miR-326-Histone Deacetylase-3 Feedback Loop Regulates the Invasion and Tumorigenic and Angiogenic Response to Anti-cancer Drugs

Histone modification is known to be associated with multidrug resistance phenotypes. Cancer cell lines that are resistant or have been made resistant to anti-cancer drugs showed lower expression levels of histone deacetylase-3 (HDAC3), among the histone deacetylase(s), than cancer cell lines that were sensitive to anti-cancer drugs. Celastrol and Taxol decreased the expression of HDAC3 in cancer cell lines sensitive to anti-cancer drugs. HDAC3 negatively regulated the invasion, migration, and anchorage-independent growth of cancer cells. HDAC3 conferred sensitivity to anti-cancer drugs in vitro and in vivo. TargetScan analysis predicted miR-326 as a negative regulator of HDAC3. ChIP assays and luciferase assays showed a negative feedback loop between HDAC3 and miR-326. miR-326 decreased the apoptotic effect of anti-cancer drugs, and the miR-326 inhibitor increased the apoptotic effect of anti-cancer drugs. miR-326 enhanced the invasion and migration potential of cancer cells. The miR-326 inhibitor negatively regulated the tumorigenic, metastatic, and angiogenic potential of anti-cancer drug-resistant cancer cells. HDAC3 showed a positive feedback loop with miRNAs such as miR-200b, miR-217, and miR-335. miR-200b, miR-217, and miR-335 negatively regulated the expression of miR-326 and the invasion and migration potential of cancer cells while enhancing the apoptotic effect of anti-cancer drugs. TargetScan analysis predicted miR-200b and miR-217 as negative regulators of cancer-associated gene, a cancer/testis antigen, which is known to regulate the response to anti-cancer drugs. HDAC3 and miR-326 acted upstream of the cancer-associated gene. Thus, we show that the miR-326-HDAC3 feedback loop can be employed as a target for the development of anti-cancer therapeutics.     

A New 2α,5α,10β,14β-tetraacetoxy-4(20),11-taxadiene (SIA) Derivative Overcomes Paclitaxel Resistance by Inhibiting MAPK Signaling and Increasing Paclitaxel Accumulation in Breast Cancer Cells

Tumor resistance due to multiple mechanisms seriously hinders the efficacy of chemotherapy drugs such as paclitaxel. The most widely studied P-glycoprotein inhibitors still have limited ability to reverse resistance in the clinic. In this study, NPB304, a novel Sinenxan A (SIA) derivative, was found to significantly sensitize resistant breast cancer cells to paclitaxel in vitro and in vivo. Treatment with NPB304 increased paclitaxel-induced apoptosis in a p53-dependent manner through PARP cleavage. Importantly, NPB304 enhanced the antitumor effect of paclitaxel in resistant breast tumor xenografts in nude mice without significantly affecting weight loss. NPB304 regulated cell resistance through inhibition of MAPK pathway components, including p-ERK and p-p38. Moreover, NPB304 increased paclitaxel accumulation by affecting P-gp function. In addition to increasing Rhodamine 123 accumulation, NPB304 promoted bidirectional permeability but decreased the efflux ratio of paclitaxel in a Caco-2 monolayer model, thereby increasing the intracellular concentration of paclitaxel. Similarly, NPB304 increased the concentration of paclitaxel in the resistant tumor tissue. Hence, NPB304 is a novel compound that promotes the sensitization of resistant cells to paclitaxel through multiple mechanisms and has the potential for use in combination therapies to treat resistant breast cancer.     

A methylene chloride fraction of Saururus chinensis induces apoptosis through the activation of caspase-3 in prostate and breast cancer cells

The aerial parts of Saururus chinensis (SC) have been used for the treatment of edema, fever, jaundice, and inflammatory diseases in Korean folk medicine for centuries. However, the mechanism by which SC exerts these anti-tumorigenic activities in human prostate and breast cancer cells has not yet been fully understood. In this study, we report on the methylene chloride fraction from SC exerting cytotoxicity against prostate and breast cancer cells in a dose-dependent manner. Specifically, SC exerted the most potent cytotoxicity in LNCaP and MCF-7 cells. SC was shown to down-regulate various angiogenetic (VEGF), proliferative (Cyclin D₁), anti-apoptotic (Bcl-2) gene products in these cells. SC also increased the number of annexin V-positive apoptotic bodies and the sub-G1 DNA contents of the cell cycle undergoing apoptosis through caspase-3 activation in both LNCaP and MCF-7 cells. We further confirmed that caspase-3 plays an important role in SC-induced apoptosis in LNCaP and MCF-7 cells through the use of the caspase-3 inhibitor. Moreover, we observed that SC potentiated paclitaxel-induced apoptosis in MCF-7 cells and sauchinone is a major active constituent of SC, which could induce apoptosis in the cells. Taken together, our data provide the evidence that SC induces apoptosis depending on caspase-3 activation and overcomes the natural biological resistance to chemotherapy found in human prostate and breast cancer cells.     

