SENSITIZATION OF HUMAN BLADDER CANCER CELLS TO FAS-MEDIATED CYTOTOXICITY BY CIS-DIAMMINEDICHLOROPLATINUM (II)

Biomarker in Cisplatin-Based Chemotherapy for Urinary Bladder Cancer

The treatment of metastasized bladder cancer has been evolving during recent years. Cisplatin based chemotherapy combinations are still gold standard in the treatment of advanced and metastasized bladder cancer. But new therapies are approaching. Based to this fact biological markers will become more important for decisions in bladder cancer treatment. A systematic MEDLINE search of the key words "cisplatin", "bladder cancer", "DNA marker", "protein marker", "methylation biomarker", "predictive marker", "prognostic marker" has been made. This review aims to highlight the most relevant clinical and experimental studies investigating markers for metastasized transitional carcinoma of the urothelium treated by cisplatin based regimens.

Molecular mechanisms of cisplatin resistance in bladder cancer

Metastatic disease is the most common mechanism of death in patients with advanced bladder cancer. As for most solid tumors, chemotherapy remains the only realistic option for palliating or curing metastatic disease. However, bladder cancer is characterized by chemoresistance. Only modest response rates are obtained using multiagent regimens including cisplatin. These low response rates and the toxicity of these regimens limit their use to patients at highest risk. Here, we review the molecular mechanisms of cisplatin resistance. These include methods to reduce cisplatin bioavailability within a cell, and defects in the machinery that produces cell death following cisplatin-induced DNA damage. While overcoming these mechanisms is a potential therapeutic approach that can increase response rates, in the short term this knowledge could be used to predict response in individual tumors.

Isolinderanolide B, a butanolide extracted from the stems of Cinnamomum subavenium, inhibits proliferation of T24 human bladder cancer cells by blocking cell cycle progression and inducing apoptosis

Isolinderanolide B (IOB), a butanolide extracted from the stems of Cinnamomum subavenium, was investigated for its antiproliferative activity in T24 human bladder cancer cells. To identity the anticancer mechanism of IOB, its effect on apoptosis, cell cycle distribution, and levels of p53, p21 Waf1/Cip1, Fas/APO-1 receptor, and Fas ligand was assayed. Enzyme-linked immunosorbent assay showed that the G0/G1 phase arrest is because of increase in the expression of p21 Waf1/Cip1. An enhancement in Fas/APO-1 and membrane-bound Fas ligand (mFasL) might be responsible for the apoptotic effect induced by IOB. This study reports the novel finding that the induction of p21 Waf1/Cip1 and activity of the Fas/mFas ligand apoptotic system may participate in the antiproliferative activity of IOB in T24 cells.

S-1: a promising new oral fluoropyrimidine derivative

S-1 is an oral fluoropyrimidine that is designed to improve the antitumor activity of 5-fluorouracil (5-FU) concomitantly with an intent to reduce its toxicity. S-1 consists of tegafur, a prodrug of 5-FU combined with two 5-FU biochemical modulators:5-chloro-2,4-dihydroxypyridine (gimeracil or CDHP), a competitive inhibitor of dihydropyrimidine dehydrogenase and oteracil potassium which inhibits phosphorylation of 5-FU in the gastrointestinal tract decreasing serious gastrointestinal toxicities,including nausea, vomiting, stomatitis and diarrhea. Being an oral agent, S-1 offers convenience of administration and prevents complications of central venous access such as infection, thrombosis and bleeding. S-1 has shown efficacy in both gastrointestinal as well non-gastrointestinal malignancies. The authors review the current literature and provide their expert opinion on the incorporation of S-1 in the treatment of solid malignancies [corrected].

The grape and wine constituent piceatannol inhibits proliferation of human bladder cancer cells via blocking cell cycle progression and inducing Fas/membrane bound Fas ligand-mediated apoptotic pathway

Piceatannol (3,3',4,5'-Tetrahydroxy-trans-stilbene) is a polyphenol present in grapes and wine. Piceatannol is a protein kinase inhibitor that modifies multiple cellular targets exerting immunosuppressive, antileukemic, and antitumorigenic activities in several cell lines and animal models. In this study, the antiproliferative activity of piceatannol was investigated. The results showed that piceatannol inhibited the proliferation of T24 and HT1376 human bladder cancer cells by blocking cell cycle progression in the G0/G1 phase and inducing apoptosis. ELISA showed that the G0/G1 phase arrest is due to an increased in the expression of p21/WAF1. An enhancement in Fas/APO-1 and membrane-bound Fas ligand (mFasL) might be responsible for the apoptotic effect induced by piceatannol. Our study reports the novel finding, that the induction of p21/WAF1 and activity of the Fas/mFasL apoptotic system may participate in the antiproliferative activity of piceatannol in T24 and HT1376 cells.

