Overcoming prostate cancer drug resistance with a novel organosilicon small molecule

A major challenge to the treatment of advanced prostate cancer (PCa) is the development of resistance to androgen-deprivation therapy (ADT) and chemotherapy. It is imperative to discover effective therapies to overcome drug resistance and improve clinical outcomes. We have developed a novel class of silicon-containing compounds and evaluated the anticancer activities and mechanism of action using cellular and animal models of drug-resistant PCa. Five organosilicon compounds were evaluated for their anticancer activities in the NCI-60 panel and established drug-resistant PCa cell lines. GH1504 exhibited potent in vitro cytotoxicity in a broad spectrum of human cancer cells, including PCa cells refractory to ADT and chemotherapy. Molecular studies identified several potential targets of GH1504, most notably androgen receptor (AR), AR variant 7 (AR-v7) and survivin. Mechanistically, GH1504 may promote the protein turnover of AR, AR-v7 and survivin, thereby inducing apoptosis in ADT-resistant and chemoresistant PCa cells. Animal studies demonstrated that GH1504 effectively inhibited the in vivo growth of ADT-resistant CWR22Rv1 and chemoresistant C4-2B-TaxR xenografts in subcutaneous and intraosseous models. These preclinical results indicated that GH1504 is a promising lead that can be further developed as a novel therapy for drug-resistant PCa.     

2-arachidonoylglycerol: a novel inhibitor of androgen-independent prostate cancer cell invasion

Endocannabinoids have been implicated in cancer. Increasing endogenous 2-arachidonoylglycerol (2-AG) by blocking its metabolism inhibits invasion of androgen-independent prostate cancer (PC-3 and DU-145) cells. Noladin ether (a stable 2-AG analog) and exogenous CB1 receptor agonists possess similar effects. Conversely, reducing endogenous 2-AG by inhibiting its synthesis or blocking its binding to CB1 receptors with antagonists increases the cell invasion. 2-AG and noladin ether decrease protein kinase A activity in these cells, indicating coupling of the CB1 receptor to downstream effectors. The results suggest that cellular 2-AG, acting through the CB1 receptor, is an endogenous inhibitor of invasive prostate cancer cells.     

Didox (a novel ribonucleotide reductase inhibitor) overcomes Bcl-2 mediated radiation resistance in prostate cancer cell line PC-3

In this study, we investigated the influence of Bcl-2 overexpression on the radiosensitizing potential of Didox (DX; 3,4-Dihydroxybenzohydroxamic acid), a novel ribonucleotide reductase inhibitor, in p53-null prostate cancer cell line PC-3. The PC-3 cells were transfected with vector alone or ectopically overexpressed with CMV-Bcl-2 construct. The effect of radiation (IR) or DX alone and in combination (pre and post IR exposure of DX) on cell survival was determined by colony-forming assay. The impact of these two treatments on the cell cycle was determined by flow cytometry. To further understand the molecular mechanism of DX-mediated radiosensitization, induction of pro-survival and pro-apoptotic factors were determined by Western blot and gel-shift assays respectively. When compared to PC-3/Bcl-2 cells (SF(2)=0.84; D(0)=437cGy), the PC-3/vector cells (SF(2)=0.4; D(0)=235cGy) were significantly sensitive to ionizing radiation (p<0.001). Exposure of DX at 5 microM concentration prior or post to radiation in both PC-3/vector and PC-3/Bcl-2 transfectants caused an increase in radiation enhancement ratios. A significant reduction in G(2)M phase was observed in cells exposed to DX post IR when compared to cells exposed to IR alone. Exposure to DX after radiation in PC-3/vector significantly abrogated radiation-induced Bcl-2 upregulation, with a concomitant induction of bax protein. In PC-3/Bcl-2 transfectants, DX exposure after IR caused an induction of bax protein. Gel shift assays indicated that in PC-3/vector cells when exposed to IR caused an induction of NFkappa-B activity however, DX down regulated the NFkappa-B activity. Radiation-induced NFkappa-B activity was abrogated in pre and post DX exposure in combination with IR. These findings indicate that DX mediates a potent radiosensitizing effect in p53 null prostate cancer cells by overcoming radiation induced NFkappa-B activity and Bcl-2 expression.     

