Induction of a multifactorial resistance phenotype by high paclitaxel selective pressure in a human ovarian carcinoma cell line

Paclitaxel (PTX) is a potent anti-neoplastic agent that is highly effective in treating ovarian cancer. Nevertheless, the emergence of PTX resistance has limited the control of this disease. To gain insight into the molecular alterations accompanying drug resistance in ovarian cancer, we generated a new stable PTX-resistant ovarian carcinoma cell line. CABA I cells, which display an intrinsic PTX resistance (IC50 = 800 ng/ml), were subjected to continuous exposure to PTX. From the residual surviving cells, the highly PTX-resistant line CABA-PTX (IC50 = 256000 ng/ml) was generated and stably maintained in vitro. Analysis of beta-tubulin expression indicated that only the HM40 and Hbeta9 isotypes were expressed in both parental and resistant cells. No specific point mutations in the HM40 were detected in either cell line, but expression levels of this isotype were significantly reduced (40%) in CABA-PTX cells. Hbeta9 levels were unchanged. In those cells, PTX resistance was associated with cross-resistance to vinblastine but not to methotrexate or 5-fluorouracil. Verapamil treatment did not reverse the intrinsic drug resistance of parental cells, but partially modulated the sensitivity of CABA-PTX cells to PTX and induced total sensitivity to vinblastine. No changes in the cell surface expression of the drug efflux pumps MRP1, MRP2 and P-glycoprotein were observed. PTX influx, monitored using a fluorescent drug derivative, was significantly reduced and delayed in CABA-PTX cells as compared to the parental cells. Together, these findings suggest that more than one mechanism is involved in PTX resistance, making CABA-PTX cell line a potentially valuable in vitro tool to study multifactorial acquired drug resistance in ovarian cancer.     

Uptake of adriamycin by human leukemic cells as measured by flow cytometry

Leukemic cells were obtained from 12 patients with acute nonlymphocytic leukemia and 2 patients with acute lymphocytic leukemia. The specimens were incubated with a range of concentrations of adriamycin (Adr) for different periods of time and then analyzed by flow cytometry. For incubations of up to 5 h, only cells exposed to 5 or more μg of Adr ml^?1 became fluorescent while cells incubated with 1 μg ml^?1 for 24 h became fluorescent. Flourescence decreased when the cells were washed and further decreased when the cells were incubated in Adr-free media. The cells from different patients exhibited a wide range of Adr uptakes and retentions. Simultaneous analysis of right angle light scatter and fluorescence intensity demonstrated that there may be subpopulations of cells whose Adr uptake and/or retention differ from the weighted mean population values. With this method rare cells which fail to take up Adr can be recognized.     

Changes in cellular glutathione content during adriamycin treatment in human ovarian cancer--a possible indicator of chemosensitivity

Patients with ovarian cancer often respond well to combination chemotherapy initially but the majority eventually relapse when, with further treatment, the initially successful regimen proves ineffectual. The cause of such failures frequently has been attributed to the development of drug resistance. Although the mechanisms of acquired resistance in situ are still poorly understood, studies in vitro have shown that cells selected for resistance to one drug often exhibit cross-resistance to other seemingly unrelated agents, suggesting a somewhat generalised mechanism of resistance. We have studied the role of glutathione (GSH) and drug transport in determining the sensitivity to adriamycin (ADR) of a panel of human ovarian cell lines established directly from biopsies of patients with diverse treatment histories. These cell lines exhibited inherent differences in sensitivity to ADR by a dose factor of up to 3; a difference that was considerably less than what has been reported when cells were selected for drug resistance in vitro. The differences in drug sensitivity reported here among the various cell lines appeared to be unrelated to drug transport, in terms of both influx and efflux. Moreover, although these cell lines have a wide range of GSH content, there was only a poor correlation between drug sensitivity and cellular GSH content per se. However, when exposed to a clinically relevant dose of ADR, the GSH content of cell lines that were 'sensitive' decreased, whereas that of cell lines that were 'resistant' increased. To take these time-dependent changes in GSH into consideration, the area under the GSH content versus time curve (AUC), with and without ADR treatment, was calculated for each cell line. When this latter factor was included in the analysis, greatly improved correlations were found between GSH kinetic parameters and responses to ADR. In particular, ADR resistance was found to be closely correlated with the positive changes in absolute GSH AUC following ADR treatment (r = 0.92; P less than 0.01). Using 35S-labelled cysteine and methionine as tracers, it was found that the essential difference between the 'resistant' and 'sensitive' lines was that the 'resistant' lines had higher steady-state rates of GSH synthesis than the 'sensitive' lines. These results demonstrate that changes in cellular GSH concentration during treatment may be an important indicator of tumour cell response to ADR.     

