RESUMO
Sphingomyelin (SM)/cholesterol liposomes are currently investigated as drug carriers in cancer therapy. However, no data is available on the influence of SM itself on P-glycoprotein (P-gp) mediated multidrug resistance. P-gp is at least partly located in sphingolipid-enriched lipid raft domains of the plasma membrane, and its activity depends on the lipid profile of the membrane, which could be altered by therapeutical SM liposomes. Therefore, the aim of this study was to analyze the effect of liposomal SM on P-gp activity, P-gp distribution in microdomains, SM content of the membrane domains, and sensitivity of human lymphoblastic CEM cells toward cytotoxic drugs in vitro. Assays were conducted in CEM and multidrug resistant CEM/ADR5000 cells. SM-only liposomes were prepared by a newly developed ethanol injection protocol and thoroughly characterized. Inclusion of SM into the membrane was analyzed by fluorescence microscopy and flow cytometry. Influence of SM liposomes on P-gp activity was assessed by rhodamine efflux and calcein assay, and sensitivity toward cytotoxic drugs was analyzed by flow cytometric 7-AAD staining. Influence on P-gp distribution was analyzed by Western blot after density gradient centrifugation. SM 16:0, 18:0, and 24:1 were quantified by liquid chromatography coupled to tandem mass spectrometry. P-gp was mainly located in nonraft fractions, which did not change upon liposome treatment. Liposomes increased SM 16:0 and SM 24:1 content in nonraft domains, but not in raft domains of multidrug resistant cells. SM-only liposomes did not influence P-gp activity and chemosensitivity. In conclusion, SM-only liposomes in therapeutic amounts did not influence P-gp mediated multidrug resistance in CEM cells.
Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/metabolismo , Lipossomos/química , Esfingomielinas/química , Western Blotting , Linhagem Celular Tumoral , Portadores de Fármacos/efeitos adversos , Portadores de Fármacos/química , Resistência a Múltiplos Medicamentos , Resistencia a Medicamentos Antineoplásicos , Citometria de Fluxo , Humanos , Lipossomos/efeitos adversos , Leucemia-Linfoma Linfoblástico de Células Precursoras , Esfingomielinas/efeitos adversosRESUMO
7-Aminoactinomycin D (7-AAD) is a DNA dye that distinguishes viable, apoptotic, and late apoptotic/dead cells in flow cytometry. Several staining protocols using 7-AAD have been described, but data on the influence of the 7-AAD concentration on the readout are not available. Therefore, we compared the results obtained by staining with 1, 5, 10, and 20µg/ml 7-AAD for 20min with the PE-Annexin V Apoptosis Detection Kit and Cell Death Detection ELISA(PLUS) in lymphocytes and CEM human leukemia cells. The results showed that 7-AAD staining with 5, 10, and 20µg/ml, but not with 1µg/ml, is suitable for quantification of apoptosis in flow cytometry.