A low but functionally significant MDR1 expression protects primitive haemopoietic progenitor cells from anthracycline toxicity

Abstract

Summary.Pgp is expressed on normal haemopoietic progenitor cells. The significance of the efflux pump in protecting normal progenitors for anthracycline toxicity is not defined and is the subject of this study. Pgp was measured in CD34 þ progenitors with a rhodamine efflux assay. A high efflux, modulated by verapamil, was only found in a distinct subpopulation (20-30%). Pgp measured by the monoclonal antibody antibody (MoAb) MRK-16 was low in the rhodamine dull, but significantly (P < 0 . 04) higher than in the rhodamine bright cells. Reverse transcriptase polymerase chain reaction (RT-PCR) of MDR1 mRNA showed a very weak signal in both populations. In a single-cell clonogenic assay, rhodamine dull cells appeared less sensitive to anthracyclines (IC 50 daunorubicin 0 . 005 mg/ml; adriamycin 0 . 03 mg/ml) compared to rhodamine bright cells (IC 50 daunorubicin 0 . 0025 mg/ml; adriamycin 0 . 01 mg/ml). Furthermore, verapamil significantly (P < 0 . 05) potentiated anthracycline toxicity only in the rhodamine dull cells, proving its Pgp-specific modulating effect. Rhodamine dull cells gave larger and more mixed colonies compatible with a more primitive origin. Although detection with MoAbs and RT-PCR revealed a low Pgp level, functionally this Pgp appeared to be very important in protecting primitive progenitors against anthracycline toxicity. This protection can be jeopardized by administration of Pgp modulators.

Breast Cancer Resistance Protein in Drug Resistance of Primitive CD34+38− Cells in Acute Myeloid Leukemia

“…Mononuclear cells were isolated by density gradient centrifugation using Ficoll 1.077 g/mL (Pharmacia Biotech, Uppsala, Sweden). Isolation, cryopreservation, and thawing procedures of cells have been previously described (19) and were identical for normal and leukemic bone marrow samples. After thawing, cells were stained with FITC-or CY5-labeled CD34 and CD38-phycoerythrin monoclonal antibodies (Becton Dickinson BV, Etten-Leur, the Netherlands) for 30 minutes at 4jC and washed in HBSS with 1% v/v heat-inactivated FCS (Hyclone, Logan, UT).…”

ATP-binding-cassette transporters in hematopoietic stem cells and their utility as therapeutical targets in acute and chronic myeloid leukemia

“…A role of ABC transporters in the protection from genetic damage by naturally occurring xenobiotics that are substrates for the transporter has been suggested for HSCs 11,18 and substantiated by the observation of increased cytotoxicity to bone marrow in ABCG2/BCRP knock-out mice. 17 The relative protective effect of ABCG2 of HSC was shown elegantly in this study using competitive repopulation assays comparing transplanted ABCG2À/À to wild-type cells.…”

“…18 This seems particularly important for HSCs, given their life-long presence in the bone marrow and high proliferative activity during this period. In this context, it is noteworthy that an anti-apoptotic role for ABCB1 has been demonstrated recently promoting cell survival by inhibiting caspase activation.…”

Idarubicin DNA intercalation is reduced by MRP1 and not Pgp

“…Isolation, cryopreservation, thawing, rhodamine staining and sorting procedures have been described previously. 23 DNA intercalation and cellular fluorescence of anthracyclines were studied by FCM in 10 4 CD34 + cells/sample.…”