Senescence In Prostate Cancer Research Articles

N6-methyladenosine-modified circRPS6KC1 regulated cellular senescence in prostate cancer via FOXM1/PCNA axis.

Prostate cancer (PCa) gradually becomes the most common cancer in men in many countries, of which circRNAs and methylated modification exert an essential role in PCa progression. However, the concrete mechanisms of N6-methyladenosine (m6A) modification of circRNAs in PCa remain unclear. In our study, we identified circRPS6KC1, a novel and up-regulated circular RNA in PCa, through circRNA sequencing. We discovered that METTL3 and YTHDF1 were involved in the m6A modification of circRPS6KC1 and the stabilization. Furthermore, we found that suppression of circRPS6KC1 contributed to cellular senescence in prostate cancer. CircRPS6KC1 acted as the miR-761 sponge to regulate the FOXM1 expression. FOXM1 mediated the transcription of PCNA and influenced the p21 degradation, which resulted in up-regulation of p21 protein in a p53-independent manner. In conclusion, our findings showed that N6-methyladenosine modification by METTL3 and YTHDF1 stabilized circRPS6KC1, and circRPS6KC1 played an essential role on cellular senescence via FOXM1/PCNA axis in prostate cancer.

Cellular senescence in metastatic prostate cancer: A therapeutic opportunity or challenge (Review).

The treatment of patients with metastatic prostate cancer (PCa) is considered to be a long‑standing challenge. Conventional treatments for metastatic PCa, such as radical prostatectomy, radiotherapy and androgen receptor‑targeted therapy, induce senescence of PCa cells to a certain extent. While senescent cells can impede tumor growth through the restriction of cell proliferation and increasing immune clearance, the senescent microenvironment may concurrently stimulate the secretion of a senescence‑associated secretory phenotype and diminish immune cell function, which promotes PCa recurrence and metastasis. Resistance to established therapies is the primary obstacle in treating metastatic PCa as it can lead to progression towards an incurable state of disease. Therefore, understanding the molecular mechanisms that underly the progression of PCa is crucial for the development of novel therapeutic approaches. The present study reviews the phenomenon of treatment‑induced senescence in PCa, the dual role of senescence in PCa treatments and the mechanisms through which senescence promotes PCa metastasis. Furthermore, the present review discusses potential therapeutic strategies to target the aforementioned processes with the aim of providing insights into the evolving therapeutic landscape for the treatment of metastatic PCa.

A GATA2-CDC6 axis modulates androgen receptor blockade-induced senescence in prostate cancer

BackgroundProstate cancer is a major cause of cancer morbidity and mortality in men worldwide. Androgen deprivation therapy (ADT) has proven effective in early-stage androgen-sensitive disease, but prostate cancer gradually develops into an androgen-resistant metastatic state in the vast majority of patients. According to our oncogene-induced model for cancer development, senescence is a major tumor progression barrier. However, whether senescence is implicated in the progression of early-stage androgen-sensitive to highly aggressive castration-resistant prostate cancer (CRPC) remains poorly addressed.MethodsAndrogen-dependent (LNCaP) and –independent (C4-2B and PC-3) cells were treated or not with enzalutamide, an Androgen Receptor (AR) inhibitor. RNA sequencing and pathway analyses were carried out in LNCaP cells to identify potential senescence regulators upon treatment. Assessment of the invasive potential of cells and senescence status following enzalutamide treatment and/or RNAi-mediated silencing of selected targets was performed in all cell lines, complemented by bioinformatics analyses on a wide range of in vitro and in vivo datasets. Key observations were validated in LNCaP and C4-2B mouse xenografts. Senescence induction was assessed by state-of-the-art GL13 staining by immunocytochemistry and confocal microscopy.ResultsWe demonstrate that enzalutamide treatment induces senescence in androgen-sensitive cells via reduction of the replication licensing factor CDC6. Mechanistically, we show that CDC6 downregulation is mediated through endogenous activation of the GATA2 transcription factor functioning as a CDC6 repressor. Intriguingly, GATA2 levels decrease in enzalutamide-resistant cells, leading to CDC6 stabilization accompanied by activation of Epithelial-To-Mesenchymal Transition (EMT) markers and absence of senescence. We show that CDC6 loss is sufficient to reverse oncogenic features and induce senescence regardless of treatment responsiveness, thereby identifying CDC6 as a critical determinant of prostate cancer progression.ConclusionsWe identify a key GATA2-CDC6 signaling axis which is reciprocally regulated in enzalutamide-sensitive and -resistant prostate cancer environments. Upon acquired resistance, GATA2 repression leads to CDC6 stabilization, with detrimental effects in disease progression through exacerbation of EMT and abrogation of senescence. However, bypassing the GATA2-CDC6 axis by direct inhibition of CDC6 reverses oncogenic features and establishes senescence, thereby offering a therapeutic window even after acquiring resistance to therapy.

