Preclinical Models Of Prostate Cancer Research Articles

Abstract B19: Induction of apoptosis and antitumor activity of the AKT inhibitor AZD5363 is enhanced by combination with hormonal therapies in preclinical models of prostate cancer

Abstract Activation of AKT by mechanisms including loss of the tumor suppressors PTEN and INPP4B is very common in prostate cancer, and has been correlated with poor prognosis and progression to androgen independent disease. Recently, a reciprocal feedback mechanism has been shown to occur between the androgen and AKT signalling axes in prostate cancer models. AZD5363 monotherapy induced apoptosis and inhibited growth of PTEN null, AR+ prostate cancer cell lines including LNCaP, C4-2 and a flutamide resistant variant of PC346C (GI50 10 – 100 nM), and showed moderate anti-proliferative activity in AR amplified, PTEN wild type VCaP cells (GI50 ∼ 1 μM). The PTEN wild type, AR negative DU-145, BPH1 and RWPE1 cell lines were relatively resistant. Monotherapy AZD5363 also caused dosedependent growth inhibition of the PTEN null, AR+ HID28 prostate cancer explant model in vivo. Treatment with AZD5363 increased expression of a panel of androgen regulated genes in LNCaP cells, whereas the same panel of genes was down-regulated when AZD5363 was combined with the novel anti-androgen MDV-3100. Combination of AZD5363 with MDV-3100 resulted in greater inhibition of growth and induction of apoptosis in vitro than monotherapy treatment with these agents, indicating a synergistic interaction. Moreover, combination of AZD5363 and bicalutamide resulted in greater efficacy than AZD5363 monotherapy in LNCaP xenografts in vivo. The data show that whilst AZD5363 has considerable monotherapy activity in AR+/PTEN null prostate cancer models, the combination with anti-androgens merits further evaluation as a possible means to achieve greater anti-tumor activity. AZD5363 is currently in Phase 1 clinical trials. Citation Format: Claire Crafter, Barry R. Davies, Christian Thomas, Francois Lamoureux, Hannah Greenwood, Juan M. Garcia-Martinez, Lorraine Mooney, Sabina Cosulich, Martin Gleave, Amina Zoubeidi. Induction of apoptosis and antitumor activity of the AKT inhibitor AZD5363 is enhanced by combination with hormonal therapies in preclinical models of prostate cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B19.

Abstract C41: Nuclear Stat5a/b predicts early recurrence and prostate cancer-specific death in patients treated by radical prostatectomy.

Abstract There is an urgent need for reliable markers to identify patients whose PCa is most likely to recur after initial therapy and progress to lethal disease. While Gleason score is considered the most accurate predictive marker for disease-specific mortality after primary treatment of localized prostate cancer (PCa), the majority of PCas cluster into intermediate group of Gleason scores 6 and 7 where there is considerable variation in treatment response, disease recurrence and disease-specific death. In this study, we analyzed the predictive value of elevated nuclear Stat5a/b expression in PCas treated by radical prostatectomy or active surveillance. The critical role of Stat5a/b in promotion of PCa growth and progression has been well-documented in preclinical PCa models. Specifically, Stat5a/b is critical for prostate cancer cell viability in vitro and for prostate tumor growth in vivo, and Stat5a/b promotes metastatic dissemination of prostate cancer in nude mice. Here, we demonstrate that in intermediate Gleason score PCas treated by radical prostatectomy, high levels of nuclear Stat5a/b predicted both early recurrence (univariate analysis; p<0.0001, multivariate analysis; HR=0.55, p=0.017) and early PCa-specific death (univariate analysis; p=0.028). In addition, high nuclear Stat5a/b predicted early disease recurrence in both univariate (p<0.0001) and multivariate (HR=0.62; p<0.01) analysis in the entire cohort of patients treated by radical prostatectomy (n=562) regardless of the Gleason score. In the second group of patients treated by active surveillance, elevated nuclear Stat5a/b expression was associated with early PCa-specific death (p=0.0453) by univariate analysis (Cox regression analysis: 60% increased risk of death, p=0.034). If confirmed in future prospective studies, nuclear Stat5a/b may become a useful independent predictive marker of recurrence of lethal PCa after radical prostatectomy for intermediate Gleason score PCas. Citation Format: Tuomas Mirtti, Benjamin E. Leiby, Pär Stattin, Anders Bergh, Marja T. Nevalainen, Junaid Abdulghani, Miia Pavela, Elina Aaltonen, Anita Mamtani, Kalle A. Alanen, Lars Egevad, Torvald Granfors, Andreas Josefsson. Nuclear Stat5a/b predicts early recurrence and prostate cancer-specific death in patients treated by radical prostatectomy [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C41.

