Radiosensitization by pemetrexed of human colon carcinoma cells in different cell cycle phases

PURPOSE: The novel folate antimetabolite Alimta (pemetrexed disodium, LY231514) exhibits antitumor activity in a broad array of human malignancies and was recently found to enhance radiation-induced cell killing in vitro. In the present study, a possible cell cycle phase-specific radiosensitization by pemetrexed was assessed. METHODS AND MATERIALS: Widr human colon carcinoma cells were synchronized by serum withdrawal/stimulation that yielded about 80% cells with G1 DNA content 6 h after replating and more than 60% S-phase cells after 22 h, as assessed by flow cytometry. The respective cultures were irradiated with doses up to 12 Gy in combination with a subtoxic pemetrexed exposure (1.06 microM for 2 h: about 80% survival), or after mock treatment. Survival curves were generated by the clonogenic assay; apoptosis was measured by sub-G1 DNA flow cytometry. RESULTS: The combination treatment of the G1 cells and of the more radioresistant S-phase cell preparations yielded survival rates that were lower than expected for independent cell killing. Radiosensitization, calculated as the ratio of the mean inactivation doses without or with drug exposure (enhancement ratio), was not significantly different for the two cell preparations (enhancement ratio of 2.1 and 2.3, respectively) and was similar to the previously reported value for log-phase cells. Pemetrexed exposure was unable to stimulate an apoptotic response of these cells to radiation. CONCLUSIONS: Radiosensitization by pemetrexed is not cell cycle phase-specific, and the relative radioresistance of S-phase cells is retained. Apoptosis seems to have no influence on radiosensitization in this cell line.     

培美曲塞对PC9肺腺癌细胞株的放射增敏作用

目的 培美曲塞是治疗非鳞癌非小细胞肺癌(non-small cell lung cancer,NSCLC)的常用药物,其对表皮生长因子受体(pithelial growth factor receptor,EGFR)敏感突变的肺腺癌是否具有放射增敏作用尚未明确.本课题研究培美曲塞在体外对EGFR 19外显子突变的人肺腺癌细胞株PC9的放射增敏作用,并初步探讨其作用机制.方法 以PC9细胞作为研究对象,采用MTT法检测培美曲塞的20%抑制浓度(20% inhibition concentration,IC20),将PC9细胞分为对照组、单独照射组、培美曲塞单药组和培美曲塞+照射组4组;采用流式细胞术检测培美曲塞联合或不联合照射对PC9细胞的凋亡率及细胞周期的影响;克隆形成实验检测培美曲塞对PC9细胞的放射效应,计算存活分数,拟合存活曲线;蛋白质印迹法检测CDC20蛋白在各组的表达.结果 MTT结果显示,PC9细胞的增殖抑制与培美曲塞呈时间-剂量依赖性,取48 h的IC20(0.084 μmol/L)的培美曲塞作为实验浓度.流式细胞术结果显示,培美曲塞单药组和单独照射组均可增加凋亡率,分别为(7.17±1.14)%和(10.78±1.52)%,而培美曲塞+照射组具有协同增效作用,凋亡率达(29.23±1.33)%,F=227.57,P<0.001;细胞周期结果显示,对照组G2/M期比例为(0.79±0.63)%,培美曲塞单药组为(0.79±0.47)%,单独照射组为(18.21±0.72)%,培美曲塞+照射组为(25.09±1.04)%,提示培美曲塞使细胞阻滞在S期,与放射线联合作用后,S期细胞比例减少,G2/M期的比例明显增多,差异有统计学意义,F=276.85,P<0.001.克隆形成实验提示,培美曲塞具有较好的放射增敏作用,其放射增敏比(sensitization enhancement ratio,SER)为1.41.培美曲塞联合照射能增加细胞周期相关蛋白CDC20的表达,F=282.12,P<0.001.结论 培美曲塞可提高EGFR 19外显子突变的PC9肺腺癌细胞的放射敏感性,其机制可能与照射引起CDC20的增加致对放射敏感的G2/M期阻滞,而照射耐受的S期比例减少有关.     

