Chemomodulation of drugs involved in multidrug resistance in chronic lymphatic leukemia of the B-cell type

Hyperforin inhibits P-gp and BCRP activities in chronic lymphocytic leukaemia cells and myeloid cells

We showed previously that hyperforin (HF), a natural phloroglucinol, stimulated apoptosis in B cell chronic lymphocytic leukaemia cells (CLL) and displayed anti-angiogenic properties. In the present work, we investigated the effects of hyperforin on the activity of P-gp/MDR1, an ABC (ATP-binding cassette) transporter putatively involved in multidrug resistance (MDR). Ex vivo treatment of CLL cells with HF markedly impaired the activity of P-gp, as measured by the inhibition of the capacity of the treated cells to efflux the rhodamine 123 probe. In addition, most CLL cells expressed breast cancer resistance protein (BCRP), another ABC transporter. The activity of BCRP was also inhibited by HF, as assessed by the impaired capacity of HF-treated CLL cells to efflux the specific probe mitoxantrone. The capacity of HF to reverse P-gp and BCRP activity was confirmed in myeloid leukaemia cell lines, notably in HL-60/DNR cells selected for their resistance to daunorubicine and overexpressing P-gp. Our results therefore suggest that HF might be of interest in the therapy of CLL and other haematological malignancies through its potential capacity to revert MDR in addition to its pro-apoptotic properties.

MPA increases idarubicin-induced apoptosis in chronic lymphatic leukaemia cells via caspase-3

The caspase family of protease is speculated to have a crucial role in apoptosis. The effect of treatment with Idarubicin (IDA) and Medroxyprogesterone acetate (MPA), used alone or in combination, on the activation of Caspase-3 in canine Chronic Lymphatic Leukaemia (CLL) cells was investigated, in order to clarify the mechanism of chemo- and hormone-therapy mediated apoptosis. Caspase activity was determined by a quantitative fluorimetric assay. Apoptosis was monitored by propidium iodide (PI) and nucleosomes assay. Treatment of CLL cells for 24 h with MPA 5 microM did not significantly activate caspase-3 but its activity was increased almost 5-fold more with IDA 1 microM (P < 0.05) than control. Treatment of CLL cells with IDA 1 microM in equimolecular association with MPA was able to increase the activation of caspase-3 induced by IDA of the 61.2% (P < 0.05) in comparison with IDA alone. The activation of caspase-3 was confirmed evaluating apoptosis by PI and nucleosomes assay. Furthermore, both caspase-3 activation and apoptosis triggered by IDA alone or in combination with MPA were significantly inhibited by specific caspase-3 inhibitor AC-DEVD-CMK. These findings provide an explanation for IDA and MPA induced-apoptosis mechanism.

Beta-tubulin and P-glycoprotein: major determinants of vincristine accumulation in B-CLL cells

Vincristine (VCR) accumulation in chronic lymphatic leukemia of B-cell origin (B-CLL) has recently been shown not to be inversely correlated to P-glycoprotein (PGP) levels. Therefore, we studied, in addition to PGP expression and accumulation of VCR, the cellular beta-tubulin content in quiescent and rhIL-2 activated B-CLL cells. VCR mediates cytotoxicity by binding to tubulin. Constitutive beta-tubulin levels in B-CLL cells varied considerably. Upon activation with rhIL-2, beta-tubulin expression increased significantly. Therefore, tubulin levels could be correlated over a wide range to VCR accumulation. When the PGP-mediated drug efflux was blocked by verapamil (VRP), tubulin levels correlated linearly to VCR accumulation. All B-CLL cases expressed PGP at different levels. There was no linear correlation between PGP expression and VCR accumulation. A modulation factor m was defined as a quotient of VCR accumulation in the presence and absence of VRP to define the extent by which VRP inhibited a steady-state accumulation of VCR. The factor allowed discrimination between B-CLLs expressing low versus high PGP, irrespective of the levels of tubulin. However, PGP and beta-tubulin levels together were predictive for VCR accumulation in steady state. There was no uniform-accumulation defect for VCR in B-cell CLL because beta-tubulin and PGP were expressed independently. Non PGP-mediated VCR transport seems to play a minor role in B-cell CLL. Leukemia-associated varying of cytoskeletal organization in B-cell CLL might be one reason for the diverse cellular responses to receptor-mediated signals.