Camptothecin analog (CPT-11)-sensitive human pancreatic tumor cell line QGP-1N shows resistance to SN-38, an active metabolite of CPT-11.

In the course of our study to determine the cross-sensitivity between CPT-11 and its active metabolite, SN-38, we found a SN-38-resistant human pancreatic tumor cell line, QGP-1N, which shows sensitivity to CPT-11. The IC50 of SN-38 was 152 times greater for QGP-1N than for SUIT-2, also a human pancreatic tumor cell line, whose IC50 of CPT-11 was similar to that for QGP-1N. The uptakes of CPT-11 and SN-38 and the intracellular conversion of CPT-11 to SN-38 could not explain the difference in sensitivity. DNA synthesis of QGP-1N cells was inhibited by CPT-11 which did not affect that of SUIT-2, while SN-38 inhibited the DNA synthesis of SUIT-2 at lower concentrations than that of QGP-1N. The inhibition test of topoisomerase I catalytic activity by CPT-11 or SN-38 revealed no difference in the biochemical properties of the topoisomerase I enzymes to the compounds between these two cell lines. These results indicate that CPT-11 should have its own inhibitory effect on DNA synthesis through a yet unknown mechanism in QGP-1N cells, although SN-38 plays an essential role in the antitumor activity of CPT-11 in SUIT-2 cells. In some cases, the antitumor effect of CPT-11 might be consequent not only on SN-38 but also on CPT-11 itself.     

Analysis of gene expression profiles associated with cisplatin resistance in human ovarian cancer cell lines and tissues using cDNA microarray

Gene expression profiles were analyzed by using cDNA microarray for a cisplatin-sensitive cell line (KF), and three- and thirty-fold cisplatin-resistant ovarian cancer cell lines (KFr and KFrP200) both showing no p53 mutation within exon 5, 6, 7, 8 and no pglycoprotein overexpression. Expression of GST-pi mRNA increased as the level of resistance to cisplatin became high. Microarray analysis revealed that DNA repair associated genes, i.e., XRCC5, XRCC6, ERCC5, hMLH1 were over-expressed in three-fold cisplatin-resistant cell line, KFr as compared to cisplatin-sensitive parental cell line, KF. Apoptosis inhibitors, i.e., IGFR type I and II were over-expressed, and apoptosis inducer, i.e., caspase 3 and BAK were underexpressed in highly cisplatin-resistant cell line, KFrP200 as compared to KFr. As for clinical cases, cDNA microarray was used to compare gene expression profiles directly between two groups, i.e., the chemotherapy (CAP) sensitive group (n = 2) and the resistant group (n = 2). Six genes such as beta tubulin, high-mobility group (nonhistone chromosomal) protein 1, connective tissue growth factor, insulin-like growth factor binding protein 2, alpha tubulin, and RAS-related gene were overexpressed in CAP therapy resistance group, whereas seven genes such as CD9 antigen, alpha-2-macroglobulin, caveolin 2, interleukin 1 receptor antagonist, Rho GTPase activating protein 1, reticulon 3, cyclin-dependent kinase 10, keratin 7 were underexpressed in CAP therapy resistance group. By increasing clinical case number and gene number of microarray to be used in the analysis of expression profile of gene cluster affecting anticancer drug resistance and sensitivity of the ovarian cancer, it would be possible to apply microarray analysis to personalization of chemotherapy such as selection of effective chemotherapy protocol and prediction of therapeutic effect in the near future.     

