Mechanisms of chemoresistance and poor prognosis in ovarian clear cell carcinoma

Clear cell carcinoma (CCC) accounts for 4% to 12% of epithelial ovarian cancer in Western countries and, for some unknown reasons, it comprises more than 20% of such cancers in Japan. CCC shows unique clinical features such as a high incidence of stage I disease, a large pelvic mass, an increased incidence of vascular thromboembolic complications, and hypercalcemia. It is frequently associated with endometriosis. Compared to serous adenocarcinoma (SAC), CCC is relatively resistant to conventional platinum, or taxane-based chemotherapy which is associated with its poor prognosis. However, the mechanisms underlying CCC's resistance to chemotherapy have not been understood. Although several mechanisms involved in drug resistance exist in CCC, including decreased drug accumulation, increased drug detoxification, and an increased DNA repair activity; however, no particular chemoresistance system has been identified. On the other hand, an in vitro study revealed that low cell proliferation may cause the insensitivity of CCC to cisplatin. The Ki-67 labeling index in CCC tumors was significantly lower than SAC. The Ki-67 labeling index for responders was significantly higher than that for non-responders in both tumor types. A multivariable analysis revealed that Ki-67 labeling index and residual tumor size were independent prognostic factors in CCC. Therefore, lower proliferation of the tumor cells may contribute to their resistance to chemotherapy. However, further investigation into the molecular biology and genetics of CCC is warranted. This review discusses the current state of knowledge of the chemoresistance mechanism in CCC and novel treatment strategies for CCC. ( Cancer Sci 2008; 99: 653–658)     

Possible mechanisms of resistance to cis-diamminedichloroplatinum (II) of human ovarian cancer cells

The mechanism of cis-diamminedichloroplatinum (II) (CDDP) resistance was examined by using a CDDP-resistant (KFr) cell line established by continuous exposure of KF cells (derived from serous cystadenocarcinoma of the ovary) to escalating doses of CDDP. When KFr cells were incubated with 66.7 microM CDDP, the uptake of CDDP was significantly inhibited and the cellular content in the KFr cells was about a half of that in KF cells after incubation for 4 h. When the KF or KFr cells were incubated for 4 h with 100 microM CDDP, the release pattern of CDDP from KFr cells was similar to that from KF cells. In addition, the DNA histogram of both KF and KFr cells revealed that KF cells seemed to contain two clones of cell population and the KFr cells may have been selected by exposure to CDDP. At 3 h after intraperitoneal administration of 0.5 mg of CDDP per mouse to nude mice with KF or KFr tumor, the CDDP content in the KFr tumor was significantly lower than that in the KF tumor. In contrast, at 6 or 9 h after CDDP administration the CDDP content in the KFr tumor was significantly higher than that in the KF tumor. Furthermore, the KFr cells had cross-resistance to various CDDP analogues including carboplatin. It was shown that cellular uptakes of two CDDP analogues into KFr cells were significantly lower than those into KF cells.     

cis-diamminedichloroplatinum(II)-resistant sublines derived from two human ovarian tumor cell lines

In two human ovarian tumor cell lines, resistance to cis-diamminedichloroplatinum(II) (CDDP) was induced by continuous exposure of the parental lines to an increasing CDDP concentration in the culture medium. In contrast, a six times repeated pulse exposure of 6.7 microM or 16.7 microM CDDP for 1 h did not result in a cell line that showed a higher survival in CDDP-containing medium. The ID50 value for CDDP was seven to eight times higher for the resistant lines and those lines were able to grow at 3.3 microM CDDP. The induced resistance was stable during at least 25 doubling times. The CDDP-resistant sublines showed cross-resistance to the CDDP-analogues cis-diammine-1,1-cyclobutane-dicarboxylateplatinum(II) and cis-dichlorobis(isopropylamine)-trans-dihydroxyplatinum(IV) indicating that resistance to the different platinum compounds is generated by a common mechanism. The resistant sublines were also cross-resistant to mitomycin C and melphalan. The degree of cross-resistance for the tested drugs varied widely between the two cell lines. Resistance to CDDP was clearly correlated to decreased amounts of platinum in the resistant cells as compared to the sensitive cells. The amplification and expression of genes encoding proteins that had been shown to be involved in multidrug resistance, e.g., the Mr 170,000 P-glycoprotein was also studied. No amplification or overexpression of these genes could be shown in the resistant cell lines.     

