Radiosensitizes Prostate Cancer Research Articles

Abstract 5085: Radiosensitization of castration-resistant prostate cancer via modulating autophagic cell death

Abstract Radioresistance markedly impair the efficacy of cancer therapy. Anti-apoptotic Bcl-2 family proteins such as Bcl-xL, Bcl-2 and Mcl-1 are overexpressed in castration-resistant prostate cancer (CRPC) and contribute to prostate tumor initiation, progression and resistance to radiotherapy. A natural BH3-mimetic, small molecule inhibitor of Bcl-2, (−)-gossypol, shows promise in ongoing Phase II clinical trials for human prostate cancer. We have recently shown that (−)-gossypol preferentially induces autophagy in CRPC cells that have high levels of Bcl-2 and are resistant to apoptosis, both in vitro and in vivo, but not in androgen-dependent cells with low Bcl-2 and sensitive to apoptosis. Our results demonstrate for the first time that (−)-gossypol can interrupt the interaction between Beclin1 and Bcl-2/Bcl-xL at the endoplasmic reticulum, thus releasing the BH3-only pro-autophagic protein Beclin1, which in turn triggers the autophagic cascade. (−)-Gossypol-induced autophagy is Beclin1- and Atg5-dependent, together with Bcl-2 downregulation and Beclin1 upregulation. (−)-Gossypol increased autophagic cell death induced by X-ray radiation in the CRPC cells. Orally administered (−)-gossypol achieved a much greater efficacy with long-term tumor regression when used in combination with ionizing radiation. We have also explored a series of gossypol derivatives and identified two novel BH3-mimetic lead compounds that are more potent than the parental compound in inducing autophagic cell death in CRPC. Taken together, (−)-gossypol significantly enhances the anti-tumor activity of radiotherapy in vitro and in vivo, and represents a promising new regime for treatment of castration-resistant human prostate cancer with overexpression of Bcl-2. Our data provide new insights into the mode of cell death induced by Bcl-2 inhibitors, which would facilitate the rational design of clinical trials by selecting patients who are most likely to benefit from the Bcl-2-targeted molecular therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5085. doi:10.1158/1538-7445.AM2011-5085

The alkylphospholipid, perifosine, radiosensitizes prostate cancer cells both in vitro and in vivo

BackgroundPerifosine is a membrane-targeted alkylphospholipid developed to inhibit the PI3K/Akt pathway and has been suggested as a favorable candidate for combined use with radiotherapy. In this study, we investigated the effect of the combined treatment of perifosine and radiation (CTPR) on prostate cancer cells in vitro and on prostate cancer xenografts in vivo.MethodsHuman prostate cancer cell line, CWR22RV1, was treated with perifosine, radiation, or CTPR. Clonogenic survival assays, sulforhodamine B cytotoxity assays and cell density assays were used to assess the effectiveness of each therapy in vitro. Measurements of apoptosis, cell cycle analysis by flow cytometry and Western blots were used to evaluate mechanisms of action in vitro. Tumor growth delay assays were used to evaluate radiation induced tumor responses in vivo.ResultsIn vitro, CTPR had greater inhibitory effects on prostate cancer cell viability and clonogenic survival than either perifosine or radiation treatment alone. A marked increase in prostate cancer cell apoptosis was noted in CTPR. Phosphorylation of AKT-T308 AKT and S473 were decreased when using perifosine treatment or CTPR. Cleaved caspase 3 was significantly increased in the CTPR group. In vivo, CTPR had greater inhibitory effects on the growth of xenografts when compared with perifosine or radiation treatment alone groups.ConclusionsPerifosine enhances prostate cancer radiosensitivity in vitro and in vivo. These data provide strong support for further development of this combination therapy in clinical studies.