Orphan receptors in prostate cancer.

The identification of new cellular receptors has been increasing rapidly. A receptor is called "orphan" if an endogenous ligand has not been identified yet. Here we review receptors that contribute to prostate cancer and are considered orphan or partially orphan. This means that the full spectrum of their endogenous ligands remains unknown. The orphan receptors are divided into two major families. The first group includes G protein-coupled receptors. Most are orphan olfactory receptors. OR51E1 inhibits cell proliferation and induces senescence in prostate cancer. OR51E2 inhibits prostate cancer growth, but promotes invasiveness and metastasis. GPR158, GPR110, and GPCR-X play significant roles in prostate cancer development and progression. However, GPR160 induces cell cycle arrest and apoptosis. The other major subset of orphan receptors are nuclear receptors. Receptor-related orphan receptor α (RORα) inhibits tumor growth, but RORγ stimulates androgen receptor signaling. PXR contributes to metabolic deactivation of androgens and inhibits cell proliferation. TLX has protumorigenic effects in prostate cancer, while its knockdown triggers cellular senescence and growth arrest. Estrogen-related receptor ERRγ can inhibit tumor growth but ERRα is protumorigenic. Dax1 and short heterodimeric partner are also inhibitory in prostate cancer. There is a "zoo" of relatively underappreciated orphan receptors that play key roles in prostate cancer.

Senescence in prostate cancer: is there sufficient evidence to move forward?

Senescence in prostate cancer: is there sufficient evidence to move forward?

Organelle homeostasis principles: How organelle quality control and inter-organelle crosstalk promote cell survival.

To survive, cells sense their surroundings and adapt to enable homeostasis. Studies dissecting this process reveal organizational principles, including quality-control pathways, changes to organelle shape, and inter-organelle communication, that facilitate metabolic or developmental remodeling. In this issue, several reviews discuss these organelle homeostasis principles and how they are altered in disease.

TIMP1 Determines the Effects of Cellular Senescence in Prostate Cancer.

Timp1 status in Pten-null prostate cancer cells dictated whether senescence was detrimental in vivo.

Senescence Reprogramming by TIMP1 Deficiency Promotes Prostate Cancer Metastasis

Metastases account for most cancer-related deaths, yet the mechanisms underlying metastatic spread remain poorly understood. Recent evidence demonstrates that senescent cells, while initially restricting tumorigenesis, can induce tumor progression. Here, we identify the metalloproteinase inhibitor TIMP1 as a molecular switch that determines the effects of senescence in prostate cancer. Senescence driven either by PTEN deficiency or chemotherapy limits the progression of prostate cancer in mice. TIMP1 deletion allows senescence to promote metastasis, and elimination of senescent cells with a senolytic BCL-2 inhibitor impairs metastasis. Mechanistically, TIMP1 loss reprograms the senescence-associated secretory phenotype (SASP) of senescent tumor cells through activation of matrix metalloproteinases (MMPs). Loss of PTEN and TIMP1 in prostate cancer is frequent and correlates with resistance to docetaxel and worst clinical outcomes in patients treated in an adjuvant setting. Altogether, these findings provide insights into the dual roles of tumor-associated senescence and can potentially impact the treatment of prostate cancer.

Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer.

The androgen receptor (AR) plays a leading role in the control of prostate cancer (PCa) growth. Interestingly, structurally different AR antagonists with distinct mechanisms of antagonism induce cell senescence, a mechanism that inhibits cell cycle progression, and thus seems to be a key cellular response for the treatment of PCa. Surprisingly, while physiological levels of androgens promote growth, supraphysiological androgen levels (SAL) inhibit PCa growth in an AR-dependent manner by inducing cell senescence in cancer cells. Thus, oppositional acting ligands, AR antagonists, and agonists are able to induce cellular senescence in PCa cells, as shown in cell culture model as well as ex vivo in patient tumor samples. This suggests a dual AR-signaling dependent on androgen levels that leads to the paradox of the rational to keep the AR constantly inactivated in order to treat PCa. These observations however opened the option to treat PCa patients with AR antagonists and/or with androgens at supraphysiological levels. The latter is currently used in clinical trials in so-called bipolar androgen therapy (BAT). Notably, cellular senescence is induced by AR antagonists or agonist in both androgen-dependent and castration-resistant PCa (CRPC). Pathway analysis suggests a crosstalk between AR and the non-receptor tyrosine kinase Src-Akt/PKB and the PI3K-mTOR-autophagy signaling in mediating AR-induced cellular senescence in PCa. In this review, we summarize the current knowledge of therapeutic induction and intracellular pathways of AR-mediated cellular senescence.

DNA Damage- But Not Enzalutamide-Induced Senescence in Prostate Cancer Promotes Senolytic Bcl-xL Inhibitor Sensitivity.

Cellular senescence is a natural tumor suppression mechanism defined by a stable proliferation arrest. In the context of cancer treatment, cancer cell therapy-induced senescence (TIS) is emerging as an omnipresent cell fate decision that can be pharmacologically targeted at the molecular level to enhance the beneficial aspects of senescence. In prostate cancer (PCa), TIS has been reported using multiple different model systems, and a more systematic analysis would be useful to identify relevant senescence manipulation molecular targets. Here we show that a spectrum of PCa senescence phenotypes can be induced by clinically relevant therapies. We found that DNA damage inducers like irradiation and poly (ADP-ribose) polymerase1 (PARP) inhibitors triggered a stable PCa-TIS independent of the p53 status. On the other hand, enzalutamide triggered a reversible senescence-like state that lacked evidence of cell death or DNA damage. Using a small senolytic drug panel, we found that senescence inducers dictated senolytic sensitivity. While Bcl-2 family anti-apoptotic inhibitor were lethal for PCa-TIS cells harboring evidence of DNA damage, they were ineffective against enzalutamide-TIS cells. Interestingly, piperlongumine, which was described as a senolytic, acted as a senomorphic to enhance enzalutamide-TIS proliferation arrest without promoting cell death. Overall, our results suggest that TIS phenotypic hallmarks need to be evaluated in a context-dependent manner because they can vary with senescence inducers, even within identical cancer cell populations. Defining this context-dependent spectrum of senescence phenotypes is key to determining subsequent molecular strategies that target senescent cancer cells.

Senolytic compounds control a distinct fate of androgen receptor agonist- and antagonist-induced cellular senescent LNCaP prostate cancer cells

