Biomedical subjects

D A Chow

Publications and source records attributed to D A Chow.

35 records · Page 2Linked to original sources

PubMed1988

Tumor progression in vitro: tumor-promoter-induced reversible decrease in natural immune susceptibility.

Growth of established murine tumor lines in media containing the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), was associated with reversible reductions in sensitivity to in vitro and in vivo parameters of natural resistance. L5178Y-F9 cells exposed to 100 ng TPA/ml for 2 days and returned to culture without TPA for 0-2 days, exhibited reductions in sensitivity to complement-mediated lysis by natural antibodies (Nab), activated macrophages and hypotonic lysis. The natural killer (NK) cell sensitive SL2-5 lymphoma was less sensitive to NK cells, complement-dependent NAb and hypotonic lysis after 2 days growth in 2 or 3 micrograms TPA/ml. Although TPA-treated L5178Y-F9 cells could acquire higher levels of serum NAb in vitro, this was complicated by the instability of the binding at 37 degrees C resulting in an effectively reduced capacity to bind NAb which was also demonstrated by TPA-treated SL2-5 cells. The tumor frequency of threshold s.c. inocula and the i.v. metastatic potential of the TPA-treated tumors was increased in syngeneic DBA/2 mice revealing possible correlations between reductions in the cellular characteristics assayed in vitro and decreased susceptibility to host-mediated defenses in vivo. Continued growth of the TPA-treated cells for a total of 2-8 days without TPA produced a reversal in the in vitro parameters, in the tumor frequency and in the metastatic potential, indicating the requirement for TPA to maintain the resistant phenotype. These data are consistent with the initial reversible nature of the promotion phase of multistage carcinogenesis. The reversible TPA-induced reductions in sensitivity to mediators of natural resistance may be an integral component of promotion, contributing to tumor survival in vivo and increasing the probability that the tumor will progress to a more malignant phenotype.

Animals↗

PubMed1987

Regulation of tumor development: the biphasic effects of silica and of lipopolysaccharide on natural resistance.

The impact on tumor development of the BRM silica and LPS was assessed through analysis of changes in NR parameters in vivo and in vitro. Although injection of the fumed silica Cab-o-sil 3 days before a threshold s.c. inoculum of L5178Y-F9 cells increased the tumor frequency in syngeneic DBA/2 mice, tumors recovered from silica-treated animals exhibited an augmented resistance to NAb and to in vivo NR. Cab-o-sil increased in vivo NR and induced a biphasic modulation of anti-tumor NAb and NK activities. The appearance of more autonomous tumors in Cab-o-sil-treated mice corresponding with a stimulation of NR parameters, suggests that the adjuvant activity of silica also contributes to its co-carcinogenic effect by accelerating tumor development. While injection of LPS 2-3 days before a threshold tumor inoculum lowered the tumor incidence, the survival of tumor cells injected within 1 day of LPS was increased. A corresponding early decrease in NAb activity occurred, in contrast with increases in NK cell and NAb levels previously observed after 5 days. This biphasic effect of LPS on NR effectors assayed in vitro was also seen on in vivo NR. Although their frequency was higher, tumors initiated during the period of LPS-induced NR abrogation exhibited greater reductions in NAb binding and sensitivity to NR than tumors from control mice. These data extend the support for NAb acting against tumor cells in vivo and reveal the dual nature of NR in tumor development, defending against small tumor foci and driving the progression of the surviving neoplasm.

Animals↗

PubMed1987

Tumor progression in vitro: the paradoxical natural antibody and complement-selected phenotype.

