The Discovery of Tumor Angiogenesis Factors: A Historical Overview

Suppressing VEGF-A/VEGFR-2 Signaling Contributes to the Anti-Angiogenic Effects of PPE8, a Novel Naphthoquinone-Based Compound

Natural naphthoquinones and their derivatives exhibit a broad spectrum of pharmacological activities and have thus attracted much attention in modern drug discovery. However, it remains unclear whether naphthoquinones are potential drug candidates for anti-angiogenic agents. The aim of this study was to evaluate the anti-angiogenic properties of a novel naphthoquinone derivative, PPE8, and explore its underlying mechanisms. Determined by various assays including BrdU, migration, invasion, and tube formation analyses, PPE8 treatment resulted in the reduction of VEGF-A-induced proliferation, migration, and invasion, as well as tube formation in human umbilical vein endothelial cells (HUVECs). We also used an aorta ring sprouting assay, Matrigel plug assay, and immunoblotting analysis to examine PPE8’s ex vivo and in vivo anti-angiogenic activities and its actions on VEGF-A signaling. It has been revealed that PPE8 inhibited VEGF-A-induced micro vessel sprouting and was capable of suppressing angiogenesis in in vivo models. In addition, PPE8 inhibited VEGF receptor (VEGFR)-2, Src, FAK, ERK1/2, or AKT phosphorylation in HUVECs exposed to VEGF-A, and it also showed significant decline in xenograft tumor growth in vivo. Taken together, these observations indicated that PPE8 may target VEGF-A–VEGFR-2 signaling to reduce angiogenesis. It also supports the role of PPE8 as a potential drug candidate for the development of therapeutic agents in the treatment of angiogenesis-related diseases including cancer.

Herbacetin suppressed MMP9 mediated angiogenesis of malignant melanoma through blocking EGFR-ERK/AKT signaling pathway

Malignant melanoma remains a challenge for clinical practice and novel therapeutic strategies are urgently needed. Herbacetin, a natural flavonoid compound that has multiple pharmacological activities, exerts anticancer effects on several human tumors. In this study, the anti-angiogenesis effect of Herbacetin in human malignant melanoma was investigated. The results indicated that Herbacetin treatment significantly suppressed tumor growth and angiogenesis of malignant melanoma both in vitro and in vivo. In melanoma A375 and Hs294T cells, Herbacetin treatment suppressed both EGF-induced and constitutive phosphorylation of EGFR, accelerated the internalization and degradation of EGFR, and subsequently suppressed the activation of the downstream kinases (AKT and ERK). Moreover, MMP9 was determined as a key angiogenic factor in Herbacetin treated melanoma cells. Knockdown of MMP9 suppressed the in vitro angiogenesis while overexpression of MMP9 in Herbacetin treated melanoma cells restored the angiogenesis ability. We concluded that Herbacetin suppressed melanoma angiogenesis through blocking EGFR-ERK/AKT-MMP9 signaling pathway and Herbacetin may be developed as a potential drug for melanoma treatment.

Knockdown of MALAT1 expression inhibits HUVEC proliferation by upregulation of miR-320a and downregulation of FOXM1 expression

Regulation of cancer angiogenesis could be a useful strategy in cancer therapy. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a long non-coding RNA (lncRNA), and can induce cancer cell proliferation, while lncRNAs, generally are able to act as microRNA (miRNA) sponges. The latter is a type of competitive endogenous RNA (ceRNA) that regulates expression of the targeting miRNAs and protein-coding genes. This study investigated the proliferative role of MALAT1 in human umbilical vein endothelial cells (HUVECs) and the underlying molecular events. The data showed that knockdown of MALAT1 expression using MALAT1 siRNA inhibited HUVEC proliferation and also significantly decreased levels of FOXM1 mRNA and protein in vitro, while knockdown of FOXM1 expression reduced HUVEC proliferation. Annotation of HUVEC microarray data revealed that seven miRNAs, including miR-320a, were upregulated after knockdown of MALAT1 expression in HUVECs. MALAT1 was shown to reciprocally interact with miR-320a, i.e., expression of one negatively regulated levels of the other, whereas knockdown of MALAT1 expression promoted miR-320a levels. Furthermore, miR-320a could directly target and inhibit FOXM1 expression in HUVECs. Knockdown of MALAT1 expression enhanced miR-320a expression but reduced FOXM1 expression resulting in downregulation of HUVEC proliferation. However, such an effect was inhibited by miR-320a depletion. In conclusion, this study demonstrates that miR-320a plays an important role in mediating the effects of MALAT1 on HUVEC proliferation by suppression of FOXM1 expression. Thus, targeting of this gene pathway could be a novel strategy in cancer therapy.