antioxidants Review Cranberries and Cancer: An Update of Preclinical Studies Evaluating the Cancer Inhibitory Potential of Cranberry and Cranberry Derived Constituents 1 2 , 3 , 4 1 , Katherine M. Weh , Jennifer Clarke and Laura A. Kresty * Department of Medicine, Division of Hematology and Oncology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA; firstname.lastname@example.org Department of Food Science and Technology, University of Nebraska, 256 Food Innovation Complex, Lincoln, NE 68588-6205, USA; email@example.com Department of Statistics, University of Nebraska, Lincoln, NE 68583, USA Quantitative Life Sciences Initiative, University of Nebraska, Lincoln, NE 68583, USA * Correspondance: firstname.lastname@example.org; Tel.: +1-414-955-2673 Academic Editor: Dorothy Klimis-Zacas Received: 30 June 2016; Accepted: 15 August 2016; Published: 18 August 2016 Abstract: Cranberries are rich in bioactive constituents reported to inﬂuence a variety of health beneﬁts, ranging from improved immune function and decreased infections to reduced cardiovascular disease and more recently cancer inhibition. A review of cranberry research targeting cancer revealed positive effects of cranberries or cranberry derived constituents against 17 different cancers utilizing a variety of in vitro techniques, whereas in vivo studies supported the inhibitory action of cranberries toward cancers of the esophagus, stomach, colon, bladder, prostate, glioblastoma and lymphoma. Mechanisms of cranberry-linked cancer inhibition include cellular death induction via apoptosis, necrosis and autophagy; reduction of cellular proliferation; alterations in reactive oxygen species; and modiﬁcation of cytokine and signal transduction pathways. Given the emerging positive preclinical effects of cranberries, future clinical directions targeting cancer or premalignancy in high risk cohorts should be considered. Keywords: cranberry; cancer; proanthocyanidin; quercetin; ursolic acid 1. Introduction Incorporation of fruit and vegetables, including cranberries, into a healthy-balanced diet is suggested for prevention of human disease. The positive health beneﬁts of cranberries and cranberry derived constituents include improvements of cardiovascular function as measured by decreases in lipid peroxidation, oxidative stress, total and low-density lipoprotein (LDL} cholesterol and high-density lipoprotein (HDL) cholesterol level increases [1,2]. Cranberry derived products can also increase immune function by increasing -T cells, NK cells and B-cells , as well as exhibit antimicrobial and anti-adhesion activities against Gram-positive bacteria , Gram-negative bacteria [5–11] and yeast [12,13]. Utilization of cranberry and cranberry derived constituents in the prevention of cancer is an underexplored area, but one with mounting preclinical in vitro and in vivo research as will be reviewed herein. To date, there have been no clinical trials conducted which utilize cranberries to prevent or delay cancer progression. The beneﬁcial effects of cranberries are attributable to the berries’ rich phytonutrient composition which has been extensively and expertly reviewed by Pappas et al. . Compositional analysis of the cranberry has resulted in identiﬁcation and characterization of over 150 different bioactive constituents and human metabolomic studies have revealed differential pharmacokinetic proﬁles for these molecules [14–17]. Included in the family of polyphenols are three ﬂavonoid classes: Antioxidants 2016, 5, 27; doi:10.3390/antiox5030027 www.mdpi.com/journal/antioxidants Antioxidants 2016, 5, 27 2 of 20 anthocyanins, ﬂavonols and proanthocyanidins. Speciﬁcally, ﬂavonoids and phenolic acids are Antioxidants 2016, 5, 27 2 of 19 detected in the urine and plasma of healthy older adults following a single dose of 54% cranberry flavonols and proanthocyanidins. Specifically, flavonoids and phenolic acids are detected in the juice . Cranberries and cranberry derived constituents are capable of exerting antioxidant and urine and plasma of healthy older adults following a single dose of 54% cranberry juice . anti-inﬂammatory functions as supported by several clinical trials investigating cardiovascular health Cranberries and cranberry derived constituents are capable of exerting antioxidant and improvements measured via increases in ﬂow mediated dilation, total antioxidant performance of anti-inflammatory functions as supported by several clinical trials investigating cardiovascular plasma, blood glutathione peroxidase levels and superoxide dismutase activity following consumption health improvements measured via increases in flow mediated dilation, total antioxidant performance of a cranberry juice cocktail [15,18–21]. of plasma, blood glutathione peroxidase levels and superoxide dismutase activity following The cancer inhibitory potential of cranberries and cranberry derived products is being elucidated consumption of a cranberry juice cocktail [15,18–21]. based on The cance multipler inhibitory po in vitro investigations tential of cranberries an and a small d cranberry de number of rive ind produc vivo studies. ts is being elucidated This review will based on multiple in vitro investigations and a small number of in vivo studies. This review will encompass a total of 34 preclinical studies utilizing 45 cancer cell lines isolated from 16 target encompass a total of 34 preclinical studies utilizing 45 cancer cell lines isolated from 16 target organs organs and studies targeting seven cancers utilizing in vivo carcinogenesis and xenograft models and studies targeting seven cancers utilizing in vivo carcinogenesis and xenograft models to to investigate mechanisms by which cranberries and cranberry derived constituents modulate or investigate mechanisms by which cranberries and cranberry derived constituents modulate or inhibit cancer-related processes. Mechanisms of cranberry-linked cancer inhibition are summarized inhibit cancer-related processes. Mechanisms of cranberry-linked cancer inhibition are summarized in Figure 1. Preclinical studies support that cranberries modulate cell viability, cell proliferation, cell in Figure 1. Preclinical studies support that cranberries modulate cell viability, cell proliferation, cell death, adhesion, inﬂammation, oxidative stress and signal transduction pathways. Many of the in vitro death, adhesion, inflammation, oxidative stress and signal transduction pathways. Many of the in studies initially focus on the effectiveness of cranberry derived constituents in cell density and viability vitro studies initially focus on the effectiveness of cranberry derived constituents in cell density and assays, as logical starting points for determining whether further mechanistic analysis is warranted. viability assays, as logical starting points for determining whether further mechanistic analysis is Collectively, these in vitro studies provide the fundamental basis for additional in vivo studies and warranted. Collectively, these in vitro studies provide the fundamental basis for additional in vivo studies and may inform the design and implementation of cancer-based clinical trials evaluating may inform the design and implementation of cancer-based clinical trials evaluating cranberries as cranberries as cancer preventive agents. cancer preventive agents. Figure 1. Cranberry and cranberry derived constituents target numerous mechanisms of cancer Figure 1. Cranberry and cranberry derived constituents target numerous mechanisms of cancer inhibition based on 34 preclinical studies. inhibition based on 34 preclinical studies. 