Degradation of basement membrane type IV collagen and lung subendothelial matrix by rat mammary adenocarcinoma cell clones of differing metastatic potentials

A series of rat 13762NF mammary adenocarcinoma cell clones and subclones of various lung metastatic potentials were examined for their abilities to degrade rat lung subendothelial matrix and purified basement membrane type IV collagen. Metastatic potentials were simultaneously determined based on the ability to form "spontaneous" lung metastases after s.c. injection or "experimental" lung metastases after i.v. injection of cells. Microvessel endothelial cells isolated from rat lung were grown in vitro, and the subendothelial matrix containing type IV collagen was metabolically labeled with [3H]proline. When mammary adenocarcinoma cells were placed on the isolated subendothelial matrix, fragmentation and solubilization of [3H]proline-labeled components were observed; highly metastatic 13762NF cells solubilized the matrix at higher rates than did poorly metastatic cells. The 13762NF cells were assayed for type IV collagenolytic activity using [3H]proline-labeled type IV collagen purified from Engelbreth-Holm-Swarm tumor as a substrate. We found excellent correlation between the type IV collagenolytic activities of living cells and their "spontaneous" lung metastatic potentials (r = 0.993). The levels of type IV collagenolytic activity in the conditioned medium depended on the cell culture conditions. In the presence or absence of acid-treated fetal bovine serum, highly metastatic cells secreted higher amounts of type IV collagenolytic enzymes in active and latent forms than did poorly metastatic cells. Incubation of procollagen type IV with medium conditioned by highly metastatic 13762NF cells and treated with trypsin resulted in the production of several large fragments characteristic of type IV collagen. The results suggest that enzymatic degradation of basement membrane type IV collagen is important in lung metastasis of 13762NF mammary adenocarcinoma cells.     

Organization of cytoskeletal structures in 13762NF rat mammary adenocarcinoma cell lines and clones of different metastatic potentials

The correlation between metastatic potential and the organization of microtubules and microfilaments in nine cell lines and clones derived from the 13762NF rat mammary adenocarcinoma was investigated using immunofluorescence techniques. Cell sizes and morphologies of cell clones isolated from the locally growing 13762NF tumor were heterogeneous; those derived from spontaneous metastases were more homogeneous. The organization of microtubules was similar in cells of various 13762NF lines and clones, and differences could not be detected with the techniques employed. The organization of microfilaments was very heterogeneous within some clones but homogeneous within others. Correlations between microfilament organization and origin of a cell line or clone or its metastatic potential were not found in this tumor system.     

Tumor-cell-platelet aggregation does not correlate with metastatic potential of rat 13762NF mammary adenocarcinoma tumor cell clones

The ability of tumor cells to induce platelet aggregation has been correlated with their capacities to colonize the lungs of experimental animals. We tested this hypothesis by studying the ability of cloned, low-passage metastatic tumor cell lines derived from rat 13762NF mammary adenocarcinoma to aggregate rat platelets in vitro and in vivo, and we then compared this activity to metastatic potential by determining the incidence of lung metastasis after subcutaneous or intravenous inoculation of the tumor cell clones into syngeneic rats. Our results failed to show a correlation between in vitro platelet-aggregating activity and metastatic potential. In this system we could not detect platelet-aggregation activity with the most metastatic tumor clone, while the least metastatic clone clearly possessed high platelet-aggregating activity. In addition, by measuring changes in blood platelet and fibrinogen concentrations at various intervals following intravenous injection of tumor cell clones, we were able to confirm in vivo the observed in vitro differences in their plateletaggregating activities. Thus, platelet aggregating activity is heterogeneously expressed among 13762NF cell clones and appears unrelated to spontaneous or experimental metastasis in this tumor system.     