Paclitaxel-Induced Apoptosis Is BAK-Dependent,but BAX and BIM-Independent in Breast Tumor

Paclitaxel (Taxol)-induced cell death requires the intrinsic cell death pathway, but the specific participants and the precise mechanisms are poorly understood. Previous studies indicate that a BH3-only protein BIM (BCL-2 Interacting Mediator of cell death) plays a role in paclitaxel-induced apoptosis. We show here that BIM is dispensable in apoptosis with paclitaxel treatment using bim^−/− MEFs (mouse embryonic fibroblasts), the bim^−/− mouse breast tumor model, and shRNA-mediated down-regulation of BIM in human breast cancer cells. In contrast, both bak ^−/− MEFs and human breast cancer cells in which BAK was down-regulated by shRNA were more resistant to paclitaxel. However, paclitaxel sensitivity was not affected in bax^−/− MEFs or in human breast cancer cells in which BAX was down-regulated, suggesting that paclitaxel-induced apoptosis is BAK-dependent, but BAX-independent. In human breast cancer cells, paclitaxel treatment resulted in MCL-1 degradation which was prevented by a proteasome inhibitor, MG132. A Cdk inhibitor, roscovitine, blocked paclitaxel-induced MCL-1 degradation and apoptosis, suggesting that Cdk activation at mitotic arrest could induce subsequent MCL-1 degradation in a proteasome-dependent manner. BAK was associated with MCL-1 in untreated cells and became activated in concert with loss of MCL-1 expression and its release from the complex. Our data suggest that BAK is the mediator of paclitaxel-induced apoptosis and could be an alternative target for overcoming paclitaxel resistance.     

miR-335 Targets SIAH2 and Confers Sensitivity to Anti-Cancer Drugs by Increasing the Expression of HDAC3

We previously reported the role of histone deacetylase 3 (HDAC3) in response to anti-cancer drugs. The decreased expression of HDAC3 in anti-cancer drug-resistant cancer cell line is responsible for the resistance to anti-cancer drugs. In this study, we investigated molecular mechanisms associated with regulation of HDAC3 expression. MG132, an inhibitor of proteasomal degradation, induced the expression of HDAC3 in various anti-cancer drug-resistant cancer cell lines. Ubiquitination of HDAC3 was observed in various anti-cancer drug-resistant cancer cell lines. HDAC3 showed an interaction with SIAH2, an ubiquitin E3 ligase, that has increased expression in various anti-cancer drug-resistant cancer cell lines. miRNA array analysis showed the decreased expression of miR-335 in these cells. Targetscan analysis predicted the binding of miR-335 to the 3′-UTR of SIAH2. miR-335-mediated increased sensitivity to anti-cancer drugs was associated with its effect on HDAC3 and SIAH2 expression. miR-335 exerted apoptotic effects and inhibited ubiquitination of HDAC3 in anti-cancer drug-resistant cancer cell lines. miR-335 negatively regulated the invasion, migration, and growth rate of cancer cells. The mouse xenograft model showed that miR-335 negatively regulated the tumorigenic potential of cancer cells. The down-regulation of SIAH2 conferred sensitivity to anti-cancer drugs. The results of the study indicated that the miR-335/SIAH2/HDAC3 axis regulates the response to anti-cancer drugs.     

Tubulin Beta3 Serves as a Target of HDAC3 and Mediates Resistance to Microtubule-Targeting Drugs

