Search

In 85 adult patients diagnosed with acute myeloid leukaemia (AML) and treated at the same institution during a 5-yr period, the clinical significance of in vitro cellular drug resistance to the anthracyclines aclarubicin (Acla) and daunorubicin (Dau) as well as the nucleoside analogue cytarabine (Ara-C) was investigated using a 4-d MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay. In 59 patients of whom 40 were treated by the combination of Acla and Ara-C we found that leukaemia cell drug resistance towards Acla was higher (by a factor 2.80) in patients who failed to enter complete remission (CR) after the first cycle of induction chemotherapy as compared to patients who entered complete remission. The relationship was significant in univariate as well as multivariate analysis (p=0.02 and 0.03, respectively). By contrast, no in vitro single drug resistance values were consistently correlated to other parameters of clinical outcome (overall CR rate, overall survival (OS), or continuous complete remission (CCR)), whereas the combined Acla and Ara-C drug resistance profile (Acla/Ara-C DRP) was of prognostic significance to overall survival of all 85 patients (p=0.004) as well as to the CCR of 39 complete responders (p=0.04). These findings remained statistically significant in multivariate analyses correcting for other variables influencing clinical outcome including patient age, leukocyte count, karyotype, FAB-subtype, and presence/absence of secondary AML. We conclude that the in vitro drug resistance of leukaemia cells at time of disease presentation appears to be independent of prognostic significance to short- and long-term clinical outcome in AML.

We investigated the cellular drug resistance to aclarubicin (Acla), cytosine arabinoside (Ara-C), daunorubicin (Dau), doxorubicin (Dox), etoposide (Etop) and mitoxantrone (Mitox) using the MTT assay at time of disease presentation in 93 cases of acute myeloid leukaemia (AML). In 31 cases we concomitantly investigated MDR1 (multiple drug resistance 1 gene) expression (semi-quantitative competitive RT-PCR) of the leukaemic cells. Drug resistance towards Dau, Dox and Etop was correlated to the MDR1 expression of the AML cells (P<0.05) with high MDR1 expression being associated with high drug resistance towards these drugs. Although the data did not allow firm conclusions to be drawn on the correlation between MDR1 expression and drug resistance towards Ara-C and Mitox, the drug resistance towards Acla clearly was not correlated to, or dependent on, the MDR1 expression level of the AML blast cells. In addition, when examining the cross-activities among the six drugs distinct patterns emerged. Thus, high to very high degrees of cross-activity were found to exist between Dau, Dox, Etop and Mitox, whereas Ara-C had moderate cross-activity with the other drugs except Acla, which showed absent to moderate cross-activity with the other drugs. We conclude that MDR1 gene expression is of significance for cellular drug resistance towards specific (MDR1-related) drugs in AML, whereas it is not of significance regarding drug resistance towards other drugs, which is the case with the anthracycline Acla. We suggest that in the place of other more or less complicated ways to circumvent MDR1-mediated drug resistance, Acla may be used to replace Dau, Dox and other MDR1-related drugs if proven as potent as the drug it is to substitute.

We have investigated the in vitro blast cell survival (viability) and drug resistance to cytosine arabinoside (Ara-C), daunorubicin (Dau), mitoxantrone (Mitox) and aclarubicin (Acla) of fresh leukaemic blast cells from 80 patients with newly diagnosed acute myeloid leukaemia (AML) employing the semiautomated colourimetric MTT(3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide)-assay. In 15 cases we concurrently investigated the relation between in vitro blast cell survival (MTT assay) and blast cell proliferation (3H-thymidine incorporation) in the presence and absence of myeloid growth factors (GFs) G-CSF, GM-CSF and IL-3 (individually and in combination). A highly significant correlation was found between blast cell survival and blast cell proliferation (r = 0.87, P < 1 x 10(-4). Furthermore, in 40 evaluable adult patients who completed intravenous induction chemotherapy and were evaluable for response to chemotherapy we found a positive correlation between in vitro blast survival (MTT assay) and response to chemotherapy with high blast survival being associated with poor response to chemotherapy (P = 0.05). Moreover, in a multivariate analysis, high blast cell survival was significantly associated with high CD13 expression and monocytic phenotype (P = 0.0003 and P = 0.02, respectively). Furthermore, we found an inverse relationship between the baseline proliferation of the blasts and the magnitude of response to the GFs (P < 0.02), indicating that cells with low baseline proliferation were more readily stimulated by growth factors. Finally, we found a significant correlation between leukaemic cell survival and cellular drug resistance towards Dau (P = 0.001) and Mitox (P = 0.03), but not towards Ara-C (P = 0.68) and Acla (P = 0.13). We conclude that high in vitro leukaemic cell survival is associated with drug resistance in vivo and in vitro, and furthermore is correlated with high blast cell proliferation and some adverse prognostic factors previously identified in AML.

The effect of stimulating acute myeloid leukemia blast cells with a combination of growth factors (G-CSF, GM-CSF, and IL-3) on cellular resistance to the antileukemia drugs Ara-C, daunorubicin, aclarubicin, and mitoxantrone was studied. For assessment of in vitro cellular drug resistance the MTT assay was employed. Stimulated cells showed enhanced sensitivity to Ara-C (p < 0.02), whereas a significant increase in cellular drug resistance to daunorubicin (p < 0.02) was observed. Variable and statistically non-significant changes in drug resistance to aclarubicin and mitoxantrone was induced by stimulation of the blast cells. We conclude on the basis of these observations that myeloid growth factors should be used with caution in combination with daunorubicin in AML treatment until further confirmatory evidence has been presented by other investigators.