Sorafenib, a multi‐kinase inhibitor, is the only standard clinical drug for patients with advanced hepatocellular carcinoma (HCC); however, development of sorafenib resistance in HCC often prevents its long‐term efficacy. Therefore, novel targets and strategies are urgently needed to improve the antitumor effect of sorafenib. In the present study, we examined the novel mechanisms of sorafenib resistance of HCC cells by investigating the difference in sorafenib sensitivity between two HCC cell lines. Sorafenib induced more apoptosis of HepG2 cells compared to Hep3B cells. Sorafenib exposure to HepG2 cells but not Hep3B cells increased the expression of proapoptotic factor PUMA, and activated PARP and caspase‐3. Notably, microRNA‐181a (miR‐181a) expression levels were lower in HepG2 cells than in Hep3B cells. Exogenous miR‐181a expression in HepG2 cells reduced apoptosis, whereas inhibition of miR‐181a in Hpe3B cells increased apoptosis. In addition, we demonstrated that miR‐181a directly targets RASSF1, a MAPK signaling factor, and knockdown of RASSF1 increased sorafenib resistance. Taken together, these results suggest that miR‐181a provokes sorafenib resistance through suppression of RASSF1. Our data provide important insight into the novel therapeutic strategy against sorafenib resistance of HCC cells by targeting of miR‐181a pathway.

The organogermanium compound 3-(trihydroxygermyl)propanoic acid (THGP) has various biological activities. We previously reported that THGP forms a complex with cis-diol structures. L-3,4-Dihydroxyphenylalanine (L-DOPA), a precursor of melanin, contains a cis-diol structure in its catechol skeleton, and excessive melanin production causes skin darkening and staining. Thus, the cosmetic field is investigating substances that suppress melanin production. In this study, we investigated whether THGP inhibits melanin synthesis via the formation of a complex with L-DOPA using mushroom tyrosinase and B16 4A5 melanoma cells. The ability of THGP to interact with L-DOPA was analyzed by ¹H-NMR, and the influence of THGP and/or kojic acid on melanin synthesis was investigated. We also examined the effect of THGP on cytotoxicity, tyrosinase activity, and gene expression and found that THGP interacted with L-DOPA, a precursor of melanin with a cis-diol structure. The results also showed that THGP inhibited melanin synthesis, exerted a synergistic effect with kojic acid, and did not affect tyrosinase activity or gene expression. These results suggest that THGP is a useful substrate that functions as an inhibitor of melanogenesis and that its effect is enhanced by combination with kojic acid.

Background/Aim: The presence of cancer stem cells (CSCs) contributes to metastasis, recurrence, and resistance to chemo/radiotherapy in hepatocellular carcinoma (HCC). The WNT signaling pathway is reportedly linked to the maintenance of stemness of CSCs. In the present study, in order to eliminate liver CSCs and improve the prognosis of patients with HCC, we explored whether small-molecule compounds targeting WNT signaling pathway suppress liver CSCs. Materials and Methods: The screening was performed using cell proliferation assay and reporter assay. We next investigated whether these compounds suppress liver CSC properties by using flow cytometric analysis and sphere-formation assays. A mouse xenograft model transplanted with CD44-positive HuH7 cells was used to examine the in vivo antitumor effect of IC-2. Results: In HuH7 human HCC cells, 10 small-molecule compounds including novel derivatives, IC-2 and PN-3-13, suppressed cell viability and WNT signaling activity. Among them, IC-2 significantly reduced the CD44-positive population, also known as liver CSCs, and dramatically reduced the sphere-forming ability of both CD44-positive and CD44-negative HuH7 cells. Moreover, CSC marker-positive populations, namely CD90-positive HLF cells, CD133-positive HepG2 cells, and epithelial cell adhesion molecule-positive cells, were also reduced by IC-2 treatment. Finally, suppressive effects of IC-2 on liver CSCs were also observed in a xenograft model using CD44-positive HuH7 cells. Conclusion: The novel derivative of small-molecule WNT inhibitor, IC-2, has the potential to suppress liver CSCs and can serve as a promising therapeutic agent to improve the prognosis of patients with HCC.

M1 macrophages are an important cell type related to tumor immunology and are known to phagocytose cancer cells. In previous studies, the organogermanium compound poly-trans-[(2-carboxyethyl)germasesquioxane] (Ge-132) and its hydrolysate, 3-(trihydroxygermyl) propanoic acid (THGP), have been reported to exert antitumor effects by activating NK cells and macrophages through the induction of IFN-γ activity in vivo. However, the detailed molecular mechanism has not been clarified. In this study, we found that macrophages differentiate into the M1 phenotype via NF-κB activation under long-term culture in the presence of THGP in vitro and in vivo. Furthermore, long-term culture with THGP increases the ability of RAW 264.7 cells to suppress B16 4A5 melanoma cell proliferation. These mechanisms indicate that THGP promotes the M1 polarization of macrophages and suppresses the expression of signal-regulatory protein alpha (SIRP-α) in macrophages and CD47 in cancers. Based on these results, THGP may be considered a new regulatory reagent that suppresses tumor immunity.

Inflammasome activity is a key indicator of inflammation. The inflammasome is activated by pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), which activate the p38-NF-κB pathway and promote IL-1β transcription (signaling step 1). Next, extracellular adenosine triphosphate (ATP) activates the inflammasome (a protein complex consisting of a signal recognition protein, an adapter protein, and Caspase-1) and secretion of inflammatory cytokines such as IL-1β (signaling step 2). Inflammasome activation causes excessive inflammation, leading to inflammasome-active diseases such as atherosclerosis and type 2 diabetes. A hydrolysate of the organogermanium compound Ge-132, 3-(Trihydroxygermyl) propanoic acid (THGP) can form a complex with a cis-diol structure. We investigated the inhibitory effect of THGP on inflammasome activity in human THP-1 monocytes. THGP inhibited IL-1β secretion and caspase-1 activation (signaling step 2) in an ATP-dependent manner. On the other hand, THGP did not suppress IL-1β secretion induced by only lipopolysaccharide (LPS) stimulation. In addition, as IL-6 is an ATP-independent inflammatory cytokine, THGP did not decrease its secretion. THGP also suppressed pyroptosis, which is a caspase-1 activity-dependent form of cell death. Therefore, THGP is expected to become a new therapeutic or prophylactic agent for inflammasome-associated diseases.

Red blood cells (RBCs) are renewed in a cyclic manner. Aging RBCs are captured and degraded by phagocytic cells, and heme metabolic pigments are subsequently excreted in feces. We evaluated the effect of an organogermanium compound on RBC metabolism and found that the phagocytosis of RAW264.7 macrophage-like cells was increased by treatment with 3-(trihydroxygermyl)propanoic acid (THGP). Additionally, consumption of Ge-132 (a dehydrate polymer of THGP) changed the fecal color to bright yellow and increased the erythrocyte metabolic pigment levels and antioxidant activity in feces. These data suggest that Ge-132 may activate macrophages in the body and promote the degradation of aged RBCs. Furthermore, Ge-132 intake promoted not only increases in RBC degradation but also the induction of erythroblast differentiation in bone marrow cells. The normal hematocrit levels were maintained due to the maintenance of homeostasis, even though Ge-132 ingestion increased erythrocyte degradation. Therefore, Ge-132 enhances the degradation of senescent RBCs by macrophages. In turn, RBC production is increased to compensate for the amount of degradation, and RBC metabolism is increased.