Effect of medium conditioned by acute myeloid leukaemia cells on normal marrow colony-forming ability and sensitivity to cytosine arabinoside

Cytosine arabinoside does not cause differentiation in vitro of CFU-GM in marrow from normal, myelodysplastic or ANLL subjects

This study examines the effect of cytosine arabinoside (Ara-C) on CFU-GM progenitor cells grown in methylcellulose culture from normal and myelodysplastic subjects and patients with acute non-lymphoblastic leukaemia. Light density marrow cells were incubated during culture with Ara-C concentrations ranging from 10(-4) M to 10(-12) M. After counting, colonies were cytospun and cells within the colonies examined for alkaline phosphatase positivity and expression of HLA-DR antigen, as indices of differentiation. Monocytes/macrophages were also enumerated in colonies using the monoclonal antibody CD14. In all subjects, 10(-4) M to 10(-6) M Ara-C caused significant reduction in CFU-GM colony formation compared with control (no Ara-C). In no instance did colony numbers increase. Ara-C across the dose curve had no effect on myeloid differentiation markers in any of the groups studied. Similarly, percentages of CD14 positive cells in colonies were not altered by exposure to Ara-C. Using this clonogenic model, these data suggest that Ara-C does not induce differentiation of CFU-GM stem cells in normal subjects or patients with myelodysplasia/acute non lymphoblastic leukemia.

Low-dose cytosine arabinoside (Ara-C) therapy in the myelodysplastic syndromes and acute leukemia

Twenty-two patients with either a myelodysplastic syndrome or acute nonlymphocytic leukemia were treated with 10-21 days of subcutaneous cytosine arabinoside (Ara-C) (5-10 mg/m2 every 12 hours). There were two complete remissions and ten partial responses. Clinically significant improvements in peripheral blood counts persisted for periods of 8 weeks to greater than 21 weeks. Responses were seen even in patients who had previously proven refractory to conventional induction regimens or high-dose Ara-C. The toxicity, however, was considerable. Nearly all patients developed significant thrombocytopenia. Platelet and red cell transfusion support was required in many cases. The response to low-dose Ara-C therapy seen in patients with the leukemic and myelodysplastic disorders may be mediated by the induction of cell differentiation or a direct cytotoxic effect on a sensitive population of cells. Low-dose Ara-C may provide an alternative therapy in the selected patient with acute nonlymphocytic leukemia or a myelodysplastic syndrome.

Low-dose cytosine arabinoside treatment for acute nonlymphocytic leukemia in elderly patients

Thirty patients older than 65 years of age with acute nonlymphocytic leukemia were treated with low-dose cytosine arabinoside (10 mg/m2 subcutaneously every 12 hours for 15 to 21 days). Fifteen achieved complete remission and five had partial remission. Treatment was more effective when initial bone marrow cellularity was low (P = 0.007). Four of six patients with secondary leukemia entered complete or partial remission. Therapy was well tolerated with reduced myelosuppression and few number of early deaths. Sixteen patients followed the whole treatment as outpatients. Six of 12 patients who achieved complete remission showed no evidence of post-therapeutic bone marrow aplasia. These data are consistent with the view that low-dose cytosine arabinoside acts on leukemic cells as a differentiating agent.

Small doses of ARA-C in the treatment of acute myeloid leukaemia: differentiation of myeloid leukaemia cells?

Three patients with acute myeloid leukaemia were treated with small doses of ARA-C (10 mg/m2/12 h, subcutaneous injections) and complete remission was obtained. The small doses of ARA-C, the progressive evolution, the absence of aplasia before remission, the simultaneous presence of normal islets of promyelocytes and leukaemic myeloblasts, favour a differentiating role for the drug rather than an antimitotic effect.

Human myeloid leukaemic cell interactions in vitro with normal myeloid colonies

To determine whether myeloid leukaemic cells could inhibit normal myeloid colony formation, leukaemic cells at concentrations ranging from 0.5 to 8 X 10(6)/ml were co-cultured in agar but separated by a 1 ml underlayer from 10(5) low-density (less than 1.077 g/ml) nonadherent normal marrow cells. Inhibition of normal-marrow myeloid colony formation occurred regularly at high cell concentrations (8 X 10(6)) at a leukaemic:normal cell ratio of 80:1. This suppression persisted with addition of indomethacin (10(-6)M). On the other hand, both low leukaemic cell numbers and irradiated leukaemic cells frequently stimulated normal colony growth. No inhibitor of colony growth could be detected in leukaemic-conditioned media, and absorption of colony-stimulating activity (CSA) with leukaemic cells improved CSA activity. These experiments point to the difficulty in unravelling the effect of leukaemic cells on normal haemopoiesis (both inhibitory and stimulatory) by in vitro agar culture.

Acute nonlymphocytic leukemia: expression in cells restricted to granulocytic and monocytic differentiation

Two patients with acute nonlymphocytic leukemia who were heterozygous for the X-chromosome-linked enzyme glucose-6-phosphate dehydrogenase were studied to determine the number and type of cells in which the disease arises. Both type A and B isoenzymes were found in normal tissues, but the myeloblasts showed only one enzyme type, indicating that at the time of study, the disease had a clonal origin. The observation in one patient that erythroid cells did not arise from this clone contrasts with conclusions reached in patients previously studied with chromosomal markers. The results suggest that in this patient, the leukemic clone suppressed expression of normal granulopoiesis but did not inhibit erythroid differentiation from normal progenitors. They suggest also that the disease is heterogeneous. In some patients, the disease is expressed in cells with differentiation restricted to the granulocyte-macrophage pathway; in others, it involves stem cells that also differentiate into erythrocytes. This heterogeneity may reflect differences in causation and could have prognostic importance.