MEK1/2 inhibition promotes Taxotere lethality in mammary tumors in vivo

Taxol (paclitaxel) and Taxotere (docetaxel) are considered as two of the most important anti-cancer chemotherapy drugs. The cytotoxic action of these drugs has been linked to their ability to inhibit microtubule depolymerization, causing growth arrest and subsequent cell death. Studies by a number of laboratories have also linked suppression of MEK1/2 signaling to enhanced Taxol toxicity in vitro and in vivo. The present study examined the interactions of the semi-synthetic taxane Taxotere with MEK1/2 inhibitors in epithelial tumor cells. In vitro colony formation studies demonstrated that Taxotere and the MEK1/2 inhibitor PD184352 interacted in a sequence dependent fashion to synergistically kill human mammary carcinoma cells (MDA-MB-231, MCF7) as well as in other tumor cell types; e.g. prostate and renal cell carcinoma. Athymic mice were implanted in the rear flank with either MDA-MB-231 or MCF7 cells and tumors permitted to form to a volume of approximately 100 mm3 prior to a two day exposure of either Vehicle, PD184352 (25 mg/kg), Taxotere (15 mg/kg) or the drug combination. Tumor volume was measured every other day and tumor growth determined over the following approximately 30 days. Transient exposure of MDA-MB-231 tumors or MCF7 tumors to PD184352 did not significantly alter tumor growth rate or the mean tumor volume in vivo approximately 15-30 days after drug administration. Transient Taxotere exposure of MDA-MB-231 or to a lesser extent MCF7, tumors modestly reduced the mean tumor volume in vivo approximately 15-30 days after drug administration. In contrast, combined treatment with PD184352 and Taxotere significantly reduced MDA-MB-231 and MCF7 tumor growth. The tumor control values for MDA-MB-231 cells and MCF7 cells were 0.43 and 0.71, respectively. Fractionated irradiation of MDA-MB-231 tumors during drug exposure or single dose irradiation prior to drug administration did not significantly further suppress tumor growth beyond that of cells exposed to Taxotere and MEK1/2 inhibitor. Single dose irradiation of tumors after drug exposure, however, caused a significant further suppression of tumor growth below that caused by drug exposure. These findings were also reflected in ex vivo colony formation analyses of isolated tumor cells. Collectively, these findings argue that Taxotere and MEK1/2 inhibitors have the potential to suppress mammary tumor growth in vivo which is enhanced by sequence-dependent exposure to ionizing radiation. Based on the cell lines used in these studies, our findings argue that the interaction of Taxotere and PD184352 is independent of p53 status, estrogen dependency, caspase 3 levels or oncogenic K-RAS expression.     

Significant anti-proliferation of human endometrial cancer cells by combined treatment with a selective COX-2 inhibitor NS398 and specific MEK inhibitor U0126

The extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway plays a critical role in the anticancer action in vitro. ERK1/2 activation or phosphorylation is responsible for increased cyclooxygenase-2 (COX-2) protein expression in some cancer cells treated with selective COX-2 inhibitor NS398. We determined the effect of NS398 on ERK signaling and the synergistic effect of combined treatment with NS398 and a specific MEK inhibitor U0126 on three human endometrial cancer cell lines: Ishikawa, HEC-1A and AN3CA cells. Results showed that NS398 and U0126 individually, and especially the combination of both exhibited profound anti-proliferation of all three cell lines in a time- and concentration-dependent manner by [3-(4, 5)-dimethylthiazol-z-yl]-2, 5-diphenyl tetrazolium bromide (MTT) assay. The phosphorylated ERK1/2 was up-regulated in HEC-1A and AN3CA cells, but the COX-2 protein expression was unchanged in the three cancer cell lines treated with NS398 alone. However, both phosphorylated ERK1/2 and COX-2 protein expression were concentration-dependently decreased in all three cell types by combined treatment with NS398 and U0126 assessed by western blot analysis. Simultaneously, the combination of NS398 and U0126 resulted in 2-fold increase in apoptosis of all three lines over that by the individual alone, and enhanced G0/G1 phase arrest of Ishikawa and HEC-1A cells induced by U0126 treatment determined by flow cytometry. The synergistic and complementary effects of combining NS398 and U0126 were found to be associated with activation of caspase-3, alterations of Bcl-2 family proteins and cell cycle regulatory proteins detected by western blot analysis. Taken together, these findings correlate with blocking MEK-ERK signaling cascade and down-regulating COX-2 protein expression in endometrial cancer cells with combination treatment of NS398 and U0126, suggesting that the combinatory use of NS398 and specific MEK inhibitors may be valuable for chemotherapy or chemoprevention of human endometrial cancer.     

