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Prostate cancer is the second most prevalent malignancy worldwide. In the early stages, the development of prostate cancer is dependent on androgens. Over time with androgen deprivation therapy, 20% of prostate cancers progress to a castration-resistant form. Novel treatments for prostate cancers are still urgently needed. Erianin is a plant-derived bibenzyl compound. We report herein that erianin exhibits anti-tumor effects in androgen-sensitive and castration-resistant prostate cancer cells through different mechanisms. Erianin induces endoplasmic reticulum stress-associated apoptosis in androgen-sensitive prostate cancer cells. It also triggers pro-survival autophagic responses, as inhibition of autophagy predisposes to apoptosis. In contrast, erianin fails to induce apoptosis in castration-resistant prostate cancer cells. Instead, it results in cell cycle arrest at the M phase. Mechanistically, C16 ceramide dictates differential responses of androgen-sensitive and castration-resistant prostate cancer cells to erianin. Erianin elevates C16 ceramide level in androgen-sensitive but not castration-resistant prostate cancer cells. Overexpression of ceramide synthase 5 that specifically produces C16 ceramide enables erianin to induce apoptosis in castration-resistant prostate cancer cells. Our study provides both experimental evidence and mechanistic data showing that erianin is a potential treatment option for prostate cancers.

Cancer recurrence poses a significant challenge. At the cellular level, recurrence takes place as a result of reactivation of dormant cancer cells residing at G

Cancer cell repopulation through cell cycle re-entry by quiescent (G0 ) cell is thought to be an important mechanism behind treatment failure and cancer recurrence. Facilitates Chromatin Transcription (FACT) is involved in DNA repair, replication and transcription by eviction of histones or loosening their contact with DNA. While FACT expression is known to be high in a range of cancers, the biological significance of the aberrant increase is not clear. We found that in prostate and lung cancer cells FACT mRNA and protein levels were low at G0 compared to the proliferating state but replenished upon cell cycle re-entry. Silencing of FACT with Dox-inducible shRNA hindered cell cycle re-entry by G0 cancer cells, which could be rescued by ectopic expression of FACT. An increase in SKP2, c-MYC and PIRH2 and a decrease in p27 protein levels seen upon cell cycle re-entry were prevented or diminished when FACT was silenced. Further, using mVenus-p27K- infected cancer cells to measure p27 degradation capacity, we confirm that inhibition of FACT at release from quiescence suppressed the p27 degradation capacity resulting in an increased mVenus-p27K- signal. In conclusion, FACT plays an important role in promoting the transition from G0 to the proliferative state and can be a potential therapeutic target to prevent prostate and lung cancer from progression and recurrence.

Cancer recurrence poses a significant challenge. At the cellular level, recurrence takes place as a result of reactivation of dormant cancer cells residing at G0 phase. The aim of the study was to identify compounds that can trap prostate and lung cancer cells in G0 phase from a new Chinese herb recipe, Astringent recipe, consisting of Radix Paeoniae Alba, Agrimonia pilosa Ledeb, Fructus Mume, Fritillaria thunbergii Miq., Ganoderma Lucidum Karst, and Astragalus membranaceus (Fisch.) Bunge. Astringent recipe impeded cell cycle progression in prostate and lung cancer cells by rounding them up at G0 phase by flow cytometric analysis of cancer cells stained with Hoechst 33342 and Pyronin Y, respectively, for DNA and RNA. The anti-cancer efficacy of the recipe was found to be attributable to Agrimonia pilosa Ledeb. Further study established that agrimol B, a polyphenol derived from Agrimonia pilosa Ledeb, contributed to the activity of the herb. The action of agrimol B on the cancer cells was likely derived from its effect on c-MYC, SKP2 and p27 by immunoblotting and immunofluorescence. Oral administration of Agrimonia pilosa Ledeb or agrimol B reduced growth of prostate cancer cell xenograft in animal. In conclusion, Agrimol B can enrich for prostate and lung cancer cells in G0 state and influence key regulators that govern G0 status.

