5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside induces accumulation of leukemia cells in S-phase

Proteinska kinaza aktivirana AMP-om (AMPK) služi kao stanični energetski senzor koji koči mTOR (ciljna molekula rapamicina u sisavaca) i zaustavlja proliferaciju. Modulatori signalnog puta AMPK/mTOR ispituju se u liječenju leukemija iako je mehanizam njihovog djelovanja samo djelomice razjašnjen. U našem istraživanju ispitali smo aktivnost signalnog puta AMPK/mTOR u sinkroniziranim leukemijskim stanicama te učinak njegovih farmakoloških modulatora na prolazak kroz stanični ciklus. Stanice akutne promijelocitne leukemije NB4 sinkronizirali smo nokodazolom. Analiza količine fosforiliranog p70S6K-a metodom Western blot u stanicama nakon otpuštanja iz nokodazolskog bloka pokazala je da je aktivnost mTOR-a niska tijekom prijelaza iz metazafe u G1-fazu te da se povećava se tijekom G1-faze. Učinak modulatora na prolazak stanica kroz stanični ciklus odredili smo protočnom citometrijom stanica označenih propidijevim jodidom. 5-aminoimidazol-4-karboksiamid-1-β-D-ribofuranozid (AICAR), metformin, rapamicin i tvar C nisu utjecali na povratak stanica iz G2/M-faze u G1-fazu 3 sata nakon otpuštanja iz nokodazolskog bloka. Međutim, AICAR je značajno povećao udio stanica u S-fazi nakon 24 sata. Rezultati našeg istraživanja pokazuju da AICAR potiče nakupljanje leukemijskih stanica u S-fazi što upućuje da bi se AICAR možda mogao koristiti u kombinaciji s drugim lijekovima za liječenje leukemija.The AMP-activated protein kinase (AMPK) is a low-energy checkpoint that inhibits mTOR (mammalian target of rapamycin) kinase and suppresses proliferation. Modulators of AMPK/mTOR have been proposed in the treatment of leukemia, but the mechanism of their action is only partially understood. In this study, we investigated the activity of AMPK/mTOR pathway in synchronized leukemia cells and the effects of pharmacological modulators on cell cycle progression. Acute promyelocytic leukemia NB4 cells were synchronized with nocodazole. Western blot analysis of the levels of Thr389-phosphorylated p70S6K in cells released from block revealed that the activity of mTOR was low during M/G1 transition and increased as the cells progressed through G1-phase. The effect of AMPK/mTOR modulators on cell cycle progression was measured using flow cytometric analysis of propidium iodide-labelled cells. The presence of 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR), metformin, rapamycin or compound C had no significant effects on return of cells to G1-phase at 3 h after release. At 24 h after release, a significant increase in the percentage of S-phase was observed in cells treated with AICAR. The results of our study demonstrate that AICAR induces the accumulation of leukemia cells in S-phase suggesting a possible role for AICAR in combination therapy of leukemia

Electrical storm and catheter ablation of ventricular tachycardia days after left ventricular assist device implantation

Ventricular arrhythmias are common complication associated with left ventricular assist devices (LVAD). We present a challenging case of a 57-year-old male LVAD recipient who developed ventricular tachycardia refractory to antiarrhythmic drugs and device therapy in the early postoperative period and was eventually successfully treated with radiofrequency catheter ablation. Ventricular arrhythmias were successfully mapped, eliminated with ablation, and remained non-inducible. This case demonstrates that ventricular arrhythmia catheter ablation can be feasible, effective, and safe in LVAD recipients with a scar-related electrical storm even days after LVAD implantation. Although optimal treatment strategy in this patient population still needs to be defined, catheter ablation should be considered in LVAD recipients with ventricular arrhythmias refractory to antiarrhythmic drugs and device therapy representing a treatment of last resort