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. Author manuscript; available in PMC: 2007 Apr 17.
Published in final edited form as: Cancer Biol Ther. 2007 Feb 5;6(2):178–184. doi: 10.4161/cbt.6.2.3577

Curcumin Induces G2/M Arrest and Apoptosis in Cisplatin-Resistant Human Ovarian Cancer Cells by Modulating Akt and p38 MAPK

Nathan M Weir 1,¥, Karuppaiyah Selvendiran 1,¥, Vijay Kumar Kutala 1, Liyue Tong 1, Shilpa Vishwanath 1, Murugesan Rajaram 1, Susheela Tridandapani 1, Shrikant Anant 2, Periannan Kuppusamy 1,*
PMCID: PMC1852522  NIHMSID: NIHMS16826  PMID: 17218783

Abstract

Curcumin, a major active component of turmeric, is known to induce apoptosis in several types of cancer cells, but little is known about its activity in chemoresistant cells. Hence, the aim of the present study was to investigate the anticancer properties of curcumin in cisplatin-resistant human ovarian cancer cells in vitro. The results indicated that curcumin inhibited the proliferation of both cisplatin-resistant (CR) and sensitive (CS) human ovarian cancer cells almost equally. Enhanced superoxide generation was observed in both CR and CS cells treated with curcumin. Curcumin induced G2/M phase cell-cycle arrest in CR cells by enhancing the p53 phosphorylation and apoptosis through the activation of caspase-3 followed by PARP degradation. Curcumin also inhibited the phosphorylation of Akt while the phosphorylation of p38 MAPK was enhanced. In summary, our results showed that curcumin inhibits the proliferation of cisplatin-resistant ovarian cancer cells through the induction of superoxide generation, G2/M arrest, and apoptosis.

Keywords: ovarian cancer, curcumin, superoxide, cell cycle, apoptosis, Akt

INTRODUCTION

Ovarian cancer is the most commonly diagnosed and lethal gynecological malignancy in the United States and Europe.1,2 The high mortality rate is attributed to the lack of early detection and also due to the development of chemoresistance.3,4 Although platinum-based compounds such as cisplatin, in combination with taxanes are initially effective, the five-year survival rates are only about 50%.5 Despite the fact that most of the ovarian tumors are sensitive to chemotherapy for the first time, the development of recurrent tumors that are resistant to cisplatin remains a major hurdle to successful therapy and is responsible for poor long-term overall survival.5,6 Cisplatin resistance is associated with defects in the apoptotic pathway including p53 and Bcl-2 family members and death receptors.7 Cisplatin resistance is also associated with the altered activation of signaling pathways which include PI3K/Akt,8 MAPK9 or JAK/STAT.10 Another suggested mechanism for the drug resistance is the increase in intracellular thiols in the redox pathway, which may inactivate and remove the platinum compounds.11,12 Several groups have targeted this redox pathway in an attempt to circumvent the thiol-induced resistance.13 Recently, we observed that a nitroaspirin derivative (NCX-4016, an NO donor) partially restored the cisplatin sensitivity by depleting thiols.14

Curcumin (diferuloylmethane) is a major constituent of turmeric powder which is extracted from the rhizomes of the plant Curcuma longa found in south and southeast tropical Asia. It has been widely used in Asian countries for centuries in daily cooking preparations.15 The medicinal value of curcumin has been well recognized for its anti-inflammatory, antimicrobial, wound healing, and anti-tumor activities.16–19 Several studies have indicated that people in southeastern Asian countries have a much lower risk of acquiring colon, gastrointestinal, prostate, breast, ovarian, and other cancers than Western populations.20,21 It is likely that constituents of their diets such as curcumin, garlic, ginger, chillies, etc., may play a role in the prevention of such cancers.21 Studies have shown the chemopreventive properties of curcumin from human malignances.22–24 Clinical evaluations of curcumin as a chemopreventive agent for many cancers including breast, prostate, colon, and lung have been carried out.25,26 The anti-carcinogenic properties of curcumin in animal models have been demonstrated.27,28 However, the molecular mechanism underlying curcumin’s chemopreventive effect has not been fully elucidated, although several mechanisms have been proposed.29

