Histological and experimental observations on the destruction of tumour cells in the blood vessels

Plasmin and Plasminogen System in the Tumor Microenvironment: Implications for Cancer Diagnosis, Prognosis, and Therapy

Simple Summary

In this review, we present a detailed discussion of how the plasminogen-activation system is utilized by tumor cells in their unrelenting attack on the tissues surrounding them. Plasmin is an enzyme which is responsible for digesting several proteins that hold the tissues surrounding solid tumors together. In this process tumor cells utilize the activity of plasmin to digest tissue barriers in order to leave the tumour site and spread to other parts of the body. We specifically focus on the role of plasminogen receptor—p11 which is an important regulatory protein that facilitates the conversion of plasminogen to plasmin and by this means promotes the attack by the tumour cells on their surrounding tissues.

Abstract

The tumor microenvironment (TME) is now being widely accepted as the key contributor to a range of processes involved in cancer progression from tumor growth to metastasis and chemoresistance. The extracellular matrix (ECM) and the proteases that mediate the remodeling of the ECM form an integral part of the TME. Plasmin is a broad-spectrum, highly potent, serine protease whose activation from its precursor plasminogen is tightly regulated by the activators (uPA, uPAR, and tPA), the inhibitors (PAI-1, PAI-2), and plasminogen receptors. Collectively, this system is called the plasminogen activation system. The expression of the components of the plasminogen activation system by malignant cells and the surrounding stromal cells modulates the TME resulting in sustained cancer progression signals. In this review, we provide a detailed discussion of the roles of plasminogen activation system in tumor growth, invasion, metastasis, and chemoresistance with specific emphasis on their role in the TME. We particularly review the recent highlights of the plasminogen receptor S100A10 (p11), which is a pivotal component of the plasminogen activation system.

Role of Operative Trauma: Explosive Metastases of Similar Size following Amputation of the Primary Leg Tumor

Trauma produced by amputation of a limb bearing the primary tumor influenced pulmonary metastases of the Carcinosarcoma of Walker 256 of the rat. This enhancement was present in 38% of the animals following the removal of a limb bearing the primary tumor; and in 29% of those in which the controlateral limb without tumor was amputated. A significant prolongation of the clotting time, an elevation of fibrinogen factor II and VII and a rapid consumption of factor VIII present soon after trauma may have been the parameter responsible for the increase of pulmonary metastases seen in this tudy.

The role of plasminogen-plasmin system in cancer

Components of the plasminogen-plasmin system participate in a wide variety of physiologic and pathologic processes, including tumor growth, invasion and metastasis, through their effect on angiogenesis and cell migration. These components are found in most tumors and their expression not only signifies their function but also carries a prognostic value. Their expression is in turn modulated by cytokines and growth factors, many of which are up-regulated in cancer. Though both tPA and uPA are expressed in tumor cells, uPA with its receptor (uPAR) is mostly involved in cellular functions, while tPA with its receptor Annexin II on endothelial surface, regulates intravascular fibrin deposition. Among the inhibitors of fibrinolysis, PAI-1 is a major player in the pathogenesis of many vascular diseases as well as in cancer. Therapeutic interventions, either using plasminogen activators or experimental inhibitor agents against PAI-1, have shown encouraging results in experimental tumors but not been verified clinically.

Pulmonary Vascular Disease

The pulmonary vasculature is an anatomic compartment that is frequently overlooked in the histologic review of lung biopsy samples, other than those obtained specifically to assess pulmonary vascular disease.1 Though often of a nonspecific nature, the histologic pattern of vascular remodeling may at times suggest its underlying pathogenesis and provide clues to the cause of pulmonary hypertension.2 Disproportionately severe vascular pathology may further indicate alternate disease processes, such as congestive heart failure or thromboemboli, contributing to the patient’s overall respiratory condition.