Blockade of cell cycle re‐entry in quiescent cancer cells is a strategy to prevent cancer progression and recurrence. We investigated the action and mode of action of CPF mixture (Coptis chinensis, Pinellia ternata and Fructus trichosanthis) in impeding a proliferative switch in quiescent lung cancer cells. The results indicated that CPF impeded cell cycle re‐entry in quiescent lung cancer cells by reduction of FACT and c‐MYC mRNA and protein levels, with concomitant decrease in H3K4 tri‐methylation and RNA polymerase II occupancy at FACT and c‐MYC promoter regions. Animals implanted with quiescent cancer cells that had been exposed to CPF had reduced tumour volume/weight. Thus, CPF suppresses proliferative switching through transcriptional suppression of FACT and the c‐MYC, providing a new insight into therapeutic target and intervention method in impeding cancer recurrence.

Hedyotis diffusa Willd. (H) and Scutellaria barbata D.Don (S) are ancient anti-cancer Chinese herb medicines. When combined, known as HS, it is one of the most commonly prescribed Chinese Medicines for cancer patients today in China.The prevention of disease progression is a dominant concern for the growing number of men with prostate cancer. The purpose of this work is to evaluate the action and mode of action of Chinese Medicine recipe HS in inhibiting prostate cancer progression in preclinical models.Effects of HS were analyzed in prostate cancer cell lines by evaluating proliferation, cell cycle profile, DNA damage and key regulators responsible for GHS treatment was observed to reduce DNA content and accumulated prostate cancer cells at the GHS acts by impeding the G

// Kaikai Shen 1, * , Zhichao Xi 1, * , Jianling Xie 4 , Hua Wang 5 , Chanlu Xie 6 , C.Soon Lee 6, 7 , Paul Fahey 6 , Qihan Dong 6, 7, 8 , Hongxi Xu 1, 2, 3 1 School of Pharmacy, Shanghai University of Traditional Chinese Medicine, Shanghai, China 2 Institute of Arthritis Research, Shanghai Academy of Chinese Medical Sciences, Guanghua Integrative Medicine Hospital/ Shanghai University of T.C.M, Shanghai, China 3 Engineering Research Center of Shanghai Colleges for TCM New Drug Discovery, Shanghai, China 4 Nutrition and Metabolism, South Australian Health and Medical Research Institute, Adelaide, Australia 5 Stanley Ho Center for Emerging Infectious Diseases, The Chinese University of Hong Kong, Hong Kong, China 6 School of Science and Health, The University of Western Sydney, Sydney, Australia 7 Central Clinical School and Bosch Institute, The University of Sydney, Sydney, Australia 8 Department of Endocrinology, Royal Prince Alfred Hospital, Sydney, Australia * These authors contributed equally to this work Correspondence to: Hongxi Xu, email: xuhongxi88@gmail.com Qihan Dong, email: q.dong@uws.edu.au Keywords: hepatocellular carcinoma, cancer metastasis, Guttiferone K, profilin1, actin Received: November 20, 2015 Accepted: July 18, 2016 Published: August 01, 2016 ABSTRACT Hepatocellular carcinoma (HCC) is an aggressive malignancy and the 5-year survival rate of advanced HCC is < 10%. Guttiferone K (GUTK) isolated from the Garcinia genus inhibited HCC cells migration and invasion in vitro and metastasis in vivo without apparent toxicity. Proteomic analysis revealed that actin-binding protein profilin 1 (PFN1) was markedly increased in the presence of GUTK. Over-expression of PFN1 mimicked the effect of GUTK on HCC cell motility and metastasis. The effect of GUTK on cell motility was diminished when PFN1 was over-expressed or silenced. Over-expression of PFN1 or incubation with GUTK decreased F-actin levels and the expression of proteins involved in actin nucleation, branching and polymerization. Moreover, a reduction of PFN1 protein levels was common in advanced human HCC and associated with poor survival rate. In conclusion, GUTK effectively suppresses the motility and metastasis of HCC cells mainly by restoration of aberrantly reduced PFN1 protein expression.