Caffeine markedly sensitizes human mesothelioma cell lines to pemetrexed

Pemetrexed is a new generation antifolate approved for the treatment of mesothelioma and non-small cell lung cancer. Caffeine is known to augment radiation or chemotherapeutic drug-induced cell killing. The current study addresses the impact of caffeine on the activity of pemetrexed in mesothelioma cell lines. Caffeine enhanced pemetrexed activity in all four mesothelioma cell lines tested (H2052, H2373, H28 and MSTO-211H). Caffeine sensitized H2052 cells in a dose- and schedule-dependent manner, and was associated with a markedly decreased clonogenic survival. Caffeine sensitization occurred only in cells subjected to pulse, but not continuous, exposure to pemetrexed. Similar pemetrexed sensitization was also observed with the clinically better tolerated caffeine analog, theobromine. Pemetrexed sensitization by caffeine was associated with an increase in pemetrexed-induced phosphorylation of ataxia-telangiectasia-mutated (ATM) and Chk1. These data indicate that caffeine and its analog, theobromine, may be a useful approach to enhance pemetrexed-based chemotherapy.     

Preferential radiosensitization of G1 checkpoint-Deficient cells by methylxanthines

To develop a checkpoint-based strategy for preferential radiosensitization of human tumors with deficient and/or mutant p53.

A 549 human lung adenocarcinoma cell lines differing in their expression of the p53 tumor suppressor gene were produced by transduction with the E6 oncogene from human papilloma virus type 16. The cells expressing E6 (E6+) lack a G1 arrest in response to ionizing radiation, are deficient in p53 and p21 expression, and exhibit a fivefold greater clonogenic survival following 10 Gy radiation.

Postirradiation incubation with millimolar concentrations of the methylxanthine pentoxifylline (PTX) results in preferential radiosensitization of the E6+ cells compared to the LXSN+ vector transduced controls. There is a threefold sensitization of the LXSN+ cells and a 15-fold sensitization of the E6+ cells, which results in equal clonogenic survival of the two lines. Flow cytometry reveals PTX abrogation of the radiation induced G2 arrest for both cell lines. PTX also prolongs G1 transit for both cell lines. Preliminary results are presented using a novel methylxanthine, lisofylline (LSF), which has similar cell cycle effects and G1 and G2 and achieves differential radiosensitization at micromolar concentrations that are sustainable in humans.

This checkpoint-based strategy is a promising approach for achieving preferential radiosensitization of p53− tumors relative p53+ normal tissues.     

Pronounced radiosensitization of cultured human cancer cells by COX inhibitor under acidic microenvironment

: To demonstrate the influence of pH on the cytotoxicity and radiosensitization by COX (cyclooxygenase) -1 and -2 inhibitors using established human cancer cells in culture.

: Nonselective COX inhibitor, ibuprofen (IB), and selective COX-2 inhibitor, SC-236, were used to determine the cytotoxicity and radiosensitization at varying pH of culture media. Human colon carcinoma cell line (HT-29) was exposed to the drug alone and in combination with radiation at different pH of the cell culture media. The end point was clonogenic ability of the single-plated cells after the treatment.

: Cytotoxicity and radiosensitization of IB increased with higher drug concentration and longer exposure time. The most significant radiosensitization was seen with IB (1.5 mM) for 2-h treatment at pH 6.7 before irradiation. The dose-modifying factor as defined by the ratio of radiation doses required to achieve the same effect on cell survival was 1.8 at 10% survival level. In contrast, SC-236 (50 μM for 2–8 h) showed no pH-dependent cytotoxicity. There was modest increase in the cell killing at lower doses of radiation.

: An acidic pH was an important factor affecting the increased cytotoxicity and radiosensitization by ibuprofen. Radiation response was enhanced at shoulder portion of the cell survival curve by selective COX-2 inhibitor.     

Schedule-dependent synergism and antagonism between pemetrexed and docetaxel in human lung cancer cell lines in vitro

