He modified SL2-B. Solid line is PS-modified SL2-B, 
dashed line is unmodified SL2-B, and dotted line is scrambled sequence. doi:10.1371/journal.pone.0050964.gAntiproliferative Activity of Aptamer on CancerFigure 6. Effect of PS-modified SL2 aptamer sequence compared to the scrambled sequence on Hep G2 cells. Low magnification view of (A) modified sequence treatment, (B) scrambled sequence treatment on Hep G2 cells after 72 hours under hypoxia condition. Scale bar = 200 mm. Close up views of (C) modified sequence treatment, (D) scrambled sequence treatment on Hep G2 cells after 72 hours under hypoxia 22948146 condition. Cellular morphology differs upon the different treatments; modified sequence treatment produces cells which are thinner with more cellular projections while the scrambled sequence treatment shows cells which appear closer to the untreated Hep G2 cells. Scale bar = 50 mm. doi:10.1371/journal.pone.0050964.gStability of SL2-B Aptamer Against Nucleases in Serum Containing MediumTo test the biostability of the unmodified and PS-modified SL2B aptamer against nucleases present in the biological fluids, both aptamers were incubated with 10 FBS for different time periods. Based on the results, the unmodified SL2-B degraded by 50 within 24 hours of incubation in serum (Figure 3). On the other hand, the PS-modified SL2-B displayed good stability, with more than 90 aptamer intact after 72 hours of incubation in the serum. The data demonstrates the importance of PS-linkages in the SL2-B sequence termini, which protects the aptamer sequence from exonuclease attack.the spectra was observed between 25uC and 37uC, this confirms the preservation of the secondary conformation at the SPR conditions (25uC) where the Kd of the aptamer was determined and at physiological conditions (37uC). However, the CD spectroscopy does not provide the complete and validated information on the structure. Advanced techniques such as nuclear magnetic resonance (NMR) and X-ray crystallography are required for further in-depth structural analysis.Antiproliferative Activity AssayThe antiproliferative property of SL2-B aptamer was studied using Hep G2 cancer cells in 23727046 hypoxia conditions. Previous studies have demonstrated that the expression of VEGF Vitamin D2 chemical information protein is potentiated in Hep G2 cells under hypoxia conditions [46]. Since no significant effect on cell proliferation was observed at 24 and 48 hours, both the unmodified and PS-modified SL2-B aptamers were tested for 72 hours duration. As shown in Figure 5, lower cell proliferation was observed at 15 mM modified SL2-B concentration after 72 hours of aptamer treatment (5262.1 ). However, no decrease in the cell proliferation was observed on further increasing aptamer concentration to 20 mM. A possible explanation for decrease in the cell proliferation could be that either the excess binding of modified SL2-B sequence to VEGF165 protein ultimately prevents the interaction of the protein to the VEGFR-2 (or KDR/Flk-1) receptor, which affects the cellular proliferation. Or aptamer after binding with VEGF protein binds with VEGFR2, undergoes cellular internalization and interferes with theStructural Analysis by Circular Dichroism (CD) SpectroscopyStructural studies have shown the impact of the conformation on the binding affinity and specificity of the aptamer for its SMER28 chemical information target [44]. If the conformation changes with temperature, then the binding affinity results obtained from SPR spectroscopy (conducted at 25uC) may not be represe.He modified SL2-B. Solid line is PS-modified SL2-B, dashed line is unmodified SL2-B, and dotted line is scrambled sequence. doi:10.1371/journal.pone.0050964.gAntiproliferative Activity of Aptamer on CancerFigure 6. Effect of PS-modified SL2 aptamer sequence compared to the scrambled sequence on Hep G2 
cells. Low magnification view of (A) modified sequence treatment, (B) scrambled sequence treatment on Hep G2 cells after 72 hours under hypoxia condition. Scale bar = 200 mm. Close up views of (C) modified sequence treatment, (D) scrambled sequence treatment on Hep G2 cells after 72 hours under hypoxia 22948146 condition. Cellular morphology differs upon the different treatments; modified sequence treatment produces cells which are thinner with more cellular projections while the scrambled sequence treatment shows cells which appear closer to the untreated Hep G2 cells. Scale bar = 50 mm. doi:10.1371/journal.pone.0050964.gStability of SL2-B Aptamer Against Nucleases in Serum Containing MediumTo test the biostability of the unmodified and PS-modified SL2B aptamer against nucleases present in the biological fluids, both aptamers were incubated with 10 FBS for different time periods. Based on the results, the unmodified SL2-B degraded by 50 within 24 hours of incubation in serum (Figure 3). On the other hand, the PS-modified SL2-B displayed good stability, with more than 90 aptamer intact after 72 hours of incubation in the serum. The data demonstrates the importance of PS-linkages in the SL2-B sequence termini, which protects the aptamer sequence from exonuclease attack.the spectra was observed between 25uC and 37uC, this confirms the preservation of the secondary conformation at the SPR conditions (25uC) where the Kd of the aptamer was determined and at physiological conditions (37uC). However, the CD spectroscopy does not provide the complete and validated information on the structure. Advanced techniques such as nuclear magnetic resonance (NMR) and X-ray crystallography are required for further in-depth structural analysis.Antiproliferative Activity AssayThe antiproliferative property of SL2-B aptamer was studied using Hep G2 cancer cells in 23727046 hypoxia conditions. Previous studies have demonstrated that the expression of VEGF protein is potentiated in Hep G2 cells under hypoxia conditions [46]. Since no significant effect on cell proliferation was observed at 24 and 48 hours, both the unmodified and PS-modified SL2-B aptamers were tested for 72 hours duration. As shown in Figure 5, lower cell proliferation was observed at 15 mM modified SL2-B concentration after 72 hours of aptamer treatment (5262.1 ). However, no decrease in the cell proliferation was observed on further increasing aptamer concentration to 20 mM. A possible explanation for decrease in the cell proliferation could be that either the excess binding of modified SL2-B sequence to VEGF165 protein ultimately prevents the interaction of the protein to the VEGFR-2 (or KDR/Flk-1) receptor, which affects the cellular proliferation. Or aptamer after binding with VEGF protein binds with VEGFR2, undergoes cellular internalization and interferes with theStructural Analysis by Circular Dichroism (CD) SpectroscopyStructural studies have shown the impact of the conformation on the binding affinity and specificity of the aptamer for its target [44]. If the conformation changes with temperature, then the binding affinity results obtained from SPR spectroscopy (conducted at 25uC) may not be represe.
