Metastasis Of B16 Melanoma Cells Research Articles

Smad4 deficiency inhibits lung metastases through enhancing phagocytosis of lung interstitial macrophages

Smad4, a critical mediator of TGF-β signaling, plays a pivotal role in regulating various cellular functions, including immune responses. In this study, we investigated the impact of Smad4 knockout specifically in macrophages on anti-tumor immunity, focusing on lung metastasis of B16 melanoma cells. Using a mouse model with Smad4 knockout in macrophages established via Lyz2-cre mice and Smad4 flox/flox mice, we demonstrated a significant inhibition of B16 metastasis in the lungs. Interestingly, the inhibition of tumor growth was found to be independent of adaptive immunity, as no significant changes were observed in the numbers or activities of T cells, B cells, or NK cells. Instead, Smad4 knockout led to the emergence of an MCHIIlow CD206high subset of lung interstitial macrophages, characterized by enhanced phagocytosis function. Our findings highlight the crucial role of Smad4 in modulating the innate immune response against tumors and provide insights into potential therapeutic strategies targeting lung interstitial macrophages to enhance anti-tumor immunity.

Cancer Prevention with Green Tea and Its Principal Constituent, EGCG: from Early Investigations to Current Focus on Human Cancer Stem Cells.

Cancer preventive activities of green tea and its main constituent, (−)-epigallocatechin gallate (EGCG) have been extensively studied by scientists all over the world. Since 1983, we have studied the cancer chemopreventive effects of EGCG as well as green tea extract and underlying molecular mechanisms. The first part of this review summarizes ground-breaking topics with EGCG and green tea extract: 1) Delayed cancer onset as revealed by a 10-year prospective cohort study, 2) Prevention of colorectal adenoma recurrence by a double-blind randomized clinical phase II trial, 3) Inhibition of metastasis of B16 melanoma cells to the lungs of mice, 4) Increase in the average value of Young’s moduli, i.e., cell stiffness, for human lung cancer cell lines and inhibition of cell motility and 5) Synergistic enhancement of anticancer activity against human cancer cell lines with the combination of EGCG and anticancer compounds. In the second part, we became interested in cancer stem cells (CSCs). 1) Cancer stem cells in mouse skin carcinogenesis by way of introduction, after which we discuss two subjects from our review on human CSCs reported by other investigators gathered from a search of PubMed, 2) Expression of stemness markers of human CSCs compared with their parental cells, and 3) EGCG decreases or increases the expression of mRNA and protein in human CSCs. On this point, EGCG inhibited self-renewal and expression of pluripotency-maintaining transcription factors in human CSCs. Human CSCs are thus a target for cancer prevention and treatment with EGCG and green tea catechins.

Biophysical Approach to Mechanisms of Cancer Prevention and Treatment with Green Tea Catechins.

Green tea catechin and green tea extract are now recognized as non-toxic cancer preventives for humans. We first review our brief historical development of green tea cancer prevention. Based on exciting evidence that green tea catechin, (−)-epigallocatechin gallate (EGCG) in drinking water inhibited lung metastasis of B16 melanoma cells, we and other researchers have studied the inhibitory mechanisms of metastasis with green tea catechins using biomechanical tools, atomic force microscopy (AFM) and microfluidic optical stretcher. Specifically, determination of biophysical properties of cancer cells, low cell stiffness, and high deformability in relation to migration, along with biophysical effects, were studied by treatment with green tea catechins. The study with AFM revealed that low average values of Young’s moduli, indicating low cell stiffness, are closely associated with strong potential of cell migration and metastasis for various cancer cells. It is important to note that treatments with EGCG and green tea extract elevated the average values of Young’s moduli resulting in increased stiffness (large elasticity) of melanomas and various cancer cells. We discuss here the biophysical basis of multifunctions of green tea catechins and green tea extract leading to beneficial effects for cancer prevention and treatment.