BackgroundThe benefit of inducing cellular senescence as a tumor suppressive strategy remains questionable due to the senescence-associated secretory phenotype. Hence, studies and development of senolytic compounds that induce cell death in senescent cells have recently emerged. Senescent cells are hypothesized to exhibit different upregulated pro-survival/anti-apoptotic networks depending on the senescent inducers. This might limit the effect of a particular senolytic compound that targets rather only a specific pathway. Interestingly, cellular senescence in prostate cancer (PCa) cells can be induced by either androgen receptor (AR) agonists at supraphysiological androgen level (SAL) used in bipolar androgen therapy or by AR antagonists. This challenges to define ligand-specific senolytic compounds.ResultsHere, we first induced cellular senescence by treating androgen-sensitive PCa LNCaP cells with either SAL or the AR antagonist Enzalutamide (ENZ). Subsequently, cells were incubated with the HSP90 inhibitor Ganetespib (GT), the Bcl-2 family inhibitor ABT263, or the Akt inhibitor MK2206 to analyze senolysis. GT and ABT263 are known senolytic compounds. We observed that GT exhibits senolytic activity specifically in SAL-pretreated PCa cells. Mechanistically, GT treatment results in reduction of AR, Akt, and phospho-S6 (p-S6) protein levels. Surprisingly, ABT263 lacks senolytic effect in both AR agonist- and antagonist-pretreated cells. ABT263 treatment does not affect AR, Akt, or S6 protein levels. Treatment with MK2206 does not reduce AR protein level and, as expected, potently inhibits Akt phosphorylation. However, ENZ-induced cellular senescent cells undergo apoptosis by MK2206, whereas SAL-treated cells are resistant. In line with this, we reveal that the pro-survival p-S6 level is higher in SAL-induced cellular senescent PCa cells compared to ENZ-treated cells. These data indicate a difference in the agonist- or antagonist-induced cellular senescence and suggest a novel role of MK2206 as a senolytic agent preferentially for AR antagonist-treated cells.ConclusionTaken together, our data suggest that both AR agonist and antagonist induce cellular senescence but differentially upregulate a pro-survival signaling which preferentially sensitize androgen-sensitive PCa LNCaP cells to a specific senolytic compound.

Deacetylation of LAMP1 drives lipophagy-dependent generation of free fatty acids by Abrus agglutinin to promote senescence in prostate cancer.

Therapy-induced senescence in cancer cells is an irreversible antiproliferative state, which inhibits tumor growth and is therefore a potent anti-neoplastic mechanism. In this study, low doses of Abrus agglutinin (AGG)-induced senescence through autophagy in prostate carcinoma cells (PC3) and inhibited proliferation. The inhibition of autophagy with 3-methyl adenine reversed AGG-induced senescence, thus confirming that AGG-triggered senescence required autophagy. AGG treatment also led to lipophagy-mediated accumulation of free fatty acids (FFAs), with a concomitant decrease in the number of lipid droplets. Lalistat, a lysosomal acid lipase inhibitor, abrogated AGG-induced lipophagy and senescence in PC3 cells, indicating that lipophagy is essential for AGG-induced senescence. The accumulation of FFAs increased reactive oxygen species generation, a known facilitator of senescence, which was also reduced in the presence of lalistat. Furthermore, AGG upregulated silent mating type information regulator 2 homolog 1 (SIRT1), while the presence of sirtinol reduced autophagy flux and the senescent phenotype in the AGG-treated cells. Mechanistically, AGG-induced cytoplasmic SIRT1 deacetylated a Lys residue on the cytoplasmic domain of lysosome-associated membrane protein 1 (LAMP1), an autolysosomal protein, resulting in lipophagy and senescence. Taken together, our findings demonstrate a novel SIRT1/LAMP1/lipophagy axis mediating AGG-induced senescence in prostate cancer cells.

Abstract 3634: Tannic acid-docetaxel scaffold nanoparticles for improved prostate cancer therapy

