Spontaneous development of drug resistance: mismatch repair and p53 defects in resistance to cisplatin in human tumor cells

Mechanism of cisplatin resistance in gastric cancer and associated microRNAs

Gastric cancer (GC) is a common malignant tumor with high morbidity and mortality rates that seriously affects human health worldwide. Although surgery is currently the preferred clinical treatment for GC, chemotherapy remains the first choice for perioperative treatment, adjuvant therapy, and palliative care for patients with advanced GC. Cisplatin (DDP) is an antineoplastic agent that has been used clinically for decades, and it is the first-line chemotherapy for many solid tumors. However, the therapeutic efficacy of DDP is often limited by resistance and the complexity of its resistance mechanisms, which involve multiple proteins and signaling pathways. It is well documented that a variety of microRNAs (miRNAs) differentially expressed in DDP-resistant GC cells play important roles in regulating or reversing DDP resistance via various pathways. In this review, we first provide an introduction to the cytotoxicity and major resistance mechanisms of DDP in GC and then discuss the role and mechanism of miRNAs in regulating the DDP resistance process in GC cells. This work demonstrates the potential of relevant miRNAs to become diagnostic and prognostic biomarkers for gastric cancer and targets of action to enhance chemosensitivity and provides directions for future research.

USP39 attenuates the antitumor activity of cisplatin on colon cancer cells dependent on p53

Cisplatin is the effective chemotherapeutic drug in colon cancer treatment, but its therapeutic efficacy is limited by intrinsic or acquired drug resistance and detrimental side effects. Therefore, improving the effect of cisplatin chemotherapy remains a great challenge. The previous study identified that USP39 was relevant to cisplatin resistance of lung cancer. However, the function and mechanisms of USP39 regulating the chemosensitivity of cisplatin in colorectal cancer remain unclear. In this study, we reveal that USP39 is associated with colon cancer cells sensitivity to cisplatin. Depletion of USP39 enhances the cisplatin-induced apoptosis in HCT116 cells. Conversely, overexpression of USP39 attenuates apoptosis in RKO cells. Furthermore, we demonstrate that USP39 depletion promotes apoptosis induced by cisplatin, which is related with the induction of oxidative stress and DNA damage response. Further studies show that USP39 regulates cisplatin-induced apoptosis dependent on p53. The underlying mechanism is demonstrated by knocking down USP39, that results in p53 upregulation, associated with its prolonged half-life. Collectively, our findings reveal that USP39 might be a negative factor of the p53 mediated cisplatin sensitivity of colon cancer, and suggest USP39 as a potential molecular target for cisplatin chemotherapy of colon cancer.

Biomarkers for chemotherapy and drug resistance in the mismatch repair pathway

Drugs targeting DNA repair have developed rapidly in cancer therapy, and numerous inhibitors have already been utilized in preclinical and clinical stages. To optimize the selection of patients for treatment, it is essential to discover biomarkers to anticipate chemotherapy response. The DNA mismatch repair (MMR) pathway is closely correlated with cancer susceptibility and plays an important role in the occurrence and development of cancers. Here, we give a concise introduction of the MMR genes and focus on the potential biomarkers of chemotherapeutic response and resistance. It has been clarified that the status of MMR may affect the outcome of chemotherapy. However, the specific underlying mechanisms as well as contradictory results continue to raise considerable controversy and concern. In this review, we summarize the current literature to provide a general overview.

Preparation of PCL Electrospun Fibers Loaded with Cisplatin and Their Potential Application for the Treatment of Prostate Cancer

Prostate cancer is a global fatal type of cancer. It is a type of cancer that affect men. Signs and symptoms of the disease include blood in the urine, pain when one micturates, and difficulties in penis erection. Cisplatin chemotherapy is a principal treatment normally given to the prostate cancer patients. Nonetheless, on its own, cisplatin loses efficacy once administered due to liver pass effects and other biochemical attacks. In this paper, we looked at preparation of PCL nanoparticles loaded with cisplatin and their potential for the treatment of prostate cancer. PCL nanoparticles protect cisplatin from biochemical attack, thus increasing drug efficacy. Incorporation of P-glycoprotein inhibitors in PCL nanoparticles (NPs) loaded with cisplatin could improve prostate cancer treatment even more.

Molecular mechanisms of chemo- and radiotherapy resistance and the potential implications for cancer treatment

Cancer is a leading cause of death worldwide. Surgery is the primary treatment approach for cancer, but the survival rate is very low due to the rapid progression of the disease and presence of local and distant metastasis at diagnosis. Adjuvant chemotherapy and radiotherapy are important components of the multidisciplinary approaches for cancer treatment. However, resistance to radiotherapy and chemotherapy may result in treatment failure or even cancer recurrence. Radioresistance in cancer is often caused by the repair response to radiation-induced DNA damage, cell cycle dysregulation, cancer stem cells (CSCs) resilience, and epithelial-mesenchymal transition (EMT). Understanding the molecular alterations that lead to radioresistance may provide new diagnostic markers and therapeutic targets to improve radiotherapy efficacy. Patients who develop resistance to chemotherapy drugs cannot benefit from the cytotoxicity induced by the prescribed drug and will likely have a poor outcome with these treatments. Chemotherapy often shows a low response rate due to various drug resistance mechanisms. This review focuses on the molecular mechanisms of radioresistance and chemoresistance in cancer and discusses recent developments in therapeutic strategies targeting chemoradiotherapy resistance to improve treatment outcomes.

Irinotecan or Oxaliplatin: Which is the First Move for the Mate?

OBJECTIVES

The aim of the present review is to discuss the potential link between RAS, BRAF and microsatellite instability (MSI) mutational patterns and chemotherapeutic agent efficacy [Irinotecan (IRI) vs. Oxaliplatin (OXA)], and how this can potentially influence the choice of the chemotherapy backbone.

METHODS

Following a review of the research literature, all pertinent articles published in the core journals were selected for the study. The inclusion criteria regarded relevant clinical and pre-clinical studies on the topic of interest (Relationship of OXA and IRI to KRAS/BRAF mutations and MSI).

RESULTS

Excision repair cross complementation group 1 (ERCC1) expression is inhibited by KRAS mutation, making tumor cells more sensitive to OXA. Results from OPUS, COIN and PRIME trials support that no conclusive data are available for BRAF mutant population because of the small number of patients. Enhanced IRI cytotoxicity to MSI cell lines is due to the participation of some of the mismatch repair (MMR) components in various DNA repair processes and their role in the maintenance of the pro-apoptotic effect of IRI and G2/M cell arrest.

CONCLUSION

OXA and IRI are indispensable drugs for mCRC treatment and their selection must be as careful as that of targeted agents. We suggest taking into consideration the interaction between known genomic alterations and OXA and IRI activity to personalize chemotherapy in mCRC patients.