U0126对MCF-7细胞株化疗敏感性及XIAP蛋白表达的影响

目的：探讨MEK抑制剂U0126对乳腺癌细胞株MCF-7的凋亡诱导和化疗增敏作用及其与X连锁凋亡抑制蛋白（XIAP）的相关性。方法：利用体外培养乳腺癌细胞株MCF-7，采用MTF比色法观察U0126、紫杉醇（PTX）、阿霉素（ADM）对MCF-7生长的影响；应用流式细胞术观察用药前后细胞周期变化和凋亡率；以Westernblot法检测用药前后XIAP蛋白表达变化。结果：与单药相比，U0126与PTX、ADM联合可显著抑制MCF-7的增殖，增加细胞的凋亡率；联合用药组XIAP蛋白的表达比单药组明显降低。结论：MEK抑制剂U0126与PTX、ADM序贯性联合应用可以协同性增加对MCF-7化疗的敏感性，其机制可能与下调XIAP的表达有关。     

Inhibitors of MEK1/2 interact with UCN-01 to induce apoptosis and reduce colony formation in mammary and prostate carcinoma cells

Recent studies have suggested that inhibition of the mitogen activated protein kinase (MAPK) pathway as well as abrogation of cell cycle check-point control can potentiate the lethal actions of chemotherapeutic drugs and radiation. We therefore investigated the impact of combined exposure to the check-point abrogator (UCN-01) in conjunction with MEK1/2 inhibitors upon survival of breast and prostate carcinoma cells. Treatment of cells with UCN-01 alone resulted in prolonged activation of the MAPK pathway. Inhibition of MEK1/2 caused modest reductions in basal MAPK activity and transiently suppressed UCN-01-stimulated MAPK activity below that of MEK1/2 inhibitor alone. Significantly, combined, but not individual, exposure of cells to UCN-01 and MEK1/2 inhibitors enhanced BAX association with mitochondria and triggered release of cytochrome c into the cytosol, accompanied by activation of effector pro-caspases, resulting in a greater than additive potentiation of apoptosis within 1 8-24h. Radiation exposure of drug treated cells did not further enhance apoptosis. Treatment of cells with both caspase 9 and caspase 8 inhibitors was required to completely inhibit apoptosis in carcinoma cells. Overexpression of Bcl-(xL) blocked cytochrome c release and cell killing induced by the drug combination. Colony forming assays demonstrated that cells exposed to both agents exhibited a substantial reduction in clonogenic survival compared to either drug alone; moreover, radiation further reduced clonogenic survival despite failing to promote additional apoptosis. Collectively, these data demonstrate that combined exposure of carcinoma cells to UCN-01 and MEK1/2 inhibitors induces apoptosis and interacts with radiation to further reduce clonogenic survival.     

