Effects of alpha-difluoromethylornithine and 5-fluorouracil on the proliferation of a human colon adenocarcinoma cell line

Because alpha-difluoromethylornithine (DFMO) reduces the incidence of experimental colon cancers, inhibits the growth of human lung cancer cells and human leukemia cells in culture, and in combination with methylglyoxal (bis)guanylhydrazone induces remission in children with leukemia, its effectiveness against a human colon adenocarcinoma cell line (Colo 205) was tested alone and in combination with 5-fluorouracil (5-FU). Both DFMO (2 X 10(-4) M) and 5-FU (10(-6) M) inhibited Colo 205 cell proliferation. Above 5 X 10(-4) M DFMO (p less than 0.001) and at 10(-4) M 5-FU (p less than 0.001), Colo 205 growth was completely inhibited. Although DFMO did not sensitize Colo 205 cells to a noninhibitory concentration of 5-FU, the effectiveness of inhibitory concentrations of 5-FU and DFMO in reducing Colo 205 cell growth was additive. DFMO (2 X 10(-4) M) caused 89 to 93% inhibition of ornithine decarboxylase activity (p less than 0.001) and reduced levels of putrescine (93%; p less than 0.01) and spermidine (57%; p less than 0.02). Growth rate and the intracellular putrescine and spermidine contents were restored by 10(-6) M putrescine. DFMO could be an effective chemotherapeutic agent against human colonic cancer because of its effects at such unusually low concentrations in vitro.     

Connexin 32 expression reduces malignant phenotype in human A549 adenocarcinoma cells: Implication of Src involvement

Recent evidence suggests that a member of the gap junction protein family, connexin (Cx) 32, acts as a tumor suppressor gene against lung adenocarcinoma. However, the precise mechanism remains unclear. In this study, we tried to explore the mechanism for the Cx32-dependent tumor-suppressive effect in lung adenocarcinoma. To perform this study, we established a stable clone of the human lung adenocarcinoma cell line, A549 in which the Cx32 gene was expressed. Cx32 expression in A549 cells reduced anchorage-independent growth and development of tumors in a xenograft model. Additionally, Cx32 induced contact inhibition of growth and reduced invasive activity in A549 cells. The tumor-suppressive effects of Cx32 depended on the inhibition of Src activity. These events were confirmed by an Src inhibitor (PP1) and siRNA for Cx32. These results suggest that the Cx32-dependent tumor-suppressive effect in A549 cells is explained by the inhibition of Src activity.     

Induction of cytotoxicity in human lung adenocarcinoma cells by 6-O-carboxypropyl-alpha-tocotrienol, a redox-silent derivative of alpha-tocotrienol

Tocotrienols are one of the most potent anticancer agents of all natural compounds and the anticancer property may be related to the inactivation of Ras family molecules. The anticancer potential of tocotrienols, however, is weakened due to its short elimination half life in vivo. To overcome the disadvantage and reinforce the anticancer activity in tocotrienols, we synthesized a redox-silent analogue of alpha-tocotrienol (T3), 6-O-carboxypropyl-alpha-tocotrienol (T3E). We estimated the possibility of T3E as a new anticancer agent against lung adenocarcinoma showing poor prognosis based on the mutation of ras gene. T3E showed cytotoxicity against A549 cells, a human lung adenocarcinoma cell line with a ras gene mutation, in a dose-dependent manner (0-40 microM), whereas T3 and a redox-silent analogue of alpha-tocopherol (T), 6-O-carboxypropyl-alpha-tocopherol (TE), showed much less cytotoxicity in cells within 40 microM. T3E cytotoxicity was based on the accumulation of cells in the G1-phase of the cell-cycle and the subsequent induction of apoptosis. Similar to this event, 24-hr treatment of A549 cells with 40 microM T3E caused the inhibition of Ras farnesylation, and a marked decrease in the levels of cyclin D required for G1/S progression in the cell-cycle and Bcl-xL, a key anti-apoptotic molecule. Moreover, the T3E-dependent inhibition of RhoA geranyl-geranylation is an inducing factor for the occurrence of apoptosis in A549 cells. Our results suggest that T3E suppresses Ras and RhoA prenylation, leading to negative growth control against A549 cells. In conclusion, a redox-silent analogue of T3, T3E may be a new candidate as an anticancer agent against lung adenocarcinoma showing poor prognosis based on the mutation of ras genes.     