流式细胞术检测肾上腺肿瘤DNA含量及临床意义

目的 明确ＤＮＡ量测定是否枳和为肾上腺肿瘤良、恶性诊断的指标之一。方法 采用ＰＣＭ技术对１３例肾肯朱嗜铬细胞列肾上腺皮质肿瘤,肾上腺转移瘤和肉眼正常肾上腺组织各５例新鲜标本进行了ＤＮＡ含量测定。结果 病理为肾上腺嗜铬细胞瘤及其瘤旁肾上腺标本ＤＮＡ含量多为非整倍体（１２／１３）,但求后无１例复发和转移,而６全 理为皮质腺瘤标本２例ＤＮＡ含量为非整倍体,其中１例术后出现肝转移而确诊为恶性,１例为二倍体     

Evaluation of nitroimidazole hypoxic cell radiosensitizers in a human tumor cell line high in intracellular glutathione

Five nitroimidazole hypoxic cell radiosensitizers were evaluated in a human lung adenocarcinoma cell line (A549) whose GSH level was 8-fold higher than Chinese hamster V79 cells. One millimolar concentrations of Misonidazole (MISO), SR-2508, RSU-1164, RSU-1172, and Ro-03-8799 sensitized hypoxic A549 cells to radiation, with Ro-03-8799 giving the highest sensitizer enhancement ration (SER) (2.3). However, MISO, SR-2508 and Ro-03-8799 were less effective in this cell line than in V79 cells, presumably due to higher GSH content of the A549 cells. Increased hypoxic radiosensitization was seen with 0.1 mM Ro-03-8799 after GSH depletion by BSO as compared to 0.1 mM Ro-03-8799 alone (SER-1.8 vs 1.3). The combination of GSH depletion and 0.1 mM Ro-03-8799 was considerably more toxic than 0.1 mM or 1.0 mM Ro-03-8799 alone. This sensitivity was much greater than has been observed for SR-2508. These data show that Ro-03-8799 was the most efficient hypoxic cell radiosensitizer in a human tumor cell line considerably higher in GSH than the rodent cell lines often used in hypoxic radiosensitization studies. Thus, Ro-03-8799 may be a more effective hypoxic cell sensitizer in human tumors that are high in GSH.     

十字孢碱促进多柔比星诱导的多药抗药性肿瘤细胞系的凋亡

 【摘要】　目的　明确蛋白激酶C（PKC）活性的抑制是否能促进化疗药物诱导的多药抗药肿瘤细胞系的凋亡。方法　选用口腔鳞癌细胞KB／S及其多药抗药株KB／VCR，常规细胞培养，比较单独或联合PKC抑制剂十字孢碱的情况下，多柔比星（ADM）诱导这2种细胞的凋亡情况。凋亡采用流式细胞术和吖啶橙荧光染色检测，并经电子显微镜观察证实。结果　ADM 0.04 μg／ml，作用36 h有96.68 % KB／S细胞凋亡，作用48 h有64.99 ％的KB／VCR细胞凋亡；将ADM质量浓度增加到0.4 μg／ml和2.0 μg／ml时，KB／VCR细胞凋亡比例分别为69.74 ％和37.18 ％；合用十字孢碱后，凋亡细胞比例分别增加到82.58 ％和47.65 ％，经统计学处理，前者χ 2 = 4.5，P＜0.05；后者χ 2 = 2.2，P＞0.05。这些结果均经电镜和吖啶橙染色证实。结论　耐受凋亡可能是肿瘤细胞多药抗药的机制之一，而PKC抑制剂可解除这种耐受。     

The mechanism of acquired resistance to cisplatin by a human ovarian cancer cell line

The present study was designed to elucidate the mechanism of resistance to cisplatin. A cisplatin-resistant cell line (KFr) was established from KF cells derived from human serous cystadenocarcinoma of the ovary. The DNA histogram revealed an increase of S-phase cells and a decrease of G1-phase cells in cultured KFr cells, compared to that in cultured KF cells. Although the cisplatin content in the KF cells incubated with cisplatin at 10 micrograms/ml increased in a time-dependent manner, that in the KFr cells remained unchanged during the experimental period. When 0.5 mg of cisplatin was administered ip to nude mice with KF or KFr tumor, the cisplatin content in the KFr tumor was significantly lower than that in the KF tumor. The KFr cells showed a cross-resistance to L-phenylalanine mustard, while no cross-resistance to vincristine or 5-fluorouracil was observed. These findings suggest that the mechanism of cisplatin resistance in the KFr cells involves a decrease of cisplatin accumulation in the tumor cells.     

