Cellular Deoxyribonucleic Acid Research Articles

Heat-induced apoptosis in human glioblastoma cell line A172.

Hyperthermia has been clinically applied to some types of brain tumors. However, the detailed mechanisms of this growth inhibition are not clear. The effect of mild hyperthermia on cultured human glioblastoma cell line, A172, was studied. A172 cells were heat treated (43-44.5 degrees C) for 1 hour in the growing phase. Cell viability was assessed by trypan blue dye exclusion assay. The presence of apoptosis was determined by the morphological changes observed using phase contrast microscopy and nuclear changes observed using HOECHST 33342 stain. For the evaluation of cellular deoxyribonucleic acid fragmentation, the TUNEL method was used. The expression of p53 and bax proteins was evaluated by Western blot, and the bax messenger ribonucleic acid was detected by Northern blot. Heat treatment induced cell death in time- and temperature-dependent manners. The nuclear staining with HOECHST 33342 demonstrated morphological changes consistent with apoptosis. The TUNEL stain also demonstrated damages in the deoxyribonucleic acid. These morphological changes were accompanied by the accumulation of p53 protein, bax protein, and messenger ribonucleic acid. These results indicate that mild hyperthermia induces apoptosis in A172 glioblastoma cells.

P53 and bcl-2 immunohistochemical alterations in prostate cancer treated with radiation therapy

Objectives. Radiation therapy is definitive treatment for localized prostate cancer. It causes cellular deoxyribonucleic acid (DNA) damage, which, if irreparable, results in apoptosis or programmed cell death. Overexpression of mutant p53 and/or bcl-2 proteins prolongs cell survival despite exposure to damaging agents. We examined whether abnormal expression of either gene could help to explain radiation therapy failures in prostate cancer. Methods. Archival tissue from patients who had failed radiation therapy as treatment for prostate cancer was obtained before and after treatment. These cancer samples were examined immunohistochemically for accumulation of p53 and bcl-2 proteins. Comparison was made with specimens from patients who had no evidence of recurrent or persistent disease at least 3 years following radiation therapy. Results. High rates of p53 immunopositivity were found in the prostate tissue from all groups studied. More patients who had failed radiation therapy were found to have bcl-2 immunopositive specimens than were those without evidence for recurrent disease (41% preradiation and 61% postradiation versus 8%, P <0.05). More patients who failed radiation therapy had both p53 and bcl-2 immunopositive prostate tissue than did those who were treated successfully (32% preradiation and 48% postradiation versus 8%). Conclusions. bcl-2 immunopositivity, with or without concomitant detection of p53, was found in significantly more cancers of patients who failed radiation therapy. Positive staining for bcl-2 may serve as a marker for determining the radiation sensitivity of a tumor and thus may help to guide treatment options. It is also notable that a high proportion of the prostate cancers examined were immunopositive for p53.

Cellular deoxyribonucleic acid fragmentation during operative course in human saphenous vein grafts

Cellular deoxyribonucleic acid fragmentation during operative course in human saphenous vein grafts

Angiotensin II and basic fibroblast growth factor induce neonatal bladder stromal cell mitogenesis.

Our aims were to establish primary stromal cell cultures from the neonatal rabbit bladder and investigate the potential mitogenic effects of angiotensin II and basic fibroblast growth factor on these cells. Primary bladder stromal cell cultures were obtained from 3-day-old rabbits, plated at a density of 3 x 10(4) cells per ml. and allowed to grow for 24 hours. Subconfluent cells were growth arrested in serum deficient (0.25% newborn calf serum) or serum-free media for 24 hours and then stimulated with 10(-7) M. angiotensin II or 10 ng./ml. basic fibroblast growth factor for an additional 48 hours. Cell counts and [3H] thymidine incorporation were done to measure cellular proliferation and deoxyribonucleic acid synthesis. Angiotensin II and basic fibroblast growth factor each stimulated neonatal bladder stromal cell proliferation and [3H] thymidine incorporation under serum deficient conditions. Angiotensin II provoked an average 26% increase in cell number (p < 0.01) and 35% increase in [3H] thymidine incorporation (p < 0.01) compared to control values. Basic fibroblast growth factor was an even more potent mitogen with a 47% increase in cell number (p < 0.01) and 180% increase in [3H] thymidine incorporation (p < 0.01) compared to controls. In contrast, angiotensin II and basic fibroblast growth factor each failed to have significant stimulatory effects under serum-free conditions. Angiotensin II and basic fibroblast growth factor induce a mitogenic response to neonatal bladder stromal cells in vitro. These mitogenic effects require the presence of serum factors. Whether angiotensin II and basic fibroblast growth factor are involved in the in vivo regulation of bladder growth associated with obstructive uropathy requires further investigation.

