Amongst the vast array of proangiogenic molecules identified, VEGF has been shown to play a pivotal role in tumor angiogenesis. VEGF is a potent stimulator of endothelial cell survival, mitogenesis, migration and differentiation [
1,
2]. Angiogenesis inhibitors targeting VEGF have shown anticancer activity in preclinical and clinical trials. Several VEGF inhibitors have been approved by the US Food and Drug administration for the treatment of tumors or age-related macular degeneration [
3,
4]. However, recently emerging reports suggest that the effects of these drugs in cancer are only transitory, not producing enduring efficacy in terms of either tumor shrinkage or dormancy or long term survival, thus resulting in eventual drug resistance, vascular recovery and relapse to progressive tumor growth [
5‐
7]. A number of contributing mechanisms have been proposed including up-regulation of fibroblast growth factor (FGF), matrix metalloproteinases (MMPs) and the induction of HIF-1α [
6,
8]. The most important mediator identified to date of the cell's response to reduced oxygen availability, HIF-1α is preserved and activated in response to reduced oxygen availability [
9]. By affecting the expression of a wide array of genes, HIF-1α plays a central role in angiogenesis and in regulating the adaptation and survival of tumors [
10,
11]. Perhaps to some extent this is because transcriptional regulation of VEGF is critically dependent on HIF-1α. Results from several studies have provided compelling evidence that hypoxia-triggered up-regulation of other proangiogenic factors in the presence of anti-VEGF agents can restimulate tumor angiogenesis through VEGF-dependent or VEGF independent pathways [
6,
12,
13]. More importantly, HIF-1α induction by hypoxia has been associated with the emergence of a more aggressive tumor phenotype [
14]. On this basis, drugs that inhibit VEGF and angiogenesis through the inhibition of HIF-1α may provide therapeutic benefit over those which target the VEGF or its signaling pathway only.
Albendazole, methyl 5-propylthio-1H-benzimidazole-2-yl carbamate, is a benzimidazole carbamate originally developed as a veterinary product back in 1975 and despite its extensive use in man and farm animals, few adverse events have been associated with its use [
15,
16]. Its anthelmintic action has been attributed to binding to the helminth β-tubulin, leading to depolymerization, cell cycle arrest and death [
17,
18]. Because of their interaction with the microtubules, in recent years, benzimidazole carbamates such as albendazole and mebendazole have been under investigation as anticancer agents. Cell culture and animal studies utilizing human cancer cells have revealed that both these agents are potent inducers of apoptosis and inhibitors of tumor growth [
19‐
23]. More recently, using an experimental model of ovarian cancer with malignant ascites formation, we demonstrated that, chronic treatment with ABZ leads to suppression of VEGF levels, inhibition of malignant ascites formation and arrest of tumor growth [
24,
25]. In the current study we sought to investigate if the observed ABZ anti-VEGF effect is mediated through the inhibition of the HIF pathway. Herein, we report that,
in vitro experiments performed using hypoxic chamber and DFO, provided evidence for the anti-HIF-1α activity of ABZ. Then, study of the effects of a single dose of ABZ on tumoral HIF-1α and VEGF expression revealed profound suppression of both HIF-1α and VEGF protein levels. Thus, results from this study demonstrate that ABZ is a potent inhibitor of HIF-1α under both
in vitro and
in vivo conditions.