Model Of Prostate Cancer Metastasis Research Articles

Abstract B050: Reproducible and effective preclinical models of prostate cancer metastasis established with PDXs

Abstract Metastatic castration resistant prostate cancer (mCRPC) is a lethal disease. Understanding the intricacy of this disease and developing targeted treatment is hampered by the lacking of clinically relevant animal models. LuCaP patient-derived xenografts (PDXs), established from advanced metastatic prostate cancer, are a large cohort that encompass the molecular and cellular heterogeneity of mCRPC. We have established four prostate cancer metastasis models from three androgen receptor (AR) positive lines (LuCaP136, LuCaP167 and LuCaP23.1) and one AR negative line LuCap145.2. The three AR positive LuCap lines metastasized to vertebrae and long bones with differing bone-associated histology while the AR negative LuCap145.2 metastasize to brain and spinal cord. The bone metastasis phenotypes of the models encompass: osteolytic (LuCaP136), mixed bone destruction and new bone formation (LuCaP167), and a highly osteoblastic histology (LuCaP23.1). LuCap136 and LuCap167 also metasize to soft tissues including adrenal, kidney and liver. Castration responses were studied on LuCap136 and LuCap167 models. Although both models are castration resistant, LuCap136 model initially are sensitive to castration with decreased tumor progression, and AR down-regulated in the metastatic sites. In contrast, tumor progression was not affected after castration in LuCap167 model. AR and ARV7 were up-regulated in metastatic cells. In summary, the LuCap PDX lines have the capacity for systemic growth in clinically accurate metastatic sites. In addition, the two AR positive models show different castration response which may be driven by different pathways. Understanding the complexity of these pathways would guide optimal selection of drug combinations to achieve the best outcome for patients with mCRPC. Citation Format: JuanJuan I. Yin, Asha Daryanani, Aian Alilin, Ross Lake, Kathy Kelly. Reproducible and effective preclinical models of prostate cancer metastasis established with PDXs [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B050.

Abstract 46: A new class of precision therapeutics that inhibit prostate cancer mediated bone destruction

Abstract The destructive nature of bone metastases dominates the clinical management of advanced prostate cancer (PCa) and is a common cause of morbidity and mortality. Our current ability to therapeutically target this process is limited. Here we describe the synthesis and functional characterization of the first-in-class Dual Acting Bone Defending agents (DABDs), which couple a small molecule therapeutic that inhibits cell movement to bone trophic bisphosphonates. Upfront in-vitro screens assessed DABD efficacy at inhibiting PCa cell migration and invasion and osteoclast mediated bone destruction. Systemic models of PCa metastasis, inclusive of intracardiac (IC) and intratibial (IT) injection models, were deployed to characterize tolerance and efficacy in-vivo. Finally, in-vitro characterization of DABD molecular mechanism of action was performed, as guided by the existing knowledge base related to the parental compounds. Results demonstrated that DABDs inhibit PCa cell migration and invasion, chemically bind hydroxyappetite, and inhibit osteoclast mediated bone destruction in vitro. Following IC injection of PCa cells, a model where cells are placed into circulation, metastasize to bone, grow and induce bone destruction, emulating the clinical scenario in humans, DABD treatment inhibited circulating PCa cells from forming new bone metastasis and prolonged life in a dose-dependent fashion. In the IT mouse models of established metastatic lesions, DABDs induce reversion of PCa cell growth and disrupt further bone destruction. DABDs at doses 1000 fold higher than those associated with efficacy are well tolerated. At the molecular level, DABDs retain the molecular mechanisms of action of their constituent chemicals. They inhibit farnesyl diphosphate synthase (FDPS), in the mevalonate pathway, leading to decreased prenylation of small GTPases, including the Ras related protein, Rap-1A, as well as inhibit Raf1 activation, inducing apoptosis and impaired cell movement, respectively. DABDs are a new class of agents that inhibit formation of new bone metastasis, revert growth of established metastasis, prolong life, and have a high potential for improving clinical outcome in humans. Citation Format: Ryan R. Gordon, Abhinandan Pattanayak, Wenqi Li, Raymond Bergan. A new class of precision therapeutics that inhibit prostate cancer mediated bone destruction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 46.

