Activation of cyclin-dependent kinases CDC2 and CDK2 in hepatocellular carcinoma

BACKGROUND: The cyclin-dependent kinases (CDKs) CDC2 and CDK2 are key regulators of the cell cycle. The expression of the CDK alone does not necessary reflect their true activities because they are highly regulated by post-translational mechanisms. Human hepatocellular carcinoma (HCC) is one of the most common cancers in the world, but the kinase activities of CDKs in HCC have not been examined. METHODS: Here we examined the protein expression and kinase activities associated with CDC2 and CDK2 in HCC and the corresponding non-tumorous liver tissues. RESULTS: CDC2 and CDK2 are activated in HCC in over 70% and 80% of the cases, respectively, but have little correlation with clinical parameters and PCNA expression. Interestingly, PCNA was readily detectable in extracts from non-tumorous liver, but more than 60% of samples contain higher concentration of PCNA in HCC than the corresponding non-tumorous tissues. CDC2 and CDK2 are generally activated in the same HCC samples, but the extent of their activation varied significantly, suggesting that the pathways leading to the activation of CDC2 and CDK2 can be regulated independently. Both positive regulators of CDK activity like cyclins and CDKs, and negative regulators of CDK activity like p21(CIP1/WAF1) and Thr14/Tyr15 phosphorylation were up-regulated in HCC. CONCLUSION: CDC2 and CDK2 are activated in HCC, and this may be due to a complex interplay between the level of the cyclin, CDK, CDK inhibitors, and inhibitory phosphorylation.     

Cyclins and cyclin-dependent kinases: comparative study of hepatocellular carcinoma versus cirrhosis

Increasing evidence has indicated that perturbation of cyclins is one of the major factors leading to cancer. The aim of this study was not only to investigate various cell cycle-related kinase activities in hepatocellular carcinoma (HCC), but also to analyze the difference of cell cycle-related kinase activity levels between hepatitis C virus (HCV)-induced HCC and HCV-induced cirrhosis. The protein levels of cyclins D1, E, A, and H, and of cyclin dependent kinase 1 (Cdk1), Cdk2, Cdk4, Cdk6, and Cdk7 in HCC and in surrounding nontumorous cirrhosis were determined by Western blot. The enzymatic activities of cyclins D1, E, A, Cdk1, Cdk4, Cdk6, Cdk7, and Wee1 were measured using in vitro kinase assays. Protein levels and kinase activities of cyclin D1, Cdk4, cyclin E, cyclin A, and Wee1 were significantly elevated in HCC compared with surrounding cirrhotic tissues. The enhanced cyclin D1-related kinase activity in HCC was accompanied by the up-regulation of Cdk4 activity, but not Cdk6 activity. The kinase activities of Cdk6, Cdk7, and Cdk1 did not differ between HCC and surrounding cirrhotic tissues. In addition, the protein levels and kinase activities of cyclin D1, Cdk4, and cyclin E were higher in poorly differentiated HCC and advanced HCC. In conclusion, the increases of cyclin D1, Cdk4, cyclin E, cyclin A, and Wee1 play an important role in the development of HCC from cirrhosis. Cyclin D1, Cdk4, and cyclin E activation may be closely related to the histopathologic grade and progression of HCC.     

S-phase delay in human hepatocellular carcinoma cells induced by overexpression of integrin β1

AIM:To clarify the mechanisms of integrin overexpression in negatively regulating the cell cycle control of hepatocellular carcinoma cells SMMC-7721.METHODS: The cell cycle pattern was determined by flow cytometry. The mRNA and protein expression levels were assayed by RT-PCR and Western blot, respectively. Stable transfection was performed by Lipofectamine 2000 reagent,and cells were screened by G418.RESULTS: Overexpression of α5β1 or β1 integrin induced S-phase delay in SMMC-7721 cells, and this delay was possibly due to the accumulation of cyclin-dependent kinase inhibitors (CKIs) p21cip1 and p27kip1. The decrease of protein kinase B (PKB) phosphorylation was present in this signaling pathway, but focal adhesion kinase (FAK) was not involved.When phosphorylation of PKB was solely blocked by wortmannin, p27kip1 protein level was increased. Moreover,S-phase delay was recurred when attachment of the parental SMMC-7721 cells was inhibited by the preparation of polyHEME, and this cell cycle pattern was similar to that of β1-7721 or α5β1-7721 cells.CONCLUSION: S-phase delay induced by overexpression of integrin β1 subunit is attributed to the decrease of PKB phosphorylation and subsequent increases of p21cip1 and p27kip1 proteins, and may be involved in the unoccupied α5β1because of lack of its ligands.     

