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Abnormal accumulation of acyl-CoA cholesterol acyltransferase-1 (ACAT-1) mediated cholesterol ester has been shown to contribute to cancer progression in various cancers including leukemia, glioma, breast, pancreatic and prostate cancers. However, the significance of ACAT-1 and cholesterol esters (CE) is relatively understudied in ovarian cancer. In this in vitro study, we assessed the expression and contribution of ACAT-1 in ovarian cancer progression. We observed a significant increase in the expression of ACAT-1 and CE levels in a panel of ovarian cancer cell lines (OC-314, SKOV-3 and IGROV-1) compared to primary ovarian epithelial cells (normal controls). To confirm the tumor promoting capacity of ACAT-1, we inhibited ACAT-1 expression and activity by treating our cell lines with an ACAT inhibitor, avasimibe, or by stable transfection with ACAT-1 specific short hairpin RNA (shRNA). We observed significant suppression of cell proliferation, migration and invasion in ACAT-1 knockdown ovarian cancer cell lines compared to their respective controls (cell lines transfected with scrambled shRNA). ACAT-1 inhibition enhanced apoptosis with a concurrent increase in caspases 3/7 activity and decreased mitochondrial membrane potential. Increased generation of reactive oxygen species (ROS) coupled with increased expression of p53 may be the mechanism(s) underlying pro-apoptotic action of ACAT-1 inhibition. Additionally, ACAT-1 inhibited ovarian cancer cell lines displayed enhanced chemosensitivity to cisplatin treatment. These results suggest ACAT-1 may be a potential new target for the treatment of ovarian cancer.

Previously, Bithionol (BT) was shown to enhance the chemosensitivity of ovarian cancer cell lines to cisplatin treatment. In the present study, we focused on the anti-tumor potential of the BT-paclitaxel combination when added to a panel of ovarian cancer cell lines. This in vitro study aimed to 1) determine the optimum schedule for combination of BT and paclitaxel and 2) assess the nature and mechanism(s) underlying BT-paclitaxel interactions. The cytotoxic effects of both drugs either alone or in combination were assessed by presto-blue cell viability assay using six human ovarian cancer cell lines. Inhibitory concentrations to achieve 50% cell death (IC50) were determined for BT and paclitaxel in each cell line. Changes in levels of cleaved PARP, XIAP, bcl-2, bcl-xL, p21 and p27 were determined via immunoblot. Luminescent and colorimetric assays were used to determine caspases 3/7 and autotaxin (ATX) activity. Cellular reactive oxygen species (ROS) were measured by flow cytometry. Our results show that the efficacy of the BT-paclitaxel combination depends upon the concentrations and sequence of addition of paclitaxel and BT. Pretreatment with BT followed by paclitaxel resulted in antagonistic interactions whereas synergistic interactions were observed when both drugs were added simultaneously or when cells were pretreated with paclitaxel followed by BT. Synergistic interactions between BT and paclitaxel were attributed to increased ROS generation and enhanced apoptosis. Decreased expression of pro-survival factors (XIAP, bcl-2, bcl-xL) and increased expression of pro-apoptotic factors (caspases 3/7, PARP cleavage) was observed. Additionally, increased expression of key cell cycle regulators p21 and p27 was observed. These results show that BT and paclitaxel interacted synergistically at most drug ratios which, however, was highly dependent on the sequence of the addition of drugs. Our results suggest that BT-paclitaxel combination therapy may be effective in sensitizing ovarian cancer cells to paclitaxel treatment, thus mitigating some of the toxic effects associated with high doses of paclitaxel.

In terms of the concept of 'drug repurposing', we focused on pharmaceutical-grade Bithionol (BT) as a therapeutic agent against ovarian cancer. Our recent in-vitro study provides preclinical data suggesting a potential therapeutic role for BT against recurrent ovarian cancer. BT was shown to cause cell death by caspases-mediated apoptosis. The present preliminary study further explores the antitumor potential of pharmaceutical-grade BT in an in-vivo xenograft model of human ovarian cancer. Nude Foxn1 mice bearing SKOV-3 human ovarian tumor xenografts were treated with titrated doses of BT and the therapeutic efficacy of pharmaceutical BT was determined using bioluminescence imaging. BT-induced changes in cell proliferation and apoptosis were evaluated by Ki-67 immunochemical staining and TUNEL assay. The effect of BT on autotaxin levels in serum, ascitic fluid, and tumor tissue was assessed by colorimetric and western blot techniques. BT treatment did not show antitumor potential or enhanced survival time at any of the doses tested. No apparent signs of toxicity were observed with any of the doses tested. Immunohistological analysis of tumor sections did not indicate a significant decrease in cellular proliferation (Ki-67 assay). An increase in apoptosis (by TUNEL assay) was observed in all BT-treated mice compared with vehicle-treated mice. Although BT did not show significant antitumor activity in the present study, the ability of BT to induce apoptosis still makes it a promising therapeutic agent. Further confirmatory and optimization studies are essential to enhance the therapeutic effects of BT.