Gene therapy with RALA/iNOS composite nanoparticles significantly enhances survival in a model of metastatic prostate cancer

BackgroundRecent approvals of gene therapies by the FDA and the EMA for treatment of inherited disorders have further opened the door for assessment of nucleic acid pharmaceuticals for clinical usage. Arising from the presence of damaged or inappropriate DNA, cancer is a condition particularly suitable for genetic intervention. The RALA peptide has been shown to be a potent non-viral delivery platform for nucleic acids. This study examines the use of RALA to deliver a plasmid encoding inducible nitric oxide synthase (iNOS) as an anti-cancer treatment.MethodsThe physiochemical properties of the RALA/DNA nanoparticles were characterized via dynamic light scattering and transmission electron microscopy. The nanoparticles were labelled with fluorophores and tracked over time using confocal microscopy with orthogonal sections to determine cellular location. In vitro studies were employed to determine functionality of the nanoparticles both for pEGFP-N1 and CMV-iNOS. Nanoparticles were injected intravenously into C57/BL6 mice with blood and serum samples analysed for immune response. PC3-luc2M cells were injected into the left ventricle of SCID mice followed by treatment with RALA/CMV-iNOS nanoparticles to evaluate the tumour response in a metastatic model of prostate cancer.ResultsFunctional cationic nanoparticles were produced with gene expression in PC-3 prostate cancer cells. Furthermore, repeated administrations of RALA/DNA nanoparticles into immunocompetent mice did not produce any immunological response: neutralization of the vector or release of inflammatory mediators. RALA/CMV-iNOS reduced the clonogenicity of PC-3 cells in vitro, and in an in vivo model of prostate cancer metastasis, systemically delivered RALA/CMV-iNOS significantly improved the survival of mice.ConclusionThese studies further validate RALA as a genetic cargo delivery vehicle and iNOS as a potent therapy for the treatment of cancer.

Organelle-Derived Acetyl-CoA Promotes Prostate Cancer Cell Survival, Migration, and Metastasis via Activation of Calmodulin Kinase II.

Although emerging evidence suggests a potential role of calcium/calmodulin-dependent kinase II (CaMKII) in prostate cancer, its role in prostate cancer tumorigenesis is largely unknown. Here, we examine whether the acetyl CoA-CaMKII pathway, first described in frog oocytes, promotes prostate cancer tumorigenesis. In human prostate cancer specimens, metastatic prostate cancer expressed higher levels of active CaMKII compared with localized prostate cancer. Correspondingly, basal CaMKII activity was significantly higher in the more tumorigenic PC3 and PC3-mm2 cells relative to the less tumorigenic LNCaP and C4-2B4 cells. Deletion of CaMKII by CRISPR/Cas9 in PC3-mm2 cells abrogated cell survival under low-serum conditions, anchorage-independent growth and cell migration; overexpression of constitutively active CaMKII in C4-2B4 cells promoted these phenotypes. In an animal model of prostate cancer metastasis, genetic ablation of CaMKII reduced PC3-mm2 cell metastasis from the prostate to the lymph nodes. Knockdown of the acetyl-CoA transporter carnitine acetyltransferase abolished CaMKII activation, providing evidence that acetyl-CoA generated from organelles is a major activator of CaMKII. Genetic deletion of the β-oxidation rate-limiting enzyme ACOX family proteins decreased CaMKII activation, whereas overexpression of ACOXI increased CaMKII activation. Overall, our studies identify active CaMKII as a novel connection between organelle β-oxidation and acetyl-CoA transport with cell survival, migration, and prostate cancer metastasis.Significance: This study identifies a cell metabolic pathway that promotes prostate cancer metastasis and suggests prostate cancer may be susceptible to β-oxidation inhibitors. Cancer Res; 78(10); 2490-502. ©2018 AACR.

α3β1 Integrin Suppresses Prostate Cancer Metastasis via Regulation of the Hippo Pathway.

Existing anticancer strategies focused on disrupting integrin functions in tumor cells or tumor-involved endothelial cells have met limited success. An alternative strategy is to augment integrin-mediated pathways that suppress tumor progression, but how integrins can signal to restrain malignant behavior remains unclear. To address this issue, we generated an in vivo model of prostate cancer metastasis via depletion of α3β1 integrin, a correlation observed in a significant proportion of prostate cancers. Our data describe a mechanism whereby α3β1 signals through Abl family kinases to restrain Rho GTPase activity, support Hippo pathway suppressor functions, and restrain prostate cancer migration, invasion, and anchorage-independent growth. This α3β1-Abl kinase-Hippo suppressor pathway identified α3 integrin-deficient prostate cancers as potential candidates for Hippo-targeted therapies currently under development, suggesting new strategies for targeting metastatic prostate cancer based on integrin expression. Our data also revealed paradoxical tumor suppressor functions for Abl kinases in prostate cancer that may help to explain the failure of Abl kinase inhibitor imatinib in prostate cancer clinical trials. Cancer Res; 76(22); 6577-87. ©2016 AACR.