Growth of rat mammary adenocarcinoma cells in semisolid clonogenic medium not correlated with spontaneous metastatic behavior: heterogeneity in the metastatic, antigenic, enzymatic, and drug sensitivity properties of cells from different sized colonies

Using rat 13762NF mammary tumor cell clones of varying spontaneous metastatic potentials and biochemical properties and known phenotypic stabilities we studied the relationship between cell colony growth in a clonogenic assay and the biological and biochemical properties of cells derived from different cell colonies. The spontaneous metastatic potential of in vivo or in vitro grown 13762NF tumor cells was not related to their in vitro cloning efficiencies; cells of both low and high metastatic potential formed colonies of various sizes and shapes during 14 days of growth in 0.3% or 0.6% semisolid agarose. A highly metastatic cell clone of relatively low growth potential in agarose was examined further. Individual tumor cell colonies derived from this cell clone were removed from agarose and their properties determined. Cells from small (less than 100-microns-diameter) or large (greater than 500-microns-diameter) agarose colonies had similar self-renewal capacities in agarose and formed variously sized cell colonies when replated in agarose medium. Metastatic potential, drug sensitivity parameters, and expression of a high Mr mucin-like glycoprotein antigen and type IV collagenolytic activity known to be associated with spontaneous metastasis of 13762NF tumor cells were dissimilar in cells from different colonies, and these characteristics were independent of original tumor cell colony size in agarose. In contrast, the expression of cell surface proteins of Mr less than 300,000 were similar among cells derived from different agarose colonies. The data indicate that heterogeneity exists in the ability of 13762NF adenocarcinoma cells of different biochemical and metastatic potentials and drug sensitivities to grow in semisolid agarose. In addition, the cells that grow in agarose to form detectable colonies (greater than 50 cells) are not necessarily those with a high potential of metastasizing spontaneously to distant sites.     

The role of polymorphonuclear leukocytes (PMN) on the growth and metastatic potential of 13762NF mammary adenocarcinoma cells

Circulating neutrophil (PMN) levels can increase in rats bearing subcutaneously growing clones of the 13762NF mammary adenocarcinoma and the level of increase correlates with the metastatic potential of the clone. In rats with poorly metastatic MTC tumors, numbers of circulating PMN did not rise, whereas PMN levels rose 50-fold in rats bearing highly metastatic MTLn3, 12-fold in rats with weakly metastatic MTLn2, and 14-fold in those with moderately metastatic MTF7 tumors. Neutrophilia was caused partly by tumor size, but metastatic potential was a stronger determinant, suggesting that PMNs may play a role in the metastatic process. To determine whether circulating PMNs indeed contribute to cellular metastatic potential, we examined effects of PMN on various aspects of the metastatic process. Experimental metastasis assays involving i.v. co-injections of PMNs yielded a dose-dependent increase in extrapulmonary metastases for MTLn3, but no change in lung colonization potential for any of the clones examined. The change in the metastatic profile was not due to any modification in in vivo distribution of i.v. injected tumor cells or in adhesion to endothelial monolayers in vitro. PMNs also had no effect on in vitro DNA, RNA or protein synthesis and were not cytolytic (E:T 100:1). However, PMNs collected from high-passage MTLn3 tumor-bearing rats had a 50% increase in heparanase and type-IV collagenolytic activity as compared to unstimulated PMNs isolated from normal rats. These results indicate that polymorphonuclear cells may contribute to the metastatic potential of highly metastatic clones from the 13762NF mammary adenocarcinoma cells by assisting in the degradation of basement membrane during extravasation.     

Phenotypic drift of metastatic and cell-surface properties of mammary adenocarcinoma cell clones during growth in vitro

