Adhesion of calcium oxalate (CaOx) crystals to kidney cells may be a key event in the pathogenesis of kidney stones associated with marked hyperoxaluria. Previously, we found that 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG), isolated from a traditional medicinal herb, reduced CaOx crystal adhesion to renal epithelial cells by acting on the cells as well as the crystal surface. Here we used the ethylene glycol (EG) - mediated hyperoxaluric rat model and found evidence of oxidant stress as indicated by decreases in the activities of the renal antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase, with increased kidney cell apoptosis and serum malondialdehyde levels, all evident by 21 days of EG treatment. These effects of hyperoxaluria were reversed by concurrent PGG treatment along with decreased urinary oxalate levels and CaOx supersaturation. Renal epithelial cell expression of the crystal binding molecule hyaluronan increased diffusely within 7 days of EG initiation, suggesting it is not a result of but precedes crystal deposition. Renal cell osteopontin (OPN) was also up regulated in EG-treated animals, and PGG significantly attenuated over expression of both OPN and hyaluronan. Thus, our findings demonstrate that PGG reduces renal crystallization and oxidative renal cell injury, and may be a candidate chemo preventative agent for nephrolithiasis.
Calcium oxalate monohydrate (COM) crystals bind avidly to the surface of proliferating and migrating renal endothelial cells, perhaps a key event in kidney stone formation. Oxalate-induced pre-oxidative stress can further promote crystal attachment cells. Natural products including gallotannins found in green teas have been studied as potentially novel treatments to prevent crystal retention and kidney stone formation. Gallotannin significantly inhibited COM crystal growth and binding to MDCK I renal epithelial cells at non-toxic concentrations and also delayed renal cell migration in a wound healing assay. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that gallotannin significantly attenuated oxalate-induced mRNA expression of monocyte chemoattractant protein 1 (MCP-1), osteopontin (OPN), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit p22phox and p47phox in human primary renal epithelial cells (HRCs). Gallotannin also reduced HRC production of reactive oxygen species (ROS) and malondialdehyde (MDA) as well as enhanced antioxidant enzyme superoxide dismutase (SOD) activity in response to oxalate. Taken together, our findings suggest that gallotannin can contribute to nephrolithiasis prevention via direct effects on renal epithelial cells including suppression of COM binding and MCP-1 and OPN expression, along with augmenting antioxidant activity.
gallotannin; renal epithelial cells; calcium oxalate monohydrate; MCP-1; osteopontin; ROS; SOD
Though tanshinone IIA and cryptotanshinone possess a variety of biological effects such as anti-inflammatory, antioxidative, antimetabolic, and anticancer effects, the precise molecular targets or pathways responsible for anticancer activities of tanshinone IIA and cryptotanshinone in chronic myeloid leukemia (CML) still remain unclear. In the present study, we investigated the effect of tanshinone IIA and cryptotanshinone on the Janus activated kinase (JAK)/signal transducer and activator of transcription (STAT) signaling during apoptotic process. We found that both tanshinone IIA and cryptotanshinone induced apoptosis by activation of caspase-9/3 and Sub-G1 accumulation in K562 cells. However, they have the distinct JAK/STAT pathway, in which tanshinone IIA inhibits JAK2/STAT5 signaling, whereas cryptotanshinone targets the JAK2/STAT3. In addition, tanshinone IIA enhanced the expression of both SHP-1 and -2, while cryptotanshinone regulated the expression of only SHP-1. Both tanshinone IIA and cryptotanshinone attenuated the expression of bcl-xL, survivin, and cyclin D1. Furthermore, tanshinone IIA augmented synergy with imatinib, a CML chemotherapeutic drug, better than cryptotanshinone in K562 cells. Overall, our findings suggest that the anticancer activity of tanshinone IIA and cryptotanshinone is mediated by the distinct the JAK/STAT3/5 and SHP1/2 signaling, and tanshinone IIA has the potential for combination therapy with imatinib in K562 CML cells.