Targeting protein geranylgeranylation slows tumor development in a murine model of prostate cancer metastasis

ABSTRACTThe isoprenoid biosynthetic pathway (IBP) plays a critical role in providing substrates and enzymes necessary for the post-translational modification and thus activation of a number of proteins involved in prostate cancer metastasis. Previous work by our lab found novel compound disodium [(6Z,11E,15E)-9-[bis(sodiooxy)phosphoryl]−17-hydroxy-2,6,12,16-tetramethyheptadeca-2,6,11,15-tetraen-9-yl]phosphonate (GGOHBP), which inhibits the IBP enzyme geranylgeranyl diphosphate synthase (GGDPS), reduced protein geranylgeranylation without altering protein farnesylation. This activity significantly reduced adrenal gland tumor burden in a murine model of human prostate cancer metastasis which relied on treatment of established disease. The present study determined the ability of GGDPS inhibition to slow the development of prostate cancer metastasis in a preventative murine model. Using tail vein injection of human derived PC-3 prostate cancer cells 4 d after initiating daily GGOHBP or vehicle treatments, we found GGOHBP significantly reduced whole body tumor burden, significantly slowed the development of tumors, and prolonged overall survival as compared to vehicle treated animals. The observed reduction in soft tissue tumor burden corresponded to a biochemical reduction in Rap1A geranylgeranylation, which for prostate cancer is important in its own merit and which serves as a surrogate marker for Rho family, i.e. Rac, protein modification. This effect was present in all treated mice pointing to strong target engagement, which was not observed in non-tumor burdened tissues or control mice. Our findings reiterate a role for protein geranylgeranylation in the development of prostate cancer metastasis in vivo.

Abstract 1572: Overexpression of Axl delays metastatic outgrowth of prostate cancer bone marrow disseminated tumor cells

Abstract The presence of detectable metastases in the bone marrow of prostate cancer patients represents lethal, incurable disease. These metastases that may emerge years or decades after prostatectomy are derived from small colonies of dormant tumor cells that disseminated from the primary tumor. Our group has previously shown that Gas6/Axl signaling is associated with disseminated tumor cell (DTC) dormancy in mouse models of prostate cancer metastasis. In this study we explored the functional significance of this association and tested the hypothesis that overexpression of Axl in prostate cancer cells would prolong their dormant phase in the bone marrow. Axl overexpression in the AR-positive Axl-negative human prostate cancer cell line C42B slowed proliferation in vitro. Select cells were completely dormant as detected by the lack of EdU incorporation over 40 hours, and this fraction was increased when co-cultured with bone-forming osteoblasts. To assess the functional effects of Axl on prostate cancer progression in vivo, we utilized a mouse model of prostate cancer metastasis in which subcutaneous tumors are established and surgically removed upon reaching 200mm3. At 10 weeks post-tumor removal, mice bearing C42B-Axl tumors did not have overt osteoblastic or osteolytic lesions in their femurs or tibiae, whereas mice bearing C42B-WT tumors had visible lesions by x-ray. Immunohistochemistry staining of mouse femurs and tibiae corroborated these findings. To confirm that the absence of metastases in mice with C42B-Axl tumors was not due to the inability of the cells to disseminate, we used immunofluorescence to detect human cells in the bone marrow of flushed femurs and tibiae. At 12 weeks post-tumor removal, fewer prostate cancer cells were detected in the bone marrow of mice with C42B-Axl tumors compared to those with C42B-WT tumors. Notably however, both groups had detectable prostate cancer cells in the bone marrow, indicating that the absence of C42B-Axl metastasis was not due to failure of primary tumor cells to disseminate. The presence of disseminated C42B-Axl cells in the bone marrow coupled with their failure to develop into clinical metastases at the time of C42B-WT metastatic outgrowth establishes a functional role for the association of Axl expression with DTC dormancy. Axl may be sufficient to induce and maintain dormancy, and ongoing experiments will address the requirement of Axl in this setting. Citation Format: Haley D. Axelrod, Kenneth C. Valkenburg, Kenneth J. Pienta. Overexpression of Axl delays metastatic outgrowth of prostate cancer bone marrow disseminated tumor cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1572.

Abstract B31: Characterization of a novel model of prostate cancer metastasis resulting from androgen receptor suppression

Abstract Background: Prostate cancer (PC) is the second leading cause of male cancer-related mortality: 30,000 men die each year from metastatic disease. The Androgen Receptor (AR) may be the earliest known example of a lineage oncogene – a master regulator of prostate cancer cell survival and growth. The AR protein is detectable at all stages of prostate cancer progression and is the primary target of pharmacological agents capable of suppressing AR signaling to extend survival in men with metastatic prostate cancer (mPC). The CYP17 inhibitor Abiraterone, and the 3rd generation AR antagonist, MDV3100 prolong the survival of men with mPC, though cures remain exceeding rare using these agents individually. In order to develop additional therapies to be used in combination with current AR inhibitors, preclinical models that mimic PC progression need to be established. Tissue microarray studies from hormone-naïve, nodal positive, prostate cancer patients revealed a significant down-regulation of AR protein level in matched nodal metastases versus primary tumors. These results suggest that loss of AR or AR activity could play a role in the progression to metastatic disease. Methods: We used a short-hairpin RNA targeting exon 1 of the AR to reduce AR protein in vivo using a doxycycline-inducible system in the non-metastatic AR-positive human prostate cancer cell line 22Rv1. This cell line model, derived from a primary tumor, is castration-resistant and enzalutamide/MDV3100-resistant. We generated xenografts using 22Rv1shARex1 and evaluated tumor growth and propensity for metastatic spread. We profiled transcriptional changes in the context of AR suppression and compared gene expression changes between grafted tumors and sites of metastatic spread. Results: Xenograft studies in NOD-SCID mice revealed that reduction of the AR protein decreased tumor proliferation rates and promoted cancer metastasis. Tumor-bearing mice exposed to continual reduction of the AR developed large liver metastases and had significantly increased disseminated tumor cells in their bone marrow. Furthermore, intratibial and intracardiac injection of 22Rv1shARex1 followed by AR reduction, resulted in an increased formation of metastases. Transcriptional analysis revealed unique signatures between untreated parental 22Rv1 xenografts, tumors with AR reduction, and liver metastases. Genes up-regulated in xenografts following AR reduction, were also up-regulated in patient metastases versus primary tumors including transcripts encoding EGF, HGF, and ZEB2. Discussion: The AR is the primary therapeutic target for mPC. However, a cure for advanced cancer and metastatic disease remains elusive. Reduction of the AR in the 22Rv1 in vivo model mimics disease progression seen in patients. Molecular changes observed during the transformation of localized cancer to metastatic disease in this model may identify new targets to be used in combination with current therapies intent on ablating AR signaling. Citation Format: Clinton K. Matson, Peter S. Nelson. Characterization of a novel model of prostate cancer metastasis resulting from androgen receptor suppression. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr B31.

Abstract A35: Axl overexpression in a prostate cancer mouse model delays metastasis and may prolong dormancy of disseminated tumor cells

Abstract The most common site of metastasis in prostate cancer (PCa) patients is the bone marrow, where disseminated tumor cells (DTCs) preferentially home to the hematopoietic stem cell niche and can undergo a state of dormancy. These PCa cells may lie dormant in the bone marrow for years after prostatectomy, but may eventually re-enter the cell cycle resulting in lethal metastatic disease. Using mouse models of PCa metastasis, our group has previously shown that Gas6/Axl signaling is associated with dormant bone marrow DTCs. In this study we investigated the requirement of Axl in initiating and maintaining the dormant phase. We hypothesized that overexpression of Axl in PCa cells would prolong dormancy. Overexpression of Axl in the bone-homing AR-positive Axl-negative human PCa cell line C42B slows proliferation in vitro. Subcutaneous injection of C42B-Axl cells in a xenograft mouse model resulted in delayed onset of tumor growth relative to WT controls. C42B-WT tumors reached an average volume of 200mm3 at 6.6 weeks, while C42B-Axl tumors reached the same volume at 11 weeks. Regions of the primary tumor with a high percentage of Axl+ cells correlated with a low number of Ki67+ cells, indicating that Axl may inhibit proliferation even in the primary tumor. Surprisingly, C42B-Axl tumors were more vascular as observed by eye, and regions of increased vasculature correlated with a high percentage of Axl+ cancer cells. Metastatic outgrowth in soft tissues reached a lethal burden ~12 weeks following C42B-WT tumor removal, while mice bearing C42B-Axl tumors did not have detectable metastases by eye at the same timepoint post-tumor removal and were apparently healthy. Metastatic outgrowth in the bone was detected by the presence of osteoblastic and osteolytic activity at 5-12 weeks post-tumor removal in the femurs and tibiae of mice bearing C42B-WT tumors. At 8-12 weeks after C42B-Axl tumor removal, however, there was no evidence of metastatic bone disease. While these experiments are still ongoing, we have shown that Axl expression in the primary tumor delayed metastatic burden in both soft tissues and in bone in a mouse model of PCa metastasis. In ongoing studies, we will compare DTC number and time to metastasis in the bone marrow of C42B-WT and C42B-Axl tumor-bearing mice. Citation Format: Haley D. Axelrod, Kenneth C. Valkenburg, Kenneth J. Pienta. Axl overexpression in a prostate cancer mouse model delays metastasis and may prolong dormancy of disseminated tumor cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A35.

Genetic engineering of platelets to neutralize circulating tumor cells

Mounting experimental evidence demonstrates that platelets support cancer metastasis. Within the circulatory system, platelets guard circulating tumor cells (CTCs) from immune elimination and promote their arrest at the endothelium, supporting CTC extravasation into secondary sites. Neutralization of CTCs in blood circulation can potentially attenuate metastases to distant organs. Therefore, extensive studies have explored the blockade of platelet–CTC interactions as an anti-metastatic strategy. Such an intervention approach, however, may cause bleeding disorders since the platelet–CTC interactions inherently rely on the blood coagulation cascade including platelet activation. On the other hand, platelets have been genetically engineered to correct inherited bleeding disorders in both animal models and human clinical trials. In this study, inspired by the physical association between platelets and CTCs, platelets were genetically modified to express surface-bound tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a cytokine known to induce apoptosis specifically in tumor cells. The TRAIL-expressing platelets were demonstrated to kill cancer cells in vitro and significantly reduce metastases in a mouse model of prostate cancer metastasis. Our results suggest that using platelets to produce and deliver cancer-specific therapeutics can provide a Trojan-horse strategy of neutralizing CTCs to attenuate metastasis.

Whole-Body and Microenvironmental Localization of Radium-223 in Naïve and Mouse Models of Prostate Cancer Metastasis.

Background:Bone-metastatic, castration-resistant prostate cancer (bmCRPC) represents a lethal stage of the most common noncutaneous cancer in men. The recent introduction of Radium-223 dichloride, a bone-seeking alpha particle (α)–emitting radiopharmaceutical, demonstrates statistically significant survival benefit and palliative effect for bmCRPC patients. Clinical results have established safety and efficacy, yet questions remain regarding pharmacodynamics and dosing for optimized patient benefit.Methods:We elucidated the biodistribution of 223Ra as well as interaction with the bone and tumor compartments in skeletally mature mice (C57Bl/6 and CD-1, n = 3–6) and metastasis models (LNCaP and PC3, n = 4). Differences in uptake were evaluated by µCT and histological investigation. Novel techniques were leveraged on whole-mount undecalcified cryosections to determine microdistribution of Radium-223. All statistical tests were two-sided.Results: 223Ra uptake in the bones (>30% injected activity per gram) at 24 hours was also accompanied by non-negligible remnant activity in the kidney (2.33% ± 0.36%), intestines (5.73% ± 2.04%), and spleen (10.5% ± 5.9%) Skeletal accumulation across strains did not correspond with bone volume or surface area but instead to local blood vessel density (P = .04). Microdistribution analysis by autoradiography and α camera revealed targeting of the ossifying surfaces adjacent to the epiphyseal growth plate. In models of PCa metastasis, radioactivity does not localize directly within tumors but instead at the apposite bone surface. Osteoblastic and lytic lesions display similar intensity, which is comparable with uptake at sites of normal bone remodeling.Conclusions:Profiling the macro- and microdistribution of 223Ra in healthy and diseased models has important implications to guide precision application of this emerging α-therapy approach for bmCRPC and other bone metastastic diseases.

Targeting geranylgeranylation reduces adrenal gland tumor burden in a murine model of prostate cancer metastasis

The isoprenoid biosynthetic pathway (IBP) is critical for providing substrates for the post-translational modification of proteins key in regulating malignant cell properties, including proliferation, invasion, and migration. Inhibitors of the IBP, including statins and nitrogenous bisphosphonates, are used clinically for the treatment of hypercholesterolemia and bone disease respectively. The statins work predominantly in the liver, while the nitrogenous bisphosphonates are highly sequestered to bone. Inhibition of the entire IBP is limited by organ specificity and side effects resulting from depletion of all isoprenoids. We have developed a novel compound, disodium [(6Z,11E,15E)-9-[bis(sodiooxy)phosphoryl]-17-hydroxy-2,6,12,16-tetramethyheptadeca-2,6,11,15-tetraen-9-yl]phosphonate (GGOHBP), which selectively targets geranylgeranyl diphosphate synthase, reducing post-translational protein geranylgeranylation. Intracardiac injection of luciferase-expressing human-derived 22Rv1 PCa cells into SCID mice resulted in tumor development in bone (100 %), adrenal glands (72 %), mesentery (22 %), liver (17 %), and the thoracic cavity (6 %). Three weeks after tumor inoculation, daily subcutaneous (SQ) injections of 1.5 mg/kg GGOHBP or the vehicle were given for one month. Dissected tumors revealed a reduction in adrenal gland tumors corresponding to a 54 % (P < 0.005) reduction in total adrenal gland tumor weight of the treated mice as compared to vehicle-treated controls. Western blot analysis of the harvested tissues showed a reduction in Rap1A geranylgeranylation in adrenal glands and mesenteric tumors of the treated mice while non-tumorous tissues and control mice showed no Rap1A alteration. Our findings detail a novel bisphosphonate compound capable of preferentially altering the IBP in tumor-burdened adrenal glands of a murine model of PCa metastasis.

Cocultures of mesenchymal stem cells and endothelial cells as organotypic models of prostate cancer metastasis.

In spite of recognized limitations in capturing species-specific responses and high costs, rodent models remain commonly used in prostate cancer metastasis research, due largely to the lack of available alternatives. We aim to develop an in vitro culture system to study prostate cancer response to a simulated bone microenvironment, which may be used to understand early events in prostate metastasis to bone or for drug screening applications. To achieve this, mesenchymal stem cells and endothelial cells were isolated and cocultured to form a vascularized bone analogue. Endothelial cells were found to exert osteopotentiating effects on mesenchymal stem cell differentiation, and reciprocal effects by the stromal cells were found to stimulate vasculogenic responses, suggesting the possible utility of this system to elicit three-way interactions between endothelial, mesenchymal, and prostate cancer cells. We further developed the use of fluorescently labeled cells which could be used to concurrently track cellular migration, proliferation, and morphometric analysis. We demonstrate the concurrent, real-time visualization of prostate cancer and endothelial cells, which may be useful for evaluation of spatiotemporal changes at a single-cell level. When prostate cancer cell proliferation on various substrates was measured, it was found that the use of coculture systems may provide a better reflection of conditions in vivo, highlighting the potential utility as a model system.

Abstract PL06-04: Targeting the tumor ecosystem: Translating the molecular biology of chemokine interactions to the clinic.

Abstract There has been an increasing recognition that the tumor microenvironment contains host non-cancer cells in addition to cancer cells, interacting in a dynamic fashion over time. The cancer cells compete and/or cooperate with non-tumor cells, and the cancer cells may compete and/or cooperate with each other. It has been demonstrated that these interactions can alter the genotype and phenotype of the host cells as well as the cancer cells. The interaction of these cancer and host cells to remodel the normal host organ microenvironment may best be conceptualized as an evolving ecosystem. Describing tumors as ecological systems defines new opportunities for novel cancer therapies (“ecological therapy”). The ecology literature is filled with stories of how changing the ecosystem resulted in the death of a species. A key method, therefore, to kill cancer cells in the tumor ecosystem may be to inhbit other cell species within the environment that are supporting the growth and survival of cancer cells. Chemokines are a family of small and secreted proteins that play pleiotropic roles in inflammation-related diseases, including cancer. Among the identified 50 human chemokines, chemokine (C-C motif) ligand 2 (CCL2) is of particular importance in cancer development since it serves as one of the key mediators of interactions between tumor and host cells. CCL2 is produced by cancer cells and multiple different host cells within the tumor microenvironment. In the bone marrow microenvironment, for example, it is produced by osteoblasts, osteoclasts, and endothelial cells. CCL2 mediates tumorigenesis in many different cancer types and has been reported to promote cancer cell proliferation, migration, invasion, and survival, via binding to its functional receptor CCR2. Most importantly, however, CCL2 induces the recruitment of monocytes to the tumor and their subsequent differentiation into tumor associated macrophages (TAMS). Upon CCL2 stimulation, CD11b(+) cells demonstrated a significant increase in the mannose receptor (CD206) and the CD14(+)/CD206(+) double-positive cells, suggesting a polarization of macrophages toward the CD206(+) M2-type phenotype. TAMs subsequently are major mediators of angiogenesis and matrix remodeling. CCL2 protects macrophages from autophagic death by activating survivin through a PI3K/AKT (phosphatidylinositol 3-kinase/protein kinase B)-dependent mechanism, increasing their ability to survive in the hypoxic tumor microenvironment. CCL2 induces up-regulation of the antiapoptotic proteins cFLIP(L) (cellular caspase-8 (FLICE)-like inhibitory protein), Bcl-2, and Bcl-X(L) and inhibits the cleavage of caspase-8 and subsequent activation of the caspase-cascade, thus protecting cells from apoptosis under serum deprivation stress. Multiple studies have revealed that inhibition of CCL2 substantially decreases macrophage infiltration, decreases osteoclast function, and inhibits prostate cancer growth in bone in preclinical animal models. In one study, for example, utilizing neutralizing antibodies to human CCL2 (CNTO888) and the mouse homologue CCL2/JE (C1142), treatment with anti-CCL2/JE antibody (2 mg/kg, twice weekly i.p.) attenuated prostate cancer cell PC-3Luc-mediated overall tumor burden in an in vivo model of prostate cancer metastasis by 96% at 5 weeks post intracardiac injection. These preclinical data have been successfully translated to the clinic. SWOG study S0916, for example, was a phase II, window trial of an anti-CCR2 antibody in patients with bone metastases. This biomarker driven study was designed to test the hypothesis that inhibiting the CCL-2-CCR2 axis in patients with cancer metastatic to bone osteoclast function would be inhibited as measured by a decrease in urinary NTX by 25% or more from baseline. Patients were given three doses of antibody two weeks apart and urinary NTX was measured at baseline, two weeks, 4 weeks, and 6 weeks. Preliminary results suggest that administration of anti-CCR2 antibody resulted in decreases in urinary NTX in a significant number of patients. These data suggest that altering the tumor microenvironment through inhibition of CCL2 may be a viable strategy for interfering with cancer cell activity and growth. This example of translation from bench to bedside demonstrating how an understanding chemokine effects on the tumor ecosystem can serve as a paradigm for other cytokines, chemokines, and cell interactions within the tumor microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr PL06-04.

Prostate cancer cells home to bone in a new in vivo model of bone metastasis

This study aimed to establish the dorsal skinfold chamber (DSC) model of prostate cancer metastasis. Metatarsals from newborn mice are engrafted into a DSC implanted a SCID mouse (5‐6 weeks old). We have demonstrated that metatarsals are rapidly vascularised by inosculation with the host vasculature by day 5‐7, with functional vessels by day 2. Vascular density was measured over a 7 day period; day 3, 455 ± 186 cm/cm2; day 5, 546 ± 305 cm/cm2 and day 7, 707 ± 370 cm/cm2. Following this fluorescently labelled prostate (PC3‐GFP) or oral (SCC4‐GFP) cancer cells (1 x 105) are injected via the heart to simulate metastatic spread. Cells initially adhere to the microvascular endothelium and/or to metatarsal matrix 5 days after injection (10 ± 7 cells/metatarsal). Bone viability has been assessed throughout the 4 week study duration and demonstrates viable tissue within the DSC. Histology of the metatarsal confirms the presence of tumour cells, viability of the metatarsal, active growth plate and new vessels formation. This model will allow homing, interactions and extravasation between the tumour and bone microenvironment to be studied in detail. Funded by Sixth European Framework Programme (PROMET).

Targeting CCL2 with Systemic Delivery of Neutralizing Antibodies Induces Prostate Cancer Tumor RegressionIn vivo

The identification of novel tumor-interactive chemokines and the associated insights into the molecular and cellular basis of tumor-microenvironment interactions have continued to stimulate the development of targeted cancer therapeutics. Recently, we have identified monocyte chemoattractant protein 1 (MCP-1; CCL2) as a prominent regulator of prostate cancer growth and metastasis. Using neutralizing antibodies to human CCL2 (CNTO888) and the mouse homologue CCL2/JE (C1142), we show that treatment with anti-CCL2/JE antibody (2 mg/kg, twice weekly i.p.) attenuated PC-3Luc-mediated overall tumor burden in our in vivo model of prostate cancer metastasis by 96% at 5 weeks postintracardiac injection. Anti-CCL2 inhibition was not as effective as docetaxel (40 mg/kg, every week for 3 weeks) as a single agent, but inhibition of CCL2 in combination with docetaxel significantly reduced overall tumor burden compared with docetaxel alone, and induced tumor regression relative to initial tumor burden. These data suggest an interaction between tumor-derived chemokines and host-derived chemokines acting in cooperation to promote tumor cell survival, proliferation, and metastasis.

IL-12 gene-modified bone marrow cell therapy suppresses the development of experimental metastatic prostate cancer

To investigate the immunomodulatory effects of interleukin-12 (IL-12) for treatment of metastatic prostate cancer, we administered adult bone marrow cells (BMC) that were genetically modified by retroviral vector-mediated IL-12 gene transduction in an experimental mouse model of prostate cancer metastasis. This therapy produced significant anti-metastatic effects in bone and lung and prolonged animal survival. Flow cytometric analysis indicated donor BMC could effectively home to bone and lung after treatment. Intensive infiltration of CD4 and CD8T cells in lung metastases and increased systemic natural killer and cytotoxic T lymphocyte activities indicated induction of a significant anti-metastatic immune response after treatment with IL-12 transduced BMC. Our results demonstrate the therapeutic potential of gene-modified BMC gene therapy.

Effects of blocking platelet-derived growth factor-receptor signaling in a mouse model of experimental prostate cancer bone metastases.

Expression of platelet-derived growth factor (PDGF) and activation (by autophosphorylation) of its receptor (PDGF-R), a tyrosine kinase, are associated with the growth of metastatic prostate tumor cells in the bone parenchyma. The tyrosine kinase inhibitor STI571 blocks the PDGF signaling pathway by inhibiting PDGF-R autophosphorylation. We examined the effects of STI571, given alone or with paclitaxel (Taxol), on tumor growth in a mouse model of prostate cancer metastasis. Human prostate cancer PC-3MM2 cells were injected into the tibias of male nude mice. Three days later the mice (20 per group) were randomly assigned to 5 weeks of treatment with oral and injected water (control), daily oral STI571, weekly injected paclitaxel, or STI571 plus paclitaxel. Lesions in bone and the surrounding muscles were then harvested and analyzed by histology, western blotting (for PDGF-R phosphorylation), immunohistochemistry (for expression of proangiogenic molecules), and double immunofluorescence (to identify endothelial cells and apoptotic tumor cells). Growth of bone lesions was monitored by digital radiography. Bone lesions from control mice were used to establish short-term cell cultures for analysis of PDGF-R phosphorylation. All statistical tests were two-sided. PC-3MM2 cells cultured from bone lesions and treated in vitro with STI571 had less phosphorylated PDGF-R than untreated cells. In control mice, bone lesions expressed high levels of PDGF and activated (i.e., phosphorylated) PDGF-R, whereas lesions in the adjacent musculature did not. Activated PDGF-R was present on the surface of endothelial cells within the bone lesions but not in endothelial cells of uninjected bone. Mice treated with STI571 or STI571 plus paclitaxel had a lower tumor incidence, smaller tumors, and less bone lysis and lymph node metastasis than mice treated with water or paclitaxel alone (P<.001 for all). Mice treated with STI571 or STI571 plus paclitaxel had less phosphorylated PDGF-R on tumor cells and tumor-associated endothelial cells, less tumor cell proliferation, statistically significantly more apoptotic tumor cells (all P<.001), and fewer tumor-associated endothelial cells (P<.001) than control mice. Endothelial cells appear to express phosphorylated PDGF-R when they are exposed to tumor cells that express PDGF. Using STI571 to inhibit PDGF-R phosphorylation may, especially in combination with paclitaxel, produce substantial therapeutic effects against prostate cancer bone metastasis.

Osteomimetic properties of prostate cancer cells: a hypothesis supporting the predilection of prostate cancer metastasis and growth in the bone environment.

Unlike most other malignancies, prostate cancer metastasizes preferentially to the skeleton and elicits osteoblastic reactions. We present a hypothesis, based upon results obtained from our laboratory and others, on the nature of progression of prostate cancer cells and their predilection to growth and metastasis in the bone microenvironment. We propose the hypothesis that osseous metastatic prostate cancer cells must be osteomimetic in order to metastasize, grow, and survive in the skeleton. The reciprocal interaction between prostate cancer and bone stromal growth factors, including basic fibroblast growth factor (bFGF), hepatocyte growth factor/scatter factor (HGF/SF), and especially the insulin growth factor (IGF) axis initiates bone tropism, and is enhanced by prostate secreted endothelin-1 (ET-1) and urokinase-type plasminogen activator (uPA). Growth factors and peptides that have differentiating activity, such as transforming growth factor beta (TGF-beta), parathyroid hormone-related protein (PTH-rp), and the bone morphogenetic proteins (BMPs), can shift local homeostasis to produce the characteristic blastic phenotype, via interaction with prostate-secreted human kalikrein 2 (hK2), and prostate-specific antigen (PSA). This proposal asserts that altering the expression of certain critical transcription factors, such as Cbfa and MSX in prostate cancer cells, which presumably are under the inductive influences of prostate or bone stromal cells, can confer profiles of gene expression, such as osteopontin (OPN), osteocalcin (OC), and bone sialoprotein (BSP), that mimic that of osteoblasts. Elucidation of common proteins, presumably driven by the same promoters, expressed by both prostate cancer and bone stromal cells, could result in the development of novel preventive and therapeutic strategies for the treatment of prostate cancer skeletal metastasis. Agents developed using these strategies could have the potential advantage of interfering with growth and enhancing apoptosis in both prostate cancer and bone stromal compartments. The selective application of gene therapy strategy, driven by tissue-specific and tumor-restricted promoters for the safe delivery and expression of therapeutic genes in experimental models of prostate cancer metastasis, is discussed.