We investigated the role of HDAC3 in anti-cancer drug-resistance. The expression of HDAC3 was decreased in cancer cell lines resistant to anti-cancer drugs such as celastrol and taxol. HDAC3 conferred sensitivity to these anti-cancer drugs. HDAC3 activity was necessary for conferring sensitivity to these anti-cancer drugs. The down-regulation of HDAC3 increased the expression of MDR1 and conferred resistance to anti-cancer drugs. The expression of tubulin β3 was increased in drug-resistant cancer cell lines. ChIP assays showed the binding of HDAC3 to the promoter sequences of tubulin β3 and HDAC6. HDAC6 showed an interaction with tubulin β3. HDAC3 had a negative regulatory role in the expression of tubulin β3 and HDAC6. The down-regulation of HDAC6 decreased the expression of MDR1 and tubulin β3, but did not affect HDAC3 expression. The down-regulation of HDAC6 conferred sensitivity to taxol. The down-regulation of tubulin β3 did not affect the expression of HDAC6 or MDR1. The down-regulation of tubulin β3 conferred sensitivity to anti-cancer drugs. Our results showed that tubulin β3 serves as a downstream target of HDAC3 and mediates resistance to microtubule-targeting drugs. Thus, the HDAC3-HDAC6-Tubulin β axis can be employed for the development of anti-cancer drugs.     

Anticancer properties and enhancement of therapeutic potential of cisplatin by leaf extract of Zanthoxylum armatum DC.

Background

Clinical use of chemotherapeutic drug, cisplatin is limited by its toxicity and drug resistance. Therefore, efforts continue for the discovery of novel combination therapies with cisplatin, to increase efficacy and reduce its toxicity. Here, we screened 16 medicinal plant extracts from Northeast part of India and found that leaf extract of Zanthoxylumarmatum DC. (ZALE) induced cytotoxicity as well as an effect on the increasing of the efficiency of chemotherapeutic drugs (cisplatin, mitomycin C and camptothecin). This work shows detail molecular mechanism of anti-cancer activity of ZALE and its potential for combined treatment regimens to enhance the apoptotic response of chemotherapeutic drugs.

Results

ZALE induced cytotoxicity, nuclear blebbing and DNA fragmentation in HeLA cells suggesting apoptosis induction in human cervical cell line. However, the apoptosis induced was independent of caspase 3 activation and poly ADP ribose polymerase (PARP) cleavage. Further, ZALE activated Mitogen-activated protein kinases (MAPK) pathway as revealed by increased phosphorylation of extracellular-signal-regulated kinases (ERK), p38 and c-Jun N-terminal kinase (JNK). Inhibition of ERK activation but not p38 or JNK completely blocked the ZALE induced apoptosis suggesting an ERK dependent apoptosis. Moreover, ZALE generated DNA double strand breaks as suggested by the induction γH2AX foci formation. Interestingly, pretreatment of certain cancer cell lines with ZALE, sensitized the cancer cells to cisplatin and other chemotherapeutic drugs. Enhanced caspase activation was observed in the synergistic interaction among chemotherapeutic drugs and ZALE.

Conclusion

Purification and identification of the bio-active molecules from the ZALE or as a complementary treatment for a sequential treatment of ZALE with chemotherapeutic drugs might be a new challenger to open a new therapeutic window for the novel anti-cancer treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s40659-015-0037-4) contains supplementary material, which is available to authorized users.     

Novel in vitro and in vivo models to study central nervous system infections due to Acanthamoeba spp.

Acanthamoeba granulomatous encephalitis is a serious human infection with fatal consequences. The most distressing aspect of Acanthamoeba granulomatous encephalitis is the limited improvement in mortality. The underlying neurobiology is at present not well understood and treatment options are often of limited efficacy. There is therefore a real need to obtain more knowledge regarding the pathogenesis and pathophysiology of Acanthamoeba granulomatous encephalitis and to develop new chemotherapeutic approaches. However, the difficulties in using mammalian models to study this infection have hindered our search for therapeutic interventions. Recent availability of the blood-brain barrier, in vitro and use of locust as an in vivo model will undoubtedly allow us to investigate disease pathogenesis, mechanisms of parasite traversal across the blood-brain barrier and new drug therapies. It is argued that the models described here can offer several advantages in terms of speed, cost, technical convenience, and ethical acceptance. Furthermore, they are extremely valuable tools to discriminate molecules participating from both sides of the host-parasite interaction and will generate potentially useful leads in the identification of new potential drugs, as well as testing drug toxicity.     