We have examined cell clones obtained from a 13762 mammary adenocarcinoma tumor and its spontaneous lung metastasis for phenotypic stability during serial culture passage in vitro. Two clones that varied markedly in their metastatic properties were chosen for further examination. One of these clones (MTC) obtained from the parental transplanted tumor initially failed to metastasize within 23 days post-injection s.c. but gained the ability to form spontaneous pulmonary metastases after several serial passages in vitro. Another clone (MTLn₃) derived from a spontaneous lung metastasis was initially highly metastatic after short-term culture, but lost the potential to form large numbers of spontaneous lung metastases with long-term culture. In contrast to MTA, clone MTLn₃ displayed lymph-node metastasis, and the frequency of lymph-node involvement increased when late-passage cultures of MTLn₃ cells were assayed in vivo. Both clones from late-passage cultures produced larger tumor sizes at the primary (mammary fat pad) injection sites compared to early passage cells. The morphologies of MTC cells changed with serial tissue culture passage, while the morphologies of MTLn₃ cells did not change. The display of fibronectin on MTC cells by immunofluorescence did not change with culture passage; fibronectin was not detected in cultures of clone MTLn₃. Fibronectin was also found on MTC cells by cell surface labelling using lactoperoxidase-catalyzed iodination-sodium dodecylsulfate polyacrylamide gel electrophoresis-autoradio-graphy. lodination of fibronectin on MTC cells did not vary with culture passage, and as in immunofluorescence experiments it was not detected on MTLn₃ cells. There was a decrease in exposure of certain cell surface proteins on MTC cells with culture passage, but we did not detect modifications with this procedure that correlated with culture passage of MTLn₃ cells. We conclude that prolonged culture in vitro can result in modifications of metastatic and cell-surface properties of tumor cell clones.     

Coexpression of cytokeratins characteristic for myoepithelial and luminal cell lineages in rat 13762NF mammary adenocarcinoma tumors and their spontaneous metastases.

We used immunohistochemical procedures to study the cellular expression and distribution of cytokeratins (CKs) in rat 13762NF mammary adenocarcinoma cells growing at mammary fat pad sites and at spontaneous lymph node and lung sites. In order to establish CK distribution in normal rat mammary epithelia, immature, resting, and lactating rat mammary glands were probed with a panel of monospecific antibodies that recognize individual CKs. Basal/myepithelial cells were distinguished by expression of CKs 5 and 14 and coexpression of vimentin from luminal cells, which expressed CKs 8, 18, and 19. Antibody to CK 7 recognized luminal epithelium of immature and resting, but not lactating, mammary glands. Myoepithelial cells of lactating mammary gland were weakly recognized by antibodies to CKs 7 and 19. Tumors formed by cell lines and clones derived from parental 13762NF tumor (MTPa, MTC, MTA, and MTF7) were not recognized by any of the anti-CK antibodies. Only vimentin was expressed in these tumors and their metastases. In tumors and metastases generated from cell lines and clones derived from lymph node (MTLY) and lung metastases (MTLn2 and MTLn3) of the 13762NF tumor we observed heterogeneous CK phenotypes. Expression of CKs 5 and 18 was greatly reduced or lacking, while CK 14 was coexpressed with CKs 7, 8, and 19 with or without vimentin. Tumors from the highly metastatic clone MTLn3 had a dominant cellular phenotype, expressing CKs 7, 8, 14, and 19 and vimentin, a pattern that did not match normal mammary epithelia, whether luminal, basal/myoepithelial, or the dual-phenotype stem cell, in which CKs 5, 8, 14, and 18 were coexpressed. MTLn3 lymph node and lung metastases expressed the same cellular phenotype as the s.c. growing MTLn3 tumor. The results appear to contradict the belief that malignant mammary tumors may be distinguished from benign tumors or hyperplastic growths by the lack of basal/myoepithelial markers.     

Purification and some properties of a lung-derived growth factor that differentially stimulates the growth of tumor cells metastatic to the lung

The ability of malignant cells to respond to growth factor(s) present in or secreted by a distant target organ may be important in tumor metastasis. We used metastatic cell lines and clones of the rat 13762NF mammary adenocarcinoma that show reproducible spontaneous metastatic behavior from the mammary fat pad to regional lymph nodes and lung sites. Whereas poorly lung metastatic MTPa and MTC cells did not grow in response to lung-conditioned medium, highly lung-metastatic MTLn3 cells responded and grew rapidly in lung-conditioned medium. The major growth-promoting factor for MTLn3 cells from porcine and rat lung-conditioned media was purified by using hydroxylapatite affinity and anion exchange chromatography, chromatofocusing, size exclusion chromatography, and preparative native gel electrophoresis. The activity in each of the purification fractions was measured by determining their ability to increase the number of MTLn3 cells in serum-deprived culture. The major component that differentially stimulated the growth of highly metastatic MTLn3 cells was a glycoprotein of Mr approximately 66,000. Under reducing conditions, its apparent Mr was approximately 72,000. This lung-derived mitogen was stable at pH 4.0-9.0, possessed a pI of 6.9-7.0, and preferentially promoted the growth of lung-metastasizing tumor lines over their poorly lung-metastasizing counterparts in rat 13762NF mammary adenocarcinoma and murine B16 melanoma tumor systems. The activity of porcine lung-derived growth factor was not affected by pretreatment with antisera to porcine insulin, human granulocyte-macrophage colony-stimulating factor, human platelet-derived growth factor, or murine epidermal growth factor. It was inactivated by reduction with dithiothreitol or exposure to high temperature (95 degrees C). The results suggest that specific organ-derived growth factors are important in metastatic colonization and organ growth of particular malignant cells.     

