Mechanism of cross-resistance to cisplatin in a mitomycin C-resistant human bladder cancer cell line

Machine learning identifies the role of SMAD6 in the prognosis and drug susceptibility in bladder cancer

BACKGROUND

Bladder cancer (BCa) is among the most prevalent malignant tumors affecting the urinary system. Due to its highly recurrent nature, standard treatments such as surgery often fail to significantly improve patient prognosis. Our research aims to predict prognosis and identify precise therapeutic targets for novel treatment interventions.

METHODS

We collected and screened genes related to the TGF-β signaling pathway and performed unsupervised clustering analysis on TCGA-BLCA samples based on these genes. Our analysis revealed two novel subtypes of bladder cancer with completely different biological characteristics, including immune microenvironment, drug sensitivity, and more. Using machine learning classifiers, we identified SMAD6 as a hub gene contributing to these differences and further investigated the role of SMAD6 in bladder cancer in the single-cell transcriptome data. Additionally, we analyzed the relationship between SMAD6 and immune checkpoint genes. Finally, we performed a series of in vitro assays to verify the function of SMAD6 in bladder cancer cell lines.

RESULTS

We have revealed two novel subtypes of bladder cancer, among which C1 exhibits a worse prognosis, lower drug sensitivity, a more complex tumor microenvironment, and a 'colder' immune microenvironment compared to C2. We identified SMAD6 as a key gene responsible for the differences and further explored its impact on the molecular characteristics of bladder cancer. Through in vitro experiments, we found that SMAD6 promoted the prognosis of BCa patients by inhibiting the proliferation and migration of BCa cells.

CONCLUSION

Our study reveals two novel subtypes of BCa and identifies SMAD6 as a highly promising therapeutic target.

Metallothionein isoforms as double agents - Their roles in carcinogenesis, cancer progression and chemoresistance

Metallothioneins (MTs) are small cysteine-rich intracellular proteins with four major isoforms identified in mammals, designated MT-1 through MT-4. The best known biological functions of MTs are their ability to bind and sequester metal ions as well as their active role in redox homeostasis. Despite these protective roles, numerous studies have demonstrated that changes in MT expression could be associated with the process of carcinogenesis and participation in cell differentiation, proliferation, migration, and angiogenesis. Hence, MTs have the role of double agents, i.e., working with and against cancer. In view of their rich biochemical properties, it is not surprising that MTs participate in the emergence of chemoresistance in tumor cells. Many studies have demonstrated that MT overexpression is involved in the acquisition of resistance to anticancer drugs including cisplatin, anthracyclines, tyrosine kinase inhibitors and mitomycin. The evidence is gradually increasing for a cellular switch in MT functions, showing that they indeed have two faces: protector and saboteur. Initially, MTs display anti-oncogenic and protective roles; however, once the oncogenic process was launched, MTs are utilized by cancer cells for progression, survival, and contribution to chemoresistance. The duality of MTs can serve as a potential prognostic/diagnostic biomarker and can therefore pave the way towards the development of new cancer treatment strategies. Herein, we review and discuss MTs as tumor disease markers and describe their role in chemoresistance to distinct anticancer drugs.

Blood transcriptional and microRNA responses to short-term exposure to disinfection by-products in a swimming pool

BACKGROUND

Swimming in a chlorinated pool results in high exposure levels to disinfection by-products (DBPs), which have been associated with an increased risk of bladder cancer.

OBJECTIVES

By studying molecular responses at the blood transcriptome level we examined the biological processes associated with exposure to these compounds.

METHODS

Whole-genome gene expression and microRNA analysis was performed on blood samples collected from 43 volunteers before and 2h after 40min swimming in an indoor chlorinated pool (PISCINAII study). Exposure to THMs was measured in exhaled breath. Heart rate and kcal expenditure were measured as proxies for physical activity. Associations between exposure levels and gene expression were assessed using multivariate normal models (MVN), correcting for age, body mass index and sex. A Bonferroni threshold at 5% was applied.

