Cell killing by actinomycin D in relation to the growth cycle of chinese hamster cells

Inhibition of interferon production and antiviral action in mouse cells by 4,5',8-trimethylpsoralen activated with near ultraviolet light. Brief report

The DNA of mammalian cells treated with 4,5',8-trimethylpsoralen (Trioxsalen) is crosslinked (preventing transcription) only after photoactivation with near ultraviolet light. Suppression of gene action in cocultivated or fused cultures, including both induction and antiviral action of fibroblast interferon, can consequently be limited to pretreated cells, an advantage over actinomycin treatment.

Induction of ovalbumin synthesis in immature chicks by actinomycin D and thioacetamide

Actinomycin D and thioacetamide induced ovalbumin synthesis and increased serum progesterone concentrations in immature chicks. The increase in progesterone induced by the carcinogens actinomycin D and thioacetamide may account for the induction of ovalbumin synthesis.

The effects of "cell age" upon the lethal effects of physical and chemical mutagens in the yeast, Saccharomyces cerevisiae

Yeast cultures progressing from the exponential to the stationary phase of growth showed changes in cell sensitivity to physical agents such as UV light, heat shock at 52 degrees C and the chemical mutagens ethyl methane sulphonate, nitrous acid and mitomycin C. Exponential phree chemicals. The increased resistance of exponential phase cells to UV light was shown to be dependent upon the functional integrity of the RAD50 gene. Treatment of growing yeast cultures with radioactively labelled ethyl methane sulphonate indicated the preferential uptake of radioactivity during the sensitive exponential stage of growth. The results indicated that the differential uptake of the chemical mutagens was responsible for at least a fraction of the variations in cell sensitivity observed in yeast cultures at different phases of growth.

Interaction between radiation and drug damage in mammalian cells. II. The effect of actinomycin-D on the repair of the sublethal radiation damage in plateau phase cells

The effect of actinomycin-D (AMD) on radiation damage repair was studied in plateau phase V79 Chinese hamster cells. Sublethal radiation damage repair, as demonstrated by survival fluctuations following two x-ray exposures separted by time, was observed in our plateau phase cells. Plateau phase cells exposed to 0.01-0.04 mug/ml AMD (a nontoxic regimen to 8 hours) between x-ray exposures were less able to repair sublethal damage. If plateau phase cells were plated at low dilutions into fresh medium (conditions for resuming exponential growth) immediately after the first x-ray dose, and exposed to 0.01--0.04 mug/ml AMD until the second dose, inhibition of sublethal damage repair and additional cell killing were observed particularly at 0.04 mug/ml AMD. It is suggested that radiation-drug damage interactions should be studied in plateau phase cells and in cells resuming exponential growth after plateau phase (possibly analogous to "recruitment"), as well as in exponential phase cultures.

A comparative study of the effects of lucanthone (miracil D) and actinomycin D on the Chinese hamster cells grown in cultures

Chinese hamster cells of an established clone line grown in monolayers were incubated for up to two hours with either lucanthone (0.3-30 mug/ml) or actinomycin D (0.06-0.10 MUG/ML) AND SUbjected to radioautographic investigations with 3H-uridine during the period of treatment. At concentration of 9 mug/ml lucanthone selectively inhibited the synthesis of nucleolar (ribosomal) RNA while the extranucleolar RNA synthesis proceeded at a high level. Similar results were obtained with 0.08 mug/ml actinomycin D. Protein synthesis and mitotic activity were also affected by lucanthone but the drug did not markedly interfere with DNA synthesis. Lucanthone appeared to be much less effective in cell killing than actinomycin D and its inhibitory effects on the nucleolar RNA synthesis and other cellular processes proved readily reversible. The results allow to conclude that lucanthone may be useful as a tool for studying RNA synthesis in animal cells.

Combined intra-arterial actinomycin D and radiation therapy for surgically unresectable hypernephroma

One primary goal of preoperative radiotherapy for hypernephroma is to reduce the volume of tumor and, therefore, improve the possibility of resection. It is important that this goal be accomplished promptly so that 4 to 6 weeks after radiation therapy nephrectomy can be attempted. A longer waiting period may allow fibrosis of the normal surrounding tissues and make surgery more difficult. In addition, longer waiting periods could theoretically increase the probability of metastasis. Therefore, we plan to continue clinical investigation on the use of combined intra-arterial actinomycin D and radiotherapy as a possible useful means of improving the possibility of prompt surgical resection, since theoretically this regimen may be a method of increasing the effective radiation dose to the hypernephroma without increasing the effective radiation dose to surrounding normal tissue, such as bowel. The method may also have merit as an improved means of palliating selected patients with metastases who are symptomatic from a bulky primary hypernephroma.