1163 POSTER A Therapeutic Sphingosine 1-phosphate Antibody Inhibits Intratumoral Hypoxia and Sensitizes to Standard Chemotherapy in a Preclinical Model of Prostate Cancer

1163 POSTER A Therapeutic Sphingosine 1-phosphate Antibody Inhibits Intratumoral Hypoxia and Sensitizes to Standard Chemotherapy in a Preclinical Model of Prostate Cancer

Tasquinimod prevents the angiogenic rebound induced by fractionated radiation resulting in an enhanced therapeutic response of prostate cancer xenografts

Tasquinimod is a novel inhibitor of tumor angiogenesis which enhances therapeutic efficacy when combined with androgen ablation and/or taxane-based chemotherapies in pre-clinical prostate cancer models. It has entered registration Phase III evaluation for the treatment of castration resistant prostate cancer. Since tasquinimod suppresses the angiogenic switch induced by tumor hypoxia as prostate cancers outgrow their blood supply, this raises the issue of whether tasquinimod also suppresses the angiogenic rebound induced by fractionated radiation thereby enhancing therapeutic response to fractionated radiation. Human endothelial and prostate cancer cells in culture and human prostate cancer xenografts growing in castrated male nude mice were evaluated for their response to radiation alone and in combination with tasquinimod. At clinically relevant drug levels, tasquinimod significantly (P < 0.05) enhances anti-cancer efficacy of fractionated radiation with optimal timing for initiating daily tasquinimod treatment being after completion of the fractionated radiation. Based upon cell culture studies and tumor tissue oxygenation (i.e., pO(2)), tumor vascular volume, and tumor blood vessel density measurements, the mechanism for such enhancement and optimal timing involves tasquinimod's ability to prevent the angiogenic rebound induced by fractionated radiation.

Targeting of αv-Integrins in Stem/Progenitor Cells and Supportive Microenvironment Impairs Bone Metastasis in Human Prostate Cancer

Acquisition of an invasive phenotype by cancer cells is a requirement for bone metastasis. Transformed epithelial cells can switch to a motile, mesenchymal phenotype by epithelial-mesenchymal transition (EMT). Recently, it has been shown that EMT is functionally linked to prostate cancer stem cells, which are not only critically involved in prostate cancer maintenance but also in bone metastasis. We showed that treatment with the non-peptide αv-integrin antagonist GLPG0187 dose-dependently increased the E-cadherin/vimentin ratio, rendering the cells a more epithelial, sessile phenotype. In addition, GLPG0187 dose-dependently diminished the size of the aldehyde dehydrogenase high subpopulation of prostate cancer cells, suggesting that αv-integrin plays an important role in maintaining the prostate cancer stem/progenitor pool. Our data show that GLPG0187 is a potent inhibitor of osteoclastic bone resorption and angiogenesis in vitro and in vivo. Real-time bioluminescent imaging in preclinical models of prostate cancer demonstrated that blocking αv-integrins by GLPG0187 markedly reduced their metastatic tumor growth according to preventive and curative protocols. Bone tumor burden was significantly lower in the preventive protocol. In addition, the number of bone metastases/mouse was significantly inhibited. In the curative protocol, the progression of bone metastases and the formation of new bone metastases during the treatment period was significantly inhibited. In conclusion, we demonstrate that targeting of integrins by GLPG0187 can inhibit the de novo formation and progression of bone metastases in prostate cancer by antitumor (including inhibition of EMT and the size of the prostate cancer stem cell population), antiresorptive, and antiangiogenic mechanisms.