Heterogeneity in the sensitivities of the 13762NF rat mammary adenocarcinoma cell clones to cytolysis mediated by extra- and intratumoral macrophages

The susceptibility of cloned cell lines of the 13762NF rat mammary adenocarcinoma to macrophage-mediated cytolysis was investigated using both intra- and extratumoral macrophages. The percentage of Fc receptor-positive cells in tumors growing s.c. in syngeneic F344 rats ranged from 8 to 20%, but we could not demonstrate a significant correlation between the number of Fc receptor-positive cells within tumors and their spontaneous metastatic potentials. In macrophage-mediated cytolysis assays, cloned 13762NF cell lines of differing metastatic potential, established from tissue culture lines, fresh tumor explants, or short-term cultures (one passage in vitro), were used as targets. Effector cells were thioglycolate-elicited peritoneal macrophages (activated in vitro with bacterial lipopolysaccharide) or intratumoral macrophages (activated in vitro with lipopolysaccharide). When the effector cells were peritoneal macrophages, established cloned 13762NF cell lines showed little correlation in their susceptibility to macrophage-mediated cytolysis and metastatic potential, while this was not observed when fresh tumor explants were used. Highly metastatic MTLn3 cells were the least sensitive, less metastatic MTF7 and MTLn2 cells were more susceptible, and the low metastatic parental MTPa cells were the most sensitive in 72-h cytolysis assays. When the effector cells were intratumoral macrophages, all 13762NF cell lines showed less sensitivity in cytolysis assays than similar assays using thioglycolate-elicited peritoneal macrophages. With the exception of line MTLn2, short-term cultures (one passage in vitro) did not differ substantially in susceptibility to intratumoral macrophages compared to fresh explants. In this system, the sensitivity of 13762NF cells to macrophage-mediated cytolysis is a function of effector as well as target cell source.     

Preferential growth stimulation of metastatic rat mammary adenocarcinoma cells by organ-derived syngeneic fibroblasts in vitro.

To determine whether organ-derived fibroblasts differentially affect the growth of cells from tumors that preferentially metastasize to specific organs, we investigated the effect of medium conditioned with primary cultured rat fibroblasts from various organs on the in vitro growth of metastatic cell lines and clones of the rat 13762NF mammary adenocarcinoma. The conditioned medium from fibroblasts derived from rat mammary fat pad differentially stimulated tumor cell growth in monolayer culture and clonogenic growth in soft agarose of the highly metastatic clone MTLn3 in a dose-dependent manner. Conditioned medium from fibroblasts derived from the lung and liver also stimulated the growth of clone MTLn3 cells but to a lesser extent than did mammary fat pad fibroblasts. In contrast, poorly metastatic cell clones (MTC, MTPa) did not respond to the growth stimulatory factor(s) from the fibroblast-conditioned medium. The factor(s) responsible for the growth stimulation were inactivated by heat and trypsin treatment and inhibited by low pH and cycloheximide. The result suggest that fibroblasts in different organs have different effects on tumor cell growth, and they may determine, in part, the organ specificity of tumor development and metastasis.     

