PC-3 Human Prostate Cancer Xenografts Research Articles

Abstract 3629: Theranostic imaging of metastatic prostate cancer

Abstract There is a compelling need to find effective treatments for metastatic prostate cancer. The ideal treatment would only target metastatic lesion while sparing normal tissue. Down-regulation of specific pathways using small interfering RNA (siRNA) provides unique opportunities to target cancer cells selectively while sparing normal tissue. Prostate-specific membrane antigen (PSMA) is a type II integral membrane protein that has abundant expression on the surface of prostate carcinomas, particularly in androgen-independent, advanced and metastatic disease [1-2]. We are developing prostate specific membrane antigen (PSMA) targeted nanoplexes carrying multimodality imaging reporters together with small interfering RNA (siRNA) and a prodrug enzyme, bacterial cytosine deaminase (bCD), for theranostic imaging of metastatic prostate cancer. We have incorporated a low molecular weight PSMA binding agent in the nanoplex to target the nanoplex to prostate cancer cells [3]. Since choline kinase (Chk) is significantly upregulated in aggressive cancer cells we have used siRNA against Chk in the nanoplex. Our prototype nanoplexes are synthesized by conjugating: (i) a low molecular weight urea-based PSMA targeting moiety (2-(3-[1-carboxy-5-[7-(2,5-dioxo-pyrrolidin-1-yloxycarbonyl)-heptanoylamino]-pentyl]-ureido)-pentanedioic acid, (ii) the prodrug-activating enzyme bCD that converts nontoxic 5-fluorocytosine (5-FC) to cytotoxic 5-fluorouracil (5-FU), (iii) the multimodal imaging reporter carrier poly-L-lysine (PLL) that carries [111In]DOTA for SPECT or [Gd3+]DOTA for MR, and a near-infrared fluorescent probe Cy5.5 for optical imaging, and (iv) the siRNA delivery vector: PEI (polyethyleneimine)-PEG (polythethyeneglycol) co-grafted-polymer. Imaging studies with PSMA targeted nanoplexes were performed with PC-3 human prostate cancer xenografts genetically engineered to overexpress PSMA (PC-3 PIP) in SCID mice. Non PSMA expressing PC-3 xenografts (PC-3 FLU) were used as controls. The addition of a low molecular weight PSMA targeting moiety allowed specific targeting of the nanoplex to PSMA expressing prostate cancer cells in vivo, which was further established with blocking studies. Initial studies established the ability of the nanoplex to effectively downregulate Chk and total choline and convert the nontoxic prodrug 5-FC to 5-FU. The strategies developed here can be extended, in the future, to down-regulate multi-drug resistance pathways, or repair enzymes to increase the efficiency of chemo- or radiation therapy. 1. Schulke, N., et al., Proc Natl Acad Sci U S A, 2003; 2. Huang, X., et al., Prostate, 2004; 3. Mease, R., et al., Clin. Cancer Res., 2008. 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 3629. doi:10.1158/1538-7445.AM2011-3629

CYP24A1 Inhibition Enhances the Antitumor Activity of Calcitriol

High systemic exposures to calcitriol are necessary for optimal antitumor effects. Human prostate cancer PC3 cells are insensitive to calcitriol treatment. Therefore, we investigated whether the inhibition of 24-hydroxylase (CYP24A1), the major calcitriol inactivating enzyme, by ketoconazole (KTZ) or RC2204 modulates calcitriol serum pharmacokinetics and biologic effects. Dexamethasone (Dex) was added to minimize calcitriol-induced hypercalcemia and as a steroid replacement for the KTZ inhibition of steroid biosynthesis cytochrome P450 enzymes. KTZ effectively inhibited time-dependent calcitriol-inducible CYP24A1 protein expression and enzyme activity in PC3 cells and C3H/HeJ mouse kidney tissues. Systemic calcitriol exposure area under the curve was higher in mice treated with a combination of calcitriol and KTZ than with calcitriol alone. KTZ and Dex synergistically potentiated calcitriol-mediated antiproliferative effects in PC3 cells in vitro; this effect was associated with enhanced apoptosis. After treatment with calcitriol and KTZ/Dex, although caspase-9 and caspase-3 were not activated and cytochrome c was not released by mitochondria, caspase-8 was activated and the truncated Bid protein level was increased. Translocation of apoptosis-inducing factor to the nucleus was observed, indicating a role of the apoptosis-inducing factor-mediated and caspase-independent apoptotic pathways. Calcitriol and KTZ/Dex combination suppressed the clonogenic survival and enhanced the growth inhibition observed with calcitriol alone in PC3 human prostate cancer xenograft mouse model. Our results show that the administration of calcitriol in combination with CYP24A1 inhibitor enhances antiproliferative effects, increases systemic calcitriol exposure, and promotes the activation of caspase-independent apoptosis pathway.

