The sensitivity of acute myeloid leukemia cells to cytarabine is increased by suppressing the expression of Heme oxygenase-1 and hypoxia-inducible factor 1-alpha.

Background: Acute myeloid leukemia (AML), a malignancy Often resistant to common chemotherapy regimens (Cytarabine (Ara-c) + Daunorubicin (DNR)), is accompanied by frequent relapses. Many factors are involved in causing chemoresistance. Heme Oxygenase-1 (HO-1) and Hypoxia-Inducible Factor 1-alpha (HIF-1α) are two of the most well-known genes, reported to be overexpressed in AML and promote resistance against chemotherapy according to several studies. The main chemotherapy agent used for AML treatment is Ara-c. We hypothesized that simultaneous targeting of HO-1 and HIF-1α could sensitize AML cells to Ara-c.

Method: In this study, we used our recently developed, Trans-Activator of Transcription (TAT) - Chitosan-Carboxymethyl Dextran (CCMD) - Poly Ethylene Glycol (PEG) - Nanoparticles (NPs), to deliver Ara-c along with siRNA molecules against the HO-1 and HIF-1α genes to AML primary cells (ex vivo) and cell lines including THP-1, KG-1, and HL-60 (in vitro). Subsequently, the effect of the single or combinational treatment on the growth, proliferation, apoptosis, and Reactive Oxygen Species (ROS) formation was evaluated.

Results: The designed NPs had a high potential in transfecting cells with siRNAs and drug. The results demonstrated that treatment of cells with Ara-c elevated the generation of ROS in the cells while decreasing the proliferation potential. Following the silencing of HO-1, the rate of apoptosis and ROS generation in response to Ara-c increased significantly. While proliferation and growth inhibition were considerably evident in HIF-1α-siRNA-transfected-AML cells compared to cells treated with free Ara-c. We found that the co-inhibition of genes could further sensitize AML cells to Ara-c treatment.

Conclusions: As far as we are aware, this study is the first to simultaneously inhibit the HO-1 and HIF-1α genes in AML using NPs. It can be concluded that HO-1 causes chemoresistance by protecting cells from ROS damage. Whereas, HIF-1α mostly exerts prolific and direct anti-apoptotic effects. These findings imply that simultaneous inhibition of HO-1 and HIF-1α can overcome Ara-c resistance and help improve the prognosis of AML patients.