Abstract Purpose: Prostate cancer (PrCa) is one of the leading causes of cancer-related deaths among men in the United States. Chemotherapy with docetaxel holds great promise and important therapeutic option for PrCa treatment. However, chemotherapy is often associated with incomplete cell death and leads to persistent senescent phenotype. Such phenotypic cancer cells survive and promotes tumor development, recurrence, and drug resistance. Altogether, targeting these cells can enhance chemotherapy outcomes. In the current study, we established a tannic acid-docetaxel scaffold nanoparticles (TDS NP) platform that allows for facile targeting and inhibition of drug induced senescence in prostate cancer. Methods: TDS NP were prepared by solvent evaporation and extrusion process using a series of tannic acid and docetaxel weight ratios. The scaffold self-assembly formation was determined using a steady-state fluorescence quenching, FT-IR, XRD, DSC, and TGA. The surface and morphological properties of TDS NPs were determined by dynamic light scattering and transmission electron microscopy. The biocompatibility assessment was characterized by hemolysis assay. C4-2 and PC-3 cell lines were used as PrCa model systems for in vitro and in vivo studies. The cellular internalization (in vitro) and accumulation (in vivo) was examined using dye-tagged TDS NPs. The superior in vitro anti-cancer and metastatic potential of TDS NPs were evaluated using proliferation, colony formation, migration, invasion, and immunoblotting assays. The anti-senescence ability of TDS NPs was examined through β-Galactosidase Staining Kit. A PC-3 xenograft mouse model was used to examine its superior therapeutic activity over free docetaxel treatment. Results: A series of physico-chemical analyses confirmed the integrity of TDS NP. An optimized formulation exhibited a spherical shape particle formulation with 124.13 ± 2.16 nm with a negative zeta potential of -14.0 mV. TDS NPs formulation exhibited superior internalization capacity in PrCa cells in a dose- and time-dependent manner. In vitro functional studies confirm superior therapeutic activity of TDS NPs over free docetaxel treatment. Enhanced pro-apoptotic while downregulating anti-apoptotic effects with treatment of TDS NPs in comparison to native drug. A profound inhibition of β-galactosidase activity was noticed with TDS NPs treatment. In vivobiodistribution studies confirm efficient accumulation of TDS NPs in mice. In addition, TDS NPs showed robust antitumor activity against PC-3 xenografts. Such improved activity was correlated with increased inhibition of senescence and induced apoptosis. Conclusion: In summary, we developed a novel tannic acid-docetaxel scaffold nanoparticle formulation that is capable of inhibiting senescence, minimizing drug resistance, and inducing apoptosis in prostate cancer. Citation Format: Prashanth Kumar Bhusetty Nagesh, Pallabita Chowdhury, Elham Hatami, Sonam Kumari, Vivek Kumar Kashyap, Bilal Hafeez, Sheema Khan, Manish Kumar Tripathi, Meena Jaggi, Subhash C. Chauhan, Murali M. Yallapu. Tannic acid-docetaxel scaffold nanoparticles for improved prostate cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3634.

Downregulation of miR-130b~301b cluster is mediated by aberrant promoter methylation and impairs cellular senescence in prostate cancer

BackgroundNumerous DNA-damaging cellular stresses, including oncogene activation and DNA-damage response (DDR), may lead to cellular senescence. Previous observations linked microRNA deregulation with altered senescent patterns, prompting us to investigate whether epigenetic repression of microRNAs expression might disrupt senescence in prostate cancer (PCa) cells.MethodsDifferential methylation mapping in prostate tissues was carried using Infinium HumanMethylation450 BeadChip. After validation of methylation and expression analyses in a larger series of prostate tissues, the functional role of the cluster miR-130b~301b was explored using in vitro studies testing cell viability, apoptosis, invasion and DNA damage in prostate cancer cell lines. Western blot and RT-qPCR were performed to support those observations.ResultsWe found that the miR-130b~301b cluster directs epigenetic activation of cell cycle inhibitors required for DDR activation, thus stimulating the senescence-associated secretory phenotype (SASP). Furthermore, overexpression of miR-130b~301b cluster markedly reduced the malignant phenotype of PCa cells.ConclusionsAltogether, these data demonstrate that miR-130b~301b cluster overexpression might effectively induce PCa cell growth arrest through epigenetic regulation of proliferation-blocking genes and activation of cellular senescence.