Synthesis and initial tumor affinity testing of iodine-123 labelled EGFR-affine agents as potential imaging probes for hormone-refractory prostate cancer

The epidermal growth factor receptor (EGFR) is over-expressed in a variety of human cancers, including in hormone-refractory prostate carcinomas, in which the EGFR has been associated with advanced disease stage, resistance to standard treatment and poor prognosis. Therefore, the EGFR is considered to be a promising molecular target for molecular imaging and therapy for hormone-refractory prostate cancer. This work describes the synthesis and initial tumor affinity testing of the EGFR antagonist 123I-mAb425 and the EGF receptor tyrosine kinase (EGFR-TK) inhibitor 123I-PD153035 as potential imaging probes for studying EGFR-expressing prostate cancer using single photon emission tomography. Methods 123I-mAb425 and 123I-PD153035 were prepared, starting from the IgG2a antibody and EGFR antagonist mAb425, that binds to the external domain of the EGF receptors, and from the EGFR-TK inhibitor PD153035, targeting the intra-endothelial tyrosine kinase domain of the EGFR, respectively. The potential of 123I-mAb425 and 123I-PD153035 to target EGFR-positive prostate carcinoma was tested on androgen-insensitive PC-3 and DU-145 prostate carcinoma cell lines, and on the androgen-sensitive LNCaP prostate cancer cell line for comparison. In vivo, the capability of 123I-mAb425 and 123I-PD153035 to target hormone-refractory prostate cancer was assessed in RNU rats or nu/nu mice bearing human PC3 prostate cancer xenografts. Results 123I-mAb425 was obtained in >90% radiochemical yield using the IODO-GEN ® method. 123I-PD153035 was synthesized by a non-isotopic [ 123I]iodo-debromination of PD153035 in 50–60% radiochemical yield in a total synthesis time including HPLC separation of 70 min. In vitro 123I-mAb425 and 123I-PD153035 accumulated highly in human PC-3 and DU-145 prostate cancer cells. Radioactivity incorporation into PC-3 and DU-145 tumor cells following 15-min incubation at 37 °C varied from 25% to 48% of the total loaded activity per 10 6 tumor cells (560–1230 cpm/1000 cells). In comparison, the uptake of the EGFR-affine probes into LNCaP prostate carcinoma cells was significantly low (105 ± 25 cpm/1000 cells). Inhibition experiments revealed that 123I-mAb425 is taken up into tumor cells via the same pathway as the naturally occurring epidermal growth factor (EGF), while 123I-PD153035 accumulation in prostate cancer cells occurs presumably via the same pathway as the selective EGFR-Tyrosine kinase antagonist AG1418. In vivo, the human prostate cancer xenografts in mouse war accurately visualized after i.v. administration of 123I-mAb425 by a gamma camera. Conclusion These data suggest that 123I-mAb425 and 123I-PD153035 are promising candidates as imaging probes for EGFR-positive prostate cancer and warrant further in vivo validations to ascertain their potential as imaging agents for clinical used.

Radiation therapy induces circulating serum Hsp72 in patients with prostate cancer

Background and purpose Hsp72 found in the extracellular milieu has been shown to play an important role in immune regulation. The impact of common cancer therapies on extracellular release of Hsp72 however, has been to date undefined. Materials and methods Serum from 13 patients undergoing radiation therapy (XRT) for prostate cancer with or without hormonal therapy (ADT) was measured for levels of circulating serum Hsp72 and pro-inflammatory cytokines (IL-6 and TNF-α) using the classical sandwich ELISA technique and the relative expression of CD8 + T lymphocytes and natural killer (NK) cells was measured using flow cytometry. Mouse orthotopic xenograft of human prostate cancer tumors (DU-145 and PC-3) were used to validate and further characterize the response noted in the clinical setting. The biological significance of tumor released Hsp72 was studied in human dendritic cells (DC) in vitro. Results Circulating serum Hsp72 levels increased an average of 3.5-fold (median per patient 4.8-fold) with XRT but not with ADT ( p = 0.0002). Increases in IL-6 (3.3-fold), TNF-α (1.8-fold), CD8 + CTL (2.1-fold) and NK cells (3.2-fold) also occurred. Using PC-3 and DU-145 human prostate cancer xenograft models in mice, we confirmed that XRT induces Hsp72 release primarily from implanted tumors. In vitro studies using supernatant recovered from irradiated human prostate cancer cells point to exosomes containing Hsp72 as a possible stimulator of pro-inflammatory cytokine production and costimulatory molecules expression in human DC. Conclusions The current study confirms for the first time in an actual clinical setting elevation of circulating serum Hsp72 with XRT. The accompanying studies in mice and in vitro identify the released exosomes containing Hsp72 as playing a pivotal role in stimulating pro-inflammatory immune responses. These findings, if validated, may lead to new treatment paradigms for common human malignancies.