Characterization of cytokeratins expressed in metastatic rat mammary adenocarcinoma cells

The expression of cytokeratins (CKs) was investigated in cell lines and clones established from the rat 13762NF mammary adenocarcinoma tumor and its spontaneous lymph node and lung metastases. Two-dimensional polyacrylamide gel electrophoresis of intermediate filament-enriched protein fractions from cultured cells revealed that clones established from spontaneous metastases contained three CKs (Mr approximately 54,000, approximately 52,000, and approximately 40,000) characteristic of simple epithelia and two CKs (Mr approximately 51,000 and approximately 47,000) characteristic of stratified epithelia. CK expression varied qualitatively and quantitatively between the different metastasis-derived cell clones. In contrast, cell clones established from the original mammary fat pad tumor expressed low or undetectable levels of CKs. Western blot analyses with a panel of anti-CK antibodies with defined specificities confirmed the observations. One-dimensional polyacrylamide gel electrophoresis of whole-cell lysates and intermediate filament-enriched extracts were transferred and probed with the panel of antibodies. The relative expression of individual CKs varied according to the cell line or clone examined and environmental conditions (low versus high passage and in vitro versus in vivo growth), whereas the amount of total CKs expressed relative to total cell protein varied according to cell line or clone and growth conditions.     

A critical step in metastasis: in vivo analysis of intravasation at the primary tumor

Detailed evaluation of all steps in tumor cell metastasis is critical for evaluating the cell mechanisms controlling metastasis. Using green fluorescent protein transfectants of metastatic (MTLn3) and nonmetastatic (MTC) cell lines derived from the rat mammary adenocarcinoma 13762 NF, we have measured tumor cell density in the blood, individual tumor cells in the lungs, and lung metastases. Correlation of blood burden with lung metastases indicates that entry into the circulation is a critical step for metastasis. To examine cell behavior during intravasation, we have used green fluorescent protein technology to view these cells in time lapse images within a single optical section using a confocal microscope. In vivo imaging of the primary tumors of MTLn3 and MTC cells indicates that both metastatic and nonmetastatic cells are motile and show protrusive activity. However, metastatic cells show greater orientation toward blood vessels and larger numbers of host cells within the primary tumor, whereas nonmetastatic cells fragment when interacting with vessels. These results demonstrate that a major difference in intravasation between metastatic and nonmetastatic cells is detected in the primary tumor and illustrate the value of a direct visualization of cell properties in vivo for dissection of the metastatic process.     

Involvement of plasminogen activator production with tumor metastasis in a rat model

The process of metastasis involves numerous steps, many of which are thought to require the action of hydrolases, such as collagenase and other proteases. In this study, we investigate the role of the protease plasminogen activator in the metastasis of the rat mammary adenocarcinoma 13762. We observed that this tumor cell line is heterogeneous with respect to plasminogen activator (PAA) production. Clonal tumor cell populations were isolated which produced various levels of PAA. This phenotypic property of these clones remained stable for long periods of in vitro culture and did not affect their tumorigenicity. When the metastatic potential of these clones was determined using the lung colony assay, a strong correlation between PAA and metastatic potential was found. Furthermore, a threshold level of PAA production was observed, above which the lung colony-forming ability of the cells increased dramatically. These studies suggest that PAA production may play an important role in tumor metastasis.     

Survival of rat mammary tumor cell clones and DNA strand damage following adriamycin treatment

Summary Tumor cell subpopulations have been shown to be heterogenous in a number of phenotypic characteristics, including responses to cytotoxic drugs. This phenotypic heterogeneity has been used here to study mechanisms associated with Adriamycin (doxorubicin HCl)-induced cytotoxicity. Clonogenic survival and alkaline elution methods were employed to examine the response of two tumor cell subpopulations to Adriamycin. The cells were derived from a primary 13762NF rat mammary adenocarcinoma (clone MTC) and a lung metastasis in the same animal (clone MTLn3). The MTC cells were significantly more resistant to Adriamycin than were the MTLn3 cells; the dose effective in reducing cell survival by 50% was 10-fold higher. Protein-associated DNA strand breakage assayed by alkaline elution was dose-dependent in both clones, and MTC cells were again more resistant to break induction than were MTLn3. These results showed that clonal tumor subpopulations isolated from a primary tumor and its metastases possessed different intrinsic survival responses to Adriamycin treatment in vitro and that this survival response correlated with Adriamycin-induced production of protein-associated DNA single-strand breaks.The investigation reported in this paper was supported in part by USPHS grants CA-32745 (SPT) and CA-23270 (REM) and NIH training grant CA-09299-06 (DPE)     

