Enhancement by drugs of metastatic lung nodule formation after intravenous tumour cell injection

Efecto bimodal de la ciclofosfamida en la terapia antineoplásica

La Ciclofosfamida (Cy) es el agente alquilante más utilizado en el tratamento quimioterápico de diversas neoplasias humanas; habitualmente se la administra em combinación con otros citostáticos para lograr una mayor eficacia terapêutica. La mayoría de los protoeolos clínicos la emplean en dosis altas y suministrada en repetidas ocaciones a lo largo del tratamento antineoplásico, con Ias ya conocidas acciones colaterales, entre ellas la inmunodepresión. Sin embargo, en diferentes modelos experimentales en animales portadores de un tumor, la administración de uma dosis única y relativamente baja en un determinado momento de la respuesta inmune antitumoral, produce inmunopotenciación, a través de una inhibieión selectiva sobre los linfocitos T supresores. Posteriormente se demostró un efecto interesante y novedoso de éstas dosis bajas de Cy: su acción preferencial sobre células tumorales com fenotipo metastásico (probablemente debido a una inmunomodulación selectiva sobre dichas subpoblaciones celulares), ya que se observo una inhibieión total en la formación de Ias metástasis sin afectar el desarrollo dei tumor primário. Estos resultados senalan el efecto bimodal de la Cy sobre el sistema inmune dei huésped cuando se la utiliza en el tratamiento antineoplásico em diferentes dosis y esquemas de administración. La utilización de sustancias naturales denominadas “modificadores de la respuesta biológica”, ha derivado en lo que se conoce como cuarta modalidad terapêutica contra el cáncer. Se propone que la Cy sea considerada también dentro de ese contexto.

DCBLD2 Mediates Epithelial-Mesenchymal Transition-Induced Metastasis by Cisplatin in Lung Adenocarcinoma

Growing evidence suggests that cisplatin and other chemotherapeutic agents promote tumor metastasis while inhibiting tumor growth, which is a critical issue for certain patients in clinical practices. However, the role of chemotherapeutics in promoting tumor metastasis and the molecular mechanism involved are unclear. Here, we investigated the roles of cisplatin in promoting tumor metastasis in lung adenocarcinoma (LUAD). We demonstrated that cisplatin promoted epithelial-mesenchymal transition (EMT), cell motility, and metastasis in vitro and in vivo. The bioinformatic analysis and molecular biology approaches also indicated that DCBLD2 (Discoidin, CUB and LCCL domain containing 2) is a key gene that mediates cisplatin-induced metastasis. DCBLD2 stabilizes β-catenin by phosphorylating GSK3β and transporting accumulated β-catenin to the nucleus to promote the expression of EMT-related transcriptional factors (TFs), ultimately resulting in tumor metastasis. We also identified that cisplatin enhanced DCBLD2 expression by phosphorylating ERK and hence the AP-1-driven transcription of DCBLD2. Furthermore, DCBLD2-specific siRNAs encapsulated by nanocarriers prominently inhibit cisplatin-induced metastasis in vivo. Therefore, DCBLD2 plays a key role in cisplatin-induced metastasis in LUAD and is a potential target for preventing chemotherapy-induced metastasis in vivo.

The Kraken Wakes: induced EMT as a driver of tumour aggression and poor outcome

Epithelial mesenchymal transition (EMT) describes the shift of cells from an epithelial form to a contact independent, migratory, mesenchymal form. In cancer the change is linked to invasion and metastasis. Tumour conditions, including hypoxia, acidosis and a range of treatments can trigger EMT, which is implicated in the subsequent development of resistance to those same treatments. Consequently, the degree to which EMT occurs may underpin the entire course of tumour progression and treatment response in a patient. In this review we look past the protective effect of EMT against the initial treatment, to the role of the mesenchymal state, once triggered, in promoting disease growth, spread and future treatment insensitivity. In patients a correlation was found between the propensity of a treatment to induce EMT and failure of that treatment to provide a survival benefit, implicating EMT induction in accelerated tumour progression after treatment cessation. Looking to the mechanisms driving this detrimental effect; increased proliferation, suppressed apoptosis, stem cell induction, augmented angiogenesis, enhanced metastatic dissemination, and immune tolerance, can all result from treatment-induced EMT and could worsen outcome. Evidence also suggests EMT induction with earlier therapies attenuates benefits of later treatments. Looking beyond epithelial tumours, de-differentiation also has therapy-attenuating effects and reversal thereof may yield similar rewards. A range of potential therapies are in development that may address the diverse mechanisms and molecular control systems involved in EMT-induced accelerated progression. Considering the broad reaching effects of mesenchymal shift identified, successful deployment of such treatments could substantially improve patient outcomes.

Prodding the Beast: Assessing the Impact of Treatment-Induced Metastasis

The arsenal of treatments for most cancers fit broadly into the categories of surgery, chemotherapy, radiation, and targeted therapy. All represent proven and successful strategies, yet each can trigger local (tumor) and systemic (host) processes that elicit unwanted, often opposing, influences on cancer growth. Under certain conditions, nearly all cancer treatments can facilitate metastatic spread, often in parallel (and sometimes in clear contrast) with tumor reducing benefits. The paradox of treatment-induced metastasis (TIM) is not new. Supporting preclinical studies span decades, but are often overlooked. With recent evidence of prometastatic effects following treatment with targeted agents blocking the tumor microenvironment, a closer inspection of this literature is warranted. The TIM phenomena may diminish the impact of effective therapies and play a critical role in eventual resistance. Alternatively, it may simply exemplify the gap between animal and human studies, and therefore have little impact for patient disease and treatment. This review will focus on the preclinical model systems used to evaluate TIM and explore the mechanisms that influence overall treatment efficacy. Understanding the role of TIM in established and emerging drug treatment strategies may help provide rationales for future drug combination approaches with antimetastatic agents to improve outcomes and reduce resistance.

The Role of TLR4 in Chemotherapy-Driven Metastasis

Tumor resistance to cytotoxic drugs is one of the main obstacles to successful cancer therapy. Emerging evidence suggests that chemoresistance is promoted by substances released from dead and damaged cells that activate the host repair program orchestrated by Toll-like receptor-4 (TLR4). TLR4 is often overexpressed in malignant and tumor-infiltrating immune cells. In addition to endogenous ligands released by therapy-induced tumor destruction, TLR4 is directly activated by paclitaxel, one of the most commonly used chemotherapeutic drugs against various human cancers. TLR4 activation promotes local and systemic inflammation, leading to induction of multiple circuits that create a regenerative environment favoring local recurrence and metastasis. Of particular importance is TLR4-mediated recruitment of endothelial progenitors derived from immature myeloid cells. These cells play a major role in rebuilding tumor-associated lymphatic and blood vessels, thereby promoting lymphatic and hematogenous metastasis. The latter is further enhanced by the premetastatic niche generated by mobilization of myeloid provascular cells to distant organs. This review summarizes the recent evidence demonstrating that paclitaxel and other clinically used anticancer drugs actively induce metastasis even while shrinking the primary tumor. Better understanding of the mechanisms underlying TLR4-dependent chemotherapy-driven metastasis might be the key to overcoming challenges of cancer eradication.

