Mode of action of chemotherapy in vivo on human acute leukemia. I. Daunomycin.

The leukocytes of 16 adult patients with acute myeloblastic leukemia were studied by autoradiographic methods to elucidate the mode of action of daunomycin. It was shown that daunomycin, at clinically useful doses, exhibits a cytolytic effect on all leukemic blasts whatever their cell-cycle phase. This cytolytic action affects, however, preferentially S-phase cells. It was shown also that blasts of patients less sensitive to daunomycin or receiving a lesser dose of the drug are temporarily blocked in G(2) phase (delayed mitosis) or in G(2) phase (prolonged generation time). Finally daunomycin appeared to hamper the passage of G(2)-blocked blasts from the bone marrow to the blood, while G(2)-phase cells crossed freely.

Chemotherapeutic sensitivity of normal and leukemic hematopoietic progenitor cells to N-[4-(9-acridinylamino)-3-methoxyphenyl]-methanesulfonamide, a new anticancer agent.

The sensitivities of hematopoietic colony-forming cells (CFC) to N-[4-(9-acridinylamino)-3-methoxyphenyl]-methanesulfonamide (NSC-249992) (m-AMSA) were measured with an in vitro clonogenic assay, a modification of the Robinson and Pike human marrow culture system. CFC derived from bone marrow and peripheral blood of normal subjects and patients with chronic myeloid leukemia (CML) were studied. Sensitivities to m-AMSA did not differ significantly between normal marrow and blood CFC, between normal and CML CFC, or between CML CFC obtained from patients with leukemias in chronic phase and blast transformation. Drug doses and exposure times producing in vitro hematopoietic inhibition were comparable to clinically employed drug dosages and schedules associated with hematopoietic toxicity.

Regulation of bone marrow myeloblast proliferation in chronic myeloid leukemia.

The in vivo [3H]thymidine-labeling index of bone marrow myeloblasts and myelocytes was determined for 9 hematologically normal individuals and 20 Ph-positive chronic myeloid leukemia (CML) patients in the chronic phase of their disease. The mean labeling index of myeloblasts from CML patients when the white blood cell (WNC) count was lower than 20,000/cu mm (42.4%) was not significantly different from that of normal myeloblasts (49.9). This index was found to be significantly (p less than 0.05) decreased to an average of 20.9% when the WBC count was higher than 40,000/cu mm. The mean labelling index of CML myelocytes was not significantly influenced by the level of WBC. The data presented indicate that such variations in the labeling index of the leukemic myeloblasts represent changes of their proliferative activity related to the level of WBC. It is concluded that the proliferation of CML myeloblasts is sensitive, to a certain degree at least, to the size of the myeloid cell population in the body or a subclass of it.

Comparison of in vitro inhibition of etoposide (VP16) on leukemic and normal myeloid, erythroid clonogenic cells.

We have compared in various clonogenic assays the in vitro sensitivity to etoposide (VP16) of 1) human leukemic precursors (leukemia colony-forming units; L-CFU), 2) normal erythroid progenitors (erythroid burst-forming units; BFU-E, and 3) normal committed myeloid progenitors (granulocyte-macrophage colony-forming units; CFU-GM and more primitive hemopoietic precursors (PPC) that adhere to cultured marrow stromal cells. Bone marrow samples were obtained from 15 normal subjects and 16 leukemic patients: 9 in the acute phase of acute nonlymphoblastic leukemia (ANLL) and 7 in complete remission. VP16 was tested at concentrations ranging from 10(-8) to 10(-3) M. The median recoveries at 10(-3) M VP16 were respectively 0%, 0.5%, 0%, and 0% for leukemic progenitors, CFU-GM from leukemic patients in complete remission, normal CFU-GM, and BFU-E, and 23% for PPC. This indicates that CFU-GM, BFU-E, and L-CFU are highly sensitive to VP16, whereas PPC, more primitive myeloid precursors, are spared. These results suggest that VP16 may be used as an "ex vivo" purging agent for autologous bone marrow.

Effect of 4-hydroperoxycyclophosphamide on leukemic and normal human myeloid progenitor cells.

The sensitivity of myeloid progenitor cells from normal subjects (N-CFU-GM) and from leukemic patients in complete remission (LR-CFU-GM) to 4-hydroperoxycyclophosphamide (4-HC) were compared to the sensitivity of leukemic progenitor cells (L-CFU) to this drug. The results were expressed as the dose of 4-HC needed to kill 90% (TD 90) of the progenitor cells. The mean TD 90 were respectively for N-CFU-GM : 59 (+/- 11 S.E.M.) nM ml-1 and for L-CFU 79 (+/- 6 S.E.M.) nM ml-1. Thus, L-CFU were equally sensitive to 4-HC as N-CFU-GM. Moreover, the mean TD 90 for LR-CFU-GM was 87 (+/- 5 S.E.M.) nM ml-1. Thus, the sensitivity of N-CFU-GM and LR-CFU-GM did not differ significantly from that of L-CFU. These results are not encouraging for the use of 4-HC in vitro to eliminate the residual leukemic cells from autologous bone marrow of AML patients in complete remission. The sensitivity of L-CFU was modified neither by previous cytoreductive therapy (different from cyclophosphamide) nor by the time elapsed since diagnosis of AML.