A MEK inhibitor (U0126) markedly inhibits direct liver invasion of orthotopically inoculated human gallbladder cancer cells in nude mice

Primary cancer of the gallbladder is not unusual. Most cases of gallbladder cancer are found at an advanced stage, accompanied by the invasion to the liver, metastases to the lymph nodes and distant organs, and peritoneal dissemination. In this study, we first examined the effect of mitogen-activated protein kinase kinase (MEK) inhibitors on the production of matrix metalloproteinases (MMPs), urokinase-type plasminogen activator (uPA), and tissue inhibitors of metalloproteinases (TIMPs) in a human gallbladder cancer cell line, NOZ cells in vitro. MEK inhibitors (PD98059 and U0126) inhibited the production of MMP-2, MMP-9 and high MW uPA, and upregulated TIMPs (TIMP-1, TIMP-2 and TIMP-3). Subsequently, we examined the effect of U0126 on invasion and metastasis of orthotopically inoculated NOZ cells in nude mice. Direct liver invasion by cancer cells was detected in all of the mice in the control group, but in only one mouse in the U0126-treated group. Most of the primary tumors in the U0126-treated group expanded to the liver, but did not invade into the liver. Vessel invasion in the liver was evident in 4 out of 5 mice in the control group, but in only one mouse in the U0126-treated group. Lymph node metastases and peritoneal dissemination were recognized in all of the mice in both groups. All 5 mice in the U0126-treated group, and 4 out of 5 mice in the vehicle control group, had metastases in the lungs. The present results suggest that a MEK inhibitor, U0126, prolonged the survival of the mice with NOZ tumor by inhibiting direct liver invasion and vessel invasion of the cancer cells via down-regulation of the matrix degrading ability of the cancer cells.     

Daurisoline suppresses esophageal squamous cell carcinoma growth in vitro and in vivo by targeting MEK1/2 kinase

Esophageal squamous cell carcinoma (ESCC) accounts for 90% of esophageal cancers and has a high mortality rate worldwide. The 5-year survival rate of ESCC patients in developing countries is <20%. Hence, there is an urgent need for developing new and effective treatments that are based on newly-discovered emerging molecules and pathways to prevent ESCC occurrence and recurrence. We investigated the effects of Daurisoline, a bis-benzylisoquinoline alkaloid extracted from the rhizome of menisperum dauricum, on ESCC cell proliferation and elucidated the molecular mechanisms underlying its functions. To explore the effects of Daurisoline on ESCC growth in vitro and in vivo, cell proliferation assays and anchorage-independent growth assays were performed and a patient-derived xenograft (PDX) model was established. Subsequently, phosphoproteomics, molecular docking analysis, pull down assays, mutation experiments and in vitro kinase assay were performed to explore the mechanism of Daurisoline's function on ESCC. Daurisoline inhibited ESCC proliferation in vitro and reduced ESCC PDX exnograft growth in vivo by reducing ERK1/2 phosphorylation. Furthermore, it directly bound to MEK1 (at Asn78 and Lys97) and MEK2 (at Asp194 and Asp212) kinases to inactivate the ERK1/2 signaling pathway. Our results suggest that Daurisoline is a dual inhibitor of MEK1 and MEK2 and suppresses ESCC growth both in vitro and in vivo by inactivating the ERK1/2 signaling pathway. This is first report on the use of MEK inhibitor for ESCC and highlights its potential applications for ESCC treatment and prevention.     

The irreversible ERBB1/2/4 inhibitor neratinib interacts with the BCL-2 inhibitor venetoclax to kill mammary cancer cells

The irreversible ERBB1/2/4 inhibitor, neratinib, down-regulates the expression of ERBB1/2/4 as well as the levels of MCL-1 and BCL-XL. Venetoclax (ABT199) is a BCL-2 inhibitor. At physiologic concentrations neratinib interacted in a synergistic fashion with venetoclax to kill HER2 + and TNBC mammary carcinoma cells. This was associated with the drug-combination: reducing the expression and phosphorylation of ERBB1/2/3; in an eIF2α-dependent fashion reducing the expression of MCL-1 and BCL-XL and increasing the expression of Beclin1 and ATG5; and increasing the activity of the ATM-AMPKα-ULK1 S317 pathway which was causal in the formation of toxic autophagosomes. Although knock down of BAX or BAK reduced drug combination lethality, knock down of BAX and BAK did not prevent the drug combination from increasing autophagosome and autolysosome formation. Knock down of ATM, AMPKα, Beclin1 or over-expression of activated mTOR prevented the induction of autophagy and in parallel suppressed tumor cell killing. Knock down of ATM, AMPKα, Beclin1 or cathepsin B prevented the drug-induced activation of BAX and BAK whereas knock down of BID was only partially inhibitory. A 3-day transient exposure of established estrogen-independent HER2 + BT474 mammary tumors to neratinib or venetoclax did not significantly alter tumor growth whereas exposure to [neratinib + venetoclax] caused a significant 7-day suppression of growth by day 19. The drug combination neither altered animal body mass nor behavior. We conclude that venetoclax enhances neratinib lethality by facilitating toxic BH3 domain protein activation via autophagy which enhances the efficacy of neratinib to promote greater levels of cell killing.     

