BACKGROUND:Triple-negative breast cancer (TNBC) is a highly diverse group that is associated with an aggressive phenotype. Its treatment has been challenging due to its heterogeneity and absence of well-defined molecular targets. Thus, there is an urgent need to identify novel agents with therapeutic application. NF-κB is over-expressed in many breast cancers; thus, inactivation of the NF-κB pathway could serve as a therapeutic target. Here we report for the first time the anti-tumor activity of panepoxydone (PP), a NF-κB inhibitor isolated from an edible mushroom, in several breast cancer cell lines. METHODS:We investigated the effects of PP on cell growth, migration-invasion, apoptosis and EMT-related proteins expression in MCF-7 and TNBC cell lines MDA-MB-231, MDA-MB-468 and MDA-MB-453. RESULTS:Significant antitumor activity was seen in all cell lines, with differential responses noted in cell-line specific manner. Treatment with PP resulted in significant cytotoxicity, decreased invasion, migration and increased apoptosis in all cell lines tested. Up-regulation of Bax and cleaved PARP and down-regulation of Bcl-2, survivin, cyclin D1 and caspase 3 were noted in PP-treated breast cancer cells. The antitumor effect of PP appeared related to its ability to inhibit the phosphorylation of inhibitor of NF-κB (IκBα) with cytoplasmic accumulation. PP treatment also down-regulated FOXM1 which resulted in a reversal of EMT. Similar results were obtained after silencing of NF-kB and FOXM1. CONCLUSION:Altogether, these studies show, for the first time the antitumor activity of PP against breast cancer cells, in particular TNBC cells. Furthermore, it highlights the concept that optimal treatment of TNBC warrants attention to the differential sensitivity of various TNBC subtypes to therapeutic agents. These results suggest that the PP may be a potentially effective chemopreventive or therapeutic agent against breast cancer. However, additional studies are required to more fully elucidate the mechanism of antitumor effect of PP.

DNA excision repair plays a significant part in platinum-based chemotherapy by removing DNA lesions caused by platinum-containing drugs. The nucleotide excision repair (NER) pathway is the mammalian DNA repair mechanism that removes bulky DNA adducts induced by DNA damaging chemotherapeutic agents. Platinum compounds induce their cytotoxic effect by binding to a DNA molecule in the form of a platinum-DNA-adduct. The NER pathway is the main mechanism responsible for platinum resistance by increased platinum-DNA-adduct removal and the excision repair cross complementing-group 1 (ERCC1) gene plays a major role in the NER-pathway because of its damage recognition and excision ability. This chapter will review mechanisms of DNA repair and platinum resistance as it relates to the NER pathway and regulation of ERCC1. A brief discussion on the role of cancer stem cells in platinum resistance is also presented.

OBJECTIVE:Aldehyde dehydrogenase (ALDH) expressing cells have been characterized as possessing stem cell-like properties. We evaluated ALDH+ ovarian cancer stem cell-like properties and their role in platinum resistance.METHODS:Isogenic ovarian cancer cell lines for platinum sensitivity (A2780) and platinum resistant (A2780/CP70) as well as ascites from ovarian cancer patients were analyzed for ALDH+ by flow cytometry to determine its association to platinum resistance, recurrence and survival. A stable shRNA knockdown model for ALDH1A1 was utilized to determine its effect on cancer stem cell-like properties, cell cycle checkpoints, and DNA repair mediators.RESULTS:ALDH status directly correlated to platinum resistance in primary ovarian cancer samples obtained from ascites. Patients with ALDHHIGH displayed significantly lower progression free survival than the patients with ALDHLOW cells (9 vs. 3 months, respectively p<0.01). ALDH1A1-knockdown significantly attenuated clonogenic potential, PARP-1 protein levels, and reversed inherent platinum resistance. ALDH1A1-knockdown resulted in dramatic decrease of KLF4 and p21 protein levels thereby leading to S and G2 phase accumulation of cells. Increases in S and G2 cells demonstrated increased expression of replication stress associated Fanconi Anemia DNA repair proteins (FANCD2, FANCJ) and replication checkpoint (pS317 Chk1) were affected. ALDH1A1-knockdown induced DNA damage, evidenced by robust induction of γ-H2AX and BAX mediated apoptosis, with significant increases in BRCA1 expression, suggesting ALDH1A1-dependent regulation of cell cycle checkpoints and DNA repair networks in ovarian cancer stem-like cells.CONCLUSION:This data suggests that ovarian cancer cells expressing ALDH1A1 may maintain platinum resistance by altered regulation of cell cycle checkpoint and DNA repair network signaling.