An in vitro model of tumor progression was employed to investigate the contribution of natural antibody (NAb) to antitumor resistance in vivo. Repeated cycles of L5178Y-F9 and SL2-5 tumor growth in the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) followed by the selective elimination of sensitive variants through complement-dependent syngeneic NAb lysis yielded tumors with a reduced sensitivity to NAb and complement, natural killer (NK) cells and the rapid elimination assay of natural resistance (NR). A dissection of the resistant phenotype revealed a reduction in the binding capacity of complement-fixing NAb and NK cells, a reduced susceptibility to hypotonic lysis and, paradoxically, increased fluorescence-detected NAb binding that correlated inversely with a reduced tumor frequency of threshold subcutaneous tumor inocula. The data distinguish tumor binding of NAb that leads to complement activation from other NAb binding and expose a difference between NR measured as the tumor frequency of threshold tumor inocula versus the rapid radiolabelled tumor elimination assay. Complement-dependent NAb lysis may not contribute significantly to the defense against small tumor foci; however, NAb-mediated processes associated with high fluorescence-detected NAb binding likely provide resistance.

Animals↗

PubMed1986

Phenotypic alterations in tumors that developed from threshold subcutaneous inocula. I. Reduced binding of natural antibodies and sensitivity to hypotonic lysis.

Tumors obtained from the injection site of threshold subcutaneous inocula of L5178Y-F9 or SL2-5 lymphomas in syngeneic mice exhibited increased tumor frequencies and reduced sensitivities to other parameters of natural immune resistance in vivo and in vitro. An examination of the resistant phenotype of cells derived through this model of tumor progression revealed that the more aggressive in vivo grown cells were less able to inhibit natural killer (NK) cell cytolysis and to bind natural antibodies (NAb) measured through fluorescence analysis, although they could not be distinguished from the starting clones by absorption of NAb for complement-mediated lysis. The in vivo grown cells also exhibited a reduced sensitivity to hypotonic lysis, which was not detectable after preincubation at 4 degrees C or upon exposure to sodium azide, procedures that reduced the lysis of the starting clones. The differential susceptibility of the in vivo grown cells was increased to control levels by treatment with cycloheximide or colchicine. These studies suggest that a decreased sensitivity to lysis associated with a reduced autolytic process and an increased counterlytic mechanism, in addition to a reduced antigen expression for binding of NK cells and certain NAb contribute to this resistant phenotype, which may characterize tumors that arise under the selective pressure of natural resistance mechanisms in the natural course of neoplastic development.

Absorption↗

PubMed1985

Characterization of tumor progression from threshold tumor inocula: evidence for natural resistance.

An examination of the variant generation and selection hypothesis of tumor progression was undertaken using the NK-sensitive, NAb-sensitive SL2-5 lymphoma in the threshold inoculum model of tumor progression. Tumor cells obtained from the i.p. injection site expressed increased heterogeneity for sensitivity to syngeneic NAb and to NR measured in the 131IUdR-labelled tumor elimination assay. Cells retrieved from the s.c. injection site exhibited reductions in sensitivity to NR which correlated with decreases in sensitivity to syngeneic NAb and NK cells in vitro. These data confirm and extend our previous observations with the NK-resistant L5178Y-F9 lymphoma and further substantiate the evidence for the participation of NAb and NK cells in host-mediated anti-tumor resistance. Characterization of the model revealed that the selection for reduced sensitivity to NR in thymus-depleted AT x BM mice and normal animals could not be distinguished, suggesting that thymus-independent mechanisms may be major contributors to the surveillance of nascent tumors. The decreases in susceptibility to NR occurred in a stepwise and time-dependent manner in accord with the sequential multistage concept of progression. Furthermore, the selection for tumor cells which exhibited reductions in sensitivity to NR correlated with selection for increased tumorigenicity, in keeping with the idea that progression is associated with development towards an increasingly autonomous tumor.

Animals↗

PubMed1984

Variant generation and selection: an in vitro model of tumor progression.

Evidence for a new in vitro model of tumor progression was sought on the basis of the variant generation and selection hypothesis. The stability of a cloned murine tumor was examined during growth in standard tissue culture or in media containing the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Analysis of subclones from the appropriate tumor populations revealed that growth of the L5178Y-F9 clone in 100 ng/ml TPA and 0.1% dimethyl sulphoxide (DMSO) for 2 days yielded a tumor which exhibited increased cellular heterogeneity for susceptibility to both syngeneic and allogeneic natural antibodies (NAb). Subsequent exposure of TPA- and DMSO-treated cells to two cycles of syngeneic NAb-mediated cytolysis resulted in tumor populations which expressed a reduced sensitivity to syngeneic NAb. Thus the elements of tumor variant generation and selection were demonstrated by means of this approach, and repeated cycles of the TPA treatment and NAb cytolysis produced tumor cells with a reduced susceptibility not only to NAb in vitro but also to anti-tumor natural resistance (NR) measured in a tumor elimination assay in vivo. These observations extend the support for the notion that tumor progression can proceed through variant generation and selection. Furthermore, the association of tumor variant generation with exposure to the combination of TPA and DMSO, both non-mutagens, offers a model for studying non-mutagenic mechanisms of tumor development.