Norsolorinic acid inhibits proliferation of T24 human bladder cancer cells by arresting the cell cycle at the G0/G1 phase and inducing a Fas/membrane-bound Fas ligand-mediated apoptotic pathway

1. Norsolorinic acid, isolated from Aspergillus nidulans, has been shown to have antiproliferative activity in T24 human bladder cancer cells by arresting the cell cycle at the G(0)/G(1) phase and inducing apoptosis. The aim of the present study was to investigate the antiproliferative activity of norsolorinic acid in T24 human bladder cancer cells. 2. The effects of norsolorinic acid (1, 5, 10 and 20 micromol/L) on the proliferation of T24 cells and on the distribution of cells within different phases of the cell cycle were investigated indirectly using an XTT assay and a flow cytometer, respectively. Factors affecting the cell cycle and apoptosis, including p53, p21, Fas receptor, Fas ligand (FasL) and caspase 8 activity, were examined using ELISA. 3. The results showed that norsolorinic acid inhibited proliferation of T24 cells in a dose-dependent manner, with an IC(50) of 10.5 micromol/L. The effect involved the induction of cell cycle arrest at the G(0)/G(1) phase and apoptosis. 4. These results demonstrate that G(0)/G(1) phase arrest is due to increased expression of p21 in cells treated with norsolorinic acid (10 and 20 micromol/L) for 24 h. Moreover, enhanced Fas and membrane-bound Fas ligand (mFasL) may be responsible for the apoptotic effect of norsolorinic acid. Thus, the present study reports, for the first time, that induction of p21 and the Fas/mFas ligand apoptotic system may participate in the antiproliferative action of norsolorinic acid in T24 human bladder cancer cells.

The Essential Role of the Mitochondria and Reactive Oxygen Species in Cisplatin-Mediated Enhancement of Fas Ligand-Induced Apoptosis in Malignant Pleural Mesothelioma

Cytotoxic chemotherapeutic drugs such as cisplatin (CDDP) synergistically interact with soluble Fas ligand (sFasL) to mediate profound induction of apoptosis in cancer cells, particularly those refractory to this death-inducing ligand. The goal of this study was to evaluate the roles of the mitochondria-dependent apoptotic cascade and the CDDP-generated reactive oxygen species (ROS) in mediating the supra-additive enhancement of cytotoxicity and apoptosis in combination-treated malignant pleural mesothelioma (MPM) cells. MPM cells were treated with sequential CDDP/sFasL in vitro. Cell viability and apoptosis were determined by MTT and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays. Stable transfectants expressing high levels of Bcl2 were created by retroviral gene transfer. Specific proteolytic activity of caspases 3, 8, and 9 were measured using fluorescent substrates. Pretreating MPM cells with CDDP increased their susceptibility to sFasL by 2- to more than 20-fold. Overexpression of either Bcl-2, the selective caspase 9 inhibitor z-LEHD-fmk, or the antioxidant N-acetylcysteine significantly abrogated combination-induced cytotoxicity and apoptosis. Moreover, the robust activation of caspase 8 in combination-treated cells was completely suppressed by Bcl-2 overexpression, thus implicating a mitochondria-mediated amplification feedback loop. As an in vivo correlate, sequential intraperitoneal administration of CDDP and sFasL significantly inhibited the growth of intraperitoneal MPM human xenografts in nude mice. Our data indicate that the mitochondria-dependent feedback loop of the caspase activation cascade and the generation of ROS are both essential in mediating profound cytotoxicity and apoptosis of MPM cells treated with CDDP and sFasL. This mechanistic study establishes a the translational framework for the clinical application of sequential CDDP/sFasL in the treatment of MPM.