CSE1L/CAS, a microtubule-associated protein, inhibits taxol (paclitaxel)-induced apoptosis but enhances cancer cell apoptosis induced by various chemotherapeutic drugs

CSE1L/CAS, a microtubule-associated, cellular apoptosis susceptibility protein, is highly expressed in various cancers. Microtubules are the target of paclitaxel-induced apoptosis. We studied the effects of increased or reduced CAS expression on cancer cell apoptosis induced by chemotherapeutic drugs including paclitaxel. Our results showed that CAS overexpression enhanced apoptosis induced by doxorubicin, 5-fluorouracil, cisplatin, and tamoxifen, but inhibited paclitaxel-induced apoptosis of cancer cells. Reductions in CAS produced opposite results. CAS overexpression enhanced p53 accumulation induced by doxorubicin, 5-fluorouracil, cisplatin, tamoxifen, and etoposide. CAS was associated with alpha-tubulin and beta-tubulin and enhanced the association between alpha-tubulin and beta-tubulin. Paclitaxel can induce G2/M phase cell cycle arrest and microtubule aster formation during apoptosis induction, but CAS overexpression reduced paclitaxel-induced G2/M phase cell cycle arrest and microtubule aster formation. Our results indicate that CAS may play an important role in regulating the cytotoxicities of chemotherapeutic drugs used in cancer chemotherapy against cancer cells.     

Methotrexate and aminopterin lack in vivo antimalarial activity against murine malaria species

The antifolate anticancer drug methotrexate (MTX) has potent activity against Plasmodium falciparum in vitro. Experience of its use in the treatment of rheumatoid arthritis indicates that it could be safe and efficacious for treating malaria. We sought to establish a murine malaria model to study the mechanism of action and resistance of MTX and its analogue aminopterin (AMP). We used Plasmodium berghei, Plasmodium yoelii yoelii, Plasmodium chabaudi and Plasmodium vinckei. None of these species were susceptible to either drug. We have also tested the efficacy of pyrimethamine in combination with folic acid in P. berghei, and data indicate that folic acid does not influence pyrimethamine efficacy, which suggests that P. berghei may not transport folate. Since MTX and AMP utilise folate receptor/transport to gain access to cells, their lack of efficacy against the four tested murine malaria species may be the result of inefficiency of drug transport.     

Histone Deacetylase-3/CAGE Axis Targets EGFR Signaling and Regulates the Response to Anti-Cancer Drugs

We have previously reported the role of miR-326-HDAC3 loop in anti-cancer drug-resistance. CAGE, a cancer/testis antigen, regulates the response to anti-cancer drug-resistance by forming a negative feedback loop with miR-200b. Studies investigating the relationship between CAGE and HDAC3 revealed that HDAC3 negatively regulated the expression of CAGE. ChIP assays demonstrated the binding of HDAC3 to the promoter sequences of CAGE. However, CAGE did not affect the expression of HDAC3. We also found that EGFR signaling regulated the expressions of HDAC3 and CAGE. Anti-cancer drug-resistant cancer cell lines show an increased expression of pEGFR^Y845. HDAC3 was found to negatively regulate the expression of pEGFR^Y845. CAGE showed an interaction and co-localization with EGFR. It was seen that miR-326, a negative regulator of HDAC3, regulated the expression of CAGE, pEGFR^Y845, and the interaction between CAGE and EGFR. miR-326 inhibitor induced the binding of HDAC3 to the promoter sequences in anti-cancer drug-resistant Malme3M^R cells, decreasing the tumorigenic potential of Malme3M^R cells in a manner associated with its effect on the expression of HDAC3, CAGE and pEGFR^Y845. The down-regulation of HDAC3 enhanced the tumorigenic, angiogenic and invasion potential of the anti-cancer drug-sensitive Malme3M cells in CAGE-dependent manner. Studies revealed that PKCδ was responsible for the increased expression of pEGFR^Y845 and CAGE in Malme3M^R cells. CAGE showed an interaction with PKCδ in Malme3M^R cells. Our results show that HDAC3-CAGE axis can be employed as a target for overcoming resistance to EGFR inhibitors.     

Leishmania (Viannia) panamensis: An in vitro assay using the expression of GFP for screening of antileishmanial drug

Promastigotes of Leishmania (Viannia) panamensis were successfully transfected with p6.5-egfp to express green fluorescent protein. The transfectants remained infective to macrophages, providing an in vitro model for screening antileishmanial drugs. This was demonstrated by flow cytometry of macrophage-associated GFP after exposure of infected cultures to known antileishmanial drugs, i.e. amphotericin B and glucantime^®. Fluorescence of GFP diminished progressively from infected cells with increasing drug concentrations used in both cases. The availability of this fluorescent assay for infection of macrophages by L. (V.) panamensis facilitates drug discovery program for the Viannia species, which differ significantly from those of the Leishmania subgenus.     

