Design, synthesis and mechanistic anticancer activity of new acetylated 5-aminosalicylate-thiazolinone hybrid derivatives.

The development of hybrid compounds has been widely considered as a promising strategy to circumvent the difficulties that emerge in cancer treatment. The well-established strategy of adding acetyl groups to certain drugs has been demonstrated to enhance their therapeutic efficacy. Based on our previous work, an approach of accommodating two chemical entities into a single structure was implemented to synthesize new acetylated hybrids (HH32 and HH33) from 5-aminosalicylic acid and 4-thiazolinone derivatives. These acetylated hybrids showed potential anticancer activities and distinct metabolomic profile with antiproliferative properties. The in-silico molecular docking predicts a strong binding of HH32 and HH33 to cell cycle regulators, and transcriptomic analysis revealed DNA repair and cell cycle as the main targets of HH33 compounds. These findings were validated using in vitro models. In conclusion, the pleiotropic biological effects of HH32 and HH33 compounds on cancer cells demonstrated a new avenue to develop more potent cancer therapies.

Epigenetic modulations in cancer: predictive biomarkers and potential targets for overcoming the resistance to topoisomerase I inhibitors.

INTRODUCTION: Altered epigenetic map is frequently observed in cancer and recent investigations have demonstrated a pertinent role of epigenetic modifications in the response to many anticancer drugs including the DNA damaging agents. Topoisomerase I (Top I) is a well-known nuclear enzyme that is critical for DNA function and cell survival and its inhibition causes DNA strand breaks and cell cycle arrest. Inhibitors of human Top I have proven to be a prosperous chemotherapeutic treatment for a vast number of cancer patients. While the treatment is efficacious in many cases, resistance and altered cellular response remain major therapeutic issues. AREAS COVERED: This review highlights the evidence available till date on the influence of different epigenetic modifications on the response to Top I inhibitors as well as the implications of targeting epigenetic alterations for improving the efficacy and safety of Top I inhibitors. EXPERT OPINION: The field of epigenetic research is steadily growing. With its assistance, we could gain better understanding on how drug response and resistance work. Epigenetics can evolve as possible biomarkers and predictors of response to many medications including Top I inhibitors, and could have significant clinical implications that necessitate deeper attention.HIGHLIGHTSEpigenetic alterations, including DNA methylation and histone modifications, play a pertinent role in the response to several anticancer treatments, including DNA damaging agents like Top I inhibitors.Although camptothecin derivatives are used clinically as Top I inhibitors for management of cancer, certain types of cancer have inherent and or acquired resistance that limit the curative potential of them.Epigenetic modifications like DNA hypomethylation can either increase or decrease sensitivity to Top I inhibitors by different mechanisms.The combination of Top I inhibitors with the inhibitors of histone modifying enzymes can result in enhanced cytotoxic effects and sensitization of resistant cells to Top I inhibitors.MicroRNAs were found to directly influence the expression of Top I and other proteins in cancer cells resulting in positive or negative alteration of the response to Top I inhibitors.lncRNAs and their genetic polymorphisms have been found to be associated with Top I function and the response to its inhibitors.Clinical trials of epigenetic drugs in combination with Top I inhibitors are plentiful and some of them showed potentially promising outcomes.

Effect of safranal on the response of cancer cells to topoisomerase I inhibitors: Does sequence matter?

