Showing papers in "Cancer Research in 1991"

Participation of p53 Protein in the Cellular Response to DNA Damage

Abstract: The inhibition of replicative DNA synthesis that follows DNA damage may be critical for avoiding genetic lesions that could contribute to cellular transformation. Exposure of ML-1 myeloblastic leukemia cells to nonlethal doses of the DNA damaging agents, gamma-irradiation or actinomycin D, causes a transient inhibition of replicative DNA synthesis via both G1 and G2 arrests. Levels of p53 protein in ML-1 cells and in proliferating normal bone marrow myeloid progenitor cells increase and decrease in temporal association with the G1 arrest. In contrast, the S-phase arrest of ML-1 cells caused by exposure to the anti-metabolite, cytosine arabinoside, which does not directly damage DNA, is not associated with a significant change in p53 protein levels. Caffeine treatment blocks both the G1 arrest and the induction of p53 protein after gamma-irradiation, thus suggesting that blocking the induction of p53 protein may contribute to the previously observed effects of caffeine on cell cycle changes after DNA damage. Unlike ML-1 cells and normal bone marrow myeloid progenitor cells, hematopoietic cells that either lack p53 gene expression or overexpress a mutant form of the p53 gene do not exhibit a G1 arrest after gamma-irradiation; however, the G2 arrest is unaffected by the status of the p53 gene. These results suggest a role for the wild-type p53 protein in the inhibition of DNA synthesis that follows DNA damage and thus suggest a new mechanism for how the loss of wild-type p53 might contribute to tumorigenesis.

Production of Large Amounts of Hydrogen Peroxide by Human Tumor Cells

Abstract: Few nonphagocytic cells are known to generate reactive oxygen intermediates. Based on horseradish peroxidase-dependent, catalase-inhibitable oxidation of fluorescent scopoletin, seven human tumor cell lines constitutively elaborated H2O2 at rates (up to 0.5 nmol/10(4) cells/h) large enough that cumulative amounts at 4 h were comparable to the amount of H2O2 produced by phorbol ester-triggered neutrophils. Superoxide dismutase-inhibitable ferricytochrome c reduction was detectable at much lower rates. H2O2 production was inhibited by diphenyleneiodonium, a flavoprotein binder (concentration producing 50% inhibition, 0.3 microM), and diethyldithiocarbamate, a divalent cation chelator (concentration producing 50% inhibition, 3 microM), but not by cyanide or azide, inhibitors of electron transport, or by agents that inhibit xanthine oxidase, polyamine oxidase, or cytochrome P450. Cytochrome b559, present in human phagocytes and lymphocytes, was undetectable in these tumor cells by a sensitive spectrophotometric method. Mouse fibroblasts transfected with human tyrosinase complementary DNA made melanin, but not H2O2. Constitutive generation of large amounts of reactive oxygen intermediates, if it occurs in vivo, might contribute to the ability of some tumors to mutate, inhibit antiproteases, injure local tissues, and therefore promote tumor heterogeneity, invasion, and metastasis.

Mutator Phenotype May Be Required for Multistage Carcinogenesis

Abstract: There is increasing evidence that the pathogenesis of cancer proceeds by sequential steps from normal cells to premalignant foci to localized tumors to invasive tumors and to metastatic lesions. The concept of stages of tumor progression was initially analyzed by Foulds (1), and a model for tumor progression based on genetic instability and clonal selection has been pro posed by Nowell (2). Individual steps in tumor progression have been operationally delineated in mouse skin by the responses of cells to different chemicals (3). A progression of phenotypic changes has been described in human tumors, the anatomical localization of which has made it feasible to obtain serial biopsies (2, 4). Sequential somatic chromosomal abnormalities have been reported in human cancers including malignant mel anoma (5), colon cancer (6), gliomas (7), adenocarcinoma of the esophagus (8), and small cell carcinomas of the lung (9). In addition, a multiplicity of different mutations has been carefully documented in human breast cancer (10). The dilemma is that there are too many mutations in human tumors. In this perspective, I will consider the relationships between mutation rates and cancer. At least two mutations are required to account for the chromosomal changes observed in certain human inherited diseases (11). An analysis of the literature indicates that the spontaneous mutation rate in cells is of sufficient magnitude to account for a two mutation hypothesis for the initiation of cancer. However, a larger number of mu tations are observed in many human tumors. The spontaneous mutation rate in somatic cells is not sufficient to account for these multiple mutations. If the multiple mutations in tumors are causally associated with and not just an accompaniment of cancer, then I argue that an early step in tumor progression is one that induces a mutator phenotype. An increased mutation rate in tumors could be the basis for the multiple mutations that characterize many cancers.

A potent specific pure antiestrogen with clinical potential.

