Specific (EMT6) and non-specific (WEHI-164) cytolytic activity by host cells infiltrating tumour spheroids

Mathematical analysis of a tumour-immune interaction model: A moving boundary problem

A spatio-temporal mathematical model, in the form of a moving boundary problem, to explain cancer dormancy is developed. Analysis of the model is carried out for both temporal and spatio-temporal cases. Stability analysis and numerical simulations of the temporal model replicate experimental observations of immune-induced tumour dormancy. Travelling wave solutions of the spatio-temporal model are determined using the hyperbolic tangent method and minimum wave speeds of invasion are calculated. Travelling wave analysis depicts that cell invasion dynamics are mainly driven by their motion and growth rates. A stability analysis of the spatio-temporal model shows a possibility of dynamical stabilization of the tumour-free steady state. Simulation results reveal that the tumour swells to a dormant level.

A mathematical model of pre-diagnostic glioma growth

Due to their location, the malignant gliomas of the brain in humans are very difficult to treat in advanced stages. Blood-based biomarkers for glioma are needed for more accurate evaluation of treatment response as well as early diagnosis. However, biomarker research in primary brain tumors is challenging given their relative rarity and genetic diversity. It is further complicated by variations in the permeability of the blood brain barrier that affects the amount of marker released into the bloodstream. Inspired by recent temporal data indicating a possible decrease in serum glucose levels in patients with gliomas yet to be diagnosed, we present an ordinary differential equation model to capture early stage glioma growth. The model contains glioma-glucose-immune interactions and poses a potential mechanism by which this glucose drop can be explained. We present numerical simulations, parameter sensitivity analysis, linear stability analysis and a numerical experiment whereby we show how a dormant glioma can become malignant.

Interactions between rnacrophage cytokines and eicosanoids in expression of antitumour activity

Cytokines and eicosanoid products of macrophages play an essential role in expression of antitumour activity of macrophages either in a cell-to-cell contact system between the effector and the target cell or as cell-free soluble products. In this review the relationship between three main monokines, namely TNF-α, IL-1 and IL-6 and the interrelationship between these monokines and eicosanoids (PGE₂, PGI₂, LTB₄, LTC₄) in their production and in expression of antitumour activity is discussed. Emphasis is given to the effect of tumour burden on production of the monokines and of the eicosanoids and on the production of these compounds by the tumour cells. Finally, the therapeutic implications drawn from animal studies and clinical trials is discussed.

Some implications of Scale Relativity theory in avascular stages of growth of solid tumors in the presence of an immune system response

We present a traveling-wave analysis of a reduced mathematical model describing the growth of a solid tumor in the presence of an immune system response in the framework of Scale Relativity theory. Attention is focused upon the attack of tumor cells by tumor-infiltrating cytotoxic lymphocytes (TICLs), in a small multicellular tumor, without necrosis and at some stage prior to (tumor-induced) angiogenesis. For a particular choice of parameters, the underlying system of partial differential equations is able to simulate the well-documented phenomenon of cancer dormancy and propagation of a perturbation in the tumor cell concentration by cnoidal modes, by depicting spatially heterogeneous tumor cell distributions that are characterized by a relatively small total number of tumor cells. This behavior is consistent with several immunomorphological investigations. Moreover, the alteration of certain parameters of the model is enough to induce soliton like modes and soliton packets into the system, which in turn result in tumor invasion in the form of a standard traveling wave. In the same framework of Scale Relativity theory, a very important feature of malignant tumors also results, that even in avascular stages they might propagate and invade healthy tissues, by means of a diffusion on a Newtonian fluid.

Travelling-wave analysis of a model of the immune response to cancer

In this paper we present a travelling-wave analysis of a mathematical model describing the growth of a solid tumour in the presence of an immune system response. From a modelling perspective, attention is focused upon the attack of tumour cells by tumour infiltrating cytotoxic lymphocytes (TICLs), in a small multicellular tumour, without necrosis and at some stage prior to (tumour-induced) angiogenesis. As we have shown in previous work, for a particular choice of parameters, the underlying reaction-diffusion-chemotaxis system of partial differential equations is able to simulate the well-documented phenomenon of cancer dormancy by depicting spatially heterogeneous tumour cell distributions that are characterized by a relatively small total number of tumour cells. This behaviour is consistent with several immunomorphological investigations. Moreover, the alteration of certain parameters of the model is enough to induce bifurcations into the system, which in turn result in tumour invasion in the form of a standard travelling wave. The work presented in this paper complements the bifurcation analysis undertaken by Matzavinos et al. [Math. Med. Biol. IMA 21 (2004) 1-34] and establishes the existence of travelling-wave solutions for the system under discussion by promoting the understanding of the geometry of an appropriate phase space.

