PI3K/Akt inhibition modulates multidrug resistance (MDR) and activates NF-kB in murine lymphoma cell lines.

GARCÍA MG, ALANIZ L, CORDO RUSSO R, ALVAREZ E, HAJOS S.

Rio de Janeiro, Brasil

Congreso; 13º Congreso Internacional de Inmunología.; 2007

Asociación Latinoamericana de Inmunología (ALAI)

Cellular responses toward cytotoxic drugs are controlled by cross-talk between oncogenic signaling pathways and resistance mechanisms. The aim of this work was to analyze the relationship between PI3K/Akt survival pathway and multidrug resistance (MDR) in murine lymphoma resistant cell lines to vincristine (LBR-V160), doxorubicin (LBR-D160) and sensitive line (LBR-). Higher PI3K/Akt activity was found in LBR-V160 and LBR-D160 compared to LBR-, analyzed through phosphatidylinositol-trisphosphate production by TLC and phosphorylated Akt (p-Akt) expression by western blot. Improved apoptosis was observed in LBR-D160 (17.7%±9.4% and 25.2%±7.3%) and LBR-V160 (17.4%±4.8% and 13.0%±5.6%) compared to LBR- (3.7%±3.4% and 4.0%±1.8%) after PI3K inhibition with wortmannin or LY294002 respectively (P<0.01 vs LBR-), evaluated by Annexin V and acridine orange-ethidium bromide staining. Both inhibitors also down-regulated survivin expression in the three cell lines while IkB phosphorylation was increased leading to down-regulation of IkB expression. Higher NF-kB activity was also observed by EMSA assay after PI3K inhibition. Vincristine (VCR) but not doxorubicin increased p-Akt expression while co-treatment with PI3K inhibitors and VCR increased apoptosis in the three cell lines. After wortmannin or LY294002 treatment, P-glycoprotein (Pgp) function was evaluated by flow cytometry showing a blockage of Pgp efflux in resistant cell lines. We conclude that PI3K/Akt pathway is involved in MDR in these lymphoma cell lines. Besides, PI3K inhibition correlates with apoptosis induction, survivin down-regulation and NF-kB activation. PI3K inhibitors, wortmannin and LY294002, modulate MDR by both PI3K/Akt and Pgp function inhibition. Therefore, PI3K/Akt signaling cascade may be considered as an attractive target for therapeutic intervention.