抗表皮生长因子受体对人肺腺癌小鼠移植瘤的放射增敏研究

目的 观察抗表皮生长因子受体药物(吉非替尼)在人肺腺癌移植瘤中有无放射增敏作用.方法 用人肺腺癌细胞A549建立移植瘤裸鼠模型,分别隔天测苗肿瘤在对照、单纯照射、单纯药物(吉非蒋尼)、照射+药物作用下(6只/组)的直径.描绘肿瘤生长曲线,计算局部肿瘤生艮抑制率、肿瘤牛长延缓时问和再牛长延缓时间.照射为5 Gy/次,1次/d,连续3 d.吉非替尼为罐胃100ms/kg,1次/d,连续14 d.结果 单纯照射、单纯吉非替尼、照射+吉非替尼的肿瘤牛长抑制率分别为22.7%、12.4%与38.2%(F=25.75,P=0.000);肿瘤生长延缓时间分别为6.0、7.8、21.6 d(F=70.49,P=0.000).照射+古非替尼、单纯照射的再牛长延缓时间分别为23.4、10.2 d(F=174.24,P=0.000).肿瘤牛长延缓的增敏比为1.5,冉生长延缓的增敏比为1.7.结论 吉非替尼对人肺腺癌小鼠移植瘤有明显的放疗增敏作用.     

Astragalus saponins induce growth inhibition and apoptosis in human colon cancer cells and tumor xenograft

Astragalus memebranaceus is used as immunomodulating agent in treating immunodeficiency diseases and to alleviate the adverse effects of chemotherapeutic drugs. In recent years, it has been proposed that Astragalus may possess anti-tumorigenic potential in certain cancer cell types. In this study, the anti-carcinogenic effects of Astragalus saponin extract were investigated in HT-29 human colon cancer cells and tumor xenograft. Our findings have shown that Astragalus saponins (AST) inhibit cell proliferation through accumulation in S phase and G2/M arrest, with concomitant suppression of p21 expression and inhibition of cyclin-dependent kinase activity. Besides, AST promotes apoptosis in HT-29 cells through caspase 3 activation and poly(ADP-ribose) polymerase cleavage, which is indicated by DNA fragmentation and nuclear chromatin condensation. Nevertheless, we also demonstrate the anti-tumorigenic effects of AST in vivo, of which the reduction of tumor volume as well as pro-apoptotic and anti-proliferative effects in HT-29 nude mice xenograft are comparable with that produced by the conventional chemotherapeutic drug 5-fluorouracil (5-FU). In addition, the side effects (body weight drop and mortality) associated with the drug combo 5-FU and oxaliplatin are not induced by AST. These results indicate that AST could be an effective chemotherapeutic agent in colon cancer treatment, which might also be used as an adjuvant in combination with other orthodox chemotherapeutic drugs to reduce the side effects of the latter compounds.     

Chemosensitization and radiosensitization of human lung and colon cancers by antimitotic agent, ABT-751, in athymic murine xenograft models of subcutaneous tumor growth

Purpose

ABT-751 is an orally active antimitotic agent that is currently in Phase II clinical trials. This agent binds to the colchicine site on ß-tubulin and inhibits polymerization of microtubules. This disruption of microtubule dynamics leads to a block in the cell cycle at the G₂/M phase, and promotes apoptosis. ABT-751, as a single agent, has antitumor activity against a series of xenograft models including non-small cell lung cancer (NSCLC) and colon cancer. The current studies were conducted to determine whether ABT-751 enhances antitumor activity of standard cytotoxic therapies currently in clinical use.