Evaluation of bombesin receptor (BB2r) targeted radiotherapy, chemotherapy, and zoledronic acid in a preclinical model of prostate cancer.

e15122 Background: The majority of patients who die of prostate cancer have metastatic castration-resistant disease (CRPC). Available therapies provide modest prolongation of survival measured in months. We have previously demonstrated that the use of BB2r targeted radiation therapy (TRT) using 177Lu-DOTA-8-AOC-BBN (7-14)NH2 in combination with chemotherapy suppressed tumor growth in SCID mice in both flank and intra-tibial models employing PC-3 cells; however, significant bone loss resulting in tibial fracture was a predominant deterrent to prolonged subject survival. Since zoledronic acid (ZA) is effective in treatment of diseases with pathologically increased osteoclast-mediated bone resorption, including metastatic bone disease, we postulated that by adding ZA, tibial fractures can be delayed resulting in improved outcomes. Methods: In a randomized study, SCID mice received intra-tibial inoculation of PC-3 cells on day (-7). Therapy (Table) was started on day(+1). Daily weight and body condition scores (BCS) and weekly radiographs were collected. Subjects were given two “21day” cycles. Subjects were removed upon reaching predetermined endpoint criteria including tibial fracture, BCS of ≤-2, significant weight loss. Results: At study termination(Day 86) 83% of the mice in Arm C(TRT+CT+ZA) and 80% of mice in Arm A(CT+ZA) had survived as compared to 29% of the mice in Arm B(CT+TRT). Health status of mice in Arm B consistently declined over the study duration, with subject removal beginning at Day 20resulting from stated endpoint criteria. Conclusions: ZA used in combination with BB2rTRT and chemotherapy is effective in prolonging short term survival in a preclinical model of CRPC. Further studies are required to ascertain if the addition of BB2r TRT to a ZA+chemotherapy regimen results in significantly improved outcomes. Therapy/day Mon Tue Wed Thu Fri Sat Sun Arm A (n=10) CT ZA CT CT CT ZA CT Rest Rest Arm B (n=7) CT CT CT TRT CT CT Rest Rest Arm C (n=6) CT ZA CT CT TRT CT ZA CT Rest Rest Control (n=2) A therapy cycle was given every 3 weeks; Chemotherapy (CT): docetaxel(ip) D1,8,15/capecitabine(po) D1-5,8-12;ZA:subcut 100mcg/kg D1,4,8,11,15,18; TRT(ip) D3,10,17.

Synergistic potentiation of antitumor immunity with light-activated drug therapy and anti-CTLA4 antibody treatment.

e13034 Background: Talaporfin sodium (TS) is a light-activated, locally cytoreductive drug in Phase 3 clinical trials for several different cancers. It is activated intratumorally with a thin, flexible LED array. TS treatment has been shown in preclinical studies to activate CD8+-dependent anti-tumor immunity in a model of metastatic breast cancer. Anti-CTLA4 antibody is an immunotherapy that acts by suppressing negative regulation of immune effectors. It has recently completed a successful Phase 3 clinical trial in melanoma patients in which it was shown to prolong survival.TS and anti-CTLA4 antibody have great potential to synergistically reduce primary tumor burden and generate systemic anti-tumor immunity. Methods: This study examined combination treatment with these two therapies in a murine prostate cancer tumor model (C57BL/6 + TRAMP C2). A large, established tumor on the left side of each mouse was treated with light-activated TS (or light-only control). One day after treatment, mice were injected intradermally with 0.5 x 106 TRAMP C2 cells on the opposite flank. Anti-CTLA4 (or vehicle control) was given on days 1, 4, 7 and 10. Progression of the untreated tumor was measured. Results: Growth of untreated tumors was prevented or significantly delayed in 55% and 33% of combination-treated animals, respectively (n = 9). In addition, contralateral tumor growth was prevented in 1 of 9 animals given talaporfin sodium alone while another animal’s tumor showed growth delay. None of the untreated controls or anti-CTLA4 only animals showed a similar response. Individual combination-treated mice with delayed tumor growth often showed an atypical tumor growth curve in which progression either tapered off or began to reverse between 30 and 40 days post treatment. Conclusions: Reduction of tumor using local treatment with a light-activated drug could potentiate the anti-tumor immune response resulting from anti-CTLA4 treatment and prevent growth of secondary tumors in a preclinical prostate cancer model.