Ethnopharmacological relevance Hedyotis diffusa Willd. (H) and Scutellaria barbata D.Don (S) are ancient anti-cancer Chinese herb medicines. When combined, known as HS, it is one of the most commonly prescribed Chinese Medicines for cancer patients today in China. Aim of the study The prevention of disease progression is a dominant concern for the growing number of men with prostate cancer. The purpose of this work is to evaluate the action and mode of action of Chinese Medicine recipe HS in inhibiting prostate cancer progression in preclinical models. Methods Effects of HS were analyzed in prostate cancer cell lines by evaluating proliferation, cell cycle profile, DNA damage and key regulators responsible for G2 to M phase transition. The transcriptional activities of these regulators were determined by RT-PCR and ChIP. The efficacy of HS in vitro was validated in an animal model. Results HS treatment was observed to reduce DNA content and accumulated prostate cancer cells at the G2/M phase. Immunolabeling for phospho-Histone H3 in association with nocodazole to capture mitotic cells confirmed that HS impeded G2 to M transition. After excluding DNA damage-induced G2 arrest, it was revealed that HS reduced expression of Cyclin B1, CDK1, PLK1 and Aurora A at both protein and mRNA levels, with concomitant reduction of H3K4 tri-methylation at their promoter-regions. Animals that received oral administration of HS with a dosage relevant to clinical application showed reduced tumor volume and weight with a reduction of Cyclin B1, CDK1, PLK1 and Aurora A protein levels. Conclusions HS acts by impeding the G2 to M transition of prostate cancer cells. It is likely that the mode of action is transcriptionally suppressing proteins governing mitotic entry, without eliciting significant DNA damage.

Cancer cell repopulation through cell cycle re-entry by quiescent (G

Aberrant increase in protein kinase B (AKT) phosphorylation (pAKT), due to a gain-of-function mutation of phosphatidylinositol-3-kinase (PI3K) or loss-of-function mutation or deletion of phosphatase and tensin homolog (PTEN), is a common alteration in prostate cancer and associated with poor prognosis. Cytosolic phospholipase A2α (cPLA2α) is a lipid modifying enzyme by catalyzing the hydrolysis of arachidonic acid from membrane phospholipid. The released arachidonic acid and its metabolites contribute to survival and proliferation of prostate cancer cells. In this mini-review, we summarize the relationship between pAKT and cPLA2α in prostate cancer cells. There was a concordant increase in pAKT and cPLA2α levels in prostate tissue of prostate epithelial-specific PTEN-knockout mice compared to PTEN-wild type mice. Restoration of PTEN expression or inhibition of PI3K action decreased cPLA2α expression in PTEN-mutated or deleted prostate cancer cells. An increase in AKT phosphorylation elevated, whereas inhibition of AKT phosphorylation diminished, cPLA2α protein levels. pAKT had no influence on cPLA2α expression at mRNA levels but stabilized cPLA2α at protein levels by protecting it from degradation. Conversely, an induction of cPLA2α expression led to an increase in pAKT levels in PTEN-mutated or deleted prostate cancer cells, while silencing of cPLA2α expression or pharmacological blocking cPLA2α action decreased pAKT levels. The diminishment of pAKT by either genetic silencing or pharmacological blocking of cPLA2α was mitigated by the addition of arachidonic acid. The stimulatory effect of arachidonic acid on pAKT levels was lessened by inhibiting the production of arachidonic acid metabolites. These studies have revealed a link between oncogenic pathway and lipid metabolism and provided potential molecular targets for treating prostate cancer.

// Mu Yao 1, 2 , Chanlu Xie 1, 2, 3 , Mei-Yee Kiang 1, 2 , Ying Teng 1, 2 , David Harman 4 , Jessamy Tiffen 5, 6 , Qian Wang 5, 6 , Paul Sved 7 , Shisan Bao 8 , Paul Witting 8 , Jeff Holst 5, 6 , Qihan Dong 1, 2, 3 1 Department of Endocrinology, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia 2 Central Clinical School and Bosch Institute, The University of Sydney, Sydney, NSW 2006, Australia 3 School of Biomedical and Health Sciences, University of Western Sydney, Parramatta, NSW 2751, Australia 4 Molecular Medicine Research Group, University of Western Sydney, Parramatta, NSW 2751, Australia 5 Origins of Cancer Laboratory, Centenary Institute, Camperdown, NSW 2050, Australia 6 Sydney Medical School, The University of Sydney, Sydney, NSW 2006, Australia 7 Department of Urology, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia 8 Department of Pathology, The University of Sydney, Sydney, NSW 2006, Australia Correspondence to: Qihan Dong, e-mail: q.dong@uws.edu.au Mu Yao, e-mail: mu.yao@sydney.edu.au Keywords: prostate cancer, phospholipase A2α, cell cycle re-entry, p27, Skp2 Received: May 15, 2015 Accepted: September 14, 2015 Published: September 24, 2015 ABSTRACT Cell cycle re-entry of quiescent cancer cells has been proposed to be involved in cancer progression and recurrence. Cytosolic phospholipase A 2 α (cPLA 2 α) is an enzyme that hydrolyzes membrane glycerophospholipids to release arachidonic acid and lysophospholipids that are implicated in cancer cell proliferation. The aim of this study was to determine the role of cPLA 2 α in cell cycle re-entry of quiescent prostate cancer cells. When PC-3 and LNCaP cells were rendered to a quiescent state, the active form of cPLA 2 α with a phosphorylation at Ser 505 was lower compared to their proliferating state. Conversely, the phospho-cPLA 2 α levels were resurgent during the induction of cell cycle re-entry. Pharmacological inhibition of cPLA 2 α with Efipladib upon induction of cell cycle re-entry inhibited the re-entry process, as manifested by refrained DNA synthesis, persistent high proportion of cells in G 0 /G 1 and low percentage of cells in S and G 2 /M phases, together with a stagnant recovery of Ki-67 expression. Simultaneously, Efipladib prohibited the emergence of Skp2 while maintained p27 at a high level in the nuclear compartment during cell cycle re-entry. Inhibition of cPLA 2 α also prevented an accumulation of cyclin D1/CDK4, cyclin E/CDK2, phospho-pRb, pre-replicative complex proteins CDC6, MCM7, ORC6 and DNA synthesis-related protein PCNA during induction of cell cycle re-entry. Moreover, a pre-treatment of the prostate cancer cells with Efipladib during induction of cell cycle re-entry subsequently compromised their tumorigenic capacity in vivo . Hence, cPLA 2 α plays an important role in cell cycle re-entry by quiescent prostate cancer cells.