Intravascular location of breast cancer cells after spontaneous metastasis to the lung

In this study, we examined the hypothesis that early pulmonary metastases form within the vasculature. We introduced primary tumors in immunocompromised mice by subcutaneous injection of murine breast carcinoma cells (4T1) expressing green fluorescent protein. Isolated ventilated and perfused lungs from these mice were examined at various times after tumor formation by fluorescent microscopy. The vasculature was visualized by counterstaining with 1,1-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI)-acetylated low-density lipoprotein. These experiments showed that metastatic cells derived by spontaneous metastases were intravascular, and that early colony formation was intravascular. The location of the tumor cells was confirmed by deconvolution analysis. This work extends our previous study(1) that sarcoma cells injected intravenously form intravascular colonies to spontaneous metastasis and to a carcinoma model system. Many of the tumor cells seen were single implying that tumor cells may travel as single cells. These results support a model for pulmonary metastasis in mice in which 1) tumor cells can attach to lung endothelium soon after arrival; 2) surviving tumor cells proliferate intravascularly in this model; and 3) extravasation of the tumor occurs when intravascular micrometastatic foci outgrow the vessels they are in.

Metastatic inefficiency: intravascular and intraperitoneal implantation of cancer cells

The term metastatic inefficiency reflects the fact that most of the cancer cells entering the metastatic process are killed; some of the evidence for this is reviewed in the case of renal and colorectal carcinomas. Although much emphasis has been placed on the rapid intravascular death of cancer cells during hematogenous metastasis, much less is known about the inefficiency associated with peritoneal carcinomatosis, and up to the present no systematic and direct numerical studies have been reported of the relative metastatic inefficiencies associated with seeding of cancer cells by intraperitoneal, vascular, and lymphatic routes. However, studies on people and laboratory animals indicate that most of the cancer cells released into the peritoneal cavity are killed. Some of the mechanisms involved in killing constitute part of cellular defense operating through the release of toxic free radicals. One of these, hydrogen peroxide, given by intraperitoneal injection, has been shown to retard the development of malignant ascites in mice previously given intraperitoneal injections of cancer cells. It is suggested that local irrigation with hydrogen peroxide during surgery for abdominal tumors may be effective in inhibiting the development of peritoneal carcinomatosis.

Analysis of the incidence of intraocular metastasis

The incidence of metastases to the uvea is compared with that in eight other (extraocular) target sites, in patients with metastatic primary carcinomas of the breast, colorectum, and lungs. The incidence of intraocular metastases from breast cancer is lower than in the eight other target organs surveyed; in the other primary cancers, the incidences were midway between those in the other sites, However, when the incidence of intraocular metastases is viewed in relation to the calculated numbers of cancer cells delivered via the arterial route, the uveal tract is the most highly favoured target site for the development of metastases per unit of delivered cancer cells.

Microscopic pulmonary tumor embolism causing subacute cor pulmonale: a difficult antemortem diagnosis

Microscopic pulmonary tumor embolism is difficult to diagnose. The most common initial clinical symptom is subacute progressive dyspnea, and the initial laboratory evaluation typically shows hypoxemia in a patient with clear lung fields on a chest roentgenogram. Another distinguishing feature may be hepatic abnormalities. In general, pulmonary angiography discloses no evidence of emboli, but multiple subsegmental peripheral perfusion defects are noted on ventilation-perfusion lung scans. The diagnosis of microscopic pulmonary tumor embolism can be confirmed by open-lung or transbronchial lung biopsy or by microvascular pulmonary cytology, a less invasive procedure that could be performed at the time of pulmonary angiography. Herein we describe two patients with unsuspected microscopic pulmonary tumor embolism that eventuated in subacute cor pulmonale and death. These cases illustrate the characteristic findings of this entity and emphasize the need for early diagnosis.