Clinical and theoretical aspects of the treatment of surgically unresectable retroperitoneal malignancy with combined intra-arterial actinomycin-D and radiotherapy

A small pilot series (eight patients) of surgically unresectable retroperitoneal tumors treated with radiotherapy and a selective, prolonged, continuous intra-arterial infusion of actinomycin-D is discussed, in addition to the possible theoretical advantages for this therapy. For such tumors, there is a very low probability of obtaining local control with conventional radiotherapy alone. However, on the basis of recent knowledge from radiobiology and molecular biology, the technique is a rational attempt to improve the local control probability. Geographic miss with radiotherapy portals is another major cause for local failure with such tumors. We also emphasize the importance of detailed tumor localization procedures. The local responses, some of the local controls, the palliation achieved, and the lack of significant morbidity with this technique have been encouraging. We therefore consider it worthy of further clinical investigation.

Kinetics of antibody production by single cells. II. The action of transcription and translation inhibitors upon the metabolism of haemolysin-secreting cells

The plaque-forming cell (PFC) population from spleens of mice at the peak of the primary immune response against sheep red blood cells has been analysed using a plaque-assay technique and automatic photographic equipment which recorded plaque formation and growth within a carboxymethyl-cellulose gel. Preliminary biochemical studies, using tritiated uridine and leucine as markers, and actinomycin D and puromycin as inhibitors of transcription and translation respectively, were performed with normal spleen cells. The effect of each of these inhibitors was then tested by means of the plaque-assay technique.

The formation and subsequent growth of a plaque within a normal gel are processes in which both transcription and translation are required for haemolysin secretion. It was found that in PFC populations, the functional lifespan of messenger RNA (m-RNA) specific for haemolysin translation has a mean value of 4 hours, while the functional lifespan of total RNA in whole spleen cell populations is not more than 2 hours. The pool of haemolysin stored in a PFC has a mean secretion time of 1.5 hours.

There was considerable heterogeneity with regard to the storage of haemolysin and to the functional lifespan of the haemolysin-specific m-RNA from one PFC to another within the spleen population. Furthermore, some PFC which displayed a high secretion rate of haemolysin were unaffected by actinomycin D, while others were inhibited within a few hours. The short-term action of each inhibitor has been studied. Puromycin was found to have a reversible action on PFC expression, while a 1-hour duration of action of actinomycin D was sufficient to inhibit irreversibly the subsequent PFC expression.

On the differential cytotoxicity of actinomycin D

Actinomycin D (AMD) at concentrations that inhibit cellular RNA synthesis by 85% or more causes an acute phase of lethal cell degeneration in HeLa cultures beginning as early as 3 hr after drug exposure, resulting in the nearly complete loss of viable cells by 12 hr. The loss of cells during this acute phase of lethality is closely dose dependent. Vero, WI38, or L cells are not susceptible to this early acute cyto-intoxication by AMD, and may begin to die only after 1-2 days. Differential susceptibility to acute cyto-intoxication by AMD, or other inhibitors of RNA synthesis (daunomycin or nogalamycin), among different types of cultured cells is analogous to that observed in vivo in certain tissues and tumors, and cannot be accounted for by differences in the effect of AMD on RNA, DNA, or protein syntheses, or by the over-all loss of preformed RNA. Actinomycin D in a dose that inhibits RNA synthesis causes an equivalent loss of the prelabeled RNA in all the cell types studied. Inhibition of protein synthesis with streptovitacin A or of DNA synthesis with hydroxyurea does not cause acute lethal injury in HeLa cells as does inhibition of RNA synthesis. Furthermore, since Vero or L cells divide at about the same rate as HeLa cells, no correlation can be drawn between the rate of cell proliferation and susceptibility to the cytotoxicity of AMD. Susceptibile cells are most vulnerable to intoxication by AMD in the G(1)-S interphase or early S phase. Inhibition of protein synthesis (which protects cells against damage by other agents affecting DNA) does not protect against AMD-induced injury. Although HeLa cells bind more AMD at a given dose than Vero or L cells, the latter cell types, given higher doses, can be made to bind proportionally more AMD without succumbing to acute cyto-intoxication. It is suggested that the differential susceptibility of these cell types to acute poisoning by AMD may reflect differences among various cells in the function or stability of certain RNA species not directly involved in translation whose presence is vital to cells. In HeLa cells, these critical species of RNA are presumed to have a short half-life.

Sedimentation of DNA released from Chinese hamster cells

Under high pH and high salt conditions, Chinese hamster cells lyse and release a DNA-containing material of large molecular weight. With increasing lysis time, a smaller material is resolved from the large one. Relative to T4 DNA, the smaller is estimated to be approximately 2 x 10(8) daltons (number average). From a comparison of radiation data, the target size of the larger is about 15 times that of the smaller (probably a lower limit estimate). In addition to concentration of alkali, temperature, and time of lysis, the resolution of the smaller from the larger material is shown to be affected by other factors. Three of these are: fluorescent light exposure during lysis, X-irradiation before lysis, and incorporation of actinomycin D before lysis. All of these treatments result in degradation of the smaller molecules if large enough exposures are used. The sedimentation patterns of both DNA materials are strongly speed dependent. This probably results from changes in molecular conformation and concomitant increases in viscous drag with speed. The speed dependence differs qualitatively for the two materials, an observation which suggests that they differ in ways in addition to size.