miR-105 Inhibits Prostate Tumour Growth by Suppressing CDK6 Levels

A significant role for micro (mi)RNA in the regulation of gene expression in tumours has been recently established. In order to further understand how miRNA expression may contribute to prostate tumour growth and progression, we evaluated expression of miRNA in two invasive prostate tumour lines, PC3 and DU145, and compared it to that in normal prostate epithelial cells. Although a number of miRNAs were differentially expressed, we focused our analysis on miR-105, a novel miRNA not previously linked to prostate cancer. miR-105 levels were significantly decreased in both tumour cell lines in comparison to normal prostate epithelial cells. To determine its potential role in prostate cancer pathogenesis, we overexpressed miR-105 in both PC3 and DU145 cells and determined its effect on various tumourigenic properties. miR-105 overexpression inhibited tumour cell proliferation, tumour growth in anchorage-independent three-dimensional conditions and tumour invasion in vitro, properties of highly aggressive tumour cells. Of potential clinical significance, miR-105 overexpression inhibited tumour growth in vivo in xenograft models using these cell lines. We further identified CDK6 as a putative target of miR-105 which is likely a main contributor to the inhibition of tumour cell growth observed in our assays. Our results suggest that miR-105 inhibits tumour cell proliferation and hence may represent a novel therapeutically relevant cellular target to inhibit tumour growth or a marker of aggressive tumours in prostate cancer patients.     

Brefeldin A enhances docetaxel-induced growth inhibition and apoptosis in prostate cancer cells in monolayer and 3D cultures

Docetaxel is a commonly used chemotherapeutic drug for patients with late stage prostate cancer. However, serious side effect and drug resistance limit its clinical success. Brefeldin A is a 16-membered macrolide antibiotic from mangrove-derived Fungus Aspergillus sp. (9Hu), which exhibited potent cytotoxicity against human cancer cells. In the present study, we determined the effect of brefeldin A on docetaxel-induced growth inhibition and apoptosis in human prostate cancer PC-3 cells. Brefeldin A in combination with docetaxel inhibited the growth of PC-3 cells in monolayer and in three dimensional cultures. The combination also potently stimulated apoptosis in PC-3 cells as determined by propidium iodide staining and morphological assessment. Mechanistic studies showed that growth inhibition and apoptosis in PC-3 cells treated with brefeldin A and docetaxel were associated with decrease in the level of Bcl-2. The present study indicates that combined brefeldin A with docetaxel may represent a novel approach for improving the efficacy of docetaxel, and Bcl-2 may serve as a target for brefeldin A to enhance the effects of docetaxel chemotherapy.     

Rapamycin enhances docetaxel-induced cytotoxicity in a androgen-independent prostate cancer xenograft model by survivin downregulation

BackgroundDocetaxel is a first-line treatment choice in castration-resistant prostate cancer (CRPC). However, the management of CRPC remains an important challenge in oncology. There have been many reports on the effects of rapamycin, which is an inhibitor of the mammalian target of rapamycin (mTOR), in the treatment of carcinogenesis. We assessed the cytotoxic effects of the combination treatment of docetaxel and rapamycin in prostate cancer cells. Furthermore, we examined the relationship between these treatments and survivin, which is a member of the inhibitory apoptosis family.MethodsProstate cancer cells were cultured and treated with docetaxel and rapamycin. The effects on proliferation were evaluated with the MTS assay. In addition, we evaluated the effect on proliferation of the combination treatment induced knockdown of survivin expression by small interfering RNA transfection and docetaxel. Protein expression levels were assayed using western blotting. PC3 cells and xenograft growth in nude mice were used to evaluate the in vivo efficacy of docetaxel and its combination with rapamycin.ResultsIn vitro and in vivo, the combination of rapamycin with docetaxel resulted in a greater inhibition of proliferation than treatment with rapamycin or docetaxel alone. In addition, in vitro and in vivo, rapamycin decreased basal surviving levels, and cotreatment with docetaxel further decreased these levels. Transfection siRNA against survivin enhanced the cytotoxicity of docetaxel in PC3 cells.ConclusionThe rapamycin-dependent enhancement of the cytotoxic effects of docetaxel was associated with the downregulation of survivin expression. Our results suggest that the combination of docetaxel and rapamycin is a candidate for the improved treatment of advanced prostate cancer.     

