In vitro sensitivity of clonogenic cells in resisting and relapsing patients with acute myelogenous leukaemia

In Vitro Chemosensitivity of Newly Diagnosed and Relapsing Acute Non-Lymphoid Leukemia Patients

We evaluated the in vitro sensitivity of circulating blasts from 25 newly diagnosed and 7 relapsing ANLL patients to drugs employed in vivo for inducing remission. Ten of the 14 newly diagnosed complete responders were in vitro sensitive to cytosine arabinoside and daunorubicin, whereas 10/11 non-responders were resistant to both agents. Although cells from all 7 relapsing patients were in vitro sensitive to the remission inducing agents, only 4 entered complete remission. Even if only indicative, these findings suggest that the poor prognosis of relapsing patients may be due, at least in part, to factors other than drug resistance. Moreover, the chemo-sensitivity test adopted is a better predictor in newly diagnosed than relapsing patients, as indicated by the concordance between in vitro and in vivo results.

Hematopoietic Growth Factors and Blast Progenitors in Acute Leukemia

Leukemic cells are maintained by a minor subpopulation of cells called leukemic stem cells (LSC) with proliferative and self-renewal capacity, both of which are detected with leukemic colony assay, with the latter being an important prognositic factor. Drug sensitivity tests employing leukemic colony assay revealed the effects of cytotoxic drugs on LSC to be diverse and that cytosine arabinoside predominantly suppresses self-renewal, which probably accounts for its effectiveness in AML therapy. Hematopoietic growth factors (HGFs) regulate the growth of LSC and various in vitro effects of HGFs on acute leukemia cells have been reported. These effects appear to reflect physiological functions of each HGF and can be categorized into groups according to their distinct functions. Endogenously produced HGFs stimulate LSC in an autocrine or a paracrine fashion, resulting in autonomous growth of these cells, which also correlates with the patients' prognosis. HGFs can enhance the cytotoxicity of anti-leukemia drugs in vitro, possibly mainly through recruitment of LSC from the dormant state into active cell cycling. HGFs have been clinically tested in leukemia therapy. Although recovery of blood leukocyte counts can consistently be accelerated with HGF treatment, the effectiveness of HGFs in sensitizing leukemia cells to chemotherapeutic agents and/or improving patient prognosis has not been clearly demonstrated. Different strategies using HGFs and related molecules must be tested in future leukemia therapy.

Prognostic significance of the blast self-renewal capacity in patients with acute myeloid leukemia

BACKGROUND

The proliferation of leukemic cells in acute myeloid leukemia (AML) is supported by a small subpopulation of leukemic blast progenitors, which can be detected in methylcellulose and suspension cultures. It is important to determine the association between the biologic properties of leukemic blast progenitors and the clinical prognosis of patients with AML.

METHODS

Ninety-five patients with AML and two patients with chronic myelocytic leukemia in blast crisis were studied. T-cell depleted mononuclear cells obtained from the peripheral blood cells were cultured in both methylcellulose and suspension cultures. In methylcellulose culture, primary blast colony formation (PE1) and secondary blast colony formation (PE2) were enumerated. The recovery of clonogenic cells was determined in suspension culture. The association between PE1, PE2, or clonogenic cell recovery in suspension and the remission induction outcome or survival duration of the patients were examined.

RESULTS

PE1 was not associated with the remission induction outcome. PE2 and clonogenic cells recovered in suspension were significantly associated with the remission induction. Furthermore, the survival duration of the patients who achieved complete remission was associated significantly with the number of clonogenic cells recovered in suspension.

CONCLUSIONS

PE1 reflects the terminal divisions of leukemic blast progenitors, whereas PE2 and the recovery of clonogenic cells in suspension culture are considered to reflect the self-renewal of leukemic blast progenitors. The results suggest that the self-renewal capacity of leukemic blast progenitors is predictive of not only remission induction outcome but also survival duration of patients with AML.

Treatment of relapsing and refractory adult acute myeloid leukemia according to in vitro clonogenic leukemic cell drug sensitivity

In an attempt to improve the results of treatment in patients with relapsing or refractory acute myeloid leukemia (AML), we conducted a pilot study using a two-drug salvage regimen according to the in vitro clonogenic leukemic cell (CFU-L) drug sensitivity. Fourteen patients were included in the study, 10 with relapsing and 4 with refractory AML. Drug exposure was assessed for daunorubicin, cytosine arabinoside, etoposide, mitoxantrone and amsacrine. The two drugs with the best inhibitory effect on CFU-L were selected for the treatment. A complete remission was achieved in only 4 patients and a partial remission in 3 patients. Although the number of patients is too small for appropriate statistical analysis and for a definite conclusion to be drawn, the observed response rate with directed therapy did not appear better than that expected from empiric salvage regimen.