Persistence of human vascular endothelium in experimental human prostate cancer bone tumors

Development of clinically relevant in vivo metastasis models using human bone discs and breast cancer patient-derived xenografts

Background

Late-stage breast cancer preferentially metastasises to bone; despite advances in targeted therapies, this condition remains incurable. The lack of clinically relevant models for studying breast cancer metastasis to a human bone microenvironment has stunted the development of effective treatments for this condition. To address this problem, we have developed humanised mouse models in which breast cancer patient-derived xenografts (PDXs) metastasise to human bone implants with low variability and high frequency.

Methods

To model the human bone environment, bone discs from femoral heads of patients undergoing hip replacement surgery were implanted subcutaneously into NOD/SCID mice. For metastasis studies, 7 patient-derived xenograft tumours (PDX: BB3RC32, ER+ PR+ HER2−; BB2RC08, ER+ PR+ ER2−; BB6RC37, ER− PR− HER2− and BB6RC39, ER+ PR+ HER2+), MDA-MB-231-luc2, T47D-luc2 or MCF7-Luc2 cells were injected into the 4th mammary ducts and metastases monitored by luciferase imaging and confirmed on histological sections. Bone integrity, viability and vascularisation were assessed by uCT, calcein uptake and histomorphometry. Expression profiling of genes/proteins during different stages of metastasis were assessed by whole genome Affymetrix array, real-time PCR and immunohistochemistry. Importance of IL-1 was confirmed following anakinra treatment.

Results

Implantation of femoral bone provided a metabolically active, human-specific site for tumour cells to metastasise to. After 4 weeks, bone implants were re-vascularised and demonstrated active bone remodelling (as evidenced by the presence of osteoclasts, osteoblasts and calcein uptake). Restricting bone implants to the use of subchondral bone and introduction of cancer cells via intraductal injection maximised metastasis to human bone implants. MDA-MB-231 cells specifically metastasised to human bone (70% metastases) whereas T47D, MCF7, BB3RC32, BB2RC08, and BB6RC37 cells metastasised to both human bone and mouse bones. Importantly, human bone was the preferred metastatic site especially from ER+ PDX (100% metastasis human bone compared with 20–75% to mouse bone), whereas ER-ve PDX developed metastases in 20% of human and 20% of mouse bone. Breast cancer cells underwent a series of molecular changes as they progressed from primary tumours to bone metastasis including altered expression of IL-1B, IL-1R1, S100A4, CTSK, SPP1 and RANK. Inhibiting IL-1B signalling significantly reduced bone metastasis.

Conclusions

Our reliable and clinically relevant humanised mouse models provide significant advancements in modelling of breast cancer bone metastasis.

Origin of the vasculature supporting growth of primary patient tumor xenografts

Background

Studies of primary patient tumor xenografts grown in immunodeficient mice have shown that these tumors histologically and genetically closely resemble the original tumors. These patient xenograft models are becoming widely used for therapeutic efficacy studies. Because many therapies are directed at tumor stromal components and because the tumor microenvironment also is known to influence the response of a tumor to therapy, it is important to understand the nature of the stroma and, in particular, the vascular supply of patient xenografts.

Methods

Patient tumor xenografts were established by implanting undisrupted pieces of patient tumors in SCID mice. For this study, formalin fixed, paraffin embedded specimens from several types of solid tumors were selected and, using species-specific antibodies which react with formalin fixed antigens, we analyzed the species origin of the stroma and blood vessels that supported tumor growth in these models. Additionally, we investigated the kinetics of the vascularization process in a colon tumor and a mesothelioma xenograft. In mice bearing a head and neck xenograft, a perfusion study was performed to compare the functionality of the human and mouse tumor vessels.

Results

In patient tumors which successfully engrafted, the human stroma and vessels which were engrafted as part of the original tumor did not survive and were no longer detectable at the time of first passage (15–25 weeks). Uniformly, the stroma and vessels supporting the growth of these tumors were of murine origin. The results of the kinetic studies showed that the loss of the human vessels and vascularization by host vessels occurred more rapidly in a colon tumor (by 3 weeks) than in a mesothelioma (by 9 weeks). Finally, the perfusion studies revealed that while mouse vessels in the periphery of the tumor were perfused, those in the central regions were rarely perfused. No vessels of human origin were detected in this model.