Background  Pemetrexed and docetaxel show clinical activities against a variety of solid tumors including lung cancers. To identify the optimal schedule for combination, cytotoxic interactions between pemetrexed and docetaxel were studied at various schedules using three human lung cancer cell lines A-549, Lu-99, and SBC-5 in vitro. Methods  Cells were incubated with pemetrexed and docetaxel simultaneously for 24 or 120 h. Cells were also incubated with pemetrexed for 24 h, followed by a 24 h exposure to docetaxel, and vice versa. Growth inhibition was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell cycle analysis. Cytotoxic interactions were evaluated by the isobologram method. Results  Simultaneous exposure to pemetrexed and docetaxel for 24 and 120 h produced antagonistic effects in all three cell lines. Pemetrexed (24 h) followed by docetaxel (24 h) produced additive effects in A-549 cells and synergistic effects in Lu-99 and SBC-5 cells. Docetaxel followed by pemetrexed produced additive effects in A-549 and Lu-99 cells and antagonistic effects in SBC-5 cells. The results of cell cycle analysis were fully consistent with those of isobologram analysis, and provide the molecular basis of the sequence-dependent difference in cytotoxic interactions between the two agents. Conclusions  Sequential administration of pemetrexed followed by docetaxel may provide the greatest anti-tumor effects for this combination in the treatment of lung cancer.     

Effect of paclitaxel (Taxol) alone and in combination with radiation on the gastrointestinal mucosa

: Paclitaxel is a potentially useful drug for augmenting the cytotoxic action of radiotherapy because it has independent cytotoxic activity against certain cancers and blocks cells in the radiosensitive mitotic phase of the cell cycle. However, all rapidly proliferating tissues, both normal and neoplastic, may be affected by this therapeutic strategy. The aim of this study was to define the in vivo response of rapidly dividing cells of the small bowel mucosa to paclitaxel given alone and in combination with radiation.

: Mice were given single IV doses of 10 or 40 mg/kg paclitaxel or four doses of 10 mg/kg paclitaxel at 6, 12, or 24 h intervals. The kinetics of mitotic arrest and apoptosis in jejunal crypts of mice at 1–24 h after treatment were defined histologically. An in vivo stem cell microcolony assay was used to assess the radiosensitizing potential of paclitaxel when radiation was delivered at the peak of mitosis and at 24 h after drug treatment.

: Paclitaxel blocked jejunal crypt cells in mitosis and induced apoptosis in a dose-dependent manner. Fractionating the paclitaxel dose over 1–4 days did not result in any greater accumulation of mitotically blocked cells than did a single dose. Mitosis peaked 2–4 h after paclitaxel and returned to near normal by 24 h. Apoptosis lagged several hours behind mitosis and peaked about 6 h later than mitosis. Despite these kinetic perturbations, there was little or no enhancement of radiation effect when single doses were delivered 2–4 after paclitaxel administration. The maximum sensitizer enhancement ratio of 1.07 observed after a single paclitaxel dose of 40 mg/kg is consistent with independent crypt cell killing. Conversely, when radiation was given 24 h after paclitaxel, a significant protective effect of the drug (SER 0.89–0.92), most probably due to a regenerative overshoot induced by paclitaxel, was observed.

: Stem cells of the jejunal mucosa determining radiation response were not radiosentized by paclitaxel with the drug concentrations and dose delivery schedules used, although additive cytotoxicity was observed with the highest drug dose. A radioprotective effect was observed when radiation was given 24 h after paclitaxel administration.     

Significance of thymidylate synthase for resistance to pemetrexed in lung cancer

Pemetrexed (MTA) is a multitargeted antifolate with promising clinical activity in lung cancer. We exposed the small cell lung cancer cell line PC6 to stepwise-increasing pemetrexed concentrations of 0.4, 1.6, and 4.0 μ m , and established three pemetrexed-resistant lung cancer cell lines: PC6/MTA-0.4, PC6/MTA-1.6, and PC6/MTA-4.0 cells. To investigate the mechanisms of acquired resistance to pemetrexed, we measured the expression levels of the thymidylate synthase ( TS ), reduced folate carrier ( RFC ), and folylpoly-gamma-glutamate synthetase ( FPGS ) genes. TS gene expression was significantly increased in PC6/MTA-1.6 and PC6/MTA-4.0 cells relative to parental cells in a pemetrexed dose-dependent manner. In contrast, the levels of RFC gene expression in PC6/MTA-0.4 cells and FPGS in PC6/MTA-1.6 cells were significantly decreased, whereas the levels of both genes were restored in PC6/MTA-4.0 cells. Knockdown of TS expression using siRNA enhanced pemetrexed cytotoxicity in PC6/MTA-4.0 cells. The expression level of the TS gene was significantly correlated with the concentration of pemetrexed for 50% cell survival (IC₅₀) in 11 non-small cell lung cancer cell lines. These results suggest that the alteration of molecular pharmacological factors in relation with pemetrexed resistance is dose-dependent, and that up-regulation of the expression of the TS gene may have an important role in the acquired resistance to pemetrexed. In addition, TS may be a predictive marker for pemetrexed sensitivity in lung cancer. ( Cancer Sci 2009)     

Effects of pemetrexed, gefitinib, and their combination on human colorectal cancer cells

Purpose

The study investigated the effects of pemetrexed, gefitinib, and their combination on human colorectal cancer cells.