Abstract: Previous studies from this laboratory have described a series of 7 alpha-alkylamide analogues of estradiol with pure antiestrogenic activity, exemplified by ICI 164,384. A new compound, 7 alpha-[9-(4,4,5,5,5-pentafluoropentylsulfinyl)nonyl]estra-1,3,5(10 )- triene-3,17 beta-diol (ICI 182,780) has now been identified which has significantly increased antiestrogenic potency and retains pure estrogen antagonist activity. The antiuterotrophic potency of ICI 182,780 in the immature rat was more than 10-fold greater than that of ICI 164,384 (50% effective doses of 0.06 and 0.9 mg/kg, respectively). This order of magnitude increase of in vivo potency was also reflected, in part, by intrinsic activity at the estrogen receptor. The relative binding affinities of ICI 182,780 and ICI 164,384 were 0.89 and 0.19, respectively, compared with that of estradiol (1.0). Similarly, the in vitro growth-inhibitory potency of ICI 182,780 exceeded that of ICI 164,384 in MCF-7 human breast cancer cells, where 50% inhibitory concentrations of 0.29 and 1.3 nM, respectively, were recorded. ICI 182,780 was a more effective inhibitor of MCF-7 growth than 4'-hydroxytamoxifen, producing an 80% reduction of cell number under conditions where 4'-hydroxytamoxifen achieved a maximum of 50% inhibition. This increased efficacy was reflected by a greater reduction of the proportion of cells engaged in DNA synthesis in ICI 182,780-treated cell cultures compared with tamoxifen-treated cells. Sustained antiestrogenic effects, following a single parenteral dose of ICI 182,780 in oil suspension, were apparent in both rats and pigtail monkeys. In vivo, antitumor activity of ICI 182,780 was demonstrated with xenografts of MCF-7 and Br10 human breast cancers in nude mice. A single injection of ICI 182,780 provided antitumor efficacy equivalent to that of daily tamoxifen treatment for at least 4 weeks. The properties of ICI 182,780 identify this pure antiestrogen as a prime candidate with which to evaluate the potential therapeutic benefits of complete estrogen withdrawal in endocrine-responsive human breast cancer.

A complex between prostate-specific antigen and alpha 1-antichymotrypsin is the major form of prostate-specific antigen in serum of patients with prostatic cancer: assay of the complex improves clinical sensitivity for cancer.

Abstract: We have studied the forms of prostate-specific antigen (PSA) in serum of patients with prostatic cancer and benign prostatic hyperplasia. Fractionation of serum by gel filtration and assay of the fractions for PSA showed that a considerable part of the PSA immunoreactivity in serum consisted of complexes that were larger than PSA. The complexes were assayed by time-resolved immunofluorometric assays based on an antibody against PSA on the solid phase and europium-labeled antibodies against various protease inhibitors as indicator antibodies. In addition to its monomeric form, PSA was found to occur in complex with alpha 1-antichymotrypsin. The proportion of the alpha 1-antichymotrypsin complex was a major form of PSA and it increased with increasing PSA concentrations, being over 85% at PSA levels exceeding 1000 micrograms/liter. A complex with alpha 1-protease inhibitor was also observed in serum of patients with prostatic cancer and very high levels of PSA. Complexes with alpha 2-macroglobulin and inter-alpha-trypsin inhibitor were detected, but their concentrations were low and similar in sera of cancer patients, normal men, and normal women, suggesting that they were not prostate derived. Commercial immunoradiometric assays for PSA were found to measure free PSA and its complexes with alpha 1-antichymotrypsin but not the complexes with alpha 2-macroglobulin and inter-alpha-trypsin inhibitor. The proportion of the PSA-alpha 1-antichymotrypsin complex was higher in patients with prostatic cancer than in those with benign hyperplasia. Therefore, assay of the complex had a higher sensitivity for cancer than assay of total PSA immunoreactivity.

Oxygenation of Human Tumors: Evaluation of Tissue Oxygen Distribution in Breast Cancers by Computerized O2 Tension Measurements

Abstract: Direct oxygen partial pressure (pO2) readings in breast cancers, in fibrocystic disease, and in the normal breast have been obtained using a novel technique which allows for the systematic evaluation of the oxygenation status as a function of pathological staging and histological grading. Measurements were performed in awake pre- and postmenopausal patients with well-defined arterial blood gas status. The measuring procedure encompasses a computerized electrode movement in the tissue which avoids significant compression artifacts and allows routine measurement in human tumors before, during, and after treatment. Using this reliable technique, pO2 measurements in the normal breast and in fibrocystic disease resulted in oxygenation patterns which were characteristic for normal, adequately supplied tissues. The median pO2 values were 65 and 67 mm Hg, respectively, with no pO2 readings below 12.5 mm Hg in the normal breast, and less than or equal to 5 mm Hg in fibrocystic disease, respectively. In contrast, in breast cancers the median pO2 value was 30 mm Hg (pooled data for pathological stages T1-T4). To date, 6 of 15 breast cancers exhibited pO2 values between zero and 2.5 mm Hg, i.e., tissue areas with less than half-maximum radiosensitivity. The oxygenation pattern in breast cancers and the occurrence of hypoxia and/or anoxia did not correlate with either the pathological stages and histological grades or with a series of clinically relevant parameters. No significant differences were found between pre- and postmenopausal tumors and between lobular and ductal carcinomas. Tumor-to-tumor variability in the oxygenation pattern was more pronounced than intra-tumor heterogeneity. pO2 variations within a tumor cannot be predicted, e.g., as a function of the measuring site (tumor center versus periphery).

Intracellular Roles of SN-38, a Metabolite of the Camptothecin Derivative CPT-11, in the Antitumor Effect of CPT-11

Abstract: It is known that 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11), a semisynthesized derivative of camptothecin (CPT), has a potent antitumor activity in vivo, but 7-ethyl-10-hydroxycamptothecin (SN-38), a metabolite of CPT-11, shows much stronger cytotoxicity in vitro than CPT-11. In this study, we demonstrated that the relaxation of SV40 DNA plasmids by type I DNA topoisomerase prepared from P388 murine leukemia cells was inhibited by 50% by SN-38 at approximately 1 microM, although CPT-11 at 1 mM slightly inhibited the relaxation. SN-38 and CPT showed strong, time-dependent inhibitory activity against DNA synthesis of P388 cells. However, CPT-11 weakly inhibited DNA synthesis independently of time with coincident inhibition of the total thymidine uptake by the cells. By alkaline and neutral elution assays, it was demonstrated that SN-38 caused much more frequent DNA single-strand breaks in P388 cells than did CPT-11. The same content of SN-38 and a similar frequency of single-strand breaks were detected in the cells treated with SN-38 at 0.1 microM or with CPT-11 at 100 microM. Therefore, single-strand breaks by CPT-11 seem to be due to SN-38 produced from CPT-11 in cells. These results indicate that CPT-11 itself possesses a marginal antiproliferative effect but that SN-38 plays an essential role in the mechanism of action of CPT-11.