Cellular resistance to platinum anticancer compounds is governed by no less than two molecular processes; DNA repair and cellular accumulation of drug. Gli1 is an upstream regulator of nucleotide excision repair, effecting this process through c-jun. We, therefore, investigated whether Gli1 plays a role in cellular accumulation of cisplatin. Using a Gli1-specific shRNA, we explored the role of Gli1 in the cellular accumulation and efflux of cisplatin, in cisplatinresistant A2780-CP70 human ovarian cancer cells. When Gli1 is inhibited, cellular uptake of cisplatin was approximately 33% of the level of uptake under control conditions. When Gli1 is inhibited, cellular efflux of cisplatin was completely abrogated, over a 12-h period of observation. We assayed nuclear lysates from these cells, for the ability to bind the DNA sequence that is the Gli-binding site (GBS) in the 5'UTR for each of five known cisplatin transmembrane transporters. Four of these transporters are active in cisplatin uptake; and, one is active in cisplatin efflux. In each case, nuclear lysate from A2780-CP70 cells binds the GBS of the respective cisplatin transport gene. We conclude that Gli1 plays a strong role in total cellular accumulation of cisplatin in these cells; and, that the combined effects on cellular accumulation of drug and on DNA repair may indicate a role for Gli1 in protecting cellular DNA from lethal types of DNA damage.

Cellular resistance to platinum anticancer compounds is governed by no less than two molecular processes; DNA repair and cellular accumulation of drug. Gli1 is an upstream regulator of nucleotide excision repair, effecting this process through c-jun. We, therefore, investigated whether Gli1 plays a role in cellular accumulation of cisplatin. Using a Gli1-specific shRNA, we explored the role of Gli1 in the cellular accumulation and efflux of cisplatin, in cisplatin-resistant A2780-CP70 human ovarian cancer cells. When Gli1 is inhibited, cellular uptake of cisplatin was approximately 33% of the level of uptake under control conditions. When Gli1 is inhibited, cellular efflux of cisplatin was completely abrogated, over a 12-h period of observation. We assayed nuclear lysates from these cells, for the ability to bind the DNA sequence that is the Gli-binding site (GBS) in the 5'UTR for each of five known cisplatin transmembrane transporters. Four of these transporters are active in cisplatin uptake; and, one is active in cisplatin efflux. In each case, nuclear lysate from A2780-CP70 cells binds the GBS of the respective cisplatin transport gene. We conclude that Gli1 plays a strong role in total cellular accumulation of cisplatin in these cells; and, that the combined effects on cellular accumulation of drug and on DNA repair may indicate a role for Gli1 in protecting cellular DNA from lethal types of DNA damage.

Abstract The transcription factor Activator Protein 1 (AP1), is an important regulator in cisplatin resistance. AP1 is comprised of the two proteins, c-jun and c-fos. The transcription factor Gli1, a member of the hedgehog signaling pathway, is also an important factor in cisplatin resistance and transcriptionally regulated c-jun. The c-jun interface with Gli1 is mediated by a 130 kDa isoform of Gli1. We have investigated whether Gli1 may regulate c-fos by selectively knocking down Gli1 expression using anti-Gli1 shRNA or by treating cells with a Hedgehog pathway inhibitor, cyclopamine. A2780-CP70 cells were treated with an IC50 dose of anti-Gli1 shRNA and the changes in RNA and protein levels were analyzed over a 72 hour time course. No changes in the expression of c-jun or c-fos RNA transcripts were observed versus control. Western blot analyses showed Gli1 protein expression was reduced at 24 hours and undetectable at 48 and 72 hours. Sonic hedgehog (Shh) protein levels were dramatically reduced by 24 hours, low but measureable at 48 hours, and undetectable at 72 hours. Indian hedgehog (Ihh) expression increased at 24 hours and remained stable for the remainder of the 72 hour time course. Treatment of A2780-CP70 cells with an IC50 dose of cyclopamine resulted in a different intracellular response than treatment with Gli1 shRNA. Cyclopamine specifically targets the cell membrane receptor Smoothened. Experiments were performed analyzing RNA and protein expression over a 72 hour time period after treatment with cyclopamine. C-jun and c-fos RNA transcript levels were higher than control 6 hours after treatment and remained high for the duration of the 72 hour experiment. Western blot analyses after cyclopamine treatment showed Gli1 protein expression gradually decreasing during the 72 hours, but were never fully depleted. Expression of Shh increased over 72 hours, while Ihh levels remained stable. The identical Gli-Binding-Site (GBS) in the c-jun promoter was found in the promoter of c-fos. We investigated whether the Gli1 isoform that binds c-jun, also binds c-fos. Simultaneous Western and Southwestern blots show only one of the known Gli1 isoform binds the promoter of c-fos. Further studies with Chromatin Immunoprecipitation (ChIP) assays confirmed the 130 kDa isoform of Gli1 binds the GBS of the c-fos promoter. We conclude that the 130 kDa Gli1 isoform binds both components of AP1, c-jun and c-fos, and modulates the cellular resistance to cisplatin. Citation Format: Lauren Amable, Kenji Kudo, Elaine Gavin, Jason Fain, Eddie Reed. A specific Isoform of Gli1 binds the promoter region of c-fos in A2780-CP70 human ovarian cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-223. doi:10.1158/1538-7445.AM2013-LB-223