Identification of novel NRAGE involved in the radioresistance of esophageal cancer cells

Tumor Biology - Radiotherapy (RT) is one main method for the treatment of esophageal squamous cell carcinoma (ESCC), and the radioresistance is the predominant cause of patients with local...     

Adenoviral-mediated PTEN transgene expression sensitizes Bcl-2-expressing prostate cancer cells to radiation

Bcl-2 is associated with resistance to radiotherapy in prostate cancer. It was recently demonstrated that transduction of LNCaP prostate cells with the PTEN gene resulted in Bcl-2 downregulation. We hypothesized that forced expression of PTEN in prostate cancer cells would sensitize cells to radiation, downregulate Bcl-2 expression, and potentiate the G2M block induced by radiation. Four cell lines - PC-3-Bcl-2 (Bcl-2 overexpression, deleted PTEN), PC-3-Neo (wild-type Bcl-2, deleted PTEN), LNCaP (Bcl-2 overexpression, deleted PTEN), and DU-145 (wild-type Bcl-2 and PTEN) - were transduced with a recombinant adenovirus-5 vector expressing the human wild-type PTEN cDNA under the control of a human cytomegalovirus promoter (Ad-MMAC). After correction for the effect of Ad-MMAC on plating efficiency, Ad-MMAC treatment reduced the surviving fractions after 2 Gy as follows: PC-3-Bcl-2, from 60.5 to 3.6%; PC-3-Neo, no reduction; LNCaP, from 29.6 to 16.3%; and DU-145, from 32.7 to 25.7%. PTEN expression was associated with the downregulation of Bcl-2 expression in PC-3-Bcl-2 and LNCaP cell lines. Ad-MMAC plus radiotherapy potentiated the G2M block seen with radiotherapy alone only in PC-3-Bcl-2 cells. These findings suggest that overexpression of Bcl-2 result in radioresistance and inability of radiation to cause its typical G2M cell-cycle arrest.     

Synergistic inhibition of breast cancer cell lines with a dual inhibitor of EGFR-HER-2/neu and a Bcl-2 inhibitor

The epidermal growth factor receptor (EGFR) (ErbB1) and HER-2/neu (ErbB2) are members of the ErbB family of receptor tyrosine kinases. These receptors are overexpressed in a variety of human tumors and overexpression generally correlates with poor prognosis and decreased survival. Lapatinib, a reversible inhibitor of both EGFR and HER-2/neu, has shown some success in achieving clinical responses in heavily pretreated advanced cancer patients. GW2974 is a reversible dual inhibitor similar to lapatinib, but GW2974 was not progressed to clinical trials due to pharmacokinetic issues. Bcl-2, an anti-apoptotic protein, is also overexpressed in a number of human tumors. Bcl-2 inhibitors induce apoptosis and sensitize cancer cells to other therapies. The purpose of this study was to assess the effects of combining ErbB and Bcl-2 inhibitors on the growth of human breast cancer cell lines. EGFR/HER-2/neu tyrosine kinase inhibitors (lapatinib and GW2974) were combined with Bcl-2 inhibitors (HA14-1 or GX15-070) and the anti-proliferative effects were determined by the MTT tetrazolium dye assay. Combinations were tested in MCF-7 human breast cancer cells, a HER-2/neu transfected MCF-7 cell line (MCF/18), and a tamoxifen-resistant MCF-7 cell line (MTR-3). A synergistic inhibitory effect was observed with the combination of inhibitors of EGFR-HER-2/neu (lapatinib or GW2974) and Bcl-2 (GX15-070 or HA14-1) on the growth of the MCF-7, MCF/18, and MTR-3 human breast cancer cell lines. This study suggests that simultaneously blocking the ErbB family of receptor tyrosine kinases and Bcl-2 family of proteins may be a benefit to breast cancer patients.     