On the effect of biochemotherapy in metastatic malignant melanoma: an immunopathological evaluation

Although immunotherapy and biochemotherapy have shown promise, producing a subset of durable responses, for the majority of patients with metastatic melanoma the prognosis is still poor. Therefore there is a great need for predictive tests to identify patients with a high probability of responding. Furthermore, there is also a need for a better understanding of the mechanisms of action during treatment in order to be able to monitor the relevant antitumour reactivity during treatment and to optimize the efficacy of future immunotherapy and biochemotherapy. In the present study histopathological regression criteria were used to study the efficacy of biochemotherapy. Thirty-two patients with metastatic malignant melanoma (18 with regional disease and 14 with systemic disease) were treated with biochemotherapy (cisplatin 30 mg/m2 intravenously on days 1-3, dacarbazine 250 mg/m2 intravenously on days 1-3 and interferon-alpha2b 10 million IU subcutaneously 3 days a week, every 28 days). Pre-treatment fine needle aspirates were obtained from metastases to analyse the number of tumour-infiltrating CD4+ lymphocytes. Therapeutic efficacy was evaluated in metastases resected after treatment using histopathological criteria of tumour regression. Comparisons were also made with metastases from 17 untreated patients, all with regional disease. Regressive changes of 25% or more (of the section area) were found in two of the 17 untreated patients with regional disease compared with 13 of the 18 patients with regional disease and 10 of the 14 patients with systemic disease after biochemotherapy. Fifty per cent of the patients with regional disease showed a high degree of regressive changes (75-100% of the section area) after biochemotherapy. These results demonstrate the occurrence of an antitumour reactivity in the majority of patients. Patients with extensive regressive changes in 75-100% of the analysed biopsies were also found to have a longer overall survival (P = 0.019). In patients with regional disease there was a close correlation between a larger number of CD4+ lymphocytes pre-treatment and a higher degree of regressive changes post-treatment (P < 0.05). Thus, immunohistochemical analysis of tumour biopsies shortly after treatment seems to be a good surrogate endpoint. This technique also allows detailed analysis of antitumour reactivity and escape mechanisms.

Loss of drug-induced activation of the CD95 apoptotic pathway in a cisplatin-resistant testicular germ cell tumor cell line

Testicular germ cell tumors (TGCTs) are unusually sensitive to cisplatin. In the present study the role of the CD95 death pathway in cisplatin sensitivity of TGCT cells was studied in Tera and its in vitro acquired cisplatin-resistant subclone Tera-CP. Cisplatin induced an increase in CD95 membrane expression, which preceded the onset of apoptosis. Cisplatin-induced apoptosis was efficiently blocked by caspase-8 inhibitor zIETD-fmk in Tera cells, but only partially in Tera-CP cells. In addition, cisplatin induced FADD and caspase-8 recruitment to the CD95 receptor in Tera cells, which was not noticed in Tera-CP cells. Moreover, overexpression of vFLIP reduced apoptosis induction by cisplatin in Tera cells. CD95L-blocking experiments revealed the involvement of CD95/CD95L interactions in cisplatin-induced apoptosis of Tera cells as well as cisplatin-sensitive 833KE TGCT cells. Tera and 833KE cells, treated with low doses of cisplatin, were sensitive for an apoptosis-inducing anti-CD95 antibody. In contrast, CD95L blocking had no effect on cisplatin-induced apoptosis in Tera-CP or Scha, an intrinsic resistant TGCT cell line, nor did anti-CD95 antibody induce additional apoptosis in cisplatin-treated Tera-CP or Scha cells. Taken together, these results show that (1) cisplatin sensitivity of TGCT cells is dependent on the activation of the CD95 death pathway and (2) loss of cisplatin-induced activation of this CD95 signaling pathway may result in resistance to cisplatin.