Abstract 5570: p53-dependent and p53-independent responses by green tea polyphenols in human prostate cancer cells

Abstract Green tea polyphenols (GTP) have been shown to provide protection against various preclinical models of prostate cancer. Recent studies conducted with GTP have provided evidence that it is effective at the initial stages of cancer development and could delay disease progression by perturbation of cell cycle and induction of apoptosis. Understanding the mechanisms that control GTP-mediated cellular responses is central to improving the therapeutic index and to encounter successfully the resistance frequently acquired during cancer therapy. p53, a tumor suppressor and a sequence-specific transcription factor senses a variety of stress signals to cells through multiple upstream signaling pathways and induces cell cycle arrest and/or apoptosis by modulating its downstream targets depending on the extent of cell damage, thus playing a central role in maintaining cellular homeostasis. p53 is either mutated or has defective signaling in most human cancers and might be one of the critical determinants for the GTP-mediated chemosensitivity of prostate tumors. We examined cell cycle and apoptosis related cellular responses to GTP exposure using human prostate cancer LNCaP cell which possess functional p53 and its variant where p53 was knocked out using shp53RNA. Exposure to various concentration of GTP (20, 40 and 80 mcg/mL) exhibited differential dose and time dependent resistance in these cells. Treatment of LNCaP cell containing empty vector with GTP caused cell cycle arrest and apoptosis which was associated with induction of p53 and its downstream cell cycle arrest and pro-apoptotic proteins p21, BIM and PUMA. In contrast, cell growth inhibition, cell cycle perturbation and induction of apoptosis in LNCaPshp53 cells was achieved at higher concentration of GTP, primarily because p53 knockdown resulted in activation of Akt phosphorylation at serine473 causing increased survival of cancer cells. To generate functional networks, protein expression of a number of genes involved in cell cycle and apoptosis, such as p21, Bad, Bax, Bcl-2, Bid, Bim, cIAP, XIAP, FAS, FADD, pFADD, p73, caspases 3, 8 and 9 was studied. Our results support the role of both p53-dependent and p53-independent responses in GTP-mediated cell cycle arrest and apoptosis of prostate cancer cells. These findings highlight the differential effect of Akt on p53 functions which seems to be responsible for the differential regulation of cell death by GTP in prostate cancer cells. Our findings become relevant as alterations in the protein expression profile could be used as in vivo markers in developing a molecular platform that could reliably monitor the responses of human prostate cancer cell populations to GTP-mediated therapeutic interventions, thereby providing clinical protocols with novel and powerful molecular tools for a more efficient and successful management of human prostate malignancies. 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 5570. doi:10.1158/1538-7445.AM2011-5570

Effect of dual inhibition of the Src and insulin-like growth factor-1 receptor (IGF-1R) pathways on antitumor effects in prostate cancer (PCa).

21 Background: The Src and IGF-1R axes are aberrantly activated in both PCa and the microenvironment of bone metastases. Dasatinib and BMS-754807 are clinically promising small molecule inhibitors with high potency against Src family kinases and IGF-1R, respectively. The aim of this study was to establish antitumor co-operativity by combining IGF-1R and Src blockade in a preclinical PCa model. Methods: LNCaP and PC3 cells were used as models for androgen-dependent and independent PCa, respectively. Inhibition of Src and IGF-1R pathways was accomplished by pharmacologic agents (dasatinib against Src and BMS-754807 against IGF-1R) as well as by shRNA. Serum IGF-1 levels were measured in patients (pts) with castration-resistant PCa (CRPC) treated with dasatinib and docetaxel in a phase II trial. Results: Src inhibition decreased proliferation of PCa cells, and migration in modified Boyden Chamber and wound assays. In contrast, IGF-1R blockade induced apoptosis (increased Sub-G1 fraction cells, Annexin-V(+) cells and PARP cleavage). Phosphorylation of Akt was partially inhibited by either drug alone and almost completely abrogated by the combination. Intraprostatic injection of shIGF-1R or shSrc PC3 cells in nude mice led to an 83% and 60% decrease in tumor size compared to control shRNA, respectively. In both cell lines, all observed antitumor effects were enhanced when dual blockade was used, relative to blocking the Src or IGF-1R pathway alone. In 9/19 (47%) pts with CRPC, treatment with dasatinib resulted in a compensatory increase of serum IGF-1 levels. Conclusions: Dual inhibition of Src and IGF-1R is effective and complementary in PCa, mediated, in part, through inhibition of the downstream target Akt. In about half of pts treated with dasatinib, an increase in soluble IGF-1 levels was observed, indicating there is a compensatory upregulation of survival pathways that might be abrogated by dual inhibition of Src and IGF-1R. The combination of dasatinib and BMS-754807 may be a rational therapeutic approach in PCa by blocking complementary processes of tumor growth and progression. [Table: see text]

Synergistic potentiation of anti-tumor immunity with light-activated drug therapy and anti-CTLA4 antibody treatment.