Cell cycle inhibition and the induction of apoptosis are common mechanism(s) proposed for the anticancer effects of curcumin.18,24,30,31 Recent studies have shown that curcumin is a potent inhibitor of tumor initiation in vivo.32,33 The antiproliferative and apoptotic effects of curcumin on tumor cells in vitro have also been reported.34 Curcumin has been shown to induce apoptosis of cancer cells via inhibition of NFκB and STAT3.32,33 Curcumin has also been shown to suppress the expression of various NFκB-regulated genes, including Bcl-2, COX-2, cyclin D1 and adhesion molecules.35 The anticancer activity of curcumin has recently been attributed to the modification of thioredoxin reductase, an enzyme that plays a key role in modulating the redox pathway.36 Although the anti-cancer effects of curcumin have been studied in various cancer cells, it remains unknown whether curcumin possesses anticancer effects on drug-resistant cells such as cisplatin-resistant ovarian cancer cells. Therefore, the aim of this study was to determine whether curcumin shows cytotoxic effects in cisplatin-resistant human ovarian cancer cells and to elucidate the mechanism of its action. Our results showed that (1) curcumin enhanced superoxide generation in ovarian cancer cells; (2) curcumin induced cell cycle arrest and apoptosis in cisplatin-resistant ovarian cancer cells; (3) the curcumin-induced apoptosis in cisplatin-resistant cells was mediated through the inhibition of Akt and an increase in the activation of p38 MAPK and p53.

MATERIALS AND METHODS

Reagents and culture materials

Curcumin ((1,7-bis[4-hy-droxy-3-methoxyphenyl]-1,6-heptadiene-3,5-dione), GSH, (L-glutamyl-L-cysteinylglycine), DMSO (dimethyl sulfoxide) and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] were obtained from Sigma (St Louis, MO). Cell culture medium (RPMI 1640), fetal bovine serum, antibiotics, sodium pyruvate, trypsin, and phosphate-buffered saline (PBS) were purchased from Gibco, BRL (Grand Island, NY). Polyvinylidene fluoride membrane (PVDF) (Millipore), and molecular weight marker were obtained from Bio-Rad, and Fluoromount-G from Southern Biotech. Lab-Tek II chamber slides were purchased from Nalge Nunc International (Naperville, IL). Antibodies against poly-adenosine diphosphate ribose polymerase (PARP), Bax, p38 MAPK, caspase-7 and cleaved caspase-3 (19 kDa and 17 kDa) and cleaved caspase-7 (20 kDa) were purchased from Cell Signaling Technology (Beverly, MA), and Akt (Ser473) and p53 from Santa Cruz Biotechnology (Santa Cruz, CA). RNase was from Promega Corporation (Madison, WI). Enhanced chemiluminescence (ECL) reagents were obtained from Amersham Pharmacia Biotech (Buckinghamshire, UK). All other reagents and compounds were analytical grades.

Cells and culture conditions

Cisplatin-resistant (CR) and cisplatin-sensitive (CS) human ovarian cancer cells were obtained from Dr. Sridhar (Howard University Medical School, Washington DC). Cells were grown in RPMI 1640 medium supplemented with 10% FBS, 2% sodium pyruvate, 1% penicillin and 1% streptomycin. Cells were grown in T-75 flasks to 80% confluence at 37°C in an atmosphere of 5% CO2 and humidified air. Cells were routinely trypsinized (0.05% trypsin/EDTA) and the cell count was determined by using a NucleoCounter, automated cell counter, (New Brunswick Scientific, Edison, NJ).

Cell proliferation assay

Cell proliferation was determined using the conversion of MTT to formazan via mitochondrial oxidation. Cells were grown in T-75 flasks to >80% confluence. They were then trypsinized, counted, and seeded in 96-well plates with an average of 7,000 cells/well. Cells were incubated overnight and then treated in triplicate with 10 or 50 uM curcumin for 12 or 24 h. All experiments were repeated at least three times.

Superoxide determination by DHE fluorescence

Cells were seeded in Chamber slides with 1 x 105 cells per chamber and incubated overnight. The following day, cells were preincubated with dihydroethidium (DHE, 10 μM) for 1 h. The cells were then washed with PBS and treated with varying doses of curcumin for 4 h. After incubation, the cells were washed and fixed with 3% paraformaldehyde supplemented with McIIvaine’s buffer for 15 min at 4°C. The paraformaldehyde was then washed off and a cover slip was fixed using Fluoromount-G. Red fluorescence, indicating superoxide formation, was detected on a Nikon Eclipse TE2000-U, using excitation/emission at 488/585 nm. Images (12 bit) were acquired using a 400 ms exposure time and the fluorescence intensity was quantified by MetaMorph software. The intensity was calculated as an average of four areas with a similar number of cells.