Lycorine is a novel inhibitor of the growth and metastasis of hormone-refractory prostate cancer

Lycorine, a natural alkaloid extracted from the Amaryllidaceae plant family, has been reported to exhibit a wide range of physiological effects, including the potential effect against cancer. However, the anti-prostate cancer (PCa) efficacy of Lycorine remains unrevealed. In this context, we figured out Lycorine''s anti-proliferative and anti-migratory properties for PCa treatment. Lycorine inhibited proliferation of various PCa cell lines, induced cell apoptosis and cell death. Here we showed that Lycorine decreased proliferation, migration, invasion, survival and EMT of prostate cancer cell lines. Subcutaneous and orthotopic xenotransplantations by ectopic implantation of the human hormone-refractory PC-3M-luc cells were used to confirm in vivo anticancer effects of Lycorine. Lycorine inhibited both growth and metastasis in multiple organs (liver, lung, kidney, spleen and bone) in vivo and improved mice survival. Lycorine prevented EGF-induced JAK/STAT signaling. Importantly, anti-cancer effects of Lycorine were dependent on STAT expression. We suggest that Lycorine is a potential therapeutic in prostate cancer.     

Antiproliferative effects of AVN944, a novel inosine 5-monophosphate dehydrogenase inhibitor, in prostate cancer cells

Inosine 5-monophosphate dehydrogenase II, a key enzyme in the de novo synthesis of purine nucleotides, is expressed in prostate tumors and prostate cancer cells. AVN944 is a new, specific, noncompetitive IMPDH inhibitor. In this study, we investigated the effects of IMPDH inhibitor AVN944 on LNCaP, CWR22Rv1, DU145 and PC-3 human prostate cancer cells. AVN944 inhibited proliferation of these 4 prostate cancer cell lines and was associated with cell cycle G1 arrest of LNCaP cells and S-phase block of androgen-independent CWR22Rv1, DU145 and PC-3 cells. AVN944 induced caspase-dependentand caspase-independent cell death in LNCaP, CWR22Rv1, and DU145 cells. AVN944 induced expression of p53-target proteins Bok, Bax and Noxa in androgen-responsive cell lines and suppressed expression of survivin in prostate cancer cells regardless of their androgen sensitivity. AVN944 also induced differentiation of androgen-independent prostate cancer cells as indicated by morphological changes and increased expression of genes coding for prostasomal proteins, keratins and other proteins, including tumor suppressor genes MIG-6 and NDRG1. AVN944-differentiated androgen-independent DU145 and PC-3 cells are sensitized to TRAIL-induced apoptosis as demonstrated by induction of caspases and PARP cleavage. In summary, AVN944 inhibited the growth of human prostate cancer cells by inducing cell cycle arrest, cell death as well as differentiation. AVN944 is a novel, promising therapeutic agent that might be combined with other agents for treatment of human prostate cancer.     

ABT-737对顺铂诱导乳腺癌T47D细胞凋亡的增敏作用

目的 探讨Bcl-2抑制剂ABT-737联合顺铂对乳腺癌T47D细胞株凋亡的影响.方法 常规培养T47D细胞,采用四甲基偶氮唑蓝(MTT)法检测ABT-737联合顺铂对T47D细胞增殖的影响,采用Western blot法检测凋亡相关蛋白的表达,采用荧光染色法观察T47D细胞凋亡的形态学变化,采用流式细胞仪检测T47D细胞的凋亡率.结果 MTT法检测结果显示,ABT-737可明显降低顺铂在T47D细胞中的IC50[由顺铂单药的(26.00±1.41) μmol/L降为联合用药的(13.00±1.11)μmol/L].ABT-737增加顺铂对T47D细胞的抑制作用,并呈剂量依赖性,而ABT-737单药对T47D细胞的抑制作用不明显.Western blot检测多聚ADP核糖聚合酶(PARP)的剪切结果显示,ABT-737明显降低了顺铂诱导T47D细胞凋亡的浓度,加快了凋亡诱导时间,ABT-737对顺铂诱导T47D细胞凋亡的增敏作用呈剂量依赖性,单药对T47D细胞的作用不明显.与单药组相比,ABT-737与顺铂联合时T47D细胞中PARP和caspase3的剪切明显增加,而Bcl-2、Bcl-XL和Bax的表达无明显变化.荧光染色和流式细胞术检测结果均显示,ABT-737联合顺铂时,T47D细胞的凋亡率明显增加.结论 ABT-737可显著提高顺铂对乳腺癌T47D细胞的凋亡诱导作用.     