RESULTS

MVN-models for the individual exposures identified 1778 genes and 23 microRNAs that were significantly associated with exposure to at least one DBP. Due to co-linearity it was not possible to statistically disentangle responses to DBP exposure from those related to physical activity. However, after eliminating previously reported transcripts associated with physical activity a large number of hits remained associated with DBP exposure. Among those, 9 were linked with bladder and 31 with colon cancer. Concordant microRNA/mRNA expressions were identified in association with DBP exposure for hsa-mir-22-3p and hsa-miR-146a-5p and their targets RCOR1 and TLR4, both related to colon cancer in association with DBP exposure.

CONCLUSIONS

Short-term exposure to low levels of DBPs shows genomics responses that may be indicative of increased cancer risk.

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.

Role of the Glutathione Metabolic Pathway in Lung Cancer Treatment and Prognosis: A Review

Inherent and acquired drug resistance is a cause of chemotherapy failure, and pharmacogenomic studies have begun to define gene variations responsible for varied drug metabolism, which influences drug efficacy. Platinum-based compounds are the most commonly used chemotherapeutic agents in the treatment of advanced stage lung cancer patients, and the glutathione metabolic pathway is directly involved in the detoxification or inactivation of platinum drugs. Consequently, genotypes corresponding to higher drug inactivation enzyme activity may predict poor treatment outcome. Available evidence is consistent with this hypothesis, although a definitive role for glutathione system genes in lung cancer prognosis needs to be elucidated. We present evidence supporting a role of the glutathione system in acquired and inherited drug resistance and/or adverse effects through the impact of either drug detoxification or drug inactivation, thus adversely effecting lung cancer treatment outcome. The potential application of glutathione system polymorphic genetic markers in identifying patients who may respond favorably, selecting effective antitumor drugs, and balancing drug efficacy and toxicity are discussed.

Metallothionein expression as prognostic factor for transitional cell carcinoma of bladder

OBJECTIVES

To determine whether metallothionein (MT) protein expression is associated with clinical outcomes in patients with transitional cell carcinoma (TCC) of the bladder.

METHODS

Archival pathologic radical cystectomy and transurethrally resected specimens and medical charts were reviewed for 123 patients with TCC. Patients were divided into groups based on the TNM stage, tumor grade, and MT protein expression in the primary tumor. Survival and disease progression were correlated with MT expression.

RESULTS

The mean patient age was 66 years (range 41 to 92). Of the 123 tumors, 21, 13, 18, 24, 17, and 30 were pathologically staged as pTa, pT1, pT2, pT3, pT4, and pTis, respectively; 28, 15, 14, and 66 tumors had a histologic grade of X, 1, 2, and 3, respectively. On univariate analysis, TNM stage and tumor grade predicted survival and progression outcomes. MT expression was detected in 69 (56.9%) of 123 bladder cancer specimens. Greater MT protein expression was associated with worse overall survival, disease-specific survival, disease-free survival, and disease-free progression (P = 0.0004, P = 0.05, P = 0.0008, and P = 0.0005, respectively).

CONCLUSIONS

MT protein expression in the primary tumor of TCC specimens appeared to be associated with overall survival, disease-specific survival, disease-free survival, and disease-free progression. This finding requires additional validation using other data sets.

Copper transporters regulate the cellular pharmacology and sensitivity to Pt drugs

Recent studies have demonstrated that the major Cu influx transporter CTR1 regulates tumor cell uptake of cisplatin (DDP), carboplatin (CBDCA) and oxaliplatin (L-OHP), and that the two Cu efflux transporters ATP7A and ATP7B regulate the efflux of these drugs. Evidence for the concept that these platinum (Pt) drugs enter cells and are distributed to various subcellular compartments via transporters that have evolved to manage Cu homeostasis includes the demonstration of: (1) bidirectional cross-resistance between cells selected for resistance to either the Pt drugs or Cu; (2) parallel changes in the transport of Pt and Cu drugs in resistant cells; (3) altered cytotoxic sensitivity and Pt drug accumulation in cells transfected with Cu transporters; and (4) altered expression of Cu transporters in Pt drug-resistant tumors. Appreciation of the role of the Cu transporters in the development of resistance to DDP, CBDCA, and L-OHP offers novel insights into strategies for preventing or reversing resistance to this very important family of anticancer drugs.