Natural Product Celastrol Destabilizes Tubulin Heterodimer and Facilitates Mitotic Cell Death Triggered by Microtubule-Targeting Anti-Cancer Drugs

Background

Microtubule drugs are effective anti-cancer agents, primarily due to their ability to induce mitotic arrest and subsequent cell death. However, some cancer cells are intrinsically resistant or acquire a resistance. Lack of apoptosis following mitotic arrest is thought to contribute to drug resistance that limits the efficacy of the microtubule-targeting anti-cancer drugs. Genetic or pharmacological agents that selectively facilitate the apoptosis of mitotic arrested cells present opportunities to strengthen the therapeutic efficacy.

Methodology and Principal Findings

We report a natural product Celastrol targets tubulin and facilitates mitotic cell death caused by microtubule drugs. First, in a small molecule screening effort, we identify Celastrol as an inhibitor of neutrophil chemotaxis. Subsequent time-lapse imaging analyses reveal that inhibition of microtubule-mediated cellular processes, including cell migration and mitotic chromosome alignment, is the earliest events affected by Celastrol. Disorganization, not depolymerization, of mitotic spindles appears responsible for mitotic defects. Celastrol directly affects the biochemical properties of tubulin heterodimer in vitro and reduces its protein level in vivo. At the cellular level, Celastrol induces a synergistic apoptosis when combined with conventional microtubule-targeting drugs and manifests an efficacy toward Taxol-resistant cancer cells. Finally, by time-lapse imaging and tracking of microtubule drug-treated cells, we show that Celastrol preferentially induces apoptosis of mitotic arrested cells in a caspase-dependent manner. This selective effect is not due to inhibition of general cell survival pathways or mitotic kinases that have been shown to enhance microtubule drug-induced cell death.

Conclusions and Significance

We provide evidence for new cellular pathways that, when perturbed, selectively induce the apoptosis of mitotic arrested cancer cells, identifying a potential new strategy to enhance the therapeutic efficacy of conventional microtubule-targeting anti-cancer drugs.     

Molecular evidence of anti-leukemia activity of gypenosides on human myeloid leukemia HL-60 cells in vitro and in vivo using a HL-60 cells murine xenograft model

We have shown that gypenosides (Gyp) induced cell cycle arrest and apoptosis in many human cancer cell lines. However, there are no reports showing that show Gyp acts on human leukemia HL-60 cells in vitro and in a murine xenograft model in vivo. In the present study effects of Gyp on cell morphological changes and viability, cell cycle arrest and induction of apoptosis in vitro and effects on Gyp in an in vivo murine xenograft model. Results indicated that Gyp induced morphological changes, decreased cell viability, induced G0/G1 arrest, DNA fragmentation and apoptosis (sub-G1 phase) in HL-60 cells. Gyp increased reactive oxygen species production and Ca²⁺ levels but reduced mitochondrial membrane potential in a dose- and time-dependent manner. Gyp also changed one of the primary indicators of endoplasmic reticulum (ER) stress due to the promotion of ATF6-α and ATF4-α associated with Ca²⁺ release. Gyp reduced the ratio of Bcl-2 to Bax due to an increase in the pro-apoptotic protein Bax and inhibited levels of the anti-apoptotic protein Bcl-2. Oral consumption of Gyp reduced tumor size of HL-60 cell xenograft mode mice in vivo. These results provide new information on understanding mechanisms by which Gyp induces cell cycle arrest and apoptosis in vitro and in vivo.     

Toxocara canis: Potential activity of natural products against second-stage larvae in vitro and in vivo

The anthelmintic activity of extracts from Chenopodiumambrosioides, Pycnanthusangolensis and Nutridesintox® was in vitro and in vivo investigated, against Toxocaracanis larvae. The in vitro assays results showed that the aqueous extract of Nutridesintox® was the most effective, followed by C. ambrosioides extracts, hexane, dichloromethane and the infusion. P. angolensis extracts showed a lower anthelmintic activity compared to the other natural products. For the in vivo assays, Nutridesintox®, the hexane extract and the infusion of C. ambrosioides were administered orally to T. canis-infected mice, in single doses, during three consecutive days. The efficacy was evaluated on the 17th day post-infection, not only by counting T. canis larvae in the tissues but also by ELISA detection of IgM and IgG antibodies and histological analysis of liver and lungs. The different treatments did not reduce the larvae burden and had no influence on the antibodies dynamic. Interestingly, a reduction on the inflammatory infiltrates was observed in the liver and lung sections of the group treated with the hexane extract of C. ambrosioides. In conclusion, the hexane extract of C. ambrosioides is of further research interest, as it showed an anthelmintic activity in vitro and a reduction on the inflammatory reaction produced by the infection of T. canis larvae in vivo.     