Methods

Efficacy of ABT-751, in combination with cisplatin, 5-FU, and radiation, was evaluated in the Calu-6 NSCLC, HT-29 colon, and HCT-116 colon carcinoma xenograft models, respectively. Tumor-bearing athymic mice were treated with ABT-751 orally once a day at 75 or 100 mg/kg/day on a 5-days-on, 5-days-off schedule for two cycles.

Results

Efficacy of ABT-751 at 100 mg/kg/day was tested in combination with cisplatin at its maximum tolerable dose (MTD) (10 mg/kg/day, i.p. x1) in Calu-6 tumor-bearing athymic mice. The percent treated/control (%T/C) tumor volume ratios on day 38 were 35, 37, and 6, and the percent tumor growth delay (%TGD) values were 71, 65, and 188 for cisplatin, ABT-751 and the combination groups, respectively. HT-29 colon tumors were used to test ABT-751 in combination with an MTD of 5-FU, 30 mg/kg/day, i.p., q.d. x5. The %T/C ratios on day 38 were 22, 28, and 5 and the %TGD values were 75, 75, and 150 for 5-FU, ABT-751, and the combination groups, respectively. Treatment of HCT-116 colon carcinoma tumors with ABT-751, concurrent with the radiation treatment, was able to both enhance radiation-induced tumor regression, and delay the time to recurrence and progression. Growth curves allowed calculation of enhancement of radiation-induced growth delay (defined as the additional time required for a treated tumor to reach four times its original size) of 2, 9, and 12 days, for ABT-751 alone, radiation alone, and the combination, respectively.

Conclusion

Collectively, these studies demonstrate that ABT-751 enhanced efficacy of standard cytotoxic therapies in a variety of tumor xenograft models, and that enhancement was at least additive in all systems.     

Sp1 inhibition-mediated upregulation of VEGF165b induced by rh-endostatin enhances antiangiogenic and anticancer effect of rh-endostatin in A549

Recombinant human endostatin (rh-endostatin), a potential antiangiogenic agent, is used in non-small cell lung carcinoma treatment and represses vascular endothelial cell growth factor (VEGF) levels in tumor cell. However, precise affection of rh-endostatin on the proangiogenic VEGF isoforms (VEGF₁₆₅) or antiangiogenic VEGF isoforms (VEGF₁₆₅b) is not clear. We therefore tested the hypothesis that rh-endostatin could alter expression of these isoforms to regulate tumor growth. A549 cells were exposed to rh-endostatin, and the expression of VEGF₁₆₅ and VEGF₁₆₅b was detected. The role of SP1 as a regulator of isoform expression was investigated. We then examined the anticancer and antiangiogenic efficacy of rh-endostatin in combination with exogenous VEGF₁₆₅b against A549 cells, EA.HY 926 cells and xenograft model of human lung cancer. rh-Endostatin reduced VEGF₁₆₅ and induced VEGF₁₆₅b as well as inhibited SP1 in A549 cells. SP1 inhibitor (betulinic acid) also developed those changes. VEGF₁₆₅b–rh-endostatin combination was highly synergistic and inhibited growth, survival, and migration of A549 cells, VEGF-mediated VEGFR2 phosphorylation in EA.HY 926 cells, and tumor growth in xenograft model of human lung cancer. rh-Endostatin downregulates proangiogenic vascular endothelial growth factor A (VEGFA) isoform and upregulates antiangiogenic VEGFA isoform, possibly through inhibition of SP1. Furthermore, VEGF₁₆₅b sensitizes A549 to rh-endostatin treatment and enhances the anticancer effect of rh-endostatin.     