Endothelialization of embolized tumor cells during metastasis formation

The reaction of the endothelial barrier to tumor cell extravasation has been studied using electron microscopy. The model system was pulmonary metastases produced by intravenous injection of B16-F10 melanoma cells. A striking difference was observed in the behavior of the endothelial lining of arterioles versus that of capillaries. In capillaries, partial retraction of endothelial cells took place following the attachment of tumor cells. The tumor cells then immediately attached to the basement membrane and the basolateral surface of the retracted endothelial cells. The endothelial cells extended to cover the tumor cells prior to complete extravasation. In the arterioles, on the other hand, endothelial retraction did not occur following tumor cell attachment. Instead the attached tumor cell emboli became encompassed by endothelial cells, outgrowing from the intact endothelial lining of the arteriole. Owing to the proliferation of the tumor cells, tumor colonies encompassed by endothelial cells expanded within the lumen. When these intravascular growths completely filled the lumen, the tumor cells extravasated from the vessel only after the original endothelial layer became mechanically disrupted and the tumor cells thereby came into contact with the basement membrane.

Mechanical aspects of the lungs as cancer cell-killing organs during hematogenous metastasis

A substantial proportion of many different types of circulating cancer cells appear to be killed during their interactions with the pulmonary microcirculation. Different tensions exist during respiration within alveolar units, and hence the pulmonary capillaries. We have calculated the effects of these tensions on the entry and subsequent fate of circulating cancer cells. Our calculations indicate that during expiration, when tension in the capillary walls is low, cancer cells can enter and travel along the capillaries without damage, because the vessels are deformed by the cells and the hydrodynamic field surrounding them. During normal inspiration when the alveoli are stretched, the increased tension within the capillary walls serves to compress the contained cancer cells. This compression, together with previously calculated blood pressure differentials between the ends of the cells, is thought in some cases, to increase their membrane tensions above the critical level for rupture, resulting in cytolysis, in accord with experimental observations. In deep inspiration, when a very substantial increase in capillary wall tension occurs, cancer cells already within the capillaries, entering them and in transit along them are expected to develop membrane tensions greatly exceeding the critical values for rupture. It is suggested that these respiration-induced effects may act as an important rate-regulating step in the metastatic process, where the development of pulmonary metastases plays a central role. Furthermore, induced deep inspiration may conceivably be utilized in the inhibition of pulmonary metastasis.

A fluid mechanical analysis of the velocity, adhesion, and destruction of cancer cells in capillaries during metastasis

Metastasis, a multistep process by which cancer disseminates through the body, mainly by intravascular routes, constitutes a major problem in cancer. When cancer cells are injected directly into the veins of animals, they are apparently arrested in the vascular bed of the first organ encountered and gradually released over the next 24 h. These interactions with the microvasculature are often associated in some manner with the death of many cancer cells, and are thought to contribute to the inefficiency of the metastatic process. We have made a theoretical analysis of cancer cells deformed into capillaries with respect to their intravascular velocity, adhesion to the vascular endothelium and intravascular destruction, in terms of the dynamics of the thin liquid film separating the surfaces of the blood vessels and cancer cells. Our calculations, which are based on previously reported experimental observations, indicate that the transit of cancer cells through the microvasculature is discontinuous, being interrupted by adhesions between the two. In addition, in some cases cell membrane rupture (and cell death) will occur when the critical membrane tension of the cancer cells is exceeded by the sum of their initial equilibrium membrane tension and the increased tension in the cancer cell membranes caused by friction generated as they move over the intraluminal surfaces of the capillaries. Our calculations on membrane rupture are consistent with previously unexplained observations by Sato and Suzuki relating cancer cell deformability to death on transpulmonary passage, and constitute a novel mechanism for "metastatic inefficiency" in terms of intravascular cancer cell death.