Adriamycin activation and oxygen free radical formation in human breast tumor cells: protective role of glutathione peroxidase in adriamycin resistance

Previous studies with Adriamycin-sensitive and -resistant (ADRR) MCF-7 human breast tumor cell lines indicated that Adriamycin formed significantly less hydroxyl radical (.OH) as the result of enhanced detoxification of reactive oxygen intermediates in the ADRR cell line. In order to further define the sites of drug activation and the role of detoxification mechanisms in free radical levels, subcellular fractions were isolated from these two cell lines and free radical formation in the presence of Adriamycin was examined by using electron spin resonance spectroscopy. Studies reported here show that considerable NADPH-cytochrome P-450 reductase and NADH dehydrogenase activities were present in microsomes and mitochondria, respectively, and in nuclei obtained from these cells, and the relative activity of NADH dehydrogenase was 2-fold higher in the mitochondrial fraction of ADRR cells compared to the mitochondrial fraction from the parental wild type cells. In the presence of Adriamycin and a reducing cofactor (NADPH or NADH), Adriamycin semiquinone free radical, superoxide anion, and .OH were detected in all these fractions. Although only a small difference in the relative amount of oxy radical formation was detected in tumor microsomes, both mitochondria and nuclei of ADRR cells showed an overall 2-fold decreased formation of oxy radicals. The formation of the free radicals was significantly inhibited by superoxide dismutase, catalase, and dimethyl sulfoxide, indicating that free .OH generation was both superoxide and hydrogen peroxide dependent. The addition of purified glutathione peroxidase likewise inhibited .OH formation in a dose-dependent fashion. Similarly, when the lysate from ADRR cells, which contains 12- to 14-fold more glutathione peroxidase than Adriamycin-sensitive cells, was added to reaction mixtures containing Adriamycin-sensitive cells and Adriamycin, the .OH formation was diminished. Decreased free radical formation in nuclei and mitochondria, as a result of detoxification of hydrogen peroxide by glutathione peroxidase, may be significant in the protection of ADRR cells from Adriamycin-induced cell killing.     

Analysis of tumor cell growth and effects of antitumor drugs on cell cycle regulation by flow cytometry

Relationship between tumor cell growth and cell cycle and influence of antitumor drugs on the cell cycle regulation were investigated by the use of murine EL-4 tumor. Cell growth curve of EL-4 cells was well related to the cell cycle pattern analyzed by two color flow cytometry both in vivo and in vitro. The ratio of S phase rapidly increased in early log phase and decreased from late log to plateau phases. The ratio of G0/G1 phase showed a reciprocal change. Minimum effective doses of 5-fluorouracil (5-FU) and CDDP on EL-4 growth in vitro were 1 x 10(-6) M and 0.5 micrograms/ml, respectively. At such doses, 5-FU showed an accumulation in early S phase and CDDP showed a partial synchronization in S phase and subsequent accumulation in late S and G2 + M phase. In case of in vivo administration with 5-FU (20 mg/kg/day) ratio of S phase was higher than in untreated control mice at day 2-3 but decreased rapidly thereafter. Mice administered with CDDP (5 mg/kg/day) showed a decrease in S phase from day 2 and completely rejected the tumors by day 5. From these results, each phase of cell cycle was influenced by the cell growth characteristics and the cell cycle pattern was dynamically changed according to the mode of action of antitumor drugs. Moreover, in vivo effects of these drugs can be evaluated adequately by the analysis of the cell cycle.     