Abstract 5481: Theranostic imaging of metastatic prostate cancer

Abstract There is a compelling need to find effective treatments for metastatic disease. The ideal therapy would target cancer cells while sparing normal tissue. With prodrug therapy, where a drug-activating enzyme is delivered to the tumor followed by the administration of a non-toxic prodrug administered systemically, side effects can be minimized. We previously synthesized a prototype agent consisting of the enzyme bacterial cytosine deaminase (bCD), that converts prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), labeled with MR and optical imaging reporters. Here we have developed a prototype targeted nanoplex that delivers bCD together with siRNA for theranostic imaging of metastatic prostate cancer. Prostate-specific membrane antigen (PSMA) has an abundant expression on the surface of prostate carcinomas. We have therefore incorporated a low molecular weight PSMA binding agent to target the nanoplex to prostate cancer cells. Since choline kinase (Chk) is significantly upregulated in aggressive prostate cancer cells we have used siRNA against Chk in the nanoplex. Our nanoplex was synthesized by conjugating three compartments: (i) the prodrug-activating enzyme bCD, (ii) the poly-L-lysine (PLL) that carries [111In]DOTA for SPECT or [Gd3+]DOTA for MRI and a near-infrared fluorescent probe Cy5.5, (iii) the siRNA delivery vector: PEI (polyethyleneimine)-PEG (polythethyeneglycol) co-grafted-polymer. These compartments are covalently conjugated and siRNA-Chk is associated with the PEI-PEG co-grafted polymer through electrostatic affiliation. For the targeted nanoplexes, a low molecular weight urea-based PSMA targeting moiety (2-(3-[1-carboxy-5-[7-(2,5-dioxo-pyrrolidin-1-yloxycarbonyl)-heptanoylamino]-pentyl]-ureido)-pentanedioic acid was used. Imaging studies with PSMA targeted nanoplexes were performed with PC-3 human prostate cancer xenografts genetically engineered to overexpress PSMA (PC-3 PIP) and with LNCaP human prostate cancer xenografts. Non-PSMA expressing PC-3 xenografts were used as controls. MR experiments were performed on a Bruker horizontal bore 9.4T animal MR scanner. SPECT/CT images were acquired on a Gamma Medica X-SPECT scanner. Initial studies with a nontargeted nanoplex carrying bCD and Chk siRNA established the ability of the nanoplex to effectively downregulate Chk and total choline and to convert the nontoxic prodrug 5-FC to 5-FU. By using SPECT and MRI, we found that the addition of a PSMA targeting moiety allowed specific targeting of the nanoplex to PSMA expressing prostate cancer cells in vivo. The targeted nanoplexes we develop will allow us to deliver siRNA together with a prodrug enzyme, under image guidance for developing theranostic imaging of metastatic prostate cancer. The strategies developed here can be extended, in the future, to down-regulate multi-drug resistance pathways, or repair enzymes to increase the efficiency of therapy. 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 5481.

Abstract 1728: Membrane androgen receptor ligands: a novel therapeutic approach for the treatment of cancer

Abstract Membrane Androgen Receptor (mAR) is a novel, yet of unknown identity, membrane receptor frequently over-expressed in aggressive prostate cancer. mAR is not related to the classical intracellular androgen receptor (AR), a well known therapeutic target for prostate cancer treatment. Consequently, mAR induces tumour cell death by apoptosis in both AR-positive and AR-negative cell lines or in the presence of anti-androgens (e.g. flutamide). Early experimental results with membrane-targeted steroids (androgen-albumin conjugates) have proved the validity of mAR as a novel target of cancer therapy, as based on the anti-cancer action observed in prostate xenograft models (reviewed in IUBMB Life. 2009 Jan;61(1):56-61). In this study, we describe novel small molecule steroidal mAR ligands that exhibit in vitro anti-cancer activity in the nanomolar range in prostate cancer cell lines. Furthermore, and as based on the identification of functional membrane androgen receptors in non-prostate cancer cells by immuno-fluorescence analysis, we show that selective novel mAR ligands exert broad anti-cancer action in additional cell line panels including colon, non-small cell lung cancer, central nervous system, breast or multi drug resistant cells. Notably, our compounds are selective for mAR binding since control displacement assays failed to identify significant interactions with recombinant Androgen Receptors. To assess the anti-cancer of our compounds in vivo, we measured the ability of a prototype mAR ligand, MDX-146, to inhibit tumour growth of human PC-3 prostate cancer xenografts. Our results show clear tumour growth inhibition effects of MDX-146 in animals and propose a potential therapeutic role of specific mAR ligands for the treatment of prostate and other cancers. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. 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 1728.