Inhibition of caspase-9 activity and Apaf-1 expression in cisplatin-resistant head and neck squamous cell carcinoma cells

We have previously reported that cisplatin induces caspase-9 (Casp9) activation in head and neck squamous cell carcinoma cells in vitro (HNSCCs). Our purpose here was to examine whether HNSCCs selected for resistance to cisplatin fail to exhibit Casp9 activation in response to cisplatin. The cisplatin-resistant HNSCCs (HSC-2CR) were selected from cisplatin-sensitive HNSCCs (HSC-2) for growth in the presence of cisplatin. Following cisplatin treatment, protelyzed Casp9 subunits were detected in HSC-2, but not detected in HSC-2CR. Using a direct enzymatic assay measuring cleavage of the synthetic peptide substrate (LEHD-AFC), Casp9 activity in cisplatin-treated HSC-2CR was less than that in cisplatin-treated HSC-2. Apoptotic protease-activating factor 1 (Apaf-1) has been shown to participate as an adaptor molecule in Casp9 activation. In the presence of cytochrome c (Cyt c) released from mitochondria, Apaf-1 binds to Casp9 and causes its activation. HSC-2 expressed 2-fold higher levels of Apaf-1 compared with HSC-2CR. On the other hand, following cisplatin treatment, the same degree of increase in cytoplasmic Cyt c was detected in both HSC-2 and HSC-2CR. These results suggest that in a certain type of HNSCCs, the inhibition of Casp9 activity and Apaf-1 expression may represent a mechanism of acquired cisplatin resistance.

Cytokine receptor as a sensitizer for targeted cancer therapy

Introducing a cytokine receptor as a sensitizer into cancer cells offers a unique opportunity for receptor-targeted cancer therapy. It has been shown that transfection of the tumor necrosis factor (TNF) receptor gene in cancer cells or exposing cancer cells to certain reagents which increase expression of TNF receptors results in enhancement of the cytotoxic effect of TNF. In addition, the literature suggests that Fas/CD95-mediated apoptotic tumor cell killing is augmented by gene transfer of Fas into cancer cells or treatment of cells with agents like cisplatin and interferon (IFN)-gamma. In contrast to these approaches, we have discovered a new approach to cancer therapy; wherein introduction of a cytokine receptor chain into cancer cells sensitizes them to receptor-directed cytotoxins. We have demonstrated that when interleukin (IL)-13 receptor (IL-13R) alpha2 chain, one of the two known IL-13 binding proteins, is introduced into cancer cells that do not express this chain the cells acquire extreme sensitivity to a chimeric fusion cytotoxin composed of IL-13 and a mutated form of Pseudomonas exotoxin (IL13-PE). Cells that do not express this chain or express low levels show limited sensitivity to IL13-PE. Acquisition of sensitivity to IL13-PE was observed both in vitro and in vivo when IL-13R alpha2-transfected human tumor cells were implanted in immunodeficient animals followed by systemic or regional IL13-PE therapy. Our third generation experiments suggest that this approach is feasible for clinical situations as intratumor administration of plasmid carrying the IL-13R alpha2 chain gene sensitized these tumors to systemic or regional IL13-PE therapy. This unique approach comprising gene transfer of cytokine receptor chain and receptor-targeted cytotoxin administration represents a novel strategy for cancer therapy.

Cisplatin-induced in vivo differentiation of human embryonal carcinoma

OBJECTIVE

To investigate the differentiation of embryonal carcinoma (EC) by cisplatin, and the underlying mechanism, as untreated metastases of nonseminomatous germ cell tumours rarely consist of fully differentiated mature somatic tissues, but such mature metastases are more common after various treatments, including chemotherapy.

MATERIALS AND METHODS

The TTSC-3 human testicular EC line heterotransplanted into nude mice was used as a target. After treating tumour-bearing mice with intraperitoneal injections of varying doses of cisplatin, the histopathology of the tumours was assessed and various gene expressions in the tumours determined by cDNA-array technology.

RESULTS

When cisplatin at 1 mg/kg/week was injected intraperitoneally into TTSC-3-bearing mice, there was no effect on tumour growth. However, injecting cisplatin at 5 mg/kg/week induced a marked regression of the tumour. In contrast, cisplatin at 3 mg/kg/week had a modest inhibitory effect on tumour growth and induced tumour dormancy. Histological examination showed that 5 weeks after injecting cisplatin (3 mg/kg/week), primitive mesenchymal-like cells increased, and 10 weeks afterward cartilage and well-developed glands (teratoma) were apparent; at > 15 weeks afterward there were no EC cells visible. cDNA probes from reverse-transcribed mRNAs of TTSC-3 treated with cisplatin or saline for 10 weeks were compared to identify genes differentially expressed in cisplatin-treated TTSC-3. Of 1176 different human cDNA transcripts in cisplatin-treated TTSC-3, three genes (tumour necrosis factor receptor 1, caspase 8 and Apaf1), which are associated with apoptosis, were expressed markedly more than after saline injection.

