While a batch of efforts are fastened on synthesizing the novel targeted anti-cancer agents, recent investigations have achieved a breakthrough in identifying a favorable anti-tumor activity for some supportive drugs, which their safety have been confirmed thus far. The results of the present study highlighted the efficacy of Aprepitant, an oral antagonist of the neurokinin-1 receptor (NK1R), against both APL (NB4) and pre-B ALL (Nalm-6) cell lines; however, a differential sensitivity pattern was found in these cells. To the best of our knowledge, this is the first time that the molecular mechanisms of resistance to Aprepitant have been investigated and, herein, we proposed that the effectiveness of Aprepitant could be overshadowed, at least partially, through over-activated nuclear factor-κB in Nalm-6 pre-B ALL cells. In contrast to Nalm-6, the cytotoxic property of Aprepitant in NB4 was divulged at the lower concentrations. Of particular interest, we found that the cytotoxicity of the inhibitor became even more evident in the synergistic experiments, where an enhanced reduction in viability was noted after treatment of NB4 cells with ATO-plus-Aprepitant. The stimulatory effect of NK1R inhibition on ATO cytotoxicity is probably mediated through up-regulation of p73, which can subsequently engage p21 and NF-κB pathway via transcriptional suppression of c-Myc. Taken together, the present study suggests that inhibition of NK1R using Aprepitant, either alone or in combination with chemotherapeutic drugs, could be a novel therapeutic strategy for the treatment of acute leukemia, especially APL, that may be clinically accessible in the near future.