H. George Mandel

Studies on the mechanism of action of the tumour inhibitory triazenes.

Abstract A series of imidazole and phenyl dialkyi triazenes were synthesized and investigated for their anti-cancer activity in experimental animals. Active triazenes had a broad spectrum of anti-tumour action and like bischloroethylnitrosourea (BCNU) were active against tumours not sensitive to conventional alkylating agents. It was confirmed that at least one N -methyl group was necessary for anti-cancer activity but there was no correlation between dealkylation by liver microsomes and activity since a diethyl triazene was readily dealkylated but not active. A factor appears to be present in normal cell cytoplasm which can detoxify triazenes but which is absent from tumours sensitive to these agents.

A simple membrane fractionation method for determining the distribution of radioactivity in chemical fractions of Bacillus cereus

A method has been devised for the rapid determination of the distribution of a labeled precursor in the chemical fractions of Bacillus cereus. The procedure involves the extraction of the cell by selective reagents, followed by filtration through collodion membranes. The distribution was then calculated by difference. By the use of suitable radioactive precursors for protein, DNA, and RNA, it was possible to examine and adapt the classical fractionation methods of Schmidt and Thannhauser and of Schneider to the membrane filter method. Complete fractionations were carried out simply and reproducibly on a few milliliters of bacterial suspension, containing less than 0.5 mg dry weight of material.

Binding of tetracycline to the 30S ribosomes and to polyuridylic acid

Abstract 1. 1. Tetracycline binds specifically to the 70S and 30S ribosomes of B. cereus and E. coli , both in vivo and in vitro . Incubation of E. coli ribosomes with ATP and amino acids reduces the amount of tetracycline bound. 2. 2. Tetracycline binds strongly to poly U in vitro . 3. 3. The binding of tetracycline to ribosomes and poly U occurs in the presence of EDTA, suggesting that this binding is not Mg++ dependent. 4. 4. It is suggested that tetracycline binds directly to mRNA, thus inhibiting the binding of sRNA to mRNA.

Differential chromatid damage induced by 6-thioguanine in CHO cells☆

Abstract Treatment of Chinese hamster ovary cells with 6-thioguanine (TG) produces severely disrupted chromatin in G2 cells, as visualized with premature chromosome condensation. In many regions of the chromosome this damage, appearing as a gapped or diffusely staining region, occurs in only one of sister chromatids. This morphology strongly supports previous reports that TG-induced cytotoxicity is related to its incorporation into DNA and that this lesion is expressed in the cell cycle following that in which drug exposure occurs.

From progress to regression: biomedical research funding

Despite great advances in health-related research and health care, major challenges remain regarding the causes and cures of many diseases; these may be overcome with further research. Our society is enthusiastic about fostering such investigations. However, available federal funds limit many such projects. Previously there have been sizable increases in the NIH budget, but because of the escalating cost of scientific investigation and the pressures of financing other much-needed governmental programs, recent growth in biomedical research funding has barely kept up with inflation. This article focuses on select attempts to sustain the record of scientific achievement enabled in the past by continued increasing investment and also suggests some solutions.

The metabolism of 1-aminocyclopentane-1-carboxylic acid in normal and neoplastic tissues☆

Abstract The distribution, excretion and metabolism of the carcinostatic amino acid derivative, 1-amino cyclo pentane-1-carboxylic acid, was investigated in normal and tumor-bearing mice. After intraperitoneal injection of 14 C-carboxyl-labeled drug, the amount of radioactivity in the blood remained constant for 4 days, while the urinary excretion of this drug also remained at a constant low level during this period of time. An insignificant quantity of 14 CO 2 was liberated. All the tissues and tumors analysed contained significant amounts of radioactivity, almost all of which was in the cold acid-soluble fraction. There was very little incorporation of the drug into protein. Chemical fractionation and chromatography of tissues, tumor cells and urine have indicated that all radioactivity present was in the form of the original compound. The significance of these results is discussed.

Trauma-induced glial proliferation: possible involvement of the immune system.