Involvement of microRNA-93, a new regulator of PTEN/Akt signaling pathway, in regulation of chemotherapeutic drug cisplatin chemosensitivity in ovarian cancer cells

The mechanisms underlying ovarian cancer cell resistance to cisplatin (CDDP) are not fully understood. MicroRNAs (miRNAs) play important roles in tumorigenesis and drug resistance. In this paper, we utilized microRNA array and real-time PCR to show that miR-93 is significantly up-regulated in cisplatin-resistant ovarian cancer cells. In vitro assays show that over-expression and knock-down of miR-93 regulate apoptotic activity, and thereby cisplatin chemosensitivity, in ovarian cells. Furthermore, we found that miR-93 can directly target PTEN, and participates in the regulation of the AKT signaling pathway. MiR-93 inversely correlates with PTEN expression in CDDP-resistant and sensitive human ovarian cancer tissues. These results may have implications for therapeutic strategies aiming to overcome ovarian cancer cell resistance to cisplatin.     

The negative feedback between miR-143 and DNMT3A regulates cisplatin resistance in ovarian cancer

Emerging evidence suggests that miR-143 plays an important role in the regulation of tumor sensitivity to chemotherapeutic agents. The study explores the underlying mechanism of miR-143 in reversing cisplatin resistance in ovarian cancer. The cisplatin-resistant ovarian cancer cell line A2780/CDDP was induced and established via treating A2780 cells by gradually increasing cisplatin concentrations. The IC₅₀ values of A2780/CDDP and A2780 to cisplatin were 218.10 ± 1.12 and 21.99 ± 1.12 μM, respectively. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that miR-143 was significantly decreased in A2780/CDDP cells compared with A2780 cells. miR-143 overexpression decreased cisplatin resistance in A2780/CDDP, and miR-143 inhibition decreased A2780 sensitivity to cisplatin. Results of qRT-PCR, Western blot analysis, and luciferase reporter assay indicated that the direct target of miR-143 was DNMT3A, which, in turn, was upregulated in A2780/CDDP. DNMT3A overexpression antagonized the sensitizing effect of miR-143 on A2780/CDDP to cisplatin. Knocking down of DNMT3A reduced cisplatin resistance in A2780/CDDP, while overexpression of DNMT3A increased cisplatin resistance in A2780. Methylation-specific polymerase chain reaction results showed that the methylation level in the promoter region of the miR-143 precursor gene was higher in A2780/CDDP cells than in A2780 cells. DNMT3A mediated the hypermethylation of the miR-143 precursor gene, resulting in miR-143 downregulation in A2780/CDDP. miR-143 inhibited cell growth of A2780/CDDP cell in nude mice. Our findings indicated the negative feedback between miR-143 and DNMT3A as a crucial epigenetic modifier of cisplatin resistance in ovarian cancer.     

Involvement of MKP-1 and Bcl-2 in acquired cisplatin resistance in ovarian cancer cells

Although cisplatin is a very effective anticancer agent against several types of cancer including ovarian cancer, the mechanisms of acquired resistance are not fully understood. By chronically exposing cisplatin to ovarian cancer cell lines, we established two cisplatin-resistant cell lines OV433 and TOV112D. Our results indicate that the mechanisms underlying their cisplatin resistance are distinct. In OV433 cells, cisplatin resistance is associated with increased expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1). By knocking down MKP-1 expression by siRNA or inhibiting MKP-1 expression by its pharmacological inhibitor triptolide, cisplatin-resistant OV433 cells became cisplatin-sensitive and subsequently increased cisplatin-induced apoptosis. In TOV112D cells, on the other hand, acquired cisplatin resistance is associated with increased levels of Bcl-2 protein. By inhibiting the activity of Bcl-2 protein with its pharmacological inhibitor gossypol or knocking down Bcl-2 expression by siRNA, cisplatin-resistant TOV112D cells became cisplatin-sensitive and subsequently increased cisplatin-induced apoptosis. Therefore, our data suggest that the mechanisms of acquired cisplatin resistance vary among ovarian cancer cells, which involve up-regulation of molecules associated with the cell survival pathways.     