Tumor interaction with hemostasis: the rationale for the use of platelet inhibitors and anticoagulants in the treatment of cancer

Clinical and experimental observations have firmly established the concept of a two-way interaction between malignancy and the hemostatic system. On the one hand, certain tumors can activate platelets and the coagulation mechanism in vivo, on the other, a convincing case has been made for the involvement of platelets and fibrin in tumor growth and metastasis. A large number of clinical and experimental studies have been conducted in order to test the efficacy of platelet inhibitors and anticoagulants as adjuvants in the treatment of cancer. Antiplatelet drugs gave variable results, depending on the drug and the tumor system tested. Prostaglandin synthetic pathways by both the host and tumor seem to be an important determinant in the response to platelet function inhibitors. Of the various anticoagulants tested, the coumarin derivatives gave somewhat consistent antitumor effect in certain human and experimental cancer. The antitumor effect of oral anticoagulants does not appear to be a primary drug effect and seems related to their role as vitamin K antagonists. It should be emphasized that although the antitumor potential of antithrombotic agents is a subject of keen interest at the present, their use in treating human cancer is still controversial.

Host resistance to metastasis from mouse mammary carcinomas

Although undisturbed primary mouse mammary tumors may give rise to overt metastases, these have generally been observed near the terminal stage of progressive tumor growth. Unlike malignant breast disease in women, metastases are seldom the cause of death in mice, and in some strains as few as 2% of mammary tumor hosts may be affected (1). Highly metastatic tumors may, of course, be found, and hosts of the mammary carcinoma WHT all develop metastases (2). Evidence from animal models suggests that host defense reactions against immunogenic tumors may affect the incidence of metastatic spread (3-5). But nonimmunogenic and weakly immunogenic tumors probably represent the majority of mammary carcinomas (2, 6, 7), and this class was once considered outside control by the host. However, natural protective factors are also known which may prevent metastasis independently of specific antitumor immunity (8-10). There are therefore most likely several different biological factors and mechanisms which prevent circulating, viable cancer cells from developing into metastases. But one can not yet generalize whether natural resistance factors or induced resistance factors are the most important, or whether any resistance factors are as important in preventing metastases as is the basic unacceptability of cells in heterotopic locations. This review will not attempt to present a comprehensive analysis of cell-mediated and humoral immunity to mouse mammary tumors because this topic has recently been exhaustively treated in the reviews by Stutman (11) and Blair (12). We will focus primarily on information from in vivo investigations of the role of host resistance in the control of mammary tumor cells progressing through successive levels of metastasis from the primary tumor, through lymphatic or hematogenous dissemination, to colonization of distant organs.

Subacute pulmonary hypertension and systemic tumour embolism from cervical cancer

Venous tumour embolization is not unusual in malignant disease (1-3) usually in the form of individual cells or small clumps. Malignant cells in the pulmonary vasculature are therefore not an uncommon finding, especially in patients with abdominal neoplasms (4-7). Arterial emboli from a malignant tumour are, however, rare (8, 9), particularly peripheral ones (9, 10) and those sufficiently large to cause organ infarction. An unusual case of pulmonary and widespread systemic tumour embolization from carcinoma of the cervix is described in which systemic dissemination of tumour emboli had apparently resulted from transpulmonary passage, without the development of pulmonary metastases.

Differing platelet aggregating effects by two tumor cell lines: absence of role for platelet-derived ADP

Two different mechanisms of aggregation of heparinized human platelet-rich plasma have been identified with two tumor cell lines: In neither case are these mechanisms dependent on platelet-derived ADP. U87MG cells from a glioblastoma line of human origin caused a single irreversible wave of aggregation simultaneously with the onset of platelet secretion, and this was inhibited by heparin and hirudin but not by apyrase or phospholipase D. In contrast, Hut 20 cells from an undifferentiated tumor cell line of murine origin gave an initial reversible wave followed by a second irreversible wave, which then led to secretion. The first wave of platelet aggregation was unaffected by heparin or hirudin but was inhibited by apyrase, and the second wave was inhibited by phospholipase D. Citrate caused irreversible inhibition with either cell line, and aggregation did not occur with gel filtered platelets. These results suggest that platelet aggregation by the Hut 20 line is initially dependent on ADP released from the tumor cells, whereas aggregation induced by the U87MG line is dependent on a procoagulant activity of the tumor cell surface.

