Abstract
The bone marrow (BM) niche impacts the progression of acute myeloid leukemia (AML) by favoring the chemoresistance of AML cells. Intimate interactions between leukemic cells and BM mesenchymal stromal cells (BM-MSCs) play key roles in this process. Direct intercellular communications between hematopoietic cells and BM-MSCs involve connexins, components of gap junctions. We postulated that blocking gap junction assembly could modify cell–cell interactions in the leukemic niche and consequently the chemoresistance. The comparison of BM-MSCs from AML patients and healthy donors revealed a specific profile of connexins in BM-MSCs of the leukemic niche and the effects of carbenoxolone (CBX), a gap junction disruptor, were evaluated on AML cells. CBX presents an antileukemic effect without affecting normal BM-CD34+ progenitor cells. The proapoptotic effect of CBX on AML cells is in line with the extinction of energy metabolism. CBX acts synergistically with cytarabine (Ara-C) in vitro and in vivo. Coculture experiments of AML cells with BM-MSCs revealed that CBX neutralizes the protective effect of the niche against the Ara-C-induced apoptosis of leukemic cells. Altogether, these results suggest that CBX could be of therapeutic interest to reduce the chemoresistance favored by the leukemic niche, by targeting gap junctions, without affecting normal hematopoiesis.
Highlights
In order to investigate the expression of Cxs in acute myeloid leukemia (AML) cells, the mRNA expression of the Cx gene family (20 genes) was investigated in 39 different AML bone marrow (BM) samples of different molecular/cytogenetic profiles and in six AML cell lines. qRT-PCR analyses revealed a high expression of three Cxs: Cx25, Cx31.9, and Cx59 in all AML primary samples with ΔCt values varying from 6 to 9 for Cx25, 7 to 10 for Cx31.9, and 7 to 10 for Cx59 (Fig. 1a)
We established a large-scale expression profile of the Cx family in leukemic cells compared with normal CD34+ hematopoietic progenitors and in leukemic BMMSCs compared with normal BM mesenchymal stromal cells (BM-MSCs)
The same Cxs were highly expressed in leukemic and normal hematopoietic cells, whereas leukemic BM-MSCs differed from their normal counterpart by overexpressing numerous Cxs, Cx25, and seven others. These new interesting data emphasize the possibility of specific gap junction interactions between AML cells and BM-MSCs in the leukemic niche, probably involving homotypic Cx25-gap junctions
Summary
In order to investigate the expression of Cxs in AML cells, the mRNA expression of the Cx gene family (20 genes) was investigated in 39 different AML BM samples of different molecular/cytogenetic profiles and in six AML cell lines. qRT-PCR analyses revealed a high expression of three Cxs: Cx25, Cx31.9, and Cx59 in all AML primary samples with ΔCt values varying from 6 to 9 for Cx25, 7 to 10 for Cx31.9, and 7 to 10 for Cx59 (Fig. 1a). Coculture experiments were performed with KG1a or primary AML blast cells, together with normal or AML BM-MSCs, to evaluate the impact of CBX exposure on niche-induced chemoresistance to Ara-C. Combination treatment of Ara-C with CBX increased the antileukemic effect of Ara-C especially by reducing the chemoresistance triggered by BMMSCs. CBX effect was promoted by direct contact of AML cells with BM-MSCs, revealing a potential role of gap junctions in the regulation of chemoresistance. Treatments with Ara-C alone, CBX alone, and even more CBX and Ara-C infusions significantly improved mice survival as shown by Kaplan–Meir analyses (Fig. 7b left) In line with these results, CBX and Ara-C infusions induced a threefold decrease in BM blastosis in untreated mice (50 ± 7% of human CD45+ cells), in which a major splenomegaly was observed in contrast to treated mice (Fig. 7b right).
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