Conclusions

In the tumors we investigated, we found no evidence that the human stromal cells and vessels contained in the original implant either survived or contributed in any substantive way to the growth of these xenografts.

Inhibition of human prostate cancer growth, osteolysis and angiogenesis in a bone metastasis model by a novel mechanism-based selective gelatinase inhibitor

Metastasis to the bone is a major clinical complication in patients with prostate cancer (PC). However, therapeutic options for treatment of PC bone metastasis are limited. Gelatinases are members of the matrix metalloproteinase (MMP) family and have been shown to play a key role in PC metastasis. Herein, we investigated the effect of SB-3CT, a covalent mechanism-based MMP inhibitor with high selectivity for gelatinases, in an experimental model of PC bone metastases. Intraperitoneal (i.p.) treatment with SB-3CT (50 mg/kg) inhibited intraosseous growth of human PC3 cells within the marrow of human fetal femur fragments previously implanted in SCID mice, as demonstrated by histomorphometry and Ki-67 immunohistochemistry. The anti-osteolytic effect of SB-3CT was confirmed by radiographic images. Treatment with SB-3CT also reduced intratumoral vascular density and bone degradation in the PC3 bone tumors. A direct inhibition of bone marrow endothelial cell invasion and tubule formation in Matrigel by SB-3CT in vitro was also demonstrated. The use of the highly selective gelatinase inhibitors holds the promise of effective intervention of metastases of PC to the bone.

Development and characterization of efficient xenograft models for benign and malignant human prostate tissue

BACKGROUND

Various research groups have attempted to grow fresh, histologically intact human prostate cancer tissues in immunodeficient mice. Unfortunately, grafting of such tissues to the sub-cutaneous compartment was found to be associated with low engraftment rates. Furthermore, xenografts could only be established using high-grade, advanced stage, but not low- or moderate-grade prostate cancer tissues.

METHODS

This paper describes methods for xenografting both benign and malignant human prostate tissue to severe combined immunodeficient (SCID) mice. We examine the efficiency and histopathologic consequences of grafting to the sub-cutaneous, sub-renal capsule, and prostatic orthotopic sites.

RESULTS

Sub-renal capsule grafting was most efficient in terms of take rate (>90%) for both benign and malignant tissue. Orthotopic grafts consistently exhibited the best histopathologic differentiation, although good differentiation with continued expression of androgen receptors (AR) and PSA was also seen in the sub-renal capsule site. Sub-cutaneous grafting resulted in low take rates and the lowest level of histodifferentiation in surviving grafts. Grafted benign tissues in all sites appropriately expressed AR, PSA, cytokeratins 8, 18, and 14 as well as p63; carcinoma tissues did not express the basal cell markers. Grafting of tissues to castrated hosts did not affect the graft take rates (but was not practical in the case of the orthotopic site). Grafting followed by host castration resulted in epithelial regression with loss PSA and reduced AR expression at all three sites.

CONCLUSIONS

These data suggest that sub-renal capsule and orthotopic grafting of human prostate tissue can be used for many basic scientific and translational studies.

Of mice and men: values and liabilities of the athymic nude mouse model in anticancer drug development

Human tumour xenografts implanted subcutaneously (s.c.) into immunosuppressed mice have played a significant role in preclinical anticancer drug development for the past 25 years. Their use as a predictive indicator of probable clinical activity has been validated for cytotoxics. A retrospective analysis for 39 compounds where both extensive xenograft testing and Phase II clinical data were available, performed by the National Cancer Institute (NCI), has shown that 15/33 agents (45%) with activity in more than one-third of xenografts showed clinical activity (P=0.04). However, with the exception of non-small cell lung cancer, activity within a particular histological type of the xenograft generally did not predict for clinical activity in the same tumour. Today, the question (largely unanswered) is how useful is the xenograft model (particularly the traditional s.c. model) in contemporary cancer drug discovery? There are many variables when conducting xenograft experiments which impact on outcome; viz, site of implantation, growth properties of the xenograft and size when treatment is initiated, agent formulation, scheduling, route of administration and dose and the selected endpoint for assessing activity. The xenograft model remains of value in current preclinical cancer drug development, especially when such studies give due consideration to the above variables and are based on sound mechanistic (e.g. status of the selected target in the chosen model) and pharmacological (e.g. use of formulated agent) principles. Dependent upon the drug target, a slowing of xenograft tumour growth (cytostatic effect) rather than tumour shrinkage might be the major observed effect. Human tumour xenografts are also particularly useful in determining pharmacodynamic markers of response for subsequent clinical application. Nevertheless, it needs to be kept in mind that the use of xenografts is relatively time-consuming and expensive, raises animal ethical issues and there are instances where the model is inappropriate as a likely predictor of clinical outcome (e.g. inhibitors of the metastatic process and anti-angiogenic strategies as the vasculature is of murine origin).