Antitumor efficacy of interleukin-2 alone and in combination with adriamycin and dacarbazine in murine solid tumor systems

Recombinant interleukin-2 (IL-2)/chemotherapy combinations have recently entered clinical trial. The rationale for sequencing has primarily been empiric or based on in vitro data. To establish in vivo models for chemoimmunotherapy trials, we investigated IL-2 alone and in combination with dacarbazine (DTIC) and adriamycin. IL-2 (as a single agent given i.v. at 1-3 x 10(5) Cetus units once daily for 5 days, repeated 7-10 days later), was highly active against an immunogenic line of colon adenocarcinoma no. 11/A [tumor growth inhibition (T/C) = 0% with cures]. It was modestly active against colon adenocarcinoma no. 38 (T/C = 39%), mammary adenocarcinoma no. 16/C (T/C = 18%), and B16 melanoma (T/C = 21%). IL-2 was inactive against colon adenocarcinoma no. 7/A (T/C = 83%). Combination trials were done using DTIC and IL-2 against colon no. 7/A and upstaged colon no. 11/A. The combination of adriamycin and IL-2 was tested against mammary adenocarcinoma no. 16/C. In the DTIC/IL-2 combination trials, the combination was superior over either agent used alone. In the IL-2/adriamycin trials, the combination was no better than adriamycin alone at optimum dosages.     

Anticancer treatment with a combination of antimetabolites of polyamine and pyrimidine

A combined efficacy of the polyamine antimetabolites, alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) with two fluorinated pyrimidines was studied. DFMO, MGBG, 5-FU and 5'-deoxy-5-fluorouridine (5'-DFUR) were administered intraperitoneally to BALB/c nu/nu mice bearing xenotransplanted human gastric cancer for 5 consecutive days. Similar antitumor efficacies were observed in 3 groups treated with DFMO plus MGBG, DFMO, MGBG plus 5-FU as well as DFMO, MGBG plus 5'-DFUR. The two groups on 5-FU or 5'-DFUR alone did not differ in antitumor effects from the control, although reasonable levels of 5-FU were involved in tumor tissues. Hepatic and splenic 5-FU levels after 5-FU administration were significantly higher than those after 5'-DFUR, and marked decrease in mouse body weight was caused by 5-FU alone as well as 5-FU plus polyamine antimetabolites for 5 consecutive days. DNA biosynthesis and spermine levels in the tumor tissues on day 2 after cessation of the treatments dropped in 3 groups with DFMO plus MGBG, DFMO, MGBG plus 5'-DFUR as well as DFMO, MGBG plus 5-FU, while on day 6 there was little difference between the control and treated groups. These data suggest that combination with 5-FU or 5'-DFUR does not enhance the antitumor activity of polyamine antimetabolites by this experimental regimen.     

5-Fluorouracil resistant colon cancer cells are addicted to OXPHOS to survive and enhance stem-like traits

Despite marked tumor shrinkage after 5-FU treatment, the frequency of colon cancer relapse indicates that a fraction of tumor cells survives treatment causing tumor recurrence. The majority of cancer cells divert metabolites into anabolic pathways through Warburg behavior giving an advantage in terms of tumor growth. Here, we report that treatment of colon cancer cell with 5-FU selects for cells with mesenchymal stem-like properties that undergo a metabolic reprogramming resulting in addiction to OXPHOS to meet energy demands. 5-FU treatment-resistant cells show a de novo expression of pyruvate kinase M1 (PKM1) and repression of PKM2, correlating with repression of the pentose phosphate pathway, decrease in NADPH level and in antioxidant defenses, promoting PKM2 oxidation and acquisition of stem-like phenotype. Response to 5-FU in a xenotransplantation model of human colon cancer confirms activation of mitochondrial function. Combined treatment with 5-FU and a pharmacological inhibitor of OXPHOS abolished the spherogenic potential of colon cancer cells and diminished the expression of stem-like markers. These findings suggest that inhibition of OXPHOS in combination with 5-FU is a rational combination strategy to achieve durable treatment response in colon cancer.     