Bcl-2-dependent modulation of Ca(2+) homeostasis and store-operated channels in prostate cancer cells

Antiapoptotic oncoprotein Bcl-2 has extramitochondrial actions due to its localization on the endoplasmic reticulum (ER); however, the specific mechanisms of such actions remain unclear. Here we show that Bcl-2 overexpression in LNCaP prostate cancer epithelial cells results in downregulation of store-operated Ca(2+) current by decreasing the number of functional channels and inhibiting ER Ca(2+) uptake through a reduction in the expression of calreticulin and SERCA2b, two key proteins controlling ER Ca(2+) content. Furthermore, we demonstrate that Ca(2+) store depletion by itself is not sufficient to induce apoptosis in Bcl-2 overexpressing cells, and that sustained Ca(2+) entry via activated store-operated channels (SOCs) is required as well. Our data therefore suggest the pivotal role of SOCs in apoptosis and cancer progression.     

Apoptosis-based treatment of glioblastomas with ABT-737, a novel small molecule inhibitor of Bcl-2 family proteins

Defects in the apoptotic signaling cascades contribute to the poor therapeutic response of malignant gliomas. As glioblastomas are characterized by high expression levels of anti-apoptotic Bcl-2 family proteins, we studied the effects of the novel Bcl-2 inhibitor, ABT-737, on malignant glioma cells. ABT-737 treatment released the pro-apoptotic Bax protein from its binding partner Bcl-2 and potently induced apoptotic cell death in glioblastoma cells in vitro and in vivo. The local administration of ABT-737 prolonged the survival in an intracranial glioma xenograft model. Downregulation of Mcl-1 and overexpression of Bcl-2 sensitized the cells to ABT-737-mediated apoptosis. Moreover, ABT-737 potentiated the cytotoxicity of the chemotherapeutic drugs vincristine and etoposide, and of the death ligand TRAIL. As glioma stem cells may play a crucial role for the tumor progression and the resistance to treatment in glioblastomas, we investigated the effects of ABT-737 on the subpopulation of glioma cells exhibiting stem cell characteristics. Inhibition of proliferation and induction of apoptosis by ABT-737 were less efficient in glioma stem cells than in non-stem cell-like glioma cells. As the resistance of glioma stem cells was associated with high Mcl-1 expression levels, ABT-737 treatment combined with downregulation of Mcl-1 could represent a promising novel approach in glioblastoma treatment.     

Bcl-2表达降低对人乳腺癌细胞米托蒽醌敏感性的影响

目的:探讨抗凋亡蛋白Bcl-2低表达后对人乳腺癌细胞米托蒽醌(mitoxantrone,MX)敏感性的影响。方法:分别用MTT法和流式细胞仪PI单染、Annexin V/PI双染法、彗星实验检测Bcl-2低表达后,MX对乳腺癌MDA-MB-435S和MDA-MB-231细胞生存率、细胞周期、凋亡和DNA损伤的影响。结果:Bcl-2表达降低后MX对乳腺癌MDA-MB-435S和MDA-MB-231细胞的增殖抑制、S期阻滞、凋亡诱导、DNA损伤均明显增加,具有统计学意义。结论:抑制Bcl-2表达可以增加乳腺癌细胞对MX的敏感性。     