Cotargeting tumor and stroma in a novel chimeric tumor model involving the growth of both human prostate cancer and bone stromal cells

Stromal-epithelial interaction contributes to local prostate tumor growth, androgen-independent progression and distant metastasis. We have established in vitro coculture and in vivo chimeric tumor models to evaluate the roles of stromal cells isolated from either osteosarcoma or normal bone, a site where prostate cancer cells frequently metastasize, in contributing to the growth and survival of human prostate cancer cells. We have evaluated extensively the effects of toxic gene therapy using luciferase-tagged chimeric human prostate cancer models both in vitro and in vivo. In the in vitro cocultured cell model, we assessed cancer cell growth and residual cellular proteins after targeting either prostate cancer epithelial cells alone or both prostate cancer and bone stromal cells. In the in vivo animal model, we measured tumor volume and serum prostate-specific antigen (PSA) in mice bearing chimeric prostate tumors comprised of human prostate tumor cells and normal bone stromal cells. Our results demonstrated that: (1) The rate of human prostate cancer cell growth in vitro is accelerated by coculturing with human and rat osteosarcoma or normal mouse bone marrow stromal cell lines. No growth stimulation was noted when cocultured with a human prostate epithelial cell line. (2) Disabling the growth of normal bone stromal cells using transgenic targeting with a bystander gene, herpes simplex virus thymidine kinase (hsv-TK), plus the pro-drug ganciclovir (GCV) or acyclovir markedly depressed the growth of cocultured human prostate cancer cells in vitro and human prostate cancer-mouse normal bone stroma chimeric tumors in vivo. (3) By cotargeting both human prostate cancer and normal mouse bone stromal cells in vitro with an adenoviral construct, Ad-hOC-TK (a replication-defective Ad5 vector with the bystander transgene hsv-TK under the control of a human osteocalcin (hOC) promoter) plus GCV4, we observed greater inhibition of tumor cell growth than by targeting a single cell compartment with Ad-PSA-TK (a vector construct similar to Ad-hOC-TK except that the transgene expression is under regulation by a full-length human PSA promoter). These results, taken together, established a basic principle that cotargeting both tumor and its supporting stroma is more efficacious than targeting a single cell compartment in the treatment of human prostate cancer bone metastasis. This principle can be applied to other clinical conditions of cancer growth where stroma contribute to the overall growth and survival potential of the cancer.

Inhibition of alpha(v)beta3 integrin reduces angiogenesis, bone turnover, and tumor cell proliferation in experimental prostate cancer bone metastases

The growth of metastatic prostate cancer cells in the bone involves an intimate interaction between the tumor cells and various elements of the bone microenvironment, resulting in increased rate of bone turnover and rapid tumor growth. The alpha(v)beta3 integrin has been shown to play an important role in tumor growth and angiogenesis, and is known to be critical to osteoclast formation and activity. This study was designed to examine the role of alpha(v)beta3 expressed by cells native to the bone in the growth and pathogenesis of prostate cancer bone metastases. Human prostate cancer cells which do not express alpha(v)beta3 or alpha(IIb)beta3 integrins were injected directly into human bone fragments previously implanted subcutaneously in SCID mice (SCID-human-bone model). At the same time treatment with anti-beta3 antibody fragment (m7E3 F(ab')2) i.p. at 300 microg/dose 3 x per week was initiated and continued for 2 weeks. In this system, m7E3 F(ab')2 only recognizes human bone-derived alpha(v)beta3. Antibody inhibition of alpha(v)beta3 integrin in vivo resulted in a specific reduction in the proportion of antigenically-human blood vessels within tumor-bearing bone implants (from 73.5% +/- 3.93 in controls to 17.74% +/- 5.64 in treated animals). Proliferation of the alpha(v)beta3-negative tumor cells was also reduced, although the overall vessel density was maintained by compensating mouse vasculature. Blockage of human bone-derived alpha(v)beta3 also significantly reduced the recruitment of osteoclasts in response to tumor cells, as well as degradation of calcified bone tissue. Together these observations confirm the importance of alpha(v)beta3 in bone metabolism and angiogenesis, and point to the role of these processes in controlling growth of metastatic prostate cancer cells in the bone.