Methods

Six human colorectal cancer cells were exposed to pemetrexed, gefitinib, and their combination. Antitumor effects were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Thymidylate synthase (TS) mRNA expression and EGFR mutation were studied by real-time RT-PCR and DNA sequence determination. Pharmacological interaction was studied using the combination index method. Cell cycle distribution and apoptosis were determined by flow cytometry. Activity assay was performed to assess the effects of drugs on TS activity, and Western blot was performed to assess the protein expression of pEGFR, pAKT, and pERK 1/2.

Results

Six colorectal cancer cells are all sensitive to pemetrexed, and TS gene expression of cells was negatively related to pemetrexed sensitivity. The cytotoxic synergism was observed in concurrent pemetrexed combined with gefitinib and sequential pemetrexed followed by gefitinib. The combination of pemetrexed and gefitinib modulated cell cycle and induced apoptosis. Pemetrexed combined with gefitinib decreased TS mRNA expression and in situ activity. Pemetrexed induced an EGFR-mediated activation of the phosphatidylinositol 3-kinase/AKT and ERK pathway, which was inhibited by gefitinib.

Conclusions

Pemetrexed is a promising agent, and pemetrexed combined with gefitinib has a significantly synergistic effect on colorectal cancer cells, which seems to present a strategy of pemetrexed combined with EGFR-TKIs in colorectal cancer treatment.     

Radiosensitizing potential of gemcitabine (2′,2′-difluoro-2′-deoxycytidine) within the cell cycle in vitro

Purpose: Gemcitabine (2′,2′-difluorodeoxycytidine; dFdCyd) is a new deoxycitidine analog which exhibits substantial activity against solid tumors and radiosensitizing properties in vitro. To examine cell cycle–specific effects of a combined treatment with gemcitabine and radiation, the in vitro clonogenic survival of two different cell lines was measured for cells from log-phase culture, G1 and S-phase cells.Methods and Materials: Chinese hamster (V79) and human colon carcinoma (Widr) cells were exposed to different radiation doses and for different points of time relative to gemcitabine treatment (2 h). Experiments were also carried out with different cell-cycle populations obtained after mitotic selection (V79) or after serum stimulation of plateau-phase cells (Widr). The resulting survival curves were analyzed according to the LQ model, and mean inactivation doses (MID) and the cell cycle–specific enhancement ratios (ER) were calculated from the survival curve parameters.Results: Effectiveness of combined treatment of log-phase cells was greatest when cells were irradiated at the end of the gemcitabine exposure [ER: 1.28 (V79), 1.24 (Widr)]. For later times after the removal of the drug, radiosensitization declined, approaching independent toxicity. From the time course of interactive-type damage decay half-life values of 75 min (V79) and 92 min (Widr) were derived. Gemcitabine did not radiosensitize G1 Widr cells or V79 cells from the G1/S border, but substantial radiosensitization was observed for the S-phase cell preparations [ER: 1.45 (V79-lateS), 1.57 (Widr)].Conclusions: Treatment of cells with gemcitabine immediately before irradiation eliminates, or at least greatly reduces, the variation in radiosensitivity during the cell cycle that is manifested by radioresistance during S phase. This reversal of S-phase radioresistance could imply that gemcitabine interferes with the potentially lethal damage repair/fixation pathway. Other approaches have been taken to overcome S-phase radioresistance, such as hyperthermia or densely ionizing radiation, and combined treatments with dFdCyd could prove of value to complement such efforts.     

