Grapefruit extract as a potential radiosensitizer of prostate cancer cells

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Prostate cancer is the most common solid cancer in men living in the United States. Grapefruit extract contains natural chemicals known as phytochemicals, which include flavonoids and vitamins, which are known to have anti-cancer properties. Previously, our laboratory found that resveratrol, a natural phenol, acts as a radiosensitizer for prostate cancer. Here, we investigate if grapefruit functions similarly. A clonogenic cell survival assay was used to investigate the role of grapefruit extract on survival of a prostate cancer cell line. Following pretreatment with 0-or 50 ng/mL grapefruit extract, the cells were irradiated with 4 grays of radiation. Pretreatment with grapefruit extract resulted in a ~60% reduction in the number of colonies compared to the control. To identify the possible molecular mechanism correlating with the observed decrease in proliferation, we analyzed mRNA expression using a reverse-transcriptase polymerase chain reaction protocol. The anti-proliferative effect of radiation therapy with grapefruit extract pretreatment correlated with the significant downregulation of mRNA expression of the following proteins involved in cell cycle regulation: cyclin B, cyclin D, cyclin-dependent kinase 2, and cyclin-dependent kinase 4. Our data indicate that the combination of grapefruit extract and radiation therapy decreases cell proliferation in PC-3 prostate cancer cells, which suggests a possible role for grapefruit as a radiosensitizer of prostate cancer.

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Prostate cancer (PCa) is the most common non-cutaneous cancer in men in the USA. Radiation therapy (RT) is widely considered the standard treatment for PCa. IL-37 is an IL-1 family member, and it has been extensively studied in immunity. However, no studies have been done regarding its potential as a radiosensitizer. This study is designed to investigate the direct effect of IL-37 on growth of DU145 and PC-3, two widely studied PCa cell lines, and to investigate whether IL-37 could be used as a radiosensitizer for PCa. Clonogenic survival and quick cell proliferation assays along with immunohistochemistry, TUNEL staining, and caspace-3 activity assay kits as well as RT-PCR were used in this study. Our results showed that IL-37 has little direct effect on growth of PCa. However, IL-37/RT enhanced RT-induced inhibition of cell proliferation and apoptosis in both cell lines. We further found that IL-37/RT upregulated the mRNA expression of p27, Fas, and Bax, while downregulating the mRNA expression of cdk2 in DU145 cells. These findings suggest that IL-37 has the potential to be used as a radiosensitizer for PCa and warrants further investigation.
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Furanocoumarins are a specific group of secondary metabolites that commonly present in higher plants, such as citrus plants. The major furanocoumarins found in grapefruits (Citrus paradisi) include bergamottin, epoxybergamottin, and 6′,7′-dihydroxybergamottin. During biosynthesis of these furanocoumarins, coumarins undergo biochemical modifications corresponding to a prenylation reaction catalyzed by the cytochrome P450 enzymes with the subsequent formation of furan rings. Because of undesirable interactions with several medications, many studies have developed methods for grapefruit furanocoumarin quantification that include high-performance liquid chromatography coupled with UV detector or mass spectrometry. The distribution of furanocoumarins in grapefruits is affected by several environmental conditions, such as processing techniques, storage temperature, and packing materials. In the past few years, grapefruit furanocoumarins have been demonstrated to exhibit several biological activities including antioxidative, -inflammatory, and -cancer activities as well as bone health promotion both in vitro and in vivo. Notably, furanocoumarins potently exerted antiproliferative activities against cancer cell growth through modulation of several molecular pathways, such as regulation of the signal transducer and activator of transcription 3, nuclear factor-κB, phosphatidylinositol-3-kinase/AKT, and mitogen-activated protein kinase expression. Therefore, based on this review, we suggest furanocoumarins may serve as bioactive components that contribute, at least in part, to the health benefits of grapefruit.
