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Biomedical subjects

Z Darzynkiewicz

Publications and source records attributed to Z Darzynkiewicz.

At least 91 records · Page 5Linked to original sources
PubMed1998

G1 arrest of U937 cells by onconase is associated with suppression of cyclin D3 expression, induction of p16INK4A, p21WAF1/CIP1 and p27KIP and decreased pRb phosphorylation.

Onconase is a 12 kDa protein homologous to pancreatic RNase A isolated from amphibian oocytes which shows cytostatic and cytotoxic activity in vitro, inhibits growth of tumors in mice and is in phase III clinical trials. The present study was aimed to reveal mechanisms by which onconase perturbs the cell cycle progression. Human histiocytic lymphoma U937 cells were treated with onconase and expression of cyclins D3 and E, as well as of the cyclin-dependent kinase inhibitors (CKIs) p16INK4A, p21WAF1/CIP1 and p27KIP1 (all detected immunocytochemically) was measured by multiparameter flow cytometry, in relation to the cell cycle position. Also monitored was the status of phosphorylation of retinoblastoma protein (pRb) by a novel method utilizing mAb which specifically detects underphosphorylated pRb in individual cells. Cell incubation with 170 nM onconase for 24 h and longer led to their arrest in G1 which was accompanied by a decrease in expression of cyclin D3, no change in cyclin E, and enhanced expression of all three CKIs. pRb was underphosphorylated in the onconase arrested G1 cells but was phosphorylated in the cells that were still progressing through S and G2/M in the presence of onconase. The cytostatic effect of onconase thus appears to be mediated by downregulation of cyclin D3 combined with upregulation of p27KIP1, p16INK4A and p21WAF1/CIP1, the events which may prevent phosphorylation of pRb during G0/1 and result in cell arrest at the restriction point controlled by Cdk4/6 and D type cyclins.

Animals↗
PubMed1998

In vitro effects and clinical evaluation of a human chorionic gonadotrophin preparation in acute leukemia.

Commercial human chorionic gonadotrophin (HCG) preparations decrease the tumorigenicity of human tumors in immunodeficient mice and induce apoptotic cell death in animal tumor models. Preliminary studies in humans have demonstrated tumor regression in patients with Kaposi's sarcoma given intralesional injections of HCG. To further evaluate HCG's antitumor activity we conducted in vitro and clinical evaluations of HCG in acute myeloid leukemia (AML). In HL-60 leukemic cell lines, a 20-40% inhibition of cell density was demonstrated by trypan blue exclusion method at low concentrations of an HCG preparation (2 x 10(-3)-2 x 10(-2)). Similar concentrations also resulted in a reduction in the proportion of cells in G2M phase of the cell cycle, as well as enhanced differentiation compared to control cells. Fifteen patients with advanced AML with marrow blast counts >30%, and five with marrow blast counts between 10 and 26% were given daily subcutaneous injections of HCG 2-4 IU and oral levamisole 50 mg weekly. Five patients with absolute blast counts in the blood ranging from 0 to 3500/microl and percent blasts in the marrow ranging from 16 to 81% were observed to have no progressive increase in either marrow or peripheral blast counts for 70-121 days. One patient with a pretreatment blast count of 10% in the marrow, no circulating blasts and minor cytopenias had a decrease in marrow blasts to less than 5% which has persisted at 550 days. No significant improvement from baseline levels of neutrophils, hemoglobin or platelets were observed in any nl the patients treated. Increases in apoptotic cell death were observed in over 50% of patients' cells with some demonstrating peak levels similar to experiences in patients treated with DNA-damaging chemotherapy. A decreased expression of bcl-2 was seen in the majority of patients ranging from 6 to 62%. These new observations suggest that HCG preparations may inhibit leukemic cell growth through enhancement of cell death mechanisms and could be used in judicious combinations with other approaches. The results confirm the pro-apoptotic effects of HCG preparations reported in patients with Kaposi's sarcoma. Identification of the active component of HCG preparations and further understanding of its growth modulatory action will be important in its development as a clinically useful agent.

Acute Disease↗
PubMed1998

Potentiation of tumor necrosis factor induced apoptosis by onconase.