Platinum Complexes in Colorectal Cancer and Other Solid Tumors

Simple Summary

Cisplatin is successfully used for the treatment of various solid cancers. Unfortunately, it shows no activity in colorectal cancer. The resistance phenotype of colorectal cancer cells is mainly caused by alterations in p53-controlled DNA damage signaling and/or defects in the cellular mismatch repair pathway. Improvement of platinum-based chemotherapy in cisplatin-unresponsive cancers, such as colorectal cancer, might be achieved by newly designed cisplatin analogues, which retain activity in unresponsive tumor cells. Moreover, a combination of cisplatin with biochemical modulators of DNA damage signaling might sensitize cisplatin-resistant tumor cells to the drug, thus providing another strategy to improve cancer therapy.

Abstract

Cisplatin is one of the most commonly used drugs for the treatment of various solid neoplasms, including testicular, lung, ovarian, head and neck, and bladder cancers. Unfortunately, the therapeutic efficacy of cisplatin against colorectal cancer is poor. Various mechanisms appear to contribute to cisplatin resistance in cancer cells, including reduced drug accumulation, enhanced drug detoxification, modulation of DNA repair mechanisms, and finally alterations in cisplatin DNA damage signaling preventing apoptosis in cancer cells. Regarding colorectal cancer, defects in mismatch repair and altered p53-mediated DNA damage signaling are the main factors controlling the resistance phenotype. In particular, p53 inactivation appears to be associated with chemoresistance and poor prognosis. To overcome resistance in cancers, several strategies can be envisaged. Improved cisplatin analogues, which retain activity in resistant cancer, might be applied. Targeting p53-mediated DNA damage signaling provides another therapeutic strategy to circumvent cisplatin resistance. This review provides an overview on the DNA repair pathways involved in the processing of cisplatin damage and will describe signal transduction from cisplatin DNA lesions, with special attention given to colorectal cancer cells. Furthermore, examples for improved platinum compounds and biochemical modulators of cisplatin DNA damage signaling will be presented in the context of colon cancer therapy.

Links between cancer metabolism and cisplatin resistance

Cisplatin is one of the most potent and widely used chemotherapeutic agent in the treatment of several solid tumors, despite the high toxicity and the frequent relapse of patients due to the onset of drug resistance. Resistance to chemotherapeutic agents, either intrinsic or acquired, is currently one of the major problems in oncology. Thus, understanding the biology of chemoresistance is fundamental in order to overcome this challenge and to improve the survival rate of patients. Studies over the last 30 decades have underlined how resistance is a multifactorial phenomenon not yet completely understood. Recently, tumor metabolism has gained a lot of interest in the context of chemoresistance; accumulating evidence suggests that the rearrangements of the principal metabolic pathways within cells, contributes to the sensitivity of tumor to the drug treatment. In this review, the principal metabolic alterations associated with cisplatin resistance are highlighted. Improving the knowledge of the influence of metabolism on cisplatin response is fundamental to identify new possible metabolic targets useful for combinatory treatments, in order to overcome cisplatin resistance.

SERCA and P-glycoprotein inhibition and ATP depletion are necessary for celastrol-induced autophagic cell death and collateral sensitivity in multidrug-resistant tumor cells

Multidrug resistance (MDR) represents an obstacle in anti-cancer therapy. MDR is caused by multiple mechanisms, involving ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp), which reduces intracellular drug levels to sub-therapeutic concentrations. Therefore, sensitizing agents retaining effectiveness against apoptosis- or drug-resistant cancers are desired for the treatment of MDR cancers. The sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) pump is an emerging target to overcome MDR, because of its continuous expression and because the calcium transport function is crucial to the survival of tumor cells. Previous studies showed that SERCA inhibitors exhibit anti-cancer effects in Bax-Bak-deficient, apoptosis-resistant and MDR cancers, whereas specific P-gp inhibitors reverse the MDR phenotype of cancer cells by blocking efflux of chemotherapeutic agents. Here, we unraveled SERCA and P-gp as double targets of the triterpenoid, celastrol to reverse MDR. Celastrol inhibited both SERCA and P-gp to stimulate calcium-mediated autophagy and ATP depletion, thereby induced collateral sensitivity in MDR cancer cells. In vivo studies further confirmed that celastrol suppressed tumor growth and metastasis by SERCA-mediated calcium mobilization. To the best of our knowledge, our findings demonstrate collateral sensitivity in MDR cancer cells by simultaneous inhibition of SERCA and P-gp for the first time.

Coexisting Molecular Determinants of Acquired Oxaliplatin Resistance in Human Colorectal and Ovarian Cancer Cell Lines

Oxaliplatin (OHP) treatment of colorectal cancer (CRC) frequently leads to resistance. OHP resistance was induced in CRC cell lines LoVo-92 and LoVo-Li and a platinum-sensitive ovarian cancer cell line, A2780, and related to cellular platinum accumulation, platinum-DNA adducts, transporter expression, DNA repair genes, gene expression arrays, and array-CGH profiling. Pulse (4 h, 4OHP) and continuous exposure (72 h, cOHP) resulted in 4.0 to 7.9-fold and 5.0 to 11.8-fold drug resistance, respectively. Cellular oxaliplatin accumulation and DNA-adduct formation were decreased and related to OCT1-3 and ATP7A expression. Gene expression profiling and pathway analysis showed significantly altered p53 signaling, xenobiotic metabolism, role of BRCA1 in DNA damage response, and aryl hydrocarbon receptor signaling pathways, were related to decreased ALDH1L2, Bax, and BBC3 (PUMA) and increased aldo-keto reductases C1 and C3. The array-CGH profiles showed focal aberrations. In conclusion, OHP resistance was correlated with total platinum accumulation and OCT1-3 expression, decreased proapoptotic, and increased anti-apoptosis and homologous repair genes.

DNA damage response and repair in ovarian cancer: Potential targets for therapeutic strategies

Ovarian cancer is among the most lethal gynecologic malignancies with a poor survival prognosis. The current therapeutic strategies involve surgery and chemotherapy. Research is now focused on novel agents especially those targeting DNA damage response (DDR) pathways. Understanding the DDR process in ovarian cancer necessitates having a detailed knowledge on a series of signaling mediators at the cellular and molecular levels. The complexity of the DDR process in ovarian cancer and how this process works in metastatic conditions is comprehensively reviewed. For evaluating the efficacy of therapeutic agents targeting DNA damage in ovarian cancer, we will discuss the components of this system including DDR sensors, DDR transducers, DDR mediators, and DDR effectors. The constituent pathways include DNA repair machinery, cell cycle checkpoints, and apoptotic pathways. We also will assess the potential of active mediators involved in the DDR process such as therapeutic and prognostic candidates that may facilitate future studies.

DNA damage repair in ovarian cancer: unlocking the heterogeneity

Treatment for advanced ovarian cancer is rarely curative; three quarters of patients with advanced disease relapse and ultimately die with resistant disease. Improving patient outcomes will require the introduction of new treatments and better patient selection. Abrogations in the DNA damage response (DDR) may allow such stratifications.

A defective DNA-damage response (DDR) is a defining hallmark of high grade serous ovarian cancer (HGSOC). Indeed, current evidence indicates that all HGSOCs harbour a defect in at least one major DDR pathway. However, defective DDR is not mediated through a single mechanism but rather results from a variety of (epi)genetic lesions affecting one or more of the five major DNA repair pathways. Understanding the relationship between these pathways and how these are abrogated will be necessary in order to facilitate appropriate selection of both existing and novel agents.

