Antisense Oligonucleotides Targeting Y-Box Binding Protein-1 Inhibit Tumor Angiogenesis by Downregulating Bcl-xL-VEGFR2/-Tie Axes

Abstract

Y-box binding protein-1 (YB-1), involved in cancer progression and chemoradiation resistance, is overexpressed in not only cancer cells but also tumor blood vessels. In this study, we investigated the potential value of amido-bridged nucleic acid (AmNA)-modified antisense oligonucleotides (ASOs) targeting YB-1 (YB-1 ASO^A) as an antiangiogenic cancer therapy. YB-1 ASO^A was superior to natural DNA-based ASO or locked nucleic acid (LNA)-modified YB-1 ASO in both knockdown efficiency and safety, the latter assessed by liver function. YB-1 ASO^A administered i.v. significantly inhibited YB-1 expression in CD31-positive angiogenic endothelial cells, but not in cancer cells, in the tumors. With regard to the mechanism of its antiangiogenic effects, YB-1 ASO^A downregulated both Bcl-xL/VEGFR2 and Bcl-xL/Tie signal axes, which are key regulators of angiogenesis, and induced apoptosis in vascular endothelial cells. In the xenograft tumor model that had low sensitivity to anti-VEGF antibody, YB-1 ASO^A significantly suppressed tumor growth; not only VEGFR2 but also Tie2 expression was decreased in tumor vessels. In conclusion, YB-1/Bcl-xL/VEGFR2 and YB-1/Bcl-xL/Tie signal axes play pivotal roles in tumor angiogenesis, and YB-1 ASO^A may be feasible as an antiangiogenic therapy for solid tumors.

Keywords: ASO; Tie; VEGFR2; YB-1; tumor angiogenesis.

Graphical abstract

Figure 1

Construction of YB-1 ASOs and Their Effects on YB-1 mRNA and Protein Expression In Vitro (A) Schematic structures of several types of YB-1 ASOs. (B) T_m values of YB-1 ASO duplexes with DNA and RNA target strands. (C) qRT-PCR of human YBX1 mRNA in HUVECs, HPAECs, and MIA PaCa-2 cells transfected with YB-1 ASOs or control ASO (normalized to B2M). n = 3. (D) Immunoblots for YB-1 protein in HUVECs, HPAECs, and MIA PaCa-2 cells transfected with YB-1 ASOs or control ASO (5 nM). β-actin is the loading control. (E) Effects of i.v. administered YB-1 ASO^A, YB-1 ASO^L, or control ASO (once per week for 3 weeks at 10 mg/kg body weight) on liver function, evaluated by alanine aminotransferase (ALT) and T. Bil values. *p < 0.01; n = 4 per group. Data are means ± SD.

Figure 2

Antitumor Efficacy of i.v. Administered YB-1 ASO^A in Mice Harboring Subcutaneous Tumor Xenografts (A) Antitumor efficacy of i.v. administered YB-1 ASO^A (once per week for 3 weeks at 10 mg/kg body weight) in mice bearing HCT116 or Suit2-GR xenografts. *p < 0.05, **p < 0.01; n = 7 per group. Black arrows represent administered time points of ASOs. (B) qRT-PCR of mouse YBX1 mRNA in liver, kidney, or tumor and human YBX1 mRNA in tumor tissues from mice harboring HCT116 and Suit2-GR xenografts and receiving YB-1 ASO^A treatments (once per week for 3 weeks at 10 mg/kg body weight). **p < 0.001; n = 7 per group. Values are normalized to those for mouse or human 18S rRNAs. Data are means ± SD.

Figure 3

i.v. Administered YB-1 ASO^A Suppresses Tumor Growth In Vivo through Antiangiogenic Effects on Host Vascular Cells (A) Representative immunostaining images showing CD31 in HCT116 and Suit2-GR tumors after YB-1 ASO^A treatment (once per week for 3 weeks at 10 mg/kg body weight). Scale bar, 200 μm. (B) Quantification of microvascular density, assessed by CD31 staining per field, in HCT116 and Suit2-GR tumor tissues. *p < 0.05, **p < 0.01; n = 6. Data are means ± SD. (C) Representative immunostaining images for YB-1 and CD31 in Suit2-GR tumor tissues in mice treated with YB-1 ASO^A or control ASO (once per week for 3 weeks at 10 mg/kg body weight). Scale bar, 20 μm. (D) Representative immunostaining images showing cleaved caspase-3 (c-caspase-3) and mouse CD31 in Suit2-GR tumor tissues from mice receiving i.v. YB-1 ASO^A treatment (once per week for 3 weeks at 10 mg/kg body weight). Yellow signal (arrowhead) in merged images represents apoptosis (c-caspase-3) in CD31-positive angiogenic endothelial cells. Scale bar, 50 μm. The fluorescent signal images (C and D) were obtained using immunofluorescence laser confocal microscopy. (E) Immunostaining of c-caspase-3 in Suit2-GR tumors from mice treated with i.v. administered YB-1 ASO^A (once per week for 3 weeks at 10 mg/kg body weight). YB-1 ASO^A-treated, but not control, tumors had apoptotic cells. Scale bar, 200 μm.

