Angiogenesis refers to the formation of new blood vessels

Angiogenesis refers to the formation of new blood vessels from pre-existing vasculature [1]. Physiological angiogenesis is necessary for key processes such as wound healing, tissue regeneration and repair. In pathological conditions, including cardiovascular diseases, diabetes, cancer, and other pathologies associated with chronic inflammation, angiogenesis represent a relevant hallmark contributing to disease insurgence and progression. Therefore, the induction of new blood vessels is a necessary condition for tumors to recruit oxygen, nutrients and disseminate to distant sites. Strategies aimed at blocking or delaying tumor angiogenesis have been employed both in therapeutic and (chemo) prevention settings and promising results have been obtained in pre-clinical models and in the clinic [2], [3]. Cancer chemoprevention offers the possibility of long-term low toxic treatments that NVP DPP 728 dihydrochloride could keep initial tumors at bay, delaying their progression to a clinically relevant tumor [4], [5], [6]. Many chemopreventive agents are directly derived from natural sources (phytochemicals) that have been reported to exert anti-proliferative, pro-apoptotic, antioxidant and anti-inflammatory activities [7]. We have demonstrated that many of these phytochemical derived agents act also as antiangiogenic and anti-inflammatory drugs, a concept we named “angioprevention” [8], [9], [10]. Substantial attention has been addressed to flavonoids and their synthetic precursors, chalcones, a class of polyphenolic compounds that, within their wide range of activity, also exhibit anti-angiogenic properties [11]. During the last decades, the prenylated chalcone Xanthohumol (XN, 1, Fig. 1) has emerged as a cancer chemopreventive agent [12]. It is the major prenylated chalcone present in the female inflorescences of the hop plant Humulus lupulus L. (Cannabaceae) employed in the brewing process to preserve and to add bitterness and flavor to beer. The beneficial properties of hops are well known from ancient times and have been used in traditional medicines since the IX century. Xanthohumol was first isolated by Power in 1913 and its structure was elucidated in 1957 by Verzele [13]. However, only in the last decades, we assisted to an increasing interest to this molecule, since it is endowed with multiple biological activities including anti-diabetic, anti-inflammatory, anti-oxidant, anti-cancer, anti-invasive, and anti-angiogenic activities [14]. Given the promising results from in vitro and in vivo preclinical studies that have pointed out the numerous benefits exerted by XN, clinical trials are currently being developed evaluating the feasibility of XN treatment in the context of metabolic syndrome and prevention of DNA damage (https://clinicaltrials.gov/) [15]. We showed that XN has stronger anti-angiogenic activity as compared to the green tea flavonoid epigallocatechin-3-gallate (EGCG) [16]. Due to the multiple beneficial activities of XN, we were interested in determining whether chemical modification of the XN-scaffold resulted in more effective inhibition of angiogenesis, to identify novel potential chemopreventive agents. Therefore, we developed a series of novel synthetic analogues of XN, compounds 2–14[17], reported in Table 1. A series of XN analogues has been recently synthesized and shown to have toxicity toward HeLa cells by inhibiting the selenoprotein thioredoxin reductases (TrxRs) [18]. We chose to replace the phenolic group on B-ring of the XN (Fig. 1) with several substituents endowed with different electronic and steric properties such as halogens, methoxy or nitro groups, to evaluate the impact of these modifications on antiangiogenic activity. The prenyl group on A-ring was left unchanged, since previous studies [19] confirmed its importance for antiangiogenic activity. Derivatives 3, 5, 7, 10 and 13 were synthesized and tested together with some analogues MOM-protected on A-ring, defined compounds 2, 4, 6, 8, 9, 11, 12 and 14. Here, we compared the antiangiogenic effects of XN and our novel synthetic derivatives in vitro, where human umbilical vein endothelial cells (HUVEC) were used as a model for cell proliferation, apoptosis, cell adhesion, migration, invasion and formation of capillary-like structures.