MEK抑制剂显著增强EGFR CAR-T细胞对口腔鳞癌的抗肿瘤活性

目的:构建靶向表皮生长因子受体（epidermal growth factor receptor,EGFR）的二代嵌合抗原受体（chimeric antigen receptor,CAR）-T细胞,以探索MEK抑制剂联合EGFR CAR-T细胞是否可以对口腔鳞癌产生显著的抗肿瘤活性。方法:免疫组化法检测口腔鳞癌患者癌和癌旁组织中EGFR的表达;流式细胞术检测口腔鳞癌细胞系中EGFR的表达;慢病毒感染法构建EGFR CAR-T细胞;生物发光法检测EGFR CAR-T细胞联合MEKi对靶细胞的杀伤活性;流式细胞术检测共孵育后效靶细胞的占比情况;活体成像监测小鼠肿瘤的生长;免疫组化法检测小鼠肿瘤组织中CD3的表达;ELISA法检测肿瘤组织中IFN-γ和GrmB的含量。结果:人口腔鳞癌组织较癌旁组织EGFR显著高表达,大部分口腔鳞癌细胞系高表达EGFR。联合MEKi在短时间的共孵育中并不能显著增强EGFR CAR-T细胞对肿瘤细胞系的杀伤活性,但在较长时间的共孵育后,联合MEKi显著增强EGFR CAR-T细胞的增殖（P＜0.01）和对肿瘤细胞的细胞毒性（P＜0.001）。体内实验也表明,联合MEKi较单独使用EGFR CAR-T细胞而言对肿瘤抑制能力更强（P＜0.01）,肿瘤组织中CD3+T细胞的浸润更多（P＜0.001）,肿瘤部位细胞因子IFN-γ（P＜0.001）和GrmB（P＜0.001）的含量也更高。结论:联合MEKi可以在体内外条件下显著增强EGFR CAR-T细胞的抗肿瘤活性,有望成为针对口腔鳞癌的潜在治疗策略。     

Differential outcome of MEK1/2 inhibitor-platinum combinations in platinum-sensitive and -resistant ovarian carcinoma cells

Deregulated pro-survival signalling plays a role in ovarian carcinoma drug resistance. Here, we show that cisplatin or oxaliplatin in combination with the MEK1/2 inhibitor CI-1040 resulted in a synergistic effect associated with enhanced apoptotic response in platinum-sensitive cells. The drug combinations were additive in platinum-resistant cells exhibiting increased phospho-ERK1/2, down-regulation of apoptosis-related factors (BAX, PUMA, FOXO1) and of phosphatases inhibiting ERK1/2 (DUSP5, DUSP6). Consistently, FOXO1 knockdown in sensitive cells reduced the efficacy of the combination treatment. Pharmacological targeting of ERK1/2 pathway increases cell sensitivity to platinum compounds by interfering with multiple events, ultimately favouring apoptosis induction in selected molecular backgrounds.     