Schedule-dependent synergism and antagonism between pemetrexed and paclitaxel in human carcinoma cell lines in vitro

Pemetrexed is a novel multitargeted antifolate with significant clinical activity against a variety of tumors. We studied the schedule-dependent cytotoxic effects of pemetrexed in combination with paclitaxel in vitro to improve our understanding of how this combination might be used clinically. Human lung cancer A549 cells, breast cancer MCF7, ovarian cancer PA1, and colon cancer WiDr cells were exposed to both pemetrexed and paclitaxel in vitro. Cell growth inhibition after 5 days was determined and the effects of drug combinations were analyzed by the isobologram method (Steel and Peckham). Simultaneous exposure to pemetrexed and paclitaxel for 24 h produced antagonistic effects in A549 and PA1 cells, additive/antagonistic effects in MCF7 cells, and additive effects in WiDr cells. Pemetrexed for 24 h followed by paclitaxel for 24 h produced synergistic effects in A549 and MCF7 cells and additive effects in PA1 and WiDr cells, while the reverse sequence produced additive effects in all four cell lines. Cell cycle analysis supported these observations. Our findings suggest that the simultaneous administration of pemetrexed and paclitaxel is suboptimal. The optimal schedule of pemetrexed in combination with paclitaxel is the sequential administration of pemetrexed followed by paclitaxel, and this schedule should be assessed in clinical trials for the treatment of solid tumors.     

Radiation survival of two human cervical carcinoma cell lines after multifraction irradiation

: Multifraction irradiation may contribute to radiation therapy treatment failure is selection of radiation resistant subpopulations occurs. We sought to determined whether surviving cells following daily fraction irradiation of two human cervical squamous cell carcinoma lines would express different radiation survival characteristics compared to the unirradiated parent.

: A late-passage line (HTB35) and an early-passage line 9RECA) received daily 2 Gy x-irradiation. Two stable HTB35 cell lines were extablished after 40 and 60 Gy (HTB3540 and HTB3560). A single line was established from RECA after 30 Gy (RECA-30). High dose rate (74 cGy/min) acute radiation survival curves were prepared from the three nre lines and the unirradiated parents. Potentially lethal damage repair (PLDR) and sublethal damage repair (SLDR) responses were detailed for HTB35, HTB3540 and HTB3560. Low dose rate (1.27 cGy/min) survival was measured dfor HTB35 and HTB3560. Clones were derived from HTB35 and from HTB3560 and the survivung fraction at 2 Gy (SF₂) values were determined.

: The two parent lines (HTB35 and RECA) differed in acute radiation survival. The surviving lines following multifraction irradiation (HTB3540, HTB3560, and RECA) showed no change in acute radiation response compared to the appropriate parent. HTB3540 and HTB3560 were repair proficient, demonstrating similar PLDR anmd SLDR recovery ratios as the parent. Likewise, low dose rate survival of HTB35 and HTB3560 was similar. Nine clones derived deom HTB35 lacked a consistent difference in SF₂ compared to the original culture. A single clone of seven derived from HTB3560 was consistently radiation resistant (SF₂ = 0.81 ± 0.06 compared to the original culture (SF₂ = 0.50 ± 0.09).

: No evidence was obtained that cell lines generated following multiple daily fractions of x-irradiation in vitro possessed acute radiation survival or repair characteristics that were different from the unirradiated parent.     

Radiosensitization by gemcitabine in p53 wild-type and mutant MCF-7 breast carcinoma cell lines.

The nucleoside analogue 2',2'-difluoro-2'-deoxycytidine (dFdCyd) is a potent radiosensitizer in several solid tumor cell lines. Radiosensitization has correlated with the dFdCyd-mediated decrease in dATP levels and is S-phase specific. Previous studies suggested that a cell line that was unable to progress through S phase after dFdCyd and radiation was not radiosensitized apparently because of the expression of wild-type p53. We have extended these results by using the MCF-7 human breast carcinoma cell line (wild-type p53) and the MCF-7/Adr subline (mutant p53) to determine whether p53 status affected radiosensitization or cell cycle progression after dFdCyd and radiation treatment. Both cell lines were sensitive to nanomolar concentrations of dFdCyd and showed significant radiosensitization, with radiation enhancement ratios of 1.6-1.8 after a 24-h exposure to either the IC(10) or IC(50) for dFdCyd. Nucleotide pool analysis demonstrated a >85% reduction in dATP pools in both cell lines within 8 h after drug addition. Both cell lines accumulated in S phase after a 24-h incubation with dFdCyd. After subsequent irradiation, MCF-7/Adr cells continued to progress through the cell cycle for at least 72 h. MCF-7 cells progressed for at least 24 h, and then exhibited a G(1) block at 48 h after drug and radiation treatment. These results demonstrate that a wild-type p53 cell line can be radiosensitized by dFdCyd, presumably because it was able to deplete dATP levels and progress through the cell cycle for at least 24 h after drug and radiation treatment.     

