Rationale and methods for the use of nude mice to study the biology and therapy of human cancer metastasis

The biology of metastatic breast cancer

Early detection and surgical removal of breast cancer are most effective in managing a disease that may affect up to one in ten women in North America and Western Europe. However, one of the most important prognostic indicators for breast cancer is the presence of neoplastic cells in the axillary lymph nodes. The dissemination of cells from a primary lesion, resulting in the progressive growth of metastatic carcinoma in distant sites (including bone, lungs, liver, and brain) is the most common cause of death in breast cancer patients. Experimental studies on the biology of metastatic breast cancer have used rodent tumor systems, and, in recent years, the transplantation of human breast carcinoma cells into athymic mice. The results of such studies, combined with clinical observations, suggest that metastasis is not a random event. The formation of secondary lesions is the result of a sequence of selective events. A better understanding of the metastatic phenotype from cellular and molecular analyses will provide a basis for rational approaches to preventing and treating this most lethal aspect of breast cancer.

Selection and characterization of human melanoma lines with different liver-colonizing capacity

Two human melanoma lines with low (HT168) and high (HT168-MI) liver metastatic capacity in immunosuppressed mice were selected in vivo from the A2058 cell line. After i.v. injection of the 2 tumor lines there was no significant difference either in the number of lung colonies or in the frequency and tissue distribution of extrapulmonary tumor deposits. These findings suggest that the selection in the spleen-liver system did not result in an overall increase in the metastatic potential of the melanoma cells, but rather that it represented an organ-preferential selection. The HT168-MI cells did not acquire an increased growth rate in vitro or in vivo, suggesting that other phenotypic alterations are responsible for the enhanced metastatic capacity. The 2 tumor lines were characterized by similar expression of HLA-A,B,C, transferrin receptor and melanoma-associated proteoglycan antigen. HT168 contained more NGF receptor, while HLA-DR appeared only on HT168-MI cells. This human metastasis model could be useful in studying the mechanisms of liver metastasis formation, as well as in revealing possible new targets of antimetastatic therapy.

Orthotopic implantation is essential for the selection, growth and metastasis of human renal cell cancer in nude mice [corrected]

Human neoplasms are heterogeneous for a variety of biological properties that include invasion and metastasis. The presence of a small subpopulation of cells with a highly metastatic phenotype has important clinical implications for diagnosis and therapy of cancer. For this reason, it is important to develop an animal model for the selection and isolation of metastatic variants from human neoplasms and for testing the metastatic potential of human tumor cells. We have implanted human renal cell carcinoma (HRCC) cells (obtained from a surgical specimen) into different organs of nude mice and then recovered the tumors and established each in culture. The 5 established lines differed in their biological-metastatic properties and had a unique karyotype, indicating that growth at different organs selects for different subpopulations of HRCC. Moreover, the HRCC did not metastasize unless they were implanted orthotopically. These findings indicate that the appropriate nude mouse model for studying the biology and therapy of HRCC must be based on the orthotopic implantation of tumor cells.

Effects of prostacyclin on hepatic metastases from human pancreatic cancer in the nude mouse

Human pancreatic cancer is an aggressive malignancy, with systemic metastases ultimately accounting for its grave prognosis. Arachidonic acid metabolites known to affect platelet function also interfere with tumor growth and metastases. We evaluated the effect of prostacyclin on the hepatic metastases of a human pancreatic cancer in a nude mouse model. The mean surface area of tumor on the liver was significantly reduced in all treatment groups. In the control group 485 mm2 of tumor was present on the liver surface. Animals treated with 200 micrograms of prostacyclin 0.5 hr prior to the injection of tumor cells had 21 mm2 of tumor present on the liver surface (P = 0.004). Similarly, 400 micrograms of prostacyclin caused a reduction of tumor surface area to 20 mm2 (P = 0.004). The maximal reduction of tumor surface area, 11 mm2, was observed when 200 micrograms of prostacyclin was given 0.5 hr prior to and 4.0 hr after the injection of tumor cells (P = 0.003). For the group given 200 micrograms of prostacyclin 4.0 hr after the injection of tumor, the surface area of tumor was 85 mm2 (P = 0.017). The number of tumor colonies on the liver surface was significantly reduced from 20 to 11 when 200 micrograms of prostacyclin was administered intraperitoneally 0.5 hr before and 4.0 hr after the injection of tumor cells (P = 0.047). These results indicate that prostacyclin has antimetastatic activity on hepatic metastases from a human pancreatic adenocarcinoma in the nude mouse.