Identification of drugs as single agents or in combination to prevent carcinoma dissemination in a microfluidic 3D environment

Experiments were performed in a modified microfluidic platform recapitulating part of the in vivo tumor microenvironment by co-culturing carcinoma cell aggregates embedded in a three-dimensional (3D) collagen scaffold with human umbilical vein endothelial cells (HUVECs). HUVECs were seeded in one channel of the device to initiate vessel-like structures in vitro prior to introducing the aggregates. The lung adenocarcinoma cell line A549 and the bladder carcinoma cell line T24 were tested. Dose-response assays of four drugs known to interfere with Epithelial Mesenchymal Transition (EMT) signaling pathways were quantified using relative dispersion as a metric of EMT progression. The presence of HUVECs in one channel induces cell dispersal in A549 which then can be inhibited by each of the four drugs. Complete inhibition of T24 aggregate dispersal, however, is not achieved with any single agent, although partial inhibition was observed with 10 μM of the Src inhibitor, AZD-0530. Almost complete inhibition of T24 dispersal in monoculture was achieved only when the four drugs were added in combination, each at 10 μM concentration. Coculture of T24 with HUVECs forfeits the almost-complete inhibition. The enhanced dispersal observed in the presence of HUVECs is a consequence of secretion of growth factors, including HGF and FGF-2, by endothelial cells. This 3D microfluidic co-culture platform provides an in vivo-like surrogate for anti-invasive and anti-metastatic drug screening. It will be particularly useful for defining combination therapies for aggressive tumors such as invasive bladder carcinoma.     

Enhanced Antitumor Effect of 5'-Deoxy-5-fluorouridine by Oral Administration with l-Cysteine

When given orally in combination with l -cysteine, 5'-deoxy-5-fluorouridine (DFUR) brought about a significant reduction in the growth of adenocarcinoma 755 and a significant prolongation of life-span in mice bearing Lewis lung carcinoma without increased toxicity to the host as compared with DFUR alone, though l -cysteine alone did not show an appreciable antitnmor activity. Moreover, the combination of DFUR and l -cysteine resulted in a marked retardation of growth of human colon tumor LS174T transplanted into nude mice. Thus, the potency of DFUR was increased by l -cysteine. Pharmacokinetic studies revealed that after DFUR administration, plasma DFUR and 5-fluorouracil (5-FU) levels rapidly declined, but that, in the combination with l -cysteine, the plasma clearances of DFUR and 5-FU were slowed down considerably. In the tumor, DFUR and 5-FU levels were similar to those in the plasma. Such a prolongation of DFUR and 5-FU levels in plasma and tumor may produce the enhancement of antitumor effect seen with the combination of DFUR and l -cysteine.     

Enhanced antitumor effect of 5'-deoxy-5-fluorouridine by oral administration with L-cysteine

When given orally in combination with L-cysteine, 5'-deoxy-5-fluorouridine (DFUR) brought about a significant reduction in the growth of adenocarcinoma 755 and a significant prolongation of life-span in mice bearing Lewis lung carcinoma without increased toxicity to the host as compared with DFUR alone, though L-cysteine alone did not show an appreciable antitumor activity. Moreover, the combination of DFUR and L-cysteine resulted in a marked retardation of growth of human colon tumor LS174T transplanted into nude mice. Thus, the potency of DFUR was increased by L-cysteine. Pharmacokinetic studies revealed that after DFUR administration, plasma DFUR and 5-fluorouracil (5-FU) levels rapidly declined, but that, in the combination with L-cysteine, the plasma clearances of DFUR and 5-FU were slowed down considerably. In the tumor, DFUR and 5-FU levels were similar to those in the plasma. Such a prolongation of DFUR and 5-FU levels in plasma and tumor may produce the enhancement of antitumor effect seen with the combination of DFUR and L-cysteine.     