Overexpression of Bcl-2 in squamous cell carcinoma of the larynx: a marker of radioresistance

Squamous cell carcinoma of the larynx can be treated using radiotherapy or surgery, either alone or in combination. Radiotherapy is preferred for early-stage tumours, as it spares the larynx and therefore preserves speech and swallowing. Unfortunately, approximately 15% of tumours treated this way will prove to be radioresistant, as manifest by tumour recurrence within the original radiotherapy field over the ensuing 12 months. By causing extensive DNA damage, radiotherapy aims to induce apoptosis and tumour regression. Our hypothesis was that defects in the mechanisms that recognise DNA damage, induce cell cycle arrest or control apoptosis, either alone or in combination, may be responsible for radioresistance. We therefore undertook an immunohistochemic analysis of pretreatment biopsies of radioresistant (n = 8) and radiosensitive (n = 13) laryngeal tumours. To minimise the impact of confounding factors, strict inclusion criteria were observed; all tumours were of the glottic subsite and all recurrences developed within 12 months of radiotherapy at the site of the original tumour. The expression of key proteins involved in DNA damage recognition (p53), cell cycle arrest (ATM, p16 and p21/WAF1) and apoptosis (Bcl-2 and BAX) were studied. Ki-67 was also assessed as a marker of cell proliferation to exclude low mitotic rate as a cause of radioresistance. A statistically significant correlation was observed between overexpression of Bcl-2 and radioresistance (p = 0.003, Fisher's exact test). We hypothesise that overexpression of the anti-apoptotic protein Bcl-2 allows tumour cells with extensive radiation-induced DNA damage to continue proliferating; the absence of an appropriate apoptotic response manifests clinically as radioresistance.     

Androgens repress Bcl-2 expression via activation of the retinoblastoma (RB) protein in prostate cancer cells

The oncogene Bcl-2 is upregulated frequently in prostate tumors following androgen ablation therapy, and Bcl-2 overexpression may contribute to the androgen-refractory relapse of the disease. However, the molecular mechanism underlying androgenic regulation of Bcl-2 in prostate cancer cells is understood poorly. In this study, we demonstrated that no androgen response element (ARE) was identified in the androgen-regulated region of the P1 promoter of Bcl-2 gene, whereas, we provided evidence that the androgenic effect is mediated by E2F1 protein through a putative E2F-binding site in the promoter. We further demonstrated that retinoblastoma (RB) protein plays a critical role in androgen regulation of Bcl-2. The phosphorylation levels of RB at serine residues 780 and 795 were decreased in LNCaP cells treated with androgens. Ectopic expression of a constitutively active form of RB inhibited expression of Bcl-2. Knockdown of endogenous RB protein by an Rb small inference RNA (siRNA) induced an increase in Bcl-2 levels. Most importantly, the effect of androgens on Bcl-2 was abolished completely by specific inhibition of RB function with a mutated E1A. Finally, androgen treatment of LNCaP cells upregulated specifically levels of the cyclin-dependent kinase inhibitors (CDKIs) p15INK4B and p27KIP1. Ectopic expression of p15INK4B and/or p27KIP1 inhibited Bcl-2 expression. Knockdown of endogenous p15INK4B or p27KIP1 protein with a pool of siRNAs diminished androgen-induced downregulation of Bcl-2 expression. Therefore, our data indicate that androgens suppress Bcl-2 expression through negatively modulating activities of the E2F site in the Bcl-2 promoter by activating the CDKI-RB axis.     