Signalling responses linked to betulinic acid-induced apoptosis are antagonized by MEK inhibitor U0126 in adherent or 3D spheroid melanoma irrespective of p53 status

MEK1/2 inhibitors like U0126 can potentiate or antagonize the antitumor activity of cytotoxic agents such as cisplatin, paclitaxel or vinblastine, depending on the drug or the target cells. We now investigated whether U0126, differentially regulates melanoma signaling in response to UV radiation or betulinic acid, a drug lethal against melanoma. This report shows that U0126 inhibits early response (ERK) kinase activation and cyclin A expression in wt p53 C8161 melanoma exposed to either UV radiation or betulinic acid. However, U0126 does not protect from UV damage, but counteracts betulinic acid-mediated apoptosis in the same cells. Protection from the latter drug by joint treatment with U0126 was also evident in wt p53 MelJuso melanoma and mutant p53 WM164 melanoma. The latter cells were the most responsive to betulinic acid, showing a selective decline in the cdk4 protein, without a comparable change in other key cell cycle proteins like cdc2, cdk2, cdk7 or cyclin A, prior to apoptosis-associated PARP fragmentation. Laser scanning cytometry also showed that betulinic acid induced a significant increase in chromatin condensation in WM164 melanoma irrespective of whether they were in adherent form or as multicellular spheroids. All these betulinic acid-induced changes were counteracted by U0126. Our data show for the first time that (a) cdk4 protein is an early target of betulinic acid-induced apoptosis and (b) unrestricted ERK signaling favours betulinic acid-induced apoptosis, but this is counteracted by U0126, partly through counteracting chromatin condensation and restoring Akt activation decreased by betulinic acid treatment.     

MEK/ERK抑制剂影响胃癌细胞对5-FU敏感性及其机制的探讨

目的:探讨MEK/ERK特异性抑制剂PD98059在5-氟尿嘧啶(5-FU)抗胃癌细胞增殖中的作用。方法:应用5-FU与MEK/ERK抑制剂(PD98059)处理胃癌细胞,MTT法检测细胞增殖状态,流式细胞术检测细胞凋亡,蛋白质印迹法检测ERK和p-ERK的表达。结果:随着5-FU浓度的增加,5-FU对3种胃癌细胞系的增殖抑制率逐渐增大。5-FU作用MGC803细胞72 h的抑制率显著高于48和24 h,t值分别为16.477和25.349,P值分别为0.002和0.001。与对照相比,5-FU作用MGC803细胞48和72 h可引起显著的凋亡,t值分别为-20.576和-40.389,P值分别为0.015和0.001。5-FU处理胃癌MGC803细胞48 h,与对照相比pERK表达一过性下降然后升高。20μmol/L的PD98059联合5-FU作用48 h,可明显抑制pERK的表达,抑制率为22%;同时可明显增加细胞凋亡,增加率为20%。结论:MEK/ERK信号传导通路在5-FU作用胃癌细胞的过程中被激活,联合应用MEK/ERK信号通路抑制剂可部分逆转ERK的活化,增加胃癌细胞凋亡,从而增加胃癌细胞对5-FU的敏感性。     

Phase I dose-escalation trial of the oral AKT inhibitor uprosertib in combination with the oral MEK1/MEK2 inhibitor trametinib in patients with solid tumors

This study aimed to determine the safety, tolerability, and recommended phase II doses of trametinib plus uprosertib (GSK2141795) in patients with solid tumors likely to be sensitive to MEK and/or AKT inhibition. This was a phase I, open-label, dose-escalation, and dose-expansion study in patients with triple-negative breast cancer or BRAF-wild type advanced melanoma. The primary outcome of the expansion study was investigator-assessed response. Among 126 enrolled patients, 63 received continuous oral daily dosing of trametinib and uprosertib, 29 received various alternative dosing schedules, and 34 were enrolled into expansion cohorts. Doses tested in the expansion cohort were trametinib 1.5 mg once daily (QD) + uprosertib 50 mg QD. Adverse events (AEs) were consistent with those reported in monotherapy studies but occurred at lower doses and with greater severity. Diarrhea was the most common dose-limiting toxicity; diarrhea and rash were particularly difficult to tolerate. Overall, 59% and 6% of patients reported AEs with a maximum severity of grade 3 and 4, respectively. Poor tolerability prevented adequate delivery of uprosertib with trametinib at a concentration predicted to have clinical activity. The study was terminated early based on futility in the continuous-dosing expansion cohorts and a lack of pharmacological or therapeutic advantage with intermittent dosing. The objective response rate was < 5% (1 complete response, 5 partial responses). Continuous and intermittent dosing of trametinib in combination with uprosertib was not tolerated, and minimal clinical activity was observed in all schedules tested.     