Engagement of αIIbβ3 (GPIIb/IIIa) with ανβ3 Integrin Mediates Interaction of Melanoma Cells with Platelets: A CONNECTION TO HEMATOGENOUS METASTASIS

A mutual relationship exists between metastasizing tumor cells and components of the coagulation cascade. The exact mechanisms as to how platelets influence blood-borne metastasis, however, remain poorly understood. Here, we used murine B16 melanoma cells to observe functional aspects of how platelets contribute to the process of hematogenous metastasis. We found that platelets interfere with a distinct step of the metastasis cascade, as they promote adhesion of melanoma cells to the endothelium in vitro under shear conditions. Constitutively active platelet receptor GPIIb/IIIa (integrin αIIbβ3) expressed on Chinese hamster ovary cells promoted melanoma cell adhesion in the presence of fibrinogen, whereas blocking antibodies to aνβ3 integrin on melanoma cells or to GPIIb/IIIa significantly reduced melanoma cell adhesion to platelets. Furthermore, using intravital microscopy, we observed functional platelet-melanoma cell interactions, as platelet depletion resulted in significantly reduced melanoma cell adhesion to the injured vascular wall in vivo. Using a mouse model of hematogenous metastasis to the lung, we observed decreased metastasis of B16 melanoma cells to the lung by treatment with a mAb blocking the aν subunit of aνβ3 integrin. This effect was significantly reduced when platelets were depleted in vivo. Thus, the engagement of GPIIb/IIIa with aνβ3 integrin interaction mediates tumor cell-platelet interactions and highlights how this interaction is involved in hematogenous tumor metastasis.

The Role of Activated Protein C in Cancer

Abstract SCI-18Activated protein C (APC) is a natural anticoagulant that blocks the amplification of the coagulation cascade via inactivation of factors Va and VIIIa. The APC/PC pathway is initiated by complex formation of thrombin, thrombomodulin (TM), and the endothelial protein C receptor (EPCR) allowing the conversion of zymogen protein C into its activated form. Based on the well-accepted view that coagulation contributes to cancer progression and that anticoagulant treatment may benefit some cancer patient groups, it has been hypothesized that the natural anticoagulant protein C pathway may also play a role in cancer progression. Interestingly, it has recently been shown that endogenous APC limits experimental metastasis of B16 melanoma cells in mouse lungs. Notably, an APC-blocking antibody dramatically increased the number of experimental lung metastasis although not due to diminished anticoagulant activity of APC but largely due to reduced APC-driven S1P1-mediated VE-cadherin-dependent vascular barrier enhancement. In line with these findings repeated administration of recombinant human APC as well as transgenic overexpression of EPCR also diminished experimental metastasis of B16 melanoma cells. It may thus be tempting to speculate that recombinant APC could be a novel treatment strategy to limit cancer progression. However, APC has however a short half-life, needs intravenous administration, and is associated with severe bleeding complications, complicating the potential clinical application of these findings. In contrast to APC, zymogen PC has a longer half-life and is associated with significantly less bleeding complications. To prove or refute the hypothesis that zymogen PC may be an attractive alternative treatment option for APC in cancer patients, we recently compared the effect of continuous overexpression of murine APC or zymogen PC in the liver by viral-mediated gene transfer in experimental metastasis. Interestingly, both APC and zymogen PC overexpression was highly effective in limiting experimental metastasis. An APC variant (APC-5A) with reduced anticoagulant but normal signaling properties did not limit experimental metastasis, whereas the protective effect of zymogen PC remained even in the absence of protease activated receptor-1 (PAR-1), which is the main mediator of APCs cytoprotective effect. Zymogen PC may thus be a novel therapeutic target to limit cancer progression. In conclusion, the natural anticoagulant APC pathway may play an important role in limiting cancer cell extravasation and interventions seeking to modulate the PC system may ultimately benefit the cancer patient. The challenge is however to confirm these findings in alternative preclinical cancer models and eventually to translate our findings into a clinical setting. Disclosures:No relevant conflicts of interest to declare.

Transcription factor Dlx2 protects from TGFβ-induced cell-cycle arrest and apoptosis

Acquiring resistance against transforming growth factor β (TGFβ)-induced growth inhibition at early stages of carcinogenesis and shifting to TGFβ's tumour-promoting functions at later stages is a pre-requisite for malignant tumour progression and metastasis. We have identified the transcription factor distal-less homeobox 2 (Dlx2) to exert critical functions during this switch. Dlx2 counteracts TGFβ-induced cell-cycle arrest and apoptosis in mammary epithelial cells by at least two molecular mechanisms: Dlx2 acts as a direct transcriptional repressor of TGFβ receptor II (TGFβRII) gene expression and reduces canonical, Smad-dependent TGFβ signalling and expression of the cell-cycle inhibitor p21(CIP1) and increases expression of the mitogenic transcription factor c-Myc. On the other hand, Dlx2 directly induces the expression of the epidermal growth factor (EGF) family member betacellulin, which promotes cell survival by stimulating EGF receptor signalling. Finally, Dlx2 expression supports experimental tumour growth and metastasis of B16 melanoma cells and correlates with tumour malignancy in a variety of human cancer types. These results establish Dlx2 as one critical player in shifting TGFβ from its tumour suppressive to its tumour-promoting functions.

Inhibition of matrix metalloproteinases related to metastasis by diosgenyl and pennogenyl saponins

Ethnopharmacological relevanceDiosgenyl and pennogenyl saponins isolated from Rhizoma Paridis, showed pro-apoptosis and immunoregulation with antitumor activity in cultured cells and animal systems. Aim of the studyTo evaluate their anti-metastatic mechanism on cancer cells and discuss their structure-activity relationship on anti-tumor effect. Materials and methodsThis research used the wound healing and migration assay to detect their anti-invasive effect on B16 melanoma cells. Through the gelatin zymography assay, immunofluorescence analysis and western blot, saponins exhibited different levels of protein expression inhibition of MMP-1, -2, -3, -9 and -14. ResultsThrough the analysis, diosgenyl and pennogenyl saponins inhibited the metastasis of B16 melanoma cells. Diosgenyl saponins also showed strong suppression of enzyme activity of MMP-2 and -9. Different saponins exhibited different levels of inhibition on MMP expression. Conclusions17-α OH increases the sensitivity of diosgenyl saponins to the membrane-bound protease which can stimulate proMMP-2 activation, but it also decreases the anti-metastatic activity of diosgenyl saponin. Furthermore, their combination might provide a potential therapeutic modality for metastasis.

Rapamycin inhibits lung metastasis of B16 melanoma cells through down‐regulating alphav integrin expression and up‐regulating apoptosis signaling

Currently available data indicate the potential application of rapamycin and its analogues in the clinic as anticancer therapeutic agents through inhibiting tumor cell growth and tumor angiogenesis. However, whether rapamycin can directly suppress tumor metastasis remains unclear. In the present study, we demonstrated that rapamycin treatment results in reduced formation of metastatic nodules in the lung by B16 cells. This is due to two mechanisms. First, the expression of alphav integrin is down-regulated by rapamycin treatment, and subsequently, the phosphorylation of focal adhesion kinase (FAK) is reduced. Second, rapamycin promotes apoptosis by up-regulating the proapoptotic molecules Bid and Bax and down-regulating Bcl-xL. Blocking the apoptosis pathway by pan-caspase inhibitor zVAD partially reversed the suppression of rapamycin in B16 metastasis. Interestingly, rapamycin up-regulates Bax and Bid in B16 cells via the S6K1 pathway and down-regulates the expression of alphav integrin via other pathway(s). In addition, our data showed that autophagy was not involved in the mechanisms of rapamycin-mediated metastasis suppression. Our findings demonstrate a potential anti-metastatic effect of rapamycin via down-regulating alphav integrin expression and up-regulating apoptosis signaling, suggesting that rapamycin might be worthy of clinical evaluation as an antimetastatic agent.

Matrix metalloproteinase inhibitor, MMI270 (CGS27023A) inhibited hematogenic metastasis of B16 melanoma cells in both experimental and spontaneous metastasis models

Matrix metalloproteinases (MMP) have been implicated in several steps of tumor metastasis, such as invasion in the extracellular matrix, intravasation, extravasation, and growth in a distant organ site. Various synthetic MMP inhibitors have been reported to suppress tumor metastasis in animal models. However, there are few reports describing which steps in the metastasis process are most critical for inhibition by MMP inhibitors. In the experimental lung colonization model by i.v. injection of mouse B16-F10 melanoma cells, we found that the daily administration of MMI270 for 2 weeks significantly decreased the number of colonies in the lung compared with the control without affecting the size of colony. Micrometastasis was monitored day 7 post-inoculation by measuring the melanin content in the lung as well as by microscopic examination of the lung tissue sections. Even only twice administrations of MMI270 on the first day after tumor injection significantly inhibited micrometastasis in the lung. In the spontaneous metastasis model using B16-BL6 melanoma cells, lung metastasis was not affected by a continuous administration of MMI270 using a mini osmotic-pump. On the contrary, when mice were subjected to popliteal lymphadenectomy on day 7 after the cell inoculation in the footpad subdermis, the continuous administration of MMI270 significantly suppressed the lung metastasis. These results suggest that the tumor cell extravasation in the target organ is the most critical step where MMPs can play their significant role in the experimental metastasis, and that the lymphatic metastasis process is less susceptible to MMI270 than the hematogenic metastasis process in the spontaneous metastasis model.

IFN-producing Killer Dendritic Cells Contribute to the Inhibitory Effect of Poly I:C on the Progression of Murine Melanoma

Toll-like receptor 3 agonist polyinosinic-polycytidilic acid (poly I:C) has been widely used as a potent adjuvant in tumor immunotherapy. In the present study, it was demonstrated that intraperitoneal injection of poly I:C could inhibit lung and liver metastasis of B16 melanoma cells in C57BL/6 mice in natural killer (NK) cells and interferon (IFN)-gamma dependent manner, leading to prolonged survival of the mice. B220 CD11c NK1.1 cells, recently defined as IFN-producing killer dendritic cells (IKDCs) were markedly increased in the spleen, lung, and liver of poly I:C-treated tumor bearing mice, compared with the control group. IFN-gamma induction by poly I:C in this unique NK cell subset indicated its critical contribution in tumor suppression in this model. Meanwhile, results of in vitro culture assay showed that poly I:C synergized with B16 cells could significantly promote IKDCs expansion in lymphocytes from different organs along with IFN-gamma production. Moreover, these ex vivo expanded IKDCs also exerted cytolytic activities against B16 cells and YAC-1 cells as conventional NK cells did. In conclusion, the findings of this study provide new insights into the role of IFN-gamma and IKDCs in the antitumor effect of poly I:C, and will possibly be helpful to explain why poly I:C may work as an adjucant to improve the antitumor effects of innate cells.

Promotion or suppression of experimental metastasis of B16 melanoma cells after oral administration of lapachol

Lapachol [2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone] is a vitamin K antagonist with antitumor activity. The effect of lapachol on the experimental metastasis of murine B16BL6 melanoma cells was examined. A single oral administration of a high toxic dose of lapachol (80–100 mg/kg) 6 h before iv injection of tumor cells drastically promoted metastasis. This promotion of metastasis was also observed in T-cell-deficient mice and NK-suppressed mice. In vitro treatment of B16BL6 cells with lapachol promoted metastasis only slightly, indicating that lapachol promotes metastasis primarily by affecting host factors other than T cells and NK cells. A single oral administration of warfarin, the most commonly used vitamin K antagonist, 6 h before iv injection of tumor cells also drastically promoted the metastasis of B16BL6 cells. The promotion of metastasis by lapachol and warfarin was almost completely suppressed by preadministration of vitamin K3, indicating that the promotion of metastasis by lapachol was derived from vitamin K antagonism. Six hours after oral administration of lapachol or warfarin, the protein C level was reduced maximally, without elongation of prothrombin time. These observations suggest that a high toxic dose of lapachol promotes metastasis by inducing a hypercoagulable state as a result of vitamin K-dependent pathway inhibition. On the other hand, serial oral administration of low non-toxic doses of lapachol (5–20 mg/kg) weakly but significantly suppressed metastasis by an unknown mechanism, suggesting the possible use of lapachol as an anti-metastatic agent.