Estimation of genetic effects of a static magnetic field by a somatic cell test using mutagen-sensitive mutants of Drosophila melanogaster

In order to estimate the genetic effects of magnetic fields, a somatic cell test was performed using mutants of the fruit fly Drosophila melanogaster which lack repair functions for damage to their cellular deoxyribonucleic acid (DNA). Young larvae of mutant and normal genotypes were exposed to a homogeneuos 0.6 T magnetic field for 24 h and were then allowed to continue development under normal culture condition until they moulted and finally emerged from their pupal cases. After eclosion, the number of surviving adults was counted. The number of adults of the mutant genotype decreased by about 8% compared with unexposed controls, while that of normal siblings remained unchanged. This suggests that exposure to a static magnetic field resulted in damage to larval cellular DNA, and that somatic cells without normal DNA repair functions failed to continue cell division which resulted in developmental lethality of mutant larvae. DNA damage occurring in normal larvae should have been repaired, so that their survival rate was not altered. The effect was compared with that of UV irradiation, and the genotoxic activity of the 0.6 T static magnetic field was estimated to be the same as that of UV light with an intensity of 0.14 mJ m −2 s −1. Possible mechanisms in which DNA damage is caused by magnetic field exposure are discussed.

Nuclear morphometric analysis of metastasis in Wilms' tumor after multimodal therapy: Comparison with primary tumor

Objectives. The outlook for children with Wilms' tumor has improved with the use of multimodal therapy, and survival rates now exceed 85%. Yet, 15% of children with tumors with favorable histologic findings continue to recur unpredictably. We previously reported that nuclear morphometry (the distribution of nuclear roundness factor [NRF], lowest values for ellipticity, and age) when combined in a multivariate analysis accurately predicted response to therapy for patients with histologically favorable Wilms' tumors. Methods. To investigate further the nuclear shape changes associated with disease recurrence, we analyzed histologic sections taken from primary tumors and postmultimodal therapy metastatic lesions for 7 children who had a recurrence with initially histologically favorable primary tumors. Results. Mean NRF was significantly lower ( P = 0.0001) in the metastatic lesion (35 ± 5) group when compared with the primary tumor group (50 ± 5). The percent coefficient of variation for NRF was also significantly lower ( P = 0.006) in the metastatic lesion when compared with the primary tumor. Nuclear area was increased ( P = 0.02), although the nuclear perimeter was unchanged ( P = 0.1). Conclusions. (1) Nuclei in metastatic lesions from Wilms' tumors with favorable histologic findings after multimodal therapy are more round and exhibit less variable distribution, suggesting clonal homogeneity within the metastatic lesion. (2) Nuclei in the metastatic lesions have greater area than in the primary tumors yet have an unchanged perimeter, which may be due to internal nuclear expansion secondary to increased cellular deoxyribonucleic acid (DNA) ploidy. Although the results of this study are promising, we are currently extending this hypothesis in a larger group of patients.

The Insertion of Foreign DNA Into Mammalian Genomes and Its Consequences: A Concept in Oncogenesis

Publisher Summary This chapter examines the consequences of foreign deoxyribonucleic acid (DNA) insertion into established mammalian genomes. In mammalian cells, the ever-present repetitive DNA sequences possibly constitute a reservoir of insertion targets whose disturbance may have less immediate functional consequences. Among the consequences of the insertion of foreign DNA into the established genomes and of the transformed cell phenotype are the de novo methylation of the foreign DNA and alterations in the existing patterns of DNA methylation in the preexisting cellular genome. Diet-ingested foreign DNA could play an important role in eliciting mutagenic and oncogenic events in mammals. In light of these findings, the postulated cellular defense mechanism by methylation of integrated foreign DNA becomes plausible. The results of studies on the model of adenovirus DNA integration in mammalian cells suggested that the insertion of foreign DNA had to be rather pliable. There is a possibility that the insertion of foreign DNA into an established mammalian genome can lead to far-reaching alterations in the patterns of cellular DNA methylation and gene expression. The classical concept of insertional mutagenesis relates to damage caused to cellular functions or genes that are encoded at the sites of foreign (adenoviral) DNA insertion into the host genome.

