Supra-additive cytotoxic effects of a combination of cytostatic drugs and antibody-induced complement activation on tumor cells in vitro.

Chemotherapy with cytostatic and cytotoxic drugs is the main treatment modality for disseminated cancer. However, despite initial clinical responses seen in certain histotypes, such as small cell lung cancer, relapses mostly occur with chemoresistant phenotypes. In order to prolong the relapse-free period, a combination of chemo- and immunotherapy might offer a new treatment strategy. Here, we have tested our hypothesis that complement activation, induced by monoclonal antibodies, in combination with cytostatic drugs may result in additive cytotoxicity in vitro. Doxorubicin, cisplatinum and etoposide were tested in combination with human complement and a murine monoclonal antibody (MAb F12) directed against the tumor-associated ganglioside antigen fucosyl GM1 on a rat hepatoma (H4-II-E) cell line which was used as tumor model. Using the MTT assay to measure cell survival, supra-additive (i.e. synergistic) cytotoxic effects were seen with each of the cytostatic drugs, the strongest being observed with doxorubicin. These results show promise for further research exploring possible prognostically favorable interactions between cytostatic drugs and monoclonal antibodies in the treatment of cancer.     

Cytotoxic and biochemical effects of thymidine and 3-deazauridine on human tumor cells

Cytotoxicity and perturbations of the deoxyribonucleoside triphosphate pools caused by thymidine were studied in thymidine-sensitive and -resistant human tumor cells. Incubation with 1 mM thymidine reduced cell viability by more than 90% in the three sensitive cell lines (two melanomas and one adrenal carcinoma) and reduced the growth rate without decreasing the viability of resistant LO melanoma cells. Thymidine (1 mM) greatly increased the ratio of the deoxythymidine 5'-triphosphate to deoxycytidine 5'-triphosphate pools in the sensitive cells compared to LO cells and also caused larger relative increases in the pool sizes of deoxyguanosine 5'-triphosphate and deoxyadenosine 5'-triphosphate in the sensitive compared to the resistant cells. 3-Deazauridine, known to inhibit synthesis of deoxycytidine 5'-triphosphate and cytidine 5'-triphosphate in other cell lines, potentiated the cytotoxicity of thymidine for thymidine-sensitive BE melanoma and LO cells. In LO cells, 3-deazauridine (50 microM) decreased the intracellular pool of deoxycytidine 5'-triphosphate to the level obtained with 1 mM thymidine. Lower concentrations of deoxycytidine as compared to cytidine were required to protect BE and LO cells against the cytotoxicity of thymidine plus 3-deazauridine. Deoxycytidine also was more effective than was cytidine in preventing loss of cell viability after exposure to thymidine or to 3-deazauridine individually. In these human melanoma cells, ribonucleotide reductase may be a major site of action of thymidine, of 3-deazauridine, and of both drugs in combination. These results indicate that in human tumor cells the cytotoxic effect of thymidine correlates with greater perturbations of the pyrimidine deoxyribonucleoside 5'-triphosphate pools and that thymidine and 3-deazauridine, which independently reduce the intracellular levels of deoxycytidine 5'-triphosphate, act synergistically against human tumor cells.     

Ascorbate exerts anti-proliferative effects through cell cycle inhibition and sensitizes tumor cells towards cytostatic drugs

Purpose

While the benefits of ascorbic acid (vitamin C, ascorbate) as an essential nutrient are well established, its effects on tumor cells and in tumor treatment are controversial. In particular, conflicting data exist whether ascorbate may increase the cytotoxic effects of antineoplastic drugs or may rather exert adverse effects on drug sensitivity during cancer treatment. Findings are further obscured regarding the distinction between ascorbate and dehydroascorbate (DHA). Thus, the purpose of this study was to evaluate and directly compare the cytotoxic efficacy of ascorbate compared to DHA, and to analyse if ascorbate at pharmacological concentrations affects the efficacy of antineoplastic agents in prostate carcinoma cells.

