Modulation of tumor cell response to chemotherapy by the organ environment

Targeting the expression of platelet-derived growth factor receptor by reactive stroma inhibits growth and metastasis of human colon carcinoma

The stromal cells within colon carcinoma express high levels of the platelet-derived growth factor receptor (PDGF-R), whereas colon cancer cells do not. Here, we examined whether blocking PDGF-R could inhibit colon cancer growth in vivo. KM12SM human colon cancer cells were injected subcutaneously (ectopic implantation) into the cecal wall (orthotopic implantation) or into the spleen (experimental liver metastasis) of nude mice. In the colon and liver, the tumors induced active stromal reaction, whereas in the subcutis, the stromal reaction was minimal. Groups of mice (n=10) received saline (control), the tyrosine kinase inhibitor imatinib, irinotecan, or a combination of imatinib and irinotecan. Four weeks of treatment with imatinib and irinotecan significantly inhibited tumor growth (relative to control or single-agent therapy) in the cecum and liver but not in the subcutis. The combination therapy completely inhibited lymph node metastasis. Imatinib alone or in combination with irinotecan inhibited phosphorylation of PDGF-Rbeta of tumor-associated stromal cells and pericytes. Combination therapy also significantly decreased stromal reaction, tumor cell proliferation, and pericyte coverage of tumor microvessels and increased apoptosis of tumor cells and tumor-associated stromal cells. These data demonstrate that blockade of PDGF-R signaling pathways in tumor-associated stromal cells and pericytes inhibits the progressive growth and metastasis of colon cancer cells.

Effect of culture conditions on the chemosensitivity of ovarian cancer cell lines

The aim of this study was to define the chemosensitivity profile of a series of human ovarian cancer cell lines representing the human primary ovarian tumours under altered culture conditions and to compare the results with those from tumour-derived cells. In this study, we used a standardized ATP-based tumour chemosensitivity assay to measure the activity of cytotoxics in the seven ovarian carcinoma cell lines and ovarian tumour-derived cells. The use of adherence-free polypropylene plates and a serum-free medium slowed down cell proliferation in all cell lines tested, mimicking the slow growth rate of solid tumours in this type of plastic. The seeding density was optimized for each cell line and was in the range of 2000-4000 cells/well. Heterogenous sensitivity to different cytotoxics was observed in the seven ovarian cancer cell lines tested in the ATP-based tumour chemosensitivity assay. The human ovarian carcinoma cell line, OVCA433, was found to be the most resistant cell line and 75% of the drugs showed an Index(SUM) above 300. Our results suggest that the use of appropriate culture conditions i.e. a serum-free culture environment, adherence-free growth and optimum seeding density can induce cell lines to behave more like tumour-derived cells in response to cytotoxic agents. On the basis of the comparison of chemosensitivity profiles of tumour-derived cells and cell lines derived from the corresponding tumour, a panel of cell lines can be selected. Such a panel could be used to screen and develop anticancer drugs.

Development of an orthotopic transplantation model in nude mice that simulates the clinical features of human lung cancer

The objective of the present study was to establish an orthotopic tumor transplantation model in nude mice that closely resembles the clinical features of human lung cancer. The human lung adenocarcinoma A549 cell line and the squamous cell carcinoma SQ5 cell line were used. Tumor cells suspended in serum-free medium were injected directly into the main bronchi of anesthetized female Balb/c athymic nude mice (7-9 weeks old) with or without simultaneous administration of 0.01 M ethylenediaminetetracetic acid (EDTA). In some experiments, lung carcinoma cells harvested from tumors transplanted subcutaneously were recultured and used for intratracheal implantation. Tumor nodules that formed in the lung were counted and confirmed by histological examination. Administration of A549 cells with EDTA resulted in a 70% engraftment rate (n = 10). Recultured A549 cells without and with EDTA resulted in 20% (n = 5) and 80% (n = 5) engraftment rates, respectively. Administration of SQ5 cells without or with EDTA formed 50% (n = 4) and 67% (n = 6) engraftment rates, respectively. Recultured SQ5 cells with EDTA further increased the engraftment rate to 100% (n = 6). Multiple tumors formed mainly in the left lung and the upper lobe of the right lung. Simultaneous administration of EDTA resulted in greater numbers of tumor nodules in the lung. Histological findings revealed that A549 tumor nodules were distributed primarily in alveoli. The SQ5 solid tumors invaded bronchioles and occupied the alveoli. This reproducible orthotopic transplantation model produced tumor growth that simulated the clinical features of human lung cancer.

Gene expression in tumor-adjacent normal tissue is associated with recurrence in patients with rectal cancer treated with adjuvant chemoradiation

Recurrence is a significant clinical problem for patients with rectal cancer treated with adjuvant chemoradiation. Previous studies have suggested that determining intratumoral gene expression of key genes may be helpful in predicting clinical outcome of patients with gastrointestinal malignancies undergoing chemotherapy. The role of molecular predictors for prediction of recurrence in the setting of adjuvant chemoradiotherapy is not well established. The present study was designed to identify a genetic profile that would be associated with recurrence in patients with rectal cancer treated with adjuvant chemoradiation therapy. A retrospective study with a longitudinal cohort and a cross-sectional cohort of 67 patients with locally advanced rectal cancer who underwent cancer resection, followed by 5-fluorouracil (5-FU) plus pelvic radiation was conducted. Total RNA was extracted from formalin-fixed, paraffin-embedded, laser-captured-microdissected tissue. We determined mRNA levels of genes involved in the 5-FU pathway (thymidylate synthase, dihydropyrimidine dehydrogenase), DNA-repair (excision-repair cross-complementing factor 1, Rad51), angiogenesis/radiation sensitivity [vascular endothelial growth factor (VEGF)] and radio-sensitivity [epidermal growth factor receptor (EGFR)] in tumor tissue and tumor-adjacent normal tissue by quantitative reverse transcriptase-polymerase chain reaction. In univariate analysis, only intratumoral gene expression level of VEGF (P = 0.055) was associated with recurrence, whereas elevated mRNA expression levels of thymidylate synthase (P = 0.008), VEGF (P = 0.023) and EGFR (P = 0.004) in tumor-adjacent normal tissue were significantly associated with recurrence. Multivariate analysis using recursive partitioning indicated that distinct groups of recurrence could be defined by elevated mRNA expression levels of VEGF, EGFR in tumor-adjacent normal tissue, and Rad51 in tumor tissue. These data suggest that the genetic profile of the tumor-adjacent normal tissue may be associated with treatment failure, indicating that tumor microenvironment may be more important in the development of recurrence of rectal tumors than formerly expected.