Docetaxel and thalidomide as a treatment option for androgen- independent, nonmetastatic prostate cancer

Prostate cancer usually presents with early-stage disease, yet a significant proportion of patients present or will progress to androgen-independent, nonmetastatic prostate cancer (AIPC). Chemotherapy has demonstrated statistically significant improvements in palliation of AIPC. Docetaxel in particular has demonstrated high response rates as a single agent. Thalidomide is effective in treating many malignancies, including prostate cancer. Thalidomide may act synergistically with docetaxel through their antiangiogenic effects. We performed a phase II trial of docetaxel with or without thalidomide in patients with AIPC and demonstrated encouraging response rates with combination therapy. We advocate further investigation of this promising combination regimen.     

Flavonoid ampelopsin inhibits the growth and metastasis of prostate cancer in vitro and in mice

The objective of this study was to evaluate the chemopreventive effect of a novel flavonoid, ampelopsin (AMP) on the growth and metastasis of prostate cancer cells. AMP showed the more potent activity in inhibiting the proliferation of androgen-sensitive LNCaP and, to less extent, androgen-independent PC-3 human prostate cancer cell lines in vitro, primarily by induction of apoptosis associated with down-regulation of bcl-2. On the other hand, AMP showed much less activity in inhibiting the proliferation of normal prostate epithelial cells than that of prostate cancer cell lines. AMP also inhibited the migration and invasion of PC-3 cells in vitro associated with down-regulation of CXCR4 expression. In the animal study using an orthotopic prostate tumor model, AMP (150 and 300 mg/kg body weight) inhibited the growth of PC-3 tumors and lymph node and lung metastases in a dose-dependent manner. Compared to the control mice, mice treated with AMP at 300 mg/kg BW had reduced final tumor weight by 49.2% (P<0.05), lymph node metastases by 54.5% (P?=?0.3) and lung metastases by 93% (P<0.05), but had no apparent alteration on food intake or body weight. The in vivo anti-growth and anti-metastasis activities of AMP were associated with induction of apoptosis and inhibition of proliferation of prostate cancer cells, reduction of prostate tumor angiogenesis, and reduction of CXCR4 expression. Our results provide supporting evidence to warrant further investigation to develop AMP as a novel efficacious and safe candidate agent against progression and metastasis of prostate cancer.     

The anti-tumor efficacy of a GM-CSF-secreting tumor cell vaccine is not inhibited by docetaxel administration

Docetaxel has demonstrated therapeutic efficacy against breast, prostate, and ovarian cancer and other solid tumors. The tumoricidal activity of docetaxel is mainly attributed to its ability to block microtubule depolymerization, thus inducing G₂-M arrest and apoptosis. Mounting evidence indicates that docetaxel also possesses immunomodulatory activity such as augmenting macrophage and lymphokine activated killer activity and inducing pro-inflammatory cytokines, suggesting that docetaxel may be a good chemotherapeutic agent to combine with cancer immunotherapies, assuming that it does not inhibit the vaccine-induced immune response. The anti-tumor activity of the combination of docetaxel and a GM-CSF-secreting B16F10 tumor cell vaccine (B16.GM) was evaluated in the murine B16 melanoma model. Dose levels of docetaxel and the B16.GM vaccine known to be ineffective when used as single agents were selected. Three iv treatments of 6 mg/kg docetaxel per injection given on days 5, 9, and 13 after tumor challenge or a single vaccination with 2–3×10⁶ B16.GM cells on day 3 were ineffective at inhibiting tumor growth when used as single agents [median survival time (MST)=24 days in both treatment groups and in control animals]. However, combination of docetaxel and B16.GM vaccine significantly delayed tumor growth, increasing MST to 45 days. A similar improvement in anti-tumor efficacy was observed using multiple treatment cycles of the B16.GM vaccine/docetaxel combination. Administration of docetaxel every 4 days between bi-weekly B16.GM vaccinations increased the median survival of tumor-bearing mice from 31 to 52 days compared to multiple B16.GM vaccinations alone. In summary, these data demonstrate that rather than inhibiting the anti-tumor effects of a GM-CSF-secreting tumor cell vaccine, docetaxel combined with a whole cell vaccine significantly inhibits tumor growth, increases survival time and does not impede T-cell activation in the murine B16F10 melanoma tumor model. GM-secreting tumor cell vaccines in combination with docetaxel may represent a new strategy for combining chemo and immunotherapy for cancer.     