Squamous cell carcinoma of the head and neck heterotransplanted to nude mice. Take rate in relation to patient survival

Biopsy specimens from 62 human single primary squamous cell carcinomas (SCC) of the head and neck were xenografted into nude mice. To evaluate the prognostic significance of successful heterotransplantation, the 62 cases were retrospectively examined for survival, adjusting for possible confounders by multivariate analysis. The recorded take rate in the first passage was 24%. Median survival in the take group was 25 months versus 74 months in the nontake group, which is not statistically significant in this material. However, the numerical difference in survival between the take groups is in accordance with the concept that human tumors accepted as xenografts on nude mice may constitute a selected group of malignancies. This has to be considered when using heterotransplanted human tumors for in vivo investigations of SCC of the head and neck.

Residual immunity of athymic NCr/Sed nude mice and the xenotransplantation of human tumors

This study assessed the residual immunity possessed by NCr/Sed (nu/nu) athymic nude mice and examined strategies to reduce it in order to enhance the transplantability of human tumors for experimentation. Adult (8-week-old) female mice had fewer T cells (11%) and more B and NK (asialo-GM1-positive [ASGM1+]) cells in their spleen than euthymic (nu/+) controls. The number of phenotypically mature T cells increased with age, peaking at 16 weeks. ASGM1+ cells also increased in number over time, although the NK-activity decreased after 12 weeks. B cells remained relatively constant in number. Athymic NCr/Sed nude mice displayed reactivity against a human squamous carcinoma xenograph (FaDu), in a Winn's test and TD50 assay. Immunity against xenografts (TD50 assay) was significantly lower (by a factor of 2) in 4-week-old than in 12-week-old nude mice. Similarly, a significant 2-fold reduction in TD50 was obtained after a single intraperitoneal injection of cyclophosphamide into 8-week-old animals. Chronic (greater than 8 weeks) exposure of the nude mice to subcutaneously administered beta-estradiol markedly reduced the number of splenic NK cells and their cytolytic activity, but the TD50 reduction was not statistically significant (p = 0.1). Six Gray whole-body irradiations (WBI) had been shown to produce a highly significant, 3-fold reduction in the TD50 for FaDu. Flow cytometric analysis of splenic lymphoid cells from whole-body-irradiated recipients revealed: (a) marked initial depletion in the absolute numbers of lymphoid cells; (b) marked and long-lasting depletion of T cells, with slow and minimal recovery only evident between 6 and 12 weeks; (c) rapid, almost complete, depletion of B cells with prompt and partial recovery after 2 weeks; (d) depletion of NK cells and NK activity, with recovery by 10 weeks. No change in the number or phagocytic capacity of resident peritoneal macrophages was seen. These data give further support to a postulated role for residual T cells in the xenoreactivity of NCr/Sed nude mice.

Studies of human breast cancer metastasis using nude mice

Athymic nude mice have been used in recent years to study the biology of human tumors and to assess therapeutic responses in vivo rather than just in vitro. Some human tumors metastasize in nude mice, providing model systems for analyzing various aspects of the metastatic phenotype of human neoplasms. For breast carcinomas, however, the tumor-take rate of surgical specimens is low, and only a limited number of cell lines proliferate in nude mice. The site of injection of the breast carcinoma cells is important; tumors grow at a lower inoculum dose and with shorter latent intervals after implantation in the mammary fatpad of nude mice than after injection in the subcutis. One breast carcinoma cell line, MDA-MB-435, metastasizes from mammary fatpad tumors to lymph nodes, lungs, and other visceral organs. In contrast, two other cell lines show lower metastatic ability. Intravenous injection and injection of tumor cells into the internal carotid artery of nude mice produces lung and brain metastases, respectively, thus simulating the arrest and organ colonizing steps of the metastatic cascade. These different techniques demonstrate the potential of experimental studies of human breast cancer growth and metastasis using nude mice.

Cytogenetic abnormalities in cancer: with special emphasis on tumor heterogeneity

There is a considerable amount of cytogenetic data available to support the statements that (1) cancer is a genetic disease; (2) most cancers are monoclonal in origin; (3) tumor cells are more genetically unstable than normal cells; (4) the genetic instability may be inherited, acquired, or both during the lifespan of the individual tumor; (5) tumor metastasis is a nonrandom, controlled process, and clonal in origin; (6) malignant tumors are genetically heterogeneous and contain multiple subpopulations that may differ in their biological properties; (7) some tumors might be difficult to treat successfully because of their resistant nature; and (8) tumor cells may acquire resistance because of gene amplification. For these reasons it is extremely important to study the biology of malignant tumor cells in order to determine their effective treatments and control this dreadful disease.

