Critical influence of an enzyme-elevating virus upon long-term remissions of mouse leukemia following asparaginase therapy

L-Glutaminase and L-Asparaginase by Extracorporeal Route in Acute Lymphoblastic Leukemia Therapy

Use of L-asparaginase by the extracorporeal route in the therapy of acute lymphoblastic leukemia (ALL) has been proposed.

Results, however, are not so satisfactory as i.v. administration of this enzyme, because the levels of L-asparagine do not fall for a sufficient length of time due to the antagonistic action of the L-asparagine-synthetase.

To avoid the L-asparagine rebound we have utilized, by extracorporeal route, L-glutaminase together with L-asparaginase, in order to reduce L-asparagine and L-glutamine levels.

We have therefore performed a series of experiments in vitro and in vivo either using L-asparaginase alone or together with L-glutaminase.

Results show that, contrary to what happens when L-asparaginase is used alone, L-asparagine levels decrease and remain low even after 24 hours from the treatment, when L-glutaminase is added to the system. Thus a lowering of L-glutamine levels, which seems to play an important role in the therapy of ALL, is obtained.

Physiological relationships among stress, viruses, and cancer in experimental animals

Anxiety-induced psychoneural stimulation, via the hypothalamic-pituitary axis, activates the adrenal cortex to release corticosteroids, which elicit various alterations of corticoid-sensitive cell-mediated immunologic processes. Stress sensitive murine tumor-host experimental models have been utilized to demonstrate various effects of stress upon aspects of tumor development. Although many of the observed anxiety-induced alterations of tumor-related parameters can be interpreted in terms of corticoid-induced modifications of immune functions, other observations are more difficult to interpret, and may be caused in part by corticosteroid-independent modulation of lymphocyte functions. In the case of tumors induced by oncogenic viruses, anxiety-induced plasma corticoid elevations may also act independently of the immune system to stimulate tumor development via hormone binding sites on proviral DNA. Rigorously controlled environmental and experimental conditions are fundamental for the demonstration and interpretation of stress-related phenomena. Technical prerequisites include protective animal facilities, special handling procedures, the use of nontraumatic stressors, and the recognition of vital psychosocial, coping and timing factors. Various biologic factors, such as sex, genetic substrain differences and common interfering viral infections, must also be controlled or taken into consideration.

Theoretical and practical considerations in the use of hemodialysis for the therapeutic removal of asparagine and other amino acids

The endogenous asparagine influx in mice undergoing asparaginase therapy can be neutralized by asparaginase activity equivalent to less than one IU/ml of plasma, as determined with a new, highly sensitive micro assay for asparaginase. It appears feasible that an asparagine influx of this magnitude may be cleared from the blood plasma by hemodialysis employing an artificial kidney apparatus with a clearance capacity somewhat greater than that routinely employed by renal patients. Application of this method for removing asparagine or other amino acids from the blood as an approach to cancer therapy ultimately depends upon the specific amino acid influx rates of the subject and upon the ability of the dialyzer to deplete the free amino acids in the blood plasma at a sufficiently high rate to lower specific amino acid concentrations in malignant tissues, or in adjoining interstitial spaces, to therapeutic levels. Based upon the data available, hemodialysis has potential therapeutic application as a means to control the removal of various free amino acids or other metabolic substrates from blood plasma.

Antibody-producing cells: virus-induced alteration of response to antigen

Spleen antibody-forming cells of mice yield a 3- to 10-fold increase in their response to sheep erythrocyte antigen if they are acutely infected by lactate dehydrogenase-elevating virus. This early stimulation is replaced by a long-term inhibition of the antibody-forming cells as the viremia goes into its persisting chronic stage. These contrasting immunological phenomena are examined as contributing factors responsible for the enhancement by this virus of asparaginase (EC 3.5.1.1; L-asparagine amidolydrolase) therapy against leukemia in mice, and for the alteration of the susceptibility of mice to various neoplastic processes.