Lung and colorectal cancers are among the leading causes of death from cancer worldwide. Although topotecan (TPT), a topoisomerase1 inhibitor, is a first- and second-line drug for lung and colon cancers, the development of drug resistance and toxicity still remain as a major obstacle to chemotherapeutic success. Accumulating evidence indicates increased efficacy and reduced toxicity of chemotherapeutic agents upon combining them with natural products. We aimed to investigate the possible interaction of safranal (SAF), a natural compound obtained from Crocus sativus stigma, with TPT when used in different sequences in colon and lung cancer cell lines. The growth inhibitory effect of the proposed combination given in different sequences was assessed using the colony formation assay. The comet assay, cell cycle distribution, Annexin-V staining, and expression of proteins involved in DNA damage/repair were utilized to understand the mechanism underlying the effect of the combination. SAF enhanced the growth inhibitory effects of TPT particularly when it was added to the cells prior to TPT. This combination increased the double-strand break induction and dysregulated the DNA repair machinery, particularly the tyrosyl-DNA phosphodiesterase 1 enzyme. In addition, the SAF + TPT combination increased the fraction of cells arrested at the G2/M checkpoint as well as enhanced the induction of apoptosis. The current study highlights the status of SAF as a natural product sensitizing the lung and colon cancer cells to the cytotoxic effects of the anticancer drug TPT. In addition, it emphasizes the importance of sequence-dependent interaction which can affect the overall outcome.

The Role of HDACs in the Response of Cancer Cells to Cellular Stress and the Potential for Therapeutic Intervention.

Throughout the process of carcinogenesis, cancer cells develop intricate networks to adapt to a variety of stressful conditions including DNA damage, nutrient deprivation, and hypoxia. These molecular networks encounter genomic instability and mutations coupled with changes in the gene expression programs due to genetic and epigenetic alterations. Histone deacetylases (HDACs) are important modulators of the epigenetic constitution of cancer cells. It has become increasingly known that HDACs have the capacity to regulate various cellular systems through the deacetylation of histone and bounteous nonhistone proteins that are rooted in complex pathways in cancer cells to evade death pathways and immune surveillance. Elucidation of the signaling pathways involved in the adaptive responses to cellular stress and the role of HDACs may lead to the development of novel therapeutic agents. In this article, we overview the dominant stress types including metabolic, oxidative, genotoxic, and proteotoxic stress imposed on cancer cells in the context of HDACs, which guide stress adaptation responses. Next, we expose a closer view on the therapeutic interventions and clinical trials that involve HDACs inhibitors, in addition to highlighting the impact of using HDAC inhibitors in combination with stress-inducing agents for the management of cancer and to overcome the resistance to current cancer therapy.

Recent advances in management of COVID-19: A review.

The coronavirus disease 2019 (COVID-19) pandemic caused and is still causing significant mortality and economic consequences all over the globe. As of today, there are three U.S Food and Drug administration (FDA) approved vaccines, Pfizer-BioNTech, Moderna and Janssen COVID-19 vaccine. Also, the antiviral drug remdesivir and two combinations of monoclonal antibodies are authorized for Emergency use (EUA) in certain patients. Furthermore, baricitinib was approved in Japan (April 23, 2021). Despite available vaccines and EUA, pharmacological therapy for the prevention and treatment of COVID-19 is still highly required. There are several ongoing clinical trials investigating the efficacy of clinically available drugs in treating COVID-19. In this study, selected novel pharmacological agents for the possible treatment of COVID-19 will be discussed. Point of discussion will cover mechanism of action, supporting evidence for safety and efficacy and reached stage in development. Drugs were classified into three classes according to the phase of viral life cycle they target. Phase I, the early infective phase, relies on supportive care and symptomatic treatment as needed. In phase II, the pulmonary phase, treatment aims at inhibiting viral entry or replication. Drugs used during this phase are famotidine, monoclonal antibodies, nanobodies, ivermectin, remdesivir, camostat mesylate and other antiviral agents. Finally, phase III, the hyper-inflammatory phase, tocilizumab, dexamethasone, selective serotonin reuptake inhibitors (SSRI), and melatonin are used. The aim of this study is to summarize current findings and suggest gaps in knowledge that can influence future COVID-19 treatment study design.

Discovery of novel class of histone deacetylase inhibitors as potential anticancer agents.