Heterogeneity of potential for hematogenous metastasis in a human pancreatic carcinoma

Human pancreatic carcinoma, a disease with grave prognosis, frequently metastasizes to the liver, with detrimental consequences for the host. Good models of experimental metastasis for this disease are lacking. We describe a model of hepatic metastasis from the fast-growing variant (FG) of the human pancreatic carcinoma COLO 357. We also show that the slow-growing variant (SG) of COLO 357 lacks the potential for forming hepatic and pulmonary metastases following injection into the spleen of the nude mouse. This expression of heterogeneity of potential for hematogenous metastases can be exploited by pursuing studies aiming at identifying differences between the cells with and without metastatic potential.

Molecular oncogenetics of metastasis

Metastasis is a complex non-stochastic process that is most likely the result of genetic and epigenetic interactions of a wide variety of genes. The search for a single gene which can encompass such a pleiotropic response as to account for the observed phenotypic characteristics of metastatic tumour populations has been unsuccessful. Particular studies involving gene transfection, subtractive hybridisation and cell fusion are beginning to identify specific genes which contribute to metastasis in some cell types. However, such analyses are complicated by the inherent genetic instability and phenotypic heterogeneity present in tumour populations. A more detailed understanding of the metastatic process may require an abandoning of current generalised approaches to metastasis in favour of concentrating on key components of the metastatic cascade such as adhesion and invasion.

Unique patterns of brain metastasis produced by different human carcinomas in athymic nude mice

The purpose of this study was to develop an in vivo model to study the growth pattern and biological behavior of brain metastases produced by different human carcinomas. To do so, human tumor cells from 8 different carcinomas of the colon, breast, kidney and lung were injected into athymic nude mice either by a direct intracerebral route or into the internal carotid artery. All carcinoma cells invaded through the blood-brain barrier and produced progressively growing lesions in the brain parenchyma. Unique patterns of growth were discernible among the carcinomas. Human colon carcinomas produced multiple lesions that spread by extension. Lung carcinoma cells produced widespread lesions throughout the brain. A very high degree of vascularization was associated with lesions produced by renal-cell carcinoma. The influence of estrogen on the growth of estrogen-receptor-positive human breast carcinoma cells was well demonstrated in this model. We conclude that the athymic nude mouse can be a useful model for studies of the biology and perhaps therapy of brain metastases produced by human carcinoma cells.

Origin and biology of cancer metastasis

Metastasis, the spread of cells from a primary neoplasm to distant sites where they grow, contributes to the death of most cancer patients. The process of metastasis is not random. Rather, the process consists of a series of linked, sequential steps that must be completed by tumor cells if a metastasis is to develop. Thus, metastatic cells must succeed in invasion and embolization, survive in the circulation, arrest in a distant capillary bed, and extravasate into and multiply in organ parenchyma. Although some of the steps in this process contain stochastic elements, as a whole metastasis favors the survival and growth of a few subpopulations of cells that preexist within the parent neoplasm. Moreover, metastases can have a clonal origin, and different metastases can originate from the proliferation of single cells. The outcome of metastasis depends on the interaction of metastatic cells with different organ environments. Organ-specific metastases have been demonstrated in a variety of experimental tumor systems, and even within one organ, site-specific tumor growth can be found. The conclusion that metastasis is a highly selective process that is influenced by both the intrinsic properties of tumor cells and by host factors is optimistic. A selective process is regulated and therefore can be studied and then manipulated.

alpha-Difluoromethylornithine inhibits liver metastasis produced by intrasplenic injection of human tumor cells into nude mice

The purpose of these studies was to examine metastatic potentials of a human colon tumor xenograft (T6) and three different human tumor cell lines (LS174T, HT29 and A549) using the intrasplenic-nude mouse model system (ISMS model system). A further objective was to study the activity of alpha-difluoromethyl-ornithine (DFMO) against primary and metastatic growth of the xenograft and the three cell lines. DFMO is an irreversible inhibitor of ornithine decarboxylase, a rate-limiting step in polyamine biosynthesis. Tumor burdens in the liver of nude mice were observed 6 weeks after the intrasplenic injection with LS174T and 12-14 weeks after intrasplenic injections with T6, HT29 and A549. Most of the mice developed primary tumor growth in the spleens. DFMO showed significant activity against liver metastases but had little or no activity against primary tumor growth in the spleens of the ISMS model and against s.c. growth of the xenograft. The studies demonstrated that the ISMS model system is an excellent system for studying metastatic behavior of human tumors and for studying the antimetastatic activity of experimental drugs.