Rat neurologlial cells proliferate following trauma to the frontal cortex. Since previous reports have indicated that activated T-lymphocytes secrete a factor which can induce the proliferation of glial cells in vitro, we investigated the effects of immunosuppression on the trauma-induced proliferation of glial cells in the rat. Animals were treated with either methotrexate (2.5 and 10 mg/kg/day), hydrocortisone (100 mg/kg/day), or saline for five days prior to lesioning of the cortex. Immunocompetence was estimated by measuring sheep red blood cell hemagglutination titers at the time of killing. On the last day of drug treatment, rats were mechanically lesioned on the frontal cortex, and the incorporation of intraventricularly injected 3H-thymidine (3H-TdR) into cortical DNA, a measure of glial cell proliferation, was determined two days after lesioning. Intraperitoneal treatment with methotrexate before the lesioning depressed 3H-TdR incorporation into brain DNA, and reduced hemagglutination titers and thymus and spleen weight. However, intramuscular hydrocortisone pretreatment, which had immunosuppressive actions similar to methotrexate, had a much smaller effect on 3H-TdR incorporation into brain DNA following trauma. Methotrexate given acutely after lesioning did not depress thymidine utilization in the lesioned rat cortex, apparently because of poor penetration of the folate analog into the brain. Thus, we conclude that inhibition of glial cell proliferation resulting from methotrexate pretreatment had been produced indirectly, probably by its severe immunosuppressive effects.

Glial DNA synthesis and cell proliferation in the lesioned frontal cortex of the rat

Proliferation of rat neurological cells was quantified following a lesion of the frontal cortex, with the rate of incorporation of intraventricularly administered [3H]thymidine ([3H]TdR) into cortical DNA serving as an index of glial proliferation. Incorporation of [3H]uridine into the corresponding RNA fractions did not serve this purpose. The intraventricular route of administration of thymidine greatly reduced the amount of [3H]TdR needed to label DNA relative to systemic injection. The rate of incorporation of [3H]TdR into DNA was linear for 75 min post-injection. Significantly more [3H]TdR was incorporated into DNA of the lesioned frontal cortex than that of the contralateral control cortex, during the first 4 days post-trauma. The majority of the acid-insoluble radioactivity (from [3H]TdR) was localized in the nuclear subcellular fraction of the cortex. Experiments indicated that the enhanced incorporation of [3H]TdR was not the result of altered metabolism or pool sizes of TdR in the lesioned cortex. Histological analysis indicated that there was a significant increase in the number of glial cells in the lesioned cortex by day 4 post-lesion, which corresponded to the increase in DNA synthetic activity. It was concluded that mechanical trauma to the frontal cortex of the rat results in an increase in the number of glial cells at and near the lesion which is accompanied by an increase in incorporation of [3H]TdR into cortical DNA. This method of measuring posttraumatic DNA synthesis has several advantages over autoradiography.

Understanding the actions of carcinostatic drugs to improve chemotherapy: 5-fluorouracil

Abstract The accumulation of additional basic knowledge about 5-fluorouracil is still required in order to improve the optimal utilization of this drug in the cancer patient. The drugs inhibitory effects on ribosome formation, already recognized as an important drug response in microorganisms and rodent tissues, has now been demonstrated for human colon tumors. However, ribosome synthesis does not occur sufficiently rapidly under the conditions of these experiments so that this assay appears to have limited promise as a predictor for human tumor responsiveness to FU. In the L1210 system, a rodent tumor model sensitive to FU, FdUMP was formed rapidly, and this metabolite persisted for several days in the tumor after a single dose of FU. DNA synthesis was inhibited simultaneously in concurrence with peak FdUMP levels, and recovery of this inhibition took place as the tissue concentration of FdUMP declined. DNA synthesis in bone marrow and gastrointestinal tract, which was also inhibited by drug treatment, recovered more rapidly than that of tumor, in line with the antitumor selectivity of FU in this tumor model. For the relatively unresponsive Walker 256 rat tumor, even higher levels of FdUMP were formed initially, but this metabolite was retained only briefly in the tumor after a single dose of FU. Inhibition of DNA formation in tumor was more transient than that in normal tissues, probably accounting for the nonselective antitumor response in that model. It is likely that tissue retention of FdUMP may serve as a major determinant for activity of FU in tumor and normal tissues, but other factors including inhibition of ribosomal maturation also play a role in the drugs cytotoxic action.

A rapid assay method for tritium in bacterial cells.

1. 1. The use of a simple bacterial filtration technique involving collodion membranes has permitted a precise means of assaying tritiated compounds. Radioassays at infinite thickness were readily converted to relative total count values. It is suggested that the method has general applicability. 2. 2. Bacterial cultures rapidly converted exogenous tritiated thymidine to thymine. [3H] diaminopimelic acid served as a more stable biochemical precursor, enabling accurate studies on the incorporation of tritium into bacterial cells.