Copper-64-diacetyl-bis(N4-methylthiosemicarbazone): An agent for radiotherapy

Systemic administration of hypoxia-selective (64)Cu-diacetyl-bis(N(4)-methylthiosemicarbazone) ((64)Cu-ATSM) has increased significantly the survival time of hamsters bearing human GW39 colon cancer tumors. Radiotherapy experiments were performed in animals bearing either 7-day-old (0.5-1.0 g) or 15-day-old (1.5-2.0 g) tumors. Studies compared animals treated with a single dose of 0, 4, 6, 7, 8, or 10 mCi of (64)Cu-ATSM (1 Ci = 37 GBq) with or without the vasodilator hydralazine. A multiple dose regimen of 3 x 4 mCi at 72-h intervals was studied also. Single doses of >6 mCi of (64)Cu-ATSM and the dose-fractionation protocol significantly increased the survival time of the hamsters compared with controls. The highest dose, 10 mCi of (64)Cu-ATSM, increased survival to 135 days in 50% of animals bearing 7-day-old tumors, 6-fold longer than control animals' survival (20 days), with only transient leucopenia and thrombocytopenia but no overt toxicity. Human absorbed doses were calculated from hamster biodistribution; the dose-critical organs were the lower large intestine (1.43 +/- 0.19 rad/mCi) and upper large intestine (1.20 +/- 0.38 rad/mCi). High-resolution MRI and positron-emission tomography using a therapeutic administration of 10 mCi were used to monitor tumor volume and morphology and to assess tumor dosimetry accurately, giving a tumor dose of 81 +/- 7.5 rad/mCi. (64)Cu-ATSM has increased the survival time of tumor-bearing animals significantly with no acute toxicity and thus is a promising agent for radiotherapy.

Multicellular spheroids: a three-dimensional in vitro culture system to study tumour biology

The growth of tumour cells as three-dimensional multicellular spheroids in vitro has led to important insights in tumour biology, since properties of the in vivo-tumour such as proliferation or nutrient gradients, can be studied under controlled conditions. While this review starts with an update of recent data on spheroid monocultures, especially concerning tumour microenvironment and therapeutic modalities, the main emphasis is put on the spectrum of heterologous cultures which have evolved in previous years. This type of culture includes tumour cell interaction with endothelial, fibroblast or immunocompetent cells. The relation of the spheroid culture model to other types of three-dimensional culture and our critical evaluation and presentation of the technical aspects of growing and analysing spheroids are included in the text. These topics are chosen to help the experimental pathologist design experiments with tumour spheroids and to stimulate discussion.

In vitro analysis of cancer prevention by a mycobacterial antigen complex and of cancer-promoted inhibition of immune reactions

The antigen complex A60 of Mycobacterium bovis bacillus Calmette-Guérin protected mice against experimental tuberculous infection, and prevented cancer development after challenge with EMT 6 cells. Although humoral and cellular immune reactions elicited by A60 in vivo remained unaffected in cases of tumor rejection, they were suppressed in the case of neoplastic growth. In the present work, these in vivo observations were analyzed by in vitro techniques. Activated macrophages played a major role, and cytolytic T lymphocytes a minor role, in A60-promoted cancer cell cytolysis leading to tumor rejection. In vitro, EMT 6 cells weakly inhibited the proliferation of A60-specific B lymphocytes and strongly inhibited the functions of activated macrophages. However, the collapse of both humoral and cellular immune reactions during the course of cancer development was also accompanied by an inhibitory action of EMT 6 cells on the multiplication and functions of A60-specific T lymphocytes. Tumor-dependent repression of macrophage activation was therefore due to both a direct action of tumor cells on macrophages and an indirect one via inhibition of macrophage-activating T cell functions. On the other hand, tumor-induced collapse of the anti-A60 Ig synthesis was mainly due to inhibition of B-cell-activating T cells, with a weaker direct effect of tumor cells on B lymphocytes. Consequently, A60 and tumor cells exert opposite effects on the immune system at several levels.