A novel combination antimetabolite, TAS-102, exhibits antitumor activity in FU-resistant human cancer cells through a mechanism involving FTD incorporation in DNA

TAS-102 is a new antimetabolite agent composed of a alpha, alpha, alpha-trifluorothymidine (FTD; 1 M) and thymidine phosphorylase inhibitor (TPI; 0.5 M). Here, we investigated the antitumor effect and mechanism of TAS-102 against 5-FU, or FdUrd, resistant human cancer cell lines. The respective tumor growth inhibition rate of orally administered FTD against 5-FU-resistant NUGC-3 was about 70% at a dose level of 200 mg/kg/day; this value was comparable to that against the parental NUGC-3. On the other hand, the tumor inhibition rates of 5-FU, FdUrd, and TS-1 against 5-FU-resistant NUGC-3 were lower than those against parental NUGC-3. Similar observations were made in an FdUrd-resistant human colorectal cancer cell line (DLD-1). TAS-102 was also effective in 5-FU-less sensitive human pancreatic cancer cell lines (PAN-12 and BxPC-3) and human esophagus cancer (T.T.) when compared with 5-FU or UFT. Our hypothesis was that a relatively short and high dosage of TAS-102 results in an additional mechanism of FTD incorporation into DNA other than thymidylate synthase (TS) inhibition. We then examined the effects of FTD on DNA at the cellular level. After treatment with FTD or FdUrd, the DNA fragmentation pattern was examined using filter elution and in situ nick translation. Treatment with FTD for 2 h resulted in marked DNA fragmentation. When the tumor cells were treated with FTD for 72 h or with FdUrd for 2 or 72 h, only a small amount of DNA fragmentation was observed, and the appearance of the tumor cells did not differ markedly from that of untreated cells. Moreover, the DNA fragmentation rate in the TAS-102 treatment group was significantly higher than that in the control group in vivo. These results suggest that when tumor cells are exposed to high concentrations of FTD for short periods of time, FTD manifests its antitumor activity primarily through the induction of DNA fragmentation after FTD incorporation into the DNA. We conclude that TAS-102 is expected to manifest antitumor effects against 5-FU-resistant tumors that are similar to those exerted in 5-FU-sensitive tumors.     

Infused L-histidinol and cisplatin: schedule, specificity, and proliferation dependence

The dose and schedule requirements found for the combination of L-histidinol and 5-fluorouracil (5-FU) were concordant with those for the combination of L-histidinol and cisplatin. Furthermore, cisplatin-L-histidinol was active against colon 26 tumor, an adenocarcinoma that developed in a BALB/c female mouse and that has been grown as a solid tumor. The toxicity of cisplatin was prevented only when cisplatin was given before L-histidinol. Studies of L-histidinol and 5-FU had similar results. For (DBA/2 X BALB/c)F1 mice, 50 mg of L-histidinol per mouse was required for protection; for hematopoietic precursor cells, protection was dependent on the dose of L-histidinol. In contrast, both L1210 leukemia cells and colon 26 adenocarcinoma cells were more efficiently killed by combinations of L-histidinol and cisplatin. This effect depended on the doses of L-histidinol and cisplatin, a finding similar to the finding for hematopoietic precursor cells.     

Toll-like Receptor 5 Agonist Inhibition of Growth of A549 Lung Cancer Cells in Vivo in a Myd88 Dependent Manner

The purpose of this study was to examine the effect of a Toll-like receptor 5 (TLR5) agonist, CBLB502, on the growth and radiosensitivity of A549 lung cancer cells in vivo. Expression of myeloid differentiation factor 88 (MyD88) or TLR5 was stably knocked down in human lung cancer cells (A549) using lentivirus expressing short hairpin RNA targeting human MyD88 or TLR5. Lack of MyD88 or TLR5 expression enhanced tumor growth in mouse xenografts of A549 lung cancer cells. CBLB502 inhibited the growth of A549 lung cancer cells, not A549-MyD88-KD cells in vivo in the murine xenograft model. Our results showed that the inhibition of A549 by CBLB502 in vivo was realized through regulating the expression of neutrophil recruiting cytokines and neutrophil infiltration. Finally, we found that activation of TLR5 signaling did not affect the radiosensitivity of tumors in vivo.     