Differential organ tissue adhesion,invasion, and growth properties of metastatic rat mammary adenocarcinoma cells

Metastatic lines and clones of the rat 13762NF mammary adenocarcinoma have been established that show reproducible spontaneous metastasis from the mammary fat pad to regional lymph node and lung. Poorly (MTC) and highly (MTLn3) metastatic cloned lines derived from tumor growing in the mammary fat pad (MTC) and its spontaneous lung metastasis (MTLn3) were tested in vitro for their abilities to attach to and invade into syngeneic organ tissue and to survive and grow in medium conditioned by target and nontarget syngeneic organ tissues. The highly metastatic MTLn3 cells adhered to and invaded target lung tissue at significantly higher rates than the MTC cells, and bound to and invaded other organ tissues although at lower rates than lung tissue. Similarly, the MTLn3 cells showed significantly higher growth stimulation by lung-conditioned medium than medium conditioned by other tissues. Poorly metastatic MTC cells were not significantly stimulated by any of the organ-conditioned media. The results are consistent with previous proposals that explain preferential organ metastasis in terms of 'seed and soil', and further suggest that metastasis of mammary tumors to specific organ secondary sites is mediated by specific properties, such as those involved in tumor-cell organ-cell adhesion, invasion, and growth.     

Heterogeneity in induced thermal resistance of rat tumor cell clones

Four 13762NF rat mammary adenocarcinoma clones were examined for their survival response to heating under conditions that induced transient thermal resistance (thermotolerance). Clones MTC and MTF7 were isolated from the subcutaneous locally growing tumor, whereas clones MTLn2 and MTLn3 were derived from spontaneous lung metastases. There was heterogeneity among these clones in thermotolerance induced by either fractionated 45 degrees C or continuous 42 degrees C heating, but the order of sensitivity was not necessarily the same. The clones developed thermal resistance at different rates and to different degrees within the same time intervals. There was heterogeneity between clones isolated from within either the primary site or metastatic lesions. However, clones derived from metastatic foci did not intrinsically acquire more or less thermotolerance to fractionated 45 degrees C or continuous 42 degrees C heating than did clones from the primary tumor. Further, there was no apparent relationship between any phenotypic properties that conferred more or less thermotolerance in vitro and any phenotypic properties that conferred enhanced metastatic success of these same clones by spontaneous (subcutaneous) or experimental (intravenous) routes in vivo. These tumor clones also differ in their karyotype, metastatic potential, cell surface features, sensitivity to x-irradiation and drugs, and ability to repair sublethal radiation damage. These results provide further credence to the concept that inherent heterogeneity within tumors may be as important in therapeutic success as other known modifiers of outcome such as site and treatment heterogeneity.     

A 6-thioguanine-resistant variant of the 13762 cell line which is no longer tumorigenic or metastatic

A 6-thioguanine resistant (TG^R) variant of the highly tumorigenic and metastatic mammary adenocarcinoma cell line 13762 was obtained. This variant was no longer tumorigenic or metastatic in normal syngeneic rats but did grow as a primary tumor in irradiated animals. Our results suggest that the TG^R cell line was rejected by an irradiation-sensitive immunological mechanism. Although the TG^R cells produced primary tumors in irradiated animals, there was no evidence of the extensive metastasis seen with the 13762 cells. This apparent inability to metastasize was confirmed by injecting the TG^R cells intravenously. Whereas the 13762 cells produced large numbers of metastatic lung foci, there was no evidence of lung metastasis with the TG^R cells, even in irradiated animals. Revertant cells for the 6-thioguanine-resistant phenotype were still non-tumorigenic and non-metastatic in normal rats, suggesting that 6-thioguanine resistance is not associated with the altered tumorigenic phenotype. From the TG^R variant, cell lines were selected with an increased ability to produce tumors in normal rats. Although some of these revertants were capable of producing limited lung metastases in normal animals, extensive metastases were always seen when the cells were injected into irradiated animals. Differences between the 13762 and the TG^R variants were also found in their ability to produce plasminogen activator. The TG^R cells released far less plasminogen activator in culture than the 13762 cells. This could be a contributing factor in their different metastatic potentials.     