Bcl‐2 mediated modulation of vascularization in prostate cancer xenografts

We previously demonstrated that Bcl-2 overexpression enhances the radiation resistance of PC-3 human prostate cancer cells and xenografts by inhibiting apoptosis, increasing proliferation, and promoting angiogenesis. To further elucidate the relationship between Bcl-2 expression and the angiogenic potential of PC-3-Bcl-2 cells, tumorigenicity, angiogenesis, and lymphangiogenesis were evaluated and compared in a Bcl-2 overexpressing clone in vitro and in vivo. Human prostate cancer cells over expressing Bcl-2 were studied in vitro and in vivo to determine the angiogenic and lymphangiogenic properties of these cells. Increased Bcl-2 expression enhanced the tumorigenicity of prostate cancer xenografts. It also enhanced the expression and secretion of key angiogenic and lymphangiogenic factors that stimulated the synthesis of CD31-positive blood vessels and LYVE-1 positive lymphatics. Specifically, the increased angiogenic and lymphangiogenic potential correlated with increased serum levels of basic fibroblast growth factor (bFGF), interleukin 8 (CXCL8), and matrix metalloproteinase (MMP 9). In vitro analysis demonstrated that Bcl-2 expressing tumor cells secreted bFGF and vascular endothelial growth factor (VEGF) into culture supernatants. Microarray analysis of Bcl-2 expressing PC-3 cells demonstrated increased transcription of genes involved in metabolism, such as interleukins, growth factors, tumor necrosis factors (TNF) family members, and peptidases. Together, these results demonstrate that Bcl-2 can regulate tumoral angiogenesis and lymphangiogenesis and suggest that therapy targeted at Bcl-2 expression, angiogenesis, and lymphangiogenesis may synergistically modulate tumor growth and confirm that Bcl-2 is a pivotal target for cancer therapy.

Humanized Radioiodinated Minibody For Imaging of Prostate Stem Cell Antigen–Expressing Tumors

Prostate stem cell antigen (PSCA) is a cell surface glycoprotein that is overexpressed in prostate cancer, including hormone refractory disease. Previous preclinical studies showed the intact anti-PSCA antibodies, 1G8 and hu1G8, localized specifically to PSCA-expressing xenografts. Optimal micro positron emission tomography (microPET) imaging using hu1G8, however, required a delay of 168 hours postinjection. In this study, the 2B3 minibody (an 80-kDa engineered antibody fragment) has been produced for rapid targeting and imaging. A gene encoding a PSCA-specific minibody, V(L)-linker-V(H)-hinge-huIgG1 C(H)3, was assembled. The minibody was expressed by secretion from mammalian cells and purified by cation exchange chromatography. Relative affinity and specificity were determined by competition ELISA and flow cytometry. Serial microPET imaging using a 124I-labeled minibody was conducted at 4 and 21 hours in mice bearing LAPC-9 AD, LAPC-9 AI, PC-3, and LNCaP-PSCA human prostate cancer xenografts. Tumor and tissue biodistribution was determined, and region of interest analysis of the images was conducted. Yields of 20 mg/L purified 2B3 minibody were obtained that showed specific binding to LNCaP-PSCA cells. Purified 2B3 minibody showed specific binding to LNCaP-PSCA cells with an apparent affinity of 46 nmol/L. Radioiodinated 2B3 minibody showed rapid nontarget tissue and blood clearance kinetics (t1/2beta = 11.2 hours). MicroPET scanning using the 124I-2B3 minibody showed both androgen-dependent and -independent tumors as early as 4 hours and excellent high contrast images at 21 hours postinjection. Imaging PSCA-positive prostate cancer is feasible using an intermediate size antibody fragment at 21 hours.

Efficacy, pharmacokinetics, tisssue distribution, and metabolism of the Myc–Max disruptor, 10058-F4 [Z,E]-5-[4-ethylbenzylidine]-2-thioxothiazolidin-4-one, in mice

c-Myc is commonly activated in many human tumors and is functionally important in cellular proliferation, differentiation, apoptosis and cell cycle progression. The activity of c-Myc requires noncovalent interaction with its client protein Max. In vitro studies indicate the thioxothiazolidinone, 10058-F4, inhibits c-Myc/Max dimerization. In this study, we report the efficacy, pharmacokinetics and metabolism of this novel protein-protein disruptor in mice. SCID mice bearing DU145 or PC-3 human prostate cancer xenografts were treated with either 20 or 30 mg/kg 10058-F4 on a qdx5 schedule for 2 weeks for efficacy studies. For pharmacokinetics and metabolism studies, mice bearing PC-3 or DU145 xenografts were treated with 20 mg/kg of 10058-F4 i.v. Plasma and tissues were collected 5-1440 min after dosing. The concentration of 10058-F4 in plasma and tissues was determined by HPLC, and metabolites were characterized by LC-MS/MS. Following a single iv dose, peak plasma 10058-F4 concentrations of approximately 300 muM were seen at 5 min and declined to below the detection limit at 360 min. Plasma concentration versus time data were best approximated by a two-compartment, open, linear model. The highest tissue concentrations of 10058-F4 were found in fat, lung, liver, and kidney. Peak tumor concentrations of 10058-F4 were at least tenfold lower than peak plasma concentrations. Eight metabolites of 10058-F4 were identified in plasma, liver, and kidney. The terminal half-life of 10058-F4 was approximately 1 h, and the volume of distribution was >200 ml/kg. No significant inhibition of tumor growth was seen after i.v. treatment of mice with either 20 or 30 mg/kg 10058-F4. The lack of significant antitumor activity of 10058-F4 in tumor-bearing mice may have resulted from its rapid metabolism and low concentration in tumors.