27 Background: Talaporfin sodium (TS) is a light-activated, locally cytoreductive drug in phase III clinical trials for several different cancers. It is activated intratumorally with a thin, flexible LED array. TS treatment has been shown in preclinical studies to activate CD8+-dependent anti-tumor immunity in a model of metastatic breast cancer. Anti-CTLA4 antibody is an immunotherapy that acts by suppressing negative regulation of immune effectors. It has recently completed a successful phase III clinical trial in melanoma patients in which it was shown to prolong survival. TS and anti-CTLA4 antibody have great potential to synergistically reduce primary tumor burden and generate systemic anti-tumor immunity. Methods: This study examined combination treatment with these two therapies in a murine prostate cancer tumor model (C57BL/6 + TRAMP C2). A large, established tumor on the left side of each mouse was treated with light-activated TS (or light- only control). One day after treatment, mice were injected intradermally with 0.5 × 106 TRAMP C2 cells on the opposite flank. Anti-CTLA4 (or vehicle control) was given on days 1, 4, 7 and 10. Progression of the untreated tumor was measured. Results: Growth of untreated tumors was prevented or significantly delayed in 55% and 33% of combination-treated animals, respectively (n = 9). In addition, contralateral tumor growth was prevented in 1 of 9 animals given talaporfin sodium alone while another animal's tumor showed growth delay. None of the untreated controls or anti-CTLA4 only animals showed a similar response. Individual combination-treated mice with delayed tumor growth often showed an atypical tumor growth curve in which progression either tapered off or began to reverse between 30 and 40 days post treatment. Conclusions: Reduction of tumor using local treatment with a light-activated drug could potentiate the anti-tumor immune response resulting from anti-CTLA4 treatment and prevent growth of secondary tumors in a preclinical prostate cancer model. [Table: see text]

Epithelial–mesenchymal transition in prostate cancer: providing new targets for therapy

Epithelial–mesenchymal transition in prostate cancer: providing new targets for therapy

Preclinical Mouse Models of Human Prostate Cancer and Their Utility in Drug Discovery

In vivo animal experiments are essential to current prostate cancer research, and are particularly critical to studying interactions between tumor cells and their microenvironment. Numerous pre-clinical animal models of prostate cancer are currently available, including transgenic mouse models and human prostate cancer xenograft mouse models. In contrast to transgenic mouse models producing more heterogeneous cohorts of tumors, xenograft mouse models provide more controlled approaches. This unit describes the detailed procedures necessary to establish several distinct pre-clinical mouse models of human prostate cancer, including an orthotopic prostate xenograft model, an orthotopic bone metastasis model, an experimental metastasis model of intra-cardiac injection, and a vossicle model of tumor-bone interaction.

657 Anti-tumor growth effect of TAK-683, a metastin analogue, in preclinical androgen-dependent prostate cancer models

657 Anti-tumor growth effect of TAK-683, a metastin analogue, in preclinical androgen-dependent prostate cancer models

Comment on “Androgen‐hypersensitive preclinical model of prostate cancer” by Kawata et al.

Comment on “Androgen‐hypersensitive preclinical model of prostate cancer” by Kawata et al.

Chemoprevention of prostate cancer with lycopene in the TRAMP model

Dietary lycopene combined with other constituents from whole tomatoes was previously found to have greater chemopreventive effects against prostate cancer as compared to pure lycopene provided in a beadlet formulation. We hypothesized that tomato paste would have greater chemopreventive effects in transgenic adenocarcinoma of the mouse prostate (TRAMP) mice relative to equivalent lycopene doses provided from lycopene beadlets. Fifty-nine TRAMP mice were randomized to a control diet or to diets providing 28 mg lycopene per kg diet from tomato paste (TP) or from lycopene beadlet (LB), and sacrificed at 20 weeks. Prostate histopathology, prostate weight and serum levels of IGF-I and IGF binding protein-3 were evaluated. The incidence of prostate cancer was significantly decreased in the LB group relative to the control group (60% vs. 95%, respectively, P = 0.0197) whereas the difference between the TP and control groups was not statistically significant (80% vs. 95%, P = 0.34). There was no difference in prostate weights between the groups. Total lycopene levels in the serum and prostate tissue were similarly elevated in the LB and TP groups relative to the control group. The ratio of 5-cis-lycopene to trans-lycopene in the serum was significantly greater in the LB group relative to the TP group (P = 0.0001). Oxidative DNA damage was significantly reduced in the livers of mice fed LB and TP diets relative to the control group. This preclinical trial suggests significant chemopreventive activity with a lycopene beadlet-enriched diet. The chemopreventive effects of lycopene from beadlets versus whole tomato products requires further testing in preclinical and clinical models of prostate cancer.