Abstract 5387: Prostate-targeted radiosensitization via aptamer-shRNA chimeras

Abstract Dose-escalated radiation therapy for localized prostate cancer (PCa) has a clear therapeutic benefit; however, escalated doses may also increase injury to non-cancerous tissues. Radiation-sensitizing agents can improve ionizing radiation (IR) potency, but without targeted delivery these agents will also sensitize surrounding normal tissues. Here we describe the development and application of prostate-targeted RNA interference agents which selectively sensitize PSMA-positive cells to IR. A high throughput siRNA screen identified DNA-PK, MAD2L2, BRCA2, NBN, RAD23B, and RAD54L as candidate DNA-repair pathway targets for prostate cancer radio-sensitization. When candidate shRNAs were conjugated to the PSMA-targeting RNA aptamer, A10-3, they were selectively delivered into PSMA positive prostate cancer cells in the absence of traditional transfection reagents. The shRNA portion was then processed by dicer to the corresponding siRNA. DNA-PK shRNAs, delivered by PSMA-targeting RNA aptamers, selectively reduced DNA-PK in PCa cells, xenografts and human prostate tissues. The mechanism of DNA-PK knock-down was confirmed to be through RNA interference by 5’-RACE assay. In tumor injection models A10-3-DNA-PK-shRNAs, combined with IR, dramatically and specifically enhanced PSMA-positive tumor response to IR. This treatment extended time to reach quadruple tumor volume by approximately 10 weeks when compared to only one week in tumors treated with radiation and control aptamer-shRNAs. A10-3-DNA-PK-shRNA and radiation had no affect on the PSMA negative PC-3 tumors. These studies support aptamer-shRNAs as selective sensitizing agents which may improve the treatment of high-risk localized PCa. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5387. doi:10.1158/1538-7445.AM2011-5387

Low-Dose Valproic Acid Enhances Radiosensitivity of Prostate Cancer through Acetylated p53-Dependent Modulation of Mitochondrial Membrane Potential and Apoptosis

Histone deacetylase inhibitors (HDI) have shown promise as candidate radiosensitizers for many types of cancers, including prostate cancer. However, the mechanisms of action are not well understood. In this study, we show in prostate cancer cells that valproic acid (VPA) at low concentrations has minimal cytotoxic effects yet can significantly increase radiation-induced apoptosis. VPA seems to stabilize a specific acetyl modification (lysine 120) of the p53 tumor suppressor protein, resulting in an increase in its proapoptotic function at the mitochondrial membrane. These effects of VPA are independent of any action of the p53 protein as a transcription factor in the nucleus, since these effects were also observed in native and engineered prostate cancer cells containing mutant forms of p53 protein having no transcription factor activity. Transcription levels of p53-related or Bcl-2 family member proapoptotic proteins were not affected by VPA exposure. The results of this study suggest that, in addition to nuclear-based pathways previously reported, HDIs may also result in radiosensitization at lower concentrations via a specific p53 acetylation and its mitochondrial-based pathway(s).

Radiosensitization of MYC-overexpressing prostate cancer cells by statins.

26 Background: Studies have shown a link between HMG-CoA reductase inhibitors (statins) and decreased cancer risk in various cancers including prostate cancer. Recent clinical studies have shown improved outcome for men on statin therapy receiving definitive radiation therapy compared to radiation therapy alone for prostate cancer. The oncogene Ras can be inhibited by statin treatment and in turn also result in targeted downregulation of Myc. Inactivation of Myc has been shown to induce tumor regression in transgenic mouse models of different cancers. Methods: Utilizing both in vitro and in vivo models, we studied in MYC over-expressing prostate cancer cells statin induced cytotoxicity and radiosensitization. We studied the effect of statin treatment with and without radiation treatment on in vitro cell death and clonogenic survival and correlated effects to levels of MYC and phospho-MYC. We constructed mutant cell lines to specifically examine the MYC-dependent effects of statins on prostate cancer cell cytotoxicity and radiosensitization. We performed similar studies in vivo using subcutaneous tumor grafts. Results: Statin treatment alone of prostate cancer cells resulted in increased cell death and decreased clonegenic survival. Statin treatment further sensitized prostate cancer cells to ionizing radiation as shown through colony formation assays. These cellular effects were associated with decreased levels of active MYC as confirmed by western and phospho-western analysis. Statin-induced cell death and decreased MYC levels could be rescued with the HMG-CoA bypass product mevalonate. Finally, flank tumor graft experiments demonstrated the ability of statins and radiation to delay tumor growth in vivo. Conclusions: Our preliminary data have implicated MYC as a potential critical target for the cytotoxic effects of statins on prostate cancer cells. The prevalence of MYC overexpression in human prostate cancers is as high as 80%. Thus the ability of statins to radiosensitize MYC overexpressing prostate cancer cells may provide a mechanistic explanation to the improved outcomes for men taking statins while on radiation therapy and now may afford us a molecular biomarker to examine this phenomenon in the clinic. No significant financial relationships to disclose.