人卵巢癌细胞系A2780肿瘤干细胞分离培养与鉴定

目的:从人卵巢癌细胞系A2780中分离培养卵巢癌干细胞,并对其特性进行鉴定.方法:将A2780细胞消化,离心制成单细胞悬液,悬浮于含有生长因子的无血清培养基(SFM)中获得肿瘤细胞微球体,流式细胞仪检测细胞表面分子标志CD44和CD133的表达;Transwell小室侵袭实验检测肿瘤微球体的体外侵袭能力;CCK-8检测微球体细胞的增殖能力,比较两种细胞的倍增时间;将肿瘤微球体置于含有血清的培养基使其诱导分化,并观察其形态学变化.结果:A2780可在SFM中形成可悬浮生长、稳定传代的肿瘤细胞微球体.与贴壁的肿瘤细胞相比,微球体高表达干细胞标志CD44和CD133(P＜0.05),具有更强的体外侵袭力(t=9.354,P＜0.05)和增殖能力(t=13.682,P＜0.05),及更短的倍增时间(t=3.773,P＜0.05),在血清环境下可分化为普通的肿瘤细胞.结论:用含有生长因子的SFM悬浮卵巢癌细胞系A2780可获得卵巢癌肿瘤细胞微球体,此细胞球体中富集有肿瘤干细胞.     

Role of cystine transport in intracellular glutathione level and cisplatin resistance in human ovarian cancer cell lines

Transport system x(c)(-) is a member of plasma membrane heterodimeric amino-acid transporters and consists of two protein components, xCT and 4F2hc. This system mediates cystine entry coupled with the exodus of intracellular glutamate and regulates the intracellular glutathione (GSH) levels in most mammalian cultured cells. We studied the activity of system x(c)(-) and GSH content in human ovarian cancer cell line (A2780) and its cisplatin (CDDP)-resistant variant (A2780DDP). The rate of cystine uptake was approximately 4.5-fold higher in A2780DDP cells than in A2780 cells and the cystine uptake in A2780DDP cells was mediated by system x(c)(-). Intracellular GSH content was much higher in A2780DDP cells but it fell drastically in the presence of excess glutamate, which inhibited the cystine uptake competitively. xCT and 4F2hc mRNAs were definitely expressed in A2780DDP cells, but far less in A2780 cells. Expression of system x(c)(-) activity by transfection with cDNAs for xCT and 4F2hc made A2780 cells more resistant to CDDP. Similar results on the cystine uptake were obtained in human colonic cancer cell lines. These findings suggest that the system x(c)(-) plays an important role in maintaining the higher levels of GSH and consequently in CDDP resistance in cancer cell lines.     

Potentiation of melphalan cytotoxicity in human ovarian cancer cell lines by glutathione depletion

The effectiveness of alkylating agents in the treatment of ovarian cancer is limited by the frequent development of drug resistance. In order to examine the mechanisms of resistance and potential ways in which this resistance could be overcome, we have developed a human ovarian cancer cell line, 1847ME, resistant to the bifunctional amino acid nitrogen mustard, melphalan. A 4-fold higher concentration of melphalan was required to produce an equivalent reduction in tumor colony formation in 1847ME cells as compared to the parent melphalan-sensitive line A1847. The magnitude of resistance in 1847ME was similar to that observed in the cell lines NIH:OVCAR-2, NIH:OVCAR-3, and NIH:OVCAR-4 which were derived from ovarian cancer patients clinically resistant to alkylating agents. There was no detectable difference in melphalan uptake between A1847 and 1847ME. The cellular content of the inactive dihydroxy melphalan metabolite, however, was two times greater in 1847ME compared to A1847. Levels of the principal intracellular thiol, glutathione, were found to be 2-fold greater in 1847ME than in A1847, and to be similarly elevated in the OVCAR lines. Depletion of glutathione by incubation of the cells in cystine-free medium or in the presence of the specific inhibitor of glutathione synthesis, DL-buthionine-S,R-sulfoximine, was accompanied by a marked increase in melphalan cytotoxicity. Doses of DL-buthionine-S,R-sulfoximine which were only minimally cytotoxic were associated with complete reversal of the induced resistance to melphalan in 1847ME. Synergism between melphalan and DL-buthionine-S,R-sulfoximine was also demonstrated in the OVCAR cell lines derived from previously treated ovarian cancer patients. The reversal of induced resistance to melphalan by modulation of glutathione levels is of potential clinical relevance. In addition, these cell lines provide a useful model system in which to study further the mechanisms of alkylating agent resistance in human tumors.     