Animals↗

PubMed1984

Tumor selection in vivo for reduced sensitivity to natural resistance and natural antibodies.

The contribution of natural antibodies (NAb) to the selective elimination of tumor variants in vivo was studied to further support the hypothesis that NAb participate in host-mediated natural resistance (NR) against neoplasia. Tumors obtained after the sc, ip, or iv inoculation of the natural killer cell-resistant, natural antibody-sensitive L5178Y-F9 tumor clone into syngeneic DBA/2 mice were tested for their sensitivity to NR in the [131I]5-iodo-2'-deoxyuridine elimination assay and to serum NAb in the presence of complement. Cells removed from the ip or sc sites of tumor inoculation exhibited a reduced susceptibility to syngeneic NR and to syngeneic but not to allogeneic NAb. Tumors recovered from the spleen, brain, and lungs after iv inoculation also expressed a decreased sensitivity to both syngeneic NR and NAb. These data suggest that NR against tumors is widely disseminated and support the hypothesis that NAb participate in this antitumor defense, including the control of metastatic spread of disease. Tumors previously selected in vivo also exhibited reduced sensitivity to complement-mediated lysis by NAb acquired in the peritoneum. The correlation observed between this sensitivity to complement and the recovery of tumor cells after the ip injection of L5178Y-F9 contribute to the evidence that NAb acts in vivo.

Animals↗

PubMed1983

In vivo generation and selection of variants with altered sensitivity to natural resistance (NR): a model of tumor progression.

The stability of a cloned murine tumor for sensitivity to NR was examined following growth in vivo in order to test the hypothesis that tumor progression proceeds through the generation and selection of variants. Clonal sensitivity to the [131I]-dUrd elimination assay of NR was assessed for the L5178Y-F9 tumor grown in syngeneic DBA/2 mice or maintained solely in tissue culture. Subclones derived from a tumor obtained from the injection site 3 1/2 weeks after the s.c. inoculation of 25 cells were less sensitive to NR in comparison with subclones derived from cells grown only in vitro. Subclones from the cells grown in vivo exhibited increased heterogeneity in sensitivity to NR in addition to their expanded range of susceptibility to complement-mediated lysis by CBA serum natural antibodies. The extent of the heterogeneity argues against tumor "adaptation" forming the basis for the phenotypic alteration while chromosomal studies eliminate the possibility that a new tumor was induced. These data support the hypothesis that tumor progression proceeds through the random generation of variants and host-mediated selection for the proliferation of clones with an increased ability to survive.

Animals↗

PubMed1981

Murine natural anti-tumor antibodies. II. The contribution of natural antibodies to tumor surveillance.

The objective of this study was to investigate whether natural anti-tumor antibodies (NAb) contributed to the surveillance of small inocula of syngeneic tumors. Experiments were designed to distinguish between NAb and NK-mediated host resistance. Four approaches were used: (1) the isolation of tumor variants differing in their tumorigenicity and susceptibility to these mechanisms, and to activated macrophages; (2) a comparison of the effects of adjuvants on the modification of both host resistance and the activity of these effectors; (3) the relationship between the ontogeny of the natural resistance mechanisms and tumorigenicity in aged mice; and (4) the use of a Winn-type assay. These studies provided support for a role in natural resistance correlated with both the ability of tumors to bind NAb, and the production of NAb in adjuvant-stimulated mice. Furthermore, the frequency of tumors observed after tumor challenge more closely correlated with the ontogeny of natural antibody than NK cells, and tumors coated with NAb were less tumorigenic than controls. The reduced tumorigenicity of an NK-sensitive tumor, when compared to an NK-resistant variant of the same line, provided evidence for NK-cell-mediated natural resistance in young adult mice. It was concluded that natural resistance to tumors is a complex phenomenon dependent on the tumor phenotype, as well as the activity of several effector mechanisms, and that natural anti-tumor antibody must be considered an important component of host resistance.