// Zhong Zheng 1,* , Xiangyi He 2,* , Chanlu Xie 3,6 , Sheng Hua 3 , Jianfang Li 4 , Tingfeng Wang 5 , Mu Yao 3 , Soma Vignarajan 3 , Ying Teng 3 , Leila Hejazi 3,6 , Bingya Liu 4 and Qihan Dong 3,6 1 Department of Gynecologic Oncology, Fudan University Shanghai Cancer Center, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China 2 Department of Gastroenterology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China 3 Central Clinical School and Bosch Institute, The University of Sydney and Department of Endocrinology and Sydney Cancer Centre, Royal Prince Alfred Hospital, Sydney, Australia 4 Shanghai Key Laboratory of Gastric Neoplasms, Department of Surgery, Shanghai Institute of Digestive Surgery, and Gastroenterology, Ruijin Hospital, Jiaotong University School of Medicine, Shanghai, China 5 Department of General Surgery, Nanhui Central Hospital. Shanghai, China 6 School of Science and Health, The University of Western Sydney, Australia * These authors contributed equally to this work Correspondence: Qihan Dong, email: // Bingya Liu, email: // Keywords : Cytosolic phospholipase A 2 α, AKT, Colorectal cancer, Efipladib Received : September 09, 2014 Accepted : October 28, 2014 Published : October 28, 2014 Abstract A constitutive activation of protein kinase B (AKT) in a hyper-phosphorylated status at Ser 473 is one of the hallmarks of anti-EGFR therapy-resistant colorectal cancer (CRC). The aim of this study was to examine the role of cytosolic phospholipase A 2 α (cPLA 2 α) on AKT phosphorylation at Ser 473 and cell proliferation in CRC cells with mutation in phosphoinositide 3-kinase (PI3K). AKT phosphorylation at Ser 473 was resistant to EGF stimulation in CRC cell lines of DLD-1 ( PIK3CA E545K mutation) and HT-29 ( PIK3CA P499T mutation). Over-expression of cPLA 2 α by stable transfection increased basal and EGF-stimulated AKT phosphorylation and proliferation in DLD-1 cells. In contrast, silencing of cPLA 2 α with siRNA or inhibition with Efipladib decreased basal and EGF-stimulated AKT phosphorylation and proliferation in HT-29. Treating animals transplanted with DLD-1 with Efipladib (10 mg/kg, i.p. daily) over 14 days reduced xenograft growth by >90% with a concomitant decrease in AKT phosphorylation. In human CRC tissue, cPLA 2 α expression and phosphorylation were increased in 63% (77/120) compared with adjacent normal mucosa determined by immunohistochemistry. We conclude that cPLA 2 α is required for sustaining AKT phosphorylation at Ser 473 and cell proliferation in CRC cells with PI3K mutation, and may serve as a potential therapeutic target for treatment of CRC resistant to anti-EGFR therapy.