What do, can and should we learn from models to evaluate potential anticancer agents?

Transfer of new anticancer agents from bench to clinical trial takes in excess of 10 years and costs up to US $500 million. Despite this massive commitment, many more new agents fail in the clinical trials than are successful. The poor performance of many investigational anticancer agents in the clinic implies that the preclinical models used to evaluate them are flawed, inappropriately used or the information they generate is misinterpreted. This article reviews current practice and the range of preclinical models available. The author provides a personal perspective on what information is needed and how in the future this might best be obtained from preclinical models to more effectively inform the transfer of novel, active agents into clinical practice.

A selective retinoid X receptor agonist bexarotene (LGD1069, targretin) inhibits angiogenesis and metastasis in solid tumours

The present study determined the influence of a retinoid X receptor agonist bexarotene on angiogenesis and metastasis in solid tumours. In the experimental lung metastasis xenograft models, treatment with bexarotene inhibited the development of the lung tumour nodule formation compared to control. In vivo angiogenesis assay utilising gelfoam sponges, bexarotene reduced angiogenesis in sponges containing vascular endothelial growth factor, epidermal growth factor and basic fibroblast growth factor to various extent. To determine the basis of these observations, human breast and non-small-cell lung cancer cells were subjected to migration and invasion assays in the presence of bexarotene. Our data showed that bexarotene decrease migration and invasiveness of tumour cells in a dose-dependent manner. Furthermore, bexarotene inhibited angiogenesis by directly inhibiting human umbilical vein endothelial cell growth and indirectly inhibiting tumour cell-mediated migration of human umbilical vein endothelial cells through Matrigel matrix. Analysis of tumour-conditioned medium indicated that bexarotene decreased the secretion of angiogenic factors and matrix metalloproteinases and increased the tissue inhibitor of matrix metalloproteinases. The ability of bexarotene to inhibit angiogenesis and metastasis was dependent on activation of its heterodimerisation partner peroxisome proliferator-activated receptor gamma. Collectively, our results suggest a role of bexarotene in treatment of angiogenesis and metastasis in solid tumours.

Human recombinant erythropoietin (rEpo) has no effect on tumour growth or angiogenesis

Tumour hypoxia has been shown to increase mutation rate, angiogenesis, and metastatic potential, and decrease response to conventional therapeutics. Improved tumour oxygenation should translate into increased treatment response. Exogenous recombinant erythropoietin (rEpo) has been recently shown to increase tumour oxygenation in a mammary carcinoma model. The mechanism of this action is not yet understood completely. The presence of Epo and its receptor (EpoR) have been demonstrated on several normal and neoplastic tissues, including blood vessels and various solid tumours. In addition, rEpo has been shown in two recent prospective, randomized clinical trials to negatively impact treatment outcome. In this study, we attempt to characterize the direct effects of rEpo on tumour growth and angiogenesis in two separate rodent carcinomas. The effect of rEpo on R3230 rat mammary adenocarcinomas, CT-26 mouse colon carcinomas, HCT-116 human colon carcinomas, and FaDu human head and neck tumours, all of which express EpoR, was examined. There were no differences in tumour growth or proliferation (measured by Ki-67) between placebo-treated and rEpo-treated tumours. In the mammary window chamber, vascular length density (VLD) measurements in serial images of both placebo-treated and Epo-treated rats revealed no difference in angiogenesis between the Epo-treated tumours and placebo-treated tumours at any time point. These experiments are important because they suggest that the recent clinical detriment seen with the use of Epo is not due to its tumour growth effects or angiogenesis. These studies also suggest that further preclinical studies need to examine rEpo's direct tumour effects in efforts to improve the therapeutic benefits of Epo in solid tumour patients.

Practices and Pitfalls of Mouse Cancer Models in Drug Discovery

Mouse models of cancer are critical tools for elucidating mechanisms of cancer development, as well as for assessment of putative cancer therapies. However, there are ongoing concerns about the value of mouse cancer models for predicting therapeutic efficacy in humans. This chapter reviews the most commonly used transplanted tumor models, including subcutaneous and orthotopic tumors in mice. It also reviews commonly utilized in vivo study endpoints. Even small improvements in predictive value achieved through careful selection of models and endpoints have the potential to have large impacts on productivity and overall drug development costs.

Therapeutic targets for antimetastatic therapy

Metastases are responsible for most cancer deaths. Despite dramatic advances in cancer therapy, the presence of metastases implies a significantly shortened survival and reduced quality of remaining life. Aside from prevention of cancer altogether, or significant improvements in early detection for most cancers, effective novel therapeutic strategies targeting metastasis should provide the greatest clinical benefit. Metastasis research has shown that many of the initial steps in metastasis are completed with a high degree of efficiency and may have occurred by the time of clinical diagnosis. Therefore, targeting the later stages of metastasis may offer a more promising therapeutic approach for the development of antimetastatic therapies. Appropriate clinical strategies include targeting dormant solitary cells, active preangiogenic metastases, or vascularised metastases. Dormancy of solitary single cells, seen clinically and experimentally, may be an explanation for cancer recurrence. Eradication or inactivation of these dormant cells could provide large benefit for patients. However, little is known about what makes cancer cells dormant and, therefore, a greater knowledge of the mechanisms of dormancy is needed. This review discusses potential biological targets, as defined by the steps in the metastatic process, for antimetastatic therapies and provides examples of clinical strategies for preventing or treating successful metastasis.

