Although ritanserin monotherapy inhibited cell proliferation and promotes apoptosis in AML cells, we discovered that exogenous PA added could rescue the suppression of AML cell growth (Fig. 3C), as well as the protein levels of SphK1 and phospho-SphK1 (Ser225) were elevated (Fig. 3E). Here, SPHK1 is linked to acute myeloid leukemia.