// Soma Vignarajan 1 , Chanlu Xie 1,6 , Mu Yao 1 , Yuting Sun 2 , Ulla Simanainen 3 , Paul Sved 4 , Tao Liu 2,5 , Qihan Dong 1,6 1 Discipline of Endocrinology, Central Clinical School, Bosch Institute, Royal Prince Alfred Hospital, and Charles Perkins Centre, The University of Sydney, Sydney, NSW, Australia 2 Children’s Cancer Institute Australia for Medical Research, Sydney, Australia 3 ANZAC Research institute, The University of Sydney, Sydney, NSW, Australia 4 Sydney Cancer Centre, Royal Prince Alfred Hospital, Camperdown, NSW, Australia 5 School of Women’s and Children’s Health, UNSW Medicine, Sydney, Australia, Australia 6 School of Science and Health, The University of Western Sydney, Sydney, Australia Correspondence: Qihan Dong, email: // Keywords : cytosolic phospholipase A2, AKT, PTEN, prostate cancer Received : June 06, 2014 Accepted : July 07, 2014 Published : July 09, 2014 Abstract Aberrant increase in pAKT, due to a gain-of-function mutation of PI3K or loss-of-function mutation or deletion of PTEN, occurs in prostate cancer and is associated with poor patient prognosis. Cytosolic phospholipase A 2 α (cPLA 2 α) is a lipid modifying enzyme by catalyzing the hydrolysis of membrane arachidonic acid. Arachidonic acid and its metabolites contribute to survival and proliferation of prostate cancer cells. We examined whether AKT plays a role in promoting cPLA 2 α action in prostate cancer cells. We found a concordant increase in pAKT and cPLA 2 α levels in prostate tissue of prostate epithelial-specific PTEN -knockout but not PTEN -wide type mice. Restoration of PTEN expression or inhibition of PI3K action decreased cPLA 2 α expression in PTEN -mutated or deleted prostate cancer cells. An increase in AKT by Myr-AKT elevated cPLA 2 α protein levels, which could be diminished by inhibition of AKT phosphorylation without noticeable change in total AKT levels. pAKT levels had no influence on cPLA 2 α at mRNA levels but reduced cPLA 2 α protein degradation. Anti-AKT antibody co-immunoprecipitated cPLA 2 α and vice versa. Hence, AKT plays a role in enhancing cPLA 2 α protein stability in PTEN-null prostate cancer cells, revealing a link between oncogenic pathway and lipid metabolism.

Proliferating cell nuclear antigen (PCNA)-Associated Factor (PAF15) is a small protein containing a PCNA interacting motif and sequences for association with ubiquitin enzymes. In interaction with PCNA, PAF15 plays a key role in recruiting DNA replicative polymerase by double monoubiquitination at Lys(15) and Lys(24). Under DNA damage conditions, PAF15 regulates the switch from DNA replicative polymerase to translesion synthesis polymerase in order to bypass the replication-blocking lesions. Overexpression of PAF15 promotes the repair of ultraviolet-induced DNA damage and prevents cell death, whereas attenuation of PAF15 decreases DNA replication and cell survival. Ectopic expression of PAF15 in mouse fibroblasts increases colony formation and tumourigenicity. PAF15 is aberrantly increased in various human malignancies with poor prognosis. Collectively, PAF15 may contribute to carcinogenesis and represents one of the potential therapeutic targets in the treatment of cancer.

We have developed a blend of food extracts commonly consumed in the Mediterranean and East Asia, named blueberry punch (BBP), with the ultimate aim to formulate a chemoprevention strategy to inhibit prostate cancer progression in men on active surveillance protocol. We demonstrated previously that BBP inhibited prostate cancer cell proliferationin vitroandin vivo. The purpose of this study was to determine the molecular mechanism responsible for the suppression of prostate cancer cell proliferation by BBP. Treatment of lymph node-metastasised prostate cancer cells (LNCaP) and bone-metastasised prostate cancer cells (PC-3 and MDA-PCa-2b) with BBP (up to 0·8 %) for 72 h increased the percentage of cells at the G0/G1phase and decreased those at the S and G2/M phases. The finding was supported by the reduction in the percentage of Ki-67-positive cells and of DNA synthesis measured by the incorporation of 5-ethynyl-2′-deoxyuridine. Concomitantly, BBP treatment decreased the protein levels of phosphorylated retinoblastoma, cyclin D1 and E, cyclin-dependent kinase (CDK) 4 and 2, and pre-replication complex (CDC6 and MCM7) in LNCaP and PC-3 cells, whereas CDK inhibitor p27 was elevated in these cell lines. In conclusion, BBP exerts its anti-proliferative effect on prostate cancer cells by modulating the expression and phosphorylation of multiple regulatory proteins essential for cell proliferation.