An orthotopic model of anaplastic thyroid carcinoma in athymic nude mice

PURPOSE

To develop an orthotopic model of anaplastic thyroid carcinoma (ATC) in athymic nude mice.

EXPERIMENTAL DESIGN

Various thyroid carcinoma cell lines were injected into the thyroid gland of athymic nude mice to determine whether such injection was technically feasible. ATC cells were then injected into the thyroid gland or the subcutis of nude mice at various concentrations, and the mice were then followed for tumor development. The tumors were examined histopathologically for local invasion or regional or distant metastasis.

RESULTS

Injection of tumor cells into the thyroid glands of nude mice was technically feasible and resulted in the formation of thyroid tumors. The ATC cell line DRO showed significantly higher tumorigenicity in the thyroid gland than in the subcutis. In contrast, oral squamous cell carcinoma cell line TU167 shows no significantly higher tumorigenicity in the thyroid gland than in the subcutis. ATC tumors established in the thyroid gland also produced symptomatic compression of the esophagus and the trachea. Local invasion of the larynx and trachea was as well as high rates of pulmonary metastasis were also observed. Immunohistochemical staining showed higher microvessel density as well as higher expression of vascular endothelial growth factor and interleukin-8 in the orthotopic thyroid tumors than in ectopic tumors.

CONCLUSION

An orthotopic model of ATC in athymic nude mice was developed that closely recapitulates the clinical findings of human ATC. This model should facilitate the understanding of the pathogenesis of ATC and aid in the development of novel therapies against ATC.

Protein biomarkers and drug design for cancer treatments

The development of new cancer treatments is quickly evolving away from traditional practices of the last 25 years. This change is occurring not only at the technical level, but also conceptually as the human genome is unravelled and decades of research contribute to our understanding of the molecular complexity of this disease. It is anticipated that disease initiation and progression is dictated by an understandable set of acquired capabilities. Knowledge of the molecular events associated with these acquired capabilities will allow the development of targeted agents coupled with new biomarkers for the prevention of cancer progression. This will have a profound influence on how drugs are developed, approved, and used by the medical community. The Food and Drug Administration (FDA) has over 400 Investigational New Drug (IND) applications for cancer in its portfolio, which increasingly involve molecular targets and genomic applications. However, only one-fifth of IND agents succeed in New Drug Application (NDA) and there is more expense and uncertainty around successful drug development than ever before. Biomarkers should help the success rate of INDs by enhancing the link between target and disease as well as in improving patient selection and monitoring response. In this review, we discuss how biomarkers can be used for target validation and pharmacodynamic modeling in preclinical drug discovery. We then explore the use of biomarkers in clinical development from proof of mechanism to proof of concept studies, as well as their use in the prevention setting.

Radiofrequency ablation: Effect of pharmacologic modulation of hepatic and renal blood flow on coagulation diameter in a VX2 tumor model

PURPOSE

To determine whether pharmacologic agents can be used to modulate blood flow in hepatic and renal tumors sufficiently to alter the extent of radiofrequency (RF)-induced coagulation.

MATERIALS AND METHODS

VX2 tumors (8-15 mm) were implanted in the liver (n = 25) or kidney (n = 8) of 33 New Zealand White rabbits. RF was applied to tumors for 6 minutes with use of conventional electrodes (125 mA +/- 35; 90 degrees C +/- 2 degrees C tip temperature). In the hepatic model, blood flow was modulated with use of halothane, epinephrine, or arsenic trioxide (2-6 mg/kg). Laser Doppler flowmetry was used to quantify changes in hepatic blood flow. Correlation of blood flow with induced coagulation diameter was performed. RF ablation was then performed in a renal model with and without arsenic trioxide.

RESULTS

For liver tumors, halothane and arsenic trioxide reduced blood flow to 40.3% +/- 17.8% and 29% +/- 15% of normal, respectively, whereas epinephrine increased blood flow to 207.8% +/- 97.9%. Correlation of blood flow to coagulation diameter was demonstrated (R(2) = 0.40). Coagulation measured 7 mm +/- 1 with epinephrine, 10 mm +/- 1 with normal blood flow, 12 mm +/- 3 with halothane, and 13 mm +/- 3 with arsenic trioxide (P <.04 compared with controls). In the renal model, arsenic trioxide decreased blood flow (44% +/- 16%) and increased coagulation diameter (10.9 mm +/- 1) compared with controls (84% +/- 11% and 7.6 mm +/- 1; P <.01, both comparisons).

CONCLUSIONS

RF-induced coagulation necrosis in rabbit hepatic and renal tumors is affected by tumor blood flow. Pharmacologic modulation of tumor blood flow may provide a noninvasive way to decrease blood flow during thermally mediated ablation therapy, potentially enabling the creation of larger zones of coagulation necrosis.

Orthotopic models of cancer for preclinical drug evaluation: advantages and disadvantages

Considering the enormous effort that has taken place over the years to discover new chemotherapeutic drugs for treating the common cancers, the conventional murine and xenograft test systems used to test efficacy for drug development have identified only a limited number of useful agents that are active clinically at well tolerated doses. In recent years, considerable effort has been made to develop more clinically relevant models by the use of orthotopic transplantation of tumour material in rodents. It has been shown that it is now possible to transplant tumour material from a variety of tumour types into the appropriate anatomical site and often these tumours will metastasise in a similar manner and to similar locations as the same tumour type will in human cancer. As yet, although a body of literature has amassed on the technique itself and its implications for metastasis, there are relatively few laboratories using these test systems in drug development programmes. Nevertheless, given the expertise now being developed and some interesting observations being made on the role of the tumour site on response to therapeutic agents, it is likely that the use of orthotopic systems will strengthen our ability to select the most appropriate molecules for recommended use in clinical studies.