Here we review the current understanding of the DDR with regard to ovarian, and particularly high grade serous, cancer, with reference to existing and emerging treatments as appropriate.

DNA damage repair in ovarian cancer: unlocking the heterogeneity

Treatment for advanced ovarian cancer is rarely curative; three quarters of patients with advanced disease relapse and ultimately die with resistant disease. Improving patient outcomes will require the introduction of new treatments and better patient selection. Abrogations in the DNA damage response (DDR) may allow such stratifications.A defective DNA-damage response (DDR) is a defining hallmark of high grade serous ovarian cancer (HGSOC). Indeed, current evidence indicates that all HGSOCs harbour a defect in at least one major DDR pathway. However, defective DDR is not mediated through a single mechanism but rather results from a variety of (epi)genetic lesions affecting one or more of the five major DNA repair pathways. Understanding the relationship between these pathways and how these are abrogated will be necessary in order to facilitate appropriate selection of both existing and novel agents.Here we review the current understanding of the DDR with regard to ovarian, and particularly high grade serous, cancer, with reference to existing and emerging treatments as appropriate.

DNA damage repair in ovarian cancer: unlocking the heterogeneity

Treatment for advanced ovarian cancer is rarely curative; three quarters of patients with advanced disease relapse and ultimately die with resistant disease. Improving patient outcomes will require the introduction of new treatments and better patient selection. Abrogations in the DNA damage response (DDR) may allow such stratifications.A defective DNA-damage response (DDR) is a defining hallmark of high grade serous ovarian cancer (HGSOC). Indeed, current evidence indicates that all HGSOCs harbour a defect in at least one major DDR pathway. However, defective DDR is not mediated through a single mechanism but rather results from a variety of (epi)genetic lesions affecting one or more of the five major DNA repair pathways. Understanding the relationship between these pathways and how these are abrogated will be necessary in order to facilitate appropriate selection of both existing and novel agents.Here we review the current understanding of the DDR with regard to ovarian, and particularly high grade serous, cancer, with reference to existing and emerging treatments as appropriate.

Asplatin enhances drug efficacy by altering the cellular response

Aspirin, a widely used anti-inflammatory drug, has been shown to be effective for the prevention and remission of cancers (Science, 2012, 337(21) 1471-1473). Asplatin, a Pt(iv) prodrug of cisplatin with the ligation of aspirin (c,c,t-[PtCl2(NH3)2(OH)(aspirin)]), demonstrates significantly higher cytotoxicity than cisplatin towards tumor cells and almost fully overcomes the drug resistance of cisplatin resistant cells. In this work, we have studied the molecular mechanism of asplatin by investigating the cellular response to this compound in order to understand the prominent inhibitory effect on the proliferation of cancer cells. The apoptosis analyses and the related gene expression measurements show that aspirin released from asplatin significantly modulates the cellular response to the platinum agent. Asplatin promotes the apoptosis via the BCL-2 associated mitochondrial pathway. The down-regulation of BCL-2 along with the up-regulation of BAX and BAK enhances the mitochondrial outer membrane permeability, resulting in the cytochrome c release from mitochondria into the cytosol. This event promotes the apoptosis by activation of caspase processing. Consequently, the ligation of aspirin significantly enhances the drug efficacy of the platinum complex in the low micromolar range. The alteration of the cellular response is probably responsible for the circumvention of the cisplatin resistance by asplatin. These results provide an insight into the mechanism of asplatin and provide information for designing new classic platinum drugs.

Cooperation of Musashi-2, Numb, MDM2, and P53 in drug resistance and malignant biology of pancreatic cancer

Our earlier work showed that Musashi (MSI)-2 promoted the development of pancreatic cancer (PC) by down-regulating Numb, which prevented murine double-minute (MDM)-2-mediated p53 ubiquitin degradation. Thus, we investigate the relationship among MSI2, Numb, MDM2, and p53 in PC in vitro and invivo, an association that has not been reported to our knowledge. MSI2 had no relationship with mutant p53 (mtp53) and wild-type p53 (wtp53) in normal PC cells. However, in response to gemcitabine or cisplatin treatment, MSI2 silencing simultaneously down-regulated MDM2 and up-regulated Numb and wtp53 protein levels. Moreover, these 4 endogenous proteins can be coimmunoprecipitated as a quaternary complex. Numb small interfering RNA (siRNA) reversed the MSI2 silencing-induced p53 increase. During treatment with chemical agents, MSI2 silencing decreased drug resistance and cell motility in vitro and inhibited tumor growth in vivo, all of which were significantly reversed by p53 siRNA. MSI2 was also negatively associated with Numb and positively associated with MDM2 expression in tissue. Overexpression of MSI2, MDM2, and mtp53 and weak expression of Numb were closely associated with aggressive clinicopathologic characteristics and poor prognosis for patients with PC. MSI2 negatively regulates wtp53 protein by up-regulating MDM2 and down-regulating Numb after treatment with chemical agents. MSI2 promotes drug resistance and malignant biology of PC in a p53-dependent manner.-Sheng, W., Dong, M., Chen, C., Wang, Z., Li, Y., Wang, K., Li, Y., Zhou, J. Cooperation of Musashi-2, Numb, MDM2, and P53 in drug resistance and malignant biology of pancreatic cancer.

[50th anniversary of cisplatin]

We have just celebrated the 50th anniversary of cisplatin cytotoxic potential discovery. It is time to take stock… and it seems mainly positive. This drug, that revolutionized the treatment of many cancer types, continues to be the most widely prescribed chemotherapy. Despite significant toxicities, resistance mechanisms associated with treatment failures, and unresolved questions about its mechanism of action, the use of this cytotoxic agent remains unwavering. The interest concerning this "old" invincible drug has not yet abated. Indeed many research axes are in the news. New platinum salts agents are tested, new cisplatin formulations are developed to target tumor cells more efficiently, and new combinations are established to increase the cytotoxic potency of cisplatin or overcome the resistance mechanisms.

Upregulation of p27Kip1 by demethylation sensitizes cisplatin-resistant human ovarian cancer SKOV3 cells

Ovarian cancer has a poor prognosis due to its chemoresistance, and p27Kip1 (p27) has been implicated in tumor prognosis and drug-resistance. However, the regulatory mechanisms of p27 in drug‑resistance in ovarian cancer remain unknown. The current study successfully established chemoresistant cell lines using paclitaxel (TAX), cisplatin (DDP) and carboplatin (CBP) in SKOV3 ovarian cancer cells. The results indicated that the expression levels of p27 were dramatically downregulated in chemoresistant cells. However, 5-aza-2'-deoxycytidine (5-aza) treatment restored p27 expression in DDP-resistant cells, and increased their sensitivity to DDP. In addition, it was observed that the methylation of DDP‑resistant cells, which was downregulated by 5‑aza treatment, was significantly higher compared with SKOV3 cells. Additionally, the overexpression of p27 arrested the cell cycle in S phase and promoted an apoptotic response to DDP. In conclusion, p27 was involved in chemoresistance of SKOV3 cells. Upregulated p27 expression induced by demethylation may enhance sensitivity to DDP through the regulation of the cell cycle.