Adjuvants, Immunologic↗

PubMed1981

Natural resistance to tumors is a heterogeneous immunological phenomenon. Evidence for non-NK cell mechanisms.

The contribution of natural killer (NK) cells to natural antitumor resistance (NR) in syngeneic DBA/2 mice was examined. Subclones from two NK-resistant tumors, P815 and L5178Y, were selected for tumorigenicity in NR assays measuring the tumor frequency of threshold doses and the elimination of 131IUdR-labelled cells. In vivo variation in sensitivity to NR did not correlate with in vitro NK cytolysis for these clones, but did for a third pair of clones from the SL2 lymphoma selected on the basis of sensitivity or resistance to NK lysis. In another series of experiments it was found that a decrease in NK cytolysis of the (NK-sensitive) SL2-5 lymphoma in aged DBA/2 contrasted with an increased rate of elimination and lower tumor frequency, suggesting that the ontogeny of these phenomena was not related. In addition, while interferon treatment of the (NK-sensitive) SL2-5 produced a corresponding decrease in susceptibility to NK cytolysis in vitro and a reduction in the in vivo elimination of 131I-labelled cells, tumor of the NK-resistant phenotype, interferon-treated in the same way, remained NK-resistant and was more rapidly eliminated. The failure to observe correlative changes in NK cytolysis associated with heterogeneity in tumorigenicity and with age-related or interferon-induced changes in NR suggest that NR cannot be due solely to an NK effector mechanism.

Animals↗

PubMed1981

Genetics, regulation, and specificity of murine natural antitumor antibodies and natural killer cells.

A concurrent study of specificity, regulation, ontogeny, and genetics of murine natural killer (NK) cell and natural antibody (NAb) activities [in DBA/2, CBA/J, A/Sn, and A/J inbred mice, Bg/Bg + mice of the inbred C57BL/6J background, (C57BL/6 x DBA/2) F1 mice, and (CBA x DBA/2) F1, (A/Sn x DBA/2)F1, and (A/J x DBA/2)F1 mice] revealed that : a) The expressions of NAb and NK cell specificities associated with the YAC-1 tumor were directly related and could not be distinguished on the basis of inhibition and absorption studies, whereas the expressions of the specificities associated with a second NK cell-sensitive tumor, the SL2 lymphoma, were not directly related. b) Treatment of mice with the adjuvants proteose peptone and lipopolysaccharide or the interferon inducers polyinosinic-polycytidylic acid and 2-amino-5-bromo-6-methyl-4-pyrimidinol resulted in increases in NAb levels and NK cells, which suggested that certain aspects of the regulation of these activities may be similar or the same. c) High NK cell activity was codominantly inherited and high serum NAb levels were recessive, which argues against the theory that the NK cell receptor is a passively acquired NAb. d) NK cell activity declined with increasing age in contrast with NAb levels that remained constant throughout adult life. e) Bg/Bg mutants that exhibit an NK Cell defect expressed normal levels of NAb. Despite the differences in their genetics, murine antitumor NAb and NK cells bear certain common features-in particular, their response to microbial products and interferon inducers and at least a portion of antigen repertoire against which they are directed.

Animals↗

PubMed1980

The generation of tumor heterogeneity in vivo.