Pyruvate dehydrogenase kinase 1 contributes to cisplatin resistance of ovarian cancer through EGFR activation

Patients with ovarian cancer frequently develop acquired drug resistance after the long-term chemotherapy, leading to disease progression. Enhanced epithelial–mesenchymal transition (EMT) has been implicated in chemoresistance of ovarian cancer cells; however, the molecular mechanisms involved are largely undefined. Pyruvate dehydrogenase kinase 1 (PDK1), a key regulatory enzyme in glucose metabolism, has been recognized as a gatekeeper of the Warburg effect, a hallmark of cancer. In this study, the function of PDK1 in cisplatin resistance of ovarian cancer in terms of growth and EMT was investigated. PDK1 was upregulated in cisplatin-resistant ovarian cancer cells. PDK1 knockdown in resistant cells led to increased sensitivity to cisplatin-induced cell death and apoptosis. PDK1 downregulation also reversed the EMT and cell motility in cisplatin-resistant cells. In a mouse xenograft model, tumors derived from PDK1-silenced ovarian cancer cells exhibited decreased tumor growth and EMT compared with control after the cisplatin treatment. Mechanistically, PDK1 overexpression led to increased phosphorylation of EGFR, and blocking EGFR kinase activity by erlotinib reversed cisplatin resistance induced by PDK1 overexpression. Furthermore, in patients with ovarian cancer, higher PDK1 and p-EGFR levels were associated with chemoresistance. These results supported that PDK1 contributes to chemoresistance of ovarian cancer by activating EGFR. Therefore, PDK1 may serve as a promising target to combat chemoresistance of ovarian cancer.     

Protein kinase CK2 is a central regulator of topoisomerase I hyperphosphorylation and camptothecin sensitivity in cancer cell lines

Topoisomerase I (topo I) is required to unwind DNA during synthesis and provides the unique target for camptothecin-derived chemotherapeutic agents, including Irinotecan and Topotecan. While these agents are highly effective anticancer agents, some tumors do not respond due to intrinsic or acquired resistance, a process that remains poorly understood. Because of treatment toxicity, there is interest in identifying cellular factors that regulate tumor sensitivity and might serve as predictive biomarkers of therapy sensitivity. Here we identify the serine kinase, protein kinase CK2, as a central regulator of topo I hyperphosphorylation and activity and cellular sensitivity to camptothecin. In nine cancer cell lines and three normal tissue-derived cell lines we observe a consistent correlation between CK2 levels and camptothecin responsiveness. Two other topo I-targeted serine kinases, protein kinase C and cyclin-dependent kinase 1, do not show this correlation. Camptothecin-sensitive cancer cell lines display high CK2 activity, hyperphosphorylation of topo I, elevated topo I activity, and elevated phosphorylation-dependent complex formation between topo I and p14ARF, a topo I activator. Camptothecin-resistant cancer cell lines and normal cell lines display lower CK2 activity, lower topo I phosphorylation, lower topo I activity, and undetectable topo I/p14ARF complex formation. Experimental inhibition or activation of CK2 demonstrates that CK2 is necessary and sufficient for regulating these topo I properties and altering cellular responses to camptothecin. The results establish a cause and effect relationship between CK2 activity and camptothecin sensitivity and suggest that CK2, topo I phosphorylation, or topo I/p14ARF complex formation could provide biomarkers of therapy-responsive tumors.     

p53 gene status and chemosensitivity in ovarian cancer.

