Objective: To explore the role of c-Myc in mesenchymal stromal cell-mediated drug resistance and elucidate the molecular mechanism of acute myeloid leukemia (AML) from the version of tumor microenvironment.
Methods: AML cell lines U937 and KG1a were co-cultured with mesenchymal stromal cells (MSC) from bone marrow of healthy donors between January to March 2012. The AML cell lines plated alone was cultured as controls. Apoptosis induced by mitoxantrone was measured by flow cytometry and Annexin V/PI double and 4'-6-diamidino-2-phenylindole (DAPI) staining. And c-Myc protein was detected by Western blot under both culturing conditions. After a pre-treatment of c-Myc inhibitor 10058-F4, the apoptosis of AML cell was also evaluated.
Results: Apoptosis of AML cells (U937 and KG1a) significantly decreased during co-culturing with MSC (9.88% ± 1.53% vs 42.83% ± 2.03%, P = 0.004;20.60% ± 2.87% vs 42.53% ± 5.29%, P = 0.030). Drug resistance was implicated. The co-culturing of AML cells with MSC significantly induced an up-regulation of c-Myc. The inhibition of c-Myc with 10058-F4 could induce apoptosis of AML cells. After an addition of 10058-F4 into the co-culture system, the apoptotic rate of KG1a cells significantly increased from 23.87% ± 1.55% to 57.23% ± 3.88% (P = 0.009). Similarly the apoptotic rates spiked from 16.07% ± 2.11% to 53.47% ± 4.08% in U937 cells (P = 0.004) to overcome the stromal cell-mediated drug resistance.
Conclusions: The co-culturing of AML cells and MSC induces an up-regulation of c-Myc protein so as to cause the emergence of chemoresistance. Therefore targeting c-Myc protein may provide a novel therapeutic strategy of AML.