Treatment with hERG1 K+ Channel Inhibitors Reduces Acute Myeloid Leukemia Cell Lines Engraftment into Nonobese Diabetic/Severe Combined Immunodeficient Mice and Prolongs Survival of Injected Mice.

Abstract

hERG1 K+ channels are expressed in a broad range of human leukemic cell lines and primary acute myeloid and lymphoid leukemias (Pillozzi S, et al Leukemia 16:1791–1798, 2002; Smith GA, et al, JBC 227:18528–18534, 2002). hERG1 activity is necessary for leukemia cell proliferation as well as migration in response to angiogenic factors (VEGF). This effect can be traced back to the assembly of a macromolecular signaling complex on the plasma membrane of leukemia cells. Such complex comprises hERG1 channels, the beta1 subunit of integrin adhesion receptors and the VEGF receptor 1, FLT-1. In vivo experiments in NOD/SCID mice injected with AML cells showed that herg1 over-expression confers a greater malignancy, witnessed by a higher bone marrow (BM) angiogenesis, and a stronger leukemia blast exit into the peripheral blood (PB) and into extramedullary organs. What is more, herg1 expression in AML patients correlates with a higher probability of relapse and shorter survival periods (Pillozzi S et al, Blood 110:1238–1250, 2007). On the whole we can conclude that hERG1 channel expression in AML represent a progression factor and can be envisaged as a novel target for therapy. We tested this latter hypothesis in NOD/SCID mice injected with AML cell lines expressing hERG1 channels at various extent, and treating injected mice with a selective hERG1 inhibitor, E4031. E4031 was administered i.p. starting one week after inoculum, at the dose of 20 mg/kg, daily for two weeks. In a first set of experiments mice were sacrificed after a total 3 weeks after inoculum. It emerged that E4031 reduced both BM engraftment and PB invasion of AML cells. In particular, BM angiogenesis was significantly lower in mice treated with E4031. In a second set of experiments, mice were treated as above and the survival time was measured. It emerged that E4031 treatment prolonged survival compared with the control-treated group. We have developed a monoclonal antibody against an extracellular loop of hERG1 channels. The immunoreactivity and activity on hERG1 channels of such antibody was first tested in leukaemia cells. Treatment of NOD/SCID mice injected with AML cell lines with this antibody is ongoing.