Protein kinase C delta involvement in mammary tumor cell metastasis.

Metastasis requires cytoskeletal remodeling for migration, adhesion, and extravasation of metastatic cells. Although protein kinase C (PKC) is involved in tumor promotion/progression and cytoskeletal remodeling, its role in metastasis has not been defined. PKCdelta levels are increased in highly metastatic 13762NF mammary tumor cells (MTLn3) compared with less metastatic, parental cell lines. To determine whether the increase in endogenous PKCdelta is functionally related to their increased metastatic potential, we prepared MTLn3 cells that express the inhibitory regulatory domain fragment of PKCdelta (RDdelta) under the control of a tetracycline-inducible promoter. RDdelta expression attenuated endogenous PKCdelta activity, as demonstrated by decreased phosphorylation of the PKCdelta substrate adducin in migrating cells. Thus, in MT cells, RDdelta appears to primarily influence cytoskeleton-dependent processes rather than cell cycle progression. To determine whether RDdelta expression influenced metastatic potential in vivo, MTLn3/RDdelta cells were either grown in the mammary fat pad or injected into the tail vein of syngeneic rats, and effects of doxycycline-induced RDdelta expression on pulmonary metastases were studied. Consistent with the in vitro data, induction of RDdelta significantly reduced the number of lung metastases without affecting growth of the primary tumor. These results suggest that interfering with endogenous PKCdelta activity by expressing the inhibitory RDdelta fragment inhibits cytoskeleton-regulated processes important for MTLn3 cell metastasis.     

Effect of host immune status on the spontaneous metastasis of cloned cell lines of the 13762NF rat mammary adenocarcinoma

The importance of host immune status on the spontaneous metastasis of cloned cell lines of the 13762NF rat mammary adenocarcinoma was examined. Cell lines MTLn3 (high metastatic potential), MTF7 and MTLn2 (intermediate metastatic potential) and MTC (low metastatic potential) were subjected to a series of in vivo assays designed to assess how manipulation of the immune system in the syngeneic F344 host would affect the ability of these cells to metastasise. Treatment of tumour bearing rats with the immunosuppressive agents cyclosporin A or cyclophosphamide had little influence on metastasis in this system. Growth of tumours in congenitally athymic nude rats resulted in reduction of observed metastases. In addition, humoral immune response was not detectable during a 23-day period of tumour growth in F344 rats. Excision of the tumour growing in situ reduced the number of metastases when the tumours were resected early (less than 10 days), but at later times tumour resection did not influence the incidence of metastasis. The importance of initial lymphatic rather than haematogenous routes of dissemination was confirmed in experiments where the draining inguinal and axillary lymph nodes were removed at different times either before, or after, subcutaneous mammary fat pad injection of metastatic tumour cells.     

Direct effects of the pyrimido-pyrimidine derivative RA 233 (Rapenton) on rat 13762NF mammary tumor cell clones in vitro

Studies with the pyrimido-pyrimidine analogue RA 233 (Rapenton) suggest that its antimetastatic action may not be mediated entirely by inhibition of platelet function. Little is known about its direct effects on tumor cells. We investigated the in vitro effects of RA 233 on clones MTLn3 and MTC of differing metastatic potentials, isolated from the 13762NF rat mammary adenocarcinoma. The results indicated that RA 233 is cytostatic (EC50 of approximately 140 microM and approximately 180 microM for MTLn3 and MTC cells, respectively) rather than cytotoxic by determining changes in viable cell number, thymidine uptake, and incorporation of thymidine and methionine. In both clones RA 233 inhibited cAMP-dependent phosphodiesterase activity and affected cAMP accumulation in intact cells. In contrast, clonal heterogeneity in drug-induced morphological changes, such as vacuole formation and altered organization of cytoskeletal structures, as well as increased tumor cell growth at 50 microM RA 233 was observed between clones MTLn3 and MTC. These data could explain the conflicting results obtained with RA 233 when evaluated as an antimetastatic agent.