MiRNA Transcriptome Profiling of Spheroid-Enriched Cells with Cancer Stem Cell Properties in Human Breast MCF-7 Cell Line

Breast cancer is the second leading cause of cancer-related mortality worldwide as most patients often suffer cancer relapse. The reason is often attributed to the presence of cancer stem cells (CSCs). Recent studies revealed that dysregulation of microRNA (miRNA) are closely linked to breast cancer recurrence and metastasis. However, no specific study has comprehensively characterised the CSC characteristic and miRNA transcriptome in spheroid-enriched breast cells. This study described the generation of spheroid MCF-7 cell in serum-free condition and the comprehensive characterisation for their CSC properties. Subsequently, miRNA expression differences between the spheroid-enriched CSC cells and their parental cells were evaluated using next generation sequencing (NGS). Our results showed that the MCF-7 spheroid cells were enriched with CSCs properties, indicated by the ability to self-renew, increased expression of CSCs markers, and increased resistance to chemotherapeutic drugs. Additionally, spheroid-enriched CSCs possessed greater cell proliferation, migration, invasion, and wound healing ability. A total of 134 significantly (p<0.05) differentially expressed miRNAs were identified between spheroids and parental cells using miRNA-NGS. MiRNA-NGS analysis revealed 25 up-regulated and 109 down-regulated miRNAs which includes some miRNAs previously reported in the regulation of breast CSCs. A number of miRNAs (miR-4492, miR-4532, miR-381, miR-4508, miR-4448, miR-1296, and miR-365a) which have not been previously reported in breast cancer were found to show potential association with breast cancer chemoresistance and self-renewal capability. The gene ontology (GO) analysis showed that the predicted genes were enriched in the regulation of metabolic processes, gene expression, DNA binding, and hormone receptor binding. The corresponding pathway analyses inferred from the GO results were closely related to the function of signalling pathway, self-renewability, chemoresistance, tumorigenesis, cytoskeletal proteins, and metastasis in breast cancer. Based on these results, we proposed that certain miRNAs identified in this study could be used as new potential biomarkers for breast cancer stem cell diagnosis and targeted therapy.

Approaches to diagnose DNA mismatch repair gene defects in cancer

The DNA repair pathway mismatch repair (MMR) is responsible for the recognition and correction of DNA biosynthetic errors caused by inaccurate nucleotide incorporation during replication. Faulty MMR leads to failure to address the mispairs or insertion deletion loops (IDLs) left behind by the replicative polymerases and results in increased mutation load at the genome. The realization that defective MMR leads to a hypermutation phenotype and increased risk of tumorigenesis highlights the relevance of this pathway for human disease. The association of MMR defects with increased risk of cancer development was first observed in colorectal cancer patients that carried inactivating germline mutations in MMR genes and the disease was named as hereditary non-polyposis colorectal cancer (HNPCC). Currently, a growing list of cancers is found to be MMR defective and HNPCC has been renamed Lynch syndrome (LS) partly to include the associated risk of developing extra-colonic cancers. In addition, a number of non-hereditary, mostly epigenetic, alterations of MMR genes have been described in sporadic tumors. Besides conferring a strong cancer predisposition, genetic or epigenetic inactivation of MMR genes also renders cells resistant to some chemotherapeutic agents. Therefore, diagnosis of MMR deficiency has important implications for the management of the patients, the surveillance of their relatives in the case of LS and for the choice of treatment. Some of the alterations found in MMR genes have already been well defined and their pathogenicity assessed. Despite this substantial wealth of knowledge, the effects of a large number of alterations remain uncharacterized (variants of uncertain significance, VUSs). The advent of personalized genomics is likely to increase the list of VUSs found in MMR genes and anticipates the need of diagnostic tools for rapid assessment of their pathogenicity. This review describes current tools and future strategies for addressing the relevance of MMR gene alterations in human disease.

Anti-apoptotic brain and reproductive organ-expressed proteins enhance cisplatin resistance in lung cancer cells via the protein kinase B signaling pathway

Background

Cisplatin‐based chemotherapy is the standard first‐line treatment for non‐small‐cell lung cancers (NSCLCs); however, the long‐term therapeutic effect is reduced by chemoresistance. Brain and reproductive organ‐expressed (BRE) proteins are overexpressed in several cancers and have an anti‐apoptotic function. However, their biological role in the development of the chemoresistant phenotype of human NSCLC remains unknown. We investigate the differential expression of the BRE gene in human lung adenocarcinoma cell lines A549 and the cisplatin‐resistant variant A549/cisplatin (DDP), and the mechanisms of cisplatin‐resistance induced by the BRE gene.

Methods

Cell counting kit‐8 assay was employed to determine the sensitivity of A549 and A549/DDP cell lines to cisplatin. BRE expression was measured using quantitative real time‐polymerase chain reaction and western blot analysis. The apoptosis rate of lung adenocarcinoma cells was determined by flow cytometry.

Results

BRE expression in A549 cells, derived from human lung cells, was markedly decreased compared with parental cisplatin‐resistant A549/DDP cells at messenger ribonucleic acid and protein levels. BRE overexpression in A549 significantly decreased sensitivity to DDP by inhibiting cell apoptosis. Conversely, BRE knockdown in A549/DDP cells increased their chemosensitivity. Importantly, we demonstrate that BRE overexpression induces the expression of phosphoprotein kinase B (p‐Akt) in lung cancer cells, while BRE silencing inhibits p‐Akt expression. Furthermore, downregulation of p‐Akt by LY294002 reversed the DDP resistance induced by BRE by increasing apoptosis. BRE enhances the DDP resistance of lung cancer cells through the Akt signaling pathway.

Conclusion

Our findings provide new insight into the mechanism of DDP resistance in NSCLC cells and suggest BRE as an attractive new target for NSCLC treatment.

DNA methylation changes in epithelial ovarian cancer histotypes

Survival after a diagnosis of ovarian cancer has not improved, and despite histological differences, treatment is similar for all cases. Understanding the molecular basis for ovarian cancer risk and prognosis is fundamental, and to this end much has been gleaned about genetic changes contributing to risk, and to a lesser extent, survival. There's considerable evidence for genetic differences between the four pathologically defined histological subtypes; however, the contribution of epigenetics is less well documented. In this report, we review alterations in DNA methylation in ovarian cancer, focusing on histological subtypes, and studies examining the roles of methylation in determining therapy response. As epigenetics is making its way into clinical care, we review the application of cell free DNA methylation to ovarian cancer diagnosis and care. Finally, we comment on recurrent limitations in the DNA methylation literature for ovarian cancer, which can and should be addressed to mature this field.