CONCLUSIONS

The intermediate dose of cisplatin inhibited tumour growth of EC by inducing differentiation and enhancing apoptosis-related gene expression. These findings suggest that cisplatin may play a significant role in the differentiation of EC in vivo.

Potentiation of the sensitivity of renal cell carcinoma cells to TRAIL-mediated apoptosis by subtoxic concentrations of 5-fluorouracil

Cytotoxic chemotherapy has shown little antitumour activity against renal cell carcinoma (RCC). Although immunotherapy is relatively effective against RCC, the response rate is approximately 20%. Therefore, there is an urgent need to increase this response rate. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2L) is one member of the tumour necrosis factor ligand family that selectively induces apoptosis of cancer cells. Since several cytotoxic anticancer drugs including 5-fluorouracil (5-FU) also mediate apoptosis, we reasoned that combined treatment of cancer cells with TRAIL and drugs might result in synergy and overcome the resistance of the cancer cell. This study has examined whether TRAIL can synergise with 5-FU in both cytotoxic and apoptotic assays against drug-resistant RCC cells. Cytotoxicity was determined by an 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis. Treatment of Caki-1 cells with TRAIL in combination with 5-FU resulted in a synergistic cytotoxic effect. Synergy was also achieved in freshly derived RCC cells from 3 patients. The enhanced cytotoxicity was obtained irrespective of the sequence of the treatment, but the highest cytotoxicity was observed when Caki-1 cells were treated with TRAIL and 5-FU simultaneously. The synergy achieved in cytotoxicity with TRAIL and 5-FU was shown to be due to apoptosis. The mechanisms responsible for the synergistic cytotoxicity and apoptosis were examined. Treatment of Caki-1 cells with 5-FU enhanced the expression of p53 and bax, but had no effect on the expression of bcl-2. Incubation of Caki-1 cells with TRAIL enhanced the intracellular accumulation of 5-FU and 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP). Treatment of Caki-1 cells with TRAIL downregulated the expression of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) modestly, and upregulated the expression of orotate phosphoribosyltransferase (OPRT). However, the expression level of thymidine phosphorylase (TP) was not affected by TRAIL. This study demonstrates that combined treatment of RCC cells with TRAIL and 5-FU overcomes their resistance. The sensitisation obtained with freshly isolated RCC cells required low subtoxic concentrations of 5-FU. These findings support the potential application in vivo of a combination of TRAIL and 5-FU in the treatment of TRAIL/5-FU-resistant RCC.

The role of Fas and FasL as mediators of anticancer chemotherapy

Fas Ligand (FasL) is a member of the TNF superfamily that induces apoptosis in susceptible cells upon cross-linking of its own receptor, Fas (Apo-1/CD95). FasL-induced apoptosis contributes to immune homeostasis and cell-mediated cytotoxicity. Several groups have suggested that it also participates in the mechanism of action of DNA-damaging anticancer drugs. However, others have disputed this hypothesis, based largely on the inability of exogenously added anti-Fas/FasL reagents to attenuate drug-induced apoptosis in their studies. In this minireview, we discuss the most recent evidence for and against the involvement of FasL/Fas in the sensitivity and resistance to chemotherapy in a variety of models. In our own model of Ewing's sarcoma (ES), we have extensively investigated the involvement of the FasL/Fas pathway in doxorubicin (Dox)-induced apoptosis. We have generated clones of the Fas-sensitive, Dox-sensitive ES cell line SK-N-MC that were either Fas-resistant or FasL-deficient, and found that they were significantly resistant to Dox. Cleavage of FasL by MMP-7 (matrilysin) protected the parental SK-N-MC cells from Dox, whereas inhibition of MMP-7 activity increased their sensitivity. Transfection of a construct encoding soluble (decoy) Fas protected SK-N-MC cells from Dox. However, incubation with anti-Fas or anti-FasL neutralizing antibodies or exogenous addition of pre-synthesized recombinant soluble Fas decoy protein had no protective effect. This raises the possibility that the proposed Fas/FasL suicidal interaction may take place in an intracellular compartment and thus is not accessible to exogenously added reagents. Therefore, commercially available Fas/FasL neutralizing reagents may not be a reliable indicator of the involvement of the Fas pathway in anticancer-drug-induced apoptosis and experiments using these agents should be carefully re-evaluated. The combined use of MMP inhibitors with conventional, cytotoxic chemotherapy may hold therapeutic benefit.