A morphological, biochemical, and radioautographic study in rats

Splenectomy has long been an establishmd surgical procedure in various conditions, including trauma. Because total splenectomy has often been correlated with sepsis, every surgeon tries to preserve as much of the injured spleen as possible. Contradictory reports have been published as to whether regeneration of the remaining splenic tissue is possible. In the present study, 28 Sprague-Dawley rats (≈ 100 g) were divided into four groups. They underwent two-thirds partial splenectomy; the remaining splenic tissue was examined after 1 day, 1 week, 1 month and 3 months postoperatively. The following parameters were determined: weight, length, and protein and deoxyribonucleic acid (DNA) content of the remaining spleen. The incorporation of 3H-thymidine into the remaining spleen tissue was also measured. Histology and radioautography were studied in parallel. Results were compared with control animals that were operated upon but with no partial splenectomy. One day, 1 week, and 1 month following partial splenectomy, a slight increase in weight, length, protein, and DNA content as well as incorporation of the radioisotope into cellular DNA was found. By 3 months after the operation, there was no difference in the above parameters between the experimental animals and controls.

Stimulatory effect of beta-alanyl-L-histidinato zinc on cell proliferation is dependent on protein synthesis in osteoblastic MC3T3-E1 cells.

The effect of beta-alanyl-L-histidinato zinc (AHZ) on bone metabolism was investigated in osteoblastic MC3T3-E1 cells. Cells were cultured for 3 days at 37 degrees C in a CO2 incubator in plastic dishes containing alpha-modified minimum essential medium supplemented with 10% fetal bovine serum. After the cultures, the medium was exchanged for that containing 0.1% bovine serum albumin plus various concentrations of AHZ or other reagents, and the cells were cultured further for appropriate periods of time. The presence of AHZ (10(-7)-10(-5) M) stimulated the proliferation of cells. AHZ (10(-6) and 10(-5) M) increased deoxyribonucleic acid (DNA) content in the cells with 48 hr-culture. This increase was completely blocked by the presence of cycloheximide (10(-6) M) or hydroxyurea (10(-3) M). Also, the presence of cycloheximide (10(-6) M) completely inhibited the AHZ (10(-5) M)-induced increase in the proliferation of cells. Meanwhile, parathyroid hormone (10(-7) M), estrogen (10(-9) M) and insulin (10(-8) M) significantly increased cellular DNA content. However, these hormonal effects clearly lowered in comparison with that of AHZ (10(-5) M). Dibutyryl cyclic AMP (10(-4) M) and zinc sulfate (10(-5) M) did not cause a significant increase in cellular DNA content. The present results support the view that AHZ has a direct specific proliferative effect on osteoblastic cells in vitro and that this effect is dependent on protein synthesis.

Circulating prostate specific antigen-positive cells correlate with metastatic prostate cancer.

Analytical flow cytometry was used to study circulating prostate specific antigen (PSA)-positive cells in 40 consecutive patients with newly diagnosed, untreated prostate cancer; 25 patients (63%) had metastatic disease confirmed by a positive bone scan. Cell suspensions were prepared for each patient from both the primary tumour and peripheral blood samples. The cells were stained with a monoclonal antibody against PSA, and analysed by flow cytometry; PSA-positive cells were sorted according to their immunofluorescence and light scatter properties. The cellular deoxyribonucleic acid (DNA) content of each specimen was also analysed to establish ploidy status. PSA-positive cells were detected in the peripheral blood of 33 patients (83%). The presence of these cells in the circulation showed a higher degree of sensitivity and specificity in predicting positive bone scans than did serum PSA levels. Circulating PSA-positive cells may represent either a subpopulation of tumour cells with distinct metastatic properties or, alternatively, host immunocytes which take up PSA in an active or passive manner.

Induction of transformational changes in normal endothelial cells by cultured human astrocytoma cells

