Correlation of MDR1 /P‐170 expression with daunorubicin uptake and sensitivity of leukemic progenitors in acute myeloid leukemia

⁴Service d'Hématologie, Hôpital Edouard Herriot, Lyon, France Abstract: Prior studies have shown that multidrug resistance gene products may be detected in acute myeloid leukemia (AML) cells, and are associated with poor response to therapy. We studied whether P‐170 expression was associated with in vitro daunorubicin (DNR) accumulation and sensitivity of leukemic clonogenic cells (CFU‐L) to DNR in 16 newly diagnosed AML samples. P‐170 expression was assessed by indirect immunofluorescence using the monoclonal antibody MRK16. DNR cellular content was measured by flow cytometry after short incubation with increasing concentrations of DNR, and was not correlated with P‐170 expression, although there was a trend for higher values in P‐170‐negative samples. The sensitivity of CFU‐L was studied in a semisolid culture assay by calculating the dose of DNR inhibiting the growth of 90% of CFU‐L (D90). The D90 was significantly higher in P‐170‐positive than in P‐170‐negative samples (mean = 1.68 ± 0.42 pg/ml versus 0.97 ± 0.35 μg/ml respectively, p< 0.005). Eight of 9 cases achieving complete remission (CR) after intensive chemotherapy were P‐170‐negative, whereas 7 of 7 nonresponders were P‐170‐positive (p< 10⁻⁵). D90 was significantly lower for patients achieving CR than for those who did not achieve CR (1.12 ± 0.55 μg/ml versus 1.59 ± 0.37 μg/ml, p = 0.04). It is concluded that P‐170 expression is correlated with in virto resistance of clonogenic cells to DNR and may be one mechanism of resistance to chemotherapy.