Calycosin, a bioactive isoflavonoid isolated from root extracts of Astragalus membranaceus, has been reported to inhibit melanogenesis, the mechanism of which remains undefined. In this study, we interrogated the mechanistic basis by which calycosin inhibits melanin production in two model systems, i.e., B16F10 melanoma cells and zebrafish embryos. Calycosin was effective in protecting B16F10 cells from α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis and tyrosinase activity. This anti-melanogenic effect was accompanied by decreased expression levels of microphthalmia-associated transcription factor (MITF), a key protein controlling melanin synthesis, and its target genes tyrosinase and tyrosinase-related protein-2 (TRP-2) in calycosin-treated cells. Mechanistically, we obtained the first evidence that calycosin-mediated MITF downregulation was attributable to its ability to block signaling pathways mediated by cAMP response element-binding protein (CREB) and p38 MAP kinase. The protein kinase A (PKA) inhibitor H-89 and p38 inhibitor SB203580 validated the premise that calycosin inhibits melanin synthesis and tyrosinase activity by regulating the PKA/CREB and p38 MAPK signaling pathways. Moreover, the in vivo anti-melanogenic efficacy of calycosin was manifested by its ability to suppress body pigmentation and tyrosinase activity in zebrafish embryos. Together, these data suggested the translational potential of calycosin to be developed as skin-lightening cosmeceuticals.

Cancer stem cells (CSCs), or tumor-initiating cells, are a small subset of cancer cells with the capacity for self-renewal and differentiation, which have been shown to drive tumor initiation, progression, and metastasis in many types of cancer. Moreover, therapeutic regimens, such as cisplatin and radiation were reported to induce the enrichment of CSCs, thereby conferring chemoresistance on cancer cells. Therefore, therapeutic targeting of CSCs represents a clinical challenge that needs to be addressed to improve patient outcome. In this context, the effectiveness of pan or class-I histone deacetylase (HDAC) inhibitors in suppressing the CSC population is especially noteworthy in light of the new paradigm of combination therapy. Evidence suggests that this anti-CSC activity is associated with the ability of HDAC inhibitors to target multiple signaling pathways at different molecular levels. Beyond chromatin remodeling via histone acetylation, HDAC inhibitors can also block key signaling pathways pertinent to CSC maintenance. Especially noteworthy is the ability of different HDAC isoforms to regulate the protein stability and/or activity of a series of epithelial-mesenchymal transition (EMT)-inducing transcription factors, including HIF-1α, Stat3, Notch1, β-catenin, NF-κB, and c-Jun, each of which plays a critical role in regulating CSCs. From the translational perspective, these mechanistic links constitute a rationale to develop isoform-selective HDAC inhibitors as anti-CSC agents. Thus, this review aims to provide an overview on the roles of HDAC isoforms in maintaining CSC homeostasis via distinct signaling pathways independent of histone acetylation.

Background: Despite recent advances in understanding the pathophysiology of cancer cachexia, prevention/treatment of this debilitating disease remains an unmet medical need.Methods: We developed an integrated, multi‐tiered strategy involving both in vitro and in vivo muscle atrophy platforms to identify traditional Chinese medicine (TCM)‐based anti‐cachectic agents. In the initial screening, we used inflammatory cytokine‐induced atrophy of C2C12 myotubes as a phenotypic screening platform to assess the protective effects of TCMs. The selected TCMs were then evaluated for their abilities to protect Caenorhabditis elegans from age‐related reduction of mobility and contractility, followed by the C‐26 colon adenocarcinoma mouse model of cachexia to confirm the anti‐muscle atrophy effects (body/skeletal muscle weights, fibre size distribution, grip strengths, and serum IL‐6). Transcriptome analysis, quantitative real‐time polymerase chain reaction, and immunoblotting were performed to gain understanding of the potential mechanism(s) by which effective TCM protected against C26 tumour‐induced muscle atrophy.Results: Of 29 widely used TCMs, Dioscorea radix (DR) and Mu Dan Pi (MDP) showed a complete protection (all P values, 0.0002) vis‐à‐vis C26 conditioned medium control in the myotube atrophy platform. MDP exhibited a unique ability to ameliorate age‐associated decreases in worm mobility, accompanied by improved total body contractions, relative to control (P < 0.0001 and <0.01, respectively), which, however, was not noted with DR. This differential in vivo protective effect between MDP and DR was also confirmed in the C‐26 mouse model. MDP at 1000 mg/kg (MDP‐H) was effective in protecting body weight loss (P < 0.05) in C‐26 tumour‐bearing mice without changing food or water intake, accompanied by the restoration of the fibre size distribution of hindleg skeletal muscles (P < 0.0001) and the forelimb grip strength (P < 0.05). MDP‐treated C‐26‐tumour‐bearing mice were alert, showed normal posture and better body conditions, and exhibited lower serum IL‐6 levels (P = 0.06) relative to vehicle control. This decreased serum IL‐6 was associated with the in vitro suppressive effect of MDP (25 and 50 μg/mL) on IL‐6 secretion into culture medium by C26 cells. RNA‐seq analysis, followed by quantitative real‐time polymerase chain reaction and/or immunoblotting, shows that MDP's anti‐cachectic effect was attributable to its ability to reverse the C‐26 tumour‐induced re‐programming of muscle homoeostasis‐associated gene expression, including that of two cachexia drivers (MuRF1 and Atrogin‐1), in skeletal muscles.Conclusions: All these findings suggest the translational potential of MDP to foster new strategies for the prevention and/or treatment of cachexia. The protective effect of MDP on other types of muscle atrophy such as sarcopenia might warrant investigations.