MUC4 mucin expression in human pancreatic tumours is affected by organ environment: the possible role of TGFbeta2

MUC4 is highly expressed in human pancreatic tumours and pancreatic tumour cell lines, but is minimally or not expressed in normal pancreas or chronic pancreatitis. Here, we investigated the aberrant regulation of MUC4 expression in vivo using clonal human pancreatic tumour cells (CD18/HPAF) grown either orthotopically in the pancreas (OT) or ectopically in subcutaneous tissue (SC) in the nude mice. Histological examination of the OT and SC tumours showed moderately differentiated and anaplastic morphology, respectively. The OT tumour cells showed metastases to distant lymph nodes and faster tumour growth (P<0.01) compared to the SC tumours. The MUC4 transcripts in OT tumours were very high compared to the undetectable levels in SC tumours. The SC tumour cells regained their ability to express MUC4 transcripts after in vitro culture. Immunohistochemical analysis using MUC4-specific polyclonal antiserum confirmed the results obtained by Northern blot analysis. Interestingly, the OT tumours showed expression of TGFβ2 compared to no expression in SC, suggesting a possible link between MUC4 and TGFβ2. The MUC4 expression, morphology, and metastasis of human pancreatic tumour cells are regulated by a local host microenvironment. TGFβ2 may serve as an interim regulator of this function.

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.

Micro-MRI at 11.7 T of a Murine Brain Tumor Model Using Delayed Contrast Enhancement

In vivo imaging methodologies allow for serial measurement of tumor size, circumventing the need for sacrificing mice at given time points. In orthotopically transplanted murine models of brain tumors, cross-section micro-MRI allows for visualization and measurement of the physically inaccessible tumors. To allow for long resident times of a contrast agent in the tumor, intraperitoneal administration was used as a route of injection for contrast-enhanced micro-MRI, and a simple method for relative tumor volume measurements was examined. A strategy for visualizing the variability of the delayed tumor enhancement was developed. These strategies were applied to monitor the growth of brain tumors xenotransplanted into nude mice and either treated with the antiangiogenic peptide EMD 121974 or an inactive control peptide. Each mouse was used as its own control. Serial imaging was done weekly, beginning at Day 7 after tumor cell implantation and continued for 7 weeks. Images obtained were reconstructed on the MRI instrument. The image files were transferred off line to be postprocessed to assess tumor growth (volume) and variability in enhancement (three-dimensional [3-D] intensity models). In a small study, tumor growth and response to treatment were followed using this methodology and the high-resolution images displayed in 3-D allowed for straightforward qualitative assessment of variable enhancement related to vascular factors and tumor age.

Development of a new in vitro chemosensitivity test using collagen gel droplet embedded culture and image analysis for clinical usefulness

The results of chemotherapy are not fully satisfactory in many cases, particularly solid cancers. Therefore, it seems useful if the effective anticancer drugs can be selected for each patient using the screening methods. In such a background, we developed a new anticancer-drug sensitivity testing method that overcame several defects in the existing method, which is the collagen gel droplet embedded culture drug sensitivity test (CD-DST) and satisfies the following requirements: a high success rate, ability to assay biopsy specimens, and quantification of the anticancer effects without contamination with fibroblasts. Under the biological exposure condition, the sensitivities of the cancers were similar to their clinical response rate and there was a statistically significant correlation between clinically reported response rates and the response rates obtained by CD-DST (P < 0.01). Furthermore, the true positive rate was 79.8%, and the true negative rate was 88.8%. Sensitivity and specificity were 88.2% and 80.6%, respectively, resulting in an overall predictive accuracy of 84.1% (154/183). The CD-DST not only shows high predictive accuracy for humans, but because of the high correlation between the results of in vitro and nude mice assays, if it also is practical as a pre-clinical screening, it can easily provide these predictions.

Human colon adenocarcinoma in the SCID/CB6 radiation chimera is susceptible to adoptive transfer of allogeneic human peripheral blood mononuclear cells

The aim of this study was to develop a murine model of human colon carcinoma (hCC) and to ascertain the potential of cellular immunotherapy in this model. Fragments of hCC obtained at surgery from 6 patients were transplanted under the kidney capsule of lethally irradiated CB6 mice radioprotected with severe combined immunodeficient (SCID) mice bone marrow. Tumor xenografts conserved their malignant behavior in the new environment, invading the mouse kidney parenchyma and expanding into the peritoneal cavity and adjacent tissues. Their growth was typically exponential, and they expanded to dimensions that allowed their subsequent fragmentation and passage to further preconditioned mice. Human carcinoembryonic antigen (hCEA) was detected on the implanted tumor and at occasionally spontaneous lung metastases. Most significantly, high levels of this tumor marker were detected in the sera of tumor-bearing mice, providing a useful tool, which allowed long-term experiments, monitoring of tumor progression, and its response to some treatment modalities. For instance, complete resection of the transplanted tumors, by means of nephrectomy, resulted in the disappearance of hCEA from mice sera within 2 weeks. Similarly, adoptive transfer of allogeneic human peripheral blood mononuclear cells (PBMC) into the peritoneum of tumor-bearing mice, resulted in their rapid engraftment, infiltration of tumor mass, and a significant drop of hCEA levels in mice serum, accounting for inhibition of tumor growth. We suggest that this novel model of human colon carcinoma affords the opportunity for in vivo evaluation of different preclinical treatment modalities, particularly, those involving manipulation with immune effector cells.