Suppression of tumor formation in lymph nodes by L-selectin–mediated natural killer cell recruitment

Natural killer (NK) cells are known to reject certain tumors in vivo; however, the ability of NK cells to prevent metastasis of tumors into secondary lymphoid organs has not been addressed. Here, we report that in tumor-bearing hosts, NK cells are recruited to regional lymph nodes in wild-type mice, but not in mice deficient for L-selectin or L-selectin ligands. By adoptive transfer and complete Freund's adjuvant stimulation experiments, we demonstrated that L-selectin on NK cells and L-selectin ligands on endothelial cells are essential for NK cell recruitment to lymph nodes. Furthermore, freshly isolated resident lymph node NK cells lysed tumors efficiently, and metastasis of B16 melanoma cells to draining lymph nodes was suppressed in wild-type or Rag-1–deficient mice, but not when NK cells were depleted. Although L-selectin–deficient NK cells efficiently lysed tumor cells in vitro, NK cell–dependent suppression of tumor metastasis was diminished in mice deficient for L-selectin or L-selectin ligands because of insufficient NK cell recruitment to lymph nodes. Moreover, tumor metastasis was substantially inhibited in L-selectin–deficient mice reconstituted with wild-type NK cells. These findings indicate that L-selectin–mediated NK cell recruitment plays a crucial role in the control of tumor metastasis into secondary lymphoid organs.

Immunomodulatory and antitumour effects of an exopolysaccharide fraction from cultivated Cordyceps sinensis (Chinese caterpillar fungus) on tumour‐bearing mice

Cordyceps sinensis (Chinese caterpillar fungus) is a fungus parasitic on the larvae of Lepidoptera and has been considered to be a precious tonic food and herbal medicine since ancient times in China. Recently, some fungal strains have been isolated from the fruiting bodies of wild C. sinensis, and some of them have been reported to show the same properties as the natural product. In the present study, an EPSF (exopolysaccharide fraction) was prepared from cultivated C. sinensis and its effects on B16 melanoma-bearing mice were investigated. Three doses of EPSF were intraperitoneally administered every 2 days after the day of tumour-cell injection. The experiment was terminated on day 28. Phagocytosis of peritoneal macrophages and proliferation of spleen and thymus lymphocytes were assayed. The tumour metastatic foci on the lung and liver surface were checked. The expression of oncoprotein Bcl-2 in livers and lungs was assayed by a immunohistochemical method. The results showed that EPSF significantly enhanced the Neutral Red uptake capacity of peritoneal macrophages (60 mg/kg, P<0.01; 120 mg/kg, P<0.001) and spleen lymphocyte proliferation (60 mg/kg, P<0.05; 120 mg/kg, P<0.001) in B16-bearing mouse. The metastasis of B16 melanoma cells to lungs (120 mg/kg) and livers (30, 60 and 120 mg/kg) was significantly inhibited by EPSF. Moreover, EPSF decreased the levels of Bcl-2 in the lungs (120 mg/kg) and livers (30, 60 and 120 mg/kg). These results suggest that EPSF has immunomodulatory function and antitumour activity.