Action of 2',2'-difluorodeoxycytidine on DNA synthesis.

Abstract: The action of the new deoxycytidine analogue 2′,2′-difluorodeoxycytidine (dFdC) on DNA synthesis was investigated in whole cells and in vitro assay systems with purified DNA polymerases. DNA synthesis in human lymphoblastoid CEM cells was inhibited by dFdC in a concentration-dependent manner that could not be reversed by exogenous deoxynucleosides. The analogue was incorporated into cellular DNA; most of the incorporated dFdC 5′-monophosphate (dFdCMP) residues were in internucleotide linkage. In vitro DNA primer extension assays demonstrated that dFdC 5′-triphosphate (dFdCTP) competed with deoxycytidine triphosphate for incorporation into the C sites of the growing DNA strand. The ratios of the apparent K m values for the incorporation of dFdCTP and dCTP into a C site of M13mp19 DNA were 21.8 and 22.9 for DNA polymerases α and e, respectively. The apparent K l values of dFdCTP were 11.2 µm for DNA polymerase α and 14.4 µm for polymerase e. After dFdCMP incorporation, the primer was extended by one deoxynucleotide before a major pause in the polymerization process was observed. This was in contrast to the action of arabinosylcytosine 5′-triphosphate, which caused both DNA polymerases α and e to pause at the site of incorporation. The 3′ → 5′ exonuclease activity of DNA polymerase e was essentially unable to excise nucleotides from DNA containing dFdCMP at either the 3′-end or at an internal position, whereas arabinosylcytosine monophosphate was removed from the 3′-terminus at 37% the rate for deoxynucleotides. The cytotoxic activity of dFdC was strongly correlated with the amount of dFdCMP incorporated into cellular DNA. Our results demonstrate qualitative and quantitative differences in the molecular actions of dFdC and arabinosylcytosine on DNA metabolism, but are consistent with an important role for such incorporation in the toxicity of dFdC.

Mammary cancer prevention by conjugated dienoic derivative of linoleic acid.

Abstract: Conjugated dienoic derivative of linoleic acid (CLA) is a collective term which refers to a mixture of positional and geometric isomers of linoleic acid. It is a naturally occurring substance in food and is present at higher concentrations in products from animal sources. The present study reports that synthetically prepared CLA is an effective agent in inhibiting the development of mammary tumors induced by dimethylbenz( a )anthracene. Rats were fed either the AIN-76A basal diet or the same diet supplemented with 0.5, 1, or 1.5% CLA by weight. These diets were started 2 weeks before carcinogen administration and continued until the end of the experiment. The total number of mammary adenocarcinomas in the 0.5, 1, and 1.5% CLA groups was reduced by 32, 56, and 60%, respectively. The final tumor incidence and cumulative tumor weight were similarly diminished in rats fed the CLA-containing diets. In general, there appeared to be a dose-dependent protection at levels of 1% CLA and below, but no further beneficial effect was evident at levels above 1%. Chronic feeding of up to 1.5% CLA produced no adverse consequences in the animals. Analysis of the phospholipid fraction from liver and mammary tumor extracts showed that only the c 9, t 11 isomer of CLA was incorporated and that the level of incorporation increased with dietary intake. An interesting property of CLA is its ability to suppress peroxide formation from unsaturated fatty acid in a test-tube model (Cancer Res., Ha et al. 50: 1097–1101, 1990). In view of this information, the amount of thiobarbituric acid-reactive substances (lipid peroxidation products) present endogenously in liver and mammary gland was quantitated. The feeding of CLA (for either 1 or 6 months) resulted in a decrease in the extent of lipid peroxidation in the mammary gland, but such a suppressive effect was not detected in the liver. It should be noted that maximal antioxidant activity was observed with only 0.25% CLA in the diet, whereas maximal tumor inhibition was achieved at about 1% CLA. Hence there is a discrepancy between the antioxidant efficacy of CLA and its anticarcinogenic potency, suggesting that some other mechanisms might be involved in cancer protection. Unlike the stimulatory effect of linoleic acid in carcinogenesis (Cancer Res., Ip et al., 45: 1997–2001, 1985), the reaction of CLA in cancer prevention is specific, and CLA is more powerful than any other fatty acid in modulating tumor development.

Tumor Invasion and Metastasis: An Imbalance of Positive and Negative Regulation

Abstract: A group of coordinated cellular processes, not just one gene product, is responsible for invasion and metastasis, the most life-threatening aspect of cancer. It is now recognized that negative factors may be just as important as positive elements. Genetic changes causing an imbalance of growth regulation lead to uncontrolled proliferation necessary for both primary tumor and metastasis expansion. However, unrestrained growth does not, by itself, cause invasion and metastasis. This phenotype may require additional genetic changes. Thus, tumorigenicity and metastatic potential have both overlapping and separate features. Invasion and metastasis can be facilitated by proteins which stimulate tumor cell attachment to host cellular or extracellular matrix determinants, tumor cell proteolysis of host barriers, such as the basement membrane, tumor cell locomotion, and tumor cell colony formation in the target organ for metastasis. Facilitory proteins may act at many levels both intracellularly or extracellularly but are counterbalanced by factors which can block their production, regulation, or action. A common theme has emerged. In addition to loss of growth control, an imbalanced regulation of motility and proteolysis appears to be required for invasion and metastasis.