GSH assay

Intracellular levels of GSH were determined by spectrophotometry using DTNB (5,5'-dithiobis(2-nitrobenzoic acid) (Ellman’s reagent, Cayman Chemical Co., Ann Arbor, Michigan) which produces a yellow color with GSH to yield TNBA (5-thio-2- nitrobenzoic acid). Cell extracts were treated with phosphoric acid, the precipitated proteins were centrifuged, and the supernatants were treated with triethanolamine to bring to neutral pH and then the DTNB reagent was added and the resulting solution was measured using a 96-well plate ELISA reader (Beckmann Coulter, AD 340) at 405 nm. All experiments were run in at least four parallels and repeated thrice. The concentration of GSH was determined from a standard curve prepared with known concentrations of GSH under similar conditions.

Cell cycle analysis by flow cytometry

Curcumin-treated cells were harvested, fixed overnight with 75% ethanol at −20°C, washed three times with PBS, treated with RNase A (1 μg/ml), and then stained with propidium iodide. After propidium iodide staining, the cells were analyzed by flow cytometry (Becton Dickinson, Franklin Lakes, NJ). The percentage of cells in the G2/M and sub-G1 apoptotic cell population was determined using CELLQuest software (Becton Dickinson).

Immunoblot analysis

Cells were lysed in RIPA buffer, phenyl-methylsulphonyl fluoride (PMSF, 0.1 mM), sodium orthovanadate (1 mM), and aprotinin and leupeptin (2 μg/ml). The lysate was centrifuged at 12000 x g for 20 min at 4°C and the supernatant was removed. The protein concentration was measured using a Bio-Rad protein assay kit. After boiling for 10 min in the presence of 2-mercaptoethanol, samples containing cell lysate protein were separated on a 10 or 15% sodium dodecyl sulfate-polyacrylamide (SDS) gel and then transferred onto equilibrated PVDF membranes. After skimmed milk blocking, the membranes were incubated with primary antibodies individually with caspase-7, PARP, cleaved caspase-3 (19 kDa and 17 kDa), phosphorylated Akt (Ser473), p38 MAPK, or p53 (1:1000 dilution). The bound antibodies were detected with horseradish peroxidase-labelled sheep anti-mouse IgG or horseradish peroxidase-labelled donkey anti-rabbit IgG (GE Health Care Corp, Piscataway, NJ). The immunoblots were then developed with enhanced chemiluminescence reagents according to manufacturer’s recommendations.

Statistical analysis

All data were expressed as mean ± SE. Comparisons among groups were performed by Student’s t-test. The significance level was set at p < 0.05.

RESULTS

Cisplatin-sensitive (CS) and cisplatin-resistant (CR) human ovarian cancer cells

The cisplatin sensitivity of the two ovarian cancer cell lines was confirmed by a cell-proliferation assay (MTT) after treating the cells with cisplatin for 24 h (Fig. 1A). The CS and CR cells exposed to cisplatin (5 μg/ml) for 24 h showed a viability of 42 and 82%, respectively, confirming their differential sensitivity to cisplatin.

Figure 1.

Figure 1

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Curcumin inhibits the growth of cisplatin-sensitive (CS) and cisplatin-resistant (CR) ovarian cancer cells. (A) To confirm cisplatin resistance, CS and CR cells were treated with cisplatin (5 μg/ml) and incubated for 24 h. Viability was determined using the MTT assay. (B) CS, CR and CHO cells were treated with varying doses of curcumin for 24 h. Cell viability was determined by MTT assay. Values are expressed as mean ± SE (n = 3). *p<0.01 vs control.

Curcumin inhibits the proliferation of CS and CR cells

The sensitivity of CR ovarian cancer cells to curcumin is unknown. To determine whether curcumin inhibits the proliferation of CR cell lines, cells were grown in the presence of varying concentrations of curcumin (0–50 μM) for 48 h and the cell proliferation was measured by MTT assay. As shown in Figure 1B, curcumin inhibited both CS and CR cell proliferation in a dose-dependent manner. The IC50 dose of curcumin for proliferation of CS and CR cells was 20 μM. Under similar conditions Chinese hamster ovary (CHO) cells (noncancer) exhibited an IC50 of 26 μM.