We demonstrate that decursin induces apoptosis via regulation of cyclooxygenase-2 (COX-2) and survivin in leukemic KBM-5 cells. By activating an apoptotic machinery, decursin is cytotoxic to KBM-5 cells. In this apoptotic process, decursin can activate caspase family members and triggers PARP cleavage. At the same time, the expression of COX-2 and survivin in the cells is downregulated. Furthermore, decursin is in synergy with COX-2 inhibitor, celecoxib or NS398 for the induction of apoptosis. Overall, these results suggest that decursin, via inhibiting COX-2 and survivin, sensitizes human leukemia cells to apoptosis and is a potential chemotherapeutic agent to treat this disease.
Decursin; Apoptosis; COX-2; Survivin; KBM-5
Background. Combination cancer therapy is one of the attractive approaches to overcome drug resistance of cancer cells. In the present study, we investigated the synergistic effect of decursin from Angelica gigas and doxorubicin on the induction of apoptosis in three human multiple myeloma cells. Methodology/Principal Findings. Combined treatment of decursin and doxorubicin significantly exerted significant cytotoxicity compared to doxorubicin or decursin in U266, RPMI8226, and MM.1S cells. Furthermore, the combination treatment enhanced the activation of caspase-9 and -3, the cleavage of PARP, and the sub G1 population compared to either drug alone in three multiple myeloma cells. In addition, the combined treatment downregulated the phosphorylation of mTOR and its downstream S6K1 and activated the phosphorylation of ERK in three multiple myeloma cells. Furthermore, the combined treatment reduced mitochondrial membrane potential, suppressed the phosphorylation of JAK2, STAT3, and Src, activated SHP-2, and attenuated the expression of cyclind-D1 and survivin in U266 cells. Conversely, tyrosine phosphatase inhibitor pervanadate reversed STAT3 inactivation and also PARP cleavage and caspase-3 activation induced by combined treatment of doxorubicin and decursin in U266 cells. Conclusions/Significance. Overall, the combination treatment of decursin and doxorubicin can enhance apoptotic activity via mTOR and/or STAT3 signaling pathway in multiple myeloma cells.
1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG), a polyphenolic compound isolated from Rhus chinensis Mill. PGG has been known to have anti-tumor, anti-angiogenic and anti-diabetic activities. The present study revealed another underlying molecular target of PGG in MDA-MB-231 breast cancer cells by using Illumina Human Ref-8 expression BeadChip assay. Through the Beadstudio v3 micro assay program to compare the identified genes expressed in PGG-treated MDA-MB-231 cells with untreated control, we found several unique genes that are closely associated with pyruvate metabolism, glycolysis/gluconeogenesis and tyrosine metabolism, including PC, ACSS2, ACACA, ACYP2, ALDH3B1, FBP1, PRMT2 and COMT. Consistent with microarray data, real-time RT-PCR confirmed the significant down-regulation of these genes at mRNA level in PGG-treated MDA-MB-231 cells. Our findings suggest the potential of PGG as anticancer agent for breast cancer cells by targeting cancer metabolism genes.
cancer metabolism; MDA-MB-231; microarray; PGG; real-time PCR
There is an urgent clinical need for chemotherapeutic and chemopreventive drugs for triple-negative breast cancer (TNBCa). Extending on our recent work, we hypothesize that the herbal compound 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) can inhibit the growth and metastasis of TNBCa xenograft and target Janus-activated kinase (JAK)-signal transducer and activator of transcription (STAT) 3-signaling axis. Daily oral gavage of 10 mg PGG/kg body wt decreased MDA-MB-231 xenograft weight by 49.3% (P < 0.01) at 40 days postinoculation, whereas weekly intraperitoneal injections of Taxol at the same dosage resulted in a 21.4% reduction (P > 0.1). PGG treatment also decreased the incidence of lung metastasis. Immunohistochemical staining detected decreased Ki-67 (proliferation) index and increased terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (apoptosis) index in PGG-treated and Taxol-treated xenografts. However, the CD34 (angiogenesis) index was decreased only in PGG-treated xenografts along with decreased phospho-STAT3. In cell culture of MDA-MB-231 cells, PGG decreased pSTAT3 and its downstream target proteins, decreased its upstream kinase pJAK1 and induced the expression of SHP1, a JAK1 upstream tyrosine phosphatase, within as early as 1 h of exposure. The phosphatase inhibitor pervanadate reversed the PGG-induced downregulation of pSTAT3 and caspase activation. Orally administered PGG can inhibit TNBCa growth and metastasis, probably through anti-angiogenesis, antiproliferation and apoptosis induction. Mechanistically, PGG-induced inhibition of JAK1-STAT3 axis may contribute to the observed in vivo efficacy and the effects on the cellular processes.