Alteration of the immune response during cancer development and prevention by administration of a mycobacterial antigen

It has been shown previously that A60, an antigen complex of Mycobacterium bovis BCG, triggers humoral and cellular immune reactions in vivo and lymphocyte-dependent macrophage activation in vitro. In the present work, the ability of A60 to prevent murine tumour development, in conjunction or not with irradiated isologous cancer cells, was explored with Taper liver tumour (TLT), a mammary-derived neoplasm (EMT6), and Lewis lung carcinoma (3LL). Repeated injections of A60 prior to challenge reduced the incidence of EMT6 and 3LL solid tumours and increased life span. This effect was enhanced by simultaneous administration of gamma-irradiated cancer cells (80-100% suppression of EMT6 and 3LL tumour growth). In mice developing or rejecting tumours, the status of humoral and cellular immunity was evaluated by A60-based immunoassays. Tumor development was accompanied by a rapid decrease of both anti-A60 IgG titre in blood and A60-triggered delayed hypersensitivity reactions. Moreover, A60-induced T lymphocyte proliferation and macrophage-dependent autologous cancer cell cytolysis declined progressively during the course of tumour growth. In case of successful immunotherapy, a pattern similar to that of unchallenged controls was observed. Our results suggest that A60 promotes cancer rejection via tumour infiltration by lymphocytes and macrophages activated by A60-specific T lymphocytes. An increased processing of tumour-specific antigens and activation of tumour-infiltrating lymphocytes is induced by administration of irradiated cancer cells in conjunction with A60.

Hydrogen peroxide lethality is associated with a decreased ability to maintain positive DNA supercoiling

Hydrogen peroxide is more toxic to mammalian cells at 37 degrees C than 0 degree C at all concentrations studied. Histone-free nuclei (nucleoids) extracted from treated cells have a reduced ability to maintain positive DNA supercoiling, with the maximum effect at the higher temperature. Prior exposure of cells to sodium ascorbate at 0 degree C increased both toxicity and the inhibition of nuclear supercoil rewinding. After exposure at 0 degrees C, normal levels of supercoiling returned with both a fast and a slow component, kinetics characteristic of DNA single-strand break repair; the fast component was eliminated when cells were exposed at 37 degrees C due to in situ rejoining. At least a portion of the lethal lesions induced by hydrogen peroxide are DNA double-strand breaks (dsb) because the dsb repair-deficient mutant, xrs-5, is approximately two to three times more sensitive than wild-type cells over the initial portion of the survival curve. However, the increased toxicity found after exposure at 37 degrees C is observed equally in both cell lines, indicating that temperature-dependent cell killing is not directly linked to DNA dsb. It is suggested that cell killing at 37 degrees C is mediated through two linked processes. First, hydrogen peroxide may disrupt cation-stabilized nuclear supercoiling by direct ion oxidation. Second, as a part of the oxidation process, hydrogen peroxide will produce potentially cytotoxic free radicals close to the DNA-linked metal site, limited in extent only by the presence of chemicals capable of reducing metal ions prior to reoxidation.

Interaction of copper(I) with nucleic acids

Poly(dG-dC) and poly(I) form particularly stable complexes with Cu(I): thus characteristic UV absorbance changes enabled demonstration of Cu(I) transfer from poly(dA-dT) to poly(dG-dC), or from DNA to poly(I). Using pulse radiolysis to generate Cu(I), a rate constant of approximately 4 x 10(7) dm3 mol-1 s-1 (per base unit) was estimated for association of Cu(I) to native DNA, and slightly higher values were found for poly(dA-dT), poly(C), poly(dG-dC) and poly(G). For native DNA and for the models poly(dA-dT) and poly(dG-dC) the addition of Cu(I) was followed by secondary absorbance changes in the time scale of 10 ms, probably due to internal Cu(I) transfer; such secondary reactions were not detectable in heat-denatured DNA or in the homopolymers of A, C, G, and I. Extraction of Cu(I) from the DNA by EDTA is slow, 0.019 s-1, and independent of EDTA concentration, indicating that dissociation of the DNA-Cu(I) complex is the rate-determining step. A tentative value can hence be given for the DNA-Cu(I) stability constant: K = k (forward)/k (reverse) approximately 2 x 10(9) dm3 mol-1. Addition of H2O2 to solutions of gamma-radiolytically generated DNA-Cu(I), at Cu(I)/base less than 0.01, resulted in DNA degradation, comparable in yield to .OH-induced degradation. In the case of poly(dA-dT) and poly(dG-dC) the reaction of H2O2 with the corresponding Cu(I) complexes produced even more damage than the reaction of .OH. The formation of DNA-Cu(I), and the deleterious reaction with H2O2, were hardly affected by RNase or BSA, when added at equal (w/v) concentration. Dismutation of O2.- by (Cu,Zn)-SOD was partly inhibited by DNA and even more by poly(I) at pH 4.4, but not at pH 7, probably by competitive complexation of Cu(I), occurring in the catalytic cycle of SOD.