Chemosensitization and delayed androgen-independent recurrence of prostate cancer with the use of antisense Bcl-2 oligodeoxynucleotides

BACKGROUND: Increased expression of the bcl-2 gene has been observed in prostate cancer cells after androgen withdrawal and has been associated with the development of androgen independence and chemoresistance. The objective of this study was to determine whether antisense Bcl-2 oligodeoxynucleotides could enhance paclitaxel cytotoxicity and delay androgen-independent progression. METHODS: Northern and western blot analyses were used to measure changes in Bcl-2 expression in mouse Shionogi tumor cells after treatment with antisense Bcl-2 oligodeoxynucleotides and/or paclitaxel. Growth inhibition and induction of apoptotic cell death were assessed with the use of standard methods. All P values are two-sided. RESULTS: Treatment of Shionogi tumor cells with 500 nM antisense Bcl-2 oligodeoxynucleotides decreased expression of Bcl-2 messenger RNA (mRNA) by approximately 85%. Paclitaxel treatment induced Bcl-2 protein phosphorylation but did not alter Bcl-2 mRNA expression. Antisense Bcl-2 oligodeoxynucleotide treatment substantially enhanced paclitaxel chemosensitivity in a dose-dependent manner. Characteristic apoptotic DNA laddering and cleavage of poly(adenosine diphosphate-ribose) polymerase were demonstrated only after combined treatment. Adjuvant in vivo administration of antisense Bcl-2 oligodeoxynucleotides and micellar paclitaxel following castration resulted in a statistically significant delay of androgen-independent, recurrent tumors compared with administration of either agent alone (P<.001, Mantel-Cox log-rank test). Combination therapy also statistically significantly inhibited the growth of established hormone-refractory tumors compared with treatment with either agent alone (P<.001, Student's t test). CONCLUSIONS. Combined treatment with antisense Bcl-2 oligodeoxynucleotides and paclitaxel could be a novel and attractive strategy to inhibit progression to androgen-independent disease as well as growth of hormone-refractory prostate cancer through deprivation of Bcl-2 function.     

RPS2: a novel therapeutic target in prostate cancer

Background

A number of studies have previously shown that the over expression of different ribosomal proteins might play an important role in cancer (i.e. S3a, L10, L16). We have previously reported that RPS2, a 33 Kda ribosomal protein was over expressed in malignant prostate cancer cell lines and in archived tumor specimens. Thus, RPS2 or other aberrantly over-expressed ribosomal proteins might promote cancer and be excellent therapeutic targets for treatment of the disease.

Methods

Western blotting and RT-PCR have been used to measure and compare the levels of expression of RPS2 in a variety of malignant prostate cancer cell lines, plus normal and benign cells lines. We have developed a ''ribozyme-like'' DNAZYM-1P ''10–23'' motif oligonucleotide and examined whether it targets RPS2 in different cell lines by RT-PCR and Western blots. Growth and apoptosis assays were carried out to measure whether DNAZYM-1P ''knock-down'' of RPS2 influenced cell proliferation or survival. We have also developed a SCID mouse tumor model with PC-3ML cells to determine whether DNAZYM-1P targeting of RPS2 compromised tumor growth and mouse survival rates in vivo.

Results

Western blots showed that PC-3ML, LNCaP, CPTX-1532, and pBABE-cmyc stably transfected IBC-10a cells all over-expressed RPS2, whereas IBC-10a parent, NPTX-1532, and BPH-1 cells or mouse NIH-3T3 cells expressed barely detectable levels of RPS2. RT-PCR assays showed that DNAZYM-1P, which targeted RPS2, ''knocked-down'' RPS2 expression in the malignant cells (i.e. PC-3ML cells) in vitro. The DNAZYM-1P also inhibited cell growth and induced apoptosis in the malignant prostate cells, but had little effect on the normal IBC-10a or NPTX-1532 cell lines. Finally, SCID mouse tumor modeling studies showed that DNAZYM-1P blocked tumor growth and metastasis by PC-3ML cells and eventually eradicated tumors following localized or systemic i.v. delivery. Mouse survival studies revealed that there was a dosage dependent increase in disease free survival rates in mice treated systemically with DNAZYM-1P (i.e. mouse survival increased from 0% to 100%).

Conclusion

In sum, we have shown for the first time that therapeutic targeting of RPS2 is an excellent approach for the eradication of prostate cancer in preclinical tumor modeling studies.