2. Materials and Methods 2. Materials and Methods A thorough bibliographic search was conducted in Pubmed through 4 June 2016 to identify all A thorough bibliographic search was conducted in Pubmed through 4 June 2016 to identify cancer focused research utilizing cranberries or cranberry derivatives. Keyword searches were all cancer focused research utilizing cranberries or cranberry derivatives. Keyword searches were performed by searching cranberry and each individual cancer target: breast, cervical, colon, performed by searching cranberry and each individual cancer target: breast, cervical, colon, esophageal, esophageal, glioblastoma, leukemia, liver cancer, lung , lymphoma, melanoma, neuroblastoma, oral glioblastoma, leukemia, liver cancer, lung, lymphoma, melanoma, neuroblastoma, oral cavity, ovarian, cavity , ovarian , prostate , renal/kidney, stomach and bladder. A secondary search was conducted prostate, renal/kidney, stomach and bladder. A secondary search was conducted using the same using the same keywords in Scopus, an abstract and citation database for peer-reviewed literature, keywords in Scopus, an abstract and citation database for peer-reviewed literature, which yielded which yielded additional manuscripts not available in Pubmed. Finally, a bibliographic search was completed in the Health Research Library provided by the Cranberry Institute using the following additional manuscripts not available in Pubmed. Finally, a bibliographic search was completed in the keywords: cancer, reactive oxygen species, anti-oxidant and oxidative stress. Health Research Library provided by the Cranberry Institute using the following keywords: cancer, reactive oxygen species, anti-oxidant and oxidative stress. Antioxidants 2016, 5, 27 3 of 20 3. In Vitro Inhibition of Cancer Processes by Cranberries Utilization of cancer cell lines to test cranberries, cranberry derived constituents and extracts has been the initial basis for deﬁning cancer inhibitory capacity of these natural components in vitro. The majority of studies have been performed following treatment of immortalized cancer cell lines with cranberry extracts or juices, while one study has determined the beneﬁt of pretreating the cells ﬁrst to measure protective capacity against oxidative stress . As summarized in Table 1, there are 31 in vitro based published reports describing cranberry linked cancer inhibition in 45 cancer cell lines derived from 16 targets. Eight mechanisms will be discussed with respect to cranberry derived extracts and constituents including cell density and viability, cell proliferation, cell cycle kinetics, cell death, signaling pathways, adhesion and migration, oxidative status and inﬂammation. 3.1. Cranberry Derived Extracts and Constituents Affect Cellular Growth and Viability A signiﬁcant amount of research shows cranberry derived constituents decrease cancer cell density, viability and proliferation. Cell density experiments are primarily based on treatment of cell lines with cranberry derived extracts followed by crystal violet staining to visualize cells remaining after treatment. While crystal violet staining indicates a qualitative difference in cellular conﬂuency based on treatment, it does not rely on active metabolic processes. Viability stains including 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and 2-(4-iodophenyl)-3- (4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt (WST-1) rely on cleavage of tetrazolium salts by the succinate-tetrazolium reductase system in metabolically active cells with an intact mitochondrial respiratory chain, whereas Calcein-acetoxymethyl (Calcein-AM) is cleaved by intracellular esterases to a ﬂuorescent molecule, which results in more reliable data when cell death involves altered mitochondrial machinery. Bromodeoxyuridine (BrdU) incorporation assays as a measurement of cell proliferation inform how cranberry derived constituents modulate S-phase cell cycle kinetics. Table 1. Summary of preclinical in vitro evaluations of cranberries or cranberry derived constituents as cancer inhibitors. Cranberry Target Cell Line(s) In Vitro Results [Reference(s)] Constituent Breast MCF-7 CE " apoptosis ; " G cell cycle arrest  # cell viability [23,24] CJE # cell viability  C-PAC # cell density  FG # cell viability  Fr6 # cell viability  Q # cell viability  UA # cell density [29,30]; # cell viability  MDA-MB-435* CJE # cell viability  Fr6 " apoptosis ; " G -M cell cycle arrest  # cell viability  UA # cell density  ME180 C-PAC # cell density  Cervix UA # cell density  Antioxidants 2016, 5, 27 4 of 20 Table 1. Cont. Cranberry Target Cell Line(s) In Vitro Results [Reference(s)] Constituent Colon Caco-2 CJE # cell viability  TP # lipid peroxidation  # pro-inﬂammatory markers TNF and IL-6  HT-29 ANTHO # cell viability  CE # cell viability [24,33] # pro-inﬂammatory marker COX-2  C-PAC " apoptosis ; # cell density  # cell viability  CJE # cell viability  Fr6 # cell viability  TP # cell viability  UA " apoptosis ; # cell density [29,30] # cell viability  HCT116 CE # cell viability  C-PAC " apoptosis ; # cell viability  UA " apoptosis ; # cell density  # cell viability  LS-513 ANTHO # cell viability  CJE # cell viability  TP # cell viability  SW460 TP # cell viability  SW620 TP # cell viability  C-PAC # cell proliferation  Esophagus CP-C C-PAC # total reactive oxygen species  JHEsoAD1 C-PAC " autophagy in acid-sensitive cells, pro-death [39,40] " necrosis in acid-resistant cells  " G -M cell cycle arrest  " total reactive oxygen species  " hydrogen peroxide levels  # cell viability [40,41] # PI3K/AKT/mTOR signaling  OE33 C-PAC " autophagy in acid-sensitive cells  " low levels of apoptosis " G -M cell cycle arrest  # cell proliferation  " total reactive oxygen species  # PI3K/AKT/mTOR signaling  OE19 C-PAC " necrosis in acid-resistant cells  " G -M cell cycle arrest with signiﬁcant S-phase delay  " total reactive oxygen species  " hydrogen peroxide levels  # PI3K/AKT/mTOR signaling  # cell viability [40,41] SF295 UA # cell density  Glioblastoma U87 C-PAC " apoptosis ; " G cell cycle arrest  # cell viability  Fr6 " apoptosis ; " G cell cycle arrest  # cell viability  K562 C-PAC # cell density  Leukemia RPMI8226 UA # cell density  HepG2 CE " reduced glutathione levels  Liver # glutathione peroxidase activity  # lipid peroxidation  # reactive oxygen species  CJE " reduced glutathione levels  # glutathione peroxidase activity  # lipid peroxidation  # reactive oxygen species  FG # cell viability  Q # cell viability  UA # cell viability  Antioxidants 2016, 5, 27 5 of 20 Table 1. Cont. Cranberry Target Cell Line(s) In Vitro Results [Reference(s)] Constituent Lung DMS114 Fr6 # cell viability  NCI-H322M UA # cell density  NCI-H460 C-PAC " apoptosis [37,42]; " G cell