Ergosterol peroxide (EP) derived from edible mushroom has been shown to exert anti-tumor activity in several cancer cells. In the present study, anti-angiogenic activity of EP was investigated with the underlying molecular mechanisms in human multiple myeloma U266 cells.
Despite weak cytotoxicity against U266 cells, EP suppressed phosphorylation, DNA binding activity and nuclear translocalization of signal transducer and activator of transcription 3 (STAT3) in U266 cells at nontoxic concentrations. Also, EP inhibited phosphorylation of the upstream kinases Janus kinase 2 (JAK2) and Src in a time-dependent manner. Furthermore, EP increased the expression of protein tyrosine phosphatase SHP-1 at protein and mRNA levels, and conversely silencing of the SHP-1 gene clearly blocked EP-mediated STAT3 inactivation. In addition, EP significantly decreased vascular endothelial growth factor (VEGF), one of STAT3 target genes at cellular and protein levels as well as disrupted in vitro tube formation assay. Moreover, EP significantly suppressed the growth of U266 cells inoculated in female BALB/c athymic nude mice and immunohistochemistry revealed that EP effectively reduced the expression of STAT3 and CD34 in tumor sections compared to untreated control.
These findings suggest that EP can exert antitumor activity in multiple myeloma U266 cells partly with antiangiogenic activity targeting JAK2/STAT3 signaling pathway as a potent cancer preventive agent for treatment of multiple myeloma cells.
ergosterol peroxide; JAK2; STAT3; angiogenesis; multiple myeloma
Sulforaphane (SFN) is an isothiocyanate found in cruciferous vegetables that exerts anti-oxidant, anti-inflammatory, anti-cancer and radio-sensitizing activities. Nonetheless, the mechanism responsible for SFN-induced cell death is not fully understood. In the present study, anti-cancer mechanism of SFN was elucidated in LNCaP prostate cancer cells.
SFN exerted cytotoxicity and increased TUNEL positive cells in a concentration-dependent manner in LNCaP cells. Proteomics study revealed that levels of nine proteins including tubulin β-2, phosphoglucomutase-3 (PGM3), melanoma-derived leucine zipper containing extra-nuclear factor, activin A type I receptor precursor, smoothelin-A, KIA0073, hypothetical protein LOC57691 and two unnamed proteins were changed over 8 folds in SFN treated LNCaP cells compared to untreated control. We have further confirmed that SFN reduced PGM3 expression with western blotting and showed that PGM3 siRNA enhanced cytotoxicity demonstrated by cell morphology and TUNEL assays in LNCaP cells.
Taken together, these findings suggest that PGM3 plays a role in mediating SFN-induced cell death in LNCaP cells, and is a potential molecular therapeutic target for prostate cancer.
We previously reported the anti-angiogenic activity of paeonol isolated from Moutan Cortex. In the present study, we investigated the negative effect of paeonol oxime (PO, a paeonol derivative) on basic fibroblast growth factor (bFGF)-mediated angiogenesis in human umbilical vein endothelial cells (HUVECs) (including tumor angiogenesis) and pro-survival activity in HT-1080 fibrosarcoma cell line.
We showed that PO (IC50 = 17.3 µg/ml) significantly inhibited bFGF-induced cell proliferation, which was achieved with higher concentrations of paeonol (IC50 over 200 µg). The treatment with PO blocked bFGF-stimulated migration and in vitro capillary differentiation (tube formation) in a dose-dependent manner. Furthermore, PO was able to disrupt neovascularization in vivo. Interestingly, PO (25 µg/ml) decreased the cell viability of HT-1080 fibrosarcoma cells but not that of HUVECs. The treatment with PO at 12.5 µg/ml reduced the levels of phosphorylated AKT and VEGF expression (intracellular and extracelluar) in HT-1080 cells. Consistently, immunefluorescence imaging analysis revealed that PO treatment attenuated AKT phosphorylation in HT-1080 cells.
Taken together, these results suggest that PO inhibits bFGF-induced angiogenesis in HUVECs and decreased the levels of PI3K, phospho-AKT and VEGF in HT-1080 cells.
Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of the aggressive and fatal disease adult T-cell leukemia. Previous studies have demonstrated that the HTLV-1-encoded Tax protein inhibits the function of tumor suppressor p53 through a Tax-induced NF-κB pathway. Given these attributes, we were interested in the activity of small-molecule inhibitor 9-aminoacridine (9AA), an anticancer drug that targets two important stress response pathways, NF-κB and p53. In the present study, we have examined the effects of 9AA on HTLV-1-transformed cells. Treatment of HTLV-1-transformed cells with 9AA resulted in a dramatic decrease in cell viability. Consistent with these results, we observed an increase in the percentage of cells in sub-G1 and an increase in the number of cells positive by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling assay following treatment of HTLV-1-transformed cells with 9AA. In each assay, HTLV-1-transformed cells C8166, Hut102, and MT2 were more sensitive to treatment with 9AA than control CEM and peripheral blood mononuclear cells. Analyzing p53 function, we demonstrate that treatment of HTLV-1-transformed cells with 9AA resulted in an increase in p53 protein and activation of p53 transcription activity. Of significance, 9AA-induced cell death could be blocked by introduction of a p53 small interfering RNA, linking p53 activity and cell death. These results suggest that Tax-repressed p53 function in HTLV-1-transformed cells is “druggable” and can be restored by treatment with 9AA. The fact that 9AA induces p53 and inhibits NF-κB suggests a promising strategy for the treatment of HTLV-1-transformed cells.
The phosphatidylinositol-3-kinase (PI3K) and AKT (Protein Kinase B) signaling pathways play an important role in regulating cell cycle progression and cell survival. In previous studies, we demonstrated that AKT is activated in HTLV-1 transformed cells and that Tax activation of AKT is linked to p53 inhibition and cell survival. In the present study, we extend these observations to identify regulatory pathways affected by AKT in HTLV-1-transformed cells. We demonstrate that inhibition of AKT reduces the level of phosphorylated Bad, an important member of the pro-apoptotic family of proteins. Consistent with the decrease of phosphorylated Bad, cytochrome c is released from the mitochondria and caspase 9 is activated. Pre-treatment of the cells with caspase-9 specific inhibitor z-LEHD-FMK or pan caspase inhibitor Ac-DEVD-CHO prevented LY294002-induced apoptosis. Of interest, p53 siRNA prevents LY294002-induced apoptosis in HTLV-1-transformed cells, suggesting that p53 reactivation is linked to apoptosis. In conclusion, the AKT pathway is involved in targeting multiple proteins which regulate caspase- and p53-dependent apoptosis in HTLV-1-transformed cells. Since AKT inhibitors simultaneously inhibit NF-κB and activate p53, these drugs should be promising candidates for HTLV-1-associated cancer therapy.
Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent for adult T-cell leukemia. The HTLV-1-encoded protein Tax transactivates the viral long terminal repeat and plays a critical role in virus replication and transformation. Previous work from our laboratory demonstrated that coactivator-associated arginine methytransferase 1, a protein arginine methytransferase, was important for Tax-mediated transactivation. To further investigate the role of methyltransferases in viral transcription, we utilized adenosine-2,3-dialdehyde (AdOx), an adenosine analog and S-adenosylmethionine-dependent methyltransferase inhibitor. The addition of AdOx decreased Tax transactivation in C81, Hut102, and MT-2 cells. Unexpectedly, we found that AdOx potently inhibited the growth of HTLV-1-transformed cells. Further investigation revealed that AdOx inhibited the Tax-activated NF-κB pathway, resulting in reactivation of p53 and induction of p53 target genes. Analysis of the NF-κB pathway demonstrated that AdOx treatment resulted in degradation of the IκB kinase complex and inhibition of NF-κB through stabilization of the NF-κB inhibitor IκBα. Our data further demonstrated that AdOx induced G2/M cell cycle arrest and cell death in HTLV-1-transformed but not control lymphocytes. These studies demonstrate that protein methylation plays an important role in NF-κB activation and survival of HTLV-1-transformed cells.