Enhanced antitumour efficacy by combining conventional chemotherapy with angiostatin or endostatin in a liver metastasis model

Background

Tumour-induced microvascular networks have become attractive targets in cancer therapy. Strategies that target both tumour cells and vasculature have not been investigated in models of early metastatic colorectal disease. The efficacy of a combination of conventional chemotherapy with a potent angiogenesis inhibitor (endostatin or angiostatin) in a murine model of early colorectal liver metastasis was studied.

Methods

Sixty-six mice were subjected to intrasplenic injection of C26 tumour cells to induce colorectal liver metastases. Control animals received phosphate-buffered saline (n = 8) or citrate buffer (n = 8). Treatment included conventional chemotherapy (n = 9), endostatin (n = 8), high-dose (n = 5) or low-dose (one-tenth of optimal dose; n = 10) angiostatin, as well as the combination of either of these drugs with chemotherapy (n &gt; 5). Clinical appearance was scored daily using a semiquantitative scale. Liver weight, macroscopic and histological tumour involvement (hepatic replacement area; HRA) were measured upon death at day 12.

Results

Treated mice displayed significantly better clinical scores than controls, except for those animals treated with low-dose angiostatin with or without chemotherapy. Treatment with conventional chemotherapy resulted in a decrease in HRA from 42·3 to 29·1 per cent (P &lt; 0·001). The addition of angiostatin or endostatin to conventional chemotherapy improved antitumoral efficacy, in a multiplicative manner, resulting in a HRA of approximately 3·5 per cent (P &lt; 0·001).

Conclusion

The addition of angiostatin or endostatin to conventional chemotherapy enhanced antitumoral efficacy in a murine model of early colorectal liver metastasis.

Dissemination and growth of cancer cells in metastatic sites

Metastases, rather than primary tumours, are responsible for most cancer deaths. To prevent these deaths, improved ways to treat metastatic disease are needed. Blood flow and other mechanical factors influence the delivery of cancer cells to specific organs, whereas molecular interactions between the cancer cells and the new organ influence the probability that the cells will grow there. Inhibition of the growth of metastases in secondary sites offers a promising approach for cancer therapy.

Heterotopic implantation alters the regulation of apoptosis and the cell cycle and generates a new metastatic site in a human pancreatic tumor xenograft model

Differences in growth and in response to antineoplastic drugs between s.c. and orthotopically implanted tumors in nude mice and between the primary tumor and the metastases in human tumors suggest that implantation site may alter the molecular regulation of tumor cells. We assessed the influence of implantation site on cell cycle and apoptotic regulation and the possible contribution of the implantation site in directing the choice of metastatic site by comparing the behavior of tumor aliquots of two human pancreatic xenografts (NP18 and NP9) implanted in the organ where the tumor grows (orthotopically), in heterotopic sites (the site of metastases (liver), and in nonmetastatic sites (subcutis and colon). We observed that implantation site changes tumor growth by altering apoptotic or cell cycle regulation in a tumor-specific manner. In the NP18 tumor it occurs by altering apoptotic induction and activation of the Bad/Bcl-XL/caspase-3 pathway through AKT and Erk regulation, but in the NP9 tumor by changing the activation and/or expression of the proteins that regulate the cell cycle (Erk, PCNA, and cyclin B1). We also observed that implantation site alters the metastatic pattern of the NP9 tumor, originating a new metastatic site.

Core biopsies can be used to distinguish differences in expression profiling by cDNA microarrays

The primary focus of this work was to determine the feasibility of obtaining representative expression array profiles from clinical core biopsies. For this purpose we performed six 16-gauge needle core biopsies and an excision biopsy on each of two different human xenografts, one from an Ewing's sarcoma cell line and the second from neuroblastoma cell line grown in Beige-Scid mice. Three of the six core biopsies were processed separately and the remaining three were pooled and processed together. As the initial RNA material isolated from the core biopsies was not sufficient for microarray analysis, an amplification procedure using a modified Eberwine protocol was performed, and the amplified products applied onto a 6000-feature human cDNA microarray. Comparisons of the array results from core biopsies (amplified RNA) and surgical specimens (non-amplified RNA) showed maintenance of the expression profile as assessed by hierarchical clustering. Gene expression profiles obtained from microarray analysis clearly differentiated the Ewing's sarcoma from the neuroblastoma with both core and excisional biopsies as starting material. Pooling the core biopsies did not improve the concordance with excisional biopsies. In conclusion, our results suggest that core biopsies can be used as a suitable and reliable material for the determination of tumor genetic profiles.

Pancreas microenvironment promotes VEGF expression and tumor growth: novel window models for pancreatic tumor angiogenesis and microcirculation

Pancreatic cancer has a poor prognosis, and treatment strategies based on preclinical research have not succeeded in significantly extending patient survival. This failure likely stems from the general lack of information on pancreatic tumor physiology, attributable to the difficulties in developing relevant, orthotopic models that accurately reflect pancreatic cancer in the clinic. To overcome this limitation, we developed abdominal wall windows suitable for intravital microscopy that allowed us to monitor angiogenesis and microvascular function noninvasively during tumor growth in vivo. We used two complementary tumor models in mice: orthotopic (human ductal pancreatic adenocarcinoma, PANC-1, grown in the pancreas), and ectopic (PANC-1 grown in the abdominal wall). We found that orthotopic PANC-1 tumors grew faster than the ectopic tumors and exhibited metastatic spread in the late stage similar to advanced pancreatic cancer in the clinic. Orthotopic PANC-1 tumors expressed vascular endothelial growth factor (VEGF)(121) and VEGF(165), contained higher levels of tumor cell-derived VEGF protein, and maintained vascular density and hyperpermeability during exponential tumor growth. Orthotopic PANC-1 tumors showed lower leukocyte-endothelial interactions in the early stage of growth. In addition, both VEGF(121) and VEGF(165) promoted the growth of PANC-1 cells in vitro. Finally, Anti-VEGF neutralizing antibody inhibited angiogenesis and tumor growth of PANC-1 tumors in both sites. We conclude that the orthotopic pancreas microenvironment enhances VEGF expression, which stimulates growth of PANC-1 tumors (compared with ectopic tumors). The mechanism is autocrine and/or paracrine and also is involved in the maintenance of blood vessels. This comparative system of orthotopic and ectopic pancreatic cancer will provide the rigorous understanding of pancreatic tumor pathophysiology needed for development of novel therapeutic strategies.