Tetrazolium-based Assays for Cellular Viability: A Critical Examination of Selected Parameters Affecting Formazan Production

Abstract: The hydrogen acceptor 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) is commonly utilized to estimate cellular viability in drug screening protocols. The present investigation was prompted, in part, by observations that reduction of MTT to its colored reaction product, MTT formazan, varied between cell lines and with culture age. A correlation was established between the D-glucose concentration of the culture medium at the time of assay and the production of MTT formazan for cell lines representing seven tumor histologies. A decrease in the concentration of D-glucose from culture medium was accompanied by a decrease in MTT specific activity (MTT formazan/microgram cell protein) for a number of cell lines. Cells which extensively metabolized D-glucose exhibited the greatest reduction in MTT specific activity. Further evidence that the D-glucose concentration of the culture medium played an important role in MTT reduction was provided by experiments which demonstrated that transfer of cells to a glucose-free medium (L-15) was accompanied by an immediate decrease in MTT reduction which was pH independent. These studies suggested that cellular transport and constant metabolism of glucose were required for maximum MTT reduction. Decreases in the cellular concentration of the reduced pyridine nucleotides NADH and NADPH were accompanied by concomitant decreases in MTT formazan production. MTT formazan varied significantly among cell lines in both the kinetics of its formation and the degree of saturability exhibited. Apparent IC50 values for Adriamycin varied, in a cell line-specific manner, with MTT exposure time. These results indicate that MTT specific activity is significantly influenced by a number of parameters and suggest that assay conditions should be established which minimize their effects.

Induction of Heme Oxygenase: A General Response to Oxidant Stress in Cultured Mammalian Cells

Abstract: Accumulation of heme oxygenase mRNA is strongly stimulated by treatment of cultured human skin fibroblasts with ultraviolet radiation, hydrogen peroxide, or the sulfhydryl reagent sodium arsenite (S. M. Keyse and R. M. Tyrrell. Proc. Natl. Acad. Sci. USA, 86: 99–103, 1989). Since this will result in a transient reduction in the prooxidant state of cells, the phenomenon may represent an important inducible antioxidant defense mechanism. To examine the generality of the response, we have measured the accumulation of the specific mRNA in a variety of human and mammalian cell types after inducing treatments. Induction by sodium arsenite is observed in all additional human cell types tested. This includes primary epidermal keratinocytes and lung and colon fibroblasts as well as established cell lines such as HeLa, TK6 lymphoblastoid, and transformed fetal keratinocytes. Strong induction of heme oxygenase mRNA is also observed following sodium arsenite treatment of cell lines of rat, hamster, mouse, monkey, and marsupial origin. The agents which lead to induction in cultured human skin fibroblasts fall into two categories: ( a ) those which are oxidants or can generate active intermediates (ultraviolet A radiation, hydrogen peroxide, menadione, and the tumor promoter, 12- O -tetradecanoylphorbol-13-acetate); ( b ) agents which are known to interact with or modify cellular glutathione levels (buthionine sulfoximine, sodium arsenite, iodoacetamide, diamide, and cadmium chloride). These observations strongly support the hypothesis that induction of the enzyme is a general response to oxidant stress in mammalian cells and are consistent with the possibility that the cellular redox state plays a key role.

Elevated expression of phosphatidylserine in the outer membrane leaflet of human tumor cells and recognition by activated human blood monocytes.

Abstract: We determined whether the presence of phosphatidylserine (PS) in the outer membrane leaflet of human tumor cells correlated with their recognition by activated human monocytes. Three tumorigenic cell lines, A375 melanoma and A431 and Colo-16 carcinomas, and a normal human epidermal keratinocyte line (NHEK) were incubated with monocytes activated to the tumoricidal state by gamma-interferon and lipopolysaccharide. Activated human monocytes bound to and lysed all tumorigenic targets, while the nontumorigenic NHEK were neither bound nor killed. Semiquantitative analysis of PS in the outer leaflet of the cells revealed that the tumorigenic cells expressed 3-7-fold more PS than did the nontumorigenic NHEK. To determine whether enhanced PS expression on the tumor cells was responsible for their recognition by activated monocytes, NHEK were supplemented with exogenously supplied analogues of PS and phosphatidylcholine. PS-labeled NHEK but not phosphatidylcholine-labeled nor control NHEK bound to activated human monocytes. These results suggest a role for PS in monocyte recognition of tumor cells.

Inhibitory effects of curcumin on in vitro lipoxygenase and cyclooxygenase activities in mouse epidermis.

Abstract: Topical application of curcumin, the yellow pigment in turmeric and curry, strongly inhibited 12- O -tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase activity, DNA synthesis, and tumor promotion in mouse skin (Huang et al. , Cancer Res., 48: 5941–5946, 1988). Chlorogenic acid, caffeic acid, and ferulic acid (structurally related dietary compounds) were considerably less active. In the present study, topical application of curcumin markedly inhibited TPA- and arachidonic acid-induced epidermal inflammation (ear edema) in mice, but chlorogenic acid, caffeic acid, and ferulic acid were only weakly active or inactive. The in vitro addition of 3, 10, 30, or 100 µm curcumin to cytosol from homogenates of mouse epidermis inhibited the metabolism of arachidonic acid to 5-hydroxyeicosatetraenoic acid (5-HETE) by 40, 60, 66, or 83%, respectively, and the metabolism of arachidonic acid to 8-HETE was inhibited by 40, 51, 77, or 85%, respectively [IC 50 (concentration needed for 50% inhibition) = 5–10 µm]. Chlorogenic acid, caffeic acid, or ferulic acid (100 µm) inhibited the metabolism of arachidonic acid to 5-HETE by 36, 10, or 16%, respectively, and these hydroxylated cinnamic acid derivatives inhibited the metabolism of arachidonic acid to 8-HETE by 37, 20, or 10%, respectively (IC 50 > 100 µm). The metabolism of arachidonic acid to prostaglandin E 2 , prostaglandin F 2α , and prostaglandin D 2 by epidermal microsomes was inhibited approximately 50% by the in vitro addition of 5–10 µm curcumin. Chlorogenic acid, caffeic acid, and ferulic acid (100 µm) were inactive. In vitro rat brain protein kinase C activity was not affected by 50–200 µm curcumin, chlorogenic acid, caffeic acid, or ferulic acid. The inhibitory effects of curcumin, chlorogenic acid, caffeic acid, and ferulic acid on TPA-induced tumor promotion in mouse epidermis parallel their inhibitory effects on TPA-induced epidermal inflammation and epidermal lipoxygenase and cyclooxygenase activities.

Genes for Epidermal Growth Factor Receptor, Transforming Growth Factor α, and Epidermal Growth Factor and Their Expression in Human Gliomas in Vivo

Abstract: Anomalies of the epidermal growth factor receptor (EGFR) gene, including amplification, rearrangement, and overexpression, have been reported in malignant human gliomas in vivo. In vitro glioma cell lines coexpress EGFR and at least one of its ligands, transforming growth factor alpha, suggesting the existence of an autocrine growth stimulatory loop. We have studied the tumor tissue from 62 human glioma patients and examined the structure and quantity of the EGFR gene and its transcripts, as well as the quantity of the receptor protein. In addition we have examined the genes and transcripts coding for the pre-pro forms of epidermal growth factor and transforming growth factor alpha, the two endogenous EGFR ligands. EGFR gene amplification was detected in 16 of the 32 malignancy grade IV gliomas (glioblastoma) studied (50%), but only in 1 of 30 gliomas of lesser malignancy grade (I-III). All tumors with an amplified gene overexpressed EGFR mRNA. More than one-half (62.5%) of the glioblastomas with amplified EGFR genes also showed coamplification of rearranged EGFR genes and concomitant expression of aberrant mRNA species. Overexpression, without gene amplification, was observed in some of the low grade gliomas, and aberrant EGFR transcripts were also seen in some cases without gene amplification or detected gene rearrangements. mRNA expression for one or both of the pre-pro forms of the ligands was detected in every tumor studied. Thus, several mechanisms for the activation of the EGFR-mediated growth stimulating pathway are possible in human gliomas in vivo: expression of a structurally altered receptor that may have escaped normal control mechanisms; and/or auto-, juxta-, or paracrine stimulating mechanisms involving coexpression of receptor and ligands, with or without overexpression of the receptor.

Mechanism of Inhibition of Cell Proliferation by Vinca Alkaloids

Abstract: We have used a structure-activity approach to investigate whether the Vinca alkaloids inhibit cell proliferation primarily by means of their effects on mitotic spindle microtubules or by another mechanism or by a combination of mechanisms. Five Vinca alkaloids were used to investigate the relationship in HeLa cells between inhibition of cell proliferation and blockage of mitosis, alteration of spindle organization, and depolymerization of microtubules. Indirect immunofluorescence staining of microtubules and 4,6-diamidino-2-phenylindole staining of chromatin were used to characterize the effects of the drugs on the distributions of cells in stages of the cell cycle and on the organization of microtubules and chromosomes in metaphase spindles. The microtubule polymer was isolated from cells and quantified using a competitive enzyme-linked immunoadsorbent assay for tubulin. We observed a nearly perfect coincidence between the concentration of each Vinca derivative that inhibited cell proliferation and the concentration that caused 50% accumulation of cells at metaphase, despite the fact that the antiproliferative potencies of the drugs varied over a broad concentration range. Inhibition of cell proliferation and blockage of cells at metaphase at the lowest effective concentrations of all Vinca derivatives occurred with little or no microtubule depolymerization or spindle disorganization. With increasing drug concentrations, the organization of microtubules and chromosomes in arrested mitotic spindles deteriorated in a manner that was common to all five congeners. These results indicate that the antiproliferative activity of the Vinca alkaloids at their lowest effective concentrations in HeLa cells is due to inhibition of mitotic spindle function. The results suggest further that the Vinca alkaloids inhibit cell proliferation by altering the dynamics of tubulin addition and loss at the ends of mitotic spindle microtubules rather than by depolymerizing the microtubules. The specific alterations of spindle microtubule dynamics appear to differ among the five Vinca congeners, and such differences may be responsible for differences in the antitumor specificities of the drugs.

E-Cadherin Expression in Squamous Cell Carcinomas of Head and Neck: Inverse Correlation with Tumor Dedifferentiation and Lymph Node Metastasis

Abstract: Tissue sections of 32 squamous cell carcinomas (SCCs) of the head and neck were investigated for the expression of the epithelium-specific cell adhesion molecule E-cadherin. We found that E-cadherin expression is inversely correlated both with the loss of differentiation of the tumor and with lymph node metastasis. The well-differentiated SCCs expressed E-cadherin, often as strongly as the normal stratified epithelium (12 cases were tested); the moderately differentiated SCCs expressed intermediate amounts of E-cadherin or were heterogeneous (15 cases were analyzed); whereas the poorly differentiated SCCs were all E-cadherin-negative (five cases were investigated). Furthermore, seven of eight infiltrated lymph nodes of SCCs were E-cadherin-negative. These data indicate that the loss of the cell adhesion molecule E-cadherin in fact plays an important role in the progression of human squamous cell carcinomas, i.e., that down-regulation of expression is associated with dedifferentiation and metastasis of the tumor cells in vivo.

Folate-binding Protein Is a Marker for Ovarian Cancer

Abstract: We describe the isolation of a complementary DNA (cDNA) sequence encoding the ovarian cancer-associated antigen recognized by monoclonal antibody MOv18 and its identification as a high-affinity folate-binding protein (FBP) Functional cDNA clones were isolated using mRNA from the ovarian carcinoma cell line SKOV3 and colon carcinoma cell line HT29, by transient expression in WOP cells and selection of expressing cells by adhesion to antibody-coated magnetic beads The cDNAs differed in the lengths of 5′- and 3′-noncoding regions, but they encoded identical peptides A database search clearly showed them to be adult high-affinity FBPs with amino acid sequences identical with those isolated from normal placenta and several carcinoma cell lines Reactivity of cell lines with MOv18 was quantitatively consistent with the expression of FBP mRNA Southern hybridizations show evidence of a family of related genes and/or pseudogenes and were mapped to chromosome 11q133–141 by fluorescent in situ hybridization using cosmid clones containing part of this region Also identified were two PstI polymorphisms of four and three alleles, respectively, and a two-allele MspI polymorphism The folate-binding protein locus was not amplified in any of the 16 carcinoma cell lines tested and in only 1 of 10 serous adenocarcinomas, indicating that overexpression of FBP in ovarian cancer cannot, in general, be due to gene amplification

Experimental Antitumor Activity of Taxotere (RP 56976, NSC 628503), a Taxol Analogue

Abstract: Taxotere (RP 56976; NSC 628503; N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyl taxol) is a new microtubule stabilizing agent. It is obtained by semisynthesis from a noncytotoxic precursor extracted from the needles of the tree, Taxus baccata L. Taxotere was evaluated for antitumor activity against a variety of transplantable tumors of mice. Taxotere had no marked schedule dependency and was found active by the i.v. and the i.p. routes. Upon i.v. administration, 9 of 11 tumor models tested responded to Taxotere. B16 melanoma was found highly sensitive to Taxotere, with a tumor growth inhibition of 0% and a 3.0 log10 tumor cell kill at the maximum tolerated dose. In the same trial, taxol produced only a 1.1 log10 tumor cell kill at the maximum tolerated dose. Taxotere cured early stage pancreatic ductal adenocarcinoma 03 (6 of 6 cures) and colon adenocarcinoma 38 (7 of 7 cures). It also effected greater than 80% complete regressions of advanced stage disease with both tumors. Taxotere was active against early and advanced stage colon adenocarcinoma 51, with 2.3 and 1.7 log10 cell kill, respectively. Four other tumors responded to a lesser extent: Lewis lung (5.5% tumor growth inhibition), Glasgow osteogenic sarcoma (27.2% tumor growth inhibition), L1210 and P388 leukemias (70 and 54% increase in life span, respectively). Because of its good preclinical activity and its unique mechanism of action, Taxotere has entered Phase I clinical trials.

Microvascular architecture in a mammary carcinoma: branching patterns and vessel dimensions.

Abstract: The objective of this work was to introduce a tumor vessel classification scheme and to provide the first quantitative measurements of vessel branching patterns and the related vascular dimensions in a mammary carcinoma. Mammary adenocarcinoma R3230AC tumors, grown in the rat ovarian tissue-isolated tumor preparation, were infused with Batson's No. 17 polymer and maintained at an intravascular pressure of 50 mm Hg during polymerization. Maceration of the tumor in KOH allowed visualization of the vasculature. The vessel branching patterns, lengths, and diameters were measured in four tumors (4-5 g). A centrifugal ordering scheme was devised specifically to account for the unique features of tumor microvascular network topology. The arterial networks revealed two types of branching patterns. One type of arteriolar network exhibited decreasing vessel diameters and lengths with increasing branch order. In a second type of network, the diameter and length of the vessels displayed fluctuations in both variables at higher generations. Avascular and poorly vascularized regions with sparse capillary supply were present in the tumors, but analysis of several capillary networks in vascularized regions revealed a nonplanar meshwork of interconnected vessels. The meshworks were composed of vessels with a mean segment length of 67 microns, a mean diameter of 10 microns, and a mean intercapillary distance of 49 microns. Capillary path lengths ranged from 0.5 to 1.5 mm. Thus, tumor capillary diameter was greater than that in most normal tissues and, in the regions where capillary networks existed, intercapillary spacing was in the normal range. In the venous network, diameters decreased from 650 to 20 microns for the first to ninth order venules. Venule length decreased from 5 to 0.5 mm for first to fourth order but was fairly uniform (less than 500 microns) for higher orders. In conclusion, solid tumor vascular architecture, while exhibiting several features that are similar to those observed in normal tissues, has others that are not commonly seen in normal tissues. These features of the tumor microcirculation may lead to heterogeneous local hematocrits, oxygen tensions, and drug concentrations, thus reducing the efficacy of present day cancer therapies.

Acceleration of human prostate cancer growth in vivo by factors produced by prostate and bone fibroblasts.

Abstract: Prostate cancer, the most prevalent cancer affecting men, frequently metastasizes to the axial skeleton where it produces osteoblastic lesions with growth rates often exceeding that of the primary tumor. To evaluate the role of tumor cell-host stromal interaction and stromal specific growth factors (GFs) in prostate cancer growth and progression, we coinoculated athymic mice with human prostate cancer cells (LNCaP) and various nontumorigenic fibroblasts s.c. LNCaP tumor formation was most consistently induced by human bone (MS) fibroblasts (62%), followed by embryonic rat urogenital sinus mesenchymal (rUGM) cells (31%) and Noble rat prostatic fibroblasts (17%), but not by NIH-3T3, normal rat kidney, or human lung CCD16 fibroblasts. Carcinomas formed preferentially in male hosts, demonstrating in vivo androgen sensitivity. The human prostate component of these tumors was confirmed with immunohistochemical staining for prostate-specific antigen (PSA), Northern analysis for PSA expression, and Southern analysis for human repetitive Alu sequences. Elevations in serum PSA paralleled the histomorphological and biochemical findings. LNCaP and fibroblast cell-conditioned media (CM) was used to determine whether autocrine and paracrine mitogenic pathways exist between LNCaP and fibroblast cells in vitro, and various defined GFs were tested to identify possible active factors. Mitogenic assays revealed a 200-300% bidirectional stimulation between LNCaP and bone or prostate fibroblast-derived CM. Lung, normal rat kidney, and 3T3 fibroblast CM were not mitogenic for LNCaP cells. Among the purified GFs tested basic fibroblast growth factor (bFGF) was the most potent mitogen, stimulating LNCaP growth 180% in a concentration-dependent manner. Transforming growth factor alpha and epidermal growth factor were both minimally mitogenic. Coinoculation of LNCaP cells with a slowly absorbed matrix (Gelfoam) absorbed with bFGF or dialyzed and concentrated rUGM or MS CM was also capable of inducing LNCaP tumor formation in vivo. These observations illustrate that fibroblasts differentially modulate prostate cancer growth through the release of paracrine-mediated GFs, possibly including bFGF, and that tumor-stromal cell interactions play an important role in prostate cancer growth and progression.

Aberrant crypts: putative preneoplastic foci in human colonic mucosa.

Abstract: Aberrant crypts were identified for the first time in whole-mount preparations of normal-appearing human colonic mucosa after staining with methylene blue. The foci of aberrant crypts varied from single altered glands to plaques of greater than 30 crypts. The mean proportion of colonic mucosa altered and the number of foci with aberrant crypts per cm2 of colonic mucosa were ( a ) higher in patients with colon cancer than in patients without colon cancer or predisposing conditions and ( b ) highest in our single case of Gardner's syndrome. Aberrant crypts are postulated to be the earliest identifiable potential precursors of colon cancer. Analysis of aberrant crypts may facilitate the study of the early pathological and molecular changes that precede colon cancer.

Overexpression and Mutation of p53 in Epithelial Ovarian Cancer

Abstract: We examined p53 expression in 107 epithelial ovarian cancers with immunohistochemical techniques using monoclonal antibody PAb1801. High level expression of nuclear p53 protein was detected in the malignant epithelium in 54 (50%) of these cancers. Expression of p53 protein was undetectable in 13 benign gynecological tissues. p53 mRNA from three cancers that overexpressed the protein were sequenced and point mutations which altered the coding sequence of the highly conserved region of the gene were found in each case. Three cancers with undetectable protein levels also were sequenced and were found to be wild-type through the same region of the gene. As in other cancers, overexpression of the p53 protein in ovarian cancer appears to correlate closely with the presence of mutation in the p53 gene. p53 overexpression did not correlate with stage, histological grade, or the ability to perform optimal cytoreductive surgery. A significant correlation (P = 0.04) was observed between p53 overexpression and aneuploidy in advanced stage (III/IV) disease. There was no significant relationship between overall survival and p53 expression. Since mutation and overexpression of p53 are common in epithelial ovarian cancers, further studies are warranted to clarify the role of p53 in ovarian tumorigenesis.

Synchronization of tumor and normal cells from G1 to multiple cell cycles by lovastatin.

Abstract: Synchronization of mammalian cells is essential for investigations involving cell proliferation. A simple method for obtaining synchrony in all types of cells, through several cycles and with minimal overall metabolic perturbations, has not yet been available. We describe a procedure for synchronizing normal as well as tumor cells reversibly in the G 1 phase of the cell cycle using Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. This method of synchronization was successful with all cell lines tested, including normal and tumor cells of mouse, hamster, and human origins. For example, when MCF-7 human breast cancer cells were synchronized with Lovastatin and released by the addition of mevalonic acid (the product of the reaction catalyzed by 3-hydroxy-3-methylglutaryl-coenzyme A reductase), 3 phases of accelerated thymidine incorporation into DNA corresponding to 3 S phases of the cell cycle occurred during a 90-h period of cell replication. Thymidine incorporation was decreased to ≤4% during the initial lag of 18 h before the first S phase, and maximum incorporation was then achieved after only 6 h. The antibody Ki-67, which detects a nuclear antigen associated with proliferation, was present in cells arrested with Lovastatin. This fact, together with the lack of thymidine incorporation during the initial lag time, indicates that the cells were arrested in the G 1 and not in the G 0 phase of the cell cycle. Furthermore, in synchronized tumor-derived human breast epithelial cells, histone H4 RNA was low after Lovastatin release and increased with the onset of DNA synthesis. Concomitant synthesis of DNA and histone H4 RNA expression could be observed for 2 cycles. Minimal perturbations of general metabolic functions occurred since the rate of RNA, protein, and initial DNA synthesis were unaffected by Lovastatin, as evidenced by [ 3 H]uridine, [ 3 H]leucine, and initial [ 3 H]thymidine incorporation. Finally, while the Lovastatin-induced synchronization was overcome by mevalonic acid, addition of squalene or cholesterol-ethanol had no such effect. Thus, Lovastatin appears to prevent formation of an early intermediate in the cholesterol pathway that is essential for progression of cells through early G 1 phase.

Wild-type p53 suppresses growth of human prostate cancer cells containing mutant p53 alleles.