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Naringenin (NAR) as one of the flavonoids observed in grapefruit has been reported to exhibit an anti-cancer activity. However, more detailed mechanism by which NAR exerts anti-cancer properties still remains unanswered. Thus, in this study, we have shown that NAR down-regulates the level of cyclin D1 in human colorectal cancer cell lines, HCT116 and SW480. NAR inhibited the cell proliferation in HCT116 and SW480 cells and decreased the level of cyclin D1 protein. Inhibition of proteasomal degradation by MG132 blocked NAR-mediated cyclin D1 downregulation and the half-life of cyclin D1 was decreased in the cells treated with NAR. In addition, NAR increased the phosphorylation of cyclin D1 at threonine-286 and a point mutation of threonine-286 to alanine blocked cyclin D1 downregulation by NAR. p38 inactivation attenuated cyclin D1 downregulation by NAR. From these results, we suggest that NAR-mediated cyclin D1 downregulation may result from proteasomal degradation through p38 activation. The current study provides new mechanistic link between NAR, cyclin D1 downregulation and cell growth in human colorectal cancer cells.
Radiation therapy (RT) is commonly used for the treatment of localized prostate cancer (PCa). However, cancer cells often develop resistance to radiation through unknown mechanisms and pose an intractable challenge. Radiation resistance is highly unpredictable, rendering the treatment less effective in many patients and frequently causing metastasis and cancer recurrence. Understanding the molecular events that cause radioresistance in PCa will enable us to develop adjuvant treatments for enhancing the efficacy of RT. Radioresistant PCa depends on the elevated DNA repair system and the intracellular levels of reactive oxygen species (ROS) to proliferate, self-renew, and scavenge anti-cancer regimens, whereas the elevated heat shock protein 90 (HSP90) and the epithelial-mesenchymal transition (EMT) enable radioresistant PCa cells to metastasize after exposure to radiation. The up-regulation of the DNA repairing system, ROS, HSP90, and EMT effectors has been studied extensively, but not targeted by adjuvant therapy of radioresistant PCa. Here, we emphasize the effects of ionizing radiation and the mechanisms driving the emergence of radioresistant PCa. We also address the markers of radioresistance, the gene signatures for the predictive response to radiotherapy, and novel therapeutic platforms for targeting radioresistant PCa. This review provides significant insights into enhancing the current knowledge and the understanding toward optimization of these markers for the treatment of radioresistant PCa.
Prostate cancer is the most common cancer in men and the second most common cause of cancer-related deaths in men. Although various drugs targeting the androgen receptor are normally used, the patients frequently undergo recurrence of the disease. To overcome these limitations, natural compounds have been researched for evidence that they suppress progression and metastasis of various cancer cells. In the present study, we investigated effects of naringenin, a natural anti-oxidant flavonoid derived from citrus, on prostate cancer cells (PC3 and LNCaP). Results of present study with PC3 and LNCaP cells revealed that naringenin inhibited proliferation and migration, while inducing apoptosis and ROS production by those cells. In addition, naringenin-induced loss of mitochondrial membrane potential and increased Bax and decreased Bcl-2 proteins in PC3 cells, but not LNCaP cells. In a dose-dependent manner, naringenin decreased phosphorylation of ERK1/2, P70S6K, S6 and P38 in PC3 cells, and reduced phosphorylation of ERK1/2, P53, P38 and JNK proteins in LNCaP cells. However, naringenin activated phosphorylation of AKT in both PC3 and LNCaP cells. Then, targeted signaling proteins associated with viability of PC3 and LNCaP cells were analyzed using pharmacological inhibitors of AKT and ERK1/2 cell signaling pathways. Moreover, we compared the apoptotic effects of naringenin and paclitaxel alone and in combination to find that naringenin enhanced the efficiency of paclitaxel to suppress progression of prostate cancer cell lines. Collectively, these results indicate that naringenin is a potential chemotherapeutic agent for treatment of prostate cancer. This article is protected by copyright. All rights reserved.
