Murine liver metastasis model using L5178Y-ML lymphoma and the effect of antitumor agents on the metastasis

Inhibition of Tumor Metastasis by a Synthetic Polymer Containing a Cell-Adhesive RGDS Peptide

A water soluble polymer containing cell adhesive Arg-Gly-Asp- Ser (RGDS) sequence, i.e., poly(carboxyethylmethacrylamide-RGDS) conjugate [poly(CEMA-RGDS)], was synthesized. Poly(CEMA-RGDS) inhibited lung metastasis of B16-BL6 melanoma cells in a dose-dependent manner (20-1000 μg) and liver metastasis of L5178YML25 lymphoma cells. A mixture of poly- (CEMA) and RGDS peptide or poly(CEMA) alone did not show any inhibitory effect on lung metastasis. The Gly-Arg-Gly-Asp-Ser (GRGDS) peptide required high doses (3000 μ g) to obtain a sufficient antimetastatic effect. An in vitro study showed that poly(CEMA-RGDS) as well as RGDS + poly(CEMA) gave similar inhibition of B16-BL6 cell invasion into reconstituted basement mem brane Matrigel. Intermittent i.v. administration of poly(CEMA-RGDS) after in oculation with B16-BL6 cells caused significant inhibition of spontaneous lung metastasis as compared with the multiple administration of RGDS, poly- (CEMA) or untreated control. These results demonstrate that the conjugation

Inhibitory effect of magnolol on tumour metastasis in mice

It has previously been reported that magnolol, a phenolic compound isolated from Magnolia obovata, inhibited tumour cell invasion in vitro. The purpose of this study was to investigate the antimetastatic effect of magnolol on tumour metastasis in vivo with experimental and spontaneous metastasis models and to clarify the mechanism. The antimetastatic effects of magnolol were evaluated by an experimental liver and spleen metastasis model using L5178Y-ML25 lymphoma, or an experimental and spontaneous lung metastasis model using B16-BL6 melanoma. Intraperitoneal (i.p.) administration of 2 or 10 mg/kg of magnolol significantly suppressed liver and spleen metastasis or lung metastasis. As for the spontaneous lung metastasis model using B16-BL6 melanoma, multiple i.p. administrations of 10 mg/kg of magnolol after and before tumour inoculation significantly suppressed lung metastasis and primary tumour growth. In addition, magnolol significantly inhibited B16-BL6 cell invasion of the reconstituted basement membrane (Matrigel, MG) without affecting cell growth. These data from the in vivo experiments suggest that magnolol possesses strong antimetastatic ability and that it may be a lead compound for drug development. The antimetastatic action of magnolol is considered to be due to its ability to inhibit tumour cell invasion.

Macrosphelide B suppressed metastasis through inhibition of adhesion of sLe(x)/E-selectin molecules

Macrosphelide B (MSB), a 16-membered macrolide from Microsphaeropsis sp. FO-5050, inhibits adhesion of sialyl Lewis(x) (sLe(x))-expressing HL-60 cells to LPS-activated (E-selectin-expressing) human umbilical vein endothelial cells (HUVECs) in vitro. This study examines MSB effects on metastasis of B16/BL6 mouse melanoma cells (B16/BL6 cells) and L5178Y-ML mouse lymphoma cells in vivo and analyzes the MSB antimetastatic activity mechanism. When administered MSB at 20 mg/kg/day, lung metastatic nodules of B16/BL6 cells were significantly decreased (T/C = 45%). However, no inhibition of metastasis of L5178Y-ML cells to the spleen and liver was observed. Flow cytometry analysis showed that B16/BL6 cells expressed high levels of sLe(x) antigen, whereas expression on L5178Y-ML cells was low. Under in vitro conditions, B16/BL6 cells demonstrated a greater degree of adhesion to LPS-activated HUVECs than L5178Y-ML cells, but adhesion was significantly inhibited by MSB and sLe(x) antibody. Combined therapy of MSB and cisplatin (CDDP) induced remarkable lung metastasis inhibition without adverse effects of CDDP to the host. All these findings suggest that MSB suppresses lung metastasis of B16/BL6 cells by inhibiting cell adhesion to endothelial cells through the sLe(x) molecule.

Antimetastatic effect of a novel indolocarbazole (NB-506) on IMC-HM murine tumor cells metastasized to the liver

IMC-HM cells were isolated from spontaneously induced ascitic IMC carcinoma cells that had been maintained intraperitoneally in CDF1 mice. Metastasis to the liver of subcutaneously implanted IMC-HM cells was detected 10 days after implantation into the flanks of mice (day 10), but metastasis to other organs was limited. Thereafter, however, tumor cells spread rapidly to lymph nodes, lung, spleen, ovary and other organs, and the mice died on day 13 to 18. We report here, together with the properties of IMC-HM cells, the effects of adriamycin, cisplatin, etoposide and a new indolocarbazole antitumor compound (NB-506) on this model of metastasis. Although these anticancer agents all inhibited the growth of the subcutaneous tumors, their effects on the life span of the tumor-bearing mice varied. Treatment with NB-506, started on day 1, more than doubled the survival period at doses 30 mg/m2 to 900 mg/m2. Further, treatment with NB-506, started on day 4 after resection of the primary tumor, inhibited growth of the metastasized tumor in the liver and other organs. Etoposide also increased the life span at a limited range of doses. However, the life-prolonging effects of adriamycin and cisplatin were marginal. These results demonstrate that IMC-HM carcinoma is a good model for spontaneous metastasis to the liver followed by lethal spread to many organs. Moreover, NB-506 was found to be highly effective against the growth not only of subcutaneous tumors, but also of tumors metastasized to the liver.

MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide, inhibits the metastasis of haematogenous and non-haematogenous tumours in mice

The antimetastatic effects of MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide (MDP), against three different types of highly metastatic murine tumour cells, B16-BL6 melanoma, colon 26-M3.1 carcinoma and L5178Y-ML25 T lymphoma, were examined in C57BL/6, Balb/c and CDF1 mice, respectively. The administration of 100 micrograms of MDP-Lys(L18) 2 or 4 days before tumour inoculation led to a significant decrease in lung metastasis of B16-BL6 melanoma or colon 26-M3.1 carcinoma cells. MDP-Lys(L18) was also effective in the inhibition of liver metastasis of L5178Y-ML25 lymphoma cells by administration 2 or 4 days before tumour inoculation. The prophylactic effect of 100 micrograms of MDP-Lys(L18) on tumour metastasis was evident for the different administration routes, i.e. subcutaneous, intravenous or intranasal injection, or oral administration. It is of prime interest that oral administration of 1 mg of MDP-Lys(L18) induced a significant decrease in lung metastasis of B16-BL6 melanoma cells. Administration of MDP-Lys(L18) 4 days before assay led to induction of tumoricidal activity by peritoneal macrophages and growth inhibition by the sera against B16-BL6 or L929 cells. When MDP-Lys(L18) was subcutaneously administered five times after tumour inoculation to test therapeutic effect in an experimental and spontaneous metastasis model using B16-BL6 melanoma, the consecutive administrations of MDP-Lys(L18) significantly inhibited lung metastasis in tumour-bearing mice. These results suggest that MDP-Lys(L18) is able to enhance host resistance to reduce tumour metastasis and is a potent immunomodulating agent which may be applied prophylactically or therapeutically for the treatment of cancer metastasis.

Inhibition of tumor metastasis by Arg-Gly-Asp-Ser (RGDS) peptide conjugated with sulfated chitin derivative, SCM-chitin-RGDS

We have synthesized a new compound in which Arg-Gly-Asp-Ser (RGDS) was conjugated with 6-O-sulfated and 6-O-carboxymethyl-chitin (SCM-chitin), i.e. SCM-chitin-RGDS, and tested the inhibitory effect on lung and liver metastases of three different types of tumors in mice. SCM-chitin-RGDS was more effective for the inhibition of liver metastasis of L5178Y-ML25 lymphoma and lung metastases of colon 26 M3.1 cells than SCM-chitin, RGDS or their mixture. GRGDS peptide, however, required a higher dose (3000 micrograms) to obtain a sufficiently antimetastatic effect. Intermittent i.v. administration of SCM-chitin-RGDS before or after the i.v. inoculation of L5178Y-ML25 cells caused significant inhibition of liver metastasis as compared with the multiple administration of RGDS, SCM-chitin or untreated control. Co-injection of lymphoma cells with SCM-chitin-RGDS or multiple treatment of SCM-chitin-RGDS after tumor inoculation showed significantly enhanced survival rate. SCM-chitin-RGDS also showed the spontaneous lung metastasis produced by intrafootpad injection of B16-BL6 melanoma cells by the multiple i.v. administrations. These results demonstrate that the conjugation of RGDS peptide with SCM-chitin led to augmentation of therapeutic potential to cancer metastasis, thus implying an importance of the conjugation of cell-adhesive RGDS peptide with structurally heparin-like SCM-chitin, which possess binding ability to the heparin-binding domain of fibronectin or laminin and extremely low anticoagulant properties.

Antimetastatic effect by anti-adhesion therapy with cell-adhesive peptide of fibronectin in combination with anticancer drugs

We have investigated the therapeutic effect of CH-271 fusion polypeptide containing both cell-binding domain (C-274) and heparin-binding domain (H-271) of fibronectin in combination with anticancer drugs such as doxorubicin (DOX) or mitomycin C (MMC) on tumor metastasis of different types of tumors. CH-271 fusion polypeptide alone significantly inhibited both liver and lung metastasis when it was co-injected with L5178Y-ML25 T-lymphoma, RAW117-H10 B-lymphoma or B16-BL6 melanoma cells, and spontaneous lung metastasis of B16-BL6 melanoma cells when administered i.v. seven times before or after surgical excision of the primary tumors. Combined treatments with CH-271 and either DOX or MMC significantly inhibited liver and lung metastasis of lymphoma or melanoma cells respectively, as compared with either treatment alone or the untreated control. Administrations of CH-271 and DOX in combination substantially prolonged the survival time of mice injected i.v. with L5178Y-ML25 cells. CH-271 or DOX was effective for inhibiting the invasion of L5178Y-ML25 cells into Matrigel in a concentration-dependent manner. Our previous study has shown that CH-271-mediated inhibition of tumor invasion may be due in part to the anti-cell adhesive property without affecting the cell growth, whereas the anti-invasive effect of DOX was established to have resulted from the growth inhibition of tumor cells. Moreover, the combination of CH-271 with DOX provided a more effective inhibition of tumor invasion into Matrigel than did either alone. Thus, we have demonstrated that the combination of anti-cell adhesive CH-271 and anticancer drugs such as DOX or MMC, i.e. anti-adhesion therapy and chemotherapy, is a new approach that offers enhanced (additive) inhibitory effects on tumor metastasis and invasion.

Deoxyribonuclease treatment prevents blood-borne liver metastasis of cutaneously transplanted tumour cells in mice

Murine L5178Y-ML cells, when transplanted subcutaneously into the flank of (BALB/c x DBA/2)F1 mice, grew locally and always formed spontaneous metastases in the liver. Even after surgical removal of the primary tumour mass 5 or 7 days after tumour cell inoculation, all mice died due to liver metastases within 18 days. Using this model of tumour metastasis, we examined whether serine protease or deoxyribonuclease I (DNase I) would affect metastasis. Spontaneous liver metastasis of L5178Y-ML cells was enhanced by systemic administration of alpha-chymotrypsin at 3, 4 and 5 days or at 5, 6 and 7 days after tumour cell inoculation. This result was consistent with a previous report on blood-borne lung metastasis. In contrast, systemic administration of DNase I at 3, 4 and 5 days or at 5, 6 and 7 days after tumour cell inoculation inhibited liver metastasis. Neither treatment affected primary tumour growth. An influence of DNase I on tumour cell arrest in the microvasculature of the liver was suggested by scanning electron microscopy. DNase I treatment resulted in a statistically significant prolongation of the survival period, however, the effect was not satisfactory. A more striking anti-metastatic treatment resulting in a greater prolongation of the survival period was achieved by combining surgical removal of the primary tumour mass with DNase I treatment. These results suggest that DNase I could be a potential therapeutic agent used in conjunction with surgery to prevent clinical blood-borne metastasis.

DT-5461, a new synthetic lipid A analogue, inhibits lung and liver metastasis of tumor in mice

We have investigated the antimetastatic effect of a new synthetic lipid A analogue, of low endotoxicity, DT-5461, against two highly metastatic tumor cell lines, L5178Y-ML25 T-lymphoma and B16-BL6 melanoma cells in mice. Four intermittent i.v. administrations of DT-5461 at intervals of 4 days resulted in a significant inhibition of liver metastasis caused by i.v. injection of L5178Y-ML25 cells and lung metastasis of B16-BL6 cells in the experimental metastasis models. Intraperitoneal and intranasal administrations as well as i.v. administration of DT-5461 were also effective in preventing lung metastasis of the melanoma cells. Multiple administrations of DT-5461 before the surgical excision of primary tumors significantly reduced the number of lung colonies of melanoma cells and primary tumor size. Similarly, this treatment modality after the surgical excision of primary tumors showed a greater reduction of lung tumor colonies as compared with lipopolysaccharide, a synthetic lipid A (No. 506) and its analogue as well as untreated control in the spontaneous lung metastasis model. Furthermore, the group that received DT-5461 after the inoculation of lymphoma or melanoma cells showed significantly enhanced survival rate compared with the untreated control. These results suggested that DT-5461 may be therapeutically useful for the inhibition of tumor metastasis.

Effects of antitumor agents on subcutaneous implants and hepatic metastases of colon carcinoma 26 in mice

We investigated the responses of experimentally produced hepatic metastases of colon carcinoma 26 tumor and subcutaneously (SC) implanted colon carcinoma 26 tumor in mice to 17 clinically-used and one under-development antitumor agents using same dose regimen. In intravenous administrations on days 7 and 14, there were no significant differences in their responses to most of the tested agents. However, there were big differences in the responses to some of the agents. Nimustine more effectively prolonged the lifespan of SC implanted tumor-bearing mice than of mice bearing hepatic metastases. Mitomycin C was, however, considerably more effective on hepatic metastases than on SC implanted tumor. ME2303, a new fluorinated anthracycline derivative, showed a similar effect to doxorubicin on both tumors. However, administrations of ME2303 on days 7, 11 and 15 showed more marked antitumor effect only on hepatic metastases than administrations on days 7 and 14. Doxorubicin was less active against both tumors for administrations on days 7, 11 and 15 than for those on days 7 and 14. These results suggest the importance of the site of tumor growth for the action of some drugs. ME2303 may be active against hepatic metastases if it is administered by multiple injections.

B30-MDP, a synthetic muramyl dipeptide derivative for tumour vaccination to enhance antitumour immunity and antimetastatic effect in mice

The effect of a muramyl dipeptide derivative (B30-MDP) on the augmentation of antitumour immunity against highly metastatic L5178Y-ML25 mouse lymphoma cells was examined in CDF1 (Balb/c x DBA/2) mice. Mice immunized with a mixture of X-irradiated tumour cells (10(3)) and B30-MDP (100 micrograms) on 7 days prior to challenge by viable tumour cells displayed a significant decrease in metastasis towards the target organs, liver and spleen, compared with that of untreated mice. Immunization of mice with the mixture on day 5 or 7 after tumour challenge, when the level of glutamic-pyruvic transaminase (GPT) and glutamic-oxaloacetic transaminase (GOT) in sera of mice inoculated with viable tumour cells was observed to be normal, caused less metastasis than immunization with X-irradiated tumour cells alone. Sensitization with X-irradiated tumour cells admixed with B30-MDP induced almost two times higher cytotoxicity of spleen cells against L5178Y-ML25 lymphoma cells than sensitization with X-irradiated tumour cells without B30-MDP. In contrast, cytotoxic activity of spleen cells against another target, L1210 lymphoma cells derived from BDF1 mice, was not observed by immunization with X-irradiated L5178Y-ML25 cells with or without B30-MDP. Specific lysis by splenic cells of the immunized mice against L5178Y-ML25 cells decreased to the normal level when T cells were deleted from the immunized spleen cells by the treatment of rabbit anti-mouse Thy1.2 antibody and rabbit complement. These results indicate that B30-MDP is able to augment a specific tumour immunity due to the enhancement of cytotoxicity mediated by T lymphocytes, and is useful as an immunopotentiating agent for active immunization of inactivated tumour cells.

Murine tumor cells metastasizing selectively in the liver: ability to produce hepatocyte-activating cytokines interleukin-1 and/or -6

Increasing evidence suggests that an intimate correlation may exist between the production of a cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF) and the ability to metastasize spontaneously in the lungs in murine transplantable tumors. In the present study, we further examined the cytokine production by tumor cells with the ability to metastasize in the liver. Four out of 8 test tumors, which produced metastasis in the lungs but not in the liver, exhibited the ability to produce GM-CSF activity in culture. Three other tumors produced metastasis in the liver but not in the lungs. These tumor cells exhibited no ability to produce GM-CSF, but two of them expressed an interleukin-6 (IL-6) mRNA and also produced IL-6 activity in the culture fluids. One of the two IL-6-producing tumors and the remaining liver metastatic tumor produced interleukin-1 (IL-1) as revealed by bioassay and neutralization test. In the tumor cells producing pulmonary metastasis, neither IL-6 gene expression nor IL-1 production could be detected. The last test tumor, which produced no metastasis either in the lungs or liver, produced neither GM-CSF, IL-1 nor IL-6. Furthermore, injection of antisera reactive to recombinant murine IL-6 caused a marked decrease of the number of liver metastases of an IL-6-producing tumor, but not lung metastases of a GM-CSF-producing tumor, which could be markedly inhibited by injection of anti-recombinant murine GM-CSF sera. These results suggest the possibility that there may be a correlation between the cytokines produced by tumor cells and their organ specificity in spontaneous metastasis, and also indicate that these tumor models may provide a useful tool for studies on the role of cytokines in tumor metastasis.

Recombinant fusion polypeptide with cell- and heparin-binding domains of fibronectin inhibits liver metastasis of L5178Y-ML25 lymphoma cells

We have investigated the effect of recombinant polypeptides with cell-binding domain (C-274) or with heparin-binding domain (H-271) and their fusion polypeptide (CH-271) on liver metastasis of murine lymphoid tumor. The polypeptides containing heparin-binding domain, H-271 and CH-271, were able to inhibit liver metastasis when co-injected i.v. with L5178Y-ML25 T-lymphoma cells, while C-274 with cell-binding domain showed much weaker antimetastatic activity. Treatment with H-271 or CH-271 substantially prolonged the survival time of mice injected i.v. with L5178Y-ML25 cells. CH-271, containing cell- and heparin-binding domains, was more antimetastatic than H-271. The reason why CH-271 was more effective in inhibiting liver metastasis than H-271 can not be explained in terms of a difference in the stability in the circulation or in the molecular size of the polypeptide. The polypeptides used in this study did not affect the tumor cell growth or viability in vitro. CH-271 was found to be still active in inhibiting liver metastasis even when natural killer cells or macrophages were removed from this system. Furthermore, multiple administrations of CH-271 after tumor implantation effectively inhibited liver metastasis and enhanced the survival rate as compared with H-271, C-274 and untreated control. Thus, the fusion of H-271 with C-274 (i.e. CH-271) augments the antimetastatic property of H-271, possibly through the interaction between tumor cells and the heparin-binding domain of fibronectin.

Inhibitory effect of antimetastatic fusion polypeptide of human fibronectin on tumor cell adhesion to extracellular matrices

We investigated the inhibitory mechanism of liver metastasis by using recombinant fragments with cell- and/or heparin-binding domains (C-274, H-271 or the fusion fragment CH-271). Intravenous co-injection of L5178Y-ML25 cells with CH-271 was more effective for the inhibition of liver metastasis than C-274, H-271 or C-274 + H-271. Reduction of the arrest and retention of the radiolabeled tumor cells in the liver of mice was found when CH-271 was co-injected with tumor cells. L5178Y-ML25 cells adhered both concentration- and time-dependently to the substrates precoated with fibronectin, laminin and reconstituted basement membrane, Matrigel. The tumor cell adhesions to the substrates were inhibited in the presence of CH-271. The tumor cell interaction with CH-271-substrate was inhibited by heparin, and monoclonal antibodies (IST-1 or IST-2) against the heparin-binding domain of fibronectin. However, monoclonal antibodies against the cell-binding domain failed to block the interaction. Similarly, CH-271-mediated antimetastatic activity was also inhibited by the treatment of CH-271 with IST-1 before the co-injection with tumor cells, whereas monoclonal antibody against the cell-binding domain had no effect. Thus, the antimetastatic effect of CH-271 fusion fragment on liver metastasis of L5178Y-ML25 cells may be partly due to interference with the adhesive interaction of tumor cells with extracellular matrix or basement membrane components by a heparin-binding domain-dependent mechanism.

