Enhanced Doxorubicin Cytotoxicity Research Articles

Enhanced chemosensitivity of drug-resistant osteosarcoma cells by lentivirus-mediated Bcl-2 silencing

The Bcl-2 gene is frequently overexpressed in malignancy and is responsible for the resistance induced by chemotherapeutic drugs. The aim of this study was to investigate whether the inhibition of Bcl-2 by lentivirus-mediated RNA interference would enhance doxorubicin cytotoxicity in the drug-resistant human osteosarcoma MG63 cells. Downregulation of Bcl-2 was confirmed by quantitative reverse transcription PCR and Western blotting. Moreover, the ratio of Bcl-2/Bax decreased due to the downregulation of Bcl-2 expression and the upregulation of Bax expression. Decreased cyclin D1 expression was also detected. Flow cytometry and MTT assays revealed that Bcl-2 knock-down increased cellular apoptosis and the MG63 cells became sensitive to doxorubicin. However, no detectable alterations in MDR1 or Bcl-xl expression were observed. Therefore, lentivirus-mediated Bcl-2 knock-down may sensitize these human osteosarcoma cells to doxorubicin and provide a potential therapeutic strategy for osteosarcoma.

Inhibition of P-glycoprotein activity by limonin and other secondary metabolites from Citrus species in human colon and leukaemia cell lines

P-glycoprotein (P-gp), a membrane transporter encoded by the MDR1 gene in human cells, mediates drug efflux from cells and plays a major role in causing multidrug resistance; which is one of the most accepted mechanisms for failure of chemotherapy in cancer treatment. In this study, we investigated the effects of nine naturally occurring compounds isolated from Citrus jambhiri Lush and Citrus pyriformis Hassk (Rutaceae) for their potential to modulate the activity of P-gp in the multidrug-resistant human leukaemia cell line CEM/ADR5000. Limonin, deacetylnomilin, hesperidin, neohesperidin, stigmasterol and ß-sitosterol- O-glucoside inhibited the efflux of the P-gp substrate rhodamine 123 in a concentration-dependent manner. Some of these compounds were more active than verapamil, which was used as a positive control. Treatment of drug-resistant Caco-2 cells with the most active C. jambhiri and C. pyriformis compounds increased their sensitivity to doxorubicin and completely reversed doxorubicin resistance, which agrees with a decreased P-gp activity. Limonin was the most potent P-glycoprotein inhibitor — when it was applied at a non-toxic concentration of 20 µM, it significantly enhanced doxorubicin cytotoxicity 2.98-fold ( P < 0.001) and 2.2-fold ( P < 0.001) in Caco2 and CEM/ADR5000 cells, respectively. These isolated Citrus compounds could be considered as good candidates for the development of novel P-gp/MDR1 reversal agents which may enhance the accumulation and efficacy of chemotherapy agents.

The therapeutic potential of p53 reactivation by nutlin-3a in ALK+ anaplastic large cell lymphoma with wild-type or mutated p53

p53 is expressed frequently, but is rarely mutated in anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) tumours. Nutlin-3a is a recently developed small molecule that targets Mdm2, a critical negative regulator of p53, and disrupts the p53-Mdm2 interaction resulting in p53 stabilization and activation. We show that nutlin-3a activates p53 in ALK+ ALCL cells carrying a wild type (wt) or mutated but partially functional p53 gene resulting in p53-dependent cell-cycle arrest and apoptosis. Cell-cycle arrest was associated with upregulation of the cyclin-dependent kinase inhibitor p21. Nutlin-3a-induced apoptotic cell death was accompanied by Bax and Puma upregulation, downregulation of Bcl-xl, survivin, and caspase-3 cleavage, and this was reduced when p53-dependent transactivation activity was inhibited by pifithrin-alpha, or when pifithrin-mu was used to inhibit direct p53 targeting of mitochondria. Nutlin-3a sensitized the activation of the extrinsic apoptotic pathway in wt-p53 ALK+ ALCL cells, in part, through upregulation of DR-5 and downregulation of c-Flip(S/L), and was synergistic with TRAIL in cell death induction. In addition, nutlin-3a treatment enhanced doxorubicin cytotoxicity against ALK+ ALCL cells harbouring mt p53, and this was associated with p73 upregulation. These data suggest that disruption of the p53-mdm2 interaction by nutlin-3a offers a novel therapeutic approach for ALK+ ALCL patients.

Synthetic Analogue of Rocaglaol Displays a Potent and Selective Cytotoxicity in Cancer Cells: Involvement of Apoptosis Inducing Factor and Caspase-12

Flavaglines constitute a family of natural anticancer compounds. We present here 3 (FL3), the first synthetic flavagline that inhibits cell proliferation and viability (IC(50) approximately 1 nM) at lower doses than did the parent compound, racemic rocaglaol. Compound 3 enhanced doxorubicin cytotoxicity in HepG2 cells and retained its potency against adriamycin-resistant cell lines without inducing cardiomyocyte toxicity. Compound 3 induced apoptosis of HL60 and Hela cells by triggering the translocation of Apoptosis Inducing Factor (AIF) and caspase-12 to the nucleus. A fluorescent conjugate of 3 accumulated in endoplasmic reticulum (ER), suggesting that flavaglines bind to their target in the ER, where it triggers a cascade of events that leads to the translocation of AIF and caspase-12 to the nucleus and probably inhibition of eIF4A. Our studies highlight structural features critical to their antineoplastic potential and suggest that these compounds would retain their activity in cells refractory to caspase activation.

