Potassium Channels as Novel Pharmacological Targets in Acute Myeloid Leukemia

Targeted therapies are considerably changing the treatment and prognosis of hematologic malignancies. The progressive elucidation of the molecular mechanisms that regulate establishment and progression of tumours is leading to more specific and efficacious pharmacological approaches. In this picture, ion channels represent a relatively unexpected, but very promising players. In particular hERG1 channel expression is altered in many primary leukemias and frequently turn out to exert pleiotropic effects on cancer cell physiology, interaction with the external matrix and stimulation of angiogenesis. hERG1 channels can also trigger intracellular signaling cascades by forming protein complexes with integrins as well as other membrane proteins. These results convey the hypothesis that drugs acting on ion channels could have therapeutic value in the treatment of cancers. Recent evidence suggests that, in certain tumours, application of channel inhibitors does in fact impair cell growth both in vitro and in vivo. A major objection to such a pharmacological approach is the presence of serious side effects, particularly cardiac arrhythmias, especially in the case of hERG1 blockers. This flaw is now being overcome by different approaches, ie the identification of non-arrhythmogenic compounds or calibration of treatment by exploitation of drug selectivity for specific channel states. We tested this possibility in a preclinical model represented by NOD-SCID mice injected with acute leukemia cells and treated with hERG1 blockers. Previous experiments, using NOD/SCID mice injected with AML cells, had shown that herg1 over-expression confers a greater malignancy (

• control group,

• E4031-treated group (i.p. starting 1 week after inoculum, 20 mg/kg, daily for 2 weeks) and

• E4031-treated group (as above, daily until the end of experiment).

Various morphometric characteristics of microvessels (density, total vascular area, several size- and shape-related parameters), highlighted through anti-CD34 staining, were quantitated in the BM. Overall, the group of mice treated with hERG1 inhibitors had decreased number of microvessels, decreased total vascular area and size-related parameters. Moreover, E4031 treated mice showed a longer survival compared to the untreated ones. Finally, we evaluated cardiac toxicity in vivo of E4031: no significant variation in ECG parameters were detected, nor gross morphological alterations. Nevertheless, we are also testing different pharmacological categories of hERG1 blockers, such the anti-psychotic drug sertindole, proven to be avoid of any cardiac side effect, despite a strong block of hERG1.