Cyclophosphamide creates a receptive microenvironment for prostate cancer skeletal metastasis

A number of cancers predominantly metastasize to bone, due to its complex microenvironment and multiple types of constitutive cells. Prostate cancer especially has been shown to localize preferentially to bones with higher marrow cellularity. Using an experimental prostate cancer metastasis model, we investigated the effects of cyclophosphamide, a bone marrow-suppressive chemotherapeutic drug, on the development and growth of metastatic tumors in bone. Priming the murine host with cyclophosphamide before intracardiac tumor cell inoculation was found to significantly promote tumor localization and subsequent growth in bone. Shortly after cyclophosphamide treatment, there was an abrupt expansion of myeloid lineage cells in the bone marrow and the peripheral blood, associated with increases in cytokines with myelogenic potential such as C-C chemokine ligand (CCL)2, interleukin (IL)-6, and VEGF-A. More importantly, neutralizing host-derived murine CCL2, but not IL-6, in the premetastatic murine host significantly reduced the prometastatic effects of cyclophosphamide. Together, our findings suggest that bone marrow perturbation by cytotoxic chemotherapy can contribute to bone metastasis via a transient increase in bone marrow myeloid cells and myelogenic cytokines. These changes can be reversed by inhibition of CCL2.

Critical Review of Preclinical Approaches to Evaluate the Potential of Immunosuppressive Drugs to Influence Human Neoplasia

Many immunosuppressive drugs are associated with an increased risk of B-cell lymphoma, squamous cell carcinoma, and Kaposi sarcoma. Thirteen immunosuppressive drugs have been tested in 2-year carcinogenicity studies (abatacept; azathioprine; busulfan; cyclophosphamide; cyclosporine; dexamethasone; everolimus; leflunomide; methotrexate; mycophenolate mofetil; prednisone; sirolimus; and tacrolimus) and in additional models including neonatal and genetically modified mice; chemical, viral, ultraviolet, and ionizing radiation co-carcinogenesis, and in models with transplanted tumor cells. The purpose of this review is to outline the mechanisms by which immunosuppressive drugs can influence neoplasia, to summarize the available preclinical data on the 13 drugs, and to critically review the performance of the models. A combination of primary tumor and metastasis assays conducted with transplanted cells may provide the highest value for hazard identification and can be applied on a case-by-case basis. However, for both small molecules and therapeutic proteins, determining the relative risk to patients from preclinical data remains problematic. Classifying immunosuppressive drugs based on their mechanism of action and hazard identification from preclinical studies and a prospective pharmacovigilance program to monitor carcinogenic risk may be a feasible way to manage patient safety during the clinical development program and postmarketing.

Anxa2 plays a critical role in enhanced invasiveness of the multidrug resistant human breast cancer cells

Multidrug resistance (MDR) is the major cause of failure in cancer chemotherapy. Recent reports even suggest that MDR is associated with elevated invasion and metastasis of tumor cells. In the current study, we used a proteomic approach to identify genes that play an important role in MDR induced cell migration. 2D-PAGE and MALDI-TOF/MS-based proteomics approach were used to separate and identify differentially expressed proteins between MCF-7 and MCF-7/ADR, a p-glycoprotein-overexpressing adriamycin-resistance breast cancer cell line. Annexin a2 (Anxa2) was identified as highly expressed in MCF-7/ADR cells, but not in MCF-7 cells. Small interference RNA-mediated gene suppression demonstrated that Anxa2 was required for enhanced cell proliferation and invasion of the MCF-7/ADR cells. Down-regulation of Anxa2 alone was not sufficient to revert the cell sensitivity to adriamycin, suggesting that Anxa2 was not required for MDR phenotype. Taken together, our results showed that expression of Anxa2 is enhanced when cancer cells, MCF-7, acquired drug resistance and it plays an essential role in MDR-induced tumor invasion.

Tumor and host-mediated pathways of resistance and disease progression in response to antiangiogenic therapy

Despite early benefits seen in cancer patients treated with antivascular endothelial growth factor (VEGF) pathway-targeted drugs, the clinical benefits obtained in terms of progression-free or overall survival have been more modest than expected. This outcome is, at least in part, due to antiangiogenic drug resistance mechanisms that involve pathways mediated largely by the tumor, whether intrinsic or acquired in response to therapy, or by the host, which is either responding directly to therapy or indirectly to tumoral cues. The focus of this review is to distinguish, where possible, between such host and tumor-mediated pathways of resistance and discuss key challenges facing the preclinical and clinical development of antiangiogenic agents, including potential differences in drug efficacies when treating primary tumors or various stages of metastatic disease.

Cyclophosphamide enhances human tumor growth in nude rat xenografted tumor models

The effect of the immunomodulatory chemotherapeutic agent cyclophosphamide (CTX) on tumor growth was investigated in primary and metastatic intracerebral and subcutaneous rat xenograft models. Nude rats were treated with CTX (100 mg/kg, intraperitoneally) 24 hours before human ovarian carcinoma (SKOV3), small cell lung carcinoma (LX-1 SCLC), and glioma (UW28, U87MG, and U251) tumor cells were inoculated subcutaneously, intraperitoneally, or in the right cerebral hemisphere or were infused into the right internal carotid artery. Tumor development was monitored and recorded. Potential mechanisms were further investigated. Only animals that received both CTX and Matrigel showed consistent growth of subcutaneous tumors. Cyclophosphamide pretreatment increased the percentage (83.3% vs 0%) of animals showing intraperitoneal tumors. In intracerebral implantation tumor models, CTX pretreatment increased the tumor volume and the percentage of animals showing tumors. Cyclophosphamide increased lung carcinoma bone and facial metastases after intra-arterial injection, and 20% of animals showed brain metastases. Cyclophosphamide transiently decreased nude rat white blood cell counts and glutathione concentration, whereas serum vascular endothelial growth factor was significantly elevated. Cyclophosphamide also increased CD31 reactivity, a marker of vascular endothelium, and macrophage (CD68-positive) infiltration into glioma cell-inoculated rat brains. Cyclophosphamide may enhance primary and metastatic tumor growth through multiple mechanisms, including immune modulation, decreased response to oxidative stress, increased tumor vascularization, and increased macrophage infiltration. These findings may be clinically relevant because chemotherapy may predispose human cancer subjects to tumor growth in the brain or other tissues.