Methods

We directly compare the effects of ascorbate (supplied as ??Pascorbin^? solution for injection??) and DHA on tumor cell viability, and determine IC₅₀ values for various cell lines. At concentrations well below the IC₅₀, ascorbate effects on cell proliferation and cell cycle are analysed. We furthermore determine changes in cellular sensitivity towards various cytostatic drugs upon pre-treatment of cells with ascorbate.

Results

We demonstrate higher therapeutic efficacy of ascorbate over DHA in various cell lines, independent of cell line-specific differences in ascorbate sensitivity, and identify the extracellular generation of H₂O₂ as critical mechanism of ascorbate action. We furthermore show that, in addition to pro-apoptotic effects described previously, ascorbate treatment already at concentrations well below the IC₅₀ exerts anti-proliferative effects on tumor cells. Those are based on interference with the cell cycle, namely by inducing a G₀/G₁ arrest. Pre-treatment of tumor cells with ascorbate leads to increased cellular sensitivity towards Docetaxel, Epirubicin, Irinotecan and 5-FU, but not towards Oxaliplatin and Vinorelbin. For Docetaxel and 5-FU, a linear correlation between this sensitizing effect and the ascorbate dosage is observed.

Conclusions

The redox-active form of vitamin C, ascorbate, shows therapeutic efficacy in tumor cells. These antitumor effects of ascorbate are mainly based on its extracellular action and, in addition to the induction of apoptosis, also include an anti-proliferative effect by inducing cell cycle arrest. Furthermore, ascorbate treatment specifically enhances the cytostatic potency of certain chemotherapeutics, which implicates therapeutic benefit during tumor treatment.     

Cytolytic and cytostatic activity on tumor cells of circulating human monocytes.

Monocytes from the peripheral blood of normal adult human donors were found to have appreciable levels of cytotoxic activity against murine and human tumor-cell lines. Adherent cells ( > 90% monocytes) were obtained from the peripheral blood of 29 normal healthy volunteers either by adherence on plastic and scraping with a rubber policeman or by adherence on microexudate-coated plastic and exposure to ethylene diamine tetra-acetic acid. Cytolytic capacity was tested by incubating effector cells for 72 h with murine and human tumor cell lines prelabelled with tritiated thy-midine. Cytostasis was evaluated by inhibition of [¹²⁵I]iododeoxyuridine (¹²⁵IdUrd) uptake. Tumor target cells employed were: a murine SV40-trans-formed kidney line (TU5), a murine chemically-induced sarcoma (1023), a human breast-cancer-derived cell line (G11) and a human lung-cancer-derived cell line (CaLu). Monocyte preparations at attacker to target cell ratios of 1:1 to 40:1, showed significant cytolytic and cytostatic activity against tumor target cells. Tumor cells showed different susceptibility to cytolytic activity, whereas comparable levels of cytostasls were observed with the various targets: TU5 and G11 tumor cells were more susceptible than 1023 and CaLu target cells to the cytolytic capacity of human monocytes and TU5 was used in most subsequent experiments. Peak isotope release from prelabelled target cells was observed after 72 h of incubation, whereas peak inhibition of [¹²⁵I]dUrd uptake occurred after 24 h of culture. The cytotoxic capacity of monocytes isolated by either of the two methods mentioned above was similar. The monocytes had higher cytotoxic activity than unseparated mononuclear cells, and non-adherent cells showed minimal cytotoxic effects. Cytotoxicity by natural killer cells did not appear to have a major role in these assays, since adherent cells did not lyse K562 cells in a 4-h ⁵¹Cr release assay. Treatment with anti-human T-cell serum and complement did not inhibit the cytotoxic capacity of the monocyte preparations, whereas exposure to silica particles significantly inhibited the cytotoxic activity. Monocyte-mediated cytotoxicity on tumor cells was expressed in the presence of both fetal bovine serum and human AB serum.     