Adenovirus E2F1 Overexpression Sensitizes LNCaP and PC3 Prostate Tumor Cells to Radiation In Vivo

We previously showed that E2F1 overexpression radiosensitizes prostate cancer cells in vitro. Here, we demonstrate the radiosensitization efficacy of adenovirus (Ad)-E2F1 infection in growing (orthotopic) LNCaP and (subcutaneous) PC3 nude mice xenograft tumors. Ad-E2F1 was injected intratumorally in LNCaP (3 × 10(8) plaque-forming units [PFU]) and PC3 (5 × 10(8) PFU) tumors treated with or without radiation. LNCaP tumor volumes (TV) were measured by magnetic resonance imaging, caliper were used to measure PC3 tumors, and serum prostate-specific antigen (PSA) levels were determined by enzyme-linked immunosorbent assay. Apoptosis was measured by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, and key proteins involved in cell death signaling were analyzed by Western blotting. Intracellular overexpression of Ad-E2F1 had a significant effect on the regression of TV and reduction of PSA levels relative to that of adenoviral luciferase (Ad-Luc)-infected control. The in vivo regressing effect of Ad-E2F1 on LNCaP tumor growth was significant (PSA, 34 ng/ml; TV, 142 mm(3)) compared to that of Ad-Luc control (PSA, 59 ng/ml; TV, 218 mm(3); p <0.05). This effect was significantly enhanced by radiation therapy (compare: Ad-E2F1+RT/PSA, 16 ng/ml, and TV, 55 mm(3) to Ad-Luc+RT/PSA, 42 ng/ml, and TV, 174 mm(3), respectively; p <0.05). For PC3 tumors, the greatest effect was observed with Ad-E2F1 infection alone; there was little or no effect when radiotherapy (RT) was combined. However, addition of RT enhanced the level of in situ apoptosis in PC3 tumors. Molecularly, addition of Ad-E2F1 in a combination treatment abrogated radiation-induced BCL-2 protein expression and was associated with an increase in activated BAX, and together they caused a potent radiosensitizing effect, irrespective of p53 and androgen receptor functional status. We show here for the first time that ectopic overexpression of E2F1 in vivo, using an adenoviral vector, significantly inhibits orthotopic p53 wild-type LNCaP tumors and subcutaneous p53-null PC3 tumors in nude mice. Furthermore, we demonstrate that E2F1 strongly sensitizes LNCaP tumors to RT. These findings suggest that E2F1 overexpression can sensitize prostate tumor cells in vivo, independent of p53 or androgen receptor status.

Prostate Cancer Radiosensitization through Poly(ADP-Ribose) Polymerase-1 Hyperactivation