S-phase delay in human hepatocellular carcinoma cells induced by overexpression of integrin β1

AIM: To clarify the mechanisms of integrin overexpression in negatively regulalting the cell cyde control of hepatocellular carcinoma cells SMMC-7721.METHODS: The cell cycle pattern was determined by flow cytometry. The mRNA and protein expression levels were assayed by RT-PCR and Western blot, respectively. Stable transfection was performed by Upofectamine 2000 reagent,and cells were screened by G418.RESULTS: Overexpression of α5β1 or β1 integrin induced S-phase delay in SMMC-7721 cells, and this delay was possibly due to the accumulaltion of cydin-dependent kinase inhibitors (CKIs) p21^cip1 and p27^kip1. The decrease of protein kinase B (PKB) phosphorylation was present in this signaling pathway, but focal adhesion kinase (FAK) was not involved.When phosphorylation of PKB was solely blocked by wortmannin, p27^kip1 protein level was increased. Moreover,S-phase delay was recurred when attachment of the parental SMMC-7721 cells was inhibited by the preparation of poly-HEME, and this cell cycle pattern was similar to that of β1-7721 or α5β1-7721 cells.CONCLUSION: S-phase delay induced by overexpression of integdn 151 subunit is attributed to the decrease of PKB phosphorylation and subsequent increases of p21^cip1 and p27^kip1 proteins, and may be involved in the unoccupied α5β1 because of lack of its ligands.     

Zoledronic acid delays disease progression of bone metastases from hepatocellular carcinoma

Aim: We conducted a retrospective cohort study to investigate the efficacy of combination therapy with radiotherapy (RT) and zoledronic acid for bone metastases from hepatocellular carcinoma (HCC). Additionally, we investigated the efficacy of zoledronic acid for non‐irradiated bone metastases. Methods: This study consisted of 31 patients who had received RT for bone metastases. Twelve of these patients with 23 sites of bone metastases were also treated with zoledronic acid (Z group). In the Z group, 14 sites received RT and nine sites did not. Nineteen patients with 38 sites of bone metastases were not treated with zoledronic acid (non‐Z group). In the non‐Z group, 22 sites received RT and 16 did not. We compared survival, pain response, time to pain progression, radiographic response, time to radiographic progression, and safety between groups. Results: While pain response rates were similar between the two groups, time to pain progression rates of irradiated and non‐irradiated bone metastases was significantly lower in the Z (0% and 20% at 6 months, respectively) than in the non‐Z group (34% and 66% at 6 months, respectively) (P = 0.045 and P = 0.005). Further, while radiographic response rates were similar between the two groups, time to radiographic progression rate of non‐irradiated bone metastases was significantly lower in the Z (29% at 3 months) than in the non‐Z group (91% at 3 months) (P = 0.009). No significant side‐effects were documented. Conclusion: Zoledronic acid delayed the pain progression of both irradiated and non‐irradiated bone metastases and the radiographic progression of non‐irradiated bone metastases from HCC.     

Reprogramming leukemic cells to terminal differentiation by inhibiting specific cyclin-dependent kinases in G1

Some tumor cells can be stimulated to differentiate and undergo terminal cell division and loss of tumorigenicity. The in vitro differentiation of murine erythroleukemia (MEL) cells is a dramatic example of tumor-cell reprogramming. We found that reentry of MEL cells into terminal differentiation is accompanied by an early transient decline in the activity of cyclin-dependant kinase (CDK) 2, followed by a decline of CDK6. Later, as cells undergo terminal arrest, CDK2 and CDK4 activities decline. By analyzing stable MEL-cell transfectants containing vectors directing inducible expression of specific CDK inhibitors, we show that only inhibitors that block the combination of CDK2 and CDK6 trigger differentiation. Inhibiting CDK2 and CDK4 does not cause differentiation. Importantly, we also show that reprogramming through inhibition of CDKs is restricted to G(1) phase of the cell cycle. The results imply that abrogation of normal cell-cycle controls in tumor cells contributes to their inability to differentiate fully and that restoration of such controls in G(1) can lead to resumption of differentiation and terminal cell division. The results also indicate that CDK4 and CDK6 are functionally distinct and support our hypothesis that the two CDKs regulate cell division at different stages of erythroid maturation.     