Radiation therapy (XRT) for treatment of localized prostate cancer (PCA) has outcomes similar to surgery and medical therapy. Toxicities of XRT and the relative radioresistance of PCA limit the effectiveness of this treatment method. Safe and effective radiosensitizing agents are lacking to enhance the effectiveness for XRT for PCA. In this study, the effect of XRT in combination with the radiosensitizing agent resveratrol (RSV) was investigated in a radioresistant PCA cell line, PC-3. Our results show the addition of RSV to XRT (XRT/RSV) synergistically enhanced XRT-induced apoptosis and inhibition of PC-3 proliferation. The antiproliferative effect of XRT/RSV treatment correlated with increased expression of p15, p21, and mutant p53 and decreased expression of cyclin B, cyclin D, and cdk2. Increased apoptosis correlated with increased expression of Fas and TRAILR1. Furthermore, XRT/RSV had little effect on the expression of p-AKT, whereas it increased the expression level of p-H2A.X, a marker for senescence. These data highlight the potential of RSV as a radiation sensitizer for PCA treatment and warrant further investigation.
Early detection and monitoring by serum prostate-specific antigen (PSA) measurement has increased the number of men presenting with potentially curable prostate cancer. Most will choose radical prostatectomy or some form of radiation therapy for treatment, but some will have evidence of biochemical disease recurrence following therapy, shown by a rising PSA level without other clinical evidence of disease. Radical prostatectomy involves the removal of all prostate tissue, causing the serum PSA to decline to undetectable levels within four to six weeks following surgery; a subsequent rise in the serum PSA to a detectable level indicates disease recurrence. Patients should be evaluated to assess whether rising PSA levels indicate local recurrence or early metastatic disease. The advantages of salvage radiation, endocrine therapy, and other treatment modalities in local disease recurrence must be weighed against potential side effects and the resulting decrease in quality of life. Radiation therapy does not immediately eradicate all PSA-producing cells; therefore the persistence of a detectable PSA does not necessarily imply residual cancer, but rising PSA levels indicate treatment failure. Salvage surgery can be performed after radiotherapy for the purpose of removing all viable cancer cells, but should be weighed against a higher incidence of surgical complications; cryoablation offers a less invasive therapeutic modality.
Naringin, an active flavonoid found in citrus fruit extracts, has pharmacological utility. The present study identified a novel mechanism of the anticancer effects of naringin in urinary bladder cancer cells. Naringin treatment resulted in significant dose-dependent growth inhibition together with G(1)-phase cell-cycle arrest at a dose of 100 microM (the half maximal inhibitory concentration) in 5637 cells. In addition, naringin treatment strongly induced p21WAF1 expression, independent of the p53 pathway, and downregulated expression of cyclins and cyclin dependent kinases (CDKs). Moreover, treatment with naringin induced phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase and c-Jun N-terminal kinase. Among the pathways examined, only PD98059, an ERK-specific inhibitor, blocked naringin-dependent p21WAF1 expression. Consistently, blockade of ERK function reversed naringin-mediated inhibition of cell proliferation and decreased cell-cycle proteins. Furthermore, naringin treatment increased both Ras and Raf activation. Transfection of cells with dominant-negative Ras (RasN17) and Raf (RafS621A) mutant genes suppressed naringin-induced ERK activity and p21WAF1 expression. Finally, the naringin-induced reduction in cell proliferation and cell-cycle proteins also was abolished in the presence of RasN17 and RafS621A mutant genes. These data demonstrate that the Ras/Raf/ERK pathway participates in p21WAF1 induction, subsequently leading to a decrease in the levels of cyclin D1/CDK4 and cyclin E-CDK2 complexes and naringin-dependent inhibition of cell growth. Overall, these unexpected findings concerning the molecular mechanisms of naringin in 5637 cancer cells provide a theoretical basis for the therapeutic use of flavonoids to treat malignancies.
Prostate Cancer -Cancer Stat Facts [Internet]. National Cancer Institute
  • A M Noone
  • N Howlader
  • M Krapcho
  • D Miller
  • A Brest
  • M Yu
  • J Ruhl
  • Z Tatalovich
  • A Mariotto
  • D R Lewis
  • H S Chen
Noone AM, Howlader N, Krapcho M, Miller D, Brest A, Yu M, Ruhl J, Tatalovich Z, Mariotto A, Lewis DR, Chen HS, Feuer EJ CK (eds). Prostate Cancer -Cancer Stat Facts [Internet]. National Cancer Institute. 2018 [cited 2018 Jul 4]. Available from: