Control of histone and DNA synthesis with canavanine, puromycin, and poliovirus

The antiproliferative and immunotoxic effects of L-canavanine and L-canaline

L-Canavanine and its arginase-catalyzed metabolite, L-canaline, are two novel anticancer agents in development. Since the immunotoxic evaluation of agents in development is a critical component of the drug development process, the antiproliferative effects of L-canavanine and L-canaline were evaluated in vitro. Both L-canavanine and L-canaline were cytotoxic to peripheral blood mononucleocytes (PBMCs) in culture. Additionally, the mononucleocytes were concurrently exposed to either L-canavanine or L-canaline and each one of a series of compounds that may act as metabolic inhibitors of the action of L-canavanine and L-canaline (L-arginine, L-ornithine, D-arginine, L-lysine, L-homoarginine, putrescine, L-omega-nitro arginine methyl ester and L-citrulline). The capacity of these compounds to overcome the cytotoxic effects of L-canavanine or L-canaline was assessed in order to provide insight into the biochemical mechanisms that may underlie the toxicity of these two novel anticancer agents. The results of these studies suggest that the mechanism of L-canavanine toxicity is mediated through L-arginine-utilizing mechanisms and that the L-canavanine metabolite, L-canaline, is toxic to human PBMCs by disrupting polyamine biosynthesis. The elucidation of the biochemical mechanisms associated with the effects of L-canavanine and L-canaline on lymphoproliferation may be useful for maximizing the therapeutic effectiveness and minimizing the toxicity of these novel anticancer agents.

L-Canavanine modulates cellular growth, chemosensitivity and P-glycoprotein substrate accumulation in cultured human tumor cell lines

L-Canavanine (L-CAV) is a naturally occurring L-arginine analog that induces the formation of non-functional proteins in a variety of organisms. Previous studies have shown that L-CAV is cytotoxic for several human tumor cell lines. In this study, we have evaluated the cytotoxicity of L-CAV for both parental and multi-drug resistant (MDR) human tumor cells. We have also determined the effect of L-CAV exposure on cellular expression and activity of the MDR P-glycoprotein (P-gp) membrane efflux pump, and the effect of L-CAV on cellular accumulation of P-gp substrates. The effect of pre-treatment with non-cytotoxic doses of L-CAV on cellular sensitivity to ten standard antineoplastic agents was also evaluated, in order to assess the chemosensitization potential of L-CAV. 3-(4,5-Dimethylthiazol-)2,5-diphenyl tetrazolium bromide (MTT) cytotoxicity assays revealed that the MDR variants of human uterine sarcoma and leukemic cells were equally sensitive to L-CAV as compared with their respective parental controls. Although the presence of free L-CAV in the uptake media did not influence cellular accumulation of P-gp substrates, cells cultured for 72 h in 250 microM L-CAV accumulated from 16 to 23% less P-gp substrate than untreated controls. Although L-CAV-cultured sarcoma cells accumulated 17% less doxorubicin (DOX) than untreated controls, they were three times more sensitive to its cytotoxic effects. L-CAV-treated cells were also significantly more sensitive to cisplatin, 5-fluorouracil, mitoxantrone and bleomycin than were untreated controls. Indirect immunofluorescence revealed that 72-h exposure to as much as 1000 microM L-CAV did not alter cellular expression of P-gp. These studies suggest that L-CAV may be equally cytotoxic for both parental and MDR tumor cells, and that L-CAV neither induces the expression of, nor is a substrate for, P-gp. The observation that L-CAV pre-treatment reduces cellular accumulation of DOX, yet sensitizes tumor cells to DOX and other DNA-targeting antineoplastic drugs, suggests a role for L-CAV as a chemosensitizer for the chemotherapy of cancer.

Canavanine resistance in Cryptococcus neoformans

All of the isolates of Cryptococcus neoformans var. gattii which we tested were resistant to greater than or equal to 3.5 mM canavanine. All of the serotype D isolates and 28% of the serotype A isolates of C. neoformans var. neoformans tested were susceptible to less than or equal to 18 microM canavanine, whereas the remaining 72% of the serotype A isolates were as resistant as the C. neoformans gattii isolates. In the naturally resistant isolates, the mechanism of resistance appeared to be decomposition of canavanine to a nontoxic product. However, in a resistant mutant derived from a naturally susceptible isolate, the mechanism of resistance was an impaired uptake system for canavanine. The toxic effect of canavanine in Cryptococcus results from the incorporation of canavanine into the protein component that is essential for the synthesis of proteins and RNAs.

The role of diet in animal models of systemic lupus erythematosus: possible implications for human lupus

Studies of diet in the mouse model of SLE have established the beneficial effects of a low calorie, low fat diet in these animals as well as the importance of the specific source of dietary fat. The role of zinc in murine and human SLE is less clear. The reported improvement of patients with SLE and other related diseases on a low phenylalanine and tyrosine diet high in fish content, and the lupus inducing capacity of a nonphysiologic amino acid present in alfalfa are also reviewed. The need for carefully controlled prospective studies of diet in patients with SLE is noted, and a diet of potential therapeutic benefit is described.

Systemic lupus erythematosus-like syndrome in monkeys fed alfalfa sprouts: role of a nonprotein amino acid

Hematologic and serologic abnormalities similar to those observed in human systemic lupus erythematosus (SLE) developed in cynomolgus macaques fed alfalfa sprouts. L-Canavanine sulfate, a constituent of alfalfa sprouts, was incorporated into the diet and reactivated the syndrome in monkeys in which an SLE-like syndrome had previously been induced by the ingestion of alfalfa seeds or sprouts.

Effect of poliovirus on deoxyribonucleic acid synthesis in HeLa cells

Ackermann, W. W. (University of Michigan, Ann Arbor), D. C. Cox, H. Kurtz, C. D. Powers, and S. J. Davies. Effect of poliovirus on deoxyribonucleic acid synthesis in HeLa cells. J. Bacteriol. 91:1943-1952. 1966.-Both poliovirus and arginine stimulated deoxyribonucleic acid (DNA) synthesis in cultures of HeLa cells which were preconditioned by incubation in a medium deficient in arginine. However, the number of cells producing DNA was unaffected. DNA synthesis in such preconditioned cells was 10 to 20% of the maximal value obtained with a full complement of amino acids. Inhibition of DNA synthesis was produced in these cultures either by increasing the multiplicity of exposure above 40 plaque-forming units of virus per cell or by increasing the concentration of the deficient amino acid at the time of virus addition. Inhibition of DNA synthesis resulted from a reduction in the fraction of cells producing DNA. The concentration of arginine required for viral inhibition of DNA synthesis is greater than that for viral multiplication.