Genetic determinants of lung cancer short-term survival: the role of glutathione-related genes

PURPOSE

Survival of lung cancer patients has been dismal. Glutathione enzymes are directly involved in the metabolism of platinum compounds, a group of important chemotherapeutic drugs in cancer treatment. We tested the hypothesis that genes encoding glutathione enzymes may predict lung cancer short-term survival.

METHODS

We studied DNA polymorphisms of 250 primary lung cancer patients at four glutathione-related loci: GSTP1, GSTM1, GSTT1 and gamma-GCS that encode glutathione-S-transferase-pi, glutathione-S-transferase-mu, glutathione-S-transferase-theta, and gamma-glutamylcysteine synthetase, respectively. Pearson's chi(2)-square tests, Kaplan-Meier survival curves, log rank tests, and Cox regression models were applied in the analysis.

RESULTS

There were 150 (60%) men and 100 (40%) women in this study. Seventeen percent of the patients had never smoked cigarettes, and 61% had stopped smoking at least 6 months prior to their lung cancer diagnosis. Among never smokers, those with null (N) or low (L) genotype experienced a better 1-year-survival rate than those with a positive (P) or high (H) genotype. Patients with P or H at two loci (PP or PH) were compared with patients with N or L at one or both loci (other). Among never smokers, 1-year-survival rates were 60-78% for patients with PP or PH genotypes compared with 89-100% for other types. The survival advantage was greater among advanced-stage patients who were NL or NN than low-stage patients. Similar results were not observed among smokers.

CONCLUSIONS

Glutathione-related genes may determine lung cancer survival. Our results, if confirmed, would suggest new directions to enhance cancer treatment, and provide easily measurable markers for clinicians to plan patient-specific therapy.

Cellular resistance to mitomycin C is associated with overexpression of MDR-1 in a urothelial cancer cell line (MGH-U1)

OBJECTIVE

To compare multidrug resistance (MDR)-1 and MDR-3 gene expression in a new urothelial cancer cell line (MGHU-1, with resistance to mitomycin C) against controls and the established (epirubicin-resistant) MDR clone, and to correlate MDR with cytotoxicity data.

MATERIALS AND METHODS

Resistance to mitomycin C was induced by the long-term exposure of wild-type MGHU-1 cells to increasing concentrations (20-400 nmol/L) of mitomycin C. The cytotoxicity of mitomycin C or epirubicin was then compared in MGHU-1, MGHU-MMC (mitomycin C-resistant) and MGHU-1R (established MDR) cells, using the tetrazolium biomass assay. The expression of MDR-1 and -3 was investigated by the reverse transcriptase-polymerase chain reaction, using cDNA-specific primers after titration, and compared with DNA and negative controls.

RESULTS

MDR-1 and -3 were significantly and equally overexpressed in MGHU-1R, and associated with a dramatic increase in the 50% inhibitory drug concentration (P < 0.001) for mitomycin C and epirubicin against controls. In MGHU-MMC, the overexpression of MDR-1 was three times greater than that of MDR-3. The cytotoxicity profile for both agents was very similar to that of MGHU-1R. Trace amounts of MDR-1, but not MDR-3, were identified in the MGHU-1 wild-type.

CONCLUSIONS

Urothelial cancer cell resistance to mitomycin C is associated with cross-resistance to epirubicin and overexpression of MDR-1, suggesting that mitomycin C falls within the MDR category. Clinical application of this methodology may allow patients to be identified who are unlikely to benefit from intravesical chemotherapy.