Involvement of RhoA in progression of human hepatocellular carcinoma

BACKGROUND AND AIM: The activation of Rho proteins has been shown to lead to loss of polarity in cancer cells, as well as reorganization of the cytoskeleton and facilitation of cell motility, possibly resulting in their malignant potential. The clinicopathological significance of RhoA, however, is not yet well known in the case of hepatocellular carcinoma (HCC). This study evaluated the clinicopathological correlation of RhoA levels with HCC. METHODS: The intratumor expression level of Rho was determined and compared with that in adjacent non-cancerous hepatic tissue using quantitative real time RT-PCR and Western blotting in 64 patients with HCC. Relationships between the level of RhoA and clinicopathological factors were examined. RhoA protein expression was confirmed by immunohistochemistry. RESULTS: RhoA immunostaining was strong in malignant tissue whereas it was minimal in benign tissue. Tumor tissue of HCC patients demonstrated a copy number of RhoA mRNA that was well correlated with its protein level in each case and was significantly higher than that found in the corresponding non-cancerous liver tissue (P < 0.01). With regard to venous invasion, satellite lesions and advanced pTNM stage, the RhoA level tended to be higher in HCC than that seen in negative tissue (P < 0.05). CONCLUSIONS: This is the first demonstration that the expression level of RhoA is correlated with tumor progression and metastasis in HCC. RhoA in tumor tissue might be expected to be not only a good candidate marker for invasive and proliferative tumor cells, but also a molecular target of these cells.     

Smoc2 potentiates proliferation of hepatocellular carcinoma cells via promotion of cell cycle progression

AIM To determine the influence of Smoc2 on hepatocellular carcinoma(HCC) cell proliferation and to find a possible new therapeutic target for preventing HCC progression.METHODS We detected expression of Smoc2 in HCC tissues and corresponding non-tumor liver(CNL) tissues using PCR, western blot, and immunohistochemistry methods. Subsequently, we down-regulated and upregulated Smoc2 expression using siR NA and lentivirus transfection assay, respectively. Then, we identified the effect of Smoc2 on cell proliferation and cell cycle using CCK-8 and flow cytometry, respectively. The common cell growth signaling influenced by Smoc2 was detected by western blot assay. RESULTS The expression of Smoc2 was significantly higher in HCC tissues compared with CNL tissues. Overexpression of Smoc2 promoted HCC cell proliferation and cell cycle progression. Down-regulation of Smoc2 led to inhibition of cell proliferation and cell cycle progression. Smoc2 had positive effect on ERK and AKT signaling.CONCLUSION Smoc2 promotes the proliferation of HCC cells through accelerating cell cycle progression and might act as an anti-cancer therapeutic target in the future.     

Transduction of human hepatocellular carcinoma cells with human alpha-interferon gene via retroviral vector

AIM:To investigate the therapeutic potential of gamma interferon (IFN-alpha) genemodified human hepatocellular carcinoma (HCC) cells.METHODS:The IFN-alpha gene was introduced retrovirally into four HCC cell lines.Secreted IFN-alpha activity was assessed using bioassay. The expression of MHC molecules was detected by FACS.Tumorigenicity was analysed by tumor formation in nude mice.RESULTS:Four IFN-alpha gene transduced HCC cell lines secreted different amounts of IFN-alpha, as in the same case of five clones derived from one HCC cell line. Transduction with IFN-alpha caused significant increase in the expression of major histocompatibility complex (MHC) antigens on HCC cells. The expression of HLA class I was increased by 2-3 times in terms of mean fluorescence intensities, while for class II expression, the percentage of positive cells augmented from < 10% to &lg 50%. When equal amount of tumor cells were injected into nude mice, the tumor igenicity some transduced cells decreased dramantically.CONCLUSION:IFN-alpha gene transduction can convert weakly imunogenic HCC cells to activate antitumor immune response, and further pave the way for the future use of such gene modified tumor cells as a modality for the cancer immunotherapy.     