The clinical experimental agent, β-lapachone (β-lap; Arq 501), can act as a potent radiosensitizer in vitro through an unknown mechanism. In this study, we analyzed the mechanism to determine whether β-lap may warrant clinical evaluation as a radiosensitizer. β-Lap killed prostate cancer cells by NAD(P)H:quinone oxidoreductase 1 (NQO1) metabolic bioactivation, triggering a massive induction of reactive oxygen species, irreversible DNA single-strand breaks (SSB), poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation, NAD(+)/ATP depletion, and μ-calpain-induced programmed necrosis. In combination with ionizing radiation (IR), β-lap radiosensitized NQO1(+) prostate cancer cells under conditions where nontoxic doses of either agent alone achieved threshold levels of SSBs required for hyperactivation of PARP-1. Combination therapy significantly elevated SSB level, γ-H2AX foci formation, and poly(ADP-ribosylation) of PARP-1, which were associated with ATP loss and induction of μ-calpain-induced programmed cell death. Radiosensitization by β-lap was blocked by the NQO1 inhibitor dicoumarol or the PARP-1 inhibitor DPQ. In a mouse xenograft model of prostate cancer, β-lap synergized with IR to promote antitumor efficacy. NQO1 levels were elevated in ∼60% of human prostate tumors evaluated relative to adjacent normal tissue, where β-lap might be efficacious alone or in combination with radiation. Our findings offer a rationale for the clinical utilization of β-lap (Arq 501) as a radiosensitizer in prostate cancers that overexpress NQO1, offering a potentially synergistic targeting strategy to exploit PARP-1 hyperactivation.

The PhScN Peptide as a Potent Agent for Targeting Both Invasion and Survival and for Increasing Radiosensitivity in Human Prostate Cancer

Purpose/Objectives(s): Metastatic invasion is caused by constitutive activation of the alpha5 beta1 integrin fibronectin receptor (FnR), and is blocked by the PHSCN peptide (Ac-PHSCN-NH2) in both preclinical models and in Phase 1 clinical trial. An endoproteinase-resistant derivative of Ac-PHSCN-NH2 was made by including D-isomers of Histidine and Cysteine to form the PhScN peptide: Ac-PhScN-NH2. Ac-PhScN-NH2 is a highly potent inhibitor of alpha5 beta1 integrin-mediated invasion and survival of human prostate cancer cells, both in vitro and in vivo.

Targeted Radiosensitization of ETS Gene Fusion-Positive Prostate Cancer

Targeted Radiosensitization of ETS Gene Fusion-Positive Prostate Cancer

Preclinical Evaluation of Sunitinib, a Multi Tyrosine Kinase Inhibitor as a Radiosensitizer for Human Prostate Cancer

Preclinical Evaluation of Sunitinib, a Multi Tyrosine Kinase Inhibitor as a Radiosensitizer for Human Prostate Cancer

Truncated E2F1 Radiosensitizes Prostate Cancer Cells by Inhibiting The E3 Ubiquitin Ligase SKP2

Ectopic overexpression of E2F1 via an adenoviral vector has been shown to induce apoptosis in cancer cells. Our earlier studies show that E2F1 overexpression sensitizes prostate cancer cells to radiation in vitro and in vivo. However, E2F1 overexpression induces proliferation and may potentiate transformation. To address this concern, a truncated version, E2F1[108], without the DP1, DNA, RB binding domains was constructed. E2F1[108] retains the binding domain for S-phase kinase associated protein 2 (SKP2), an F-box protein that degrades cell-cycle regulators and proapoptotic factors (FOXO) by ubiquitin dependent mechanism.

Abstract 5541: Daidzein protects against genistein-induced lymph node metastasis, and serve as a radiosensitizer in prostate cancer