Recent studies suggest that drug induced apoptosis relates to the sensitivity. p53 gene, which has a pivotal role in inducing apoptosis, frequently mutates in ovarian cancer. Therefore, p53 gene status and chemosensitivity in epithelial ovarian cancer is discussed. Nonresponders to chemotherapy had mutations of the p53 gene more frequently (83% for nonresponders vs. 16% for responders) in patients with epithelial ovarian cancer undergoing platinum-base chemotherapy. Apoptotic index was significantly greater in tumors with wild-type p53 gene than those without the gene. p53 gene transduction markedly enhanced the sensitivity to cisplatin (CDDP) and CDDP-induced apoptosis, but did not affect the sensitivity to paclitaxel (PTX) nor PTX-induced apoptosis in ovarian cancer cells without p53 gene. The combination treatment with a recombinant adenovirus carrying a wild-type p53 gene (AxCAp53) and CDDP significantly suppressed tumor growth of ovarian cancer cells with and without p53 gene, compared with a single treatment of either AxCAp53 or CDDP in ovarian cancer xenograft. Apoptotic index was significantly higher and proliferating cell nuclear antigen labeling index was relatively lower in an ovarian cancer xenograft without p53 gene receiving combination treatment, compared with a single treatment of either CDDP or AxCAp53, suggesting that the transduction of p53 gene induces apoptosis, but does not enhance the DNA repair system. A significant survival advantage was observed in the combination treatment compared with other treatments in carcinoma peritonitis models. In conclusion, p53 gene status contributes the sensitivity to CDDP in ovarian cancer. Additionally, combination treatment of p53 gene transduction and CDDP may be an effective therapeutic modality for ovarian cancer without wild-type p53 gene.     

Simple non-ion-paired high-performance liquid chromatographic method for simultaneous quantitation of carboxylate and lactone forms of 14 new camptothecin derivatives

SN-38 (7-ethyl-10-hydroxycamptothecin) is an active metabolite derived from the semi-synthetic compound camptothecin (CPT) named Irinotecan (CPT-11). The antitumor activity of SN-38 is 1000-fold more potent than the parent CPT-11. Fourteen new derivatives of camptothecin have recently been developed by Yakult Honsha (Tokyo, Japan). Here we describe a simple and cost-effective high-performance liquid chromatography (HPLC) method without an ion-pairing agent, which allows the simultaneous determination of both lactone and carboxylate forms of SN-38 and other camptothecin derivatives. A weak linear relationship between the HPLC retention factors (ln k') and the cellular concentrations of these compounds was observed. These results suggest that low-polarity compounds easily accumulate in cancer cells and may circumvent drug resistance. The HPLC analysis herein described is expected to greatly assist in derivative synthesis and chemical modification of camptothecin-based antitumor drugs.     

Drug-Resistant Urothelial Cancer Cell Lines Display Diverse Sensitivity Profiles to Potential Second-Line Therapeutics

Combination chemotherapy with gemcitabine and cisplatin in patients with metastatic urothelial cancer of the bladder frequently results in the development of acquired drug resistance. Availability of cell culture models with acquired resistance could help to identify candidate treatments for an efficient second-line therapy. Six cisplatin- and six gemcitabine-resistant cell lines were established. Cell viability assays were performed to evaluate the sensitivity to 16 different chemotherapeutic substances. The activity of the drug transporter ATP-binding cassette transporter, subfamily B, member 1 (ABCB1, a critical mediator of multidrug resistance in cancer) was evaluated using fluorescent ABCB1 substrates. For functional assessment, cells overexpressing ABCB1 were generated by transduction with a lentiviral vector encoding for ABCB1, while zosuquidar was used for selective inhibition. In this study, 8 of 12 gemcitabine- or cisplatin-resistant cell lines were cross-resistant to carboplatin, 5 to pemetrexed, 4 to methotrexate, 3 to oxaliplatin, 5-fluorouracil, and paclitaxel, and 2 to cabazitaxel, larotaxel, docetaxel, topotecan, doxorubicin, and mitomycin c, and 1 of 12 cell lines was cross-resistant to vinflunine and vinblastine. In one cell line with acquired resistance to gemcitabine (TCC-SUP^rGEMCI²⁰), cross-resistance seemed to be mediated by ABCB1 expression. Our model identified the vinca alkaloids vinblastine and vinflunine, in Europe an already approved second-line therapeutic for metastatic bladder cancer, as the most effective compounds in urothelial cancer cells with acquired resistance to gemcitabine or cisplatin. These results demonstrate that this in vitro model can reproduce clinically relevant results and may be suitable to identify novel substances for the treatment of metastatic bladder cancer.     