Onconase (ONC) a ribonuclease from amphibian oocytes is cytostatic and cytotoxic to many human tumor lines, shows in vivo antitumor activity in mouse tumor models and is in Phase III clinical trials. The mechanism of antitumor activity of ONC is presumed to be due to its internalization, degradation of intracellular RNA and suppression of protein synthesis. Since apoptosis triggered by TNF-alpha is known to be potentiated by inhibitors of protein synthesis, we have hypothesized that it also may be potentiated by ONC. Indeed, preincubation of U-937 or HL-60 leukemic cells with 0.17 microM ONC rendered them more sensitive to induction of apoptosis by TNF-alpha or antibody to CD95 (Fas). The mechanism by which ONC amplifies the effect of TNF-alpha may involve suppression of induction of the survival genes whose expression is triggered by activation of NFkB by this factor.

Animals↗
PubMed1998

Enhanced in vitro cytotoxicity and cytostasis of the combination of onconase with a proteasome inhibitor.

In proliferating cells the turnover rate of proteins responsible for regulation of the cell cycle progression, namely cyclins and inhibitors of the cyclin-dependent kinases (CDKs) and phosphatases, is rapid and their cellular level is modulated at the transcriptional, translational and/or degradation (via proteasome pathway) stages. Inhibition of proteasome function results in accumulation of rapidly turning over proteins and, thus, causes an imbalance of the cell cycle regulatory components, and loss of their regulatory function. Indeed, it has been shown that proteasome inhibitors perturb the cell cycle progression. Onconase, a novel RNase which has anti-tumor activity and is in clinical trials, has previously been shown to suppress protein synthesis, presumably by degradation of intracellular RNA, preferentially tRNA. By interfering with regulation of expression of cyclins and/or CDK-inhibitors, onconase also may induce the imbalance of these proteins and potentiate the effect of proteasome inhibitors. In the present study, we observed that the combinations of onconase with peptide-aldehyde inhibitors of calpain and proteasome such as the N-acetyl-leucinyl-leucinyl-norleucinal (LLnL) and the N-acetyl-leucinyl-valinyl-phenylalaninal (LVP), but not N-acetyl-leucinyl-leucinyl-methioninal (LLM), were synergistic in suppressing cell proliferation and inducing apoptosis in three human tumor cell lines: A-549 lung adenocarcinoma, DU-145 prostatic carcinoma, and MDA-MB-231 breast carcinoma. The observed cytotoxicity may also be a result of prevention of the induction of the 'survival' genes by the nuclear factor kappaB (NFkappaB) by onconase and proteasome inhibitors. The data indicate that such combinations should be further tested as potential anti-cancer regimens.

Antineoplastic Agents↗
PubMed1998

Critical aspects in the analysis of apoptosis and necrosis.

Despite that large number of methods to analyze cell death, in particular apoptosis, that have been developed, identification of the mode of cell death and its quantitation is not always simple or straightforward. The difficulties, potential pitfalls and traps in quantitation of dead cells, whether apoptotic or necrotic are reviewed. The following are common flaws in the measurement of cell death, which include incorrect assumptions, erroneous data interpretation and shortcomings of the methodology: 1) Misclassification of apoptotic bodies or chromatin fragments as individual apoptotic cells based on cellular DNA content analysis by flow cytometry; 2) Assumption that the quantity of fragmented DNA extracted from cells represents the frequency of apoptosis; 3) Conjecture that the apoptotic index represents the cell death rate; 4) Assumption that apoptotic cells must exhibit classical features of apoptosis e.g. internucleosomal DNA fragmentation; 5) Inadequacy of methods that presume to discriminate between late apoptotic and necrotic cells; 6) Possibility of a selective enrichment or loss of apoptotic cells during cell separation on density gradients, during trypsinization or other procedures of cell collection; and 7) Inability to distinguish between live, nonapoptotic cells phagocytizing apoptotic bodies and genuine apoptotic cells by flow cytometric methods. Many of the problems stem from the difficulty in identifying apoptotic or necrotic cells. Because apoptosis and necrosis have been originally defined based on morphological criteria it is essential to confirm the mode of cell death by microscopy. Laser scanning cytometry (LSC), which combines the advantages of flow and image cytometry, offers the possibility of morphological examination of apoptotic cells. By virtue of this attribute LSC appears to be the instrument of choice for analysis of apoptosis.

Apoptosis↗
PubMed1998

Analysis of apoptosis in solid tumors by laser-scanning cytometry.