cycle arrest  # cell density ; # cell viability  # cell proliferation  UA # cell density [29,30] Lymphoma Rev-2-T-6 NDM # cell viability  # extracellular matrix invasion  M14 C-PAC # cell density  Melanoma UA # cell density  SK-MEL5 Fr6 # cell viability  Neuroblastoma IMR-32 C-PAC # cell viability  SH-Sy5Y C-PAC # cell viability  SK-N-SH C-PAC # cell viability  SMS-KCNR C-PAC " apoptosis ; " G -M cell cycle arrest  " reactive oxygen species  # PI3K/AKT/mTOR signaling  # cell viability [44,45] Oral Cavity CAL27 CE " apoptosis ; # cell adhesion  # cell density ; # cell viability  TP # cell viability  HSC2 CJE " reduced glutathione levels  # cell viability  KB CE # cell viability  TP # cell viability  SCC25 CE " apoptosis ; # cell adhesion  # cell density  Ovary OVCAR-8 C-PAC " G -M cell cycle arrest ; # cell viability  SKOV-3 C-PAC " apoptosis [48,49]; " G -M cell cycle arrest [48,49] " reactive oxygen species  # AKT signaling  # cell proliferation [45,49] # cell viability [45,48,49] Prostate 22Rv1 CE # cell viability  TP # cell viability  DU-145 CE " G cell cycle arrest  # cell viability [50,51] C-PAC " apoptosis  " MAPK signaling  # cell viability [26,36,51,52] # matrix metalloprotease activity  # PI3K/AKT signaling  Fr6 # cell viability [28,36] LNCaP CE # cell viability  PC3 CJE " G cell cycle arrest  # cell viability  C-PAC # cell density  UA # cell density  RWPE-1 CE # cell viability  C-PAC # cell viability  TP # cell viability  RWPE-2 CE # cell viability  C-PAC # cell viability  TP # cell viability  Antioxidants 2016, 5, 27 6 of 20 Table 1. Cont. Cranberry Target Cell Line(s) In Vitro Results [Reference(s)] Constituent Renal RXF393 UA # cell density  SN12C UA # cell density  TK-10 UA # cell density  AGS CJE # cell viability  Stomach SGC-7901 CE " apoptosis  # cell proliferation  # cell viability  Cranberry derived constituents are abbreviated as follows: anthocyanins (ANTHO), organic-soluble cranberry extract (CE), cranberry juice extract (CJE), cranberry proanthocyanidin-rich fraction (C-PAC), ﬂavonoid-rich fraction 6 (Fr6), ﬂavonoid glycosides (FG), non-dialyzable material from cranberry juice concentrate (NDM), total polyphenolic fraction (TP), quercetin (Q) or ursolic acid fraction (UA). Additional abbreviations: Phosphoinositide 3-kinase (PI3K), Protein Kinase B (AKT), mechanistic Target of Rapamycin (mTOR), mitogen-activated protein kinase (MAPK). Note: MDA-MB-435* was misidentiﬁed as a breast cancer cell line, but is now conﬁrmed to be of melanoma origin. Three cranberry derivatives inhibit the growth of 43 human cancer cell lines. For the purpose of this review, growth inhibitory (GI ) concentrations are presented for cancer cell lines where cranberry treatment results in 50% growth inhibition. Speciﬁcally, cranberry derived ursolic acid, proanthocyanidins and an organic-soluble cranberry extract inhibit the growth of breast, colon, cervical, glioblastoma, leukemia, lung, melanoma, oral cavity, prostate and renal cancer cell lines [26,29,30,46]. The GI concentration for ursolic acid is 1.2–11.2 M in renal cancer cell lines RXF393, SN12C and TK-10, with similar results observed in breast (MCF-7; 1.4–1.9 M), colon (HCT116; 1.5–3.5 M) and lung (NCI-H322M; 1.2–9.8 M) cancer cell lines when cell density is measured following a 48 h treatment [29,30]. The cell density of lung (NCI-H460; 20.0 g/mL) and cervical (ME180; 30.0 g/mL) cancer cell lines are similarly susceptible to cranberry proanthocyanidin treatment, while breast (MCF-7), melanoma (M-14), leukemia (K562) and prostate (PC3) cancer cell lines have GI values greater than 70.0 g/mL . An organic soluble cranberry extract is effective at reducing cell density of two oral cancer cells lines, CAL27 and SCC25, at fairly similar GI concentrations, 40.0 g/mL and 70.0 g/mL, respectively . While cell density experiments support a reduction in conﬂuency following treatment with cranberry derivatives, these assays do not take metabolic activity, functional enzyme processes or mechanisms associated with cell death into consideration. Extending beyond simple density studies, multiple cranberry derived extracts and constituents signiﬁcantly inhibit the viability of cancer cell lines. In breast cancer cell lines, an organic-soluble cranberry extract, cranberry juice extract, a ﬂavonoid rich fraction (with and without glycosides), quercetin and ursolic acid are all effective at decreasing the viability of MCF-7 and MDA-MB-435 cells [23–25,27,28]. The GI concentration of a combination ﬂavonoid and glycoside fraction (FG; 23.9 M) is the most efﬁcacious against MCF-7 cells . Several cranberry extracts inhibit the viability of colon cancer cell lines including an organic-soluble cranberry extract, cranberry juice extract, cranberry proanthocyanidins, a ﬂavonoid rich fraction, a total polyphenolic fraction and ursolic acid [24,25,32,33,35,36]. Cranberry proanthocyanidins and ursolic acid are most effective at inhibiting the viability of HCT116 colon cancer cells, with GI concentrations of 25 g/mL for both constituents . LS-513 colon cancer cells are particularly susceptible to viability reductions following exposure to a total polyphenolic fraction (3.8–92.9 g/mL) and anthocyanins (4.3–75.5 g/mL) when compared to a cranberry juice extract (38.11–113.0 g/mL) . Cranberry proanthocyanidins also decrease the viability of neuroblastoma, esophageal adenocarcinoma and ovarian cancer cells [40,41,44,45,48,49]. All four neuroblastoma cancer cell lines (IMR-32, SH-Sy5Y, SK-N-SH and SMS-KCNR) show signiﬁcant reductions in viability when treated with 12.5–25.0 g/mL of cranberry proanthocyanidins [44,45]. In comparison, a signiﬁcant reduction in viability of esophageal adenocarcinoma and ovarian cancer cells is observed with 25.0–50.0 g/mL and 50.0–200.0 g/mL Antioxidants 2016, 5, 27 7 of 20 cranberry proanthocyanidins, respectively [40,41,45,48,49]. Reductions in viability of glioblastoma and melanoma cancer cell lines occur following treatment with a ﬂavonoid rich extract, with the GI for U87 glioblastoma cells about half of the GI for SK-MEL5 melanoma cells after a 96h treatment . A signiﬁcant decrease in viability is observed for HepG2 liver cancer cells when treated for 4 days with a cranberry ﬂavonoid glycoside extract (GI = 49.2 M), quercetin (GI = 40.9 M) or ursolic acid 50 50 (GI = 87.4 M); where quercetin was the most effective of the three constituents . Lastly, NCI-H460 cells are more susceptible to a lower dose of cranberry proanthocyanidins (50.0–100.0 g/mL) than DMS114 cells treated with a ﬂavonoid rich extract; however, both extracts are capable of signiﬁcantly reducing cell viability of lung cancer cell lines [28,37]. A single study utilized non-dialyzable material isolated from cranberry juice reporting signiﬁcant reductions in the viability of Rev-T-2-6 lymphoma cells following a 48h treatment . The non-dialyzable material contains high molecular weight polyphenolic compounds, likely containing both proanthocyanidins and smaller quantities of anthocyanins ; however, structural characterization was not conducted due to the inability to hydrolyze the high molecular weight components into smaller oligomeric components for MALDI analysis . Cancer cell lines originating from the oral cavity are susceptible to reduced viability following treatment with cranberry extract (50.0–180.6 g/mL), cranberry juice extract (150.0 g/mL) and a total polyphenolic fraction (200.0 g/mL) with cranberry extract (50.0 g/mL) treatment of CAL27 cells having the lowest GI [24,33,47]. Ten studies have documented the effectiveness of a cranberry extract, cranberry juice extract, a ﬂavonoid rich extract and cranberry proanthocyanidins at signiﬁcantly reducing the viability of prostate cancer cells [24–26,28,33,36,45,50–52]. The most efﬁcacious constituent appears to be a cranberry proanthocyanidin extract, which inhibits the viability of RWPE-1 and RWPE-2 prostate cancer cell lines with a GI of approximately 6.5 g/mL . In contrast, prostate cancer cells are not particularly sensitive to inhibition by a ﬂavonoid rich extract as the GI concentration for DU-145 (234.0 g/mL) cancer cells is comparatively 1.6–3.0 fold higher compared to the GI for glioblastoma (77.0 g/mL), melanoma (147.0 g/mL) and breast (147.0–212.0 g/mL) cancer cell lines . Finally, two studies report cranberry and cranberry juice extract decrease the viability of stomach cancer cell lines AGS and SGC-7901 [25,53]. The majority of in vitro studies have characterized the ability of cranberry derived extracts and constituents to inhibit cancer cell line density and viability. Cranberry derived proanthocyanidins and ursolic acid tend to have lower GI values compared to the organic-soluble cranberry extracts and total phenolic fractions. It is difﬁcult to make comparisons to the results observed for the cranberry juice extracts because concentrations are reported as L/mL and may vary widely in concentrations of inhibitory constituents based on the starting product [25,32,47]. Furthermore, direct comparisons for speciﬁc constituents is challenging due to a lack of protocol standardization for the generation and isolation of any cranberry derived extracts or constituents. Taken together, these data show that cranberry derivatives are capable of inhibiting the viability of 31 cancer cell lines. 3.2. Modulation of Cell Proliferation and Cell Cycle Processes by Cranberry Constituents The ability of cranberry derived extracts and constituents to modulate cell proliferation and cell cycle kinetics is highlighted by studies conducted in nine different target organs. Cell proliferation, as measured by BrdU incorporation, is decreased in colon, lung, ovarian and OE33 esophageal cancer cell lines following treatment with 25.0–125.0 g/mL cranberry proanthocyanidins [37,39,45,49]. Additional esophageal adenocarcinoma cells treated with cranberry proanthocyanidins responded with an S-phase delay , potentially linked to induction of cell death via necrosis. A decrease in cell proliferation of stomach cancer cells is also noted following treatment with a cranberry extract but at a much higher concentration of 10.0 mg/mL . Ten studies present data for modulation of cell cycle progression by cranberry derivatives. In breast cancer cells, an organic-soluble cranberry extract and a ﬂavonoid rich extract induce G and G -M cell cycle arrest, respectively [23,28]. In esophageal adenocarcinoma cells, cranberry 2 Antioxidants 2016, 5, 27 8 of 20 proanthocyanidins (50.0–100.0 g/mL) induce G -M cell cycle arrest in acid-sensitive JHEsoAd1 and OE33 cells as well as in acid-resistant OE19 cells . However, cranberry proanthocyanidins induce a signiﬁcant S-phase delay in acid-resistant OE19 cells. In lung cancer cells, cranberry proanthocyanidins (50.0 g/mL) induce a G cell cycle arrest . Cranberry proanthocyanidins induce a G -M cell cycle 1 2 arrest in neuroblastoma (20.0 g/mL) and ovarian (75.0–100.0 g/mL) cancer cells [44,48,49]. Organic soluble cranberry extracts (25.0 g/mL) and cranberry juice extracts (25.0 L/mL) are both effective at inducing G cell cycle arrest in prostate cancer cells [25,50]. Finally, cranberry proanthocyanidins are more effective than a ﬂavonoid rich extract at inducing G cell cycle arrest in glioblastoma cells in a time and dose-dependent manner . 3.3. Cranberry Derived Extracts and Constituents Induce Cell Death Pathways Induction of cell death pathways by cranberry constituents has been investigated in nine target organs. An organic soluble cranberry extract induces apoptosis in stomach (5.0 mg/mL) and breast (15.0 mg/mL) cancer cell lines at high concentrations, whereas cancer cell death was induced at much lower concentrations (range of 50.0–70.0 g/mL) in SCC25 and CAL27 oral cancer cell lines [23,46,53]. Treatment of esophageal adenocarcinoma, lung, colon, glioblastoma, neuroblastoma and ovarian cancer cells with cranberry proanthocyanidins results in apoptosis induction [35–37,39,42,44,48,49]. Ursolic acid (25.0 g/mL) induces apoptosis in colon cancer cells and a ﬂavonoid rich extract (100.0–400.0 g/mL) induces late apoptosis in glioblastoma cells [28,35]. Finally, a ﬂavonoid rich extract (200.0–400.0 g/mL) from the cranberry is also responsible for induction of apoptosis in MDA-MB-435 cancer cells . In esophageal adenocarcinoma cells, the primary form of cell death appears linked to an acid sensitive or acid resistant phenotype. Speciﬁcally, treatment with an equimolar concentration of ﬁve bile salts (taurocholic, glycocholic, glycodeoxycholic, glycochenodeoxycholic and deoxycholic acids) in acidiﬁed medium (pH 4.0) induces rapid apoptosis of esophageal adenocarcinoma cells except in the case of constitutively resistant OE19 cells were exposure to an acidiﬁed bile salt mixture has little impact on cell viability. In acid sensitive JHEsoAD1 and OE33 cell lines, cranberry proanthocyanidins induce autophagy through inactivation of Phosphoinositide 3-kinase /Protein Kinase B/mechanistic Target of Rapamycin (PI3K/AKT/mTOR) signaling pathways, but with low levels of apoptosis [39,40]. Conversely, intrinsically acid resistant OE19 cells die mainly through necrosis following treatment with cranberry proanthocyanidins. Acid sensitive JHEsoAd1 cells can be pushed to acid resistance following repeated exposure to an acidiﬁed bile cocktail resulting in a switch from autophagic to necrotic cell death . The concentration of cranberry proanthocyanidins necessary to inhibit the viability of acid-resistant cells through necrosis is similar to the concentration inducing autophagy in acid-sensitive cells . It is important to note that autophagy induction in JHEsoAD1 cells is a pro-death mechanism and not a pro-survival response [40,41]. In contrast to esophageal adenocarcinoma cells, the primary form of cell death induced by cranberry proanthocyanidins in neuroblastoma cells is apoptosis . Interestingly, treatment of SMS-KCNR neuroblastoma (25.0 g/mL) cancer cells for 18 h with cranberry proanthocyanidins also resulted in inactivation of PI3K/AKT/mTOR signaling pathways and at concentrations lower than those necessary for similar effects in esophageal adenocarcinoma (50.0 g/mL) cancer cells [39,44]. The caspase apoptotic machinery in esophageal adenocarcinoma cells is expressed at low basal levels, which may explain why acid sensitive cells die primarily through autophagy . Furthermore, treatment of acid sensitive esophageal adenocarcinoma cell lines with cranberry proanthocyanidins results in cell death through Beclin-1 independent autophagy induction and is largely caspase-independent despite low levels of apoptosis [39,40]. Conversely, western blot data from untreated neuroblastoma cells show that the apoptotic machinery is present . Thus, cranberry proanthocyanidins modulate cell death via inactivation of the PI3K/AKT/mTOR signaling axis, but may be dependent on available cell death machinery. A decrease in signaling through the AKT pathway is also observed in SKOV-3 ovarian cancer cells treated with cranberry proanthocyanidins . Antioxidants 2016, 5, 27 9 of 20 Furthermore, cranberry proanthocyanidins (25.0 g/mL) increase mitogen-activated protein kinase (MAPK) signaling and decrease PI3K/AKT signaling in prostate cancer cells, suggesting a common cell death mechanism with esophageal adenocarcinoma, ovarian and neuroblastoma cancer cells . 