Abstract: Evidence supporting a broad role for the inactivation of the p53 gene in human tumorigenesis has been provided by studies showing that the p53 gene is mutated in many human cancers. In this study, we report on the mutational status of the p53 gene in prostate cancer cells and provide functional evidence that the wild-type p53 gene may have a role in suppressing prostatic tumorigenesis. Sequence analysis of exons 5-8 of the p53 gene reveals that three of five prostate cancer cell lines (TSUPr-1, PC3, DU145) contain mutations which alter the amino acid sequence of this most highly conserved portion of the gene. One of two primary prostatic cancer specimens examined also contained a mutation in this region. Transfection of the wild-type p53 gene versus a mutated p53 gene into two cell lines with p53 mutations results in reduced colony formation. Wild-type p53 gene expression is apparently incompatible with continued growth of these tumor cells inasmuch as none of the colonies which formed after wild-type transfections retain the transfected p53 sequences. Immunocytochemical data indicate that prostate carcinoma cells expressing the transfected wild-type p53 gene are growth arrested because they exhibit a reduced level of thymidine incorporation into DNA. This study is the first report of p53 gene mutations in prostate cancer cells and suggests a functional role for the p53 gene in suppressing prostatic tumorigenesis.

Variant Human Breast Tumor Estrogen Receptor with Constitutive Transcriptional Activity

Abstract: Since progesterone receptor (PgR) is normally induced by estrogen, breast cancers lacking estrogen receptor (ER) would also be expected to lack PgR. However, a small percentage of breast cancers are ER- yet PgR+. These tumors might possess an ER which is defective in estrogen binding but is still functional in stimulating estrogen-responsive genes such as PgR. We have now detected such a variant, lacking exon 5 of the hormone-binding domain, using complementary DNA amplified by the polymerase chain reaction. This variant was the predominate ER RNA expressed in three ER-/PgR+ tumors. Furthermore, the variant ER constitutively activates transcription of a normally estrogen-dependent gene construct in yeast cells. The variant ER could explain the expression of PgR in certain tumors and have therapeutic implications.

Toxicity and antitumor activity against solid tumors of micelle-forming polymeric anticancer drug and its extremely long circulation in blood.

Abstract: Toxicity and in vivo antitumor activity against five solid tumors (C 26, C 38, M 5076, MKN-45, MX-1) of Adriamycin (ADR)-conjugated poly(ethylene glycol)-poly(aspartic acid) block copolymer (PEG-P[Asp(ADR)]) were evaluated, and its pharmacokinetic behavior in blood and biodistribution by i.v. injection were obtained. PEG-P[Asp(ADR)] was revealed to express higher antitumor activity than ADR against all the examined tumors except MKN-45. Especially against C 26, PEG-P[Asp(ADR)] expressed critical suppression of tumor growth and considerably prolonged life span of the treated mice. PEG-P[Asp(ADR)] was observed in blood at much higher concentrations with a longer half-life than ADR after the i.v. injection. PEG-P[Asp(ADR)] was known to form a micellar structure with a diameter of approximately 50 nm and a narrow distribution in phosphate-buffered saline. Therefore, the stabilized circulation of ADR residue in blood by binding to the block copolymer was considered to result from the micellar structure which possesses the hydrated outer shell composed of the poly(ethylene glycol) chains.

Programmed cell death during regression of the MCF-7 human breast cancer following estrogen ablation.

Abstract: To study the mechanism of regression of human mammary cancer following estrogen ablation, estrogen-responsive MCF-7 human mammary adenocarcinoma cells were inoculated into ovariectomized female nude mice supplemented with exogenous 17 beta-estradiol (E2) via an E2 implant. Implants were then removed when MCF-7 tumors were 400 mm3 in size. Removal of the E2 implants resulted in a 50% tumor regression by 2 weeks following E2 ablation. Associated with this regression is a rapid (i.e., within 1 day following E2 ablation) enhanced expression of the transforming growth factor beta 1 and TRPM-2-genes, two genes the expression of which has been previously demonstrated to be enhanced in a variety of cell types induced to undergo programmed cell death (i.e., apoptosis). The enhanced expression of transforming growth factor beta 1 and TRPM-2 is not a nonspecific response since the expression of other genes, like c-fos, c-H-ras, and pS2, decrease following E2 ablation. Fragmentation of tumor DNA into nucleosomal oligomers and histological appearance of apoptotic bodies are characteristic early events that precede the dramatic reduction in tumor volume following E2 ablation. These results demonstrate that the regression of MCF-7 human mammary cancers in nude mice following estrogen ablation is due to a sequence of biochemical and morphological changes that result in both the cessation of cell proliferation and activation of programmed death or apoptosis of these MCF-7 cancer cells. Clarification of the biochemical pathway involved in the activation of this programmed cell death should identify new targets of therapy for even estrogen-independent human mammary cancer cells.

Topoisomerase II-reactive chemotherapeutic drugs induce apoptosis in thymocytes.

Abstract: The effects of topoisomerase II-reactive epipodophyllotoxins etoposide and teniposide as well as amsacrine on the viability of thymocytes in primary culture has been examined. All three drugs were shown to produce DNA cleavage detectable by resolving isolated DNA by pulsed field agarose gel electrophoresis. The DNA cleavage was found to have two components. The first was due to the interaction of the drugs with topoisomerase II, whereas the second component was due to endonuclease cleavage caused by the drug-induced entry of the thymocytes into programmed cell death or apoptosis. This second component of the DNA cleavage was also detected in thymocytes undergoing apoptosis following exposure to the glucocorticoid analogue, dexamethasone. The effect of the drugs on programmed cell death is dependent upon new protein and RNA synthesis, indicating that topoisomerase II has a role in the very first stages of the process. These results are discussed in terms of the use of this class of topoisomerase II-reactive drugs in chemotherapy.