CK2-Mediated Hyperphosphorylation of Topoisomerase I Targets Serine 506, Enhances Topoisomerase I–DNA Binding,and Increases Cellular Camptothecin Sensitivity

Topoisomerase I is the target for a potent class of chemotherapeutic drugs derived from the plant alkaloid camptothecin that includes irinotecan and topotecan. In this study we have identified a novel site of CK2-mediated topoisomerase I (topo I) phosphorylation at serine 506 (PS506) that is relevant to topo I function and to cellular responses to these topo I-targeted drugs. CK2 treatment induced hyperphosphorylation of recombinant topo I and expression of the PS506 epitope, and resulted in increased binding of topo I to supercoiled plasmid DNA. Hyperphosphorylated topo I was approximately three times more effective than the basal phosphorylated enzyme at relaxing plasmid supercoils but had similar DNA cleavage activity once bound to DNA. The PS506 epitope was expressed in cancer cell lines with elevated CK2 activity, hyperphosphorylated topo I, and increased sensitivity to camptothecin. In contrast, PS506 was not detected in normal cells or cancer cell lines with lower levels of CK2 activity. By experimentally manipulating CK2 activity in cancer cell lines, we demonstrate a cause and effect relationship between CK2 activity, PS506 expression, camptothecin-induced cellular DNA damage, and cellular camptothecin sensitivity. Our results show that the PS506 epitope is an indicator of dysregulated, hyperphosphorylated topo I in cancer cells, and may thus serve as a diagnostic or prognostic biomarker and predict tumor responsiveness to widely used topo I-targeted therapies.     

TXNL1-XRCC1 pathway regulates cisplatin-induced cell death and contributes to resistance in human gastric cancer

Cisplatin is a cytotoxic platinum compound that triggers DNA crosslinking induced cell death, and is one of the reference drugs used in the treatment of several types of human cancers including gastric cancer. However, intrinsic or acquired drug resistance to cisplatin is very common, and leading to treatment failure. We have recently shown that reduced expression of base excision repair protein XRCC1 (X-ray repair cross complementing group1) in gastric cancerous tissues correlates with a significant survival benefit from adjuvant first-line platinum-based chemotherapy. In this study, we demonstrated the role of XRCC1 in repair of cisplatin-induced DNA lesions and acquired cisplatin resistance in gastric cancer by using cisplatin-sensitive gastric cancer cell lines BGC823 and the cisplatin-resistant gastric cancer cell lines BGC823/cis-diamminedichloridoplatinum(II) (DDP). Our results indicated that the protein expression of XRCC1 was significantly increased in cisplatin-resistant cells and independently contributed to cisplatin resistance. Irinotecan, another chemotherapeutic agent to induce DNA damaging used to treat patients with advanced gastric cancer that progressed on cisplatin, was found to inhibit the expression of XRCC1 effectively, and leading to an increase in the sensitivity of resistant cells to cisplatin. Our proteomic studies further identified a cofactor of 26S proteasome, the thioredoxin-like protein 1 (TXNL1) that downregulated XRCC1 in BGC823/DDP cells via the ubiquitin-proteasome pathway. In conclusion, the TXNL1-XRCC1 is a novel regulatory pathway that has an independent role in cisplatin resistance, indicating a putative drug target for reversing cisplatin resistance in gastric cancer.     