Suppressive effect of Zedoariae rhizoma on pulmonary metastasis of B16 melanoma cells

The inhibitory effect of Curcuma zedoaria Roscoe (WE-CZ) on experimental pulmonary metastasis of B16 melanoma cells was investigated. The intake of WE-CZ at doses of 250 and 500 mg/kg for 6 weeks from 2 weeks before tumor inoculation significantly reduced the number of metastatic surface nodules in the lung, resulting in an extended life span. When the duration of WE-CZ intake was examined, survival time was not affected by pre-intake before B16 melanoma cell inoculation and was slightly extended by post-intake after B16 melanoma cell inoculation, although the life span was prolonged by intake throughout the experiment. To address the mechanism underlying the anti-metastatic effect of WE-CZ, we examined the issue of whether WE-CZ modulated macrophage function, which is involved in killing tumor cells. The intake of WE-CZ for 6 weeks increased nitric oxide (NO) production by macrophages following stimulation with lipopolysaccharide in a dose-dependent manner. The elevated NO was found to serve as a cytotoxic mediator against B16 melanoma cells in co-culture with macrophages. On the contrary, B16 melanoma-conditioned medium reduced NO production by macrophages. However, WE-CZ treatment significantly reversed the reduction in NO production by the conditioned medium. These findings indicate that WE-CZ possesses anti-migratory effects on B16 melanoma cells and that the macrophage function-modulating activity by WE-CZ appears to underlie its anti-metastatic activity, which leads to a decrease in the number of lung metastatic surface nodules and the extension of life span. These results suggest that WE-CZ may play important roles in the inhibition of cancer metastasis.

Inhibition of lung metastasis of B16 melanoma cells exposed to blue light in mice

The effects of blue light on B16 melanoma cells and on the metastasis of these cells to the lungs were investigated in mice. The exposure of B16 melanoma cells to blue light in two 20-min sessions resulted in marked suppression of cell growth measured at 7 days after exposure. When these cells were harvested, re-inoculated into medium and incubated for a further 7 days, their growth activity returned to almost the same level as that of cultured cells from the non-exposure control group. The melanoma cells harvested after 7 days of incubation were injected intravenously into mice. In the non-exposure group, black nodules developed on the lung surface and the nodules increased in size over time. In the blue-light-exposure group, the development of such black nodules on the lung surface was delayed, and the nodules were smaller. Histopathological examination revealed that blue light suppressed the growth of metastatic tumor cells, and no increase in the number of melanin-containing cells or atypical cells was induced in the metastatic lesions. These results suggest that blue light suppresses the metastasis of B16 melanoma cells.

Suppressive effect of Shichimotsu-koka-to (Kampo medicine) on pulmonary metastasis of B16 melanoma cells.

Shichimotsu-koka-to (SKT) is a Kampo (traditional Japanese herbal) medicine, which is used in Japan to treat hypertension and atherosclerosis. We investigated the inhibitory effect of SKT on experimental pulmonary metastasis of B16 melanoma cells. The intake of SKT at a dose of 430 mg/kg for 6 weeks from 2 weeks before tumor inoculation significantly reduced the number of metastatic surface nodules in the lung and extended the life span. When the duration of SKT intake was examined, survival time was not affected by preintake before B16 melanoma cell inoculation and was slightly extended by postintake after B16 melanoma cell inoculation, although the life span was prolonged by intake throughout the experiment. To address the mechanism underlying the antimetastatic effect of SKT, we studied whether SKT modulated macrophage function, which is involved in killing tumor cells. The intake of SKT for 6 weeks dose dependently increased nitric oxide (NO) production by macrophages following stimulation with lipopolysaccharide. The elevated NO was found to serve as a cytotoxic mediator against B16 melanoma cells in co-culture with macrophages. On the contrary, B16 melanoma-conditioned medium reduced NO production by macrophages. However, SKT treatment reversed the reduction in NO production by the conditioned medium significantly. These findings may suggest that macrophage function-modulating activity by SKT appears to underlie its antimetastatic activity, which leads to a decrease in the number of lung metastatic surface nodules and the extension of life span.

Antimetastatic activity of acteoside, a phenylethanoid glycoside.