Two human melanoma xenografts with different metastatic capacity and glycosaminoglycan pattern

Two human melanoma xenografts were compared with respect to their in vivo growth and metastatic potentials as well as glycosaminoglycan patterns. The less differentiated HT 168 tumor showed faster growth at primary sites and a more pronounced capacity for metastasis into the liver. Although chondroitin sulfate was the dominant glycosaminoglycan subtype in both tumors, the more invasive xenograft had a higher heparan sulfate/chondroitin sulfate (HS/CS) ratio. We suggest that tumor progression is influenced by this ratio in this human melanoma system.

Intraperitoneal and subcutaneous xenografts of human ovarian carcinoma in nude mice and their potential in experimental therapy

Human ovarian carcinomas (HOC) were established s.c. and i.p. in nude mice and the biological characteristics were investigated for 4 xenografts. HOC8 and HOC18, derived respectively from a primary tumor of the ovary and a pleural effusion (from 2 different patients) were established s.c. in nude mice. HOC10 and HOC22, derived from the ascites of 2 patients, were directly established as ascites after i.p. injection in nude mice. The s.c. and i.p. growth behavior of the 4 HOC lines was investigated. HOC18, HOC8 and HOC22 cells produced progressively growing tumor after s.c. injection but HOC10 ascites would not grow s.c. The cell suspension derived from HOC18 only produced carcinomatosis upon i.p. injection, while HOC8 cells produced both ascites and carcinomatosis. The 2 ascites HOC10 and HOC22 produced ascites in nude mice, but only HOC22 formed i.p. carcinomatosis. Histopathological characteristics of the patients' primary tumors persisted in nude mice, regardless of the site of tumor implantation. DNA histograms of the xenografts closely matched the patients' tumors and remained stable at different passages. Cisplatin, adriamycin and cyclophosphamide given i.v. were tested against HOC8 and HOC18 growing s.c. and HOC22 and HOC10 growing i.p. HOC8 showed a significant response to DDP and almost no sensitivity to ADR and CTX. HOC18 showed only moderate growth delay with all 3 drugs. Mice bearing HOC10 and HOC22 ascites had a prolonged survival time after DDP and ADR treatment.

Determination of subcutaneous tumor size in athymic (nude) mice

The athymic (nude) mouse is a useful model for studying the biology and response to therapies of human tumors in vivo. A survey of recent literature revealed the use of 19 different formulas for determining the size of subcutaneous tumors grown as xenografts in nude mice (2 for determining tumor area, 3 for tumor diameter, and 14 for calculating tumor volume). We compared the volumes, areas, and diameters predicted by each of the 19 formulas with the actual weights of 50 tumors ranging from 0.46 to 22.0 g established in nude mice as xenografts from human cell lines. In addition to determining how well each formula predicted relative tumor size, we analyzed how well each formula estimated actual tumor mass. The ellipsoid volume formulas (pi/6 x L x W x H and 1/2 x L x W x H) were best for estimating tumor mass (r = 0.93), whereas measurements of diameter correlated poorly with tumor mass (r less than 0.66). Although determination of tumor area correlated well with tumor mass in small tumors (r = 0.89), correlations of area with tumor mass for large tumors were poor (r = 0.41). We conclude that determination of the ellipsoid volume from measurements of three axes consistently yields the most accurate estimations of both relative and actual tumor mass.

In vivo selection of human renal cell carcinoma cells with high metastatic potential in nude mice

Studies were made to determine whether the orthotopic implantation of human renal cell carcinoma cells (HRCC) into nude mice will produce distant metastases, thus allowing for the selection of variant cells with high metastatic potential. The parental SN12C line was established in culture from a surgical specimen of HRCC. The renal subcapsule (RSC) of adult nude mice was injected with SN12C cells; the mice were killed when they became moribund. Cell lines were established from either single or multiple lung HRCC metastases. The intravenous injection of many (but not all) of the metastasis-derived lines produced significantly more experimental metastases than did the parental cells. The injection of cells into the RSC demonstrated that, in general, cells derived from spontaneous metastases were more metastatic than cells of the parental line. Hence adult nude mice can be used to select HRCC cells with high metastatic potential. These HRCC variant lines offer a good model for studying the cell properties of metastatic HRCC.