Apoptosis (programmed cell death) plays an important role in tissue physiology and pathology. First, tumor development and progression is often associated with defective regulation of apoptotic pathways, and measurement of apoptosis might be equally important for the analysis of cell proliferation. Second, tumor cells die by apoptosis during chemotherapy or radiotherapy, so monitoring the level of apoptosis might prove useful in modulating treatment or in predicting the biologic behavior of the tumor. Flow cytometry (FC), in conjunction with DNA strand-break labeling assays, is commonly used to assess apoptosis, but unless combined with cell sorting, FC results cannot correlate with morphology. Also, analysis by FC is associated with cell loss during preparation of the specimen. In this study, we identified apoptotic cells by in situ DNA strand-break labeling in solid tumors and then analyzed those cells by laser-scanning cytometry (LSC). LSC provides data comparable to those obtained by FC, but because the cells are prepared and measured on a slide, there is no cell loss. Also, with LSC, each measured cell can be relocated and examined visually by conventional or fluorescence microscopy to confirm its identity. With use of this approach, we analyzed apoptosis in 30 primary solid tumors of different types. The number of cells with DNA strand breaks varied from tumor to tumor and ranged from 0.5 to 28.1% (average, 7.0%). FC on the same tumors gave similar results. More than 95% of the relocated cells with DNA strand breaks either had the typical appearance of late apoptosis or showed strong green fluorescence within or at the periphery of the nucleus. Our results suggest that different morphologic variants of apoptosis might be common in different tumor types and that cytometric quantification might provide biologically useful information not otherwise easy to obtain.

Adult↗
PubMed1998

Laser scanning cytometry quantification of estrogen receptors in breast cancer.

OBJECTIVE: To describe the laser scanning cytometry (LSC) processing and analysis developed for the quantitative analysis of estrogen receptor (ER) content in routine paraffin sections of breast carcinomas. STUDY DESIGN: Histologic sections of archival, paraffin-embedded tissues from 30 breast carcinomas were labeled for ER with fluoresceinated monoclonal antibody. ER expression was quantified by LSC and expressed as percent positive tumor cells and as histogram distributions of receptor expression per cell. Duplicate sections of the same tumors were stained for ER by a conventional immunoperoxidase reaction and percent positive tumor cells counted visually. RESULTS: Percent ER-positive tumor cells by LSC of immunofluorescence-stained sections correlated well with conventional (visual) counts of immunoperoxidase-stained duplicate sections when the latter were categorized as low, intermediate or high percent of positive cells. In addition, the marked variation in relative number of ER binding sites per cell could be quantified by LSC and displayed in histogram distribution. CONCLUSION: LSC measurements are fast and objective and can be carried out on sections of paraffin-embedded tissue after routine processing in the pathology laboratory. In addition, LSC data provide the relative number of ER binding sites per unit of DNA; that may reveal clinically significant skewed distributions or subpopulations of tumor cells.

Breast Neoplasms↗
PubMed1997

Laser scanning cytometry distinguishes lymphocytes, monocytes, and granulocytes by differences in their chromatin structure.

By providing rapid measurements of cellular fluorescence in addition to morphometric analysis, the novel microscope-based multiparameter laser scanning cytometer (LSC) combines advantages of flow and image cytometry. Analysis of the integrated fluorescence intensity (IF) versus peak fluorescence intensity (maximal fluorescence per pixel; FP) versus fluorescence area (FA) of the cells stained with the DNA intercalating fluorochrome propidium iodide (PI) made it possible to discriminate lymphocytes, monocytes, and granulocytes in samples of peripheral blood of normal individuals. Lymphocytes, characterized by maximally condensed chromatin, had the highest FP and lowest values of FA. Granulocytes had the lowest FP and the highest FA. They also had increased IF compared to lymphocytes and monocytes. The difference in IF between granulocytes and monocytes/lymphocytes was abolished after exposure of cells to 0.1 M HCl at 0-4 degrees C, which is known to dissociate histones from DNA in chromatin. Monocytes were characterized by intermediate values of peak and area fluorescence intensity compared to lymphocytes and granulocytes. Thus, although all three classes of white blood cells have the same DNA content, they can be distinguished based on differences in structure of their chromatin after staining with PI. Discrimination of these cells by LSC is similar to that provided by flow cytometry based on differences in forward and side light scatter properties.

Cell Separation↗
PubMed1997

Monitoring uptake of ellipticine and its fluorescence lifetime in relation to the cell cycle phase by flow cytometry.