Combination of vasostatin gene therapy with cyclophosphamide inhibits growth of B16(F10) melanoma tumours

Angiogenesis, i.e. formation of new blood vessels out of pre-existing capillaries, is essential to the development of tumour vasculature. The discovery of specific antiangiogenic inhibitors has important therapeutic implications for the development of novel cancer treatments. Vasostatin, the N-terminal domain of calreticulin, is a potent endogenous inhibitor of angiogenesis and tumour growth. In our study, using B16(F10) murine melanoma model and electroporation we attempted intramuscular transfer of human vasostatin gene. The gene therapy was combined with antiangiogenic drug dosing schedule of a known chemotherapeutic (cyclophosphamide). The combination of vasostatin gene therapy and cyclophosphamide administration improved therapeutic effects in melanoma tumours. We observed both significant inhibition of tumour growth and extended survival of treated mice. To our knowledge, this is one of the first reports showing antitumour efficacy of electroporation-mediated vasostatin gene therapy combined with antiangiogenic chemotherapy.     

Targeted Notch1 inhibition with a Notch1 antibody,OMP-A2G1, decreases tumor growth in two murine models of prostate cancer in association with differing patterns of DNA damage response gene expression

Notch plays a protumorigenic role in many cancers including prostate cancer (PCa). Global notch inhibition of multiple Notch family members using γ-secretase inhibitors has shown efficacy in suppressing PCa growth in murine models. However, global Notch inhibition is associated with marked toxicity due to the widespread function of many different Notch family members in normal cell physiology. Accordingly, in the current study, we explored if specific inhibition of Notch1 would effectively inhibit PCa growth in a murine model. The androgen-dependent VCaP and androgen-independent DU145 cell lines were injected subcutaneously into mice. The mice were treated with either control antibody 1B7.11, anti-Notch1 antibody (OMP-A2G1), docetaxel or the combination of OMP-A2G1 and docetaxel. Tumor growth was measured using calipers. At the end of the study, tumors were assessed for proliferative response, apoptotic response, Notch target gene expression, and DNA damage response (DDR) expression. OMP-A2G1 alone inhibited tumor growth of both PCa cell lines to a greater extent than docetaxel alone. There was no additive or synergistic effect of OMP-A2G1 and docetaxel. The primary toxicity was weight loss that was controlled with dietary supplementation. Proliferation and apoptosis were affected differentially in the two cell lines. OMP-A2G1 increased expression of the DDR gene GADD45α in VCaP cells but downregulated GADD45α in Du145 cells. Taken together, these data show that Notch1 inhibition decreases PCa xenograft growth but does so through different mechanisms in the androgen-dependent VCaP cell line vs the androgen-independent DU145 cell line. These results provide a rationale for further exploration of targeted Notch inhibition for therapy of PCa.     

Alteration in the Balance of Prosurvival and Proapoptotic Signalling Pathways Leads to Sequence-Dependent Synergism Between Docetaxel and Sorafenib in Human Non-small Cell Lung Cancer Cell Lines

To examine the antiproliferative effect of the combination of docetaxel and sorafenib, applied to the representative non-small cell lung cancer cell line A549 cells either wild type or with acquired resistance to docetaxel (A549/D). The aim of this study is to evaluate the synergistic effect of combination treatment on cell growth inhibition and to elucidate the involved molecular mechanisms. A549 cells with acquired resistance to docetaxel were established by continuous exposure to docetaxel. We examined the effect of different combinatorial treatment on cell proliferation and cell cycle distribution. In addition, the effect of combinatorial treatments on proliferative and apoptotic signalling pathway were studied. Our results showed that the synergistic effect presented when A549 cells were treated with docetaxel followed by sorafenib or when A549/D cells were treated in reverse sequence. Furthermore, we suggested that synergistic effect in A549/D cells was caused by inhibiting P-gp function and altering in the balance of growth and apoptotic signalling pathways. Our data suggested a potential role of sorafenib in chemosensitizing docetaxel-resistant cancer cells. This study also provides molecular evidence for applying different therapeutic strategies for patients with different genetic and proteomic profile.     

