Qi Su

Objectives: Gastric cancer (GC) is often associated with high invasiveness, epithelial-mesenchymal transition (EMT), and resistance to 5-fluorouracil (5-FU), highlighting the need for novel therapeutic targets. This study explored whether diallyl disulfide (DADS) upregulates retinoic acid-related orphan receptor alpha (ROR) to weaken the protein kinase C alpha (PKC)/RORα-mediated RORα/β-catenin pathway, thereby inhibiting GC cell invasion, epithelial-mesenchymal transition (EMT), and enhancing 5-FU sensitivity. Methods: Human GC cell lines MGC-803 and SGC7901 were treated with DADS, RORα agonist SR1078/antagonist T0901317, and PKCα agonist TPA/antagonist GO6976. Cell proliferation (MTT), migration (scratch assay), invasion (Transwell), protein expression (Western blot), protein interactions (coimmunoprecipitation), and localization (immunofluorescence) were detected. Apoptosis and 5-FU sensitivity-related proteins were examined. Experiments were triplicated; statistics used t-test/ANOVA (p < 0.05). Results: DADS/SR1078 inhibited GC cell proliferation/migration/invasion, upregulated RORα/E-cadherin, downregulated nuclear β-catenin/TGF-β1/Rac1/Vimentin, and weakened EMT (reversed by T0901317). DADS/TPA upregulated RORα/p-RORα/PKCα/p-PKCα, promoted PKCα-RORα binding, and downregulated RORα/β-catenin target genes (counteracted by GO6976). DADS upregulated caspase-3 and downregulated Bcl-2/P-gp/XIAP via RORα, promoting apoptosis and 5-FU sensitivity. Conclusion: DADS inhibits GC progression and enhances 5-FU sensitivity by PKCα/RORα-mediated downregulation of RORα/β-catenin signaling, paralleling SR1078/TPA effects. It may act as a novel RORα agonist for GC therapy.

Overactivation of Wnt/β-catenin pathway due to dysfunction of retinoid-related orphan receptor α (RORα) is related to cancer development and progression. Diallyl disulfide (DADS), an active component of garlic, has been reported in our previous study for upregulation of RORα expression in gastric cancer (GC) cells. It remains to be elucidated the role and mechanism of RORα in DADS against GC. This study revealed that DADS treatment resulted in reduced expression levels of Wnt1, β-catenin, TCF-4, intranuclear β-catenin and p-β-catenin in GC cells, concomitant with the compromised expression of β-catenin target genes (Axin, c-Jun, and c-Myc). RORα overexpression augmented DADS-induced downregulation of Wnt1/β-catenin pathway, G2/M phase arrest, and cell growth inhibition in vitro and in vivo. Contrarily, knockdown of RORα attenuated these effects of DADS. Interestingly, DADS induced an increase in the binding of RORα to β-catenin, which may lead to reduction of β-catenin phosphorylation and nuclear translocation. This interplay modulated by DADS may affect β-catenin target gene expression for that the opposite results were observed in DADS-treated RORα knockdown and overexpression cells. DADS caused a decrease in vimentin, snail and MMP-9, as well as an increase in E-cadherin and TIMP3 expression, which restricted epithelial‑mesenchymal transition (EMT), migration, and invasion. The aforementioned effects of DADS were weakened simultaneously when the suppression of DADS on the Wnt1/β-catenin pathway was resisted by knockdown of RORα. In contrast, overexpression of RORα enhanced the effects of DADS. Therefore, RORα-mediated downregulation of Wnt1/β-catenin pathway could undertake an important role in anticancer activity of DADS against GC cell proliferation, EMT, migration, and invasion.

Cofilin is associated with cell differentiation; however, to the best of our knowledge, no data have indicated an association between the cofilin 1 pathway and leukemia cell differentiation. The present study investigated the involvement of the cofilin 1 signaling pathway in diallyl disulfide (DADS)‑induced differentiation and the inhibitory effects on the proliferation, migration, and invasion of human leukemia HL‑60 cells. First, it was identified that 8 µM DADS suppressed cell proliferation, migration and invasion, and induced differentiation based on the reduced nitroblue tetrazolium ability and increased CD11b and CD33 expression. DADS significantly downregulated the expression of cofilin 1 and phosphorylated cofilin 1 in HL‑60 leukemia cells. Second, it was verified that silencing cofilin 1 markedly promoted 8 µM DADS‑induced differentiation and the inhibitory effect on cell proliferation and invasion. Overexpression of cofilin 1 obviously suppressed 8 µM DADS‑induced differentiation and the inhibitory effect on cell proliferation and invasion. Third, the present study examined the mechanisms by which 8 µM DADS decreases cofilin 1 expression and activation. The results revealed that 8 µM DADS inhibited the mRNA and protein expression of Rac1, Rho‑associated protein kinase 1 (ROCK1) and LIM domain kinase 1 (LIMK1) as well as the phosphorylation of LIMK1 in HL‑60 cells, while 8 µM DADS enhanced the effects of the Rac1‑ROCK1‑LIMK1 pathway in cells overexpressing cofilin 1 compared with that in control HL‑60 cells. These results suggest that the anticancer function of DADS on HL‑60 leukemia cells is regulated by the Rac1‑ROCK1‑LIMK1‑cofilin 1 pathway, indicating that DADS could be a promising anti‑leukemia therapeutic compound.

Retinoid-related orphan receptor alpha (RORα) is involved in tumor development. However, the mechanisms underlying RORα inhibiting epithelial-to-mesenchymal transition (EMT) and invasion are poorly understood in gastric cancer (GC). This study revealed that the decreased expression of RORα is associated with GC development, progression, and prognosis. RORα suppressed cell proliferation, EMT, and invasion in GC cells through inhibition of the Wnt/β-catenin pathway. RORα overexpression resulted in the decreased Wnt1 expression and the increased RORα interaction with β-catenin, which could lead to the decreased intranuclear β-catenin and p-β-catenin levels, concomitant with downregulated T-cell factor-4 (TCF-4) expression and the promoter activity of c-Myc. The inhibition of Wnt/β-catenin pathway was coupled with the reduced expression of Axin, c-Myc, and c-Jun. RORα downregulated vimentin and Snail and upregulated E-cadherin protein levels in vitro and in vivo. Inversely, knockdown of RORα attenuated its inhibitory effects on Wnt/β-catenin pathway and its downstream gene expression, facilitating cell proliferation, EMT, migration, and invasion in GC cells. Therefore, RORα could play a crucial role in repressing GC cell proliferation, EMT, and invasion via downregulating Wnt/β-catenin pathway.

To investigate the inducing effect of down-regulation of MCL-1 by diallyl disulfide(DADS) on the G2/M arrest of human leukemia K562 cells and its mechanisms. CCK-8 was used to detect the effect of DADS on proliferation of K562 cells, flow cytometry was employed to observe the effect of cycle arrest by DADS and RNAi silencing MCL-1 gene in K562 cells. The expressions of MCL-1, PCNA and CDK1 in K562 cells treated with DADS were detected by Western blot. The amphigamy of MCL-1 with PCNA and CDK1 was detected by Coimmunoprecipitation. CCK-8 detection showed that the inhibition rates of K562 cells treated with 15, 30, 60, 120, 240 µmol/L DADS were 32.48%, 59.34%, 66.42%, 77.06%, 81.05% respectively (P<0.05). Flow cytometry analysis revealed that the perecentages of G2/M cells were increased to 18.6% and 34.4%, 17.5% and 28.5%, respectively at 24 and 48 h after treating K562 cells with 60 and 120 µmol/L DADS (P<0.05). And the perecentage of G2/M cells of silencing MCL-1 was significantly increased (P<0.05). Silencing effects of MCL-1+DADS on the cells were enhanced more significantly as compared with DADS or MCL-1 alone (P<0.05). Western blot exhibited that DADS could markedly downregulate the expression of MCL-1, PCNA and CDK1(P<0.05). Coimmunoprecipitation revealed that MCL-1 bound with PCNA and CDK1, then forming heterodimers, which were downregulated respectively more significantly than that in the control group after treating K562 cells with DADS for 8 h (P<0.05). DADS can inhibit the K562 cell proliferation and induce them arrest G2/M through downregulation of MCL-1, then decreasing the expression of PCNA and CDK1 in hunan leukemia K562 cells. Moreover, silencing MCL-1 can enhance the effect of DADS.

Transforming growth factor‑β1 (TGF‑β1) has been demonstrated to promote epithelial‑mesenchymal transition (EMT), invasion and proliferation in tumors via the activation of Rac1 and β‑catenin signaling pathways. The present study investigated the effects of diallyl disulfide (DADS) on TGF‑β1‑induced EMT, invasion and growth of gastric cancer cells. TGF‑β1 treatment augmented EMT and invasion, concomitantly with increased expression of TGF‑β1, Rac1 and β‑catenin in gastric cancer cells. DADS downregulated the expression levels of TGF‑β1, Rac1 and β‑catenin. DADS, TGF‑β1 receptor inhibitor as well as Rac1 inhibitor antagonized the upregulation of the TGF‑β1‑induced expression of these genes, abolishing the enhanced effects of TGF‑β1 on EMT and invasion. Blocking the TGF‑β1 receptor through inhibition resulted in the decreased expression of Rac1 and β‑catenin. Rac1 inhibitor reduced the TGF‑β1‑induced β‑catenin expression. In addition, DADS and the aforementioned inhibitors attenuated the TGF‑β1‑induced tumor growth and the expression changes of E‑cadherin, vimentin, Ki‑67 and CD34 in nude mice. These data indicated that the blockage of TGF‑β1/Rac1 signaling by DADS may be responsible for the suppression of EMT, invasion and tumor growth in gastric cancer.

This study aimed to explore whether the downregulation of LIM kinase 1 (LIMK1)-actin depolymerization factor (ADF, also known as destrin)/cofilin by diallyl disulfide (DADS) inhibited the migration and invasion of colon cancer. Previous studies have shown that silencing LIMK1 could significantly enhance the inhibitory effect of DADS on colon cancer cell migration and invasion, suggesting that LIMK1 was a target molecule of DADS, which needed further confirmation. This study reported that LIMK1 and destrin were highly expressed in colon cancer and associated with poor prognosis of patients with colon cancer. Also, the expression of LIMK1 was positively correlated with the expression of destrin. The overexpression of LIMK1 significantly promoted colon cancer cell migration and invasion. DADS obviously inhibited migration and invasion by suppressing the phosphorylation of ADF/cofilin via downregulation of LIMK1 in colon cancer cells. Furthermore, DADS-induced suppression of cell proliferation was enhanced and antagonized by the knockdown and overexpression of LIMK1 in vitro and in vivo, respectively. Similar results were observed for DADS-induced changes in the expression of vimentin, CD34, Ki-67, and E-cadherin in xenografted tumors. These results indicated that LIMK1 was a potential target molecule for the inhibitory effect of DADS on colon cancer cell migration and invasion.

Diallyl disulfide (DADS) is a primary component of garlic, which has chemopreventive potential. We previously found that moderate doses (15-120 µM) of DADS induced apoptosis and G2/M phase cell cycle arrest. In this study, we observed the effect of low doses (8 µM) of DADS on human leukemia HL-60 cells. We found that DADS could inhibit proliferation, migration and invasion in HL-60 cells, and arrested cells at G0/G1 stage. Then, cell differentiation was displayed by morphologic observation, NBT reduction activity and CD11b evaluation of cytometric flow. It showed that DADS induced differentiation, reduced the ability of NBT and increased CD11b expression. Likewise, DADS inhibited xenograft tumor growth and induced differentiation in vivo. In order to make sure how DADS induced differentiation, we compared the protein expression profile of DADS-treated cells with that of untreated control. Using high resolution mass spectrometry, we identified 18 differentially expressed proteins after treatment with DADS, including four upregulated and 14 downregulated proteins. RT-PCR and western blot assay showed that DJ-1, cofilin 1, RhoGDP dissociation inhibitor 2 (RhoGDI2), Calreticulin (CTR) and PCNA were decreased by DADS. These data suggest that the effects of DADS on leukemia may be due to multiple targets for intervention.