Characterization of a chlorambucil-resistant human ovarian carcinoma cell line overexpressing glutathione S-transferase mu

Ovarian carcinoma cells 10-fold resistant to the alkylating agent chlorambucil (CBL) were isolated after repeated exposure of the parent cells to gradually escalating concentrations of the drug. The resistant variant, A2780(100), was highly cross-resistant (9-fold) to melphalan and showed lower-level resistance to other cross-linking agents. The resistant A2780(100) cells had almost 5-fold higher glutathione S-transferase (GST) activity than the parental A2780 cells with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. The pi-class GST(s) was the major isoform(s) in both cell lines. However, the resistant A2780(100) cells had at least 11-fold higher GST mu as compared with the parental cells, in which this isoform was barely detectable. A significant induction of GST mu was observed in A2780 cells, but not in the resistant cells, 18 hr after a single exposure to 100 microM CBL. The induction of GST mu by CBL was both time- and concentration-dependent. Assays of the conjugation of CBL with GSH showed that the human mu-class GST had 3.6- and 5.2-fold higher catalytic efficiency relative to the pi- and alpha-class GSTs, respectively. This difference was reflected in the relatively higher (about 6-fold) efficiency of CBL conjugation in A2780(100) cells as compared with the parental cells. These results have demonstrated for the first time a near-linear correlation between CBL resistance and overexpression of mu-class GSTs and suggest that this overexpression maybe responsible, at least in part, for the acquired resistance of ovarian carcinoma cells to CBL, and possibly the other bifunctional alkylating agents. Consistent with this hypothesis, we found evidence for decreased formation of DNA lesions in A2780(100) compared with the drug-sensitive A2780 cells after exposure to CBL.

Effects of the Bowman-Birk inhibitor on clonogenic survival and cisplatin- or radiation-induced cytotoxicity in human breast, cervical, and head and neck cancer cells

Bowman-Birk inhibitor (BBI) is a soybean-derived anticarcinogenic protease inhibitor previously shown to potentiate cisplatin-induced cytoxicity in human lung and ovarian cancer cells. To further assess the potential of BBI as a sensitizing agent for cancer radiotherapy and chemotherapy, we evaluated the effects of BBI and a soybean concentrate enriched in BBI known as BBI concentrate (BBIC) on clonogenic survival and radiation- or cisplatin-induced cell killing in MCF7 human breast carcinoma cells, SCC61 and SQ20B human head and neck carcinoma cells, HeLa, HeLa-R1, and HeLa-R3 human cervical carcinoma cells, MCF10 nontumorigenic human epithelial cells, HTori-3 nontumorigenic human thyroid epithelial cells, and C3H10T1/2 mouse fibroblast cells. BBI and BBIC significantly suppressed the clonogenic survival of MCF7 and SCC61 cells. BBIC also suppressed the survival of SQ20B cells and enhanced radiation-induced cell killing in SCC61 and SQ20B cells and cisplatin-induced cell killing in HeLa, HeLa-R1, and HeLa-R3 cells. In contrast, BBI and/or BBIC did not enhance radiation-induced cell killing in MCF10 cells or cisplatin-induced cell killing in C3H10T1/2 cells. BBI did not significantly affect the survival of SQ20B cells or enhance radiation-induced cell killing in SCC61 and SQ20B cells. The clonogenic survivals of MCF10 and C3H10T1/2 cells were not adversely affected by treatment with BBI or BBIC. The clonogenic survival of HTori-3 cells was only moderately suppressed by treatment with BBIC at > or = 80 micrograms/ml. These results suggest that BBIC could be a useful agent for the potentiation of radiation- and cisplatin-mediated cancer treatment without significant adverse effects on surrounding normal tissues.