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) is a green fluorescent plant alkaloid that inhibits DNA topoisomerase II activity and possesses pharmacologic activity toward both murine and human leukemias in vivo. In this flow cytometric study, the uptake of ellipticine was monitored as a function of cell volume and cell cycle phase in viable human promyelocytic (HL-60) cells costained with the DNA fluorochrome Hoechst 33342. Uptake of ellipticine was time and dose dependent; however, drug content was quantitatively similar in all phases of the cell cycle when normalized for DNA content or similar to cell size when correlated with cell volume. The fluorescence lifetime values of ellipticine in HL-60 cells, as analyzed by novel flow cytometric analysis, reached a plateau when the intra-cellular ellipticine intensity was still rising with increasing drug concentration. Since the free drug and the different subcellular ellipticine complexes, including DNA and RNA, had different lifetime values, the changes in the lifetime values appear to reflect differing proportions of unbound drug to that bound to different cellular constituents in the cells. Further development of phase-sensitive flow cytometry will provide for multiple lifetime determinations so that quantitation of drugs bound to the different cellular components can be performed along with the simultaneous determination of total drug uptake and cell cycle position. Such analyses should provide useful information for the design of drugs with greater affinity for cytotoxic targets.

Antineoplastic Agents↗
PubMed1997

Immunoseparation and immunodetection of nucleic acids labeled with halogenated nucleotides.

A novel methodology for labeling, isolation, and detection of nucleic acids is described. Nucleic acid isolation is based on in vivo or in vitro incorporation of BrU or BrdU to either RNA or DNA, respectively, followed by immunoprecipitation of the labeled nucleic acid utilizing anti-BrdU MoAb, which crossreacts with BrU, attached to solid particles. Filter-bound bromine-labeled DNA or RNA was detected by immunoblotting with anti-BrdU MoAb, by a combined Southern/Western or Northern/Western approach, respectively. This method was applied to isolate and detect rRNA and mRNA from human cells, plasmid DNA from bacterial cells, and in vitro synthesized DNA. Newly transcribed BrU-labeled mRNA was recovered from the immunoprecipitates and analyzed by RT-PCR to study phorbol ester-mediated regulation of interleukin 1 gene transcription in human leukemic HL-60 or lymphoma U937 cells. The plasmid DNAs were isolated by immunoprecipitation from transformed bacterial cultures that were grown in the presence of BrdU and were detected immunochemically on filters. Likewise, the products of RT-PCR and Klenow polymerase-catalyzed DNA synthesis in which dTTP was replaced with BrdUTP were detected by immunoblotting. Since the method allows one to selectively separate or detect nucleic acids only synthesized during a pulse of the precursor, it can uniquely be used to identify nascent gene transcripts or the transcripts synthesized within specific time windows, e.g., after induction of differentiation, carcinogenesis, or drug treatment, and distinguish such transcripts from preexisting ones. In addition, this approach offers a simple and inexpensive alternative for preparing labeled DNA as well as RNA probes for use in a variety of hybridization protocols. Due to the low toxicity of BrU and BrdU, this approach can be used in analysis of gene transcription or DNA replication in vivo.

Antibodies, Monoclonal↗
PubMed1997

Activation-induced expression of human programmed death-1 gene in T-lymphocytes.

The Programmed Death-1 (PD-1) gene is a member of the immunoglobulin superfamily of genes. Murine PD-1 mRNA expression has been shown to correlate with activation-induced apoptosis in a mouse T-cell hybridoma cell line and in murine thymocytes. Here we report that expression of the human homolog, hPD-1, seems to correlate with activation of T lymphocytes rather than apoptosis. We observed a time-dependent upregulation of hPD-1 mRNA and protein levels in Jurkat cells during phorbol ester (12-O-tetradecanoylphorbol 13-acetate, TPA)-induced differentiation. Human PD-1 protein was also induced during lectin-stimulated activation of human peripheral blood mononuclear cells. Additionally, TPA stimulation of Jurkat cells induces tyrosine phosphorylation of hPD-1, putatively on its cytoplasmic tail signal transduction motif. These data suggest a role for hPD-1 during activation and differentiation of T-lymphocytes.

Antigens, CD↗
PubMed1997

Correlation between DNA replication and expression of cyclins A and B1 in individual MOLT-4 cells.