The role of DNA repair pathways in cisplatin resistant lung cancer

Platinum chemotherapeutic agents such as cisplatin are currently used in the treatment of various malignancies such as lung cancer. However, their efficacy is significantly hindered by the development of resistance during treatment. While a number of factors have been reported that contribute to the onset of this resistance phenotype, alterations in the DNA repair capacity of damaged cells is now recognised as an important factor in mediating this phenomenon. The mode of action of cisplatin has been linked to its ability to crosslink purine bases on the DNA, thereby interfering with DNA repair mechanisms and inducing DNA damage. Following DNA damage, cells respond by activating a DNA-damage response that either leads to repair of the lesion by the cell thereby promoting resistance to the drug, or cell death via activation of the apoptotic response. Therefore, DNA repair is a vital target to improving cancer therapy and reduce the resistance of tumour cells to DNA damaging agents currently used in the treatment of cancer patients. To date, despite the numerous findings that differential expression of components of the various DNA repair pathways correlate with response to cisplatin, translation of such findings in the clinical setting are still warranted. The identification of alterations in specific proteins and pathways that contribute to these unique DNA repair pathways in cisplatin resistant cancer cells may potentially lead to a renewed interest in the development of rational novel therapies for cisplatin resistant cancers, in particular, lung cancer.

The expression of p21 is upregulated by forkhead box A1/2 in p53-null H1299 cells

The expression of the cell cycle inhibitor p21 is increased in response to various stimuli and stress signals through p53-dependent and independent pathways. We demonstrate in this study that forkhead box A1/2 (FOXA1/2) is a crucial transcription factor in the activation of p21 transcription via direct binding to the p21 promoter in p53-null H1299 lung carcinoma cells. In addition, histone deacetylase inhibitor trichostatin A (TSA)-mediated upregulation of p21 expression was repressed by knockdown of FOXA1/2 in H1299 cells. Consequently, these results suggest that FOXA1/2 is required for p53-independent p21 expression.

Antitumor effects of a novel small molecule targeting PCNA chromatin association in prostate cancer

Proliferating cell nuclear antigen (PCNA) plays an essential role in DNA replication and repair. Tumor cells express high levels of PCNA, identifying it as a potentially ideal target for cancer therapy. Previously, we identified nine compounds termed PCNA inhibitors (PCNA-Is) that bind directly to PCNA, stabilize PCNA trimer structure, reduce chromatin-associated PCNA, and selectively inhibit tumor cell growth. Of these compounds, PCNA-I1 is most potent. The purposes of this study were to further investigate the effects of targeting PCNA chromatin association on DNA damage and cytotoxicity and to evaluate the therapeutic potential of PCNA-I1 against tumors in mice. Given the important roles of tumor suppressor p53 in regulating sensitivity of tumor cells to chemotherapeutics, we performed studies in two human prostate cancer cell lines differing in p53 expression: LNCaP cells (wild-type p53) and PC-3 cells (p53-null). PCNA-I1 induced DNA damage and apoptosis in both LNCaP and PC-3 cells and enhanced DNA damage and apoptosis triggered by cisplatin. PCNA-I1 also induced autophagy in PC-3 cells. A short-term pretreatment with PCNA-I1 reduced colony formation by 50% in both cell lines. These data suggest that, unlike many other cytotoxic drugs, the effects of PCNA-I1 on tumor cells do not depend on expression of p53. Intravenous administrations of PCNA-I1 significantly retarded growth of LNCaP tumors of in nude mice without causing detectable effects on mouse body weight and hematology profiles. These data provide proof of concept that targeting PCNA chromatin association could be a novel and effective therapeutic approach for treatment of cancer.

Systems biology of cisplatin resistance: past, present and future

The platinum derivative cis-diamminedichloroplatinum(II), best known as cisplatin, is currently employed for the clinical management of patients affected by testicular, ovarian, head and neck, colorectal, bladder and lung cancers. For a long time, the antineoplastic effects of cisplatin have been fully ascribed to its ability to generate unrepairable DNA lesions, hence inducing either a permanent proliferative arrest known as cellular senescence or the mitochondrial pathway of apoptosis. Accumulating evidence now suggests that the cytostatic and cytotoxic activity of cisplatin involves both a nuclear and a cytoplasmic component. Despite the unresolved issues regarding its mechanism of action, the administration of cisplatin is generally associated with high rates of clinical responses. However, in the vast majority of cases, malignant cells exposed to cisplatin activate a multipronged adaptive response that renders them less susceptible to the antiproliferative and cytotoxic effects of the drug, and eventually resume proliferation. Thus, a large fraction of cisplatin-treated patients is destined to experience therapeutic failure and tumor recurrence. Throughout the last four decades great efforts have been devoted to the characterization of the molecular mechanisms whereby neoplastic cells progressively lose their sensitivity to cisplatin. The advent of high-content and high-throughput screening technologies has accelerated the discovery of cell-intrinsic and cell-extrinsic pathways that may be targeted to prevent or reverse cisplatin resistance in cancer patients. Still, the multifactorial and redundant nature of this phenomenon poses a significant barrier against the identification of effective chemosensitization strategies. Here, we discuss recent systems biology studies aimed at deconvoluting the complex circuitries that underpin cisplatin resistance, and how their findings might drive the development of rational approaches to tackle this clinically relevant problem.

[Expression and significance of IKBKB in pulmonary adenocarcinoma A549 cells and its cisplatin-resistant variant A549/DDP]

背景与目的

肺癌顺铂耐药在临床治疗中广泛存在，严重影响了肺癌患者的治疗效果，因此研究肺癌耐药机制对新药的研发和解决临床肿瘤耐药有十分重要的意义。IKBKB是组成IKK复合物重要的催化亚基之一，其对核转录因子NF-κB的激活起到重要调控作用。本研究旨在探讨IKBKB基因在肺腺癌顺铂耐药细胞株（A549/DDP）与其亲本肺腺癌A549细胞株中的表差异及其调控肺腺癌顺铂耐药的机制。

方法

应用MTT法检测A549和A549/DDP细胞株顺铂敏感性及IKBKB基因对A549细胞株顺铂耐药性的影响。Real-time PCR检测肿瘤细胞中IKBKB基因mRNA变化，流式细胞学检测肿瘤细胞凋亡率，双荧光素酶报告基因实验检测NF-κB的活性。

结果

A549细胞与A549/DDP细胞在IC₅₀和凋亡率方面均有统计学差异，IKBKB基因在A549/DDP细胞株中mRNA表达水平明显高于A549。与对照组比较，pcDNA3.1/IKBKB转染A549细胞后，IKBKB基因在mRNA水平明显升高，A549细胞顺铂耐药性明显增加，IC₅₀增加2.85倍，凋亡率减少59%，NF-κB的活性明显升高。

结论

IKBKB基因通过激活NF-κB信号通路抑制细胞凋亡，从而导致细胞耐药性增加，这一研究结果对新抗肿瘤药物的研发和解决肿瘤耐药难题有重要意义。

TP53 K351N mutation-associated platinum resistance after neoadjuvant chemotherapy in patients with advanced ovarian cancer

OBJECTIVE

TP53 K351N mutation is associated with acquired cisplatin resistance in ovarian cancer cells following exposure to cisplatin. We investigated the effect of TP53 K351N mutation on outcome in patients with epithelial ovarian cancer (EOC) who received platinum-based chemotherapy.

METHODS

We assessed TP53 K351N mutations by allele specific real-time PCR (AS-PCR) and DNA sequencing in tumor samples of 153 patients with stage IIIC/IV EOC. Clinicopathologic and follow-up data were collected by a retrospective chart review.

RESULTS

TP53 K351N mutations were detected in 8 (11.27%) of 71 patients who underwent neoadjuvant chemotherapy with interval debulking surgery (NACT-IDS) but not in 82 patients who underwent primary debulking surgery (PDS) (P<0.01). In patients with relapse within 6 months, the relapse rate was 14 (19.72%) of 71 patients for NACT-IDS compared to 15 (18.29%) of 82 patients for PDS (P=0.49), and TP53 K351N mutation was observed in 8 of NACT-IDS 14 patients (57.14% P<0.01). In the patients retreated at first recurrence within 6 months, 7 with TP53 K351N mutation of 14 NACT-IDS patients exhibited progression of disease, compared to 2 of PDS 15 patients (50.00% vs. 13.33%, P=0.04). The median disease-free survival (DFS) for NACT-IDS was 13.0 months compared to 15.0 months for PDS (P=0.02). In multivariate analysis, TP53 K351N mutation is an independent factor for shorter DFS in the patients who underwent NACT-IDS (HR=19.05; P=0.01).

CONCLUSIONS

TP53 K351N mutation may be associated with induction of platinum resistance after NACT in advanced EOC.

DNA-bound platinum is the major determinant of cisplatin sensitivity in head and neck squamous carcinoma cells

PURPOSE

The combination of systemic cisplatin with local and regional radiotherapy as primary treatment of head and neck squamous cell carcinoma (HNSCC) leads to cure in approximately half of the patients. The addition of cisplatin has significant effects on outcome, but despite extensive research the mechanism underlying cisplatin response is still not well understood.

METHODS

We examined 19 HNSCC cell lines with variable cisplatin sensitivity. We determined the TP53 mutational status of each cell line and investigated the expression levels of 11 potentially relevant genes by quantitative real-time PCR. In addition, we measured cisplatin accumulation and retention, as well as the level of platinum-DNA adducts.

RESULTS

We found that the IC50 value was significantly correlated with the platinum-DNA adduct levels that accumulated during four hours of cisplatin incubation (p = 0.002). We could not find a significant correlation between cisplatin sensitivity and any of the other parameters tested, including the expression levels of established cisplatin influx and efflux transporters. Furthermore, adduct accumulation did not correlate with mRNA expression of the investigated influx pumps (CTR1 and OCT3) nor with that of the examined DNA repair genes (ATR, ATM, BRCA1, BRCA2 and ERCC1).

CONCLUSION

Our findings suggest that the cisplatin-DNA adduct level is the most important determinant of cisplatin sensitivity in HNSCC cells. Imaging with radio-labeled cisplatin might have major associations with outcome.

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.

DNA damage and repair in human cancer: molecular mechanisms and contribution to therapy-related leukemias

Most antitumour therapies damage tumour cell DNA either directly or indirectly. Without repair, damage can result in genetic instability and eventually cancer. The strong association between the lack of DNA damage repair, mutations and cancer is dramatically demonstrated by a number of cancer-prone human syndromes, such as xeroderma pigmentosum, ataxia-telangiectasia and Fanconi anemia. Notably, DNA damage responses, and particularly DNA repair, influence the outcome of therapy. Because DNA repair normally excises lethal DNA lesions, it is intuitive that efficient repair will contribute to intrinsic drug resistance. Unexpectedly, a paradoxical relationship between DNA mismatch repair and drug sensitivity has been revealed by model studies in cell lines. This suggests that connections between DNA repair mechanism efficiency and tumour therapy might be more complex. Here, we review the evidence for the contribution of carcinogenic properties of several drugs as well as of alterations in specific mechanisms involved in drug-induced DNA damage response and repair in the pathogenesis of therapy-related cancers.

Molecular mechanisms of cisplatin resistance

Platinum-based drugs, and in particular cis-diamminedichloroplatinum(II) (best known as cisplatin), are employed for the treatment of a wide array of solid malignancies, including testicular, ovarian, head and neck, colorectal, bladder and lung cancers. Cisplatin exerts anticancer effects via multiple mechanisms, yet its most prominent (and best understood) mode of action involves the generation of DNA lesions followed by the activation of the DNA damage response and the induction of mitochondrial apoptosis. Despite a consistent rate of initial responses, cisplatin treatment often results in the development of chemoresistance, leading to therapeutic failure. An intense research has been conducted during the past 30 years and several mechanisms that account for the cisplatin-resistant phenotype of tumor cells have been described. Here, we provide a systematic discussion of these mechanism by classifying them in alterations (1) that involve steps preceding the binding of cisplatin to DNA (pre-target resistance), (2) that directly relate to DNA-cisplatin adducts (on-target resistance), (3) concerning the lethal signaling pathway(s) elicited by cisplatin-mediated DNA damage (post-target resistance) and (4) affecting molecular circuitries that do not present obvious links with cisplatin-elicited signals (off-target resistance). As in some clinical settings cisplatin constitutes the major therapeutic option, the development of chemosensitization strategies constitute a goal with important clinical implications.

α-TEA cooperates with chemotherapeutic agents to induce apoptosis of p53 mutant, triple-negative human breast cancer cells via activating p73

Introduction

Successful treatment of p53 mutant, triple-negative breast cancers (TNBC) remains a daunting challenge. Doxorubicin (DOXO) and cisplatin (CDDP) are standard-of-care treatments for TNBC, but eventually fail due to acquired drug resistance and toxicity. New treatments for overcoming drug resistance and toxicity in p53 mutant, TNBC are therefore badly needed. Unlike p53, p73 - a member of the p53 family - is usually not mutated in cancers and has been shown to regulate p53-mediated apoptotic signaling in p53-deficient cancers. Therefore, identification of anticancer agents that can activate p73 in p53-deficient cancers may provide a chemotherapeutic approach for treatment of p53 mutant cancers. Here we report on the reconstitution of the p53 tumor suppressor pathway in a p53-independent manner via p73 with combination treatments of α-TEA, a small bioactive lipid, plus DOXO or CDDP.

Methods

p53 mutant, TNBC cell lines MDA-MB-231, BT-20 and MDA-MB-468 were used to evaluate the anticancer effect of chemotherapeutic drugs and α-TEA using annexin V (FITC)/PI staining, western blot analyses, RT-PCR and siRNA knockdown techniques.

Results

Combination treatments of α-TEA plus DOXO or CDDP act cooperatively to induce apoptosis, caspase-8 and caspase-9 cleavage, p73, phospho-c-Ab1 and phospho-JNK protein expression, and increase expression of p53 downstream mediators; namely, death receptor-5, CD95/APO-1 (Fas), Bax and Noxa, as well as Yap nuclear translocation - plus reduce expression of Bcl-2. Knockdown of p73, c-Abl, JNK or Yap using siRNAs shows that p73 plays a critical role in combination treatment-enhanced apoptosis and the expression of pro-apoptotic and anti-apoptotic mediators, and that c-Abl, JNK and Yap are upstream mediators of p73 in combination treatment responses.

Conclusions

Data show that α-TEA in combination with DOXO or CDDP synergistically enhances apoptosis in TNBC via targeting p53-mediated genes in a p73-dependent manner, and that p73 responses are downstream of c-Abl, JNK and Yap.

Epigenomics and ovarian carcinoma

Ovarian cancer is the leading cause of death among gynecological cancers. It is now recognized that in addition to genetic alterations, epigenetic mechanisms, such as DNA methylation, histone modifications and nucleosome remodeling, play an important role in the development and progression of ovarian cancer by modulating chromatin structure, and gene and miRNA expression. Furthermore, epigenetic alterations have been recognized as useful tools for the development of novel biomarkers for diagnosis, prognosis, therapeutic prediction and monitoring of diseases. Moreover, new epigenetic therapies, such as DNA methyltransferase inhibitors and histone deacetylase inhibitors, have been found to be a potential therapeutic option, especially when used in combination with other agents. Here we discuss current developments in ovarian carcinoma epigenome research, the importance of the ovarian carcinoma epigenome for development of diagnostic and prognostic biomarkers, and the current epigenetic therapies used in ovarian cancer.

Cellular responses to Cisplatin-induced DNA damage

Cisplatin is one of the most effective anticancer agents widely used in the treatment of solid tumors. It is generally considered as a cytotoxic drug which kills cancer cells by damaging DNA and inhibiting DNA synthesis. How cells respond to cisplatin-induced DNA damage plays a critical role in deciding cisplatin sensitivity. Cisplatin-induced DNA damage activates various signaling pathways to prevent or promote cell death. This paper summarizes our current understandings regarding the mechanisms by which cisplatin induces cell death and the bases of cisplatin resistance. We have discussed various steps, including the entry of cisplatin inside cells, DNA repair, drug detoxification, DNA damage response, and regulation of cisplatin-induced apoptosis by protein kinases. An understanding of how various signaling pathways regulate cisplatin-induced cell death should aid in the development of more effective therapeutic strategies for the treatment of cancer.

NSC109268 potentiates cisplatin-induced cell death in a p53-independent manner

BACKGROUND

Ovarian cancer is the leading cause of death among gynecological cancers. Cisplatin is one of the most effective anticancer drugs used in the treatment of ovarian cancer. Development of resistance to cisplatin limits its therapeutic use. Most of the anticancer drugs, including cisplatin, are believed to kill cancer cells by inducing apoptosis and a defect in apoptotic signaling can contribute to drug resistance. The tumor suppressor protein p53 plays a critical role in DNA damage-induced apoptosis. During a yeast-based drug screening, NSC109268 was identified to enhance cellular sensitivity to cisplatin. The objective of the present study is to determine if p53 is responsible for cisplatin sensitization by NSC109268.

RESULTS

NSC109268 enhanced sensitivity of ovarian cancer 2008 cells and its cisplatin resistant counterpart 2008/C13* cells which express wild-type p53. The potentiation of cisplatin sensitivity by NSC109268 was greater in 2008/C13* cells compared to 2008 cells. Cisplatin caused a concentration-dependent increase in p53 in 2008 and 2008/C13* cells, and the induction of p53 correlated with cisplatin-induced apoptosis as determined by the cleavage of PARP. NSC109268 alone had no effect on p53 but it enhanced p53 level in response to cisplatin. Knockdown of p53 by siRNA, however, did not attenuate cell death in response to cisplatin or combination of NSC109268 and cisplatin.

CONCLUSIONS

These results demonstrate that NSC109268 enhances sensitivity of ovarian cancer 2008 cells to cisplatin independent of p53.

The effect of paclitaxel alone and in combination with cycloheximide on the frequency of premature centromere division in vitro

Premature centromere division (PCD) can be viewed as a manifestation of chromosome instability. In order to evaluate the ability of Paclitaxel (Ptx) and Cycloheximide (Cy) to induce PCD we used a cytokinesis block micronucleus assay (CBMN), fluorescent in situ hybridization (FISH), and the chromosome aberration (CA) assay in human peripheral blood lymphocytes. Results showed that Ptx can induce PCD alone or in combination with Cy. These findings call us to pay more attention to PCD as a parameter of genotoxicity in the pre-clinical research of mono and/or combinational therapies for cancer treatment.

Utility of gene promoter methylation in prediction of response to platinum-based chemotherapy in epithelial ovarian cancer (EOC)

The aim was to determine whether promoter methylation of BRCA1, MGMT, MLH1, RASSF1A, and p16 genes could predict response to platinum-based chemotherapy. Thirty-five subjects with epithelial ovarian cancer (EOC) treated by platinum-based chemotherapy were recruited. Methylation-specific polymerase chain reaction was carried out and the methylation index (MI) was also derived. Response to platinum-based chemotherapy was documented clinically, radiologically, and by serial CA125 levels. Methylated BRCA1 (p = .037) and a higher MI (p = .045) were associated with primary chemosensitivity. A better outcome was predicted by a higher MI (p = .032). In EOC, BRCA1 gene promoter methylation is useful in the prediction of response to chemotherapy.

MLH1 expression sensitises ovarian cancer cells to cell death mediated by XIAP inhibition

BACKGROUND

The X-linked inhibitor of apoptosis protein (XIAP), an endogenous apoptosis suppressor, can determine the level of caspase accumulation and the resultant response to apoptosis-inducing agents such as cisplatin in epithelial ovarian cancer (EOC). In addition, the mismatch repair protein, hMLH1, has been linked to DNA damage-induced apoptosis by cisplatin by both p53-dependent and -independent mechanisms.

METHODS

In this study, hMLH1 expression was correlated with clinical response to platinum drugs and survival in advanced stage (III-IV) EOC patients. We then investigated whether MLH1 loss was a determinant in anti-apoptosis response to cisplatin mediated by XIAP in isogenic and established EOC cell lines with differential p53 status.

RESULTS

The percentage of cells undergoing cisplatin-induced cell killing was higher in MLH1-proficient cells than in MLH1-defective cells. In addition, the presence of wild-type hMLH1 or hMLH1 re-expression significantly increased sensitivity to 6-thioguanine, a MMR-dependent agent. Cell-death response to 6-thioguanine and cisplatin was associated with significant proteolysis of MLH1, with XIAP destabilisation and increased caspase-3 activity. The siRNA-mediated inhibition of XIAP increased MLH1 proteolysis and cell death in MLH1-proficient cells but not in MLH1-defective cells.

CONCLUSION

These data suggest that XIAP inhibitors may prove to be an effective means of sensitising EOC to MLH1-dependent apoptosis.

Pharmaco(epi)genomics in ovarian cancer

Ovarian cancer shows considerable variability in its chemoresponse, however, the prospect of individualized medicine holds high hopes for improving patient survival. The influence of interindividual genomic polymorphisms on drug response (pharmacogenomics) is well established, and a variety of candidate loci in ovarian tumors have been identified, including ERCC1, ABCB1 and p53 variants. Recently pharmacoepigenomic modulators of key genes and pathways, such as promoter methylation (MLH1 and BRCA1 genes) and microRNA regulation (PTEN/AKT and NF-κB pathways) have been implicated in ovarian cancer chemoresponse. Epigenomic studies have until now mainly focused on tumor-specific changes, although germ-line epigenetic change may also be of importance. However, assessing the relevance of these potential pharmaco(epi)genomic biomarkers in clinical trials requires well powered studies in homogeneous populations, with independent validation sets, to distinguish real associations from false-positives. In addition, the selection of one gene or locus as having sufficient phenotypic effect to impact on clinical outcome may be an oversimplification. Integrated approaches that identify stable pharmacogenomic and epigenomic patterns and their relationship with expression patterns and gene function will be increasingly necessary.

