2.1. Anticancer Activity
The development of cancer therapeutics from steroidal compounds has been an attractive choice for medicinal chemists and many active molecules have emerged [2, 26].
In this context, several preclinical studies investigated the effects of the diosgenin as a chemopreventive/therapeutic agent against cancers of several organs, and this has demonstrated the high interest of this molecule as a potential antitumor agent [5, 7]. In fact, the anticancer effect of diosgenin has been studied in various tumoural cell lines and it was evidenced that this bioactivity depends both on the cell type and on concentration. Thus, for example, diosgenin has antiproliferative activity, namely, in prostate cancer (PC-3 and DU-145 cells) [23], colon carcinoma (HCT-116 and HT-29 cells) [24], erythroleukemia (HEL cells) [27], squamous carcinoma (A431, Hep2, and RPMI 2650 cells) [28], hepatocellular carcinoma (HepG2 and HCC cells) [6, 25, 29], gastric cancer (BGC-823 cells) [30], lung cancer (A549 cells) [31], breast cancer (MCF-7) [6, 32-34], and human chronic myeloid leukemia (CML) (K562 cells) [1]. Moreover, several studies suggested that the known anticancer mechanisms of action of diosgenin are associated with a modulation of multiple cell signalling events involved in cell growth/proliferation, differentiation, epithelial-mesenchymal transition migration, and apoptosis, as well as oncogenesis and angiogenesis [12]. Within the various phases of tumorigenesis, diosgenin seems to be critical in inducing apoptotic cell death and avoiding their malignant transformation [3, 5, 12]. More specifically, the diosgenin antitumor effects have been demonstrated, for example, to be mediated through p53 activation, immune-modulation, cell cycle arrest, modulation of caspase-3 activity, and activation of the transcription STAT3 signalling pathway [6, 7, 25]. In this context, important studies have shown that diosgenin inhibits the proliferation of osteosarcoma cells by inducing apoptosis and cell cycle arrest in G1 phase [35] and also inhibits the proliferation of breast cancer cells (MCF-7 cells) through the induction of the proapoptotic p53 protein and an increase of caspase-3 levels [6, 36]. In addition, the proliferation of PC-3 human prostate cancer cells is inhibited by diosgenin in a dose-dependent manner, reducing cell migration and invasion by decreasing matrix metalloproteinase expression which reveals the potential of this compound in antimetastatic therapy [23]. Diosgenin, due to its antioxidant activity, affects the growth of A549 lung cancer cell line and downregulates hTERT gene expression in these cells in a time dependent manner. Therefore, this sapogenin could constitute an interesting approach for lung cancer therapy [31, 37]. The diosgenin-induced apoptosis of HEL cells (human erythroleukemia cell line) was related to COX-2 upregulation. In addition, this apoptosis induction was accompanied by an increase in Bax/Bcl-2 ratio, PARP cleavage, and DNA fragmentation [38]. In the COX-2 deficient K562 cells, the inhibition of NF-kappa B nuclear binding and p38 MAPK activation are involved in the diosgenin-mediated signal cascades for inducing/regulating DNA fragmentation [39]. Other authors also demonstrated that this steroid inhibits the proliferation of this leukemia cell line via cell cycle G2/M arrest and apoptosis, with disruption of Ca2+ homeostasis and mitochondrial dysfunction playing vital roles [40]. Moreover, diosgenin not only produces cytotoxic effect on human chronic myeloid leukemia cells (K562 and BaF3-WT) but also induces autophagy accompanied by reactive oxygen species (ROS) generation and mammalian target of rapamycin (mTOR) signalling pathway inhibition. Further studies also demonstrated that the inhibition of autophagy potentiated the diosgenin-induced apoptosis [1]. Diosgenin inhibits the STAT3 signalling pathway in the human hepatocellular carcinoma (HCC) cells, leading to the suppression of cell proliferation and to chemosensitization, and caused arrest at the G1 phase of the cell cycle and induced apoptosis through caspase-3 activation and PARP cleavage occurred [41]. In HepG2 hepatic cells, this steroid induces apoptosis through the Bcl-2 protein family (Bcl-2, Bax, and bid) mediated by the mitochondrial/caspase 3-dependent pathway. Furthermore, diosgenin also generates ROS and leads to oxidative stress which might induce apoptosis [25]. Furthermore, the colorectal adenocarcinoma cell line HT-29 is sensitized by diosgenin to TRAIL (TNF-related apoptosis-inducing ligand) induced apoptosis [24].
Diosgenin also has antimetastatic effects; for example, it was demonstrated that it can inhibit the migration of human breast cancer MDA-MB-231 cells, at least partially, by suppressing Vav2 protein activity [42]. Additionally, angiogenesis is an essential process for the development, invasiveness, and metastasis of solid tumours and is dependent on the action of angiogenic factors, namely, integrin and VEGF. In this context, it has been reported that VEGF expression in PC-3 cells is reduced by diosgenin in a dose-dependent manner, suggesting that this steroid can inhibit angiogenesis by interfering with this factor [23]. All of these results have shown significantly the potential use of this compound as a new therapeutic agent against various types of cancer. Thus, there has been considerable effort to continue assessing the role of diosgenin and some of its chemical analogues as well as combinations of diosgenin with other bioactive compounds in modulating growth and proliferation of various types of human tumours and in the evaluation of its potential mechanism of action. As a relevant example, the combination of diosgenin and thymoquinone has antiproliferative and apoptotic effects on squamous cell carcinoma (SCC), in a synergistically way, and thus could be a novel strategy for the development of potential antineoplastic therapies against squamous cell carcinoma [28].
An interesting novelty in this topic is the integration of diosgenin, as well as other interesting potential drugs, into nanoparticles, in order to drive diosgenin to its site of action and to increase its pharmacological bioavailability. In fact, diosgenin functionalized iron oxide nanoparticles, as well as hollow manganese ferrite nanocarriers encapsulating tamoxifen and diosgenin, were developed as potential therapeutic tools against breast cancer [34, 43]. Also in this context, Li et al. [44] prepared, characterized, and evaluated a nanoparticle platform based on poly(ethylene glycol)diosgenin conjugates for codelivery of anticancer drugs as a promising drug delivery system for cancer therapy.
