key protein required for progression of tumor from benign to malignant phenotype. In this study, we investigated the binding affinity of a previously selected 26-mer DNA aptamer sequence (SL2-B) against heparin binding domain (HBD) of VEGF165 protein. The SL2-B was first chemically modified by introduction of phosphorothioate linkages (PS-linkages). Subsequently, surface plasmon resonance (SPR) spectroscopy and circular dichroism (CD) were used to determine the binding affinity, specificity and to deduce the conformation of PS-modified SL2-B sequence. Finally, antiproliferative activity of the modified SL2-B sequence on Hep G2 cancer cells was investigated. Our results demonstrate a marked enhancement in the biostability of the SL2-B sequence after PS modification. The modified SL2-B sequence also exhibits enhanced antiproliferative activity against Hep G2 cancer cells in hypoxia conditions. In addition, modified SL2-B sequence inhibits the expression of Jagged-1 protein, which is one of the ligands to VEGF linked delta/jagged-notch signaling pathway.
Highlights
Cancer is one of the leading causes of death worldwide and accounted for 7.6 million deaths in 2008 [1,2]
We demonstrated that, compared to unmodified SL2-B aptamer, the PS-modified SL2-B aptamer is an improved sequence in terms of serum stability and antiproliferative activity without sacrificing the binding affinity and specificity for VEGF165 protein
As reported previously in our study, the unmodified SL2-B aptamer displayed a Kd = 0.5 nM to heparin binding domain (HBD) of VEGF165 protein determined via surface plasmon resonance (SPR) technique (Table 1) [37]
Summary
Cancer is one of the leading causes of death worldwide and accounted for 7.6 million deaths in 2008 [1,2]. Monoclonal antibodies are one of the most advanced therapeutic agents for cancer treatment in the market. In 1990, an in vitro selection process called systematic evolution of ligands by exponential enrichment (SELEX) was developed to screen single stranded nucleic acid molecules from random pool of library against the target ligand [13,14]. These classes of single stranded molecules are referred as ‘‘aptamers’’. They possess high binding affinity and specificity that are comparable to monoclonal antibodies. Based on the promising results in preclinical studies, two cancer targeting aptamers, ACT-GRO-777 (or AS1411) - a G-rich DNA aptamer targeting nucleolin for treatment of acute myeloid leukemia (AML) and NOX-A12 L-RNA aptamer targeting CXCL12 for treatment of multiple myeloma and lymphoma are already in clinical trials [16,17]
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