Clear cell histology as a poor prognostic factor for advanced epithelial ovarian cancer: a single institutional case series through central pathologic review

Objective

Compared with serous adenocarcinoma (SAC), clear cell carcinoma (CCC) often shows chemo-resistance, which would potentially lead to a poor prognosis. On the other hand, there have been arguments over prognoses of CCC and SAC disease. In the present study, multivariate analysis to compare prognosis of CCC patients with that of SAC was aimed for the patients selected from central pathologic review.

Methods

Between 1984 and 2009, a total of 500 ovarian cancer patients were treated at our university hospital. Among them, 111 patients with CCC and 199 patients with SAC were identified through central pathological review. Overall survival and progression-free survival were compared using Kaplan-Meier method, and prognostic factors were investigated by multiple regression analyses.

Results

Median age was 52 years for CCC and 55 years for SAC (p=0.03). The ratio of stage I patients were significantly higher in CCC compared with SAC (55% vs. 13%, p<0.01). Among evaluable cases, response rate was significantly lower in CCC than that in SAC (32% vs. 78%, p<0.01). No significant differences of progression-free survival and overall survival were observed in stage I patients; however, prognoses of CCC were significantly poorer than those of SAC in advanced-stage disease. In stage II-IV patients, not only residual tumors and clinical stages, but also clear cell histology were identified as predictors for poor prognosis.

Conclusion

Clear cell histology was identified as a prognostic factor for advanced-stage ovarian cancers. Histologic subtypes should be considered in further clinical studies, especially for advanced epithelial ovarian cancers.     

Clinical characteristics of clear cell carcinoma of the ovary: a distinct histologic type with poor prognosis and resistance to platinum-based chemotherapy

BACKGROUND: A retrospective review of treatment results comparing women with clear cell carcinoma of the ovary (CCC) with a group with serous adenocarcinoma of the ovary (SAC) was conducted. METHODS: Between 1988-1998, 662 patients with epithelial ovarian carcinoma were identified through the medical records department and the tumor registry at 4 institutions. After the central pathologic review, 101 patients with pure or dominant (>/= 90%) CCC (15.3%) were entered into the current study. Two hundred thirty five patients with pure SAC were selected as a group for comparison. All patients underwent staging laparotomy followed by platinum-based chemotherapy. Distribution of the International Federation of Gynecology and Obstetrics (FIGO) disease stage, response to chemotherapy, and prognosis for patients with CCC were compared with the same values in patients with SAC. RESULTS: Patients with CCC were significantly more likely to have FIGO Stage I disease than were patients with SAC (48.5% vs. 16.6%). A high recurrence rate was noted in those patients with Stage IC CCC (37%). In those patients with Stage IC disease, the survival rates for patients with CCC were lower than those for patients with SAC. The 3-year and 5-year survival rates for Stage III CCC patients were significantly lower compared with Stage III SAC patients. The response rate to platinum-based chemotherapy in patients with CCC was significantly lower than that in patients with SAC. CONCLUSIONS: CCC is an intriguing histologic type of epithelial ovarian cancer that demonstrates a clinical behavior distinctly different from that of SAC.     

Molecular signature linked to acquired resistance to cisplatin in esophageal cancer cells

To clarify the molecular basis of acquired cisplatin (CDDP) resistance in esophageal squamous cell carcinoma (ESCC), we used cDNA microarray technology. A CDDP-resistant cell line (YES-2/CDDP), which shows a 7.5-fold increase in resistance to CDDP and a 3-fold decrease in CDDP accumulation compared with the parental YES-2 ESCC cell line, was generated from YES-2 by exposure to increased concentrations of CDDP. By cDNA microarray analysis, we identified 44 genes with significantly different expression levels between YES-2/CDDP and YES-2 cells. Interestingly, 15 of these 44 genes encoded ribosome-related proteins, almost all of which were underexpressed in YES-2/CDDP cells. Our present data suggest that many ribosome-related genes may be involved in the acquired resistance to CDDP in ESCC and that such information may allow us to better understand the mechanism of CDDP resistance.     