Experimentation with the progenitor/stem cells in adult prostate epithelium can be inconvenient due to a tight time line from tissue acquisition to cell isolation and to downstream experiments. To circumvent this inconvenience, we developed a simple technical procedure for culturing epithelial cells derived from human prostate tissue. In this study, benign prostate tissue was enzymatically digested and fractionated into epithelium and stroma, which were then cultured in the medium designed for prostate epithelial and stromal cells, respectively. The cultured cells were analyzed by immunocytochemical staining and flow cytometry. Prostate tissue-regenerating capacity of cultured cells in vitro was determined by co-culturing epithelial and stromal cells in dihydrotestosterone-containing RPMI. Cell lineages in formed acini-like structures were determined by immunohistochemistry. The culture of epithelial cells mainly consisted of basal cells. A minor population was negative for known lineage markers and positive for CD133. The culture also contained cells with high activity of aldehyde dehydrogenase. After co-culturing with stromal cells, the epithelial cells were able to form acini-like structures containing multiple cell lineages. Thus, the established culture of prostate epithelial cells provides an alternative source for studying progenitor/stem cells of prostate epithelium.

Aberrant increase in protein kinase B (AKT) phosphorylation (pAKT), due to a gain-of-function mutation of phosphatidylinositol-3-kinase (PI3K) or loss-of-function mutation or deletion of phosphatase and tensin homolog (PTEN), is a common alteration in prostate cancer and associated with poor prognosis. Cytosolic phospholipase A2α (cPLA2α) is a lipid modifying enzyme by catalyzing the hydrolysis of arachidonic acid from membrane phospholipid. The released arachidonic acid and its metabolites contribute to survival and proliferation of prostate cancer cells. In this mini-review, we summarize the relationship between pAKT and cPLA2α in prostate cancer cells. There was a concordant increase in pAKT and cPLA2α levels in prostate tissue of prostate epithelial-specific PTEN-knockout mice compared to PTEN-wild type mice. Restoration of PTEN expression or inhibition of PI3K action decreased cPLA2α expression in PTEN-mutated or deleted prostate cancer cells. An increase in AKT phosphorylation elevated, whereas inhibition of AKT phosphorylation diminished, cPLA2α protein levels. pAKT had no influence on cPLA2α expression at mRNA levels but stabilized cPLA2α at protein levels by protecting it from degradation. Conversely, an induction of cPLA2α expression led to an increase in pAKT levels in PTEN-mutated or deleted prostate cancer cells, while silencing of cPLA2α expression or pharmacological blocking cPLA2α action decreased pAKT levels. The diminishment of pAKT by either genetic silencing or pharmacological blocking of cPLA2α was mitigated by the addition of arachidonic acid. The stimulatory effect of arachidonic acid on pAKT levels was lessened by inhibiting the production of arachidonic acid metabolites. These studies have revealed a link between oncogenic pathway and lipid metabolism and provided potential molecular targets for treating prostate cancer.

p27(Kip1) is an inhibitor of a broad spectrum of cyclin-dependent kinases (CDKs), and the loss of a single p27(Kip1) allele is thereby sufficient to increase tumor incidence via CDK-mediated cell cycle entry. As such, down-regulation of p27(Kip1) protein levels, in particular nuclear expressed p27(Kip1), is implicated in both disease progression and poor prognosis in a variety of cancers. p27(Kip1) expression is positively regulated by the transcription factor MENIN, and inhibited by oncogenic transcription factors MYC and PIM. However, regulation of p27(Kip1) protein expression and function is predominantly through post-translational modifications that alter both the cellular localization and the extent of E3 ubiquitin ligase-mediated degradation. Phosphorylation of p27(Kip1) at Thr(187) and Ser(10) is a prerequisite for its degradation via the E3 ubiquitin ligases SKP2 (nuclear) and KPC (cytoplasmic), respectively. Additionally, Ser(10) phosphorylated p27(Kip1) is predominantly localized in the cytoplasm due to the nuclear export protein CRM1. Another E3 ubiquitin ligase, PIRH2, degrades p27(Kip1) in both the cytoplasm and nucleus independent of phosphorylation state. As such, inhibition of cell cycle entry and progression in a variety of cancers may be achieved with therapies designed to correct p27(Kip1) localization and/or block its degradation.