Curcumin induces superoxide generation in ovarian cancer cells

To determine whether curcumin induces superoxide generation in CS and CR cell lines, cells were grown on chamber slides for 24 h. The cells were then preincubated with DHE (10 μM) for 1 h, followed by curcumin (10 μM) for 3 h. The nonfluorescent DHE is converted by superoxide into fluorescent hydroethidine which can be measured by fluorescence microscopy. Greater fluorescence intensity would indicate more superoxide was present. Both CS and CR cells showed intense fluorescence (Fig. 2), suggesting the generation of superoxide during curcumin treatment. CS cells treated with curcumin showed a significantly higher fluorescence intensity compared to the CR cells (p < 0.01) (Fig. 2). Cells pretreated with N-acetylcysteine (NAC, 10 mM), an antioxidant, exhibited significantly lower levels of superoxide compared to the cells not treated with NAC. The superoxide generation in CHO cells treated with curcumin was significantly lower compared to the cancer cells and NAC completely abolished the fluorescence intensity.

Figure 2.

Figure 2

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Curcumin induces superoxide generation in CS and CR cells. CS, CR or CHO cells were grown in chamber slides and were pretreated with dihydroethidium (10 μM) for 30 min and then exposed to curcumin (10 μM) for 3 h. All experiments were performed with and without NAC (10 mM). The florescence was monitored using a Nikon fluorescence microscope equipped with a rhodamine filter. Top, Representative micrographs from triplicate experiments are shown. Bottom. Fluorescence intensity in curcumin treated CR, CS and CHO cells with and without NAC are shown. Values are expressed as mean ± SE (n = 3). *p<0.01 vs curcumin.

Curcumin increases glutathione levels in ovarian cancer cells

The effect of curcumin on glutathione synthesis in CS and CR cells was determined by measuring the levels of intracellular GSH by spectrophotometry. Glutathione levels in the untreated CR cells were significantly higher (p < 0.01) compared to CS cells (Fig. 3). Both CS and CR cells incubated with curcumin (10 or 50 μM) for 24 h showed increased glutathione levels. Compared to controls, there were a 214 and 271% increase in glutathione levels in CS cells and a 168 and 235% increase in CR cells treated with 10 and 50 μM of curcumin, respectively.

Figure 3.

Figure 3

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Curcumin induces glutathione synthesis in CS and CR cells. CS and CR were treated with curcumin (10 and 50 μM) and incubated for 24 h. Values are expressed as mean ± SE (n = 3). *p < 0.01 vs CS cells; **p < 0.05 vs control; #p < 0.01 vs control.

Curcumin causes G2/M Phase cell cycle arrest and induces apoptosis in CR cells

To determine whether curcumin inhibits the cell cycle progression of CR cells, cells were grown to 70% confluence and the cell cycle distribution was analyzed by flow cytometry after a 12- and 24-h exposure to curcumin (50 μM). It was observed that the percentage of cells in G2/M phase with curcumin treatment was 51.5% after 12 h of incubation and decreased to 20.1% after 24 h. The percentage of cells in sub-G0/G1 phase was 3.2% and 35.8% after 12 and 24 h of incubation, respectively. In control cells the percentage of cells in G2/M and Sub-G0/G1 phase was 20.5% and 1.2% respectively.

Immunoblotting of CR cells treated with curcumin showed increased caspase-7 activity and cleavages of caspase-3 (19 and 17 kDa), caspase-7 (20 kDa), and PARP (89 kDa) after 12 h and were even higher after 24 h of incubation (Fig. 5). Quantification of cleaved caspase-3 and cleaved PARP, done by measuring the relative band intensities, showed that cleaved caspase-3 and PARP levels were significantly higher in CR cells incubated with curcumin for 12 (p < 0.01) and 24 h (p < 0.001) of incubation (Fig. 5B and C). This data indicated that curcumin induced cell cycle arrest within 12-h of incubation and apoptosis after 24 h of incubation. Preincubation of CR cells with NAC significantly attenuated the curcumin-induced increase of cleaved caspase-3 and cleaved PARP. Thus, the data clearly showed that curcumin induced G2/M phase cell-cycle arrest and apoptosis.

Figure 5.

Figure 5

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Curcumin activates procaspases and PARP degradation in CR cells. CR cells were treated with curcumin (50 μM) for 12 and 24 h and then Western blot analysis was performed for cleaved caspase-3, caspase-7, and PARP. Top: Representative blot from 3 independent experiments. Bottom: Quantification of band intensities. Values are expressed mean ± SE (n=3).