INTRODUCTION: Cancer progression and tumorigenesis have been linked to alterations in cellular metabolic pathways of lipid and cholesterol synthesis in many cancers. Increased levels of cholesterol esters (CE) have been reported in breast cancer, leukemia, glioma and prostate cancer, but not exploited in detail in ovarian and endometrial cancers. Inside cells, excess free cholesterol is esterified by acyl-CoA cholesterol acyltransferase (ACAT) and stored as cholesteryl ester (CE) in lipid droplets (LDs). Cholesteryl ester accumulation may be a consequence of loss of tumor suppressor PTEN and subsequent activation of PI3K/AKT pathway as observed in pancreatic cancer. In the present study, we focused on the role of ACAT and cholesterol esters in altered cholesterol metabolism in ovarian/endometrial cancer cell lines. METHODS: We studied the effect of abrogation of cholesterol esterification either by an ACAT-1 inhibitor/shRNA knockdown or via inhibition of PI3K/AKT/mTOR pathways and subsequent effect on ovarian/endometrial cancer cells proliferation, invasion, cell migration and tumorigenesis. The expression of ACAT was studied at the protein and mRNA levels in a panel of ovarian/ endometrial cancer cell lines and also in normal and ovarian cancer clinical samples. ACAT expression was assessed by western blotting, ELISA, quantitative RT-PCR and immunostaining techniques. RESULTS: Our results reveal an elevated expression of ACAT-1 at both protein and mRNA levels in ovarian and endometrial cancer cell lines as compared to primary cells. Our results also provide preliminary data on involvement of ACAT and cholesterol esters in the progression and metastasis of ovarian cancer. CONCLUSION: These studies may aid in the development of new biomarkers or treatment targets for ovarian/endometrial cancer. Citation Format: Vijayalakshmi N. Ayyagari, Xinjia Wang, Laurent Brard. Studies on role of acyl-CoA cholesterol acyltransferase (ACAT) expression in ovarian/endometrial cancer progression - An invitro study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4416. doi:10.1158/1538-7445.AM2017-4416

Background Drug resistance is a cause of ovarian cancer recurrence and low overall survival rates. There is a need for more effective treatment approaches because the development of new drug is expensive and time consuming. Alternatively, the concept of ‘drug repurposing’ is promising. We focused on Bithionol (BT), a clinically approved anti-parasitic drug as an anti-ovarian cancer drug. BT has previously been shown to inhibit solid tumor growth in several preclinical cancer models. A better understanding of the anti-tumor effects and mechanism(s) of action of BT in ovarian cancer cells is essential for further exploring its therapeutic potential against ovarian cancer. Methods The cytotoxic effects of BT against a panel of ovarian cancer cell lines were determined by Presto Blue cell viability assay. Markers of apoptosis such as caspases 3/7, cPARP induction, nuclear condensation and mitochondrial transmembrane depolarization were assessed using microscopic, FACS and immunoblotting methods. Mechanism(s) of action of BT such as cell cycle arrest, reactive oxygen species (ROS) generation, autotaxin (ATX) inhibition and effects on MAPK and NF-kB signalling were determined by FACS analysis, immunoblotting and colorimetric methods. Results BT caused dose dependent cytotoxicity against all ovarian cancer cell lines tested with IC50 values ranging from 19 μM – 60 μM. Cisplatin-resistant variants of A2780 and IGROV-1 have shown almost similar IC50 values compared to their sensitive counterparts. Apoptotic cell death was shown by expression of caspases 3/7, cPARP, loss of mitochondrial potential, nuclear condensation, and up-regulation of p38 and reduced expression of pAkt, pNF-κB, pIκBα, XIAP, bcl-2 and bcl-xl. BT treatment resulted in cell cycle arrest at G1/M phase and increased ROS generation. Treatment with ascorbic acid resulted in partial restoration of cell viability. In addition, dose and time dependent inhibition of ATX was observed. Conclusions BT exhibits cytotoxic effects on various ovarian cancer cell lines regardless of their sensitivities to cisplatin. Cell death appears to be via caspases mediated apoptosis. The mechanisms of action appear to be partly via cell cycle arrest, ROS generation and inhibition of ATX. The present study provides preclinical data suggesting a potential therapeutic role for BT against recurrent ovarian cancer.