RNAi-mediated knockdown of ERK1/2 inhibits cell proliferation and invasion and increases chemosensitivity to cisplatin in human osteosarcoma U2-OS cells in vitro

Osteosarcoma is the most common primary malignancy of the bone. There have been some advances in surgical and chemotherapeutic strategies, but it is still a tumor with a high mortality rate in children and young adults. Mitogen-activated protein kinase/extracellular signal regulated kinase (ERK) pathway plays an essential role in the development and progression of various tumors. ERK1/2 is a key component of this pathway and hyperactivated in different tumors including osteosarcoma. This study aimed to investigate whether downregulation of ERK1/2 by siRNA (small interfering RNA) could inhibit cell proliferation and invasion and increase chemosensitivity to cisplatin in human osteosarcoma U2-OS cells in vitro. Results showed that the downregulation of ERK1/2 expression by siRNA in human osteosarcoma cells significantly inhibited cell proliferation and invasion in vitro. Furthermore, ERK1/2 knockdown led to cell arrest in the G1/G0 phase of the cell cycle, and eventual apoptosis and chemosensitivity enhancement in tumor cells. Our data reveal that RNAi-mediated downregulation of ERK1/2 expression can lead to potent antitumor activity and chemosensitizing effects in human osteosarcoma.     

Antitumor activities of JTP-74057 (GSK1120212), a novel MEK1/2 inhibitor, on colorectal cancer cell lines in vitro and in vivo

The MAPK pathway is one of the most important pathways for novel anticancer drug development. We performed high-throughput screening for compounds that induce expression of p15INK4b, and identified JTP-74057 (GSK1120212), which is being evaluated in ongoing phase I, II and III clinical trials. We characterized its antitumor activities in vitro and in vivo. JTP-74057 strongly inhibited MEK1/2 kinase activities, but did not inhibit another 98 kinase activities. Treatment by JTP-74057 resulted in growth inhibition accompanied with upregulation of p15INK4b and/or p27KIP1 in most of the colorectal cancer cell lines tested. Daily oral administration of JTP-74057 for 14 days suppressed tumor growth of HT-29 and COLO205 xenografts in nude mice. Notably, tumor regression was observed only in COLO205 xenografts, and COLO205 was much more sensitive to JTP-74057-induced apoptosis than HT-29 in vitro. Treatment with an Akt inhibitor enhanced the JTP-74057-induced apoptosis in HT-29 cells. Finally, JTP-74057 exhibited an additive or a synergistic effect in combination with the standard-of-care agents, 5-fluorouracil, oxaliplatin or SN-38. JTP-74057, a highly specific and potent MEK1/2 inhibitor, exerts favorable antitumor activities in vitro and in vivo. Sensitivity to JTP-74057-induced apoptosis may be an important factor for the estimation of in vivo efficacy, and sensitivity was enhanced by an Akt inhibitor. These results suggest the usefulness of JTP-74057 in therapeutic applications for colorectal cancer patients.     

