Combination Therapy of Anti-Cancer Drug with FNIII14 Peptide of Fibronectin Effectively Overcome Cell Adhesion Mediated-Drug Resistance of Acute Myelogenous Leukemia.

Abstract

We have previously reported that in acute myelogenous leukemia (AML), drug resistance is induced by the attachment of α4β1-integrin (very late antigen (VLA)-4) on leukemic cells (AML cells) to fibronectin (FN) on bone marrow (BM) stromal cells, and this interaction is crucial in BM minimal residual disease (MRD) and prognosis after chemotherapy (Matsunaga T et al, Nature Med 2003, 9, 1158–1165). We also reported a successful overcome of drug resistance in human AML cells transplanted mice with the use of anti-VLA-4 antibody. However, a drawback of progressive multifocal leukoencephalopathy by anti-VLA-4 antibody administration was reported in multiple sclerosis and Chron's disease patients. Therefore, in this study, we examined whether FNIII14, a 22-mer peptide derived from FN which was reportedly potent to block the interaction between FN and VLA-4, VLA-5 or αvβ3-integrin (Fukai F et al. Clin Cancer Res 2002, 8, 2455–2462), can overcome cell adhesion mediated drug resistance (CAM-DR) induced by VLA-4/FN interaction in AML cells. By in vitro culturing system, FNIII14 dose dependently inhibited adhesion of two AML cell lines (U937 cells, HL-60 cells) and fresh AML cells from patients to FN, and significantly circumvented CAM-DR of these AML cells to cytosine arabinoside (Ara C). The mechanism for this circumvention of CAM-DR involved conformational inactivation of β1-integrin as revealed by FACS through inside out inhibitory signal from complex FNIII14/its 50kDa receptor resulting in down regulation of FAK/Akt/Bcl-2 signal which is responsible for VLA-4/FN induced CAM-DR. In a mouse model of MRD, a 100% survival rate was achieved by combining FNIII14 and Ara C, in contrast to a slight prolongation of survival by Ara C alone. These results indicate that combination treatment of anticancer drugs and FNIII14 is the potent modality for eradication of MRD in BM, and should improve the prognosis of AML.