Dual blockade of VEGFR1 and VEGFR2 by a novel peptide abrogates VEGF-driven angiogenesis, tumor growth, and metastasis through PI3K/AKT and MAPK/ERK1/2 pathway

Poly(1-vinylimidazole) polyplexes as novel therapeutic gene carriers for lung cancer therapy

The present work explores the ability of poly(1-vinylimidazole) (PVI) to complex small interfering RNA (siRNA) silencing vascular endothelial growth factor (VEGF) and the in vitro efficiency of the formed complexes in A549 lung cancer cells. The polyplex formed was found to exhibit 66% complexation efficiency. The complexation was confirmed by gel retardation assays, FTIR and thermal analysis. The blank PVI polymer was not toxic to cells. The polyplex was found to exhibit excellent internalization and escaped the endosome effectively. The polyplex was more effective than free siRNA in silencing VEGF in lung cancer cells. The silencing of VEGF was quantified using Western blot and was also reflected in the depletion of HIF-1α levels in the cells treated with the polyplex. VEGF silencing by the polyplex was found to augment the cytotoxic effects of the chemotherapeutic agent 5-fluorouracil. Microarray analysis of the mRNA isolated from cells treated with free siRNA and the polyplex reveal that the VEGF silencing by the polyplex also altered the expression levels of several other genes that have been connected to the proliferation and invasion of lung cancer cells. These results indicate that the PVI complexes can be an effective agent to counter lung cancer.

Vascular PPARβ/δ Promotes Tumor Angiogenesis and Progression

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors, which function as transcription factors. Among them, PPARβ/δ is highly expressed in endothelial cells. Pharmacological activation with PPARβ/δ agonists had been shown to increase their angiogenic properties. PPARβ/δ has been suggested to be involved in the regulation of the angiogenic switch in tumor progression. However, until now, it is not clear to what extent the expression of PPARβ/δ in tumor endothelium influences tumor progression and metastasis formation. We addressed this question using transgenic mice with an inducible conditional vascular-specific overexpression of PPARβ/δ. Following specific over-expression of PPARβ/δ in endothelial cells, we induced syngenic tumors. We observed an enhanced tumor growth, a higher vessel density, and enhanced metastasis formation in the tumors of animals with vessel-specific overexpression of PPARβ/δ. In order to identify molecular downstream targets of PPARβ/δ in the tumor endothelium, we sorted endothelial cells from the tumors and performed RNA sequencing. We identified platelet-derived growth factor receptor beta (Pdgfrb), platelet-derived growth factor subunit B (Pdgfb), and the tyrosinkinase KIT (c-Kit) as new PPARβ/δ -dependent molecules. We show here that PPARβ/δ activation, regardless of its action on different cancer cell types, leads to a higher tumor vascularization which favors tumor growth and metastasis formation.

Apatinib induces 3-hydroxybutyric acid production in the liver of mice by peroxisome proliferator-activated receptor α activation to aid its antitumor effect

Apatinib, an antiangiogenic agent, shows efficient antitumor activity in a broad range of malignancies. Considering tumor is a type of metabolic disease, we investigated the metabolomics changes in serum and tumor after apatinib treatment and the molecular mechanism of characteristic changes associated with its antitumor efficacy. Molecules in serum and tumor tissue were extracted and analyzed by a gas chromatography-mass spectrometry metabolic platform. Apatinib significantly inhibited e tumor growth and alleviated metabolic rearrangement in both serum and tumor of A549 xenograft mice. Among these endogenous metabolites, 3-hydroxybutyric acid (3-HB) was significantly increased in serum, tumor and liver after apatinib treatment. Interestingly, giving exogenous 3-HB also inhibited tumor growth. Gene expression, dual luciferase reporter gene assay and molecular docking analysis all indicated that apatinib could induce 3-HB production through the dependent activation of peroxisome proliferator-activated receptor α (PPARα) and promotion of fatty acid utilization in the liver. Therefore, increased content of 3-HB induced by PPARα activation in the liver partially contributed to the antitumor effect of apatinib. It may provide clues to another potential mechanism underlying the antitumor effect of apatinib besides its antiangiogenic effect through inhibiting vascular endothelial growth factor receptor 2.

Autophagy, cancer and angiogenesis: where is the link?