Approaches to modeling stromal-epithelial interactions

PURPOSE Techniques that can be used to examine the molecular mechanisms of stromal-epithelial interactions are described. MATERIALS AND METHODS A historical perspective of available techniques is provided. Recent developments and examples are used to illustrate and provide descriptive literature references for these methods. Since the possibilities for manipulating experimental systems are enormous and rapidly expanding, the reader should be aware that this review is an overview of how data have been and could be obtained rather than a comprehensive listing of what has been achieved. This review focuses on studies performed in the organs of the urogenital tract to illustrate techniques that are available.RESULTS Recent technological innovations have impacted our ability to manipulate specific components and pathways of stromal-epithelial interactions. They include rapid developments in transgenic and gene knockout mouse technology, and the development of highly efficacious gene delivery and expression systems. CONCLUSIONS These technologies have the potential to transform our understanding of the mechanistic basis of intercellular communication and point the way toward new therapeutic approaches for benign and malignant proliferative conditions.

Interactive gene expression pattern in prostate cancer cells exposed to phenolic antioxidants

Dietary phenolic compounds are known to elicite vital cellular responses such as cell cycle arrest, apoptosis and differentiation by activating a cascade of molecular events. As there is an increasing interest to improve the efficacy of these compounds for use as potential chemopreventive agents, we wanted to understand the impact of phenolic compounds on target genes in prostate cancer. In this study we used human cDNA microarrays with 2400 clones consisting of 17 prosite motifs to characterize alterations in gene expression pattern in response to the phenolic antioxidants ellagic acid (EA) and resveratrol (RE). Over a 48-hr exposure of androgen - sensitive LNCaP cells to EA and RE, a total of 593 and 555 genes respectively, showed more than a two fold difference in expression. A distinct set of genes in both EA-and RE-treated cells may represent the signature profile of phenolic antioxidant-induced gene expression in LNCaP cells. Although extensive similarity was found between effects of EA - and RE - responsive genes in prostate cancer cells, out of 246 genes with overlapping responses, 25 genes showed an opposite effect. Quantitative RT-PCR was used to verify and validate the differential expression of selected genes identified from cDNA microarrays. In-depth analysis of the data from this study provided insight into the alterations in the p53 - responsive genes, p300, Apaf-1, NF-kBp50 and p65 and PPAR families of genes, suggesting the activation of multiple signaling pathways that leads to growth inhibition of LNCaP cells. This is a first study to look for changes in a large number of human genes in response to dietary compounds.

Mechanisms governing bone metastasis in prostate cancer

Why does prostate cancer metastasize to bone? Why is there increased turnover of the bone matrix in the presence of prostate cancer? A recent autopsy study supports a traditional hypothesis that gross, anatomic patterns of blood flow influence the distribution of metastatic deposits. On the other hand, recent developments in animal models of prostate cancer bone metastasis have renewed interest in the traditional 'seed and soil' hypothesis: several studies point to specific biological interactions between prostate cancer cells and the bone microenvironment that can explain the tendency of prostate cancer cells to colonize bone and grow into clinically relevant metastatic deposits. Some studies implicate mechanisms including chemoattraction and enhanced adherence to bone endothelium. Additional data suggest that prostate cancer cells are 'osteomimetic', that is, they take on the properties and behaviors of osteoblasts or osteoclasts upon arrival in bone. These activities lead to enhanced turnover of the bone matrix and may explain the propensity of prostate cancer to grow in bone. Finally, a series of studies have implicated other molecular markers as distinguishing characteristics of bone-metastatic prostate cancer tissue.