Cyclins A and B1 activate cyclin-dependent kinases CDK2 and CDC2, which regulate cell progression through S and G2. Expression of these cyclins is generally measured in populations of synchronized cells, by immunoblotting. Such studies neither provide information regarding intercellular variability in cyclin expression nor yield precise data on a time relationship between initiation and termination of DNA replication in relation to cyclin expression. Furthermore, cell synchronization by DNA polymerase inhibitors or excess of thymidine induces cell growth imbalance and alters expression of cyclins, thereby introducing an experimental bias. Using a novel flow cytometric method of detection of incorporated bromodeoxyuridine (BrdUrd) in the present study, we have been able to correlate expression of immunocytochemically discerned cyclins A and B1 with incorporation of BrdUrd and the cell cycle position of individual MOLT-4 cells. On the basis of differences in amount of incorporated BrdUrd and DNA content, the following cohorts of cells in narrow windows of the cell cycle were identified: (a) cells initiating and (b) terminating DNA replication during a 1-h pulse of BrdUrd; (c) cells replicating DNA throughout the duration of BrdUrd pulse; (d) G1 cells; and (e) G2 cells that remained in G2 for at least 1 h after exiting S phase. These populations were characterized with respect to expression of cyclins A and B1. Expression of cyclin A was an early event of S phase, and 84% of cells entering S phase during 1 h of exposure to BrdUrd were already cyclin A positive. More than 95% of S-phase cells, as well as the cells exiting S during BrdUrd pulse, were also cyclin A positive. The maximal rate of accumulation of cyclin A was seen during the first hour of progression through S phase. In contrast, the maximal accumulation rate of cyclin B1 showed cells during the first hour of progression through G2. A strong correlation between expression of cyclin A and the rate of DNA replication, estimated by the degree of BrdUrd incorporation (r = 0.99), was observed.

Cell Cycle↗
PubMed1997

Cytometry in cell necrobiology: analysis of apoptosis and accidental cell death (necrosis).

The term cell necrobiology is introduced to comprise the life processes associated with morphological, biochemical, and molecular changes which predispose, precede, and accompany cell death, as well as the consequences and tissue response to cell death. Two alternative modes of cell death can be distinguished, apoptosis and accidental cell death, generally defined as necrosis. The wide interest in necrobiology in many disciplines stems from the realization that apoptosis, whether it occurs physiologically or as a manifestation of a pathological state, is an active mode of cell death and a subject of complex regulatory processes. A possibility exists, therefore, to interact with the regulatory machinery and thereby modulate the cell's propensity to die in response to intrinsic or exogenous signals. Flow cytometry appears to be the methodology of choice to study various aspects of necrobiology. It offers all the advantages of rapid, multiparameter analysis of large populations of individual cells to investigate the biological processes associated with cell death. Numerous methods have been developed to identify apoptotic and necrotic cells and are widely used in various disciplines, in particular in oncology and immunology. The methods based on changes in cell morphology, plasma membrane structure and transport function, function of cell organelles, DNA stability to denaturation, and endonucleolytic DNA degradation are reviewed and their applicability in the research laboratory and in the clinical setting is discussed. Improper use of flow cytometry in analysis of cell death and in data interpretation also is discussed. The most severe errors are due to i) misclassification of nuclear fragments and individual apoptotic bodies as single apoptotic cells, ii) assumption that the apoptotic index represents the rate of cell death, and iii) failure to confirm by microscopy that the cells classified by flow cytometry as apoptotic or necrotic do indeed show morphology consistent with this classification. It is expected that flow cytometry will be the dominant methodology for necrobiology.

Apoptosis↗
PubMed1997

Cell cycle specificity of apoptosis during treatment of leukaemias.