Selective inhibition of histone deacetylases (HDACs) is an important strategy in the field of anticancer drug discovery. However, lack of inhibitors that possess high selectivity toward certain HDACs isozymes is associated with adverse side effects that limits their clinical applications. We have initiated a collaborative initiatives between multi-institutions aimed at the discovery of novel and selective HDACs inhibitors. To this end, a phenotypic screening of an in-house pilot library of about 70 small molecules against various HDAC isozymes led to the discovery of five compounds that displayed varying degrees of HDAC isozyme selectivity. The anticancer activities of these molecules were validated using various biological assays including transcriptomic studies. Compounds 15, 14, and 19 possessed selective inhibitory activity against HDAC5, while 28 displayed selective inhibition of HDAC1 and HDAC2. Compound 22 was found to be a selective inhibitor for HDAC3 and HDAC9. Importantly, we discovered a none-hydroxamate based HDAC inhibitor, compound 28, representing a distinct chemical probe of HDAC inhibitors. It contains a trifluoromethyloxadiazolyl moiety (TFMO) as a non-chelating metal-binding group. The new compounds showed potent anti-proliferative activity when tested against MCF7 breast cancer cell line, as well as increased acetylation of histones and induce cells apoptosis. The new compounds apoptotic effects were validated through the upregulation of proapoptotic proteins caspases3 and 7 and downregulation of the antiapoptotic biomarkers C-MYC, BCL2, BCL3 and NFĸB genes. Furthermore, the new compounds arrested cell cycle at different phases, which was confirmed through downregulation of the CDK1, 2, 4, 6, E2F1 and RB1 proteins. Taken together, our findings provide the foundation for the development of new chemical probes as potential lead drug candidates for the treatment of cancer.

Induction of DNA damage, apoptosis and cell cycle perturbation mediate cytotoxic activity of new 5-aminosalicylate-4-thiazolinone hybrid derivatives.

Modulation of several targets in cancer cells enhances the effect of anti-cancer drugs. This can be achieved by using combinations of anti-cancer drugs or by designing new drugs with novel pharmacophore structures that target different molecules within cancer cells. We developed a panel of such compounds by accommodating two chemical entities (5-Aminoslicylic acid and thiazolin-4-one) known to have anti-cancer activities into a single framework structure. Using a panel of 7 cancer cell lines, two compounds (HH3 and HH13) showed efficient cytotoxic effects on some types of cancer comparable to the standard anti-cancer drug doxorubicin with tumor specificity and minimal effects on normal fibroblasts. Investigating the molecular mechanisms of the two compounds revealed (i) induction of DNA damage, (ii) cell cycle arrest in G2/M phase and (iii) induction of apoptosis as indicated by annexin-V staining and activation of caspases. These effects were more prominent in HH compounds-sensitive cells (with IC50 < 0.5µM) than -resistant or normal cells (with IC50 > 1µM). Moreover, both compounds modulate the expression and activity of several factors in the DNA damage response pathway (γ-H2AX, ATM, ATR, CHK1, CHK2), cyclins/cyclin dependent kinases and CDC25 phosphatase. Altogether, our results show that both HH3 and HH13 compounds are good candidates as anti-cancer drug leads for certain types of cancer and worth further detailed investigations of their safety and effectiveness on animal/xenograft models.

Inhibition of SHP2 by new compounds induces differential effects on RAS/RAF/ERK and PI3K/AKT pathways in different cancer cell types.

Kinases and phosphatases are important players in growth signaling and are involved in cancer development. For development of targeted cancer therapy, attention is given to kinases rather than phosphatases inhibitors. Src homology region 2 domain-containing protein tyrosine phosphatase2 (SHP2) is overexpressed in different types of cancers. We investigated the SHP2-inhibitory effects of two new 5-aminosalicylate-4-thiazolinones in human cervical (HeLa) and breast (MCF-7 & MDA-MB-231) cancer cells. In-silico molecular docking showed preferential affinity of the two compounds towards the catalytic over the allosteric site of SHP2. An enzymatic assay confirmed the docking results whereby 0.01 µM of both compounds reduced SHP2 activity to 50%. On cellular level, the two compounds significantly reduced the expression of SHP2, KRAS, p-ERK and p-STAT3 in HeLa but not in the other two cell lines. Phosphorylation of AKT and JNK was enhanced in HeLa and MCF7. Both compounds exhibited anti-proliferative/anti-migratory effects on HeLa and MCF7 but not in MDA-MB-231 cells. These results indicate that inhibition of SHP2 and its downstream pathways by the two compounds might be a promising strategy for cancer therapy in some but not all cancer types.