Abstract We have previously reported that genistein, the major bioactive isoflavone of soybeans, acts as a radiosensitizer for prostate cancer (PCa) both in vitro and in orthotopic mouse models in vivo. However, pure genistein promoted increased spontaneous metastasis to regional lymph nodes, when administered alone in vivo. In contrast to genistein, a natural formulation of soy isoflavones mixture (43% genistein, 21% daidzein and 2% glycitein) did not cause increased metastasis, but like genistein, the soy mixture potentiated the therapeutic effect of radiation. We have now tested whether daidzein, the second main isoflavone of soybeans, could negate genistein-induced lymph node metastasis in PC-3 orthotopic prostate tumors in nude mice. Mice were treated with purified daidzein, or genistein or both combined; and also in conjunction with prostate tumor irradiation. Either daidzein or genistein alone or both combined caused the same extent of prostate tumor growth inhibition than the soy mixture. Treatment with daidzein alone did not increase metastasis to regional lymph nodes but still acted as a potent radiosensitizer for prostate tumors. Treatment with both genistein and daidzein combined did not cause an increase in lymph node metastasis, which is consistent with the findings obtained with the soy mixture. These studies show that pure daidzein could be the component of the soy isoflavones mixture that protects against genistein-induced lymph node metastasis. In order to gain further mechanistic insight on how daidzein negates the adverse effects of genistein, we compared the effects of each isoflavone and the soy mixture in vitro using PC-3 (androgen receptor AR-) and C4-2B (AR+) androgen independent PCa cell lines. We found that daidzein inhibited tumor cell growth and synergized with radiation in clonogenic assays but at doses higher than genistein or the soy mixture. We have previously demonstrated that genistein or the soy mixture cause tumor cell apoptosis and enhance radiation killing by inhibiting cell survival pathways activated by radiation including the repair enzyme/redox activator APE1/Ref-1 and the transcription factors HIF-1α and NF-κB. Compared to the effect of genistein or the soy mixture, daidzein treatment caused milder effects on PARP cleavage, inhibition of expression of APE1/Ref-1 and HIF-1α; and lower inhibition of HIF-1α and NF-κB DNA binding activities. These effects were reproduced in both PC-3 and C4-2B cell lines. Based on these results, we conclude that APE1/Ref-1, NF-κB and HIF-1α molecular pathways were also affected by daidzein, although to a lesser extent than genistein and soy mixture, in both AR+ and AR- PCa cancer cell lines, suggesting that this is an AR-independent mechanism. The protective effect of daidzein against lymph node metastasis induced by genistein appears to be independent of HIF-1α and NF-κB pathways, and remains to be clarified. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5541.

Abstract 1398: Aurora kinase A inhibition with MLN8054 radiosensitizes prostate cancer by inducing cell cycle arrest leading to increased prolonged DNA damage and apoptosis

Abstract The purpose of this study is to investigate a potential new radioenhancer for the treatment of prostate cancer. Despite multiple promising treatment modalities, prostate cancer remains a significant cause of diminished quality of life and cancer death, indicating the need for more aggressive, targeted therapy. Aurora kinase A (AURKA) is a promising treatment target, but its inhibition has never been investigated in combination with radiotherapy in prostate cancer. Using the selective AURKA inhibitor, MLN8054, we performed clonogenic assay to investigate in vitro radiosensitization, cell cycle analysis to observe changes induced by AURKA inhibition, tumor growth delay to study in vivo effects, and histologic active caspase staining to measure apoptosis. We demonstrated radiosensitizing effects in vitro in PC3 and DU145 prostate cancer cell lines, which was confirmed in vivo by tumor growth delay in PC3 xenografts in nude mice. In addition, we investigated a potential mechanism for radiosensitization. We report that MLN8054 induces cell cycle arrest at G2/M and polyploidy in both prostate cancer cell lines, which is associated with sustained DNA damage from radiation as seen by increased immunofluorescence for γ-H2AX, a measure of DNA double-strand breaks. Staining for caspase-3 in xenograft samples showed increased apoptosis in irradiated samples pre-treated with MLN8054 compared to irradiation or inhibitor alone. Our findings support the potential use of AURKA inhibition with MLN8054 to enhance the effectiveness of radiation therapy for the treatment of prostate cancer, and suggest a potential mechanism underlying its radiosensitization effects. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1398.