Invasion and metastasis following orthotopic transplantation of human pancreatic cancer in the nude mouse

A good experimental model for metastasis of human pancreatic cancer would be a valuable tool for the study of this process, which contributes significantly to morbidity and mortality. Models of experimental metastasis using injection of tumor cells into the portal or systemic circulation bypass some important steps of the metastatic process. We describe invasion and metastasis following orthotopic transplantation of human pancreatic carcinoma into nude mice. Tumor pieces were used as xenografts in this study, and metastases were observed in the regional lymph nodes, liver, lungs, and distant lymph nodes of the animals. Peritoneal implants and ascites were not observed in this study. Orthotopic transplantation of human pancreatic cancer in the nude mouse appears to be a promising model of spontaneous metastasis relevant to clinical reality.

Use of the Membrane Invasion Culture System (MICS) as a screen for anti-invasive agents

The Membrane Invasion Culture System (MICS) assay was adapted for relatively rapid screening of compounds and used to identify anti-invasive drugs that inhibit human and murine tumor cell migration through a reconstituted basement membrane in vitro. Cell lines demonstrating low and high invasive and metastatic potentials were tested with all compounds for tumoricidal effects prior to evaluation in MICS at non-cytotoxic doses. The effect on invasive potential in the MICS assay was determined in 3 categories: (1) 48 hr drug pre-treatment prior to seeding in the MICS (exceptions: 90 min pre-treatment with pertussis toxin and, for some studies, continuous exposure for 2-7 days); (2) peptide or prostaglandins 2 hr after seeding and attachment to the membranes in MICS followed by continuous exposure; and (3) cells receiving neither drug nor peptide treatment and serving as controls in each MICS chamber. Since invasion involves cellular motility and deformability, some cytoskeleton disrupting agents were selected. Of these, vincristine, colcemid and colchicine inhibited invasion but taxol did not. Pre-treatment with cAMP agonists produced conflicting results: dibutyryl cAMP and 8-(4-chloro-phenylthio) cAMP resulted in 50% and 38% reduction in invasion, respectively, whereas 8-bromo cAMP stimulated invasive potential by 30%. Forskolin and cholera toxin both significantly reduced invasiveness. Pre-treatment with 5-azacytidine and araC, to consider the role of methylation and proliferations decreased invasive ability. Anti-metastatic drugs such as gamma-interferon and razoxane inhibited invasive potential but to varying degrees. Treatment of cells with prostaglandins E2, F2 alpha, A2, and D2 were ineffectual; however, indomethacin mildly inhibits invasion (less than 30%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the immunomodulator PSK on growth of human prostate adenocarcinoma in immunodeficient mice

Tumor growth alterations were studied using an immunomodulator, PSK. Four human prostate tumor lines were grown in two types of immunodeficient mice. Two of the lines were selected because they are able to metastasize to lungs in host animals. Outbred NIH Swiss athymic mice having normal natural killer cells and athymic Beige mice deficient in natural killer cells were used as animal hosts. PSK treatment was given to tumor-bearing hosts to some animals soon after solid tumors were injected and to others after solid tumors were well-established. Low dose cyclophosphamide was given to some animals to decrease host natural killer cells and polyinosinic-polycytidylic acid (poly I:C) was given to other animals to increase natural killer cell activity. Measurement of tumor doubling times, host survival and metastatic capabilities showed that either poly I:C or PSK treatment in NIH Swiss animals soon after tumor cells were injected significantly increased tumor doubling times and host survival and decreased the incidence and number of metastatic lung lesions. Two of the tumor lines incapable of metastasizing in NIH Swiss mice were metastatic in the Beige athymic, natural killer-cell-deficient animals.

Altered biodistribution of indium-111-labeled monoclonal antibody 96.5 to tumors and normal tissues of nude mice bearing human melanoma xenografts in visceral organs

Human melanoma xenografts were produced in the subcutis, kidney, cecum and liver of different nude mice. An 111In-labeled anti-(human melanoma) monoclonal antibody (96.5) or an 111In-labeled nonspecific control monoclonal antibody (ZCE-025) was injected intravenously in separate groups of mice. Radioactive antibody accumulation was measured in tumor, blood, viscera, and carcasses. mAb 96.5 targeted specifically to tumor tissue regardless of site of growth. Tumors in the liver exhibited significantly (P less than 0.05) higher tumor-to-blood ratios (45 +/- 6, mean +/- SEM) than xenografts at other visceral organs, the lowest value being found for subcutaneous melanoma (2.6 +/- 0.5). The differences in tumor-to-blood ratio were due to significant alterations of antibody biodistribution, since the actual antibody concentration in the different tumor sites was similar. The percentage of recovered anti-melanoma antibody per milliliter of blood in mice with visceral lesions (4.6 +/- 1.1% ml) was significantly lower than that found in mice with subcutaneous tumors (9.5 +/- 1.4%/ml, P less than 0.05). Moreover, significantly higher levels (18.2 +/- 3.2%/g, 31.0 +/- 5.1%/g, respectively) of the melanoma mAb 96.5 were found in normal liver and spleen tissue recovered from mice with visceral tumors as compared to tissue from mice with subcutaneous tumors (9.2 +/- 0.9%/g, 13.5 +/- 1.9%/g, respectively; P less than 0.05). These results demonstrate that the presence of visceral tumor can significantly affect tumor-to-blood ratios, blood levels, and biodistribution of 111In-labeled mAb 96.5.