Endothelial cell proliferation is a significant biological feature of malignant astrocytomas. The ability of the cells of these tumors to elaborate mitogenic angiogenesis factors has been well documented. However, less is known about the transformational effects that neoplastic astrocytes may have on the endothelial cells within malignant astrocytomas. In this study, the hypothesis that humoral factors elaborated by cells derived from malignant astrocytomas induce transformational changes in normal endothelial cells in vitro is investigated. Conditioned medium (CM) was prepared from exponentially growing cultures of a human glioblastoma cell line (UW18) and from two rat brain-tumor cell lines: an anaplastic astrocytoma (R175A) and a glioblastoma with sarcomatous elements (9L). Subconfluent target bovine aortic arch endothelial cells (BAEC's) were exposed for 48 hours to varying concentrations of CM prepared from each of these tumors, and then evaluated for transformational changes. Different molecular weight (MW) fractions of UW18 CM were prepared by molecular ultrafiltration, and each fraction was tested for transforming activity. Transformation endpoints included changes in cellular deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) content and distribution (measured by differential flow cytometry) and changes in de novo DNA synthesis determined by 3H-thymidine incorporation. Significant changes in the amount and distribution of DNA and RNA were observed in the BAEC's treated with UW18 CM compared to untreated BAEC's. At 10% concentrations of UW18 CM, changes in the RNA profile of target BAEC's were evident, and at 30% concentrations of UW18 CM, an irregular bimodal distribution was well established. Patterns of DNA were also altered in a concentration-dependent manner, with significant aneuploidy developing at UW18 CM concentrations of 20%. The DNA synthesis in BAEC's increased with increasing CM concentrations, up to a maximum of about 250% of control values at 30% concentrations of UW18 CM. The transformational changes induced after exposure of BAEC's to CM prepared from R175A and 9L were significantly less than those observed with UW18 CM. Molecular ultrafiltration was used to prepare UW18 CM fractions with MW cutoffs of less than 10 kD, 10 to 30 kD, and greater than 30 kD. Transformational activity was significant only in CM's with an MW of 10 to 30 kD. It is concluded that the UW18 human glioblastoma cell line elaborates a soluble factor, or group of factors, with an MW in the 10- to 30-kD range, capable of inducing transformational alterations in target normal endothelial cells, and that such transformation may account for some of the abnormal endothelial cell changes associated with malignant astrocytomas.

Flow cytometric analysis of cellular deoxyribonucleic acid content of nine renal oncocytomas

The cellular deoxyribonucleic acid content of formalin-fixed, paraffin-embedded tissue from nine renal oncocytomas was determined using an Epics-C flow cytometer. The tissues were all from surgical specimens, and all neoplasms met stringent light and electron microscopic criteria for the diagnosis of oncocytoma. Thirteen samples of pure tumor, 5 of tumor and normal kidney, and 3 of normal kidney alone were analyzed. All oncocytomas had single, sharp G1 peaks with no evidence of aneuploidy, and this peak was similar to that of normal renal parenchyma. This was true even for three oncocytomas that had multiple major chromosomal anomalies on karyotyping. These data support the concept that renal oncocytomas are euploid neoplasms, consistent with their benign biologic behavior. The apparent discrepancy between the results of flow cytometry and karyotyping is discussed.

Expression of cytokine receptors and markers of differentiation in human papillomavirus-infected cervical tissues

Human papillomavirus infection of the uterine cervix is associated with a spectrum of benign, premalignant, and malignant epithelial lesions, a process that appears to require the coordinated effects of secondary cellular and environmental events. We have used flow cytometry and immunohistochemistry to examine the expression of the cellular markers for proliferation (interleukin-1, epidermal growth factor receptor, and transferrin receptor) and the markers of cellular differentiation (filaggrin and low-molecular-weight cytokeratin) in normal and human papillomavirus-infected human cervical tissues representing the natural range of human papillomavirus-induced disease. The results were correlated with the histologic grade of disease, human papillomavirus type, cellular deoxyribonucleic acid content, and cell cycle status. Interleukin-1 and transferrin receptor were slightly increased in high-grade dysplasias and in squamous cell carcinomas. Filaggrin expression was found to be inversely related and cytokeratin and epidermal growth factor receptor expression directly related to the degree of neoplasia. These findings indicate that cytokeratin and epidermal growth factor receptor are useful markers of cell proliferation in human papillomavirus-infected tissues and that their expression may directly increase as a result of infection.

DNA probes in the quality control of pharmaceutical products purified from bovine brain tissue

The presence of contaminating endogenous and viral deoxyribonucleic acid (DNA) was evaluated by dot-blot hybridization in products derived from intermediate steps of an industrial process for extraction of gangliosides from bovine brain tissue and from several final production lots. The hybridization was performed with probes specific for calf thymus DNA and with two recombinant DNA plasmids specific for bovine herpes virus I (BHV-I) and bovine leukaemia virus (BLV). These probes were labelled with 32P. The hybridization was also evaluated by means of a biotin-labelled calf thymus DNA probe. Traces of cellular DNA were identified in the starting raw material and in the products which were obtained after the early purification steps. No hybridization was detected in any of the final preparations within the limits of sensitivity of the assay. The two specific viral DNA probes did not show any hybridization signal even in the starting raw material. The limit of detection was well below the maximum allowed values. These results indicate that the purification procedure used to obtain pharmaceutical-grade bovine gangliosides reduces DNA to undetectable levels and that the assay used is applicable to the analytical screening of products purified from biological sources on an industrial scale.