Abstract 1503: PSMA Aptamer-targeted siRNAs selectively Eehance prostate cancer radiation sensitivity

Abstract The application of dose escalated radiation therapy for localized prostate cancer has a clear therapeutic benefit; however, its clinical use is hampered by the increased risk of damage to surrounding normal tissues. One attractive alternative to elevated doses is radiation sensitizing agents. Prostate cancer cells can be made radiosensitive by targeted reductions of DNA repair proteins via RNA interference. However, without tissue-selective targeting, these agents will also sensitize surrounding tissue, leading to increased adverse effects. Here we describe a strategy where prostate-targeted RNA interference is used to selectively radio-sensitize prostate cancer cells. A high throughput siRNA screen was completed to identify DNA-repair pathway targets for prostate cancer radio-sensitization. Candidate siRNAs were then conjugated to PSMA-targeted RNA aptamers for selective delivery of siRNAs to Prostate cancer cells. In vitro and in vivo data support PSMA and aptamer-specific targeting and gene knock-down. These studies support continued development of this technology as a path to enhance radiotherapeutic outcomes for men with Prostate cancer and it is the first report of targeted, prostate-specific siRNAs for radio-sensitization. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1503.

Daidzein Effect on Hormone Refractory Prostate Cancer In Vitro and In Vivo Compared to Genistein and Soy Extract: Potentiation of Radiotherapy

Genistein, the major bioactive isoflavone of soybeans, acts as a radiosensitizer for prostate cancer (PCa) both in vitro and in vivo. However, pure genistein promoted increased metastasis to lymph nodes. A mixture of soy isoflavones (genistein, daidzein, glycitein) did not cause increased metastasis, but potentiated radiotherapy. We tested whether daidzein could negate genistein-induced metastasis. Mice bearing PC-3 prostate tumors were treated with daidzein, genistein or both, and with tumor irradiation. Primary tumors and metastases were evaluated. The effects of each isoflavone and soy were compared in vitro using PC-3 (AR-) and C4-2B (AR+) androgen-independent PCa cell lines. Daidzein did not increase metastasis to lymph nodes and acted as a radiosensitizer for prostate tumors. Daidzein inhibited cell growth and enhanced radiation in vitro but at doses higher than genistein or soy. Daidzein caused milder effects on inhibition of expression and/or activities of APE1/Ref-1, HIF-1alpha and NF-kappaB in PC-3 and C4-2B cells. Daidzein could be the component of soy that protects against genistein-induced metastasis. Daidzein inhibited cell growth and synergized with radiation, affecting APE1/Ref-1, NF-kappaB and HIF-1alpha, but at lower levels than genistein and soy, in AR+ and AR- PCa cells, suggesting it is an AR-independent mechanism.

Synergistic Effect Between Curcumin (diferuloylmethane) and Radiation on Clonogenic Cell Death Independent of p53 in Prostate Cancer Cells

Radiotherapy is a common treatment for prostate cancer, but failure is observed 30 to 40% of the time. It is more common in patients with abnormal p53. The phytochemical diferuloylmethane (curcumin) a naturally occurring fl avinoid derived from the rhizome of Curcuma longa, shows potential radiosensitizing effects. In the present study, the effect of curcumin and radiation on cell viability, apoptosis and clonogenic cell death was examined in LNCaP (wild type p53) and PC3 (mutant p53) prostate cancer cells. The expression of p53 and p53 target genes was examined using RNase protection assay and Western blot analysis. Cell cycle and apoptosis was evaluated by fl ow cytometry. Cell viability and colony formation was examined using MTT assay and clonogenic assay respectively. The expression of p53, p21 and gadd45 increased in LNCaP cells after radiation exposure. In PC3 cells, there was no change in expression in mutant p53 after radiation or curcumin treatment. However, the expression of p21 and gadd45 increased after curcumin treatment in PC3 cells independent of p53. Curcumin induced cell growth arrest and apoptosis in both the cell lines. The cell viability and cell proliferation decreased in presence of both curcumin and radiation as compared to curcumin or radiation alone in both the cell lines. Regardless of p53 status, combination treatment with curcumin (2.5 to 10 μM) and radiation (2 Gy) had a synergistic effect on clonogenic cell death in both LNCaP and PC3 cells. Conclusion: Curcumin appears to radiosensitize prostate cancer cells and may be a possible adjuvant to radiotherapy in the treatment of prostate cancers.