Lymphocytic infiltration and cytotoxicity under hypoxic conditions in the EMT6 mouse mammary tumor

Infiltration of lymphocytes, neutrophils and macrophages was evaluated in hypoxic and well-oxygenated areas of the EMT6 mouse mammary adenocarcinoma, by in vivo staining with the fluorescent dye Hoechst 33342 followed by cell sorting on the basis of fluorescence intensity. Tumors were grouped by days post-injection (days 11-14, 15-17 and 20-27). As lymphocytes are the only host cell population in this tumor model to possess lytic activity against EMT6 tumor cells, the ability of sensitized T lymphocytes to lyse syngeneic EMT6 cells was examined under conditions of varying oxygen concentrations. Infiltrating lymphocytes were detected to the same extent in cell fractions from both areas in all tumors. In contrast, neutrophils were found in significantly higher percentages in the hypoxic population than in the well-oxygenated cell fraction of all but the largest tumors. Macrophages were present in significantly higher percentages in the well-oxygenated fraction than in the hypoxic fraction of day-11 to -14 tumors. Extreme radiobiological hypoxia (0% O2) resulted in a significant decrease in T-cell-mediated lysis of EMT6 tumor cells, compared to lysis in room air (20% O2), but lysis was not impaired under conditions of mild radiobiological hypoxia (1% O2). Our study indicates that host-cell infiltration into areas of differing oxygenation may be quantitated via in situ Hoechst staining followed by cell sorting; in the EMT6 tumor, lymphocytes appear to infiltrate hypoxic areas to the same extent as well-oxygenated areas, and T-lymphocyte killing of syngeneic tumor cells is significantly reduced, although still present, under these hypoxic conditions.

Hyperthermic modulation of macrophage-tumor cell interactions

Hyperthermia in the febrile (less than or equal to 41 degrees C) or tumor therapeutic (greater than or equal to 42 degrees C) ranges is known to alter tumor-host interactions: there are reports of either inhibitory or enhancing effects on tumor metastasis and various host defense mechanisms. Historically, this has been an area of conflicting and often anecdotal reports, and there are still significant gaps in our knowledge of the effects of temperature on tumor-host interactions. However, we believe that the tools are now available to further our understanding of the complex relationships between febrile episodes or therapeutically applied heat and various tumor-host cytotoxic mechanisms, and that potentially important and exploitable relationships can be defined. In this review we give an overview of the current status of this field and the factors that have shaped it. We also describe our recent experimental work with macrophages and their monokines, primarily tumor necrosis factor (TNF), which we feel offers new scientific and clinical opportunities for future studies.

Tumor necrosis factor-mediated cytotoxicity by tumor-associated macrophages

We have directly demonstrated that macrophages present within solid EMT6 mammary tumors (of BALB/c origin) produce TNF-alpha (TNF). These tumor-associated macrophages lysed WEHI-164, a TNF-sensitive cell line, very efficiently. This cytotoxicity was abrogated in the presence of anti-TNF antisera. In contrast, EMT6 cells, the tumor from which the macrophages were obtained, were not effectively lysed by the macrophages and were 100-fold less sensitive to lysis by recombinant mouse TNF. Thus, marked heterogeneity exists among tumors regarding sensitivity to TNF-mediated cytotoxicity. Similarly, macrophages which infiltrate into EMT6 multicellular spheroids implanted into the peritoneal cavity as well as free cells within the cavity exhibited TNF-mediated cytotoxicity of WEHI-164 cells, but failed to lyse EMT6 cells. The kinetics of lysis by these cells was similar to that of recombinant mouse TNF.

Cell and environment interactions in tumor microregions: the multicell spheroid model

Abnormal vascularization of malignant tumors is associated with the development of microregions of heterogeneous cells and environments. Experimental models such as multicell spheroids and a variety of new techniques are being used to determine the characteristics of these microregions and to study the interactions of the cells and microenvironments. The special cellular microecology of tumors influences responsiveness to therapeutic agents and has implications for future directions in cancer research.