Flow Cytometric Evaluation of Multicystic Dysplastic Kidneys

The most appropriate management of the multicystic dysplastic kidney remains controversial. At issue is the long-term risk of the development of malignancy in the multicystic dysplastic kidney. The association between renal dysplasia and neoplasia has not been confirmed, with only 6 cases of malignancy reported. Nephroblastomatosis, a probable precursor of Wilms tumor, has been found in 5 to 7% of the cases of multicystic dysplastic kidney when specifically sought.In an attempt to determine whether a relationship exists between renal dysplasia and neoplasia in terms of abnormalities of cellular deoxyribonucleic acid content we performed flow cytometric evaluation on 30 formalin fixed, paraffin embedded archival specimens of multicystic dysplastic kidneys. None of the kidneys had evidence of malignancy. Nuclear deoxyribonucleic acid ploidy studies were performed on single dissociated nuclei prepared by the technique of McLemore and associates and stained with propidium iodide. All specimens demonstrated a diploid pattern of deoxyribonucleic acid, including 3 specimens with nephroblastomatosis or extensive papillary growth, and no specimen demonstrated a tetraploid or aneuploid pattern. The mean G0/G1 fraction was 85.94% (standard deviation 4.59) and the mean S/G2/M fraction was 12.54% (standard deviation 4.72). These findings do not support or negate the potential for neoplasm associated with multicystic dysplastic kidney, since a diploid deoxyribonucleic acid pattern does not eliminate the possibility of the future development of malignancy.

Differential inhibitory effects of some catechin derivatives on the activities of human immunodeficiency virus reverse transcriptase and cellular deoxyribonucleic and ribonucleic acid polymerases

The two components of Camellia sinensis (tea plant) [i.e., (-)-epicatechin gallate and (-)-epigallocatechin gallate] were found to differentially inhibit the activities of reverse transcriptase and cellular DNA and RNA polymerases. Under the assay conditions optimized for each enzyme species, the strongest inhibition by these compounds was observed with reverse transcriptase. The concentrations of (-)-epicatechin gallate and (-)-epigallocatechin gallate required for 50% inhibition of the activity of human immunodeficiency virus (HIV) reverse transcriptase were in the range of 0.01-0.02 microgram/mL. On the other hand, neither (-)-epicatechin, (-)-epigallocatechin, nor gallic acid, the constituents of (-)-epicatechin gallate and (-)-epigallocatechin gallate, was inhibitory to the activity of HIV reverse transcriptase at concentrations up to 1 microgram/mL. The mode of inhibition of reverse transcriptase and other DNA polymerases by these compounds was competitive with respect to the template-primer, whereas the mode of inhibition of RNA polymerase was competitive with respect to the nucleotide substrate. The Ki values of HIV reverse transcriptase for (-)-epicatechin gallate and (-)-epigallocatechin gallate were determined to be 7.2 and 2.8 nM, respectively, which are smaller by 1-2 orders of magnitude than the Ki's of other DNA and RNA polymerases for these compounds.

Human uterus-derived growth substances for rat bone cells and fibroblasts

The effects of extracts from normal human uteri on tritiated thymidine incorporation and cell number were studied in primary cultures of isolated fetal rat calvarial osteoblasts and fetal rat skin fibroblasts. In this study crude uterine extracts were shown to stimulate tritiated thymidine incorporation into cellular deoxyribonucleic acid in osteoblast-like and fibroblast-like cell cultures above controls levels. This effect, which began after 6 hours, was maximal after 24 hours of incubation. In addition, the number of osteoblast-like and fibroblast-like cells increased above control levels after 1, 3, and 5 days of incubation. The above effects were dose-dependent, and maximal stimulation of uterine extracts was comparable with the stimulation achieved by 10% fetal bovine serum. The degree of stimulation by uterine extracts, expressed as percent above controls, was not dependent on the concentration of fetal bovine serum in cell culture medium. The above results are consistent with the view that uterine extracts contain mitogen(s) for bone cells and fibroblasts. These mitogens could play an important role in bone physiology and uterine pathophysiology.

