Introduction

Recently, more and more attention has been placed on the use of nutraceuticals as therapeutic agents for cancer prevention, as well as supplements to conventional therapy because of their promising effects and a low rate of toxicity [1–3]. A number of natural compounds have been found to inhibit one or more pathways that contribute to proliferation of cancer cells and metastatic processes [4]. The most investigated and promising compounds studied in the last years include: curcumin [5], resveratrol [6], and indole-3-carbinol [7], which are naturally present in some species of fruit and vegetables. Fermented wheat germ extract (FWGE; trade name FWGE ) is a product of industrial fermentation of wheat germ. Its production process is patented and is derived from the extraction of wheat germ and fermentation by Saccharomyces cerevisiae, followed by separation of the fermentation liquid, drying, and then granulation. As with other nutraceuticals, FWGE contains various molecules, but recent studies assume that the two quinones, 2-methoxy benzoquinone and 2, 6-dimethoxy benzoquinone, which are present in wheat germ as glucosides, are likely to be responsible for some of the biological properties of FWGE [8,9]. Quinones are cyclic organic compounds containing two carbonyl groups (C=O) linked to the cyclic structure of a conjugated system. Several anticancer compounds, e.g., Mitomycin C, Mitotraxan, Doxorubicin, and Daunorubicin, are quinone derivatives [10,11]. The anticancer characteristics of FWGE have been deeply investigated, and results have suggested its metabolic, antiproliferative, and antimetastatic effects [12–14].

 Recently, more and more attention has been placed on the use of nutraceuticals as therapeutic agents for cancer prevention, as well as supplements to conventional therapy because of their promising effects and a low rate of toxicity [1–3]. A number of natural compounds have been found to inhibit one or more pathways that contribute to proliferation of cancer cells and metastatic processes [4]. The most investigated and promising compounds studied in the last years include: curcumin [5], resveratrol [6], and indole-3-carbinol [7], which are naturally present in some species of fruit and vegetables. Fermented wheat germ extract (FWGE; trade name FWGE ) is a product of industrial fermentation of wheat germ. Its production process is patented and is derived from the extraction of wheat germ and fermentation by Saccharomyces cerevisiae, followed by separation of the fermentation liquid, drying, and then granulation. As with other nutraceuticals, FWGE contains various molecules, but recent studies assume that the two quinones, 2-methoxy benzoquinone and 2, 6-dimethoxy benzoquinone, which are present in wheat germ as glucosides, are likely to be responsible for some of the biological properties of FWGE [8,9]. Quinones are cyclic organic compounds containing two carbonyl groups (C=O) linked to the cyclic structure of a conjugated system. Several anticancer compounds, e.g., Mitomycin C, Mitotraxan, Doxorubicin, and Daunorubicin, are quinone derivatives [10,11]. The anticancer characteristics of FWGE have been deeply investigated, and results have suggested its metabolic, antiproliferative, and antimetastatic effects [12–14].

The antimetabolic effects of FWGE on cancer cells seems to be due to a hypermetabolic state of the cancer cells and their upregulated utilization of glucose [15,16]. The antimetastatic effect of FWGE, besides the immune-reconstitution, may also be due to its cell adhesion inhibitory, cell proliferation inhibitory, apoptosis enhancing, and antioxidant characteristics, which have also been observed in some in vitro experiments [17]. The antiproliferative action has been investigated in in vitro and in vivo studies performed on various human cancer cell lines and animal models, and results have shown a reduction of tumor growth in a dose-dependent manner [8,17–19]. The antimetastatic effect of FWGE investigated in vitro and in vivo by several studies appears to be promising for FWGE to be used alone or in association with traditional anticancer agents [8,17]. The aim of this systematic review is to summarize the data available in the scientific literature concerning the in vitro activity of FWGE on malignant cells.

Materials and Methods

This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [20]. A systematic review of English articles in electronic databases (PubMed, Scopus, and Web of Science) was performed independently by two authors (KZ and GT) using search terms: (FWGE OR “wheat germ extract”) AND (cancer OR antitumoral OR anticancer). No restrictions were imposed on the study designs. The criterion for inclusion in this systematic review was in vitro original studies on human tumor cell lines where the effects of FWGE have been evaluated. No restriction on publication dates was applied. 