Oxaliplatin activity in selected and unselected human ovarian and colorectal cancer cell lines

Oxaliplatin is used for treatment of colon cancer in combination with 5-fluorouracil or irinotecan. Oxaliplatin has similar, but also different resistant mechanisms as cisplatin. We studied the activity of oxaliplatin in ovarian and colon cancer cells with different resistance patterns to cisplatin. The 40-fold cisplatin-resistant cell line ADDP was only 7.5-fold resistant to oxaliplatin. The gemcitabine-resistant AG6000 cell line, 9-fold resistant to cisplatin, was not cross-resistant. LoVo-175X2, with mutant p53 showed no resistance compared to the empty vector control. However, LoVo-Li, with inactive p53, was 3.6-fold resistant corresponding to decreased accumulation and Pt adducts. Accumulation and DNA adducts formation showed no significant correlation with oxaliplatin sensitivity. Cell cycle distribution after exposure to oxaliplatin showed arrest in G2/M (A2780) or in S-phase (LoVo-92) for wt-p53 cells. ADDP and LoVo-Li showed G1 arrest followed by S-phase arrest and no changes in distribution, respectively. The cell cycle related proteins Cyclins A and B1 and (p)CDC25C were marginally affected by oxaliplatin. Expression of hCTR1 was decreased in ADDP, LoVo-Li and AG6000, OCT1 decreased in ADDP and AG6000 and OCT3 in LoVo-175X2, compared to the parental cell lines. In ADDP and LoVo-175X2 ATP7A and B were decreased but were increased in AG6000. From this study it can be concluded that changes in cell cycle distribution were cell line dependent and not related to changes in expression of Cyclin A or B1. Oxaliplatin accumulation was related to hCTR1 and, at low concentration, ATP7A to DNA adducts formation while the retention was related to hCTR1, OCT2 and ATP7B.

Low hMLH1 expression prior to definitive chemoradiotherapy predicts poor prognosis in esophageal squamous cell carcinoma

The present study evaluated the pretreatment expression patterns of hMLH1, MDM2, p53, and pRb protein to determine whether these could predict the outcome of definitive concurrent chemoradiotherapy (CCRT) in 51 patients with stage I-IVa esophageal squamous cell carcinoma. High immunoreactivies of hMLH1, MDM2, p53, and pRb were detected in 90.2%, 19.6%, 27.5%, and 66.7% of entire patients, respectively. High hMLH1 expression was found to favor earlier stage, less locoregional failure, and longer cause-specific survival, and all were with significance. However, the expressions of MDM2, p53, and pRb were not found to be clinically significant. Thirty-three patients with high hMLH1 and pRb expression tended to survive longer than four patients with low hMLH1 and pRb expression. We suggest that the expression of hMLH1 is a potential marker of tumor response and survival. Determinations of this protein expression might be useful for selecting esophageal squamous cell carcinoma patients for definitive CCRT.

Paclitaxel resistance in untransformed human mammary epithelial cells is associated with an aneuploidy-prone phenotype

Despite its increasing clinical use, almost no data are currently available about paclitaxel effects on non-cancerous mammary epithelial cells. We have previously established paclitaxel-resistant sub-cell lines (paclitaxel-surviving populations, PSPs; n=20), and sensitive controls (control clones, CCs; n=10), from the untransformed human mammary epithelial cell line HME1. In this study, we aimed to establish whether paclitaxel resistance was associated with a modified sensitivity to paclitaxel-induced aneuploidy. For this purpose, we analysed basal and paclitaxel-induced chromosome missegregation, apoptosis and aberrant spindle multipolarisation as well as microtubular network composition for each subline. PSP sublines showed higher basal and paclitaxel-induced chromosome missegregation than the CC sublines. This phenomenon was associated with resistance to paclitaxel-induced apoptosis. No significant difference in paclitaxel-induced spindle pole abnormalities between CC and PSP sublines was found. Besides, we showed that a majority of PSPs display a constitutively disrupted microtubular network composition due to aberrant tubulin expression and post-translational modifications. These results clearly indicate that paclitaxel resistance in untransformed human mammary epithelial cells is related to an increased susceptibility to acquire aneuploidy in response to this agent. The consequences of these paclitaxel-associated alterations could be deleterious as they can potentially trigger tumorigenesis.

Mismatch repair deficiencies transforming stem cells into cancer stem cells and therapeutic implications

For the exceptional self-renewal capacity, regulated cell proliferation and differential potential to a wide variety of cell types, the stem cells must maintain the intact genome. The cells under continuous exogenous and endogenous genotoxic stress accumulate DNA errors, drive proliferative expansion and transform into cancer stem cells with a heterogeneous population of tumor cells. These cells are a common phenomenon for the hematological malignancies and solid tumors. In response to DNA damage, the complex cellular mechanisms including cell cycle arrest, transcription induction and DNA repair are activated. The cells when exposed to cytotoxic agents, the apoptosis lead to cell death. However, the absence of repair machinery makes the cells resistant to tumor sensitizing agents and result in malignant transformation. Mismatch repair gene defects are recently identified in hematopoietic malignancies, leukemia and lymphoma cell lines. This review emphasizes the importance of MMR systems in maintaining the stem cell functioning and its therapeutic implications in the eradication of cancer stem cells and differentiated tumor cells as well. The understanding of the biological functions of mismatch repair in the stem cells and its malignant counterparts could help in developing an effective novel therapies leaving residual non-tumorigenic population of cells resulting in potential cancer cures.

A human cell-based assay to evaluate the effects of alterations in the MLH1 mismatch repair gene

We describe a new approach to investigate alterations in the human MLH1 mismatch repair (MMR) gene. This is based on complementation of the phenotype of a MLH1-defective subclone of the ovarian carcinoma A2780 cells by transfection of vectors encoding altered MLH1 proteins. Measurements of resistance (tolerance) to methylating agents, mutation rate at HPRT, microsatellite instability (MSI), and steady-state levels of DNA 8-oxoguanine were used to define the MMR status of transfected clones. The approach was validated by transfecting cDNA of wild-type (WT) MLH1, cDNAs bearing two previously identified polymorphisms (I219V and I219L) and two with confirmed hereditary nonpolyposis colorectal cancer (HNPCC) syndrome mutations (G224D and G67R). A low-level expression of two MLH1 polymorphisms partially reversed methylation tolerance and the mutator phenotype, including MSI. Higher levels of I219V resulted in full restoration of these properties to WT. Increased expression of I129L did not fully complement the MLH1 defect, because there was a simultaneous escalation in the level of oxidative DNA damage. The findings confirmed the important relationship between deficient MMR and increased levels of oxidative DNA damage. Mutations from Italian HNPCC families (G224D, G67R, N635S, and K618A) were all ineffective at reversing the phenotype of the MLH1-defective A2780 cells. One (K618A) was identified as a low penetrance mutation based on clinical and genetic observations.