The dietary isothiocyanate sulforaphane modulates gene expression and alternative gene splicing in a PTEN null preclinical murine model of prostate cancer

BackgroundDietary or therapeutic interventions to counteract the loss of PTEN expression could contribute to the prevention of prostate carcinogenesis or reduce the rate of cancer progression. In this study, we investigate the interaction between sulforaphane, a dietary isothiocyanate derived from broccoli, PTEN expression and gene expression in pre malignant prostate tissue.ResultsWe initially describe heterogeneity in expression of PTEN in non-malignant prostate tissue of men deemed to be at risk of prostate cancer. We subsequently use the mouse prostate-specific PTEN deletion model, to show that sulforaphane suppresses transcriptional changes induced by PTEN deletion and induces additional changes in gene expression associated with cell cycle arrest and apoptosis in PTEN null tissue, but has no effect on transcription in wild type tissue. Comparative analyses of changes in gene expression in mouse and human prostate tissue indicate that similar changes can be induced in humans with a broccoli-rich diet. Global analyses of exon expression demonstrated that sulforaphane interacts with PTEN deletion to modulate alternative gene splicing, illustrated through a more detailed analysis of DMBT1 splicing.ConclusionTo our knowledge, this is the first report of how diet may perturb changes in transcription induced by PTEN deletion, and the effects of diet on global patterns of alternative gene splicing. The study exemplifies the complex interaction between diet, genotype and gene expression, and the multiple modes of action of small bioactive dietary components.

Increased potency of the PHSCN dendrimer as an inhibitor of human prostate cancer cell invasion, extravasation, and lung colony formation

Activated alpha5beta1 integrin occurs specifically on tumor cells and on endothelial cells of tumor-associated vasculature, and plays a key role in invasion and metastasis. The PHSCN peptide (Ac-PHSCN-NH(2)) preferentially binds activated alpha5beta1, to block invasion in vitro, and inhibit growth, metastasis and tumor recurrence in preclinical models of prostate cancer. In Phase I clinical trial, systemic Ac-PHSCN-NH(2) monotherapy was well tolerated, and metastatic disease progression was prevented for 4-14 months in one-third of treated patients. We have developed a significantly more potent derivative, the PHSCN-polylysine dendrimer (Ac-PHSCNGGK-MAP). Using in vitro invasion assays with naturally serum-free basement membranes, we observed that the PHSCN dendrimer was 130- to 1900-fold more potent than the PHSCN peptide at blocking alpha5beta1-mediated invasion by DU 145 and PC-3 human prostate cancer cells, whether invasion was induced by serum, or by the Ac-PHSRN-NH(2) peptide, under serum-free conditions. The PHSCN dendrimer was also approximately 800 times more effective than PHSCN peptide at preventing DU 145 and PC-3 extravasation in the lungs of athymic mice. Chou-Talalay analysis suggested that inhibition of both invasion in vitro and extravasation in vivo by the PHSCN dendrimer are highly synergistic. We found that many extravasated DU 145 and PC-3 cells go onto develop into metastatic colonies, and that a single pretreatment with the PHSCN dendrimer was 100-fold more affective than the PHSCN peptide at reducing lung colony formation. Since many patients newly diagnosed with prostate cancer already have locally advanced or metastatic disease, the availability of a well-tolerated, nontoxic systemic therapy, like the PHSCN dendrimer, which prevents metastatic progression by inhibiting invasion, could be very beneficial.