Site-specific growth of the prostate xenograft line UCRU-PR-2

A xenografted small-cell, undifferentiated prostate (SCUCP) cancer line, UCRU-Pr-2, was implanted at different sites within nude mice to examine the effect of local environmental factors on tumor growth and behavior. All tumors that grew were small-cell carcinomas. Fragments implanted within muscle and under the kidney capsule were locally invasive; however, tumors that grew subcutaneously or intraperitoneally showed no invasion. UCRU-Pr-2 did not grow in the spleen or the liver. No induced metastases were observed in the lung after intravenous injection. The sites of implantation did not allow the outgrowth of subpopulations as detected by the parameters used: light and electron microscopy, expression of tumor markers, levels of hormone production, and DNA flow cytometry. Electron microscopy, which showed both glandular and neuroendocrine differentiation within the same cell, does not support a dual-cell origin of SCUCP.

Patterns of metastasis by the human prostate cancer cell line PC-3 in athymic nude mice

Cells from the PC-3 human prostate cancer cell line were evaluated in athymic nude mice in order to determine the influence of size of the primary tumor and site inoculation on the incidence and pattern of metastasis. At autopsy, all organs, including the skeleton, were evaluated for metastasis. Subcutaneous injections resulted in metastases to the draining axillary lymph node and lungs (56% and 13%, respectively), and were correlated with size of the primary tumor. Tail vein injection resulted in a high incidence of lung metastasis, while injection into the peritoneal space, spleen, and seminal vesicles resulted in intraabdominal tumor growth, liver metastasis, and large tumors within the seminal vesicles, respectively. Skeletal metastases were not observed in any of the animals studied. We conclude that injection of PC-3 cells into various sites results in different patterns of metastasis, but may not constitute an entirely suitable animal model of human prostate cancer due to the lack of metastasis to the skeleton.

Growth and metastasis of human tumors in nude mice following tumor-cell inoculation into a vascularized polyurethane sponge matrix

Growth and metastasis of human tumor cells in immunodeficient nude mice were improved when tumor cells were inoculated within a vascularized artificial polyurethane sponge matrix. The sponges had been implanted 7-10 days earlier and were vascularized at the time of cell injection. All cell lines tested, including colon carcinoma-derived lines from primary tumors (HT29, PT3 and PT4) or from liver metastasis (LM3), and a metastatic variant from a melanoma (MeWo-Met) grew in a high percentage (78-94%) of the inoculated sponge grafts. When growth in sponge grafts is compared with growth at a subcutaneous site, the sponge matrix appears to increase tumorigenicity, at least for some cell lines. Regular formation of metastases was observed when cells had been injected into sponges. Most metastases were found in a second sponge graft implanted at a contralateral site, but some were also found at other s.c. sites. In vivo depletion of NK cells by pre-treatment with cyclophosphamide could not further enhance the formation of metastasis. Tumor cells from fresh surgical specimens could be propagated in sponge matrix grafts and subsequently established as cell lines in tissue culture.

Human tumor xenografts as model for drug testing

This paper reviews the history of xenografts, the endpoints commonly used to evaluate response and chemotherapeutic results obtained with serially maintained human tumor xenografts from different laboratories, and discusses the potential clinical relevance of the heterotransplant model for cancer chemotherapy. Specifically, an attempt is made to correlate the published xenograft data with the clinical data. Drug testing with different types of xenotransplanted tumors has shown that the response of xenografts obtained in immune-deficient animals is comparable to that in clinical practice. In addition, xenografts of a particular tumor type are able to identify agents of known clinical activity against that disease.