Interplay between Epigenetics, Expression of Estrogen Receptor- α, HER2/ERBB2 and Sensitivity of Triple Negative Breast Cancer Cells to Hormonal Therapy.

Triple negative breast cancer (TNBC) cells are resistant to hormonal/targeted therapies. This study aims to investigate epigenetic differences between TNBC and other types of breast cancer and the effect of epigenetic modulation on the response of TNBC cells to hormonal therapy. Thus, we investigated (i) the expression of different epigenetic markers, (ii) the effect of epigenetic modifying agents on the expression of ERα and HER2/ERBB2 and (iii) the effect on the response to tamoxifen in four breast cancer cell lines with different hormonal receptor status. Our results revealed a differential expression patterns of epigenetic markers in the four breast cancer cells. In TNBC cells, histone deacetylases (HDAC) 1 and 2 were less expressed, whereas HDACs 4 and 6 were overexpressed. Interestingly, treatment with epigenetic modifiers resulted in (i) a pronounced increase in the expression of ERα and HER2/ERBB2 along with (ii) an increase in the sensitivity of TNBC cells to tamoxifen. Collectively, this study indicates a different epigenetic background for TNBC cells, which represses the expression of ERα and HER2/ERBB2. Furthermore, we provide here the rationale for the use of epigenetic modifiers to enhance the response of TNBC to hormonal therapy through upregulation of ERα.

Inhibition of exosome release by ketotifen enhances sensitivity of cancer cells to doxorubicin.

Exosomes released from cancer cells support metastasis and growth of recipient cells and increase their resistance to chemotherapy. Therapeutic targeting of exosomes is a promising area in cancer research. Our aim is to test the effect of the mast cell stabilizer ketotifen on exosomes release from cancer cells and how this can modify their response to doxorubicin. Exosomes release from three cancer cell lines (MCF7, HeLa and BT549) was assessed by scan electron microscope and exosomes quantification kit. Doxorubicin export within exosomes was monitored flurometrically and cellular sensitivity to doxorubicin ± ketotifen was measured by sulphorhodamine-B and colony formation assays. The three cell lines release different amounts of exosomes with the highest quantity released from BT549 followed by MCF7 and then HeLa. Ketotifen (10 µmol L-1) reduced exosomes release in all three cell lines with different efficiency (HeLa>MCF7>BT549). Doxorubicin export via exosomes was highest in BT549, lower in HeLa and lowest in MCF7 cells. Pretreatment with ketotifen sensitized the cells to doxorubicin (HeLa>MCF7>BT549) with a sensitization factor of 27, 8 and 1.25 respectively. Increased sensitivity of cells to doxorubicin by ketotifen was proportional to its effect on exosomes release. Our data is the first report of ketotifen modulating exosomes release from cancer cells and opens the avenue for exosomes-targeting cancer therapy. The differential effects of ketotifen on doxorubicin exosomal export in the cell lines studied, suggests an opportunity of pharmacological enhancement of doxorubicin anti-tumor activity in some but not all cancer types.

In-silico screening for DNA-dependent protein kinase (DNA-PK) inhibitors: Combined homology modeling, docking, molecular dynamic study followed by biological investigation.