Inhibitory mechanisms of Agaricus blazei Murill on the growth of prostate cancer in vitro and in vivo

Agaricus blazei Murill (A. blazei) has been conventionally used as a health food for the prevention of cancer. However, little is known about the direct effects and action mechanisms of A. blazei on human prostate cancer. In the present study, the effects of A. blazei on the growth of human prostate cancer were examined in vitro and in vivo. A. blazei, especially the broth fraction, inhibited cell proliferation in both androgen-dependent and androgen-independent prostate cancer cell lines. The broth of A. blazei induced lactate dehydrogenase leakage in three cancer cell lines, whereas the activities of caspase 3 and the DNA fragmentation were enhanced the most in androgen-independent PC3 cells. The protein expressions of apoptosis-related molecules were elevated by the broth of A. blazei in PC3 cells. Oral supplementation with the broth of A. blazei (with the higher ratio of beta-glucan) significantly suppressed tumor growth without inducing adverse effects in severe combined immunodeficient mice with PC3 tumor xenograft. Tumor xenografts from A. blazei-fed mice showed decreased proliferating cell nuclear antigen-positive cells and reduced tumor microvessel density. Based on these results, we found that the broth of A. blazei may directly inhibit the growth of prostate cancer cell via an apoptotic pathway and suppress prostate tumor growth via antiproliferative and antiangiogenic mechanisms. We therefore suggest that A. blazei might have potential therapeutic use in the prevention and treatment of human prostate cancer.     

Cidofovir administered with radiation displays an antiangiogenic effect mediated by E6 inhibition and subsequent TP53-dependent VEGF repression in HPV18+ cell lines

Therapeutic administration of the antiviral agent cidofovir with radiation markedly enhanced the antitumor effect of ionizing radiation in cells of two HPV18+ human cervical carcinoma cell lines. Although this potent radiosensitizing effect was associated with repression of the viral oncoproteins E6/ E7 and restoration of TP53 as shown previously, additional mechanisms may be involved. In the present study, we investigated the antiangiogenic effect of the combination of cidofovir and radiation in cells of two HPV18+ cervical cancer cell lines, HeLa and ME180, and assessed the molecular mechanisms associated with the antiangiogenic effect observed. Cells were exposed to cidofovir (10 microg/ml) and irradiated (1-9 Gy). The angiogenic response was studied in vitro by a matrigel invasion assay. Modulations of E6, TP53 and VEGF mRNA and protein levels were studied by real-time RT-PCR, Western blot analysis and ELISA, respectively. Then a double RNA interference approach was used to analyze the connection between E6/TP53 and VEGF. The combination of cidofovir and radiation had a potent antiangiogenic effect. It induced E6 inhibition, restoration of TP53, and reduction of the proangiogenic phenotype of HPV18+ cells associated with VEGF inhibition. A siRNA strategy showed an anti-VEGF action of the combination mediated directly by E6 inhibition and TP53 restoration, since E6 siRNA inhibited VEGF whereas co-transfection with E6 and TP53 siRNA abrogated the anti-VEGF effect. This study showed that the combination of cidofovir with ionizing radiation has an antiangiogenic effect associated with VEGF inhibition subsequent to E6 inhibition and TP53 restoration.     