Cytotoxic and cytostatic effects of the streptococcal preparation OK-432 and its subcellular fractions on human ovarian tumor cells

Previous studies have indicated that OK-432 is a potent biologic response modifier (BRM) and that it augments immune responses to tumor cells. We studied the direct effect of OK-432 on tumor cells. Established and freshly derived human ovarian carcinoma lines were examined for their susceptibility to OK-432 or its subcellular fractions in direct cytotoxicity, cytostatic activity, and inhibition of metabolic activity. OK-432 was cytotoxic to 13 of 15 freshly derived ovarian carcinoma lines in a 24-hour chromium-51 (51Cr) release assay. The optimal effect was noticed at OK-432 concentrations between 0.1 and 1.0 Klinishe Einhert (KE) per milliliter. The cytostatic effect on two established lines and one fresh line correlated with the cytotoxic activity. In all three lines, however, the metabolic activities (DNA, RNA, and protein synthesis) were inhibited by OK-432, suggesting that cell lysis by OK-432 may not be directly correlated with the inhibition of metabolic activities. Several subcellular fractions were derived from OK-432 and only the cytoplasmic and protoplast membrane fractions showed cytotoxic activity against the OK-432-sensitive tumor cell lines, although the cytotoxicity obtained was greatly less than the whole microorganism OK-432. The direct binding of 14C-OK-432 to tumor cells was examined. Binding took place rapidly after 1 hour of incubation and reached a maximum activity at 37 degrees C. Binding in all three lines ranged between 1.7 and 2.7 pg/cell. These results demonstrate the direct cytotoxic effect of OK-432 and some subcellular fractions on human ovarian carcinoma lines. These results also show that the BRM OK-432 may exert its effect by both potentiating the antitumor response and directly inhibiting tumor cell growth.     

Three-dimensional co-culture of human monocytes and macrophages with tumor cells: Analysis of macrophage differentiation and activation

Here we report on an experimental system for generating TAM in vitro by culturing human MO and MO-derived macrophages (MAC) within 3-dimensional multicellular tumor spheroids (MCS). MO as well as MO-derived MAC migrate into tumor spheroids and spread throughout the entire spheroid within 16 hr. In contrast, fibroblast-spheroids were not infiltrated. The regular expression of MAC maturation-associated antigens on infiltrating MO was suppressed within MCS of the undifferentiated bladder carcinoma line J82 with regard to carboxypeptidase M (CPM), MAX.3 antigen and CD105. However, MAC within spheroids of highly differentiated papillary RT4 cells failed only the single antigen CD51, whereas MAC expressed the complete maturation-associated phenotype within nontumorigenic HCV29 spheroids. Interestingly, the suppressive effect of J82 carcinoma cells could only be observed in 3-dimensional but not in monolayer cultures. The J82-MCS induced suppression of CPM and MAX.3 expression was only seen to be operative on infiltrating blood MO: MO first differentiated for 2 days and subsequently co-cultured with J82-MCS showed normal expression of MAX.3 and CPM within the spheroid. Besides the modulation of MAC phenotype, the cytokine response of intraspheroidal MAC was analyzed: upon co-culture MO secreted high IL-1β and IL-6 but low amounts of TNF-α as compared to MAC. This MO typical cytokine pattern remained constant for up to B days in culture, again indicating a disturbed MO to MAC maturation within tumor spheroids. In conclusion, a 3-dimensional interaction with tumor cells in vitro results in significant changes in the phenotype and function of the spheroid-associated MO and MAC. © 1996 Wiley-Liss, Inc.     

Chemosensitivity of solid tumor cells in vitro is related to activation of the CD95 system