DNA-dependent protein kinase (DNA-PK) is a key enzyme in non-homologous DNA end joining (NHEJ) repair pathway. The targeted inhibition of such enzyme would furnish a valuable option for cancer treatment. In this study we report the development of validation of enzyme homology model, and the subsequent use of this model to perform docking-based virtual screening against a database of FDA-approved drugs. The nominated highest ranking hits (Praziquantel and Dutasteride) were subjected to biological investigation. Additionally, molecular dynamic study was carried-out for binding mode exploration. Results of the biological evaluation revealed that both compounds inhibit the DNA-PK enzymatic activity at relatively high concentration levels with an IC50 of 17.3µM for praziquantel and >20µM for dutasteride. Furthermore, both agents enhanced the anti-proliferative effects of doxorubicin and cisplatin on breast cancer (MCF7) and lung cancer (A549) cell lines. This result indicates that these two hits are good candidate as DNA-PK inhibitors and worth further structural modifications to enhance their enzyme inhibitory effects.

The Role of Eukaryotic and Prokaryotic ABC Transporter Family in Failure of Chemotherapy.

Over the years chemotherapy failure has been a vital research topic as researchers have been striving to discover reasons behind it. The extensive studies carried out on chemotherapeutic agents confirm that resistance to chemotherapy is a major reason for treatment failure. "Resistance to chemotherapy," however, is a comprehensive phrase that refers to a variety of different mechanisms in which ATP-binding cassette (ABC) mediated efflux dominates. The ABC is one of the largest gene superfamily of transporters among both eukaryotes and prokaryotes; it represents a variety of genes that code for proteins, which perform countless functions, including drug efflux - a natural process that protects cells from foreign chemicals. Up to date, chemotherapy failure due to ABC drug efflux is an active research topic that continuously provides further evidence on multiple drug resistance (MDR), aiding scientists in tackling and overcoming this issue. This review focuses on drug resistance by ABC efflux transporters in human, viral, parasitic, fungal and bacterial cells and highlights the importance of the MDR permeability glycoprotein being the mutual ABC transporter among all studied organisms. Current developments and future directions to overcome this problem are also discussed.

Inhibition of topoisomerase IIα sensitizes FaDu cells to ionizing radiation by diminishing DNA repair.

Despite the high efficiency of ionizing radiation (IR) to inactivate malignant tumours in general, an appreciable number of individual patients cannot be cured by standard IR. Head and neck tumours are not likely to be cured even by high-dose radiotherapy or chemotherapy. Accordingly, combined therapy is one of the most applicable strategies. Topoisomerase IIα is a ubiquitous enzyme that removes knots and tangles from the genetic material by generating and subsequently resealing of transient double-strand breaks. Due to its unique mechanism of action, topoisomerase IIα is the target of many chemotherapeutic agents such as etoposide. The aim of the present study is to examine the effect of inhibiting topoisomerase IIα by etoposide on the response of squamous cell carcinoma to IR. Results of the present study demonstrated a radiosensitizing effect for the topoisomerase IIα inhibitor etoposide on exponentially growing squamous cell carcinoma (FaDu) cell line especially at low radiation doses. This effect was found to be due to inhibition, by etoposide, of the repair of radiation-induced DNA damage. Cell cycle studies showed that the concentration of etoposide that sensitized the cells to radiation had no effect on the distribution of cells at different phases of the cell cycle. Synchronization of FaDu cells in different cell cycle phases revealed that proliferating G1 and G2 cells are responsible for sensitization of cells at low doses of ionizing radiation. It might, therefore, be concluded that topoisomerase II enzyme may be involved in the repair of radiation-induced DNA damage and consequently its inhibition constitute a strategy for sensitizing tumour cells to ionizing radiation.

Epigenetics and miRNA as predictive markers and targets for lung cancer chemotherapy.