Molecularly Targeted Radiosensitization of Human Prostate Cancer by Modulating Inhibitor of Apoptosis

The inhibitor of apoptosis proteins (IAP) are overexpressed in hormone-refractory prostate cancer, rendering the cancer cells resistant to radiation. This study aims to investigate the radiosensitizing effect of small-molecule IAP inhibitor both in vitro and in vivo in androgen-independent prostate cancer and the possible mechanism of radiosensitization. Radiosensitization of SH-130 in human prostate cancer DU-145 cells was determined by clonogenic survival assay. Combination effect of SH-130 and ionizing radiation was evaluated by apoptosis assays. Pull-down and immunoprecipitation assays were employed to investigate the interaction between SH-130 and IAPs. DU-145 xenografts in nude mice were treated with SH-130, radiation, or combination, and tumor suppression effect was determined by caliper measurement or bioluminescence imaging. Nuclear factor-kappaB activation was detected by luciferase reporter assay and quantitative real-time PCR. SH-130 potently enhanced radiation-induced caspase activation and apoptosis in DU-145 cells. Both X-linked IAP and cIAP-1 can be pulled down by SH-130 but not by inactive SH-123. Moreover, SH-130 interrupted interaction between X-linked IAP/cIAP-1 and Smac. In a nude mouse xenograft model, SH-130 potently sensitized the DU-145 tumors to X-ray radiation without increasing systemic toxicity. The combination therapy suppressed tumor growth more significantly than either treatment alone, with over 80% of complete tumor regression. Furthermore, SH-130 partially blocked tumor necrosis factor-alpha- and radiation-induced nuclear factor-kappaB activation in DU-145 cells. Our results show that small-molecule inhibitors of IAPs can overcome apoptosis resistance and radiosensitize human prostate cancer with high levels of IAPs. Molecular modulation of IAPs may improve the outcome of prostate cancer radiotherapy.

Targeting Cdc37 Radiosensitizes Prostate Cancer Cells by Inhibiting Multiple Kinase Cascades

Targeting Cdc37 Radiosensitizes Prostate Cancer Cells by Inhibiting Multiple Kinase Cascades

Triple Suicide Gene Therapy Radiosensitizes Prostate Cancer Cells

The double suicide gene therapy strategy combining herpes simplex virus type-1 thymidine kinase (HSV-1 TK) and cytosine deaminase (CD) with ganciclovir (GCV) and 5-fluorocytosine (5-FC) had been carried out in a phase I clinical trail for prostate cancer. The objective of the present study was to ascertain whether co-expression of HSV-1 TK, CD, and uracil phosphoribosyltransferase (UPRT) in conjunction with GCV and 5-FC treatment, a triple suicide gene therapy strategy, would be more effective at killing and radiosensitizing prostate cancer cells than double suicide gene therapy.

Immunosuppressive drug FTY720 sensitizes prostate cancer cells to radiotherapy by inhibition of sphingosine kinase‐1.

A sphingolipid analogue FTY720 is a novel immunosuppressive drug – an agonist of sphingosine 1‐phosphate (S1P) receptors. Recently we identified S1P as a therapy target in prostate cancer. In the current study we have demonstrated that FTY720 can radiosensitize prostate cancer in cell and animal models.FTY720 has induced apoptosis in several hormone‐ and radio‐resistant prostate cancer cell lines. FTY720 treatment induced a sustained inhibition of prosurvival sphingosine kinase‐1 (SK1) and a decrease in the intracellular S1P content. Enforced expression of SK1 in prostate cancer cells rendered them resistant to FTY720. In vitro sub‐lethal concentrations of FTY720 have dramatically sensitized PC‐3 cells to radiotherapy in p53‐independent manner.Mice orthotopically engrafted with fluorescent PC‐3 cells were treated with FTY720 with or without ã‐Irradiation. FTY720 has demonstrated a synergy with ã‐irradiation significantly reducing tumor size, angiogenesis and formation of micrometastases as demonstrated by fluorescent in vivo imaging.In conclusion, FTY720 can sensitize prostate cancer cells to radiotherapy both in vitro and in vivo, through inhibition of SK1 and modification of intracellular levels of lipid second messengers.