Figure 4

Involvement of YB-1 in Proliferation, Apoptosis, and Tube Formation in Vascular Endothelial Cells HUVECs and HPAECs were transfected with YB-1 ASO^A or control ASO^A (5 nM) and subjected to the following analyses. (A) Cell proliferation analysis with the WST-8 assay. *p < 0.05, **p < 0.01; n = 3. (B) Cell-cycle distribution, analyzed in HUVEC and HPAEC by staining the DNA content with propidium iodide. The distribution was measured by flow cytometry. *p < 0.05, **p < 0.01; n = 3. (C) Western blot analysis shows robustly increased c-caspase-3 (apoptosis) and decreased YB-1 levels in YB-1 ASO^A-transfected cells. β-actin is the loading control. (D) Cytochrome c release from the IMS was detected in HUVECs and HPAECs transfected with YB-1 ASO^A in the presence of a pan-caspase inhibitor, Z-VAD-FMK, under immunofluorescence laser confocal microscopy. Data were obtained from 50 cells in each of three independent experiments. Quantitated levels of released cytochrome c were higher in cells with YB-1 ASO^A transfection than in controls. *p < 0.001. (E) Representative images showing tube formation in HUVEC and HPAEC cultures transfected with YB-1 ASO^A or control. Scale bar, 200 μm. (F) Quantitation of total tube length in 10 randomly chosen images using ImageJ software. *p < 0.001. Data are means ± SD.

Figure 5

YB-1 ASO^A-Induced Apoptosis and Inhibition of Tube Formation Are Mediated by Bcl-xL Reduction in Vascular Endothelial Cells (A) Heatmap analysis of cDNA microarray data showing highly downregulated Bcl-xL expression, among Bcl-2 family genes, in HUVECs and HPAECs transfected with YB-1 ASO^A (5 nM). (B) Downregulation of Bcl-xL expression was confirmed by qRT-PCR analysis (normalized to values for 18S). *p < 0.01; n = 3. Data are means ± SD. (C) Immunoblots for Bcl-xL and YB-1 in HUVECs and HPAECs transfected with YB-1 ASO^A or control ASO (5 nM). β-actin is the loading control. (D) Western blot analysis shows an increase in c-caspase-3 but no change in YB-1 protein levels in HUVECs and HPAECs transfected with Bcl-xL siRNA (5 nM). (E) Cell proliferation, assessed by WST-8 assay, was decreased in HUVECs and HPAECs by transfection with Bcl-xL siRNA. *p < 0.05, **p < 0.01. (F) Capillary-like tube formation was inhibited by transfection with Bcl-xL siRNA or YB-1 ASO^A in HUVECs and HPAECs. Scale bar, 200 μm.

Figure 6

Knockdown of YB-1/Bcl-xL Downregulates VEGFR2 and Tie-1/-2 Expression in Angiogenic Endothelial Cells in Tumor Microenvironments (A and B) Western blot analysis showing inhibition of VEGFR2 and Tie-1/-2 expression in HUVECs or HPAECs transfected with YB-1 ASO^A (5 nM) (A) or Bcl-xL siRNA (20 nM) (B). β-actin is the loading control. (C) Antitumor efficacy of YB-1 ASO^A treatment (once per week for 4 weeks at 10 mg/kg body weight) was superior to that of bevacizumab (twice per week for 4 weeks at 10 mg/kg body weight) in mice bearing Suit2-GR xenografts. *p < 0.05; n = 9. Data are means ± SD. Red and black arrows represent administered time points of bevacizumab and ASOs, respectively. (D) Immunohistochemistry for VEGFR2, Tie2, and CD31 in the Suit2-GR tumors using laser confocal microscopy. The images show inhibition of Tie2 signals in CD31-positive angiogenic endothelial cells in tumor tissues treated with i.v. administered YB-1 ASO^A (once per week for 4 weeks at 10 mg/kg body weight), but not in the controls. Scale bar, 20 μm.

Figure 7

Antitumor Efficacy of i.p. Administered YB-1 ASO^A in Mice Harboring Peritoneal Dissemination (A) qRT-PCR analysis shows an inhibition of mouse and human YBX1 expression in peritoneally disseminated RMG-1 tumors treated with i.p. administered YB-1 ASO^A. *p < 0.05; n = 3. Values are normalized to those for mouse and human 18S rRNAs. (B) Disseminated RMG-1 tumor growth was inhibited on day 21 in mice treated with YB-1 ASO^A (once per week for 3 weeks at 10 mg/kg body weight) compared with control ASOs. *p < 0.05; n = 5. Data are means ± SD. (C) Immunohistochemistry for CD31 and YB-1 or c-caspase-3 using laser confocal microscopy. The images show decreased YB-1 and increased c-caspase-3 levels in not only CD31-positive angiogenic endothelial cells but also most disseminated RMG-1 cancer cells after i.p. administration of YB-1 ASO^A. Scale bar, 50 μm.