An orthotopic model of murine osteosarcoma with clonally related variants differing in pulmonary metastatic potential

To provide an investigative tool for the study of osteosarcoma (OSA) biology we have developed a syngeneic (balb/c) murine model of OSA, using cell lines derived from a spontaneously occurring murine OSA (Schmidt et al. Differentiation 1988; 39: 151-60). This model is characterized by orthotopic primary tumor growth, a period of minimal residual disease, spontaneous pulmonary metastasis, and clonally related variants (K7M2 and K12) that differ in pulmonary metastatic potential. Primary tumor and pulmonary metastasis histology was consistent with OSA in human patients. Expression of bone sialoprotein, biglyan, decorrin, and osteopontin was suggestive of bone lineage cells. The development and use of a more aggressive OSA cell line (K7M2) resulted in spontaneous metastasis to the lungs in over 90% of mice, whereas metastases were seen in only 33% of mice when a less aggressive OSA cell line (K12; Schmidt et al. Differentiation 1988; 39: 151-60) was used. Death from metastasis occurred at a median of 76 days using K7M2 whereas no median was achieved after 140 days using K12. Angiogenic potential, characterized by CD31 and factor VIII staining of primary tumors and pulmonary metastases, was greater in the K7M2 model compared to the K12 model. No significant differences in the in vitro or in vivo expression of angiogenesis associated genes (flt1, flt4, TIE1, TIE2, and VEGF) was found between K7M2 and K12. This well characterized and relevant model of OSA will be a valuable resource to improve our understanding of the biology and treatment of metastasis in OSA.

Rapid and quantitative assessment of cancer treatment response using in vivo bioluminescence imaging

Current assessment of orthotopic tumor models in animals utilizes survival as the primary therapeutic end point. In vivo bioluminescence imaging (BLI) is a sensitive imaging modality that is rapid and accessible, and may comprise an ideal tool for evaluating antineoplastic therapies. Using human tumor cell lines constitutively expressing luciferase, the kinetics of tumor growth and response to therapy have been assessed in intraperitoneal, and subcutaneous, and intravascular cancer models. However, use of this approach for evaluating orthotopic tumor models has not been demonstrated. In this report, the ability of BLI to noninvasively quantitate the growth and therapeutic-induced cell kill of orthotopic rat brain tumors derived from 9L gliosarcoma cells genetically engineered to stably express firefly luciferase (9LLuc) was investigated. Intracerebral tumor burden was monitored over time by quantitation of photon emission and tumor volume using a cryogenically cooled CCD camera and magnetic resonance imaging (MRI), respectively. There was excellent correlation (r=0.91) between detected photons and tumor volume. A quantitative comparison of tumor cell kill determined from serial MRI volume measurements and BLI photon counts following 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) treatment revealed that both imaging modalities yielded statistically similar cell kill values (P=.951). These results provide direct validation of BLI imaging as a powerful and quantitative tool for the assessment of antineoplastic therapies in living animals.

Antigen-specific immunotherapy for human papillomavirus 16 E7-expressing tumors grown in the liver

BACKGROUND/AIMS

We have previously reported a recombinant vaccinia-based vaccine (vac-Sig/E7/LAMP-1) that demonstrated a significant anti-tumor effect in a subcutaneous tumor challenge model. Since the liver is one of the most common sites for tumor metastasis and organ microenvironments may modulate tumor cell responses to therapies, the aim of the present study was to evaluate the potency of vac-Sig/E7/LAMP-1 in treating E7-expressing tumors grown in the liver.

METHODS

For in vivo tumor prevention experiments, mice were vaccinated intraperitoneally with vac-Sig/E7/LAMP-1 followed by intrahepatic tumor challenge. For in vivo tumor regression experiments, mice were first challenged with tumor cells and then vaccinated with vac-Sig/E7/LAMP-1 intraperitoneally. In addition, enzyme-linked immunospot assays were used to determine the frequency of E7-specific T cell precursors.

RESULTS

For in vivo tumor protection experiments, tumor growth was observed in all of the mice vaccinated with wild-type vaccinia and 60% of the mice vaccinated with wild-type E7 vaccinia. All of the mice vaccinated with vac-Sig/E7/LAMP-1 remained tumor-free 30 days after tumor challenge. For the tumor regression assays, all of the mice vaccinated with vac-Sig/E7/LAMP-1 remained tumor-free 30 days after vaccination. In contrast, all of those mice receiving culture medium, wild-type vaccinia, or wild-type E7 vaccinia developed tumors in the liver. In addition, mice vaccinated with vac-Sig/E7/LAMP-1 had the highest E7-specific CD8+ T cell precursors.

CONCLUSIONS

Our data suggest that vac-Sig/E7/LAMP-1 is an effective vaccine for controlling E7-expressing tumors grown in the liver and our model suggests that antigen-specific immunotherapy may represent a powerful tool for treating liver tumors with characterized tumor-specific antigens. In addition, our data indicate that the number of E7-specific CD8+ T cell precursors directly correlated with the anti-tumor effect generated by Sig/E7/LAMP-1 vaccinia.