Therapeutic Potential of Adult Bone Marrow–Derived Mesenchymal Stem Cells in Prostate Cancer Bone Metastasis

Current evidence indicates that an osteoblast lesion in prostate cancer is preceded by osteolysis. Thus, prevention of osteolysis would reduce complications of bone metastasis. Bone marrow-derived mesenchymal stem cells have the ability to differentiate into osteoblast and produce osteoprotegerin, a decoy receptor for the receptor activator for nuclear factor kappaB ligand, naturally. The present study examined the potential of unmodified mesenchymal stem cells to prevent osteolytic bone lesions in a preclinical mouse model of prostate cancer. The human prostate cancer cell line PC3 was implanted in tibiae of severe combined immunodeficient mice. After establishment of the tumor, either unmodified or genetically engineered mesenchymal stem cells overexpressing osteoprotegerin was injected at the site of tumor growth. The effects of therapy were monitored by bioluminescence imaging, micro-computed tomography, immunohistochemistry, and histomorphometry. Data indicated significant (P < 0.001) inhibition of tumor growth and restoration of bone in mice treated with unmodified and modified mesenchymal stem cells. Detailed analysis suggested that the donor mesenchymal stem cell inhibited tumor progression by producing woven bone around the growing tumor cells in the tibiae and by preventing osteoclastogenesis. Overcoming the limitation of the number of mesenchymal stem cells available in the bone can provide significant amelioration for osteolytic damage without further modification.

Identification of novel truncated androgen receptor (AR) mutants including unreported pre-mRNA splicing variants in the 22Rv1 hormone-refractory prostate cancer (PCa) cell line

Advanced prostate cancer (PCa) has emerged as a public health concern due to population aging. Although androgen deprivation has proven efficacy in this condition, most advanced PCa patients will have to face failure of androgen deprivation as a treatment. Mutations in the androgen receptor (AR) from tumor cells have been shown to induce androgen independency both in PCa cell lines and in the clinic. We have investigated the molecular events leading to androgen independency in the 22Rv1 cell line, a commonly used preclinical model of PCa. Besides AR mutants that have been described so far, including nonsense mutations, recent data have focused on AR pre-mRNA aberrant splicing as a new mechanism leading to constitutively active truncated AR variants. In this article, we describe two novel variants arising from aberrant splicing of AR pre-mRNA, characterized by long mRNA transcripts that encode truncated, constitutively active proteins. We also describe several new nonsense mutants that share ligand independency and transcriptional activity. Finally, we show that alongside these mutants, 22Rv1 cells also express a mutant AR lacking exon 3 tandem duplication, a major feature of this cell line. By describing unreported AR mutants in the 22Rv1 cell line, our data emphasize the complexity and heterogeneity of molecular events that occur in preclinical models, and supposedly in the clinic. Future work on the 22Rv1 cell line should take into account the concomitant expression of various AR mutants.

Continuous and intermittent dosing of lonafarnib potentiates the therapeutic efficacy of docetaxel on preclinical human prostate cancer models

Lonafarnib is a potent, selective farnesyltransferase inhibitor (FTI) undergoing clinical studies for the treatment of solid tumors and hematological malignancies. Preclinically, a number of FTIs, including lonafarnib, interact with taxanes to inhibit cancer cell growth in an additive/synergistic manner. These observations provided rationale for investigating the effects of combining lonafarnib and docetaxel on preclinical prostate cancer models. To date, docetaxel is the only chemotherapeutic agent in clinical use for hormone-refractory prostate cancer. In vitro experiments with 22Rv1, LNCaP, DU-145, PC3 and PC3-M prostate cancer cell lines showed significantly enhanced inhibition of cell proliferation and apoptosis when lonafarnib was added to docetaxel. In human tumor xenograft models, continuous coadministration of lonafarnib with docetaxel caused marked tumor regressions (24-47%) in tumors from all of the cell types as well as parental CWR22 xenografts. Intermittent dosing of lonafarnib (5 days on then 5 days off) coadministered with docetaxel produced similar regressions in hormone-refractory 22Rv1 tumors. 22Rv1 tumors progressing on docetaxel treatment also responded to treatment with intermittent lonafarnib (5 days on then 5 days off). Moreover, animals did not exhibit any signs of toxicity during coadministration of lonafarnib and docetaxel. In conclusion, coadministration of continuous and intermittent lonafarnib enhanced the antitumor activity of docetaxel in a panel of prostate cancer models. An intermittent dosing schedule of lonafarnib coadministered with docetaxel may allow enhanced efficacy to that of continuous dosing by improving the tolerability of higher doses of lonafarnib.