MP55-11 SYNTHETIC LETHAL METABOLIC TARGETING OF CELLULAR SENESCENCE IN PROSTATE CANCER WITH METFORMIN

You have accessJournal of UrologyProstate Cancer: Basic Research III1 Apr 2015MP55-11 SYNTHETIC LETHAL METABOLIC TARGETING OF CELLULAR SENESCENCE IN PROSTATE CANCER WITH METFORMIN Michael L. Blute, Bing Yang, Nathan Damaschke, Dudley Lamming, F. Michael Hoffman, and David F. Jarrard Michael L. BluteMichael L. Blute More articles by this author , Bing YangBing Yang More articles by this author , Nathan DamaschkeNathan Damaschke More articles by this author , Dudley LammingDudley Lamming More articles by this author , F. Michael HoffmanF. Michael Hoffman More articles by this author , and David F. JarrardDavid F. Jarrard More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.2054AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Cellular senescence occurs in response to sub-lethal stress after androgen deprivation therapy, radiation and chemotherapy whereby cells exit the cell cycle and develop distinct morphologic and biochemical characteristics. Senescence is a therapeutic approach, however potentially deleterious consequences make elimination of these cells important. The objective of this study was to determine whether the increased gluconeogenesis induced during senescence could be exploited to synergistically eliminate PCa cells using metformin (Met), an oral biguanide hyperglycemic approved for type II diabetes. METHODS High throughput screening of small molecule collections identified two novel robust senescence inducing agents, AZQ (diaziquone) a quinone and AZD5438 a novel CDK inhibitor. Senescence was confirmed using beta-galactosidase staining, cell arrest and increased size by flow cytometry. mTOR a serine-threonine protein kinase activity was evaluated using western. PCa cells were seeded on 96-well plates, low(L) and high(H) AZQ (0.1 and 0.25 microM) or AZD 5438 (0.1 and 0.4 microM) concentrations administered and after 3 days of senescence induction Met (1 and 5mM) added. Cells were collected 24 and 72h later and stained with Hoechts to evaluate the cell number. CalcuSyn software (Biosoft, Cambridge, UK) modeled synergism. RESULTS AZQ and AZD robustly increased beta-galactosidase staining, cell size and p27 and p16 induction in Du145, PC3, PPC1 cell lines. mTOR signaling through mTOR complex 1 significantly increased in AZQ-induced senescent cells. Used alone, AZD(L) and AZQ(L) demonstrate a 30% reduction in cell number and Met(L) alone 18%. Met after senescence induction (72h) decreased cell number 70% and 55% (AZD and AZQ respectively). CalcuSyn calculations revealed moderate synergistic effects with combinations of either AZD(H) or AZQ (L and H) and Met(L and H) at 24hr. A strong synergistic decrease in cell viability was demonstrated at 72h with AZQ(H) and Met(L) (CI= 0.267). CONCLUSIONS Senescent cells targeted by metformin may offer an alternative treatment strategy for removing castrate-resistant PCa cells. Increased gluconeogenesis during senescence represents a novel ‘Achilles heel’ for these dormant/arrested cancer cells. mTOR activity is activated during the conversion of cells to senescence, and Met inhibition of this pathway is a putative mechanism. Our results suggest that combination treatment with a senescence-inducing drug and metformin may be a feasible targeted therapeutic approach. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e677 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Michael L. Blute More articles by this author Bing Yang More articles by this author Nathan Damaschke More articles by this author Dudley Lamming More articles by this author F. Michael Hoffman More articles by this author David F. Jarrard More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Orphan nuclear receptor TLX functions as a potent suppressor of oncogene-induced senescence in prostate cancer via its transcriptional co-regulation of the CDKN1A (p21(WAF1) (/) (CIP1) ) and SIRT1 genes.