We have identified the CD95 system as a key mediator of chemotherapy-induced apoptosis in leukemia and neuroblastoma cells. Here, we report that sensitivity of various solid tumor cell lines for drug-induced cell death corresponds to activation of the CD95 system. Upon drug treatment, strong induction of CD95 ligand (CD95-L) and caspase activity were found in chemosensitive tumor cells (Hodgkin, Ewing's sarcoma, colon carcinoma and small cell lung carcinoma) but not in tumor cells which responded poorly to drug treatment (breast carcinoma and renal cell carcinoma). Blockade of CD95 using F(ab′)₂ anti-CD95 antibody fragments markedly reduced drug-induced apoptosis, suggesting that drug-triggered apoptosis depended on CD95-L/receptor interaction. Moreover, drug treatment induced CD95 expression, thereby increasing sensitivity for CD95-induced apoptosis. Drug-induced apoptosis critically depended on activation of caspases (ICE/Ced-3-like proteases) since the broad-spectrum inhibitor of caspases zVAD-fmk strongly reduced drug-mediated apoptosis. The prototype substrate of caspases, poly(ADP-ribose) polymerase, was cleaved upon drug treatment, suggesting that CD95-L triggered autocrine/paracrine death via activation of caspases. Our data suggest that chemosensitivity of solid tumor cells depends on intact apoptosis pathways involving activation of the CD95 system and processing of caspases. Our findings may have important implications for new treatment approaches to increase sensitivity and to overcome resistance of solid tumors. Int. J. Cancer 76:105–114, 1998.© 1998 Wiley-Liss, Inc.     

蟾蜍灵对宫颈癌细胞的增殖抑制作用及其机制研究

背景与目的：宫颈癌仍然是妇科肿瘤致死病因的第二位,部分原因为化疗耐药。蟾蜍灵是传统中药蟾酥的成分之一,目前在国内广泛应用于肿瘤的治疗中。该研究旨在探讨蟾蜍灵对宫颈癌细胞ME180和C33A的增殖抑制作用及相关机制。方法：采用CCK8(cell counting kit-8)法检测蟾蜍灵对宫颈癌细胞增殖的抑制作用,采用葡萄糖检测分析试剂盒(glucose assay kit)进行细胞内糖代谢检测分析,采用实时荧光定量聚合酶链反应(quantitative real-time polymerase chain reaction,qRT-PCR)检测细胞内葡萄糖转运蛋白1(glucose transporter 1,GLUT1)和己糖激酶2(hexokinase 2,HK2)的mRNA的表达水平,采用蛋白［质］印迹法(Western blot)检测原癌基因C-MYC和缺氧诱导因子1α(Hif-1α)表达的变化。结果：CCK8法结果显示,蟾蜍灵能明显抑制宫颈癌细胞ME180和C33A细胞增殖(P=0.027,P=0.018)。糖代谢检测结果显示,蟾蜍灵处理组葡萄糖代谢水平显著降低(P=0.034,P=0.036)。qRT-PCR检测结果显示,蟾蜍灵处理组糖代谢相关指标GLUT1(P=0.019,P=0.016)和HK2(P=0.039,P=0.041)的表达水平明显下调。Western blot检测结果显示,蟾蜍灵处理后宫颈癌细胞内C-MYC和Hif-1α蛋白表达水平显著下调。结论：蟾蜍灵可以通过降低宫颈癌细胞ME180和C33A糖代谢水平,从而抑制细胞增殖。     

Role of tumor necrosis factor in macrophage activation and tumoricidal activity

Tumor necrosis factor (TNF)-sensitive (LM) and -insensitive (P815) target cell lines were used to examine the role of TNF in both the activation and lytic phases of macrophage-mediated lysis. LM cells were lysed spontaneously by thioglycolate-elicited macrophages in an 18-h assay (media or activating agents added with targets) or 36-h assay (macrophages cultured with media or activating agents for 18 h, washed, and targets added for a subsequent 18 h). In contrast, P815 cells were lysed only in the 36-h assay by macrophages exposed to appropriate activation signals. Using antibody to murine TNF, it was shown that lysis of LM cells but not P815 cells was TNF mediated. The addition of lipopolysaccharide (LPS) to the 18-h assay resulted in augmented LM killing. This was probably due to the fact that LPS stimulates macrophages to produce TNF. Conversely, when macrophages were pretreated with LPS for 18 h, washed, and assessed for lytic activity during the subsequent 18 h, lysis of LM cells was reduced relative to the endogenous level. Although macrophage lysis of P815 was not mediated by TNF, the addition of TNF to macrophage activation cultures facilitated LPS triggering of cytolytic activity against P815. Similarly, the addition of TNF to the activation cultures partially prevented the LPS-induced reduction in macrophage-mediated LM cell lysis. Taken together, these data suggest that TNF may act as an autocrine signal during macrophage activation, in addition to being directly lytic to a select number of sensitive target cell lines.     