Inhibition of duck hepatitis B virus replication by 2′,3′-dideoxycytidine: A potent inhibitor of reverse transcriptase

The effect of 2′,3′-dideoxycytidine, a potent antiviral agent, which, following anabolic phosphorylation, inhibits the reverse transcriptase of the human immunodeficiency virus in vitro, was assessed in 16 Pekin ducks chronically infected with the duck hepatitis B virus. Nine ducks were given 11 mg/m2 of dideoxycytidine intravenously every 6 h, and 7 ducks received no treatment. Serum duck hepatitis B virus deoxyribonucleic acid and deoxyribonucleic acid polymerase activity decreased in every duck treated with dideoxycytidine. The mean inhibition of deoxyribonucleic acid polymerase and duck hepatitis B virus deoxyribonucleic acid on the third day of treatment measured 64% (p < 0.01) and 73% (p < 0.01), respectively. The inhibition of deoxyribonucleic acid polymerase persisted after treatment was stopped, and 4 ducks continued to show >50% inhibition 12 days after stopping treatment. Duck hepatitis B virus deoxyribonucleic acid, which was measured in total cellular deoxyribonucleic acid extracted from liver biopsy specimens obtained before and on the last day of treatment with dideoxycytidine, showed an average inhibition of 96% in 3 ducks treated with dideoxycytidine, but showed no decrease in the remaining 5 ducks. Thus, dideoxycytidine has potent antiviral activity against duck hepatitis B virus and warrants further evaluation as an antiviral agent in the treatment of chronic hepatitis B virus infection in humans.

Flow-cytometric DNA analysis and immunohistochemical measurement of Ki-67 and BUdR labeling indices in human brain tumors

Cell proliferation potential was assessed by measuring the labeling indices of the monoclonal antibody Ki-67 and of 5-bromodeoxyuridine (BUdR), and the cellular deoxyribonucleic acid (DNA) content in 48 human brain tumors. The diagnostic and prognostic value of flow-cytometric DNA analysis was also evaluated using ethanol-fixed paraffin-embedded BUdR-labeled specimens; these were the same specimens as were used for measuring the BUdR and Ki-67 labeling indices. Both the Ki-67 and the BUdR labeling indices correlated with the degree of malignancy estimated from conventional histological preparations. The Ki-67 labeling index was 1.7 times greater than the BUdR labeling index. The relationship of DNA aneuploidy to the labeling indices or to morphology in cases of glioma was examined. All of the tumors with an aneuploid line corresponded to malignant glioma classified by histological criteria, although malignant glioma did not always show DNA aneuploidy. In addition, the cases with aneuploid lines showed high BUdR and Ki-67 labeling indices. The cell kinetic data, which indicate the biological character of tumors, allowed prediction of the prognosis of the patients with gliomas. In contrast, despite the presence of an aneuploid line, three of 13 meningiomas showed a benign histological pattern without an aggressive clinical course, and neither the Ki-67 nor the BUdR labeling index was high. These results indicate an unequivocal relationship between DNA aneuploidy and clinical behavior; in general, both labeling indices may prove to be objective indicators of the outcome of patients with brain tumors.

Differential inhibitory effects of various herb extracts on the activities of reverse transcriptase and various deoxyribonucleic acid(DNA) polymerases.

Forty preparations of the extracts from 28 kinds of Asian herbs were tested for ability to inhibit the activities of murine retroviral reverse transcriptase and human deoxyribonucleic acid (DNA) polymerases. Among the 40 extracts, 35 inhibited reverse transcriptase activity and 29 inhibited DNA polymerase alpha activity. The inhibitory potencies of these extracts were expressed as the 50% inhibition concentrations (IC50), at which the enzyme activities were inhibited by 50%. Very strong inhibitions were observed with the extracts from Millettia pachycarpa (Leguminosae) and Mallotus apelta (Euphorbiaceae) as shown by their low IC50 values for reverse transcriptase (0.4-0.5 micrograms/ml) and DNA polymerase alpha (0.9-1.4 micrograms/ml). Enzyme kinetic analysis revealed that the mode of inhibition of reverse transcriptase by these two extracts was competitive with respect to the template.primer [poly(rA).oligo(dT)] and noncompetitive with respect to deoxythymidine triphosphate (dTTP) substrate. Besides reverse transcriptase and DNA polymerase alpha, DNA polymerase I and ribonucleic acid (RNA) polymerase from E. coli were inhibited by these two extracts. These results indicate that the herb extracts contain as yet unidentified substance(s) which inhibit the activities of reverse transcriptase and cellular DNA polymerases.