Howard E. Skipper

Chromatographic studies of purine metabolism. I. The effect of azaserine on purine biosynthesis in E. coli using various C14-labeled precursors☆☆☆

Abstract It has been observed that levels of azaserine capable of only partial reduction in the growth rate of E. coli are sufficient to cause partial inhibition of the de novo synthesis of purine-containing nucleotides and concomitant intracellular accumulation of formylglycinamide ribotide and formylglycinamide riboside. Azaserine inhibited the incorporation of the radioactivity of formate-C14, glycine 1-C14, glycine-2-C14, and serine-3-C14 into all the purine-containing compounds observable on two-dimensional papergrams of extracts of noninhibited cells. Azaserine failed to inhibit the assimilation of hypoxanthine-8-C14, adenine-8-C14, and guanine-2-C14 and the interconversion of these substrates to other purine derivatives. These results indicate that a major site of action of azaserine in E. coli is the blockade of de novo purine nucleotide synthesis at a point subsequent to the formation of formylglycinamide ribotide. A procedure is presented for the application of known chromatographic-radiographic procedures to the determination of inhibition mechanisms.

Biochemical, biological, pharmacologic, toxicologic, kinetic and clinical (subhuman and human) relationships

Questions are posed regarding the marked differences in clinical response of different types of cancer to chemotherapeutic agents in the light of the quite similar sensitivity of many different types of cancer cells to such agents when they are exposed in log‐phase cultures in vitro (the cell‐culture paradox). Thymidine index data, cell‐culture response data, data on the relative sensitivity of “resting” vs. log phase leukemia cells and in vivo tumor responses are presented. Consideration of these diverse results suggest that biochemical differences exploited by some chemotherapeutic agents often may be largely quantitative—associated with the ratio of proliferating to nonproliferating cells in a normal or neoplastic tissue—thus the ratio of cells carrying out vulnerable biochemical reactions to cells not carrying out vulnerable biochemical reactions when both are exposed to drug in vivo.

Studies with mustards. III. In vivo fixation of C14 from nitrogen mustard-C14H3 in nucleic acid fractions of animal tissues

Abstract Experimental evidence is presented which strongly suggests that C 14 from injected nitrogen mustard-C 14 H 3 is fixed in the nucleic acid fractions of animal tissues chiefly as a result of the combination of the nitrogen mustard with nucleic acid moieties. The specific activity of the RNA purine fraction was consistently higher than that of any other nucleic acid fraction examined.

Studies on the mode of action of azaserine

Abstract 1. 1. Azaserine-induced inhibition of E. coli was significantly prevented by (a) 4-amino-5-imidazolecarboxamide (AIC), adenine, guanine, hypoxanthine, or xanthine; (b) methionine; and (c) glutamine; and, as has already been observed by others, by phenylalanine, tyrosine, or tryptophan. 2. 2. In studies carried out on the effect of azaserine on purine synthesis in the tumors, intestines, livers, and spleens of mice bearing Sarcoma 180, it was found that azaserine inhibited utilization of formate-C14 and glycine-1-C14 for purine synthesis, failed to affect utilization of C14-labeled adenine, AIC, and hypoxanthine, and failed to affect utilization of formate for thymine biosynthesis. Azaserine also inhibited utilization of formate-C14 and glycine-1-C14 for purine synthesis by heterologous implants of a human sarcoma growing in the rat. 3. 3. The results indicate that azaserine inhibits purine synthesis in the intact animal at a stage prior to the formation of 5-amino-4-imidazole-carboxamide ribotide.