Introduction: ‘Drug Repurposing’ promises to be a successful concept for the treatment of many diseases. We focused on Bithionol (BT), a clinically approved antiparasitic drug for use as a therapeutic agent against ovarian cancer. BT has been shown to inhibit solid tumor growth in several preclinical cancer models by targeting autotaxin (ATX). Methods: In the present study, we determined the anti-tumor effect of BT and its mechanism of action against a panel of ovarian cancer cell lines. First, we studied the cytotoxic effect of BT against a panel of ovarian cancer cell lines (A2780 & A2780-CDDP OVACAR-3, SKOV-3, IGROV-1, and IGROV-1CDDP). We identified the type of cell death i.e. apoptotic vs. necrosis, and examined markers of apoptosis and necrosis. Mechanism(s) of action were studied in terms of reactive oxygen species (ROS) generation, autotoxin (ATX) inhibition and MAPK signaling. In addition, we studied the sensitizing effect of BT on cisplatin cytotoxicity. Results: Our results have shown that BT causes dose dependent cytotoxicity against all the cell lines tested with IC50 values ranging from 20μM - 60μM. The order of ranking in terms of sensitivity to BT is A2780 > SKOV-3 > OVACAR-3>, IGROV-1. Cisplatin resistant variants of A2780 and IGROV-1 have shown almost similar IC50 values to their sensitive variant. Apoptotic cell death was observed at low concentration and early time points whereas necrosis was observed at high concentrations and later time points. Apoptotic cell death was shown by expression of caspases 3,7, increased homogenous caspases 3/7 activity, loss of mitochondrial potential, cPARP expression, DNA condensation, up-regulation of p38 and down regulation of XIAP. At higher concentrations, BT caused down-regulation of caspases3/7 activity and increased LDH activity indicative of necrosis. Sensitization studies with BT showed that pre-treatment of ovarian cancer cell lines with BT for 24 hrs enhanced cisplatin cytotoxicity by 20 - 80%. Interestingly, cisplatin resistant variants of A2780 and IGROV-1 were more sensitive to cisplatin upon BT pre-treatment as compared to their sensitive variants. The order of ranking in terms of enhanced sensitivity to cisplatin upon BT pre-treatment was A2780-CDDP > A2780 > OVCAR-3 > IGROV-1CDDP > IGROV-1 >SJOV-3. BT treatment resulted in increased ROS generation. Treatment with antioxidant ascorbic acid resulted in partial restoration of cell viability. In addition, dose and time dependent inhibition of ATX was observed. Conclusions: Our results demonstrate the cytotoxic effect of BT on various ovarian cancer cells and the mechanism of actions appears to be partly via ROS generation and inhibition of ATX. Pre-treatment with BT resulted in enhanced cytotoxicity to cisplatin especially in cisplatin resistant variants. In view of these results, BT can be an effective adjunct agent along with cisplatin for ovarian cancer treatment. Citation Format: Vijayalakshmi N. Ayyagari, Laurent Brard. Studies on antitumor effects of bithionol on 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 2121. doi:10.1158/1538-7445.AM2013-2121

Background Combination drug therapy appears a promising approach to overcome drug resistance and reduce drug-related toxicities in ovarian cancer treatments. In this in vitro study, we evaluated the antitumor efficacy of cisplatin in combination with Bithionol (BT) against a panel of ovarian cancer cell lines with special focus on cisplatin-sensitive and cisplatin-resistant cell lines. The primary objectives of this study are to determine the nature of the interactions between BT and cisplatin and to understand the mechanism(s) of action of BT-cisplatin combination. Methods The cytotoxic effects of drugs either alone or in combination were evaluated using presto-blue assay. Cellular reactive oxygen species were measured by flow cytometry. Immunoblot analysis was carried out to investigate changes in levels of cleaved PARP, XIAP, bcl-2, bcl-xL, p21 and p27. Luminescent and colorimetric assays were used to test caspases 3/7 and ATX activity. Results The efficacy of the BT-cisplatin combination depends upon the cell type and concentrations of cisplatin and BT. In cisplatin-sensitive cell lines, BT and cisplatin were mostly antagonistic except when used at low concentrations, where synergy was observed. In contrast, in cisplatin-resistant cells, BT-cisplatin combination treatment displayed synergistic effects at most of the drug ratios/concentrations. Our results further revealed that the synergistic interaction was linked to increased reactive oxygen species generation and apoptosis. Enhanced apoptosis was correlated with loss of pro-survival factors (XIAP, bcl-2, bcl-xL), expression of pro-apoptotic markers (caspases 3/7, PARP cleavage) and enhanced cell cycle regulators p21 and p27. Conclusion In cisplatin-resistant cell lines, BT potentiated cisplatin-induced cytotoxicity at most drug ratios via enhanced ROS generation and modulation of key regulators of apoptosis. Low doses of BT and cisplatin enhanced efficiency of cisplatin treatment in all the ovarian cancer cell lines tested. Our results suggest that novel combinations such as BT and cisplatin might be an attractive therapeutic approach to enhance ovarian cancer chemosensitivity. Combining low doses of cisplatin with subtherapeutic doses of BT can ultimately lead to the development of an innovative combination therapy to reduce/prevent the side effects normally occurring when high doses of cisplatin are administered. Electronic supplementary material The online version of this article (doi:10.1186/s12885-016-3034-2) contains supplementary material, which is available to authorized users.