Superior in vivo inhibitory efficacy of methylseleninic acid against human prostate cancer over selenomethionine or selenite

Methylselenol has been implicated as an active anticancer selenium (Se) metabolite. However, its in vivo efficacy against prostate cancer (PCa) has yet to be established. Here, we evaluated the growth inhibitory effects of two presumed methylselenol precursors methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) in comparison with selenomethionine (SeMet) and selenite in DU145 and PC-3 human PCa xenografts in athymic nude mice. Each Se was given by a daily single oral dose regimen starting the day after the subcutaneous inoculation of cancer cells. We analyzed serum, liver and tumor Se content to confirm supplementation status and apoptosis indices and tumor microvessel density for association with antitumor efficacy. Furthermore, we analyzed lymphocyte DNA integrity to detect genotoxic effect of Se treatments. The data show that MSeA and MSeC exerted a dose-dependent inhibition of DU145 xenograft growth and both were more potent than SeMet and selenite, in spite of less tumor Se retention than in the SeMet-treated mice. Selenite treatment increased DNA single-strand breaks in peripheral lymphocytes, whereas the other Se forms did not. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) and cleaved caspase-3 indices (apoptosis) from MSeC-treated tumors were higher than tumors from control mice or MSeA-treated mice, whereas the microvessel density index was lower in tumors from MSeA-treated mice. In the PC-3 xenograft model, only MSeA was growth inhibitory at a dose of 3 mg/kg body wt. In summary, our data demonstrated superior in vivo growth inhibitory efficacy of MSeA over SeMet and selenite, against two human PCa xenograft models without the genotoxic property of selenite.

Diallyl Trisulfide Suppresses Growth of PC-3 Human Prostate Cancer Xenograft In vivo in Association with Bax and Bak Induction

The present study was undertaken to determine the effect of garlic constituent diallyl trisulfide (DATS) on growth of PC-3 human prostate cancer xenograft in vivo. DATS was given orally (6 micromoL, thrice weekly) to male athymic mice s.c. implanted with PC-3 cells. Tumor sections from control and DATS-treated mice were examined for apoptotic bodies by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. Protein levels of apoptosis and cell cycle regulating proteins in tumor tissues of control and DATS-treated mice were determined by immunoblotting. The effect of DATS treatment on in vivo angiogenesis was determined by immunohistochemical analysis of CD31 in tumors. Oral gavage of DATS significantly retarded growth of PC-3 xenografts in athymic mice without causing weight loss. For instance, 20 days after starting therapy, the average tumor volume in control mice was approximately 3-fold higher compared with DATS-treated mice. Tumors from DATS-treated mice exhibited a markedly higher count of apoptotic bodies compared with control tumors. Consistent with the results in cultured PC-3 cells, the DATS-mediated suppression of PC-3 xenograft growth correlated with induction of proapoptotic proteins Bax and Bak. Although DATS treatment inhibited migration of cultured PC-3 cells in association with down-regulation of vascular endothelial growth factor receptor-2 protein, formation of new blood vessels was comparable in tumors of control and DATS-treated mice as judged by CD31 immunostaining. The present study indicates that DATS administration inhibits growth of PC-3 xenografts in vivo in association with induction of Bax and Bak.

An oriental herbal cocktail, ka-mi-kae-kyuk-tang, exerts anti-cancer activities by targeting angiogenesis, apoptosis and metastasis

Rigorous and systematic pre-clinical studies are necessary and essential to establish the efficacy and safety of Oriental herbs and formulas in order to transform traditional herbal practices into evidence-based medicine. Here we evaluated the anti-cancer activities of the ethanol extract of Ka-mi-kae-kyuk-tang (KMKKT), a formula of ten Oriental herbs, with a battery of in vitro and in vivo mechanism-based biomarkers involving angiogenesis, apoptosis and metastasis. The results show that KMKKT suppressed the vascular endothelial responses by inhibiting basic fibroblast growth factor (bFGF)-induced ERK1/2 phosphorylation, cell migration as well as tube formation in the human umbilical vein endothelial cell model, and decreased the hypoxia-induced HIF1alpha and vascular epithelial growth factor (VEGF) expression in the mouse Lewis lung carcinoma (LLC) cells in vitro, and inhibited the bFGF-induced angiogenesis in chick chorioallantoic membrane model, and in the Matrigel plugs in mice. Intraperitoneal delivery of KMKKT potently inhibited the growth of the subcutaneously inoculated LLC cells in syngenic mice. In addition, KMKKT inhibited the invasion ability of the mouse colon 26-L5 cancer cells in vitro and decreased their formation of liver metastasis when intraportally inoculated in syngenic mice. Furthermore, KMKKT suppressed the growth of the human PC-3 prostate cancer xenografts in athymic nude mice and averted the cancer-related body weight loss. The in vivo cancer growth suppression was associated with a decreased microvessel density and VEGF abundance as well as an increased PARP cleavage and the TUNEL-positive apoptosis. Together, our data support broad-spectra in vivo anti-cancer activities of KMKKT targeting angiogenesis, apoptosis and metastasis without any adverse effect on the body weight. This formula merits serious consideration for further evaluation for the chemoprevention and treatment of cancers of multiple organ sites.