Lung cancer cells show inherent and acquired resistance to chemotherapy. The lack of good predictive markers/novel targets and the incomplete understanding of the mechanisms of resistance limit the success of lung cancer response to chemotherapy. In the present study, we used an isogenic pair of lung adenocarcinoma cell lines; A549 (wild-type) and A549DOX11 (doxorubicin resistant) to study the role of epigenetics and miRNA in resistance/response of non-small cell lung cancer (NSCLC) cells to doxorubicin. Our results demonstrate differential expression of epigenetic markers whereby the level of HDACs 1, 2, 3 and4, DNA methyltransferase, acetylated H2B and acetylated H3 were lower in A549DOX11 compared to A549 cells. Fourteen miRNAs were dys-regulated in A549DOX11 cells compared to A549 cells, of these 14 miRNAs, 4 (has-mir-1973, 494, 4286 and 29b-3p) have shown 2.99 - 4.44 fold increase in their expression. This was associated with reduced apoptosis and higher resistance of A549DOX11cells to doxorubicin and etoposide. Sequential treatment with the epigenetic modifiers trichostatin A or 5-aza-2'-deoxycytidine followed by doxorubicin resulted in: (i) enhanced sensitivity of both cell lines to doxorubicin especially at low concentrations, (ii) enhanced doxorubicin-induced DNA damage in both cell lines, (iii) dysregulation of some miRNAs in A549 cells. In conclusion, A549DOX11 cells resistant to DNA damaging drugs have epigenetic profile and miRNA expression different from the sensitive cells. Moreover, epigenetic modifiers may reverse the resistance of certain NSCLC cells to DNA damaging agents by enhancing induction of DNA damage. This may open the door for using epigenetic profile/miRNA expression of some cancer cells as resistance markers/targets to improve response of resistant cells to doxorubicin and for the use of combination doxorubicin/epigenetic modifiers to reduce doxorubicin toxicity.

Induction and repair of DNA double-strand breaks using constant-field gel electrophoresis and apoptosis as predictive markers for sensitivity of cancer cells to cisplatin.

This study was designed to evaluate some parameters that may play a role in the prediction of cancer cells sensitivity to cisplatin (CIS). Sensitivity, induction and repair of DNA double-strand breaks (DSB), cell cycle regulation and induction of apoptosis were measured in four cancer cell lines with different sensitivities to CIS. Using a sulphorhodamine-B assay, the cervical carcinoma cells (HeLa) were found to be the most sensitive to CIS followed by breast carcinoma cells (MCF-7) and liver carcinoma cells (HepG2). Colon carcinoma HCT116 cells were the most resistant. As measured by constant-field gel electrophoresis (CFGE), DSB induction, but not residual DSB exhibited a significant correlation with the sensitivity of cells to CIS. Flow cytometric DNA ploidy analysis revealed that 67% of HeLa cells and 10% of MCF-7 cells shift to sub-G1 phase after incubation with CIS. Additionally, CIS induced the arrest of MCF-7 cells in S-phase and the arrest of HepG2 and HCT116 cells in both S phase and G2/M phase. Determination of the Fas-L level and Caspase-9 activity indicated that CIS-induced apoptosis results from the mitochondrial (intrinsic) pathway. These results, if confirmed using clinical samples, indicate that the induction of DNA DSB as measured by CFGE and the induction of apoptosis should be considered, along with other predictive markers, in future clinical trials to develop predictive assays for platinum -based therapy.

Antagonism between curcumin and the topoisomerase II inhibitor etoposide: a study of DNA damage, cell cycle regulation and death pathways.