Copper efflux transporter (ATP7B) contributes to the acquisition of cisplatin-resistance in human oral squamous cell lines

Acquired resistance to cisplatin (CDDP) is an issue in cancer chemotherapy. This resistance has been reported to be correlated with the expression of the Cu influx copper transporter 1 (CTR1) and two copper efflux transporters (ATP7A, ATP7B). We investigated the correlation between the expression of these transporters and the sensitivity to CDDP using three pairs of parent cell lines and resistant cell lines derived from various types of invasive oral squamous cell carcinoma (OSCC). Using multiple steps, each of the CDDP-resistant cell lines, HSC-4-R, OSC-19-R, HOC313-R, was selected from HSC-4 cells derived from a cancer with medium invasiveness, OSC-19 cells derived from a cancer with high invasiveness and HOC313 cells derived from a cancer with the highest invasiveness. Resistant cell lines had a stronger expression of ATP7B in conjunction with the acquisition of CDDP-resistance than parent cell lines. Furthermore, OSC-19-R cells transfected with the ATP7B siRNA had a 10.6-fold higher sensitivity to CDDP compared to OSC-19-R cells transfected with a nonsense siRNA. These results suggest that each of the resistant cell lines had acquired resistance to CDDP due to the overexpression of ATP7B. On the other hand, the expression of CTR1 was the same between sensitive cell lines and resistant cell lines and ATP7A mRNA expression was barely noted. We conclude that ATP7B is correlated with the acquisition of CDDP resistance more closely than either CTR1 or ATP7A. ATP7B may be a key determinant in the acquired resistance to CDDP in OSCC.     

AKT1 amplification regulates cisplatin resistance in human lung cancer cells through the mammalian target of rapamycin/p70S6K1 pathway

Cisplatin [cis-diaminodichloroplatinum (II) (CDDP)] is one of the most widely used and effective therapeutic agents for many kinds of cancers. However, its efficiency is limited due to development of drug resistance. In this study, we showed that CDDP resistance was associated with AKT1 overexpression and gene amplification in human lung cancer cells that acquired the drug resistance. We showed that AKT1 forced expression in the cells was sufficient to render the cells CDDP resistant, and that AKT1 inhibition by its dominant negative mutant reversed the CDDP-resistant cells to be CDDP sensitive. These results show that AKT1 activity is essential for regulating CDDP resistance in cultured lung cancer cells. To study whether these results were correlated with human lung cancer tumors, we randomly selected tumor samples from human lung cancer patients to study the correlation of AKT activation and CDDP resistance in clinical tumor samples. We showed that AKT activation was highly related to CDDP chemosensitivity in human tumor tissues. Our results further showed that AKT1 induced lung cancer cells to become resistant to CDDP through the mammalian target of the rapamycin (mTOR) signaling pathway. These studies conclude that AKT amplification and the mTOR pathway play an important role in human lung cancer cells acquiring CDDP resistance, which represents a new mechanism for acquiring CDDP resistance and a potential novel therapeutic target for overcoming CDDP resistance in human cancer in the future.     

Inhibition by 5-fluorouracil of cis-diamminedichloroplatinum(II)-induced DNA interstrand cross-link removal in a HST-1 human squamous carcinoma cell line.

To elucidate the mechanism of the synergistic cytotoxicity of 5-fluorouracil (5-FU) and cis-diamminedichloroplatinum(II) (CDDP), we studied the interaction of these agents using a human squamous carcinoma cell line (HST-1). Exposure to 5-FU for 24 h and to CDDP for 1 h produced a 50% inhibitory concentration of 1.0 micrograms/ml (7.7 microM) and 2.5 micrograms/ml (8.3 microM), respectively. The cytotoxic action of CDDP was augmented, and a greater than additive effect was observed when the cells were exposed to 5-FU (1.0 micrograms/ml; 7.7 microM) for 24 h before the CDDP treatment. This synergistic activity was maximal when the interval between 5-FU and CDDP exceeded 24 h. In contrast, the cytotoxicity of CDDP was attenuated when it preceded the exposure to 5-FU. Thymidine did not alter the 5-FU-CDDP interaction. Evaluation of the kinetics of the removal of DNA interstrand cross-links, measured by alkaline elution, showed a significant reduction of this removal in the cells exposed to 5-FU followed by CDDP with a drug-free interval of 48 h, as compared with cells exposed to CDDP alone, or to 5-FU immediately followed by CDDP, although no differences were found in the formation of DNA interstrand cross-links by CDDP among these cells. No significant differences in the accumulation of intracellular platinum were detected by atomic absorption spectrophotometry. These findings suggest that 5-FU modulates the repair of platinum-DNA adducts, thereby potentiating the antitumor activity of CDDP.     