In order to determine whether host factors may contribute to the generation of tumor heterogeneity, the phenotypic stability of cells from a cloned tumor was examined during proliferation in tissue culture and in the syngeneic host. Growth of this cloned tumor was initiated both in vivo and in vitro, and the tumor populations were sampled at different time intervals by subcloning. The susceptibility of these tumor subclones to the cytotoxic action of natural antibodies and complement was used as a marker of their membrane phenotype. The extent of phenotypic variation of the clones in one sample was considered to be a measure of tumor heterogeneity. Following these procedures, we observed that a clone of the L5178Y murine lymphoma maintained its homogeneity during 5 months of in vitro culture. In contrast, a single passage of the same tumor clone for 3 1/2 weeks or 3 months in the syngeneic host resulted in the generation of a population of cells exhibiting a significant increase in heterogeneity. This relative instability of tumor phenotype in vivo suggests that the host milieu may allow the generation of tumor heterogeneity. Genetic or epigenetic mechanism(s) may be involved although the high frequency of new phenotypes argues against a role for somatic mutation.

Animals↗

PubMed1979

Macrophage-dependent, NK-cell-independent "natural" surveillance of tumors in syngeneic mice.

The present study, which was designed to further characterize the "natural" T-independent rejection of syngenetic tumours (Greenberg and Greene, 1976), has revealed the following points: (1) no detectable DBA/2 NK cell activity was demonstrated against the syngeneic tumour lines studied, and these tumours were indensitive to NK cells from high-activity strains; (2) in addition the tumour frequencies in old and young mice receiving small tumour inocula were identical, in contrast with the reported decline in NK cell activity with age, suggesting that the surveillance of small inocula of these tumours was NK-cell-independent; (3) injection of silica intraperitoneally enhanced the frequency of tumours in normal and immunodeficient AT x BM mice, suggesting that the rejection mechanism was macrophage-dependent; (4) the effects of silica injection were maximal if administered 3 days prior to tumour injection, indicating that the period of time in which the rejection mechanism must act was very limited; (5) silica markedly decreased the survival of AKR mice dying of spontaneous tumours, providing evidence that the effect of this agent was not limited to model systems but would influence the appearance of spontaneous tumours; (6) reticuloendothelial stimulants such as mycobacterium butyricum and proteose peptone decreased the tumour frequency of small tumour inocula, indicating that the effector mechanism can be stimulated; and (7) soluble tumour antigen enhanced the tumour frequency in normal and immunodeficient mice, suggesting that the specific receptor molecule of the surveillance mechanism was not thymus-dependent.

Animals↗

PubMed1978

Surface membrane changes of T cells induced by syngeneic tumour cells. I. Formation and uptake of complexes of Ig and tumour antigens by T cells.

A large dose of tumour cells (10(7)) from two different tumours produced a significant increase of Ig-bearing spleen cells 6 h after intraperitoneal administration in syngeneic mice, like conventional antigens previously tested. Incubation of normal spleen cells in serum taken 6 h after administration of tumour cells reproduced in vitro the changes observed in the spleen cell population of the serum donors, demonstrating the presence of a cytophilic Ig, which was shown to be taken up by T cells. Serum collected 6 h after tumour cell inoculation contains also a 4S factor which can generate in vitro cytophilic Ig for T cells in the presence of a foreign soluble protein or tumour antigen. Extracts obtained from tumours cells, which were shown to contain tumour antigens, were labelled with 125I and mixed with the 4S factor and normal 7S Ig. Upon fractionation of the mixture, high molecular weight material containing radioactivity and 7S Ig were eluted in the void volume, well ahead of the position of both the tumour cell preparation and the 7S Ig. This material contained Ig cytophilic for splenic T cells and it is likely that it represents cytophilic complexes of Ig and tumour antigens. It is postulated that the cytophilic Ig detected in the serum of animals 6 h after injection of a large number of tumour cells represents cytophilic complexes of Ig and tumour antigens formed through the mediation of a soluble factor.

Animals↗

PubMed1978

Surface membrane changes of T cells induced by syngeneic tumour cells. II. T-cell defects induced by small tumour cell inocula or tumour cell antigens.