Synergistic anti-tumor activity of isochaihulactone and paclitaxel on human lung cancer cells

Drug resistance frequently develops in tumors during chemotherapy. Therefore, to improve the clinical outcome, more effective and tolerable combination treatment strategies are needed. Here, we show that isochaihulactone (K8) enhanced paclitaxel-induced apoptotic death in human lung cancer cells, and the enhancing effect was related to increased NSAID-activated gene-1 (NAG-1) expression. CalcuSyn software was used to evaluate the synergistic interaction of K8 and paclitaxel on human lung cancer cells; the synergistic effect of K8 in combination with paclitaxel was increased more than either of these drugs alone. Furthermore, the activity of ERK1/2 was enhanced by the combination of K8 and paclitaxel, and an ERK1/2 inhibitor dramatically inhibited NAG-1 expression in human lung cancer cells. Therefore, this synergistic apoptotic effect in human lung cancer cells may be directly associated with K8-induced NAG-1 expression through ERK1/2 activation. Moreover, over-expression of NAG-1 enhanced K8/paclitaxel-induced apoptosis in human lung cancer cells. In addition, treatment of nude mice with K8 combined with paclitaxel induced phospho-ERK1/2 and NAG-1 expression in vivo. Targeting of NAG-1 signaling could enhance therapeutic efficacy in lung cancer. Our results reveal that activation of NAG-1 by K8 enhanced the therapeutic efficacy of paclitaxel in human lung cancer cells via the ERK1/2 signaling pathway.     

Cancer/Testis Antigen CAGE Exerts Negative Regulation on p53 Expression through HDAC2 and Confers Resistance to Anti-cancer Drugs

The role of the cancer/testis antigen CAGE in drug resistance was investigated. The drug-resistant human melanoma Malme3M (Malme3M^R) and the human hepatic cancer cell line SNU387 (SNU387^R) showed in vivo drug resistance and CAGE induction. Induction of CAGE resulted from decreased expression and thereby displacement of DNA methyltransferase 1(DNMT1) from CAGE promoter sequences. Various drugs induce expression of CAGE by decreasing expression of DNMT1, and hypomethylation of CAGE was correlated with the increased expression of CAGE. Down-regulation of CAGE in these cell lines decreased invasion and enhanced drug sensitivity resulting from increased apoptosis. Down-regulation of CAGE also led to decreased anchorage-independent growth. Down-regulation of CAGE led to increased expression of p53, suggesting that CAGE may act as a negative regulator of p53. Down-regulation of p53 enhanced resistance to drugs and prevented drugs from exerting apoptotic effects. In SNU387^R cells, CAGE induced the interaction between histone deacetylase 2 (HDAC2) and Snail, which exerted a negative effect on p53 expression. Chromatin immunoprecipitation assay showed that CAGE, through interaction with HDAC2, exerted a negative effect on p53 expression in Malme3M^R cells. These results suggest that CAGE confers drug resistance by regulating expression of p53 through HDAC2. Taken together, these results show the potential value of CAGE as a target for the development of cancer therapeutics.     

Chemosensitization by phenothiazines in human lung cancer cells: impaired resolution of ��H2AX and increased oxidative stress elicit apoptosis associated with lysosomal expansion and intense vacuolation

Chemotherapy resistance poses severe limitations on the efficacy of anti-cancer medications. Recently, the notion of using novel combinations of ‘old'' drugs for new indications has garnered significant interest. The potential of using phenothiazines as chemosensitizers has been suggested earlier but so far our understanding of their molecular targets remains scant. The current study was designed to better define phenothiazine-sensitive cellular processes in relation to chemosensitivity. We found that phenothiazines shared the ability to delay γH2AX resolution in DNA-damaged human lung cancer cells. Accordingly, cells co-treated with chemotherapy and phenothiazines underwent protracted cell-cycle arrest followed by checkpoint escape that led to abnormal mitoses, secondary arrest and/or a form of apoptosis associated with increased endogenous oxidative stress and intense vacuolation. We provide evidence implicating lysosomal dysfunction as a key component of cell death in phenothiazine co-treated cells, which also exhibited more typical hallmarks of apoptosis including the activation of both caspase-dependent and -independent pathways. Finally, we demonstrated that vacuolation in phenothiazine co-treated cells could be reduced by ROS scavengers or the vacuolar ATPase inhibitor bafilomycin, leading to increased cell viability. Our data highlight the potential benefit of using phenothiazines as chemosensitizers in tumors that acquire molecular alterations rendering them insensitive to caspase-mediated apoptosis.