ON THE MECHANISM OF ACTION OF 6-MERCAPTOPURINE

Elion et al.’ put forward the suggestion that a hypoxanthine-containing metabolite may be an intermediate in the conversion of adenine to guanine in L. casei, and that its transformation to a guanine-containing substance might be viewed as a possible site of action of 6-mercaptopurine (6-MP). These authors observed that a 6-meraptopurine-resistant strain of L. casei (MPR), unlike the wild strain, was incapable of using hypoxanthine for growth and grew poorly on adenine in a folic acid-free medium containing thymine, suggesting the scheme presented as FIGURE 1. When the wild and MPR strains were grown in the presence of 8-C14-adenine, the MPR strain accumulated large amounts of inosine, appreciable amounts

The Forty-Year-Old Mutation Theory of Lurla and Delbrück and Its Pertinence to Cancer Chemotherapy

Publisher Summary This chapter explains the 40-year-old mutation theory and its persistence to cancer chemotherapy. Mathematical relationships derived by Lloyd and Skipper et al . have been of help in the study of (1) the behavior of drug sensitive tumor cell populations during repetitive dose treatment and (2) the variables that affect the rate of the selection and overgrowth of drug-resistant neoplastic cell populations. The mathematical model of Goldie and Coldman has been of help in the application of the fundamental implications of the mutation theory in the area of cancer treatment. The 40-year-old somatic mutation t0heory (or law) appears to be pertinent to problems faced in increasing the cure rates of disseminated cancers today—even those cancers that are relatively refractory to most available single drugs. New and quantitative approaches to the interpretation of available chemotherapeutic results—and the planning of new combination chemotherapy regimens—are essential to accelerate progress in curing disseminated cancers.

General motors cancer research foundation awards. Charles F. Kettering Award. Stepwise progress in the treatment of disseminated cancers

Remarkable progress has been made in curing a significant number of disseminated cancers, but at times the pace has seemed discouragingly slow. When I look back at both the successes and failures, and relate them to current concepts, I cannot help but wonder if the rate of future progress might be accelerated by application of basic tenets of the 40‐year‐old somatic mutation theory. By this I mean serious consideration of the implications of this theory in interpretation of available data and in the design of future therapeutic regimens.

On the metabolic stability of nucleic acids in mitotically inactive adult tissues labeled during embryonic development

Abstract [8-14C]adenine was administered to pregnant mice in order to incorporate isotope into DNA and RNA of dividing fetal tissue (brain and liver) that subsequently becomes mitotically inactive in the adult animal. The radioactivity in the DNA and RNA purines of these and other tissues from the offspring were determined at periods from nine days to one year after birth. During this period there was no loss of 14C from the DNA purines of brain and liver, whereas the RNA of these tissues did lose radioactivity. These results further confirm the metabolic stability of DNA and indicate that radioactive atoms incorporated into DNA of the liver and brain of embryos may remain fixed for the life of the animal.

Anticancer Activity of Purine Antagonists and Their Ribosides. I. Comparative Studies with 6-Mercaptopurine and 6-Mercaptopurine Riboside.

Summary (1) 6-Mercaptopurine riboside has been assayed for inhibitory activity against Adenocarcinoma 755 in mice and has been found to be of approximately the same activity as 6-mercaptopurine. (2) Lines of S. faecalis resistant to 6-mercaptopurine have been found to be cross-resistant to 6-mercaptopurine riboside. (3) A line of Adenocarcinoma 755 selected for resistance to 6-mercaptopurine showed cross-resistance to 6-mercaptopurine riboside.

Chromatographic studies of purine metabolism. II. The mechanism of E. coli inhibition by A-methopterin.

Abstract The observed effect of A-methopterin upon Escherichia coli metabolism has been the intracellular accumulation of 5-amino-4-imidazole-carboxamide ribotide, with the concomitant exclusion of formate-C 14 and glycine-C 14 from purine derivatives. Correlation between the observed amount of intracellular accumulation of aminoimidazolecarboxamide ribotide and the degree of growth inhibition by various levels of A-methopterin provided evidence that blockade of the de novo synthesis of purines was the primary site of A-methopterin inhibition. The metabolic sequence from formate to the various purine ribotides was apparently the same for an A-methopterin-resistant strain of E. coli as for its parent strain.