Combined effect of sodium selenite and docetaxel on PC3 metastatic prostate cancer cell line

Docetaxel and sodium selenite are well known for their anticancer properties. While resistance to docetaxel remains an obstacle in prostate cancer chemotherapy, sodium selenite, has been exploited as a new therapeutic approach. Currently, development of therapies affecting a multitude of cell targets, have been proposed as a strategy to overcome drug resistance. This association may reduce systemic toxicity counteracting a wide range of side effects.Here we report the effect of docetaxel and sodium selenite combination on the PC3 prostate cancer cell line, derived from bone metastasis. Therefore we evaluate cell growth, cell cycle progression, viability, mitochondria membrane potential, cytochrome C, Bax/Bcl2 ratio, caspase-3 expression and reactive oxygen species production.Our results suggest that sodium selenite and docetaxel combination have a synergistic effect on cell growth inhibition (67%) compared with docetaxel (22%) and sodium selenite (24%) alone. This combination also significantly induced cell death, mainly by late apoptosis vs necrosis, which is correlated with mitochondria membrane potential depletion. On the other hand, cytochrome C, Bax/Bcl2 ratio and caspase-3, known as proapoptotic factors, significantly increased in the presence of sodium selenite alone, but not in the presence of docetaxel in monotherapy or in combination with sodium selenite.These findings suggest that docetaxel and sodium selenite combination may be more effective on prostate cancer treatment than docetaxel alone warranting further evaluation of this combination in prostate cancer therapeutic approach.     

γ-Tocopherol inhibits human prostate cancer cell proliferation by up-regulation of transglutaminase 2 and down-regulation of cyclins

To establish a system to study differentiation therapy drugs, we used the androgen-independent human prostate PC-3 tumor cell line as a target and α- and γ-tocopherol as inducers. Effects of α- and γ-tocopherol on the cell cycle, proliferation and differentiation, were examined. A more significant growth inhibition activity for γ- than for α-tocopherol was observed. Flow cytometry analysis of α- and γ-tocopherol-treated prostate carcinoma PC3 cells showed decreased progression into the S-phase. This effect, particularly evident for γ-tocopherol, was associated with an up-regulation and increased activity of transglutaminase 2 (TG2), a reduced DNA synthesis and a remarkable decreased levels of cyclin D1 and cyclin E. Activation of TG2 suggests that γ-tocopherol has an evident differentiative capacity on PC3 cells, leading to an increased expression of TG2, and reduced cyclin D1 and cyclin E levels, affecting cell cycle progression. It is feasible that up-regulation and activation of TG2, associated with a reduced proliferation, are parts of a large-scale reprogramming that can attenuate the malignant phenotype of PC3 cells in vitro. These data suggest further investigation on the potential use of this γ-form of vitamin E as a differentiative agent, in combination with the common cytotoxic treatments for prostate cancer therapy.     

Potentiating effects of GHRH analogs on the response to chemotherapy

Growth hormone releasing hormone (GHRH) from hypothalamus nominatively stimulates growth hormone release from adenohypophysis. GHRH is also produced by cancers, acting as an autocrine/paracrine growth factor. This growth factor function is seen in lymphoma, melanoma, colorectal, liver, lung, breast, prostate, kidney, bladder cancers. Pituitary type GHRH receptors and their splice variants are also expressed in these malignancies. Synthetic antagonists of the GHRH receptor inhibit proliferation of cancers. Besides direct inhibitory effects on tumors, GHRH antagonists also enhance cytotoxic chemotherapy. GHRH antagonists potentiate docetaxel effects on growth of H460 non-small cell lung cancer (NSCLC) and MX-1 breast cancer plus suppressive action of doxorubicin on MX-1 and HCC1806 breast cancer. We investigated mechanisms of antagonists on tumor growth, inflammatory signaling, doxorubicin response, expression of drug resistance genes, and efflux pump function. Triple negative breast cancer cell xenografted into nude mice were treated with GHRH antagonist, doxorubicin, or their combination. The combination reduced tumor growth, inflammatory gene expression, drug-resistance gene expression, cancer stem-cell marker expression, and efflux-pump function. Thus, antagonists increased the efficacy of doxorubicin in HCC1806 and MX-1 tumors. Growth inhibition of H460 NSCLC by GHRH antagonists induced marked downregulation in expression of prosurvival proteins K-Ras, COX-2, and pAKT. In HT-29, HCT-116 and HCT-15 colorectal cancer lines, GHRH antagonist treatment caused cellular arrest in S-phase of cell cycle, potentiated inhibition of in vitro proliferation and in vivo growth produced by S-phase specific cytotoxic agents, 5-FU, irinotecan and cisplatin. This enhancement of cytotoxic therapy by GHRH antagonists should have clinical applications.     