Proteomic analysis of cisplatin resistance in human ovarian cancer using 2-DE method

Platinum-based chemotherapy, such as cisplatin, is the primary treatment for human ovarian cancer. However, overcoming drug resistance has become an important issue in cancer chemotherapy. In this study, we performed 2-DE and ESI-Q-TOF MS/MS analysis to identify differential proteins expression between cisplatin-sensitive (A2780S) and cisplatin-resistant (A2780-CP) ovarian cancer cell lines. Of the 14 spots identified as differentially expressed (±over twofold, P < 0.05) between the two cell lines, ten spots (corresponding to ten unique proteins) were positively identified by ESI-Q-TOF MS/MS analysis. These proteins include capsid glycoprotein, fructose-bisphosphate aldolase C, heterogeneous nuclear ribonucleoproteins A2/B1, putative RNA-binding protein 3, Ran-specific GTPase-activating protein, ubiquitin carboxyl-terminal hydrolase isozyme L1, stathmin, ATPSH protein, chromobox protein homolog3 and phosphoglycerate kinase 1. The proteins identified in this study would be useful in revealing the mechanisms underlying cisplatin resistance and also provide some clues for further research.     

ISG15 suppresses translation of ABCC2 via ISGylation of hnRNPA2B1 and enhances drug sensitivity in cisplatin resistant ovarian cancer cells

Cisplatin-based chemotherapies have long been considered as a standard chemotherapy in ovarian cancer. However, cisplatin resistance restricts beneficial therapy for patients with ovarian cancer. The ubiquitin-like protein interferon-stimulated gene 15 (ISG15) encodes a 15-kDa protein, that is implicated in the post-translational modification of diverse proteins. In this work, we found that ISG15 was downregulated in cisplatin resistant tissues and cell lines of ovarian cancer. Functional studies demonstrated that overexpression of wild type (WT) ISG15, but not nonISGylatable (Mut) ISG15 increased cell responses to cisplatin in resistant ovarian cancer cells. Furthermore, we found that WT ISG15 decreased ABCC2 expression at the protein level. Importantly, overexpression of ABCC2 blocked sensitizing effect of ISG15 on cisplatin. In addition, we identified that hnRNPA2B1 was recruited to 5′UTR of ABCC2 mRNA and promoted its translation, which was blocked by ISG15. We further demonstrated that hnRNPA2B1 could be ISGylated, and ISGylation blocked its recruitment to ABCC2 mRNA, thereby suppressed translation of ABCC2. Altogether, our data support targeting ISG15 might be a potential therapeutic strategy for patients with cisplatin-resistant ovarian cancer.     

Antiproliferation effect of Rosemary (Rosmarinus officinalis) on human ovarian cancer cells in vitro

Rosemary (Rosmarinus officinalis L.) is a popular culinary/medicinal herb. Recent studies have shown it has pharmacologic activities for cancer chemoprevention and therapy. This study evaluated the antiproliferation activity of rosemary extract (RE) against human ovarian cancer cells, and whether the extract and its three main active ingredients carnosol (CS), carnosic acid (CA) and rosmarinic acid (RA) can enhance the antiproliferation activity of cisplatin (CDDP). Our study showed that RE has significant antiproliferation activity on human ovarian cancer A2780 and its CDDP resistant daughter cell line A2780CP70, with IC(50) (50% inhibitory concentration) estimated at 1/1000 and 1/400 dilutions respectively. RE enhanced the antiproliferation effect with CDDP on both A2780 and A2780CP70 cells. A2780 cells were consistently more sensitive to CS, CA, and RA than A2780CP70 cells between 2.5 and 20μg/ml. CS and RA also showed synergistic antiproliferation effect with CDDP on A2780 cells at some concentrations. RE treated by ultrafiltration, dialysis, and removal of phenolics lost the antiproliferation activity suggested that the activity resides in phenolics with MW<1000Da. Apoptosis array study of A2780 cells treated with RE showed that the expression of a number of genes regulating apoptosis were modulated by the treatment. This study showed that RE inhibited the proliferation of ovarian cancer cell lines by affecting the cell cycle at multiple phases. It induced apoptosis by modifying the expression of multiple genes regulating apoptosis, and holds potential as an adjunct to cancer chemotherapy.     