We examined the antimetastatic effect of acteoside, a phenylethanoid glycoside widely distributed in the plant kingdom, on lung metastasis using a mouse model injected with B16 melanoma cells intravenously. Male C57BL/6 mice were injected intravenously with 2 x 10(5) of B16 melanoma cells, while acteoside at a dose of 50 mg/kg was administered intraperitoneally every other day from 13 d before B16 melanoma cell injection until all mice had succumbed to the metastatic tumor burden in the lung. Administration of acteoside prolonged survival time significantly and the average survival time was 63.3 +/- 3.4d compared with 52.1 +/- 2.5d in control mice. This result suggests that acteoside showed suppressive effect on lung metastasis of B16 melanoma cells.

An attempt to isolate genes responsible for spontaneous and experimental metastasis in the mouse model.

Cancer develops and progresses as genetic alterations occur subsequently. Onset process of cancer has become well understood in some types of cancer, such as colorectal cancers. In this process, responsible alterations were identified in numbers of oncogenes such as k-ras, and tumor suppressor genes such as p53, as Vogelstein proposed earlier in the multistage carcinogenesis theory. In contrast, our understanding remains short to draw such an adequate diagram for the process during which cancer becomes more malignant, i.e., metastatic. To examine the molecular basis for this progression step, mouse metastasis models have been established where tumor cell lines are inoculated into mice and metastasize to specific organs. The model using B16 melanoma cells is one of the most developed. BL6 subline, one of the most metastatic, was obtained from F10 subline simply through six rounds of in vitro selection. Nonetheless, BL6 cells metastasize lungs much more heavily than F10 cells when injected subcutaneously. The difference in gene expression between the two sublines is considered rather small but relevant for spontaneous metastasis. We began our research by elaborating a method for the construction of subtracted cDNA libraries, and made it applicable to BL6 and F10 cells. As a result, we were able to isolate a couple of genes that were expressed differently between the two sublines. As might be expected, each of the genes appeared to play a role more or less in distinct aspects of spontaneous metastasis of B16 melanoma cells. Moreover, similar roles were expected for the genes in the process by which human melanoma cells metastasize.

Perforin-dependent NK cell cytotoxicity is sufficient for anti-metastatic effect of IL-12.

IL-12 exerts a potent anti-tumor effect, which is possibly mediated by multiple mechanisms including activation of NK and NKT cells, induction of cytotoxic T lymphocytes, and inhibition of angiogenesis. In the present study, we characterized the cytotoxic effector cells and mechanisms responsible for the anti-metastatic effect of IL-12. Administration of IL-12 had a comparable inhibitory effect on experimental lung metastasis of B16 melanoma cells in wild-type C57BL/6 mice and RAG-2-/- mice that lack T and NKT cells, which was abolished by depletion of NK cells. Cytotoxic activity of liver and splenic mononuclear cells against B16 was induced by IL-12 administration in RAG-2-/- mice at a level comparable to that in wild-type mice, which was also abolished by depletion of NK cells. Moreover, the anti-metastatic effect of IL-12 was abrogated by perforin deficiency, but not by Fas ligand deficiency, in association with a lack of IL-12-induced cytotoxic activity of liver and splenic mononuclear cells against B16. These results suggest that perforin-dependent cytotoxicity of IL-12-activated NK cells is sufficient for the anti-metastatic effect of IL-12.

Effect of restraint stress on immune system and experimental B16 melanoma metastasis in aged mice

An overnight restraint stress was given to young and old mice and its effect was examined in terms of the number and function of T cells and natural killer (NK) cells in spleen and patterns of lung metastasis of B16 melanoma cells. A great decrease was observed in the number and proliferative activity of splenic T cells in old mice after the stress. The decrease in young mice was rather temporary with a quick recovery. The number of NK cells in spleen was not different between young and old mice before giving the stress, but a significant decrease was observed in the old after the stress. NK activity was always much lower in old than in young throughout the experiment. The pattern of metastasis of B16 melanoma cells was different between young and old mice. Metastatic colonies in lungs were larger in number and bigger in size in young mice than in old mice. After the stress, the number increased and the size unchanged in old mice, while the size increased and the number remained unchanged in young mice. It was shown that the same restraint stress resulted in a more serious influence on the immune cells in old than in young mice and gave rise to a differential effect on the pattern of tumor metastasis between young and old mice.