重组诱导性质粒Egr1-XPO4 的构建及其与5-FU 联合对肝癌细胞SKHep1的协同抑制作用

目的：构建重组诱导性质粒Egr1-XPO4,探讨其与5-FU联合对肝癌细胞SK-Hep1 的协同抑制作用。方法: 将XPO4基因插入带诱导性启动子Egr1 的质粒载体中,构建Egr1-XPO4 重组质粒。将Egr1-XPO4 质粒转染肝癌细胞SK-Hep1 并经化疗药物5-FU诱导,采用Western blotting 检测转染细胞中XPO4 蛋白表达水平,CCK法检测转染诱导后SK-Hep1 细胞的增殖水平,Annexin V-FITC/PI 流式细胞仪检测SK-Hep1 细胞凋亡情况。动物实验观察Egr1-XPO4 质粒联合5-FU对裸鼠移植瘤的治疗效果。结果: 成功构建携XPO4 基因和启动子Egr1 的重组诱导性质粒Egr1-XPO4,重组质粒转染SK-Hep1 细胞并经5-FU诱导后,细胞中XPO4 蛋白表达量明显增加,且与5-FU的质量浓度明显依赖。Egr1-XPO4 转染联合5-FU诱导对SK-Hep1 细胞增殖抑制明显强于单纯转染或5-FU诱导（P<0.05）,同时导致SK-Hep1 细胞的早期凋亡率显著高于单纯转染或诱导（P<0.05）。以Egr1-XPO4 质粒联合5-FU 治疗后,裸鼠肝癌移植瘤的体积明显小于Egr1-XPO4 或5-FU 单独治疗（P<0.05)。结论: 重组诱导性质粒Egr1-XPO4联合5-FU对肝癌细胞SK-Hep1 产生协同抑制作用。     

5-Fluorouracil and Interleukin-2 Immunochemotherapy Enhances Immunogenicity of Non-Small Cell Lung Cancer A549 Cells through Upregulation of NKG2D Ligands

Background: The aim of this study was to investigate the anti-cancer effects and mechanisms ofimmunochemotherapy of 5-fluorouracil (5-FU) and interleukin-2 (IL-2) on non-small cell lung cancer (NSCLC)A549 cells. Materials and Methods: In order to detect whether 5-FU+IL-2 could effectively inhibit tumorgrowth in vivo, we established an A549-bearing nude mouse model. The cytotoxicity of natural killer (NK) cellswas evaluated using a standard chromium release assay. To evaluate the relevance of NK cells in 5-FU+IL-2-mediated tumor inhibitory effects, we depleted NK cells in A549-bearing mice by injecting anti-asialo-GM-1antibodies. Effects of 5-FU+IL-2 on the expression and promoter activity of NKG2D ligands (MICA/MICB) inA549 cells in vitro were also assessed. Results: In A549-bearing nude mice, combination therapy significantlyinhibited tumor growth in comparison with monotherapy with 5-FU or IL-2 and enhanced the recognitionand lysis of tumor cells by NK cells. Further study of mechanisms showed that NK cells played a vital role inthe anticancer immune response of 5-FU+IL-2 immunochemotherapy. In addition, the combination therapysynergistically stimulated the expression and promoter activity of MICA/MICB. Conclusions: 5-FU and IL-2immunochemotherapy significantly inhibited tumor growth and activated NK cytotoxicity in vivo, and theseeffects were partly impaired after depleting NK cells in tumor-bearing mice. Combination treatment of 5-FUand IL-2 upregulated the expression and the promoter activity of MICA/MICB in A549 cells, which enhancedthe recognition of A549 cells by NK cells. All of the data indicated that immunochemotherapy of 5-FU and IL-2may provide a new treatment option for patients with lung cancer