The ubiquitin-conjugating enzymes 2C (UBE2C) is an integral component of the ubiquitin proteasome system. UBE2C consists of a conserved core domain containing the catalytic Cys residue and an N-terminal extension. The core domain is required for ubiquitin adduct formation by interacting with the ubiquitin-fold domain in the E1 enzyme, and contributes to the E3 enzyme binding. UBE2C N-terminal extension regulates E3 enzyme activity as a part of an intrinsic inhibitory mechanism. UBE2C is required for the destruction of mitotic cyclins and securin, which are essential for spindle assembly checkpoint and mitotic exit. The UBE2C mRNA and/or protein levels are aberrantly increased in many cancer types with poor clinical outcomes. Accumulation of UBE2C stimulates cell proliferation and anchorage-independent growth. UBE2C transgenic mice are prone to develop spontaneous tumors and carcinogen-induced tumor with evidence of chromosome aneuploidy.

Cell cycle re-entry by quiescent cancer cells is an important mechanism for cancer progression. While high levels of c-MYC expression are sufficient for cell cycle re-entry, the modality to block c-MYC expression, and subsequent cell cycle re-entry, is limited. Using reversible quiescence rendered by serum withdrawal or contact inhibition in PTENnull/p53WT (LNCaP) or PTENnull/p53mut (PC-3) prostate cancer cells, we have identified a compound that is able to impede cell cycle re-entry through c-MYC. Guttiferone K (GUTK) blocked resumption of DNA synthesis and preserved the cell cycle phase characteristics of quiescent cells after release from the quiescence. In vehicle-treated cells, there was a rapid increase in c-MYC protein levels upon release from the quiescence. However, this increase was inhibited in the presence of GUTK with an associated acceleration in c-MYC protein degradation. The inhibitory effect of GUTK on cell cycle re-entry was significantly reduced in cells overexpressing c-MYC. The protein level of FBXW7, a subunit of E3 ubiquitin ligase responsible for degradation of c-MYC, was reduced upon the release from the quiescence. In contrast, GUTK stabilized FBXW7 protein levels during release from the quiescence. The critical role of FBXW7 was confirmed using siRNA knockdown, which impaired the inhibitory effect of GUTK on c-MYC protein levels and cell cycle re-entry. Administration of GUTK, either in vitro prior to transplantation or in vivo, suppressed the growth of quiescent prostate cancer cell xenografts. Furthermore, elevation of FBXW7 protein levels and reduction of c-MYC protein levels were found in the xenografts of GUTK-treated compared with vehicle-treated mice. Hence, we have identified a compound that is capable of impeding cell cycle re-entry by quiescent PTENnull/p53WT and PTENnull/p53mut prostate cancer cells likely by promoting c-MYC protein degradation through stabilization of FBXW7. Its usage as a clinical modality to prevent prostate cancer progression should be further evaluated.

Active surveillance is an emerging management option for the rising number of men with low-grade, clinically localized prostate cancer. However, 30-40% of men on active surveillance will progress to high-grade disease over 5 y. With the ultimate aim of developing a food-based chemoprevention strategy to retard cancer progression in these otherwise healthy men, we have developed a blend of food extracts commonly consumed in Mediterranean countries and East Asia. The effect of the food extracts known as Blueberry Punch (BBP) on prostate cancer cell growth and key signaling pathways were examined in vitro and in vivo. BBP reduced prostate cancer cell growth in a dose-dependent manner (0.08-2.5%) at 72 h in vitro due to the reduction in cell proliferation and viability. Prostate cancer cell xenograft-bearing mice, administered 10% BBP in drinking water for 2 wk, had a 25% reduction in tumor volume compared with the control (water only). In vitro, BBP reduced protein concentrations in 3 signaling pathways necessary for the proliferation and survival of prostate cancer cells, namely androgen receptor, phospho-protein kinase B/protein kinase B, and phospho-cytosolic phospholipase A(2)alpha. The downstream effectors of these pathways, including prostate-specific antigen and glycogen synthase kinase 3beta, were also reduced. Thus, this palatable food supplement is a potential candidate for testing in clinical trials and may ultimately prove effective in retarding the progression of low-grade, early-stage prostate cancer in men managed by active surveillance.