Abstract
BackgroundOvarian cancer is the most lethal gynecologic malignancy characterized by the frequent development of resistance to platinum chemotherapy. Finding new drug combinations to overcome platinum resistance is a key clinical challenge. Thymoquinone (TQ) is a component of black seed oil that exerts multiple anti-tumorigenic effects on cells, including inhibition of NF-κB and promotion of DNA damage. We aimed to determine whether TQ enhances cisplatin cytotoxicity in cultured ovarian cancer cells and in an established murine syngeneic model of ovarian cancer.MethodsOvarian cancer cell viability in vitro was measured by sulforhodamine B (SRB) assays, and drug interactions tested for synergism by isobologram analysis. ID8-NGL mouse ovarian cancer cells stably expressing an NF-κB reporter transgene were injected intra-peritoneally into C57BL/6 mice. After 30 day TQ and/or cisplatin treatment, we measured the following indices: tumor burden (ascites volume, number of peritoneal implants and mesenteric tumor mass); NF-κB reporter activity (luciferase assay); protein expression of the double-strand DNA break marker, pH2AX(ser139), the proliferation markers, Ki67/mib-1 and PCNA, and the apoptosis markers, cleaved caspase-3, cleaved PARP and Bax; and mRNA expression of NF-κB targets, TNF-α and IL-1β. Two-tailed Mann–Whitney tests were used for measuring differences between groups in mouse experiments.ResultsIn SRB assays, TQ and cisplatin synergized in ID8-NGL cells. In mice, cisplatin significantly reduced cell proliferation and increased apoptosis in tumors, resulting in decreased overall tumor burden. Combining TQ with cisplatin further decreased these indices, indicating co-operative effects between the drugs. TQ treatment promoted cisplatin-induced pH2AX expression in cultured cells and in tumors. While NF-κB inhibition by TQ induced anti-tumor effects in vitro, we made the unexpected observation that TQ alone increased both tumor NF-κB activity and formation of ascites in vivo.ConclusionsTQ enhanced cisplatin-mediated cytoxicity in ovarian cancer cells in vitro and in a mouse syngeneic model, effects associated with increased DNA damage. However, our results strongly caution that TQ treatment alone may have an overall deleterious effect in the immunocompetent host through stimulation of ascites. Since TQ is a potential candidate for future clinical trials in ovarian cancer patients, this finding has considerable potential relevance to the clinic.Electronic supplementary materialThe online version of this article (doi:10.1186/s13048-015-0177-8) contains supplementary material, which is available to authorized users.
Highlights
Ovarian cancer is the most lethal gynecologic malignancy characterized by the frequent development of resistance to platinum chemotherapy
TQ enhances anti-tumor effects of cisplatin in cultured ovarian cancer cells Here, we aimed to determine whether TQ can sensitize ovarian cancer cells cultured in vitro to the cytotoxic effect of cisplatin
The combination of TQ and cisplatin was tested in sulforhodamine B (SRB) cell growth and viability assays
Summary
Ovarian cancer is the most lethal gynecologic malignancy characterized by the frequent development of resistance to platinum chemotherapy. The development of resistance to platinum chemotherapy (carboplatin and cisplatin) is common in advanced disease [3]. Multiple molecular mechanisms of action have been described for the demonstrated ability of TQ to reduce tumor growth and survival in these preclinical studies These include activation of tumor suppressor genes such as PTEN and p21, reducing pro-inflammatory and angiogenic signals via inhibition of NF-κB signaling, an important molecular link between inflammation and cancer [8,9,10,11,12,13], and induction of DNA damage through generation of reactive oxygen species (ROS) [4,5,6]. Definitive trials for establishing safe and effective doses of TQ in cancer patients are currently lacking, but are well supported by preclinical data [4,5,6,7]
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