β-榄香烯逆转人乳腺癌MCF-7/ADM细胞对阿霉素耐药性的研究

目的　探讨 β 榄香烯 (β ELE)逆转人乳腺癌MCF 7/ADM细胞对阿霉素 (ADM)的耐药性。方法　采用MTT法测定β ELE对人乳腺癌MCF 7/ADM细胞药物敏感性的影响。经荧光分光光度法检测 β ELE对细胞内化疗药物ADM积累的影响 ,应用流式细胞术观察耐药细胞的凋亡抑制蛋白bcl 2改变。结果　β ELE对MCF 7/ADM的耐药性有明显逆转作用 ,非细胞毒性剂量 (6 μg/ml)及低毒剂量 (13μg/ml)的 β ELE逆转倍数分别为 1.4倍及 2 .2倍。β 榄香烯作用后 ,MCF 7/ADM的细胞内ADM浓度明显增加 (P <0 .0 1) ,bcl 2由 90 .2 %降至 70 .0 % (P <0 .0 5 )。结论　β ELE可部分逆转MCF 7/ADM细胞的耐药性 ,逆转机制与增加细胞内药物积累及降低bcl 2的表达有关。     

The role of glutathione in resistance to cisplatin in a human small cell lung cancer cell line

The role of glutathione (GSH) in resistance to cisplatin (CDDP) was studied in a human small cell lung carcinoma cell line (GLC4) and a CDDP-resistant subline (GLC4-CDDP). In addition to studying the steady state of GSH, the kinetics of this defence system were also studied via the monitoring of the GSH status of the cells under continuous pressure of CDDP. GLC4-CDDP maintained its elevated GSH level whereas GLC4 (under pressure of CDDP) quickly synthesised GSH to about twice its initial level, corresponding with 80% of the GSH level of GLC4-CDDP. D,L-buthionine-S,R-sulphoximine (BSO) was used to analyse the role of GSH in resistance to CDDP. Pretreatment with BSO (48 h, 50 microM, GSH not detectable) increased the CDDP-induced cytotoxicity 2.8-fold in GLC4-CDDP and 1.7-fold in GLC4. In GLC4 no changes in the amount of platinum (Pt) bound to DNA could be observed after GSH depletion. Changes in formation of interstrand cross-links or the main Pt-containing intrastrand cross-link in digested DNA, the Pt-GG adduct, were also not observed. In GSH depleted GLC4-CDDP cells, an increase in the amount of Pt bound to DNA and in the Pt-GG adduct was observed. Pretreatment with BSO substantially reduced the repair of Pt bound to DNA in both cell lines. We conclude that an increased GSH level and GSH synthesis capacity were demonstrated in CDDP resistant cells. The observations after BSO treatment suggest two roles for GSH in CDDP resistance, namely that of a cytosolic elimination resulting in less DNA platination and a nuclear effect on the formation and repair of DNA platinum adducts.     

Isolation of tumor cell growth-inhibiting factors from a human rhabdomyosarcoma cell line

Two types of growth-modulating factors were derived from the serum-free conditioned media of a human rhabdomyosarcoma cell line, A673. One type, Mr 18,000 to 22,000, competes for binding to epidermal growth factor receptors and enhances the growth of normal and tumor cells in soft agar. It has all of the biological properties ascribed to transforming growth factor type alpha (TGF alpha). A673 cells also produce factors which inhibit the growth of human tumor cells in soft agar and in monolayer cultures. These tumor cell growth-inhibiting factors (TIFs) are acid- and heat-stable peptides. The major TIF activities have molecular weights in the ranges of greater than 28,000, 18,000 to 22,000, 10,000 to 16,000, and 5,000 to 10,000 and do not possess the antiviral activity associated with interferon. Partially purified preparations of TIF-1 (Mr 10,000 to 16,000) inhibit the growth of all human tumor cell lines tested and stimulate the growth of normal human fibroblasts and epithelial cells in monolayer cultures. The growth of human lung carcinoma A549 cells in soft agar, which was enhanced by treatment with TGF alpha from A673-conditioned media, was inhibited by treatment with TIF-1 derived from the same media. The ratio of the two types of tumor cell-derived, growth-modulating factors (TIFs and TGF alpha), which are antagonistic in their biological effects, may determine the capacity of tumor cells for anchorage-independent growth.     