Injection of a large number of tumour cells, like other strong immunogenic challenges, is followed within 6 h by the uptake of cytophilic Ig (probably complexes) by a subpopulation of T cells. This phenomenon, known as the "6-hour T-cell response" is abrogated when small tumour cell inocula (10(2)), or small amounts of a preparation from tumour cells, which contains tumour antigens, are injected prior to the immunogenic challenge Abrogation of the "6-hour T-cell response" resulted in a decrease in specific anti-tumour cell immunity as tested in vitro by measuring growth inhibition (cytostasis). It has also resulted in loss of the amplifying function on antibody formation against sheep erythrocytes, normally detected in a T-B cell co-operative system when T cells are used 6 h after priming with sheep erythrocytes. It is postulated that this T-cell defect may represent a mechanism by which tumour cells, in the early stages of their growth, interfere with inductive stages of the immune response for a sufficient period of time to allow the tumour to grow beyond immune control.

Animals↗

PubMedDate not supplied

p21ras independent down-regulation of ras-induced increases in natural antibody binding during tumor progression.

Selective outgrowth of v-H-ras-infected 10T1/2 cells based on the cointroduction of a gene for resistance to geneticin (G418), yielded cells which exhibited an increased capacity to bind polyclonal serum natural antibody (NAb). This demonstrated an NAb-susceptible phase of tumor development which would be a basic requirement for NAb-mediated surveillance of tumors. The ras-oncogene dependence of the high-NAb-binding phenotype provided a model for assessing NAb resistance against ras transformants in vivo and for a comparative analysis of phenotypic and genetic alterations contributing to the progression of ras transformants. Variants were developed through in vitro and in vivo models of tumor progression. T24-H-ras and v-H-ras transformants were isolated in vitro through more rigorous growth conditions, focus formation in the presence of untransformed cells with no selecting drug. These clones expressed p21ras but exhibited little or no increase in NAb binding. Variants recovered following growth from intravenous or threshold subcutaneous (s.c.) inocula of high-NAb-binding ras transformants in syngeneic C3H/HeN mice exhibited decreases in NAb binding but no uniform change in p21ras. Concurring inverse correlations between NAb binding and s.c. tumorigenicity were exhibited by the T24-H-ras transformant clones, the ras transformants grown in vivo, and the v-H-ras-transformed clones isolated in the presence versus the absence of untransformed cells. This consistent inverse correlation, together with the reduced NAb binding of the ras transformants grown in vivo, provides strong evidence that NAb participates in the defense against ras-transformed cells in vivo. The lack of any direct correlation between p21ras expression and the reduction in NAb binding or the increase in tumorigenicity of cells generated through progression in vivo suggested the regulatory action of additional genes. Hybridization studies between high- and low-NAb-binding clones implicated the activation of an additional oncogene and inactivation of an antioncogene in the down-regulation of the ras-induced increases in NAb binding associated with tumor progression.

Animals↗

PubMedDate not supplied

Phorbol ester tumor promoter regulation of natural antitumor antibody binding depends on protein kinase C and an intact microfilament system.

Phorbol ester tumor promoter treatment produced a biphasic effect on the binding of polyclonal whole-serum natural antibody (NAb) by L5178Y-F9 murine lymphoma cells. In vitro tumor growth in 100 ng/ml 12-O-tetradecanoylphorbol-13-acetate (TPA) produced a rapid decrease followed by a reversible and unstable increase in NAb binding detected at 4 degrees C. The latter was associated with a functional decrease in NAb binding at 37 degrees C and increases in the tumorigenic and metastatic potentials in vivo. Colchicine, cytochalasin B and sodium azide inhibited the NAb binding of TPA-treated cells, while only colchicine reduced the binding of controls, suggesting the dependence of the TPA-induced increase in NAb binding on microfilament organization and active energy production. The non-tumor-promoting, non-PKC-activating TPA analogue 4-O-Me-TPA failed to alter NAb binding, arguing against nonspecific effects of TPA. The non-tumor-promoting, PKC-activating diacylglycerol, OAG, reproduced the initial decrease in NAb binding but was unable to mimic the subsequent TPA-induced increase. The PKC inhibitor H-7, but not HA1004, could block the TPA-induced increase in NAb binding. Together the data argue that PKC activation is required for both TPA-induced changes in NAb binding but that it is not sufficient to generate the energy- and microfilament-system-dependent, unstable high-NAb-binding phenotype associated with increased tumor progression.

Actin Cytoskeleton↗