Abstract Purpose: Triple-negative breast cancer (TNBC), representing up to 20% of all breast cancer cases, is a highly diverse group of cancer that is associated with an aggressive phenotype, with affected patients having a poorer prognosis. Its treatment has been challenging due to its heterogeneity and the absence of well-defined molecular targets. Thus, there is an urgent need to identify novel agents with therapeutic application. Nuclear factor kappa-B (NF-κB), a transcription factor, has been shown to be significantly increased in TNBC, consistent with the aggressiveness of these tumors. Thus, inactivation of the NF-κB pathway, could serve as therapeutic targets for treatment of TNBC. Panepoxydone (PP), a compound isolated from Lentinus crinitus (an edible mushroom), has been shown to interfere with NF-κB mediated signal transduction by inhibiting the phosphorylation of IκBα. Here we evaluate the antitumor activity of panepoxydone in several breast cancer cell lines. Experimental Design: Estrogen receptor positive (MCF-7) and three triple negative breast cancer cell line subtypes (MDAMB-231, MDAMB-468 and MDAMB-453) were treated with increasing concentrations of panepoxydone or DMSO (final concentration, 0.2%). Results: Significant antitumor activity was seen in all the breast cancer cell lines, with differential responses noted in a cell-line specific manner. Whereas treatment with PP resulted in significant cytotoxicity, along with decreased invasion and migration in all the cell lines tested, with IC50 of 4-15 μM, MDAMB-453 cells were the most sensitive, whereas MDAMB-231 were almost 4-fold less sensitive. PP treatment also induced apoptosis in a cell-line specific manner, with minimal effect noted in MCF7 and MDAMB-231 cells, but a 35.8% and 40.8% increase in apoptotic cells noted in MDAMB-453 and MDAMB-468 cells, respectively. Differential response to PP treatment was also noted in the decreased expression of the apoptosis-related proteins Bcl-2, survivin, and cyclin D1, with MDAMB-453 again having at least a 3-fold greater decrease in expression when compared to the other TNBC cell lines. The antitumor effect of PP, appeared in part, to be related to its ability to inhibit phosphorylated IκBα, with accumulation of IκBα noted in a dose-dependent manner in all the cell lines. This resulted in reduced translocation of NF-kB from cytoplasm to nucleus as analyzed via immunofluorescence. Conclusion: Altogether, these studies show, for the first time the antitumor activity of PP against breast cancer cells, in particular TNBC cells. Furthermore, it highlights the concept that optimal treatment of TNBC warrants attention to the differential sensitivity of various TNBC subtypes to therapeutic agents. Additional studies are required to further elucidate the antitumor effect of panepoxydone, but these studies provide support for the further evaluation of PP as a therapeutic agent in the treatment of TNBC. Citation Format: Ritu Arora, Bernard D. Gary, Steven McClellan, Yaguang Xi, Gary Piazza, Eddie Reed, Laurie Owen, Windy Dean-Colomb. Antitumor activity of a novel natural therapeutic agent against triple negative breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5571. doi:10.1158/1538-7445.AM2013-5571

β-Elemene, originally derived from plants, has been recently investigated as a new anticancer agent. The purpose of this study was to explore the efficacy and mechanisms of action of the combined use of β-elemene plus a taxane as an antitumor therapeutic strategy for ovarian cancer and other carcinomas. The interaction of β-elemene with paclitaxel or docetaxel produced additive to moderately synergistic effects against the platinum-resistant ovarian cancer cell line A2780/CP70 and its parental cell line A2780, and showed moderately synergistic activity against PC-3 prostate cancer cells. In addition, the co-administration of β-elemene and a taxane at low-micromolar concentrations dramatically increased the rate of micronucleus formation and the percentage of mitotic arrest in both ovarian cancer cell lines, as compared with treatment with either agent alone. The highest synergy towards the ovarian cancer cells was observed with β-elemene plus docetaxel. Consistent with these data, treatment of A2780/CP70 cells with β-elemene plus a taxane strikingly reduced cell viability and increased cell apoptosis, as assessed by annexin V binding. Moreover, β-elemene plus docetaxel induced elevated levels of caspase-9 and p53 proteins in A2780/CP70 cells, and the combination of β-elemene plus a taxane caused marked cell-cycle arrest at the G2/M phase in these cells. One possible mechanism to account for the enhanced cytotoxic efficacy of this combination treatment is a β-elemene-induced increase in taxane influx into cancer cells. These observations indicate that combination therapy with β-elemene and taxanes has synergistic antitumor activity against ovarian and prostate carcinomas in vitro. This promising new therapeutic combination warrants further pre-clinical exploration for the treatment of chemoresistant ovarian cancer and other types of tumors.

Cisplatin, a platinum-based chemotherapy agent, is commonly used in treating cancers that may affect women of childbearing age, including cervical cancer, triple-negative breast cancer, and pediatric tumors in adolescents. The authors found that platinum was undetectable in breast milk at 66 hours and beyond following a 70-mg dose of intravenous cisplatin. Relative infant dose of platinum was calculated to be between 0.29% and 0.40% of the maternal dose corrected for body weight. This case demonstrates minimal exposure to platinum via breast milk, following a single 70-mg intravenous dose of cisplatin.

The development of effective agents for overcoming platinum chemoresistance in lung carcinoma continues to have high priority. We have demonstrated recently that β-elemene, a novel antitumor compound, enhances cisplatin activity by triggering lung cancer cell death via apoptosis. Here, we investigated whether β-elemene acts synergistically with cisplatin to inhibit non-small cell lung cancer (NSCLC) cell proliferation by blocking cell cycle progression. β-Elemene substantially increased the suppressive effect of cisplatin on cell growth and proliferation in the NSCLC cell lines H460 and A549. Furthermore, β-elemene augmented cisplatin in the cell cycle arrest of NSCLC cells at G(2)/M. This was associated with upregulated checkpoint kinase (CHK2) expression and reduced CDC2 activity (i.e., increased phosphorylation of CDC2 on Tyr-15 and decreased phosphorylation of CDC2 on Thr-161). Moreover, β-elemene and cisplatin in combination clearly decreased the protein levels of cyclin B1 and CDC25C and increased the levels of p21(Cip1/Waf1), p27(Kip1), and GADD45 in these cells, compared with the effects of either agent alone at the same concentration. These results suggest that the β-elemene-enhanced inhibitory effect of cisplatin on lung carcinoma cell proliferation is regulated by a CHK2-mediated CDC25C/CDC2/cyclin B1 signaling pathway and leads to the blockade of cell cycle progression at G(2)/M. A comparison of the cytotoxic efficacies of β-elemene and three synthetic analogs (β-elemenol, β-elemenal, and β-elemene fluoride) in the two lung cancer cell lines revealed that β-elemenol and β-elemene fluoride had the same antitumor efficacy as β-elemene, whereas β-elemenal was appreciably more potent than β-elemene. Thus, although all three synthetic analogs of β-elemene considerably suppressed NSCLC cell growth and proliferation, β-elemenal may have greater potential as an anticancer alternative to β-elemene in treating lung cancer and other tumors.

Cisplatin-based combination treatment is the most effective systemic chemotherapy for bladder cancer; however, resistance to cisplatin remains a significant problem in the treatment of this disease. β-Elemene is a new natural compound that blocks cell-cycle progression and has a broad spectrum of antitumor activity. This study was conducted to explore the potential of β-elemene as a chemosensitizer for enhancing the therapeutic efficacy and potency of cisplatin in bladder cancer and other solid carcinomas. β-Elemene not only markedly inhibited cell growth and proliferation but also substantially increased cisplatin cytotoxicity towards human bladder cancer 5637 and T-24 cells. Similarly, β-elemene also enhanced cisplatin sensitivity and augmented cisplatin cytotoxicity in small-cell lung cancer and carcinomas of the brain, breast, cervix, ovary, and colorectal tract in vitro, with dose-modifying factors ranging from 5 to 124. β-Elemene-enhanced cisplatin cytotoxicity was associated with increased apoptotic cell death, as determined by DNA fragmentation, and increased activities of caspase-3, -7, -8, -9, and -10 in bladder cancer cell lines. Collectively, these results suggest that β-elemene augments the antitumor activity of cisplatin in human bladder cancer by enhancing the induction of cellular apoptosis via a caspase-dependent mechanism. Cisplatin combined with β-elemene as a chemosensitizer warrants further pre-clinical therapeutic studies and may be useful for the treatment of cisplatin-resistant bladder cancer and other types of carcinomas.

β-Elemene is a promising new plant-derived drug with broad-spectrum anticancer activity. It also increases cisplatin cytotoxicity and enhances cisplatin sensitivity in resistant human carcinoma cells. However, little is known about the mechanism of its action. To explore the potential therapeutic application of β-elemene as a drug-resistance modulator, this study investigated the underlying mechanism of β-elemene activity in cisplatin-resistant ovarian cancer cells. β-Elemene enhanced cisplatin sensitivity to a much greater extent in chemoresistant A2780/CP70 and MCAS human ovarian carcinoma cells compared to the chemosensitive parental cell line A2780. The dose-modifying factors for cisplatin were between 35 and 60 for A2780/CP70 cells and between 1.6 and 2.5 for A2780 cells. In the cisplatin-resistant ovarian carcinoma cells, β-elemene abrogated cisplatin‑induced expression of excision repair cross-complementation group‑1 (ERCC-1), a marker gene in the nucleotide excision repair pathway that repairs cisplatin-caused DNA damage. In addition, β-elemene not only reduced the level of X-linked inhibitor of apoptosis protein (XIAP), but also downregulated cisplatin-mediated XIAP expression in chemoresistant cells. Furthermore, β-elemene blocked the cisplatin-stimulated increase in the level of phosphorylated c-Jun NH2-terminal kinase (JNK) in these cells. These novel findings suggest that the β-elemene enhancement of cisplatin sensitivity in human chemoresistant ovarian cancer cells is mediated at least in part through the impairment of DNA repair activity and the activation of apoptotic signaling pathways, thereby making resistant ovarian cancer cells susceptible to cisplatin-induced cell death.

Triple negative breast cancer (TNBC) is generally diagnosed by immunohistochemical methods that result in negative staining for the estrogen and progesterone receptors, and human epidermal growth factor receptor 2, which are targets for the most successful treatments for breast cancer. African American women are particularly affected by the disease, and among those in this ethnic group who develop breast cancer there is a 20 to 40 percent chance of it being triple‐negative. Although the use of DNA damaging agents is standard therapy in the treatment of multiple classes of cancers, growing studies suggest that pathways that seek to repair DNA damage might also be fruitful targets. This lecture will address modulation of DNA damage and DNA repair pathways in treating TNBC, with a particular focus on nucleotide excision repair.

e13566 Background: It is well known that most cancer cells display a Warburg effect, a state of active glycolysis with lactate production under aerobic conditions. NF-κB has been shown to play a role in modulating cancer metabolism and control the balance between glycolysis and mitochondrial respiration. We have previously shown that panepoxydone (PP), a compound isolated from an edible mushroom, interferes with NF-κB mediated signal transduction. Additionally, we have shown that PP decreases cell viability and proliferation in breast cancer cells. To further characterize the antitumor effect of PP, here we have evaluated it ability to modulate cancer metabolism. Methods: The metabolic action of PP was evaluated in estrogen receptor positive (MCF-7) and triple negative (MDAMB-231) breast cancer cell lines. Cytotoxicity was determined by the cell titer glow assay and expressed as IC50. Metabolic activity, expressed as basal oxygen consumption rate (OCR, an indicator of oxidative phosphorylation) and extracellular acidification rate (ECAR, an indicator of lactate acid production), was measured in real-time using the XF24 Extracellular Flux Analyzer. Mitochondrial membrane potential (MMP) alteration was determined through flow cytometry and LDH-A expression was analyzed via western blot. Results: Significant antitumor activity with PP was seen in both MCF-7 (IC50 5 µM) and MDAMB-231 cells (IC50 15 µM). This correlated to a significant dose-dependent reduction in OCAR in MCF-7 (2-fold, p<0.05) and MDAMB-231 cells (3.5-fold, p<0.01). However, while a decrease in ECAR (1.5-fold, p<0.05), along with decreased LDHA expression was noted in the 231 cells (3.5-fold, p<0.01), this was not seen with the MCF-7 cells. A similar trend was noted with increased damaged mitochondria noted in 231-cells, but again no significant difference in MCF-7 cells. Conclusions: Taken together, these results indicate that PP has the potential to modulate metabolism in breast cancer cells, especially triple negative cells, as noted by its ability to inhibit glycolysis. The inhibition of glycolysis has become an important strategy in treating cancer and development of novel glycolytic inhibitors, such as PP, warrants its further investigation in breast cancer treatment.

Objectives Although it does not alter the ERCC1 phenotype, the ERCC1 500C>T (rs11615) polymorphism has undergone a myriad of investigations into its role as a marker for nucleotide excision repair (NER) function in different races, diseases and treatment outcomes. The goal of our study was to test the hypothesis that 500C>T is in linkage disequilibrium (LD) with causative alleles, and that these haplotypes are more frequent in Caucasians with melanoma than in healthy Caucasians or African Americans. Design In this case–control study, we selected race-specific ERCC1 single-nucleotide polymorphism (SNPs), conducted LD analysis with ERCC1 500C>T and compared the frequency of ERCC1 diplotypes in Caucasians with melanoma (n=165), healthy Caucasians (n=150) and healthy African Americans (n=159). The haplotype was further studied using a fusion gene containing multiple ERCC1 SNPs. Setting Large cancer institute in the USA. Participants A total of 165 Caucasian melanoma patients, 159 healthy Caucasian controls and 159 African American healthy controls. Men and women were enrolled in the clinical trial; however, since the screening trial included prostate cancer screening in addition to screening for other cancers, only male controls were available. Outcome measures The outcome measures were melanoma risk in Caucasians, and LD between ERCC1 SNP, N118N and other race-specific allelic variants. Results When compared to ERCC1 500C>T alone, a race-specific three-SNP variant haplotype in ERCC1 (comprised of rs11615, rs3212950 and rs3212948) was even more frequent in Caucasians with melanoma than in healthy Caucasians (p=0.0034) or African Americans (p<0.0001). A plasmid containing the variant haplotype was not differentially expressed. Conclusions We demonstrate that ERCC1 500C>T participates in a previously characterised cancer-risk haplotype found more frequently in Caucasians, while LD is weak in African Americans; this haplotype appears to also be related to melanoma. It is therefore likely that ERCC1 500C>T is only a valid NER, disease or treatment outcome marker in Caucasians.

Cancer cells with the surface marker profile CD44+/CD24− have previously been described to possess cancer stem cell-like properties. This manuscript evaluates those properties in ovarian cancer cell lines. The proportion of CD44+/CD24− cells corresponded to the clinical aggressiveness of each ovarian cancer cell line histologic subtype. CD44+/CD24− cells demonstrated enhanced progressive differentiation as well as showing a 60-fold increase in Matrigel invasion in both SKOV3 and OV90 cell lines (p < 0.001 each) compared to other phenotypes. CD44+/CD24− demonstrated significant resistance to all chemotherapy agents used in all cell lines, with a 71–93 % increase in resistance compared with baseline. Using a threshold of 25 % CD44+/CD24– ovarian cancer cells found in ascites, patients with >25 % CD44+/CD24− were significantly more likely to recur (83 vs. 14 %, p = 0.003) and had shorter median progression-free survival (6 vs. 18 months, p = 0.01). In conclusion, the CD44+/CD24− phenotype in ovarian cancer cells demonstrate cancer stem cell-like properties of enhanced differentiation, invasion, and resistance to chemotherapy. This CD44+/CD24− phenotype correlates to clinical endpoints with increased risk of recurrence and shorter progression-free survival in patients with ovarian cancer.