Background

Autophagy is a catabolic process for degradation of intracellular components. Damaged proteins and organelles are engulfed in double-membrane vesicles ultimately fused with lysosomes. These vesicles, known as phagophores, develop to form autophagosomes. Encapsulated components are degraded after autophagosomes and lysosomes are fused. Autophagy clears denatured proteins and damaged organelles to produce macromolecules further reused by cells. This process is vital to cell homeostasis under both physiologic and pathologic conditions.

Main body

While the role of autophagy in cancer is quite controversial, the majority of studies introduce it as an anti-tumorigenesis mechanism. There are evidences confirming this role of autophagy in cancer. Mutations and monoallelic deletions have been demonstrated in autophagy-related genes correlating with cancer promotion. Another pathway through which autophagy suppresses tumorigenesis is cell cycle. On the other hand, under hypoxia and starvation condition, tumors use angiogenesis to provide nutrients. Also, autophagy flux is highlighted in vessel cell biology and vasoactive substances secretion from endothelial cells. The matrix proteoglycans such as Decorin and Perlecan could also interfere with angiogenesis and autophagy signaling pathway in endothelial cells (ECs). It seems that the connection between autophagy and angiogenesis in the tumor microenvironment is very important in determining the fate of cancer cells.

Conclusion

Matrix glycoproteins can regulate autophagy and angiogenesis linkage in tumor microenvironment. Also, finding details of how autophagy and angiogenesis correlate in cancer will help adopt more effective therapeutic approaches.

Suppression of migratory and metastatic pathways via blocking VEGFR1 and VEGFR2

BACKGROUND

Vascular endothelial growth factor (VEGF) A and B are endothelial cell mitogens whose ligation to VEGFR1/VEGFR2 drives tumor angiogenesis and metastasis, and epithelial-mesenchymal transition (EMT). Blockade of these signaling axes could be obtained by disturbing the interactions between VEGFA and/or VEGFB with VEGFR1 and/or VEGFR2.

METHODS

A 14-mer peptide (VGB) that recognizes both VEGFR1 and VEGFR2 were investigated for its inhibitory effects on the VEGF-induced proliferation and migration using MTT and scratch assay, respectively. Downstream signaling pathways were also assessed by quantitative estimation of gene and protein expression using real-time PCR and immunohistochemistry (IHC).

RESULTS

We investigated the inhibitory effects of VGB on downstream mediators of metastasis, including epithelial-cadherin (E-cadherin), matrix metalloprotease-9 (MMP-9), cancer myelocytomatosis (c-Myc), and nuclear factor-κβ (NF-κβ), and migration, comprising focal adhesion kinase (FAK) and its substrate Paxilin. VGB inhibited the VEGF-induced proliferation of human umbilical vein endothelial cells (HUVECs), 4T1 and U87 cells in a time- and dose-dependent manner and migration of HUVECs. Based on IHC analyses, treatment of 4T1 mammary carcinoma tumor with VGB led to the suppression of p-AKT, p-ERK_1/2, MMP-9, NF-κβ, and activation of E-cadherin compared with PBS-treated controls. Moreover, quantitative real-time PCR analyses of VGB-treated tumors revealed the reduced expression level of FAK, Paxilin, NF-κβ, MMP-9, c-Myc, and increased expression level of E-cadherin compared to PBS-treated controls.

CONCLUSIONS

Our results demonstrated that simultaneous blockade of VEGFR1/VEGFR2 is an effective strategy to fight solid tumors by targeting a wider range of mediators involved in tumor angiogenesis, growth, and metastasis.

A cyclic peptide reproducing the α1 helix of VEGF-B binds to VEGFR-1 and VEGFR-2 and inhibits angiogenesis and tumor growth

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are pivotal regulators of angiogenesis. The VEGF–VEGFR system is therefore an important target of anti-angiogenesis therapy. Based on the X-ray structure of VEGF-B/VEGFR-1 D2, we designed a cyclic peptide (known as VGB1) reproducing the α1 helix and its adjacent region to interfere with signaling through VEGFR-1. Unexpectedly, VGB1 bound VEGFR-2 in addition to VEGFR-1, leading to inhibition of VEGF-stimulated proliferation of human umbilical vein endothelial cells and 4T1 murine mammary carcinoma cells, which express VGEFR-1 and VEGFR-2, and U87 glioblastoma cells that mostly express VEGFR-2. VGB1 inhibited different aspects of angiogenesis, including proliferation, migration and tube formation of endothelial cells stimulated by VEGF-A through suppression of extracellular signal-regulated kinase 1/2 and AKT (Protein Kinase B) phosphorylation. In a murine 4T1 mammary carcinoma model, VGB1 caused regression of tumors without causing weight loss in association with impaired cell proliferation (decreased Ki67 expression) and angiogenesis (decreased CD31 and CD34 expression), and apoptosis induction (increased TUNEL staining and p53 expression, and decreased Bcl-2 expression). According to far-UV circular dichroism (CD) and molecular dynamic simulation data, VGB1 can adopt a helical structure. These results, for the first time, demonstrate that α1 helix region of VEGF-B recognizes both VEGFR-1 and VEGFR-2.