Accelerated metastasis after short-term treatment with a potent inhibitor of tumor angiogenesis

Herein we report that the VEGFR/PDGFR kinase inhibitor sunitinib/SU11248 can accelerate metastatic tumor growth and decrease overall survival in mice receiving short-term therapy in various metastasis assays, including after intravenous injection of tumor cells or after removal of primary orthotopically grown tumors. Acceleration of metastasis was also observed in mice receiving sunitinib prior to intravenous implantation of tumor cells, suggesting possible "metastatic conditioning" in multiple organs. Similar findings with additional VEGF receptor tyrosine kinase inhibitors implicate a class-specific effect for such agents. Importantly, these observations of metastatic acceleration were in contrast to the demonstrable antitumor benefits obtained when the same human breast cancer cells, as well as mouse or human melanoma cells, were grown orthotopically as primary tumors and subjected to identical sunitinib treatments.

Cyclophosphamide promotes pulmonary metastasis on mouse lung adenocarcinoma

Cyclophosphamide (CTX), as a common use of chemotherapeutic agent, has some side effects in clinical treatment. In our experiments, we studied CTX-treated T739 mice using histopathology, immunohistochemistry, reverse transcription polymerase chain reaction and Western blot for markers of proliferation, angiogenesis, tumor progression and distant metastasis. As a result, CTX increased the number and area of metastases and tumor embolus in lungs by effecting on the expression of matrix metalloproteinase-2, intercellular adhesion molecule-1 and tissue inhibitor of metalloproteinase-2. Taken together, it indicated that CTX enhanced the process of pulmonary metastasis by the synergistic effect of matrix-degrading proteases and adhesion proteins.

Induction of cancer metastasis by cyclophosphamide pretreatment of host mice: an opposite effect of chemotherapy

Although side effects of cancer chemotherapy are well known, "opposite effects" of chemotherapy that enhance the malignancy of the treated cancer are not well understood. In this report, we describe the induction of intravascular proliferation, extravasation, and colony formation by cancer cells, critical steps of metastasis, by pretreatment of host mice with the commonly used chemotherapy drug cyclophosphamide. In contrast, in the unpretreated mice, most cancer cells remained quiescent in vessels without extravasation. HT1080 human fibrosarcoma cells, labeled in the nucleus with green fluorescent protein and red fluorescent protein in the cytoplasm for imaging, were injected into the epigastric cranialis vein of nude mice. Twenty-four hours before cancer cell injection, cyclophosphamide was given i.p. Double-labeled cancer cells were imaged at the cellular level in live mice with the Olympus OV100 Small Animal Imaging System with variable magnification. Cyclophosphamide seems to interfere with a host process that inhibits intravascular proliferation, extravasation, and extravascular colony formation. Cyclophosphamide does not directly affect the cancer cells because cyclophosphamide has been cleared by the time the cancer cells were injected. This report shows an important unexpected "opposite effect" of chemotherapy that enhances critical steps in malignancy rather than inhibiting them, suggesting that certain current approaches to cancer chemotherapy should be modified.

Enhanced in vitro invasiveness and drug resistance with altered gene expression patterns in a human lung carcinoma cell line after pulse selection with anticancer drugs

The human lung carcinoma cell line DLKP was exposed to sequential pulses of 10 commonly used chemotherapeutic drugs (VP-16, vincristine, taxotere, mitoxantrone, 5-fluorouracil, methotrexate, CCNU, BCNU, cisplatin and chlorambucil); resulting cell lines exhibited resistance to the selecting agents (ranging approx. 1.5- to 36-fold) and, in some cases, cross-resistance to methotrexate (approx. 1.4- to 22-fold), vincristine (1.6- to 262-fold), doxorubicin (Adriamycin, approx. 1.1- to 33-fold) and taxotere (approx. 1.1- to 36-fold). Several of the variants displayed collateral sensitivity to cisplatin. A marked increase in in vitro invasiveness and motility was observed with variants pulsed with mitoxantrone, 5-fluorouracil, methotrexate, BCNU, cisplatin and chlorambucil. There was no significant change in invasiveness of cells pulsed with VP-16, vincristine, taxotere or CCNU. All of the pulse-selected variants showed elevated levels of MDR-1/P-gp protein by Western blot analysis, although mdr-1 mRNA levels were not increased (except for DLKP-taxotere). In DLKP-taxotere, MRP1 protein levels were also greatly elevated, but mrp1 mRNA levels remained unchanged. BCRP was upregulated in DLKP-mitoxantrone at both the mRNA and protein levels. Gelatin zymography, Western blot and RT-PCR showed that DLKP and its variants secreted MMPs 2, 9 and 13. MMP inhibition assays suggested that MMP-2 plays a more important role than MMPs 9 and 13 in cell invasion of these DLKP drug-resistant variants in vitro. These results indicate that drug exposure may induce not only resistance but also invasiveness in cancer cells.

Antimetabolite-induced increases in the invasive capacity of murine leukaemia L1210 cells

Pretreatment of murine leukaemia L1210 cells with non-lethal concentrations of various antimetabolites increased the in vitro invasive capacity of these cells into monolayers of rat embryo fibroblasts. The increase in invasive capacity was partly correlated with the induced cell cycle arrest. The concomitant increase in cell surface fucosylation and inhibition of invasion with sulphate indicate a role for glycoproteins in this process. Our results suggest that treatment with antimetabolites may lead to a more aggressive phenotype by altering cell surface properties.

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis. 1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner. 2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis. 3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-alpha. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis. 4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

Cancer cell interactions with injured or activated endothelium

Blood vessels and lymphatics are the most important pathways for dissemination of cancer cells but the entry and exit of these cells into and from the vasculature requires that they pass through barriers formed by the endothelium and its basement membrane. This review summarizes evidence that this step in metastasis can be regulated by microenvironmental influences which alter the properties of this barrier. These phenomena can be attributed to both 'passive' and 'active' responses of the endothelium. The microvasculature is susceptible to perturbation from environmental agents, host cells and cancer cells. There is clinical and experimental evidence that this can upregulate the metastatic process. Using established animal models of pulmonary microvascular injury it has been shown that endothelial damage promotes the localization and metastasis of circulating cancer cells to the lung and that this effect is lost after endothelial repair. Oxidative stress is an effector of vascular damage in several of the experimental models. While endothelial cells appear to be directly susceptible to free radical attack, basement membranes are not. However, oxidative injury of endothelial cells causes release of proteases which can then degrade the basement membrane. This event is associated with generation of tumor cell chemoattractants and enhances cancer cell invasion of vascular basement membranes in vitro. Vascular endothelial cells are also susceptible to stimulation by systemic mediators including cytokines, thrombin, or endotoxin which induce a series of active responses in the vessel wall. These perturbed endothelial cells synthesize and express cell surface adhesion molecules which can interact with cancer cells. They also release chemoattractants which stimulate cancer cell motility. We postulate that such responses endow the vessel wall with the potential to act as a determinant of metastatic rate.

Effects of gamma irradiation on cultured rat and mouse microvessel endothelial cells: metastatic tumor cell adhesion, subendothelial matrix degradation, and secretion of tumor cell growth factors

The effects of gamma-irradiation on the properties of microvessel endothelial cells were studied in vitro. After incubating confluent endothelial cell monolayers in low serum-containing medium for 24 h, the monolayers were irradiated with 137Cs. Survival of rat lung microvessel endothelial (RLE) and mouse brain microvessel endothelial (MBE) cells were similar after irradiation (Do = 2.17 and 1.75 Gy, Dq = 4.44 and 5.67 Gy, and n = 7.8 and 25 for RLE and MBE cells, respectively). We examined the effects of gamma-irradiation on endothelial cell morphology, adhesion of syngeneic rat lung or mouse brain metastasizing tumor cells, release of the subendothelial matrix-degrading enzyme heparanase, and secretion of soluble mitogenic factors that stimulated the growth of syngeneic metastatic tumor cells. The effects of gamma-irradiation were not apparent until several hours after irradiation, and by 24 h doses of greater than or equal to 10 Gy caused limited endothelial cell retraction and reorganization of the endothelial monolayer. By 24 h after irradiation there was also increased adhesion of metastatic tumor cells to RLE but not MBE cells. We also examined the effects of gamma-irradiation on the release from endothelial cells of enzymes that solubilize the subendothelial matrix. Radiation resulted in a significant increase in the release of matrix-degrading enzyme (heparanase) that solubilized [35S]-labeled heparan sulfate from subendothelial matrix. This was most pronounced in the 24 h sample from gamma-irradiated endothelial cells. Finally, we examined the gamma-irradiation-induced release of mitogenic factors from endothelial cells that could stimulate the growth of metastatic cells in serum-limiting medium. The medium from RLE but not MBE cells stimulated the growth of a rat mammary carcinoma cell line. The results suggest that gamma-irradiation of microvessel endothelial cells can affect the interactions of tumor cells with endothelial cells and their subendothelial matrix; these processes could facilitate metastasis formation in irradiated tissues such as the lung.

Radiation enhancement of metastasis: a review

Virtually every modality employed in the treatment of cancer has demonstrated an adverse effect upon metastasis under some conditions. This review surveys the experimental and clinical literature pertaining to the untoward effects of ionizing radiation upon metastatic processes. Two processes are described: (1) enhancement of metastases following local tumor irradiation; (2) localization of metastasis in previously irradiated normal tissues. In the first process the experimental evidence indicates a local effect of irradiation upon the tumor-stroma interface. It predominates under conditions of non-curative radiation doses. There is no proof that this process occurs in clinical practice, but a review of data provides suggestive evidence for its existence following non-curative therapy. The second process is documented both experimentally and clinically. It requires the presence of viable, circulating tumor cells and appears mediated through vascular damage. The few clinical reports suggest that this effect is rare in practice. The clinical significance of both processes appears small under conditions of effective tumor therapy, but it is speculated that inadequate tumor irradiation, or irradiation of normal tissues with uncontrolled tumor elsewhere, may be deleterious.

Lectin-resistant variants of mouse Lewis lung carcinoma cells. I. Selection and in vivo properties

The availability of lectin-resistant cell lines with altered carbohydrate moieties in cell surface glycoproteins and glycolipids has greatly facilitated study of the involvement of cellular glycoconjugates in tumor growth and metastasis. We present here a new animal model for metastasis study based on mouse Lewis lung carcinoma LL2 in vitro cell line. From this line, five lectin-resistant variant sublines were selected with the following lectins: wheat germ agglutinin (WGAR), Ricinus communis agglutinin II (RCA IIR) and Aleuria aurantia agglutinin (AAAR). The correlation of the lectin resistance with their in vitro and in vivo growth properties, and especially lung colonizing ability, were investigated. Three WGAR variants with well-preserved tumorigenicity revealed reduced metastatic ability, both spontaneous, after subcutaneous (s.c.) administration and experimental, after intravenous (i.v.) administration. The RCA IIR variant also possessed reduced spontaneous and experimental metastatic ability, but exhibited higher growth rate of local s.c. tumors. The AAAR variant possessed reduced spontaneous metastatic ability but its ability to colonize the lungs after i.v. administration was five-fold higher than that of the parent LL2 line, whereas its tumorigenicity remained unchanged. The relative differences among WGAR variants and parent LL2 line, concerning their experimental metastatic ability, remained similar in cyclophosphamide-modified mice to those in normal recipients.

An assessment of the effects of swainsonine on survival of mice injected with B16-F10 melanoma cells

Systemic administration of swainsonine, an indolizidine alkaloid, inhibits the experimental metastasis of B16-F10 murine melanoma cells. This activity can be attributed primarily to swainsonine-mediated enhancement of host natural killer cell activity. As one next step towards investigating the potential therapeutic utility of this drug, its efficacy in enhancing host survival in the same B16-F10 model system has been assessed. In studies employing intravenously injected tumor cells, pretreatment of mice with swainsonine-containing drinking water provided a reproducible protective effect for the host. This prolongation of survival was substantially enhanced when swainsonine was administered in combination with either of two other immunomodulators, polyinosinic: cytidylic acid (poly-IC) or interleukin-2. In studies in which combinations of these agents were administered after intravenous injection of tumor cells, or after subcutaneous implantation, a greatly reduced effect on host survival was observed. However, when used in combination with cyclophosphamide (to block the effects of suppressor T cells), swainsonine did increase mean survival time. The implications of these results for the use of swainsonine in treatment of metastatic or localized disease, together with its potential mechanism(s) of action, are discussed.

Evidence of a role for NK cells in oxazaphosphorine-mediated tumor regression

The present studies showed that nude mice xenotransplanted with L5222 leukemia responded as did syngeneic BD IX rats to low doses of mafosfamide or cyclophosphamide. Unlike rats, nude mice rarely showed resistance to a second tumor challenge. The observation that concurrent treatment of rats with cyclosporin A did not alter the rate of survival clearly indicated a T-cell-independent mechanism of tumor defense. The incidence of lung colonies from i.v. injected Lewis lung-tumor cells could be enhanced by a high dose pretreatment with mafosfamide or cyclophosphamide, whereas pretreatment at low doses was inhibitory. Since identical experiments carried out in NK-cell-deficient C57Bl/6 "beige" mice did not show such an effect, NK cells appeared to represent a possible effector cell in oxazaphosphorine-mediated antitumor effects. This assumption was further supported by the fact that enhanced NK cell activity could be observed in the 51Cr release assay using spleen cells from mafosfamide-treated L5222-bearing rats. The transplantation of the unrelated syngeneic ovarian carcinoma OV-342 to animals that had previously been cured of L5222 leukemia did not lead to the rejection of this tumor. This indicates that a specific resistance against L5222 leukemia had developed. In contrast, a T-cell-dependent antitumor effect was demonstrated for mafosfamide in the MOPC-315 mouse plasmocytoma. Therefore, we conclude that the effector cell for tumor rejection depends on the type of tumor. This, of course, does not exclude a common target cell for the immunopharmacological activity of oxazaphosphorines.

Combined modality treatment with radiotherapy and chemotherapy

Combined modality treatment with radiotherapy and chemotherapy is used increasingly for the primary management of a variety of human tumours, with the aim of improving both local and distant control. The present paper reviews methodological issues related to the evaluation of combined modality therapy. Reports that patients have superior outcome in single-arm studies as compared to historical controls treated with radiation alone have limited value because of several types of bias including patient selection, stage migration, the tendency to publish positive results, or inadequate follow-up as compared to the historical series. The observation that response to chemotherapy predicts for survival after combined treatment also conveys no proof that combined treatment is superior to radiation alone. Randomized controlled trials provide the only rigorous method for evaluating combined therapy, but are also subject to misinterpretation. The majority of published trials report negative results but are too small to detect clinically important differences in survival. Even large trials may give spurious results if they seek small benefits of treatment in a spectrum of patients with widely differing prognosis. Some randomized trials have demonstrated improved local control and increased toxicity from combined treatment, a result that might have been achieved by increasing the effective radiation dose. Ideally, combined treatment should be compared with radiotherapy alone at equal levels of normal tissue damage. A review of published data for patients with cancers of the head and neck, lung, gastrointestinal tract and bladder reveals very few trials which have adequately evaluated the role of combined modality therapy (with or without surgery). Most of the large randomized trials have demonstrated no benefit from the use of radiation and chemotherapy, although some of them suggest small therapeutic gains from using thoracic radiation with chemotherapy in small-cell-lung cancer of limited extent, or from combined modality treatment after resection of rectal cancer. Possible reasons for the failure of active drugs to lead to easily detected gains in therapeutic index include insufficient reduction in cell survival from chemotherapy, selective killing of radiosensitive subpopulations, stimulation of the proliferation of surviving cells, or enhancement of metastasis. With the possible exception of radiation and concurrent 5-fluorouracil for squamous cancers of the anal canal, there are no convincing data to mandate the routine combined use of radiotherapy and chemotherapy in any of the above sites.

Interactions between cancer cells and the microvasculature: a rate-regulator for metastasis

Hematogenous metastasis is a major consideration in the staging, treatment and prognosis of patients with cancer. Key events affecting hematogeneous metastasis occur in the microvasculature. This is a brief, selective review of some interactions involving cancer cells and the microvasculature in pathologic sequence, specifically: (1) intravasation of cancer cells; (2) the arrest of circulating cancer cells in the microvasculature; (3) cancer cell trauma associated with arrest; (4) microvascular trauma; (5) the inflammatory; and (6) the hemostatic coagulative responses associated with arrest, and finally (7) angiogenesis, leading to tumor vascularization. The evidence shows that through a series of complex interactions with cancer cells, the microvasculature acts as a rate-regulator for the metastatic process, in addition to providing routes for cancer cell dissemination and arrest sites for cancer cell emboli.

Non-cytotoxic asialo-GM1-positive cells exert antimetastatic activity

Metastasis can be inhibited by asialo-GM1-positive spleen cells, and in this paper we show that there are two such spleen cell populations. One population is adherent and non-cytotoxic to YAC cells, whereas the other population is non-adherent and cytotoxic to YAC cells. Both cell populations exert an antimetastatic activity in cyclophosphamide-treated mice that are inoculated with LL2 Lewis lung carcinoma cells. We conclude that the antimetastatic activity is not only exerted by cytotoxic asialo-GM1-positive cells (apparently natural killer cells), but also by adherent, non-cytotoxic asialo-GM1+, Thy1.2-, IgG- cells. This means that the latter exert their antimetastatic activity by a non-cytotoxic mechanism.

Radiation enhancement of lung nodule formation in mice is not potentiated by treatment with a perfluorochemical emulsion and carbogen

The ability of intravenously-injected mouse mammary tumor cells to form lung tumors is increased by irradiation of the thorax 24 h previously. We examined the effects of treatment with a perfluorochemical emulsion (Fluosol-DA, 20%) plus carbogen before and during irradiation on the radiation-induced enhancement of lung nodule formation. We found no evidence that treatment with Fluosol plus carbogen altered the development of tumor nodules in irradiated mouse lungs.

Contributions of host and donor T cells to the inflammatory process in murine lymphocytic choriomeningitis

The severe inflammation characteristic of the infection of adult mice with murine lymphocytic choriomeningitis virus (LCMV) is induced earlier in unsuppressed, virus-infected recipients by the adoptive transfer of class I MHC-compatible, CD4- CD8+ LCMV-immune spleen cell populations. The time to onset of fatal LCM may also be slightly diminished, though not to the extent that would be expected from the enhanced kinetics of the extravasation of cells into cerebrospinal fluid. The development of symptoms is thus not solely related to the magnitude of the inflammatory process. The majority of the T lymphocytes in the inflammatory exudate are of host origin and have the size characteristics of resting cells, while the minority population of donor T cells show more of a lymphoblast morphology. The findings are consistent with the idea that relatively few CD8+ virus-immune effectors trigger an inflammatory process which consists largely of secondarily recruited host T cells and monocyte/macrophages.

In vivo emergence of a highly metastatic tumour cell line from a rat rhabdomyosarcoma after treatment with an alkylating agent

Rats bearing a transplanted nickel-induced rhabdomyosarcoma (RMS 9-4/0), treated with chlorozotocin (CZT), an alkylating agent, showed an amplified metastatic invasion of the lung (median of 165 lung tumour nodules, compared to 3 for untreated controls). A higher level of metastatic invasion (200 nodules) was reached spontaneously after the grafting of the S4T line, which was obtained by successive in vivo passages of RMS 9-4/0 cells in CZT treated rats. S4T tumour cells also invaded the liver and a considerable proportion of the lymph nodes. The NT4T line, obtained by successive in vivo passages in untreated rats, showed a lesser degree of enhancement of metastatic capacity (57 nodules). Both derived lines proved to be more aggressive than the parental, proliferated more rapidly, and were resistant to CZT toxicity. Only the non-treated lineage became more resistant to NK lysis. The S4T line lost its myogenic differentiation and was best described as a fibrohistiosarcoma, whereas NT4T did not. Chromosome analysis demonstrated a reduced range of chromosome number per cell in both lines. We conclude that both S4T and NT4T tumours became more metastatic than RMS 9-4/0 as the result of tumour progression through in vivo passages, and that in addition S4T acquired a spontaneously higher metastatic potential, similar to that which occurred in rats grafted with RMS 9-4/0 or NT4T tumours and treated by CZT. This suggests an inheritable mutation in the S4T line.

Preferential growth of metastatic tumors at the pleural surface of mouse lung

In an experimental model of lung metastasis we have observed that more metastatic tumors are located on the pleura of the lung than in the parenchyma. To study possible reasons for this differential pattern we have now related the initial distribution of injected tumor cells to the later location and growth rate of metastases in different regions of the lung in C57bl/6 mice. It was found that labeled murine fibrosarcoma cells were evenly distributed throughout the lungs 24 h after intravenous injection into controls and animals previously treated with bleomycin or by exposure to hyperoxia. These treatments, known to induce pulmonary endothelial injury, were associated with increased tumor cell localization in the lung. In all cases, using morphometric methods, we found that after 2 weeks, approximately 75 per cent of metastatic tumors were located at the pleura. By [3H]thymidine labeling in autoradiographs, pleural tumors in all experimental groups had a growth rate 14 times the growth rate of tumors located in the internal regions of the lung. In vitro, the fibrosarcoma cells proliferated more rapidly on connective tissue matrices prepared from normal pleuras than they did on matrices from the remainder of the lung. Protease digestion of these matrices indicated differences in composition with more insoluble collagen, probably type I collagen, present at the pleura. These data suggest that, in spite of the initial random distribution and localization of tumor cells in the lung, there is preferential growth of metastatic tumors at the pleura which may be related to regional differences in the composition of the extracellular matrix.

Can cancer chemotherapy enhance the malignant behaviour of tumours?

Cancer chemotherapy is currently undergoing an intensive reappraisal because of its unimpressive performance against the major common cancers. There are a number of possible reasons for this lack of success; one considered here is that under some circumstances anti-neoplastic drug treatment actually increases the malignant behaviour of tumours. Support for this idea comes mainly from experimental studies in which drug treatments increased metastatic spread. Investigation of this phenomenon shows that drug induced modifications of the host, including immunosuppression and vascular damage, can indeed facilitate metastasis. In addition, new data are presented demonstrating that the direct action of drugs on the tumour cells themselves can have similar enhancing effects. The possible mechanisms underlying such direct effects are discussed and the ability of anti-cancer drugs to cause genetic mutations, amplify genes, and alter gene expression are considered. While the nature and extent of this facilitation of tumour malignancy is not fully understood, it is suggested that this possibility should be considered in the design of treatment protocols.

The effectiveness of cis-platinum, cyclophosphamide and melphalan in treating disseminated tumor cells in mice

Both B16 melanoma and Lewis lung carcinoma growing in C57/Bl mice spontaneously metastasize to the lungs and other organs. When the tumors are grown in the mouse tail to a specific volume and amputated, the spontaneously disseminated tumor cells can then be independently treated. The effects of a single dose of cyclophosphamide (200 mg/kg), cis-platinum (6 mg/kg) and melphalan (10 mg/kg) on the appearance of pulmonary and other metastases were measured. The cis-platinum treatment was shown to reduce the number and incidence of metastases of both tumors at various times after treatment. The antimetastatic effectiveness of cis-platinum against these two tumors was increased when 2.4 mg/kg was administered each day for five consecutive days after amputation of the primary. Cyclophosphamide, when administered at two-thirds maximum tolerated dose, had a small promoting effect on the number and incidence of pulmonary metastases of Lewis lung carcinoma, whereas, applied in the same dose, it had efficacy in the treatment of disseminated B16 melanoma and inhibited appearance of both pulmonary and lymph-node metastases. When melphalan was administered in single- and multiple-dose regimens, the number and incidence of metastases of both tumors increased at various times after primary tumor amputation. These data suggest that melphalan can promote the growth of disseminated tumor cells in both the lungs and other sites and that some systemic chemotherapies may result in promotion instead of suppression of metastatic disease.

Effects of injury and repair of the pulmonary endothelium on lung metastasis after bleomycin

Acute endothelial injury induced by bleomycin has been shown to enhance the localization and metastasis of circulating tumour cells. In the present study we wished to determine whether increased metastases to the lung is related to the degree of endothelial damage as indicated by morphology and protein leakage to alveoli and whether the progression to repair with pulmonary fibrosis also effects metastatic tumour growth. C57b1/6 mice were injected with a single intravenous dose of bleomycin (120 mg/kg). After 5 days, severe enothelial injury was demonstrated by morphology and by increased levels of protein in lung lavage fluid. When [131I]-iododeoxyuridine labeled syngeneic fibrosarcoma cells were injected intravenously at this time, a 9-fold increase in their localization was detected 24 h later in bleomycin-treated lungs compared with saline controls. By electron microscopy tumour cells were observed at sites of denuded vascular basement membrane. There was also a significant increase in the number of gross metastases which developed subsequently and in the percentage of lung occupied by tumour in the bleomycin group. Animals examined 10 days after bleomycin showed less endothelial damage and a smaller increase in tumour cell localization and metastases. At 21 days, when endothelial structure and alveolar protein levels had returned to normal, and at 6 weeks, when there was focal fibrosis, no increase in tumour cell localization or metastases was found. It is concluded that damage to the pulmonary endothelium is a key factor in enhancing the trapping of circulating tumour cells and increasing metastatic tumour growth after bleomycin.

Enhanced experimental metastatic capacity of a murine melanoma following pre-treatment with anticancer drugs

The effect of in vitro pretreatment of B16 murine melanoma cells with various cancer chemotherapeutic agents on their subsequent experimental metastatic capacity has been examined. Methotrexate, cytosine arabinoside, 5-azacytidine and aphidicolin all produced significant increases in the number of lung nodules formed following the i.v. injection of tumour cells. This effect was not seen with melphalan or 5-fluorouracil. Since the doses of melphalan and 5-fluorouracil used produced similar levels of cell kill to cytosine arabinoside and aphidicolin it appears that a cytotoxic effect was not sufficient to produce increased lung nodule formation. Analysis of the perturbations in the cell cycle induced by the drugs did not reveal any consistent differences between those drugs which enhanced experimental metastasis and those which did not. The precise mechanisms underlying this phenomenon remain to be elucidated but the results are consistent with the possibility that anticancer agents may play a role in assisting tumour progression.

Enhancement of experimental metastasis by pretreatment of tumour cells with hydroxyurea

The effect of treatment with hydroxyurea (HU), on subsequent experimental metastasis formation by cells of 3 murine melanoma lines has been examined. In vitro treatment of B16-F1, B16-F10 and K-1735-clone 19 cells with 0.1 mM or 0.3 mM HU, followed by a period of recovery in drug-free medium, resulted in a significant increase in the number of lung nodules formed in syngeneic mice following i.v. injection of the cells. The maximum effect obtained was observed when cells were injected 6 hr after removal of HU and it occurred in spite of the cytotoxicity of the doses used. Six hours after release from treatment with 0.3 mM HU cells were synchronized in the G2 phase of the cell cycle but the consequent increase in cell volume was not responsible for increased metastasis through enhancement of tumour-cell arrest, since lodgement of 51Cr-labelled, HU-treated cells was no greater than that of control cells. The results obtained suggest that the chemotherapeutic agent HU may facilitate tumour progression via a direct action on neoplastic cells.

Tumour invasion and metastasis: therapeutic implications?

Invasion and metastasis is the hallmark of tumour malignancy. Some aspects of invasion and metastasis with potential implications for tumour therapy are reviewed: the value of laboratory models; the acquisition of invasiveness and metastatic capability during carcinogenesis; the relationship between growth and invasion; clinical and experimental anti-invasive and antimetastatic agents. The value of joint experimental and clinical research is underscored.

Effect of a perfluorochemical emulsion on the development of artificial lung metastases in mice

Intravenous infusions of perfluorochemical emulsions, combined with administration of inspired oxygen or carbogen have been found to improve tumor oxygenation and increase the response of solid tumors in animals to radiotherapy. Fluosol-DA 20 per cent, the only perfluorochemical emulsion currently approved for testing in humans in the United States, has recently entered clinical trials as an adjunct to radiotherapy in the treatment of head and neck carcinoma. The studies reported here were undertaken as part of our laboratory evaluation of the safety and clinical potential of this oxygen-transport fluid as an adjunct to cancer therapy; they asked whether single or multiple treatments with Fluosol and an oxygen-enriched atmosphere produced immunologic perturbations, pulmonary damage, or other effects which altered the development of artificial lung metastases in experimental animals. Neither single nor multiple treatments with clinically relevant regimens of Fluosol and carbogen (95 per cent O2/5 per cent CO2) had any effect on the development of lung nodules from intravenously injected EMT6 tumor cells.

The influence of prior total body irradiation on the tissue distribution of mouse lymphoma/leukemia

The effect of a single dose of 10 Gy X rays on the distribution of subsequently injected mouse lymphoma/leukemia cells was studied. The organ distribution of an acute myeloid leukemia (A46) was not affected by prior (90 days) administration of 10 Gy X rays. A T-cell lymphoblastic lymphoma/leukemia (A55) and a B-cell lymphoblastic lymphoma/leukemia (A31) produced enhanced infiltration of the lung when 10 Gy of total body irradiation (TBI) was given 90 days before the tumor cells. The infiltration was predominantly in the peribronchiolar and perivascular spaces. Enhancement was not seen in any tissues other than lung. The possibility is raised that in those acute lymphoblastic leukemia patients whose treatment includes TBI, residual circulating cells may be encouraged to infiltrate the lung.

Enhancement by misonidazole of metastatic tumor nodule formation in the lungs of mice

Investigations were performed to determine whether misonidazole, a hypoxic cell radiosensitizer, influences formation of tumor nodules in the lung of C3Hf/Kam mice and whether it affects the enhancement of tumor nodule formation caused by local thoracic irradiation (LTI). Cells from a chemically-induced fibrosarcoma (FSa) and a spontaneously-developed fibrosarcoma (NFSa) formed twice as many tumor colonies in the lungs of mice that received misonidazole as in untreated mice. The effect was observed only with doses of misonidazole of 1 mg/g or higher given within 2 days prior to i.v. injection of tumor cells. A similar twofold amplification of the effect of LTI occurred when 1 mg/g misonidazole was given 30 min before or 0.5 to 2 hours after irradiation. This increase was independent of the dose of LTI and the absolute number of tumor nodules in the lung. The mechanistic possibilities and clinical relevance of the misonidazole effect are discussed.

Influence of thorax irradiation on the survival of mice with spontaneous or artificial lung metastases from a transplantable mammary adenocarcinoma

The effect of thorax irradiation on lung metastases, either occurring spontaneously from a primary mammary adenocarcinoma (M8013X) transplanted on the leg or artificially induced by intravenous injection of tumor cells was studied. Increasing the interval between the moment at which lung metastases are supposed to originate and the thorax irradiation resulted in a rapid decrease of the effectiveness of this treatment in preventing the development of lung metastases. Early treatment of the mice not only resulted in a considerable number of animals that were cured, but also in a significant decrease in the number of tumor localizations in the lung of those animals still developing metastases. Thorax irradiation performed later was much less effective; at autopsy the lung showed a large number of small metastases. Increasing the radiation dose led to an increased number of cures; however, an increased number of mice dying of lethal lung damage was also observed. Irradiation of the lungs of mice with 5 or 10 Gy, 24 hours, 7 days or 14 days prior to i.v. injection with tumor cells, did not significantly increase the number of mice with lung metastases. Immunological resistance against the tumor played a role in our experiments with both spontaneous and artificial lung metastases.

Investigation of a new murine model of regional lymph node metastasis: characteristics of the model and applications

The RC tumor, originally a renal adenocarcinoma very sensitive to different classes of chemotherapeutic agents, maintained in CDF 1 mice, was examined for its ability to metastasize. When inoculated into the foot (with 10(7) tumor cells), bulky metastases developed in the popliteal and para-aortic lymph nodes, in a constant and reproducible pattern, producing a massive microscopic invasion of the liver, the lungs and the spleen. The antigenicity tests demonstrated a low immunogenicity of the tumor. Chemotherapy assays showed that adriamycin and vincristine were effective against metastatic dissemination when administered early after tumor cell inoculation and principally when combined with excision of the tumor-bearing leg. The RC model appears to be suitable for the study of lymph node metastasis and could be used in chemotherapy trials of new drugs potentially effective against metastases of the lymphatic system.

Enhancement of artificial lung metastases by misonidazole

The effect of treatment with the hypoxic cell radiosensitizer misonidazole on the formation of artificial lung metastases was examined. Both single treatments with large doses of misonidazole and fractionated treatments with smaller doses of misonidazole were found to increase the number of lung tumors developing after intravenous injection of EMT6 mouse mammary carcinoma cells. The immunologic and physiologic effects of the nitroimidazole were postulated to be responsible for the enhancement of lung tumor formation.

Role of plasma, platelets, and endothelial cells in tumor metastasis

This review studies interactions of tumor cells with a particular host system which is normally responsible for hemostasis and the physiological integrity of the blood vessel luminal surface. With malignancy components of this system are frequently activated, producing abnormalities of blood coagulation, increased platelet responses, and conditions favoring tumor growth and metastasis. Activation of the clotting cascade is mediated by tumor and macrophage procoagulants, acting via Factor X or VII. Thrombin and fibrin are formed. Thrombin also interacts with platelets and the endothelium, potentiating or decreasing coagulation. Generation of thrombin or other tumor mechanisms activate platelets, leading to direct aggregation or secretion of ADP, serotonin, and/or intermediates of the arachidonate metabolism. Vascular lesions caused by tumor attack, platelet secretion, or exogenous agents promoting metastasis may also activate the hemostatic system. It is not yet fully understood how activation of the clotting system, including platelets, contributes to metastasis. Secretion of platelet products appears, however, to be heavily involved. Based on putative mechanisms of action, anticoagulants, platelet inhibitors, thrombocytopenic or vascular repairing agents have been used to control tumor spread. Results depended on the agent and experimental model of metastasis used. Except for coumarin, which was beneficial even against spontaneous metastases, other anticoagulants and platelet inhibitors, excluding perhaps Nafazatrom, gave equivocal results. Thrombocytopenic agents, however, were effective in every tumor system and with any experimental model of metastasis, indicating that platelets play a role in this process. Also consistent were the inhibitory effects of leech salivary gland extract (probably a vascular repairing agent) against lung tumor colonization promoted by ionizing radiation, cyclophosphamide, and cortisone.

Pattern of organ colonization of metastasizing mouse L929-MM4 cells and the stimulation of lung tumor formation by cyclophosphamide

The pattern of lung colonization of L929-MM4 metastasis-derived cells was studied in C3HA/Hab mice. The incidence of mice with lung tumors and the number of tumor foci increased with the number of tumor cells in the i.v. inoculum until a 'plateau' was reached. However, some 30 per cent of the animals continued to show no macroscopic or microscopic evidence of metastases. Twenty days after the i.v. injection of 2.5 X 10(5) L929-MM4 cells, viable tumor cells were recovered from 80-90 per cent of the animals as judged by in vivo or in vitro assay methods, even though survival of mice under these conditions was 50 per cent at the end of a 3-month period. These results are discussed in relation to possible tumor dormant states. Cyclophosphamide stimulated both the incidence and the number of lung tumor foci after i.v. injection of tumor cells, if the drug was administered before the tumor cell inoculum. On the basis of the observed time dependency of this effect, and the low immunogenicity of L929-MM4 cells in C3HA/Hab mice, the results could be explained on the basis of drug damage to normal cells.

Studies on the antitumor activities of pyrimidinone-interferon inducers. Part 2. Potentiation of antitumor resistance mechanisms

In continuation of studies on antitumor activities of pyrimidinone interferon inducers, we report here that 2-amino-5-bromo-6-mF-phenyl-4(3H)-pyrimidinone (ABmFPP) is similarly effective to 2-amino-5-bromo-6-phenyl-4-pyrimidinone (ABPP) in its ability to reduce the number of metastatic nodules of a spontaneous fibrosarcoma (NFSa) and a spontaneous mammary carcinoma (MCa-K) in the lungs of C3Hf/Kam mice. Both compounds were more effective when given to mice prior to, rather than after, intravenous transplantation of tumor cells. In studies on the mechanism of the antitumor activity of pyrimidinones, 2-amino-5-iodo-6-phenyl-4-pyrimidinone (AIPP) was used in addition to ABPP and ABmFPP. These agents were capable of activating peritoneal macrophages that thus became capable of lysing in vitro 3T12 transformed cells but not syngeneic BALB/c embryo fibroblasts. Also, these agents were capable of augmenting significantly the natural killer (NK) cell activity in the spleen of C3Hf/Kam mice. Spleen cells from treated mice admixed to NFSa cells inhibited in vivo tumor take of these cells when the admixture was injected subcutaneously. Pyrimidinones were also effective against the development of NFSa nodules in the lungs of T-cell deficient mice implying that the presence of T-cells is not a prerequisite for the induction of antitumor activity by these agents. A further observation was that pyrimidinone compounds reduced the metastasis formation enhancing effect of cyclophosphamide. Therefore, pyrimidinone interferon inducers exhibit an appreciable antimetastatic activity mediated through antitumor resistance mechanisms involving activation of macrophages and stimulation of NK-cells.

Influence of implantation site on formation of metastases

It has been suggested that local factors at the site of growth of a primary tumor might influence the outcome of the metastatic process. Compilation of the data from the literature revealed that growth of tumor cells in the selective medium of the intraperitoneal cavity, of the lymph node and/or of the spleen leads to progression towards a population of cells with a higher metastatic capacity. In search for an experimental model with transplantable rodent tumors that could be used to study the influence of the anatomic site of an implant on the formation of spontaneous metastases, we have considered heterogeneity of microenvironmental conditions in the subcutaneous milieu. For the MO4 mouse fibrosarcoma, a primary tumor growing subcutaneously in the tail was highly metastatic to lymph nodes and lungs while it failed to produce metastases when growing in the pinna. Implantation of a spheroidal aggregate of MO4 tumor cells, alternatively in the tail and in the pinna of syngeneic C3H/He mice, might be an appropriate model, which is discussed in this review.

Immunology of metastasis. Can the immune response cope with disseminated tumor?

The application of immunologic methods to the treatment of neoplasia has been a goal of research in tumor immunology. Unfortunately, no clearly defined success for such therapy has been achieved. However, the most recent advances in tumor biology have provided for a more valid conceptual framework upon which to plan further research in this area. The more general awareness of tumor progression and heterogeneity, particularly in the context of tumor metastasis, while imposing a sense of gloom regarding all therapeutic modalities, shifted immunologic thinking toward the development of nonspecific modalities. We herein propose that this 'shift' may be premature and that immunotherapy using cytolygic T cells could still be feasible. Our views are based on newer approaches for selecting immunogenic variants of malignant tumors and a better understanding of the relationship of the immune response to metastases.

Comparison of metastatic disease after local tumour treatment with radiotherapy or surgery in various tumour models

Spontaneous metastases in lymph nodes and/or the lung were obtained after tumour cell inoculation of four mouse tumours and one rat tumour into the foot-pads of syngeneic animals or their F1 hybrids. Following local radiotherapy with doses of 45-80 Gy, significantly more mice died with metastases than following local amputation of the tumour-bearing foot when the 2661 carcinoma was involved. No significant difference was observed after these treatments for the other tumours. The enhancement of metastastic growth after local radiotherapy in the 2661 carcinoma seems not to be due to incomplete killing of tumour cells in the foot. The presence of irradiated normal structures and tumour tissue after radiotherapy promoted the outgrowth of 261 carcinoma cells which were outside the radiation field at the time of treatment. Evidently, even under similar experimental conditions, radiotherapy may enhance the growth of metastases from some tumours and not from others.