Enhanced sensitivity of bladder cancer cells to tumor necrosis factor related apoptosis inducing ligand mediated apoptosis by cisplatin and carboplatin

PURPOSE

The development and acquisition of multiple drug resistance in cancer cells are a consequence of cancer chemotherapy and remain a major obstacle in treatment. Therefore, there is an obvious need for alternative approaches, such as immunotherapy and gene therapy. Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is one of the tumor necrosis factor ligand families and it selectively induces apoptosis against cancer cells. Several cytotoxic anticancer drugs also mediate apoptosis and may share the common intracellular pathways leading to apoptosis. We reasoned that combination treatment of cancer cells with TRAIL and drugs may overcome this resistance. We evaluated whether bladder cancer cells are sensitive to TRAIL mediated cytotoxicity and whether TRAIL may synergize with anticancer agents in cytotoxicity and apoptosis against bladder cancer cells.

MATERIALS AND METHODS

Cytotoxicity was determined by a 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis.

RESULTS

Human T24 bladder cancer line was relatively resistant to TRAIL and TRAIL was not cytotoxic against normal bladder cells. Treatment of T24 cells with TRAIL in combination with 5-fluorouracil or mitomycin C did not overcome resistance to these agents. However, treatment of T24 cells with a combination of TRAIL and cisplatin resulted in a synergistic cytotoxic effect. Synergy was also achieved in the cisplatin resistant T24 line (T24/CDDP), 2 other bladder cancer lines and 3 freshly derived bladder cancer cells. The combination of TRAIL and carboplatin resulted in a synergistic cytotoxic effect on T24 cells. However, the combination of TRAIL and trans-diamminedichloroplatinum (II) resulted in an antagonistic cytotoxic effect. The synergy achieved in cytotoxicity with TRAIL and cisplatin was also achieved in apoptosis. Treating T24 cells with cisplatin enhanced the expression of bax but not bcl-2. Incubation of T24 cells with TRAIL increased the intracellular accumulation of cisplatin.

CONCLUSIONS

This study demonstrates that combination treatment of bladder cancer cells with TRAIL and cisplatin overcomes their resistance. The sensitization obtained with established cisplatin resistant and freshly isolated bladder cancer cells required low subtoxic concentrations of cisplatin, supporting the in vivo potential application of a combination of TRAIL and cisplatin for treating TRAIL resistant and cisplatin resistant bladder cancer.

Effect of anticancer agents on Fas-mediated cytotoxicity against bladder cancer cells

Fas and Fas ligand play an important role in cytotoxic T lymphocyte-mediated cytotoxicity. Like Fas ligand, anti-Fas monoclonal antibody (mAb) induces apoptosis of cells expressing Fas and mimics tumor necrosis factor-alpha (TNF-alpha) in its cytotoxic activity, but not in regard to other TNF-alpha-mediated activities. Since combination treatment with TNF-alpha and some anticancer chemotherapeutic agents results in synergistic cytotoxicity against various cancer cells, anti-Fas mAb may also synergize with anticancer agents in exerting cytotoxicity. The present study examined this hypothesis using bladder cancer cells. Cytotoxicity was examined by a 1-day microculture tetrazolium dye assay. Treatment of T24 cells with anti-Fas mAb in combination with mitomycin C, methotrexate, or 5-fluorouracil did not overcome their resistance to these agents. However, combination treatment with anti-Fas mAb and adriamycin (ADR) resulted in a synergistic cytotoxic effect on T24 cells, three other bladder cancer lines, and fresh bladder cancer cells derived from four patients. Treatment with ADR enhanced the expression of Fas on T24 cells. The expression of P-glycoprotein was not affected by the antibody-mediated sensitization. This study showed that combination treatment of bladder cancer cells with anti-Fas mAb and ADR can overcome their resistance and that the upregulation of Fas expression by ADR may play a role in the enhanced cytotoxicity.