Rationale and experimental design for the VA Cooperative Study of Anticoagulation (Warfarin) in the Treatment of Cancer

Anticoagulants have been demonstrated to reduce tumor growth in certain experimental animal systems. Inhibition of clot formation interferes with tumor growth and spread while enhancement of coagulation promotes tumor growth and spread. The fact that the coagulation mechanism is commonly activated in human malignancy together with preliminary reports of therapeutic efficacy of anticoagulants suggests that the coagulation mechanism may be of pathophysiologic significance also in the growth of human tumors. A VA Cooperative Study has been established to test the hypothesis that warfarin anticoagulation will modify the course of malignancy in man. The purpose of this paper is to present the rationale and experimental design for this study with emphasis on management of anticoagulant administration in cancer patients. This paper serves as the basis for forthcoming reports of toxicity and therapeutic efficacy of warfarin in human malignancy.

[The significance of fibrin/fibrinogen for growth and metastasis of malignant tumors (author's transl)]

It seems evident that fibrinogen and fibrin representing the final substrate und product of clotting system act as pathogenetic connecting links for development and spread of malignant tumors. The results reported demonstrate the influence of fibrin on the initial phase of haematogenic metastasis particularly. Several tumor-specific mechanisms are shown to cause frequently an accumulation of fibrin in malignant tumors. The results discussed here stress the importance of fibrin in tumors for tumor cells and tumor cell units. In the literature a large number of indications to fibrin depositions in experimental tumors is found, an attempt is made to compare these findings semiquantitatively. The last part of this article discusses the therapeutic and diagnostic consequences based on the possible key position of fibrin-(ogen) in the tumor pathology.

Microscopic pulmonary tumor emboli associated with dyspnea

A syndrome is described in which severe, clinically unexplained dyspnea is found at autopsy to be caused by multiple microscopic tumor emboli. Such a situation was found in 8 of 16 cases of multiple microscopic tumor emboli in the pulmonary arteries without significant lymphatic or parenchymal involvement of the lungs. The origins oftumor emboli included carcinomas of the prostate, breast, stomach, pancreas, and liver. In the 8 cases that presented with unexplained dyspnea, initial physical, roentgenographic, and electrocardiographic examinations were not diagnostic. Clinical or morphological evidence of car pulmonale was pre emboli did not invade the walls of pulmonary vessels but were frequently associated with thrombi. Recognition of this clinicopathologic entity becomes important as progress is made in cancer therapy.

Techniques for inhibiting tumor metastases

Of the four major biological mechanisms of cancer spread, hematogenous dissemination is perhaps the most significant, as it usually heralds a fatal outcome for the patient. Recent experimental approaches have shown ways of altering the metastatic process and even totally inhibiting it in some animal models. It appears that these models may be applicable to certain human cancers. To prevent hematogenous metastasis formation the process must be inhibited at any one of four levels: 1) growth of the primary; 2) invasion of vessel walls; 3) release of viable tumor cells; or 4) entrapment and growth in distant organs. Judicious handling of the primary can decrease metastasis by minimizing the shedding of tumor cells. New experimental agents prevent the release of tumor cells from the primary by normalizing the blood vessels of the tumor. Warfarin, heparin, and fibrinolytic agents inhibit the entrapment of circulating tumor cells, presumably by their effect on coagulative mechanisms. A better understanding of the benefits of combined approaches to cancer using chemotherapy, irradiation, and immunotherapy, alone and as adjuncts to surgery, offers new opportunity to study methods of controlling metastatic disease.

Effect of Growth of Walker 256 Carcinosarcoma on the Fibrinolytic System of the Rat Plasma and Urine

Growth of a transplanted Walker 256 carcinosarcoma in rats was accompanied by: 1) An increase in plasma fibrinogen and urinary trypsin inhibitors; 2) A significant decrease in plasma plasminogen and hematocrit; 3) A decrease in urokinase activity in urine; 4) A decrease in fibrinolytic activity of the euglobulin fraction of plasma and serum. There was no significant change in the plasma inhibitors for trypsin or bovine fibrinolysin.