3.4. Modulation of Oxidative Status by Cranberries Consistent with the antioxidant properties of cranberry and cranberry derived extracts in human trials for cardiovascular disease, markers of reactive oxygen species (ROS) decrease in a number of cranberry treated cancer cell lines [15,18,21]. Speciﬁcally, malondialdehyde lipid peroxidation levels decrease in colon cancer lines following treatment with a total polyphenolic fraction (250.0 g/mL) for 24 h . An organic soluble cranberry extract and cranberry juice extract decrease malondialdehyde lipid peroxidation levels in HepG2 liver cancer cells . Furthermore, an organic soluble cranberry extract and cranberry juice extract increase reduced glutathione levels and decrease glutathione peroxidase activity in HepG2 cells, respectively . Total ROS levels also decrease in HepG2 liver cancer cells following treatment with an organic soluble cranberry extract (0.5 g/mL) and cranberry juice extract (25.0 g/mL) for 20 h . Conversely, increases in ROS are reported in select cancer cell lines treated with cranberry derivatives. Specifically, cranberry proanthocyanidins increase ROS levels in esophageal adenocarcinoma (100.0 g/mL), neuroblastoma (20.0 g/mL) and ovarian (75.0 g/mL) cancer cell lines [38,44,49]. The increase in JHEsoAD1 esophageal adenocarcinoma cells was partially due to increases in hydrogen peroxide levels . While these data may seem counterintuitive, several drugs including cisplatin, cyclophosphamide and fenretinide used to treat cancer rely on the production of ROS as a mechanism to inhibit cancer cell viability [55,56]. Interestingly, ROS levels decrease in premalignant Barrett’s esophageal CP-C cells following treatment with cranberry proanthocyanidins, also resulting in cell death induction [38,57,58]. Given the differences observed between ROS production in premalignant Barrett’s and esophageal adenocarcinoma cells following treatment with cranberry proanthocyanidins, it is possible that basal oxidative stress levels or stage of carcinogenesis may inform functional cell death machinery and cell fate. The mechanism of cell death for premalignant esophageal cells treated with cranberry derived constituents remains to be investigated. However, immortalized “normal” Het1A esophageal cells are less susceptible to C-PAC induced cell death compared to esophageal adenocarcinoma and premalignant Barrett’s esophageal cell lines when treated with the same cranberry proanthocyanidin fraction at equivalent concentrations . 3.5. Additional Biological Processes Modulated by Cranberry Derived Extracts and Constituents Modulation of pro-inﬂammatory markers, cellular adhesion, matrix metalloprotease activity and invasion of the extracellular matrix are the remaining biological processes that have been examined in cancer cell lines treated with cranberry based derivatives. Specifically, TNF and IL-6 levels decrease following treatment with a total cranberry polyphenolic fraction (250.0 g/mL) in colon cancer cells [31,34]. A soluble cranberry extract (50.0 g/mL) reduces the expression of cyclooxygenase-2 (COX-2), an enzyme responsible for conversion of arachidonic acid into prostaglandins thus mitigating downstream inﬂammatory responses . The ability of oral cancer cells to settle, adhere and establish colonies is inhibited by an organic soluble cranberry extract in a dose dependent manner . In prostate cancer cells, cranberry proanthocyanidins (250.0 g/mL) decrease matrix metalloprotease activity preventing cleavage of extracellular matrix proteins and migration of cancer cells . Finally, a non-dialyzable material extract isolated from cranberry juice (50.0 g/mL) is capable of decreasing invasion of Rev-2-T-6 lymphoma cells . While these ﬁnal studies describe distinctly different processes, they provide additional mechanistic information for how cranberry derived extracts and constituents modulate cancer cells in vitro and provide a foundation to support additional in vivo investigations. Antioxidants 2016, 5, 27 10 of 20 3.6. In Vitro Summary Collectively, data from the in vitro studies support that cranberries successfully inhibit three hallmarks of cancer: resisting cell death, sustaining proliferative signaling and activating invasion and metastasis . These studies provide the preclinical basis for cancer inhibitory investigations of cranberry derived constituents utilizing in vivo models and may inform future clinical trials in high risk human cohorts. Protocol standardization for extraction and isolation of constituents from cranberries will be vital for reproducibility of data and for development of standardized products for use in human clinical trials. Cranberry proanthocyanidins appear to be among the most potent cranberry derived constituents based upon the completed in vitro research evaluating a large panel of cancer cell lines and multiple inhibitory mechanisms. Low concentrations of cranberry derived ursolic acid also favorably impacts cancer cell viability and induces apoptosis, but additional signaling networks have yet to be assessed. However, it is important to recognize that both the starting cranberry product, processing and extraction methods differed greatly across the summarized studies making direct comparisons difﬁcult. It is interesting to note that included in the in vitro studies is the evaluation of cranberry derived constituents in MDA-MB-435 (misidentiﬁed as breast) and M14 melanoma cancer cell lines. Controversy regarding the origin of these two cancer cell lines has been debated since 2003 when microarray studies suggested that the MDA-MB-435 cell line was not of breast origin . Through extensive genetic and expression analyses, it has been established that the MDA-MB-435 cell line is of melanoma origin and is very likely a clone of the M14 melanoma cancer cell line . This ﬁnding has broader implications for the scientiﬁc community, but herein expands the inhibitory effects of cranberries to include inhibition of melanoma cancer cell viability, modulation of cell cycle kinetics and provides mechanistic insight into mode of cell death induction [25,28,29]. Additional research is necessary for improved understanding of the molecular mechanisms by which