Oncogene-induced senescence is an important tumour-suppressing mechanism to prevent both premalignant transformation and cancer progression. Overcoming this process is a critical step in early cancer development. The druggable orphan nuclear receptor TLX (NR2E1) is characterized as an important regulator of neural stem cells and is also implicated in the development of some brain tumours. However, its exact functional roles in cancer growth regulation still remain unclear. Here we report that TLX can act as a promoter of tumourigenesis in prostate cancer by suppressing oncogene-induced senescence. We determined that TLX exhibited an increased expression in high-grade prostate cancer tissues and many prostate cancer cell lines. Functional studies revealed that TLX could perform an oncogenic function in prostate cancer cells, as its knockdown triggered cellular senescence and cell growth arrest in vitro and in vivo, whereas its over-expression promoted the malignant growth of prostate cancer cells. Furthermore, enhancement of TLX activity, by either ectopic expression or ligand stimulation, could potently prevent doxorubicin-induced senescence in prostate cancer cells and also allow prostatic epithelial cells to escape oncogene-induced senescence induced either by activated oncogene H-Ras(G12V) or knockdown of tumour suppressor PTEN, via a mechanism of direct but differential transcriptional regulation of two senescence-associated genes, repression of CDKN1A and transactivation of SIRT1. Together, our present study shows, for the first time, that TLX may play an important role in prostate carcinogenesis through its suppression of oncogene-induced senescence, and also suggests that targeting the senescence-regulatory TLX is of potential therapeutic significance in prostate cancer.

Induction of DNA damage and p21-dependent senescence by Riccardin D is a novel mechanism contributing to its growth suppression in prostate cancer cells in vitro and in vivo

Our previous studies had shown that Riccardin D (RD) exhibited cytotoxic effects by induction of apoptosis and inhibition of angiogenesis and topoisomerase II. Here, we reported that apoptosis is not the sole mechanism by which RD inhibits tumor cell growth because low concentrations of RD caused cellular senescence in prostate cancer (PCa) cells. Low concentrations of RD were used to treat PCa cells in vitro and in vivo, and senescence-associated β-galactosidase activity, DNA damage response markers, and/or colony-forming ability, cell cycle were analyzed, respectively. We then used siRNA knockdown to identify key factor in RD-triggered cellular senescence. RD treatment caused growth arrest at G0/G1 phase with features of cellular senescence phenotype such as enlarged and flattened morphology, increased senescence-associated-beta-galactosidase staining cells, and decreased cell proliferation in PCa cells. Induction of cellular senescence by RD occurred through activation of DNA damage response including increases in the phosphor-H2AX, inactivation of Chk1/2, and suppression of repair-related Ku70/86 and phosphor-BRCA1 in PCa cells in vitro and in vivo. Analysis of expression levels of p53, p21(CIP1), p16(INK4a), p27(KIP1), pRb and E2F1 and genetic knockdown of p21(CIP1) demonstrated an important role of p21(CIP1) in RD-triggered cellular senescence. Involvement of the DNA damage response and p21(CIP1) defines a novel mechanism of RD action and indicates that RD could be further developed as a promising anticancer agent for cancer therapy.

Decreased Skp2 Expression Is Necessary but Not Sufficient for Therapy-Induced Senescence in Prostate Cancer

Therapy-induced senescence (TIS), a cytostatic stress response in cancer cells, is induced inefficiently by current anticancer agents and radiation. The mechanisms that mediate TIS in cancer cells are not well defined. Herein, we characterize a robust senescence response both in vitro and in vivo to the quinone diaziquone (AZQ), previously identified in a high-throughput senescence-induction small-molecule screen. Using AZQ and several other agents that induce senescence, we screened a series of cyclin-dependent kinase inhibitors and found that p27(Kip1) was induced in all investigated prostate cancer cell lines. The ubiquitin-ligase Skp2 negatively regulates p27(Kip1) and, during TIS, is translocated to the cytoplasm before its expression is decreased in senescent cells. Overexpression of Skp2 blocks the effects of AZQ on senescence and p27(Kip1) induction. We also find that stable long-term short hairpin RNA knockdown of Skp2 decreases proliferation but does not generate the complete senescence phenotype. We conclude that Skp2 participates in regulating TIS but, alone, is insufficient to induce senescence in cancer cells.

