Expression of metastatic potential of tumor cells in young nude mice is correlated with low levels of natural killer cell-mediated cytotoxicity

Characterization of mouse natural killer cell activating factor (NKAF) induced by OK-432: evidence for interferon- and interleukin 2-independent NK cell activation

The bacterial immunopotentiator OK-432 induced natural killer cell activating factor (NKAF) from mouse spleen cells. OK-432-induced NKAF showed a single peak with an apparent mol. wt of 70 Kd by Sephadex G-100 chromatography and OK-432-induced interleukin 2 (IL-2) had the same mol. wt as NKAF. However, OK-432-induced interferon (IFN) showed molecular heterogeneity with two peaks at 90 Kd and 45 Kd. Further purification was achieved by Blue Sepharose affinity chromatography which copurified NKAF and IFN. The affinity-purified NKAF, however, was stable to heat (56 degrees C) and acid (pH 2) treatments. Moreover, anti-IFN failed to abolish NKAF activity and this activity was not absorbed by IL-2 dependent T cells. From isoelectric focusing analysis, a dissociation of NKAF and IFN was observed over the range of pI 6.5 to 8.0. Based on these results, KNAF appears to be a new kind of cytokine distinguishable from IFN and IL-2.

Prospective study of natural cytotoxicity in peripheral blood of patients with nonlymphoid solid malignancies

Natural killer (NK) cells have been implicated as an initial immunosurveillance mechanism for carcinogenesis in humans. Work in the murine system as well as the findings of depressed NK activity in patients with advanced malignancies and the discovery of increased incidences of cancer in humans congenitally deficient in NK ability have supported this. Few prospective studies have demonstrated a prognostic change in NK activity with respect to malignant disease course. In 32 healthy donors, NK activity against K562 was determined. No race or sex difference existed with respect to NK cell function. Esophageal (5), bronchogenic (3), breast (3), cervical (3), and endometrial (1) cancer patients who had received no prior chemotherapy were compared to controls. All patients subsequently received radiotherapy. Prior to such treatment NK activity could not be associated with stage of malignancy. Of the 15 patients studied, 11 were sequentially followed. Five of eight patients with stable or improving clinical courses as assessed by weight and Karnofsky scores were found to have increasing NK activity. Two of three patients with poor clinical courses presented with subnormal killing which never rose to normal while the third declined to subnormal before expiring. Esophageal, cervical, and endometrial carcinoma patients all presented with low or subnormal NK activity. Of these, only cervical and endometrial cancer patients exhibited an increase to normal levels.

Considerations in the use of nude mice for cancer research

Transplants of human tumors in nude mice have shown a progressive increase during the past 15 years as an experimental model for cancer research. A variety of factors, including relatively fragile health, have been identified that require appropriate experimental controls if the investigator is obtain consistent results. Not all tumors grow in nude mice. The frequency of tumor 'take' varies according to tumor origin, tumor type, inoculation site, age and conditioning of the mouse host, and a variety of other factors. Manipulation of these variables has led to successful propagation of almost every known variety of human malignancy. Following transplant, changes in characteristics have been documented, but the frequency and degree of such changes remains uncertain. Tumor growth rate probably increases after transplantation, requiring great care in the interpretation of chemotherapy experiments, but biochemical characteristics may be more stable. The nude mouse offers great interest as a model for the in vivo study of metastasis, as a number of experimental variables, mainly immunological, have been shown to affect this process. Spontaneous tumors have been shown to arise in these animals, but the controversy over their frequency relative to the thymus-bearing background strain is unresolved. We conclude that the nude mouse/tumor xenograft model, while requiring meticulous experimental controls, is nevertheless an extremely useful tool for cancer research.

Analysis of metastatic spread and growth of tumor cells in mice with depressed natural killer activity by anti-asialo GM1 antibody or anticancer agents

The mechanism of artificial and spontaneous metastases of tumor was analyzed in B16 melanoma cells and C57BL/6 mice by using anti-asialo GM1 antibody and anticancer agents. Single administrations of 500 micrograms anti-asialo GM1 antibody resulted in significantly decreased NK activity in spleen cells of C57BL/6 mice, lasting 10 days from the day following administration. Treatment with anti-asialo GM1 antibody never decreased the function of T lymphocytes measured by blastogenesis with phytohemagglutinin or T cell growth factor. The tumoricidal functions of activated macrophages but not of resident macrophages were decreased by in vivo treatment with anti-asialo GM1 antibody. The anti-asialo GM1 antibody was evaluated in terms of the enhancing effect on pulmonary metastases with regard to the timing of administration. Treatment with anti-asialo GM1 antibody 1 day before or on the day of tumor inoculation resulted in a substantial increase in the number of artificial pulmonary metastases. In the experimental system of spontaneous metastases, anti-asialo GM1 antibody most effectively increased the number of pulmonary metastases when administered 1-2 weeks before the removal of primary tumor, when the tumor cells are thought to be released into blood circulation from the primary site. In addition, accelerated growth of transplanted tumors at the primary site was observed in mice treated with anti-asialo GM1 antibody. These results strongly suggest that anti-asialo GM1 antibody enhances the incidence of in vivo tumor metastases and the growth of transplanted tumor mainly by suppressing the function of NK cells. The maximum effective dose (MED) of mitomycin C or its derivative (M-83) suppressed NK activity significantly, and pretreatment with these anticancer agents enhanced the growth of the artificial pulmonary and liver metastases. In contrast, the MED of cDDP showed no effect on the NK activity or the numbers of pulmonary and liver metastases. These results indicate that the depression of NK activity induced by chemotherapy results in the promotion of metastatic disease. From these studies it can be concluded that NK cells have a key role in the control of metastases of malignant disease, and that support of NK activity is very important for the prevention of metastases.

Cell surface molecules and tumor metastasis. Regulation of metastatic phenotypic diversity

Metastatic tumor cells are characterized by quantitative alterations in cell surface and other properties that confer to these cells their abilities to invade, disseminate, implant, survive and grow at secondary sites. Metastasis is also determined by a variety of host factors that prevent, allow or even stimulate metastatic processes. The emergence of diversified cell subpopulations in malignant tumors insures that some cells will ultimately become highly metastatic, resulting in tumor progression towards characteristics which are the most favorable for survival and growth. Unknown mechanisms appear to stimulate and then to control phenotypic diversification of tumor cell subpopulations. These mechanisms may be altered by genetic (mutational) and/or epigenetic (non-mutational) modifications that individually influence cells within a malignant neoplasm.

The experimental and clinical implications of cellular heterogeneity in malignant tumors

The growing body of evidence showing that malignant tumors are heterogeneous and contain diverse subpopulations of tumor cells is reviewed, with particular emphasis being given to the presence of tumor-cell subpopulations with differing metastatic properties. The factors that may influence the evolution of cellular diversity at different stages in the progression of malignant neoplasms are discussed. Emphasis is given to the possibility that interactions occurring amongst the constituent subpopulations of a malignant tumor may influence the rate at which new variant subpopulations emerge. Metastatic heterogeneity poses significant problems for experimental efforts to identify features unique to metastatic cells and also for the therapy of metastatic disease.

Murine non-lymphoid tumors are lysed by a combination of NK and NC cells

Natural cell-mediated cytotoxicity (NCMC) against a variety of tumor targets is mediated by a heterogeneous group of effector cells with the natural killer (NK) and natural cytotoxic (NC) cells being the predominant prototypes in mice. This report shows that non-lymphoid tumor targets, mostly derived from chemically induced fibrosarcomas, are susceptible to either (1) NK-mediated lysis with all the activity being the function of a poly-IC augmentable Qa-5+ effector cell; (2) NC-mediated lysis with all activity being the function of a Qa-5- cell not augmented by poly-IC; and (3) a combination of NK-and NC-mediated lysis with activity being the function of both Qa-5+ and Qa-5- cells, the NK (Qa-5+) augmented by poly-IC. These studies further support the view that murine NC and NK cells are distinct and collectively make up the NCMC system, and also that the previous association of NK cells with lymphoid tumor lysis and NC cells with non-lymphoid tumor lysis is not a valid one.

The role of natural killer cells in the intravascular death of intravenously injected murine tumour cells

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Studies of the thymus in mice bearing the Lewis lung carcinoma. II. Modulation of thymic natural killer activity by thymulin (FTS-Zn) and the antimetastatic effect of zinc

Modulation of thymic natural killer (NK) cell activity by the serum thymic factor (thymulin or FTS-Zn) was demonstrated in mice carrying the Lewis lung carcinoma (3LL). Thymulin decreased the increased NK activity found in amputated (tumor) tumor-bearing mice and induced a significant NK activity in nonamputated mice, normally devoid of such activity. Zinc had no effect in either case. Histological studies revealed that zinc prevented the tumor-induced thymic atrophy. A clear-cut decrease in the number of lung metastases was observed in zinc-treated mice. This effect was suppressed by concomitant administration of thymulin to amputated mice. The thymic dependency of the anti-metastatic action of zinc as well as the mode of action of thymulin on NK cell activity in tumor-bearing animals is discussed.

Studies of the thymus in mice bearing the Lewis lung carcinoma. I. Thymic natural killer cell activity in 3LL tumor-bearing mice

Natural killer (NK) cell activity of spleen and thymus was studied in Lewis lung carcinoma (3LL)-bearing mice. A high level of hydrocortisone-sensitive NK cell cytotoxicity was found in the thymus after excision of the primary tumor, but not in nonamputated mice. Conversely, splenic NK cell activity was diminished in nonamputated tumor-bearing mice and remained unmodified in amputated tumor-bearing mice. Excision of the primary tumor prevented tumor-induced thymic atrophy and splenomegaly. Histological study of the thymus revealed the presence of metastatic cells within the cortex. These data suggest that NK cells or their precursors are present in the thymus and can be triggered or unmasked in situ by tumor cells migrating from the primary tumor.

Inhibition of experimental and spontaneous lung metastases of highly metastatic Syrian hamster sarcoma cells by non-activated bone marrow and peritoneal exudate cells

The possibility of inhibiting local tumor growth (experimental and spontaneous lung metastases) of the selected highly-metastatic Syrian hamster sarcoma of STHE-LM8 subline by means of non-activated syngeneic and allogeneic spleen, bone marrow (BMC) and peritoneal exudate (PEC) cells was studied. Retroorbital inoculation of Syrian hamsters with native, or lethally irradiated allogeneic BMC and PEC, but not spleen cells, or hamster embryo cells effectively inhibited the development of experimental and spontaneous lung metastases induced by STHE-LM8 cells in the animals. Spontaneous lung metastases were effectively inhibited in about 50% of STHE-LM8 tumor-bearing animals (with or without tumor excision) inoculated with BMC five times at 5- to 7-day intervals beginning from 1-10 days after subcutaneous palpable tumor appearance. Experimental lung metastases were inhibited in 20-80% of animals inoculated with BMC or PEC once 5-7 days before the tumor cells, simultaneously with them, or during the 5-7 days following the inoculation of tumor cells, thus demonstrating that BMC metastasis-inhibiting activity was expressed during 10-14 days against single tumor cells, or small clusters of tumor cells, and was not effective at the stage of micro-, or macrometastasis formation. BMC and PEC of normal allogeneic donors were significantly more active in metastasis inhibition than the same cells of tumor-bearing animals. BMC of inbred normal Syrian hamsters of the ICV line were significantly less active, or did not inhibit experimental lung metastases either in syngeneic or in random-bred allogeneic hamsters, thus apparently demonstrating an unknown genetic defect of their NR system.

Natural killer cell activity and spontaneous development of lymphoma. Effects of single and multiple injections of interferon into young and aged C57BL/6 mice

The capacity of interferon (IFN) given once or repeatedly to augment natural killer (NK) cell activity in the spleen was tested in young and aged C57BL/6 mice. Multiple injections of 10(4) u IFN i.p. into 3-month-old or 12-month-old mice did not augment cytotoxicity mediated by NK cell activity; rather it reduced this activity in relation to the effect obtained with a single injection. When T and B cells or macrophages were removed in vitro, no restoration of NK-cell activity, and therefore no suppressor cells, could be found in this system. In a long-term experiment, B6 mice were chronically injected with 10(4) u of IFN or mock-IFN from 5 months of age until death. No difference in the modification of NK-cell activity was observed after IFN and mock-IFN, regardless of the duration of treatment. However, the capacity of spleen cells to generate cytotoxic T cells after allogeneic stimulation in vitro or in vivo was increased in IFN-treated mice. The median survival time was improved by 7 weeks through treatment with IFN compared to mock-IFN, but was reduced by 9 weeks compared to the survival after treatment with saline. No significant difference in the incidence of spontaneous lymphoma resulted from IFN treatment, but the percentage of tumors observed in mice receiving mock-IFN (68.1%) was higher than that in mice receiving saline (44.1%). These results indicate that, while a stimulating effect resulting in a delay in mortality and in tumor development can be attributed to IFN itself, the contaminating antigenic products are plausibly responsible for the deleterious effect of the total preparation.

Susceptibility of human ocular melanoma cells to spontaneous and interferon-augmented natural cytotoxicity

Due to the current interest in natural killer (NK) cells as a host defence mechanism against neoplasia, we have investigated the susceptibility of short-term cultures of human ocular melanoma cells to spontaneous and interferon (IFN)-augmented natural cytotoxicity. Cultures of ocular melanoma cells were readily established and identified as bipolar and multipolar pigmented melanoma cells. In short-term cytotoxicity assays these cell lines demonstrated a weak susceptibility to spontaneous human PBL natural cytotoxicity, and increased killing was observed using IFN-augmented cytotoxic effector cells. These findings may be pertinent in relation to the role of NK cells in vivo.

Metastasis of a human pancreatic adenocarcinoma (RWP-1) in nude mice

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Natural killer (NK) activity in peripheral blood lymphocytes of patients with benign and malignant breast disease

Previous studies of natural killer (NK) activity in the peripheral blood of breast cancer patients have failed to show a reduction in cytotoxicity, an observation at variance with results obtained in other malignancies. Interpretation of the data however is complicated by the presence of treated and post-mastectomy patients in the groups studied.In this study, lymphocytes from preoperative blood samples of untreated women with benign and malignant breast disease were tested at various effector-to-target ratios for cytotoxicity activity against the NK sensitive erythromyeloid cell line, K562.A significant reduction in NK activity was observed between carcinoma patients and the control group (P=0·02). When the carcinoma group was further divided into pre- and postmenopausal patients, the reduction was found to be a feature only of premenopausal women (P=0·002). The levels of NK activity in patients with benign breast disease were not significantly different from those in controls, irrespective of menstrual status. There was no correlation between NK activity and tumour size, oestrogen-receptor or lymph-node status in the carcinoma patients.A preliminary analysis of NK activities in the control group suggests that women donating blood in the first half of their menstrual cycle show significantly reduced NK activity in comparison with those in the second half (P=0·001). This finding, coupled with the variation in NK activity shown between pre- and postmenopausal breast carcinoma patients, suggests that hormonal effects in conjunction with malignancy determine the level of NK activity in breast cancer.

Environmental and genetic factors determine the level of NK activity of nude mice and affect their suitability as models for experimental metastasis

In these studies we have evaluated the effects of age, genetic background, and housing conditions on the NK-cell activity of nude mice measured in vitro and resistance to tumor metastasis in vivo. BALB/cAnN nude mice exhibited lower levels of NK-cell-mediated cytotoxicity than age-matched N:NIH(S) nude mice maintained under similar housing conditions. The stronger response of N:NIH(S) nude mice was observed also after experimental activation of NK cells by Corynebacterium parvum. Nude mice maintained under barrier conditions have weaker NK-cell activity than mice maintained under conventional conditions. The incidence of experimental pulmonary metastases of allogeneic tumors injected into nude mice was inversely correlated with the levels of NK-cell-mediated cytotoxicity. Thus, 3-week-old BALB/cAnN nude mice raised under barrier conditions were more sensitive to development of experimental metastasis than age-matched N:NIH(S) nude mice maintained under barrier conditions or nude mice of either strain maintained under conventional conditions. In both strains, however, the relative differences in metastatic potential among the tumor cell lines observed in syngeneic recipients were maintained. We conclude that young BALB/cAnN nude mice raised under barrier conditions may provide a valuable in vivo model for studying metastasis of neoplasms.

Role of NK cells in the control of metastatic spread and growth of tumor cells in mice

The ability of BALB/c nude and C57BL/6 mice to eliminate tumor cells from the blood stream was severely impaired after a single inoculation of 0.2 ml of anti-asialo BMI (asGMI) serum, diluted 1:40 to 1:320. The number of i.v.-inoculated YAC-I cells surviving in the lungs of BALB/c nude mice pretreated with anti-asGMI serum was 28 times higher than in the control nude mice. In this respect, nude mice treated with anti-asGMI behaved similarly to beige mice. The increase in the initial survival of tumor cells in the mice that was induced by pre-treatment with anti-asGMI resulted in a substantial increase in the number of artificial lung metastases that developed. In C57BL/6 +/+ mice treated with anti-asGMI and in C57BL/6 beige mice, i.v. inoculation of B16 melanoma cells induced 10 times more metastatic foci in the lungs than in the control C57BL/6 +/+ mice. In contrast, in nude mice which possess higher levels of NK reactivity, metastatic growth was suppressed 7-fold in comparison with intact C57BL/6 +/+ mice. In beige mice and in C57BL/6 +/+ mice treated with anti-asGMI, multiple metastatic foci developed in the liver, whereas in control C57BL/6 +/+ and nude mice, no extrapulmonary metastases were found. These data indicate that B16 melanoma cells are able to grow in the liver, but their growth is ordinarily prevented by NK cells. The antimetastatic defense of C57BL/6 mice treated by anti-asGMI could be restored by transplantation of 40 X 10(6) normal spleen cells. This antimetastatic effect of transplanted spleen cells was mediated by asGMI-bearing cells, since after in vitro pre-treatment of normal spleen cells with anti-asGMI and complement, they lost their ability to inhibit the development of artificial metastases in the lungs of C57BL/6 mice. Suppression of NK reactivity by multiple injections of anti-asGMI (every 4 to 5 days), in C57BL/6 mice inoculated intrafootpad (i.f.p.) with B16 melanoma or 3LL tumor cells, did not influence the growth of local tumors, but dramatically accelerated the development of spontaneous pulmonary metastases. These data demonstrate that NK cells may play an important role in resistance to the dissemination of tumor cells, and therefore contribute to the control of metastasis formation in mice.

Experimental systems for analysis of the malignant phenotype

Identification of the cellular and subcellular alterations responsible for the metastatic behavior of malignant tumor cells and development of reliable screening programs for detecting new therapeutic agents for improved treatment of metastatic disease both depend crucially on the availability of experimental systems that can serve as relevant models of human cancer. Recent advances in our understanding of the pathogenesis of cancer metastasis have raised serious doubts about the usefulness of many of the experimental approaches that have long been used in the study of metastasis. Recent findings showing that metastases are caused by specific subpopulations of metastatic tumor cells, and that not all cells in a malignant primary tumor possess metastatic properties, are of profound importance for experimental efforts to understand the mechanism of metastatic phenotype among cells from the same tumor means that the traditional, and widely used, approach of analyzing primary tumors and cultured cell lines containing multiple, phenotypically heterogeneous, subpopulations of cells may provide little or no insight into the properties of the metastatic subpopulations, particularly if they represent only a minor fraction of the entire population. Similarly, the practice of screening potential therapeutic modalities for their ability to reduce the mass and/or growth rate of a primary tumor may be inadequate in predicting the responsiveness of metastatic lesions. Solution of these problems requires that new methods must be devised to isolate and characterize the specific subpopulations of tumor cells endowed with metastatic potential. In addition, knowledge of how the extraordinary phenotypic diversity found in tumor cell subpopulations from the same tumor is generated and how subpopulation diversity is regulated during progressive growth of both the primary tumor and its metastases are of fundamental importance if we are to design meaningful experimental systems for studying the metastatic process. This article reviews our current understanding of these complex issues and their implications for the experimental analysis of the malignant phenotype. The merits and shortcomings of different experimental systems are discussed in detail together with the identification of areas in which new experimental strategies and models are now needed.'

Role of natural killer cells in control of cancer metastasis

There is a close association between levels of natural killer (NK) cell activity and the ability of the host to eliminate circulating tumor cell emboli. Mice that exhibit low levels of NK-cell-mediated cytotoxicity (3-week-old syngeneic mice, 3-week-old allogeneic nude mice, cyclophosphamide- or beta-estradiol-treated mice, and beige mice) also exhibit enhanced survival of tumor cells in the vascular bed of the lung and increased incidence of pulmonary tumor metastasis. Conversely, hosts with high NK cell activity (adult nude mice and syngeneic mice treated with NK-cell-stimulating biological response modifiers (BRM) ) are very resistant to metastasis. Lymphoid adoptive transfer studies have shown that the effector cell responsible for the antimetastatic activity is the NK cell. In these studies, NK cells were highly effective in destroying circulating tumor cells before their extravasation into the organ parenchyma, whereas they exerted only a minimal inhibiting effect on already established micrometastases. The ability to activate NK cells selectively (without subsequently inducing suppressor macrophages) provides a valuable tool for the evaluation of the role of activated NK cells in therapy of tumor metastasis. The validity of this approach is supported by the finding that NK cells activated by BRM are effective in killing, both in vivo and in vitro, solid tumor cells that developed NK-cell-resistance as a result of adaptive growth in vivo or selection during the metastatic process. An understanding of the mechanisms that regulate NK cell activation or suppression as well as elucidation of the circulatory patterns and anatomical compartmentalization of activated NK cells will help achieve a sustained systemic and/or in situ activation of NK cells which may prove effective in the control of cancer metastasis.

Natural killer cells: their roles in defenses against disease

Natural killer cells are a recently discovered subpopulation of lymphoid cells that are present in most normal individuals of a range of mammalian and avian species. Natural killer cells have spontaneous cytolytic activity against a variety of tumor cells and some normal cells, and their reactivity can be rapidly augmented by interferon. They have characteristics distinct from other types of lymphoid cells and are closely associated with large granular lymphocytes, which comprise about 5 percent of blood or splenic leukocytes. There is increasing evidence that natural killer cells, with the ability to mediate natural resistance against tumors in vivo, certain virus and other microbial diseases, and bone marrow transplants, may play an important role in immune surveillance.