In vitro cytocidal effect of L-glutaminase on leukaemic lymphocytes

Effects of phenylacetate on cells from patients with B-chronic lymphocytic leukemia

Peripheral blood mononuclear cells from 11 patients with untreated B-chronic lymphocytic leukemia (CLL) were exposed to sodium phenylacetate (NaPA) in culture to assess its ability to induce differentiation. We found no evidence of cellular differentiation or induction of tartrate resistant acid phosphatase activity, as seen when B-CLL cells were treated with phorbol ester. We observed a striking decrease in the viability of the B-CLL cells in a time and dose dependent fashion when exposed to NaPA. After six days of culture, control cells from the 11 patients studied had a median viability of 90%, whereas cells exposed to NaPA at 5 and 10 mM concentrations had median viabilities of 39 and 16%, respectively. The cells treated with NaPA developed prominent cytoplasmic vacuoles. NaPA binds and depletes glutamine which is an important amino acid for lymphocyte metabolism. Although the mechanism of the cytocidal effects demonstrated in this study are unknown, they may relate at least partially to glutamine deprivation.

Kinetic properties and inhibition of Acinetobacter glutaminase-asparaginase

Kinetic parameters, substrate specificity and exclusivity of ligands at binding sites of L-glutaminase-L-asparaginase purified from Acinetobacter glutaminasificans were studied in order to gain knowledge about the dual activities of this enzyme and its inhibition by structural analogs. Both L-glutamine and L-asparagine, which showed similar Km (4 approximately 7 X 10(-5) M) and Vmax (molecular activity 1.0 min-1) values, were competitive with each other for the substrate binding site. The products, L-glutamic acid and L-aspartic acid, showed competitive inhibition with respect to either L-glutamine or L-asparagine as substrates. Multiple inhibition of the glutaminase activity by L-glutamic acid and L-aspartic acid indicated that these ligands are mutually exclusive at the product-releasing site. The initial rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in decreasing order of activity): 6-diazo-5-oxo-L-norleucine (DON), L-methionine sulfoximine, azaserine, and Acivicin. DON and azaserine inhibited both the asparaginase and glutaminase activities in a time-dependent and irreversible manner. The kinetic data suggest an ordered mechanism with glutamine or asparagine as the first substrate and glutamic acid or aspartic acid, respectively, as the last product. These results also suggest that a single mechanism and a single set of binding sites are responsible for catalyzing both of the enzyme's activities. The data also showed that succinylated enzyme, which has a 10-fold increase of plasma half-life in animals and humans and, thus, has benefit as a cancer chemotherapeutic agent, retained its catalytic activity and maintained Km and Vmax values similar to the native enzyme.

L-Asparagainases from Citrobacter freundii

Three enzymes which catalyze the hydrolysis of L-asparagine have been identified in extracts of Citrobacter freundii. One of these (asparaginase-glutaminase (EC 3.5.1.1) also shows substantial glutaminase activity. This enzyme is extremely labile, is sensitive to inactivation by p-chloromercuribenzoate, and is not protected by dithiothreitol. A second enzyme (asparaginase B) is also sensitive to mercurials but is protected from inactivation by dithiothreitol. This enzyme has a relatively low affinity for L-asparagine (Km = 1.7-10(-3) M). The third enzyme (asparaginase A) is insensitive to inactivation by mercurials, is stable upon long term storage and has a relatively high affinity for L-asparagine (Km = 2.9-10(-5) M). This enzyme has been purified to homogeneity and has a molecular weight of approx. 140 000; the subunit weight being approx. 33 000. The C. freundii asparaginase A produced significant increases in the survival time of C3H/HE mice carrying the 6C3HED lymphoma tumor.

Chronic lymphocytic leukemia: correlation of clinical course and therapeutic response with in vitro testing and morphology of lymphocytes

Forty-two patients with chronic lymphocytic leukemia (CLL) were studied for morphology of lymphocytes by light and electron microscopy (EM), in vitro responses of lymphocytes to a battery of physical and chemical agents, overall clinical status, immunologic status, course, and response to therapy. CLL lymphocytes could be classified by EM into four groups on the basis of cell size and nuclear contour and by light microscopy into two groups, small cells and large cells (lymphosarcoma cells). Patient survival did not vary with cell size or morphology as determined by light or electron microscopy. In vitro testing of CLL lymphocytes following exposure to X-ray, PHA, DMSO 2 hr at 43 degrees C, prednisolone, glutaminase, and asparaginase permitted a separation of patients into categories of normal and abnormal in vitro responses. A normal in vitro response predicted a good response to therapy but an abnormal in vitro response did not preclude a good response to therapy. Following therapy, normalization of abnormal EM morphology and in vitro response was seen in some patients. Most patients tested had decreased serum immunoglobulins and abnormal PHA responses. There was a high incidence of infections and second neoplasms. Immunologic deficits could not be correlated with variations in lymphocyte morphology or in vitro response.

Bacterial glutaminase in treatment of acute leukaemia

A glutaminase-asparaginase enzyme from Achromobacter sp has antitumour activity in vitro and in animals. Glutaminase was administered in doses of 3500-20 000 IU/m2 body surface area/day to six patients with acute lymphoblastic leukaemia (ALL) and three patients with acute myeloid leukaemia (AML). The enzyme had a blood half life of 80 minutes but depletion of blood glutamine persisted for 12 hours after single doses. Seven patients, including four (two with AML and two with ALL) resistant to asparaginase, received repeated doses of glutaminase. Antileukaemic effects were observed in all seven; one elderly patient developed metabolic acidosis. Study of this new antileukaemic agent in patients with acute leukaemia at an earlier stage of their disease is now justified.

The effects of arginine deficiency on lymphoma cells

When L5178Y and L1210 mouse lymphosarcoma cells were incubated with rat or beef liver arginase there was up to 100% cell destruction in 24 hours. This was reversed specifically with arginine and partially with arginino-succinic acid, citrulline and ornithine. The concentration of arginine was critical; at 8 μmol/l the cells remained viable and reversible inhibition could be shown; below this level cells died. L5178Y cells were grown in medium containing from 0 to 80 μmol/l arginine for 24 hours then transferred to fresh medium for 24 hours. Viable cell counts and mitotic indices were determined, and cells were pulsed with (3)H-thymidine, (3)H-uridine, (14)C-leucine and (14)C-arginine at various times. Thymidine uptake was affected most and preceded parallel changes in viable cell numbers. It was concluded that arginine is required by these cells even in a "resting" state and despite some evidence for their capacity to utilize precursors, the tumour cells underwent rapid and extensive destruction when available arginine was severely depleted.