cranberry derivatives inhibit cancer cells in vitro including to what extent reactive oxygen species play a role in cell death induction and whether downregulation and inactivation of the PI3K/AKT/mTOR pathway is a common mechanism. The latter is of particular importance for the potential development of neoadjuvant applications combining therapeutic drugs with natural inhibitors . Natural products including quercetin, curcumin, resveratrol and lycopene reportedly impact multiple cancer-associated processes, with clinical trial results supporting the efﬁcacy of lycopene at reducing colon cancer tumor size . In addition, Singh et al. found that cranberry proanthocyanidins acted synergistically with paraplatin to inhibit SKOV-3 ovarian cancer cell viability and proliferation . Importantly, pretreatment of SKOV-3 ovarian cancer cells with cranberry proanthocyanidins signiﬁcantly reduced the IC following paraplatin treatment. Utilization of natural products in conjunction with chemotherapy drugs may also be useful in treating patients who have developed resistance to chemotherapeutic drugs . Finally, in esophageal adenocarcinoma JHEsoAD1 cells, pharmacologic inhibition of mTOR using cranberry proanthocyanidins or rapamycin induces autophagy resulting in cell death and survival, respectively . Therefore, understanding the mechanisms of cancer inhibition by cranberry constituents is critical for evaluation of cranberries in human clinical trials with a cancer prevention focus or possibility for use in combination with chemotherapeutic agents. 4. In Vivo Inhibition of Cancer Using Cranberry Products There are only nine published studies assessing the preclinical efﬁcacy of cranberry products in animal models. These studies are summarized in Table 2 and will be reviewed by target organ in the following section. Antioxidants 2016, 5, 27 11 of 20 Table 2. Summary of preclinical in vivo evaluations of cranberry products as cancer inhibitors. Target Organ In Vivo Models/Cranberry Product and Mode of Delivery/Results [Reference] Bladder Nitrosamine-induced tumors in female F344 rats for eight weeks; following a one-week break, treatment with 0.5 mL/rat or 1.0 mL/rat with cranberry juice  concentrate by gavage daily for six months; 31% reduction in bladder tumor weight and 38% reduction in cancerous lesion formation. Colon AOM-induced ACF in male F344 rats three weeks after initiation of cranberry juice treament; ad libitum access to 20% cranberry juice in water for 15 weeks;  77% reduction in AOM-induced ACF with reductions in the proximal and distal colon versus untreated controls; signiﬁcantly increased levels of liver glutathione-S-transferase versus controls. HT29 (5.0 10 cells) xenografts in female NCR NU/NU mice; treatment with  cranberry proanthocyanidins (100.0 mg/kg body weight) intraperitoneally three times weekly for 24 days; signiﬁcant inhibition of explant growth versus controls. DSS induced experimental colitis in male Balb/c mice at weeks three and six; Treatment with cranberry extract powder (0.1% or 1.0%) or 1.5% freeze dried whole cranberry powder in diet ad libitum from start until six weeks; cranberry extract  powder (1.0%) and 1.5% dried whole cranberry powder treatment normalized stool consistency, decreased blood in fecal samples versus controls and reduced late onset colitis; all treatments decreased serum TNF levels. Esophagus OE19 (1.25 10 cells) xenografts in male athymic NU/NU mice; treatment with cranberry proanthocyanidins (250.0 g/mouse) by oral gavage six days/week for  19 days; 67% decrease in mean tumor volume versus controls and treatment modulated multiple cancer signaling pathways including inactivation of the PI3K/AKT/mTOR pathway. Glioblastoma U87 (1.0 10 cells) xenografts in female NCR NU/NU mice; treatment with cranberry proanthocyanidins (100.0 mg/kg body weight) or a ﬂavonoid rich  cranberry fraction (250.0 mg/kg body weight) intraperitoneally three times a week; signiﬁcant inhibition of explant growth by both fractions versus controls Lymphoma Rev-2-T-6 (5.0 10 cells) xenografts in female Balb/C mice; treatment with  non-dialyzable material from cranberry juice concentrate (160.0 mg/kg body weight) intraperitoneally three times a week; signiﬁcant inhibition of explant growth. Prostate DU-145 (4.0 10 cells) xenografts in female NCR NU/NU mice; treatment with cranberry proanthocyanidins (100.0 mg/kg body weight) intraperitoneally three  times a week; signiﬁcant inhibition of explant growth by cranberry proanthocyanidin fraction. Stomach SGC-7901 (5.0 x 10 cells) xenografts in Balb/c NU/NU mice; SGC-7901 cells were  pre-treated with cranberry extract prior to xenograft implantation; increased tumor latency and reduced tumor size in a dose-dependent manner. Abbreviations: azoxymethane (AOM), athymic nude mice (NCR NU/NU), dextran sodium sulfate (DSS). Antioxidants 2016, 5, 27 12 of 20 4.1. Cranberry Juice Concentrate and Bladder Cancer Despite extensive research focused on cranberries and improved urinary tract health, including prevention of urinary tract infections, there is little research on cancer inhibition in vivo. Prasain et al. performed the only in vivo investigation to assess the efﬁcacy of cranberries as inhibitors of bladder cancer . Bladder cancer was induced in female Fischer-F344 rats following administration of N-butyl-N-(4-hydroxybutyl)-nitrosamine twice a week for eight weeks. Starting one week after the ﬁnal carcinogen treatment, rats were gavaged daily for six months with cranberry juice concentrate (0.5 mL/rat or 1.0 mL/rat) or water. The cranberry juice concentrate utilized in this study was made available from Ocean Spray Cranberries, Inc. (City, US State, USA) and described to contain 9.57 0.5 mg vanillic acid equivalent/mL of total phenolics. At the end of the six month study, bladder lesions were weighed showing that administration of high dose cranberry juice concentrate (1.0 mL/rat/day) reduced bladder tumor weight by 31%. Both doses of cranberry juice concentrate resulted in a decrease in urinary bladder tumor weight, but only the higher volume of cranberry juice concentrate (1.0 mL/rat/day) resulted in a 38% reduction in cancerous lesion formation in the bladder . These data are promising supporting that an orally administered cranberry juice concentrate is non-toxic when delivered over a period of six months and that a behaviorally achievable concentration signiﬁcantly inhibits progression events resulting in reduced bladder cancer [15,68]. 