Pharmacologic Basis for the Enhanced Efficacy of Dutasteride against Prostatic Cancers

Prostatic dihydrotestosterone (DHT) concentration is regulated by precursors from systemic circulation and prostatic enzymes of androgen metabolism, particularly 5alpha-reductases (i.e., SRD5A1 and SRD5A2). Therefore, the levels of expression SRD5A1 and SRD5A2 and the antiprostatic cancer growth response to finasteride, a selective SRD5A2 inhibitor, versus the dual SRD5A1 and SRD5A2 inhibitor, dutasteride, were compared. Real-time PCR and enzymatic assays were used to determine the levels of SRD5A1 and SRD5A2 in normal versus malignant rat and human prostatic tissues. Rats bearing the Dunning R-3327H rat prostate cancer and nude mice bearing LNCaP or PC-3 human prostate cancer xenografts were used as model systems. Tissue levels of testosterone and DHT were determined using liquid chromatography-mass spectrometry. Prostate cancer cells express undetectable to low levels of SRD5A2 but elevated levels of SRD5A1 activity compared with nonmalignant prostatic tissue. Daily oral treatment of rats with the SRD5A2 selective inhibitor, finasteride, reduces prostate weight and DHT content but did not inhibit R-3327H rat prostate cancer growth or DHT content in intact (i.e., noncastrated) male rats. In contrast, daily oral treatment with even a low 1 mg/kg/d dose of the dual SRD5A1 and SRD5A2 inhibitor, dutasteride, reduces both normal prostate and H tumor DHT content and weight in intact rats while elevating tissue testosterone. Daily oral treatment with finasteride significantly (P < 0.05) inhibits growth of LNCaP human prostate cancer xenografts in intact male nude mice, but this inhibition is not as great as that by equimolar oral dosing with dutasteride. This anticancer efficacy is not equivalent, however, to that produced by castration. Only combination of dutasteride and castration produces a greater tumor inhibition (P < 0.05) than castration monotherapy against androgen-responsive LNCaP cancers. In contrast, no response was induced by dutasteride in nude mice bearing androgen-independent PC-3 human prostatic cancer xenografts. These results document that testosterone is not as potent as DHT but does stimulate prostate cancer growth, thus combining castration with dutasteride enhances therapeutic efficacy.

Low-Dose Metronomic Daily Cyclophosphamide and Weekly Tirapazamine: A Well-Tolerated Combination Regimen with Enhanced Efficacy That Exploits Tumor Hypoxia

The recent clinical successes of antiangiogenic drug-based therapies have also served to highlight the problem of acquired resistance because, similar to other types of cancer therapy, tumors that initially respond eventually stop doing so. Consequently, strategies designed to delay resistance or treat resistant subpopulations when they arise have assumed considerable importance. This requires a better understanding of the various possible mechanisms for resistance. In this regard, reduced oxygenation is thought to be a key mediator of the antitumor effects of antiangiogenic therapies; accordingly, increased hypoxia tolerance of the tumor cells presents a potential mechanism of resistance. However, hypoxia can also be exploited therapeutically through the use of hypoxic cell cytotoxins, such as tirapazamine. With this in mind, we measured the oxygenation of PC-3 human prostate cancer xenografts subjected to chronic low-dose metronomic (LDM) antiangiogenic chemotherapy using cyclophosphamide given through the drinking water. We found that LDM cyclophosphamide impairs the oxygenation of PC-3 xenografts even during relapse, coinciding with reduced microvessel density. Combination of LDM cyclophosphamide with tirapazamine results in significantly improved tumor control in the PC-3, HT-29 colon adenocarcinoma, and MDA-MB-231 breast cancer human xenograft models without having a negative effect on the favorable toxicity profile of LDM cyclophosphamide. These results provide further evidence that reduced vascular dependence/increased hypoxia tolerance may be a basis for eventual resistance of tumors exposed to long-term LDM chemotherapy.

Low-dose Metronomic Combined with Intermittent Bolus-dose Cyclophosphamide Is an Effective Long-term Chemotherapy Treatment Strategy

Metronomic chemotherapy refers to the close, regular administration of comparatively low doses of cytotoxic drugs, with minimal or no drug-free breaks, over prolonged periods. It is thought to have an antiangiogenic basis. However, whereas surprisingly durable and potent tumor responses have been observed in a number of preclinical tumor models, relapses usually eventually occur using this type of treatment strategy. We therefore decided to test modified metronomic chemotherapy regimens that might significantly delay such relapses, but still maintain modest and acceptable toxicity profiles. Here, we show that repeated administration of bolus doses (BDs) of cyclophosphamide every 3 or 6 weeks, combined with a daily oral low-dose metronomic (LDM) regimen (20 mg/kg/d cyclophosphamide), improves efficacy and significantly delays progression of transplanted PC-3 human prostate cancer xenografts, syngeneic transplanted EMT-6 breast tumors, and "spontaneous" murine erythroleukemia. Efficacy was superior whereas toxicity was mild and comparable to the LDM regimen, the latter assessed by body weight, neutrophil, lymphocyte, and total white blood counts. Antiangiogenic activity, measured by reduction in circulating endothelial precursor cells, revealed that the greatest degree of suppression occurred using the combination treatment. Overall, our results indicate that the administration of intermittent BD combined with chronic oral LDM cyclophosphamide is a potent treatment regimen for controlling tumor growth, which has a low toxicity profile, over prolonged periods of time.