Simultaneous exposure of transformed cells to SRC family inhibitors and CHK1 inhibitors causes cell death

The present studies were initiated to determine in greater molecular detail the regulation of CHK1 inhibitor lethality in transfected and infected breast cancer cells and using genetic models of transformed fibrobalsts. Multiple MEK1/2 inhibitors (PD184352, AZD6244 (ARRY-142886)) interacted with multiple CHK1 inhibitors (UCN-01 (7-hydroxystaurosporine), AZD7762) to kill mammary carcinoma cells and transformed fibroblasts. In transformed cells, CHK1 inhibitor -induced activation of ERK1/2 was dependent upon activation of SRC family non-receptor tyrosine kinases as judged by use of multiple SRC kinase inhibitors (PP2, Dasatinib; AZD0530), use of SRC/FYN/YES deleted transformed fibroblasts or by expression of dominant negative SRC. Cell killing by SRC family kinase inhibitors and CHK1 inhibitors was abolished in BAX/BAK -/- transformed fibroblasts and suppressed by over expression of BCL-XL. Treatment of cells with BCL-2/BCL-XL antagonists promoted SRC inhibitor + CHK1 inhibitor -induced lethality in a BAX/BAK-dependent fashion. Treatment of cells with [SRC + CHK1] inhibitors radio-sensitized tumor cells. These findings argue that multiple inhibitors of the SRC-RAS-MEK pathway interact with multiple CHK1 inhibitors to kill transformed cells.     

Comparative in vitro cytotoxicity of taxol and Taxotere against cisplatin-sensitive and-resistant human ovarian carcinoma cell lines

Summary Using the sulforhodamine B assay, we compared the cytotoxic properties of the novel microtubule agent taxol and the semi-synthetic related compound Taxotere in nine human ovarian-carcinoma cell lines, including three pairs of cell lines rendered resistant to cisplatin or carboplatin. In addition, the cytotoxicity of the commonly used anticancer drugs cisplatin and adriamycin and the topoisomerase II inhibitor etoposide was determined. The results of continuous drug exposure showed that taxol [mean concentration producing 50% growth inhibition (IC₅₀), 1.1×10^–9 m; range, 2.8×10^–9–5×10^–10 m and Taxotere (mean IC₅₀, 5.1×10^–10 m; range, 7.2–3.3×10^–10 m) were >1,000 times more cytotoxic than either cisplatin (mean IC₅₀, 3.1×10^–6 m;P<0.05) or etoposide (mean IC₅₀, 2.3×10^–6 m;P<0.05) and >100 times more cytotoxic than Adriamycin (mean IC₅₀, 6.9×10^–8 m;P<0.05). Taxotere was more cytotoxic than taxol; following continuous exposure, the mean difference across the cell lines was 2 orders of magnitude (range, 1.1–3.9 orders of magnitude for individual lines). Although this difference did not reach statistical significance for any individual cell line (P values ranged from 0.17 for HX/62 to 0.9 for OVCAR-3), when all IC₅₀ values for the 96-h experiments were pooled, Taxotere was found to be significantly more potent than taxol (P=0.05). Following 2 h exposure, the mean cytotoxicity of Taxotere was 3.9-fold > that of taxol across the nine lines (range, 0.75- to 10-fold;P<0.05 for the CH1 cell line; overall pooled IC₅₀ data,P=0.05). Although a 71-fold range of sensitivity to cisplatin was observed across the six parent cell lines (IC₅₀ most resistant line/IC₅₀ most sensitive line), this was largely abolished by treatment with taxol (5.6-fold range) and Taxotere (2.2-fold rante). Following continuous exposure of the three pairs of lines exhibiting acquired resistance to platinum, no cross-resistance with either Taxotere or taxol was found (resistance factors, <1.5). In the 41M and 41McisR pair of lines, in which previous studies have shown resistance to be due to reduced platinum accumulation, taxol and Taxotere exhibited some collateral sensitivity (resistance factors, 0.69 and 0.66, respectively). Taxotere and, particularly, taxol showed a pronounced concentration times exposure duration (CxT) dependence as compared with cisplatin (P<0.05). The mean loss in potency across the nine lines for 2 vs 96 h exposure was 97 for taxol, 35 for Taxotere, 30 for Adriamycin and only 9.9 for cisplatin. However, these differences in potency loss observed between taxol and Taxotere did not reach statistical significance (P=0.18). These data indicate that Taxotere is approximately 2 times more cytotoxic than taxol and shows an encouraging lack of cross-resistance in three cell lines exhibiting acquired resistance to cisplatin and carboplatin.This study was supported by grants to the Institute of Cancer Research, Royal Cancer Hospital, from the Cancer Research Campaign and, through the European Organisation for Research and Treatment of Cancer (EORTC) Clonogenic Assay Screening Group, by grant 90031 from Rhone-Poulenc Rorer.     