 Flowchart of the selection process for the studies inclusion. 3.1. Characteristics of Included Studies and Primary Outcomes All sixteen studies selected for the review were in-vitro studies published in English. The effects of FWGE were investigated on the following cell lines: (1) Jurkat leukemic T cells were studied by three studies [18,21,32] and the treatment resulted in cytotoxic effects, alteration of the cell cycle, antiproliferative effects, and induction of apoptosis; (2) Lymphoma cells were subjected to the treatment and the effects investigated by three studies [21,27,32] showed growth inhibition, induction of apoptosis, antiproliferation, and cytotoxic effects; (3) Gastric cancer cell line experiments reported in three papers [22,25,26] found antiproliferative, cytotoxic, cytostatic, and growth-delay effects; (4) Ovarian cancer cell lines, when subjected to treatment with FWGE , showed cytotoxic effects [23], antiproliferative activity [25], and suppression of cell proliferation [29]; (5) Breast cancer cell lines appeared to undergo cytotoxicity and apoptosis [24–26,32], while, in one study [33] investigating the combined administration of FWGE and cytostatics, the treatment with FWGE resulted in no increase or decrease of cell viability compared to untreated cells; (6) When applied to colon cancer cell lines, FWGE showed antiproliferative activity [25], cytotoxicity, cytostasis, and induction of cell apoptosis [31];(7) The treatment of hepatic cancer cells appeared to cause cytotoxicity, apoptosis [32], and an inhibition of proliferation [25,28];

FWGE is a nutraceutical that has been reported to possess unique “cancer-fighting” characteristics [13]. Its antiproliferative and cytotoxic activity, as well as its induction of apoptosis in human cancer cells, have been affirmed by several studies [18,21,24]. Some studies [18,26,34] investigated the metabolic changes in tumor cells in response to the treatment with FWGE and revealed important alterations in enzymes involved in direct glucose oxidation (G6PDH), non-oxidative glucose utilization (transketolase) toward nucleic acid synthesis, glycolysis (LDH), and glucose activation (HK). The inhibition of the key pathways of sugar metabolism and DNA-synthesis seems to contribute to the proliferation inhibiting capacity of FWGE. Saiko et al. [19] found that treatment with FWGE carried a direct enzyme attenuation of ribonucleotide reductase, which was demonstrated to be significantly up-regulated in tumor cells. In another study [21], some early biochemical events, such as tyrosine phosphorylation and the increase of intracellular Ca2+ concentration, occurred in response to the treatment and was associated with increased apoptosis of the tumor cells. Judson et al. [23] have also identified genes and molecular signaling pathways associated with FWGE activity on investigated cells and these pathways include hedgehog signaling, activin A signaling regulation, and regulation of GAP 1/Synthesis (G1/S) phases transition. Moreover, some of the studies included in this review suggested that FWGE could potentially inhibit cancer cell migration and invasive capacities [30].

 Such actions can be important especially for some types of tumors, such as the oral squamous cell carcinoma [37,38], for which the highest mortality is due to the ability of lymph node metastasis or metastasis to distant organs. Imir et al. [22] investigated the ability of FWGE to inhibit angiogenesis and obtained very encouraging results stating that FWGE exerts anti-angiogenic effects by inhibiting VEGF and Cox-2 gene expression. This mechanism of action has already been proposed for the anti-angiogenic activity of polyphenols and polyphenol-rich foods in “in vitro” and “in vivo” models of angiogenesis [39].Another important finding was that the treatment with FWGE  results in widespread apoptosis in lymphoid tumor cells, but it does not induce apoptosis of healthy resting mononuclear cells [21]. In some studies, the association of FWGE with conventional anticancer drugs has also been investigated in order to search for possible solutions to overcome the drug resistance that frequently occurs during anticancer chemotherapy and limit the side effects that traditional treatments entail. The results are promising for the addition of this natural compound to cisplatin chemotherapy of epithelial ovarian cancer cell lines [23,29] and hepatocellular carcinoma cells [28], to tamoxifen in the treatment of breast cancer cells [24], to docetaxel in ovarian carcinoma cells [29], to 5-Fluorouracil (5-FU) in colon cancer cells [25], and to the treatment of hepatocellular carcinoma cells [28]. Only one study [33] reported poor results for simultaneous use of FWGE and Dacarbazine, 5-fluorouracyl, or Adriblastina, where the addition of the nutraceutical did not increase nor decrease the viability of any of the cell cultures.