Growth inhibition and apoptosis induction of tanshinone Ⅱ-A on human hepatocellular carcinoma cells

AIM: To evaluate the effects of tanshinone II-A on inducing growth inhibition and apoptosis of human hepatocellular carcinoma (HCC) cells. METHODS: The human hepatocellular carcinoma cell line SMMC-7721 was used for the study. The cells were treated with tanshinone II-A at different doses and different times. Cell growth and proliferation were measured by MTT assay, cell count and colony-forming assay. Apoptosis induction was detected by microscopy, DNA ladder electrophoresis and flow cytometry. RESULTS: In MTT assay, the inhibitory effect became gradually stronger with the passage of time, 24, 48, 72 and 96 h after treatment with tanshinone II-A, and the most significant effect was observed at 72 h. On the other hand, the increase of doses (0.125, 0.25, 0.5, 1.0 mg/L tanshinone II-A) resulted in enhanced inhibitory effect. The growth and proliferation of SMMC-7721 cells were obviously suppressed in a dose- and time-dependent manner. The results of cell count were similar to that of MTT assay. In colony-forming assay, the colony-forming rates were obviously inhibited by tanshinone II-A. In tanshinone II-A group, the morphology of cellular growth inhibition and characteristics of apoptosis such as chromatin condensation, crescent formation, margination and apoptotic body were observed under light and transmission electron microscopes. DNA ladder of cells was presented in electrophoresis. The apoptosis index (AI) was 16.9% (the control group was 4.6%) in flow cytometry. The cells were arrested in G(0)/G(1) phase, and the expressions of apoptosis-related genes bcl-2 and c-myc were down-regulated and fas, bax, p53 up-regulated. CONCLUSION: Tanshinone II-A could inhibit the growth and proliferation of HCC cell effectively in vitro by apoptosis induction, which was associated with up-regulation of fas, p53, bax, expression and down-regulation of bcl-2 and c-myc.     

Chemokine ligand 20 enhances progression of hepatocellular carcinoma via epithelial-mesenchymal transition

AIM: To identify the mechanisms of chemokine ligand 20(CCL20)-induced hepatocellular carcinoma(HCC) metastasis and evaluate it as a prognostic marker. METHODS: Expression of CCL20 was evaluated by immunohistochemistry in HCC tissues from 62 patients who underwent curative resection. The relationship between CCL20 expression and clinicopathologic features was analyzed. Univariate and multivariate analyses were performed to evaluate its predictive value for recurrence and survival of HCC patients. The expression levels ofepithelial-mesenchymal transition(EMT)-and signaling pathway-related proteins were evaluated by Western blotting and immunocytochemistry. The effects of CCL20 on HCC cell proliferation and migration were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenoltetrazolium bromide(MTT) and Transwell assays. RESULTS: CCL20 immunoreactivity was detected in all 62 patient specimens. CCL20 expression was associated with preoperative alpha-fetoprotein level(P = 0.043), tumor size(P = 0.000), tumor number(P = 0.008), vascular invasion(P = 0.014), and tumor differentiation(P = 0.007). Patients with high CCL20 expression had poorer recurrence-free and overall survivals compared to those with low CCL20 expression(both P 0.001). CCL20 induced EMT-like changes in HCC cells and increased their proliferation and migration ability(P 0.05). Western blotting and immunofluorescence staining showed that CCL20 induced an EMT-like phenotype in HCC cells, and increased expression of phosphorylated AKT, β-catenin and vimentin, and decreased E-cadherin expression(P 0.05). The correlation analysis revealed that high CCL20 expression in HCC tissue specimens was negatively correlated with E-cadherin expression(13.33%, 4/30), and positively correlated with vimentin(90.0%, 27/30), β-catenin(96.67%, 29/30) and p-AKT(76.67%, 23/30) expression.CONCLUSION: CCL20 expression is associated with HCC recurrence and patient survival and promotes HCC cell proliferation and migration by inducing EMT-like changes via PI3K/AKT and Wnt/β-catenin pathways.     

CDK5在肝细胞癌中的异常表达

目的:研究周期素依赖性激酶5(cyclin-dependent kinase5.CDK5)在肝细胞癌(hepatocellular carcinoma,HCC)发生发展中的异常表达.方法:应用反转录聚合酶链式反应(RT-PCR)检测CDK5 mRNA的表达水平;免疫组织化学技术检测CDK5蛋白在正常肝组织、肝硬化和HCC组织中的表达:分析CDK5与临床病理学特征的关系.结果:CDK5 mRNA在HCC中呈上调表达,阳性表达率在正常肝组织、肝硬化和HCC组织中分别为35.3%、64.3%、89.7%;正常肝组织与HCC组织有显著差异(P<0.05),肝硬化组织与HCC组织也有显著差异(P<0.01).CDK5蛋白在HCC中高表达,阳性表达率在人正常肝组织、肝硬化和HCC组织之间分别为29.4%.64.3%,89.7%,三组之间差异有统计学意义(x2=58.095,P<0.01).HCC组织中CDK5蛋白表达强度与肿瘤的病理学分级显著相关(x2=19.330,P<0.01).结论:CDK5在HCC中上调表达,他的异常表达在HCC的发生发展过程中发挥重要的作用,且与肿瘤的分化程度相关.     