Cellular heterogeneity. Explanation for changing of tumor phenotype and biologic behavior in soft tissue sarcomas

Many human soft tissue sarcomas are known to show variable structures in a given tumor and to be able of changing the histological feature during the course of the disease. These facts prompted an experimental study in order to ascertain if by use of long-term cultures of an established rat fibrosarcoma cell line (RFS) in respective inoculation tumors a histological picture different from the original fibrosarcoma could be produced. It was found that inoculation tumors generated by later subcultures partly corresponded to tumors with features of malignant histiocytomas and malignant fibrous histiocytomas. In a further experiment we attempted to initiate metastatic dissemination of a primarily non-metastasizing xenotransplanted RFS sarcoma in nude mice. By repeated diminution operations comparable to inadequate tumor surgery in human metastasis formation in lung parenchyme was attained. Taking into account cellular heterogeneity as basically responsible for the phenomena observed, different causal aspects concerning the experimental results are discussed. We deduce from our findings that the concept of histogenetic classification of soft tissue sarcomas should be replaced by an interpretation according to the actual differentiation. This also applies to malignant fibrous histiocytomas which are at least in part mesenchymal tumors and not descendants of mononuclear phagocytic cells and may originate by a dedifferentiation process of otherwise defined sarcoma types.

The biology of melanoma metastasis

The process of cancer metastasis is sequential and selective and contains stochastic elements. The growth of melanoma metastases represents the endpoint of many lethal events that few tumor cells can survive. Primary tumors consist of multiple subpopulations of cells with heterogeneous metastatic properties, and the outcome of metastasis depends on the interplay of metastatic tumor cells with various host factors. This viewpoint is more optimistic than that of metastasis as a random process. A selective biological process is regulated by the interaction of tumor cells with their host, and these complex interactions can now be studied and manipulated.

Organ specificity of tumor metastasis: role of preferential adhesion, invasion and growth of malignant cells at specific secondary sites

The locations of distant secondary tumors in many clinical cancers and animal tumors are nonrandom, and their distributions cannot be explained by simple anatomical or mechanical hypotheses based on the simple lodgment or trapping of tumor cell emboli in the first capillary bed encountered. Evidence from certain experimental tumor systems supports Paget's 'seed and soil' hypothesis on the nonrandom distributions of metastases, in which the unique properties of particular tumor cells ('seeds') and the different characteristics of each organ microenvironment ('soil') collectively determine the organ preference of metastasis. Experimentally, differential tumor cell adhesion to organ-derived microvessel endothelial cells and organ parenchymal cells, differential invasion of basement membranes and organ tissues, and differential responses to organ-derived growth-stimulatory and -inhibitory factors all appear to be important determinants in explaining the organ preference of metastasis. Each tumor system may achieve organ specificity because of its own unique set of multiple metastasis-associated properties and responses to host microenvironments. As neoplasms progress to more highly malignant states multisite metastases are more likely and organ-specific metastases may be masked or circumvented owing to stochastic events, tumor cell diversification, host selection processes, and increased production of tumor autocrine molecules that may modulate adhesion, invasion, growth, and other properties important in metastasis. The importance of each of these properties, however, appears to vary considerably among different metastatic tumor systems. These and other tumor cell and host properties may eventually be used to predict and explain the unique metastatic distributions of certain human malignancies.

A new experimental metastasis model in athymic nude mice, the human malignant melanoma LOX

The human tumor line LOX was established as an s.c. xenograft in nude mice from a lymph-node metastasis of a patient with malignant melanoma. I.v. injection into adult nude mice of single-cell suspensions prepared from xenografts resulted in progressively growing lung tumor colonies that killed the animals. No difference in colony formation was seen between cells taken from lung colonies and s.c. xenografts. An in vitro cell line, LOX-L, was established from lung colonies, and the monolayer cells, detached with EDTA, retained the same ability to form experimental lung metastases. In a total of 14 experiments, 82 of 89 mice receiving 1 X 10(6) viable tumor cells died with a mean survival time of 34.1 +/- 4.8 days. Long-term passaging in vivo and in vitro did not result in any alteration of the lung-colonizing potential of the LOX cells, whereas trypsinization of the cells before i.v. injection reduced lung colony formation. The life span was inversely related to the number of LOX cells injected, permitting estimation of the cell kill caused by chemotherapy. Mice injected i.v. with the LOX cells showed the same relative response to cis-diamminedichloroplatinum (CDDP) and mitozolomide (MZA) as did animals carrying s.c. xenografts. The LOX cells have shown a remarkable stability and similarity to the cells of the patient's tumor with respect to morphology, karyotype and chemosensitivity. The LOX model may be useful for testing effects of therapy on lung micro- and macrometastases, and the activity of antimetastatic agents, as well as for studying mechanisms involved in the metastatic process.