UNLABELLED: The use of combinations of chemotherapy and natural products has recently emerged as a new method of cancer therapy, relying on the capacity of certain natural compounds to trigger cell death with low doses of chemotherapeutic agents and few side effects. The current study aims to evaluate the modulatory effects of curcumin (CUR), Nigella sativa (NS) and taurine on etoposide (ETP) cytotoxicity in a panel of cancer cell lines and to identify their underlying mechanisms. CUR alone showed potent antitumor activity, but surprisingly, its interaction with ETP was antagonistic in four out of five cancer cell lines. Neither taurine nor Nigella sativa affect the sensitivity of cancer cells to ETP. Examination of the DNA damage response machinery (DDR) showed that both ETP and CUR elicited DNA double-strand breaks (DSB) and evoked γ-H2AX foci formation at doses as low as 1 µg/ml. Cell cycle analysis revealed S phase arrest after ETP or CUR application, whereas co-treatment with ETP and CUR led to increased arrest of the cell cycle in S phase (MCF-7 cells) or the accumulation of cells in G 2/M phases (HCT116, and HeLa cells). Furthermore, cotreatment with ETP and CUR resulted in modulation of the level of DNA damage induction and repair compared with either agent alone. Electron microscopic examination demonstrated that different modalities of cell death occurred with each treatment. CUR alone induced autophagy, apoptosis and necrosis, whereas ETP alone or in combination with CUR led to apoptosis and necrosis. CONCLUSIONS: Cotreatment with ETP and CUR resulted in an antagonistic interaction. This antagonism is related, in part, to the enhanced arrest of tumor cells in both S and G 2/M phases, which prevents the cells from entering M-phase with damaged DNA and, consequently, prevents cell death from occurring. This arrest allows time for the cells to repair DNA damage so that cell cycle -arrested cells can eventually resume cell cycle progression and continue their physiological program.

Interaction of celecoxib with different anti-cancer drugs is antagonistic in breast but not in other cancer cells.

Celecoxib, an inhibitor of cyclooxygenase-2, is being investigated for enhancement of chemotherapy efficacy in cancer clinical trials. This study investigates the ability of cyclooxygenase-2 inhibitors to sensitize cells from different origins to several chemotherapeutic agents. The effect of the drug's mechanism of action and sequence of administration are also investigated. The sensitivity, cell cycle, apoptosis and DNA damage of five different cancer cell lines (HeLa, HCT116, HepG2, MCF7 and U251) to 5-FU, cisplatin, doxorubicin and etoposide±celecoxib following different incubation schedules were analyzed. We found antagonism between celecoxib and the four drugs in the breast cancer cells MCF7 following all incubation schedules and between celecoxib and doxorubicin in all cell lines except for two combinations in HCT116 cells. Celecoxib with the other three drugs in the remaining four cell lines resulted in variable interactions. Mechanistic investigations revealed that celecoxib exerts different molecular effects in different cells. In some lines, it abrogates the drug-induced G2/M arrest enhancing pre-mature entry into mitosis with damaged DNA thus increasing apoptosis and resulting in synergism. In other cells, it enhances drug-induced G2/M arrest allowing time to repair drug-induced DNA damage before entry into mitosis and decreasing cell death resulting in antagonism. In some synergistic combinations, celecoxib-induced abrogation of G2/M arrest was not associated with apoptosis but permanent arrest in G1 phase. These results, if confirmed in-vivo, indicate that celecoxib is not a suitable chemosensitizer for breast cancer or with doxorubicin for other cancers. Moreover, combination of celecoxib with other drugs should be tailored to the tumor type, drug and administration schedule.

Targeting DNA double-strand break repair: is it the right way for sensitizing cells to 5-fluorouracil?

Inhibition of the repair of 5-fluorouracil (FU)-induced DNA lesions may improve the response of many tumors to this anticancer agent. Despite the identified associations between DNA strand breaks and the lethality of thymidylate synthase inhibitors, the role of DNA double-strand break (DSB) repair pathways in a cellular response to 5-FU treatment has not been studied yet. Isogenic cell lines defective (irs1SF), wild type (AA8), or reconstituted (1SFK8) in the DSB repair protein XRCC3 were used to investigate the effect of defective DSB repair on the overall sensitivity of cells to 5-FU and to see how targeting DSB repair may affect other cellular responses to 5-FU. Treatment with 5-FU resulted in (i) similar induction of DSB in both cell lines as indicated by the formation of gamma-H2AX (a marker for DSB). The repair of these breaks was complete in AA8 but not in irs1SF cells. (ii) Concentration-dependent reduction in the survival of both cell lines. The AA8 cells were six times more sensitive to 5-FU than the irs1SF cells. (iii) An earlier and more prolonged G(1)/S phase arrest in AA8 compared with the irs1SF cells. (iv) Induction of apoptosis as indicated by sub-G(1) cells and caspase-3 activity in AA8 but not in irs1SF cells. XRCC3 complementation of irs1SF cells restored the wild-type phenotype. This result shows that targeting DSB repair is not always associated with increased sensitivity to DNA damaging agents such as 5-FU because it may affect other cellular responses such as cell cycle regulation and induction of apoptosis.