A study of human small-cell lung carcinoma (hSCLC) cell lines with different sensitivities to detect relevant mechanisms of cisplatin (CDDP) resistance

The cisplatin(CDDP)-resistant cell line GLC4-CDDP shows a variety of differences from the parent line GLC4. The aim of this study was to determine which of the observed changes correlated with the degree of resistance and was therefore relevant to the phenomenon of CDDP resistance. For these experiments we used cells of the sensitive hSCLC cell line GLC4 and the in vitro-acquired CDDP-resistant sublines GLC4-CDDP3 and GLC4-CDDP11, with a resistance factor (RF) of 3 and 11 respectively for CDDP and of 1.8 and 7.4 respectively for carboplatin. Carboplatin was used, in addition to CDDP in seeking relevant mechanisms. No consistency was found between the RF and the growth pattern or antigen expression, cellular volume, doubling time, cellular or nuclear platinum (Pt) content or the level of Pt-non-histone chromatin protein (NHCP) binding. A correlation was found between the RF and the level of glutathione (GSH), and a trend was found for the level of Pt-DNA binding, Pt-GG adduct content and the amount of interstrand cross-links (ISC). These changes might therefore be relevant for the development of resistance. These findings are compatible with a GSH-induced reduction of the amount of reactive Pt in the resistant cell, resulting in a lower net platination and toxic Pt-DNA adduct formation.     

N-acetylcysteine modifies cis-dichlorodiammineplatinum-induced effects in bladder cancer cells.

We previously demonstrated a role of reactive oxygen species (ROS) in cytotoxicity induced by cis-dichlorodiammineplatinum (CDDP) in combination with glutathione (GSH) depletors in bladder cancer cells. However, the relationship between CDDP and ROS is still unclear, although many mechanisms of drug resistance have been well characterized. The present study was undertaken to investigate the effects of N-acetylcysteine (NAC), a GSH precursor, on the CDDP-induced effects in bladder cancer cells (KU1). The cytotoxic effects of CDDP were significantly blunted by NAC (1 mM) in KU1 cells. The IC50 of CDDP only (10.2+/-1.2 microM) is significantly lower than that of CDDP with NAC (IC50: 20.3+/-1.6 microM) in KU1 cells. NAC also significantly increased the intracellular concentration of GSH in KU1 cells (37.2+/-1.6 nmol/10(6) cells), compared to controls (15.9+/-7.6 nmol/10(6) cells). While CDDP produced a significant increase in ROS as measured in terms of dichlorofluorescein (DCF) production in KU1 cells in a time-dependent manner, pretreatment with NAC significantly reduced CDDP-induced intracellular DCF in KU1 cells. Moreover, TdT-mediated dUTP-biotin nick-end labeling (TUNEL) assay showed that CDDP-induced apoptosis (31.1+/-3.8%) was significantly inhibited by pretreatment with NAC in KU1 cells (11.2+/-2.6%). These results demonstrated that NAC scavenges CDDP-induced ROS and inhibits CDDP-induced cytotoxicity, suggesting that ROS mediate the CDDP-induced cytotoxicity in bladder cancer cells.     

The Mechanism of the Difference in Cellular Uptake of Platinum Derivatives in Non-small Cell Lung Cancer Cell Line (PC-14) and Its Cisplatin-resistant Subline (PC-14/CDDP)

A cisplatin-resistant non-small cell lung cancer cell line, PC-14/CDDP, was established from PC-14 by stepwise escalation of CDDP concentrations in vitro . PC-14/CDDP cells were 11.4-fold more resistant to CDDP compared with PC-14 cells. This resistant cell line was cross-resistant to platinum analogues, such as carboplatin (CBDCA) (X 3.5), cis -diammine(glycolate-O, O')platinum(II) (254-S) (X 5.6) and cis -dichloro(ethylenediammine)platinum(II) (cis-DEP) (X 4.2). On the other hand, relative resistance value to ormaplatin was only 1.4-fold. To elucidate the mechanism(s) of CDDP resistance and of its circumvention by ormaplatin, we investigated the characteristics of this cell line. Total sulfhydryl content was slightly elevated in PC-14/CDDP cells compared with PC-14 cells. There was no significant difference in the DNA repair ability between the two cell lines. Cellular accumulations of CDDP, CBDCA, 254-S, and cis-DEP in PC-14/CDDP cells were markedly decreased to 23%, 27%, 29%, and 32% of those in PC-14 cells, respectively. However, the accumulation of ormaplatin in PC-14/CDDP was almost the same as that in PC-14. To elucidate the mechanisms of uptake of these platinum analogs in the cells, we studied the effects of ouabain, an Na⁺, K⁺ -ATPase inhibitor, on cellular drug uptake in both cell lines. Preincubation with 300 n M ouabain for 1 h inhibited approximately 60% of CDDP accumulation in PC-14. However ouabain preincubation at any concentration up to 300 n M did not affect CDDP accumulation in PC-14/CDDP. The accumulation of ormaplatin was not inhibited by ouabain in either of the cell lines. These data suggest that the mechanism of the uptake of ormaplatin is different from that of CDDP, and that ormaplatin exerts a cytotoxic effect in CDDP-resistant cells which have defective cisplatin accumulation.     