This review summarizes our observations on the mechanism of induction of apoptosis in vitro in leukaemic cell lines and in vivo in patients with leukaemia undergoing chemotherapy, in relation to the cell cycle. Multiparameter flow cytometric methods allowed us to identify apoptotic cells and position them with respect to their cell cycle phase. Several antitumor agents of different classes have been characterized in terms of the cell cycle phase specificity of induction of apoptosis. Three types of apoptosis could be distinguished in relation to the initial damage to the cell vis-a-vis cell cycle position: (1) homo-phase apoptosis where the cells underwent apoptosis during the same phase in which they were initially affected; (2) homo-cycle apoptosis, where the cells underwent apoptosis during the same cell cycle in which they were initially affected, i.e., prior to or during the first mitosis, and (3) post-mitotic apoptosis, where cells underwent apoptosis during the cell cycle(s) subsequent to that in which the cell was initially affected, most likely at the G1 or G2 checkpoints of these cycle(s). Four ranges of drug concentration can be distinguished in vitro for most drugs, where either: (1) no immediate effects; (2) cytostasis or post-mitotic apoptosis; (3) homo-cycle or homo-phase apoptosis; or (4) necrosis are observed. Analysis of cell death of blast cells from peripheral blood or bone marrow of over 250 leukaemia patients (AML, ALL, CML in blast crisis) treated with various drugs during routine chemotherapy reveals that in the case of DNA topoisomerase inhibitors (e.g., mitoxantrone, VP-16) apoptosis is often rapid (peaks at 1-2 days after drug administration) and has features of homo-phase apoptosis. In contrast, cell death observed after administration of paclitaxel (taxol) or cytarabine (cytosine arabinoside) occurs later and has features of post-mitotic apoptosis: the cells divide but die in G1 of the subsequent cycle(s).

Journal Article↗
PubMed1997

Phase I clinical and laboratory evaluation of topotecan and cytarabine in patients with acute leukemia.

PURPOSE: To determine the maximal-tolerated dose (MTD) of topotecan with cytarabine in acute leukemia patients, and to evaluate leukemia cell apoptosis in these patients. PATIENTS AND METHODS: Fifty-three patients with acute leukemia not responsive to standard therapy were treated at eight dose levels of topotecan (2.5 mg/m2/d to 7.75 mg/m2/d). Topotecan was given as a 30-minute infusion daily with cytarabine 1 g/m2/d, both for 5 days. Using a flow-cytometric technique, the percent apoptotic cells in blood and bone marrow samples was determined, and the cell cycle distribution of the leukemic cells studied. RESULTS: Oropharyngeal mucositis was dose-limiting. The MTD of topotecan was 4.75 mg/m2/d for 5 days in high-risk patients and 7.0 mg/m2/d for 5 days in low-risk patients. The mean percent apoptotic cells in the peripheral blood reached a peak of 18.8%, a median of 48 hours following the first dose of topotecan. Patients with higher S-phase fractions, either before treatment or following cytarabine, were more likely to achieve bone marrow aplasia than those with lower S-phase fractions (P = .01 and P < .05, respectively). Clinical responses were seen in four of 39 patients with acute myelogenous leukemia (AML; of whom 32 had received prior high-dose cytarabine), three of six with acute lymphoblastic leukemia (ALL), and one of eight with chronic myelogenous leukemia in blast phase (CML-BP). CONCLUSION: The recommended phase II dose of topotecan with intermediate-dose cytarabine is 4.75 mg/m2/d for high-risk patients and 7.0 mg/m2/d for low-risk patients. The percentage of cells in S phase was important in determining response to treatment.

Adult↗
PubMed1997

Laser scanning cytometric analysis of cyclin B1 in primary human malignancies.

Cyclins are key components of the cell cycle progression machinery. They activate their partner-dependent kinases (CDKs) and target them to respective substrate proteins within the cell. CDK-mediated phosphorylation of specific sets of proteins drives the cell through particular phases or checkpoints of the cell cycle. During unperturbed growth of normal cells, the timing of expression of several cyclins is discontinuous, occurring at discrete and well-defined periods of the cell cycle. Immunocytochemical detection of cyclins in relation to cell cycle position (DNA content) by multiparameter flow cytometric techniques has provided a new approach to cell cycle studies. This approach, like no other method, can be used to detect the "unscheduled" expression of cyclins, namely, the presentation of G1 cyclins by cells in G2/M and of G2/M cyclins by G1 cells, without the need for cell synchronization. By use of multiparameter flow cytometric and laser scanning cytometric analysis, we correlated the expression of cyclin B1 with cell cycle position in normal lymphocytes stimulated to proliferate by the mitogen phytohemagglutinin and in 28 primary human tumors of different organ and type. Eighteen of the 28 tumors expressed the cyclin B1 in more than 5% of cells (B1 positive), and the rest showed cyclin expression from 2.1 to 5% (B1 negative). In normal lymphocytes, the expression of cyclin B1 was restricted to very late S and G2 + M phases of the cell cycle. In 15 of 18 primary tumors studied, the expression of cyclin B1 was "unscheduled" (unrestricted to particular phases of the cycle). The data suggest that the "unscheduled" expression of cyclin B1 might be a common defect in neoplasia.

Adrenal Gland Neoplasms↗