Curcumin inhibits Akt and enhances p38 MAPK activation

To investigate the effect of curcumin on Akt activity in CR cells, we examined the regulation of Akt phosphorylation by curcumin. The results showed increased phosphorylation of Akt in CR cells, which was inhibited by curcumin (50 μM) after 12 and 24 h (p < 0.001) of incubation (Fig. 6). A marked increase in the p38 MAPK and p53 phosphorylation (p < 0.001) was observed following curcumin exposure for 12 and 24 h (Fig. 6). Pretreatment of the cells with NAC attenuated the curcumin-induced inhibition of Akt, and activation of p38 MAPK and p53.

Figure 6.

Figure 6

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Curcumin inhibits Akt phosphorylation and enhances the p38 MAPK and p53 phosphorylation. Cells were treated with curcumin (50 μM) for 24 h and then Western blot analysis was performed for phospho-Akt (Ser473), phospho-p38 MAPK and phospho-p53. Top: A representative blot from 3 independent experiments is shown. Bottom: Quantification of band intensities. Values are expressed mean ± SE (n = 3). *p < 0.001 vs control; **p < 0.001 vs curcumin.

DISCUSSION

The present study demonstrated that curcumin induced cytotoxicity in both cisplatin-sensitive (CS) and cisplatin-resistant (CR) human ovarian cancer cells. Both cells exhibited similar responses to curcumin. We also observed that curcumin induced G2/M cell cycle arrest leading to apoptosis, possibly by down-regulating anti- apoptotic Akt signaling and/or also by activating the pro-apoptotic p38 MAPK in parallel with the generation of superoxide radicals.

Reactive oxygen species (ROS) such as superoxide radicals are implicated as important mediators of apoptotic cell death. MAPK is considered as one of the most important signaling molecules in ROS-mediated apoptosis in cancer cells.37,38 The results of the present study indicate that curcumin induces superoxide generation in both CS and CR cells but not in CHO cells. The amount of superoxide generation by curcumin in CR cells was significantly less than in CS cells. This could be due to the higher levels of endogenous thiol in CR cells as observed in the current study and also in our earlier study.14 On the other hand, curcumin was less effective in CHO cells wherein the superoxide production was observed to be significantly less. Curcumin-induced ROS generation has been reported in tumor cells such as rat histiocytoma (AK-5), human renal carcinoma cell line (Caki cells), human submandibular gland caracinoma (HSG) was others.39,40 The accumulation of intercellular superoxide may lead to the disruption of the mitochondrial membrane potential, release of cyctochrome c into the cytosol, with subsequent activation of the caspase cascade, and apoptosis.41 Therefore, the curcumin-induced superoxide generation may be critical for the modulation of the apoptotic signaling pathways.

Our study demonstrated that curcumin inhibited the cisplatin-resistant ovarian cancer cell proliferation by inducing G2/M cell cycle arrest leading to apoptotic cell death. Recent studies suggested that caspase-3 plays an important role in several key events causing DNA fragmentation during apoptosis.42,43 It has been suggested that the cleavage of procaspase-3 is an early event in apoptosis induced by chemotherapeutic agents.44 The activation of caspase-3 leads to the cleavage of PARP, which serves as a “death substrate”.45 In our study, cleavages of caspase-7, caspase-3, and PARP were observed in CR cells treated with curcumin. These results are in agreement with the published reports, which indicate that curcumin induces apoptosis in cancer cells.18,31 Pretreatment with NAC attenuated the curcumin-induced cleavage of caspase-3 and 7, and PARP. In colon carcinoma cells, curcumin induced apoptotic cell death by cell cycle arrest in the S and G2/M phases, whereas in the MCF-7 breast cancer cell line this occurred at the G2 or M phases.30,46 Previous studies have shown that curcumin blocks the proliferation of various cancer cells by downregulating the expression of the cyclin D1 protein.47 In vitro studies have shown that curcumin has multiple biological and biochemical targets which may be related to its anticancer and antitumor activities.18,48 These functions include inhibition of PI3 kinase activities and induction of G2/M cell cycle arrest along with the down-regulation of vascular endothelial growth factor (VEGF).48 Curcumin induces caspase-3-independent apoptosis in human multidrug-resistant cells such as human lymphoblastic leukemia cell line and the human colon-carcinoma cell line.49