A quantitative analysis of vascularization and perfusion of human glioma xenografts at different implantation sites

The effect of tissue site of implantation of four different human gliomas on tumor vascularity and perfusion was examined. Vascular parameters of gliomas implanted subcutaneously in the nude mouse and intracerebrally in the nude rat were analyzed. Tumor vessels were stained with an antibody to collagen type IV and perfusion was investigated with the perfusion marker Hoechst 33342. Characteristic vascular patterns were observed in both intracerebral and subcutaneous xenografts belonging to the same tumor line. Major differences in vascular architecture and in the degree of vascularization were noted in comparisons of the two implantation sites for the same tumor line. Tumor perfusion was highly variable for both locations of tumor growth. Distinct differences between the implantation sites of similar tumor lines in vascular perfusion, intervascular distance, and vascular density were present. Incomplete perfusion of vascular structures, as seen in this study, may result in reduced delivery of oxygen to tumor areas. Therefore, measurements of vascular density and intervascular distance alone, without knowledge of the perfusion status, may not be sufficient to estimate the degree of tumor oxygenation. Furthermore, differences in vascular parameters may have important consequences for treatment modalities such as radiotherapy and chemotherapy. Thus, the findings in our study suggest that care has to be taken in extrapolating therapy results obtained with subcutaneous glioma tumor models to the original growth location of gliomas, the brain, due to major differences in vasculature.

Heterogeneous suppression of experimentally induced colon cancer metastasis in rat liver lobes by inhibition of extracellular cathepsin B

Metastatic rat colon cancer cells but not normal rat hepatocytes showed activity of cathepsin B on their plasma membranes. Activity was visualized in living cells with a new fluorogenic substrate, [Z-Arg]2-cresyl violet, and confocal microscopy. When these cancer cells were injected into the portal vein of rats, the animals developed tumors in the liver in a heterogeneous fashion. Three- to four-fold more tumors were found in the small caudate lobe than in the other three large lobes of the liver. Oral treatment with a selective water-soluble inhibitor of extracellular cathepsin B, Mu-Phe-homoPhe-fluoromethylketone, resulted in 60% reduction of the number of tumors and 80% reduction of the volume of tumors in the three large lobes whereas tumor development was not affected in the small caudate lobe. This study supports the conclusions that (a) extracellular cathepsin B plays a crucial but complex role in liver colonisation by rat colon carcinoma cells in vivo, (b) its selective inhibition suppresses tumor growth heterogeneously in the liver and (c) the caudate lobe of the liver is a relatively large risk factor for tumor development.

Overexpressed human CD44s promotes lung colonization during micrometastasis of murine fibrosarcoma cells: facilitated retention in the lung vasculature

Normally nonmetastatic murine sis-transformed BALB/c 3T3 cells, transfected with human CD44s gene (hCD44s), acquire spontaneous metastatic capacity to the lung. The mechanism(s) of this facilitated micrometastasis was analyzed in an experimental metastasis model. Human CD44s overexpression promoted the earliest stages severalfold (initial implantation and subsequent stabilization of tumor cells) but was irrelevant for later stages (subsequent outgrowth) of lung experimental micrometastasis. By injecting mixed populations of parental (nonmetastatic) and CD44s-transfected cells, it was shown that cell-cell adhesion between tumor and parental cells was not promoted by hCD44s but that promotion of cell-cell adhesion to lung endothelium or specifically between transfected cells (via hyaluronan) are likely mechanisms. Results obtained with hCD44s-negative primary tumor cells and hCD44s-positive or -negative variants of lung micrometastatic cells (after s.c. injection of transfectants) confirmed the importance of CD44s overexpression for early but not late stages of experimental lung metastasis. Therefore, CD44s represents a metastasis-facilitating molecule that is irrelevant for primary tumor outgrowth but that promotes micrometastasis to the lungs at the very earliest stages.

Direct correlation between DNA repair capacity and metastatic potential of K-1735 murine melanoma cells

The purpose of this study was to determine whether the ability of K-1735 murine melanoma cells to repair DNA damage correlates with their metastatic potential. Three nonmetastatic clones, four metastatic clones, and three somatic-cell hybrids between metastatic and nonmetastatic clones were exposed to incident ultraviolet (UV) light (254 nm). Cell survival was determined by the microculture tetrazolium assay, which measures cell metabolic activity. DNA repair capacity was determined with a host-cell reactivation assay, which measures the activities of chloramphenicol acetyltransferase encoded by the reporter gene in both UV-damaged and undamaged plasmid (control) pCMV cat 40 h after transfection. No discernible differences in transfection efficiencies were found between K-1735 clones with low and high metastatic potential or between cells transfected with UV-damaged and control plasmids. DNA repair capacity directly correlated with cell survival (p < 0.05) and with metastatic potential in the K-1735 clones and somatic cell hybrids (p < 0.05). These data suggest that the intrinsic resistance of melanoma metastases to systemic chemotherapy may be due, in part, to the cells' enhanced DNA repair capacity.

Differential effect of taxol in rat primary and metastatic prostate tumors: site-dependent pharmacodynamics

PURPOSE

This study compared the sensitivity of rat prostate MAT-LyLu primary and lymph node metastatic tumors to taxol.

METHODS

Tumors were established by subcutaneous implantation of tumor cells in a hind leg (primary site) of male Copenhagen rats. Lymph node metastases were used for serial transplantation. Eleven pairs of primary and metastatic tumors between the sixth and twentieth generations were harvested and maintained as 3-dimensional histocultures. The effects of taxol (24 hr treatment at 1 nM to 10 microM) were measured by the appearance of apoptotic cells, and by the inhibition of DNA precursor (thymidine) incorporation. To determine the basis of differential sensitivity of primary and metastatic tumors to the DNA inhibition, we examined the expression of multidrug resistance pglycoprotein (Pgp) and the accumulation of 3H-taxol after 24 hr exposure and the retention after a 48 hr washout period.