1alpha,25-Dihydroxyvitamin D3 enhances proliferation of rat prostate cancer cells in the presence of living bone

1alpha,25-Dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) is known to inhibit prostate cancer cells in vitro. Its effects on proliferation in the presence of living bone have not been reported, but are especially relevant since much of the morbidity and mortality associated with prostate cancer is due to metastatic bone disease. We investigated the effect of 1alpha,25(OH)(2)D(3) on MatLyLu-beta(2) cells (MatLyLu cells), a rat prostate cancer line, co-cultured in transwells with living rat calvaria. Cultures of MatLyLu cells with living calvaria treated with 1alpha,25(OH)(2)D(3) exhibited a statistically significant increase in proliferation (range 1.4 to 1.7-fold; p<0.05). Cultures of MatLylu cells alone, with spleen cells, muscle tissue, or with living or inactivated calvarial bone showed no differences in proliferation. To investigate the mechanism for enhanced proliferation, Galardin, a matrix metalloproteinase (MMP) inhibitor, or pamidronate, an antiresorptive agent, was added. Enhanced proliferation was prevented by either agent, but not to an equal extent. The presence of 1alpha,25(OH)(2)D(3) may lead to proteolytic release or activation of growth factors from bone. These results may explain the variability in reports on the in vivo effects of Vitamin D and suggest a potential concern in using Vitamin D or its analogs alone in patients with metastatic prostate cancer.     

CUDC‐907, a novel dual PI3K and HDAC inhibitor,in prostate cancer: Antitumour activity and molecular mechanism of action

Targeting the androgen receptor (AR) signalling pathway remains the main therapeutic option for advanced prostate cancer. However, resistance to AR‐targeting inhibitors represents a great challenge, highlighting the need for new therapies. Activation of the PI3K/AKT pathway and increased expression of histone deacetylases (HDACs) are common aberrations in prostate cancer, suggesting that inhibition of such targets may be a viable therapeutic strategy for this patient population. Previous reports demonstrated that combination of PI3K inhibitors (PI3KIs) with histone deacetylase inhibitors (HDACIs) resulted in synergistic antitumour activities against preclinical models of prostate cancer. In this study, we demonstrate that the novel dual PI3K and HDAC inhibitor CUDC‐907 has promising antitumour activity against prostate cancer cell lines in vitro and castration‐resistant LuCaP 35CR patient‐derived xenograft (PDX) mouse model in vivo. CUDC‐907‐induced apoptosis was partially dependent on Mcl‐1, Bcl‐xL, Bim and c‐Myc. Further, down‐regulation of Wee1, CHK1, RRM1 and RRM2 contributed to CUDC‐907‐induced DNA damage and apoptosis. In the LuCaP 35CR PDX model, treatment with CUDC‐907 resulted in significant inhibition of tumour growth. These findings support the clinical development of CUDC‐907 for the treatment of prostate cancer.     

R115777 (Zarnestra)/Zoledronic acid (Zometa) cooperation on inhibition of prostate cancer proliferation is paralleled by Erk/Akt inactivation and reduced Bcl-2 and bad phosphorylation

Zoledronic acid (ZOL) has proved activity in bone metastases from prostate cancer through inhibition of mevalonate pathway and of prenylation of intracellular proteins. We have reported that ZOL synergizes with R115777 farnesyltransferase inhibitor (FTI, Zarnestra) in inducing apoptosis and growth inhibition on epidermoid cancer cells. Here, we have studied the effects of the combination of these agents in prostate adenocarcinoma models and, specifically, on androgen-independent (PC3 and DU145) and -dependent (LNCaP) prostate cancer cell lines. We have found that ZOL and R115777 were synergistic in inducing both growth inhibition and apoptosis in prostate adenocarcinoma cells. These effects were paralleled by disruption of Ras-->Erk and Akt survival pathways, consequent decreased phosphorylation of both mitochondrial bcl-2 and bad proteins, and caspase activation. Finally, ZOL/R115777 combination induced cooperative effects also in vivo on tumor growth inhibition of prostate cancer xenografts in nude mice with a significant survival increase. These effects were paralleled by enhanced apoptosis and inactivation of both Erk and Akt. In conclusions, the combination between ZOL and FTI leads to enhanced anti-tumor activity in human prostate adenocarcinoma cells likely through a more efficacious inhibition of ras-dependent survival pathways and consequent bcl-related proteins-dependent apoptosis.     