4.2. Colon Cancer and Cranberries Two studies have investigated the ability of cranberry products to reduce or inhibit colon carcinogenesis. In the ﬁrst study, male F344 rats were administered either 20% cranberry juice or water ad libitum for 15 weeks with two weeks of azoxymethane (AOM) administration in weeks 4 and 5 to induce aberrant crypt foci (ACF) and colon cancer . There was a 77% reduction in the number of AOM-induced ACF in rats administered cranberry juice, with reductions in both the proximal and distal colon. Finally, animals had signiﬁcantly higher levels of liver glutathione-S-transferase activity compared to untreated controls supporting that cranberry juice may activate cell protection mechanisms against oxidative stress in the context of colon cancer. In a study performed by Ferguson et al., the colon carcinoma cell line HT-29 was utilized to establish xenografts in female NCR NU/NU mice . Speciﬁcally, HT-29 (5.0 10 ) cells were subcutaneously injected into the right ﬂank of mice and tumors were monitored every other day. Cranberry proanthocyanidins (100.0 mg/kg) were administered intraperitoneally 2–3 times per week for a total of ten injections over 24 days. Mice treated with cranberry proanthocyanidins had signiﬁcantly lower body weights early in the study but weights returned to normal in the last ﬁve days of the study raising the question of initial toxicity at the administered concentration. Importantly, cranberry proanthocyanidins signiﬁcantly inhibited the growth of HT-29 tumor xenografts in mice. The ﬁnal colon related study utilized a dextran sodium sulfated (DSS)-induced mouse model of colitis . DSS-induced colitis is widely accepted as an animal model of irritable bowel syndrome, a condition linked to elevated risk for colorectal cancer development . In this study, male Balb/C mice were fed a diet containing either cranberry extract (0.1% or 1%) or 1.5% dried whole cranberry powder in the food ad libitum. On the third and sixth weeks of the study, the water was replaced with 1% w/v of DSS solution for one week. Animals fed either the cranberry extract or the dried whole cranberry powder had a signiﬁcantly lower disease activity index (more normal stool consistency and decreased blood in fecal samples) compared to controls for both DSS treatment periods. Furthermore, 1% cranberry extract and the 1.5% dried whole cranberry powder diets delayed the onset of colitis. In addition, inﬂammatory markers including TNF (signiﬁcant in all cranberry treatments) and IL-1 (1.5% dried whole cranberry powder only) were decreased in colonic tissues, suggesting that cranberry derived extracts and powders exert an anti-inﬂammatory role in vivo. These data parallel in vitro data for cell death induction, antioxidant effects and anti-inﬂammatory properties of cranberries and cranberry derived constituents. In the studies by Boateng et al. and Xiao et al. [66,67], the cranberry products were administered throughout the entire bioassay Antioxidants 2016, 5, 27 13 of 20 and although encouraging consideration in future studies should be given to discerning whether cranberry products possess both anti-initiation as well as anti-promotion/progression properties in vivo. As colon cancer and a western diet are reportedly linked, regular inclusion of cranberries may impart cancer preventative advantages . 4.3. Cranberry Proanthocyanidins and Esophageal Adenocarcinoma The cancer inhibitory potential of cranberry proanthocyanidins against esophageal adenocarcinoma was investigated by Kresty et al. using murine xenografts . Acid-resistant OE19 (1.25 10 ) cells were subcutaneously implanted in each ﬂank of twelve male NU/NU athymic mice and tumors were established (150 mm ) prior to initiation of cranberry proanthocyanidin treatment. Five days after cell injection, mice were randomized for treatment with cranberry proanthocyanidins (250.0 g/mouse) or vehicle by oral gavage six days a week. There was a signiﬁcant difference in tumor volume between vehicle and cranberry proanthocyanidin treated mice by day 12, with the study ending on day 19 due to large tumor size among vehicle treated controls. Mean tumor volume in cranberry proanthocyanidin treated mice was reduced by 67.6% and showed reduced inﬂammation compared to tumors isolated from control mice. Importantly, tumor lysates from cranberry proanthocyanidin treated mice showed inactivation of PI3K/AKT/mTOR signaling as was observed in vitro utilizing a panel of esophageal adenocarcinoma cell lines . Interestingly, acid-sensitive JHAD1 and OE33 cells were not able to form tumors in this xenograft model, suggesting that the OE19 cells are phenotypically more aggressive and that acid-resistance may support tumor development. 4.4. Glioblastoma and Cranberry Derived Constituents The efﬁcacy of cranberry proanthocyanidins and a ﬂavonoid rich cranberry extract for prevention of glioblastoma tumors was evaluated by Ferguson et al. in a murine xenograft model . U87 (1.0 10 ) glioblastoma multiforme cancer cells were injected subcutaneously into the right ﬂank of female NCR NU/NU mice and tumors were monitored every other day. Mice were administered cranberry proanthocyanidins (100.0 mg/kg body weight) or a ﬂavonoid rich extract (250.0 mg/kg body weight) intraperitoneally 2–3 times per week for a total of ten injections. Both cranberry fractions were able to slow tumor growth by up to 40%. These data suggest that cranberry derived extracts may be effective against glioblastoma muliforme but the mechanisms remain to be characterized. 4.5. Non-Dialyzable Material from Cranberry Juice and Lymphoma Inhibition of lymphoma xenograft growth by cranberry juice in a murine model was investigated by Hochman et al. . Rev-2-T-6 (5.0 10 ) lymphoma cancer cells were injected into female Balb/C mice and animals were subsequently treated with cranberry juice constituents (130.0 mg/kg body weight) intraperitoneally every other day for two weeks. The treatment consisted of non-dialyzable material from cranberry juice with a molecular weight range of 12–30 kDa. Mice treated with non-dialyzable material did not form tumors with 80% of control mice developing lymphomas. This study is positive for the prevention of lymphoma by cranberry juice but due to study design the results fail to discriminate between failed xenograft implementation and prevention of tumor growth. 4.6. Prostate Cancer and Cranberry Proanthocyanidins Utilizing a murine xenograft model with prostate cancer cells, Ferguson et al. showed that cranberry proanthocyanidins inhibit tumors in vivo . DU-145 (4.0 10 ) prostate cancer cells were subcutaneously implanted in the right ﬂank of female NCR NU/NU mice. On day 2, mice were administered cranberry proanthocyanidins (100.0 mg/kg body weight) intraperitoneally every 2 or 3 days for a total of 10 injections. Cranberry proanthocyanidins signiﬁcantly inhibited the growth of tumors compared to control mice and two of the mice had tumor regression by 108 days post implant. These data are encouraging for the inhibition of prostate tumor development by cranberry Antioxidants 2016, 5, 27 14 of 20 proanthocyanidins, but additional experiments are necessary for investigating the mechanism of tumor regression. 4.7. Whole Cranberry Extract and Stomach Cancer Efﬁcacy of a whole cranberry extract inhibiting stomach cancer tumor growth was evaluated in a murine xenograft model developed by Liu et al. . Balb/C NU/NU mice were subcutaneously injected with SGC-7901 (5.0 10 ) gastric adenocarcinoma cells in the right ﬂank region. Prior to implantation, SGC-7901 cells were pretreated with a whole cranberry extract (0–40.0 mg/mL) for 48 h. Tumors in control mice developed by the tenth day of the experiment with a delay of 3–7 days for cells pretreated with 5.0–20.0 mg/mL of cranberry extract. Xenograft tumors did not develop from SGC-7901 cells pretreated with 40.0 mg/mL cranberry extract but in vitro data presented in the same study supported that these cells were likely undergoing high levels of apoptosis with reduced viability. Therefore, additional studies will be necessary to determine how a whole cranberry extract inhibits the growth of stomach cancer in animal models, including those which model gastric carcinogenesis as a result of chronic Helicobacter pylori infection . 