RESULTS

The fraction of apoptotic cells increased linearly with the logarithm of taxol concentration to a maximal value of 25%; the concentration-response curves for primary and metastatic tumors were superimposable. Taxol produced a sigmoidal, concentration-dependent inhibition of thymidine incorporation; the maximal inhibition of approximately 40% was reached at 0.1 and 1 microM for primary and metastatic tumors, respectively. Within the primary or metastatic subgroups, the IC30 (drug concentration that produced a 30% inhibition of DNA synthesis) among consecutive generations varied by < 5 fold, but the primary tumor consistently showed a lower IC30 than the daughter or the parent metastatic tumor (mean, 20-fold; median, 15-fold; range, 6- to 56-fold). The finding that the lower drug sensitivity in metastatic tumors was not exhibited in its daughter primary tumor but was regained in its daughter metastatic tumors suggests that the chemoresistant phenotype is maintained only in lymph nodes and not in the primary site. There were no differences in the Pgp status (neither tumor expressed Pgp), accumulation and retention of taxol in primary and metastatic tumors.

CONCLUSIONS

Taxol induced apoptosis and inhibited DNA synthesis in the rat MAT-LyLu primary and lymph node metastatic tumors. The apoptotic effect was not different among the two tumors, whereas the primary tumor was more sensitive to the inhibition of DNA synthesis. The differential sensitivity of the two tumors to the DNA effect is not associated with a difference in Pgp expression, drug accumulation nor drug retention, and appears to be associated with changes that are linked to lymph node metastasis.

Oncogene-dependent expression of CD44 in Balb/c 3T3 derivatives: correlation with metastatic competence

Oncogene-dependent regulation and tumor relatedness of CD44 expression were investigated in Balb/c 3T3 cells and their derivatives transformed with different ras oncogenes (metastatic tumor model) or the human c-sis oncogene (non-metastatic model). Ras transformants using either the Harvey or Kirsten oncogenes expressed high levels of cell surface CD44 protein that bound fluoresceinated hyaluronan (HA). Much lower levels of CD44 were expressed in parental 3T3 cells, ras- revertants generated from Kirsten-transformed cells, or c-sis transformants, confirming the significance of the ras oncogene in this upregulation. To determine whether endogenous HA regulates these parameters, hyaluronidase treatment of ras transformants exposed more cell surface CD44 to anti-CD44 antibody and increased fluoresceinated HA binding; this did not occur with 3T3 or c-sis transformants. CD44 expression and its HA-binding function were conserved in a panel of in vivo primary and lung metastatic tumor cell lines derived from ras transformants. Ras transformants also retained the ability to downregulate CD44 protein levels in confluent cultures which occurred through a translational or post-translational mechanism (as CD44 mRNA levels were not reduced). These results taken together demonstrate that ras-dependent regulation of CD44 may correlate with tumor progression and metastasis in vivo, possibly (although not exclusively) supporting CD44's importance in metastatic progression.

Modulation of tumor cell gene expression and phenotype by the organ-specific metastatic environment

The mechanistic basis of a metastatic cell's ability to proliferate in the parenchyma of certain organs and develop organ-specific metastases is under intense investigation. Signals from paracrine or autocrine pathways, alone or in combination, may regulate tumor cell proliferation with the eventual outcome dependent on the net balance of stimulatory and inhibitory factors. This article summarizes recent reports from our laboratory and others demonstrating that the organ microenvironment can profoundly influence the pattern of gene expression and the biological phenotype of metastatic tumor cells, including induction of melanocyte stimulating hormone receptor and production of melanin, regulation of terminal differentiation and apoptosis, resistance to chemotherapy, and regulation of growth at the organ-specific metastatic site. These recent data from both murine and human tumor models support the concept that the microenvironment of different organs can influence the pattern of gene expression and hence the phenotype of tumor cells at different steps of the metastatic process. These findings have obvious implications for the therapy of neoplasms in general and metastases in particular.

The role of fibroblasts in tumor behavior

The prominent desmoplastic or stromal reaction seen in many invasive carcinomas suggests that stromal cells play a role in cancer pathogenesis. Investigations based on cell typing, using antibodies to cytoskeletal constituents, have revealed that most tumors contain various types of fibroblasts. Stromal cells with myofibroblastic differentiation features are the predominant cell type at the periphery of epithelial tumors. These tumor-activated fibroblasts play a major role in tumor development and spread, affecting the proliferation, differentiation, invasion or regression of cancer cells. This review considers the events inducing the different fibroblastic responses and the role of tumor-activated fibroblasts in both tumor development and anti-cancer treatments.

Fibronectin and integrins in invasion and metastasis

The adhesive glycoprotein fibronectin and integrin receptors appear to play important roles in the progression of metastatic disease. Fibronectin is a multifunctional extracellular glycoprotein that has at lest two independent cell adhesion regions with different receptor specificities. The cell adhesive region in the central portion of fibronectin is comprised of at least two minimal amino acid sequences--an Arg-Gly-Asp (RGD) sequence and a Pro-His-Ser-Arg-Asn (PHSRN) sequence--which function in synergy. Another cell adhesive region is located near the carboxy-terminus in the alternatively spliced IIICS module. The critical minimal sequences for this region Leu-Asp-Val (LDV) and Arg-Glu-Asp-Val (REDV) which function in an additive rather than synergistic fashion. Integrins are heterodimeric, transmembrane cell adhesion receptors for fibronectin and other extracellular matrix molecules. Several different integrins bind to fibronectin. The alpha 5 beta 1 fibronectin-specific integrin binds to the central RGD/PHSRN site. The alpha 4 beta 1 integrin binds to the IIICS site. Fibronectin-integrin interactions are important in tumor cell migration, invasion, and metastasis. In addition to promoting cell adhesion to the extracellular matrix, these proteins may also function in chemotaxis and control of proliferation. Peptide and antibody inhibitors of fibronectin and integrin functions have been shown to be effective inhibitors of metastasis, and are potentially important reagents for the study and control of cancer.