Positive transcription elongation factor (P-TEFb), which is composed of CDK9 and cyclin T1, plays an important role in cellular and viral gene expression. Our lab has recently demonstrated that P-TEFb is required for Tax transactivation of the viral long terminal repeat (LTR). P-TEFb is found in two major complexes: the inactive form, which is associated with inhibitory subunits 7SK snRNA and HEXIM1, and the active form, which is associated with, at least in part, Brd4. In this study, we analyzed the effect of Brd4 on human T-lymphotropic virus type 1 (HTLV-1) transcription. Overexpression of Brd4 repressed Tax transactivation of the HTLV-1 LTR in a dose-dependent manner. In vitro binding studies suggest that Tax and Brd4 compete for binding to P-TEFb through direct interaction with cyclin T1. Tax interacts with cyclin T1 amino acids 426 to 533, which overlaps the region responsible for Brd4 binding. In vivo, overexpression of Tax decreased the amount of 7SK snRNA associated with P-TEFb and stimulates serine 2 phosphorylation of the RNA polymerase II carboxyl-terminal domain, suggesting that Tax regulates the functionality of P-TEFb. Our results suggest the possibility that Tax may compete and functionally substitute for Brd4 in P-TEFb regulation.
In this study, we demonstrate that the coactivator-associated arginine methyltransferase 1 (CARM1), which methylates histone H3 and other proteins such as p300/CBP, is positively involved in the regulation of Tax transactivation. First, transfection studies demonstrated that overexpression of CARM1 wild-type protein resulted in increased Tax transactivation of the human T-cell lymphotropic virus type 1 (HTLV-1) long terminal repeat (LTR). In contrast, transfection of a catalytically inactive CARM1 methyltransferase mutant did not enhance Tax transactivation. CARM1 facilitated Tax transactivation of the CREB-dependent cellular GEM promoter. A direct physical interaction between HTLV-1 Tax and CARM1 was demonstrated using in vitro glutathione S-transferase-Tax binding assays, in vivo coimmunoprecipitation, and confocal microscopy experiments. Finally, chromatin immunoprecipitation analysis of the activated HTLV-1 LTR promoter showed the association of CARM1 and methylated histone H3 with the template DNA. In vitro, Tax facilitates the binding of CARM1 to the transcription complex. Together, our data provide evidence that CARM1 enhances Tax transactivation of the HTLV-1 LTR through a direct interaction between CARM1 and Tax and this binding promotes methylation of histone H3 (R2, R17, and R26).
A novel immunostimulating factor (ISTF) of Actinobacillus actinomycetemcomitans ATCC 29522 was isolated and characterized as inducing proliferation of mouse B cells and human peripheral blood mononuclear cells. This factor was isolated from the bacterial culture medium and purified by size exclusion chromatography, dye-ligand affinity chromatography, immunoaffinity chromatography using monoclonal antibodies, and preparative electrophoresis. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the purified ISTF migrated as a single band corresponding to a molecular mass of 13 kDa. ISTF was a proteinaceous material distinct from lipopolysaccharide; it directly induced the proliferation of B lymphocytes but had no effect on the proliferation of T lymphocytes, even in the presence of antigen-presenting cells. A B-lymphocyte-mitogenic activity of ISTF was also shown by flow cytometric analysis of responding cell subpopulations. Immunoblot analysis revealed that ISTF was a component of the outer membranes of bacteria, could exist as a soluble form, and was released by growing and/or lysed bacteria. These results suggest that ISTF produced by A. actinomycetemcomitans may play an important role in immunopathologic changes associated with A. actinomycetemcomitans infections.
The aim of this study is to determine anti-cancer effect of Icariside II purified from the root of Epimedium koreanum Nakai on human acute myeloid leukemia (AML) cell line U937.
Icariside II blocked the growth U937 cells in a dose- and time-dependent manner. In this anti-proliferation process, this herb compound rendered the cells susceptible to apoptosis, manifested by enhanced accumulation of sub-G1 cell population and increased the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells. Icariside II was able to activate caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP) in a time-dependent manner. Concurrently, the anti-apoptotic proteins, such as bcl-xL and survivin in U937 cells, were downregulated by Icariside II. In addition, Icariside II could inhibit STAT3 phosphorylation and function and subsequently suppress the activation of Janus activated kinase 2 (JAK2), the upstream activators of STAT3, in a dose- and time-dependent manner. Icariside II also enhanced the expression of protein tyrosine phosphatase (PTP) SH2 domain-containing phosphatase (SHP)-1, and the addition of sodium pervanadate (a PTP inhibitor) prevented Icariside II-induced apoptosis as well as STAT3 inactivation in STAT3 positive U937 cells. Furthermore, silencing SHP-1 using its specific siRNA significantly blocked STAT3 inactivation and apoptosis induced by Icariside II in U937 cells.