Sef downregulation by Ras causes MEK1/2 to become aberrantly nuclear localized leading to polyploidy and neoplastic transformation

Subcellular trafficking of key oncogenic signal pathway components is likely to be crucial for neoplastic transformation, but little is known about how such trafficking processes are spatially controlled. In this study, we show how Ras activation causes aberrant nuclear localization of phosphorylated mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK; MEK) MEK1/2 to drive neoplastic transformation. Phosphorylated MEK1/2 was aberrantly located within the nucleus of primary colorectal tumors and human colon cancer cells, and oncogenic activation of Ras was sufficient to induce nuclear accumulation of phosphorylated MEK1/2 and ERK1/2 in intestinal epithelial cells. Enforced nuclear localization of MEK1 in epithelial cells or fibroblasts was sufficient for hyperactivation of ERK1/2, thereby driving cell proliferation, chromosomal polyploidy, and tumorigenesis. Notably, Ras-induced nuclear accumulation of activated MEK1/2 was reliant on downregulation of the spatial regulator Sef, the reexpression of which was sufficient to restore normal MEK1/2 localization and a reversal of Ras-induced proliferation and tumorigenesis. Taken together, our findings indicate that Ras-induced downregulation of Sef is an early oncogenic event that contributes to genetic instability and tumor progression by sustaining nuclear ERK1/2 signaling.     

PD98059对肝癌HepG2细胞Tec信号转导作用的初步研究

Objective： To investigate the effect of MEK1 inhibitor PD98058 on Tec and ERK2 in HepG2 hepatoma cells. Methods： The expression of mRNA and protein of Tec and ERK2 in HepG2 cells was detected by immunocytochemistry assay. After various concentration of PD98059 treatment, the expression of Tec and ERK2 mRNA in HepG2 cells was detected by RT-PCR and Western blotting. Results： Tec and ERK2 expressed highly in HepG2 cells. PD98059 obviously inhibited the expression of mRNA and protein of Tec and ERK2 in a dose-dependent manner, in which 40 μmol/L of PD98059 exhibited the strongest inhibiting effect. Conclusion： PD98058, as MEK1 inhibitor, can inhibit Tec, block the signal route of Ras/Raf/ERK and to impede the signal transduction in HepG2 cells. Tec may be the signal protein in the upper stream of Ras/Raf/ERK in hepatocarcinoma cells and is supposed to interact with the signal way of Ras/Raf/ERK.     

ITAC转染乳腺癌细胞系4T1的体内外生物学行为研究

目的:观察转染ITAC对乳腺癌细胞系4T1体内及体外生物学行为的影响。方法:构建pcDNA3-ITAC真核表达质粒,基因转染的方法建立稳定表达ITAC的乳腺癌细胞系ITAC-4T1。体外及体内观察ITAC-4T1细胞的生长情况。RT-PCR检测肿瘤组织ITACmRNA转录水平。杀伤实验检测脾细胞杀伤活性,FACS检测CD8 T细胞IFN-γ的分泌。结果:体外ITAC-4T1细胞的生长与未转染及转染空载体的4T1细胞没有差别(P>0.05)。体内ITAC-4T1细胞形成的肿瘤生长较对照组明显减慢(P<0.05)。ITAC-4T1肿瘤组织检测到较高水平的ITACmRNA转录(P<0.01)。接种ITAC-4T1细胞的小鼠脾细胞杀伤率显著高于对照组(P<0.05),CD8 T细胞IFN-γ分泌明显增加(P<0.05)。结论:ITAC基因转染可以抑制4T1细胞体内生长,与ITAC诱导Th1型细胞免疫应答,增强效应细胞特异性杀伤活性相关。