Penta-O-galloyl-beta-D-glucose induces G1 arrest and DNA replicative S-phase arrest independently of cyclin-dependent kinase inhibitor 1A, cyclin-dependent kinase inhibitor 1B and P53 in human breast cancer cells and is orally active against triple negative xenograft growth.
BACKGROUND
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 G(1) 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 druggable targets.


METHODS
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 20mg PGG/kg body weight by daily gavage starting 4 days after cancer cell inoculation.


RESULTS
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 G(1) arrest. Higher levels of PGG induced more caspase-mediated apoptosis in MCF-7, in strong association with induction of P53 Ser(15) phosphorylation, than in MDA-MB-231 cells. The cell cycle arrests were achieved without an induction of cyclin dependent kinase (CDK) inhibitory proteins P21(Cip1) and P27(Kip1). PGG treatment led to decreased cyclin D1 in both cell lines and over-expressing cyclin D1 attenuated G(1) 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 G(1)-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.


CONCLUSIONS
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.
Chai
Yubo
Y
The Hormel Institute, University of Minnesota, Austin, MN 55912, USA.
Lee
Hyo-Jeong
HJ
Shaik
Ahmad Ali
AA
Nkhata
Katai
K
Xing
Chengguo
C
Zhang
Jinhui
J
Jeong
Soo-Jin
SJ
Kim
Sung-Hoon
SH
Lu
Junxuan
J
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D005260:Female; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects*; D006801:Humans; D047348:Hydrolyzable Tannins / Q000008:administration & dosage / Q000494:pharmacology*; D061986:MCF-7 Cells; D051379:Mice; D008819:Mice, Nude; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D059807:S Phase Cell Cycle Checkpoints / Q000187:drug effects*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D047348:Hydrolyzable Tannins; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D016159:Tumor Suppressor Protein p53; D050760:Cyclin-Dependent Kinase Inhibitor p27; C435084:pentagalloylglucose; D066246:ErbB Receptors
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