Radiation-induced apoptosis in different pH environments in vitro

: The effect of environmental pH on the radiation-induced apoptosis in tumor cells in vitro was investigated.

: Mammary adenocarcinoma cells of A/J mice (SCK cells) were irradiated with γ-rays using a ¹³⁷Cs irradiator and incubated in media of different pHs. After incubation at 37°C for 24–120 h the extent of apoptosis was determined using agarose gel electrophoresis, TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, flow cytometry, and release of ³H from ³H-thymidine labeled cells. The clonogenicity of the cells irradiated in different pH medium was determined, and the progression of cells through the cell cycle after irradiation in different pHs was also determined with flow cytometry.

: Irradiation with 2–12 Gy of γ-rats induced apoptosis in SCK cells in pH 7.5 medium within 48 h as judged from the results of four different assays mentioned. Radiation-induced apoptosis declined as the medium pH was lowered from 7.5 to 6.4. Specifically, the radiation-induced degradation of DNA including the early DNA breaks, as determined with the TUNEL method, progressively declined as the medium pH was lowered so that little DNA fragmentation occurred 48 h after irradiation with 12 Gy in pH 6.6 medium. When the cells were irradiated and incubated for 48 h in pH 6.6 medium and the medium was replaced with pH 7.5 medium, DNA fragmentation promptly occurred. DNA fragmentation also occurred even in pH 6.6 medium when the cells were irradiated and maintained in pH 7.5 medium for 8 or longer post-irradiation before incubation in pH 6.6 medium. The radiation-induced G₂ arrest in pH 6.6 medium lasted markedly longer than that in pH 7.5 medium.

: Radiation-induced apoptosis in SCK cells in vitro is reversibly suppressed in an acidic environment. Taking the results of four different assays together, it was concluded that early step(s) in the apoptotic pathway, probably the DNA break or upstream of DNA break, is reversibly halted by an acidic environment in irradiated cells. Radiation-induced G₂ arrest is prolonged in an acidic environment indicating that the suppression of radiation-induced apoptosis and prolongation of radiation-induced G₂ arrest in an acidic environment are related.     

Loss of reduced folate carrier function and folate depletion result in enhanced pemetrexed inhibition of purine synthesis.

Pemetrexed is a novel antifolate with polyglutamate derivatives that are potent inhibitors of thymidylate synthase (TS) and to a lesser extent glycinamide ribonucleotide formyltransferase (GARFT). Conditions that might modulate relative suppression of these sites were assessed by the pattern of hypoxanthine and thymidine protection. When grown with 25 nmol/L racemic 5-formyltetrahydrofolate, thymidine alone fully protected wild-type HeLa cells to at least 1 micromol/L pemetrexed, but protection of a reduced folate carrier (RFC)-null subline required both thymidine and hypoxanthine above a concentration of 30 nmol/L pemetrexed. As medium 5-formyltetrahydrofolate was decreased, protection by thymidine alone decreased, and was further diminished when HeLa cells were grown in dialyzed serum. There was little protection by thymidine of RFC-null HeLa cells under the latter conditions. Thymidine alone was not protective, and hypoxanthine alone produced only a small (2-fold) increase in IC(50), in a HeLa-derived line 8-fold resistant to pemetrexed due to a modest increase in TS. Finally, in MCF-7 breast cancer cells there was greater protection with thymidine alone than in HeLa cells when cells were grown in medium containing a low concentration of 5-formyltetrahydrofolate. These observations indicate that as intracellular folates decrease in HeLa cells, due to decreased extracellular reduced folate, or loss of RFC function, pemetrexed inhibition of GARFT increases. These data support the concept that the contribution to pemetrexed activity by inhibition of GARFT, particularly at low folate levels, is a contributing factor to drug activity but relative inhibition of TS and GARFT may vary among human tumors and cell lines.     