Synergistic Enhancement of Cisplatin Cytotoxicity by SN-38, an Active Metabolite of CPT-11, for Cisplatin-resistant HeLa Cells

A cisplatin ( cis -diamininedichloroplatinuin(II); CDDP)-resistant HeLa cell line (HeLa/CDDP cells), which showed more than 8-fold resistance to CDDF compared to the parent cells, was newly established for this study. HeLa/CDDP cells accumulated 50% less platinum than the parent cells. There was no difference in intracellular glutathione (GSH) content between the parent and HeLa/ CDDP cells. The dose modification factor by DL-buthionine-S, R-sulfoximine (BSO) pretreatment was similar in both cell lines. HeLa/CDDP cells had cross-resistance to diammine (l, l-cyclobutanedicarboxylato)platinum(II) (CBDCA), ( cis -diammine (glycolato)platinum (254-S), but not to (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platinum(II) (DWA2114R), adriamycin, or VP-16. HeLa/CDDP cells showed a collateral sensitivity to 7-ethyl-10-hydroxycampto-thecin (SN-38), an active metabolite of 7-ethyl-10-[4-(l-piperidino)-l-piperidino]carbonyloxycamptothecin (CPT-11). Furthermore, isobologram analysis indicated synergistic interaction of CDDP and SN-38 only for HeLa/CDDP cells. The present study suggests that combination therapy with CDDP and CPT-11 may he potentially useful in the treatment of some patients with CDDP-resistant cancer.     

In vitro susceptibility to anticancer agents of the human KB carcinoma cell line transfected with COX-2 cDNA

In order to investigate the malignant phenotype of cyclooxygenase (COX)-2 overexpressing cancer cells, a human epidermoid KB carcinoma cell line minimally expressing COX-2 protein was transfected with human COX-2 cDNA. In this study, we used a COX-2 transfected clone KB/COX-2 and a neomycin-transfected clone KB/neo as the control. When we examined the susceptibility to anticancer agents, there was no difference between these two clones in vincristine, bleomycin and 5-fluorouracil, although KB/COX-2 showed a 2.5-fold resistance to cisplatin (CDDP) as compared with KB/neo. The IC50 for CDDP was 4.3 microM in KB/COX-2 and 1.7 microM in KB/neo. Treatment with small interfering RNA (siRNA) mediated the inhibition of COX-2 significantly increasing the level of susceptibility to CDDP in COX-2 siRNA as compared to that of the control siRNA. The expression of MRP1 and MRP2 was stronger in KB/COX-2 than in KB/neo by Western blot analysis. In addition, apoptosis induction by CDDP was at a lower level in KB/COX-2 (31%) than in KB/neo (38%). These results suggested that the overexpression of COX-2 increases the intracellular production of MRP1 and MRP2 and causes drug resistance to CDDP.     

Interaction between CD44 and hyaluronate induces chemoresistance in non-small cell lung cancer cell

CD44s is a principle hyaluronate (HA) receptor and has been reported to play an important role in cancer cell invasion and metastasis. The aim of our study is to determine if the interaction between HA and CD44s influences in vitro chemosensitivity of non-small cell lung cancer (NSCLC). NSCLC cell line, H322 cells, transfected with the CD44s gene (H322/CD44s) cultured on HA coated plates were more resistant to cisplatin (CDDP) than that on bovine serum albumin. Multidrug resistance protein2 (MRP2) expression was induced in H322/CD44s cells cultured on HA. MRP2 inhibitor, MK571, not only suppressed MRP2 expression but also reversed CDDP resistance. These results suggest that the interaction between CD44s and HA play a pivotal role in acquired resistance to CDDP in NSCLC and MRP2 could be involved in this potential mechanism.