Use of NeoR B16F1 murine melanoma cells to assess clonality of experimental metastases in the immune-deficient chick embryo

Recent work on molecular and genetic aspects of metastasis has emphasized the need for assays in immune-deficient animal hosts. The commonly used assays in athymic nude mice may not always be appropriate, and assays in other hosts are required. We have developed a metastasis assay in the naturally immune-deficient chicken embryo. As part of our characterization of this assay we have examined the clonality of individual experimental (i.v.-derived) metastases in this host. For these studies we developed a cell line, B16-Neo, from parental B16F1 murine melanoma cells. B16-Neo cells carry a stable drug-resistance marker, the bacterial neo gene, which confers resistance to the drug G418, but are unaltered in experimental metastatic properties in the chick embryo relative to parental B16F1 cells. We observe that the majority of individual liver tumors that arise following i.v. injection of mixtures of these cells contain cells of a single marker phenotype and are likely to be clonal in origin. These results are similar to those obtained by others for metastases in immune-competent mice, suggesting similar mechanisms of metastasis formation in these two systems. In both hosts it should be noted, however, that a small but significant proportion of metastases appear not to be clonal in origin.

Biological characterization and oncogene expression in human colorectal carcinoma cell lines

To establish well-characterized cellular reagents for the study of colon carcinoma, we have examined 19 human colorectal carcinoma cell lines with regard to morphology, ultrastructure, expression of tumor-associated antigens, proliferative capacity in vitro, anchorage-independent growth, oncogene expression, tumorigenicity and malignant potential. Cell lines examined were cultured under identical conditions, and in vitro and in vivo analyses were performed in parallel on replicate cultures. Three classes of colorectal cell lines were defined according to their tumorigenicity in nude mice. Class-1 lines formed rapidly progressing tumors in nearly all mice at an inoculum of 10(6) cells. Cell lines belonging to class-2 were less tumorigenic, producing tumors later and at a slower growth rate. Class-3 lines were non-tumorigenic under all experimental conditions tested. By Northern analysis, the oncogenes c-myc, H-ras, K-ras, N-ras, myb, fos and p53 were expressed in nearly all cell lines examined. In contrast, transcripts for abl, src and ros were not detected. The best in vitro predictor of tumorigenicity was colony formation in soft agar. There was no detectable correlation between tumorigenicity and metastatic potential, doubling time in vitro, production of tumor-associated markers, xenograft histology or expression of specific oncogenes.

The nude mouse for the study of human colorectal carcinoma

The tumorigenicity and metastatic behaviour of human colorectal tumors have been assessed in athymic nude mice. Surgical specimens were obtained from colorectal carcinomas or from metastases of different patients. Primary colorectal tumors and their synchronous liver metastases were obtained from three patients. After intramuscular (i.m.) injection into nude mice, tumor cells originating from metastases showed a higher take than those from primary tumors. In general, metastasis-derived tumors had a shorter doubling time than primary-derived tumors. This growth pattern was not associated with the production of spontaneous metastases in nude mice. To investigate the malignant potential of colorectal neoplasms in the nude mouse, tumor cells were injected intravenously (i.v.) (artificial lung metastases) and in the spleen (artificial liver metastases). Colorectal-derived tumor cells produced lung colonies after i.v. injection, but the most dramatic expression of malignancy was the tumor cells' ability to grow in the liver after intrasplenic (i.s.) injection. The ability to grow in the liver of nude mice appeared to be a distinct characteristic of each tumor cell population. Human colorectal tumors were maintained as continuous lines subcutaneously (s.c.) in nude mice. Phenotypic differences, including malignant potential, were generally maintained at different passages. Human colorectal tumors with a definite pattern of malignant behaviour (i.e. to the liver) in the nude mouse provide a unique experimental system for the study of the biology and the therapy of cancer metastases.

Microscopic metastasis of a human lung carcinoma cell line in athymic nude mice: isolation of a metastatic variant

A human lung carcinoma cell line, UCP3, was carried as subcutaneous xenotransplants in athymic mice. Autopsies of these animals showed rare foci of microscopically visible metastases to any of the other organs. A metastatic variant, 522, was established serendipitously in vitro as a continuous cell line by blind isolation of the pulmonary metastatic foci, at the time of autopsy, from the lungs of the animals that carried subcutaneous xenotransplants of the parental cell line. The parental UCP3 and the metastatic variant 522 were examined by karyotypic and isoenzyme analysis and shown to be human and related. The metastatic variant, 522, metastasizes spontaneously from subcutaneous sites (like the parental UCP3). However, it forms larger subcutaneous xenotransplants and forms more metastatic foci in the lungs of the animals than does the parental cell line. Comparisons of the cell surface glycolipids show many similarities and a few differences. This model system may now be used for further investigations into the processes of metastasis of this human neoplasm.