Recombinant human granulocyte colony-stimulating factor inhibits the metastasis of hematogenous and non-hematogenous tumors in mice

We studied the effects of in vivo administrations of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on the metastasis of murine hematogenous and non-hematogenous tumors in spontaneous and experimental metastasis models. Spontaneous lung metastasis caused by intra-footpad injections of B16-BL6 melanoma and Lewis-lung-carcinoma (3LL) cells were inhibited by intravenous (i.v.) and subcutaneous (s.c.) injections of rhG-CSF after excision of the primary tumors. Recombinant hG-CSF significantly inhibited liver metastasis when administered i.v. after i.v. injection of L5178Y-ML25 T-lymphoma cells. Multiple i.v. administration of rhG-CSF after the tumor inoculation prolonged the survival times of mice inoculated i.v. with L5178Y-ML25 lymphoma cells. Recombinant hG-CSF did not directly affect the growth of B16-BL6 and L5178Y-ML25 cells in vitro. During the administration periods, both i.v. and s.c. injections of rhG-CSF increased the number of total white blood cells (WBC) in peripheral blood to approximately 3 times the normal level in normal and tumor-bearing mice. We also found that the administration of rhG-CSF stimulates neutrophils to become cytostatic against these tumor cells. Our results indicate that the injection of rhG-CSF is effective in inhibiting lung and liver metastases by activating neutrophils and increasing cell number.

A correlation between GM-CSF gene expression and metastases in murine tumors

Using 14 transplantable murine tumors, we investigated a possible correlation between their ability to produce the cytokine GM-CSF and the spontaneous metastatic potential when mice were subcutaneously inoculated. The following results were obtained: (1) seven tumors, which produced severe pulmonary metastases and metastatic swelling of lymph nodes, exhibited the ability to produce GM-CSF activity in culture. The cell population analysis revealed that the cells producing GM-CSF were tumor cells themselves, but that contaminating macrophages/granulocytes and T lymphocytes did not produce GM-CSF. The mRNA for GM-CSF was also found in all of these highly metastatic tumors tested. In mice inoculated with a highly metastatic tumor, the GM-CSF mRNA was also found in lungs; (2) in 3 other tumors, which produced histological but not macroscopical pulmonary metastases, no GM-CSF activity could be detected in the culture fluids. GM-CSF mRNA was, however, detected in the tumor cells in the presence of an mRNA-stabilizing agent, cycloheximide, suggesting the possibility that the tumor cells of this type were transcribing GM-CSF gene, and secreting it in undetectable levels; (3) in culture of the 4 remaining poorly or non-metastatic tumors, neither CSF activity nor GM-CSF mRNA could be detected even in the presence of cycloheximide. GM-CSF mRNA was also not found in lungs of tumor-bearing mice. Our results indicate that there may be a correlation between GM-CSF gene expression in tumor cells and spontaneous metastases.

Structure-activity relationship of polyamine derivatives of 1,3-dichloroacetone-thiosemicarbazone: induction of metastases and increase in sialylation of murine lymphoma L5178Y-R cells

A number of polyamine (PA) derivatives of thiosemicarbazone of 1,3-dichloroacetone (TDA) have been prepared and their effect on growth in vivo of tumorigenic but not metastatic cell strain (LY-R) of mouse lymphoma L5178Y has been investigated. Polyamine derivatives of TDA (PDT) were injected i.p. every third day (4 times, 10 or 25 mg/kg per injection) into DBA/2 mice inoculated i.p. or s.c. with LY-R cells. It has been found that disubstituted putrescine (Put), spermidine (Spd) and spermine (Spm) derivatives TDA exhibit a prometastatic activity as indicated by the appearance of solid tumor foci in subcutaneous tissues, liver and spleen. This activity depends mainly on the structure of the PA fragment and the presence of TDA. An increase in lipid bound sialic acid content after treating LY-R cells in vitro and in vivo with a Spm derivative has been found. These findings suggest that disubstituted PA derivatives of TDA and LY-R cells may be a useful model for investigation of the final steps in formation of metastases by lymphoma cells.