A peptide mimicking the binding sites of VEGF-A and VEGF-B inhibits VEGFR-1/-2 driven angiogenesis, tumor growth and metastasis

Interfering with interactions of vascular endothelial growth factors (VEGFs) with their receptors (VEGFRs) effectively inhibits angiogenesis and tumor growth. We designed an antagonist peptide of VEGF-A and VEGF-B reproducing two discontinuous receptor binding regions of VEGF-B (loop 1 and loop3) covalently linked together by a receptor binding region of VEGF-A (loop3). The designed peptide (referred to as VGB4) was able to bind to both VEGFR1 and VEGFR2 on the Human Umbilical Vein Endothelial Cells (HUVECs) surface and inhibited VEGF-A driven proliferation, migration and tube formation in HUVECs through suppression of ERK1/2 and AKT phosphorylation. The whole-animal fluorescence imaging demonstrated that fluorescein isothiocyanate (FITC)-VGB4 accumulated in the mammary carcinoma tumors (MCTs). Administration of VGB4 led to the regression of 4T1 murine MCT growth through decreased expression of p-VEGFR1 and p-VEGFR2 and abrogation of ERK1/2 and AKT activation followed by considerable decrease of tumor cell proliferation (Ki67 expression) and angiogenesis (CD31 and CD34 expression), induction of apoptosis (increased p53 expression, TUNEL staining and decreased Bcl2 expression), and suppression of metastasis  (increased E-cadherin and decreased N-cadherin, NF-κB and MMP-9 expression). These findings indicate that VGB4 may be applicable for antiangiogenic and antitumor therapy.

Effects of VEGFR1+ hematopoietic progenitor cells on pre-metastatic niche formation and in vivo metastasis of breast cancer cells

The pre-metastatic niche has been shown to play a critical role in tumor metastasis, and its formation is closely related to the tumor microenvironment. However, the underlying molecular mechanisms remain unclear. In the present study, we successfully established a mouse model of lung metastasis using luciferase-expressing MDA-MB-435s cells. In this model, recruitment of vascular endothelial growth factor receptor-1 (VEGFR1)⁺CD133⁺ hematopoietic progenitor cells (HPCs) was gradually increased in lung but gradually decreased after the formation of tumor colonies in lung. We also established a highly metastatic MDA-MB-435s (MDA-MB-435s-HM) cell line from the mouse model. Changes in protein profiles in different culture conditions were investigated by protein microarray analysis. The levels of CXC chemokine ligand 16, interleukin (IL)-2Rα, IL-2Rγ, matrix metalloproteinase (MMP)-1, MMP-9, platelet-derived growth factor receptor (PDGFR)-α, stromal cell-derived factor (SDF)-1α, transforming growth factor (TGF)-β, platelet endothelial cell adhesion molecule (PECAM)-1 and vascular endothelial (VE)-cadherin were significantly greater (> fivefold) in the culture medium from MDA-MB-435s-HM cells than in that from MDA-MB-435s cells. Moreover, the levels of MMP-9, PDGFR-α, and PECAM-1 were significantly greater in the co-culture medium of MDA-MB-435s-HM cells and CD133⁺ HPCs than in that from MDA-MB-435s-HM cells. Differentially expressed proteins were validated by enzyme-linked immunosorbent assay, and expression of their transcripts was confirmed by quantitative real-time polymerase chain reaction. Moreover, inhibition of MMP-9, PDGFR-α, and PECAM-1 by their specific inhibitors or antibodies significantly decreased cell migration, delayed lung metastasis, and decreased recruitment of VEGFR1⁺CD133⁺ HPCs into lung. Intra-hepatic growth of HPCs enhanced the invasive growth of MDA-MB-435s-HM cells in the liver. Our data indicate that VEGFR1⁺CD133⁺ HPCs contribute to lung metastasis.