培美曲塞联合序贯与同步放疗治疗中晚期非小细胞肺癌疗效的对比研究

目的:比较培美曲塞联合同步与序贯放疗治疗中晚期非小细胞肺癌疗效及不良反应。方法:67例初次治疗的中晚期非小细胞肺癌患者接受培美曲塞联合放疗,分别采用同步放化疗和序贯放化疗。化疗方案为培美曲塞单药500mg/m2,第1天,21天为1个周期,共2个周期。放疗采用多叶光栅技术,直线加速器6MV X线放疗,2Gy/次,5次/周,总剂量DT=66Gy,引流区淋巴结总剂量为58~60Gy。结果:同步组总有效率（76.5%,26/34）高于序贯组（54.5%,18/33）,同步组中位疾病进展时间(14.1个月)长于序贯组(11.6个月)(P＜0.05);两组中位生存期分别为21.3个月和19.6个月(P＞0.05)。不良反应为骨髓抑制、恶心呕吐、疲劳、放射性食管炎和放射性肺炎等。结论:培美曲塞联合放疗,同步放射治疗中晚期非小细胞肺癌较序贯放射治疗疗效好,不良反应可耐受,该方案治疗中晚期非小细胞肺癌值得进一步临床研究。     

培美曲塞对不同miR-21表达水平人肺癌细胞凋亡影响的实验研究

目的 检测不同miR-21表达水平的人肺癌细胞对培美曲塞的药物敏感性,并探讨可能作用机制。方法 采用Annexin V-EGFP荧光染色法定性检测及流式细胞术定量检测培美曲塞对不同miR-21表达水平的A549人肺癌细胞凋亡诱导作用,级联酶底物显色法检测caspase-3的活化状态,蛋白免疫杂交法检测凋亡相关蛋白Bcl-2、 Bax的表达水平变化。结果 20μmol／L培美曲塞作用24h可以诱导高表达miR-21的A549人肺癌细胞（A549-21H0）和低表达miR-21的A549细胞（A549-21L0）的凋亡,且A549-21L0处于细胞凋亡晚期,而A549-21H0处于细胞凋亡早期。5μmol／L培美曲塞作用24h可以诱导65.3％的A549-21L0 细胞早期凋亡,仅诱导2.8％的A549-21H0细胞早期凋亡。5μmol／L培美曲塞作用6h即可引起A549-21L0细胞中caspase-3活化,与作用前相比活化效应超过2倍（P＜0.01）;在9h时活化效应最强,活化效应超过7倍（P＜0.01）;18h后活化效应超过6倍（P＜0.01）;至24h时活化效应仍在5倍以上（P＜0.01）。同样条件下,5μmol／L培美曲塞作用18h才引起A549-21H0细胞中caspase-3活化,与作用前相比活化效应接近3倍（P＜0.01）,至24h活化效应在4倍以上（P＜0.01）。5μmol／L培美曲塞作用于A549-21L0细胞9h即可引起Bax表达水平显著性升高和Bcl-2表达水平明显下降。结论 A549-21L0人肺癌细胞对培美曲塞诱导的细胞凋亡具有更高的敏感性。培美曲塞可引起A549-21L0细胞中caspase-3活化,并可通过调控Bax和Bcl-2表达水平诱导凋亡,这种效应具有一定的时间-效应关系。     

培美曲塞联合舒尼替尼对肝癌细胞生物学行为的影响

目的:探讨培美曲塞联合舒尼替尼对肝癌细胞增殖、细胞周期和细胞凋亡的影响。方法:以培美曲塞和舒尼替尼单药或联合处理肝癌SK-Hep1细胞后,MTT法检测细胞的增殖抑制率,FCM检测细胞的周期变化和凋亡率,Western blot检测蛋白激酶B（AKT）、磷酸化蛋白激酶B（p-AKT）、增殖细胞核抗原（PCNA）、B淋巴细胞瘤-2基因（Bcl-2）和切割型半胱天冬酶3（Cleaved caspase-3）蛋白的表达。结果:培美曲塞和舒尼替尼均能够呈时间-浓度依赖性抑制SK-Hep1细胞增殖,72 h IC50分别为（2.89±0.20）μmol/L和（2.12±0.12）μmol/L（P＜0.05）;培美曲塞和舒尼替尼均能够诱导SK-Hep1细胞凋亡（P＜0.05）;培美曲塞使SK-Hep1细胞周期阻滞于S期,舒尼替尼使细胞周期阻滞于G0/G1期（P＜0.05）;培美曲塞和舒尼替尼均可使p-AKT、PCNA、Bcl-2的表达下降,Cleaved caspase-3表达升高。两药联用使SK-Hep1细胞阻滞在G2/M期,细胞增殖抑制率和细胞凋亡率较单药更加明显,且p-AKT、PCNA、Bcl-2表达下降及Cleaved caspase-3表达升高更为显著（P＜0.05）。结论:培美曲塞联合舒尼替尼可抑制SK-Hep1细胞增殖,并诱导SK-Hep1细胞周期阻滞和凋亡,其作用机制可能与下调p-AKT、PCNA、Bcl-2表达和上调Cleaved caspase-3表达有关。     