流式细胞术检测肿瘤相关蛋白在人卵巢上皮性肿瘤裸鼠冻融卵巢组织移植中的意义

目的 通过对人卵巢上皮性肿瘤裸鼠原位移植瘤的癌旁组织相关蛋白的检测,探讨癌旁正常卵巢组织筛选的标准及冻融卵巢组织移植的可行性.方法 将人卵巢上皮性肿瘤OVCAR3细胞于裸小鼠颈背部近腋窝处皮下种植获取瘤源,行卵巢原位移植后,取癌组织、癌旁近端组织、癌旁中段组织、癌旁远端组织及正常裸鼠卵巢组织,采用流式细胞术检测各组织中的细胞角蛋白-7（CK-7）、CA125、p53、Survivin、基质金属蛋白酶-2（MMP-2）、金属蛋白酶组织抑制物-2（T1MP-2）的表达量;分别取全部指标阴性组、CK-7（-）CA125（-）Survivin（-）组、CK-7（＋）CA125（＋）Survivin（＋）组的组织、癌组织和冻融正常裸鼠卵巢组织进行移植,分析各组移植后的癌变率及CA125水平变化,同时检测原位移植后不同病变程度的裸鼠血清CA125水平.结果 从52份人卵巢上皮性肿瘤裸鼠原位移植瘤模型中获取46份（88.5％）活组织检查正常的癌旁残余卵巢组织;仅卵巢种植裸鼠血清CA125水平高于正常裸鼠（P＜0.01）,低于卵巢外种植裸鼠（P＜0.05）.原位移植瘤组织中CK-7、CA125、p53、Survivin、MMP-2及TIMP-2的表达率分别为93.3 ％（28/30）、93.3 ％（28/30）、86.7％（26/30）、86.7％（26/30）、83.3％（25/30）、83.3％（25/30）,癌旁近端组织的表达率分别为70.0％（21/30）、70.0％（21/30）、63.3％（19/30）、63.3％（19/30）、60.0％（18/30）、56.7％（17/30）,癌旁中段组织的表达率分别为33.3％（10/30）、30.0％（9/30）、30.0％（9/30）、30.0％（9/30）、26.7％（8/30）、23.3％（7/30）,癌旁远端组织的表达率分别为26.7％（8/30）、23.3％（7/30）、26.7％（8/30）、26.7 ％（8/30）、30.0％（9/30）、30.0％（9/30）;20份原位移植正常卵巢组织上述指标均为阴性.癌旁近端组织中CK-7、CA125、p53、Survivin、MMP-2及TIMP-2的表达率低于癌组织（P＜0.05）,高于癌旁中段组织及癌旁远端组织（P＜0.01）;癌旁中段组织及癌旁远端组织表达率差异无统计学意义（P＞0.05）.癌旁组织CK-7、CA125、Survivin的强阳性表达率明显高于p53、MMP-2、TIMP-2（P＜ 0.05）.全部指标表达阴性组或CK-7（-）CA125（-）Survivin（-）组的组织移植后,未发现癌变,其癌变率及CA125水平低于CK-7（＋）CA125（＋）Survivin（＋）组（P＜0.01,P＜0.05）.结论 CK-7、CA125、p53、Survivin、MMP-2及TIMP-2等分子指标的表达向无癌方向呈递减趋势,这些肿瘤相关基因表达全部阴性或主要指标CK-7、CA125、Survivin阴性均可作为筛选癌旁残余正常卵巢组织的标准,流式细胞术可作为筛查残留癌灶及隐匿转移的有效方法;人卵巢上皮性肿瘤裸鼠冻融卵巢组织移植安全、可行.     

Biochemical characterization of resistance to mitoxantrone and adriamycin in Caco-2 human colon adenocarcinoma cells: a possible role for glutathione S-transferases.

Cytotoxicity of Adriamycin on human colon adenocarcinoma cell lines was investigated. Concentrations of Adriamycin producing 50% inhibition were very similar in HT29, Sw480, Sw620, and Sw1116 cells, whereas Caco-2 cells were relatively insensitive. As compared to the Sw1116 cell line, Caco-2 cells were also insensitive to mitoxantrone. Sensitivity to cisplatin, 5-fluorouracil, or ethacrynic acid was comparable in both cell lines. To find the mechanism for this mitoxantrone and Adriamycin resistance, several potential Adriamycin-detoxifying systems were characterized and quantified in both Sw1116 and Caco-2 cells. No dramatic differences in glutathione content and expression of both selenium dependent- and independent glutathione peroxidase, UDP-glucuronyltransferase, and cytochrome P-450 were found. However, highly significant differences in glutathione S-transferase activity were present, the expression of both class pi and class alpha glutathione S-transferases being much higher in the Caco-2 cell line. In addition, a slightly higher content of P-170 glycoprotein was present in the Caco-2 cells. These findings suggest that glutathione S-transferases, and to a lesser extent the P-170 glycoprotein, may be involved in mitoxantrone and Adriamycin resistance of Caco-2 colon carcinoma cells.