Synthesis and in-vitro biological activity of macrocyclic urea Chk1 inhibitors

A variety of macrocyclic urea compounds were prepared as potent Chk1 inhibitors by modifying the C5 position of the benzene ring of the macrocyclic urea with ether moieties, aliphatic carbon chains, amide and halides. Enzymatic activity less than 20 nM was observed in 29 of 40 compounds. Compounds 14, 46d, and 48j provided the best overall results in the cellular assays as they abrogated doxorubicin-induced cell cycle arrest (IC 50 = 3.31, 3.08, and 3.13 μM) and enhanced doxorubicin cytotoxicity (IC 50 = 0.54, 1.27, and 0.96 μM) while displaying no single agent activity, respectively.

Different effectiveness of piperidine nitroxides against oxidative stress induced by doxorubicin and hydrogen peroxide

The piperidine nitroxides Tempamine and Tempace have been studied for their effect on doxorubicin (DOX) and hydrogen peroxide (H(2)O(2)) cytotoxicity in immortalized B14 cells, a model for neoplastic phenotype. The significance for nitroxide performance of the substituent in position 4 of the piperidine ring was evaluated. The cells were exposed to DOX/H(2)O(2) alone or in combination with the nitroxides Tempamine or Tempace. Two other piperidine nitroxides, Tempo and Tempol, were used for comparison. All the nitroxides except Tempamine modestly reduced DOX cytotoxicity. Tempamine evoked a biphasic response: at concentrations lower than 200 micromol/L the nitroxide decreased DOX cytotoxicity, while at concentrations higher than 200 micromol/L, it enhanced DOX cytotoxicity. In contrast to Tempo and Tempol, Tempamine and Tempace ameliorated hydrogen peroxide cytotoxicity, but none of the nitroxides influenced TBARS stimulated by hydrogen peroxide. The cytoprotective effect of Tempace, Tempo and Tempol in DOX-treated cells correlated with the inhibition of DOX-induced lipid peroxidation. The bioreduction rates of the investigated nitroxides differed significantly and were variously affected by DOX depending on the nitroxide substituent. In combination with DOX, Tempo and Tempol were reduced significantly more slowly, while no influence of DOX on Tempamine and Tempace bioreduction was observed. Our results suggest that the structure of the 4-position substituent is an important factor for biological activity of piperidine nitroxides. Among the investigated nitroxides, Tempace displayed the best protective properties in vitro but Tempamine was the only nitroxide that potentiated cytotoxicity of DOX and did not influence DOX-induced lipid peroxidation. However, this nitroxide showed different performance depending on its concentration and conditions of oxidative stress.

G3139 antisense oligonucleotide directed against antiapoptotic Bcl‐2 enhances doxorubicin cytotoxicity in the FU‐SY‐1 synovial sarcoma cell line

Synovial sarcoma (SS) is a highly aggressive, periarticular soft tissue sarcoma that causes death in more than half of affected children, adolescents, and young adults. Five- and 10-year survival rates are as low as 36 and 20%, respectively. Bcl-2, a negative regulator of apoptosis, is overexpressed in up to 90% of SS. Increased Bcl-2 expression not only leads to the development of cancer, but also to resistance of many anticancer chemotherapeutic agents. We hypothesized reducing Bcl-2 expression in SS should enhance doxorubicin cytotoxicity. Cell cultures representing two human sarcomas (FU-SY-1 SS and the pleomorphic SW982) and a primary human dermal fibroblast comparator (NHDF) were exposed in vitro to doxorubicin, or to doxorubicin preceded by Bcl-2 (G3139) antisense oligonucleotides, and assayed for cell survival, apoptosis, and modulations in Bcl-2 and Bcl-xL mRNA and protein content. SW982 sarcoma cells proved most susceptible to doxorubicin, while NHDF mesenchymal cells were least sensitive to doxorubicin. Treatment of FU-SY-1 SS with G3139 reduced Bcl-2 mRNA and protein levels, which enhanced doxorubicin-induced cell killing. There was a concurrent reduction in Bcl-xL mRNA following G3139 application in FU-SY-1 and NHDF cultures, but not in SW982. G3139 anti-Bcl-2 intervention sensitized the FU-SY-1 SS to doxorubicin, due to increased apoptosis. G3139 intervention was ineffective in the two non-SS cell lines.