Synergistic antiangiogenic effects of stathmin inhibition and taxol exposure

Stathmin is one of the key regulators of the microtubule cytoskeleton and the mitotic spindle in eukaryotic cells. It is expressed at high levels in a wide variety of human cancers and may provide an attractive target for cancer therapy. We had previously shown that stathmin inhibition results in the abrogation of the malignant phenotype. The microtubule-interfering drug, taxol, has both antitumorigenic and antiangiogenic properties. We had also shown that the antitumor activities of taxol and stathmin inhibition are synergistic. We hypothesized that taxol and stathmin inhibition may also have synergistic antiangiogenic activities. A replication-deficient bicistronic adenoviral vector that coexpresses green fluorescent protein and an anti-stathmin ribozyme was used to target stathmin mRNA. Exposure of endothelial cells to anti-stathmin adenovirus alone resulted in a dose-dependent inhibition of proliferation, migration, and differentiation into capillary-like structures. This inhibition was markedly enhanced by exposure of transduced endothelial cells to very low concentrations of taxol, which resulted in a virtually complete loss of proliferation, migration, and differentiation of endothelial cells. In contrast, exposure of nontransduced endothelial cells to taxol alone resulted in a modest inhibition of proliferation, migration, and differentiation. Our detailed analysis showed that the antiangiogenic effects of the combination of stathmin inhibition and taxol exposure are synergistic. Our studies also showed that the mechanism of this synergistic interaction is likely to be mediated through the stabilization of microtubules. Thus, this novel combination may provide an attractive therapeutic strategy that combines a synergistic antitumor activity with a synergistic antiangiogenic activity.     

Chemical Biology Drug Sensitivity Screen Identifies Sunitinib as Synergistic Agent with Disulfiram in Prostate Cancer Cells

Background

Current treatment options for castration- and treatment-resistant prostate cancer are limited and novel approaches are desperately needed. Our recent results from a systematic chemical biology sensitivity screen covering most known drugs and drug-like molecules indicated that aldehyde dehydrogenase inhibitor disulfiram is one of the most potent cancer-specific inhibitors of prostate cancer cell growth, including TMPRSS2-ERG fusion positive cancers. However, the results revealed that disulfiram alone does not block tumor growth in vivo nor induce apoptosis in vitro, indicating that combinatorial approaches may be required to enhance the anti-neoplastic effects.

Methods and Findings

In this study, we utilized a chemical biology drug sensitivity screen to explore disulfiram mechanistic details and to identify compounds potentiating the effect of disulfiram in TMPRSS2-ERG fusion positive prostate cancer cells. In total, 3357 compounds including current chemotherapeutic agents as well as drug-like small molecular compounds were screened alone and in combination with disulfiram. Interestingly, the results indicated that androgenic and antioxidative compounds antagonized disulfiram effect whereas inhibitors of receptor tyrosine kinase, proteasome, topoisomerase II, glucosylceramide synthase or cell cycle were among compounds sensitizing prostate cancer cells to disulfiram. The combination of disulfiram and an antiangiogenic agent sunitinib was studied in more detail, since both are already in clinical use in humans. Disulfiram-sunitinib combination induced apoptosis and reduced androgen receptor protein expression more than either of the compounds alone. Moreover, combinatorial exposure reduced metastatic characteristics such as cell migration and 3D cell invasion as well as induced epithelial differentiation shown as elevated E-cadherin expression.

Conclusions

Taken together, our results propose novel combinatorial approaches to inhibit prostate cancer cell growth. Disulfiram-sunitinib combination was identified as one of the potent synergistic approaches. Since sunitinib alone has been reported to lack efficacy in prostate cancer clinical trials, our results provide a rationale for novel combinatorial approach to target prostate cancer more efficiently.