Cytotoxic and cytostatic effects of arecoline and sodium nitrite on human cells in vitro

Arecoline, an active alkaloid of Areca catechu L., and sodium nitrite, a food additive, are highly cytotoxic and cytostatic on the Hep 2 cell line when administered in an acidic environment (pH 4.2) in the presence of S-9 mixture. Hep 2 cells (10(6)) were treated with either 0.145, 0.725 or 1.449 mM sodium nitrite or 0.042, 0.085 or 0.339 mM arecoline or sodium nitrite (0.145 mM) plus varied concentrations of arecoline (0.042, 0.085 or 0.339 mM). Their effects were additive in nature. Hep 2 cells exposed to this combination showed reduced cell survival, and lower rates of DNA and protein syntheses. Involvement of N-nitroso derivatives of arecoline is suggested to explain the results. On the basis of these studies, we speculate that N-nitroso compounds derived from arecoline can (weakly) interact with DNA.     

The cytostatic and cytotoxic effects of oridonin (Rubescenin), a diterpenoid from Rabdosia rubescens, on tumor cells of different lineage

Rabdosia rubescens is a herbal medicine used to treat esophageal cancer in China. In this study, the sesquiterpene oridonin, an isoprenoid, was isolated from Rabdosia rubescens. Mass spectroscopy and carbon 13 NMR spectroscopy were used to identify the structure of the purified compound. It was then evaluated for biological activity against human cell lines derived from prostate (DU-145, LNCaP), breast (MCF-7), and ovarian (A2780 and PTX10) cancers. Oridonin exhibited anti-proliferative activity toward all cancer cell lines tested, with an IC50 estimated by the MTT cell viability assay ranging from 5.8+/-2.3 to 11.72+/-4.8 microM. Flow cytometric analysis demonstrated that oridonin induced a G1 phase arrest in androgen receptor-positive LNCaP cells containing wt p53, while it blocked the cell cycle at G2 and M phases in androgen receptor-negative DU-145 cells with mutated p53; the arrest in M was verified by examination of cell morphology and by the increased frequency of cells with Ser-10 phosphorylated histone H3. The increased incidence of apoptosis, identified by characteristic changes in cell morphology, was seen in tumor lines treated with oridonin. Notably, at concentrations that induced apoptosis among tumor cells, oridonin failed to induce apoptosis in cultures of normal human fibroblasts. Western blot analysis was used to determine the protein expression of cancer suppressor genes, p53 (wt) and Bax, and the proto-oncogene, Bcl-2 in LNCaP cells following treatment with oridonin. Oridonin up-regulated p53 and Bax and down-regulated Bcl-2 expression in a dose-dependent manner. To further explore the possible interaction between oridonin and DNA, its absorption spectrum was measured in the presence and absence of double stranded (ds) DNA. Spectral shifts and an increase in absorption band intensity were observed indicating interaction of oridonin with DNA bases. The nature of the binding is not clear at present though no evidence of histone H2AX phosphorylation on Ser-139 was apparent in DU-145 cells treated with oridonin that would indicate the induction of ds DNA breaks. In conclusion, oridonin inhibits cancer cell growth in a cell cycle specific manner and shifts the balance between pro- and anti-apoptotic proteins in favor of apoptosis. The present data suggest that further studies are warranted to assess the potential of oridonin in cancer prevention and/or treatment.     