Intracochlear infusion of buthionine sulfoximine potentiates carboplatin ototoxicity in the chinchilla

The aim of this experiment was to determine if buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, enhances the ototoxicity of carboplatin. Osmotic pumps were used to infuse BSO into the right cochleas of 12 adult chinchillas for 14 days. The left cochleas served as controls. Animals were assigned to three groups: a drug control group that did not receive carboplatin, a group that received a single dose of carboplatin (25 mg/kg i.p.), and a group that received a double dose of carboplatin (25 mg/kg i.p. x 2), with 4 days between injections. Carboplatin was administered after three days of BSO pre-treatment. Ototoxicity was assessed with evoked potentials recorded from electrodes implanted in the inferior colliculi (ICPs), distortion product otoacoustic emissions (DPOAEs), and cochleograms. BSO infusion itself caused no long-term functional or morphological changes. One of four animals treated with it single dose of carboplatin showed a significant loss of inner hair cells (IHCs), with greater loss in the BSO-treated ear. All animals in the double-dose carboplatin group showed marked differences between BSO-treated and control ears. Average IHC losses were 59% in BSO-treated ears vs. 18% in control ears. Moreover, BSO-treated ears sustained significantly greater outer hair cell (OHC) losses than control ears (37% vs. 2%, respectively). ICP and DPOAE response amplitudes were reduced slightly in BSO-treated ears relative to control ears, consistent with their greater hair cell loss. The results clearly show that BSO can enhance carboplatin ototoxicity in the chinchilla, supporting a role of GSH and reactive oxygen species in platinum ototoxicity.

Growth inhibition and cytotoxicity induced by Bowman-Birk inhibitor concentrate in cisplatin-resistant human ovarian cancer cells

Bowman-Birk inhibitor (BBI) is a soybean-derived anticarcinogenic protease inhibitor that was shown to potentiate the cytotoxicity of cisplatin in our previous studies. To assess the potential of BBI as a sensitizing agent for the chemotherapy of cisplatin-resistant cancers, we evaluated the effects of a soybean concentrate enriched in BBI (known as BBI concentrate or BBIC) on cell growth and clonogenic survival of a human ovarian cancer cell line, A2780, and its cisplatin-resistant sublines, C30, and C200. The presence of BBI and BBIC in the cell culture, medium reduced the clonogenic survival of the A2780, C30, and C200 cells in a dose-dependent manner and enhanced cisplatin-induced growth inhibition and/or cytotoxicity. BBIC alone showed greater inhibitory effects on growth in the cisplatin-resistant cell lines. These results suggest that BBI and BBIC could be useful agents for the treatment of cancers, especially with cisplatin, in tumors resistant to this important anticancer agent.

Biochemical characterization of a mitomycin C-resistant human bladder cancer cell line

This study describes characteristics of a mitomycin C (MMC)-resistant human bladder cancer cell line, J82/MMC-2, which was established by repeated in vitro exposures of a 6-fold MMC-resistant variant (J82/MMC) to 18 nM MMC. A 9.6-fold higher concentration of MMC was required to kill 50% of the J82/MMC-2 sub-line compared with parental cells (J82/WT). NADPH cytochrome P450 reductase and DT-diaphorase activities were significantly lower in J82/MMC-2 cells compared with J82/WT, suggesting that reduced sensitivity of J82/MMC-2 cells to MMC resulted from impaired drug activation. Consistent with this hypothesis, the formation of MMC-alkylating metabolites was significantly lower in J82/MMC-2 cells compared with J82/WT. Furthermore, DT-diaphorase activity in J82/MMC-2 cells was significantly lower compared with the 6-fold MMC-resistant variant. Glutathione (GSH) levels were comparable in all 3 cell lines. Although GSH transferase (GST) activity was significantly higher in the J82/MMC-2 cells compared with J82/WT, this enzyme activity did not differ between 6- and 9.6-fold MMC-resistant variants. Whereas DNA polymerase alpha mRNA expression was comparable in these cell lines, levels of DNA ligase I mRNA were slightly lower in both MMC-resistant variants relative to J82/WT. However, the DNA polymerase beta mRNA level was markedly higher in the J82/MMC-2 cell line compared with either J82/WT or J82/MMC. Thus, emergence of a higher level of resistance to MMC in J82/MMC-2 cells compared with J82/MMC may be attributed to (i) impaired drug activation through further reduction in DT-diaphorase activity and (ii) enhanced DNA repair through over-expression of DNA polymerase beta.