Our results demonstrated that via targeting STAT3-related signaling, Icariside II sensitizes U937 cells to apoptosis and perhaps serves as a potent chemotherapeutic agent for AML.
Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various cellular processes such as cell survival, angiogenesis and proliferation. In the present study, we examined that betulinic acid (BA), a triterpene from the bark of white birch, had the inhibitory effects on hypoxia-mediated activation of STAT3 in androgen independent human prostate cancer PC-3 cells.
BA inhibited the protein expression and the transcriptional activities of hypoxia-inducible factor-1α (HIF-1α) under hypoxic condition. Consistently, BA blocked hypoxia-induced phosphorylation, DNA binding activity and nuclear accumulation of STAT3. In addition, BA significantly reduced cellular and secreted levels of vascular endothelial growth factor (VEGF), a critical angiogenic factor and a target gene of STAT3 induced under hypoxia. Furthermore, BA prevented in vitro capillary tube formation in human umbilical vein endothelial cells (HUVECs) maintained in conditioned medium of hypoxic PC-3 cells, implying anti-angiogenic activity of BA under hypoxic condition. Of note, chromatin immunoprecipitation (ChiP) assay revealed that BA inhibited binding of HIF-1α and STAT3 to VEGF promoter. Furthermore, silencing STAT3 using siRNA transfection effectively enhanced the reduced VEGF production induced by BA treatment under hypoxia.
Taken together, our results suggest that BA has anti-angiogenic activity by disturbing the binding of HIF-1α and STAT3 to the VEGF promoter in hypoxic PC-3 cells.
Natural herbal compounds with novel actions different from existing breast cancer (BCa) treatment modalities are attractive for improving therapeutic efficacy and safety. We have recently shown that penta-1,2,3,4,6-O-galloyl-β-D-glucose (PGG) induced S-phase arrest in prostate cancer (PCa) cells through inhibiting DNA replicative synthesis and G1 arrest, in addition to inducing cell death at higher levels of exposure. We and others have shown that PGG through intraperitoneal (i.p.) injection exerts a strong in vivo growth suppression of human PCa xenograft models in athymic nude mice. This study aims to test the hypothesis that the novel targeting actions of PGG are applicable to BCa cells, especially those lacking proven drugable targets.
Mono-layer cell culture models of p53-wild type estrogen receptor (ER)-dependent MCF-7 BCa cells and p53-mutant ER-/progesterone receptor (PR)- and Her2-regular (triple-negative) MDA-MB-231 BCa were exposed to PGG for a comprehensive investigation of cellular consequences and molecular targets/mediators. To test the in vivo efficacy, female athymic mice inoculated with MDA-MB-231 xenograft were treated with 20 mg PGG/kg body weight by daily gavage starting 4 days after cancer cell inoculation.
Exposure to PGG induced S-phase arrest in both cell lines as indicated by the lack of 5-bromo2'-deoxy-uridine (BrdU) incorporation into S-phase cells as well as G1 arrest. Higher levels of PGG induced more caspase-mediated apoptosis in MCF-7, in strong association with induction of P53 Ser15 phosphorylation, than in MDA-MB-231 cells. The cell cycle arrests were achieved without an induction of cyclin dependent kinase (CDK) inhibitory proteins P21Cip1 and P27Kip1. PGG treatment led to decreased cyclin D1 in both cell lines and over-expressing cyclin D1 attenuated G1 arrest and hastened S arrest. In serum-starvation synchronized MCF-7 cells, down-regulation of cyclin D1 was associated with de-phosphorylation of retinoblastoma (Rb) protein by PGG shortly before G1-S transition. In vivo, oral administration of PGG led to a greater than 60% inhibition of MDA-MB231 xenograft growth without adverse effect on host body weight.
Our in vitro and in vivo data support PGG as a potential drug candidate for breast cancer with novel targeting actions, especially for a triple negative BCa xenograft model.