Adenosine enhances cisplatin sensitivity in human ovarian cancer cells

Ovarian cancer is the deadliest gynecologic cancer due to lack of early effective diagnosis and development of resistance to platinum-based chemotherapy. Several studies reported that adenosine concentrations are higher in tumor microenvironment than in non-tumor tissue. This finding inspired us to study the role of adenosine in ovarian cancer cells and to investigate if adenosine pathways offer new treatment options urgently needed to prevent or overcome chemoresistance. The ovarian cancer cell lines HEY, A2780, and its cisplatin-resistant subline A2780CisR were used in this study. Expression and functional activity of adenosine receptors were investigated by RT-PCR, Western blotting, and cAMP assay. A1 and A2B adenosine receptors were expressed and functionally active in all three cell lines. Adenosine showed moderate cytotoxicity (MTT-IC₅₀ values were between 700 and 900 μM) and induced apoptosis in a concentration-dependent manner by increasing levels of sub-G1 and cleaved PARP. Apoptosis was diminished by QVD-OPh, confirming caspase-dependent induction of apoptosis. Forty-eight hours pre-incubation of adenosine prior to cisplatin significantly enhanced cisplatin-induced cytotoxicity in a synergistic manner and increased apoptosis. SLV320 or PSB603, selective A1 and A2B antagonists, was not able to inhibit adenosine-induced increase in cisplatin cytotoxicity or apoptosis whereas dipyridamole, a nucleoside transporter inhibitor, completely abrogated both effects. Mechanistically, adenosine increased pAMPK and reduced pS6K which was prevented by dipyridamole. In conclusion, application of adenosine prior to cisplatin could be a new therapeutic option to increase the potency of cisplatin in a synergistic manner and thus overcome platinum resistance in ovarian cancer.     

Concentration-dependent collateral sensitivity of cisplatin-resistant gastric cancer cell sublines

The cisplatin-resistant gastric cancer cell sublines, SNU-601/Cis2 and /Cis10, were 49 and >530 times more resistant to cisplatin, respectively, compared with the drug-sensitive cells, SNU-601/WT. The SNU-601/Cis2 showed cross-resistance to carboplatin, heptaplatin, doxorubicin, mitomycin C, and 5-fluorouracil compared with the SNU-601/WT whereas the SNU-601/Cis10 displayed collateral sensitivity to these drugs with the exception of cisplatin compared with the SNU-601/Cis2, suggesting that the cross-resistance and collateral sensitivity of cisplatin-resistant gastric cancer cells are dependent upon cisplatin concentrations. Altered expression of the antioxidant and transporter genes (metallothionein, catalase, superoxide dismutases, P-glycoprotein, and the breast cancer resistance protein) was involved in these phenotypes of the cisplatin-resistant gastric cancer cell lines.     

Correlation between expression of oncogene products and resistance to anticancer drugs in cultured ovarian cancer cell lines

Despite recent advances in the application of chemotherapy to ovarian cancer, the development of alternative therapies that retain activity against drug-resistant-tumors remains a high priority. We analyzed a number of cultured ovarian cancer cell lines of different tissue types for the presence or absence of sensitivity to various anticancer drugs as well as expression patterns of oncogene products (erbB-2, EGFR, bcl-2). As a result, we identified oncogene products that were related to resistance. Using 9 cultured cell lines of ovarian cancers (serous, mucinous, endometrioid, clear, undifferentiated), sensitivities to anticancer drugs were investigated using the MTT assay. The phenotypes of oncogene products expressed by the above cultured cell lines were analyzed by Western blotting. The oncogene products involved in resistance to anticancer drugs were identified by multivariate analysis. Positive correlation between the resistance to anticancer drugs and the oncogene products was obtained by multivariate analysis for (a) CDDP and erbB-2 (b) x p-16 and erbB-2, and (c) MMC and EGFR. Correlation between resistance to anticancer drugs and expression of certain oncogene products was obtained in ovarian cancers, suggesting that sensitivity to anticancer drugs could be predicated prior to chemotherapy.