The PI3-kinase/Akt pathway contributes to the tumor formation by elevating the activity of the anti-apoptotic action of Akt. Akt inhibits apoptosis through phosphorylation of Bad, GSK3, and caspase-9 and activation of transcriptional factors such as Forkhead (FOXO1) and NFκB.50,51 The present study showed increased phosphorylation of Akt in CR cells and curcumin inhibited Akt phosphorylation. The phosphorylation of Akt is routinely used as readout for the Akt activation. The inhibition of Akt phosphorylation by curcumin is an important mechanism of action in CR ovarian cancer cells. Similar results were also observed by others in human mantle cell lymphoma (MCL).32 Suppression of Akt activation could lead to p53 activation, which in turn may lead to the activation of pro-apoptotic signaling pathways.52 The regulation of p53 by Akt is a critical determinant of cisplatin-induced chemoresistance in ovarian cancer cells.53 In the current study, the observation of an increase in the phosphorylation of p53 in CR cells treated with curcumin is supported by the PI3K-Akt pathway.

The p38 MAPK pathway is implicated in cancer cell apoptosis and is induced by several chemotherapeutic drugs.54 Oxidative stress has been reported to play a role in p38 MAPK activation.38 We found a marked increase in the phosphorylation of p38 MAPK following curcumin treatment in CR cells. The increased super-oxide production induced by curcumin subsequently activated p38 MAPK resulting in the activation of caspases, PARP cleavage, followed by cell death. These findings imply that the ROS trigger is an upstream signal which initiates the series of apoptotic events induced by curcumin. Pretreatment with NAC attenuated the curcumin-induced p38 MAPK activation. These results suggest that the activation of the p38 MAPK pathway plays a causal role in the curcumin-induced apoptosis in CR cells. Thus, the increased superoxide generation by curcumin may contribute to the enhanced p38 MAPK activity in resistant cells. It was also reported that the loss of the capacity to activate p38 MAPK in response to cisplatin treatment may be one of the mechanisms of chemoresistance.55 Thus, activation of p38 MAPK and an increase in the caspase-3 activities appears to contribute to the proapoptotic effect of curcumin in CR cells. Taken together, our results indicate that curcumin produces a profound effect on chemoresistant ovarian cancer cell proliferation. The inhibition of Akt, the activation of p38 MAPK and p53 and the increase in caspase-3 activity appear to contribute to the proapoptotic effects of curcumin.

The chemoresistance of ovarian cancer was also linked to increased cellular glutathione content.14,56–58 Depletion of cellular glutathione has been shown to sensitize the resistant cancer cells to cisplatin and other anticancer drugs.14,59,60 In the present study we observed that curcumin significantly enhanced the intracellular GSH levels in both CR and CS cells and but not in CHO cells. However, the anti-proliferative efficacy of curcumin on CR cells was not significantly different from that of CS cells. These results indicate that in CR cells, curcumin induces apoptosis through non-glutathione dependent pathways. The exact mechanism of the enhanced glutathione synthesis in resistant cells is not yet known and warrants further investigation. In a similar fashion, Piwocka et al, demonstrated the Jurkat cells treated with curcumin showed increased intracellular GSH levels.49 Curcumin has also been shown to increase the levels of GSH in kidney cells,61 and rat hepatocytes.62

In summary, the current study demonstrated that curcumin induces G2/M arrest and apoptosis in cisplatin-resistant human ovarian cancer cells. Further, we showed that curcumin induces superoxide generation and enhances p38 MAPK and p53 phosphorylation. The increase in Akt activity in cisplatin-resistant ovarian cancer cells was attenuated by curcumin. Our results highlight the importance of Akt and p53 signaling pathways as the new targets for the development of therapeutic strategies against drug-resistant cancer cells, in general, and cisplatin-resistant cancer cells, in particular. Our results indicate that curcumin may be a promising compound, especially for the treatment of chemo-resistant human ovarian cancer.

Figure 4.

Figure 4

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Curcumin causes G2/M arrest of CR cells. Flow cytometric analysis of the PI staining of CR cells after 24 h of growth in the presence of DMSO (control) vehicle or curcumin (50 μM). Representative values of three experiments are shown. Top: The distribution of total cells in M1-M4 gate in the flow cytometry plot. Bottom: The percentage of distribution of total cells in sub-G0-G1, G0/G1, S, and G2/M phase.

Acknowledgments

We acknowledge the financial support from the NIH grant CA 102264.

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