The senescence pathway in prostatic carcinogenesis

Prostate cancer is a disease of the old and with increasing life expectancy, its incidence will continue to increase in the future. Control of prostate cancer has involved androgen ablation as a routine form of therapy. However, after an initial response, therapy-resistant clones can appear and result in cancer progression and metastasis with high mortality. The precise mechanisms for the development of androgen resistance are yet uncertain. It appears to be multi-factorial and relates not only to newly acquired genomic capabilities of the cancer cells but also to their interaction with their microenvironment. Overcoming cellular senescence is essential for oncogenesis. Although it seems to be a protective response for normal cells to avoid malignant transformation, senescence can on the other hand promote tumour progression. Interaction of senescent cancer cells with their microenvironment may be the key link to survival or regression of neoplastic cells. Hence, there is speculation that senescence may be a useful new target for therapy in the future. We review the role of senescence in prostate cancer and the effect of tumour microenvironment on androgen resistance.

1185 SENESCENCE AS CYTOSTATIC THERAPY: DRUG-INDUCED SENESCENCE IN PROSTATE CANCER CELLS REQUIRES SKP2-REGULATED P27KIP1 EXPRESSION

You have accessJournal of UrologyProstate Cancer: Basic Research VI1 Apr 20101185 SENESCENCE AS CYTOSTATIC THERAPY: DRUG-INDUCED SENESCENCE IN PROSTATE CANCER CELLS REQUIRES SKP2-REGULATED P27KIP1 EXPRESSION Jonathan Ewald, Josh Desotelle, F. Michael Hoffman, and David Jarrard Jonathan EwaldJonathan Ewald More articles by this author , Josh DesotelleJosh Desotelle More articles by this author , F. Michael HoffmanF. Michael Hoffman More articles by this author , and David JarrardDavid Jarrard More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.686AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Traditional approaches to cancer treatment have relied on cytotoxic strategies. In contrast, cellular senescence is a terminal cytostatic phenotype induced in normal and transformed cells by stress. Drug-induced senescence in cancer may provide an effective therapeutic alternative to cytotoxic treatments by reducing toxicity and immune stimulation. The development of senescence for therapy has been hindered by a lack of compounds that efficiently induce this response in cancer as well as defined molecular pathways. METHODS We utilized a novel high-throughput whole cell assay to screen for agents from a 4600 compound library that induce senescence based on growth arrest, senescence-associated β-galactosidase(SA-β-gal) staining, and morphology(JBS 30;2009). We then examined AZQ-induced senescence in prostate cancer cell lines in vitro and DU145 xenograft tumors in vivo, monitoring cell/tumor growth, viability, and senescence. The role of cyclin-dependent kinase inhibitors (CDKI) inhibitors was tested in senescence. RESULTS The quinone diazequone(AZQ) was selected as a lead compound for its ability to induce senescence at low concentrations. In multiple prostate cancer cell lines, AZQ induced a terminal growth arrest, SA-β-gal and other senescence markers (Glb2, Cspg2 and BRAK). In all cell lines a consistent accumulation of the CDKI p27kip1 was identified with AZQ-induced senescence. The induction of p27kip1 resulted from decreased ubiquitylation mediated primarily by decreased Skp2, a ubiquitin ligase. Skp2 loss of expression was found after exposure to AZQ and other senescence-inducing compounds including doxorubicin and 5-azacytidine. Knockdown of Skp2 by siRNA in DU145 and PC3 cells increased p27Kip1 expression and decreased proliferation after 72 hours, while enforced expression of Skp2 disrupts the growth-inhibitory effects of AZQ. AZQ was found to be a potent inducer of senescence in prostate cancer xenografts and generated improved survival compared to controls(14 vs 8wk; p<0.5) with minimal side effects. CONCLUSIONS A novel high-throughput screen has generated a potent lead compound for further development. AZQ is a novel agent that induces senescence growth arrest in prostate cancer cells both in vitro and in xenograft tumors. Moreover, Skp2-regulated expression of p27Kip1 is a novel pathway regulating chemically-induced senescence in cancer. Madison, WI© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e459 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Jonathan Ewald More articles by this author Josh Desotelle More articles by this author F. Michael Hoffman More articles by this author David Jarrard More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...