Altered expression of proliferation-inducing and proliferation-inhibiting genes might contribute to acquired doxorubicin resistance in breast cancer cells.

This study was designed to investigate the molecular changes that may develop during exposure of breast cancer cells to anticancer agents and that may lead to acquired resistance. We used two breast cancer cell lines, a parental (MCF7/WT) and a doxorubicin-resistant (MCF7/DOX) one. Cell survival, cell cycle distribution and RT-PCR expression level of genes involved in DNA damage response, MDR1, GST and TOPOIIalpha were measured. MCF7/DOX cells were five-fold more resistant to doxorubicin (DOX) than the MCF7/WT cells. DOX treatment causes arrest of MCF7/DOX cells in G1 and G2 phases of cell cycle whereas MCF7/WT cells were arrested in S-phase. The molecular changes in both cell lines due to DOX treatment could be classified into: (1) the basal level of p53, p21, BRCA1, GST and TOPOIIalpha mRNA was higher in MCF7/DOX than MCF7/WT. During DOX treatment, the expression level of these genes decreased in both cell lines but the rate of down-regulation was faster in MCF7/WT than MCF7/DOX cells. (2) The expression level of MDR1 was the same in both cell lines but 48 and 72 h of drug treatment, MDR1 disappeared in MCF7/WT but still expressed in MCF7/DOX. (3) There was no change in the expression level of BAX, FAS and BRCA2 in both cell lines. Conclusively, after validation in clinical samples, overexpression of genes like BRCA1, p53, p21, GST, MDR1 and TOPOIIalpha could be used as a prognostic biomarker for detection of acquired resistance in breast cancer and as therapeutic targets for the improvement of breast cancer treatment strategies.

Apoptosis is the most efficient death-pathway in tumor cells after topoisomerase II inhibition.

OBJECTIVE: To compare the efficiency of apoptosis and other modes of cell death in killing tumor cells after the induction of DNA damage by topoisomerase inhibitors like etoposide. METHODS: This study was carried out in the Tumor Biology Department, National Cancer Institute, Cairo University, Cairo, Egypt, from September 2005 to August 2007. The breast cancer MCF7, the cervix carcinoma, human cervical adenocarcinoma Hela, and the brain tumor U251 cell lines were exposed to etoposide. Apoptosis was detected using the flow cytometry and the DNA ladder formation methods. Cell viability was determined by a colorimetric assay, and the residual DNA double-strand breaks dsb were measured by gel electrophoresis. RESULTS: The Hela cells were the most, the MCF7's were moderately, whereas the U251's were the least sensitive to etoposide. Apoptosis was detected only in Hela cells whereas the other 2 cell lines showed a very low level of apoptosis only 3% increase above the control cells. At equitoxic drug concentrations namely IC50, the Hela cells showed the lowest amount of non-repaired DNA dsb, and the MCF7's showed the highest amount, whereas the U251 cells showed a moderate amount. CONCLUSION: These results indicate that although other modes of cell death exist, apoptosis is the most efficient and requires lower drug concentrations and fewer numbers of non-repaired dsb to give the same killing effect. Clinically, this means that tumors that can execute apoptosis may require lower doses of topoisomerase inhibitors than those that lost the ability to exercise apoptosis.