4.8. In Vivo Summary The in vivo studies described here provide preliminary evidence for the preclinical efﬁcacy of multiple cranberry derived extracts against seven cancer targets. Except for the studies in esophageal adenocarcinoma and colon cancer, the majority of completed in vivo studies reporting inhibition of tumor development or growth, fail to include further mechanistic assessments. Of the nine in vivo studies, three studies used carcinogens or chemicals to induce cancer in animal models. In the bladder, delivery of a cranberry juice concentrate by gavage following carcinogen treatment supports anti-promotion/progression effects of cranberries against chemically-induced bladder cancer. Two studies in the colon assessed the efﬁcacy of cranberry juice, cranberry extract powder and a dried whole cranberry powder in a full carcinogenesis schematic, where dietary administration of cranberries began prior to carcinogen initiation and continued throughout, after carcinogen or chemical treatment was completed. In regard to mode of delivery, four of the in vivo studies delivered the cranberry product by orally, either in water, diet or gavage with efﬁcacy suggesting that the compounds or their metabolites hold promise as orally bioavailable cancer inhibitors. Administration of cranberry products via intraperitoneal injection also showed cancer inhibitory efﬁcacy in four in vivo studies, but as a mode of delivery is less relevant for primary or secondary cancer prevention efforts in human cohorts. Overall, the in vivo results expand upon in vitro observations and importantly support that long-term administration of cranberry products is well tolerated and cancer inhibitory in various animal models. However, additional research focused on bioavailability, metabolic fate and additional cancer inhibitory mechanisms of cranberry products is warranted for informing clinical focused cancer prevention efforts. To date only a few human studies have characterized cranberry metabolites in plasma or urine and often these studies are limited to quantifying molecules that have previously been identified [15,16,72–75]. A recent study by McKay et al. reported that ﬂavonoids, phenolic acids and proanthocyanidins can be detected in the urine or plasma of individuals who consumed a 54% cranberry juice cocktail . Recent advances in standards used for identiﬁcation and quantiﬁcation of cranberry metabolites has resulted in the identiﬁcation of 60 metabolites from the urine and plasma of healthy men after consumption of a cranberry juice cocktail that contained 787 mg of polyphenols . The ability to detect and quantitate proanthocyanidins in the urine and plasma is not consistent from study to study, but this should improve with the recent development of a new cranberry proanthocyanidin standard that more closely reﬂects the structural heterogeneity of proanthocyanidins present in fresh cranberries . Cranberry proanthocyanidins are large, complex molecules with recent data supporting that the intestinal microbiome is responsible for the metabolism of cranberry proanthocyanidins into smaller active metabolites . Additional research will be necessary to Antioxidants 2016, 5, 27 15 of 20 assess the bioavailability and metabolism of cranberries in humans and recent advances in standards and the radiolabeling of cranberry products will provide new tools to aid investigations. 5. Conclusions Evaluation of cranberries and cranberry derived constituents in preclinical in vitro and in vivo studies evaluating cancer inhibition is key for the future development of cranberry-based interventions in high-risk human cohorts. The data presented in this review strongly support the anti-proliferative and pro-death capacities of cranberries in a multitude of cancer cell lines and select in vivo models including xenograft and chemically induced cancer models. The precise cancer inhibitory mechanisms associated with cranberries in speciﬁc targets are still be elucidated, but preclinical studies utilizing cranberry proanthocyanidins show inactivation of the PI3K/AKT/mTOR pathways and modulation of MAPK signaling in esophageal, neuroblastoma, ovarian and prostate cancer cells and in esophageal xenografts [39,44,49,52]. Moreover, cranberry proanthocyanidins have recently been shown to induce autophagic markers in vitro and in vivo , suggesting an alternative mode of cell death induction and tumor inhibition that requires further evaluation in additional cancer targets. A recent study published by The Cancer Genome Atlas Network showed that a large number of genetic alterations were shared across 279 patients with head and neck squamous cell carcinomas including activating mutations in PIK3CA, the gene encoding the catalytic subunit of phosphatidylinositol 3-kinase (PI3K) . Cranberry proanthocyanidins are also known to mitigate inﬂammatory responses of oral epithelial cells and to inhibit oral bioﬁlm formation [12,78]; thus, cranberry derived constituents may be particularly efﬁcacious inhibitors targeting oral premalignancy. Researchers should continue to deﬁne the mechanisms of cancer inhibition in vitro and in vivo with the goal of informing mechanistically driven human clinical trials. It should be noted that the efﬁcacy of natural products in head and neck, esophageal and colon cancers has been demonstrated by black raspberries . The use of cranberries and cranberry derived constituents in cancer prevention is at an early stage. Still, results are highly promising considering positive preclinical results following treatment at relatively low, behaviorally achievable, concentrations when administered in a drink formulation, consumed as food or as a supplement. A recent study by Marette et al. reported cranberry polyphenols protect from diet-induced obesity, insulin resistance and intestinal inﬂammation . The latter research ﬁndings were associated with a shift in fecal microbiome proﬁles and although cancer was not an outcome under evaluation, further assessments of cranberries targeting obesity-linked cancers seems logical. In conclusion, additional research focused on issues of metabolism, bioavailability, pharmacokinetics, pharmacodynamics, active fractionation, optimum dose, formulation, routes of delivery and duration are required to inform the cancer preventive utility of cranberries in high risk human cohorts. Acknowledgments: We thank the National Institutes of Health and National Cancer Institute for funding support via grant (R01-CA158319) and Advancing a Healthier Wisconsin (5220296), both awarded to Laura A. Kresty. Author Contributions: Katherine M. 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Antioxidants – Multidisciplinary Digital Publishing Institute
Published: Aug 18, 2016