Mechanisms of hepatocellular carcinoma progression

Hepatocellular carcinoma(HCC) is the most common primary malignancy of the liver. It is the second leading cause of cancer-related deaths worldwide, with a very poor prognosis. In the United States, there has been only minimal improvement in the prognosis for HCC patients over the past 15 years. Details of the molecular mechanisms and other mechanisms of HCC progression remain unclear. Consequently, there is an urgent need for better understanding of these mechanisms. HCC is often diagnosed at advanced stages, and most patients will therefore need systemic therapy, with sorafenib being the most common at the present time. However, sorafenib therapy only minimally enhances patient survival. This review provides a summary of some of the known mechanisms that either cause HCC or contribute to its progression. Included in this review are the roles of viral hepatitis, non-viral hepatitis, chronic alcohol intake, genetic predisposition and congenital abnormalities, toxic exposures, and autoimmune diseases of the liver. Well-established molecular mechanisms of HCC progression such as epithelial-mesenchymal transition, tumor-stromal interactions and the tumor microenvironment, cancer stem cells, and senescence bypass are also discussed. Additionally, we discuss the roles of circulating tumor cells,immunomodulation, and neural regulation as potential new mechanisms of HCC progression. A better understanding of these mechanisms could have implications for the development of novel and more effective therapeutic and prognostic strategies, which are critically needed.     

Mast cells and human hepatocellular carcinoma

AIM: TO Investigate the density of mast cells (MCs) in human hepatocellular carcinoma (HCC), and to determine whether the MCs density has any correlations with histopathological grading, staging or some baseline patient characteristics.METHODS: Tissue sections of 22 primary HCCs were histochemically stained with toluidine blue, in order to be able to quantify the MCs in and around the neoplasm using a computer-assisted image analysis system. HCC was staged and graded by two independent pathologists. To identify the sinusoidal capillarisation of each specimen 3μm thick sections were histochemically stained with siriusred, and semi-quantitatively evaluated by two independent observers. The data were statistically analysed using Spearman‘‘s correlation and Student‘‘s t-test when appropriate.RESULTS: MCs density did not correlate with the age or sex of the patients, the serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels, or the stage or grade of the HCC. No significant differences were found between the MCs density of the patients with and without hepatitis C virus infection, but they were significantly higher in the specimens showing marked sinusoidal capillarisation.CONCLUSION: The lack of any significant correlation between MCs density and the stage or grade of the neoplastic lesions suggests that there is no causal relationship between MCs recruitment and HCC. However, as capillarisation proceeds concurrently with arterial blood supply during hepatocarcinogenesis, MCs may be considered of primary importance in the transition from sinusoidal to capillary-type endothelial cells and the HCC growth.     

Growth inhibition and apoptosis induction of tanshinone Ⅱ-A on human hepatocellular carcinoma cells

AIM: To evaluate the effects of tanshinone Ⅱ-A on inducing growth inhibition and apoptosis of human hepatocellular carcinoma (HCC) cells.METHODS: The human hepatocellular carcinoma cell line SMMC-7721 was used for the study. The cells were treated with tanshinone Ⅱ-A at different doses and different times.Cell growth and proliferation were measured by MTT assay,cell count and colony-forming assay. Apoptosis induction was detected by microscopy, DNA ladder electrophoresis and flow cytometry.RESULTS: In MTT assay, the inhibitory effect became gradually stronger with the passage of time, 24, 48, 72and 96 h after treatment with tanshinone Ⅱ-A, and the mostsignificant effect was observed at 72 h. On the other hand, the increase of doses (0.125, 0.25, 0.5, 1.0 mg/L tanshinone Ⅱ-A) resulted in enhanced inhibitory effect.The growth and proliferation of SMMC-7721 cells were obviously suppressed in a dose- and time-dependent manner. The results of cell count were similar to that of MTT assay. In colony-forming assay, the colony-forming rates were obviously inhibited by tanshinone Ⅱ-A. In tanshinone Ⅱ-A group, the morphology of cellular growth inhibition and characteristics of apoptosis such as chromatin condensation, crescent formation, margination and apoptotic body were observed under light and transmission electron microscopes. DNA ladder of cells was presented in electrophoresis. The apoptosis index (AI) was 16.9% (the control group was 4.6%) in flow cytometry. The cells were arrested in G0/G1 phase, and the expressions of apoptosisrelated genes bcl-2 and c-myc were down-regulated and fas, bax, p53 up-regulated.CONCLUSION: Tanshinone Ⅱ-A could inhibit the growth and proliferation of HCC cell effectively in vitro by apoptosis induction,which was associated with up-regulation of fas, p53, bax,expression and down-regulation of bcl-2and c-myc.     

Increases in src-related protein tyrosine kinases in human liver cirrhosis and hepatocellular carcinoma

We examined the involvement of src-related tyrosine kinases (RTK) in various human liver diseases, such as chronic hepatitis (CH), liver cirrhosis (LC) and hepatocellular careinoma (HCC), by Western blot and immunohistochemical analysis using an anti-src-RTK polyclonal antibody (α-416). Our results showed that src-RTK were rarely found in the liver tissues from CH patients, while they were found at high amounts in those from LC and HCC patients. In addition, src-RTK were expressed more strongly in HCC than in LC. These results indicate that src-RTK may play important roles in the occurrence and development of LC and HCC.     

Proteasome inhibition sensitizes hepatocellular carcinoma cells, but not human hepatocytes, to TRAIL

TRAIL exhibits potent anti-tumor activity on systemic administration in mice. Because of its proven in vivo efficacy, TRAIL may serve as a novel anti-neoplastic drug. However, approximately half of the tumor cell lines tested so far are TRAIL resistant, and potential toxic side effects of certain recombinant forms of TRAIL on human hepatocytes have been described. Pretreatment with the proteasome inhibitor MG132 and PS-341 rendered TRAIL-resistant hepatocellular carcinoma (HCC) cell lines but not primary human hepatocytes sensitive for TRAIL-induced apoptosis. We investigated the different levels of possible MG132-induced interference with resistance to apoptotic signal transduction. Although proteasome inhibition efficiently suppressed nuclear factor-kappaB (NF-kappaB) activity, specific suppression of NF-kappaB by mutIkappaBalpha failed to sensitize TRAIL-resistant cell lines for TRAIL-induced apoptosis. In contrast to the previously reported mechanism of sensitization by 5-fluorouracil (5-FU), cellular FLICE-inhibitory protein (cFLIP)(L) and cFLIP(S) were markedly upregulated in the TRAIL death inducing signaling complex (DISC) by proteasome inhibitor pretreatment. Compared with 5-FU pretreatment, caspase-8 was more efficiently recruited to the DISC in MG132 pretreated cells despite the presence of fewer death receptors and more cFLIP in the DISC. But downregulation of cFLIP by short interference RNA (siRNA) further sensitized the HCC cell lines. In conclusion, these results show that otherwise chemotherapy-resistant tumor cells can be sensitized for TRAIL-induced apoptosis at the DISC level in the presence of high levels of cFLIP, which suggests the existence of an additional factor that modulates the interaction of FADD and the TRAIL death receptors. Of clinical relevance, proteasome inhibitors sensitize HCC cells but not primary human hepatocytes for TRAIL-induced apoptosis.     

Docetaxel shows radiosensitization in human hepatocellular carcinoma cells

AIM: To determine the radiosensitizing potential of docetaxel in human hepatocellular carcinoma SMMC-7721 cells and its mechanisms. METHODS: SMMC-7721 cells were incubated with docetaxel at 0.125, 0.25, and 0.5 nmoL/L for 24 h and at 0.125 and 0.25 nmol/L for 48 h before irradiation. Radiation doses were given from 0 to 10 Gy. Cell survival was measured by a standard clonogenic assay after a 9-d incubation. The reactive oxygen species (ROS) and glutathione (GSH) are detected after being given the same dose of docetaxel for the same time. RESULTS: The sensitization enhancement ratios (SER) for SMMC-7721 cells determined at the 50% survival level were 1.15, 1.21 and 1.49 at 0.125, 0.25, and 0.5 nmol/L for pre-incubation of 24 h, respectively; the SER were 1.42, 1.67 at 0.125 and 0.25 nmol/L, for pre-incubation of 48 h, respectively. The ROS of SMMC-7721 cells increased and GSH decreased after pretreatment with the same doses of docetaxel for 24 or 48 h. CONCLUSION: A radiosensitizing effect of docetaxel could be demonstrated unambiguously in this cell line used. In addition, our data showed that the mechanism of radiopotentiation by docetaxel probably does not involve a G2/M block in SMMC-7721 cells, and ROS generation and GSH deletion may play a key role in the radiosensitizing effect of docetaxel.