Growth and biochemical effects of unsymmetrically substituted polyamine analogues in human lung tumor cells 1

Three unsymmetrically substituted polyamine analogues demonstrate significant and selective antitumor effects. Each of the analoguesN ¹-ethyl-N ¹¹-propargyl-4,8-diazaundecane (PENSpm),N ¹-ethyl-N ¹¹-(cyclobutyl)methyl-4,8-diazaundecane (CBENSpm), andN ¹-ethyl-N ¹¹-(cyclopropyl)methyl-4,8-diazaundecane (CPENSpm) is cytotoxic to a representative non-small-cell lung carcinoma line, NCI H157, while being only growth-inhibitory to a representative small-cell-lung carcinoma line, NCI H82. Cytotoxicity is accompanied by a significant increase in expression of the polyamine catabolic enzyme spermidine/spermineN ¹-acetyltransferase (SSAT) at the levels of activity and steady-state mRNA. These new analogues are significant both for their cell-type-specific activity and as synthetic prototypes for the addition of SSAT-activated functional groups.     

Direct toxic effects of immunopotentiators on monocytic, myelomonocytic, and histiocytic or macrophage tumor cells in culture.

Four murine monocyte, myelomonocyte, and histiocyte or macrophage tumor cell lines adapted to culture were growth inhibited by one or more of the following macrophage-activating substances: Mycobacterium bovis, Bacillus Calmette-Guérin strain, zymosan, lipopolysaccharide, and dextran sulfate, as well as tuberculin purified protein derivative, but not latex beads. Lipopolysaccharide was effective with one line at 4 ng/ml. All four lines actively phagocytosed zymosan and latex beads. In many cases the growth inhibition was apparently immediate but only cytostatic, and cell proliferation resumed upon removal of the drug. Bacillus Calmette-Guérin, live or boiled, was toxic to some of the tumor lines. Synthesis of lysozyme by all the cell lines in the monocyte series and production of granulocyte colony-stimulating factor by the myelomonocytic leukemia were not inhibited during several days of zero growth conditions in the presence of drugs. Since these agents had no direct effect on other hematopoietic tumor types (myeloma, T-lymphoma, mastocytoma) at the same or up to 10(4) higher concentrations, it is proposed that the sensitive tumors retain specific receptors for immunostimulants, either at the cell surface or within the cell in the case of phagocytosable particles. The binding of these agents to physiological receptors leads to stimulation and mitogenesis in normal macrophages and lymphocytes but leads to growth inhibition without affecting differenetiated functions in the corresponding tumor lines.     

Constitutive integrin activation on tumor cells contributes to progression of leptomeningeal metastases

Leptomeningeal metastases are a serious neurological complication in cancer patients and associated with a dismal prognosis. Tumor cells that enter the subarachnoid space adhere to the leptomeninges and form tumor deposits. It is largely unknown which adhesion molecules mediate tumor cell adhesion to leptomeninges. We studied the role of integrin expression and activation in the progression of leptomeningeal metastases. For this study, we used a mouse acute lymphocytic leukemic cell line that was grown in suspension (L1210-S cell line) to develop an adherent L1210 cell line (L1210-A) by selectively culturing the few adherent cells in the cell culture. beta1, beta2, and beta3 integrins were in a constitutively high active state on L1210-A cells and in a low, but inducible, active state on L1210-S cells. Expression levels of these integrins were comparable in the two cell lines. Static adhesion levels of L1210-A cells on a leptomeningeal cell layer were significantly higher than those of L1210-S cells. All mice that were injected intrathecally with L1210-A cells died rapidly of leptomeningeal leukemia. In contrast, 45% long-term survival was seen after intrathecal injection of mice with L1210-S cells. Our data indicate that constitutive integrin activation on leukemic cells promotes progression of leptomeningeal leukemia by increased tumor cell adhesion to the leptomeninges. We argue that an aberrantly regulated inside-out signaling pathway underlies constitutive integrin activation on the adherent leukemic cell population.     