Discovery and preclinical evaluation of a novel class of small-molecule compounds in hormone-dependent and -independent cancer cell lines

We discovered a series of salicylhydrazide class of compounds with remarkable anticancer activity against a panel of hormone receptor-positive and -negative cell lines. In the present study, we evaluated the in vitro activity of SC21 and SC23 against a range of human tumor cell types and the in vivo efficacy of compound SC21 in a PC3 human prostate cancer xenograft model in mice. We also determined the effects of SC21 on cell cycle regulation and apoptosis. Our in vitro results show that salicylhydrazides are highly potent compounds effective in both hormone receptor-positive and -negative cancer cells. SC21 induced apoptosis and blocked the cell cycle in G(0)/G(1) or S phase, depending on the cell lines used and irrespective of p53, p21, pRb, and p16 status. SC21 effectively reduced the tumor growth in mice without apparent toxicity. Although the mechanism of action of SC21 is not completely elucidated, the effect on cell cycle, the induction of apoptosis and the activity against a panel of tumor cell lines of different origins prompted us to carry out an in-depth preclinical evaluation of SC21.

Sulforaphane-induced Cell Death in Human Prostate Cancer Cells Is Initiated by Reactive Oxygen Species

We have shown previously that sulforaphane (SFN), a constituent of many edible cruciferous vegetables including broccoli, suppresses growth of prostate cancer cells in culture as well as in vivo by causing apoptosis, but the sequence of events leading to cell death is poorly defined. Using PC-3 and DU145 human prostate cancer cells as a model, we now demonstrate, for the first time, that the initial signal for SFN-induced apoptosis is derived from reactive oxygen species (ROS). Exposure of PC-3 cells to growth-suppressive concentrations of SFN resulted in ROS generation, which was accompanied by disruption of mitochondrial membrane potential, cytosolic release of cytochrome c, and apoptosis. All these effects were significantly blocked on pretreatment with N-acetylcysteine and overexpression of catalase. The SFN-induced ROS generation was significantly attenuated on pretreatment with mitochondrial respiratory chain complex I inhibitors, including diphenyleneiodonium chloride and rotenone. SFN treatment also caused a rapid and significant depletion of GSH levels. Collectively, these observations indicate that SFN-induced ROS generation is probably mediated by a nonmitochondrial mechanism involving GSH depletion as well as a mitochondrial component. Ectopic expression of Bcl-xL, but not Bcl-2, in PC-3 cells offered significant protection against the cell death caused by SFN. In addition, SFN treatment resulted in an increase in the level of Fas, activation of caspase-8, and cleavage of Bid. Furthermore, SV40-immortalized mouse embryonic fibroblasts (MEFs) derived from Bid knock-out mice displayed significant resistance toward SFN-induced apoptosis compared with wild-type MEFs. In conclusion, the results of the present study indicate that SFN-induced apoptosis in prostate cancer cells is initiated by ROS generation and that both intrinsic and extrinsic caspase cascades contribute to the cell death caused by this highly promising cancer chemopreventive agent.

A New High Affinity Technetium Analogue of Bombesin Containing DTPA as a Pharmacokinetic Modifier

The bombesin (BN)/gastrin-releasing peptide (GRP) receptor is expressed in high density on the cell surface of a variety of tumors. This makes the receptors accessible as a molecular target for the detection of lesions in which they are expressed. In this study, we describe a high affinity hydrophilic (99m)Tc-labeled BN analogue, [DTPA(1), Lys(3)((99m)Tc-Hx-DADT), Tyr(4)]BN, having diethylenetriaminepentaacetic acid (DTPA), as a build-in pharmacokinetic modifier, to direct its excretion through the urinary system in order to lower abdominal background activity. In vitro binding studies using [(125)I-Tyr(4)]BN (K(d), 0.1 nM) and human prostate cancer PC-3 cell membranes showed that the inhibition constant (K(i)) of [DTPA(1), Lys(3)((99)Tc-Hx-DADT), Tyr(4)]BN was 19.9 +/- 8.0 nM. Biodistribution studies in normal mice showed fast blood clearance (0.15 +/- 0.01% ID/g, 4 h postinjection), low intestinal accumulation (9.16 +/- 2.35% ID/g, 4 h postinjection), and significant uptake in BN/GRP receptor rich tissues such as the pancreas (21.83 +/- 2.88% ID/g, 15 min postinjection). The pancreas/blood, pancreas/muscle, and pancreas/liver ratios were highest at 2 h postinjection at 23, 74, and 8.4, respectively. The uptake in the pancreas could be blocked by BN (11.96 +/- 1.17 vs 0.65 +/- 0.16% ID/g), partially blocked by neuromedin B (11.96 +/- 1.17 vs 6.66 +/- 0.51% ID/g), but not affected by somatostatin (11.96 +/- 1.17 vs 12.91 +/- 2.53% ID/g), indicating that the binding of [DTPA(1), Lys(3)((99m)Tc-Hx-DADT), Tyr(4)]BN to the receptors was specific. Scintigraphic imaging of human PC-3 prostate cancer xenografts in SCID mice gave a high target to nontarget ratio on the image. Thus, [DTPA(1), Lys(3)((99m)Tc-Hx-DADT), Tyr(4)]BN has the potential for imaging BN/GRP receptor-positive lesions.