Synthesis and biological evaluation of 1-(2,4,5-trisubstituted phenyl)-3-(5-cyanopyrazin-2-yl)ureas as potent Chk1 kinase inhibitors

Based on the X-ray crystallography of our lead compound 1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-cyanopyrazin-2-yl)urea in the checkpoint kinase 1 (Chk1) enzyme, we modified R 4, and to a lesser extent, R 2, and R 5 of the phenyl ring, and made a variety of N-aryl- N′-pyrazinylurea Chk1 inhibitors. Enzymatic activity less than 20 nM was observed in 15 of 41 compounds. Compound 8i provided the best overall results in the cellular assays as it abrogated doxorubicin-induced cell cycle arrest (IC 50 = 1.7 μM) and enhanced doxorubicin cytotoxicity (IC 50 = 0.44 μM) while displaying no single agent activity.

Enhancement of doxorubicin cytotoxicity by polyunsaturated fatty acids in the human breast tumor cell line MDA-MB-231: relationship to lipid peroxidation.

Exogenous polyunsaturated fatty acids modulate the cytotoxic activity of anti-cancer drugs. In this study, we examined whether lipid peroxidation is a potential mechanism through which fatty acids enhance drug cytotoxicity. We measured cell viability in the human breast cancer cell line MDA-MB-231 exposed to doxorubicin in the presence of non-cytotoxic concentrations of various polyunsaturated fatty acids for 6 days. To determine the role of lipid peroxidation, the hydroperoxide level was measured in cell extracts. Among all polyunsaturated fatty acids tested, docosahexaenoic acid (DHA, 22:6n-3) was the most potent in increasing doxorubicin cytotoxicity: cell viability decreased from 54% in the presence of 10(-7) M doxorubicin alone to 21% when cells were incubated with doxorubicin and DHA. After addition of an oxidant system (sodium ascorbate/2-methyl-1,4-naphthoquinone) to cells incubated with doxorubicin and DHA, cell viability further decreased to 12%. Cell hydroperoxides increased commensurately. The effect of DHA on doxorubicin activity and lipid hydroperoxide formation was abolished by a lipid peroxidation inhibitor (dl-alpha-tocopherol) or when oleic acid (a non-peroxidizable fatty acid) was used in place of DHA. No effect was observed with mitoxantrone, a drug with a low peroxidation-generating potential. Thus, DHA may increase the efficacy of oxyradical-producing drugs through a mechanism involving a generation of lipoperoxides. This may lead in vivo to a modulation of tumor cell chemosensitivity by DHA and oxidant agents.

Enhancement of doxorubicin cytotoxicity by polyunsaturated fatty acids in the human breast tumor cell line MBA‐MB‐231: Relationship to lipid peroxidation

Enhancement of doxorubicin cytotoxicity by polyunsaturated fatty acids in the human breast tumor cell line MBA‐MB‐231: Relationship to lipid peroxidation

Mechanism of action and spectrum of cell types susceptible to doxorubicin photochemotherapy.

We have shown that, whereas argon ion laser irradiation alone is not cytocidal for L929 cells, it greatly increases the cytotoxicity of intracellular doxorubicin. The present study showed that light enhancement of doxorubicin cytotoxicity was not restricted to stock L929 cells, but could also be demonstrated using L929 cells selected for doxorubicin resistance and several standard cell lines that are relatively resistant to doxorubicin prior to selection. Light-enhanced cytotoxicity resulted in extensive nuclear DNA loss and was strongly inhibited by anoxia. These findings suggest that the mechanism by which light exposure enhances doxorubicin cytotoxicity involves DNA damage by intranuclear generation of reactive oxygen species.

Structure-activity relationship of verapamil analogs and reversal of multidrug resistance

We studied the relationship between the chemical structure and multidrug resistance (MDR) reversal activity of racemic verapamil (VER) and 14 VER analogs (VAs). The LoVo-R human colon carcinoma cell line was used as an experimental model. This cell line exhibited a typical MDR phenotype and overexpressed the MDR1 gene products. Key structural features were identified as being related to MDR reversal and cytotoxic activity. In particular, we demonstrated that the methoxy groups in the VER molecule structure [1.7-Bis-(3.4-dimethoxyphenyl) -3-methylaza-7-cyan-8-methyl-nonane] prevented cytotoxicity when the VAs were used alone, whereas the 7-cyan-8-methyl groups were important for MDR reversal activity and interaction with P-glycoprotein (P-gp). Among the VAs tested, the most active compounds were gallopamil, R-isomer of VER (R-VER), and nor-VER, which potentiated doxorubicin (DOX) cytotoxicity by 52.3 ± 7.2 ( n = 3 ± SD), 38.9 ± 6.4 ( n = 4 ± SD), and 35.4 ± 4.3 ( n = 3 ± SD) times, respectively. The reversal activity of these compounds was similar to that of VER, which enhanced DOX cytotoxicity by 41.3 ± 5.0 ( n = 3 ± SD) times. The potentiation of DOX cytotoxicity was associated with an increase in DOX uptake in LoVo-R cells and with an increased [ 3H]azidopine P-gp photolabeling inhibition. Some compounds that had a high reversal potency (i.e. R-VER and nor-VER) showed a lower calcium antagonist activity than VER, and seem useful candidates for the treatment of MDR in cancer patients.