Regulatory T cells control macrophage accumulation and activation in lymphoma

Strategies of manipulating immunosuppressive regulatory T cells (Treg) in cancer patients are currently evaluated in clinical trials. Treg suppress immune responses of tumor‐specific T cells; yet, relatively little is known about the impact of Treg on innate immune cells in tumor models in vivo. Many tumors lose expression of MHC class I. Therefore, our study aimed at defining strategies to strengthen immune responses against a high tumor burden of the MHC class I‐deficient mouse lymphoma RMA‐S. We demonstrate that Treg depletion in mice led to tumor rejection that was dependent on T cells, NK cells and IFN‐γ. In the absence of Treg elevated levels of IFN‐γ were produced by tumor‐infiltrating T cells and NK cells. Tumor rejection observed in the absence of Treg correlated with a substantial IFN‐γ‐dependent increase in the numbers of tumor‐infiltrating leukocytes. The most abundant cell population in the tumors was macrophages. Tumor‐infiltrating macrophages from Treg‐depleted mice expressed increased amounts of MHC class II, produced highly enhanced levels of pro‐inflammatory cytokines and inhibited tumor cell proliferation. It was reported that tumor‐infiltrating macrophages have multi‐faceted functions promoting or counteracting tumor growth. In our study, high numbers of macrophages infiltrating RMA‐S tumors in the absence of Treg correlated with tumor rejection suggesting that macrophages are additional targets for Treg‐mediated immune suppression in cancer.     

Cytolytic activity against tumor cells by macrophage cell lines and augmentation by macrophage stimulants

Previous studies have shown that macrophage cell lines retained the ability to phagocytize, to secrete lysosomal enzymes, and to function as effector cells in antibody-dependent cellular cytoxicity. In this paper, the cytolytic activity of murine macrophage cell lines against tumor target cells was assessed using an 18-h 51Cr release assay. Of the macrophage cell lines tested, RAW 264, PU5-1.8 and IC-21 had intermediate to high levels of spontaneous cytolytic activity, P388D, and J774 had low to intermediate levels, while /WEHI-3 showed little or no cytolytic activity against RBL-5, MBL-2 and TU-5 target cells. Tumor-cell killing by macrophage cell lines could be augmented by the addition of macrophage stimulants, such as bacterial lipopolysaccharide and poly I:C, indicating that the activation of macrophages by these stimulants does not require the participation of other cell types. Treatment with interferon also augmented the tumor-cell killing by macrophage cell lines. Although the mechanism by which these cell lines exert their spontaneous or boosted cytotoxic activity is not clear, it does not appear to be due to depletion of nutrients since cell lines with high metabolic and proliferative activities, such as WEHI-3 and RBL-5, showed little or no cytotoxicity and supernatants from the macrophage cell lines did not exert any cytotoxic effects in their essay. Thus, it appears that the different macrophage cell lines represent different levels of activation and/or differentiation and may be useful for studying the development of these processes as well as providing a useful tool for analyzing the mechanisms of macrophage-mediated cytolysis.     

Molecular mechanisms for activated macrophage recognition of tumor cells

The biological heterogeneity of tumor cells requires a therapeutic modality that recognizes and kills resistant as well as susceptible tumor cells but does not harm normal cells. Tumoricidal macrophages appear to be able to fulfill these criteria. The mechanisms by which macrophages recognize tumor cells are not known, but they recognize carbohydrates and proteins that may be relevant for binding to tumor cells. In addition, phospholipids appear to be involved in the macrophage-tumor cell interaction. The abnormal presence of phosphatidylserine (PS) on the outer leaflet of tumor cells correlates with enhanced binding and cytotoxicity by macrophages.     

Dimethylarsinic acid effects on DNA damage and oxidative stress related biochemical parameters in B6C3F1 mice.

Adult female B6C3F1 mice were given 720 mg/kg of DMA by oral gavage at one of three times (2 h, 15 h, or at both 21 and 4 h) before sacrifice. Significant (P < 0.05) decreases in liver GSH and GSSG contents (15-37%) were observed. Some evidence of DMA-induced hepatic DNA damage (at the P < 0.10 level only) was observed. Pulmonary and hepatic ODC activities were reduced (19-59%) by DMA treatment. Overall, these biochemical studies show that mice are much less responsive to DMA than rats.