Cytotoxic effects of pemetrexed in gastric cancer cells

Pemetrexed is a newly developed multitargeted antifolate with promising clinical activity in many solid tumors including gastric cancer. The aim of the present study was to evaluate the cytotoxicity of pemetrexed and its mode of interaction with cisplatin in gastric cancer cell lines, and to identify genes associated with sensitivity to pemetrexed. The cytotoxic activity of pemetrexed was assessed by tetrazolium-based colorimetric assay (MTT assay) and the interaction between pemetrexed and cisplatin was evaluated by the isobologram method. Western immunoblotting and real time RT-PCR analysis of thymidylate synthase (TS), folylpoly-gamma-glutamate synthetase (FPGS) and reduced folate carrier (RFC1) were performed in order to determine whether sensitivity to pemetrexed would be predictable by protein or mRNA expression levels. Pemetrexed was more cytotoxic than 5-fluorouracil, with IC50 between 17 and 310 nM in most of the gastric cancer cell lines examined and the pemetrexed/cisplatin combination resulted in additive or synergistic interaction. The protein expressions of TS, FPGS, and RFC1 were significantly associated with IC50 for 5-fluorouracil, but no such association was found for pemetrexed chemosensitivity. The mRNA expressions of RFC1, FPGS and other target and resistance related genes revealed no significant association with pemetrexed sensitivity. In conclusion, pemetrexed is active against gastric cancer cell lines and the pemetrexed/cisplatin combination showed a synergistic or additive interaction, supporting its clinical use in gastric cancer. Drug sensitivity toward pemetrexed could not be predicted by the expressions of TS, RFC1, or FPGS and we suggest that it is determined by interactions between multiple genes.     

Combination of vascular targeting agents with thermal or radiation therapy

: The most likely clinical application of vascular targeting agents (VTAs) is in combination with more conventional therapies. In this study, we report on preclinical studies in which VTAs were combined with hyperthermia and/or radiation.

: A C3H mammary carcinoma grown in the right rear foot of female CDF1 mice was treated when at 200 mm³ in size. The VTAs were combretastatin A-4 disodium phosphate (CA4DP, 25 mg/kg), flavone acetic acid (FAA, 150 mg/kg), and 5,6-dimethylxanthenone-4-acetic acid (DMXAA, 20 mg/kg), and were all injected i.p. Hyperthermia and radiation were locally administered to tumors of restrained, nonanesthetized mice, and response was assessed using either a tumor growth or tumor control assay.

: Heating tumors at 41.5°C gave rise to a linear relationship between the heating time and tumor growth with a slope of 0.02. This slope was increased to 0.06, 0.09, and 0.08, respectively, by injecting the VTAs either 30 min (CA4DP), 3 h (FAA), or 6 h (DMXAA) before heating. The radiation dose (±95% confidence interval) that controls 50% of treated tumors (the TCD₅₀ value) was estimated to be 53 Gy (51–55 Gy) for radiation alone. This was decreased to 48 Gy (46–51 Gy), 45 Gy (41–49 Gy), and 42 Gy (39–45 Gy), respectively, by injecting CA4DP, DMXAA, or FAA 30–60 min after irradiating. These values were further decreased to around 28–33 Gy if the tumors of VTA-treated mice were also heated to 41.5°C for 1 h, starting 4 h after irradiation, and this effect was much larger than the enhancement seen with either 41.5°C or even 43°C alone.

: Our preclinical studies and those of others clearly demonstrate that VTAs can enhance tumor response to hyperthermia and/or radiation and support the concept that such combination studies should be undertaken clinically for the full potential of VTAs to be realized.