Treatment of poor risk acute leukemia with sequential high-dose ARA-C and asparaginase

1-beta-D-Arabinofuranosylcytosine (ara-C), 2 or 3 g/sq m, was administered as a 1-hr i.v. infusion every 12 hr for 10 or 12 doses to patients with acute leukemia and refractory lymphoma. Four of seven patients with relapsed or refractory acute myelocytic leukemia and two of four patients with previously untreated acute myelocytic leukemia achieved complete remission. Of five treatment failures, two patients had leukemia which was clearly resistant to high-dose ara-C, and three patients died of infections or hemorrhagic complications during periods of pancytopenia. Three patients with acute myelocytic leukemia in remission received high-dose ara-C as consolidation therapy following previous courses of intensive, multiagent consolidation chemotherapy. Two of these three patients had prolonged thrombocytopenia following high-dose ara-C. Five patients with refractory acute lymphocytic leukemia were treated. Three patients achieved partial remission, and two patients had drug-resistant disease. Complete or partial disappearance of measurable disease parameters was seen in three of three patients with refractory lymphoma. Response was seen in five of five patients with meningeal leukemia, including complete response in one patient with extensive meningeal infiltration. Toxicity of this regimen was generally moderate and limited to pancytopenia and mild nausea. Patients who had received prior multiagent consolidation chemotherapy appeared to be at greater risk for hematopoietic toxicity. Patients who had received prior cranial irradiation or intrathecal chemotherapy appeared to be at greater risk for neurological toxicity. Plasma levels of ara-C immediately after completion of the infusion were 17.96 +/- 8.02 (S.D.) and 35.0 +/- 2.8 micrograms/ml for doses of 2 and 3 g/sq m, respectively. From 160 to 720 min following completion of the infusion, the plasma levels of drug were comparable to steady-state levels achieved with a continuous infusion of ara-C at 100 mg/sq m over 24 hr. A high degree of penetration into the central nervous system was demonstrated. High-dose ara-C has substantial activity against leukemic and lymphomatous cell populations, including cell populations resistant to conventional doses of the drug, and is an effective treatment modality for patients with these diseases. The high degree of penetration into the central nervous system suggests that this drug regimen may be useful as consolidation therapy for patients at high risk for central nervous system disease.

https://cancerres.aacrjournals.org/content/canres/42/4/1587.full.pdf

A pilot study of high-dose 1-beta-D-arabinofuranosylcytosine for acute leukemia and refractory lymphoma: clinical response and pharmacology.

Does treatment with ARA-C in low dosage cause differentiation of leukemic cells?

The mechanisms of resistance to nucleoside analogues established in preclinical models are rarely found in primary tumors resistant to therapy with these agents. We tested the hypothesis that cells sense sublethal incorporation of analogues into DNA during replication and react by arresting further DNA synthesis and cell cycle progression. After removal of drug, cells may be able to repair damaged DNA and continue proliferation, thus escaping nucleoside analogue toxicity. As a corollary, we evaluated whether dysregulation of this mechanism causes cell death. Using gemcitabine as a model of S-phase-specific nucleoside analogues in human acute myelogenous leukemia ML-1 cells, we found that DNA synthesis decreased, cells arrested in S-phase transit, and 60-70% of the population accumulated in S-phase in response to cytostatic conditions. Proliferation continued after washing the cells into drug-free medium. S-phase-arrested cells were then treated with otherwise nontoxic concentrations of UCN-01, which caused rapid onset of apoptosis without cell cycle progression specifically in cells with an S-phase DNA content. Thus, S-phase arrest by nucleoside analogues sensitizes cells to UCN-01, which appears to activate signaling for death mechanisms and/or inhibit survival pathways. These results differ from those in cells arrested at the G2 checkpoint, in which UCN-01 abrogates cell cycle arrest, permitting cells to progress in the cell cycle before apoptosis.

https://cancerres.aacrjournals.org/content/canres/61/3/1065.full.pdf

S-Phase arrest by nucleoside analogues and abrogation of survival without cell cycle progression by 7-hydroxystaurosporine.