Hedgehog-interacting protein is highly expressed in endothelial cells but down-regulated during angiogenesis and in several human tumors.

BackgroundThe Hedgehog (Hh) signaling pathway regulates a variety of developmental processes, including vasculogenesis, and can also induce the expression of pro-angiogenic factors in fibroblasts postnatally. Misregulation of the Hh pathway has been implicated in a variety of different types of cancer, including pancreatic and small-cell lung cancer. Recently a putative antagonist of the pathway, Hedgehog-interacting protein (HIP), was identified as a Hh binding protein that is also a target of Hh signaling. We sought to clarify possible roles for HIP in angiogenesis and cancer.MethodsInhibition of Hh signaling by HIP was assayed by measuring the induction of Ptc-1 mRNA in TM3 cells treated with conditioned medium containing Sonic hedgehog (Shh). Angiogenesis was assayed in vitro by EC tube formation on Matrigel. Expression of HIP mRNA was assayed in cells and tissues by Q-RT-PCR and Western blot. HIP expression in human tumors or mouse xenograft tumors compared to normal tissues was assayed by Q-RT-PCR or hybridization of RNA probes to a cancer profiling array.ResultsWe show that Hedgehog-interacting protein (HIP) is abundantly expressed in vascular endothelial cells (EC) but at low or undetectable levels in other cell types. Expression of HIP in mouse epithelial cells attenuated their response to Shh, demonstrating that HIP can antagonize Hh signaling when expressed in the responding cell, and supporting the hypothesis that HIP blocks Hh signaling in EC. HIP expression was significantly reduced in tissues undergoing angiogenesis, including PC3 human prostate cancer and A549 human lung cancer xenograft tumors, as well as in EC undergoing tube formation on Matrigel. HIP expression was also decreased in several human tumors of the liver, lung, stomach, colon and rectum when compared to the corresponding normal tissue.ConclusionThese results suggest that reduced expression of HIP, a naturally occurring Hh pathway antagonist, in tumor neo-vasculature may contribute to increased Hh signaling within the tumor and possibly promote angiogenesis.

Allyl isothiocyanate, a constituent of cruciferous vegetables, inhibits growth of PC-3 human prostate cancer xenografts in vivo.

We have shown previously that allyl isothiocyanate (AITC), a constituent of cruciferous vegetables, significantly inhibits survival of PC-3 and LNCaP human prostate cancer cells in culture, whereas proliferation of a normal prostate epithelial cell line is minimally affected by AITC even at concentrations that are highly cytotoxic to the prostate cancer cells. The present studies were designed to test the hypothesis that AITC administration may retard growth of human prostate cancer xenografts in vivo. Bolus i.p. injection of 10 micromol AITC, three times per week (Monday, Wednesday and Friday) beginning the day of tumor cell implantation, significantly inhibited the growth of PC-3 xenograft (P < 0.05 by two-way ANOVA). For example, 26 days after tumor cell implantation, the average tumor volume in control mice (1025 +/- 205 mm3) was approximately 1.7-fold higher compared with AITC-treated mice. Histological analysis of tumors excised at the termination of the experiment revealed a statistically significant increase in number of apoptotic bodies with a concomitant decrease in cells undergoing mitosis in the tumors of AITC-treated mice compared with that of control mice. Western blot analysis indicated an approximately 70% reduction in the levels of anti-apoptotic protein Bcl-2 in the tumor lysate of AITC-treated mice compared with that of control mice. Moreover, the tumors from AITC-treated mice, but not control mice, exhibited cleavage of BID, which is known to promote apoptosis. Statistically significant reduction in the expression of several proteins that regulate G2/M progression, including cyclin B1, cell division cycle (Cdc)25B and Cdc25C (44, 45 and 90% reduction, respectively, compared with control), was also observed in the tumors of AITC-treated mice relative to control tumors. In conclusion, the results of the present study indicate that AITC administration inhibits growth of PC-3 xenografts in vivo by inducing apoptosis and reducing mitotic activity.