Cytosine arabinoside (araC) has proven efficacy in acute myeloid leukemia (AML), but its place in the treatment of acute lymphoblastic leukemia (ALL) and T lymphoblastic lymphoma is uncertain. The therapeutic potential of araC has been assessed in patients with AML, ALL, and T lymphoblastic lymphoma by measuring the conversion of araC to its active metabolite, the 5'-triphosphate of araC (araCTP), in purified blasts from patients as well as in normal polymorphs and lymphocytes. In all leukemias, araCTP was the major intracellular metabolite of araC. The highest araCTP formation was in blasts from T lymphoblastic lymphoma, which formed threefold more nucleotide than myeloblasts, and in turn myeloblasts formed twofold more araCTP than lymphoblasts from ALL. The mean araCTP formation in myeloblasts was sixfold greater than polymorphs, but in contrast, lymphoblasts and lymphocytes formed low and similar amounts of this nucleotide. Reasons for the sixfold range in araCTP accumulation in the various leukemic blasts were studied. The mean size of myeloblasts was 35-70% larger than lymphoblasts when compared on the basis of protein or intracellular water content, but T lymphoblastic lymphoma blasts and lymphoblasts were the same size. Activities of deoxycytidine kinase, deoxycytidylate deaminase, and pyrimidine nucleoside monophosphate kinase were not different between any of the leukemic cell types. The number of nucleoside transport sites on blasts was estimated by measuring the equilibrium binding of [3H]nitrobenzylthioinosine (NBMPR), which binds with high affinity to the transporter. Scatchard analysis yielded mean values of 27,500 sites/cell for T lymphoblastic lymphoma blasts, 10,000 sites/cell for myeloblasts, and 2,300 sites/cell for lymphoblasts. Our previous work has shown that araC influx correlates with the maximum number of 3H-NBMPR binding sites in leukemic and normal white cells. A strong correlation was observed between the number of nucleoside transport sites per leukemic blast cell and the accumulation of intracellular araCTP from extracellular araC at 1 microM. Membrane transport of araC at the low concentrations (approximately 1 microM), which are achieved therapeutically, is a major rate-limiting step in its conversion to araCTP by leukemic blast cells. Myeloblasts form more araCTP than lymphoblasts because of both higher nucleoside transport capacity and larger cell size. The highest nucleoside transport capacity and largest conversion of araC to araCTP is in T lymphoblastic lymphoma, which suggests that araC may be effective in the treatment of this disease.

/pdf/cytosine-arabinoside-transport-and-metabolism-in-acute-3p4fgkmt7n.pdf

Cytosine arabinoside transport and metabolism in acute leukemias and T cell lymphoblastic lymphoma.

1 The pharmacokinetics of cytosine arabinoside were studied after a single i.v. bolus of 2 mg/kg ara-C in patients with newly diagnosed untreated AML, using a bioassay and GC-MS method to measure the plasma concentrations. 2 Most patients showed a bi- or tri-phasic decline in plasma concentrations with time. Plasma clearance was 3.9 to 18.1 l/min as measured by the GC-MS method, and terminal half-lives varied from 7--107 min. 3 There was poor correlation of the GC-MS assay with the bioassay, probably because the latter was interfered with by the release of endogenous nucleosides from blasts after after ara-C. 4 Plasma concentrations were measured by GC-MS during continuous infusions in 14 patients. Plasma clearances were much lower than after a bolus, 0.39 to 5.25 l/min. 5 There was no correlation of response (remission or fall in peripheral blast count) with exposure to ara-C calculated from infusion dose, clearance and duration of infusion. 6 This study shows that ara-C pharmacokinetics varies markedly from patient to patient and that there is a wide range in the plasma concentrations associated with therapeutic response.

https://bpspubs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2125.1979.tb01005.x

Pharmacokinetics of cytosine arabinoside in patients with acute myeloid leukaemia.

1. The conversion of cytosine arabinoside into its active metabolite cytosine arabinoside triphosphate, and catabolism by deamination to uracil arabinoside, was measured in intact marrow myeloblasts from patients with acute myeloid leukaemia. The ratio of uracil arabinoside/cytosine arabinoside triphosphate ranged from 0.32 to 19.11. 2. The effect of tetrahydrouridine, and inhibitor of cytosine arabinoside deamination, on cytosine arabinoside triphosphate production was studied. The greatest increase of cytosine arabinoside triphosphate production caused by addition of tetrahydrouridine was 27%. 3. The increase in cytosine arabinoside triphosphate production wad not related to the ratio of uracil arabinoside/cytosine arabinoside triphosphate or to the deaminase activity per 10(6) cells. It wa proportional to the percentage change of cytosine arabinoside in the incubation medium. 4. The sensitivity of DNA synthesis to inhibition by cytosine arabinoside was measured in myeloblasts from 11 patients. Addition of tetrahydrouridine did not increase the sensitivity of the marrow to cytosine arabinoside. 5. Cytosine arabinoside deamination is unlikely to be an important mechanism of resistance in myeloblasts in vivo, although it may produce apparent resistance in vitro.

Cytosine arabinoside deamination in human leukaemic myeloblasts and resistance to cytosine arabinoside therapy.

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Pharmacokinetics of cytosine arabinoside in patients with acute myeloid leukaemia.

Cytosine arabinoside deamination in human leukaemic myeloblasts and resistance to cytosine arabinoside therapy.